PWM Inverter Current Control Using Predictive Switching Times
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Solution Overview
Problem
Current methods for controlling pulse width modulated power converters in electrical machines face challenges in achieving efficient and precise current control, particularly due to sensitivity to changes in engine parameters, which affects accuracy and stability.
Innovation Solution
A method that involves detecting actual current values at discrete sampling times and calculating predictive and updated sets of switching times for each phase, allowing for dynamic control by switching between predictive and recalculated sets based on current and nominal values, minimizing delay and preventing inconsistencies in voltage output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If predictive current control is used to compensate delay and increase bandwidth, then control response speed is improved, but sensitivity to engine parameter changes increases affecting accuracy and stability
Solution Approach 1:
The patent applies preliminary action by calculating a first set of switching times in advance for a subsequent interval based on current actual and predicted values. This allows the control system to have switching times ready before the next interval begins, compensating for computational delays while maintaining stability through validation checks.
Solution Approach 2:
The patent implements feedback by validating the first set of switching times against a second set calculated with updated current values. This feedback mechanism ensures that predicted values remain accurate and stable by comparing them with actual measured values, preventing divergence due to parameter changes.
2Productivity
If switching times are calculated for subsequent intervals in advance, then control bandwidth is increased, but inconsistencies in voltage output may occur
Solution Approach 1:
The system calculates switching times for subsequent intervals in advance to increase control bandwidth and reduce delays. This preliminary calculation allows the control system to operate at higher frequencies without sacrificing accuracy.
Solution Approach 2:
The patent uses feedback validation to prevent inconsistencies by comparing the first set of switching times (calculated in advance) with a second set (calculated with updated values). If they differ significantly, the system adjusts to maintain voltage output consistency.
Solution Approach 3:
The system dynamically adjusts between using predicted switching times and recalculated switching times based on actual measurements. This dynamic approach allows the control bandwidth to be increased while maintaining stability by adapting to real-time conditions.
3Ease of manufacture
If discrete sampling is used to measure actual current, then measurement simplicity is maintained, but control delay increases
Solution Approach 1:
The patent applies preliminary action by calculating switching times in advance for subsequent intervals based on current sampling data. This eliminates the delay caused by waiting for the next sampling point, as the control values are already computed and ready.
Solution Approach 2:
The system dynamically uses predicted current values between sampling points to generate control signals. This maintains the simplicity of discrete sampling while reducing control delay by interpolating and predicting values rather than waiting for the next measurement.
Data Source
AI summary
The present invention relates to a method for the current control of a pulse width modulated power converter for an electric machine, in particular a pulse width modulated inverter connected to the electric machine. The machine and the inverter thereby comprise a plurality of phases, and the current control is carried out by means of a control loop comprising a modulator for the calculation of switching times for a pulse generator for producing a pulse width modulated control voltage for each phase. Furthermore, the present invention relates to a corresponding device for current control of an inverter connected to an electric machine.