What do you need to know about photovoltaic inverters?

1.1 Classification and main technical performance indicators of inverters

        Usually, the process of converting AC power into DC power is called rectification, the circuit that completes the rectification function is called rectifier circuit, and the device that realizes the rectification process is called rectifier equipment or rectifier. Correspondingly, the process of converting DC power into AC power is called inverter, the circuit that completes the inverter function is called inverter circuit, and the device that realizes the inverter process is called inverter equipment or inverter.

Modern inverter technology is a science and technology that studies the theory and application of inverter circuit. It is a practical technology based on industrial electronic technology, semiconductor device technology, modern control technology, modern power electronic technology, semiconductor inverter technology, pulse width modulation (PWM) technology and other disciplines. It mainly includes three parts: semiconductor power integrated devices and their applications, inverter circuits and inverter control technology.

1.1. 1 Classification of inverters

1. According to the scope of inverter application

According to the scope of inverter application, it can be divided into the following categories.

(1) Ordinary inverter. DC 12V or 24V input, AC 220V, 50Hz output, power 75 ~ 5000W, some models have AC-to-current conversion (UPS) function.

(2) Inverter-charging integrated inverter. Such inverters can use various forms of power to power AC loads. For example, when there is alternating current, the inverter uses alternating current to power the load, or charges the battery: when there is no alternating current, the electric energy falling into the battery is inverted into alternating current to power the AC load. It can be used in combination with various power sources, such as batteries, generators, solar panels and wind turbines.

(3) Special inverter for communication. It provides high-quality 48V power supply for communication. Its product has good performance and high reliability. It adopts modular structure (the module is 1kW), has N+1 redundancy function and is expandable (the power is 2 ~ 20kW).

(4) Special inverters for aviation and military. This kind of inverter has a DC 28V input, can provide AC output voltages of 26V, 115V, and 230V. Its output frequency can be 50Hz or 60 ~ 400Hz, and its output power can range from 30 to 3500VA.

(5) Photovoltaic power inverter. According to the photovoltaic power generation method, it can be divided into: independent photovoltaic power generation system inverter and grid-connected photovoltaic power generation system inverter.

2. Divide according to the waveform output by the inverter

According to the waveform output by the inverter, it can be divided into the following categories.

(1) Square wave inverter. The AC voltage waveform output by square wave inverter is square wave. This kind of inverter can be realized by different inverter topologies, but its common feature is that the circuit is relatively simple and the number of power switching tubes used is small. Its design power is generally between 100 watts and kilowatts. The advantages of square wave inverters are: simple circuit, low price, and convenient maintenance: the disadvantages are: because the output square wave voltage contains a large number of high-order harmonics, it will be used in load electrical appliances with iron core inductors or transformers. Additional losses will be generated, interfering with audio and some communication equipment. In addition, this kind of inverter has insufficient voltage regulation range, imperfect protection function and relatively loud noise.

(2) Step wave inverter. The AC voltage waveform output by this kind of inverter is step wave. Because step wave inverter has many different circuit structures, the number of steps in the output waveform is very different. The advantages of step wave inverter are: the output waveform is significantly improved compared with square wave, and the content of higher harmonics is reduced. When the number of steps reaches more than 17, the output waveform can realize quasi-sine wave. When the output without transformer is adopted, the whole machine is very efficient. High. The disadvantage is: the power used by the ladder wave superposition line is open

There are a large number of off-tubes, and some circuit forms also require multiple sets of DC power inputs, which is unfavorable to the grouping and wiring of solar cell arrays and the balanced charging of batteries. In addition, the ladder wave voltage still has some high-frequency interference to audio and some communication equipment.

(3) Sine wave inverter. The AC voltage waveform output by the sine wave inverter is a sine wave. The advantages of sine wave inverter are: good output waveform, low distortion, little interference to audio and communication equipment, and low noise. In addition, it has complete protection functions, strong adaptability to inductive and capacitive loads, and high efficiency of the whole machine. The disadvantages are: the circuit is relatively complex, requires high maintenance technology, and the price is high.

3. According to the AC power output by the inverter

According to the frequency of AC power output by the inverter, it can be divided into: power frequency inverter (inverter with a frequency of 50 ~ 60Hz): intermediate frequency inverter (the frequency of intermediate frequency inverter is generally 400Hz to more than ten kilohertz): high-frequency inverter (the frequency of high-frequency inverter is generally more than ten kilohertz to megahertz).

4. Divide according to the number of phases output by the inverter

According to the number of phases output by the inverter, it can be divided into: single-phase inverter, three-phase inverter and multi-phase inverter.

5. According to the direction of the electric energy output by the inverter

According to the direction of the output power of the inverter, it can be divided into: active inverter and passive inverter. Any inverter that transmits the electric energy output by the inverter to the industrial power grid is called an active inverter: any inverter that transmits the electric energy output by the inverter to a certain electrical load is called a passive inverter.

6. According to the form of the inverter main circuit

According to the form of the main circuit of the inverter, it can be divided into: single-ended inverter, push-pull inverter, half-bridge inverter and full-bridge inverter.

7. According to the type of inverter main switch tube

According to the type of inverter main switching tube, it can be divided into: thyristor inverter, transistor inverter, field effect inverter, and insulated gate bipolar transistor (IGBT) inverter. It can also be classified into two categories: "semi-controlled" inverters and "fully controlled" inverters. The "semi-controlled type" inverter does not have self-shutdown capability, and the components lose control after being turned on, so it is called "semi-controlled type".

Ordinary thyristors belong to this category: "fully controlled" inverters have self-turn-off capabilities, that is, the conduction and turn-off of components can be controlled by the control pole, so they are called "fully controlled". Power field effect transistors and insulated almost bipolar transistors (IGBTs) all belong to this category.

8. According to inverter DC power supply

According to the inverter DC power supply, it can be divided into: voltage source inverter (VSI) and current source inverter (CSI). Because the VSI DC voltage is approximately constant, the output voltage is an alternating square wave, while the CSI DC current is also approximately constant, so the output current is also an alternating square wave.

9. According to the inverter control method

According to the inverter control method, it can be divided into: frequency modulation (PFM) inverter and pulse width modulation (PWM) inverter.

10. According to the working mode of the inverter switch circuit

According to the working mode of the inverter switching circuit, it can be divided into: resonant inverter, hard switching inverter and soft switching inverter.

11. According to the inverter commutation mode

According to the inverter conversion method, it can be divided into: load converter inverter and self-converter inverter.

12. According to the inverter isolation method

According to the inverter isolation method, it can be divided into: isolated inverter and non-isolated inverter.