Inverter Common-Mode Voltage Control for Circulating Current Reduction
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Solution Overview
Problem
Parallel-connected inverters experience circulating currents due to phase shifts in switching patterns, leading to undesirable strain on the inverter and output filter, and existing solutions like communication links and current sensors are costly and bulky.
Innovation Solution
Measuring common-mode voltage to control the cycle length of switching cycles in inverter bridges or active rectifier bridges, synchronizing modulation without additional sensors or communication, thereby minimizing circulating currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If communication links are used to synchronize parallel-connected inverters, then circulating currents are reduced, but device complexity and cost increase
Solution Approach 1:
The inverter synchronizes its switching cycle automatically by detecting the common-mode voltage generated by other parallel inverters and adjusting its own switching cycle length accordingly. This self-service mechanism eliminates the need for external communication links or current sensors, reducing device complexity while effectively minimizing circulating currents between parallel-connected inverters
Solution Approach 2:
The control unit continuously monitors the common-mode voltage signal and uses this feedback to dynamically adjust the switching cycle length. This closed-loop feedback mechanism enables automatic synchronization without requiring additional communication infrastructure, resolving the contradiction between circulating current reduction and device complexity
2Object-generated harmful factors
If current sensors are used to measure circulating current, then circulating currents are minimized, but device complexity and cost increase
Solution Approach 1:
The patent uses common-mode voltage as an intermediary signal that indirectly reflects the circulating current state. Instead of directly measuring circulating current with sensors, the system measures the common-mode voltage generated by switching patterns and uses this intermediate measurement to synchronize switching cycles, thereby eliminating the need for additional current sensors while achieving circulating current minimization
Solution Approach 2:
The patent replaces the mechanical/electrical measurement system (current sensors) with an electrical signal processing approach. By substituting direct current measurement with common-mode voltage detection and processing, the system achieves the same synchronization goal without requiring additional sensing hardware, reducing device complexity
3Adaptability or versatility
If switching frequencies of modulators differ or have phase shifts, then inverter operation is flexible, but circulating currents increase
Solution Approach 1:
The patent implements dynamic adjustment of the switching cycle length based on real-time common-mode voltage detection. Instead of using fixed switching frequencies, the system continuously adapts the switching cycle duration to match the phase and frequency characteristics of other parallel inverters, maintaining synchronization flexibility while eliminating circulating currents caused by phase shifts
Data Source
AI summary
The present disclosure discloses a method and an apparatus implementing the method for minimizing a circulating current of parallel-connected inverters. The method can include, for at least one parallel-connected inverter, measuring a common-mode voltage of the inverter, and controlling a cycle length of the switching cycle on the basis of the common-mode voltage.