Abstract This paper introduces the functional structure of the power drive circuit of AC induction motor controller, the working principle and design method of each part, and details the working principle of the power factor control chip MC34262 with circuit power factor correction as the core. It also presents the schematic diagram of the boost type active power factor correction (APFC) circuit, as well as the parameter design and selection method of each part of the circuit. Keywords: Power drive, power factor correction, AC induction motor, power supply Classification number: TM383.6 Design of Power Stage Board for Low-power AC Induction Motor [align=right]Penglai of Shandong Xiaoya Washing Equipment Co., Ltd. Yong-Xia Wang Zip code 265607 Penglai City in Shandong Province Chinese medicine hospitals Yan-Min Sun Zip code 265600 Penglai of Shandong Xiaoya Washing Equipment Co., Ltd. Xiao-Dong Jiang Zip code 265607 山东蓬莱小鸭洗设备有限公司王永霞邮编265607 山东省蓬莱市中医院孙艳敏邮编265600 山东蓬莱小鸭洗设备有限公司姜晓东邮编265607[/align] Abstract : This paper first introduces the functional configuration of the power stage for AC induction motor controller, followed by the description of the operating principles and design methods for each part of the configuration. Then, the operating principle of MC34262, a A monolithic power factor control IC is presented in great detail centered by PFC (Power Factor Correction). Lastly, the schematic design for boost-type APFC (Active Power Factor Correction) circuit is given, along with the parameter design and selection for each part of the circuit. Keywords: power stage, power factor correction, induction motor, power supply 1. Overview In recent years, with the development of high-performance digital IC and DSP technology, vector control of AC motors has become a hot topic in motor control. The main circuit of the power stage of AC motor controller generally adopts AC-DC-AC control mode [1]. That is, AC is first converted into stable DC through rectification and filtering, and then AC with frequency conversion or amplitude conversion required for motor control is obtained by using inverter circuit. Therefore, a stable and fast-responding power drive stage design is the key to realizing AC motor controller. The entire power drive stage circuit includes four components: AC-DC conversion circuit supporting power factor correction, DC-AC inverter circuit, voltage and current sampling circuit, and auxiliary power supply. 2. AC-DC conversion circuit supporting power factor correction Supplied by rectification from 220V AC power grid to DC power is a basic power conversion scheme widely used in power electronics technology and electronic instruments. For example, at the input end of AC-DC switching power supply, after full-wave rectification of AC power, a large capacitor is connected to obtain a relatively flat DC voltage, and then the required voltage is obtained through DC-DC converter. Rectifier-capacitor filter is a combination of nonlinear components and energy storage components. Although the input AC voltage is sinusoidal, the waveform of the input AC current is severely distorted and pulsed [2]. The extensive use of rectifier circuits requires the power grid to supply severely distorted non-sinusoidal current, resulting in a decrease in the power factor at the input end. Therefore, relevant international standards, such as MIL2STD21399, Bell2co re001089 and IEC55522, have made corresponding provisions for the amount of harmonics generated by electrical equipment. To increase the power factor and reduce pollution to the power grid, this paper adopts an active power factor correction (APFC) circuit based on critical conduction mode. Many companies offer integrated chips for active power factor correction based on critical conduction mode design, such as ST's L6561, Fairchild's FAN7527, Onsemi's MC34262, and TI's UCC28050. These can all be used in multiplier-based boost active power factor correction circuits with constant on-time control technology. This paper uses the MC34262, which has a simple external circuit and is based on a transconductance error amplifier. 2.1 Power Factor Correction Circuit Principle The MC34262 is a high-performance, critical conduction, current-mode power factor controller manufactured by Motorola, featuring high power factor, zero-current conduction of the power switch, low power diode losses, and a simple control circuit. The MC34262 (Figure 1) mainly includes: a multiplier, a zero-current detection circuit, a current comparator amplifier, a low-frequency feedback error amplifier, a reference voltage, an overvoltage protection circuit, and an undervoltage lockout circuit. The APFC boost converter circuit of the MC34262 (Figure 2) mainly consists of the controller IC chip MC34262, a rectifier bridge D1, a MOSFET power transistor Q1, a boost inductor L1, a boost diode D2, an output filter capacitor C6, and a feedback loop. [align=center] Figure 1 Block diagram of MC34262 Figure 2 APFC boost converter circuit of MC34262[/align] The working principle of the APFC converter is to control the switching of the MOSFET Q1, making the current and voltage in the boost inductor L1 form an impedance state, thereby achieving power factor control. The working process is as follows: 1) Initially, the current detection is 0, the power switch Q1 is turned on, the current in the main inductor L1 increases linearly, the inductor stores energy, the diode D2 is in reverse cutoff, and the load is powered by the output capacitor C6. 2) When the current detected by the power switch Q1 at current detection pin 4 reaches the output of the multiplier, the power switch Q1 is turned off. At this time, L1 generates a sudden potential change, causing D2 to be forward biased and turned on. The power supply and the main inductor L1 are connected in series to supply power to the load, the capacitor C6 is charged, and the current in the inductor decreases linearly. 3) When the current in the inductor drops to zero, the current in the power switch also drops to zero accordingly. The zero-voltage detection circuit detects that the current is 0, and another switching cycle begins immediately. The power switch is turned on in the zero-current state. 