Systematic Testing Solution of PV Inverter

As the "heart" of a photovoltaic (PV) power generation system, the performance, efficiency, and reliability of the PV inverter directly determine the power generation revenue and lifespan of the entire power plant. Therefore, comprehensive and accurate testing is an indispensable part of every stage of inverter development, from R&D and production to on-site operation and maintenance.

The following will systematically explain PV inverter testing solutions from four aspects: testing scenarios, key testing items, core testing equipment and solutions, and development trends.

Core Testings

R&D and Verification Testing

Purpose: To verify the design of new products and ensure they conform to theoretical models, performance indicators, and various international/national standards.

Features: Most comprehensive and in-depth testing, the highest precision requirements, and allows for destructive testing.

Production and Quality Inspection Testing

Purpose: To perform rapid and automated functional and performance verification on each inverter before shipment, ensuring product consistency.

Features: Fast testing speed, high degree of automation, focuses on pass/fail determination, and is non-destructive.

Certification and Type Testing

Purpose: To obtain market access certificates (such as China CQC, Europe VDE, and North America UL). Features: Strictly adheres to specific standards (such as IEC 62109, IEC 62116, NB/T 32004, etc.), and is performed by an authoritative third-party laboratory.

On-site Installation and Operation Testing

Purpose: To ensure correct on-site installation, troubleshooting, and to conduct regular performance evaluations.

Features: Portable equipment, complex testing environment, emphasis on safety, and basic functional verification.

Key Test Items

A. Electrical Performance Testing

Efficiency Testing

Maximum Efficiency: The inverter's efficiency at its optimal operating point.

Weighted Efficiency (European Efficiency, CEC Efficiency): Calculated by weighting operating time under different illumination conditions, more accurately reflecting actual power generation.

MPPT Efficiency: Measures the inverter's ability to track the maximum power point of photovoltaic modules, crucial for power generation.

MPPT Dynamic Performance Testing

Simulates environments with rapid changes in illumination and temperature to test the inverter's MPPT algorithm response speed and accuracy.

Power Quality Testing

Harmonics and Interharmonics: Analyze the distortion of the output current, which must comply with standards (e.g., IEC 61727, IEEE 1547).

DC Injection: Prevent the inverter from injecting DC into the grid, protecting transformers and equipment.

Power Factor and Reactive Power Regulation Capability: Test the inverter's ability to participate in grid regulation at the grid connection point.

Protection Function Testing

Grid Connection Protection: Such as over/under voltage, over/under frequency, and anti-islanding protection. This is the core of safety testing.

Input Side Protection: DC side overvoltage, reverse connection protection, etc.

Self-Protection: Over-temperature, over-current protection, etc.

B. Safety and Compliance Testing

Insulation Resistance Test: Detect the insulation performance of the DC and AC sides.

Withstand Voltage Test (Dielectric Strength Test): Verify that clearances and creepage distances meet requirements.

Leakage Current Test: Assess leakage current to ground to ensure personal safety.

Environmental and Reliability Testing

• Temperature Rise Test: Measure the temperature of critical components under rated load.
• High and Low Temperature Operation/Storage Test: Verify the inverter's adaptability to extreme environments.
• Damp Heat Test, Salt Spray Test, etc.

C. Grid Support Function Testing (Smart Inverters)

With increasing photovoltaic penetration, modern inverters need stronger grid interaction capabilities.

Low Voltage Ride-Through: In the event of a grid fault, the inverter cannot immediately disconnect from the grid and needs to support the grid for a period of time.

Active Power Derating and Frequency Support: Adjust output power according to grid commands.

Automatic Voltage Regulation: Stabilize the grid connection point voltage by adjusting reactive power.

III. Core Testing Equipment and Solutions

For different testing scenarios and projects, the following equipment needs to be used in combination:

1. Core Testing Platform: Photovoltaic Simulator + Grid Simulator + Test Analysis Software

This is the gold standard for R&D and certification laboratories.

Photovoltaic Simulator

Function: Replaces real photovoltaic modules, accurately simulating I-V curves under different light and temperature conditions, and can simulate complex scenarios such as shading and aging.

Advantages: Repeatable, high precision, not limited by weather or site.

Representative Manufacturers: Ainuo, Keysight, Chroma.

Grid Simulator

Function: Simulates various grid conditions, including normal and abnormal conditions (such as voltage dips and frequency fluctuations), for testing the grid connection performance and protection functions of inverters.

Advantages: Can create various test scenarios to verify the grid adaptability of inverters.

Representative Manufacturers: Ainuo, Keysight, Chroma.

Power Analyzer

Function: High-precision measurement of all electrical parameters on the DC/AC side, including voltage, current, power, efficiency, and harmonics.

Advantages: High precision (up to 0.01% or higher), the cornerstone of efficiency testing.

Representative Manufacturers: Ainuo Yokogawa, Keysight.

Automated Testing Software

Function: Integrates hardware devices to automatically execute complex test sequences (such as efficiency curve scanning, LVRT testing) through programming and generates reports.

Advantages: Improves testing efficiency, ensures data consistency, and traceability.

2. Production Testing Solutions

Automated Testing System: Integrates multiple testing instruments (AC/SOURCE, DC LOAD, insulation withstand voltage tester, etc.), controlled by PLC or PC, completing a full inspection of an inverter within tens of seconds to minutes.

Features: Modular design, high throughput, barcode binding, and data upload to the MES system.

3. Field Testing Equipment

I-V Curve Tracker: Tests the I-V characteristics of photovoltaic strings on-site to troubleshoot component problems.

Power Quality Analyzer / Portable Power Analyzer: Measures voltage, current, power, harmonics, etc. at the grid connection point to evaluate actual operating performance.

General electrical tools such as insulation resistance testers and clamp meters.

IV. Development Trends and Challenges

High Power, High Voltage: With 1500V systems becoming mainstream, testing equipment requires higher voltage and power ratings.

Integrated Energy Storage: The demand for testing photovoltaic-storage hybrid inverters is surging, requiring the simulation of more complex charging and discharging scenarios and energy management strategies.

Higher Grid Adaptability Requirements: Testing weak and high-impedance grids presents new challenges.

Digitalization and AI: Utilizing big data and AI algorithms to analyze test data, optimize testing processes, and even predict potential faults.

Increasingly Stringent Safety Requirements: Testing, especially DC arcing detection, has become mandatory.

Summary

A complete photovoltaic inverter testing solution needs to be customized according to specific testing objectives (R&D/production/certification/O&M). Its core is an accurate simulation (PV simulator, grid simulator) and precise measurement (power analyzer). Selecting mature and reliable testing equipment and solutions is crucial to ensuring inverter product quality, enhancing market competitiveness, and guaranteeing the safe and efficient operation of photovoltaic power plants.