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　　A low-cost, high-reliability inverter power circuit design

　　How to integrate the cheapest components while ensuring their reliability is the key to circuit design. This article introduces the design of a single-input and three-output inverter, which can drive three-phase cage asynchronous motors below 1kW. After slight modification, it can be used to drive brushless DC motors. The article also introduces the selection of key components in the design to help engineers achieve high reliability with the cheapest components.

　　This article summarizes the design points of a relatively mature circuit obtained after nearly a hundred modifications, including microprocessors, power devices, half-bridge drivers, overcurrent protection, control methods, test results, etc. The variable frequency speed regulation achieved by this circuit can greatly expand its application scope due to its low cost, and can be used to drive brushless DC motors with slight modifications.

　　The design of the inverter circuit is similar, generally using the AC-DC-AC method, which consists of four parts: rectification, intermediate DC link, inverter and control. The industrial frequency AC power supply is first converted into DC power supply through the rectifier, and then the DC power supply is converted into a DC power supply. The power is converted into AC power with controllable frequency and voltage to supply the motor. Frequency converters generally use intelligent power modules (IPM), and many electronics companies have their reference designs. As long as the software and hardware are used, there is not much design risk, but there is a cost, which limits the use of frequency converters in applications such as industrial sewing machines and desktops. Drilling machines and other applications that require speed control but are cost-sensitive. In low-power situations, using 6 discrete field effect tubes or IGBTs is a good choice, which can greatly reduce costs, but its reliability issues are very prominent, and tube explosion is the biggest headache for designers. How to integrate the cheapest components from different companies while ensuring their reliability is the key to circuit design.

　　Main circuit design

　　1. Selection of half-bridge drive solution

　　There are two types of half-bridge drive circuits: isolated and non-isolated. The non-isolated solution has a simple circuit, but the high voltage of the main circuit can easily escape into the control circuit and cause an accident. Using the IR2105 bipolar SPWN modulation method, it is still very difficult to drive a motor below 370W. reliable. The isolation solution increases the cost. Isolation drivers include transformer drive and optocoupler drive. The transformer switching speed is fast, but when the duty cycle of the inverter output changes between 0% and 100%, modulation method must be used. Low-power The occasion is not necessary. Although the switching speed of the optocoupler driver is slower, the switching time is about 0.5μS. The allowed switching speed of IGBT is generally below 40kHz. In practical applications, it does not necessarily have to be so high. Therefore, optocoupler isolation is used to drive the upper tube and is used below 1kW. The motor is a cost-effective solution.

　　2. Use of driver chips

　　IR210x is one of IR's many driver IC families. It can work in circuits with bus voltages up to 600V, and the price is only 2 yuan. The driving signal is compatible with TTL and MOS levels. An IR210x can be used to complete the driving task of two power components. It uses bootstrap technology internally, so that the driving circuit of the power component only needs one input stage DC power supply, which can realize the power MOSFET and IGBT. The driver also has certain protection functions. The circuit is shown in Figure 1.

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