Parallel Inverter DC Voltage Control for Cross Current Suppression
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Solution Overview
Problem
In parallel power conversion systems, cross current control methods can lead to unexpected harmonic currents due to voltage differences between power conversion apparatuses, necessitating careful specification of coupling reactors to prevent harmonic current flow.
Innovation Solution
A power conversion system that controls DC output voltages of converters based on detected current differences between inverters, using current detectors and difference current controllers to minimize cross currents and suppress harmonic currents by synchronizing the fundamental wave outputs of inverters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If coupling reactor specification is increased to prevent harmonic current, then harmonic current is suppressed, but system complexity and cost increase
Solution Approach 1:
The invention converts the control approach itself into the solution rather than using the coupling reactor as a passive filter. By actively controlling DC voltages to prevent harmonic generation at the source, the system eliminates the need for oversized coupling reactors, transforming the problem from one requiring passive component scaling to one solved by active control
2Object-generated harmful factors
If DC output voltages of converters are controlled based on current differences, then cross current is suppressed and harmonic currents are prevented, but control system complexity increases
Solution Approach 1:
The invention implements a feedback control mechanism where the actual output currents of the inverters are measured and fed back to the converter control units. The control units calculate current differences and adjust DC output voltages accordingly, creating a closed-loop system that automatically suppresses cross current and prevents harmonic generation through continuous feedback adjustment
Solution Approach 2:
The invention merges the cross current suppression function into the existing converter control structure rather than adding a separate control system. By utilizing the converter's existing voltage control capability and integrating current measurement and differential calculation into the control logic, the system achieves harmonic prevention using existing infrastructure
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively prevents unexpected harmonic currents from flowing between power conversion apparatuses operated in parallel, ensuring stable and efficient operation by adjusting DC output voltages in response to current differences.
Implementation Method 1
outputs of the first inverter and the second inverter are connected in parallel via a coupling reactor
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A power conversion system that has two power conversion apparatuses 2 each including a converter 21 that can control a DC voltage and an inverter 22 and that drives the AC motor 4 by connecting the outputs of the two inverters 22A and 22B in parallel is provided. The output voltage of one of the converters is controlled according to the difference between the detection currents detected by the two current detectors 6A and 6B for detecting the output currents of the two inverters 22A and 22B, respectively, so that a cross current flowing through the two inverters 22A and 22B is suppressed.