Bidirectional Power Conversion System for Single-Phase Loads
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Solution Overview
Problem
Existing bidirectional power conversion systems for single-phase electric loads face challenges with current fluctuations due to voltage differences, requiring additional converters that increase size and cost, and existing solutions either use multiple converters or additional conversion stages that complicate the system.
Innovation Solution
A bidirectional power conversion system with a 3-stage DC/AC power conversion stage, including interleaved converters with inductive circuits and PWM modulation, which generates a controlled square-wave output voltage to minimize current fluctuations without needing an additional converter, using a transformer to smooth the output voltage and reduce fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If multiple converters are used to eliminate current fluctuations, then current fluctuation is reduced, but system volume and cost increase
Solution Approach 1:
The patent merges multiple converter functions into a single converter by using multiple bridge arms (first bridge arm, second bridge arm, third bridge arm, fourth bridge arm) that operate in parallel with different phase shifts. This combination eliminates current fluctuations without requiring multiple separate converters, thus reducing system volume while maintaining the benefit of fluctuation elimination.
Solution Approach 2:
The converter is segmented into multiple independent bridge arms that can be controlled separately with different phase shifts relative to the grid voltage. Each bridge arm contributes to power transfer with a specific phase relationship, and their combined effect smooths current fluctuations while keeping the overall system compact.
2Object-generated harmful factors
If additional conversion stages are added to eliminate current fluctuations, then current fluctuation is reduced, but device complexity increases
Solution Approach 1:
The single converter with multiple bridge arms performs multiple functions simultaneously: it transfers power bidirectionally, regulates voltage, and eliminates current fluctuations through phase-shifted control. This multi-functionality avoids the need for additional dedicated conversion stages, reducing device complexity while achieving fluctuation elimination.
Solution Approach 2:
The converter uses dynamic phase-shift control where the phase shift between each bridge arm and the grid voltage can be independently adjusted. This dynamic control mechanism allows the system to adaptively eliminate current fluctuations without requiring additional static conversion stages, thereby reducing complexity.
3Power
If voltage levels are kept at nominal levels in DAB converters, then power transfer is maintained, but current fluctuations appear when voltage difference becomes large
Solution Approach 1:
The patent changes the control parameter from fixed nominal voltage levels to variable phase shifts. By adjusting the phase shift of each bridge arm relative to the grid voltage, the system can accommodate large voltage differences while maintaining power transfer and eliminating current fluctuations through coordinated phase-controlled power exchange.
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 eliminates significant current fluctuations, reduces system volume and cost, and provides faster voltage regulation by interleaving converters with inductive circuits and using a transformer to smooth the output voltage, ensuring efficient power transfer between the DC power bus and the single-phase load.
Implementation Method 1
using a transformer to smooth the output voltage and reduce fluctuations
Implementation Method 2
interleaved converters with inductive circuits
Data Source
Figure 1a~1d
Figure 2
Figure 3a~3b
AI summary
This bidirectional power conversion system for single-phase electrical loads is designed to be connected to a DC power bus supplying a single DC supply voltage and to deliver to the load an AC output voltage (Vac) substantially in the shape of a square wave. It comprises a set of interleaved converters capable of jointly delivering a control voltage (Uac). The phase shift of the fundamental component of this control voltage relative to the output voltage is intended to control the power transfer between the converters and the load. The converters are controlled such that the amplitude of the average value of the control voltage (Uac) corresponds to the amplitude of the AC output voltage, and such that the control voltage has amplitudes suitable for reducing fluctuations in the current flowing between the voltage converters and the load.