Parallel Power Converter Control for Reactive Power Balancing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In AC systems like microgrids, parallel-connected power converters face challenges in maintaining frequency and voltage stability, especially when one converter fails, and traditional master-slave configurations are unreliable.
Innovation Solution
A control system that forms reactive power indicators, calculates an arithmetic average, and adjusts alternating voltage amplitude references based on unbalance indicators, eliminating the need for a centralized master controller by distributing control among converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a master-slave configuration is used for reactive power balancing, then reactive power sharing is achieved, but system reliability deteriorates because a master failure renders the whole system inoperable
Solution Approach 1:
The centralized master control function is segmented and distributed to all slave converters. Each converter independently calculates its own voltage amplitude reference based on its measured reactive power and the average reactive power of all converters, eliminating the single point of failure while maintaining coordinated control.
Solution Approach 2:
Each converter serves itself by autonomously determining its voltage amplitude reference using its own reactive power measurement and the calculated average. This self-service approach eliminates dependency on a master converter, improving reliability while reducing control structure complexity.
2Reliability
If a master-slave configuration is used for reactive power balancing, then reactive power sharing is achieved, but control structure complexity increases due to the need for dynamic master changing mechanisms
Solution Approach 1:
The control function is segmented such that each converter performs the same calculation algorithm independently. This segmentation eliminates the need for complex master-slave switching mechanisms, as all converters operate symmetrically with equal capability to determine voltage references.
Solution Approach 2:
All converters are designed with universal control capability to determine voltage amplitude references. Each converter can independently perform the reactive power balancing function, making the system more robust and eliminating the need for specialized master converter hardware or complex switching logic.
3Ease of operation
If individual converters control their voltage independently, then converter autonomy is improved, but voltage and frequency stability of the AC grid deteriorates
Solution Approach 1:
Each converter uses feedback from the actual reactive power it supplies to the AC grid to adjust its voltage amplitude reference. This feedback mechanism ensures that individual autonomous converters collectively maintain AC grid voltage and frequency stability by coordinating their reactive power output through the calculated average.
4Reliability
If reactive power balancing is implemented, then reactive power sharing is improved, but AC voltage amplitude stability deteriorates due to unbalance indicators affecting voltage amplitude
Solution Approach 1:
The control approach applies local quality by having each converter adjust only its voltage amplitude based on its local unbalance indicator, while the overall AC voltage stability is maintained through the collective effect of all converters using the calculated average reactive power as a reference.
Data Source
AI summary
A control system for controlling parallel connected power converters includes 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.