DTC Induction Motor Drive
Implement direct torque and flux control (DTC) induction motor drive model
Description
The DTC Induction Motor Drive (AC4) block represents an improved scalar control drive for induction motors with direct torque and flux control. This drive features closed-loop speed control using hysteresis-band torque and flux controllers. The speed control loop outputs the reference electromagnetic torque and stator flux of the machine. The torque and flux references are compared with their estimated values, respectively, and the errors are fed to hysteresis-band controllers. The outputs of the hysteresis-band controllers are then used to obtain the required gate signals for the inverter through an optimal switching table.
The main advantage of this drive compared to other scalar-controlled drives is its improved dynamic response. This drive can reduce the impact of torque variation on the flux and conversely through an optimal switching table. Therefore, this drive is less sensitive to the inherent coupling effect (between the torque and flux) present in the machine. However, this drive requires similar signal processing as in vector-controlled drives, which makes its implementation complex compared to closed-loop Volts/Hertz controlled drives.
Note
In Simscape™
Electrical™ Specialized Power Systems software, the DTC Induction Motor Drive
block is commonly called the AC4
motor drive.
The DTC Induction Motor Drive block uses these blocks from the Electric Drives / Fundamental Drive Blocks library:
Speed Controller (AC)
Direct Torque Controller
DC Bus
Inverter (Three-Phase)
Remarks
The model is discrete. Good simulation results have been obtained with a 2 µs time step. In order to simulate a digital controller device, the control system has two different sampling times:
The speed controller sampling time
The D.T.C. controller sampling time
The speed controller sampling time has to be a multiple of the D.T.C. sampling time. The latter sampling time has to be a multiple of the simulation time step.
Parameters
General
- Output bus mode
Select how the output variables are organized. If you select
Multiple output buses
(default), the block has three separate output buses for motor, converter, and controller variables. If you selectSingle output bus
, all variables output on a single bus.- Mechanical input
Select between the load torque, the motor speed, and the mechanical rotational port as mechanical input. Default is
Torque Tm
.If you select and apply a load torque, the output is the motor speed according to the following differential equation that describes the mechanical system dynamics:
This mechanical system is included in the motor model.
If you select the motor speed as mechanical input, then you get the electromagnetic torque as output, allowing you to represent externally the mechanical system dynamics. The internal mechanical system is not used with this mechanical input selection and the inertia and viscous friction parameters are not displayed.
For the mechanical rotational port, the connection port S counts for the mechanical input and output. It allows a direct connection to the Simscape environment. The mechanical system of the motor is also included in the drive and is based on the same differential equation.
- Use signal names as labels
When you select this check box, the
Motor
,Conv
, andCtrl
measurement outputs use the signal names to identify the bus labels. Select this option for applications that require bus signal labels to have only alphanumeric characters.When this check box is cleared (default), the measurement output uses the signal definition to identify the bus labels. The labels contain nonalphanumeric characters that are incompatible with some Simulink® applications.
Asynchronous Machine Tab
The Asynchronous Machine tab displays the parameters of the Asynchronous Machine block of the Fundamental Blocks (powerlib) library.
Converters and DC Bus Tab
The Rectifier section of the Converters and DC Bus tab displays the parameters of the Rectifier block of the Fundamental Blocks (powerlib) library. For more information on the rectifier parameters, refer to the Universal Bridge reference page.
- Capacitance
The DC bus capacitance (F). Default is
2000e-6
.
- Resistance
The braking chopper resistance used to avoid bus over-voltage during motor deceleration or when the load torque tends to accelerate the motor (Ω). Default is
8
.- Chopper frequency
The braking chopper frequency (Hz). Default is
4000
.- Activation voltage
The dynamic braking is activated when the bus voltage reaches the upper limit of the hysteresis band. The following figure illustrates the braking chopper hysteresis logic. Default is
320
.- Shutdown voltage
The dynamic braking is shut down when the bus voltage reaches the lower limit of the hysteresis band. Default is
310
. The Chopper hysteresis logic is shown below:
The Inverter section of the Converters and DC Bus tab displays the parameters of the Inverter block of the Fundamental Blocks (powerlib) library. For more information on the inverter parameters, refer to the Universal Bridge reference page.
Controller Tab
- Regulation type
This parameter allows you to choose between speed and torque regulation. Default is
Speed regulation
.- Modulation type
Select hysteresis or space vector modulation. The default modulation type is
Hysteresis
.- Schematic
When you click this button, a diagram illustrating the speed and current controllers schematics appears.
