DN0005 Design note A three phase induction motor drive using a V/F control Designs from our labs describe tested circuit designs from ST labs which provide optimized solutions for specific applications. For more information or support, visit www.st.com By Dennis Nolan Main components STM8S Mainstream 8-bit MCU with Advanced Timer L6391 High-voltage high and low side driver Specification Speed control with acceleration and deceleration limit Over current protection Over voltage protection Over temperature protection on power IGBT Operating voltage (AC mains input) 90 – 130V Motor current up to 1A RMS Circuit description For loads where the load curve is well known, such as a fan, a simple V/F drive can provide good efficiency and reasonable speed control without the need for any speed feedback. In such an application, the actual rotation speed is the commanded speed less the slip. This is the same operating mode as if a motor were connected directly to the mains, but we have the added advantage of being able to control the drive frequency and therefore we have a low cost and easily implemented speed control. The original application of this board was a small fan used in a residential heating system. February 2014 DN0005 Rev 2 1/5 www.st.com The example software generates a three phase sine drive for the motor in voltage mode. The software uses a simple V/F algorithm where the amplitude of the applied sine wave is increased proportional to the drive frequency over the operating range. In the example software, the desired speed is set using potentiometer R32 that is read by one of the analog inputs on the microcontroller. The V/F constant can be estimated from the motor rating. For example, if the motor is rated at 120V for 60 Hz operation, the starting point for selecting the V/F constant is simply 120V/60Hz. For most applications this will be the appropriate value. The acceleration and deceleration limit can be set empirically as appropriate for the application. For the board, the most important parameter is to select a deceleration limit so that when decelerating with the load, the high voltage power supply is not forced above the over voltage trip point. The V/F constant, the acceleration rate and the deceleration rate are all set using #DEFINE statements in the header so they can easily be set for the motor. The circuit implements the V/F control using the advanced timer of the 8-bit microcontroller, the STM8S103F3, to generate the three phase PWM signals with dead time to drive the power bridge. The power stage is a three phase bridge using discrete IGBTs, T1-T6 and half bridge gate driver ICs, U3, U5 and U8. The power supply for the controller and gate drivers are derived from the high voltage supply using a VIPer12, U1, in a buck configuration. It regulates 15 V for the gate drivers and supplies a linear regulator, U2, that regulates 5V for the microcontroller and other associated circuitry. Over current protection, over voltage protection and over temperature protection are implemented using the internal comparators in the L6391 gate driver IC. One input of each comparator input is biased at 0.5V by R19 and R23. The other inputs are connected to sense the voltage across the current sense resistor, R31, the temperature feedback from the thermistor, NCT1, and the bus voltage from the lower resistor, R6, of the voltage divider. If any of these three voltages exceed the 0.5V reference, the comparator will activate the smart shutdown on one of the L6391 and pull the SD pin low. Since all three of the SD pins are connected together, all of the bridge drivers will be turned off. As configured, the board will detect a fault for