The primary function of a solar inverter is to convert the direct current (DC) generated by solar panels into alternating current (AC) for household appliances. All the electricity generated by the solar panels must be processed by the inverter before being output. Through a full-bridge circuit, typically using an SPWM processor, the inverter performs modulation, filtering, and voltage boosting to obtain a sinusoidal AC power supply that matches the frequency and rated voltage of the lighting load for use by the system's end users. With an inverter, DC batteries can be used to provide AC power to electrical appliances.
Inverter Function
An inverter is a power conversion device whose main function is to convert the DC power from a battery into AC power. Through a full-bridge circuit, typically using an SPWM processor, the AC power is modulated, filtered, and boosted to obtain a sinusoidal AC power that matches the load frequency and rated voltage for use by the system's end users.
I. Classification by Application Scope
1. Standard inverter: DC 12V or 24V input, AC 220V, 50Hz output, power from 75W to 5000W, some models have AC/DC conversion, i.e. UPS function.
2. Inverter/Charger All-in-One: In this type of inverter, users can use various forms of power to supply AC loads: when AC power is available, the inverter uses AC power to supply the load or charge the battery; when AC power is unavailable, the battery supplies the AC load. It can be used in conjunction with various power sources, such as batteries, generators, solar panels, and wind turbines.
3. Telecommunications-Specific Inverters: Providing high-quality 48V inverters for telecommunications and postal services. These products are of high quality and reliability, are modular (1KW per module), and have N+1 redundancy and are expandable (power from 2KW to 20KW).
4. Aviation and military-specific inverters: These inverters have a 28Vdc input and can provide the following AC outputs: 26Vac, 115Vac, and 230Vac. Their output frequencies can be 50Hz, 60Hz, and 400Hz, and their output power ranges from 30VA to 3500VA. There are also DC-DC converters and frequency converters specifically for aviation applications.
II. Output Waveform Classification
1. Square Wave Inverter: A square wave inverter outputs a square wave AC voltage waveform. While the inverter circuitry used in these inverters isn't entirely identical, they share the common characteristics of relatively simple circuitry and a small number of power switching transistors. Design power is generally between hundreds of watts and kilowatts. The advantages of square wave inverters are: simple circuitry, low price, and easy maintenance. The disadvantages are: because the square wave voltage contains a large number of high-order harmonics, it will generate additional losses in loads with iron-core inductors or transformers, and it can interfere with radios and some communication equipment. Furthermore, this type of inverter also has disadvantages such as a narrow voltage regulation range, inadequate protection functions, and relatively high noise levels.
2. Stepped-Wave Inverters: These inverters output a stepped-wave AC voltage waveform. There are various circuits for achieving stepped-wave output, with a wide range of steps. The advantages of stepped-wave inverters are a significantly improved output waveform compared to square waves, reduced high-order harmonic content, and the ability to achieve a quasi-sine wave when there are 17 or more steps. When using transformerless output, the overall efficiency is very high. The disadvantages are that stepped-wave circuits use more power switches, and some circuit configurations require multiple DC power inputs. This complicates the grouping and wiring of the solar cell array and the equalization charging of the batteries. Furthermore, stepped-wave voltage still causes some high-frequency interference to radios and certain communication equipment.
3. Sine Wave Inverter: A sine wave inverter outputs an AC voltage waveform that is sinusoidal. The advantages of a sine wave inverter are: excellent output waveform, very low distortion, minimal interference to radios and other equipment, and low noise. Furthermore, it offers comprehensive protection functions and high overall efficiency. The disadvantages are: relatively complex circuitry, higher technical requirements for maintenance, and higher price.
The above classification of inverters into three types helps designers and users of photovoltaic and wind power systems to identify and select the right inverter. In reality, inverters with the same waveform can differ significantly in their circuit principles, components, and control methods.
