impedance source inverters - download.e-bookshelf.de€¦ · hongpeng liu † zichao zhou † yuhao...

Hongpeng Liu · Zichao Zhou · Yuhao Li · Wentao Wu · Jiabao Jiang · Enda Shi

Impedance Source Inverters

Hongpeng Liu • Zichao Zhou • Yuhao Li •

Wentao Wu • Jiabao Jiang • Enda Shi


123

Hongpeng LiuNortheast Electric Power UniversityJilin, China

Zichao ZhouAalborg UniversityAalborg, Denmark

Yuhao LiDelta Electronic Enterprise Management(Shanghai) Co., LtdShanghai, China

Wentao WuChina Southern Power Grid Co., LtdShenzhen Power Supply BureauShenzhen, China

Jiabao JiangState Grid Zhejiang Electric PowerCompany Hangzhou Power SupplyCompanyHangzhou, China

Enda ShiHarbin Institute of TechnologyHarbin, China

ISBN 978-981-15-2762-3 ISBN 978-981-15-2763-0 (eBook)https://doi.org/10.1007/978-981-15-2763-0

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https://doi.org/10.1007/978-981-15-2763-0

Contents

1 Research Status and Development . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Traditional Source Inverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Energy Situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1.2 Traditional Power Inverter Topologies . . . . . . . . . . . . . . . 5

1.2 Impedance Source Inverters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101.3 Classification and Future Trends . . . . . . . . . . . . . . . . . . . . . . . . . 15

1.3.1 Classification of Impedance Source Inverters . . . . . . . . . . . 151.3.2 Future Trend of Impedance Source Inverters . . . . . . . . . . . 19

1.4 Contents Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2 Z-Source Inverter and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292.1 Voltage-Fed Z-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . 29

2.1.1 Structure and Equivalent Circuit . . . . . . . . . . . . . . . . . . . . 292.1.2 Circuit Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312.1.3 Quasi-Z-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.2 Modulation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352.2.1 Simple Boost Pulse-Width Modulation . . . . . . . . . . . . . . . 352.2.2 Maximum Boost Pulse-Width Modulation . . . . . . . . . . . . . 392.2.3 Other Boost Pulse-Width Modulation . . . . . . . . . . . . . . . . 40

2.3 Closed-Loop Control of Shoot-Through Duty Ratio . . . . . . . . . . . 412.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412.3.2 Single-Loop Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422.3.3 Dual-Loop Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432.3.4 Non-linear Control Methods . . . . . . . . . . . . . . . . . . . . . . . 43

2.4 Current-Fed Z-Source Inverter and Control . . . . . . . . . . . . . . . . . 432.4.1 Structure of Current-Fed Z-Source Inverter . . . . . . . . . . . . 432.4.2 Modes of Current-Fed Z-Source Inverter . . . . . . . . . . . . . . 442.4.3 Modulation of Current-Fed Z-Source Inverter . . . . . . . . . . 452.4.4 Closed-Loop Control of Current-Fed Z-Source

Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

v

2.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

3 Developments of Impedance Source Inverters . . . . . . . . . . . . . . . . . . 513.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513.2 Topology Improvements with Constant Boost Ratio . . . . . . . . . . . 52

3.2.1 Z-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523.2.2 Improved Z-Source Inverters . . . . . . . . . . . . . . . . . . . . . . 533.2.3 Neutral Point Z-Source Inverters . . . . . . . . . . . . . . . . . . . . 553.2.4 Reduced Leakage Current Z-Source Inverters . . . . . . . . . . 573.2.5 Quasi-Z-Source Inverters . . . . . . . . . . . . . . . . . . . . . . . . . 583.2.6 Other Basic Z-Source Inverters . . . . . . . . . . . . . . . . . . . . . 58

3.3 Topology Developments to Improve Boost Ratio . . . . . . . . . . . . . 603.3.1 Switched Components Z-Source Inverters . . . . . . . . . . . . . 603.3.2 Tapped Inductor Z-Source Inverters . . . . . . . . . . . . . . . . . 613.3.3 Cascaded Quasi-Z-Source Inverters . . . . . . . . . . . . . . . . . . 623.3.4 Coupled Inductor Z-Source Inverters . . . . . . . . . . . . . . . . . 63

3.4 Multilevel and Multiplex Topologies . . . . . . . . . . . . . . . . . . . . . . 633.4.1 Three-Level Z-Source Inverters . . . . . . . . . . . . . . . . . . . . 633.4.2 Five-Level Z-Source Inverters . . . . . . . . . . . . . . . . . . . . . 643.4.3 Cascaded Multilevel Z-Source Inverters . . . . . . . . . . . . . . 643.4.4 Multiplex Z-Source Inverters . . . . . . . . . . . . . . . . . . . . . . 64

3.5 Parameter Optimization of Topologies . . . . . . . . . . . . . . . . . . . . . 643.5.1 High-Frequency Transformer Isolated Z-Source

Topologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643.5.2 Inductor Z-Source Topologies . . . . . . . . . . . . . . . . . . . . . 653.5.3 Extended Quasi-Y-Source Topologies . . . . . . . . . . . . . . . . 653.5.4 Low DC-Link Voltage Spikes Y-Source Topologies . . . . . 65


4 Dual-Winding Impedance Source Inverters . . . . . . . . . . . . . . . . . . . 734.1 T-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734.2 Trans-Quasi-Z-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . 754.3 Improved Trans-Quasi-Z-Source Inverter . . . . . . . . . . . . . . . . . . . 764.4 Transformer Quasi-Z-Source Inverter . . . . . . . . . . . . . . . . . . . . . . 784.5 Inductor–Capacitor–Capacitor–Transformer ZSI . . . . . . . . . . . . . . 784.6 C-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

