Working principle and scheme of three-phase motor programming control

This paper introduces a method of realizing a position sensorless drive of a surface mounted permanent magnet synchronous motor (SPMSM) by using the MC16C/28 series CPU products of Renesas Company and using 120o trapezoidal wave alternation to estimate the rotor position through the zero crossing point of the motor induced voltage .

Digital control of the speed and position of AC motors through frequency conversion technology and pulse width modulation technology is the development trend of motor control . Permanent magnet synchronous motor (PMSM) has the advantages of simple structure, small size, easy control and excellent performance. Using single chip microcomputer to digitally control the motor is the most common means to achieve digital control of the motor.

Motor Control

Figure 1 Three-phase motor drive

Figure 2 Block diagram of motor control hardware

Inverter control

Electrical energy (commercial power ) is generally provided through a power supply system. In this case, the voltage, frequency and phase of the commercial power are fixed at a precise level under strict control. If a commercial power supply is directly supplied to the motor load, an induction motor (IM) can be started, while a synchronous motor (such as a permanent magnet synchronous motor PMSM) cannot be started.

In the inverter control process, the commercial power supply is not connected to the load. A conversion device first converts the alternating current (AC) current into direct current (DC) power, and then an inverter converts the DC power into AC power in order to deliver AC power with the desired voltage and frequency to the motor. If the output voltage and frequency are controlled according to the load and disturbance, this will enable the synchronous motor to start and rotate and achieve energy saving.

Table 1 Control methods

Table 2 A/D conversion

Table 3 Interrupt functions

Induced voltage

Electric motors can act as generators. Therefore, when you connect a lamp to a motor and rotate the motor shaft, the lamp will glow. This is because an induced electromotive force is generated, and the voltage generated is called "induced voltage".

When the motor is stopped, no induced voltage is generated. Therefore, when the motor is started, it is forced to rotate in a certain direction to find the position of the rotor.

In the motor control using 180° sinusoidal wave alternation, the induced voltage generated in the motor cannot be directly monitored because the current flows continuously in the motor. Therefore, in the position sensorless control, the rotor position is estimated by the motor current.

Hardware and software specifications for motor control

Hardware composition

Surface mounted permanent magnet synchronous motor (SPMSM)
A/D converter
Three-phase PWM output
Zero point detection of induced voltage

The four-part block diagram is shown in Figure 2.

Software Features

The software controls are shown in Table 1.

Functional description of CPU and peripheral devices for motor control

A/D conversion

The A/D conversion description is shown in Table 2.

Three-phase PWM output

Sawtooth wave is used for modulation and three-phase mode 0 is adopted to realize 120o alternating drive motor.

In the 120° alternating trapezoidal wave, the speed is basically proportional to the voltage.

Zero-crossing detection of induced voltage in three-phase motor

In this software, the zero crossing point of the induced voltage is detected by configuring the external interrupt function according to Table 3.

Using trapezoidal wave alternation to realize the position sensorless type of SPMSM

Driver software description

The software describes how to use the 120° alternation of the trapezoidal wave to realize the sensorless drive of the SPMSM. Contents include:

(1) The rotor position is detected by the induced voltage in the motor and the rotation speed is controlled within the range of ±500 rpm~3000 rpm using a 120° trapezoidal wave.

(2) Description of the eight control modules.

A/D converter
Detection of induced voltage
Calculation of actual speed Calculation
of target speed
Calculation of PWN duty cycle
Determination of output mode
Initial startup processing
Other CPU monitoring and detection of system abnormality.

(3) Storage transformation of CPU registers

The CPU has 13 registers: data register, address register, frame register, interrupt table register, program pointer register, user stack pointer (USP) register, interrupt stack pointer (ISP) register, status register, flag register (carry flag register, debug flag register, 0 flag register, sign flag register, register group selection flag register, overflow flag register, interrupt enable flag register.) Stack pointer selection flag register, processor interrupt priority register, reserved domain register.

Storage transformations include:

Address allocation for linear address space, fixed interrupt vectors, internal RAM, SFR area, special page vectors, etc.
Used for storage conversion and segment configuration of this software

(4) Main software modules of the system

(5) Initial setting values ​​of SFR related to three-phase output

AD converter control register 0-2 settings
Motor induction voltage detection
Three-phase output PWM settings (24 registers)

(6) Implementing the SPMSM sensorless drive control process through 120° trapezoidal wave alternation

Main processing for realizing sensorless drive of SPMSM by 120° trapezoidal wave alternation
Initialization processing
PWM interrupt processing
Stop processing
Start processing
Normal processing
Actual speed calculation processing
Speed ​​command calculation processing
Bus Voltage calculation processing
Motor lock detection processing
Stop detection processing