Implement two-quadrant three-phase rectifier DC drive

Electric Drives/DC drives

The Two-Quadrant Three-Phase Rectifier DC Drive (DC3) block represents a two-quadrant, three-phase, thyristor-based (or phase controlled) drive for DC motors. This drive features closed-loop speed control with two-quadrant operation. The speed control loop outputs the reference armature current of the machine. Using a PI current controller, the thyristor firing angle corresponding to the commanded armature current is derived. This firing angle is then used to obtain the required gate signals for the rectifier through a thyristor bridge firing unit.

The main advantage of this drive, compared with other DC drives, is its implementation simplicity. However, for all two-quadrant DC drives, reversible and regenerative operations (reverse motoring and forward regeneration), which are required in most DC drives, cannot be obtained.

In Simscape™
Power Systems™ software, the Two-Quadrant Three-Phase Rectifier DC Drive block is
commonly called the `DC3`

motor drive.

The Two-Quadrant Three Phase Rectifier DC Drive block uses these blocks from the Electric Drives/Fundamental Drive Blocks library:

Speed Controller (DC)

Regulation Switch

Current Controller (DC)

Bridge Firing Unit (DC)

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 a three-phase rectifier controlled by two PI regulators. Armature current oscillations are reduced by a smoothing inductance connected in series with the armature circuit.

The average-value converter represents the average behavior of a three-phase rectifier for continuous armature current. This model is thus not suitable for simulating DC drives under discontinuous armature current conditions. The converter outputs a continuous voltage value equal to the average-value of the real-life rectified voltage. The armature voltage, armature current, and electromagnetic torque ripples are thus not represented. The input currents have the frequency and amplitude of the fundamental current component of the real-life input currents.

The model is discrete. Good simulation results have been obtained with a 20-µs time step. The control system (speed and current controllers) samples data following a user-defined sample time in order to simulate a digital controller device. Keep in mind that this sampling time has to be a multiple of the simulation time step.

The average-value converter allows the use of bigger simulation time steps since it does not generate small time constants (due to the RC snubbers) inherent to the detailed converter. For a controller sampling time of 100-µs good simulation results have been obtained for a simulation time step of 100 µs. This time step cannot be higher than the controller time step.

**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:

$${T}_{e}=J\frac{d}{dt}{\omega}_{r}+F{\omega}_{r}+{T}_{m}$$

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.

**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.

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

The **Rectifier** section of the **Converter** tab
displays the parameters of the Universal Bridge block
of the Fundamental Blocks (powerlib) library. For more information
on the thyristor converter parameters, refer to the Universal Bridge reference
page.

**Smoothing inductance**The smoothing inductance value (H). Default is

`50e-3`

.**Field DC source**The DC motor field voltage value (V). Default is

`150`

.

**Phase-to-phase rms voltage**Phase-to-phase rms voltage of the three-phase voltage source connected to the A,B,C terminals of the drive (V). This parameter is not used when using the detailed rectifier. Default is

`220`

.**Frequency**Frequency of the three-phase voltage source connected to the A,B,C terminals of the drive (Hz). This parameter is not used when using the detailed rectifier. Default is

`50`

.**Source inductance**Source inductance of the three-phase voltage source connected to the A,B,C terminals of the drive (H). This parameter is not used when using the detailed rectifier. Default is

`1e-6`

.**Phase angle of phase A**Phase angle of phase A of the three-phase voltage source connected to the A,B,C terminals of the drive (deg). This parameter is not used when using the detailed rectifier. Default is

`0`

.

**Regulation type**This pop-up menu allows you to choose between speed and torque regulation. Default is

`Speed regulation`

.**Sampling time (s)**The controller (speed and current) sampling time (s). The sampling time has to be a multiple of the simulation time step. Default is

`100e-6`

.**Schematic**When you click this button, a diagram illustrating the speed and current controllers schematics appears.

**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`

.**Proportional gain**The proportional gain of the PI speed controller. Default is

`80`

.**Integral gain**The integral gain of the PI speed controller. Default is

`200`

.**Acceleration**The maximum change of speed allowed during motor acceleration (rpm/s). Too great a value can cause armature over-current. Default is

`250`

.**Deceleration**The maximum change of speed allowed during motor deceleration (rpm/s). Too great a value can cause armature over-current. Default is

`-250`

.

**Low-pass filter cutoff frequency**Cutoff frequency of the low-pass filter used to filter the armature current measurement (Hz). Default is

`50`

.**Reference limit**Maximum current reference value (pu). 1.5 pu is a common value. Default is

`1.5`

.**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`5*746`

. Default for**Voltage**is`240`

.**Proportional gain**The proportional gain of the PI current controller. Default is

`1`

.**Integral gain**The integral gain of the PI current controller. Default is

`80`

.

**Alpha min**Minimum firing angle value (deg.). 20 degrees is a common value. Default is

`20`

.**Alpha max**Maximum firing angle value (deg.). 160 degrees is a common value. Default is

`160`

.**Frequency of synchronization voltages**Frequency of the synchronization voltages used by the discrete synchronized 6-pulse generator block (Hz). This frequency is equal to the line frequency of the three-phase power line. This parameter is not used when using the average-value converter. Default is

`50`

.**Pulse width**The width of the pulses applied to the six thyristor gates (deg.). This parameter is not used when using the average-value converter. Default is

`10`

.

`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 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 three-phase converter measurement vector. It 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 detailed rectifier bridge can be visualized with the mulimeter block

`Ctrl`

The controller measurement vector. This vector contains:

The armature current reference

The firing angle computed by the current controller

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.

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 | 220 V | 460 V | |

Frequency | 50 Hz | 60 Hz | |

| |||

Power | 5 hp | 200 hp | |

Speed | 1750 rpm | 1750 rpm | |

Voltage | 240 V | 500 V |

The `dc3_example`

illustrates the three-phase rectifier drive used with the
200-hp drive parameter set during torque regulation.

[1] Sen, P.C., *Thyristor DC Drives*,
J.Wiley and Sons, 1981.

[2] Nondahl, Thomas A., *Microprocessor
Control of Motor Drives and Power Converters*, *tutorial
course*, IEEE Industry Application Society, October 1993,
pp. 7.1-7.26.

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