5 Three-Winding Impedance Source Inverter . . . . . . . . . . . . . . . . . . . 835.1 Y-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835.2 Improved Y-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

vi Contents

5.3 Extended Quasi-Y-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . 875.3.1 Startup Current Suppression . . . . . . . . . . . . . . . . . . . . . . . 885.3.2 Operational States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895.3.3 Current Ratings and Core Size of Coupled Inductor . . . . . . 925.3.4 Component Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 965.3.5 Loss of ST Duty Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . 975.3.6 DC-Link Voltage Spikes . . . . . . . . . . . . . . . . . . . . . . . . . 1005.3.7 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

5.4 Modified Y-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1065.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

6 Technology of DC-Link Voltage Spikes Suppression . . . . . . . . . . . . 1196.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1196.2 Dual Diodes Capacitor–Diode Absorbing Circuits . . . . . . . . . . . . 120

6.2.1 Operational Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1236.2.2 Current Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1256.2.3 Voltage Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1276.2.4 Switching Loss Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 1316.2.5 Simulation and Experimental Results . . . . . . . . . . . . . . . . 1346.2.6 Extension of Topologies Range . . . . . . . . . . . . . . . . . . . . 141

6.3 Single Diode Capacitor–Diode Clamping Circuits . . . . . . . . . . . . . 1426.4 Embedded Capacitor–Diode Absorbing Circuits . . . . . . . . . . . . . . 143

6.4.1 Operational States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1446.4.2 Current Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1486.4.3 Voltage Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1526.4.4 Voltage and Current Stress Analysis . . . . . . . . . . . . . . . . . 1546.4.5 Simulation and Experimental Results . . . . . . . . . . . . . . . . 154

6.5 Cascaded Quasi-Z-Network Clamping Circuits . . . . . . . . . . . . . . . 1596.5.1 Operational Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1606.5.2 Current Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1636.5.3 Voltage Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1676.5.4 Stresses and Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1716.5.5 Extra Power Loss Analysis . . . . . . . . . . . . . . . . . . . . . . . . 1726.5.6 Simulation and Experimental Results . . . . . . . . . . . . . . . . 174


7 Impedance Source Inverters Analysis . . . . . . . . . . . . . . . . . . . . . . . . 1837.1 Traditional Analysis of Voltage and Current Stresses . . . . . . . . . . 1837.2 Novel Method to Analyze Voltage and Current Stresses . . . . . . . . 187

7.2.1 Current Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1877.2.2 Voltage Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1897.2.3 Method Applied to Other Converters . . . . . . . . . . . . . . . . 190

Contents vii

7.3 Transient Analysis Based on Impedance Source Inverter . . . . . . . . 1927.3.1 Derivation of the Novel Model . . . . . . . . . . . . . . . . . . . . . 1937.3.2 Switching Transient Analysis . . . . . . . . . . . . . . . . . . . . . . 1997.3.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204


8 Reliability Research on Impedance Source Inverters . . . . . . . . . . . . 2118.1 Existing Reliability Analysis Methods . . . . . . . . . . . . . . . . . . . . . 211

8.1.1 Basic Concept of Reliability and Evaluation Index . . . . . . 2118.1.2 Method for Predicting Device Reliability . . . . . . . . . . . . . 2158.1.3 The Method for System Reliability Prediction . . . . . . . . . . 217

8.2 Failure Mechanism of Power Devices . . . . . . . . . . . . . . . . . . . . . 2228.2.1 Structure of IGBT Module . . . . . . . . . . . . . . . . . . . . . . . . 2238.2.2 Failure Mechanism of IGBT Module . . . . . . . . . . . . . . . . 2258.2.3 Structure of Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . 2298.2.4 Failure Mechanism of Capacitor . . . . . . . . . . . . . . . . . . . . 233

8.3 Thermal Model of Power Devices . . . . . . . . . . . . . . . . . . . . . . . . 2378.3.1 Thermal Model of IGBT . . . . . . . . . . . . . . . . . . . . . . . . . 2378.3.2 Thermal Model of Capacitor . . . . . . . . . . . . . . . . . . . . . . 245

8.4 Life Prediction of Impedance Source Inverters . . . . . . . . . . . . . . . 2478.4.1 Lifetime Models of IGBT Module . . . . . . . . . . . . . . . . . . 2478.4.2 Lifetime Models of DC-Link Capacitors . . . . . . . . . . . . . . 249

8.5 Reliability Analysis of Life Distribution . . . . . . . . . . . . . . . . . . . . 2518.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253

9 Application of Impedance Source Inverters . . . . . . . . . . . . . . . . . . . 2559.1 Application of Power Decoupling . . . . . . . . . . . . . . . . . . . . . . . . 255

9.1.1 Power Decoupling Characteristics . . . . . . . . . . . . . . . . . . . 2559.1.2 Application of Impedance Source Inverter

in Power Decoupling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2599.2 Application in Photovoltaic Power Generation . . . . . . . . . . . . . . . 265

9.2.1 Photovoltaic Power Characteristics . . . . . . . . . . . . . . . . . . 2659.2.2 MPPT Control and System Control Methods . . . . . . . . . . . 2669.2.3 Example Demonstration . . . . . . . . . . . . . . . . . . . . . . . . . . 267

9.3 Application in Wind Power Generation . . . . . . . . . . . . . . . . . . . . 2769.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2769.3.2 Z-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2779.3.3 Quasi-Z-Source Inverter . . . . . . . . . . . . . . . . . . . . . . . . . . 2829.3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284

9.4 Application on Motor Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2849.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2849.4.2 Z-Source Inverter-Based Permanent Magnet

Brushless DC Motor Drive . . . . . . . . . . . . . . . . . . . . . . . . 285

viii Contents

9.4.3 Z-Source Inverter-Based Permanent MagnetSynchronous Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285

9.4.4 Z‐Source Inverter-Based Switched Reluctance Motor . . . . . 2869.4.5 Modified Z-Source Inverter-Based Three-Phase

Induction Motor Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . 2869.4.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288

Contents ix

Chapter 1Research Status and Development

Abstract Significant developments on highly performance, highly reliable andhighly efficient power electrical inverters are underway for renewable energy andother industrial occasions. This chapter introduces the background of renewableenergy and traditional source inverters which are widely applied in solar PV andwind power. Then current research status and advanced technologies related toimpedance source inverters are presented, including the concepts, classification, andfuture trends as well as the advantages compared with traditional source inverters.

