Elgar SW5250A Service Manual download pdf (Page 19)

SERVICE MANUAL THEORY OF OPERATION

1-9

The PFC module is a two–board assembly consisting of a PFC Power and a PFC

Control board. The single–phase AC input voltage enters the PFC power board where it

is rectified by the full-wave bridge rectifier circuit, developing a raw 380 Vdc bus. The

raw 380 Vdc bus is then delivered through a soft–start relay to the PFC circuit, which is

comprised of a boost converter. The output of the PFC, a regulated 380 Vdc bus, is

then delivered to the DC/DC stage of the power module. The 380 Vdc bus is also

converted down to a 24 Vdc bus used to power the control circuitry for the PFC power

and control boards.

CAUTION

When the PFC module is configured for the INTERNATIONAL input

configuration, the input neutral must be connected. Failure to do so

will result in catastrophic damage to the PFC input.

1.7.3 DC/DC CONVERTER

The DC/DC converter module, or just DC/DC, is a two–board assembly consisting of a

DC/DC Converter Power and a DC/DC Converter Control board. The DC/DC serves two

purposes. First, to provide isolation between the 3 phase input voltage and the eventual

output voltage used by the customer. Second, to generate the two isolated 290 Vdc

buses used by the amplifier and a 48 Vdc bus used by the HSKP board and fan panel

assembly. The DC/DC converter circuit is rated for 2000 watts and consists of a PWM

controlled full H-bridge, which chops (switches) the 380 Vdc bus supplied by the

rectifier or PFC input stage at a rate of 140 kHz. The output transformer and three full-

wave bridge rectifier circuits then generate the two 290 Vdc and 48 Vdc buses. The

output transformer and associated rectifier circuitry also produces a 27 Vdc bus which

provides power for the DC/DC PWM control circuit.

1.8 AMPLIFIER MODULE

The amplifier module is a four board assembly consisting of an Amplifier Power, an

Amplifier Control and two Gate Drive boards. The amplifier module is in fact comprised

of two 156 V / 6.5 A amplifiers (upper and lower) which can be series or paralleled by

relay K1 on the Amplifier Power board to produce a single 312 V / 6.5 A or 156 V / 13 A

output. Relay K2 is the amplifier output relay but breaks only the line connection to the

output filter and not the neutral. The drive circuits for K1 and K2 are located on the

amplifier control board and respond to commands from the Analog board. Both the

upper and lower amplifiers consist of identical full H-bridges that vary only in the

method in which the bridge current is measured. The lower bridge uses a shunt resistor

to monitor the bridge current while the upper bridge uses a hall-effect current

transformer to provide isolation.

The amplifier control board contains the PWM circuit that generates the drive

waveforms to the upper and lower H-bridges from the input voltage reference signal

sent by the Analog board and the current feedback signals from the upper and lower

bridges. The amplifier runs at a frequency of 200 kHz, interleaved, which equates to an

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Elgar SW5250A Service Manual Page 19