Model Predictive Current Control With Dead-Time Cycle Segmentation
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Solution Overview
Problem
Current model predictive control (MPC) systems in power conversion face deviations in current prediction due to dead time, especially when the switching cycle of the output voltage is equal to or less than the dead time, leading to increased current ripple and switching frequency, which are not effectively addressed by existing methods.
Innovation Solution
The system divides the switching cycle of the output voltage into two periods based on the ratio between dead time and the switching cycle, performs a dead time judgment to set appropriate voltage vectors, and calculates predicted currents for each period to determine the optimal command voltage vector, thereby reducing the deviation caused by dead time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the switching cycle of the output voltage is shortened to improve current control performance, then the current control accuracy is improved, but the dead time influence becomes more significant and causes prediction deviation
Solution Approach 1:
The switching cycle is divided into multiple prediction periods, allowing the system to perform current predictions at different time points within the cycle. This segmentation enables the system to account for dead time effects more accurately by predicting currents at the beginning and end of the switching cycle separately, thus resolving the contradiction between short switching cycles and dead time influence.
2Reliability
If the switching cycle is lengthened to reduce the influence of dead time, then the current prediction accuracy is improved, but the current control performance deteriorates
Solution Approach 1:
By dividing the switching cycle into multiple prediction periods, the system achieves accurate current predictions without requiring a long overall switching cycle. The segmented approach allows each prediction to be accurate while maintaining a short total cycle for good control performance.
Solution Approach 2:
The system performs preliminary current predictions at the beginning of the switching cycle to determine the optimal voltage vector before the cycle ends. This preliminary action ensures accurate current control is achieved in advance, eliminating the need to extend the switching cycle duration.
3Speed
If the switching cycle is set equal to or less than the dead time, then the response speed is improved, but the predicted current deviates significantly from actual current
Solution Approach 1:
The switching cycle is divided into multiple prediction periods, enabling the system to perform predictions at different stages. This segmentation allows the system to maintain fast response while compensating for dead time effects by predicting currents at multiple points rather than relying on a single prediction.
Solution Approach 2:
The system uses predicted currents from multiple prediction periods as feedback to determine the optimal voltage vector. This feedback mechanism allows the system to correct for dead time effects and maintain accurate current predictions even when the switching cycle is very short or equal to the dead time.
Data Source
AI summary
A higher control unit 1 generates a command current i* based on a command value. A model predictive control unit 2 sets a plurality of assumed voltage vectors for each switching cycle of an output voltage, divides the switching cycle of the output voltage into two periods according to a ratio between a dead time and the switching cycle of the output voltage, calculates a predicted current of the assumed voltage vector for each of the two periods obtained by the two-dividing, determines an evaluation function between the assumed voltage vector and the predicted current, sets the assumed voltage vector which has highest evaluation function result, as a command voltage vector. A gate signal g for outputting a voltage expressed by the command voltage vector from the power converter is output. The power converter is driven and controlled based on the gate signal.