1.1 Traditional Source Inverters

1.1.1 Energy Situation

Greenhouse gas emissions over the next decade have been projected in the ParisAgreement and global average temperature rise is requested well below 2 °C, whichmeans the conventional generations should be replaced by decarbonized powernetworks [1–3]. Building on the impetus of trend toward decarbonization, energyindustry steps in the era of distributed renewable energy resources (DRERs), suchas solar photovoltaic (PV), wind generation (WG), hydropower turbines,bio-power, ocean power, concentrating solar power (CSP), and geothermal powerthat all demand for hybrid inverters [4, 5].

Figure 1.1 reveals the annual global renewable power capacity in the level ofgigawatts (GW) from 2007 to 2017 [5]. It is obvious that the world total renewablepower capacity has reached 2,195 GW in 2017, which is almost twice than that in2007. Hydropower accounts for the largest share and is growing every year, whilethe composition of solar PV and wind power increases significantly annually andbecomes one of the most important parts in the renewable power capacity. Otherrenewable powers like bio-power, ocean, CSP, and geothermal power are devel-oping which will be further studied in the future.

The solar PV global capacity and annual additions from 2007 to 2017 are shownin Fig. 1.2 [5]. The total global capacity of solar PV reaches 402 GW in 2017 which

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has increased 98 GW than the last year. Besides, the annual additions of solar PVare almost keeping growing in the past decades, while that of wind power are nearlyconstant as shown in Fig. 1.3 which illustrates the wind power global capacity andannual additions from 2007 to 2017 [5]. However, both energies contribute moreand more capacity to that of total global renewable power. In 2017, the world totalcapacity of wind power generation has reached 539 GW, which almost constitutesone-quarter of the global renewable power capacity. In order to realize the 100%renewable energy as [2] mentioned, the solar PV and wind power will be stillregarded as key development objects in the years ahead.

However, the renewable energy still have various issues. As for the solar PV, theoutput power is restricted to load variations, temperature, and irradiance [6, 7]. Theload is variable whether the solar PV system is connected to the grid or off the grid.

Fig. 1.1 Annual global renewable power capacity from 2007 to 2017 [5] (Source Reproducedwith the permission of REN21)

Fig. 1.2 Solar PV global capacity and annual additions from 2007 to 2017 [5] (SourceReproduced with permission of REN21)

2 1 Research Status and Development

Thus, the maximum power point tracking (MPPT) technique is applied and thesolar PV could output maximum power in a single point of operation when thecorresponding insolation is given [8]. Besides, as the temperature and irradiance areinfluenced by weather, nighttime, shadow on the PV panels, and so on, the outputpower maybe decreased and even down to zero. Battery storage is integrated intothe PV system to avoid the discontinuous electric supply to the load [9, 10].Moreover, direct current to direct current (DC–DC) converters are requested whenthe power level of output mismatches with that of PV panels. And the existing loadsare almost alternating current (AC), inverters that perform direct current to alter-nating current (DC–AC) transition are always regarded as the final link to the loadsor grid [11, 12].

Figure 1.4 illustrates various configurations of PV systems, where the inverters’outputs are given to the AC loads or grid [13]. Figure 1.4a shows one PV panelconnected with inverter, while a DC–DC converter added to it becomes Fig. 1.4b,which enhances the output power level. Furthermore, several PV panels connectedwith inverters can be combined into module-based inverters that also improve thepower rating [12]. Figure 1.4c, d, e displays the structure of string inverters, whereevery string contains two or more PV panels. Centralized inverters are shown inFig. 1.4f, whose each string provides high voltage so that no further amplification isneeded. However, the centralized inverters would cause power loss and poor powerquality due to the centralized MPPT. Besides, the configurations that containone-stage converter make the inverter sustain all tasks like MPPT and currentcontrol, which may cut its lifespan [13]. Therefore, the structures of Fig. 1.4b, d, ewhich have two-stage converters are widely utilized.

Similarly with solar PV, wind power is almost up to weather and geographiclocation [14]. Wind speed and wind direction are checkered over time, which leadsto wind power fitful, random, and uncontrollable. In order to address these prob-lems, some inverter interfaces that can improve safety and quality when wind power

Fig. 1.3 Wind power global capacity and annual additions from 2007 to 2017 [5] (SourceReproduced with permission of REN21)

1.1 Traditional Source Inverters 3

synchronizes and closes have been proposed [15]. The variable speed systems arewidely used among the current inverter interfaces because maximum wind powercan be extracted by the various speed operations [16]. Among them, the doubly fedinduction generator (DFIG) system and permanent magnet synchronous generator(PMSG) system are two typical various speed systems [17], which are mainlycomposed of wind turbine (WT), generator, and power electronic converters.

The abridged general view of DFIG wind power system is shown in Fig. 1.5, ofwhich the gearbox is designed to adjust speed. It is obvious that the stator of DFIGconnects to the grid directly while the rotor link with grid through power electronicconverters, which makes the power electronic converter work in partial scale.Therefore, the capacity of power converters can be reduced and expected effect canbe reached at a fraction of the cost. Besides, the parallel power converter canachieve separate active and reactive power regulation [15]. It is worth mentioningthat the power converter in Fig. 1.5 is designed as back-to-back (BTB) converter,which is widely used in traditional DFIG wind power system. The rotor side

DC-AC DC-ACDC-AC

DC-DC

DC-AC

DC-DC

DC-AC

(a) (b) (c)

(d) (f)

DC-AC

DC-DC

(e)

DC-DC

Fig. 1.4 Various configurations of PV systems [13] (Source Reproduced with permission ofIEEE)

WT

gearbox

DFIG

AC-DC DC-AC

grid

Fig. 1.5 Abridged general view of DFIG wind power system


converter undertakes the functions that adjusting electromagnetic torque and pro-viding part of reactive power to insure the magnetization of motor, whereas the gridside converter regulates the direct current (DC) link voltage. However, sharpfluctuations in output power of this system are easily caused by unbalanced voltagewhen the stator of DFIG directly connects to the grid [18]. Thus, [15] proposed aseries way on the basis of traditional parallel, which controls the DC-link voltage byincreasing an inverter at the link between output of AC-DC and grid.

