MPE XR III series, Руководство оператора

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6.0 PRINCIPLE OF OPERATION
Power is fed through ac fuses and is distributed to the auxiliary power supply, inrush limiter, and
main 3
φ contactor. The auxiliary power supply operates off the ac mains supplies power to the
other printed circuit boards in the system. The inrush limiter is a step start device which is used
to initially charge capacitors on the input dc bus and limit the inrush of current. The inrush
limiter is initiated when the power supply is switched from a standby to a power state. After the
charge cycle, the main 3
φ contactor is energized and power is allowed to flow to the load. The
EMI filter filters common mode and differential mode noise emanating from the supply.
Output power is controlled through a polyphase chopper. For a 6 kW XR Series power supplies,
three choppers, phased 120° apart, provide a current source to a current fed inverter. The 4 kW
XR Series power supplies uses two choppers, phased 180° apart, and the 2 kW supplies uses only
one chopper. The choppers are controlled with current mode, pulse width modulation (PWM).
This modulation scheme provides a quick response for transients and filtering harmonics on the
dc bus. As illustrated, chopper output current is monitored for balancing and for sensing overload
current conditions. The polyphase chopper has been engineered to eliminate harmonic
components minimizing currents circulating in the power supply.
The polyphase chopper produces a controlled dc bus which is connected to dc link inductors and
current fed, IGBT inverter. The inverter, which operates above 20 kHz, excites the main
transformer at higher than normal line frequencies. This operation produces ohmic isolation
between the input and output of the power supply using a transformer of dramatically reduced
size.
The inverter operates with a 50% duty cycle and its frequency operation is transparent to the
performance of the power supply.
The output of the main power transformer is converted to dc via rectifiers. Low voltage versions
of the XR Series power supply use midpoint diode configurations and higher voltage versions use
bridge configurations.
The dc output voltage is filtered with a pie section filter. This, in combination with the dc link
inductors, form a double stage inductive capacitive (LC) filter.
The gate driver board supports a synchronized modulation scheme which integrates power
semiconductor switching of the switching power supply, polyphase chopper, and IGBT inverter.
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