INVERTER

THREE PHASE INVERTER

Here is the detailed explanation of the three-phase inverter project with all codes and details.

Introduction

An inverter is an essential electrical device primarily used to convert direct current (DC) into alternating current (AC). Also referred to as a variable frequency drive, this device is crucial in a variety of applications, including variable frequency drives and high-power environments such as high voltage direct current (HVDC) power transmission. Its main purpose is to regulate the torque and speed of electric motors, making it indispensable in numerous industrial and commercial settings. Inverters are also key in HVDC power transmission, where they convert the DC power generated by power plants or offshore wind farms into AC power suitable for long-distance transmission.

In this role, inverters contribute to reducing energy losses and enhancing the efficiency of electricity distribution across vast distances. In the following sections, we will explore the circuit design and operation of inverters, various types of inverters, their advantages, limitations, and applications.

Three Phase Inverter

A three-phase inverter is a device that converts DC power into AC power in a three-phase format. This type of inverter is commonly used in industrial and commercial applications where three-phase power is needed. The three-phase inverter works by using switches, typically transistors or IGBTs, to generate AC output from a DC input. It creates three separate AC waveforms that are 120 degrees out of phase with each other, which is necessary for driving three-phase motors or other equipment.

Types of Three Phase Inverter

Three-phase inverters are categorized based on their features and characteristics. Some common types include:

1. Voltage Source Inverter (VSI)

A voltage source inverter converts a DC source voltage into an AC output voltage. It is suitable for situations where the DC source has low impedance. VSIs are often used in Variable-Frequency Drive (VFD) systems to control the speed of three-phase motors. These inverters are typically powered by battery banks or photovoltaic (PV) cells.

2. Current Source Inverter (CSI)

A current source inverter converts a DC current source into AC current at the desired frequency. The input current remains constant, making these inverters ideal for boost operations. They are used in applications such as starting synchronous motors, power factor correction, and speed control of AC motors.

3. Cascaded Multilevel Inverter

This type of inverter is designed for high-voltage applications and uses multiple voltage levels to create a stepped waveform. It typically consists of multiple H-bridges and DC capacitors, making it suitable for renewable energy systems and high-voltage power transmission.

4. Hybrid Multilevel Inverter

The hybrid multilevel inverter combines elements of both current-source and voltage-source inverters, making it suitable for medium voltage and high power applications. It is used in high-power industrial settings and electric vehicle charging stations.

5. Pulse Width Modulated Inverter (PWM)

PWM inverters use pulse-width modulation to precisely control output frequency and voltage. They generate high-quality AC power with minimal harmonic distortion, making them ideal for renewable energy systems and motor drives.

Working of Three Phase Inverter

A three-phase inverter converts a DC input into a three-phase AC output using a circuit with three separate single-phase inverter switches. Each switch is connected to three load terminals. The inverter operates with a 120-degree phase shift between its three arms, ensuring a balanced AC output. The circuit typically includes a single fuse and a shared DC power source, simplifying control and protection mechanisms.

Conduction Modes:

  1. 1. 180-Degree Conduction Mode

    In this mode, each switch conducts for 180 degrees, activating at 60-degree intervals. This balanced load arrangement ensures precise control of current flow and is used in applications requiring balanced three-phase AC power.

  2. 2. 120-Degree Conduction Mode

    Each switch operates for 120 degrees, suitable for delta-connected loads. This mode generates a six-step waveform with precise control over the phase voltages, providing a balanced output across the phases.

Project Schematics

Below is the schematic diagram of the 3-phase inverter used in this project:

3-Phase Inverter Schematic

Sample Code

Here is a portion of the code used to control the 3-phase inverter:


        // Example of a simple inverter control loop in C++
        // Define Arduino pins for inverter switches
#define SU_PLUS 3  // Upper switch for phase U
#define SU_MINUS 9 // Lower switch for phase U
#define SV_PLUS 5  // Upper switch for phase V
#define SV_MINUS 10 // Lower switch for phase V
#define SW_PLUS 6  // Upper switch for phase W
#define SW_MINUS 11 // Lower switch for phase W

// #define FREQUENCY 50
// #define PERIOD_US (1000000 / FREQUENCY) // 20ms in microseconds

// // Switching angles in degrees
// float a1 = 8.7426;
// float a2 = 24.3975;
// float a3 = 27.7622;

// // Convert angles to microseconds
// unsigned long angleToTime(float angle) {
//   return (unsigned long)((angle / 360.0) * PERIOD_US);
// }

// // Timing points for switching
// unsigned long t1 = angleToTime(a1);
// unsigned long t2 = angleToTime(a2);
// unsigned long t3 = angleToTime(a3);

void pulseout(int a, int b){
  digitalWrite(a, HIGH);
  delayMicroseconds(900);
  digitalWrite(a, LOW);
  delayMicroseconds(10);
  digitalWrite(b, HIGH);
  delayMicroseconds(500);
  digitalWrite(b, LOW);
  delayMicroseconds(10);
  digitalWrite(a, HIGH);
  delayMicroseconds(500);
  digitalWrite(b, LOW);
  delayMicroseconds(10);
  digitalWrite(b, HIGH);
  delayMicroseconds(800);
  digitalWrite(b, LOW);
  delayMicroseconds(10);
  digitalWrite(a, HIGH);
  delayMicroseconds(150);
  digitalWrite(a, LOW);
  delayMicroseconds(10);
}

void setup() {
  // Set pins as outputs
  pinMode(SU_PLUS, OUTPUT);
  pinMode(SU_MINUS, OUTPUT);
  pinMode(SV_PLUS, OUTPUT);
  pinMode(SV_MINUS, OUTPUT);
  pinMode(SW_PLUS, OUTPUT);
  pinMode(SW_MINUS, OUTPUT);

  // Initialize all switches to LOW
  digitalWrite(SU_PLUS, LOW);
  digitalWrite(SU_MINUS, LOW);
  digitalWrite(SV_PLUS, LOW);
  digitalWrite(SV_MINUS, LOW);
  digitalWrite(SW_PLUS, LOW);
  digitalWrite(SW_MINUS, LOW);
}

void loop() {
  pulseout(SU_PLUS, SU_MINUS);
  pulseout(SV_PLUS, SV_MINUS);
  pulseout(SW_PLUS, SW_MINUS);
  pulseout(SU_MINUS, SU_PLUS);
  pulseout(SV_MINUS, SV_PLUS);
  pulseout(SW_MINUS, SW_PLUS);
}

Conclusion

Understanding the basics of 3-phase inverters is essential for engineers and technicians involved in power electronics and electrical engineering. The concepts discussed here provide a foundation for further study and application in various fields.



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