instantaneous active and reactive power … active and reactive power control in off-grid smart...

INSTANTANEOUS ACTIVE AND REACTIVE POWER CONTROLIN OFF-GRID SMART HOUSE

Takashi Oki1, Hidehito Matayoshi1, Hayato Tahara1, Gul Ahmad Ludin1,Sharma Aditya1 and Tomonobu Senjyu1

1Faculty of Engineering, University of the Ryukyus,Okinawa, Japan 903-0213

ABSTRACT

Reduction of carbon dioxide emissions is a big chal-lenge for the entire world. Therefore, a residentialphotovoltaic (PV) system has recently begun to spreadand the increasing penetration rate of the renewableenergy is expected. However, output power from PVdepends on isolation condition and entails uncertainty.So if many PV systems are integrated into the elec-trical power system, voltage and frequency fluctua-tion in the power system will occur. Therefore, re-duction of PV generation or isolation from the powersystem is required to the demand side. In this study,the completely off-grid smart house which is not con-nected with the power system is proposed. In thehouse, off-grid PV system, storage battery, electricalvehicle (EV), and Home Energy Management System(HEMS) are introduced.

INTRODUCTION

The carbon dioxide reduction is a big challenge forthe entire world. Accordingly, the energy efficiency ofhousehold is recognized major problem. As a methodto this problem, Home Energy Management System(HEMS) is presented in (Yoshikawa and Awai, 2011;Niyato et al., 2011; Han and Lim, 2010; Son et al.,2010; Jin and Kunz, 2011). HEMS automatically per-form energy saving without manual action. In off-grid smart house, the power from PV system and thechanges of consumption causes steep fluctuation of thepower supply voltage. This fluctuation have adverseeffect to the home electric appliances. In previousstudies, related to inverter control, the inverter is op-erated with feedback control based on the root meansquare or average value of voltage in (Jung et al., 2007;Hu et al., 2011; Tirumala et al., 2002). These con-trol methods cat not suppress steep voltage fluctuation.For solving this problem,this research study appliesthe inverter control method based on single phase dqtransformation system (Yamauchi et al., 2012; Miyagiet al., 2014). In order to put the off-grid smart houseinto practice, a consideration of the state of charge(SOC) for a fixed battery is needed. In this study,the HEMS adjusts the energy consumption of elec-tric appliances considering the battery remaining ca-pacity to avoid the shortage of energy. Furthermore,efficient operation of PV is performed by Maximum

Power Point Tracking (MPPT) (Esram and Chapman,2007). The effectiveness of this study is verified byMATLAB/SimPowerSystems.

SYSTEM MODELThe smart house model is shown in Figure 1. In thismodel, HEMS is able to control electric appliances.The communication between HEMS and appliancesis performed by wireless communication techniques.The fixed battery with a capacity of 2 kWh and an in-verter with a rated output of 3kW has been introduced.Simulation circuit is illustrated in Figure 2. The DC-DC buck-boost converter which is connected to PVpanels executes the MPPT control of PV. To keep avoltage in the DC-Link, the DC-DC boost converteris connected to the DC-Link. Moreover, a fixed bat-tery is also connected to the DC-Link. In this way, thepower losses can be decreased, because the power in-verter for a battery is not required. There is another ad-vantage that it will maintain the level of output powerfrom PV.

PV SystemThe model of the PV array is simulated by basic equa-tion and current source (Itako and Mori, 2005). Table1 shows the parameters of PV. The Single-Ended Pri-mary Inductance Converter (SEPIC) is used as a DC-DC converter for PV (Duran et al., 2011). Figure 3illustrates SEPIC. SEPIC has both advantages protec-tion for the occurrence of a short-circuit and same po-larity of input and output voltages.

Fixed Battery SystemA fixed battery is connected to DC-DC boost con-verter, which is shown in Figure 4. The DC-DC con-verter boosts the output voltage of a battery from 200Vto 350V. The Droop control method is applied for thepurpose of maintaining the voltage in the DC-Link.The current command value for the DC-DC converteris determined by the PI control using SOC for a fixedbattery. The bttery control system is shown in Fig-ure 5. The allowable voltage range in the DC-Link is±20V (VDC=330∼370V).

INVERTER CONTROL METHODIn this section, the inverter control method based oninstantaneous active and reactive power is explained.

Proceedings of BS2015: 14th Conference of International Building Performance Simulation Association, Hyderabad, India, Dec. 7-9, 2015.

