- Control circuit of the inverter
The main circuit of the inverter needs to have a control circuit to achieve, generally there are two control methods of square wave and sine wave. The inverter circuit of square wave output is simple and low in power, but the efficiency is low, and the wave component is large. Sine wave output is the development trend of inverters. With the development of microelectronic technology, microprocessors with PWM function have also come out, so the inverter technology of sine wave output has matured.
(1) Inverter control integrated circuit with square wave output
Inverters with square wave output currently mostly use pulse width modulation integrated circuits, such as SG3525, TL494 and so on. Practice has proved that using the SC3525 integrated circuit and using the power field effect transistor as the switching power element can realize the inverter with relatively high performance and price. Because the SG3525 has the ability to directly drive the power FET, and has the internal reference source and operational amplifier and under-voltage protection function, its peripheral circuit is very simple.
(2) Inverter control integrated circuit with sine wave output
The control circuit of the inverter with sine wave output can be controlled by a microprocessor, such as B0C196MC produced by INTEL, MP16 produced by Motorola and pic16c73 produced by Microchp, etc. These microcontrollers all have multi-channel PWM generators, and are equipped with Set the dead time between the upper and lower bridge arms.
- Selection of inverter power devices
The selection of the main power components of the inverter is very important. At present, the most used power components are Darlington power transistors (GTR), power field effect transistors (MOSFET), insulated gate transistors (IGBT) and Turn off the thyristor (GTO), etc. In small-capacity low-voltage systems, more devices are used as MOSFETs because of their lower on-state voltage drop and higher switching frequency. In high-voltage and large-capacity systems, IGBT modules are generally used, because the on-state resistance of MOSFET increases as the voltage increases, the withstand voltage is limited (generally not more than 500V), and the power of a single MOSFET It is not big. In large-capacity speed changers, multiple parallel connections are required, and IGBTs have absolute advantages in high-voltage and large-capacity systems.