SPWM on ESP32

Sine Pulse Width Modulation (SPWM) is a technique used to generate a sinusoidal AC waveform from a DC supply. On the ESP32, the built-in LEDC (LED Controller) peripheral is ideal for generating high-resolution PWM signals.

The core idea is to vary the duty cycle of a high-frequency PWM signal sinusoidally over time. By filtering this PWM signal (e.g., with an LC filter), a smooth sinusoidal voltage can be obtained.

How it Works:

• Modulation Index (Ma): Controls the amplitude of the output sine wave. A higher `Ma` (up to 1.0) results in a larger output voltage.
• Output Sine Wave Frequency: The desired frequency of the generated AC waveform (e.g., 50 Hz or 60 Hz).
• Number of Samples per Sine Cycle: Determines the number of discrete duty cycle values that approximate one full sine wave. A higher number of samples leads to a smoother sine wave and reduced harmonic distortion, but requires more memory for the lookup table.
• PWM Carrier Frequency: This is the frequency at which the PWM pulses themselves are generated. A higher carrier frequency results in a smaller ripple voltage and allows for smaller output filter components. The ESP32 LEDC can operate at very high frequencies.
• PWM Resolution (bits): Defines the number of distinct duty cycle steps available. For example, 10-bit resolution means 1024 (0-1023) possible duty cycle values. Higher resolution means finer control and better sine wave fidelity.
• GPIO Pin: The physical pin on the ESP32 where the PWM signal will be output.

Code Structure:

The generated code utilizes the ESP32’s LEDC driver.
1. A lookup table is pre-calculated based on the sine wave parameters (Modulation Index, Samples, Resolution). 2. In `setup()`, the LEDC channel is configured with the chosen PWM carrier frequency and resolution, and then attached to the specified GPIO pin. 3. In `loop()`, a timer-based mechanism (using `micros()`) is used to iterate through the lookup table at a rate that produces the desired output sine wave frequency. For each step, `ledcWrite()` is called to update the duty cycle.
This code generates a **unipolar PWM signal**. For driving a full H-bridge (to get a bipolar AC output), you would typically use this signal for one leg and a complementary signal (or another phase-shifted SPWM) for the other leg.

Note: This code provides a basic SPWM implementation. For real-world applications, consider adding dead-time insertion for H-bridge drivers, current/voltage feedback loops, overcurrent protection, and more robust timing mechanisms (e.g., hardware timers for precise sample updates).