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DC

DC

PV

DC

AC

Power

Conditioner

DC

DC

Battery

HEMSPower Control

Wi-FiZigBee

DC-DC

Converter

Loads

Figure 1 Configuration of smart house

PV

200V

Battery

VDC

DC

DC

L3

Vr =

iL

S1

S2

S3

S4

DC

DC

ipv

ib

Lf

Cf

L1L2

L4100VVp =

100VVn =

200V

10Ah

2kW

2kWh

3kW

Lf

6kVA

Figure 2 Simulation circuit

IPV

C3

C 2L1

S

D1

PV

+

-

L2

C 1

IDC

VDC

VPV

VPV

IPV

MPPT control+

-

Vmax

PI PWM

SEPIC

Figure 3 SEPIC

S2

Ldc

Cdc

S1

Battery200V

Figure 4 Battery converter

VDC

V*

DC

Rb

ξb

ξ*

b

PI2

I*

b+

+

+

+

-

PWM

I*

b

- -

+PI1

Ib

PI3+

-Droop control

Figure 5 Battery control system

Phase DetectionThe voltage of power supply in the smart house is af-fected by the fluctuation of PV output power. Hence,

Table 1 PV panel constantsPV short-circuit current[A] 18.3PV open circuit voltage[V] 230.0Diode saturation current[A] 1.94×10−16

PV Short-circuit currentat18.3

at standard temperature[A]Diode saturation current

1.94 ×10−16

at standard temperature[A]Standard cell temperature[K] 298Amount of solar radiation[kW/m2] 1Area of a solar panel [m2] 1.47Number of solar panels 14The total area of solar panels [m2] 20.58Energy gap[V] 1.767 ×10−19

Elementary charge[C] 1.6 ×10−19

Boltzmann’s constant 1.38 ×10−23

Constant independent of temperature 2.0 ×10−2

Junction constant1.95

(determined by the materialConstant determined by the material 2.8

the Phase-locked loop circuit that can estimate phasein a high accuracy is required. This research uses theALOF-PLL circuit to estimate the phase (Han et al.,2009).

The Single Phase dq Transformation SystemThe root mean square value (RMS) VRMS is calcu-lated from AC voltage v =

√2V sin(ωt) as follows:

VRMS =

√1

T

∫ T

0

v2dt

=

√1

T

∫ T

0

(√2V sinωt)2dt (1)

If this equation is used to estimate the phase of thevoltage, the command signal is delayed. The delayhas the risk of an accident with appliances. The con-trol method using the single-phase dq transformation,estimates an instantaneous voltage value. Figure 6 il-lustrates Single-phase dq transformation system. In-put voltage V is converted into digital signals v andv′. Where, the digital signal v′ is delayed δθ from v inthe phase by a delay block. Figure 7 shows the digitalsignals v and v′. The ∆v that is difference between vand v′ can be calculated as follows:

∆v = v − v′ =√2V sinωt−

√2V sin(ωt− δθ)

=√2V sinωt−

√2V sinωt cos δθ

+√2V cosωt sin δθ (2)

where, V sinωt and V sinωt cos δθ are eliminatedin the analogue/digital conversion processing. Then,only

√2V cosωt sin δθ keep remains. Moreover, ∆v

is obtained as shown in Figure 8. The β axis com-ponent vβ can be obtained by holding the ∆v for 10µs and multiplying by K = 1/ sin(δθ) as shown in


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Delayv β

vα vα

2+vβ

2Vd

_ K Hold

Circuit

10µs5µs

AD

100ksps

vv

v’ ∆v

Figure 6 Single-phase dq transformation system

0.29995 0.3 0.3001-20

-10

0

10

Time t [s]

v , v

’[V

] v

v’

0.30015

Figure 7 v and v′

0.29995 0.3 0.30010

0.5

1

Time t [s]

∆v[V

]

0.30015

Figure 8 Differntial value , ∆v

0.29995 0.3 0.30010

100

200

300

400

Time t [s]

vβ[V

]

0.30015

Figure 9 beta axis component, vβ

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8-500

0

500

v[V

]

Time t [s]

Figure 10 Input voltage, v

Figure 9. By defining v as the α-axis component, thed-axis component Vd and q-axis component Vq are ob-tained as follows:

Vd = vα sinωt+ vβ cosωt =√v2α + v2β (3)

Vq = vα cosωt− vβ sinωt = 0 (4)

