Inverter LVRT Control via Reactive Current Compensation
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Solution Overview
Problem
Existing methods for controlling Low Voltage Ride Through (LVRT) in photovoltaic grid-connected inverters fail to manage current fluctuations effectively during voltage dips, leading to reduced active power generation and increased risk of large-scale power cuts and grid instability.
Innovation Solution
A method and apparatus that control the inverter to output a current with smaller fluctuations by judging voltage levels and adjusting active and reactive current values, using a combination of MPPT and PI control algorithms, to maintain stability and reliability during voltage dips.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photovoltaic power station is removed immediately from the power supply network when voltage dip occurs (passive protection), then the photovoltaic power station is protected from damage, but active power generation decreases greatly and may cause large-scale power cuts
Solution Approach 1:
Instead of immediately disconnecting the photovoltaic power station during voltage dips (passive protection), the invention inverts the approach by maintaining connection and using active control strategies. The inverter continues to operate and even provides reactive current support during voltage dips, transforming from a passive victim to an active participant in grid stabilization, thus preventing large-scale power cuts while protecting the system.
Solution Approach 2:
The invention changes the operating parameters of the inverter during voltage dips by dynamically adjusting the reactive current output based on the severity of the voltage dip. When voltage dips occur, the inverter modifies its current output characteristics to provide reactive power support, enabling it to ride through the voltage dip while continuing to contribute to active power generation, thereby resolving the contradiction between protection and productivity.
2Device complexity
If existing LVRT control methods are used without current control, then the control system is simple, but current fluctuations are serious and output electric energy quality is severely affected
Solution Approach 1:
The invention implements a feedback control mechanism where the inverter continuously monitors grid voltage conditions and adjusts its reactive current output accordingly. During voltage dips, the inverter detects the voltage level and dynamically modifies its current injection to provide support, ensuring stable operation and high-quality power output. This feedback-based approach improves energy quality without requiring overly complex control systems.
Data Source
AI summary
A method and an apparatus for controlling a Low Voltage Ride Through of a photovoltaic grid-connected inverter. The method for controlling comprises: judging whether a voltage value of a grid is smaller than an upper limit of a low voltage value and is not greater than a lower limit of the low voltage value; when it is judged that a root mean square value of the voltage in the grid is smaller than the upper limit of the low voltage value and greater than the lower limit of the low voltage value, controlling an active current value outputted from the inverter to be equal to a target active current value and controlling a reactive current value outputted to be equal to a target reactive current value, so that a comparison difference between a total current outputted by the inverter in a Low Voltage Ride Through state and a current outputted by the inverter in a normal state is smaller than a preset value. The method and apparatus settle problem that the poor stability is caused since control on the waveform and amplitude of the current is ignored in the Low Voltage Ride Through control on the inverter, such that the total current changes slightly before and after a voltage dip, which can support and stabilize the grid.