Documentation

DTC Induction Motor Drive

Implement direct torque and flux control (DTC) induction motor drive model

Library

Electric Drives/AC drives

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™ 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 select Single 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:

Te=Jddtωr+Fωr+Tm

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.

See Mechanical Coupling of Two Motor Drives.

Use signal names as labels

When you select this check box, the Motor, Conv, and Ctrl 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 Aynchronous Machine tab displays the parameters of the Aynchronous Machine block of the Fundamental Blocks (powerlib) library.

Converters and DC Bus Tab

Rectifier Section

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.

DC Bus Section

Capacitance

The DC bus capacitance (F). Default is 2000e-6.

Braking Chopper Section

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:

Inverter Section

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 Controller Section

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.

DTC Controller Section

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.

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 or Wm

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 or S

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.

Introduced in R2006a

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