The sine wave inverter is a conversion device that converts direct current into alternating current. It converts direct current into alternating current by controlling the on and off of semiconductor power switching devices (such as SCR, GTO, GTR, IGBT and power MOSFET, etc.). The circuit that controls the turn-on and turn-off of the power switch tube is the control circuit of the inverter. The control circuit outputs a certain voltage pulse to make the power switch tube in the power conversion circuit turn on and off according to a certain rule. At this time, the power main circuit The output is a specific harmonic combination, and finally the required voltage waveform is obtained through the filter circuit.
The input of the inverter is usually direct current (or direct current obtained through rectification and filtering of mains power), which includes direct current grid, storage battery, photovoltaic cell and other means of direct current. Usually, these electrical energies cannot be directly used as the voltage on the input side of the inverter, but are used as the input of the inverter after passing through a certain filter circuit and EMC circuit.
Convert Main Circuit
The main circuit of the inverter is a power conversion circuit composed of power switching devices. There are many structural forms of the main circuit. Under different input and output conditions, the main circuit form is different. Each power conversion circuit has its advantages and disadvantages. , the most suitable circuit topology should be considered as the main circuit structure in actual design.
According to the requirements of the inverter output, the control circuit generates one or more groups of pulse voltages through a certain control technology, and acts on the power switch tubes through the drive circuit, so that the power switch tubes are turned on or off according to the specified order, and finally in the main The desired voltage waveform is obtained at the output of the circuit. The role of the control circuit is crucial to the inverter system, and the performance of the control circuit directly determines the quality of the inverter output voltage waveform.
The output circuit generally includes an output filter circuit and an EMC circuit. If the output is DC, a rectifier circuit should be added later. For inverters with isolated output, there should be an isolation transformer in the front stage of the output circuit. According to whether the output needs a voltage regulator circuit, the output circuit can be divided into open-loop and closed-loop control. The output of the open-loop system is only determined by the control circuit, while the output of the closed-loop system is also affected by the feedback loop to make the output more stable.
Some parts or chips of the control circuit and input and output circuits have specific input voltage requirements, and the auxiliary power supply can meet the specific voltage requirements in the circuit. Usually, the auxiliary power supply is composed of one or several DC-DC converters. In the case of AC input, the auxiliary power supply is completed by combining the rectified voltage and the DC-DC converter.
Protect the Circuit
Protection circuits usually include input overvoltage, undervoltage protection, output overvoltage, undervoltage protection, overload protection, overcurrent and short circuit protection. There are other protections for inverters working in specific occasions. For example, temperature protection is required in places where the temperature is very low or high, air pressure protection is required in certain air pressure changes, and protection is required in humid environments. Humidity protection etc.
Read more: Understand the Working Principle of Inverter