direct torque control of a 6-phase switched reluctance motor · direct torque control of a 6-phase...
TRANSCRIPT
Direct Torque Control of a 6-Phase
Switched Reluctance Motor
Xu Deng, Prof. Barrie Mecrow and Dr. Shady Gadoue
Electrical Power Research Group
School of Electrical and Electronic Engineering
Newcastle University
• Background
• Conventional SRM Control Method
• Direct Torque Control Method for a 6-phase SRM
• Simulation
• Conclusion
Outline
Rotor: no winding or permanent magnet. Stator: concentric windings. Advantages: Simplest structure of all electrical motors with high fault-tolerant. rotor of a six phase SRM stator of a six phase SRM
Background
Applications: aerospace, electric vehicles, high-speed drives, small automotive applications, cooling fans and pumps
Background
relationship between rotor position, current and torque
relationship between rotor position, flux and current
Disadvantages:
Doubly salient structure
Highly unlinear magnetization characteristics
Ununiform torque output
Large torque ripple:
vibration of stator
main source of noise
application limited
0 0.005 0.01 0.015 0.028
9
10
11
12
13
14
15
16
Time(s)
Torque Output(Nm)
30%
Conventional SRM Control Method
Torque command
Current or voltage
reference profile
Torque sharing function
(TSF)
0
10
20
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.050
5
10
15
Time(s)
12 A 14 A18 A16 A
10 A
Torque output of single phase()Nm
Current of single phase(A)
-500
0
500
Voltage of single phase/(V)
0 0.005 0.01 0.015 0.02 0.0250
10
20
30
Time(s)
Torque output of single phase(Nm)
Single phase torque output driven by Current Chopping Control
Single phase torque output driven by Angle Position Control
-500
0
500
Voltage of single phase/(V)
0 0.005 0.01 0.015 0.02 0.0250
10
20
30
Time(s)
Torque output of single phase(Nm)0
10
20
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.050
5
10
15
Time(s)
12 A 14 A18 A16 A
10 A
Torque output of single phase()Nm
Current of single phase(A)
Q1: If we can control instantaneous torque directly,
rather than by controlling current or voltage,
can we achieve a better torque performance?
Q2: How can we control the torque directly?
Current Torque
Conventional SRM Control Method
Torque equation of SRMs on steady sate
>0 , T>0, flux acceleration
Basic Principle of DTC in SRMs
<0 , T<0, flux deceleration
Basic principle of DTC in SRMs
(a) Stator flux linkage vector of the motor is kept at a constant by selecting an
suitable voltage vector.
(b) Torque can be controlled by accelerating or decelerating the stator flux vector
relative to the rotor movement.
Current in SRM is unipolar, i is positive.
flux linkage discrete expression
the change of stator flux linkage is
be controlled by selecting an
suitable voltage vector
N2
N1
N3 N4
N5
N6
N7
N8
N9 N10
N12
N11
DTC Method for a 6-phase SRMs
U1
U2(ϕb)
U3
U4(ϕc)
U5
U6(ϕd)
U7
U12(ϕa)
U11
U10(ϕf)
U9
U8(ϕe)
x
y
Space Voltage Vectors
U1 (+1,+1,-1,-1,-1,-1)
U3 (-1,+1,+1,-1,-1,-1)
U5 (-1,-1,+1,+1,-1,-1)
U7 (-1,-1,-1,+1,+1,-1)
U9 (-1,-1,-1,-1,+1,+1)
U11 (+1,-1,-1,-1,-1,+1)
U2 (+1,+1,+1,-1,-1,-1)
U4 (-1,+1,+1,+1,-1,-1)
U6 (-1,-1,+1,+1,+1,-1)
U8 (-1,-1,-1,+1,+1,+1)
U10 (+1,-1,-1,-1,+1,+1)
U12 (+1,+1,-1,-1,-1,+1)
Flux and voltage vector arrangement
ϕs Asymmetric Half Bridge
Converter (AHB)
“+1” = +Vdc
“-1” =-Vdc
Zone1~Zone12 are defined to locate stator flux
DTC Method for a 6-phase SRMs
N2
N1
N3 N4
N5
N6
N7
N8
N9 N10
N12
N11
U1
U2(ϕb)
U3
U4(ϕc)
U5
U6(ϕd)
U7
U12(ϕa)
U11
U10(ϕf)
U9
U8(ϕe)
ϕs
Operation example
Assume:
1. Stator flux rotates along anticlockwise and
locates in Zone1.
2. Both flux and torque feedbacks are lower than
reference value.
How can we choose voltage vectors?
Step1: Select voltage vector to increase stator flux
U11, U12, U1, U2, U3
Step2: Select Voltage vectors to increase torque
U2, U3
ϕs
Current Chopping Control(CCC)
N=1000rpm Vdc=560V
Torque reference=13 N·m
Current reference=12A
Direct Torque Control(DTC)
N=1000rpm Vdc=560V
Torque reference=13 N·m
Flux reference=0.52 Wb
Simulation
Current
Hysteresis
Controller
I_ref AHB
Converter M
I_real
+
-
Torque
Hysteresis
Controller T_ref
AHB
Converter M
T_real
+
-
Flux
Hysteresis
Controller
Flux_ref Voltage
vector
controller
Flux_real
+
-
Control diagram of current chopping control
Control diagram of direct torque control
Flux Position
Simulation
Current(A)
Flux Linkage(Wb)
Torque(N·m)
0
0.2
0.4
0.6
0
5
10
15
0 0.005 0.01 0.015 0.02
0
2
4
6
8
Time(s)
0
0.1
0.2
0.3
0.4
0
5
10
15
0 0.005 0.01 0.015 0.02
0
5
10
15
Current(A)
Flux Linkage(Wb)
Torque(N·m)
Time(s)
Current Chopping Control Direct Torque Control
Simulation
0 0.005 0.01 0.015 0.020
2
4
6
8
10
12
14
16
Time(s)
Current Chopping Control
Direct Torque Control
33.3% 11.5%
Stator flux linkage vector comparison Torque output comparison
X-Y stationary frame
Highly linear trajectory
Relatively rounded
-1 -0.5 0 0.5 1-1
-0.5
0
0.5
1
X Axis(Wb)
Y A
xis
(Wb)
X Y Plot
Direct Torque Control
Current Chopping Control
Same average torque output =13.1Nm
Torque ripple sharply reduced
DTC method has been used on a 6-phase SRM
By using DTC method, producing a same average torque, the torque ripple of
DTC method is sharply reduced.
The challenges of DTC method is to select reasonable voltage vectors and
chose flux and torque reference value properly to ensure the efficiency.
Conclusion