Nevertheless, the full-scale power converter is easier to satisfy the requirementof grid connection and more flexible to adjust reactive power [19]. Thus, the PMSGsystem that contains full-scale power converter becomes more and more attractive.Figure 1.6 displays the abridged general view of PMSG wind power system, wherethe gearbox is optional and PMSG is connected with grid through a BTB converterthat can be changed as other power electronic converters according to the rating ofPMSG WTs [20]. Diagrammatic drawing in Fig. 1.6 is adopted when the rating ofWTs is below 0.75 megawatts (MW). Otherwise, when the rating is above0.75 MW, the high power capacitor is required to be handled. To address this issue,the BTB converters connected in parallel, employing multiphase PMSGs, adoptingdistributed power converters are put into practice. Besides, BTBneutral-point-clamped (NPC) power converter that can reduce switch loss andoutput ripples is applied in above 3 MW rating [20]. Moreover a BTB converterwith intermediate boost converter has been proposed in [21, 22] to increase theDC-link voltage at a suitable power rating. Therefore, power converters especiallypower inverters are vital parts whatever in the solar PV or wind power systems.

1.1.2 Traditional Power Inverter Topologies

Traditional power inverters can be classified as voltage source inverters (VSIs) andcurrent source inverters (CSIs), whose basic topologies are illustrated in Fig. 1.7.The basic topology of VSIs shown in Fig. 1.7a is three-phase two-level voltagesource inverter that consists of DC source, input capacitor, three phase legs, outputfilter, and three-phase load. Each leg contains two power transistors with

WT

gearbox PMSG AC-DC DC-AC

grid

Fig. 1.6 Abridged general view of PMSG wind power system


antiparallel diode in series [23]. The inverter is capable of output variable frequencyvariable amplitude sinusoidal waveform and the size of input and output filters canbe reduced when the power transistors are operating at high frequency. Thus, thethree-phase two-level voltage source inverter has been applied in AC motor driver[24], active power filters [25], PV systems [26], and wind power systems [27].

However, high current ripple always exists in applications of VSIs, whichrequires larger capacitors [28]. Besides, shoot-through between two power tran-sistors of the same leg is forbidden [29]. In order to address these issues, a basictopology of CSIs shown in Fig. 1.7b is proposed [30], which has higher reliabilityand inherent over current protection. Besides, multilevel techniques are introducedinto CSIs to decrease the output current’s harmonic content and total harmonicdistortion (THD) [31]. Although CSIs have more benefits than VSIs, the latter aremore widely wielded because the voltage control is easier to implement.

Similarly with CSIs, multilevel voltage source inverters turn up to reduce theharmonic content and THD of output current because the staircase output voltagewaveform is nearly sinusoidal [32, 33]. Besides, compared with two-level voltagesource inverters, multilevel voltage source inverters have lower switching stresses,lower switching frequency, reduced switching losses, lower dv/dt, and EMI.Moreover, multilevel voltage source inverters can produce high voltage levels andbe used for high voltage applications. Cascaded H-bridge (CHB) topology [34],neutral-point-clamped (NPC) topology [35], and flying capacitor (FC) topology[36] are three earlier proposed multilevel voltage source inverters.

S1

S2

S3

S4S6

S5

C1Vdc

Filte

r

Load

or g

ridvavb

vc

(a)

S1

S2

S3

S4S6

S5

Filte

r

Load

or g

rid

vavb vc

Lin

D1

D6

D3

D4 D2

D5C1Idc

(b)

Fig. 1.7 Basic topologies of traditional power inverter


The NPC topology and FC topology both develop gradually from three-levelinverters while CHB topology starts from five-level inverters [37]. Figure 1.8displays five-level CHB inverter where every bridge is able to provide three levelsof voltages. The number of voltage level can be defined as 2m + 1, where mrepresents the number of bridge. One biggest advantage of this topology is thatthere are no additional capacitors and diodes. Thus, the CHB inverter can generatethe same voltage levels by fewer components. Besides, as every bridge of CHBtopology requires one separate DC source, the CHB topology is modularizedeffortlessly. However, the number of separate DC source grows in proportion withthe increase of voltage levels and every source needs real power conversion.

The structure of three-level NPC inverter is illustrated in Fig. 1.9, which adds sixdiodes, six power transistors modules, and one capacitor on the basis of two-level

V1 C1

S11 S13

S14S12

V2 C2

S41 S43

S44S42

S31 S33

S34S32

S61 S63

S64S62

S51 S53

S54S52

S21 S23

S24S22

vavb vc Fi

lter

Load

or g

rid

Fig. 1.8 Five-level cascaded H-bridge inverter

Vdc

S11

S12

S41

S42

S31 S51

S32 S52

S21 S61

S22 S62

C1

C2

D1

D4

D3

D2

D5

D6 Load

or g

ridvavb

vc

Fig. 1.9 Three-level neutral-point-clamped inverter


voltage source inverter. The power transistor is not under full voltage of DC sourceas the capacitors split source into two parts. Thus, the power rating of device can bereduced. Besides, the NPC inverter has high efficiency and need not any filters toreduce harmonics. And it is worth mentioning that reactive power flow can becontrolled [37]. However, the topology of NPC is difficult to be modularized andmore number of diodes is needed for higher levels. As shown in Fig. 1.10, onephase leg of five-level NPC inverter has four diodes and four power transistors morethan that of three-level NPC inverter [38]. Moreover, five-level NPC inverterrequires four capacitors to divide DC source, from which the expression betweenthe number of voltage levels and capacitors can be derived as s + 1, where s rep-resents the number of capacitors.

