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Application Report
SLUA076 - July 2000
1
A Simplified Approach to dc Motor Modeling
for Dynamic Stability Analysis
Edited by Mickey McClure Power Supply Control Products
ABSTRACT
When we say that an electric motor is a device that transforms electric power into mechanical
power, we say two things. First, that the motor is – and behaves as – a transformer. Second,
that it stands at the dividing line between electrical and mechanical phenomena. In the case
of permanent magnet (PM) motors, this power transformation works in both directions so that
the elecrical impedance depends on the mechanical load, while the mechanical behavior of
the motor depends on the conditions at the electrical end. This being the case, it should be
possible to represent a motor’s mechanical load, on the electrical side, by a set of familiar
electrical components such as capacitors or resistors.
Contents
1 Choosing a Unit System 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 The Motor as a Transformer 3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 A Motor Model 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.1 Measuring the Components 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2 The Motor’s Transfer Function 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 A Disk Drive Example 7. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
