In this DIY electronics project, we will design and build a high-power DC-AC inverter using the SGT15T60SD1F, a silicon carbide (SiC) MOSFET. This component is ideal for high-efficiency power conversion due to its fast switching capabilities, high voltage tolerance, and reduced power loss compared to traditional silicon-based transistors. The goal is to create a DC to AC inverter that can convert a 24V DC input (such as from a solar panel or battery) into a 120V AC output, which is suitable for powering household appliances or other AC devices.

This inverter will be designed to provide a stable output for small to medium power applications, such as powering lights, fans, or charging other devices. With its SiC MOSFET-based design, the inverter will offer enhanced performance, especially under high loads or varying conditions, making it suitable for off-grid systems or as a backup power source.

Materials and Components:

1. SGT15T60SD1F (SiC MOSFET) – The primary switching element for the inverter.

2. Transformer – Used to step up the DC voltage to AC and deliver the appropriate output voltage (120V AC).

3. Capacitors – For filtering and stabilizing the input and output voltage.

4. Resistors – For biasing, limiting current, and setting feedback.

5. Diodes – To protect the circuit and rectify the signal.

6. Inductors – Used to reduce high-frequency noise and filter the output signal.

7. Heat Sinks – For cooling the SiC MOSFET and other power components.

8. PWM Controller IC – Used to generate the pulse-width modulation signal that drives the SiC MOSFET.

9. Voltage Regulation Circuit – To stabilize the output voltage and ensure steady performance under varying load conditions.

10. PCB or Veroboard – To mount and organize all components neatly.

11. Fuse – For safety and overcurrent protection.

Project Overview:

The aim of this project is to create a reliable DC to AC inverter using the SGT15T60SD1F MOSFET, which is a Silicon Carbide (SiC) MOSFET. The advantage of SiC MOSFETs lies in their ability to handle high voltages and currents, switching at very high frequencies with minimal energy loss. This makes them ideal for power conversion applications where efficiency is crucial.

This inverter will use a high-frequency transformer to step up the voltage from the DC input (24V) to an AC output (120V) with the help of pulse-width modulation (PWM) to control the output waveform. The design will incorporate modern components like the SiC MOSFET for high efficiency, and the entire system will be built to handle continuous power in the 200-500W range, depending on the size of the transformer and the other components.

Step 1: Understanding the SGT15T60SD1F SiC MOSFET

Before starting the project, it’s essential to understand the SGT15T60SD1F and why it’s chosen for this inverter. The SGT15T60SD1F is a Silicon Carbide (SiC) MOSFET designed for high-voltage and high-power switching applications. SiC MOSFETs are known for:

● High Voltage Tolerance: The SGT15T60SD1F can handle up to 600V, which is ideal for stepping up the voltage in this DC to AC inverter application.

● High Efficiency: Due to their reduced switching losses and low conduction resistance, SiC MOSFETs are highly efficient, which is crucial for power conversion systems.

● Fast Switching: The SiC MOSFETs can switch at much higher frequencies than silicon-based MOSFETs, which helps in reducing the size of the passive components (like the transformer and capacitors) in the circuit.

● Thermal Performance: SiC devices tend to generate less heat than their silicon counterparts at the same power levels, reducing the need for extensive heat dissipation.

These features make the SGT15T60SD1F the perfect choice for this inverter project, allowing us to design a system that is not only efficient but also compact and capable of operating at high power levels.

Step 2: Power Supply Design

The power supply for the inverter is the starting point for our project. It’s essential to provide stable and filtered DC voltage to the SGT15T60SD1F SiC MOSFETs.

1. DC Input: The input power can come from a 24V DC battery, solar panel, or any regulated DC power source. The voltage is then fed to the PWM controller that generates the switching signal for the MOSFETs.

2. Capacitors: To ensure that the DC input is smooth and free of noise, large electrolytic capacitors (100µF to 470µF) should be placed across the input to filter any ripple in the DC voltage.

