Low-power permanent magnet synchronous motor speed sensorless controller

In traditional AC vector transformation control systems, speed sensors are essential. For ordinary AC motors, the speed sensor has three functions: one is to obtain the speed feedback signal to realize the closed-loop control of the speed; the other is to add the slip angle frequency to obtain the stator current angular frequency reference value for frequency control; The third is to observe the rotor flux with a current model in the low-speed range and perform field-oriented control. If the vector control of the PMSM is implemented such that the direction of the stator current is spatially orthogonal to the direction of the magnetic flux generated by the permanent magnet, a position sensor is also needed to determine the rotor pole position, according to the position information, through the control circuit, with the correct phase and phase sequence. Power is supplied to the three-phase stator windings, and a constant torque is generated by the alternating stator currents, thereby achieving precise control of the system. Most of the detection of motor speed and magnetic pole position use mechanical sensors such as photoelectric encoders or resolvers. In practical applications, the following problems exist:

(1) High-precision speed sensors are expensive, and for some small-capacity devices, the cost of system development (including sensors and electronic circuits) is significantly increased.

(2) The speed sensor is difficult to install, and there is a problem of concentricity. Only in a specially machined motor can the problem be satisfactorily solved. In a general motor, the speed sensor often becomes the fault source of the system due to the installation problem. The mechanical robustness of the system is greatly reduced, which also brings difficulties to maintenance.

(3) The transmission of the speed signal is limited by the distance. If the distance is long, it will bring a lot of interference signals, so it is limited to some high-performance occasions, which greatly limits the application range:

(4) When selecting the frequency converter, the parameters of the speed sensor must be taken into account to make it match, and the interchangeability is poor;

(5) In the harsh environment, since most of the internal and output signals of the sensor are weak, the ability to resist electromagnetic interference is poor, and the effects of temperature, humidity, vibration, etc. may cause the performance of the sensor to be small and stable, and the accuracy of the detection is restricted. If a resolver is used, the speed and magnetic pole position information are obtained through signal processing, and the demodulation process is complicated, which increases the complexity of the hardware and software and the difficulty of the control strategy:

(6) All sensors produce a certain degree of static and dynamic friction on the drive shaft of the motor, and are attached to the motor shaft with a certain inertia.

The permanent magnet synchronous motor (PMSM) made of the third generation permanent magnet material NdFeB has the advantages of small size, light weight, low loss, high efficiency, flexible and diverse motor shape and size. Agricultural production, aerospace, defense and daily life are increasingly widely used. At the same time, China's rare earth resources are abundant. Therefore, research and development of high-efficiency rare earth permanent magnet synchronous motors, export of rare earth resources to high value-added rare earth permanent magnet motor products, Promote product structure adjustment and replacement in the motor industry and fan and pump industry, thus creating huge economic benefits. Therefore, the research and development of permanent magnet synchronous motor controller has good application value.

AVR microcontroller introduction and IRMCF341 chip

This program is intended to be implemented using ATMEL's ATmega64 microcontroller and IRMCF341, a high-performance home appliance with a sensorless sine wave motor control IC.

ATmega64:

High reliability, strong function, high speed, low power consumption and low price have always been an important indicator to measure the performance of single-chip microcomputers. It is also a necessary condition for the single-chip computer to occupy the market and survive.

The early MCUs were mainly due to low process and design level, high power consumption and poor anti-interference performance. Therefore, a conservative solution was adopted: the higher frequency division factor was used to divide the clock, which made the instruction cycle long and the execution speed slow. Future CMOS microcontrollers have adopted measures such as increasing the clock frequency and reducing the division factor, but this state has not been completely changed (51 and 51 compatible). Although some RISCs have been introduced here, they still follow the practice of clock division.

The introduction of AVR microcontroller completely breaks the old design pattern, abolishes the machine cycle, abandons the complicated instruction computer (CISC) and pursues the instruction completeness; adopts the reduced instruction set, uses the word as the instruction length unit, and the content-rich operands The opcode is arranged in one word (this is the case for most single-cycle instructions in the instruction set). The instruction fetch cycle is short, and the instruction can be prefetched to realize the pipeline operation, so the instruction can be executed at high speed. Of course, this speed increase is backed by high reliability.

Atmel's RISC microcontroller AVR, which was developed in 1997, has taken advantage of the PIC and 8051 series of microcontrollers, and has made some major improvements in the internal structure. The main advantages are as follows:

Built-in high-quality FLASH program memory, can be repeatedly erased and written, support ISP and IAP, easy to debug, develop, produce, update, embed long-life EEPROM, long-term preservation of critical data, to avoid loss of power. The large-capacity RAM on the chip not only satisfies the general use, but also supports the use of high-level language development system programs more effectively.

High speed, low power consumption, with SLEEP function. One instruction cycle of the AVR can be up to 50ns, while power consumption is between 1uA and 2.5mA. The AVR uses the Harvard architecture and the pre-fetching function of the first-stage pipeline, that is, different data buses are used for program read and data operations. Therefore, when an instruction is executed, the next instruction is pre-fetched from the program memory. This allows instructions to be executed every clock cycle.

Rich peripherals. AVR microcontrollers include SPI, EEPROM, RTC, watchdog timer, ADC, PWN and on-chip oscillator, which can be truly single.

Good anti-interference. There is a watchdog timer (WDT) safety protection to prevent the program from flying and improve the anti-interference of the product. In addition, the power supply anti-interference can be recorded very strong.

Highly confidential. The FLASH that can be programmed multiple times has multiple password protection lock (LOCK) function, so it can be quickly commercialized at low price, and the program can be changed multiple times (product upgrade), which facilitates system debugging without wasting IC or circuit board. Greatly improve product quality and competitiveness.

Strong driving ability. With high current: 10~20mA (output current) or 40mA (current sink), it can directly drive LED, SSR or relay.

Low power consumption. With six sleep functions, it can wake up quickly from low power modes.

Super-function reduced instructions. With 32 general purpose working registers (equivalent to 32 accumulators of 8051), it overcomes the bottleneck caused by single accumulator data processing.

The interrupt vector is rich. With 34 interrupt sources, different interrupt vector entry addresses are different and can respond quickly to interrupts.

High reliability. The AVR MCU has a power-on power-on counter. When the system RESSET is reset and powered up, the internal RC watchdog timer can be used to delay the MCU from officially starting the program after the system power supply and external circuit have stabilized, thus improving the system operation. Reliability, while also saving additional reset delay circuits. In addition, the built-in power-on reset (POR) and power-drop detection (BOD) also improve the reliability of the microcontroller.