Motor Drive Harmonic Current Prediction for Active Filter Control
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Solution Overview
Problem
Existing control devices face challenges in effectively suppressing harmonic currents generated by inverters in electric vehicles while maintaining a reasonable processing load, as feedback control is inefficient and feedforward control increases processing demands.
Innovation Solution
A control device that includes a prediction unit to forecast harmonic currents based on motor control information and a command value determination unit to generate compensation currents with opposing polarity, reducing processing load by optimizing prediction points and intervals according to the carrier cycle length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If feedback control is used to control the compensation current from the active filter, then the control stability is improved, but the responsiveness of the compensation current to the harmonic current deteriorates
Solution Approach 1:
The patent performs preliminary calculation of the compensation current command value based on predicted harmonic current before the actual harmonic current occurs. By calculating the compensation current in advance using prediction values and storing it, the system achieves both responsiveness (since the compensation is ready before needed) and stability (through controlled execution). This preliminary action resolves the contradiction by preparing the control signal beforehand rather than reacting in real-time.
2Speed
If feedforward control is used to control the compensation current from the active filter, then the responsiveness of the compensation current to the harmonic current is improved, but the processing load of the control device increases
Solution Approach 1:
The patent performs prediction and calculation only for the next carrier cycle rather than continuous real-time prediction. By limiting the prediction scope to a partial timeframe (one carrier cycle ahead) and calculating compensation current at specific intervals rather than continuously, the system achieves feedforward responsiveness while significantly reducing the processing load. This partial action approach avoids the excessive computational burden of continuous full-range prediction.
3Manufacturing precision
If the number of prediction points is increased to improve prediction accuracy, then the manufacturing precision of harmonic current suppression is improved, but the processing load of the control device increases
Solution Approach 1:
The patent concentrates prediction resources on critical timing points (prediction points strategically positioned before carrier cycle transitions) rather than uniformly distributing prediction across all time points. By identifying and focusing computational effort on locally important prediction moments where harmonic current characteristics change significantly, the system achieves high prediction accuracy at key moments without the excessive processing load of continuous high-frequency prediction across all time points.
Data Source
AI summary
A control device includes: a prediction unit configured to predict the harmonic current at each of prediction points comprised in a predetermined prediction target period after current time, based on control information of the motor in at least a next carrier cycle of the inverter, and a command value determination unit configured to output, to the active filter unit, a current command value for generating a compensation current having a polarity opposite to a polarity of a harmonic current at a prediction point, at a timing corresponding to the prediction point comprised in the next carrier cycle in the prediction target period, based on a prediction result of the prediction unit. Each of the prediction points is provided at a predetermined time interval since start time of the prediction target period. The time interval is longer as the next carrier cycle is longer.