PWM Rectifier Control Using Differential Tracking for Grid Imbalance
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Solution Overview
Problem
Existing control methods for three-phase active front-end rectifiers are sensitive to power grid frequency fluctuations, leading to deteriorated control performance and high memory consumption.
Innovation Solution
A method and apparatus using a differential tracker to calculate a 90° lagged grid voltage, followed by instantaneous power calculation and power converter voltage determination, to suppress grid voltage imbalance, eliminating the need for arrays and making the system insensitive to grid frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If repetition controller is used to track six-fold frequency components, then (6n±1)th harmonic suppression is improved, but control performance deteriorates when grid frequency fluctuates and memory consumption increases
Solution Approach 1:
The patent changes the control parameter from fixed-frequency repetition control to variable-frequency differential tracking. The differential tracker dynamically adjusts to grid frequency fluctuations by computing the derivative of the grid voltage, which inherently provides the 90° lagged voltage component without requiring fixed-frequency assumptions. This resolves the contradiction by making the harmonic suppression adaptive to frequency changes.
Solution Approach 2:
The patent replaces the mechanical array-based storage system with a computational differential tracking system. Instead of storing large arrays of pre-computed values in memory, the system uses real-time differential computation to generate the required 90° lagged voltage component. This substitution eliminates the memory consumption issue while maintaining harmonic suppression effectiveness.
2Measurement precision
If arrays are used for repetition control, then six-fold frequency component tracking is achieved, but memory consumption increases significantly
Solution Approach 1:
The patent extracts only the essential computational element (differential computation) needed for frequency component tracking, eliminating the need for large memory arrays. By taking out the core mathematical operation (derivative calculation) that provides the 90° phase shift, the system achieves accurate tracking with minimal memory resources.
Solution Approach 2:
The patent substitutes the physical memory array structure with a computational differential operator. Instead of storing values in memory arrays, the system computes the required values on-the-fly using differential calculus, replacing a memory-intensive mechanical approach with a computation-efficient mathematical approach.
3Object-generated harmful factors
If proportional-integral controller, repetition controller, and resonance controller are used together, then comprehensive harmonic suppression is achieved, but device complexity increases
Solution Approach 1:
The patent merges the functions of multiple controllers into a unified differential tracking framework. Instead of separately implementing PI control for fundamental current tracking, repetition control for six-fold frequency components, and resonance control for third harmonic suppression, the system integrates all these functions through a single differential tracker that computes the 90° lagged voltage component needed for comprehensive harmonic suppression.
Solution Approach 2:
The differential tracker serves multiple functions simultaneously: it provides the 90° lagged voltage component for instantaneous power calculation, enables harmonic suppression across multiple frequency components, and adapts to frequency variations. This multi-functional approach replaces the need for multiple specialized controllers, reducing overall system complexity.
Data Source
AI summary
The present application provides a method and apparatus for suppressing grid voltage imbalance. By obtaining a 90° lagged grid voltage through a differential tracker, calculating instantaneous power using the 90° lagged grid voltage, and then calculating a power converter voltage according to the instantaneous power, the suppression of grid voltage imbalance may be achieved.