DN0005
Design note
A three phase induction motor
drive using a V/F control
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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
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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
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February 2014
DN0005 Rev 2
5/5
www.st.com