UPS DC Bus Voltage Control via Instantaneous Power Difference
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Solution Overview
Problem
Existing power conversion circuitry in UPS systems faces challenges in achieving a balance between power factor correction and dynamic response, resulting in poor transient response of DC bus voltage due to slow voltage control loops, which leads to significant overshoots and undervoltages.
Innovation Solution
A method that determines the difference in instantaneous load power between successive cycles and adjusts the DC bus voltage based on this difference, employing a cumulative power difference to improve transient response time, allowing for control of the DC bus voltage in less than one cycle, thereby reducing voltage excursions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a voltage control loop with relatively slow response time is employed to reduce harmonics and improve power factor, then power factor is improved, but the transient response of DC bus voltage deteriorates with wider deviations, greater overshoot and undershoot
Solution Approach 1:
The control system performs preliminary action by detecting instantaneous load power changes and proactively adjusting the DC bus voltage before significant deviations occur. The controller compares instantaneous load power with average load power and generates control signals in advance to prevent overshoot and undershoot, rather than reacting after voltage deviations have already occurred.
Solution Approach 2:
The system implements feedback by continuously monitoring the DC bus voltage and load power, comparing instantaneous values with average values, and adjusting the voltage control loop accordingly. The feedback mechanism enables the system to detect power changes and respond dynamically, improving transient response while maintaining power factor correction.
2Object-generated harmful factors
If a feedback control system with slow frequency response is used to meet harmonic standards, then harmonic compliance is achieved, but the DC bus voltage exhibits poor transient response with large overvoltages and undervoltages
Solution Approach 1:
The control system detects instantaneous load power changes and proactively adjusts DC bus voltage before significant deviations occur. By comparing instantaneous power with average power and generating control signals in advance, the system prevents large overvoltages and undervoltages during transient conditions while maintaining harmonic compliance.
Solution Approach 2:
The system transitions from a static, slow-response voltage control loop to a dynamic control mechanism that responds to instantaneous load power changes. The controller dynamically adjusts the DC bus voltage based on real-time power comparisons, enabling fast transient response while maintaining steady-state harmonic performance.
3Speed
If the transient response time of DC bus voltage is reduced to less than one cycle, then voltage excursions are reduced, but the complexity of the control system increases
Solution Approach 1:
The system introduces an intermediary control mechanism that compares instantaneous load power with average load power and uses this comparison to generate control signals for the DC bus voltage. This intermediary power comparison stage simplifies the control logic by providing a straightforward method to detect transient conditions and trigger appropriate voltage adjustments without requiring complex control algorithms.
Data Source
AI summary
A UPS includes an AC output, power factor control circuitry; and a DC bus coupled to the power factor control circuitry where the power factor control circuitry is configured to determine a difference in instantaneous power supplied to the AC output and to adjust a voltage of the DC bus based, at least partly, on the difference. In one embodiment, the UPS includes a single phase AC input. In another embodiment, the power factor control circuitry is configured to determine a cumulative difference in instantaneous power supplied to the AC output.