Delay-Compensated Current Regulator for AC Motor Stability
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Solution Overview
Problem
Conventional synchronous frame current regulators for AC motors experience instability and sub-harmonic issues due to low sampling frequency to fundamental frequency ratios, particularly at high motor speeds, leading to challenges in maintaining stable current regulation.
Innovation Solution
The implementation of a delay-compensated and anti-windup offset-based current regulation system, which includes a processor to sample commanded and synchronous frame currents, compensate for delays, and adjust voltages to maintain stability, even at low sampling frequency to fundamental frequency ratios, using complex vector current regulation with active damping and low-pass filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the sampling frequency is reduced to limit switching device stress and processor throughput, then device complexity and energy use are reduced, but current regulation stability deteriorates due to digital delays and sub-harmonics
Solution Approach 1:
The system performs preliminary actions by predicting future current values and calculating required voltage adjustments before the actual sampling interval elapses. The lead-lag compensator proactively adjusts the voltage command based on predicted current trends, and the anti-windup mechanism preemptively prevents integrator saturation by detecting when voltage limits are approaching. This preliminary action allows the system to maintain stability with lower sampling frequencies by not waiting for errors to fully develop before correcting them.
Solution Approach 2:
The system implements dynamic adaptation by adjusting the lead-lag compensator parameters and anti-windup thresholds based on operating conditions such as motor speed, load, and current error magnitude. The compensator dynamically modifies its phase lead/lag characteristics to optimize performance across different fundamental frequencies, allowing the regulator to maintain stability whether operating at low speeds with high pole counts or at higher speeds with better sampling ratios.
2Power
If the pole count is increased to produce high torque within limited volume, then power density is improved, but the fundamental frequency increases making current regulation more difficult at maximum speed
Solution Approach 1:
The system changes parameters dynamically by adjusting the lead-lag compensator time constants and gains based on the fundamental frequency, which varies with motor speed and pole count. The anti-windup threshold parameters are also adapted based on the voltage limits and operating point. This parameter adaptation allows the same hardware to effectively regulate current for high pole-count motors producing high torque while maintaining stability across the full speed range despite the increased fundamental frequency challenging the fixed sampling rate.
Data Source
AI summary
Methods and systems are provided for controlling an AC motor via an inverter. The method includes determining a delay-compensated offset based on a synchronous frame current, producing a current error based on a synchronous frame current and a commanded current, producing a voltage error based on an anti-windup offset and the current error, producing a commanded voltage based on the delay-compensated offset and the voltage error, and providing the inverter with the commanded voltage.