7
half-bridge topology is that leakage inductance spikes are easily clamped to the DC
supply bus and any energy stored in the leakage inductance is returned to the input
bus instead of having to be dissipated in some resistive element.
The topology works as follows. Q1 and Q2 are switched on at alternate half cycles.
The junction voltage of Q1 and Q2 is a high frequency rectangular waveform. This
rectangular wave through the LC filter will become a standard sine wave.
3.5. Bypass and INV converting circuit
The unit performs bypass and INV converting via an inverter relay and a bypass SCR.
The bypass mode: the utility power is supplied to the output terminals of the unit via
the input NFB, the inverter relay contact (generally closed) and the load-detecting
transformer.
The INV mode: the inverter output is supplied to the output terminals of the unit via the
filter choke, the inverter relay contact (generally open, closed when in INV mode) and
the load-detecting transformer.
If the INV fails, then the bypass SCR will be driven to be on and the INV bypass
converting can be realized without interruption.
3.6. Control circuit
Utility power sense circuit
This is a typical line sense circuit on the control board. The sense signals adopt
difference input these signals through some multiple attenuation, which can get a new
signal. The new signal send to the I/O port of DSP via a protect circuit. The new signal
also compare to a reference voltage in the comparator. The comparator generates a
rectangular waveform that goes high at the signal become lower than the reference
voltage and low at the signal become higher than the reference voltage. The signal of
LINE V sense the form of the line. The signal of LINE.Z sense the frequency of the line.
