Grid solar inverter

Date: 2010/5/13      Source: Zhejiang Tress Electronic Technology Co.,Ltd.     Views: 8669

Inverter with generally divided into photovoltaic inverter, wind power generator, inverter, power equipment and network equipment, inverters and other power grid inverter. 

1, photovoltaic inverter with 

As the construction of the diversity, will inevitably lead to the diversity of solar panels installed in order to make the most efficient solar energy conversion while taking into account the shape of beautiful architecture, which requires the diversification of our inverter, the best way to achieve solar conversion. More common now in the world of solar energy inverter way: focus on inverter, group string inverter, multiple string inverters and inverter components, will now use several occasions inverter analyzed. 

Centralized inverter 

Figure. Focus on general use and large-scale photovoltaic inverter power stations (> 10kW) systems, many parallel strings of PV group was connected to the same concentration of inverter DC input terminal, the general use of large power IGBT three-phase power module, the use of smaller power field-effect transistor, while using the DSP converter controller to improve the quality of electrical energy output, it is very close to sine wave currents. Most prominent feature is the system of power and low cost. But by the photovoltaic group of string matching and some shading effects, the overall PV system efficiency and power capacity. At the same time the reliability of the photovoltaic power generation system by a group of photovoltaic cells adversely affect working conditions. The latest research is to use space vector modulation control and the development of new inverter topology to connect, to get some of the load in case of high efficiency. 

Concentrated in the Tres inverter, you can attach a solar array interface box, a string of photovoltaic panels on each string to monitor, such as a string which does not work correctly, the system will be to pass this information to the remote controller, and a string through the remote control to stop this work, which will not be a string of photovoltaic string of failures and impact of the PV system reduces the work and energy output. 

Group string inverter 

Figure. Group series inverter has become the international market is now the most popular inverter. Group string inverter is based on the concept based on modular, each PV group string (1kW-5kW) through an inverter, the DC-side with maximum peak power tracking, parallel and network in the exchange side. Many large-scale photovoltaic power plants group string inverter. Advantage of the module from group differences between strings and shading effects, while reducing the optimal working point of PV modules 

And inverter mismatch, thereby increasing capacity. These technical advantages of the system not only reduces costs, increases system reliability. Meanwhile, in the group between the introduction of string "master - slave" concept, allows a single string of energy in the system can not make the work of a single inverter case, several groups of PV group strung together, so that one or more of work to produce more power. The latest concept for several inverters each other to form a "team" instead of "master - slave" concept, making system reliability one step further. Currently, transformerless string inverters group already has a dominant position. 

Multiple string inverters 

Figure. Multiple string inverter is set to take a centralized inverter and the advantages of string inverters, to avoid its shortcomings, can be applied to a few kilowatts of photovoltaic power stations. In the multiple string inverters, contains a different single peak power tracking and DC to DC converter, the DC to DC through a regular AC inverter into alternating current electricity grid to the Internet. PV strings of different rating group (for example: different rated power, each string the number of different components, different component manufacturers, etc.), different sizes or different technology of photovoltaic components, in different directions group string (such as: East, South and West), a different angle or shading, can be connected in a common inverter, the same string in each group are working in their respective peak at maximum power. 

Meanwhile, the DC cable length reduction between the group string shader effects and because the differences between groups string minimize losses caused. 

Component inverter 

Components of each inverter is the PV module is connected with an inverter, and each component has a maximum power of the peak single track, so components and better match the inverter. Often used to 50W to 400W photovoltaic power stations, the overall efficiency of less than group string inverter. Because it is paralleled in the exchange, which increased the exchange side of the connection of the complexity, maintenance difficulties. Another need to be addressed is how to more effectively and to network with the network, the simple way is directly through ordinary AC outlet to the grid, so that you can reduce the cost and installation of equipment, but often the safety standards throughout the network may not allow to do so, the power companies may oppose the power plant directly and ordinary home users connected to the ordinary socket. Another security-related factors and the need to use isolation transformers (high or low), or allows the use of transformerless inverter. The inverter of solar glass curtain grid inverter photovoltaic inverter wall in the most widely used. 

