Photovoltaic Inverter System Capacitance Measurement
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Solution Overview
Problem
Existing methods for determining system capacitance in photovoltaic systems are complex, limited to small systems, and unable to accurately measure capacitance during night hours or with integrated electronics, leading to potential tripping of residual current circuit breakers and reduced energy yield.
Innovation Solution
A method using an intermediate circuit voltage to measure system capacitance by short-circuiting the DC input and analyzing the temporal waveform of measured voltages, allowing for accurate determination during night hours and with energy storage devices connected, while also considering insulation resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compensation methods are used to prevent tripping of residual current circuit breakers, then reliability is improved, but device complexity increases
Solution Approach 1:
The photovoltaic inverter automatically measures its own system capacitance and performs self-compensation by adjusting its operating parameters, eliminating the need for external compensation devices and complex control systems while preventing RCCB tripping
Solution Approach 2:
The patent replaces complex mechanical/electrical compensation devices with an electronic control approach where the inverter's control unit adjusts operating parameters based on measured capacitance values, substituting physical compensation mechanisms with electronic control
2Reliability
If system capacitance is determined before connection, then reliability is improved, but loss of time increases
Solution Approach 1:
The system performs preliminary capacitance measurement and evaluation before connecting to the supply network, allowing the inverter to assess whether connection conditions are met and prepare appropriate control parameters in advance
Solution Approach 2:
The measurement and connection process is made dynamic and conditional - the inverter continuously monitors system capacitance and automatically adjusts connection timing based on real-time measurements, optimizing the balance between reliability and time loss
3Object-affected harmful factors
If RCCB is triggered to protect the system, then safety is improved, but productivity decreases
Solution Approach 1:
The inverter implements continuous feedback monitoring of system capacitance and leakage currents, using this information to dynamically adjust operating parameters and prevent RCCB tripping before it occurs, thereby maintaining continuous energy production
Solution Approach 2:
The system takes preliminary protective action by measuring system capacitance before connection and evaluating potential leakage current risks, allowing the inverter to adjust parameters in advance to prevent RCCB tripping and maintain continuous operation
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
Enables fast and reliable determination of system capacitance and insulation resistance, preventing unintended tripping of residual current circuit breakers and optimizing energy yield by ensuring safe and efficient connection to the supply network.
Implementation Method 1
determining the system capacitance from the temporal waveform of the measured voltages
Implementation Method 2
whereby the intermediate circuit voltage is applied to the DC input in the reverse direction
Data Source
AI summary
A method and a photovoltaic inverter determines the system capacitance of a photovoltaic system relative to ground. The voltage required for the measurement can be provided by the intermediate circuit in the form of the intermediate circuit voltage, and the measuring device is designed to actuate an input short-circuit switch for short-circuiting the DC input with the AC disconnector open, as a result of which the intermediate circuit voltage can be applied to the DC input in the reverse direction, and the measuring device is configured to determine the system capacitance from the temporal waveform of the measured voltage after the switch of the voltage divider is closed.