The sunlight power stations

                                       
                                         

Therefore, power inverter , General requirements below 10kVA inverter efficiency> 90% over 10kVA inverter efficiency> 95 %. 2) small waveform distortion, high power factor and grid-connected the sunlight power stations output associated with the outside grid inverter output waveform must be consistent with the outer grid. Requirements waveform distortion <5%, high harmonic content <3%, power factor close to 1. The independent type the sunlight power plant with the waveform distortion of the inverter can be a large number (<10%), however, in order to reduce transmission line losses, but also desired waveform close to sine wave, the power factor is close to 1, and to reduce the reactive power loss. 3) to meet the conditions of use requirements of the majority of independent the sunlight power stations for remote mountainous areas and islands, the inverter can withstand the harsh conditions of use, while ensuring the long-term work in less maintenance conditions. Because the most grid sunlight electromagnetic interference power station for families require inverter does not affect peoples living environment, and does not prevent the normal work of other household appliances. Of course, the sun power stations inverter according to market requirements, and other commodities, meet the requirements of the premise, the pursuit of high performance and low cost, low cost, small size and light weight.

 

Generally in accordance with the output of the insulation in the form of sunlight power stations with the main circuit of the inverter is divided into frequency transformer insulation; manner of high-frequency transformer insulation; without transformer insulation method; Forward transformer insulation method. Below the requirements of the inverter according to the sunlight power stations, each of these four kinds of the main circuit are introduced. 1.1-frequency transformer insulation using frequency transformer enter the solar cell matrix, and the output of the power grid insulation, the main circuit structure shown in Figure 1, is divided into two kinds of voltage and current. Generally use voltage-frequency inverter. Large capacity and input low voltage high current work uses current-frequency inverter, the input string with large inductance withstand voltage stress favor switching devices. Power frequency transformer insulation way circuit, the transformation is only a high efficiency, low manufacturing costs. General power frequency inverter SPWM control output moments waveform, after powerful filtering measures, in order to make the output sine waveform distortion <5%. Since the circuit of the semiconductor device is small, can be adapted to the relatively harsh conditions of use.

The switching frequency is low, the electromagnetic interference generated. The main transformer and filter inductor bulky, but low-frequency material can be used, the cost is not high. This way the main inverter for the independent type sunlight power stations. 1.2 high-frequency transformer insulating manner using the high-frequency transformer with the input grid of a solar cell matrix and an output terminal insulated, the main circuit structure shown in Figure 2, transformation is divided into two. Figure 2 (a) in the first stage for SPWM high frequency inverter, high frequency transformer rectifier filter, and then through the second stage working frequency inverter becomes-frequency sine wave voltage output. Figure 2 (b), the first stage for the high frequency PWM inverter, the high-frequency transformer and the second-level Frequency converter, directly into power frequency sinusoidal output voltage, nor as general Frequency converter as is required by the switching device bidirectional, unidirectional operation can be achieved to transform, although the reduction of the rectifying filtering links, high efficiency, however, than in Figure 2 (a) of the circuit and control complexity. Figure 2 (c) circuit for household sunlight power stations with the main circuit of the inverter, the basic structure and Figure 2 (a), in order to eliminate the zero line current, single-phase three-wire output. High-frequency transformer than the power frequency the transformer small size, light weight, low cost. However, the two transform efficiency problem is more prominent, as long as the low-loss snubber circuit and the careful selection of electromagnetic components, you can still make more than 90% efficiency. SPWM control and transform Frequency output waveform distortion, no strong filtering, but the serious problem of high-frequency electromagnetic interference suppression measures such as filtering and shielding. This way the inverter for grid sunlight power stations. 1.3 without transformer insulation method in order to further reduce costs, improve efficiency, and has developed sunlight power stations with a transformerless no way insulated inverter main circuit, the circuit structure shown in Figure 3. Wherein the front of the Figure 3 (a) circuit for the boost circuit, followed SPWM frequency inverter. Boost circuit can be provided and the different output voltage of the solar cell match, the output voltage of the solar cell increases to about 370V, although due to changes in the weather factors, the solar cell output voltage to change, with the booster section, can guarantee the inverter part The input voltage is relatively stable. While increasing the voltage, reducing the current to the inverter part of the loss can be reduced. The boosting circuit can also be performed on the input power factor correction. Figure 3 (b) circuit for the output circuit of the single-phase three-wire, after a simple transformation, it can be changed to three-phase output circuit of Figure 3 (c). The transformerless inverter main circuit insulation method can not enter the solar cell output power grid insulation, so the positive and negative input solar cells can not be directly ground. The solar cell matrix area is large, and the capacitance to ground in the work will occur equivalent capacitance charge and discharge currents. Wherein the low frequency part, may cause the leakage of the power supply circuit switch malfunction, and causing blackout. This can be eliminated by controlling the switching mode of the inverter switching devices. The high-frequency part of the distribution line to other electrical equipment caused by electromagnetic interference, and affect the normal work of other electrical equipment, therefore, to add in the inverter output inductor-capacitor filter to eliminate it. Also CARICOM mode filter, to prevent electromagnetic interference of the solar cells by high-frequency inverter.

