Hybrid Vehicle Inverter Control for Capacitor Stress Reduction
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Solution Overview
Problem
Existing power shunt circuit systems in hybrid vehicles generate high-frequency harmonics that stress the filtering capacitor, leading to premature aging due to RMS current, and require optimization of pulse-width modulation control to minimize current waves and harmonics.
Innovation Solution
The system employs time-shifted and vectorial pulse-width modulation control for the inverters, allowing them to operate as motor/motor or generator/generator, with a DC-DC converter to optimize voltage and reduce RMS current, using scalar, vectorial, overmodulated, and full-wave modulation modes based on speed and torque requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional pulse-width modulation control is used for the inverters, then the control is simple, but the RMS current through the capacitor increases and harmonics are not minimized
Solution Approach 1:
The patent applies dynamic control strategies including scalar PWM, vectorial PWM, overmodulated PWM, and full-wave rectification modes that adapt to different operating conditions. The control unit dynamically selects and switches between these modes based on real-time requirements, transforming the static PWM control into a dynamic system that optimizes performance while reducing capacitor stress
Solution Approach 2:
The patent changes key control parameters including modulation index, switching frequency, and phase relationships. By varying these parameters according to operating conditions, the system minimizes RMS current through the capacitor and reduces harmonic content, thereby extending capacitor lifespan without excessive complexity
2Ease of operation
If the capacitor filters high-frequency harmonics from PWM chopping, then the current to the storage element is made as direct as possible, but the capacitor ages prematurely due to heating from RMS current
Solution Approach 1:
The patent converts the harmful high-frequency harmonics generated by PWM chopping into beneficial effects by using resonant circuits and selective filtering. Instead of simply suppressing all harmonics, the system exploits specific frequency relationships to cancel harmful harmonics while maintaining efficient power transfer, thereby reducing capacitor heating without compromising current quality
Solution Approach 2:
The patent employs periodic switching patterns and synchronized PWM techniques where the switching frequency is carefully selected to create constructive and destructive interference patterns. This periodic action naturally filters certain harmonics while maintaining the desired current waveform, reducing the burden on the capacitor
3Loss of energy
If two electric machines operate as motor/generator or generator/motor for power shunting, then power can be recovered from the drive, but high-frequency harmonics are generated that stress the capacitor
Solution Approach 1:
The patent merges the control of two electric machines operating in motor/generator or generator/motor modes under a unified control strategy. By coordinating their operation and synchronizing their PWM patterns, the system recovers energy from the drive while the combined effect of the two machines produces harmonic cancellation, reducing stress on the capacitor
Data Source
AI summary
A device for controlling a power shunt circuit of a hybrid vehicle, including inverters, including DC sides linked to a DC voltage storage unit and AC sides intended to be linked to polyphase electrical machines. The polyphase electrical machines are able to operate in engine/engine or generator/generator modes. A control unit controls chopping switches of the second inverter in a way that is temporally offset relative to chopping switches of the first inverter in such a case, the control unit of the inverters controlling their chopping switches by pulse width vector modulation.