The primary function of an inverter, also called inverter, is the conversion of DC voltage into, usually sinusoidal, AC voltage. Some devices also transform the input voltage upwards. So is z. B. the use of 12 or 24 volts DC one car batteryto operate a device designed for 220 volts AC. Depending on the circuit, a inverter generate single-phase or three-phase (three-phase) AC voltage. Models based on semiconductor technology achieve an efficiency of up to 98 percent (ratio of output to input power). However, the use of an inverter is not limited to operating electrical equipment designed for AC power in locations where only DC power is available. Rather, today is another important application in the supply of direct current, such as photovoltaic systems, in a AC or three-phase network.

Chopper or oscillator – the technologies of inverter

Electromechanical choppers provide a rectangular output voltage, which is then transformed. These devices can be considered the origin of inverter technology. However, they are susceptible to faults and are almost no longer used today. In motor generators, an electric motor is operated with the DC voltage, which drives a generator. The latter supplies the output voltage of the inverter as AC voltage. The most common today inverter are electronic devices that are based on semiconductor technology and operate on the principle of oscillators (oscillating systems) or astable multivibrators (systems that cycle independently or externally between two states).

Self- or externally controlled – the control more up-to-date inverter

Self-controlled (also self-guided) inverter control with transistors. They are also called island inverters. In these models, a clock generated by the device itself triggers the blocking and enabling of the flow passage. Reference pulses from the power grid are therefore not required in this variant of the inverter and the devices themselves determine the phase position of the output AC voltage. In this way, a so-called island grid can be built. These are locally limited networks for the operation of electrical equipment without connection to a public power grid. The supply voltage is supplied by a rechargeable battery in isolated networks. Another important application area is uninterruptible power supplies. Emergency power supplies also often operate on this principle.

Third-party or grid-controlled inverters usually also control with semiconductors, wherein in addition to transistors, thyristors (semiconductors for switching higher power in one direction) or triacs (bidirectionally switching thyristors) are used. A main field of application of the foreign-controlled inverters is the feeding of electrical energy into an already existing AC voltage network. To make this network-synchronous, the existing network controls the phase position of the inverter output voltage. A typical application example is the supply of electrical energy from a photovoltaic system. Another main field of application of externally controlled inverters are so-called frequency converters (often simply referred to as inverters). In these devices, the input voltage is an AC voltage that is rectified and then operates an inverter. This can be used to connect AC networks that are not synchronized or even operated with different network frequencies. Another field of application are wind turbines with variable generator voltage (due to changing speeds) and a DC voltage intermediate circuit. 2-quadrant frequency converters provide energy recovery when braking energy is used.

The different characteristics of the output voltage

Depending on the form of the output voltage inverters are divided into corresponding categories. Sine inverters are suitable for all common devices, such. As switching power supplies, compact fluorescent lamps, LED lamps, TV, hi-fi systems and small electrical appliances. As a rule, these are sinusoidal voltages with low noise components, which however are unproblematic in these applications. However, pure sinusoidal voltages for highly sensitive devices can also be generated by correspondingly high-quality inverters. The operation of square and trapezoidal inverters can cause problems for many electrical devices, especially for home appliances that are internally controlled with triacs, such as: Some modern ones vacuum cleaneror coffee machines. You perform limited or often not even when operating with rectangular or trapezoidal AC voltage. In general, inverters can produce single-phase or three-phase (three-phase) output voltage, depending on the design.

Efficiency and performance

The high efficiency of high-quality inverters depends on the power. If this is relatively small (for example, with photovoltaic systems and cloudy weather) it can fall significantly with conventional inverters. However, specialized solar inverters are optimized to operate highly efficiently over a wide power spectrum.