a motor current over 2A, a high voltage supply voltage over 200V, or a temperature on the NTC over 110oC. The trip point for any of the three can be adjusted by changing the values of resistors on the board. The microcontroller can sense that a fault has occurred by looking for a falling edge on the SD pin and take action appropriate to shut down when a fault occurs. P1 is power in from the AC mains. (120V, 60 Hz). P2 is the SWIM programming connection for the STM8S103. P3 is the motor terminal connection. February 2014 DN0005 Rev 2 2/5 www.st.com R23 3K R19 27K SHUTDOWN ENABLE +5V CD3 1uF CD2 1uF +15V 1uF C31 27K R13 R16 6K8 1uF CD4 100nF C17 2N2222 Q1 3K3 R9 1 N Temp 100nF C18 +15V 20K R7 HEADER 2 SW NEU 2 2 1 P5 100nF C19 1nF C11 1% R42 82E NTC1 10K 1nF C12 X1 1nF C13 MOV 125V +5V CH BH AH 0.1uF C29 @97degC , NTC 1 = 741E REF LINE FILTER 10E NTC2 3 1k 1k 1k IR8GBU06 4 + - R43 47K +15V 100nF C30 R38 R26 47K +15V 100nF C20 R21 R17 47K +15V 100nF C14 R10 1 L1 D2 2 7 6 5 4 3 2 1 7 6 5 4 3 2 1 7 6 5 4 3 2 1 U8 U5 U3 GND NC DT VCC HIN SD LIN CP- CP+ LVG NC OUT HVG VBOOT CP- CP+ LVG NC OUT HVG VBOOT L6391 GND NC DT VCC HIN SD LIN CP- CP+ LVG NC OUT HVG VBOOT L6391 GND NC DT VCC HIN SD LIN L6391 CP4 470uF/200V 8 9 10 11 12 13 14 8 9 10 11 12 13 14 8 9 10 11 12 13 14 0.1uF/400V REF 18E R40 18E R39 0.47uF/50V C28 100pF C21 REF 18E R24 18E R22 0.47uF/50V C16 REF VBUS 18E R14 18E R11 0.47uF/50V C10 C8 4.7k R2 D13 D11 D8 D7 D6 D5 C4 22nF 1N4148WS 47E R41 1N4148WS 47E R36 R31 47K R27 47K R18 47K R44 1% 0.25E/2W 1N4148WS 47E R25 1N4148WS 47E R20 1N4148WS 47E R15 C3 Vdc Vdc T6 T5 Vdc T4 T3 T2 T1 3 FB STTA1R06U 1N4148WS 22uF/25V 1N4148WS 47E R8 ZD1 C5 15V D3 D1 STGB7NC60HD STGB7NC60HD STGB7NC60HD VD D 4 0.23V + - DRA IN SOUR C E +5V Note: O/C protection O/V protection O/T protection C25 0.1uF 3 2 1 P3 RES SET VIPER12AS U1 15v REGULATEDSUPPLY 8 7 6 5 R29 100E 1 2 - 2A - 200V - 110degC 0.1uF C27 Fref ZD2 VBUS 18V Q2 2N2222 4 3 2 1 10K PB1 @Vbus = 0.5V , Vdc = 404V CP1 R12 4 HEADER P2 0.1uF C15 +5V STTA1R06U D4 1mH L1 100uF/25V 1 2 P1 Y1 680pF C26 R34 10K 2K2 R30 C22 +5V U7 +5V 0.1uF CD1 0.1uF C7 0.1uF C9 0.1uF 16.00MHZ R35 2K2 +5V Ceramic resonat or 510E R6 3K3 R5 R4 100K/2W 100K/2W R1 NEC2501 R28 3 2 9 8 7 18 4 5 6 1 5V ZD3 D10 200E +15V 4 3 MAIN RECTIFIER R32 5k STGB7NC60HD STGB7NC60HD STGB7NC60HD 1 2 U2 +5V U6 PD6 / RxD PD5 / TxD VDD VCAP VSS SWIM U4 8K2 R37 NEC2501 10K R33 PC7/PWMV PC6/PWMU PC3/PWMU PB5/BKIN PD3/AIN4 PD2/AIN3 PC4/AIN2 PA3 PB4 PC5 PD4 10uF/25V Vdclink Vdc +15V +5V CP2 3 STM8S103F3P3 Vo LF50 NRST OSC1/PA1 OSC2/PA2 Vi 1 2 1 2 3 4 4 HEADER 17 16 13 11 20 19 14 10 12 15 1 P4 CH BH AH SHUTDOWN Fref Vdclink Temp ENABLE TP2 TP1 TP3 1 GND 4 4 DN0005 Rev 2 3 1 February 2014 1 AC POWER IN Figure 1. Circuit diagram 3/5 www.st.com 22uF/25V Variations The board includes an isolated serial (UART) interface that could be used to send on/off and/or speed commands to the board. This is not implemented in the example software. Support material Related design support material STSW-DRIVE001, 3-phase VF example source code for DN0005 Documentation Datasheet: STM8S103F3, Mainstream Access line 8-bit MCU Datasheet: L6391, High-voltage high and low side driver Datasheet: VIPer12A, Fixed frequency off line converter Revision history Date Version Changes 30-May-12 1 Initial release 24-Feb-14 2 Revised schematic February 2014 DN0005 Rev 2 4/5 www.st.com Please Read Carefully Information in this document is provided solely in connection with ST products. STMicroelectronics NV and its subsidiaries (“ST”) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described herein at anytime, without notice. 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