MOSFET based 500 watt PWM INVERTER with solar battery charger controller (my b.tech (EEE) final year project)

Circuit No. 1 (Oscillator Circuit and feedback circuit)

Circuit No. 2 (MOS DRIVER CIRCUIT)

FINAL PRODUCT: -

  • WORKING OF THE CIRCUIT No.1 (Oscillator Circuit and feedback circuit)

 

This Inverter is based on the Pulse Width Modulation technology.

Working principle of various section of this INVERTER is explained next:-

1.Oscillator section:- 

This section generates the 50 Hz frequency required for inverter output. This section uses a common oscillator IC KA3524 (IC6) for this purpose.

2.Circuit Description:-

Pin15 of the IC6 is connected to the battery through an ON/OFF switch. Pin8 is connected to the ground.Pin6 and 7 are oscillator section pin of IC6. Timing capacitor C18 is connected to pin-7. Timing resistor R60 and VR8 is connected to pin6. Resistance and capacitors at pin6 and 7 decide the 50Hz of IC6.VR8 at pin6 can be used to change the frequency. Pin4 and 5 are connected to ground and pin12 and 13 are given battery voltage.Pin2 is given a stable 5v reference voltage from pin16 of this same IC6.Pin1 is provide with error sample voltage. Pin3 and 10 are not used in this circuit.

3.Working principle:-

Based on the value of resistor and capacitors connected to the pin6 and 7 internal oscillator of IC6 generates a fixed frequency signal. Internally this signal goes to the flip-flop section inside the IC. From the flip-flop this signal gets converter into two signals with changing polarity. By changing polarity we mean, when the first signal is positive, the second signal will be negative and when the first signal becomes negative, the second signal becomes positive. These changing polarity signals are output from output pin11 and 14 of IC6. These signals are known as MOS drive signal. These MOS drive signals are between 3v and 4v. Outputs on both the pin should be same value but with opposite polarity, otherwise the MOSFETs at the output section could get damaged.

MOS drive signal at pin 11 and 14 of IC6 is given to the pin5 and 11 of and gate IC5.

Pin5 is input pin of one of the AND gate of IC5, other two pins of this AND gate are 3 and 4. Pin6 is the output pin for this gate. Pin11 is input pin of another AND gate of IC5, other two input pins of this AND gate are 12 and 13. Pin10 is the output for this gate

This circuit uses only two AND gates from the three AND gates of IC5. Each of these AND gates have three input pins and one output pin. As a rule when all the inputs of AND gate are high, the output will be high, otherwise the output will be low. Pin3 and 13 of IC5 receive positive supply through R65. Pin4 and 12 receive positive supply through R66, D33. Pin5 and 11 receive MOS drive signal from pin11 and 11 of IC6. As the IC5 is an AND gate IC,Mos drive signal at its input pins 11 and 5 will go to output pins 10 and 6 of IC5. Pin14 of IC5 receive supply and pin7 is grounded AND gate using pin1, 2, 8 and 9 are not used in this circuit. MOS drive signal at pin10 and 6 of IC5 are given to driver transistors T7 and T8 for amplification.

4.WORK OF IC5 (CD4073)

AND gate IC5 is used in this circuit as an electronic switch between the MOS drive voltage at pin11 and 14 of oscillator of IC6 and MOS drive transistors T7 and T8. Using this switch the MOS drive signals can be sending or stopped going to the MOS drive transistors. This facility is used to stop the INVERTER output (INVERTER shutdown) during the overload, no-load, low battery etc. conditions,

  • MOS DRIVER SECTION

 

MOS drive signal at the output pin10 and 6 of IC5 are not powerful enough to drive the output MOSFETs. These signals are given to the diver transistor T7 and T8 to amplify them to a level that be able to drive the MOSFETs.

1.Circuit Description (MOS DRIVER SECTION)

MOS drive signal from pin10 of IC5 is given to the base of T7, and the MOS drive signal at the pin6 is given to the base T8. This will start two channels of MOS drive voltage. Collectors of T7 and T8 are connected to the ground. Base of these transistors are given negative biasing by connecting them to the ground through 10k resistor each.

2.WORKING PRINCIPLE (MOS DRIVER SECTION)

MOS drive signal amplified by T7 and output at its emitter, reach the gate of MOSFETs T13 and T14 through D50, R84, R93 and R86. MOS drive signal amplified by T8 and output at its emitter, reach the gate of MOSFETs T17 and T19 through D53,R98,R101 and R104 Value of the components used in the both  channels of MOS drive signals must be same, so that the voltage level of both channels remain same, otherwise the MOSFETs could get damaged.

  • OUTPUT SECTION

IN the driver section, the MOS drive signals reach the gates of MOSFETs through 20E resistors.

