Variable Frequency Drive System Apparatus and Method for Reduced Ground Leakage Current and Transistor Protection
First Claim
1. A method of reducing ground leakage current in a VFD system comprising:
- floating a neutral point on a DC bus of the VFD, anddisposing an electrically insulating plate which has high thermal conductivity, a low dielectric constant, and high dielectric strength between a VFD power semiconductor module and a cooling plate.
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Abstract
As applications of variable frequency drives (VFD) (50) continue to grow so do challenges to provide VFD (50) systems meeting application specific requirements. For multiple reasons to include safety standards and electromagnetic interference, reduced ground leakage current is desirable. Building high output voltage VFDs (50) using transistors rated at voltages lower than the VFD output voltage is desirable for economic reasons. The apparatus and method described herein meet these challenges and others, in part by placing an electrically insulating plate (cp176) having high thermal conductivity, a low dielectric constant, and high dielectric strength between the heat sink plate of a VFD power semiconductor module and a grounded cooling plate (80 TE). The positive effects of this plate installation include reducing ground leakage current induced by system capacitances to ground upon high frequency voltage steps and increasing the effective dielectric strength of the VFD'"'"'s (50) transistor modules engaging in high reliable VFD (50) voltage output for a given transistor rating.
38 Citations
21 Claims
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1. A method of reducing ground leakage current in a VFD system comprising:
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floating a neutral point on a DC bus of the VFD, and disposing an electrically insulating plate which has high thermal conductivity, a low dielectric constant, and high dielectric strength between a VFD power semiconductor module and a cooling plate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of reducing ground leakage current in a medium voltage VFD system comprising:
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floating a neutral point on a DC bus of the VFD; and disposing an electrically insulating plate which has high thermal conductivity, a low dielectric constant, and high dielectric strength between a VFD power semiconductor module and a cooling plate, wherein the ground leakage current is reduced to less than 1.5 amps.
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11. A medium voltage VFD system having low ground leakage current comprising:
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a DC bus which has a floating neutral point; an inverter bridge, of a VFD power semiconductor module, electrically connected to the DC bus; an electrically insulating plate which has high thermal conductivity, a low dielectric constant, and high dielectric strength; and a cooling plate, wherein the VFD power semiconductor module is mounted on the electrically insulating plate, having high thermal conductivity, a low dielectric constant, and high dielectric strength; wherein the insulating plate is mounted on the cooling plate; and wherein the cooling plate is grounded. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A medium voltage VFD system comprising:
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a DC bus which has a grounded neutral point; VFD power semiconductor modules, wherein transistor modules of an inverter bridge are connected in series, the inverter bridges is electrically connected to the DC bus, and an insulation of transistor modules is rated at less than half of a full maximum DC bus voltage rating; an electrically insulating plate which has high thermal conductivity, a low dielectric constant, and high dielectric strength; and a grounded cooling plate, wherein the VFD power semiconductor module is mounted on the electrically insulating plate, having high thermal conductivity, a low dielectric constant, and high dielectric strength; wherein the insulating plate is mounted on the grounded cooling plate; and
wherein an effective insulation capability to ground of the VFD system is increased.
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Specification