Single-Phase Sine-Wave Inverter using SPWM and LC Filter

Inverters convert DC (battery, solar) to AC, but the waveform quality decides what they can safely power. The simplest inverters output a square wave — fine for a resistive heater, but motors run hot and noisy on it, transformers saturate, and sensitive electronics misbehave. A sine-wave inverter synthesizes a smooth waveform by switching an H-bridge with sinusoidal pulse-width modulation (SPWM): the pulse widths follow a sine reference, and an LC filter averages the high-frequency switching into a clean 50 Hz sine. This modulation-plus-filter architecture is the foundation of UPS systems, solar inverters and motor drives. This project implements it on a bench scale: an Arduino generates complementary SPWM with dead-time, drives a MOSFET full bridge, and an LC filter plus step-up transformer delivers mains-frequency AC with overload and low-battery protection.

1. The Arduino's firmware generates two complementary SPWM streams: a 50 Hz sine reference modulated onto a high-frequency carrier, with dead-time between the two halves.
2. Isolated gate drivers level-shift these signals to drive the high-side and low-side MOSFETs of the full H-bridge.
3. The bridge chops the DC bus (12/24 V battery) into a high-frequency pulse train whose average follows the sine reference.
4. The LC low-pass filter averages the pulse train, attenuating carrier harmonics and reconstructing a 50 Hz sine wave at low voltage.
5. A step-up transformer raises the filtered output to usable AC mains level for the demo load.
6. Output voltage and current are sensed continuously; on overload the firmware disables all gate drives, latches the fault and shows it on the LCD until reset.
7. If the battery voltage falls below cut-off, the inverter shuts down cleanly and re-arms when the battery recovers.

Tech stack:

• Arduino Uno/Nano (ATmega328P)
• MOSFET full H-bridge with isolated gate drivers
• LC low-pass output filter (inductor + capacitor)
• Step-up transformer for mains-level output
• Output voltage and current sensing stage
• 16x2 character LCD
• Arduino IDE (C/C++ firmware)
• 12/24 V battery source and demo AC load

• [Sinusoidal PWM generation] The Arduino synthesizes SPWM by comparing a 50 Hz sine reference against a high-frequency carrier in firmware, with the modulation index adjustable for output voltage control.
• [Full-bridge MOSFET stage] Four MOSFETs in an H-bridge, driven through isolated gate drivers, switch the DC bus into the modulated waveform.
• [Dead-time insertion] A programmed blanking interval between high-side and low-side switching prevents shoot-through — a key inverter design detail, documented in the report.
• [LC output filter] A series inductor and shunt capacitor low-pass filter attenuates the switching-frequency harmonics, leaving the 50 Hz fundamental at the output.
• [Overload and short-circuit shutdown] Output current sensing trips the bridge on overload, with a latched fault that needs a manual reset — demonstrating inverter protection behavior.
• [Battery low-voltage cut-off] The inverter shuts down when the DC input sags below the set threshold, protecting the battery from deep discharge, and restarts with hysteresis.
• [Live output readout] An LCD shows DC input voltage, AC output voltage and frequency, and fault status.

• Working sine-wave inverter prototype (Arduino, H-bridge, gate drivers, LC filter, transformer, sensors, LCD)
• Complete firmware source code (SPWM generation, dead-time, protections, LCD)
• Circuit and wiring documentation with filter design notes
• Component list with voltage/current ratings
• Tuning procedure (buyer-run: set modulation index, verify waveform on oscilloscope, set protection thresholds)
• Project report PDF (inverter topologies, SPWM theory, filter design, methodology, test procedure)
• PPT presentation for final review
• Viva Q&A preparation document (SPWM, modulation index, dead-time, LC filter, shoot-through)
• Setup and demonstration guide

• This is an academic demonstration prototype at modest power; it is not a UPS replacement and must not back-feed or parallel with mains supply under any circumstances.
• Output voltage regulation, waveform quality and efficiency are design targets verified by the buyer's own oscilloscope tests — nothing is pre-measured at build.
• The transformer and heatsinking size the practical demo load; sustained full-load running needs the thermal notes followed.
• Battery sizing and runtime are the buyer's selection; the report gives the calculation method rather than a claimed backup time.
• No galvanic output isolation beyond the transformer itself; standard bench high-voltage precautions apply during demo.