The ESC is like an intermediate regulator between the battery and the motor. It controls the speed of the motor through time-controlled electrical signals. It can also convert the DC power from the battery into the three-phase AC power required by the motor through the switch system.
The throttle control of a vehicle can be used to change the rotation of an electric motor, whether it is an electric car, a plane, or a drone. Increasing the throttle increases the output power of the motor, which changes the rate at which the switch in the ESC circuit opens and closes.
At present, the commonly used protocols of ESC are: PWM, Oneshot, Multishot and Dshot. The main difference between these protocols is that the signals they transmit use different frequencies. The higher the frequency of the signal, the better the maneuverability of the drone. In addition, the Dshot protocol differs from other protocols in that it sends a digital signal instead of an analog signal, which is inherently less sensitive to electrical noise, making the signal more accurate and with higher resolution, which we will discuss in more detail later in this article. Introduce this.
【ESC components】
There are many important components within an ESC, including microcontrollers, gate drivers, MOSFETs, and in some cases battery equivalent circuits and device management adapters.
(1) Microcontroller (MCU)
The microcontroller has three main functions in the operation of the ESC:
Acts as a firmware carrier to parse the signals from the controller and feed the parsed signals into the control loop.
Track the position of the motor and make sure it accelerates smoothly.
Send a pulse signal to the gate driver to implement the desired command.
The firmware used in ESCs is usually pre-installed by the manufacturer, and open source versions are also available from third parties. The pre-installed firmware in hobby drones is usually a variant of BLHeli (BLHeli_S or BLHeli_32), but other software such as SimonK and KISS can also be used. But the firmware must be compatible with its hardware as it will determine the performance of the ESC as well as the supported application protocols.
The microcontroller can also determine the position of the motor through a sensored or sensorless system. The sensing system uses electronic sensors in the motor to track the position of the rotor, which works well for low-speed, high-torque applications such as ground vehicles. More widely used sensorless systems use back EMF to determine the position of the rotor relative to the stator. This works well in high-speed scenarios, but once the motor turns at a lower speed and the back EMF is small, the sensorless system will not work properly. For propeller applications there are generally not too many problems, especially high-speed applications, and sensorless systems are more efficient, cheaper, and more reliable.
(2) Gate driver
The role of the gate driver is to act as a middleman between the controller and the gate of the MOSFET. After receiving the low voltage signal from the microcontroller, the gate driver amplifies the signal and transmits the high voltage signal to the MOSFET. The gate driver has lower resistance than the microcontroller and can therefore supply higher currents, thereby amplifying the speed of the signal. This allows for faster switching and lower heat generation. Some ESCs have an insulating optical chip between the low-voltage microcontroller and the high-voltage transistor, which we generally call an Opto-ESC.
(3) Field effect transistor
Metal-oxide-semiconductor field-effect transistors, or MOSFETs, are selective switches that power motors. The ESC has a total of six of these transistors, and each wire from the motor goes to two of them. The MOSFET receives a signal from the microcontroller and then powers the motor to put each coil in one of three phases: high voltage, low voltage, or off/ground.
As the motor spins, a signal from the MOSFET switches the phase of the coil, keeping the rotor spinning. ESCs use direct current coupled with a switching system to provide alternating three-phase currents. The higher the throttle input, the faster the switching frequency, which makes the motor rev higher. There are a variety of signaling protocols currently supporting the control of the above process, each with different capabilities and signaling frequencies.
(4) Battery Eliminator Circuit
ESCs typically have a built-in battery canceller circuit (BEC), which instead of eliminating the need for a battery, provides the functionality of a voltage regulator to eliminate the need for a separate battery for integrated electronics. Power through the BEC is dropped to a lower voltage, typically 5V, to safely power the throttle receiver and any other electronics of the integrated system.
(5) Device Management Adapter (DMA)
A Device Management Adapter (DMA) helps users connect their ESC to a computer to download firmware and update it to use advanced programming options to customize their device. This keeps the ESC always up to date, while providing advanced settings features such as voltage cutoff, throttle calibration mode, and motor direction.
A Device Management Adapter (DMA) is usually a feature only available on certain brands of ESCs and is not available for all ESCs.