Converter Filter Cell MPC for Low-Speed Harmonic Control
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Solution Overview
Problem
Existing control schemes for 3L(A)NPC+AF converter topologies struggle with optimized hardware design, reliable operation, and fail to effectively manage low-speed and stand-still operations, leading to high computational demand and increased total harmonic distortion and losses.
Innovation Solution
A method combining pattern determination and model predictive control to optimize switching instants of main and filter cell stages, using pulse width modulation and model predictive control to minimize flux error and balance cell voltages, reducing computational burden and harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optimized pulse patterns are used for medium to high speed operation, then power quality is improved, but control effectiveness deteriorates at low speed and stand-still operation
Solution Approach 1:
The control method dynamically adapts between two different control modes: using pre-computed optimized pulse patterns for medium to high speed operation, and switching to carrier-based model predictive control for low speed and stand-still operation. This dynamic adaptation ensures optimal performance across the entire operating range without compromising power quality or control effectiveness.
Solution Approach 2:
The invention changes the control parameters and methodology based on operating conditions. At medium to high speeds, the system uses fixed optimized pulse patterns with specific switching angles. At low speeds and stand-still, it transitions to model predictive control that continuously optimizes switching instants based on real-time flux trajectory requirements, thereby maintaining adaptability across all speed ranges.
2Measurement precision
If model predictive control is applied to optimize switching instants, then flux error is minimized, but computational demand increases
Solution Approach 1:
The control strategy is segmented into two distinct operational modes: for medium to high speed operation, pre-computed optimized pulse patterns are used which require minimal real-time computation; for low speed and stand-still operation, model predictive control is activated to minimize flux error. This segmentation reduces overall computational demand by applying intensive MPC only when necessary.
Solution Approach 2:
Instead of applying full model predictive control across all operating conditions, the invention applies MPC partially - only during low speed and stand-still operation where traditional optimized pulse patterns are ineffective. This partial application reduces computational burden while maintaining sufficient control precision where needed.
3Reliability
If filter cells are added to reduce voltage steps and harmonic distortion, then power quality is improved, but device complexity increases
Solution Approach 1:
The filter cells in the 3L(A)NPC+AF topology serve multiple functions: they reduce voltage steps at the converter output, minimize harmonic distortion in the output voltage, and improve overall power quality. By making the filter cells multi-functional, the added device complexity is justified by multiple performance benefits rather than a single function.
Solution Approach 2:
The active filter cells incorporate feedback control through the carrier-based model predictive control scheme, which continuously monitors the flux trajectory and adjusts the switching instants of the filter cells to minimize deviations from the desired flux path. This feedback mechanism optimizes the performance of the added filter cells, ensuring they effectively reduce harmonic distortion and improve power quality.
Data Source
AI summary
An electrical converter comprises a main stage adapted for converting a DC voltage into an intermediate voltage comprising at least two voltage levels and a filter cell for each phase of the intermediate voltage, each filter cell being adapted for adjusting a cell voltage with the intermediate voltage. A control method comprises: determining a main pulse pattern for the main stage, wherein the main pulse pattern comprises switching instants for the main stage over a modulation period; and determining a cell pulse pattern, wherein the cell pulse pattern comprises switching instants for the filter cells over the next modulation period. The method additionally comprises: modifying the main pulse pattern and the cell pulse pattern by moving at least one transition time of a switching instant and applying at least a next switching instant from the main pulse pattern and the cell pulse pattern.