Parallel Power Converter Voltage Control for Reactive Power Sharing
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Solution Overview
Problem
In AC microgrids, parallel-connected power converters face challenges in balancing reactive power without a master unit, leading to potential system instability and failure in case of master unit failure, and existing solutions require complex mechanisms for dynamic master switching.
Innovation Solution
A control system that calculates reactive power indicators, forms an arithmetic average, and generates unbalance indicators to adjust alternating voltage amplitude references, allowing for decentralized control and redundancy among power converters, ensuring stable AC voltage without relying on a single master unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a master-slave control mechanism is used to balance reactive power between parallel connected power converters, then reactive power balancing is achieved, but system reliability deteriorates due to single point of failure
Solution Approach 1:
The control system is segmented into multiple independent control units, each capable of autonomously calculating its own unbalance indicator and adjusting its voltage amplitude reference. This eliminates the need for a centralized master unit and enables distributed control, where each power converter operates independently while maintaining overall system balance.
Solution Approach 2:
Each power converter performs self-control by autonomously measuring its own reactive power, calculating its unbalance indicator relative to the arithmetic average, and adjusting its own voltage amplitude reference without requiring instructions from a master unit. This self-service mechanism ensures continuous operation even if other units fail.
2Reliability
If dynamic master switching mechanism is implemented to handle master unit failure, then system reliability is improved, but device complexity increases
Solution Approach 1:
The system eliminates the need for dynamic master switching by implementing self-service control in each power converter. Each unit independently determines its control actions based on real-time measurements and the unbalance indicator calculation, removing the complexity of master selection, switching mechanisms, and associated control logic while maintaining continuous system operation.
3Ease of operation
If reactive power balancing control is applied to each power converter, then reactive power distribution is optimized, but AC voltage amplitude stability deteriorates due to cumulative unbalance effects
Solution Approach 1:
The control system employs feedback by continuously measuring the reactive power of each power converter, calculating the unbalance indicator based on the deviation from the arithmetic average, and using this feedback to adjust the voltage amplitude reference. This closed-loop control ensures that reactive power balancing is achieved while maintaining AC voltage amplitude stability within acceptable limits.
Solution Approach 2:
The system dynamically changes the voltage amplitude reference parameter based on the calculated unbalance indicator. By adjusting this key parameter in real-time according to the reactive power distribution status, the system optimizes reactive power balancing while preventing excessive voltage amplitude deviations that would compromise stability.
Data Source
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AI summary
A control system for controlling parallel connected power converters comprises a data processing system (101-103) configured to form, for each power converter, a reactive power indicator (Ireact_n) based on data indicative of reactive power (Q_n) of the power converter, form an arithmetic average (Ireact_ave) of the reactive power indicators of the power converters, form, for each of the power converters, an unbalance indicator (edm_n) based on a difference (Ireact_n - Ireact_ave) between the reactive power indicator of the power converter and the arithmetic average, and control an alternating voltage amplitude reference (UAC,ref_n) of a converter stage of each of the power converters based on at least the unbalance indicator of the power converter. The use the arithmetic average reduces undesired voltage drift of the power converters when balancing the reactive powers of the power converters.