Based on the analysis of the mathematical model of elevator asynchronous motor in synchronous rotating coordinate system when iron loss is considered, the optimal control of vector-controlled variable frequency speed regulating asynchronous motor is realized by studying the relationship between motor loss and rotor flux linkage under different operating conditions. In order to further improve the speed regulation performance of motor, according to the basic principle of motor vector control, the hardware implementation of vector control is given by using digital signal processor and intelligent power module, and the software implementation method of the system is expounded. Experiments show that the vector control variable frequency speed regulation system of asynchronous motor for elevator runs smoothly, has good static and dynamic characteristics, and can be widely used in the electric drive system driven by motor for elevator.
Keywords: asynchronous motor for elevator; Vector control; Iron loss; optimal control
Optimal control of VVVF speed regulating motor for elevator
Based on DSP& inches per minute (abbreviation of inches per minute)
Introduction to 0
With the development of urban construction industry, the requirements for elevator motor speed regulation system in high-rise buildings are getting higher and higher. Due to the limitation of digital analysis methods and tools, iron loss is usually ignored when establishing the dynamic mathematical model and simulation model of asynchronous motor for elevator. The asynchronous motor for elevator does have iron loss, which will make the output torque deviate and affect the control accuracy [1]. At the same time, the realization of vector control needs to complete many functions in real time, such as coordinate transformation, current and speed detection, flux estimation, PWM signal generation and fault protection, so the control algorithm involves a lot of real-time calculations. In the past, the realization structure of this high-performance asynchronous motor control system for AC elevators was quite complicated [2]. In recent years, due to the progress of microelectronics and computer technology, especially the appearance of digital signal processor (DSP) and intelligent power module (1PM) with powerful computing power, it is possible to design a vector system with simple structure. In this paper, the hardware composition of vector control system and the software design method of optimization algorithm are described in detail. The experimental results show that the vector control system has excellent dynamic and static speed regulation performance, and it is a speed regulation system with strong real-time performance and excellent performance at present. Frequency conversion speed regulating elevator has the advantages of energy saving, fast lifting speed, accurate leveling and good comfort, which provides power guarantee.
1 control principle
1. 1 Mathematical model of asynchronous motor for elevator considering iron loss in dq axis of synchronous rotating coordinate system.
According to the theory of AC motor, the asynchronous motor for elevator can be equivalent to a two-phase motor model on the dq axis of synchronous rotating coordinate system through coordinate transformation. Compared with the conventional dq-axis motor model, two equivalent windings of iron loss are added to the stator, so that the equivalent circuit of asynchronous motor in synchronous rotating coordinate system with iron loss considered as shown in figure 1 can be obtained [3].
Figure 1 dq axis equivalent circuit of asynchronous motor considering iron loss in synchronous rotating coordinate system
Let the rotational speed of the dq axis be equal to the synchronous angular velocity ω 1 of the stator, the angular velocity ω r of the rotor, and the angular velocity ω s of the DQ axis relative to the rotor = ω1-ω r, that is, slip. Then, according to the above equivalent circuit, the mathematical model of asynchronous motor in arbitrary two-phase synchronous rotating coordinate system is deduced:
Equations (a) ~ (e) constitute a dynamic mathematical model of asynchronous motor in any synchronous rotating coordinate system when iron loss is considered.
1.2 flux optimization module
Because the total loss of the motor is equal to the difference between the input power and the output power, that is
From the above formula, it can be seen that the controllable loss of asynchronous motor is related to the magnitude of rotor flux linkage at a certain rotor angular frequency and a certain load torque Te, assuming that the motor parameters are unchanged. Ignoring mechanical loss and stray loss, the efficiency of asynchronous motor is the highest when the output power is constant [4].
The convex function of loss, so the derivative of the above formula is equal to zero, and the optimal magnetic flux with minimum loss can be obtained; In ...
2 based on DSP &；; System hardware design of intelligent power module
The hardware structure of the elevator asynchronous motor vector control system is shown in Figure 2. The whole system mainly consists of three modules: the main circuit power conversion module with the intelligent power module PS2 1867 as the core; An operation control module with DSP as the main component; The signal detection module consists of an incremental photoelectric encoder and a Hall sensor.
Hardware structure diagram of elevator asynchronous motor vector control system.
2. 1 power conversion module
The main circuit of the system adopts AC -DC- AC voltage source frequency conversion and transformation circuit. The inverter power supply device adopts the IPM(PS2 1867) of Mitsubishi's small dual in-line package format. This new DIP-IPM adopts the latest fifth-generation IGBT technology, which greatly improves its static and dynamic performance. And because of the most advanced sub-micron power chip design technology and optimized module design technology and packaging technology, it can not only be directly connected to the control MCU and bootstrapped by a single power supply, but also effectively change its input logic from low level to high level. Thereby greatly simplifying the interface circuit design and improving the cost performance of the inverter system.
