Nine-Phase Phase-Shifting Autotransformer for UPS Harmonic Reduction
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Solution Overview
Problem
Conventional high-power power-frequency UPS systems generate significant power harmonic pollution due to input side rectification, which is costly and inefficient, and require bulky isolation transformers for 18-pulse rectification, limiting their economic and spatial benefits.
Innovation Solution
A symmetric-type UPS power system based on a nine-phase phase-shifting autotransformer with a unique symmetric structure, utilizing a three-phase AC power input and output, a synchronized control device, and a power-frequency isolation transformer with coupled isolation of four ports, achieving 18-pulse rectification and reducing grid-side current harmonics without the need for balance reactors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a full-isolation phase-shifting transformer based on Δ/Y-type and Δ/Δ-type structure is adopted for 12-pulse rectification, then grid-side current harmonic is suppressed, but the transformer becomes large and heavy and costly
Solution Approach 1:
The patent combines the phase-shifting function and isolation function into a single nine-phase phase-shifting autotransformer. This merging of functions achieves 18-pulse rectification with harmonic suppression while eliminating the need for bulky balance reactors and multiple separate transformers, thereby reducing overall weight and cost.
Solution Approach 2:
The nine-phase phase-shifting autotransformer serves multiple purposes simultaneously: it provides phase shifting for 18-pulse rectification, electrical isolation, and harmonic suppression. This multi-functionality replaces what would traditionally require separate components, reducing system complexity and weight.
2Object-generated harmful factors
If an isolation transformer is used to realize nine-phase phase-shift power supply for 18-pulse rectification, then grid-side current harmonic is further reduced, but the isolation transformer becomes bulky and economic benefit decreases
Solution Approach 1:
The patent merges the phase-shifting function and isolation function into a single nine-phase phase-shifting autotransformer. This merging of functions achieves 18-pulse rectification with harmonic suppression while eliminating the need for bulky balance reactors and multiple separate transformers, thereby reducing overall weight and cost.
3Device complexity
If conventional six-pulse rectifier is used, then system structure is simple, but quintuple and septuple harmonic pollution is severe
Solution Approach 1:
The patent segments the rectification process into three separate six-pulse rectifier circuits that are phase-shifted relative to each other. By dividing the single rectification path into multiple segmented paths with different phase angles, the system achieves 18-pulse rectification that suppresses harmonics while maintaining reasonable structural complexity.
Solution Approach 2:
The patent introduces a phase dimension to the rectification system by creating three sets of rectifier circuits with different phase shifts (0°, +20°, -20°). This dimensional expansion from a single phase to multiple phases enables harmonic cancellation while maintaining system manageability.
4Object-generated harmful factors
If 18-pulse rectification technology is implemented using conventional methods, then grid-side current harmonic is reduced, but the system becomes complex and requires balance reactors
Solution Approach 1:
The patent combines the phase-shifting function and isolation function into a single nine-phase phase-shifting autotransformer. This merging of functions achieves 18-pulse rectification with harmonic suppression while eliminating the need for bulky balance reactors and multiple separate transformers, thereby reducing overall weight and cost.
Solution Approach 2:
The nine-phase phase-shifting autotransformer serves multiple purposes simultaneously: it provides phase shifting for 18-pulse rectification, electrical isolation, and harmonic suppression. This multi-functionality replaces what would traditionally require separate components, reducing system complexity.
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
The system effectively suppresses quintuple, septuple, elevenfold, and thirteenfold harmonics, reduces seventeenfold and nineteenfold harmonic content, and provides a compact, cost-effective solution with high reliability and redundancy, suitable for wide power range UPS systems above 500 KVA.
Implementation Method 1
a nine-phase phase-shift autotransformer... the nine-phase phase-shifting autotransformer is provided with three groups of three-phase AC output terminals, namely output terminals A1, B1 and C1 in an advance group, output terminals A0, B0 and C0 in an original group, and output terminals A2, B2 and C2 in a hysteresis group respectively
Implementation Method 2
a power-frequency isolation transformer... the power-frequency isolation transformer is provided with three groups of three-phase input terminals... the output terminals U, V and W of the power-frequency isolation transformer are connected to the three-phase AC power output terminal
Data Source
AI summary
A symmetric-type UPS power system based on a nine-phase phase-shifting autotransformer includes a three-phase AC power input terminal, a three-phase AC power output terminal, a nine-phase phase-shift autotransformer, a synchronized control device for controlling output of a three-phase inverter, a power-frequency isolation transformer and three circuits of output devices; wherein the three-phase AC input terminal of the nine-phase phase-shifting autotransformer is connected to the three-phase AC power input terminal, each circuit of the output devices includes a zero-sequence suppression commutating inductor, a three-phase six-pulse rectifier, a three-phase inverter and a filter inductor which are connected with each other in sequence, each circuit of the zero-sequence suppression commutating inductor is connected to the three-phase AC output terminal of the phase-shifting autotransformer, each circuit of the filter inductor is connected to the input terminal of the power-frequency isolation transformer.