Tres photovoltaic inverter specification, the existing small group of string inverter power, but also centralized power inverter, as China's PV market is developing rapidly, Tres inverse Transformer is bound to be more and more Chinese customers. 

Second, wind power generator inverter 

Characteristics of wind power generation system for the design in parallel with the PWM power inverter control system, the system uses the current instantaneous feedback directly to mains voltage synchronization signal for the inverter output current to track orders, through the network side of the current closed-loop tracking control in order to achieve unity power factor power feed to the grid. On the stability of the system is analyzed, experimental results show that the inverter control system is feasible and correct. 

Key words wind power inverter with power factor 

1 Introduction 

With the strengthening of environmental awareness and demand for renewable energy, wind power technology and more attention. As the wind with instability and randomness, wind turbine power is given voltage, frequency changes randomly alternating current, the power to take effective measures before we can transform the wind power into the grid. In order to improve the operation of wind turbine power generation system performance, developed in recent years based on the AC - DC - AC inverter variable speed wind power system. 

In the AC - DC - AC variable speed wind power system, inverter control technology is the key, at home and abroad have begun research in this area. [2] ~ [5] which are of special study. Several documents in this article of the above advantages of inverter, a new inverter control scheme. The inverter directly to the power grid voltage synchronization signal for the inverter output current tracking signal, enabling fast track the grid voltage output current. The control system is simple, experimental results show that the control system can achieve unity power factor output, and output current harmonic content is low. 

2 AC - DC - AC Variable Speed Wind Generation System Introduction 

AC - DC - AC variable speed wind power generation system shown in Figure 1, Figure in rectifier and inverter with diode rectifier and were based on full-controlled PWM inverter device. To address the low wind speed when the voltage after rectification low amplitude, frequency changes too fast, a larger dc ripple, voltage spikes and other issues, the rectifier and inverter DC link between the joined part, the link is l pressure and voltage regulator functionality. Inverter to convert DC into AC for the grid conditions before or directly into the grid through the transformer. 

This AC - DC - AC system the most prominent feature is the connection between wind turbines and power buffer circuit, when the grid is no current impact, not only can adjust the voltage inverter, frequency, and can adjust the output power, is a stable and nets. 

3 PWM Inverter Control 

PWM inverter topology shown in Figure 2a. Inverter DC input and the output connected to the input voltage to DC voltage regulator after the udc, through the filter inductor on the output after the grid for wind power generator inverter systems, the output phase voltage, phase current and electromotive force to meet the power vector relations shown in Figure 2b. 

For the infinite public grid, the grid as a current source inverter power to the power grid. Therefore, on the control of inverter output current can be achieved by controlling the output power purposes. Can see from Figure 2b, in order not to generate harmonic pollution of public power, must each phase inverter output current and grid voltage inverting, in order to achieve unity power factor inverter output.To achieve this purpose, as shown in Figure 3 is designed inverter control system. 

4 controller and its parameter design 

Because the PWM switching frequency is much larger than the common power grid power frequency, as shown in Figure 3, the control system plan, shown in Figure 4 can be a passing phase current closed-loop diagram. 

5 and Inverter Test 

Figure 6a for the battery voltage with a phase current waveform diagram, Figure 6b is a phase voltage and current waveform. Figure 6c for the output current spectrum. The results show that stability in the battery voltage conditions, the inverter output current is a steady sine wave, and the opposite phase with the grid voltage, thus achieving a unity power factor in transmission of electricity. Inverter fundamental output current frequency is 50Hz. Reached the harmonic content and network requirements. 

6 Conclusion 

In this paper, the inverter control system directly to the grid voltage as the inverter output current reference signal, using the current instantaneous feedback, the control system is not only simple, but also to achieve unity power factor output, reduce the output current of the power grid caused harmonics. The grid inverter control system design for the wind power and network technology to provide the conditions. 

3, inverter power equipment and network 

Power Equipment inverter with a power inverter with internal combustion engines, etc., in daily life with a wide range of applications.