Inverter Switching Synchronization for Common Mode Noise Reduction
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Solution Overview
Problem
Existing inverter devices for motors face challenges in reducing common mode noise due to neutral point potential fluctuations, which can be exacerbated by discontinuous modulation methods, leading to narrow modulation widths and increased heat generation.
Innovation Solution
An inverter device employing a discontinuous modulation method that synchronizes switching timings of upper and lower arm switching elements to cancel phase voltage changes, reducing the number of switchings and suppressing neutral point potential fluctuations, while maintaining high modulation rates and cooling the switching elements effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If discontinuous modulation method is used to reduce switching losses, then switching frequency is reduced and heat generation is decreased, but modulation width becomes narrow and motor drive area is limited
Solution Approach 1:
The patent dynamically switches between continuous modulation mode and discontinuous modulation mode based on operating conditions. The control device determines whether to apply discontinuous modulation to two phases or continuous modulation to all three phases, allowing the system to adapt between low loss and high adaptability requirements
2Object-generated harmful factors
If discontinuous modulation is applied to reduce common mode noise, then neutral point potential fluctuation is reduced, but modulation width becomes narrow
Solution Approach 1:
The control device dynamically selects between continuous and discontinuous modulation modes based on whether common mode noise reduction is the priority. When discontinuous modulation is applied to two phases, common mode noise is reduced; when continuous modulation is applied to all three phases, modulation width is maintained
3Object-generated harmful factors
If switching timings are synchronized to cancel phase voltage changes, then common mode noise is reduced, but timing errors increase noise
Solution Approach 1:
The patent employs redundant control mechanisms where the control device continuously monitors switching timing accuracy and can switch between continuous and discontinuous modulation modes to maintain noise suppression effectiveness even when timing errors occur
Data Source
AI summary
An inverter device is provided which is based on a discontinuous modulation method and makes it possible to further reduce common mode noise. A control device 21 includes a phase voltage command operation unit 33 which calculates a continuous modulation voltage command value, an inter-line modulation operation unit 34 which calculates a discontinuous modulation voltage command value which fixes an ON/OFF state of a switching element of one phase of an inverter circuit 28 and modulates an ON/OFF state of switching elements of the other two phases, and a PWM signal generation unit 36 which performs PWM control on the inverter circuit. The control device synchronizes switching timings of the switching elements of the two phases in which the ON/OFF state is modulated, and cancels out a change in a phase voltage applied to a motor 8 by a change in another phase voltage.