Figure 1.11 shows the topology of three-level FC inverter, which replaces thediodes of three-level NPC inverter by several capacitors. Similarly with NPCinverter, there are no filters implemented to reduce harmonics. And when poweroutage appears, the FC inverter can provide extra ride through capability. Besides,both real and reactive power flows are controllable [37]. However, as the capacitorsare introduced into the topology, the switching frequency and power losses will behigh for real power transmission [39]. Moreover, the number of components is also

Vdc

S11

S12

S13

S14

C1

C2

D1

D4

va

S61

S62

S63

S64

C3

C4

D2

D5

D3

D6

Fig. 1.10 One phase leg offive-levelneutral-point-clampedinverter


increasing with the voltage level growth, which leads to low efficiency andexpensive cost.

With the development of multilevel inverters, several novel topologies havebeen proposed [40]. For example, P2 [41] and active NPC (ANPC) [42] topologiesare two improved multilevel inverters. Figure 1.12a displays one phase leg of P2topology which integrates NPC topology and FC topology. That makes theimproved inverter inherit advantages of both topologies and can balance the dc-linkvoltage without any extra assistant circuits. Besides, the P2 topology is widelyapplied in PV generation when the capacitors are all replaced by PV panels.Similarly, Fig. 1.12b shows one phase leg of ANPC that possesses the robustnessof NPC topology and flexibility of FC topology.

Beyond those topologies, there are many other hybrid multilevel inverters, suchas one improved cascade inverter as shown in Fig. 1.13. The H-bridge of originalcascade inverter is replaced by blocking diodes scheme, while the H-bridge can alsobe substituted by flying capacitors scheme [43]. These inverters could generatemore voltage levels by less DC source which means fewer modules needed.Besides, soft-switched technology has been introduced into multilevel inverters toreduce switching loss. The insertion of soft-switched assistant circuits makes theswitch work in zero voltage or zero current stage, which results in less energy loss.

Moreover, more and more novel topologies are proposed to improve perfor-mance and adapt in various occasions. In order to analyze the novel topologiesproposed and further research more advanced topologies, several sub-modules arereviewed and summarized from original topologies [40]. Every sub-module has itsown switching characters and different voltages could be output. Therefore, noveltopologies can be proposed through connecting the sub-modules in series, in par-allel, or in other way.

Vdc

S11

S12

S41

S42

S31 S51

S32 S52

S21 S61

S22 S62

C1

C2

Load

or g

ridvavb

vc

C3

C4 C5

Fig. 1.11 Three-level flying capacitors inverter


1.2 Impedance Source Inverters

Traditional VSIs and CSIs can only work in buck (step-down) mode or boost(step-up) mode, respectively, because of the inherited features. Besides, the deadtimes for VSIs and overlap delays for CSIs have to be inserted with the compromiseof slight output waveform distortions. Moreover, the growth of renewable energyrequires wider voltage gain range which is difficult for traditional inverters.Although two-stage traditional inverters that inserting a DC–DC converter betweenthe renewable sources and inverter bridge are proposed to adjust voltage gain range,the complexity and size of system, in turn, increase [44–46]. To address these

Vdc

S1

S2

S3

S4

C1

C2

vaC3

S5 S7

S6 S8

Vdc

S1

S2

S3

S4

C1

C2

va

S5

S6

C3

(a)

(b)

Fig. 1.12 Two improvedmultilevel inverters: a P2topology, b ANPC topology


problems, various single-stage impedance source inverters that can both buck andboost voltages without demanding for dead times or overlap delays have beenproposed [47]. Thus, the impedance source inverters have been introduced into PVpower generation [48–54], wind power generation [55–62], electric vehicles [63–67], and so on.

The earliest topology among impedance source inverters is Z-source inverter(ZSI), which can buck or boost its dc-link voltage by changing the shoot-through(ST) time of the same phase leg [68]. Therefore, the ZSI is less affected by inad-vertent short circuit and waveform distortions caused by dead times and overlapdelays. Figure 1.14 shows the topology of one-phase ZSI, which contains DCsource, impedance network, H-bridge, output filter, and AC load. The impedancenetwork is a two-port network that consists of two inductors (L1 and L2) and twocapacitors (C1 and C2) connected in X shape, which makes the ZSI have inheritedfeatures of impedance source inverters. By simply embedding the impedance

V1

S11

S12

S41

S42

S31

S32

S21

S22

C1

C2

D1

D4

D3

D2

V2

S11

S12

S41

S42

S31

S32

S21

S22

C1

C2

D1

D4

D3

D2

va

Fig. 1.13 Improved cascadeinverter that embraces NPCtopology

1.2 Impedance Source Inverters 11

network between the input source and inverter bridge of traditional three-phasesource inverter, three-phase impedance source inverter is produced. Besides, it isworth mentioning that the impedance network can be transplanted to AC–DC, AC–AC, and DC–DC power conversion so that similar function could be realized.Therefore, the impedance network is the most vital part of impedance sourceinverters and even impedance source converters.

In order to briefly analyze the structure of ZSI, the H-bridge, output filter, and ACload are simplified as a switch SW and a current source Io in parallel shown inFig. 1.15. The ZSI can be divided into ST state and non-shoot-through (NST) stateaccording to whether the power transistors of same phase leg are conductingsimultaneously. When the inverter steps into ST state, the equivalent switch SW turnson thus the current source Io is short-circuited and inactive. The SW turns off whenZSI turns to the NST state, and Io is active at this time which represents AC load isconnected with source and works steadily. Figure 1.16a illustrates the ST operatingstate of ZSI, while NST state of that is shown in Fig. 1.16b. The switch state of diodeD1 is contrary to SW and then voltage and current stresses of ZSI could be derived.

