1. Introduction

In the ever - expanding landscape of renewable energy, photovoltaic (PV) power generation has become a significant contributor to the global energy mix. However, the stable integration of PV systems into the power grid faces various challenges, and one of the most critical among them is the low - voltage ride - through (LVRT) capability of photovoltaic inverter systems. When voltage sags occur in the grid, such as during short - circuit faults or other disturbances, PV inverters without adequate LVRT capabilities may disconnect from the grid prematurely. This not only reduces the power generation efficiency of PV systems but also poses a threat to the stability and reliability of the entire power grid. Therefore, formulating an effective LVRT capability improvement plan is of great significance for promoting the large - scale and stable operation of PV power generation. This plan will comprehensively analyze the current situation, propose specific improvement measures, and outline the implementation steps and evaluation methods to enhance the LVRT performance of PV inverter systems.

2. Current Situation Analysis of LVRT Capability of PV Inverter Systems

2.1 Existing Problems

Many existing PV inverter systems still have obvious deficiencies in LVRT capabilities. Some inverters lack the necessary control strategies to respond to voltage sags. When the grid voltage drops, they cannot adjust their output power in a timely and appropriate manner, resulting in power fluctuations and potential disconnection from the grid. For example, in some regions with weak grids, even small - scale voltage sags can cause a large number of PV inverters to trip, disrupting the normal power supply order.

In addition, the hardware design of some PV inverter systems is not optimized for LVRT requirements. The insufficient capacity of energy storage devices and the improper configuration of power electronic components limit the inverter's ability to ride through low - voltage conditions. Without sufficient energy storage, the inverter cannot maintain stable power output during voltage sags, and the lack of suitable power electronic components may lead to over - current or over - voltage problems, further endangering the safe operation of the inverter.

2.2 Impact on the Power Grid

The poor LVRT capability of PV inverter systems has a series of negative impacts on the power grid. Premature disconnection of PV inverters during voltage sags reduces the total power supply capacity of the grid, increasing the load pressure on other power - generation units. This may lead to a chain reaction, potentially causing the collapse of local power grids in severe cases. Moreover, the sudden disconnection and reconnection of PV inverters can generate large - scale power fluctuations, which not only affect the power quality of the grid but also interfere with the normal operation of other electrical equipment connected to the grid, such as motors and transformers. These fluctuations can cause additional losses in the grid and reduce the overall efficiency of power transmission and distribution.

3. Technical Solutions for Improving LVRT Capability

3.1 Control Strategy Optimization

3.1.1 Voltage - Oriented Control

The voltage - oriented control (VOC) strategy can be further optimized to enhance the LVRT performance of PV inverters. By improving the accuracy of voltage detection and the speed of response, the inverter can quickly sense voltage sags in the grid. Advanced algorithms can be used to adjust the d - q axis components of the output current in real - time, ensuring that the inverter can provide reactive power support to the grid during voltage sags. For example, when the grid voltage drops, the inverter can increase the reactive power output to help stabilize the grid voltage, while at the same time, adjusting the active power output to avoid over - current and over - power situations.

3.1.2 Model Predictive Control

Model predictive control (MPC) is a powerful control method that can be applied to PV inverters for LVRT improvement. MPC predicts the future behavior of the system based on the current state and model parameters, and then calculates the optimal control strategy in advance. In the context of LVRT, MPC can predict the development trend of grid voltage sags and adjust the inverter's output power and current accordingly. It can consider multiple constraints, such as the maximum current limit of the inverter, the capacity of energy storage devices, and the power quality requirements of the grid, to achieve the best balance between grid support and inverter safety during low - voltage conditions.

3.2 Hardware Upgrade

3.2.1 Energy Storage Device Expansion

Adding or upgrading energy storage devices in PV inverter systems is an effective way to improve LVRT capabilities. Lithium - ion batteries or supercapacitors can be integrated into the system. During voltage sags, the energy storage devices can release stored energy to supplement the power output of the inverter, ensuring continuous power supply to the grid. For example, a properly configured supercapacitor can quickly respond to sudden voltage drops, providing a large amount of current in a short time to support the inverter's operation. At the same time, the control system of the energy storage device needs to be coordinated with the inverter control system to ensure seamless integration and efficient operation.

