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M-AI-VT-001-EN Rev.C.1
Overview of the VTT Compressor
Figure 7
Basic Block Diagram
To provide an overview, the main drive module
components are grouped into three categories:
The control logic section, logic to power
interface, and power section. The sequence of
operation description describes these sections
in greater detail while explaining how power
and control signals move throughout the drive
module.
Drive Module Logic to
Power Interface
The logic to power interface isolates the high-
voltage components of the power section from
the low voltage signals of the control logic
section. The power interface section consists of
the power card and gate driver card.
The control card handles the fault processing for
output short circuit and earth fault conditions as
well as scaling of current and voltage feedback.
The power card provides conditioning of these
signals and the circuitry for controlling the speed
of the cooling fans.
The gate drive signals from the control card to
the insulated gate bipolar transistors (IGBTs) are
isolated and buffered on the gate drive card.
Power Section
The high-voltage power section consists of AC
input and motor output terminals, fuses, wiring
harness, AC and DC bus bars, and optional
components. The power section (See figure 7)
also contains circuitry for the silicon controlled
rectifier (SCR); the DC bus filter circuitry
containing the DC coils and the output IGBT
modules.
The inrush circuit controls the firing of the SCRs
in the rectifier. When power is applied, the
SCRs limit the charging rate of the DC capacitors.
Once the capacitors are charged, the inrush
circuit sequences the firing of the SCRs to
maintain the proper charge on the DC capacitors.
The DC bus circuitry regulates the pulsating DC
voltage created by the input AC supply.
The DC bus capacitors are arranged into a
capacitor bank along with bleeder and balancing
circuitry.
DC
