Grid-Connected Inverter Switching Control for Zero-Voltage Turn-On
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Solution Overview
Problem
Conventional grid-connected inverters face significant turn-on losses due to hard-switching control methods, hindering advancements in high-frequency and high-efficiency operations.
Innovation Solution
A grid-connected inverter control method that determines a switching period meeting zero-voltage switching conditions, utilizing a closed-loop regulation mechanism to control switching transistors, and employs a mapping relationship between capacitance and voltage differences to minimize turn-on losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If hard-switching control method is used, then the inverter can operate at utility frequency, but the switching transistor experiences significant turn-on loss
Solution Approach 1:
The patent applies preliminary action by pre-charging the output capacitor of the switching transistor before turning on the transistor. The control method determines a switching period that includes a capacitor charging stage where the output capacitor is charged to the DC input voltage before the switching transistor is turned on, ensuring zero-voltage switching and eliminating turn-on losses
Solution Approach 2:
The patent changes the switching parameter from fixed utility-frequency switching to variable switching period that satisfies zero-voltage switching conditions. The control method calculates and adjusts the switching period based on the relationship between capacitor charging time and the required voltage difference between DC input and grid voltage, transforming the switching mode from hard-switching to soft-switching
2Productivity
If switching frequency is increased for high-frequency operation, then productivity improves, but switching losses increase significantly
Solution Approach 1:
The patent implements preliminary action by preparing the switching transistor's output capacitor to be charged to the appropriate voltage level before each switching event. The control method ensures that the capacitor charging stage completes before the transistor turns on, enabling high-frequency operation with minimal losses by maintaining zero-voltage switching conditions throughout operation
Solution Approach 2:
The patent applies continuity of useful action by making the capacitor charging process an integral part of the switching cycle rather than a separate preparatory step. The charging stage continuously prepares the capacitor for the next switching event, ensuring that the transistor is always ready for zero-voltage switching without interruption or additional loss-inducing transitions
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 method achieves zero-voltage switching, reducing switching transistor losses and enhancing the efficiency and frequency capabilities of grid-connected inverters.
Implementation Method 1
an output capacitor C1 to C4 connected in parallel with the switching transistors
Implementation Method 2
a filter inductor L1 and a filter capacitor Co2 connected to the bridge arm where the switching transistor S1/S2 is located
Data Source
AI summary
A grid-connected inverter control method comprises: determining a calculation rule of the switching period meeting the zero-voltage switching condition and a mapping relationship between the capacitance value of the output capacitor and a voltage difference between a DC input voltage and a grid voltage; according to the polarity of the grid-connected reference current, determining the switching transistor operating at high frequency; according to the grid-connected current and the grid-connected reference current, determining the duty ratio; calculating the switching period according to the calculation rule of the switching period, the mapping relationship, the DC input voltage, the grid voltage, the grid-connected reference current and the duty ratio; and controlling the zero-voltage switching of the switching transistor according to the switching period and the duty ratio.