VSCF Voltage Regulation Circuit for Parallel Power Transfer
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Solution Overview
Problem
Circulating current between two systems operating in parallel can be challenging due to small phase differences or amplitude differences, leading to undesirable large currents and DC components in inverter systems.
Innovation Solution
A circuit comprising a slow voltage loop, a fast voltage loop, a current control loop, and switches that toggle gains between normal and power transfer modes, along with a DC content compensation circuit with different gains for AC and DC content, to manage and reduce circulating currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If two systems are operated in parallel, then power transfer capability is improved, but circulating current increases due to phase difference or amplitude difference
Solution Approach 1:
The patent applies preliminary action by detecting voltage parameters (phase angle and amplitude) before power transfer occurs and pre-adjusting the inverter output to match the bus voltage. The controller calculates required adjustments and applies them in advance, ensuring voltage synchronization before closing the transfer switch, thereby preventing circulating current from arising in the first place
Solution Approach 2:
The patent implements feedback by continuously monitoring the inverter output voltage and bus voltage, comparing their phase angles and amplitudes, and using this information to dynamically adjust the inverter control signals. This closed-loop feedback ensures voltage matching is maintained during power transfer, eliminating circulating current caused by voltage mismatches
2Power
If inverter system operates with DC component, then power transfer is enabled, but system stability deteriorates due to undesirable DC content
Solution Approach 1:
The patent applies the taking out principle by explicitly extracting and addressing the DC component issue through separate control mechanisms. The controller detects DC content in the inverter output and applies specific correction signals to eliminate it, separating the DC component management from the normal AC power transfer control, thereby maintaining system stability while enabling power transfer
3Speed
If voltage amplitude is adjusted rapidly, then response speed is improved, but voltage loop stability may be compromised
Solution Approach 1:
The patent applies segmentation by dividing the voltage control into two independent loops: a fast voltage loop for rapid response to voltage deviations and a slow voltage loop for maintaining overall voltage level and stability. Each loop operates with appropriate bandwidth and gain settings, allowing the fast loop to correct transient errors quickly while the slow loop ensures long-term stability, preventing oscillations that would result from a single high-gain controller
Data Source
AI summary
A variable speed constant frequency electric voltage regulation circuit may include a slow voltage loop detecting and adjust an amplitude of an output signal of the circuit. A fast voltage loop of the circuit may include an error amplifier detecting a difference between a reference sine wave signal and the output signal. A current control loop may include a current controller and an inverter. A first switch may toggle a gain of the circuit between a gain associated with a normal mode and a gain associated with a power transfer mode based on a power transfer command signal. A second switch may toggle control between the current control loop in the power transfer mode and the fast and slow voltage loops in the normal mode. The sample/hold circuit eliminates the slow voltage loop from regulating the output during the power transfer.