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Three Phase Inverter Motors
Ben Kemink
Three Phase Inverter Motor
At the end of this training session you will have
learned;
1. There are different three-phase measurements.
2. Pulse Width Modulation.
3. Inverter Driven Applications mess-up with Period
Time T.
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Three Phase Systems
A One-Phase System, also called a Single-Phase (SP)
System works very much similar to a DC network and can
be considered so far at any particular moment in time.
Electrical Systems comprising two or more phases are
also called Multi-Phase or Poly-Phase (PP) systems.
The voltage amplitudes and frequencies in the individual
system circuits are the same, but they have definite
phase differences.
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Why Poly-Phase?
The technical complications and economical investments
are small compared to the enormous advantages of a
Poly-Phase system:
1. Same size generator or motor, higher output.
2. Same energy transmission less copper required.
3. PP motors have uniform torque, SP have pulsating
torque *).
4. PP motors are self-starting, SP are not *).
5. Polyphase generators work fine parallel, SP not.
*) Single Phase commutator motors are exception.
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Why 3 Phase and not 7?
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Three Phase is ideal
Source: Advanced Electrical Technology by H.Cotton
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Three-Phase Three-Wire
Total Power calculation based on Two-Watt-meter method
3 wires – 1 = 2 power meters required
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Three-Phase Four-Wire
4 wires - 1 = 3 Watt meters are required
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Three-Voltage Three-Current
Calculation based on Two-Watt meter method.
Third Phase measurements are added.
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Three-Phase Three-Wire with PT & CT
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Introduction
 What is Three phase?


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Three phase = three signals
Phase shift: 1200
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Figure 1: Phase shift 1200
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Pulse Width Modulation of a Sine Wave
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Demonstration circuit
Demonstration circuit consists of:
Frequency inverter;
 3-Phase Electromotor;
 Power meter;

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Figure 2: Demonstration circuit
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Demonstration circuit
 Freq. inverter
Step 1:
 Step 2:

AC → DC
DC → 3-Phase
T
T
Control unit
0 Hz →
50 Hz
L1(mains)
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Figure 3: Block diagram 1phase inverter
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Demonstration circuit
 Freq. inverter

Step 1: rectifying
AC → DC
Performed by rectifier;
 DC-signal is smoothened
by capacitor;
 In 3phase mains the output
of the rectifiers is
connected to the same
capacitor;
Example:
Single phase rectifying

t→
Figure 4: rectifier
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Demonstration circuit
 Freq. inverter
 Step 2: regeneration of 3-Phase-signals

Six switches
Generate periodic pulse-trains;
 Insulated Gate Bipolair Transistor (IGBT);
 High frequency switches;

New Period T
U
t
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t
Figure 5: Inverter step 2: regeneration of AC-signals
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Demonstration circuit
 Freq. inverter
YEF-HQ Test Motor
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Figure 6: Output of Freq. Inverter: 1-phase, current (green) / voltage (yellow)
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Running the motor
CW
 Direction

Direction (CCW or CW)

U
Can be changed by
manipulating the pulses
V
W
CCW
U
V
W
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Running the motor
 Speed
T
Slow
 Depends on the switching
frequency
U
V
W
Two times faster
T
U
V
W
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Running the motor
 Speed:

20

Slow

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voltage (yellow) and current (green)
1s time window
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Faster

1s time window
Figure 7: Output of Freq. Inverter at different speeds
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Now you have learned;
1. There are different three-phase measurements.
2. What Pulse Width Modulation is.
3. Why Inverters mess-up with Period Time T.
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Thank you for your attention
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