Three-Phase LLC Power Module Phase Shifting for Power Balancing
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Solution Overview
Problem
Conventional three-phase solid-state transformers face challenges in designing complex systems with numerous cells, leading to double frequency power fluctuations and inefficiencies due to limited voltage adjustment schemes, which result in increased losses and difficulty in power balancing among modules.
Innovation Solution
A phase-shift control method for power modules, where multiple inverter units output AC voltages that are cascaded and connected to a post-stage rectifier circuit, allowing for alternative phase-shift sequences to control AC voltages, thereby inhibiting double frequency fluctuations and achieving balanced power sharing within a wide voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional three-phase solid-state transformers use numerous single-phase cells in ISOP configuration, then output voltages with wide ranges can be achieved, but the device complexity increases and system integration becomes difficult
Solution Approach 1:
The patent combines three single-phase LLC circuits into a single three-phase LLC circuit, merging previously separate components into an integrated structure. This reduces the number of cells from 3N to N while maintaining the ability to achieve wide output voltage ranges through phase-shift control among the three phases.
Solution Approach 2:
The three-phase LLC circuit performs multiple functions simultaneously: it provides wide output voltage adjustment through phase-shift control, maintains ZVS for high efficiency, and enables power balancing among phases. The single circuit structure serves as a universal solution replacing multiple separate single-phase circuits.
2Adaptability or versatility
If single-phase cells with LLC circuits are used, then output voltage can be adjusted, but double frequency power fluctuations occur causing additional losses and requiring complex control algorithms
Solution Approach 1:
The patent creates homogeneous current waveforms in the three-phase resonant cavity by using phase-shift control, making the currents consistent and eliminating the double frequency fluctuations that occur in single-phase systems. This homogenization reduces additional losses and simplifies control requirements.
3Adaptability or versatility
If frequency modulation is used for output voltage adjustment, then wide voltage range is achieved, but system efficiency decreases
Solution Approach 1:
Instead of changing frequency for voltage adjustment, the patent changes the phase shift angle among the three phases as the control parameter. This parameter change maintains resonant operation and ZVS conditions while achieving wide output voltage ranges without increasing system losses.
4Adaptability or versatility
If phase shifting or duty cycle regulation is used for voltage adjustment, then output voltage can be controlled, but ZVS of inverter circuits is lost increasing loss
Solution Approach 1:
The patent dynamically adjusts the phase shift angles among the three phases while maintaining resonant operation. This dynamic control enables wide voltage regulation without losing ZVS, as the phase-shifted three-phase operation keeps the inverter circuits operating in their optimal switching zones throughout the adjustment range.
Data Source
AI summary
A power module includes N inverter units outputting N AC voltages and being coupled to N high-frequency AC terminals, wherein the N high-frequency AC terminals are cascaded and connected to a post-stage rectifier circuit. A phase-shift control method for the power module includes: setting at least two phase-shift sequences, wherein phase sequence numbers of the N AC voltages of the N inverter units are different in the at least two phase-shift sequences; in one switching period, controlling the N AC voltages of the N inverter units to shift a first angle according to a first phase-shift sequence of the at least two phase-shift sequences; and in another switching period, controlling the N AC voltages of the N inverter units to shift the first angle according to a second phase-shift sequence of the at least two phase-shift sequences.