Because of the demand for renewable energy, solar power inverter (photovoltaic inverter) market is growing. These inverters need high efficiency and reliability. 。 In this paper, these inverter circuits used in power for the inspection, and recommend against switching and rectifier of the best choice.
Photoelectric inverter the general structure as shown in Figure 1, there are three different inverter to choose from. Sunlight through the series connected solar modules, each module includes a set series of solar cells (solar) module. The DC solar modules (DC) voltage in the number of V-class hundreds, according to specific numerical module array of light conditions, battery temperature and the number of modules in series on.
This type of inverter is the primary function of the DC voltage to enter into a stable value. The function through the boost converter to achieve, and the need to boost switch and boost diode.
In the first structure, step-up level of isolation followed by a full-bridge converter. Full-bridge transformer role is to provide isolation. Output on the second full-bridge converters are used to from the first-class full-bridge DC converter DC transform into exchange (AC) voltage. The output and then an additional two-contact relay switch connected to the AC power grid network before the filtering, is aimed at fault in the incident providing security at night and isolation and quarantine power grid.
The second structure of the non-separation programme. The AC-level exchanges boost output voltage from the DC voltage directly.
The third structure of power switches and power diode innovative topology, to boost exchanges and AC have a part in integrating the functions of a dedicated topology. 原文位置 Original location
Original Location 1: solar power inverter system Principle of
Although the solar panels of the conversion efficiency is very low, so that the efficiency of inverter as close as possible to 100 percent is very important. In Germany, installed in the south on the roof of 3 kW series estimated annual power generation module 2550 kWh. If the inverter efficiency from 95 percent to 96 percent, generating more than a year will be 25 kWh. And the use of additional solar modules that produce 25 kWh and increase the cost of an inverter is. As the efficiency from 95 percent to 96 percent will not make the cost of doubling inverter, is the more efficient investment in the inverter is the inevitable choice. The new design, the most cost-effective to improve the efficiency of inverter is the key to the design guidelines. Original location
As for the inverter reliability and cost are two other design criteria. Greater efficiency can reduce the load on the cycle of temperature fluctuation, thereby enhancing reliability, therefore, these guidelines is actually associated. The module will also improve the reliability of use.
Figure 1 shows all the topology need rapid conversion of the power switches. Boost-class and full-bridge needs fast-changing conversion diodes. In addition, specifically for low-frequency (100 Hz) and optimize the conversion of these switch topology also very useful. For any particular silicon technology, optimized for rapid conversion of the switch than the low-frequency conversion applications optimized for the switch has a higher conduction losses.
II.Boost for class switches and diodes
Boost-general design for continuous current mode converters. According to inverter used by the solar array module in the number of election to the use of 600 V or 1200 V devices.
Power switches are the two choices MOSFET and IGBT. Generally speaking, MOSFET than IGBT can work at a higher switching frequencies. In addition, we must always consider the impact of diodes: in the case of boost-no question, because the normal mode of operation does not lower body diode conduction. MOSFET on-loss under-resistance RDS (ON) to calculate, given the MOSFET series, which is effective die area proportional relationship. When rated voltage from 600 V to 1200 V at the changes, MOSFET conduction of the loss will be greatly increased, so, even if rated RDS (ON) is, 1200V MOSFET is not available or the price is too high.
Rated 600 V for the boost switch, can be super-node MOSFET. The high-frequency switching applications, the technology is the best on-loss. There are currently using TO-220 package, RDS (ON) is lower than 100 milliohms and the use of the MOSFET TO-247 package, RDS (ON) is lower than the 50 cents Europe MOSFET.
The need to switch the 1200 V solar power inverter, IGBT is an appropriate choice. The more advanced IGBT technology, such as the NPT and the NPT trenches to stop the field, are directed against lower conduction losses to the optimization, but the price is higher switching losses, which makes them less suitable for high-frequency step-up under the application.
