Power Conversion Apparatus Fixed Interval Current Detection
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Solution Overview
Problem
Conventional power conversion systems face challenges in accurately detecting currents due to varying sampling intervals and high frequency of current detection, leading to distortion, torque ripple, sound, and vibration, especially during zero-voltage vector periods with small or large application voltages.
Innovation Solution
A power conversion apparatus with an inverter unit, current detecting unit, and control unit that adjusts the duty instruction value to ensure current detection at fixed intervals, correcting phase currents based on positive and negative-side current detection values, thereby reducing ripple current and current detection errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current detection is performed at carrier peak timings with symmetrical sampling, then current detection accuracy is improved, but sampling intervals become variable and device complexity increases
Solution Approach 1:
The patent changes the parameter of sampling timing from variable (symmetrical around carrier peak) to fixed (predetermined intervals). This is achieved by adjusting the duty instruction value to ensure active voltage vector intervals are sufficiently long, allowing current detection at fixed intervals without requiring complex variable timing control.
2Measurement precision
If current detection frequency is increased to four times per PWM cycle, then measurement precision is improved, but distortion and torque ripple increase
Solution Approach 1:
Instead of performing current detection four times per PWM cycle, the patent uses partial action by detecting current only once per PWM cycle at fixed intervals. This reduces the excessive detection frequency that causes distortion and torque ripple while still obtaining sufficient measurement data for control.
3Reliability
If zero-voltage vector period is extended for small or large application voltages, then reliability is improved, but current detection cannot be performed properly
Solution Approach 1:
The patent dynamically adjusts the duty instruction value based on application voltage conditions. For small or large voltages where zero-voltage vector periods are naturally long, the system increases the active voltage vector interval to ensure current detection can be performed at fixed intervals, maintaining both reliability and detection capability.
4Measurement precision
If duty instruction value is adjusted to ensure fixed interval sampling, then measurement precision is improved, but active voltage vector interval becomes variable
Solution Approach 1:
The patent changes the control parameter by adjusting the duty instruction value to prioritize fixed sampling intervals. The active voltage vector interval duration becomes a secondary parameter that varies to accommodate the fixed sampling requirement, ensuring measurement precision is maintained while allowing natural variation in vector interval duration.
Data Source
AI summary
A power conversion apparatus includes: an inverter unit having high and low potential-side switching elements corresponding to each phase of a winding of a rotating electrical machine; a current detecting unit; a current obtaining unit obtaining a current detection value with a fixed interval sampling timing; and a control unit controlling the switching elements based on a PWM reference signal and a duty instruction value. The control unit includes: a phase current computing device; a voltage instruction value computing device; and a duty computing device. The phase current computing device computes a correction current based on positive and negative side corrected current detection values. The positive-side corrected current detection value is obtained when a duty is adjusted to a positive side, and the negative-side corrected current detection value is obtained when the duty is adjusted to a negative side.