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Isolated Photovoltaic Grid - connected Inverter

Author: Source: Datetime: 2016-10-05 01:00:16
In the PV solar power generator system, the main function of the inverter is to convert the direct current from the PV array into alternating current with the same frequency of the grid and feed the power into the grid. Usually a transformer can be used to isolate the grid and the PV array, photovoltaic grid-connected system will have a grid-connected inverter isolation transformer and grid-connected inverter, according to the type of transformer can be isolated photovoltaic grid-connected inverter The device is divided into two types: power frequency isolated PV grid-connected inverter and high-frequency isolated PV grid-connected inverter.

In the frequency isolation photovoltaic grid-connected inverter system, the PV array output of the DC inverter from inverter to AC, after the transformer step-up and isolation and people after the power grid. The use of frequency transformers for voltage conversion and electrical isolation, has the following advantages: simple structure, high reliability, impact resistance solar power generator, good safety performance, no DC current problems. This type of structure DC circuit voltage, the lower limit of the ratio range is generally less than 3 times. However, because the system uses a frequency transformer, so there are bulky, heavy, high noise, low efficiency and other shortcomings.

The conventional topologies of grid-connected PV grid-connected inverters are single-phase, three-phase and three-phase multi-structures. Single-phase structure of the power-frequency isolation photovoltaic grid-connected inverter shown in Figure 4-6, can generally use full-bridge and half-bridge structure. This single-phase structure is commonly used in several kilowatts of power level of the PV solar power generator systems, including DC voltage is generally less than 600V, the efficiency is less than 96%. Three-phase structure of the power-frequency isolation PV grid-connected inverter shown in Figure 4-7, can generally use full-bridge and three-level half-bridge structure. Such three-phase structure is commonly used in dozens or even hundreds of kilowatts of power levels of photovoltaic grid-connected systems. Among them: three-phase full-bridge structure of the DC voltage is generally 450-820V, the working efficiency of up to 97%; and three-level half-bridge structure of the DC voltage is generally 600-1000-, the work efficiency of up to 98% , Three-level half-bridge structure can achieve better waveform quality.
It is worth mentioning that this three-phase multi-structure can be based on changes in solar irradiance, the combination of photovoltaic arrays and inverters to switch the combination to mention the inverter operating efficiency, such as solar irradiance is small, all Array into an inverter, and when the solar irradiance is large enough, only two inverters into operation solar power generator. In addition, this three-phase multi-structure when the two inverters can also work simultaneously using the transformer secondary winding or X connection to eliminate low harmonic current; or the use of phase shift multiplexing technology to increase the equivalent switching frequency, The switching losses of each inverter.

In the specific circuit structure, the conversion type high-frequency chain PV solar powered portable generator inverter high-frequency inverter part of its pre-level can be used push-pull, half-bridge and full-bridge conversion circuit form, Part of the device can be half-bridge and full-bridge conversion circuit and other forms. In general: push-pull circuit for low-voltage input conversion occasions; half-bridge and full-bridge circuit for high-voltage input occasions. Practical application can be based on the final output voltage level and power to determine the appropriate size of the circuit topology. The following full-bridge topology as an example to expand the specific elaboration. Full-bridge conversion high-frequency chain PV grid-connected inverter consists of a high-frequency voltage full-bridge inverter, a high-frequency transformer, an uncontrollable bridge diode full-wave rectifier solar powered portable generator, a DC filter inductor and a polarity inversion Variable bridge composition. Among them: The high-frequency voltage full-bridge inverter adopts the modulation mode, and inverts the DC voltage from the photovoltaic array into a bipolar three-level ^ high-frequency pulse signal. High-frequency transformer will boost the signal after the transfer to the uncontrollable bridge diode full-wave rectifier circuit. TAG: Multi-Storage Reliability Shell Manganese 200MW Ørsted Micro ABB Programs Volvo 65MW Porsche Largest Volkswagen Lease