Photovoltaic Inverter Capacitor Pre-Charging Control
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Solution Overview
Problem
Inverters in photovoltaic installations face high charging currents and structural complexity when connecting to power grids due to capacitors, which can damage semiconductor components and increase operational risks.
Innovation Solution
A method involving pre-charging capacitors via the photovoltaic generator to a first voltage, then discharging them to a second voltage matching the inverter's maximum operating voltage, allowing safe connection to the power grid without excessive voltages or currents, and using a control device to manage the inverter and switching elements for controlled voltage adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitors are pre-charged to high voltage via the PV generator before grid connection, then high charging currents are prevented, but the inverter may be damaged by excessive voltage
Solution Approach 1:
The capacitor is pre-charged to a first voltage (potentially high voltage) before the inverter is connected to the PV generator. This preliminary charging action prevents high charging currents when the inverter later connects to the grid. The key is that this pre-charging occurs before the inverter is exposed to the voltage, eliminating the harmful effect while maintaining the beneficial current protection.
Solution Approach 2:
The connection process is segmented into distinct phases: first connecting the capacitor to the PV generator for pre-charging, then disconnecting the inverter from the PV generator, and finally connecting the inverter to the grid. This temporal segmentation allows the capacitor to be charged to high voltage without exposing the inverter to damaging voltages, as the inverter connection is delayed until after charging is complete and the voltage is reduced to a safe level.
2Reliability
If a separate pre-charging device is provided, then high charging currents are prevented, but structural complexity increases
Solution Approach 1:
The capacitor serves multiple functions: it acts as a pre-charging device for itself, a buffer for voltage stabilization, and a protective element against high charging currents. By making the capacitor multi-functional, the patent eliminates the need for separate pre-charging devices, transformers, or additional circuitry, thereby reducing structural complexity while maintaining reliability.
Solution Approach 2:
The capacitor performs its own pre-charging function by connecting directly to the PV generator before the inverter is connected. This self-service approach eliminates the need for external pre-charging devices, as the capacitor uses the available PV generator output to charge itself to the appropriate voltage level, simplifying the overall system architecture.
3Device complexity
If the inverter is connected directly to the PV generator, then simple connection is achieved, but high charging currents flow into the capacitors
Solution Approach 1:
Before the inverter is connected to the PV generator, the capacitor is pre-charged to an appropriate voltage level. This preliminary action ensures that when the inverter subsequently connects to the grid, the voltage difference is minimized, preventing high charging currents from flowing into the capacitor. The sequence of operations is carefully controlled to achieve this protective effect.
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 method reduces the risk of damaging inverter components by avoiding high voltages and currents during connection, simplifies the structural complexity, and ensures efficient operation by controlling the intermediate circuit voltage to optimal levels.
Implementation Method 1
a photovoltaic installation having a photovoltaic generator (1), a direct voltage intermediate circuit (3) with at least one capacitor (3) and an inverter (5)
Implementation Method 2
Inverters have (buffer) capacitors located in their direct current input circuit or in a direct voltage intermediate circuit to smooth the direct voltage despite the pulsed electricity consumption
Data Source
AI summary
The disclosure relates to a method for connecting a photovoltaic installation to a power supply grid, the photovoltaic installation comprising a photovoltaic generator, a direct voltage intermediate circuit with at least one capacitor, and an inverter. The method including connecting the direct voltage intermediate circuit to the photovoltaic generator and the capacitor is pre-charged to a first voltage. The direct voltage intermediate circuit is then separated from the photovoltaic generator and the capacitor is discharged to or below a second voltage that corresponds to a maximum operating voltage of the inverter. The inverter is then connected to the power supply grid, an inverter bridge of the inverter is clocked, and the direct voltage intermediate circuit is connected to the photovoltaic generator.