Multi-Inverter PWM Synchronization for EV Ripple Current Reduction
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Solution Overview
Problem
Existing electric vehicle systems with multiple electric motors experience high ripple currents due to uncontrolled phase shifts between pulse-width modulated control signals, leading to power losses and increased demands on the battery and onboard power supply.
Innovation Solution
A method for controlling at least two electric machines in a vehicle, where a synchronization signal is used to adjust the phase relationship between pulse-width modulated control signals output by different inverters, thereby reducing ripple currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple electric motors are operated with uncontrolled PWM signals, then system complexity is reduced and control is simplified, but high ripple currents occur causing power losses and increased demands on the battery and power supply system
Solution Approach 1:
The system uses synchronization signals that provide feedback information about the phase and frequency of PWM control signals from one inverter to another. This feedback mechanism enables the inverters to coordinate their switching operations, reducing ripple currents in the DC voltage source by aligning their switching phases appropriately.
Solution Approach 2:
The invention changes the phase relationship parameter between PWM control signals from random/uncontrolled to controlled/synchronized. By adjusting the phase shift parameter between inverters based on synchronization signals, the system reduces ripple currents while maintaining operational simplicity.
2Ease of operation
If multiple electric motors are operated with uncontrolled PWM signals, then control implementation is simplified, but the battery and onboard power supply system experience increased stress and require higher capacity design
Solution Approach 1:
A synchronization signal acts as an intermediary between inverters, carrying phase and frequency information that enables coordinated operation. This intermediary mechanism allows inverters to maintain reliable power supply operation without requiring complex direct communication or control coordination between all inverters.
3Ease of manufacture
If high ripple currents occur due to uncontrolled phase shifts, then component design must accommodate higher stress, but this increases component costs and reduces system efficiency
Solution Approach 1:
The synchronization mechanism establishes periodic alignment between PWM signals from different inverters. By coordinating switching phases periodically, the system reduces ripple current magnitude and frequency, allowing components to be designed for lower stress conditions while maintaining manufacturing simplicity.
Data Source
AI summary
A first electric machine is controlled by a first pulse-width modulated control signal output by a first inverter and having a first signal parameter, and a second electric machine is controlled by means of a second pulse-width modulated control signal output by a second inverter and having a second signal parameter. The first signal parameter is output from the first inverter to the second inverter via a separate synchronization line. A third pulse-width modulated control signal having a third signal parameter is modulated by the second inverter. The third signal parameter is determined based on the first signal parameter and a predeterminable synchronization parameter. The third pulse-width modulated control signal having the third signal parameter is output by the second inverter to the second electric machine. The first pulse-width modulated control signal and the third pulse-width modulated control signal have a phase relationship predeterminable by the predeterminable synchronization parameter.