GE Industrial Solutions AF-600 FP High Power (460V_575V 150HP and above) User Manual
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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 3-3) 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
DC bus circuitry smooths the pulsating DC voltage created by the conversion from the AC supply.
The DC coil is a single unit with 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 aids
in the reduction of mains harmonics.
The DC bus capacitors are arranged into a capacitor bank along with bleeder and balancing circuitry. Due to the requirement for higher power capacity, some
frequency converters have two capacitor banks connected in parallel.
The inverter section is made up of six IGBTs, commonly referred to as switches. One switch is necessary for each half phase of the three-phase power, for a total
of six. The six IGBTs are contained in a single module. Due to higher current handling requirements, some models contain two or three larger six-pack style modules.
In these units, each switch (half phase) is made up of two or three IGBTs in parallel.
A Hall effect type current sensor is located on each phase of the output to measure motor current. This type of device is used instead of more common current
transformer (CT) devices in order to reduce the amount of frequency and phase distortion that CTs introduce into the signal. With Hall sensors, the average, peak,
and earth leakage currents can be monitored.
Illustration 3.3: Typical Power Section
AF-650 GP and AF-600 FP High Power Service Manual
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