However, the ZSI still has some drawbacks that affect performance of inverter.Thus, several improvements are gradually introduced to ZSI. For example, thebidirectional ZSI (BZSI) was proposed to exchange energy between AC and DC inboth directions [69]. The high-performance improved ZSI (HP-IZSI) proposed in

AC Load

S1

S2

S3

S4

Lf

Cf

D1

Vin

vdc

L1

L2

C2C1

Fig. 1.14 Topology of Z-source inverter

D1

Vin

L1

L2

C2C1 SWvdc

Io

Fig. 1.15 Equivalent circuit of Z-source inverter


[70] can limit its inrush current at startup and reduce stresses across its capacitors.And the quasi-ZSI (QZSI) has been proposed in [71] to obtain a continuous inputcurrent. Besides, in order to realize a higher boost with the same ST duty ratio,switched inductor and switched capacitor ZSI emerged [72, 73]. However, thehigher voltage is required, the more diodes, inductors, or capacitors are needed. Theextra components increase complexity and cost, and hence lead to the switchedcomponent ZSI unprepossessing. Similarly, extended boost ZSI which boosts widerrange voltage through combination of some impedance networks [74]. Thisincreases the number of components, which may also lower efficiency of inverter.

To reduce components without compromising gain, coupled inductor impedancesource inverters (CISIs) have been proposed in [75–81], such as T-source inverter(TSI), gamma-Z-source inverter (ГSI), Y-source inverter (YSI), and so on.Each CISI embedded coupled inductor boosts the output voltage by altering theturns ratio of the coupled inductors. Besides, CISIs can achieve a higher boost evenin a small ST duty ratio compared with other impedance source inverters. However,the introduction of coupled inductor renders the appearance of leakage inductancewhatever cores or winding techniques are employed, which induces operatingproblems. For instance, when the CISI transfers from ST to NST state, a greatvoltage spike will occur at the dc-link due to a sharp change in current through theleakage inductors. Thus, higher rated switches are required to avoid damages whichwill push up the production cost. Moreover, part of ST duty ratio will be lost whentransferring from NST to ST state. Thus, some energy is wasteful, in turn, the

Vin

L1

L2

C2C1SW

vdcIo

Vin

L1

L2

C2C1SW

vdcIo

(a)

(b)

Fig. 1.16 Operating states of Z-source inverter: a ST state, b NST state


efficiency of inverters deceases. Obviously, these issues limit practical applicationof CISIs, unless the DC-link voltage spikes could be avoided and the lost energy onthe leakage inductors can be recycled.

One of themethods that is reducingDC-link voltage spikes is changing the structureof coupled inductors. The method brought up in [82] decreases the leakage inductanceas well as series resistance on each winding of three-winding CISI by applying a Δ-connection rather than Y-connection. But the third winding depends on the other twowindings using the Δ-connection structure. Thus, the voltage regulating degree offreedom of coupled inductors decreases which results in the three-winding coupledinductors to perform quite similarly with dual-winding coupled inductors. Besides, thismethod cannot reduce the DC-link voltage spikes totally causing the leakage inductorsstill exist in the circuit.

Another method is adding an extra absorbing circuit, which can either be of theactive or passive type, even if the common purpose of both types is providing a way toabsorb the lost energy caused by the leakage inductors. For instance, an active DC–DCbuck converter has been applied to the inverter for recycling leakage energy to thecapacitors or source [83]. However, the introduction of buck converter also increasesone power transistor, which in turn leads to the higher control complexity and cost.Therefore, the passive type without any extra power transistors is more appealing.

One of the passive absorbing circuits also proposed in [83] relies on capacitors anddiodes for clamping the DC-link voltage, as shown in Fig. 1.17a. The absorbingcircuit is drawn in red, while Lcouple represents the coupled inductors which can bedual winding or three winding. However, a huge current will flow through the inputvoltage Vin, diode DS2, capacitor CS1, and shorted phase leg in the ST state, sincethere are no series-wound sizable limiting inductance. Then the current is instanta-neously large and in turn may damage power transistors or other semiconductordevices unintentionally. To limit this large current, an improved absorbing circuit isproposed in [84] where a series inductance is introduced into the ST loop. The diodeDS1 conducts only during the transition of ST to NST state, which can clamp thedc-link voltage in series with CS1 and C1 as shown in Fig. 1.17b.

Figure 1.17c illustrates a simplified absorbing circuit which can realize thefunction similarly with circuit 2 shown in Fig. 1.17b [85]. The spiky DC-linkvoltage can be clamped during the transfer from ST to NST state by DS in serieswith capacitors C1 and C2. However, the usable range of both circuit 2 and circuit 3shown in Fig. 1.17c is limited. They are only suitable for several specific CISIs.[86] introduces a novel passive absorbing circuit which clamps the dc-link voltageby diode DS and capacitors (CS and C2) in series. This absorbing circuit can begeneralized to all CISIs and has various configurations when it is applied to onespecific topology, one of which has been displayed in Fig. 1.17d. Besides, neotericpassive absorbing circuits embedding other enhanced functions are gradually pro-posed. One clamping circuit that can also increase voltage gain is proposed in [87].As shown in Fig. 1.17e, it almost could be regarded as the CISI cascaded withQZSI, thus the voltage gain is further enhanced. Detailed introduction and othermore novel absorbing circuits will be presented in Chap. 6.


Vin

D

CS1

CS2

DS1DS2

C

Lcouple

vdc

Lin

Vin

D

CS1

DS2DS1

Lcouple

C2

C1vdc

Lin

Vin

D

DS

Lcouple

C2

C1vdc

Lin

Vinvdc

C2

C1

D1DS

CS

C2

C1

D1

Lin

Vin

CS2

DS

CS1

LS

vdc

(a) (b)

(c) (d)

(e)

Fig. 1.17 Illustration of passive absorbing a circuit 1 [83], b circuit 2 [84], c circuit 3 [85],d circuit 4 [86], e circuit 5 [87]

Therefore, more and more improvements of impedance source inverters withoutthe compromise of inherited excellent features are turning up. In order to rightlyanalyze and design the impedance source inverters, it requires more uniformly validsteady and transient analysis methods. Besides, the reliability research on impedancesource inverters is noteworthy to work steadfastly. Moreover, impedance sourceinverters have not only been applied in photovoltaic power generation and windpower generation, but also introduced to application of power decoupling, motordrive, and so on. All of these will be introduced in detail in the latter chapters.

