ESC-S25

Firmware for a 3-phase brushless DC (BLDC) electronic speed controller (ESC), built for the ESP32 with ESP-IDF and the MCPWM peripheral. It drives a 6-PWM half-bridge gate driver with complementary outputs and hardware dead time.

Developed by the Electrium Mobility ESC team (Spring 2025).

Status: feature complete. Trapezoidal 120, sinusoidal and space-vector modulation, open-loop and hall-based closed-loop speed control, throttle input and a PID are implemented. The firmware has not been compiled or run on hardware yet, so expect to tune the gains and check hall wiring on the bench.

Features

• Three modulation schemes, switched with the global modulation: Trapezoid_120, Sinusoidal, Space_Vector (min/max injection, about 15% more usable voltage than plain sine).
• Open-loop speed control (VelocityOpenLoop) that integrates the angle from real elapsed time.
• Closed-loop speed control: hall sensors give position and speed, a PID sets the q-axis voltage.
• Potentiometer throttle on an ADC1 pin with filtering, deadband, start/stop hysteresis and an acceleration limit.
• Protection: phase voltage clamped to what the supply and modulation can deliver, gate driver enable pin, shutdown on invalid hall code or throttle release.

Control mode and tuning constants (pole pairs, speed limit, voltages, PID gains) are in main/inc/main.h. Set CONTROL_MODE to CONTROL_OPEN_LOOP or CONTROL_CLOSED_LOOP.

Architecture

flowchart TD
    T["Throttle pot<br/>SpeedInput"] --> M["main.cpp<br/>control_task"]
    HS["HallSensor"] --> M
    M --> P["PID<br/>speed loop"]
    P --> M
    M --> C["Motor controller<br/>SetPhaseVoltage"]
    C -- "Va, Vb, Vc" --> B["BLDC6PWMDriver"]
    B --> D["BLDC6PWMmcpwm<br/>MCPWM_set_duty"]
    D --> E["ESP32 MCPWM unit 0<br/>3 timers with dead time"]
    E --> F["6 PWM outputs"]
    F --> G["Gate driver and<br/>3-phase inverter"]
    G --> H(("BLDC motor"))
    H -. "hall signals" .-> HS

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Class structure

classDiagram
    class BLDCDriver {
        <<abstract>>
        +int pwm_freq
        +float voltage_limit
        +float voltage_power_supply
        +init()
        +enable()
        +disable()
        +setPwmVoltage(Va, Vb, Vc)
    }
    class BLDC6PWMDriver {
        +int pin_A_PWM_H
        +int pin_A_PWM_L
        +int pin_B_PWM_H
        +int pin_B_PWM_L
        +int pin_C_PWM_H
        +int pin_C_PWM_L
        +int pin_CAP0
        +int pin_CAP1
        +int pin_CAP2
        +int enable_pin
    }
    class PID {
        +float kp
        +float ki
        +float kd
        +update(error, dt)
        +reset()
    }
    class HallSensor {
        +init()
        +update()
        +getElectricalAngle()
        +getElectricalVelocity()
    }
    class SpeedInput {
        +init()
        +read()
    }
    BLDCDriver <|-- BLDC6PWMDriver

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Commutation (120° trapezoidal)

flowchart LR
    A["angle"] --> B["NormalizeAngle(angle + PI/6)"]
    B --> C["sector = 6 * angle / 2PI<br/>(0..5)"]
    C --> D["lookup trap_120_map[sector]<br/>+1 / -1 / 0 per phase"]
    D --> E["Vx = Vsupply/2 + map * Vq"]
    E --> F["driver.setPwmVoltage()"]
    F --> G["duty = 100 * V / Vsupply"]

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A hand-drawn flowchart is also in Motor FlowChart.drawio and ESC-S25/Untitled Diagram.drawio.

Repository layout

ESC-S25/
├── CMakeLists.txt            ESP-IDF project file
├── sdkconfig                 Target config (ESP32)
├── diagram.json, wokwi.toml  Wokwi simulation setup
├── scrap.cpp                 Scratch notes, not part of the build
└── main/
    ├── CMakeLists.txt
    ├── inc/                  Headers (main.h, PWM/, motor/, motor/drivers/, misc/)
    └── src/
        ├── main.cpp                         Entry point and control task
        ├── control/PID.cpp                  PID with anti-windup and ramp
        ├── sensors/HallSensor.cpp           Hall position and speed
        ├── input/SpeedInput.cpp             Throttle ADC input
        ├── PWM/BLDC6PWMmcpwm.cpp            MCPWM pin, timer and duty setup
        └── motor/
            ├── BLDC6PWMmotor_controller.cpp Modulation (trapezoidal 120)
            └── drivers/BLDC6PWMDriver.cpp   6-PWM driver

Pin map

Signal	GPIO	Signal	GPIO
Phase A high / low	18 / 19	Capture 0	26
Phase B high / low	21 / 22	Capture 1	27
Phase C high / low	23 / 25	Capture 2	32
Gate driver enable	4	Throttle (ADC1)	34

The capture pins double as the three hall sensor inputs. If the motor runs backwards in closed loop, swap two hall wires or set hall.reversed.

Pins are defined in main/inc/main.h.

Build and flash

Requires ESP-IDF v5.4.x.

cd ESC-S25
idf.py set-target esp32
idf.py build
idf.py -p <PORT> flash monitor

The MCPWM code uses the legacy driver/mcpwm.h API, which is deprecated in ESP-IDF 5.x but still supported. Do not mix it with the newer mcpwm_prelude.h API in the same firmware.

Safety

This drives power electronics. Test with a current-limited bench supply and no propeller or load attached first. Verify dead time on a scope before connecting a motor. There is no current or temperature sensing, so rely on the bench supply's current limit.