Micro Inverter Feedforward Control for Output Capacitor Reactive Current
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Solution Overview
Problem
The reactive current generated by a capacitor at the output terminal of micro inverters in photovoltaic systems significantly impacts the grid current, affecting the quality of grid-connected current.
Innovation Solution
A micro inverter design that includes a controller, a primary H-bridge, a transformer, a bi-directional switch arm, and a capacitor arm, where the controller determines the reactive current based on grid voltage, equivalent capacitance, and grid angle, and adds it to the given current to generate internal and external phase-shift angles, thereby reducing the impact on the grid-connected current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitor is added at the output terminal of the micro inverter, then the power factor is improved, but a reactive current is generated that has a great impact on the grid current
Solution Approach 1:
The controller calculates the reactive current in advance based on grid voltage, equivalent capacitance, and grid angle, then adds this calculated reactive current to the given current before generating control signals. This preliminary compensation action counteracts the reactive current impact before it affects the grid current, resolving the contradiction between improving power factor and reducing reactive current impact.
Solution Approach 2:
The system performs feedforward control by pre-calculating the reactive current component and incorporating it into the control current before the reactive current actually flows into the grid. This preliminary action allows the system to proactively compensate for the capacitor's reactive current effect, maintaining both improved power factor and reduced grid current impact.
2Reliability
If feedforward control is used to add reactive current compensation, then the quality of grid-connected current is improved, but the control complexity increases
Solution Approach 1:
The controller autonomously calculates the reactive current compensation based on readily available parameters (grid voltage, equivalent capacitance, grid angle) without requiring external intervention or complex coordination. The system self-regulates by internally generating the compensation current and applying it through the control algorithm, simplifying the overall control architecture while maintaining high current quality.
Data Source
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AI summary
A micro inverter, a photovoltaic system and a method for controlling a micro inverter are provided. The micro inverter includes a controller, a primary H-bridge, a transformer, a bi-directional switch arm and a capacitor arm. The controller is configured to: determine a reactive current based on a grid voltage, an equivalent capacitance of an output terminal of the inverter and a grid angle; add the reactive current to a given current to generate an internal phase-shift angle and an external phase-shift angle from a new given current obtained through the addition, where the internal phase-shift angle refers to a phase-shift angle between two arms of the primary H-bridge and the external phase-shift angle refers to a phase-shift angle between the primary H-bridge and the bi-directional switch arm.