Photovoltaic Inverter PID Prevention Using DC Link Capacitor
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Solution Overview
Problem
Existing photovoltaic systems incur unnecessary costs and inefficient energy utilization due to the requirement of additional modules for applying reverse voltage to prevent potential-induced degradation (PID) in solar cell arrays, which also fail to effectively utilize residual energy stored in DC link capacitors.
Innovation Solution
A photovoltaic inverter design that incorporates a controller and switch unit to determine whether to apply the DC voltage or its reverse voltage to the solar cell array based on driving conditions, eliminating the need for separate modules and efficiently utilizing open-circuit voltage to reduce polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an additional offset box is used to apply reverse voltage to the solar cell array, then PID degradation is reduced, but device complexity and cost increase
Solution Approach 1:
The patent combines the reverse voltage application function into the existing photovoltaic inverter by utilizing the DC link capacitor that is already present in the system. The controller manages the switching of existing components (DC link capacitor, power conversion stage) to apply reverse voltage during shutdown periods, eliminating the need for a separate offset box while maintaining PID prevention capability
Solution Approach 2:
The DC link capacitor, originally designed for voltage stabilization during operation, is made multi-functional by enabling it to serve dual purposes: (1) voltage stabilization during photovoltaic generation, and (2) reverse voltage application during shutdown periods to prevent PID. This universal utilization of existing components resolves the contradiction by avoiding additional hardware
2Reliability
If residual energy in the DC link capacitor is discharged through a rapid discharge circuit, then safety is improved, but energy utilization efficiency deteriorates
Solution Approach 1:
The patent converts the potentially harmful rapid discharge of residual energy into a beneficial reverse voltage application. Instead of dissipating energy harmlessly through a discharge resistor, the controller redirects the residual energy from the DC link capacitor to apply reverse voltage to the solar cell array during shutdown periods, thereby preventing PID while utilizing the otherwise wasted energy
Solution Approach 2:
The system recovers and reuses the residual energy that would normally be discarded through rapid discharge. By controlling the switching of power conversion stage components, the system captures the residual energy in the DC link capacitor and applies it as reverse voltage to the solar cell array, transforming waste energy into a useful function for PID prevention
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
This solution effectively prevents degradation in photovoltaic generation efficiency by dynamically managing voltage application, reducing costs, and optimizing energy utilization within the photovoltaic system.
Implementation Method 1
The DC link capacitor 11 stores a DC voltage output from the photovoltaic array 13
Implementation Method 2
If such a potential difference lasts, polarization occurs, i.e., some electrons generated in the solar cell array flow out through the metal frame. Such polarization degrades the efficiency of power generation
Data Source
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AI summary
Disclosed herein is a photovoltaic inverter (100) that prevents degradation in the efficiency of photovoltaic generation by applying a reverse voltage of a DC voltage stored in a DC link capacitor to a solar cell array. The photovoltaic inverter includes: a DC link capacitor configured to store a DC voltage output from the solar cell array; a power conversion stage configured to generate an AC power by using the DC voltage stored in the DC link capacitor to transmit the generated AC power to a power system; and a controller configured to apply the DC voltage stored in the DC link capacitor to the power conversion stage or apply a reverse voltage of the DC voltage stored in the DC link capacitor to the solar cell array depending on whether a driving value of the solar cell array satisfies a predetermined driving condition.