What is the inverter?
Introduction
Inverter is a device that converts direct current energy into alternating current (generally 220V, 50Hz sine wave), which consists of inverter bridge, control logic and filter circuit. Inverter is a DC-to-AC transformer, which is actually a process of voltage inversion with converter.
Converter is to convert the AC voltage of power grid into stable DC output, while inverter is to convert the DC voltage output by equipment into high-frequency and high-voltage AC.
Inverters are widely used in air conditioners, home theaters, electric grinding wheels, electric tools, sewing machines, DVDs, VCD, computers, televisions, washing machines, range hoods, refrigerators, video recorders, massagers, fans, lighting and so on.
Characteristic:
- high conversion efficiency and quick start function;
- Good safety performance: the product has various protection functions such as short circuit, overload, over/under voltage and over temperature;
- Good physical properties: the product is made of all-aluminum shell, which has good heat dissipation performance, hard oxidation treatment on the surface, good friction resistance, and can resist extrusion or impact by certain external forces;
- Strong adaptability and stability under load.
Structure of inverter
The inverter consists of three parts: inverter circuit, logic control circuit and filter circuit, mainly including input interface, voltage starting circuit, MOS switch tube, PWM controller, DC conversion circuit, feedback circuit, LC oscillation and output circuit, load, etc.
Classification according to wave string properties
There are two main types, one is sine wave inverter and the other is square wave inverter.
The sine wave inverter outputs sine wave alternating current that is the same as or even better than the power grid we use everyday, because it does not have electromagnetic pollution in the power grid.
The output of square-wave inverter is the square-wave alternating current with poor quality, and its positive maximum value and negative maximum value are generated almost at the same time, thus causing severe unstable influence on the load and the inverter itself. At the same time, its load capacity is poor, only 40-60% of the rated load, so it can’t carry inductive load. If the load is too large, the third harmonic component contained in the square wave current will increase the capacitive current flowing into the load, which will seriously damage the power filter capacitor of the load.
In view of the above shortcomings, quasi-sine wave (or modified sine wave, modified sine wave, analog sine wave, etc.) inverter appears, and its output waveform has a time interval from the positive maximum to the negative maximum, which improves the use effect. However, the quasi-sine wave waveform is still composed of broken lines, belonging to the square wave category, and its continuity is not good.
To sum up, sine wave inverter can provide high-quality alternating current and drive any kind of load, but the technical requirements and cost are high. Quasi-sine wave inverter can meet most of our electricity demand, with high efficiency, low noise and moderate price, so it has become the mainstream product in the market. The square wave inverter is made by simple multivibrator.