KR-20260062204-A - APPARATUS FOR CONTROLLING INVERTER FOR PHOTOVOLTAIC SYSTEM

Abstract

The present invention relates to a photovoltaic power generation inverter output control device, and more specifically, to a photovoltaic power generation inverter output control device capable of managing the Total Harmonic Distortion (THD), a key indicator of power quality management, within a reference value (5%) by individually controlling the output of the inverters in a photovoltaic power generation system using multiple inverters. The photovoltaic power generation inverter output control device according to the present invention is a photovoltaic power generation inverter output control device for limiting the output of an inverter in a photovoltaic power generation system equipped with a plurality of inverters, characterized by individually limiting the output of each inverter within a range that satisfies the total harmonic distortion rate standard of each inverter for the requested total active power limit.

Inventors

• 박상욱
• 이강주
• 송준영
• 이강준

Assignees

• 주식회사 에이치티솔루션

Dates

Publication Date

20260507

Application Date

20241025

Claims (2)

1. In a photovoltaic power generation inverter output control device that limits the output of an inverter in a photovoltaic power generation system equipped with multiple inverters, A photovoltaic power inverter output control device characterized by individually limiting the output of each inverter within a range that satisfies the total harmonic distortion rate standard of each inverter for the requested total active power limit.
2. In paragraph 1, A photovoltaic power inverter output control device characterized by evaluating and learning the installation conditions and operating status of a photovoltaic power generation system to calculate output limiting conditions for each inverter for active power limiting and individually limiting the output of each inverter.

Description

Photovoltaic Inverter Output Control Device {APPARATUS FOR CONTROLLING INVERTER FOR PHOTOVOLTAIC SYSTEM} The present invention relates to a photovoltaic power generation inverter output control device, and more specifically, to a photovoltaic power generation inverter output control device capable of managing the Total Harmonic Distortion (THD), a key indicator of power quality management, within a reference value (5%) by individually controlling the output of the inverters in a photovoltaic power generation system using multiple inverters. Generally, a solar power system includes solar modules and inverters. Solar modules can generate electricity by converting sunlight into direct current (DC). The inverter performs the role of converting the DC power produced by the solar modules into alternating current (AC). The DC power produced by the solar modules passes through the inverter, is converted into AC power, and output to the grid. Meanwhile, when using multiple inverters, it is necessary to control each inverter to operate properly, manage power flow, and maintain grid safety. The cases in which surplus power is limited in a solar power generation system differ depending on whether it is a self-generation facility or a power generation facility. In the case of self-generation facilities, power flow fluctuates according to load variations. Under light-load conditions, if the power demanded by the load is less than the amount of solar power generated, surplus power is produced. If this surplus power flows back into the grid, the reverse power relay may activate, potentially causing the power system to be cut off. To prevent this, self-generation facilities manage surplus power through a power limiting function. This is primarily achieved by controlling the output of the inverter to reduce the amount of generated power. In the case of power generation facilities, power limiting is primarily required to maintain the stability of the power grid. Supplying power in excess of the amount required by the grid can place a burden on the system. In such situations, a request for power limiting may be received from the grid, and multiple inverters are coordinated to adjust the output. A key aspect of this process is power quality management. When using multiple inverters, each inverter must be synchronized with others to limit power while maintaining power quality; to achieve this, communication between inverters and a cooperative control system are required. In this way, a system can be established that maintains grid safety and improves power quality, even when surplus power is generated. In a photovoltaic (PV) power generation system, the inverter interacts with the power grid to adjust frequency, voltage, and phase, thereby maintaining a stable power supply. In addition to frequency, voltage, and phase, Total Harmonic Distortion (THD) is a key electrical characteristic of the solar inverter and serves as a major indicator for power quality management, which is strictly controlled. Although THD is evaluated and managed only during the facility's rated output, power generation fluctuates depending on sunlight levels due to the nature of solar power facilities; consequently, operation at rated capacity accounts for less than 50% of total operating time. While an increase in THD can lead to power quality degradation—such as overheating, reduced efficiency, and inductive fields in power-receiving devices—there is no way to suppress these issues due to the inherent characteristics of the PV system. Although the THD of solar inverters is managed to remain within 5% based on rated output, a decrease in power generation can cause THD to increase significantly, potentially degrading power quality. Referring to Figure 1, which shows a graph of THD measurements relative to the output of a solar inverter, it can be seen that the THD increases when the output of the solar inverter decreases. Figure 2 shows a conventional power limiting method for multiple solar inverters. The solar inverters receive an output limiting command from an upper control unit and perform power limiting. The upper control unit requests output limiting from the solar inverters in operation based on the total power to be limited, and executes power limiting uniformly and identically. Due to the characteristics of the solar inverters, if power generation is below the rated value, the THD increases, and if the power generation is significantly limited compared to the rated value, the THD can increase by more than 5%. Referring to Fig. 2, in a photovoltaic power generation system that generates a total of 293 kW of power with three inverters each having a power generation capacity of 100 kW, 95 kW, and 98 kW, when the active power limit must be set to 30%, the conventional power limiting method of the existing photovoltaic inverter, which limits the power generation capacity of the three inverters collectively to 30 kW, 30 kW, and 30 kW, which is 30% of th