Glossary term
Inverter
A power electronic converter that transforms DC electrical power into AC power with controlled voltage, frequency, and waveform.
Definition
deviceAn inverter is a power electronic converter that converts direct current into alternating current.
Inverters synthesize AC output by switching semiconductor devices from a DC link or battery source. They can control voltage, frequency, phase, and waveform, making them central to solar power systems, battery storage, motor drives, uninterruptible power supplies, electric vehicles, grid converters, and variable-frequency drives. Their engineering performance depends on topology, modulation, switching devices, filters, thermal design, protection, electromagnetic compatibility, and control strategy.
An inverter converts DC power into AC power. The DC source may be a battery, photovoltaic array, rectified supply, fuel cell, or DC link. The AC output may feed a motor, local load, transformer, microgrid, or utility grid. Unlike a passive transformer, an inverter uses actively controlled semiconductor switches to create the desired waveform.
The simplest single-phase topology is a full bridge, often an H-bridge. Three-phase inverters use six main switches arranged in three legs. By switching these devices in a controlled sequence, the inverter applies positive, negative, or zero voltage states to the load. Pulse-width modulation shapes the average output voltage and frequency over each switching period.
Main applications
In motor drives, inverters control motor speed and torque by changing output frequency and voltage. In solar and battery systems, grid-tied inverters synchronize with grid voltage, regulate power export, manage reactive power, and meet protection requirements. In uninterruptible power supplies, inverters maintain AC output when the input supply fails. In electric vehicles, traction inverters convert battery energy into controlled three-phase power for the motor.
Engineering considerations
Important inverter design variables include DC-link voltage, output current, switching frequency, modulation method, device technology, filter design, control bandwidth, cooling method, short-circuit protection, isolation, leakage current, and electromagnetic emissions. Semiconductor losses include conduction loss and switching loss. These losses determine efficiency and junction temperature.
The output waveform is not perfectly sinusoidal before filtering. Harmonic distortion, common-mode voltage, bearing currents, cable reflections, acoustic noise, and electromagnetic interference can all be design constraints. For grid-connected inverters, synchronization, anti-islanding, fault ride-through, power-factor control, grid-code compliance, and weak-grid stability become critical.
Common mistakes
A common mistake is specifying inverter power without checking the load profile. Motor startup, overload, regenerative braking, thermal cycling, altitude, ambient temperature, cable length, and switching frequency can all change the required rating. Another mistake is treating an inverter as an ideal AC source. Real inverters have current limits, control delays, harmonic content, protection states, and stability limits that must be considered in system design.