Power Section - GE AF-650 GP Operating Instructions Manual

High Power Service Manual for Unit Sizes 6x

3.2.3 Power Section

The high voltage power section consists of AC input terminals, AC and DC bus bars, fusing, harnessing, AC output, and optional components. The power section
(see illustration below) also contains circuitry for the soft charge and SCR/diode modules in the rectifier; the DC bus filter circuitry containing the DC coils, often
referred to as the intermediate or DC bus circuit; and the output IGBT modules which make up the inverter section.
In conjunction with the SCR/diode modules, the soft charge circuit limits the inrush current when power is first applied and the DC bus capacitors are charging.
This is accomplished by the SCRs in the modules being held off while charging current passes through the soft charge resistors, thereby limiting the current. The
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DC bus circuitry smooths the pulsating DC voltage created by the conversion from the AC supply.
Each unit contains one DC coil per inverter module. Therefore the 61/63 units contain two DC coils and the 62/64 units contain three. The DC coil has two coils
wound on a common core. One coil resides in the positive side of the DC bus and the other in the negative. The coil reduces mains harmonics.
The DC bus capacitors are arranged into a capacitor bank along with bleeder and balancing circuitry. Each inverter module contains two DC capacitor banks.
The inverter section is made up of six IGBTs, commonly referred to as switches. Two switches are necessary for each phase of the three-phase power, for a total
of six switches per IGBT module (half-phase per switch). Three IGBT modules run in parallel are contained in each inverter due to the high current handling
requirements. Each inverter can be paralleled with one or two additional inverter modules to provide the required current for the power size.
A Hall effect type current sensor is located on each phase of the inverter module output to measure motor current. This type of device is used instead of more
common current transformer (CT) devices to reduce the frequency and phase distortion that CTs introduce into the signal. With Hall sensors, the average, peak,
and earth leakage currents can be monitored. The current sensors from each inverter module are summed with the same phase of the other inverter modules
by the MDCIC to provide one current level to the control card.
Illustration 3.3: Typical Power Section
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