2.2 Operation control unit
The control system is controlled by digital signal processor TMS320F2407A. TMS320F240 is a new generation microcontroller specially designed for motor control. It has a high-performance C2xLP kernel with the highest computing power of 40MIPS, and adopts an improved Harvard structure and four-stage pipeline operation. The on-chip integrated event manager includes three independent bidirectional timers, each of which has an independent comparison register, which supports PWM output that produces programmable dead zone; Two of the four capture ports can be directly connected with orthogonal coded pulses from photoelectric encoders; Two independent 10-bit 16 A/ D converters can complete the conversion of two analog inputs simultaneously and in parallel; On-chip integrated serial communication interface (SCI) and serial peripheral interface (SPI) can be used to communicate with hosts, peripherals and multiprocessors. These outstanding characteristics of TMS320F240 provide an ideal solution for high-performance motor control [2].
2.3 signal detection module
Because the controlled motor adopts star connection, it is only necessary to detect the two-phase current () [2]. Considering the conversion speed and accuracy, the system uses Hall sensor to measure the stator currents ia and ib of the motor, converts ia and ib into voltage signals, and then sends them to level conversion circuit, converts bipolar current signals into 0-3.3 V unipolar level, and sends them to A/D conversion ports ADCIN2 and ADCIN3 of TMS320LF2407A for sampling, then converts analog signals into digital signals, and then carries out data processing. The detection circuit adopts two-stage operational amplifier LM358. In the speed sampling system, an incremental encoder with the accuracy of 1024p/r is used to detect the rotor position, and two orthogonal pulse signals output by the photoelectric encoder are directly connected to QEP 1 and QEP 2 of DSP after differential amplification.
Software implementation of the system
After using intelligent power module, the main circuit of the system is relatively simple, and all control algorithms can be completed in real time in TMS320LF2407A DSP. The software of LF2407A DSP control part of the system is written in assembly language under the DSP integrated development environment CCS. The whole software mainly includes initialization program and underflow interrupt service subroutine. Its software structure is shown in Figure 5 and Figure 6. Initialization program completes the initialization of DSP hardware and software variables, and enables interrupts. Interrupt service program consists of several functional modules, such as current and speed detection signal processing, speed and flow adjustment, flow estimation, coordinate transformation, PWM signal generation and so on. Each functional module is executed in a fixed time period according to a certain sequence relationship, and the program is started by the overflow interrupt of T 1CNT.
Fig. 3 flow chart of initialization program
Fig. 4 Flow chart of underflow interrupt service subroutine
3. Design of1pi regulator
PI regulation is the most commonly used controller in motor control system. The purpose of the regulator is to eliminate the deviation between the output and the input. The algorithm after digital discretization is as follows:
Where KP is proportional gain, KI is integral gain and t is sampling time. Its principle is shown in Figure 5.
Fig. 5 PI regulator for preventing integral saturation
3.2 Optimization of controller design
The purpose of optimizing the output of the controller is to improve the efficiency of the program. The mixed programming of C and assembly is adopted, and the subroutine of division and extraction is written in assembly language. Firstly, the optimal magnetic flux is obtained, and then the optimal excitation current is obtained according to the steady state.
3.3 Calculation of Rotor Flux Position
The control performance of vector control system depends largely on the precision of magnetic field orientation. The system uses the current speed model in the rotor flux coordinate system to estimate the rotor flux position angle, so as to realize the correct magnetic field orientation. The equation of flux observation model is: where is rotor time constant, Fs is the ratio of rotor flux angular frequency to rated angular frequency, ωn is electrical rated angular frequency, and n is the ratio of actual rotor speed to rated rotor speed.
3.4 SVPWM module
Each event manager of TMS320LF2407A has three complete comparison units, which can output six PWM waveforms with programmable dead zones. When the component and sector number of stator phase voltage vector are known, PWM control signal can be generated by voltage space vector SVPWM technology to control the inverter.
4 experimental results and analysis
The experimental prototype is a 2.2KW variable frequency drive elevator vector control asynchronous motor speed regulation system, and its steady-state operation experiment is carried out by using efficiency optimization control strategy.
In this experiment, the motor runs at no load, and the initial speed is set to 1600 r/min, and after stable operation, 1.4s is set to 1400 r/min. Figs. 6 and 7 are experimental waveforms of output line current and output line voltage, respectively.
Figure 6 Output Line Current
Figure 7 Output Line Voltage
It can be seen from the experimental results in Figures 6 and 7 that the output current is a good sine wave and the output voltage is a pulse width modulated sine wave. The fundamental wave is the absolute main component, and the harmonic component is less. The effectiveness and feasibility of the control method proposed in this paper are proved.
5 conclusion
On the basis of analyzing the mathematical model and flux optimization algorithm of asynchronous motor considering iron loss, a vector control variable frequency speed regulation system based on DSP and IPM is designed, which effectively solves the real-time problem caused by excessive calculation in actual vector control implementation. The control system has the advantages of simple hardware structure, stability and reliability, fast dynamic response and high control accuracy. It is an ideal vector control scheme, which can be widely used in electric drive with elevator motor as driving device, so as to obtain high-precision speed control performance and provide power guarantee for elevator energy saving, fast lifting speed, accurate leveling and good comfort.
refer to
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Wang Xiaoming, Wang Ling. DSP control of motor [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2004.
[3] Mars, Shi Weiguo. Study on operating efficiency and energy-saving control of variable frequency motor [J]. Electric drive automation,1999,21(1): 21-25.
Cui Naxin. Research on fast response control of asynchronous motor driven by frequency conversion with minimum loss [D]. Shandong: School of Control Science and Engineering, Shandong University, 2005.