 1.Circuit Description (OUTPUT SECTION)

MOSFETs T13 and T14 make first channel and T17 and T19 make the second channel of the output section. Drain of T13 and T14 are joined together and connected to one end of bifilar winding of mains transformer TR2. Drain of T17 and T19 are joined together and connected to other end of bifilar winding of mains transformer TR2. Source of the four MOSFETs are joined together and grounded through a shunt. A 3 inch piece of 20 gauge copper wire is used for making shunt. Center taping of the bifilar winding is connected to the positive supply of the 12v battery.

2.WORKING PRINCIPLE (OUTPUT SECTION)

MOS drive signals of different polarity reach the gate of each MOSFET channels. As the polarities of signals are different, when first channel is ON, the second channel will be OFF and when the second is ON, the first channel will be OFF, Each channels will be ON/OFF alternatively. This ON/OFF process takes place 50 times per second. As these MOSFETs are connected to the primary of the mains transformer, continues ON/OFF wil produce an alternating current (AC) in the primary winding of TR2. AC current in the primary of TR2 will induce an AC voltage in the secondary of TR2.This Ac voltage is sent to the INVERTER output socket through an ON/OFF switch.

  • PWM (Pulse width Modulation)

PWM is used to keep the output supply of inverter constant. The PWM technology changes the width of 50Hz frequency signal to keep the output supply constant. In the battery mode some part of the AC supply received by the mains transformer TR2 is given to the pin5 of connector CN4. This AC voltage at pin5 of CN4 is given to the bridge rectifier (D28, D29, D30 and D31) through R22. Bridge rectifier converts the AC supply into DC supply. The positive DC supply is given to the pin1 of IC7 and negative DC supply is given to pin2 of IC7. IC7 is an opto-coupler IC. In this IC, a LED is connected between pin1 and pin2 and a photo –transistor is connected at pin4,5, and 6. Collector of photo-transistor, inside the IC7, is connected to the pin5. This pin is given 12v supply.

Photo-transistors emitter is connected to pin4 of IC7 pin3 and 6 of IC7 are not used in this circuit. In the battery mode when the DC supply from bridge rectifier reaches pin1 and 2 of IC7, the LED inside the IC starts to glow. Light from the LED reach the base of photo-transistor inside the IC7 and the photo-transistor switch on. This will makes the supply at the collector, reach the emitter i.e.pin4 of IC7. This voltage at pin4 is used as error voltage sample and given to the pin1 of IC6, through R62. Pin1,2 and 9 of IC6 are part of an operational amplifier(op-amp) which is known as error amplifier. Pin1 and 2 are input pins of this error amplifier and pin9 is the output pin. Error voltage at pin4 of IC7 is given to the pin1 of IC6. 5V regulated supply at pin16 of IC6 is given to the pin2 of IC6 through R59 as reference voltage. As the load at the output of Inverter change, the output AC supply value also changes. Change in the output supply will change the value of error voltage at pin4 of IC7. The error voltage at pin4 of IC7 is one way represents the AC voltage output value of INVERTER. As the error voltage at pin4 of IC7 change, the voltage at pin1 of IC6 also changes. As the voltage at pin1 change, the output of error amplifier inside this IC also changes accordingly. Error amplifier output pin9 of IC6 is connected to the duty cycle control section, inside the IC. This duty cycle control section controls the width of 50 Hz signals, generated by the oscillator. As the width of 50Hz signals is controlled by the error amplifier output, the INVETER output socket will always give a stable output, whatever be the load value. If the PWM error voltage amplifier section stops working, the INVERTER output AC supply will vary according to the load connected to the output. PWM adjustment preset VR7 connected to pin4 of IC7 can be used to change the error voltage given to pin4 of this IC. This will adjust the INVERTER output supply value.

  • Additional safety circuits

Any fault in the PWM control section will stop the PWM control section, and the MOS drive voltage at pin11 and 14 of IC6 will increase. This will results in increase in MOS drive voltage at pin10 and 6 of IC5. Any increase in the MOS drive voltage could damage the MOSFETs. So to save MOSFETs from this type of faults, an additional safety circuit for MOSFETs is made using T10 and T21.

1.Circuit Description (Additional safety circuits)

Amplified MOS drive voltage at emitter of T8 is given to the collector of protection transistor T21, through R98. MOS drive signal at the emitter of MOS driver transistor T8 is given to the base of protection transistor T21, through R107, and four diodes D56, D57, D58 and D59. This same protection circuit is made for the other MOSFET channel using the T10 protection transistor.