Fairchild plane in the old NPT technology on the basis of the development of a high switching frequency can improve the efficiency of the step-up circuit devices FGL40N120AND, with 43 uJ and the EOFF, compared to adopt more advanced technology devices for the EOFF 80 uJ and A, but To get this performance is very difficult. FGL40N120AND the shortcomings of the device is saturated pressure drop VCE (SAT) (3.0V compared to 125 oC the 2.1 V) higher, but its high-frequency boost switch the advantage of low switching losses have been sufficient to make up for it. The device also incorporates anti-parallel diode. Boost in normal work, not on-the diode. However, during the launch or transient circumstances, the step-up circuit may be driven into the work mode, then the anti-parallel diodes conducts. As IGBT does not have the inherent body diodes, the need for such a total package of diodes to ensure a reliable work.
To boost diodes, need to covert operations . Or carbon silicon diodes such a fast recovery diodes. Carbon silicon diode with a very low forward voltage and loss. But now their prices are very high.
In choosing boost diode, the reverse recovery must take into account the current (or carbon-silicon junction capacitance diode) switch to boost the impact, because it will lead to additional wear and tear. Here, the new covert operations FFP08S60S II diodes can deliver higher performance. When VDD = 390V, ID = 8A, di / dt = 200A and us, and the case temperature of 100 oC, calculated FFP08S60S switching losses below the parameters 205 mJ. ISL9R860P2 used covert operations diodes, this value amounted to 225 mJ. It would also raise the inverter in the high switching frequency efficiency.
III For the bridge and special-class switches and diodes
After filtering, create a bridge output of 50 Hz sine voltage and current signals. A common programme is to achieve a standard full-bridge structure (Figure 2). If the plans in the upper left and lower right corner of the switch-on, between the loading terminal in about a positive voltage; the top right and bottom left of the switch-on, between the loading terminal in about a negative voltage.
For such applications, in a certain time there is only one switch-on. A switch can be switched to high-frequency PWM, another switch in the low frequency of 50 Hz. As bootstrap circuit dependent on the conversion of low-end devices, the low-end device was switched to high-frequency PWM, and high-end device was switched to low frequency of 50 Hz. Original location
2: MOSFET full-bridge
This application using a 600 V power switch, the super-node 600 V MOSFET suitable for this very high-speed switching devices. As a result of these switching devices in the switch-on will bear all the other devices reverse recovery current, super-fast guitar devices such as the restoration of 600 V FCH47N60F is a very good choice. The RDS (ON) was 73 cents in Europe, compared with other similar devices quickly resume its on-loss is very low. When this device in under 50 Hz conversion, without the use of rapid recovery characteristics. These devices have excellent dv / dt and di / dt of more standard super-node MOSFET can improve the reliability of the system.
Another option is worth exploring the use of FGH30N60LSD devices. It is a saturation voltage VCE (SAT) only 1.1 V of 30 A/600V IGBT. EOFF off its loss is very high, reaching 10 mJ, is only suitable for low-frequency conversion. A Europe of 50 cents in the work of MOSFET temperature-resistance RDS (ON) of 100 milliohms. Therefore, in 11 A, and IGBT with the VCE (SAT) the same VDS. As a result of this IGBT based on the breakdown of the older technology, VCE (SAT) as the temperature changes little. Therefore, this can reduce the output IGBT bridge in the overall loss, thereby enhancing the overall efficiency inverter.
。 FGH30N60LSD IGBT in each half-cycle power conversion technology from a switch to another kind of topology for the practice is also very useful. IGBT IGBT here to be used as topology switch.。 In the more rapid conversion when the use of conventional and rapid resumption of ultra-end devices.
For 1200 V dedicated topology and full-bridge structure, the aforementioned FGL40N120AND is very suitable for solar power inverter new high-frequency switching.When the special technology needs diodes, covert operations II, Hyperfast? Carbon II diodes and silicon diode is a very good solution.