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INV 2500 SERIES MANUAL REV 1 1/13
SECTION 4
TROUBLE SHOOTING
4.1
THEORY OF OPERATION
The INV 2500 series utilizes high frequency, switched mode, power conversion to convert
the incoming DC to an AC output. The first stage is a DC to DC converter which “steps - up”
the input voltage to a reg/- 200 Vdc. This voltage is applied to a second high
frequency “housekeeping” supply and the output inverter. The housekeeping supply provides
operating voltages for the output inverter and alarm circuits. The output section consists of
a crystal controlled sine wave oscillator and class “D” power amplifier. The crystal derived
clock frequency is divided down and applied to a counter, PROM, D/A converter
combination. The resulting sine wave at the output frequency is applied to the power
amplifier and boosted to the 120 VAC level required on the output.
The power amplifier consists of a pulse width modulated ( PWM ) “half bridge” circuit utilizing
IGBT output devices. The devices are switched at a rate of 20 KHZ and modulated with the
sine wave information. The result is a 400V p/p pulse train at the output that contains the
original sine wave information. The 20 KHz “carrier” frequency is removed by a low pass LC
filter . This provides an amplified version of the original modulation signal to the output
terminals. The control circuitry on the output inverter assembly also provides output
regulation and protective functions. The output voltage RMS value is monitored and used to
keep the output regulated. Output current is measured and used to provide fold back type
limiting in the event of an overload. Output short circuits will disable the inverter stage,
requiring the input power to be recycled to return proper operation.
The alarm and bypass circuits ( if provided ) allow for external monitoring of input and output
status. The AC input/ bypass feature allows the AC power line to be applied to the model INV
2500 and sent directly to the output terminals. In the event the AC is interrupted, a relay will
switch the output to the inverter. Units supplied with the D1 option will switch the line through
when the DC is not available or the inverter has a fault. The AC input is fused at 30 amps.
Figure 4-1 INV 2500 Block Diagram ( with By-pass option)
