Variable-Level Inverter Balancing DC Bus Voltages
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Solution Overview
Problem
Split DC link inverter arrangements in UPS systems face challenges with voltage imbalances due to unbalanced loads, which existing balancer circuits may not adequately address, leading to inefficiencies and potential flickering in AC voltage waveforms.
Innovation Solution
A power conversion apparatus and method that utilizes an inverter circuit coupled to DC busses and a neutral node, along with an inductor, to selectively couple the DC busses and neutral node to generate AC voltage, transitioning between inverter level modes to compensate for imbalances by routing current through capacitors and inductors, eliminating the need for separate balancer circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a split DC link inverter arrangement is used, then the inverter can generate AC voltage from DC sources, but voltage imbalances occur on the DC link busses due to unbalanced loads
Solution Approach 1:
The inverter circuit itself performs the balancing function by selectively coupling DC busses to the AC output during specific half-cycles. The circuit uses its own switching elements to detect and correct voltage imbalances without requiring a separate balancer circuit, making the system self-sufficient for both power conversion and voltage balancing tasks.
Solution Approach 2:
The balancing operation is performed periodically during specific half-cycles of the AC waveform. The control circuit identifies when voltage imbalances occur and activates balancing sequences during appropriate half-cycles, using periodic AC cycles to gradually equalize DC bus voltages while maintaining continuous power delivery.
2Stability of the object's composition
If separate balancer circuits are added to address DC bus imbalances, then voltage balance can be maintained, but device complexity increases
Solution Approach 1:
The inverter circuit is designed to perform multiple functions: primary AC voltage generation and secondary DC bus balancing. The same switching elements and control circuitry that generate the AC output are also used to detect and correct voltage imbalances, eliminating the need for dedicated balancer circuits and reducing overall system complexity.
Solution Approach 2:
The balancing function is merged with the power conversion function within a single integrated inverter circuit. The control circuit combines both AC generation control and DC bus balancing control into one unified system, sharing common components such as switching elements, sensors, and control logic to reduce device complexity.
3Adaptability or versatility
If unbalanced loads are connected to the inverter, then the inverter can serve diverse power requirements, but voltage imbalances and potential flickering occur
Solution Approach 1:
The control circuit continuously monitors DC bus voltages and AC output characteristics to detect imbalances caused by unbalanced loads. Based on this feedback, the control circuit dynamically adjusts switching sequences and coupling configurations to correct voltage imbalances and maintain stable AC voltage waveforms, ensuring reliable operation with diverse loads.
Solution Approach 2:
The inverter circuit dynamically adapts its switching sequence and DC bus coupling configuration based on real-time load conditions. When unbalanced loads are detected, the circuit dynamically changes its operation mode to prioritize balancing, and when loads are balanced, it returns to standard AC generation mode, providing versatile and reliable performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively balances DC bus voltages and maintains stable AC voltage waveforms, particularly in UPS systems with unbalanced loads, by using stored energy in inductors to equalize DC bus voltages, thereby enhancing power conversion efficiency and reducing the need for additional balancing circuits.
Implementation Method 1
an inductor configured to be coupled to a load... the inverter circuit uses a switching sequence wherein the first DC bus, the second DC bus and the neutral node are successively coupled to a first terminal of the inductor
Implementation Method 2
Discharge of the inductor may counteract an imbalance of the first and second DC busses with respect to the neutral node
Data Source
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AI summary
A power conversion apparatus, such as an uninterruptible power supply, included first and second DC busses, a neutral node and an inductor configured to be coupled to a load. The apparatus further includes an inverter circuit coupled to the first and second DC busses, to the neutral node and to the inductor and configured to selectively couple the first and second DC busses and the neutral node to a first terminal of the inductor to generate an AC voltage at a second terminal of the inductor such that, in a given half-cycle of the AC voltage, the inverter circuit uses a switching sequence wherein the first DC bus, the second DC bus and the neutral node are successively coupled to the first terminal of the inductor.