2-2-2 Power cell
The power cell is a basic cell of medium voltage drive for realizing variable voltage and
frequency output. It is mainly comprised of fast acting fuses, a rectification bridge, DC bus
capacitance, IGBT inverting bridge, and etc.
The input terminal of the power cell is connected with the three-phase winding of the
secondary side of the phase-shift transformer, the three phase diode provides full-wave
rectification to charge the DC bus capacitance, and the voltage on the capacitance is
provided to the H-bridge single-phase bridge inverter circuit formed by 4 IGBTs.
The power cell receives signals by means of optical fibers, and controls the closing and
opening of the S1~S4 IGBTs by using PWM modulation mode to output a single-phase
impulse modulated waveform. Each cell only has three possible output states: when S1 and
S4 are closed, the state of the output voltage Vuv is Vdc, when S2 and S3 are closed, the
output voltage Vuv is -Vdc, and when S1 and S3 or S2 and S4 are closed, the output voltage
Vuv is 0.
Fig. 2-10 shows the waveform diagram of the output voltage waveform of each power
cell and the superimposed output phase voltage waveform when 6 cells are connected in
series. As shown in the figure, 13 voltage levels are obtained through connecting the 6 power
cells in series. The increasing number of the voltage levels reduces the distortion content of
the output voltage and simultaneously lowers the risk of damaging the motor insulation
caused by dv/dt. Fig. 2-11 and Fig. 2-12 are the waveform diagram of the output voltage &
current of the MVD when loaded by a motor.
Fig. 2-10 Output & phase voltage diagram
Fig. 2-11 Output line-to-line voltage waveform Fig. 2-12 Output current waveform
Summary of Contents for MVF2000 Series
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