Multilevel Converter MPC With Reduced Switching States
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Solution Overview
Problem
Current methods for capacitor balancing and common-mode voltage reduction in silicon-carbide (SiC) based dual T-type drive systems face challenges with high computation time and increased harmonic content, which affect the performance and efficiency of induction motors.
Innovation Solution
The implementation of a reduced switching state model predictive control (MPC) system that incorporates common-mode voltage reduction (CMVR) and capacitor balancing, using a reduced set of switching states to minimize computation time and improve performance by generating optimal gating signals for silicon carbide (SiC) semiconductor switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a full set of switching states is used for model predictive control, then control precision is improved, but computation time increases
Solution Approach 1:
The patent segments the complete set of switching states into multiple groups based on their impact on capacitor voltage balancing. By dividing the switching states into different categories (e.g., states that charge/discharge specific capacitors), the controller can selectively evaluate only the relevant subset of switching states for each control objective, thereby reducing computation time while maintaining control precision.
Solution Approach 2:
The patent changes the parameter of switching state selection by introducing a reduced set of switching states that are pre-identified based on their effectiveness in capacitor balancing. This parameter change allows the system to work with a smaller, more efficient subset of switching states, reducing the computational burden while preserving the essential control functions.
2Stability of the object's composition
If capacitor balancing control is implemented, then capacitor voltage stability is improved, but computation time increases
Solution Approach 1:
The patent segments switching states into groups based on their capacitor balancing effect. By identifying and selecting only those switching states that have a positive impact on capacitor voltage balancing, the system achieves effective capacitor voltage stability control while minimizing the number of switching states that need to be evaluated, thus reducing computation time.
Solution Approach 2:
The patent performs preliminary classification of switching states into different groups based on their capacitor balancing characteristics. This preliminary action allows the controller to pre-identify the most effective switching states for capacitor balancing, so that during real-time operation, only these pre-selected states need to be evaluated, reducing computation time while maintaining stability control effectiveness.
3Duration of action of stationary object
If common-mode voltage reduction is implemented, then bearing lifetime is improved, but harmonic content increases
Solution Approach 1:
The patent changes the parameter of switching state selection by incorporating common-mode voltage considerations into the cost function. By adjusting the weighting factor for common-mode voltage in the cost function, the system can prioritize bearing protection while managing the trade-off with harmonic content, achieving an optimized balance between these two objectives.
4Loss of time
If a reduced set of switching states is used, then computation time is reduced, but control performance may deteriorate
Solution Approach 1:
The patent changes the parameter of switching state evaluation by introducing a comprehensive cost function that incorporates multiple control objectives (torque control, flux control, capacitor balancing, and common-mode voltage reduction). By carefully selecting and weighting the parameters in the cost function, the system ensures that the reduced set of switching states still achieves satisfactory control performance across all objectives.
Data Source
AI summary
Reduced computation time for model predictive control (MPC) of a five level dual T-type drive considering the DC link capacitor balancing, the common-mode voltage (CMV) along with torque control of an open-ends induction motor based on determining a reduced set of switching states for the MPC. The reduced set of switching states are determined by considering either CMV reduction (CMVR) or CMV elimination (CMVE). Cost function minimization generates a voltage vector, which is used to produce gating signals for the converter switches. The reduced switching state MPC significantly reduces computation time and improves MPC performance.