20kW Grid-Connected Solar Battery Interaction Test and Harmonic Distortion Rate and Insulation Impedance Test Plan

　　I. Test Background and Core Objectives

　　With the widespread application of photovoltaic energy storage technology in distributed energy systems, 20kW grid-connected solar batteries serve as core devices for energy storage and grid interaction. Their operational stability, power quality compatibility, and electrical safety directly impact the reliable operation of the grid and the lifecycle of the equipment. This test focuses on three key dimensions to verify that the equipment meets the technical requirements for grid-connected operation:

　　Ensuring the interoperability of the equipment with the grid during grid-connection interaction and avoiding grid shocks caused by power fluctuations and grid switching;

　　Controlling harmonic distortion in power output to ensure that the power quality connected to the grid meets national standards;

　　Verifying the insulation performance of the equipment to eliminate safety hazards such as leakage and insulation failure, providing a basis for the long-term safe operation of the equipment.

　　II. Grid Interaction Testing

　　1. Test Significance

　　Grid interaction is the core component of the 20kW solar battery's interoperability with the grid. This test simulates the full "charging - discharging - grid-connected power supply" scenario in actual operation to verify the device's ability to respond to changes in grid parameters and prevent abnormal interactions from causing grid frequency or voltage fluctuations or device downtime.

　　2. Core Test Indicators and Implementation Standards

　　Grid-connected power regulation capability: The reference standard is GB/T 37408-2019. Qualified requirements include a power regulation range of 0-20kW and a response time of no more than 1s.

　　Grid fault low voltage ride-through: The reference standard is GB/T 19964-2012. Qualified requirements include a continuous support time of no less than 0.15s when the voltage drops to 0%.

　　Off-grid/grid-connected automatic switching: The reference standard is GB/T 34120-2017. Qualified requirements include a switching time of no more than 50ms and no significant voltage surge during the switching process.

　　Grid-connected current phase matching: The reference standard is IEC 61727:2004. Qualified requirements include a power factor of no less than 0.95, with either lagging or leading phases acceptable.

　　3. Test Method

　　A simulated power grid test platform was built, equipped with a grid simulator with adjustable voltage and frequency. The platform simulated normal grid conditions, voltage drops (10%-90% of rated voltage), and frequency fluctuations (49.5Hz-50.5Hz).

　　The solar battery was controlled to switch between charge and discharge modes at different power levels (20%/50%/100% of rated power), and the device output power, grid-connected current, and grid parameter change curves were recorded.

　　A grid power outage was simulated to test the device's off-grid switching logic. After the grid was restored, the accuracy and stability of the automatic grid connection were verified.

　　III. Harmonic Distortion Rate Test

　　1. Test Significance

　　When solar batteries are connected to the grid, their internal power electronic devices, such as inverters, are prone to generating harmonic currents. If the harmonic distortion rate exceeds the specified value, it can distort the grid voltage waveform, interfere with the normal operation of nearby electrical equipment (such as precision instruments and communications equipment), and even accelerate the aging of grid equipment such as transformers and cables. This test focuses on controlling total harmonic distortion (THD) and the content of each characteristic harmonic.

　　2. Core Test Indicators and Implementation Standards

　　Based on GB/T 14549-1993 "Power Quality - Public Grid Harmonics" and GB/T 37408-2019 "Technical Requirements for Grid-Connected Photovoltaic Energy Storage Systems":

　　Total Harmonic Distortion (THD): Under rated power (20kW) output conditions, grid-connected current THD ≤ 5%;

　　Harmonic current content: 3rd harmonic ≤ 4%, 5th harmonic ≤ 3%, 7th harmonic ≤ 2%, 9th and higher harmonics ≤ 1% (all based on rated current).

　　3. Test Method

　　Connect a high-precision power quality analyzer (such as the Fluke 6100B) to the grid-connected output of the device (the point where the inverter connects to the grid). Set the sampling frequency to ≥ 2kHz and the sampling duration to ≥ 10 grid cycles.

　　Test the device's harmonic data at 25%, 50%, 75%, and 100% of rated power, recording the total harmonic distortion (THD) and the current amplitude and phase of harmonics 3-31.

　　Compare to standard limits and analyze the harmonic sources (such as inverter switching frequency and filter circuit parameters). If these values exceed the standard, propose optimization suggestions for the filtering solution (such as adding an LC filter).

　　IV. Insulation Impedance Test

　　1. Test Significance

　　Insulation impedance is a key indicator for measuring the electrical safety of solar cells and is directly related to the risk of electric shock to equipment operators and nearby personnel. During long-term operation, factors such as high temperatures, humidity fluctuations, and electrolyte leakage can cause insulation degradation. If insulation resistance is too low, this can easily lead to leakage, short circuits, and even fire. This test covers the equipment's critical electrical circuits to ensure that insulation performance meets safe operation requirements.

　　2. Core Test Indicators and Implementation Standards

　　Based on GB/T 17215.301-2007 "AC Current Measuring Equipment - Particular Requirements - Part 1: Active Energy Meters" and IEC 62109-2:2011 "Safety Requirements for Photovoltaic Inverters - Part 2":

　　Insulation resistance between the positive and negative terminals of the battery and the device housing: ≥ 10MΩ at a DC 500V test voltage;

　　Insulation resistance between the inverter output (AC side) and the housing: ≥ 5MΩ at an AC 1000V test voltage;

　　Adaptability to hot and humid environments: After 48 hours in an environment with a temperature of 40°C and a relative humidity of 90%, the insulation resistance must still meet the above requirements.

　　3. Test Method

　　Before testing, disconnect all external power supplies and ground connections to ensure the test circuit is independent.

　　Use an insulation resistance tester (such as the KEW 3125) to apply the specified test voltage to the "battery positive - case," "battery negative - case," and "AC output - case" connections for 1 minute, then read the impedance values.

　　Place the device in a constant temperature and humidity chamber to simulate a hot and humid environment, then repeat the test to verify the stability of the insulation performance.

　　If the impedance value is below the standard limit, investigate for insulation damage or moisture on the terminal blocks. Repair the problem and retest.

　　V. Test Summary and Application Value

　　This 20kW grid-connected solar battery underwent three core tests, establishing a device performance verification system based on the three dimensions of "grid interoperability, power quality, and electrical safety":

　　The grid interaction test ensures the device can adapt to grid fluctuations, ensuring the grid-connected stability of the distributed PV system;

　　The harmonic distortion test controls electrical pollution, helping the grid maintain high-quality power supply and reducing interference with downstream equipment;

　　The insulation impedance test mitigates safety risks at the source, providing a solid safety barrier for device installation, operation, maintenance, and long-term operation.

　　The test results can be directly used for device factory certification, project acceptance, and subsequent optimization and upgrades. They also provide data support for the design of grid access solutions for PV energy storage systems, promoting the safe and efficient integration of distributed energy resources with the grid.

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