DC Machine

Implement wound-field or permanent magnet DC machine

• 

Libraries:
Simscape / Electrical / Specialized Power Systems / Electrical Machines

Description

The DC Machine block implements a wound-field or permanent magnet DC machine.

For the wound-field DC machine, you can access the field terminals (F+, F−) to use the machine model as a shunt-connected or a series-connected DC machine. The Simulink^® input T_L provides the torque applied to the shaft.

The armature circuit (A+, A−) consists of an inductor La and resistor Ra in series with a counter-electromotive force (CEMF) E.

The CEMF is proportional to the machine speed.

E = KEω

(1)

K_E is the voltage constant and ω is the machine speed.

In a separately excited DC machine model, the voltage constant K_E is proportional to the field current I_f:

KE = LafIf,

(2)

L_af is the field-armature mutual inductance.

The electromechanical torque that the DC Machine block develops is proportional to the armature current I_a.

Te = KTIa,

(3)

K_T is the torque constant. The sign convention for T_e and T_L is:

Te , TL > 0: Motor mode Te, TL < 0: Generator mode

(4)

The torque constant is equal to the voltage constant.

KT = KE.

(5)

The armature circuit is connected between the A+ and A− ports of the DC Machine block. It is represented by a series Ra La branch in series with a Controlled Voltage Source and a Current Measurement block.

In the wound-field DC machine model, the field circuit is represented by an RL circuit. It is connected between the F+ and F− ports of the DC Machine block.

In the permanent magnet DC machine model, there is no field current as the magnets establish the excitation flux. K_E and K_T are constants.

The mechanical part computes the speed of the DC machine from the net torque applied to the rotor. The block uses the speed to implement the CEMF voltage E of the armature circuit.

The mechanical part implements this equation:

$$J\frac{d\omega }{dt}=T_e-T_L-B_m\omega -T_f,$$

where J is the inertia, B_m is the viscous friction coefficient, and T_f is the Coulomb friction torque.

Examples

Starting a DC Motor

The starting of a 5 HP 240V DC motor with a three-step resistance starter.

• Open Model

Ports

Input

TL — Mechanical load torque, N*m

scalar

Mechanical load torque, in N*m.

Dependencies

To enable this port, set Mechanical input to Torque TL.

w — Machine speed, rad/s

scalar

Speed of the machine, in rad/s.

Dependencies

To enable this port, set Mechanical input to Speed w.

Output

m — Measurement signals

four elements vector

Vector of measurement signals. To demultiplex these signals, use the Bus Selector block in the Simulink library.

Name	Definition	Units
w	Speed wm	rad/s
iA	Armature current ia	A
iF	Field current if	A
Te	Electrical torque Te	N.m

Conserving

A+ — Positive terminal of armature

specialized electrical

Specialized electrical conserving port associated with the positive terminal of the armature circuit.

A- — Negative terminal of armature

specialized electrical

Specialized electrical conserving port associated with the negative terminal of the armature circuit.

F+ — Positive terminal of field circuit

specialized electrical

Specialized electrical conserving port associated with the positive terminal of the field circuit.

Dependencies

To enable this port, set Field type to Wound.

F- — Negative terminal of field circuit

specialized electrical

Specialized electrical conserving port associated with the negative terminal of the field circuit.

Dependencies

To enable this port, set Field type to Wound.

S — Machine shaft

mechanical rotational

Mechanical rotational conserving port associated with the machine shaft.

Dependencies

To enable this port, set Mechanical input to Mechanical rotational port.

Parameters

Configuration

Preset model — Set of predetermined electrical and mechanical parameters for DC machine

No (default) | 01: 5HP 240V 1750RPM Field:300V | 02: 5HP 240V 1750RPM Field:150V | 03: 5HP 500V 1750RPM Field:300V | 04: 10HP 240V 1750RPM Field:300V | 05: 10HP 500V 1750RPM Field:300V | 06: 20HP 240V 1750RPM Field:300V | 07: 20HP 500V 1750RPM Field:300V | 08: 30HP 240V 1750RPM Field:300V | 09: 30HP 500V 1750RPM Field:300V | 10: 40HP 240V 1750RPM Field:300V | 11: 40HP 500V 1750RPM Field:300V | 12: 50HP 240V 1750RPM Field:300V | 13: 50HP 500V 1750RPM Field:300V | 14: 75HP 500V 1750RPM Field:300V | 15: 100HP 500V 1750RPM Field:300V | 16: 125HP 500V 1750RPM Field:300V | 17: 150HP 500V 1750RPM Field:300V | 18: 175HP 500V 1750RPM Field:300V | 19: 200HP 440V 1184RPM Field:310V | 20: 200HP 500V 1750RPM Field:150V | 21: 200HP 500V 1750RPM Field:300V | 22: 225HP 500V 1750RPM Field:300V | 23: 250HP 500V 1750RPM Field:300V

Option to choose a set of predetermined electrical and mechanical parameters for various DC machine ratings of power (HP), DC voltage (V), rated speed (rpm), and field voltage (V).

Select one of the preset models to load the corresponding electrical and mechanical parameters in the entries of the dialog box. Select No if you do not want to use a preset model, or if you want to modify some of the parameters of a preset model.

