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Implementation methods for Vector controlled PMSM Drive System
Control of Servo Motors
Implementation methods for Vector controlled PMSM Drive System
Power Circuit
Detection (Current, Voltage, Speed, Position)Control (Analog , Digital)
Power Circuit
PMSM
P W M
Inverter
Full bridge rectifier ( Six diodes)
- 3-phase AC voltage DC voltage
- Harmonics : 6th times to source frequency
Filtering capacitor
- For suppressing the harmonics in DC Voltage- Electrolytic Capacitor : High capacity & Low cost
Initial charging circuit for filtering capacitor
- To prevent the rush current in the capacitor at start-up of power circuit
- Charging through resistor at initial condition
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Implementation methods for Vector controlled PMSM Drive System
Control of Servo Motors
PWM inverter
Driver circuit- To drive the switching device
The structure of driver circuit- Opto-coupler : Isolation between the signal ground and the power ground
- Driver circuit : Increasing current or changing voltage level
- Separate dc power source is required
-Six switching devices in anti-parallel with diodes.
a
b
c
A+
C-A-
C+
B-
B+
a
b
c
PWM
+Vcc
Driver
Circuit
+VSSOpto-Coupler
(A+)
A+
Driver circuit
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Implementation methods for Vector controlled PMSM Drive System
Control of Servo Motors
Switching device
Discrete - type
Module - type
IPM (Intelligent Power Module)
-Six or seven switching devices
(one switching device for
dynamic braking)
- Drive circuit
- Protector circuit for overcurrent,
under or over voltage
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Detection method for PMSM drive system
Control of Servo Motors
Sensing devices
Current sensors
Three-phase ac currents & dc link current
Voltage sensorsThree-phase ac voltage & dc capacitor voltage
Speed & position sensor
Requirement of sensor
Accuracy
Range (Measurement)
Nonlinearity
Isolation (Ground of signal is separated from that of power circuit)
Type of output signal
(voltage, current, number of pulse, duty cycle of pulse)
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Current sensor
Control of Servo Motors
Current sensor
- Sensing ac and dc currents
- Hall-effect current sensor
Hall element
B
I C
V H
I Cd
BBId
KV CH
Output voltage of hall element
- The Hall voltage is proportional to flux
- The polarity of hall voltage Direction of flux
IAMP.
Vout
Hall device
Hall effect current sensor
Structure of hall effect current sensor
- DC power supply : +15V, -15V
- Measuring both ac and dc current
- Isolation from power circuit
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Current sensor
Control of Servo Motors
Output voltage versus current
( Ex. 4V/100A Hall-effect sensor)
- Magnitude of output voltage is proportional to current
Block diagram for current measurement circuit for digital control
Current100 A-100 A
+4V
-4V
Output voltage
Type of Hall-CT
Hall-CTLow-Pass
FilterAmplifier
A/D
Converter
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Voltage sensor
Control of Servo Motors
Voltage sensor : Measuring three-phase ac voltages and dc capacitor voltage
Measuring three-phase ac voltages
Transformer for isolation and magnitude control
Vab+
-
Vo+
-
N1 N2
abc
Transfomer
- Signal ground is isolated from power ground
- Output voltage (Secondary winding voltage) of transformer
aboV
NNV
12
- Frequency response of transformer is not good
- Ferrite core is used to improve the frequency performance
- The transformer cant be used to measure the dc voltage
Output voltage is adjusted by winding ratio.
C l f S M
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Voltage sensor
Control of Servo Motors
Isolation amplifier
- Measuring both ac and dc voltage
- Isolation- Amplification factor : 1:1 or 1:8 It is difficult to control the magnitude of voltage
Block diagram for voltage measurement circuit using isolation amplifier
Internal structure of isolation amplifier
(AD 202)
Isolation Low-Pass
FilterAmplifier
A/D
ConverterAmplifier
R1
R2 Vi
+
-
Vab
+
-
abiV
RR
RV
21
2
C t l f S M t
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Speed measurement methods
Control of Servo Motors
Tachogenerator
Speed measurement methods
- Tachogenerator
- Incremental encoder
- Linearity is not good
- LPF, amplification, A/D converter are required for digital control
- DC generator type
- DC Output voltage is generated by speed
Speed
Output voltage
Control of Servo Motors
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Control of Servo Motors
Structure of incremental encoder
- Output signals : A, B, Z pulses
- A and B pulses : Many pulses are outputted at one revolutionEx. 2048 P/R (pulses per revolution)
Phase difference between A and B is 90
- Z pulse : One pulse is outputted at one revolution
A
B
Z
Output signals of encoder
Speed measurementusingIncremental encoder
Control of Servo Motors
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Control of Servo Motors
Direction of rotor speed
- Checking whether the rotor rotates at forward direction or reverse direction using D
F/F.
