Four switches, a clever timing pattern and a filter turn a battery into AC power for real appliances.
A power inverter converts DC from a battery or solar panel into AC that runs everyday equipment. The switching method decides whether the output is a crude square wave or a clean sine wave.
What Is a Power Inverter?
A power inverter is an electronic converter that changes DC voltage into AC voltage at a set frequency, usually 50 Hz in India. It is the heart of every UPS, solar system and motor drive.
The basic building block is the H bridge, four switches arranged so current can flow through the load in either direction. Switching the diagonal pairs alternately creates AC.
The switches are usually MOSFETs at low voltage or IGBTs at higher power. They must switch fast to keep losses low.
Many home units also include a transformer or boost stage to raise battery voltage to 230 V AC. Modern designs often boost DC first and then invert at high voltage.
5 Steps Inside a Power Inverter
Control.com explains that a microcontroller switches the power with varying pulse widths to build a stair stepped approximation of a sine wave. An LC filter then smooths it.
Gate drivers deliver the fast, strong pulses the switches need, described in MOSFET gate driver ICs.
3 Power Inverter Output Waveforms Compared
Simple on and off switching with high harmonic content.
Stepped waveform with a zero period between pulses.
PWM plus filtering gives grid quality sine output.
Control.com ranks efficiency from square wave down to pure sine, the reverse of output quality. The filtering and fast switching of pure sine designs add some losses.
The hidden tradeoff is harmonics. Square and modified waves carry large harmonic content, measured as THD, which heats motors and causes buzzing.
Battery Current and Backup Formula
Backup time = (Ah × V × Depth of discharge) ÷ (Load W ÷ Efficiency)
Worked example:
800 VA at 0.8 power factor = 640 W
12 V battery, efficiency 85 percent
Battery current = 640 ÷ (12 × 0.85) = 62.7 A
150 Ah battery, 80 percent usable = 1440 Wh
Backup = 1440 ÷ (640 ÷ 0.85) ≈ 1.9 hours
High battery current explains why larger inverters move to 24 V or 48 V systems. Doubling voltage halves current and cable losses.
For UPS sizing, compare with our guides on battery backup time and UPS kVA calculation.
How a Power Inverter Uses PWM
The switching frequency is typically tens of kHz, far above 50 Hz. The LC filter passes 50 Hz and blocks the switching frequency.
The same sine PWM method drives motors in every VFD, but with variable frequency instead of fixed 50 Hz.
Higher switching frequency allows smaller filters but increases switching loss. Designers balance the two for efficiency and size.
Power Inverter Types by Application
| Type | Input | Output | Typical Use |
|---|---|---|---|
| Home inverter | 12 V or 24 V battery | 230 V AC | Backup during outages |
| Solar string inverter | PV strings | Grid AC | Grid tied solar |
| Online UPS | Rectified mains and battery | Clean AC | Critical loads |
| VFD inverter stage | DC bus | Variable frequency AC | Motor speed control |
| Microinverter | Single PV panel | Grid AC | Rooftop solar |
Online UPS systems run the inverter continuously for the cleanest supply, compared in UPS topology comparison.
Grid tied solar inverters also synchronize with the grid and include anti islanding protection. Off grid inverters create their own reference.
Where a Power Inverter Is Used
Battery health strongly affects backup, as explained in causes of battery failure. Deep discharges shorten battery life.
Always size the inverter for motor starting surges, which can be several times running power. Pure sine models handle these loads best.
Power Inverter Backup Calculator
Real backup falls at high discharge rates because battery capacity drops. Use the battery maker discharge tables for accurate sizing.
- Runs motors and pumps smoothly.
- Low harmonic content.
- Quiet operation of fans and transformers.
- Safe for sensitive electronics.
- Higher cost than modified sine.
- Slightly lower efficiency.
- Needs larger filter components.
- High battery current at low voltage.
TI Pure Sine Inverter Reference Design
How Inverters Work Video
Power Inverter FAQ
Related Articles
- UPS Working Principle
- UPS Topology Comparison
- Calculate Battery Backup Time
- IGBT Working Principle
- Boost Converter Working Principle
External References
- 800VA Pure Sine Inverter Reference Design, Texas Instruments
- Converting DC to AC, Control.com
- How Inverters Work, The Engineering Mindset
- Inverter, Wikipedia
What We Learn Today
- An H bridge reverses current through the load to create AC from DC.
- PWM and an LC filter turn switching pulses into a clean sine wave.
- Output quality, efficiency and battery current are the key tradeoffs.