dc to ac inverter with dsc

8/10/2019 DC to AC Inverter With DSC

1/23

TM

Freescale Semiconductor Confidential and Proprietary Information. Freescale and the Freescale logo are trademarks

of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. Freescale Semiconductor, Inc. 2006.

Stanislav Arendrik, (Aug 2010)

DC to AC Inverter for Solar Panel


2/23

TMFreescale Semiconductor Confidential and Proprietary Information. Freescale and the Freescale logo are trademarks


Main Topics

Main topics:

Solar panel description and characteristics Main parameters of the inverter

Structure and block schematic of the inverter

Blocks description

1


3/23



Solar cell simple description

Photons in sunlight hit the solar panel

and are absorbed by semiconductor

materialsilicon.

Electrons (negatively charged) are

knocked loose from their atoms, allowing

them to flow through the material to

produce electricity. Due to special

composition of solar cell, the electrons

are only allowed to move in a single

direction.

An array of the solar cells converts

solar energy into a usable amount ofdirect current (DC) electricity.

2

source: wikipedia


4/23



Solar cell characteristics

A solar cell may be modeled by a current source in parallel witha diode, shunt and series resistances.

IL represents the max current of the solar panel (short current)

Diode forms the I-V characteristic

Shunt resistor represents the leakage currents (very small)

Series resistance represents the wiring losses

3


5/23



Solar cell characteristics - variations

For most crystalline silicon solar cells the change

in VOC

with temperature is about -0.50%/C

Impact of the product of the series resistor andshort-circuit current (I

SCRS) is about 25mV/cell.

Impact of the parallel resistance is small.

4


6/23



Solar cell characteristics example

The maximum power point (MPP) on the I-V curve varies with real working conditions

high dependency on the irradiance and lower dependency on the temperature.

5


7/23



Maximum Power Point

In the technical parameters of the solar cellpanel are defined:

VMP

voltage at MPP

IMP

current at MPP

The Inverter for the solar cell panel must

achieve the operation on the MPP. Thismethod is called as MPPTmaximum power

point tracking.

The presented inverter has implemented the

P&O (perturb & observe) algorithm for MPPT.

To get maximum power from a PV panel

required operating at the optimum voltage.

6


8/23



Selected range of the solar panels

The amount of the solar cells is used to build one solar panel. Usually 72, 36, or other.

For this design was selected panel with 72 cells, this implies MPP at 36V, which fairlycorresponds to 3 x 12V lead acid batteries in series as the back-up for the power source for

the inverter. This battery is used as the energy accumulator for the off-grid inverter usage.

The characteristic of the selected solar panel:

PMAX

= 180W

VSC

= 44.4V

VMP

= 36V

ISC

= 5.25A

IMP

= 5A

7


9/23



Inverter structure

8

PV String

PV Panel

MPPT

Charger Battery

Booststage

Inverter

Isolation

Outputfilter GRID

Isolation

DEMO Inverter

Main HW/SW

Option

Selected design way

Possible design way


10/23


of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. Freescale Semiconductor, Inc. 2009. 9

Main Parameters of DC to AC Inverter

Input voltage source Voltage level from solar panel V

MP= +36V

Solar energy can be stored in Lead-Acid batteries

Battery charger can be implemented (phase 2) Selected 3 pcs Lead-Acid batteries in series

Output voltage This design aims 1-phase 230V 50Hz (115V 60Hz optional); Single design, just different power components; Tolerance +5% to -10%;

Output power 400VA;

Harmonic distortion of the output voltage Lower than 3%;

Fault Protection Output over-current, over-voltage, short-circuit; Input under-voltage;

Signal output Serial link RS-485 to main system


11/23


of Freescale Semiconductor, Inc. All other product or service names are the property of their respective owners. Freescale Semiconductor, Inc. 2009. 10

Block Diagram of DC to AC Inverter

Block Diagram of Inverter The whole DC to AC inverter consists of main power parts:

MPP Tracking for solar panel outputsoftware implemented DC low voltage to DC high voltage converter DC high voltage to AC sine output voltage inverter Output filter Isolated RS-485 line

Associated control and fault detection circuits Both DC-DC converter and DC-AC inverter is controlled by one DSC MC56F8023.


12/23



DC to DC Converter

Push-Pull type with bridge rectifier on the isolated secondary sideAdvantage:

Simple transformer windings Simple control

Good efficiency

MPPT algorithm integrated in the software control loop

11

L1T1

Q1

PWM1

Q2PWM2

+400V DCBus

+ C2+

C1

0V DCBus

0V DC In

+36V DC In

D2

D1


13/23


14/23



DC to AC Inverter

Full-bridge type inverter Advantages:

Simple +400V DCBus used to generate 230V AC Simple PWM control

Simple reconstruction filter for AC line output

Can be controlled by half-bridge drivers or isolated gate transformers

Power MOSFETs or IGBTs can be used

13

DRIVERDRIVER

+400V DCBus

PWM3PWM4

AC Line_1

AC Line_2

L2Q3

Q4

Q5

Q6

C3

0V DCBus


15/23



DC to AC Inverter

Full-bridge type inverter control signals:

