I. Overview of Development of Large Photovoltaic Desert Power Stations According to the data of planned installations announced by the state in 2014, this explosive growth trend has not been reduced. At present, the final installed capacity after adjustment is 14 GW (6 GW for terrestrial photovoltaic power plants and 8 GW for distributed photovoltaic power plants). This is almost equivalent to the total installed capacity of domestic photovoltaic power plants in all previous years. The development trend of the desert power station is moving towards an increasingly larger capacity of the individual power stations and an increasing voltage level of access. II. Power Quality Problems of Large Photovoltaic Desert Power Stations 1. How are harmonics generated? The generation of harmonics in PV power plants is mainly caused by inverters, DC bus fluctuations, transformer core saturation nonlinearity, and power grid distortion. The harmonics generated by the inverter are mainly composed of two parts: one is caused by the dead time, including low harmonics such as 3, 5, 7, and 9; the other part is generated by the modulation process, and the groups are distributed at integer multiples of the switching frequency. nearby. DC bus disturbance is also a source of generating harmonics. The DC bus voltage has a transient adjustment process. The influence of its current waveform can only be weakened by improving the MPPT method, but it cannot be eliminated. The saturation nonlinearity of the iron core of an isolation transformer also leads to the generation of harmonics. At the same time, if the power grid distortion is serious, if the inverter emits an ideal sinusoidal voltage, a harmonic voltage difference will be generated in the reactance, resulting in a corresponding current in the grid-connected current. Harmonic components. The large-capacity photovoltaic grid-connected system will generate a large number of current and voltage harmonics when the low-power and weak-grid power grids are connected. The large desert power station is composed of multiple inverters. When an access point is incorporated into the power grid, the inverters will affect each other and interact with each other. Therefore, there will be problems of superposition of various harmonics. In low-light situations, the inverter load rate is usually below 10%, the grid-connected current THD is usually more than 5%, and the capacity of super-large photovoltaic power plants may reach 100 megawatts. Even if the load rate is 10%, the output capacity will reach 10MW. At the time, the photovoltaic power plant will become a huge source of harmonics and seriously threaten the stable operation of the power grid. 2. How does resonance occur? The output harmonic current of large-scale grid-connected photovoltaic power plants has wide frequency domain and high-frequency characteristics, and is connected to the power grid through long-distance transmission cables. Therefore, the influence of distributed capacitance of transmission lines cannot be ignored. When the harmonic current is matched with the parameters of the transmission line of the power grid, a parallel resonance will occur, which will cause the amplification of the harmonic current and further increase the harmonic content of the system. When the background harmonic voltage matches the parameters of the transmission line, a series resonance will result in serious harmonic voltage amplification. The 200-300km transmission line is easy to resonate with the 3rd harmonic voltage, and there is about 5 times amplification at the resonance point. The 100-200km transmission line is easy to generate resonances at 5 and 7 times, and has nearly 10 times amplification at the resonance point, and has no amplification for other times of harmonic voltage. Transmission lines within 100 km may generate resonances at harmonics of 11, 13 and higher, and the amplification factor may exceed 20. Because the background harmonic voltage is mostly low order 3, 5, 7, etc., it is necessary to pay attention to the influence of the transmission line over 100 km, and the resonance will cause the transmission line harmonic voltage to be too high, which will seriously affect the stable operation of the photovoltaic power plant. Therefore, the reactive power compensation device supported by the large-scale photovoltaic desert power station has the need for harmonic compensation and resonance suppression. III. Harmonic Compensation and Resonance Suppression Technology of Static Var Generator TBEA Static VAR Generator uses external CT to measure the load current or grid current to the signal board for processing. The high-performance FPGA harmonic detection algorithm is used to quickly and accurately calculate the load harmonic current. Through the independent control of the fundamental wave current and the harmonic current in the rotating coordinate system, a closed-loop control loop for harmonic current compensation is formed, and a PWM drive signal is generated to the power device for modulation, and targeted harmonics can be compensated specifically. , The required compensation current is output to the grid, the harmonic filtering function is completed, and the harmonic compensation ability of 25 times or less is achieved. At the same time, the real-time detection of the harmonic current of the load and the harmonic voltage of the grid point, the virtual harmonic impedance is adjusted to control, and the resonance is effectively suppressed. By investing in the VTOE static var generator, using its harmonic compensation and resonance suppression technology, the power quality of the large desert photovoltaic power station is effectively improved, and the system stability of the photovoltaic power station and transmission network is improved. Lens Ring,Lens Ring Joint Gasket ,Lens Gasket,Lens Ring Gasket WENZHOU JINGWEI SEAL TECHNOLOGY CO., LTD , https://www.ringjoint-gasket.com
Figure 1. Domestic PV installation capacity 
Figure 2. System topology of a desert power station 
Figure 3. Inverter output current measured under low light 
Figure 4. Measured harmonic curves of photovoltaic power plant 
Figure 5. Series resonance analysis of overhead lines 
Figure 6. Photovoltaic dedicated outdoor container 
Figure 7. The measured secondary current at 35KV before the operation of the VSEA static var generator (ratio of 800:5) 
Figure 8. The measured 35KV secondary current after the VSEA's static var generator is put into operation (electric transformation ratio 800:5)