UPS Current Reference Signal Modification for THD Reduction
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Solution Overview
Problem
Existing uninterruptible power supply (UPS) systems face challenges in achieving low total harmonic distortion (THD) and efficient power factor correction (PFC), leading to increased harmonic terms and asymmetrical current waveforms, which affect the reliability and efficiency of power distribution.
Innovation Solution
The implementation of a UPS system with a positive and negative boost circuit configuration, utilizing current loop control circuits and controllers to generate modified current reference signals with predetermined zero values prior to period ends, ensuring the current error amplifiers come out of saturation and into the active region before activating the boost circuits, thereby reducing THD and achieving symmetrical current waveforms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional PFC schemes are used to improve power factor, then power factor is improved, but total harmonic distortion increases and current waveforms become asymmetrical
Solution Approach 1:
The input circuit is divided into separate positive boost circuit and negative boost circuit, each with its own current loop control. This segmentation allows independent control of positive and negative half-cycles, enabling symmetrical current waveforms while maintaining power factor correction
Solution Approach 2:
The current reference signal is modified to have predetermined zero values prior to period ends (approximately 0.8 milliseconds before), which prepares the current error amplifiers to come out of saturation and into the active region before the boost circuits activate, preventing harmonic distortion
2Reliability
If current loop control is used to control input current, then power factor correction is achieved, but current waveforms become asymmetrical and harmonic terms increase
Solution Approach 1:
The patent intentionally introduces asymmetry in the control approach by modifying the current reference signal with predetermined zero values before period ends, which compensates for the inherent asymmetry in boost circuit operation and achieves symmetrical overall current waveforms
Solution Approach 2:
Current loop control circuits continuously monitor and adjust the input current to follow the modified current reference signal, providing feedback control that maintains waveform symmetry while achieving power factor correction
Data Source
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AI summary
According to a first aspect, an uninterruptable power supply is provided. In one example, the uninterruptable power supply comprises a controller configured to provide a first current reference signal, the first current reference signal having a periodic waveform including a first half period and a second half period, each half period having a period end, the waveform comprising a substantially rectified sine wave modified such that a value of the rectified sine wave is equal to zero for a predetermined period of time prior to the period end of the second half period, a positive current loop control circuit configured to receive the first current reference signal and provide an output signal to the positive boost circuit, and a negative current loop control circuit configured to provide an output signal to a negative boost circuit.