1.3 Classification and Future Trends

1.3.1 Classification of Impedance Source Inverters

The impedance source inverters have become very attractive since their appearance.Navigating through the history of impedance source inverters, there are severalcontrol techniques proposed to improve the performance of impedance source


inverters. Simple boost PWM (SBPWM) is the earliest control technique proposedin [88], which is also the simplest. However, the voltage stresses of switches arehigh. Thus, maximum boost PWM (MBPWM) is introduced to limit the highvoltage stresses of switches [88]. But low-frequency high-magnitude ripples relatedto the dc-link voltage fundamental frequency result in the size of impedance net-work to increase. In order to address both issues produced by SBPWM andMBPWM, constant boost PWM (CBPWM) is born, which can decrease the rippleswith relatively low voltage stresses [89].

Besides, modified space vector PWM (MSVPWM) is applied to the impedancesource inverters with the extensional principle of space vector PWM [90, 91]. Theoperational range of linear relations is wider under the control of MSVPWM.Moreover, [92] proposes a novel control technology that named discontinuousPWM (DCPWM), which separates the boosting factor and modulation index so thatthe impedance source inverter could operate in a relative high stable status.However, the improvement of control technology still has small effect on theperformance of impedance source inverters. The structure advancement of impe-dance source inverters impacts the their capability greatly.

There are multiple generations of impedance source inverters with the devel-opment of technology, as shown in Fig. 1.18. Since the impedance source invertersare improved from traditional voltage source and current source inverters byinserting an impedance network, they can be classified into voltage-fed andcurrent-fed impedance source inverters. Besides, the vital inserted impedance net-work allows the inverters to operate in ST state and adjust output voltage freely;therefore, almost all improvements are about the impedance network.

As is shown in Fig. 1.18, the impedance network topologies could be dividedinto four categories, i.e., constant boost ratio topologies, improved boost ratiotopologies, multilevel and multiplex topologies, and parameter optimizationtopologies. The impedance source inverters which contain constant boost ratiotopologies have the common feature that the boost factors are all the same as that ofbasic ZSI. And the constant boost ratio topologies can be further subdivided into sixsorts. The first sort is Z-source topologies, which mainly contains basic ZSI [68].

And the second sort of constant boost ratio topologies is improved Z-sourcetopologies, which is based on the ZSI, such as BZSI [69], high-performance ZSI(HP-ZSI) proposed in [93], improved ZSI (IZSI) proposed in [94], and so on.Among them, HP-IZSI is produced by combining the IZSI and HP-ZSI [70].Besides, series Z-source inverter (SZSI) and quasi-resonant soft-switching ZSI(QRSSZSI) are modified from IZSI [95, 96]. While the third sort that neutral pointZ-source topologies mainly includes four-wire ZSI (FWZSI) [97], four-leg ZSI(FLZSI) [98], dual ZSI (DuZSI) [99], and neutral point ZSI (NPZSI) [100].

The fourth sort of constant boost ratio topologies is reduced leakage currentZ-source topologies, which is divided into ZSI with diode (ZSI-D) and ZSI withswitch (ZSI-S) [101, 102]. In order to make the input power source and the dc-linkshare common ground, the fifth sort quasi-Z-source topologies are proposed [71].Moreover, there are other basic Z-source topologies that distributed ZSI (DiZSI)


[103], embedded ZSI (EZSI) [104], and bidirectional QZSI (BQZSI) [65], whichbelongs to the sixth sort. All the impedance source inverters consisting of constantboost ratio topologies will be presented in Sect. 1.2 of Chap. 3.

Impedance network

topologies

Voltage fed

Current fed

Constant boost ratio topologies

Improved boost ratio topologies

Multilevel and multiplex topologies

Parameter optimization topologies

Z-source topologies

Improved Z-source topologies

Neutral point Z-source topologies

Reduced leakage current Z-source topologies

Quasi-Z-source topologies

Other basic Z-source topologies

Switched components Z-source topologies

Tapped inductor Z-source topologies

Cascaded quasi-Z-source topologies

Coupled inductors Z-source topologies

Three-level Z-source topologies

Five-level Z-source topologies

Cascaded multilevel Z-source topologies

multiplex Z-source topologies

High-frequency transformer isolated Z-source topologies

Inductor Z-source topologies

Extend quasi-Y-source topologies

Low dc-link voltage spikes Y-source topologies

Other optimized topologies

Fig. 1.18 Classification of impedance source inverters

1.3 Classification and Future Trends 17

As for the improved boost ratio topologies, which are opposite to the constantboost ratio topologies, the boost factor of these type impedance source inverters isenhanced. Generally, they can be divided into four sorts, i.e., switched componentsZ-source topologies, tapped inductor Z-source topologies, cascaded quasi-Z-sourcetopologies, and CISIs, where the switched components could further be subdividedinto switched inductor and switched capacitor Z-source topologies [72, 73]. Theswitched inductor or switched capacitor is a cell composed of inductor or capacitorwith diodes. Then the switched inductor Z-source topologies are produced when theinductors of constant boost ratio topologies are displaced by switched inductorcells, while the switched capacitor Z-source topologies are similarly replaced byswitched capacitor cells [105–112].

Similarly with switched inductor Z-source topologies, tapped inductor Z-sourcetopologies replace the inductors by tapped inductor cells, which consist of tappedinductors and diodes [113, 114]. As the quasi-Z-source topology processes thecapability of extending boost factor without extra active switches, thequasi-Z-source topology could be an extended passive boost cell, so that the cas-caded quasi-Z-source topologies are proposed [115–117]. Besides, the cascadedquasi-Z-source topologies are subdivided into capacitor-assisted (CA) anddiode-assisted (DA) topologies whether the connecting component ofquasi-Z-source cell is capacitor or diode. These three improved boost ratiotopologies mentioned will be introduced in Sect. 1.3 of Chap. 3.

