PWM Optimization Module for Electric Drive Noise Reduction
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Solution Overview
Problem
Existing power electronic inverter systems in electric vehicles face challenges in reducing noise, vibration, and harshness (NVH) associated with electric machines, particularly due to high pitched whining and whistling noises caused by PWM switching frequencies within the audible spectrum, which often result in increased switching losses and decreased fuel efficiency when attempting to mitigate noise.
Innovation Solution
A PWM optimization module (POM) utilizing an optimized pseudorandom period pattern (PPP) to spread noise energy in the frequency spectrum, allowing for carrier period changes at various intervals, independent of electric machine current and torque requirements, thereby reducing audible noise and inverter losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If PWM switching frequency is increased to reduce audible noise, then noise reduction is improved, but switching losses increase and fuel efficiency decreases
Solution Approach 1:
The patent implements dynamic switching between synchronous and asynchronous PWM control modes based on operating conditions. The system automatically transitions between control strategies to optimize the balance between noise reduction and switching losses, rather than using a fixed high-frequency approach that always increases energy consumption.
Solution Approach 2:
The patent changes the carrier frequency parameter dynamically - using synchronous PWM with integer multiples of base frequency for noise-critical operations, and asynchronous PWM with arbitrary frequencies for efficiency-critical operations. This parameter flexibility allows the system to avoid consistently high switching frequencies that cause excessive losses.
2Object-affected harmful factors
If synchronous PWM control is used for noise reduction, then noise control is improved, but device complexity increases due to requiring multiple control circuits
Solution Approach 1:
The patent designs a unified control device that can perform both synchronous and asynchronous PWM control functions. Rather than requiring separate control circuits for each mode, the single control device dynamically selects and implements the appropriate control strategy based on real-time operating conditions, reducing overall system complexity.
Solution Approach 2:
The control device dynamically switches between synchronous and asynchronous control modes based on operating conditions such as torque and speed requirements. This dynamic adaptability allows the system to use the simpler asynchronous mode when noise is less critical, reducing the need for complex synchronous control circuitry to be continuously active.
3Object-affected harmful factors
If carrier frequency is randomized around 7.5 kHz to mitigate switching noise, then noise mitigation is improved, but switching losses increase and fuel economy decreases
Solution Approach 1:
Instead of randomly varying carrier frequency around a high base value (7.5 kHz), the patent uses integer multiples of a lower base carrier frequency in synchronous mode or arbitrary frequencies in asynchronous mode. This parameter strategy achieves noise reduction by spreading spectral energy while operating at lower average frequencies, thereby reducing switching losses and improving fuel efficiency.
4Adaptability or versatility
If PWM strategy is changed based on current and torque conditions, then adaptability is improved, but real-time processing complexity increases
Solution Approach 1:
The control device dynamically adapts PWM strategy based on simple thresholds of electric current and torque. Rather than implementing complex real-time algorithms, the system uses straightforward conditional logic to switch between synchronous and asynchronous modes, reducing real-time processing complexity while maintaining adaptability to operating conditions.
Data Source
AI summary
An optimized pseudo-random period pattern can reduce audible noise in a system that includes an inverter circuit configured to provide power to an electric machine. A system can include a PWM optimization module (POM) comprising the PPP. A carrier period for a carrier signal used to provide PWM inverter drive signals can be selected in accordance with the PPP. The PPP can be expressed as an array of 200-400 elements, each element a period belonging to a finite set of 2 or more predetermined periods. A period can be selected by index from the array, and the index incremented to progress through the PPP, which can be repeated upon its completion. The PPP can be optimized to reduce audible noise while mitigating inverter losses. Modeling techniques can determine the number of array elements, the number of possible periods, and the period values that optimize the PPP.