SimPowerSystems

DC Machine

Implement a separately excited DC machine

Library

Machines

Description

This block implements a separately excited DC machine. An access is provided to the field terminals (F+, F-) so that the machine model can be used as a shunt-connected or a series-connected DC machine.

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

The CEMF is proportional to the machine speed.

K_E is the voltage constant and is the machine speed.

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

where L_af is the field-armature mutual inductance.

The electromechanical torque developed by the DC machine is proportional to the armature current Ia

where K_T is the torque constant. The sign convention for T_e is

The torque constant is equal to the voltage constant.

The armature circuit is connected between the A+ and A- ports of the DC Machine block. It is represented by a Series RLC Branch block in series with a Controlled Voltage Source and a Current Measurement block.

The field circuit is represented by an RL circuit. It is connected between the F+ and F- ports of the DC Machine block.

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

The mechanical part is represented by Simulink blocks that implement the equation

Measurements

Four internal signals are multiplexed on the Simulink measurement output vector returning

• Rotor speed in rad/s
• Armature current in A
• Field current in A
• Electromechanical torque in N.m

Dialog Box

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

The armature resistance Ra, in ohms, and the armature inductance La, in henries.

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

The field resistance Rf, in ohms, and the field inductance Lf, in henries.

Field-armature mutual inductance Laf (H):

The field armature mutual inductance, in henries.

Total inertia J (kg.m^2)

The total inertia of the DC machine, in kg.m².

Viscous friction coefficient Bm (N.m.s)

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

Coulomb friction torque Tf (N.m)

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

Initial speed (rad/s)

Specifies an 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 TL must be proportional to the initial speed.

Example

The psbdcmotor.mdl demo illustrates the starting of a 5 HP 240 V DC machine with a three-step resistance starter.

The Motor Starter subsystem is

Reference

Reference Analysis of Electric Machinery, Krause et al., pp. 89-92.

See Also

Asynchronous Machine, Synchronous Machine

Current Measurement

DC Voltage Source