The instantaneous magnitude√2V of input voltage v

can be obtained calculating Vd using vα and vβ . Theinput voltage v is shown in Figure 10. Furthermore,Figure 11 illustrates magnitude of input voltage Vm ascalculated by the proposed system and the RMS valueVRMS which is calculated by conventional method.It is obvious that output response of the single-phasedq transformation system is faster than the system re-sponse using RMS value.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

100

200

300

Vm, V

RMS[V

]

Time t [s]

Vm = V

d / 2

VRMS

Figure 11 Magnitude of input voltage, Vm and VRMS

Vm

Im

θ

from ALOF-PLL sinθ

cosθ

P=VmImcosθ

Q=VmImsinθ

Figure 12 Active and reactevi power detection circuit

Active and Reactive Power DetectionFigure 12 shows the active and reactive powers detec-tion circuit. This circuit calculate active and reactivepowers P , Q using the single-phase dq transformationsystem, and phase difference, θ, between Vr and Iinvas follows:

Pinv = VmIm cos θ (5)Qinv = VmIm sin θ (6)

Command Value Determination for Inverter Con-trolA single-phase inverter, controls the magnitude andphase of the output current. In this research, due to us-ing PQ feedback control, the current command valueis determined by the PQ information that has beendetected by the active and reactive powers detectioncircuit. Then, rearranging Equations (5) and (6), themagnitude of the output current command value Icomand the phase difference θ are calculated as follow:

Icom =

√P 2inv +Q2

inv

Vm(7)

θ = arcsinQinv

VmIm(8)

By substituting the command values P ∗inv, Q

∗inv for

Pinv , Qinv in above equation, the inverter output cur-rent command can be determined as follow:

Iref =√2Icom sin(ωHt∗ + θ) (9)

In this study, the inverter uses control method based onthe instantaneous active and reactive powers feedbackcontrol. The inverter control system is shown in Figure13. The load voltage Vr and DC-Link voltage VDC arecontrolled by the inverter using PWM control.


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Pinv

Qinv

VDC

*

Vr*

Vr =Vm

VDC PI

+-

Pinv*2

+Qinv*2

VmVm

Iref

Pinv*

Qinv*

sin(ωHt*+θ)

ωHt*

PWM

fs=20kHz

ωUt

++

+

-

-

+

Im

Before phase synchronization

PI

After phase synchronization

Figure 13 Inverter control system

SOC < 70%

Limit load according to load priority

Turn off according to load priority

Yes

Yes

No

No

SOC < 50%

SOC < 70.02%

Yes

Turn on / No limit load

No

Figure 14 Load management algorithm for HEMS

HEMSEnergy management in the proposed smart house isachieved by the HEMS. The algorithm of energy man-agement is shown in Figure 14. The power consump-tion of appliances are adjusted considering SOC forthe battery. The adjusting of power consumption isperformed based on priority level of all appliances.

SIMULATION RESULTSIn the proposed smart house, in order to avoid deple-tion of the SOC for a storage battery, HEMS adjuststhe power consumption based on priority of loads. Thepriority of critical loads in order of highest to lowest isL1, L2, L3, L4. L1 is supplied with a stable powerduring all the time. In order to confirm load controlby the HEMS during simulation time that is 4 sec-onds, the initial value of SOC for the storage batteryis set 70.003%. When the SOC for the storage bat-tery is less than 70%, the loads are controlled by theHEMS. The simulation result is illustrated in Figures15∼26. Figure 15 shows the inverter output currentIinv. The inverter output current is decreased by the

0 0.5 1 1.5 2 2.5 3 3.5 4−20

−10

0

10

20

Time t [s]

Iin

v [

A]

Figure 15 Inverter output current, Iinv

0 0.5 1 1.5 2 2.5 3 3.5 4−400

−200

0

200

400

Time t [s]

Vr [

V]

Figure 16 Receiving voltage, Vr

0 0.5 1 1.5 2 2.5 3 3.5 4-1000

0

1000

2000

3000

Time t [s]

Pin

v [

W]

, Q

inv [

var]

