Solid-State Transformer PV Grid Interface for Fast Fault Protection
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Solution Overview
Problem
Existing power conversion systems connecting photovoltaic plants to the electric grid face inefficiencies due to high material costs, bulky components, slow response times in voltage regulation and protection, and limited flexibility, which hinder the ability to optimize energy production and efficiently transmit large amounts of power at higher voltage levels.
Innovation Solution
The implementation of a power conversion system utilizing solid-state transformers and a medium voltage DC-AC inverter, which reduces the use of expensive conductor materials, enables faster fault protection, and provides greater flexibility and modularity by operating at higher frequencies, thereby achieving higher power density and lower installation costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If solid-state transformers operating at higher frequencies are used, then power density is improved, but device complexity increases
Solution Approach 1:
The solid-state transformer is divided into multiple functional modules including DC-AC converters, medium frequency transformers, and AC-DC rectifiers. Each module operates independently at optimized frequencies, allowing the system to achieve high power density while managing complexity through modular design. The segmentation enables parallel processing of power conversion tasks across multiple stages.
Solution Approach 2:
The system operates at medium frequency ranges (2-20 KHz) instead of standard grid frequency, fundamentally changing the operating parameters of the transformers. This frequency parameter change enables smaller transformer sizes and higher power density while the control system adapts to manage the increased complexity through automated frequency synchronization and voltage regulation.
2Loss of energy
If medium voltage DC-AC inverters are used, then transmission efficiency is improved, but ease of operation deteriorates
Solution Approach 1:
The medium voltage DC-AC inverter incorporates multiple feedback control mechanisms including voltage feedback, current feedback, and frequency feedback. These feedback loops continuously monitor system parameters and automatically adjust operating conditions to maintain optimal transmission efficiency. The feedback systems manage the operational complexity by providing automated control rather than manual intervention.
Solution Approach 2:
The system replaces mechanical voltage regulation and frequency control mechanisms with electronic control through the DC-AC inverter. This substitution eliminates the need for mechanical transformers and switchgear operations, improving transmission efficiency while the electronic control interface simplifies operation through automated digital controls rather than manual mechanical adjustments.
3Power
If higher frequency operation is implemented, then power density is improved, but loss of time in voltage regulation decreases
Solution Approach 1:
The medium frequency operation (2-20 KHz) implements periodic switching action in the solid-state transformers, allowing voltage regulation to occur in rapid cycles. This periodic action enables the system to achieve high power density while the fast cycling provides frequent adjustment opportunities, reducing the effective response time for voltage regulation compared to low-frequency systems.
Solution Approach 2:
The control system performs preliminary voltage regulation adjustments through the medium frequency switching before power disturbances affect the output. By anticipating and pre-adjusting voltage levels through the high-frequency switching capability, the system maintains stable output while the preliminary actions reduce the need for corrective time, improving both power density and response characteristics.
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 results in a more compact, cost-effective, and versatile power conversion system capable of efficiently transmitting several tens of megawatts of power with faster fault protection and improved electromagnetic compatibility, enhancing the safety and efficiency of power transmission.
Implementation Method 1
Each solid-state transformer includes a primary stage and a secondary stage. The primary stage includes at least one DC-AC converter, each arranged to receive low voltage DC power from a power generation unit, and one or more primary medium frequency transformer windings.
Implementation Method 2
The secondary stage includes at least one AC-DC rectifier, each arranged to receive AC power from a respective secondary medium frequency transformer winding.
Implementation Method 3
The medium voltage DC-AC inverter is configured to receive medium voltage DC power from one or more AC-DC rectifiers and output medium voltage AC power.
Data Source
AI summary
A power conversion system includes one or more solid state transformers, and a medium voltage DC-AC inverter. Each solid state transformer includes a primary stage, including at least one DC-AC converter, each arranged to receive low voltage DC power from a power generation unit, and one or more primary medium frequency transformer windings, and a secondary stage, including at least one AC-DC rectifier, each arranged to receive AC power from a respective secondary medium frequency transformer winding. The medium voltage DC-AC inverter is configured to receive medium voltage DC power from one or more rectifiers and output medium voltage AC power.