Getting lower output voltage than expected in 5 level inverter

Question

I am making a 5 level inverter using an Arduino Mega. I am using an IRFZ44N MOSFET for switching and also an MCT2E as a MOSFET driver.

The problem I am facing is that I am a getting a lower output voltage than expected: the actual output should be 24V, but I am getting 12 - 13V as output.

Can anyone help me out with this problem?

This is the schematic:

This is the code I am using:

float f = 50;
float t = (1 / f) * 1000000;
float a1 = 10;
float a2 = 40;
float a1p1 = (a1 * t) / 360;
float a1p2 = (a2 * t) / 360;
float d = 5;

int pin1 = 1;
int pin2 = 2;
int pin3 = 3;
int pin4 = 4;
int pin5 = 5;
int pin6 = 6;
int pin7 = 7;
int pin8 = 8;

void setup() {
  pinMode(pin1, OUTPUT);
  pinMode(pin2, OUTPUT);
  pinMode(pin3, OUTPUT);
  pinMode(pin4, OUTPUT);
  pinMode(pin5, OUTPUT);
  pinMode(pin6, OUTPUT);
  pinMode(pin7, OUTPUT);
  pinMode(pin8, OUTPUT);
}

void loop() {
  digitalWrite(pin1, HIGH);
  digitalWrite(pin2, HIGH);
  digitalWrite(pin5, HIGH);
  digitalWrite(pin6, HIGH);
  delayMicroseconds(a1p1 - d);                                                                                                                                                                                                                                   

  digitalWrite(pin2, LOW);
  delayMicroseconds(d);
  digitalWrite(pin4, HIGH);
  delayMicroseconds(a1p2 - a1p1 - d);

  digitalWrite(pin6, LOW);
  delayMicroseconds(d);
  digitalWrite(pin8, HIGH);
  delayMicroseconds(t / 2 - (2 * a1p2) - d);

  digitalWrite(pin5, LOW);
  delayMicroseconds(d);
  digitalWrite(pin7, HIGH);
  delayMicroseconds(a1p2 - a1p1 - d);

  digitalWrite(pin1, LOW);
  delayMicroseconds(d);
  digitalWrite(pin3, HIGH);
  delayMicroseconds((2 * a1p1) - d);

  digitalWrite(pin4, LOW);
  delayMicroseconds(d);
  digitalWrite(pin2, HIGH);
  delayMicroseconds(a1p2 - a1p1 - d);

  digitalWrite(pin8, LOW);
  delayMicroseconds(d);
  digitalWrite(pin6, HIGH);
  delayMicroseconds(t / 2 - (2 * a1p2) - d);

  digitalWrite(pin7, LOW);
  delayMicroseconds(d);
  digitalWrite(pin5, HIGH);
  delayMicroseconds(a1p2 - a1p1 - d);

  digitalWrite(pin3, LOW);
  delayMicroseconds(d);
  digitalWrite(pin1, HIGH);
  delayMicroseconds(a1p1);
}
```

Answer 1

To keep the high-side FETs turned on their Gates need to go above the battery voltage by >=10 V. However you must also ensure that they don't receive more than 20 V between Gate and Source, so you can't just boost the battery voltage by 10 V because then the total would be 22 V which could blow up the FETs.

One way to do it is with an isolated DC/DC converter such as the Recom ROL-1212S, powered by the battery being switched and with its output connected between the optocoupler positive supply and FET Source. You will need one converter per high-side FET.

For testing you could use PP9 dry cell batteries, which should last a long time at the low current your Gate driver draws.

Apart from that your circuit and program appear to be correct. The rms output voltage should be ~20 V.