Four-Quadrant Chopper DC Drive

Implement four-quadrant chopper DC drive

Description

The Four-Quadrant Chopper DC Drive (DC7) block represents a four-quadrant, DC-supplied, chopper (or DC-DC PWM converter) drive for DC motors. This drive features closed-loop speed control with four-quadrant operation. The speed control loop outputs the reference armature current of the machine. Using a PI current controller, the chopper duty cycle corresponding to the commanded armature current is derived. This duty cycle is then compared with a sawtooth carrier signal to obtain the required PWM signals for the chopper.

The main advantage of this drive, compared with other DC drives, is that it can operate in all four quadrants (forward motoring, reverse regeneration, reverse motoring, and forward regeneration). In addition, due to the use of high switching frequency DC-DC converters, a lower armature current ripple (compared with thyristor-based DC drives) is obtained. However, four switching devices are required, which increases the complexity of the drive system.

Note

In Simscape™ Electrical™ Specialized Power Systems software, the Four-Quadrant Chopper DC Drive block is commonly called the DC7 motor drive.

The Four-Quadrant Chopper DC Drive block uses these blocks from the Electric Drives/Fundamental Drive Blocks library:

Speed Controller (DC)
Regulation Switch
Current Controller (DC)
Chopper

Remarks

The machine is separately excited with a constant DC field voltage source. There is thus no field voltage control. By default, the field current is set to its steady-state value when a simulation is started.

The armature voltage is provided by an IGBT converter controlled by two PI regulators. The converter is fed by a constant DC voltage source. Armature current oscillations are reduced by a smoothing inductance connected in series with the armature circuit.

The model is discrete. Good simulation results have been obtained with a 1-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 current controller sampling time

The speed controller sampling time has to be a multiple of the current sampling time. The latter sampling time has to be a multiple of the simulation time step.

General

Output bus mode

Select how the output variables are organized. If you select Multiple output buses, 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.

Model detail level

Select between the detailed and the average-value inverter. Default is Detailed

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:

$T_{e} = J \frac{d}{d t} ω_{r} + F ω_{r} + T_{m}$

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.

DC Machine Tab

The DC Machine tab displays the parameters of the DC Machine block of the Fundamental Blocks (powerlib) library.

Converter Tab

Smoothing Inductance and Excitation Circuit Section

Smoothing inductance: The smoothing inductance value (H). Default is 10e-3.
Field DC source: The DC motor field voltage value (V). Default is 150.

IGBT/Diode Device Section

The IGBT/Diode device section of the Converter tab displays the parameters of the Universal Bridge block of the Fundamental Blocks (powerlib) library. For more information on the Universal Bridge block parameters, refer to the Universal Bridge reference page.

Controller Tab

Regulation type: This pop-up menu allows you to choose between speed and torque regulation. Default is Speed regulation.
Schematic: When you click this button, a diagram illustrating the speed and current controllers schematics appears.

Controller — Speed Controller Subtab

Nominal speed: The nominal speed value of the DC motor (rpm). This value is used to convert motor speed from rpm to pu (per unit). Default is 1750.
Initial speed reference: The initial speed reference value (rpm). This value allows the user to start a simulation with a speed reference other than 0 rpm. Default is 0.
Low-pass filter cutoff frequency: Cutoff frequency of the low-pass filter used to filter the motor speed measurement (Hz). Default is 40.
Sampling time: The speed controller sampling time (s). This sampling time has to be a multiple of the current controller sampling time and of the simulation time step. Default is 100e-6.
Proportional gain: The proportional gain of the PI speed controller. Default is 10.
Integral gain: The integral gain of the PI speed controller. Default is 50.
Acceleration: The maximum change of speed allowed during motor acceleration (rpm/s). Too great a value can cause armature over-current. Default is 1000.
Deceleration: The maximum change of speed allowed during motor deceleration (rpm/s). Too great a value can cause armature over-current. Default is -1000.

Controller — Current Controller Subtab

Low-pass filter cutoff frequency: Cutoff frequency of the low-pass filter used to filter the armature current measurement (Hz). Default is 500.
Reference limit: Symmetrical current reference (pu) limit around 0 pu. 1.5 pu is a common value. Default is 1.5.
PWM switching frequency: The switching frequency of the four IGBT devices (Hz). Default is 5e3.
Sampling time: The current controller sampling time (s). This sampling time has to be a submultiple of the speed controller sampling time and a multiple of the simulation time step. Default is 20e-6.
Power and Voltage nominal values: The DC motor nominal power (W) and voltage (V) values. These values are used to convert armature current from amperes to pu (per unit). Default for Power is 200*746. Default for Voltage is 440.
Proportional gain: The proportional gain of the PI current controller. Default is 2.
Integral gain: The integral gain of the PI current controller. Default is 200.

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.
Vcc, Gnd: The DC voltage source electric connections. The voltage must be adequate for the motor size.
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 is composed of two elements:

The armature voltage
The DC motor measurement vector (containing the speed, armature current, field current, and electromagnetic torque values). Note that the speed signal is converted from rad/s to rpm before output.

Conv

The IGBT/Diode device measurement vector. This vector includes the converter output voltage. The output current is not included since it is equal to the DC motor armature current. Note that all current and voltage values of the converter can be visualized with the Multimeter block.

Ctrl

The controller measurement vector. This vector contains:

The armature current reference
The duty cycle of the PWM pulses
The speed or torque error (difference between the speed reference ramp and actual speed or between the torque reference and actual torque)
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 5 hp and a 200-hp drive parameter set. The specifications of these two drives are shown in the following table.

5 HP and 200 HP Drive Specifications

		5 HP Drive	200 HP Drive
Drive Input Voltage
	Amplitude	280 V	500 V
Motor Nominal Values
	Power	5 hp	200 hp
	Speed	1750 rpm	1184 rpm
	Voltage	240 V	440 V

Examples

The dc7_example example illustrates the four-quadrant chopper drive used with the 200-hp drive parameter set during speed regulation.

References

[1] Boldea, Ion, and S.A. Nasar, Electric Drives, CRC Press LLC, 1999.

[1] Séguier, Guy, Electronique de puissance, Dunod, 1999.