Modular Multi-Level Converter Valve Control for Circulating Current Suppression
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Solution Overview
Problem
Modular multi-level converters for HVDC transmission systems face limitations in circulating current suppression and harmonic control, especially during unbalanced voltage conditions, which affect the stability and efficiency of energy transmission.
Innovation Solution
A driving apparatus and method that independently control each valve of the modular multi-level converter using current reference values, error calculations, and voltage reference calculations to suppress circulating currents and harmonics, allowing for distributed control and improved operation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a typical control method is used for modular multi-level converter, then the converter can operate, but circulating current is not suppressed and harmonics are induced in the DC-grid under unbalanced voltage conditions
Solution Approach 1:
The control method is segmented into independent valve-level controllers rather than a centralized controller. Each valve controller independently calculates its own voltage reference value based on local current measurements and control parameters, enabling distributed control that suppresses circulating currents while maintaining converter operation under unbalanced conditions
Solution Approach 2:
The invention changes the control parameters by using valve-specific current reference values and measured current values to calculate error values and voltage reference values for each valve independently. This parameter-based distributed control approach enables circulating current suppression and harmonic reduction without compromising converter operation stability
2Ease of operation
If a centralized controller is used to control all valves, then comprehensive control is achieved, but the operation speed is reduced due to large amount of operations required
Solution Approach 1:
The centralized controller is segmented into multiple independent valve controllers, with each valve controller handling only its own valve's control calculations. This segmentation distributes the computational load, maintaining comprehensive control capability while significantly improving operation speed by eliminating the need for a single controller to process all valve operations
Solution Approach 2:
Each valve controller performs self-service by independently calculating its own voltage reference value based on its own current measurements and control parameters. This self-service approach eliminates the need for complex inter-valve communication and centralized processing, thereby improving operation speed while maintaining comprehensive control
Data Source
AI summary
The present invention relates to a driving method for a modular multi-level converter. The driving method include inputting a current reference value (i*pj2) of the upper valve of the modular multi-level converter, measuring a current value (ipj2) of the valve, calculating an error value (errpj2) between the current reference value and the measured current value of the upper valve, measuring a DC link voltage value (Vdc2) of the modular multi-level converter, measuring a AC-grid voltage value (Esj) of the modular multi-level converter, and calculating a voltage reference value (u*pj2) using the current reference value (i*pj2), the measured current value (ipj2), the error value (errpj2), the DC link voltage value (Vdc2), and the AC-grid voltage value (Esj).