Parallel Inverter Current Balancing via Feedback Control
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Solution Overview
Problem
Existing systems for driving inverters in parallel face output current unbalance issues due to time differences in communication and variations in power semiconductor features, leading to inefficiencies and the need for derating, which results in oversized inverter designs to ensure safety.
Innovation Solution
A system utilizing a proportional-integral controller, limiter, and output adder to balance output currents among inverters by compensating for differences through proportional and integral control, limiting values, and summing pulse width values to ensure balanced current output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single master controller and multiple slave controllers are used to control inverters in parallel, then the system can be controlled through communication, but output current unbalance occurs due to time differences in communication and variations in power semiconductor features
Solution Approach 1:
The patent implements a feedback mechanism where the master controller receives output current information from each slave controller and calculates correction values. The correction values are sent back to the respective slave controllers to adjust their output currents, thereby eliminating the unbalance caused by communication time differences and power semiconductor variations.
Solution Approach 2:
The patent dynamically adjusts the PWM duty cycle parameters of each inverter based on real-time output current measurements. By changing the control parameters (duty cycle) of each slave controller individually, the system compensates for differences in power semiconductor features and communication delays, achieving balanced output currents.
2Device complexity
If inverters are driven in parallel with the same PWM signals, then the system structure is simple, but output current unbalance occurs requiring derating and oversized inverter designs
Solution Approach 1:
The master controller performs preliminary calculations to determine the correction values needed for each slave controller before the inverters operate. By pre-calculating the appropriate duty cycle adjustments based on expected load conditions and inverter characteristics, the system prevents output current unbalance before it occurs, ensuring reliable operation without requiring oversized inverters.
Solution Approach 2:
The patent transitions from static PWM signal generation to dynamic adjustment of PWM parameters. The system continuously monitors output currents and dynamically modifies the duty cycle of each inverter in real-time, allowing the control structure to adapt to changing conditions and maintain balanced operation, thereby improving reliability without increasing hardware complexity.
3Reliability
If derating factor is applied to ensure safety in parallel inverter systems, then system reliability is maintained, but inverter capacity is reduced requiring bigger inverters than theoretically calculated
Solution Approach 1:
The feedback mechanism enables real-time monitoring and adjustment of each inverter's output current. By continuously measuring actual output currents and applying correction values, the system ensures that each inverter operates within safe limits while maximizing its capacity utilization. This eliminates the need for conservative derating, allowing inverters to operate at their full theoretical capacity safely.
Data Source
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AI summary
A system for driving inverters in parallel includes a master controller (210), a plurality of slave controllers (220), and a plurality of inverters (230) controlled correspondingly by each of the slave controllers (220). The system further includes a control signal creation unit to create control signals for the slave controllers (220) by using data transmitted and received between the master controller (210) and the slave controllers (220) to enable the plurality of inverters to create balanced output currents.