A
B
D F/FD Q F / R
[1] Forward rotation
- A pulse leads by 90 to B pulse The output of D F/F is 1A
B
F / R
[2] Reverse rotation
- B pulse leads by 90 to A pulse The output of D F/F is 0A
B
F / R
Speed measurementusingIncremental encoder
Control of Servo Motors
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Control of Servo Motors
Calculation of speed
- To increase the frequency of encoder pulse
Improvement of resolution of speed calculation- AB The frequency of encoder pulse is increased by twice.
- Monostable The frequency of encoder pulse is increased by four times.
A
B
A B
Monostable
Method of speed calculation by encoder pulse T method
M method M/T method
Speed measurementusingIncremental encoder
Control of Servo Motors
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Control of Servo Motors
T method
- The one period of encoder pulse is measured by counting the high frequency clock & speed is calculated.
- Motor speed The period of encoder pulse Resolution of speed calculation - Motor speed The period of encoder pulse Resolution of speed calculation
Overflow in counter may be generated
Encoderpulse
High frequencyClock
1 Period
M method
- The speed is calculated by counting the encoder pulse during speed sampling time.
- Motor speed The number of encoder pulse Resolution of speed calculation - Motor speed The number of encoder pulse Resolution of speed calculation
* Resolution is dependent on P/R of encoder, speed sampling period, and speed.
Speed measurementusingIncremental encoder
Control of Servo Motors
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f
M method
- The speed is calculated by counting the encoder pulse during speed sampling time.
- Motor speed The number of encoder pulse Resolution of speed calculation - Motor speed The number of encoder pulse Resolution of speed calculation
* Resolution is dependent on P/R of encoder, speed sampling period, and speed.
Encoderpulse
Speed Sampling Time(T )s
Ex.) 1024 P/R encoder, Speed sampling time = 10ms, Motor speed =1800rpm .
What is no. of encoder pulse for counter ?
* # of encoder pulse for sampling period = (1800/60)[rps] * (1024*2) * 0.01 = 614
Equation of speed
)(#*2*)/(
60][ pulseencoderof
TRPrpm
s
r
Where Ts
= speed sampling time.
Speed measurementusingIncremental encoder
Control of Servo Motors
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Incremental encoder for Speed measurement
f
Resolver
- 2-axis stator winding and rotating transformer
- sin t costare applied totwo stator winding, respectively. Output voltage of rotating transformer
R/D converter for digitization
Position measurementmethods
)sin()sincoscos(sin)sincos( 4_32_12_1 tKttKtEtEKE ssR
Control of Servo Motors
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Incremental encoder for Speed measurement
Incremental encoder
- Frequency of encoder pulse is increased by twice using exclusive OR
- Z-pulse is generated at the center of N-pole of rotor flux. (at the position =0) External interrupt is generated by Z-pulse
Advantage
- Digital value of position can be obtained
- The low cost and simple structure
- Both the position and speed are measured with one incremental encoder
Disadvantage
- The absolute position of rotor can not be available at any time
- The position should be compensated, whenever the Z-pulse is generated
Position measurementmethods
A
B
A B
Z
N
Control of Servo Motors
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Incremental encoder for Speed measurement
Absolute encoder
- Multi layer : 12-bit absolute encoder12 layers
Structure of absolute encoder
Position measurementmethods
Advantage
- Digital value of position can be obtained
- The absolute position can be available at any time Disadvantage
- The number of output lines is too many
- The cost is high
- Number of bit Cost and resolution
Control of Servo Motors
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Incremental encoder for Speed measurement
Output data of absolute encoder
- Grey code is used to prevent the measurement error
Position measurementmethods
310000111111
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110111011010101111001010
91011010010
80011000010
70010011100
61010001100
51110010100
40110000100
30100011000
21100001000
11000010000
00000000000
DecimalGray CodeNatural Binary Code
Grey code
- Only one bit is changed
At transition from 7 to 8
* binary code :
00111b(7) 01111b (15) or 00000b(0)* Grey code :
00100b(7) 01100b(8) or 00100b(7)
Table for binary code and grey code (5-bit)