With the development of grid-connected photovoltaic power generation, more and more grid-connected power generation systems are integrated into the grid. Due to the characteristics of the grid itself, strict testing requirements are put forward for the performance of grid-connected photovoltaic inverters. In this paper, aiming at the grid frequency response test, anti-islanding effect test and low voltage traversal test of grid-connected inverters, the functions of ADMIRE POWER standard AC power supply APA1000 series and intelligent AC power supply APA2000 series are introduced.

一．Photovoltaic grid-connected inverters
The grid-connected photovoltaic inverter is the core of energy conversion and control of photovoltaic system. It is a device that converts DC output from solar cells into AC which meets the requirements of the grid and then inputs it into the grid. The efficiency of the inverter affects the efficiency of photovoltaic power generation system. Therefore, the performance guarantee of the inverter is very important.

二．Test requirements of grid-connected photovoltaic Inverters
Since the grid-connected photovoltaic inverters directly convert the energy into sinusoidal current of the same frequency and phase with the grid, any change of the grid will affect the normal operation of the photovoltaic inverters, so the response of the inverters to the changes of the grid is a very important test item in the test of the performance of the inverters. Next, the frequency response test, anti-islanding effect test and low voltage traversal test of the inverter power grid are introduced in detail.
Frequency response test of power grid: test whether the inverter can work normally in the prescribed frequency range (under normal voltage); stop grid-connected power supply after the prescribed time of the normal operation of the inverter in the prescribed frequency range; consider that the grid frequency is abnormal outside the prescribed frequency range, and grid-connected inverters stop working. Its frequency response time must meet the requirements of the table below.

Frequency range	Inverter Response
<48Hz	The Inverter Stops Operating within 0.2S
48~49.5Hz	The Inverter Stops Operating after Running 10M
49.5~50.2Hz	Normal Operation of Inverter
50.2~50.5Hz	The Inverter Stops Operating after Running 2M
>50.5Hz	Within 0.2S, the inverters stop supplying power to the power grid.

Anti-islanding effect test: "islanding" refers to the existence of photovoltaic inverters after the power supply of the public power grid is stopped, so that some lines in the power outage area of the power grid remain live, forming "islanding" of power supply. This state may bring a series of potential safety hazards and accident disputes, endanger personal safety and cause equipment damage, so there is a test standard of anti-island effect. The standard requirements include: when the grid loses voltage, the protection against islanding effect must be completed in 2 seconds, and the photovoltaic system should be disconnected from the grid.

The detection of anti-islanding effect can be divided into passive mode and active mode. Passive islanding detection method detects whether the output of the inverter deviates from the grid-connected standard, but it can not detect the islanding effect when the output power of the inverter is balanced with the local load power. Active islanding detection method controls the output voltage and frequency of the inverters and the voltage and frequency of the power grid have certain errors (the error is within the standard allowable range). When the power grid works normally, the error between the output voltage frequency of the inverters and the voltage frequency of the power grid is always within a small range due to the correction of the phase-locked circuit; but when the power grid fails, the error between the output voltage frequency of the inverters and the voltage frequency of the power grid is always Errors accumulate, which leads to further increase of errors until they exceed the non-standard requirements and trigger the islanding effect protection circuit. This method has high detection accuracy and small blind area, so it is more used. Active detection method needs a programmable AC power supply which can continuously adjust the voltage and frequency of the analog power grid.

Low Voltage Traverse (LVRT) Testing: For photovoltaic power plants, when grid-connected voltage sags are caused by power system accidents or disturbances, within a certain range of voltage sags and time intervals, photovoltaic power plants can ensure continuous operation without disconnection and support grid restoration until the grid returns to normal, thus "traversing" this low voltage area.
From the introduction of the above test projects, it can be found that in order to achieve these performance tests of grid-connected photovoltaic inverters, it is necessary to provide a powerful AC power supply, which can meet the needs of simulating the above characteristics of the grid.

三、ADMIRE POWER Electronics standard APA1000 series and intelligent APA2000 series AC power supply
ADMIRE POWER Electronics has been devoted to the research of power supply and power supply testing for many years. Aiming at the larger range and more complex changing characteristics of AC, we have developed and introduced standard AC power supply APA1000 series and intelligent AC power supply APA2000 series . These two series AC power supply can simulate all kinds of normal and abnormal AC power input, and can measure the important electrical performance parameters of the object to be measured. To meet the above test requirements of grid-connected photovoltaic inverters, better research and development and manufacturing.

The voltage specifications of standard AC power APA1000 series and intelligent AC power APA2000 series are 0 ~ 300V (0 ~ 600V selection), and the frequency is adjustable in the range of 45Hz ~ 500Hz, which meets the voltage and frequency requirements of power grid simulation. Users can set and observe real-time characteristic curves of voltage, frequency, power, power factor, current, peak current, temperature, electricity, time, phase angle, impedance value, voltage and current (touch screen display); voltage, current, power, power factor, frequency, peak current and time (LCD display). According to the need to simulate various normal and abnormal conditions of the grid, the performance test of grid-connected inverters can be implemented more effectively.