3.2.2 Power Electronic Component Reinforcement

Selecting high - performance power electronic components is crucial for enhancing the LVRT ability of PV inverters. Components with higher voltage and current ratings, better thermal stability, and faster switching speeds should be used. For instance, upgrading IGBTs to those with higher voltage withstand capabilities can prevent the IGBTs from being damaged during voltage sags, and using high - frequency capacitors and inductors can improve the dynamic response performance of the inverter, enabling it to better adapt to the rapidly changing grid conditions during low - voltage events.

4. Implementation Steps of the Improvement Plan

4.1 System Design and Simulation

First, based on the proposed technical solutions, a detailed system design for the improved PV inverter is carried out. This includes the design of the control circuit, the selection of components, and the integration of energy storage devices. Then, using simulation software such as MATLAB/Simulink, a simulation model of the PV inverter system is established. Different types of voltage sags are simulated in the model, and the performance of the improved system under various conditions is tested and analyzed. By adjusting the parameters of the control strategy and the configuration of hardware components in the simulation, the optimal design scheme can be obtained to ensure the effectiveness of the LVRT improvement measures.

4.2 Prototype Development and Testing

After the simulation verification, a prototype of the improved PV inverter system is developed. During the development process, strict quality control measures are implemented to ensure the reliability of the hardware and the accuracy of the software. Once the prototype is completed, a series of laboratory tests are carried out. These tests include low - voltage ride - through performance tests under different voltage sag levels and durations, power quality tests to ensure that the inverter's output meets the grid requirements during LVRT, and safety tests to verify the protection functions of the inverter. According to the test results, any problems or deficiencies in the prototype are identified and rectified in a timely manner.

4.3 Field Installation and Commissioning

After passing the laboratory tests, the improved PV inverter system is installed in the actual PV power plant. During the installation process, attention should be paid to the correct connection of electrical circuits and the proper placement of components to ensure the normal operation of the system. After installation, commissioning work is carried out, including parameter setting, system calibration, and communication connection testing. The LVRT performance of the system is also tested in the actual grid environment to verify whether it meets the design requirements. If necessary, on - site adjustments and optimizations are made to ensure that the PV inverter system can operate stably and effectively in the field.

5. Evaluation and Monitoring of LVRT Capability Improvement

5.1 Evaluation Indicators

To comprehensively evaluate the effectiveness of the LVRT capability improvement plan, a series of evaluation indicators are established. These include the minimum voltage level that the PV inverter can ride through without disconnection, the reactive power support capacity during voltage sags, the recovery time of the inverter after the voltage returns to normal, and the power quality parameters such as total harmonic distortion (THD) and voltage unbalance during LVRT. By comparing these indicators before and after the implementation of the improvement plan, the degree of improvement in the LVRT performance of the PV inverter system can be accurately measured.

5.2 Monitoring System Establishment

A real - time monitoring system is established to continuously monitor the LVRT performance of PV inverter systems in operation. The monitoring system can collect data such as grid voltage, inverter output current, power, and temperature in real - time. Through data analysis and processing, it can detect abnormal conditions in a timely manner and provide early warnings. In addition, historical data can be stored and analyzed to summarize the operation characteristics and performance trends of the PV inverter system, providing a basis for further optimization and improvement of the LVRT capability.

6. Conclusion

The improvement of the low - voltage ride - through capability of photovoltaic inverter systems is a complex and systematic project that requires comprehensive consideration of control strategy optimization, hardware upgrade, implementation steps, and performance evaluation. By implementing the proposed improvement plan, it is expected to significantly enhance the LVRT performance of PV inverter systems, ensuring their stable operation during grid voltage sags, and promoting the large - scale and reliable integration of PV power generation into the power grid. In the future, with the continuous development of power electronics technology and control theory, the LVRT capability of PV inverter systems will be further improved, making greater contributions to the sustainable development of the global energy industry.