Multi Modular Converter Voltage Balancing via Energy Transfer
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Solution Overview
Problem
Existing power converters for three-phase AC transmission networks face challenges with voltage unbalance and the need for over-rated converters due to unbalanced loads, leading to increased costs and losses from extra switching cells required for redundancy.
Innovation Solution
A method and converter arrangement that selectively connect energy storage elements to phase legs based on voltage reference signals, allowing for energy transfer between phase legs to balance voltages and reduce the number of required energy storage elements, thereby minimizing costs and losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If extra switching cells are included in the phase legs for redundancy to compensate for unbalanced conditions, then the converter can handle unbalanced loads, but the costs and losses increase due to the additional components
Solution Approach 1:
The patent applies multi-functionality by enabling switching cells to serve dual purposes: primarily for voltage synthesis in balanced conditions, and secondarily for energy transfer between phase legs during unbalanced conditions. The controller dynamically reconfigures the circuit topology to allow switching cells to function either as voltage sources or as energy transfer mediators, eliminating the need for dedicated redundant cells while maintaining reliability under unbalanced loads.
2Reliability
If extra switching cells are included in the phase legs for redundancy, then the converter can handle unbalanced loads, but the costs increase due to additional components
Solution Approach 1:
The patent applies multi-functionality by enabling switching cells to serve dual purposes: primarily for voltage synthesis in balanced conditions, and secondarily for energy transfer between phase legs during unbalanced conditions. The controller dynamically reconfigures the circuit topology to allow switching cells to function either as voltage sources or as energy transfer mediators, eliminating the need for dedicated redundant cells while maintaining reliability under unbalanced loads.
3Device complexity
If a fixed number of energy storage elements are used in each phase leg, then the converter structure is simple, but the voltages become unbalanced under unbalanced load conditions
Solution Approach 1:
The patent applies dynamics by transitioning from a static, fixed circuit topology to a dynamic, reconfigurable topology. The controller continuously monitors voltage levels across energy storage elements and dynamically switches between different operational modes: normal voltage synthesis mode and energy transfer mode. This dynamic reconfiguration allows the system to adapt to unbalanced load conditions by transferring energy between phase legs, thereby maintaining voltage balance without requiring a fixed, over-rated structure.
Solution Approach 2:
The patent applies parameter changes by allowing the operational parameters of the converter to vary dynamically. Specifically, the circuit configuration and energy distribution parameters are adjusted in real-time based on load conditions. During unbalanced conditions, the controller modifies the switching patterns and energy transfer parameters to equalize voltages across phase legs, whereas under balanced conditions, the system operates with standard parameters. This parameter adaptability enables voltage balance maintenance without structural complexity.
4Reliability
If the number of series connected cells is increased to compensate for unbalanced conditions, then the converter can handle zero sequence voltage, but the total number of switching cells and costs increase
Solution Approach 1:
The patent applies multi-functionality by enabling switching cells to serve dual purposes: primarily for voltage synthesis in balanced conditions, and secondarily for energy transfer between phase legs during unbalanced conditions. The controller dynamically reconfigures the circuit topology to allow switching cells to function either as voltage sources or as energy transfer mediators, eliminating the need for dedicated redundant cells while maintaining reliability under unbalanced loads.
Solution Approach 2:
The patent applies merging by combining the functions of voltage synthesis and zero-sequence voltage compensation into a single, integrated circuit structure. Instead of having separate redundant switching cells dedicated solely to zero-sequence compensation, the patent merges this function with the existing switching cells used for normal operation. The same switching cells that synthesize phase voltages also participate in energy transfer and zero-sequence voltage generation when needed, achieving functional integration and reducing component quantity.
Data Source
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AI summary
A converter arrangement (1) and a method of controlling a three-phase converter arrangement connected to a transmission grid is provided. The converter arrangement (1) comprises three phase legs (10, 20, 30) and an energy transfer circuit (40). The method comprises providing a varying respective output phase (A, B, C) voltage to the transmission grid by selecting (206) energy storage elements (12A-n, 21A-n, 31A-n, 44) of both the phase legs (10, 20, 30) and the energy transfer circuit (40) and connecting (210) the selected energy storage elements (12A-n, 21A-n, 31A-n, 44) to the transmission grid output (15, 25, 35). The method further comprises selecting (208) energy storage elements (12A-n, 21A-n, 31A-n, 44) for performing a transfer of energy between the energy storage elements (12A-n, 21A-n, 31A-n, 44) during the control period.