- Speed ramps — Acceleration
The maximum change of speed allowed during motor acceleration (rpm/s). An excessively large positive value can cause DC bus under-voltage. This parameter is used in speed regulation mode only. Default is
1800
.- Speed ramps — Deceleration
The maximum change of speed allowed during motor deceleration (rpm/s). An excessively large negative value can cause DC bus overvoltage. This parameter is used in speed regulation mode only. Default is
-1800
.- Speed cutoff frequency
The speed measurement first-order low-pass filter cutoff frequency (Hz). This parameter is used in speed regulation mode only. Default is
100
.- Speed controller sampling time
The speed controller sampling time (s). The sampling time must be a multiple of the simulation time step. Default is
100e-6
.- PI regulator — Proportional gain
The speed controller proportional gain. This parameter is used in speed regulation mode only. Default is
5
.- PI regulator — Integral gain
The speed controller integral gain. This parameter is used in speed regulation mode only. Default is
10
.- Torque output limits — Negative
The maximum negative demanded torque applied to the motor by the current controller (N.m). Default is
-17.8
.- Torque output limits — Positive
The maximum positive demanded torque applied to the motor by the current controller (N.m). Default is
17.8
.
- Hysteresis bandwidth — Torque
The torque hysteresis bandwidth. This value is the total bandwidth distributed symmetrically around the torque set point (N.m). Default is
0.5
. The following figure illustrates a case where the torque set point is Te* and the torque hysteresis bandwidth is set to dTe.- Hysteresis bandwidth — Flux
The stator flux hysteresis bandwidth. This value is the total bandwidth distributed symmetrically around the flux set point (Wb). Default is
0.01
. The following figure illustrates a case where the flux set point is ψ* and the torque hysteresis bandwidth is set to dψ.Note
This bandwidth can be exceeded because a fixed-step simulation is used. A rate transition block is needed to transfer data between different sampling rates. This block causes a delay in the gate signals, so the current may exceed the hysteresis band.
- Initial machine flux
The desired initial stator flux established before the DTC drive module begins to produce an electromagnetic torque. This flux is produced by applying a constant voltage vector at the motor terminals (Wb). Default is
0.3
.- DTC sampling time
The DTC controller sampling time (s). The sampling time must be a multiple of the simulation time step. Default is
20e-6
.- Maximum switching frequency
The maximum inverter switching frequency (Hz). Default is
20000
.- Show/Hide Autotuning Control
Click to show or hide the parameters of the Autotuning Control tool.
- Desired damping [zeta]
Specify the damping factor used for the calculation of the Kp and Ki gains of the speed controller. Default is
0.707
.- Desired response time @ 5% [Trd (sec)]
Specify the desired settling time of the speed controller. This is time required for the controller response to reach and stay within a 5 percent range of the target value. Default is
0.01
.- Bandwidth ratio (InnerLoop/SpeedLoop)
Specify the ratio between the bandwidth and natural frequency. Default is
30
.- Calculate PI regulator gains
Compute the Proportional gain and Integral gain parameters of the Speed Controller (AC) block. The computation is based on the Desired damping [zeta], Desired response time @ 5%, and Bandwidth ratio (InnerLoop/SpeedLoop) parameters. The computed values are displayed in the mask of the Drive block. Click Apply or OK to confirm them.
Block Inputs and Outputs
SP
The speed or torque set point. The speed set point can be a step function, but the speed change rate will follow the acceleration / deceleration ramps. If the load torque and the speed have opposite signs, the accelerating torque will be the sum of the electromagnetic and load torques.
Tm
orWm
The mechanical input: load torque (Tm) or motor speed (Wm). For the mechanical rotational port (S), this input is deleted.
A, B, C
The three phase terminals of the motor drive.
Wm
,Te
orS
The mechanical output: motor speed (Wm), electromagnetic torque (Te) or mechanical rotational port (S).
When the Output bus mode parameter is set to Multiple output buses, the block has the following three output buses:
Motor
The motor measurement vector. This vector allows you to observe the motor's variables using the Bus Selector block.
Conv
The three-phase converters measurement vector. This vector contains:
The DC bus voltage
The rectifier output current
The inverter input current
Note that all current and voltage values of the bridges can be visualized with the Multimeter block.
Ctrl
The controller measurement vector. This vector contains:
The torque reference
The speed error (difference between the speed reference ramp and actual speed)
The speed reference ramp or torque reference
When the Output bus mode parameter is set to Single output bus, the block groups the Motor, Conv, and Ctrl outputs into a single bus output.
Model Specifications
The library contains a 3 hp and a 200-hp drive parameter set. The specifications of these two drives are shown in the following table.
Drive Specifications
3 HP Drive | 200 HP Drive | ||
---|---|---|---|
Drive Input Voltage | |||
Amplitude | 220 V | 460 V | |
Frequency | 60 Hz | 60 Hz | |
Motor Nominal Values | |||
Power | 3 hp | 200 hp | |
Speed | 1705 rpm | 1785 rpm | |
Voltage | 220 V | 460 V |
Examples
The ac4_example
example illustrates the simulation of an AC4
motor drive with standard load condition.
References
[1] Bose, B. K. Modern Power Electronics and AC Drives. Upper Saddle River, NJ: Prentice-Hall, 2002.
[2] Grelet, G. and G. Clerc. Actionneurs électriques. Paris: Éditions Eyrolles, 1997.
[3] Krause, P. C. Analysis of Electric Machinery. New York: McGraw-Hill, 1986.
Version History
Introduced in R2006a