Photovoltaic Inverter Startup Control Using Fan Load and Dynamic Thresholds
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Solution Overview
Problem
The existing methods for startup control of photovoltaic inverters, which determine grid-connected operation based solely on input voltage magnitude, lead to repeated startup and shutdown, reducing the service life of grid-connected relays.
Innovation Solution
A method that involves starting a fan as a load when the input voltage exceeds a threshold, measuring the voltage drop, and initiating grid-connected operation only if the voltage drop is within a dynamic threshold adjusted based on power determination thresholds, thereby avoiding unnecessary startups and shutdowns.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If grid-connected operation is determined based solely on input voltage magnitude, then the startup control is simple, but repeated startup and shutdown occur reducing relay service life
Solution Approach 1:
The patent changes the determination parameters from only voltage magnitude to a combination of voltage magnitude and power magnitude. By introducing power as an additional parameter, the system avoids repeated startup and shutdown operations, thereby extending relay service life while maintaining reasonable control complexity.
Solution Approach 2:
The patent implements dynamic threshold adjustment where the voltage threshold is modified based on power determination results. When power meets requirements, the voltage threshold is lowered to enable startup; when power is insufficient, the threshold is raised to prevent premature startup. This dynamic adjustment reduces relay operations and extends service life.
2Productivity
If voltage threshold is lowered to enable startup at lower voltages, then more startup opportunities are available, but startup occurs at inappropriate conditions with small power levels
Solution Approach 1:
The patent changes from single-parameter (voltage) control to two-parameter (voltage and power) control. This ensures that even when voltage threshold is lowered, startup only occurs when both voltage and power meet requirements, preventing inappropriate startup at small power levels while maintaining high startup frequency when conditions are favorable.
Solution Approach 2:
The patent performs preliminary power detection before finalizing the startup decision. By checking power magnitude in advance and adjusting the voltage threshold accordingly, the system ensures that startup occurs only when both voltage and power conditions are appropriate, avoiding premature startup while capturing valid startup opportunities.
3Reliability
If voltage threshold is raised to prevent inappropriate startup, then operational reliability improves, but legitimate startup opportunities are missed
Solution Approach 1:
The patent implements dynamic threshold adjustment where the voltage threshold is not fixed but adapts based on real-time power detection. When power is sufficient, the threshold is lowered to capture legitimate startup opportunities; when power is insufficient, the threshold is raised to prevent inappropriate startup. This maintains high operational reliability while maximizing startup frequency.
Solution Approach 2:
The patent dynamically changes the voltage threshold parameter based on power magnitude. This allows the system to lower the threshold when conditions are favorable (increasing startup frequency) and raise it when conditions are poor (maintaining reliability), thereby resolving the contradiction between reliability and productivity.
Data Source
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AI summary
A method for start control of photovoltaic inverter, a system thereof, and a photovoltaic power generation system are provided. A fan of the photovoltaic inverter is controlled to operate in a case that input voltage of the photovoltaic inverter is greater than a start threshold, and the fan operation is used as a load. Input voltage drop before and after the fan operates is obtained, and in a case that the input voltage drop is less than or equal to a voltage determination threshold, the photovoltaic inverter is controlled to start a grid connection. Using the fan of the photovoltaic inverter as the load in the solution, no external connective dummy load of direct current or alternating current is needed, and cost of additional hardware is reduced; in addition, the voltage determination threshold is amended based on a power determination threshold of the photovoltaic inverter, the voltage determination threshold is allowed to be a dynamic threshold, which varies with an actual situation, and the problem of service life reduction caused by frequent startup of the photovoltaic inverter in case of appropriate voltage and small power is avoided.