3. PWM Controller: The PWM controller is used to generate a square wave signal at a frequency of 20kHz to 50kHz, which will control the switching of the SiC MOSFETs. The duty cycle of this square wave will be varied to regulate the output voltage.

4. Gate Driver Circuit: Since the SGT15T60SD1F MOSFET is a high-voltage device, it requires a gate driver to supply the appropriate voltage to turn the MOSFET on and off. A suitable gate driver IC is needed to ensure that the MOSFET switches cleanly and rapidly.

5. Fuse Protection: A fuse should be placed on the input side of the circuit to prevent damage in case of a short circuit or overload condition.

Step 3: Designing the Output Stage

The output stage of the inverter is responsible for converting the high-frequency PWM signal into a clean AC signal, which is then stepped up to the desired voltage using a transformer.

1. SGT15T60SD1F Switching Stage: The SGT15T60SD1F MOSFETs are placed in a push-pull configuration. In this configuration, two MOSFETs alternate in switching the voltage between positive and negative, which creates a full AC waveform. The switching frequency of these MOSFETs will be driven by the PWM controller.

2. Transformer: After the switching stage, the voltage is stepped up using a high-frequency transformer. The transformer steps up the 24V DC input to 120V AC. The transformer is essential for converting the DC into a high-voltage AC signal that can be used to power household appliances.

3. Inductors and Capacitors: The output from the transformer may still contain high-frequency switching noise, so filtering capacitors and inductors are used to smooth the AC waveform and remove any residual ripple. These components are placed at the output of the transformer to reduce noise and ensure a stable AC output.

4. Feedback Loop: A feedback loop is implemented to regulate the output voltage of the inverter. This feedback ensures that the inverter can handle varying loads and maintain a constant output voltage.

5. Output Protection: To prevent back EMF or voltage spikes from damaging the components, diodes are used to protect the circuit. These diodes are placed across the MOSFETs and the transformer to protect them from reverse voltage conditions that can occur when inductive loads like motors are connected to the inverter.

Step 4: Heat Management

Because high-power switching elements like the SGT15T60SD1F can generate significant heat during operation, effective heat dissipation is crucial. Here are some key points to consider:

1. Heat Sinks: Attach heat sinks to the SGT15T60SD1F SiC MOSFETs to prevent overheating. SiC MOSFETs are more efficient than silicon-based devices, but they still generate heat under high loads. A large fin-type heat sink will help to dissipate the heat efficiently.

2. Thermal Monitoring: It’s advisable to include thermal sensors or a temperature cutoff to ensure that the inverter does not overheat. This feature can protect the circuit from damage if the operating temperature exceeds safe levels.

Step 5: Testing and Calibration

Once the inverter is assembled, testing is an essential step to ensure that everything is functioning correctly.

1. Initial Power-Up: Initially, power on the circuit without any load to check for any excessive heat or irregularities. Use a multimeter to measure the input and output voltages.

2. Load Testing: After confirming the inverter operates without issues under no load, connect a small resistive load (such as a light bulb or fan) to the output. Gradually increase the load to check the inverter's performance under real-world conditions.

3. Output Waveform: Use an oscilloscope to check the output waveform. The waveform should be a clean sinusoidal or modified sine wave, depending on the complexity of your design. If the waveform shows significant distortion, check the PWM signal and filter components.

4. Adjusting the Duty Cycle: If the output voltage is not stable or the output is lower than expected, adjust the PWM controller's duty cycle to increase the voltage.

Conclusion

Building a high-power DC-AC inverter using the SGT15T60SD1F SiC MOSFET is a rewarding project that demonstrates the advantages of modern semiconductor technologies in power conversion. By carefully selecting components such as the SiC MOSFET, transformer, and filtering network, this inverter can provide reliable, efficient power for a variety of applications.

The finished inverter can be used for off-grid power systems, backup power, or even small home appliances. Its high efficiency, thanks to the use of SiC MOSFETs, ensures minimal energy loss, making it a practical choice for anyone looking to build a sustainable and reliable power inverter. With proper heat management, protection, and feedback regulation, this inverter can operate continuously at high loads, providing clean and stable AC power.