 

Also, in order to prevent the solar cell, the positive and negative ground, causing damage to the inverter main circuit, ground current through the current transformer or Hall detector for detecting the solar battery positive, the negative, if it exceeds a predetermined value, and immediately cut inverter main circuit protection. Transformerless inverter Insulation way the main circuit-frequency transformer insulating complex than the high-frequency transformer insulation simple, single-stage transformation efficiency. No transformer, small size, light weight, low cost, is by far the better of a main circuit. 1.4 Forward transformer insulation way inverters without transformers insulated way the main circuit of the indicators is better, however, solar cells, and outside the grid without insulation isolation, there is insecurity, in order to protect and prevent electromagnetic interference, to take protective measures. Therefore, recently developed a main circuit of the inverter forward transformer insulation, as shown in Figure 4, the booster circuit in Figure 3 (a), the inductor becomes the forward transformer, while boosting and insulation isolation, while maintaining the advantages of main circuit transformer insulation method to increase the insulation isolation, to make the work more secure. Of course, to increase the forward transformer, so that the volume, weight, cost increase, from the trial samples of view, however, the AC output 100V 200V direct input, under the conditions of the carrier frequency of 20kHz, the output waveform is close to a sine wave, power factor close 1, from no-load to full 3kVA, the efficiency of> 90%, the cost is still acceptable for users. 2.1-frequency electromagnetic components sunlight power stations inverter transformer inverter main circuit-frequency transformer insulation, electromagnetic components play a role of insulation and power conversion frequency transformer. Core E-type cold-rolled grain-oriented silicon steel punching majority piled up. Enamelled copper wire coil is made of high strength. In order to reduce the iron loss and copper loss, core operating flux density take 1.1 ~ 1.1T, the operating current density of the coil taken 1.5A/mm2.

 

Therefore,power inverter, the frequency transformer bulky, heavy weight. Frequency transformer insulation from foreign workers sunlight power generation inverter prototype of view, which accounts for about 50% of the total weight of the inverter frequency transformer, inverter efficiency is about 90%. According to reports, the United States 10kVA frequency transformer insulation sunlight power station with inverter, frequency transformer magnetic core of iron-based amorphous alloy winding iron loss only cold-rolled grain-oriented silicon steel laminated core 1 / 5, the overall efficiency can reach 95%. Working flux density take the 1.3T, the volume and the weight ratio of silicon steel core. Therefore, we can predict in the the sunlight above 10kVA power station, due to the switching device operating current, the switching frequency should not be high, using frequency inverter transformer insulation, its frequency transformer winding-type iron-based amorphous alloy core or lap-core, high-efficiency, low cost, is a better indicator of a comprehensive program. 2.2 high-frequency transformer in the inverter using the main circuit of the high-frequency transformer insulation from the insulation and power conversion components of electromagnetic high-frequency transformer, as majority MnZn soft ferrite cores. A large number of high frequency inverter transformer insulation used for the sunlight power plants of the family. Its switching devices using IGBT, the operating frequency of 20 ~ 40kHz, in the low end of the high-frequency range,Grid tie inverter, and can not give full play to the advantages of MnZn soft ferrite. Therefore, we can consider another program, using the ring and CD of the iron-based amorphous alloy cores to produce the high-frequency transformer in the inverter. For example, the newly developed iron-based cobalt amorphous alloy 1K104, saturation flux density 1 �� 86T Curie temperature of 457 �� C and the magnetostriction coefficient 1.49% 26; # 215; 10-6. After heat treatment, http://www.gridtieinverter.de/, the loss under 200kHz/0.2T 3.7W/kg 20kHz/0.5T under loss 25.6W/kg loss less than 40W/kg 40kHz/0.5T under. MnZn soft ferrite saturation flux density of 0.4T Curie temperature 180 ��, the magnetostriction coefficient 14% 26; # 215; 10-6, at 20kHz/0.2T for loss as 12.5W/kg. Performance comparison of these two materials can be seen 1K104 iron-based amorphous alloy sunlight power stations with high-frequency transformer, high operating flux density up to 0.5T, its size and weight than the soft ferrite, total loss of small, high-efficient than soft ferrite. Its high Curie temperature, the effects of temperature changes within the range of from -70 �� C to +100 �� C by small impact than the soft ferrite. Its magnetostriction coefficient is small, low electromagnetic interference generated than the soft ferrite. Therefore, the operating frequency to 20kHz ~ 40kHz inverter ideal high-frequency transformer core material. 2.3 The driving transformer in the inverter, the electromagnetic component of the signal converting and driving the switching device is a drive transformer. Power frequency drive transformer using cold rolled grain oriented silicon steel core stacked punching. HF driver transformer MnZn ferrite cores. The drive transformer Parameters with the drive circuit. Figure 5 is a circuit schematic waveform diagram of a drive IGBT. Driving the transformer primary and secondary sides are working under the sine wave voltage, in the sine wave voltage is higher than the threshold voltage, the IGBT conduction below the threshold voltage, Grid tie inverter , disconnected. Regulator DZ determine the size of the threshold voltage Vth, making the amplitude of the output voltage of the secondary side of similar, so that the switch device is turned on nearly 180% 26; # 176; In such a drive circuit, the drive transformer loss of the work under the sine wave voltage is small, the size and weight are small, and not produce electromagnetic interference. As a drive transformer in the inverter circuit of the high frequency SPWM, carrier frequency is generally higher than 20kHz, but also a sinusoidal pulse width modulation (SPWM). The drive circuit and the drive transformer complex than in Figure 5, the design principles, however, is still reduce the loss, reduce the size, weight and manufacturing costs. MnZn ferrite cores are generally used to produce SPWM drive transformer. 2.4 filter inductor inverter, high harmonic electromagnetic components from the elimination of the DC and AC filter inductor. DC filter inductor is connected to the input terminal of the inverter, to withstand the superposition of DC and AC, the working current, inductance, the core having a constant magnetic permeability characteristics, at least same parameters AC filter inductor capacity times.