Three-Phase Inverter With Scott Transformer Reduces Capacitance
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Solution Overview
Problem
Existing three-phase inverters for photovoltaic power generators often require large capacitances to achieve high grid conformity, which can be inefficient and costly.
Innovation Solution
A three-phase inverter design utilizing a Scott transformer with two primary windings and at least three secondary windings, coupled with an inverter circuitry featuring a split DC link and two inverter half-bridges, reduces capacitance needs by offsetting single-phase alternating voltages, allowing for high grid conformity with minimal switches and capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing three-phase inverter designs are used to achieve high grid conformity, then the output power quality is improved, but the capacitance requirements and device complexity increase
Solution Approach 1:
The inverter circuitry is divided into two separate half-bridges that independently generate single-phase alternating voltages with a fixed phase offset. This segmentation allows each half-bridge to operate with reduced capacitance requirements while the transformer combines their outputs to achieve high grid conformity. The split DC link is also segmented into two separate capacitor sets, one for each half-bridge, reducing the total capacitance needed compared to a unified inverter design.
Solution Approach 2:
A transformer with two primary windings and at least three secondary windings serves as an intermediary device between the two half-bridges and the three-phase power grid. The transformer combines the two single-phase alternating voltages with fixed phase offset into a balanced three-phase alternating voltage, achieving high grid conformity without requiring large capacitances in the inverter circuitry. The transformer effectively mediates the phase relationships and voltage transformations needed for grid connection.
2Reliability
If more switches and capacitors are added to improve power conversion efficiency, then the grid conformity is improved, but the device complexity and cost increase
Solution Approach 1:
The inverter uses only two half-bridges with a total of four switches (two per half-bridge) to generate the two single-phase alternating voltages needed for the transformer. This segmented approach with minimal switches, combined with the transformer's phase-combining capability, achieves high power conversion efficiency and grid conformity without requiring a larger number of switches and capacitors that would increase device complexity and cost.
3Device complexity
If a split DC link with two inverter half-bridges is used, then the capacitance needs are reduced, but the transformer configuration becomes more specific
Solution Approach 1:
The transformer with two primary windings and at least three secondary windings serves multiple functions: it combines the two single-phase alternating voltages with fixed phase offset, performs voltage transformation, and generates balanced three-phase alternating voltage for grid connection. This multi-functional transformer design reduces capacitance requirements in the inverter circuitry while maintaining adaptability for three-phase power generation applications.
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 solution provides a three-phase AC output with high grid conformity using fewer switches and capacitors, reducing the overall complexity and cost while maintaining efficient power conversion.
Implementation Method 1
a transformer (12) having two primary windings (10, 11) and at least three secondary windings (5, 6, 7), the transformer (12) being configured for transforming two single phase alternating voltages at a fixed phase offset which are applied to its two primary windings (10, 11) into a three-phase alternating voltage present at its secondary windings (5, 6, 7)
Implementation Method 2
The half bridges alternately connect their centre points each connected to one terminal of one of the primary windings of the transformer to the two electric potentials of the direct current link
Data Source
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AI summary
A three-phase inverter (1) for converting DC power from a generator (2) into three-phase AC power comprises a transformer (12) for transforming two single phase alternating voltages with a fixed phase offset present at corresponding two primary windings (10, 11) of the transformer (12) into a three-phase alternating voltage present at secondary windings (5-7) of the transformer (12). An inverter circuitry (20) for receiving a direct voltage of the generator (2) between two input lines (8, 9) and for supplying the two single phase alternating voltages to the two primary windings (10, 11) of the transformer (12) is included in the three-phase inverter (1) and comprises a split DC link (25) having a centre point (25) connected to both input lines (8, 9) via corresponding capacitors (21, 22) and connected to a first terminal (17, 18) of each primary winding (10, 11) of the transformer (12), and two inverter half-bridges (23, 24) connected to both input lines (8, 9), wherein a centre point of each half bridge (23, 24) is connected to a second terminal (26, 27) of a corresponding one of the primary windings (10, 11) of the transformer (12).