When you select a preset model, the electrical and mechanical parameters in the Parameters section of the dialog box become unmodifiable (unavailable). To start from a given preset model and then modify machine parameters:

1. Select the preset model that you want to initialize the parameters.

2. Change the Preset model parameter value to No. This does not change the machine parameters. By doing so, you break the connection with the particular preset model.

3. Modify the machine parameters as you want, then click Apply.

Dependencies

To enable this parameter, set Field type to Wound.

Mechanical input — Mechanical input

Torque TL (default) | Speed w | Mechanical rotational port

Torque applied to the shaft or the rotor speed as a Simulink input of the block, or represent the machine shaft by a Simscape™ rotational mechanical port:

• Torque TL — Specify a torque input, in N*m. The block determines the machine speed by using the machine Inertia J and the difference between the applied mechanical load torque TL and the internal electromagnetic torque Te. The sign convention for the mechanical torque is: when the speed is positive, a positive torque signal indicates motor mode and a negative signal indicates generator mode.

• Speed w — Specify a speed input, in rad/s. The block imposes the machine speed and ignores the mechanical part of the model (inertia J). Use the speed as the mechanical input to model a mechanical coupling between two machines.

  The next figure indicates how to model a stiff shaft interconnection in a motor-generator. The speed output of machine 1 (motor) is connected to the speed input of machine 2 (generator), while machine 2 electromagnetic torque output Te is applied to the mechanical load torque input TL of machine 1. The Kw factor takes into account speed units of both machines (rad/s) and gear box ratio. The KT factor takes into account torque units of both machines (N.m) and machine ratings. Also, as the inertia J2 is ignored in machine 2, J2 referred to machine 1 speed must be added to machine 1 inertia J1.

  

• Mechanical rotational port — Add to the block a Simscape mechanical rotational port that allows connection of the machine shaft with other Simscape blocks having mechanical rotational ports.

  The next figure indicates how to connect an Ideal Torque Source block from the Simscape library to the machine shaft to represent the machine in motor mode, or in generator mode, when the rotor speed is positive.

  

Field type — Field type of machine

Wound (default) | Permanent magnet

Whether to model a wound-field machine or a permanent magnet DC machine.

Measurement output

Use signal names to identify bus labels — Whether to use signal names in measurement output

off (default) | on

Whether to use the signal names in the measurement output to identify the bus labels. Select this parameter for applications that require bus signal label to have only alphanumeric characters.

When you clear this parameter, the measurement output uses the signal definition to identify the bus labels. The labels contain non alphanumeric characters that are incompatible with some Simulink applications.

Parameters

Armature resistance and inductance [Ra (ohms) La (H) ] — Armature resistance and inductance

[ 0.6 0.012] (default)

Armature resistance Ra, in ohms, and armature inductance La, in henries.

Field resistance and inductance [Rf (ohms) Lf (H) ] — Field resistance and inductance

[ 240 120] (default)

Field resistance Rf, in ohms, and field inductance Lf, in henries.

Dependencies

To enable this parameter, in the Configuration section, set Field type to Wound.

Field-armature mutual inductance Laf (H) — Field-armature mutual inductance

1.8 (default)

Field-armature mutual inductance, in henries.

Dependencies

To enable this parameter, in the Configuration section, set Field type to Wound.

Specify — Machine constant for block parameterization

Torque constant (N.m/A) (default) | Back-emf constant (V/rpm)

For a permanent magnet DC machine, select the machine constant that you want to specify for block parameterization.

Dependencies

To enable this parameter, in the Configuration section, set Field type to Permanent magnet.

Back-emf constant (V/rpm) — Voltage per speed constant

1.8 (default)

Voltage per speed constant of the permanent magnet DC machine, in V/rpm.

Dependencies

To enable this parameter, in the Configuration section, set Field type to Permanent magnet and, in the Parameters section, set Specify to Back-emf constant.

Torque constant (N.m/A) — Torque per current constant

1.8 (default)

Torque per current constant of the permanent magnet DC machine, in N.m/A.

Dependencies

To enable this parameter, in the Configuration section, set Field type to Permanent magnet and, in the Parameters section, set Specify to Torque constant.

Total inertia J (kg.m^2) — Total inertia of DC machine

1 (default)

Total inertia of the DC machine, in kg.m².

Viscous friction coefficient Bm (N.m.s) — Total friction coefficient of DC machine

0 (default)

Total friction coefficient of the DC machine, in N.m.s.

Coulomb friction torque Tf (N.m) — Coulomb friction torque constant of DC machine

0 (default)

Total Coulomb friction torque constant of the DC machine, in N.m.

Initial speed (rad/s) — Initial speed for DC machine

1 (default)

Initial speed for the DC machine, in rad/s, in order to start the simulation with a specific initial speed. To start the simulation in steady state, the initial value of the input torque signal T_L must be proportional to the initial speed.

Advanced

Sample time (-1 for inherited) — Sample time of block

-1 (default)

Sample time that the block uses. To inherit the sample time specified in the Powergui block, set this parameter to −1.

References

[1] Analysis of Electric Machinery, Krause et al., pp. 89–92.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced before R2006a