Photovoltaic Inverter DC Link Voltage Control During Network Faults
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Solution Overview
Problem
Photovoltaic inverters face the risk of damage during network faults due to increased DC link voltage, which can lead to unnecessary energy losses and reduced current supply capability, as existing solutions like the brake chopper may not effectively manage voltage fluctuations.
Innovation Solution
A method and system for controlling photovoltaic inverters that detect voltage dips and activate an energy dissipation device to maintain the DC link voltage within a predetermined range, using the saturation voltage as the upper limit to prevent damage and optimize energy dissipation, thereby enabling reliable ride-through of network faults with reduced losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inverter remains connected to the network during a fault to provide short-circuit current, then the reliability of the power supply network is improved, but the DC link voltage increases to dangerous levels that can damage power semiconductor switches
Solution Approach 1:
The patent introduces a crowbar circuit as an intermediary protective device between the PV generator and the inverter. This circuit includes a controllable switch and a brake resistor that can be activated during faults to clamp the DC link voltage to a safe level, preventing damage to power semiconductor switches while allowing the inverter to remain connected and provide fault ride-through current
Solution Approach 2:
The patent implements prior cushioning by pre-configuring the crowbar circuit with energy dissipation capabilities before faults occur. The brake resistor is sized and positioned to absorb and dissipate the excess energy that would otherwise cause dangerous voltage spikes, providing a safety buffer that activates automatically when voltage thresholds are exceeded
2Object-affected harmful factors
If a brake chopper is used to clamp the DC link voltage during faults, then the power semiconductor switches are protected from overvoltage, but energy is dissipated as thermal losses in the brake resistor
Solution Approach 1:
The patent applies dynamics by implementing intelligent, adaptive control of the crowbar circuit based on real-time fault conditions. The controllable switch activates only when DC link voltage exceeds predetermined thresholds and deactivates when voltage returns to safe levels, optimizing the balance between protection and energy efficiency. The control system dynamically adjusts the energy dissipation based on the severity and duration of the fault
Solution Approach 2:
The patent utilizes parameter changes by monitoring and responding to voltage threshold conditions. The system changes the operational state of the crowbar circuit based on DC link voltage parameters, activating protection only when necessary and transitioning between protective and normal operating modes based on real-time electrical parameters
3Loss of energy
If the DC link voltage is allowed to increase naturally during faults, then energy dissipation losses are reduced, but the current supply capability of the inverter is limited
Solution Approach 1:
The patent implements feedback control by continuously monitoring the DC link voltage and using this information to control the crowbar circuit operation. The system measures the actual voltage, compares it to threshold values, and adjusts the crowbar switch state accordingly, creating a closed-loop control system that optimizes both protection and energy efficiency based on real-time conditions
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 solution allows photovoltaic energy generation plants to remain connected to the network and supply required short-circuit currents during faults while minimizing energy losses and protecting power semiconductor switches, ensuring efficient operation and compliance with network directives.
Implementation Method 1
a series circuit consisting of a controllable switch and a brake resistor which is connected to the DC voltage link parallel to the PV generator to dissipate energy from the PV generator and convert it into thermal energy in the brake resistor
Data Source
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AI summary
A method of controlling an inverter, which is connected between a photovoltaic generator and a power supply network for ride-through of a network fault, is disclosed. A voltage dip is detected in the network voltage and the voltage (Udc) of a DC voltage link of the inverter is monitored. When it is detected that the DC link voltage (Udc) exceeds an upper limit value (UTHup), an operating mode for ride-through of the network fault (FRT) is started. The upper limit value (UTHup) corresponds to a saturation voltage Udc,nom(max) in the specific Iac/Udc characteristic curve of the inverter, above which the maximum AC output current Iac,max of the inverter decreases. In the FRT operating mode, an energy dissipation device is activated, which is adapted to dissipate power from the DC voltage link, if necessary, and is controlled to keep the DC link voltage (Udc) within a range (Udc - ΔU < Udc < Udc,nom(max)) below the saturation voltage (Udc,nom(max)). An inverter system for a photovoltaic plant which implements the method according to the invention is also disclosed.