Power Conversion Device Grid Impedance Control
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Solution Overview
Problem
Monitoring the impedance of a power grid during operation of a power generation system is challenging, especially when the point of interconnection between the transformer and the grid is inaccessible or economically difficult to measure, which affects the control of reactive power and voltage regulation in grid-connected PV systems.
Innovation Solution
A power conversion system with a sensor and system controller that measures voltage levels at a first point of interconnection and determines the impedance of the power grid, allowing for closed-loop control of reactive power output based on grid strength, using an equivalent power system model to estimate voltage levels at inaccessible points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage measurement is performed at the point of interconnection between transformer and power grid, then voltage regulation and reactive power control are improved, but the system complexity and measurement cost increase due to inaccessibility of the measurement point
Solution Approach 1:
The patent uses the transformer as an intermediary element to indirectly measure the voltage at the inaccessible point of interconnection. By measuring voltages at accessible points (primary and secondary sides of the transformer) and using the known transformer turns ratio, the system calculates the voltage at the grid connection point without direct physical access to that location.
Solution Approach 2:
The system creates a virtual copy of the voltage measurement at the inaccessible point by using mathematical relationships based on transformer characteristics. Instead of directly measuring at the grid connection point, the controller calculates the voltage value that would exist at that point based on measurements taken at accessible transformer terminals.
2Measurement precision
If direct measurement at the high-voltage side of the transformer is implemented, then measurement precision is improved, but the ease of operation and economic feasibility deteriorate due to inaccessibility
Solution Approach 1:
The transformer serves as a mediator that allows indirect measurement of high-voltage side parameters through low-voltage side measurements. The accessible low-voltage terminals of the transformer are used as intermediate measurement points, and the known transformation relationship enables accurate determination of the inaccessible high-voltage parameters.
Solution Approach 2:
The patent replaces the mechanical/physical measurement approach (direct voltage sensing at the high-voltage point) with a computational/mathematical approach. The system uses mathematical relationships based on transformer theory to substitute for direct physical measurement, eliminating the need for physical access to the high-voltage connection point.
3Reliability
If reactive power output is increased to support grid voltage, then power factor correction is improved, but the risk of overloading the power conversion device increases
Solution Approach 1:
The system implements feedback control by continuously monitoring the calculated grid connection point voltage and adjusting the reactive power output accordingly. The controller receives feedback about the actual voltage conditions and modifies the reactive power injection to maintain voltage within acceptable ranges while preventing device overload through closed-loop control.
Solution Approach 2:
The patent employs dynamic adjustment of reactive power output based on real-time voltage conditions. Rather than operating at fixed reactive power levels, the system dynamically varies the reactive power injection to match changing grid conditions, allowing optimal power factor correction while adapting to prevent device overload as conditions change.
Data Source
AI summary
A power conversion system configured to provide alternating current (AC) power to a transformer is described. The power conversion system includes a power conversion device that includes a device input and a device output. The power conversion device is configured to receive power from a power source at the device input and the device output is configured for coupling to a transformer input. The power conversion system also includes a sensor coupled at a first point of interconnection between the device output and the transformer input and is configured to measure a voltage level at the first point of interconnection. The power conversion system also includes a system controller communicatively coupled to the power conversion device and the sensor. The system controller is configured to determine an impedance of the power grid based at least partially on the voltage level at the first point of interconnection.