Micro Inverter Feedforward Control for Reactive Current Compensation
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Solution Overview
Problem
The reactive current generated by the capacitor at the output terminal of a micro inverter has a significant impact on the grid current, affecting the quality of grid-connected current.
Innovation Solution
A micro inverter system is designed with a controller that determines a reactive current based on grid voltage, equivalent capacitance, and grid angle, and adds this current to a given current to generate internal and external phase-shift angles, compensating for the reactive current through feedforward control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a capacitor is placed at the output terminal of the micro inverter, then the inverter can maintain voltage and stabilize operation, but reactive current is generated that significantly impacts the grid current quality
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 harmful reactive current effect before it impacts the grid current quality.
Solution Approach 2:
The system performs feedforward control by pre-calculating the reactive current component and incorporating it into the control current before the actual grid connection occurs. This preliminary action ensures that the reactive current effect is compensated in advance, improving grid current quality without waiting for the harmful effect to manifest.
2Object-generated harmful factors
If feedforward control is implemented to compensate reactive current, then the quality of grid-connected current is improved, but the control system complexity increases
Solution Approach 1:
The controller introduces an intermediate calculated current component (the sum of given current and calculated reactive current) that serves as a mediator between the simple capacitive structure and the grid connection. This intermediary allows the harmful reactive current effect to be compensated through mathematical calculation and control signal adjustment, rather than requiring complex hardware modifications.
Data Source
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.