“At present, new energy power generation has become a mainstream power generation method, and the attention of all walks of life to it is gradually increasing. But how to test the power generation core inverter, the difficulty of the test and how to perform the performance diagnosis of the inverter? This article will take you through it quickly.
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1. Development of new energy power generation in 2020
New energy mainly includes wind energy, solar energy, biomass energy, nuclear energy and so on. In recent years, under the background of increasingly tight supply of traditional energy and increasing pressure on environmental protection, new energy has become an important energy strategy in my country. During the 13th Five-Year Plan period, the country will still “mainly focus” on low-carbon green. From an industrial perspective, clean power generation industries such as photovoltaics, wind power and nuclear power will benefit.
Figure 1 2008-2018 Global PV History Newly Installed Changes
2. Difficulties in testing core equipment inverters
As the two main forms of new energy power generation, photovoltaic wind power, as the core equipment of power generation, the improvement of inverter power and conversion efficiency has become the focus of design and production. Here, we will share with you the difficulties of testing for photovoltaic wind power generation.
Figure 2 Test diagram of photovoltaic wind power industry power generation
Difficulty 1: Power and Efficiency Test
When the photovoltaic wind power is converted by the inverter, the waveform signal is easily distorted. These distorted waveforms are all non-sinusoidal signals, such as rich in high frequency harmonic components. Without high sampling rate and high bandwidth, high frequency components cannot be accurately measured, so there is a huge gap between the measured value and the true value.
Difficulty 2: Low Voltage Ride Through (LVRT) testing in photovoltaic and wind power industries
Low voltage ride-through stipulates that when the grid voltage drops for a period of time, grid-connected devices such as solar inverters or wind power generation still need to maintain output until the grid power returns to normal. During the test, all the waveforms of this process should be recorded. It is necessary to record for a long time under the condition of ensuring the sampling rate, and then analyze the data.
Difficulty 3: Harmonic Test Standard
Harmonic and inter-harmonic measurement methods and technical standards for measuring instruments of power supply systems and grid-connected equipment are the standards that can accurately measure power grid harmonics in international power quality measurement standards. Because the power generated by photovoltaic wind power generally contains a large number of harmonics , so it needs to pass the harmonic test standard before it can be connected to the grid.
3. Solutions:
1. Power and efficiency test
Figure 3 Schematic diagram of photovoltaic power generation test
As shown in Figure 3, we can see that the focus of photovoltaic power generation testing lies in the power and efficiency values of photovoltaic inverters. The PA8000 power analyzer adopts a new data acquisition technology and has a breakthrough power measurement accuracy of 0.01%, which can realize the conversion An accurate measure of efficiency.
At the same time, the PA power analyzer supports simultaneous testing of 7 channels of voltage and current. One instrument can perform power measurement at multiple points at the same time, which can provide strong data support for the efficiency testing of photovoltaic inverters and wind converters.
2. Low Voltage Ride Through (LVRT) test in photovoltaic and wind power industry
The process of low voltage ride through in the photovoltaic industry is as follows:
Figure 4 Schematic diagram of low voltage ride through test in photovoltaic industry
According to the requirements of GB/T 19964-2012, the PV industry low voltage ride through test needs to meet the following requirements:
(1) When the voltage of the grid-connected point drops to 0, if it can recover to 20% of the rated voltage within 150ms, the inverter must ensure that it will not be disconnected from the grid within this 150ms.
(2) If the voltage of the grid-connected point can recover from 20% of the rated voltage within 0.625s after the drop occurs, the inverter must ensure that it will not be disconnected from the grid and run continuously for 625ms.
(3) If the voltage of the grid-connected point can be restored to 90% of the rated voltage within 2s after the drop occurs, the inverter can ensure that it will not be disconnected from the grid and continue to operate.
The low voltage ride through process in the wind power industry is as follows:
Figure 5 Schematic diagram of low voltage ride through test in wind power industry
According to the requirements of GB/T 19963-2011, the low voltage ride-through test of wind power converters needs to meet the following requirements:
(1) When the output voltage of the wind generator set drops to 20% of the rated voltage, the wind generator set can ensure continuous operation for 625ms without being disconnected from the grid.
(2) When the output terminal voltage of the wind turbine can recover to 90% of the rated voltage within 2s after the drop, the wind turbine should be able to ensure continuous operation without being disconnected from the grid.
Figure 6 PAM management software LVRT data analysis
As shown in Figure 6, Zhiyuan Electronics has added a special test function to the software for the photovoltaic and wind power industries, which can not only solve the problem of low voltage ride through test in the photovoltaic industry, but also specially add the low voltage ride through test function of the wind power industry. It can help users in the wind power industry to independently conduct low voltage ride-through tests on wind power converters.
3. Harmonic Test Standard
IEC61000-4-7 Harmonic Test Standard
IEC61000-4-7 is a technical standard for harmonic and inter-harmonic measurement methods and measuring instruments for power supply systems and grid-connected equipment. It is a standard that can accurately measure power grid harmonics in international power quality measurement standards. Whether the harmonic content of the measured object exceeds the standard can be analyzed according to the harmonic limit standard in the standard.
The frequency spectrum analysis interval of the IEC harmonic measurement standard is 5Hz, and the amplitude of the harmonic is determined by the root mean square of the harmonic subgroup. It conforms to the distribution of harmonic content in the real power grid. With the standard analysis of harmonic content in IEC61000-4-7,
Figure 7 IEC61000-4-7 Harmonic Test Standard
VDE-AR-N4105 German Harmonic Test Standard
VDE-AR-N4105 is a newly promulgated German low-voltage power supply grid-connected operation management regulation. The difficulty of its detection is that the measurement equipment must provide measurement results up to the 178th harmonic for harmonic analysis. Because the VED-AR-N4105 low-voltage grid-connected standard requires that the harmonic measurement range covers the entire low frequency domain (about 9KHz), the number of tests is 8900/50=178 (50Hz is the 0th harmonic).
PA6000H series power analyzers can support both IEC and N4105 German standard harmonic test standards, and can support up to 500 harmonic measurements, which can truly present each harmonic component and harmonic distortion factor (THD).
Figure 8 VDE-AR-N4105 standard
4. Flicker impedance angle test
Conventional inverter grid-connected flicker test requires RLC load, but for large inverters, it is unrealistic to use RLC load, so the IEC61400-21 standard provides a method for flicker impedance angle test under simulated grid conditions. The PA power analyzer and PAM host computer software can quickly measure the short flicker value and flicker coefficient under different flicker angles. In addition, we also optimized the phase-locking algorithm in a targeted manner, which solved the step jitter well and achieved better accuracy.
The Links: FS50R06KE3 G170EG01-V1