Transformerless Power Conversion Circuit for Grid-Connected Systems
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Solution Overview
Problem
Conventional DC to AC power conversion circuits require transformers for isolation, leading to increased size, cost, and reduced efficiency due to the need for ground isolation, which is prohibited in many interconnection rules and results in DC current flowing into the grid, affecting device size, cost, and conversion efficiency.
Innovation Solution
A transformerless power conversion circuit utilizing a buck-boost converter to generate two DC power levels and at least one half-bridge inverter to convert these levels into AC power for grid interconnection, eliminating the need for transformers and addressing common ground issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transformer is connected between the power conversion circuit and grid for isolation, then ground isolation is provided to prevent DC current flowing into the grid, but device size, manufacturing cost increase and conversion efficiency decreases
Solution Approach 1:
The patent removes the transformer component from the power conversion circuit by implementing a transformerless topology. The circuit achieves ground isolation through a different mechanism - using a floating DC link voltage and controlled switching of power devices to prevent DC current injection into the grid, thereby eliminating the need for the transformer while maintaining reliability.
Solution Approach 2:
The patent replaces the electromagnetic isolation mechanism of the transformer with an electronic control mechanism. By using controlled power semiconductor switches and a specific circuit topology that maintains a floating DC link, the system achieves ground isolation through electronic means rather than mechanical/electromagnetic transformation, reducing device size and improving efficiency.
2Reliability
If a transformer is connected between the power conversion circuit and grid for isolation, then ground isolation is provided to prevent DC current flowing into the grid, but manufacturing cost increases
Solution Approach 1:
The transformer component is completely removed from the circuit architecture. The isolation function previously performed by the transformer is achieved through a transformerless topology with controlled switching, eliminating the need for expensive magnetic components and reducing manufacturing costs.
Solution Approach 2:
The patent uses solid-state power semiconductor switches and electronic control components instead of expensive, bulky transformers. These electronic components are generally more cost-effective, have longer operational lifetimes, and require less maintenance, thereby reducing overall manufacturing and operational costs.
3Reliability
If a transformer is connected between the power conversion circuit and grid for isolation, then ground isolation is provided to prevent DC current flowing into the grid, but conversion efficiency decreases
Solution Approach 1:
By removing the transformer from the power conversion circuit, the patent eliminates energy losses associated with magnetic core hysteresis, eddy currents, and copper losses in the transformer windings. The transformerless topology directly converts DC to AC through power semiconductor switching, significantly improving conversion efficiency.
Solution Approach 2:
The patent replaces the electromagnetic energy transformation in the transformer with direct electronic switching and voltage synthesis. This substitution eliminates the inefficiencies of magnetic energy conversion and achieves higher efficiency through controlled power electronic switches operating at higher frequencies with lower losses.
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 significantly reduces device size, manufacturing cost, and power loss while improving conversion efficiency by eliminating the transformer and using fewer active switches, effectively addressing the common ground problem and enhancing overall circuit performance.
Implementation Method 1
a buck-boost converter converting the input DC power into two sets of DC power levels
Implementation Method 2
at least one half-bridge inverter converting the two sets of DC power levels into the AC power for feeding into the grid
Data Source
AI summary
A transformerless power conversion circuit is interconnected with an electric grid and converts an input DC power provided by a power generator into an AC power and feeding the AC power into the grid. The power conversion circuit includes a buck-boost converter converting the input DC power into two sets of DC power levels; and at least one half-bridge inverter converting the two sets of DC power levels into the AC power for feeding into the grid. The isolating transformer can be eliminated and the common ground problem for DC side and AC side is also solved. The power conversion circuit has significant improvement for device size, manufacture cost and conversion efficiency.