Inverter Modulator Synchronization via Circulating Current Feedback
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Solution Overview
Problem
In high-power applications with parallel-connected inverter units, circulating currents occur due to phase switch misalignment, causing stress on converters and input inductors, and existing solutions like isolation transformers are cumbersome and expensive, while common PWM modulators require complex arrangements.
Innovation Solution
Synchronize inverter unit-specific modulators using current measurement data, specifically measuring modulation-frequency circulating currents caused by phase differences in zero components of three-phase voltage patterns, allowing for standard unit implementation without additional electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If inverter unit-specific PWM modulators are used independently for each parallel-connected inverter unit, then each unit can operate autonomously, but circulating currents occur due to phase switch misalignment causing stress on converters and input inductors
Solution Approach 1:
The patent employs feedback by measuring the circulating current between parallel-connected inverter units and using this measurement to adjust the PWM modulation phases. The control system continuously monitors the circulating current and modifies the modulation signals to minimize the circulating current, thereby maintaining autonomous operation while eliminating harmful effects.
Solution Approach 2:
The patent changes the phase parameters of the PWM modulation signals dynamically based on the measured circulating current. By adjusting the phase shift between modulators of different inverter units, the system optimizes the switching timing to prevent circulating currents while preserving autonomous operation capability.
2Object-affected harmful factors
If isolation transformers are used to prevent circulating currents, then circulating currents are eliminated, but the solution becomes cumbersome and expensive with large space requirements
Solution Approach 1:
The patent replaces the mechanical/isolation transformer solution with an electronic control system. Instead of using physical transformers to block circulating currents, the system uses PWM modulator phase adjustment based on current measurements to electronically eliminate circulating currents, thereby avoiding the space and cost penalties of isolation transformers.
3Reliability
If a common PWM modulator is used for all parallel inverter units, then synchronization is achieved, but complex arrangements are required for modulator distribution
Solution Approach 1:
The patent segments the PWM modulation function into independent unit-specific modulators rather than using a single common modulator. Each inverter unit has its own modulator that operates autonomously but is synchronized through phase adjustment based on circulating current measurements, thereby achieving synchronization without complex distribution arrangements.
Data Source
AI summary
A method for the synchronization of parallel-connected inverter units (INU1, INU2) or frequency converters and an inverter apparatus or a frequency converter apparatus wherein the inverter units are provided with inverter-specific modulators, in which method the circulating current between the inverter units is measured, and the modulators are synchronized to each other on the basis of the current measurement data.