Pinv

Qinv

Figure 17 Output active and reactive power of inverter,Pinv , Qinv

HEMS due to low SOC for the storage battery. Figure16 shows receiving voltage Vr which is 200V. Accord-ing to Figure 16, regardless of the adjusting of load,the receiving voltage was maintained at a 200V. Theinverter output active and reactive powers Pinv , Qinv

are shown in Figure 17. In Figure 17, it is clear that in-verter output active and reactive powers are decreasingduring low consumption of load. Figures 18, 19 showsthe DC-Link voltage VDC and the output current of thestorage battery, Ib respectively. The DC-Link voltageVDC is maintained at a 350V by the control of the in-verter and the storage battery. Figure 20 shows theSOC ξb for the storage battery. The different SOCsfor the storage battery are illustrated due to with orwithout load control. The frequency of receiving volt-age fH is shown in Figure 21. According to Figure21, the frequency of receiving voltage is maintained at60Hz. Figures 22, 23, 24 show the amount of solarradiation, IN , the output current of the PV, IPV , andthe output voltage of the PV, VPV respectively. TheMPPT control is performed by using the hill climb-ing method in 1.4s cycles. Figure 25 shows the loadcurrents IL1, IL2, IL3, IL4 with load control. In thisFigure, it is clear that the load currents IL2, IL3 andIL4 are limited by HEMS when SOC of battery is low.On the other hand, Figure 26 shows the load currentsIL1, IL2, IL3, IL4 without load control. In this Figure,the load currents are constant.


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0 0.5 1 1.5 2 2.5 3 3.5 4250

300

350

400

Time t [s]

VD

C [

V]

Figure 18 DC-Link voltage, VDC

0 0.5 1 1.5 2 2.5 3 3.5 4−5

0

5

10

Time t [s]

Ib [

A]

With load control

Without load control

Figure 19 Output current of storage battery, Ib

0 0.5 1 1.5 2 2.5 3 3.5 469.97

69.98

69.99

70

70.01

Time t [s]

ξb [

%]

With load control

Without load control

Figure 20 State of charge for storage battery, ξb

0 0.5 1 1.5 2 2.5 3 3.5 40

20

40

60

80

Time t [s]

fH

[H

z]

Figure 21 Frequency of receiving voltage, fH

0 0.5 1 1.5 2 2.5 3 3.5 4

0.7

0.8

0.9

1

Time t [s]

IN

[kW

/m2]

Figure 22 Insolation, IN

0 0.5 1 1.5 2 2.5 3 3.5 4−10

0

10

20

Time t [s]

IP

V [

A]

Figure 23 Output current of PV, IPV

CONCLUSIONIn this paper, the completely off-grid smart housewhich is not connected with the power system is pro-posed. The off-grid PV system, storage battery, EV,

0 0.5 1 1.5 2 2.5 3 3.5 4−100

0

100

200

300

Time t [s]

VP

V [

V]

Figure 24 Putput voltage of PV, VPV

0 0.5 1 1.5 2 2.5 3 3.5 4−10

−5

0

5

10

Time t [s]

IL

1 [

A]

(a) Load current with control, IL1

0 0.5 1 1.5 2 2.5 3 3.5 4−4

−2

0

2

4

Time t [s]

IL

2 [

A]

(b) Load current with control, IL2

0 0.5 1 1.5 2 2.5 3 3.5 4−10

−5

0

5

10

Time t [s]

IL

3 [

A]

(c) Load current with control, IL3

0 0.5 1 1.5 2 2.5 3 3.5 4−10

−5

0

5

10

Time t [s]

IL

4 [

A]

(d) Load current with control, IL4

Figure 25 Load currents with control

and HEMS have been introduced into the smart house.In the off-grid smart house, the bad influence to appli-ances due to fluctuation of the PV output power is rec-ognized problem. Furthermore, because the house cannot receive the electric power from power grid, the de-pletion of energy in storage battery should be avoided.By applying the dq transformation system to controlthe inverter instead of conventional control system,instantaneous inverter control is achieved. This hassuppressed the voltages and frequency fluctuation ofpower supply. Moreover, in order to save the elec-tric energy, the HEMS controlled power consumptionof electric appliances considering SOC for the storagebattery.


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0 0.5 1 1.5 2 2.5 3 3.5 4−10

−5

0

5

10

Time t [s]

IL

1 [

A]

(a) Load current without control, IL1

0 0.5 1 1.5 2 2.5 3 3.5 4−4

−2

0

2

4

Time t [s]

IL

2 [

A]

(b) Load current without control, IL2

0 0.5 1 1.5 2 2.5 3 3.5 4−10

−5

0

5

10

Time t [s]

IL

3 [

A]

(c) Load current without control, IL3

0 0.5 1 1.5 2 2.5 3 3.5 4−10

−5

0

5

10

Time t [s]

IL

4 [

A]

(d) Load current without control, IL4

Figure 26 Load currents without control

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instantaneous active and reactive power … active and reactive power control in off-grid smart...

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