The PWM3and PWM4are complementary

The duty-cycle varies ideal from zero to full

period in sine amplitude and power line

frequency

Real duty-cycle varies from 5% to 95% of the

period

When the duty-cycle is 50%, the positive part

of the output sine voltage is generated

14

t

t

U

U

PWM Duty-cycle variation

PWM period T

+Umax -Umax

PWM 4

PWM 3

PWM 4 = PWM 3

D = (5% - 95%) T


16/23


17/23



PV

HW Comparator

0V

+36V

+36V DC/DC

DC/DC

+3.3V

DC/DC

+5VA

+12V

0V

0VA

+3.3V

+5VA

DRIVERS

ANALOG

PARTs

DSC

MOSFET MOSFETs

+12V0V

DC/DC+12V

ISOL

DRIVERS

IGBT

TR

PUSH-PULL

FULL-

BRIDGE

DC/DC

0VA-ISO

+5VA-ISO

+5VAANALOG

+12V-ISO

PARTs

0V-ISO

DC/DC

+5VA

ISOL

0V-ISOA

+5VA-ISOA

ANALOG

PARTs

BAT Relay +

3 x 12V

Auxiliary Power Supplies

The HW comparator enables the first

DC/DC converter if the input voltage is >

18V DC from PV panel

If the battery is connected, the inverter

runs from battery and battery is charged by

the solar panel

The main +12V DC power supply acts as

the source for all other DC/DC converters

Two isolated power supplies provide the

power for the isolated secondary side of the

inverter

The control DSC is placed on the primary

low voltage side

16

Auxiliary power supplies power the on-board circuitry

Isolated circuitry


18/23



Control circuits

DSC MC56F8023used

Controls the DC/DC converter and DC/AC inverter

MPPT software algorithm for the solar panel implemented Battery charger controlas option

RS-485 line interface for supervisors line communication

Output over-current, over-voltage, short-circuit and input under-voltage fuses implemented

ON-GRID or OFF-GRID mode

17


19/23



Inverter view

18

Full-Bridge Inverter

+ L-C FilterPush-Pull

Primary side

DSC MC56F8023

Control Board

Battery Charger HW

DCBus +400VOutput Filter

Solar Panel

Connectors

Power

Output

Battery

present

relay

Low power

DC-DC converters

For control circuitry

Battery connector

RS-485 Line


20/23



Conclusion

One standard DSC MC56F8023used for whole inverter control

Possibility of use as the ON-GRID or OFF-GRID connected inverter

Possibility of use of wide range of the solar panels:

One piece of the 36V type with the output power up to 450W

Two pieces of the 18V types in series with the total output power up to 450W

Inverters can be connected in parallel at the output to boost the output power in the OFF-GRID usage

The inverter starts run when the sufficient amount of the power is available from the solar panel (if battery

not connected)

The 3 x 12V lead-acid batteries in series are used as the energy accumulator

19


21/23



DEMO Connection

Switch OFF both switches (down position)

Connect load bulb (60W to 100W) at output

Connect the solar panel The green LED shines, red LED not

Put OFF-GRID switch ON (up position)

Switch ON the main switch

The Fault LED indicates the over-currentwhen

shines, switch OFF the main switch, wait about 20-

30 sec and switch ON the main switch.

20

DEMO Start-up sequence:


22/23



Literature

[1]: http://www.solarserver.com/knowledge/basic-knowledge/photovoltaics.html

[2]: http://www.nikhef.nl/~h73/kn1c/praktikum/phywe/LEP/Experim/4_1_09.pdf

[3]: http://en.wikipedia.org/wiki/Solar_cell

[4]: http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=56F802X&tid=mDHp

[5]: http://www.simosolar.com/uploadfile/learn/uploadfile/200904/20090417030623524.pdf

21
http://www.solarserver.com/knowledge/basic-knowledge/photovoltaics.htmlhttp://www.nikhef.nl/~h73/kn1c/praktikum/phywe/LEP/Experim/4_1_09.pdfhttp://en.wikipedia.org/wiki/Solar_cellhttp://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=56F802X&tid=mDHphttp://www.simosolar.com/uploadfile/learn/uploadfile/200904/20090417030623524.pdfhttp://www.simosolar.com/uploadfile/learn/uploadfile/200904/20090417030623524.pdfhttp://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=56F802X&tid=mDHphttp://en.wikipedia.org/wiki/Solar_cellhttp://www.nikhef.nl/~h73/kn1c/praktikum/phywe/LEP/Experim/4_1_09.pdfhttp://www.solarserver.com/knowledge/basic-knowledge/photovoltaics.htmlhttp://www.solarserver.com/knowledge/basic-knowledge/photovoltaics.htmlhttp://www.solarserver.com/knowledge/basic-knowledge/photovoltaics.html


23/23

TM

dc to ac inverter with dsc

Documents