2.Working Principle (Additional safety circuits)

When the PWM section is working properly, the strength of the MOS drive signal at Pin11 and 14 of IC6 is very low and these signals do not provide enough biasing to the base of T10 and T21. Without enough biasing the transistor stay OFF and the MOS drive signals reach the MOSFETs gate and the INVERTER work properly. If the PWM section inside the IC6 stops working, the value of the MOS drive voltage output at pin11 and 14 will increase suddenly. This increased voltage will give enough biasing to T10 and T21 and turn then ON. This increased voltage will give enough biasing to T10 an T21 and turn then ON. This will results in the MOS drive signals reaching the collector of both these transistors going to the ground and the MOS drive signals will not reach the gate of MOSFETs. Without MOS drive signals, the MOSFETs will stop working and the INVERTER will turn off. This will protect the MOSFETs from getting damaged.

High Voltage Spike Protection Circuits

With the MOS drive signal Pin11 and 14 of PWM controller IC6 sometimes produce spikes, high voltage pulse of very small duration. When these spikes reach MOSFET gate or drain, they could damage the MOSFET. A filter circuits is used to protect the MOSFETs from the high voltage spikes. MOS drive signal from emitter of driver transistor T8 is given to the anode of D49 and R82 of filter circuit, through R107 and D54. Anode of D49 is also connected to the drain of the MOSFETs of this channel. In This same manner, MOS drive signal from emitter of driver transistor T7 is given to the anode of D48 and R81 of filter circuit, through R85 and D51. Anode of D48 is also connected to the drain of the MOSFETs of this channel. Cathodes of D48 and D49 are joined together and a filter circuit with R81, R82 and C24 is also used in this junction.

1.Working principle

Any high voltage spikes generated by IC6 go to the junction of D48 and D49. The filter circuit at this junction grounds the high voltage spikes reaching here. This protects the MOSFETs from getting damaged due to these high voltage spikes.

  • 5V Regulated Supply

 

IC6 contains a 5V regulated supply section. This section regulates any supply given as input at its pin15 and provides +5V regulated output at pin16.

This +5V regulated supply is used as:

  1. Reference voltage to pin2 of IC6
  2. Reference voltage to pin5 and 9 of IC1

 

  • Circuit diagram of Solar Charger Controller:- 

Principle of Operation of Solar charger controller:-

  • Description of  Master Control Card: –

Voltage Regulator IC LM 317T (IC6) on the Control Card (CC1) provides stabilized voltage 9.0 volt as Vcc for operating all the ICs and other semiconductor devices. This voltage can be adjusted by potentiometer P4. LM 7805 generates stabilized voltage of 5.0 volt which provides reference for the different comparator circuits on the Control Card.

Battery voltage is sensed and divided by potential divider network R1, R2, and R3 at pin 3 of Comparator LM 324 (IC1) & is compared with attenuated reference voltage at pin 2 (VR) of the same IC to control over-charging of Battery. Depending upon levels of two voltages, the output (pin 1) of the IC goes High or Low. Whenever this output goes from ‘Low’ to ‘High’ or ‘High’ to ‘Low’ State, the output of “EX-OR” gate of IC 4070 (IC 4) at pin 11 provides trigger pulse. This trigger pulse (of a microsecond duration) triggers monostable multivibrator IC 4098 (IC 3) at pin 12. The output of multivibrator CD 4098 from pin 9 acts as a clock pulse input for JK flip-flop CD 4027 (IC 2) at pin 13. The output of flip-flop (IC2) at pin 15 control conduction through transistor 2N2907 (Q2).

This transistor provides Control Signals from Connector pins 5 for switching ‘OFF’ and ‘ON’ of Green LED (through Relay & Status Indication Card (CC2) and to drive Charging Relay (through base of Transistor 2N3019 (Q4).

Battery voltage is also sensed through divider networks R6, R11, P2 and R14, R12 and P3 at pin 5 and 12 respectively of comparator IC LM 324. These attenuated voltages are compared with reference & voltage (Vref) at pin 6 and 13 of IC1 (LM 324) to sense Battery Low to protect battery from deep-discharge and similarly to protect load from battery voltage exceeding 15 volt accidentally, due to failure of charge control circuitry.

Whenever the Battery voltage is between 11.4 volt and 15 volt, the voltage at pin 7 of IC1 is high and pin 14 of IC1 is low. The logic at pin 14 is inverted by “EX-0R” gate CD 4070 (IC4). The output at pin 4 (IC4) is high whenever battery voltage is less than 15 volt. This inverted output and output from pin 7 of IC1 is fed to input of NAND GATE CD 4011 of (IC5) and output at pin 10 is high, whenever any of inputs is low, the transistor (Q3) is conduction mode. The Transistor 2N3019 (Q3) Cut-off the drive signal to the Relay coil (through Transistor 2N3019 (Q5) in CC2 Card). And Load is ‘OFF’. If both the input at NAND GATE (i.e. pin 8 and 9 of IC 5) is high, then transistor Q3 will be ‘OFF’ and drive will be provided to Load Relay in CC2 Card.

