Power Conversion Device Offset Voltage Control for Ripple Reduction
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Solution Overview
Problem
The existing power conversion devices face excessive ripple current in capacitors due to the repetition of states where voltage vectors from two inverter sections are simultaneously effective or zero, leading to increased vibrations and noise.
Innovation Solution
A power conversion device with two three-phase coils and a control unit that calculates and applies offset voltages to the coils, ensuring that one inverter section outputs effective vectors while the other outputs zero vectors during specific periods of the carrier wave signal, thereby reducing capacitor ripple current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the phase difference of the switching reference signal is set to 180 degrees and the neutral point voltage is controlled to be half the capacitor voltage, then the vibration and noise are reduced, but the ripple current of the capacitor becomes excessively large due to repeated simultaneous effective vectors and zero vectors
Solution Approach 1:
The patent dynamically adjusts the neutral point voltage control strategy based on the duty ratio. When the duty ratio is greater than a first prescribed value, the neutral point voltage is controlled to be half the capacitor voltage to reduce vibrations and noise. When the duty ratio is equal to or lower than the first prescribed value, the control is switched to a different strategy (controlling neutral point voltage to be equal to the capacitor voltage) to prevent excessive ripple current. This dynamic adjustment resolves the contradiction by adapting the control parameter to operating conditions.
Solution Approach 2:
The patent changes the control parameter (neutral point voltage reference value) based on the duty ratio condition. By monitoring the duty ratio and switching between different neutral point voltage control strategies (half capacitor voltage vs. equal to capacitor voltage), the system optimizes performance across different operating ranges, reducing both vibrations/noise and capacitor ripple current under different conditions.
2Productivity
If the duty ratio is low (equal to or lower than first prescribed value), then the power conversion operates in a specific mode, but controlling the neutral point voltage to be half the capacitor voltage causes excessive ripple current
Solution Approach 1:
The patent changes the neutral point voltage control parameter based on the duty ratio. When the duty ratio is low (≤ first prescribed value), the neutral point voltage is controlled to be equal to the capacitor voltage rather than half, preventing excessive ripple current while maintaining proper power conversion operation. This parameter adaptation allows the system to operate efficiently across different duty ratio ranges.
Solution Approach 2:
The control system dynamically switches between different neutral point voltage control strategies based on the duty ratio condition. This dynamic control adaptation ensures that the system maintains optimal performance and avoids excessive ripple current generation under low duty ratio operating conditions.
Data Source
AI summary
A first offset voltage which is added to voltage commands in a first three-phase voltage command calculated on the basis of a control command for an AC rotary machine, and a second offset voltage which is added to voltage commands in a second three-phase voltage command calculated on the basis of a control command for the AC rotary machine, are set in such a manner that a period during which one of a first power converter and a second power converter outputs an effective vector and the other thereof outputs a zero vector occurs during a carrier period of a first carrier wave signal and a second carrier wave signal.