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28 Operation principle and hardware description
AC voltage and current waveforms
The AC line current of the drive is sinusoidal with power factor equal to 1. The IGBT
supply unit does not generate characteristic current or voltage overtones like a
traditional 6- or 12-pulse bridge does.
The Total Harmonic Distortion (THD) in current is given in
(page 128). The THD in voltage depends slightly on the Short Circuit Ratio in the
Point of Common Coupling (PCC). The high frequency switching and high d
slightly distort the voltage waveform at the input of the converter.
Typical line current (
Example spectra of the current and voltage distortion at the output of the
transformer are shown below. Each harmonic is presented as compared to
fundamental voltage (reference value = 1). n denotes the ordinal number of the
harmonic.
Test 13
Phase current (A)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Motor control
The motor control is based on the Direct Torque Control (DTC) method. Two phase
currents and DC link voltage are measured and used for the control. The third phase
current is measured for earth fault protection.
i
u
) and voltage (
) waveforms are shown below.
u (V)
i (A)
IL1 [A]
n
Input power connection
t (ms)
t (ms)
Test 13
Line-to-line voltage (%)
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
u
t
/d
UL12 [%]
n
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