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Want your drone to fly more stably and longer? It is enough to read this article

ESC module is a very important subsystem in non military UAV; If the user needs the operator to learn to find and eliminate the problem, the following analysis is made on the problem: to achieve a more efficient model with longer flight time, better dynamic behavior and smoother and more stable performance, it is very suitable to use this kind of module. Ti adopts electronic governor (ESC), which is usually used in unmanned aerial vehicles (UAVs) or unmanned aerial vehicles

speed control is completed by sensorless method, and the electric frequency of the motor is as high as 1.2kHz (12krpm for 6-pole motor) using FOC speed control technology

the high-speed sensorless FOC reference design of UAV ESC has the first-class implementation of FOC algorithm, which can achieve longer flight time, better dynamic performance, and higher integration, so the circuit board size is smaller and the BOM components are fewer

the sensorless high-speed FOC control technology uses ti's fatm software observer, using instaspin motion TM c2000tm launchpadtm and drv8305 boosterpacktm

features

instaspin foc ™ Sensorless FOC can achieve higher dynamic performance. Tested up to 12000 RPM (using 3 lithium polymer batteries)

high dynamic performance: reach 1 krpm to 10 krpm (electrical frequency 100Hz to 1kHz) speed in less than 0.2S, which can realize high-performance deflection and pitch action

fast turnover ability suitable for completing turnover action

due to higher FOC efficiency on block switching, longer flight time can be achieved

higher PWM switching frequency (tested as high as 60KHZ) can reduce current/torque ripple for low inductance high-speed motors and avoid ultrasonic sensors

due to the automatic motor parameter identification of instaspin FOC, the time to market is shortened: automatically tune the sensorless FOC solution

the motor temperature is estimated according to the change of winding resistance to protect the motor from damage under temporary overload

application fields

UAV and UAV

high speed motor

battery powered power tools

1 System description

for UAV, the different subsystems included in the complete UAV flight system usually involve the following module definitions

UAV flight system module

(1) ESC functional requirements of UAV

esc defines the dynamic motion performance and flight time of UAV. Some motion modes that the UAV must be able to complete include:

precise motion mode: navigation, hovering

fast motion mode: 360 ° rotation in the x/y/z direction, horizontal maximum speed flight, vertical maximum speed flight

in order to provide these functions, it is necessary to use excellent ESC to control the lift generated by the motor at all speeds. In this way, the stabilization algorithm based on the position sensor module can compensate the vibration and external forces that affect the UAV

the faster the motor speed that can be changed, the less the speed change that the stability algorithm needs to execute; Therefore, the energy used is less than that required when the UAV operates at a highly variable speed (this is the case when using the less dynamic ESC)

(2) sinusoidal control ESC module

measures the magnetic field angle of the rotor with a minimum accuracy of 1 to 5 degrees, so as to use FOC algorithm to ensure the maximum torque, or estimate the rotor magnetic angle according to the phase voltage and phase current of the motor (sensorless algorithm)

the figure below shows the typical PWM high side and low side graphics of three phases, and shows the corresponding ideal filtered phase voltage after eliminating PWM carrier when running the motor in sinusoidal control mode

generate ideal PWM sinusoidal phase voltage

in open-loop control, the synchronous motor (BLDC or blac) is blindly driven by the control signal, and it is assumed that the motor will follow the specified control action

in order to ensure the correct operation of the motor, it is necessary to apply a current greater than the ideal current on the winding to force the movement. Finally, this is the main reason why the efficiency of the open-loop control motor is lower than that of the closed-loop control motor

in closed-loop control, the motor control system can test whether the motor operates as expected. If it cannot operate as expected, the control loop will automatically compensate by machining 1 inspection rod to reduce or increase the current

whether closed-loop control or sensorless algorithm is used, current and voltage signals must be measured in order to use these signals as feedback signals

for sinusoidal control, a maximum of three shunt currents should be measured. When measuring voltage, you should choose whether to measure DC link voltage only or measure three-phase voltage and DC link voltage at the same time

(3) electronic governor (ESC)

the engine running speed of the UAV must be determined according to the weight of the UAV and the size of the propeller, so as to generate the lift required for the UAV flight. The typical three-phase brushless motor designed for UAV has the following common characteristics:

low inductance

low resistance

two to eight pole pairs

1000Hz or higher electrical frequency

the motor is optimized and can be powered by a Keng polymer battery containing two to six batteries (i.e. 7.4v to 22.2v DC voltage). These voltages are used to design the maximum speed of the selected motor

a common problem here is to run the motor close to VEUs at the maximum speed, because the FOC algorithm and sensorless algorithm here must be excellent enough to support this operation mode

the ESC used in this report is applicable to three-phase brushless motor using sensorless algorithm. The components of the ESC module are shown in the figure below

block diagram of UAV ESC

2 System specification

this system requires a three-phase half bridge power level with sensing ability in order to generate the feedback signal required by the sensorless algorithm

this power level must be powered by a Keng polymer battery containing two to six batteries (i.e. VEUs is 7.4v to 22.2v)

because the motor and the frequency dependent sensor have lower time constants, the PWM frequency is higher; Typical current designs use PWM frequencies of about 45khz to 60KHZ, and there is a trend of further increase. Secondly, it needs a way to communicate with the flight controller, which can be completed by using duty cycle or serial communication

3. Principle block diagram

system block diagram

4 Core device

(1) TM s320f2806xf

f2806xf piccolotm series microcontroller (MCU) integrates the performance of c28x core and control law accelerator (CLA) with highly integrated control peripherals into low pin count devices

an internal voltage regulator realizes single power rail operation. The high-resolution pulse width modulator (hrpwm) module has been strengthened to realize double edge control (frequency modulation). The device also adds an analog comparator with 10 bit internal reference, which can be directly connected to control the epwm output

a3. The ground around and at the bottom of the fuselage should be kept clean at all times. DC can be converted within a fixed full-scale range of OV to 3.3V, and supports proportional vrefhi/vreflo benchmarks. ADC interfaces have been optimized for low overhead and latency

the device includes special motor control software in the ROM dedicated for execution to realize the instaspin FOC solution, and provides system software support through motorware

(2) drv8305

drv8305 is a gate driver IC suitable for three-phase motor drive applications. The device provides three half bridge drivers with high-precision trimming and temperature compensation. Each driver can drive a high side and low side enhancement mode n-channel MOSFET

drv8305 has three current detection amplifiers based on current devices, which can realize accurate current measurement, support 100% duty cycle, and have multi-level protection. The gate driver can be programmed through serial peripheral interface (SPI)

(3) lmr16006

the PWM DC/DC step-down regulator has a wide input voltage range of 4V to 60V, which is suitable for the power regulation of non regulated power supply in a wide range of applications from industry to automobile. The standby current of the regulator in eco mode is 28 μ a. It is very suitable for battery powered systems

(4) csd18540q5b

this 60V 1.8m ω son 5mm × 6mm nexfet ™ Power MOSFET can be used to minimize losses in power conversion applications

BOM

b

the following figure shows the top and bottom pictures of launchpad and boosterpack PCB respectively

picture of complete system circuit board (top view)

picture of launchpad circuit board (top view)

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