3-Phase Inverter Control Reducing Audible Noise
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Solution Overview
Problem
3-phase inverters using PWM control generate harmonic frequency components that cause audible noise and increase switching losses, with existing solutions either failing to reduce noise effectively or increasing switching losses by raising switching frequency.
Innovation Solution
A control apparatus for a 3-phase inverter that designates phases based on voltage levels, keeping the highest phase voltage phase switched state fixed and increasing switching frequency only for the lowest phase, thereby reducing switching losses and moving harmonic frequencies above the audible range without significant loss increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the switching frequency is increased above 20 kHz to eliminate audible noise, then the harmonic frequency components are moved above the audible range, but the switching losses increase significantly
Solution Approach 1:
The patent segments the three-phase switching control into independent control of two phases, where only two switching devices are actively modulated while the third phase's switching state is held fixed. This segmentation allows the system to achieve noise reduction benefits without the full switching loss penalty of conventional three-phase PWM control
Solution Approach 2:
The patent applies partial action by performing PWM modulation on only two phases instead of all three phases. This partial modulation approach is sufficient to push harmonic frequencies above the audible range while avoiding the excessive switching losses that would result from modulating all three phases at high frequency
2Loss of energy
If 2-phase modulation is used to reduce switching losses, then the switching frequency can be maintained at lower levels, but the audible noise problem is not effectively reduced
Solution Approach 1:
The patent changes the control parameters by selectively holding the switching state of one phase fixed while actively modulating the other two phases. This parameter change in the switching control strategy enables the system to achieve both reduced switching losses and effective noise suppression by optimizing which phases are modulated
Data Source
AI summary
An inverter control apparatus performs PWM control of a 3-phase inverter connected to a rotary machine, by operating switching devices corresponding to respective phases. In each of successive processing periods, the PWM control is applied such as to satisfy first and second conditions. The first condition is that the state of switching devices corresponding to a highest-voltage phase of the inverter during the processing period is held fixed throughout the processing period. The second condition is that switching devices corresponding to a lowest-voltage phase of the inverter undergoes a greater number of switching operations during the processing period than switching devices corresponding to an intermediate-voltage phase of the inverter. The frequency of harmonic components in AC currents flowing in the rotary machine can thereby be raised above the audible range, to suppress audible mechanical noise, without significantly increasing the amount of switching losses.