Moreover, the latest improved boost ratio topologies, namely, CISIs are widelyemployed because the coupled inductors reduce the quantity of passive componentsneeded in the impedance network [118]. Therefore, the power density of CISIs can beimproved and the cost is reduced accordingly. There are various topologies belongingto CISIs, such as TSI [83], trans-quasi-Z-source inverters (trans-QZSI) [75], improvedtrans-QZSI [84], transformer ZSI (TZSI) [79], inductor-capacitor-capacitor-transformer ZSI (LCCT-ZSI) [77], ГSI [78], YSI [80], improved YSI (IYSI) [81],and so on. All of these topologies will be recommended in Chaps. 4 and 5.

The multilevel technology can also be applied to impedance source inverters liketraditional inverters, thus the multilevel and multiplex topologies emerge at theright time. Similarly, the multilevel topologies contain three-level and five-leveleven more level topologies [119–123]. Besides, the multilevel ZSI could be cas-caded to get higher voltage gain and system reliability [124, 125]. Moreover,dual-input or dual-output ZSIs have been proposed for specific application [126,127]. The detailed introduction of multilevel and multiplex topologies will bepresented in Sect. 1.4 of Chap. 3.

In order to make the impedance source inverters fit different occasions, plentifulimproved researches have been underway. For example, high-frequency trans-former isolated ZSI (HFTI-ZSI) proposed in [128] can achieve electrical isolationand reduced device stresses. Besides, the inductor Z-source inverter (L-ZSI) whichavoids the disadvantages caused by capacitors is proposed in [129]. As mentionedin last section, great DC-link voltage spikes and ST duty loss of CISIs always existswhich might damage devices. Therefore, extended quasi-Y-source inverter (par-ticular introduction in Chap. 5) [130] and various low DC-link voltage spikes


Y-source inverters (detailed presentation in Chap. 6) emerge. Without doubt, moreand more optimized impedance source inverters are being studied to achieve higherperformance and are generalized to more applications.

1.3.2 Future Trend of Impedance Source Inverters

Obviously, the mentioned improvements of impedance source inverters are almostabout impedance network and little amelioration is concentrated on the followinginverter bridge. Although the impedance source inverters which contain multileveland multiplex topologies are improved by changing the inverter bridge’s structure,they could be further developed in the following stages. For example, the inverterbridge of multilevel impedance source inverter can be not only the diode NPCstructure, but also FC structure, cascade H-Bridge, P2 structure, ANPC structure, oreven more novel hybrid multilevel structure.

Moreover, with the development of wide bandgap semiconductors, powerelectronics field is vibrant. The bandgap semiconductors provide more interestingfeatures than traditional silicon (Si) semiconductors, such as reduced energy loss ofswitching, high blocking voltage, and less influence by temperature [131].Therefore, higher power density and efficiency of power electronic systems can berealized. On the basic of wide band gap semiconductors, impedance sourceinverters can also develop towards higher efficiency and higher power density.

Besides, the reliability of power electrical systems is also important because itrelates to the life of systems. However, current reliability analysis focuses on thecomponents other than the whole impedance source inverters or even the PVsystems that contain the impedance source inverters. Therefore, the reliabilityanalysis of PV systems or wind power systems composed of impedance sourceinverters and other power electricity will be one direction of development.Moreover, the power rate of impedance source inverters will be further improvedwith the development of PV generation and wind power generation.

The above mentioned are about the hardware improvements of impedancesource inverters; however, the control of impedance source inverters is also onefuture direction. The traditional control technologies of impedance source inverterscan be perfect and proposing one novel control method. And the control tech-nologies could also be combined with technologies implemented on originalapplications, such as the combination with MPPT of PV generation.

1.4 Contents Outline

Obviously, concepts, advantages, classification, and future trend of impedancesource inverters have been summarized in this chapter. Then Chap. 2 introducesand analyzes in detail the original Z-source inverter including its operation

1.3 Classification and Future Trends 19

mechanism, modulation, and closed-loop control. The developments of impedancesource inverters are presented in Chap. 3 later, where improvements such as boostability enhancement and parameter optimization are presented based on whichmany popular and practical derived topologies from original Z-source inverter areintroduced systematically. After that, dual-winding impedance source inverters andthree-winding impedance source inverters are introduced in detail in Chap. 4 andChap. 5, respectively. The suppression methods of DC-link voltage spikes and dutyloss which would be a problem for most researchers are summarized and imple-mented in Chap. 6. Common current and voltage analysis method that is givenalong with the introduction of a new efficient way of calculation stresses is intro-duced in Chap. 7. After this, failure mechanism and lifetime prediction of impe-dance source inverters are discussed to guarantee their reliability, which ismentioned in Chap. 8. For conclusion, the impedance source inverter powerdecoupling method and applications in different occasions are given in examples forpractical purposes.

In general, in this book, the suppression methods of DC-link voltage spikes andduty loss which would be a problem for most researchers are summarized andimplemented. Novel, efficient steady-state and transient analysis methods of sig-nificant practical value which are proposed originally will be covered by specificcalculation examples. Other than that, the reliability of impedance source invertersis first introduced which adopts methodology from reliability engineering to studythe reliability in components and system of impedance source inverters. Manyexamples are given for the application of impedance source inverters which helpengineers to directly use them in practice.

Moreover, the book is organized in a clear and coherent way which summarizesall the existing topologies of impedance source inverter more thoroughly than anypublished books up to date. The book will give the readers an in-depth knowledgeon the advantages and disadvantages of these impedance source inverters throughcomparative discussions, tables, and figures. Examples given in the book will havefull explanation along with detailed calculation to help understanding. Confirmatorysimulations and experiments will be given in the book to strengthen thepersuasiveness.

References

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impedance source inverters - download.e-bookshelf.de€¦ · hongpeng liu † zichao zhou † yuhao...

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