4) The output voltage signal is compared with the reference voltage of the error amplifier through the feedback loop, and a voltage signal containing the output voltage error information is obtained through the error amplifier compensation loop. Since the bandwidth of the error amplifier is very low, the output voltage signal of the error amplifier is approximately a constant value within one power frequency cycle. The sampling signal of the input voltage serves as the basis for the shaping of the input current. It is multiplied with the output of the error amplifier in the multiplier to obtain the output voltage signal containing the phase information of the output voltage and the input voltage. 5) The output of the multiplier serves as the current reference. It is compared with the current feedback signal in the switch and the zero current detection signal. The power switch is controlled by the pulse width modulator. This achieves the purpose of ensuring the stability of the output voltage and making the phase of the input current track the input voltage. Figure 3 shows the current waveform in the main inductor in half a power frequency cycle under the critical conduction mode with constant conduction time. [align=center] Figure 3 Inductor current waveform and MOS gate voltage drive waveform [/align] 2.2 Power factor correction circuit parameter design 2.2.1 Boost inductor design The primary coil of the transformer is the boost inductor of the APFC pre-adjuster. The secondary coil of the transformer has two functions: (1) as a zero current detection sensor, (2) as an auxiliary power supply circuit of the power drive board. Peak inductor current: Substituting the data into equation (2), the inductance is 250uH. The core size and number of turns of the winding can be determined using conventional design methods. The voltage of the secondary winding of the boost inductor is 15V, and the number of turns of this winding is taken as 1:10 of that of the primary winding. 2.2.2 Calculation of other parameters 1) Calculation of R1 and R2: Where: VCS——current detection threshold value, taken as 0.5V From equation (5), R7 is 0.069Ω, taken as 0.06Ω. 5) Calculation of output capacitor: The value of the output capacitor is determined by the following formula: The actual selection is 330μF, the withstand voltage is not less than 450V, and it is required to have a small equivalent series resistance (ESR). 3. DC-AC inverter circuit The DC-AC inverter circuit adopts an intelligent power module IRAMS10UP60A from International Rectifier (IR). This module is designed and optimized for electronically driven variable speed motor control, providing a very compact, high-performance AC driver in a single isolated package. The IRAMS10UP60A integrates six IGBT high-voltage gate drivers and incorporates diverse protection functions. Its internal block diagram is shown in Figure 4. [align=center] Figure 4 Internal Block Diagram of IRAMS10UP60A[/align] Compared to distributed IGBT drive methods, the IRAMS10UP60A integrated circuit, in addition to its compact structure and high reliability, also has the following characteristics: 1) Low di/dt gate driver with good noise suppression and low power consumption when the switching transistor operates at high frequency. 2) Integrated gate driver and bootstrap diode, simple circuit connection: simply connect V+ to the high-voltage end of the DC, Le1, Le2, and Le3 to the low-voltage end of the DC, and connect the three phases of the motor to U, V, and W respectively. The six PWM signals from the controller are connected to the corresponding positions of pins 15 to 21, and the appropriate frequency bus capacitor can be selected to control the output of U, V, and W. 3) Control method with dead-time control prevents the upper and lower IGBTs from conducting simultaneously. It automatically shuts down when the circuit experiences overcurrent or overvoltage. 4) Provides pins for temperature and current detection. 4. Current sampling circuit To accurately measure the phase current of the induction motor, this module connects a 3W precision resistor R in series with the ground terminals of U, V, and W. The phase current of the motor can be obtained based on the resistance value of R and the voltage difference measured across it. The principle diagram of voltage difference measurement is shown in Figure 5, where: [align=center] Figure 5 Current detection principle diagram[/align] Ra=R4006=R4007 Rb=R4000=R4001 R4006 is connected to 1.65V V[sub]ref[/sub], R4000 is connected to the high end of the input voltage, R4001 is connected to the low end of the input voltage, V[sub]d[/sub] is the voltage difference to be measured, and Vout is the measured voltage. According to the working principle of the op-amp, we have: (10) V[sub]d[/sub] can be obtained from equation (10). 5. Auxiliary Power Supply To provide a reliable and stable DC power supply for the driver chip and sampling chip, the circuit structure shown in Figure 6 is adopted. The AC signal is obtained through the auxiliary winding of the PFC inductor, rectified, filtered, and then supplied with 15V power to the control circuit via the 7815 chip. The 5V power required by the sampling chip is provided by the 7815 and then converted to a 7805. The 1.65V reference voltage in the sampling circuit is obtained through LM317 and variable resistor adjustment. [align=center]Figure 6 Auxiliary DC power supply using 7815[/align] 6. Conclusion Experiments have proven that the APFC circuit of this power drive stage can provide a stable high-voltage DC power supply with 5% ripple and a power factor of 0.99. Combined with a self-designed controller based on the Freescale 56F8356 DSP, it can drive a 300W AC induction motor to operate stably, realizing vector control of the AC induction motor. References [1] Er Guihua, Dou Yuexuan, Motion Control System [M], Beijing: Tsinghua University Press, October 2002 [2] Zhang Zhansong, Cai Xuansan, Principles and Design of Switching Power Supply [M], Beijing: Electronic Industry Press, 2002 [3] Sha Zhanyou et al., Latest Application Technology of Special Integrated Power Supply [M], Beijing: People's Posts and Telecommunications Press, 2002 [4] Nave, Mark J. Power line filter design for switched-mode power supplies [M], New York, Van Nostrand Reinhold, 1991 Author Introduction: Wang Yongxia: Born in 1970, Senior Engineer, Senior Mechanical Designer in Industrial Washing Industry Sun Yanmin: Born in 1976, Network Engineer, Weak Current Control Expert Jiang Xiaodong: Born in 1974, Electrical Engineer, Senior Electrical Designer in Industrial Washing Industry