The control card (CC1) provides the supply voltage Vcc to Status Relay & Indication Card (CC2). The hysteresis is provided between low voltage disconnect voltage and low voltage reconnect voltage through resistance R8, and charging ‘OFF’ and ‘ON’ by resistance R4.

  • Description of  Relay & Indication Card (CC2) : –

i) The drive signal from pin 5 of master control card (CC1) switch ‘ON’ and ‘OFF’ Transistor 2N 3019 (Q4). If drive signal is zero, Q5 is in cut-off mode and Charging is off through Relay. And if drive signal is high, Q4 is in conduction mode and charging is ON through relay.

ii) The drive signal from pin 9 of master control card (CC1) switch ‘ON’ and ‘OFF’ Transistor 2N 3019 (Q5). If drive signal is zero, Q5 is in cut-off mode and load is off through Relay. And if drive signal is high, Q5 is in conduction mode and load is ON through relay.

iii) This card also has four indications of status of the system: -

  1. Red LED for Over-voltage Load cut-off indication
  2. Red LED for  Battery deep-discharge  Load cut-off indication
  3. Green LED for Load on indication
  4. Green LED for Battery Charging indication.

High Voltage charging cut-off                     : 14.2 V

Reconnect (ON)                                             : 13.2 V

 

Low Voltage Load cut-off                            : 11.4 V

Reconnect (ON)                                             : 12.0 V

 

Preset P4                    : use for setting Vcc Voltage

 

Preset P1                    : use for setting battery Over-charging cut off

 

Preset P2                    : use for setting battery deep-discharge

 

Preset P3                    : use for setting Over-voltage cut-off.

 

1. When the Charging voltage below 14.2V Pin 1 of LM324 (IC1) is LOW, due to this pin 3 of CD4070 (IC4) is HIGH on account of this pin15of CD4027 (IC2) is LOW & transistor Q2 is ON & give drive voltage for to ON charging circuit through Tr. 2N3019 (Q4) & Relay.

 

2. When the Charging voltage Above 14.2V Pin 1 of LM324 (IC1) is HIGH, due to this pin 10 of IC2 goes HIGH & pin 3 of CD4070 (IC4) is LOW & pin 11 of IC4 change from HIGH to LOW on account of this IC CD4098 (IC3) give CLK at pin 9 which goes to pin 13 of CD4027 (IC2) this Time pin 15 of IC2 goes HIGH & transistor Q2 is OFF & give drive voltage zero for to OFF charging circuit through Tr. 2N3019 (Q4) & Relay.

 

3. When the Battery  voltage Above 11.4V Pin 7 of LM324 (IC1) is HIGH, due to this pin 10 of CD4011 (IC5) is HIGH on account of this pin10 of IC4 is HIGH & pin 3 of IC5 is LOW this time transistor Q3 is OFF & give drive voltage for to ON the Load circuit through Tr. 2N3019 (Q5) & Relay.

 

4. When the Battery  voltage Below 11.4V Pin 7 of LM324 (IC1) is LOW, due to this pin 10 of CD4011 (IC5) is LOW on account of this pin10 of IC4 is also LOW & pin 3 of IC5 is HIGH this time transistor Q3 is ON condition & give drive voltage LOW for to OFF the  Load circuit through Tr. 2N3019 (Q5) & Relay.

 

5. When the Battery  voltage Below 15V Pin 14 of LM324 (IC1) is LOW, due to this pin 4 of CD4070 (IC4) is HIGH on account of this pin10 of IC5 is also LOW & pin10 of IC4 is HIGH & pin 3 of IC5 is LOW this time transistor Q3 is OFF & give drive voltage for to ON the Load circuit through Tr. 2N3019 (Q5) & Relay.

 

6. When the Battery  voltage Above 15V Pin 14 of LM324 (IC1) is HIGH, due to this pin 4 of CD4070 (IC4) is LOW on account of this pin10 of IC5 is also HIGH & pin10 of IC4 is LOW & pin 3 of IC5 is HIGH this time transistor Q3 is ON & give drive voltage zero for to OFF the Load circuit through Tr. 2N3019 (Q5) & Relay.

 

 

  • Description of  Main Components used in Solar charger controller ckt:-
  1. CD 4070
  2. CD 4027
  3. CD 4011
  4. LM324
  5. CD4098
  6. LM 317
  7. 12 volt Relay

 

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