Inverter PWM Control for Leakage Current Reduction
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Solution Overview
Problem
Inverters using pulse width modulation (PWM) control generate leakage current due to neutral point voltage fluctuations, leading to potential malfunctions and electric shocks, particularly in automotive and renewable energy applications, where stray capacitance between motors and ground causes high-frequency leakage currents.
Innovation Solution
An apparatus and method that shift the pulse width modulation (PWM) control signal for a three-phase drive motor inverter, allowing the rising and falling edge timings of different phases to be distinct, and adjusting pulse widths to maintain consistent output line voltages, thereby reducing leakage current and noise by preventing simultaneous on-states of multiple phases within a carrier cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If PWM control is used to control the three-phase motor, then the motor control precision and efficiency are improved, but leakage current is generated due to neutral point voltage fluctuation
Solution Approach 1:
The patent applies periodic action by implementing two-phase modulation that alternates between different phase combinations (UV, VW, WU) in a cyclic manner. The modulation wave is applied to two phases while the third phase remains at zero voltage, creating a periodic pattern that maintains neutral point stability while delivering continuous motor control. This periodic switching between phase pairs prevents the neutral point voltage fluctuation that occurs in conventional three-phase PWM.
Solution Approach 2:
The patent changes the modulation parameters by applying the modulation wave to only two phases instead of three, and by dynamically adjusting which two phases receive the modulation signal based on the operating condition. This parameter change from three-phase to two-phase modulation fundamentally alters the voltage application pattern, eliminating the neutral point potential variation that causes leakage current while maintaining effective motor control.
2Power
If three-phase modulation is used, then the power output is improved, but the average leakage current remains greater than two-phase modulation due to neutral point potential variation
Solution Approach 1:
The patent implements periodic action through cyclic switching between different two-phase modulation patterns (UV phase pair, VW phase pair, WU phase pair). Each phase pair is activated in sequence, creating a periodic modulation pattern that maintains neutral point stability. This periodic alternation allows the system to deliver continuous power output while avoiding the sustained neutral point potential variation that occurs in conventional three-phase modulation.
Solution Approach 2:
The patent applies dynamics by dynamically selecting which two phases receive the modulation signal based on real-time operating conditions. The system adaptively switches between different phase pairs (UV, VW, or WU) to optimize performance while maintaining low leakage current. This dynamic phase selection allows the inverter to respond to varying load conditions while preserving the fundamental advantage of reduced neutral point potential variation.
3Stability of the object's composition
If pulse shifting is applied to reduce leakage current, then the neutral point potential stability is improved, but the on-period for current sensing may become insufficient
Solution Approach 1:
The patent adjusts the pulse width parameter to ensure that the on-period for current sensing meets the minimum required duration. By carefully controlling the pulse width of the modulation signal, the system maintains adequate time for accurate current measurement while preserving the neutral point potential stability achieved through two-phase modulation. This parameter optimization balances the competing requirements of stability and sensing accuracy.
Data Source
AI summary
An apparatus that reduces leakage current and noise in various environments. The apparatus includes a motor, an inverter to supply power to the motor and a plurality of switching elements configured to convert input DC power into three-phase AC power, and a processor to control the plurality of switching elements. The processor generates a carrier, obtains a rising and falling edge timing of a PWM control signal of each phase based on superposition of a zero phase voltage, and drives a motor by shifting the PWM control signal of each phase to allow a rising edge timing and a falling edge timing of a PWM control signal of one phase among the PWM control signal of the each phase to be different from a rising edge timing and a falling edge timing of a PWM control signal of other phase among the PWM control signal of the each phase.