MMC Current Control via Dynamic Inductance Compensation
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Solution Overview
Problem
Traditional current control methods for three-phase modular multilevel converters (MMC) fail to accurately manage inductance changes, leading to current oscillations and distortion due to the lack of consideration for inductance variations during abc-to-dq vector conversions.
Innovation Solution
A division-summation (D-Σ) method that calculates equivalent inductance values and adjusts submodule operations in real-time, eliminating the need for coordinate conversions and sector judgments, allowing for precise control of submodule numbers and duty ratios to mitigate inductance-related distortions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional abc-to-dq vector conversion method is used for current control, then the control method can be implemented, but current oscillation and distortion occur due to inductance changes not being considered
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the inductance value parameter based on actual current measurements. The inductance value is updated in real-time according to the relationship between current magnitude and inductance, allowing the control system to adapt to inductance variations and eliminate the resulting current oscillations and distortions.
2Reliability
If D-Σ control method of two-level converter is directly applied to MMC, then inductance changes can be considered, but complex multilevel space phasor-order modulation is required with memory and calculation greatly increased
Solution Approach 1:
The patent extracts the essential function of inductance change compensation from the complex two-level converter D-Σ control method. By separating the inductance compensation function from the overall control system and implementing it through a simplified calculation approach that directly uses current measurements to update inductance parameters, the patent achieves accurate current control without requiring complex multilevel space phasor-order modulation.
3Ease of operation
If inductance changes are not considered in abc-dq conversion, then the control implementation is simple, but error on current control happens
Solution Approach 1:
The patent applies dynamics by making the inductance parameter dynamic rather than fixed. The inductance value is continuously updated based on the measured current, allowing the control system to adapt to changing operating conditions. This dynamic approach maintains simplicity of implementation while significantly improving current control accuracy under varying inductance conditions.
Data Source
AI summary
Current of a three-phase multilevel modular converter (MMC) is controlled. The control is a division-summation (D-Σ) method yet uses integration to replace the two steps of division and summation. Common D-Σ characteristic equations are used for all areas. Inductance changes are considered in the characteristic equations. Current source is used to control converter. Therefore, the current of the converter can be traced to sinusoidal reference current even when the inductance changes become big. The modulation method and the capacitor-voltage balancing method are submodule unified pulse width modulation (SUPWM) and sorted voltage-balancing method, respectively. The current control directly obtains a law of the current change on each conducting module of an arm. It does not need complex sector judgments and table look-ups. Thus, the amount of computation and memory for a processor can be relatively reduced.