阅读说明：本技术 一种感应电机恒压频比调速系统的能效优化方法 (Energy efficiency optimization method of constant-voltage frequency ratio speed regulation system of induction motor ) 是由 夏加宽 梁宗伟 宋孟霖 刘思琪 张子璇 于 2020-11-17 设计创作，主要内容包括：一种感应电机恒压频比调速系统的能效优化方法,它是在感应电机考虑铁耗的数学模型的基础上,分析转矩输入功率比与感应电机控制系统中转速和转差关系的表达式,并求出转矩输入功率比最大时对应的最优转差频率,用这个最优转差频率来调节电机的运行,达到提高电机运行能效水平的目的与传统的最优转差计算方法相比,本方法考虑更全面,既考虑了感应电机中铁耗的影响,又通过一定负载转矩下使电机输入功率最小,来达到减小电机损耗的目的。提高了电机的能效水平,增强了系统的稳定性和抗干扰能力,而且易于实现。(The energy efficiency optimizing method for constant voltage-frequency ratio speed regulating system of induction motor is characterized by that on the basis of mathematical model of iron loss of induction motor the expression of relationship between torque input power ratio and rotating speed and slip in induction motor control system is analyzed, and the optimum slip frequency correspondent to maximum torque input power ratio is obtained, and said optimum slip frequency can be used for regulating operation of motor so as to attain the goal of raising energy efficiency level of motor operation. The energy efficiency level of the motor is improved, the stability and the anti-interference capability of the system are enhanced, and the system is easy to realize.)

1. An energy efficiency optimization method of a constant voltage-frequency ratio speed regulation system of an induction motor is characterized by comprising the following steps: the method comprises the following steps:

firstly, starting a motor at a constant voltage-frequency ratio K, and setting the rotating speedWith the actual speed omega_rAfter passing through the PI regulator, the difference is added with the actual rotation speed to obtain the synchronous rotation speed omega₁；

Second, synchronous speed omega₁Obtaining the voltage amplitude U at the moment through a voltage-frequency ratio calculation module_s；

Thirdly, calculating a compensation voltage U'_sI.e. the above-mentioned U_sAfter voltage compensation, with omega₁The value of the voltage is sent to a PWM module, and the PWM module modulates pulse voltage meeting the control requirement and inputs the pulse voltage to the motor.

2. The energy efficiency optimization method of the constant voltage-frequency ratio speed regulating system of the induction motor according to claim 1, characterized in that:

calculating the compensation voltage in the third stepU′_sThe method comprises the following steps:

the second step obtains the voltage amplitude U at this time_sSending the real-time rotating speed of the motor into an optimal slip calculation module to calculate the current optimal slip Making a difference with the real-time slip of the motor, sending the difference value into a compensation voltage PI regulator, and calculating a compensation voltage U'_s。

3. The energy efficiency optimization method of the constant voltage-frequency ratio speed regulating system of the induction motor according to claim 2, characterized in that:

calculating the current optimum slipThe calculation formula of (A) is as follows:

wherein ω is_rIs the rotor speed angular frequency; r_s、R_rAnd R_mRespectively a stator resistor, a rotor resistor and an iron loss equivalent resistor; l is_s、L_r、L_mThe self inductance and mutual inductance of the stator and the rotor are respectively.

4. The energy efficiency optimization method of the constant voltage-frequency ratio speed regulating system of the induction motor according to claim 3, characterized in that:

based on the principle of maximum torque to input power ratio, the ratio of torque to input power considering iron loss is expressed as:

wherein:

and orderCalculation formula for obtaining optimal slip

Wherein the torque equation: t is_e＝Aω_sli_sd ²The motor input power equation: p_input＝u_sdi_sd+u_sqi_sq；ω_sl＝ω₁-ω_rIs the angular frequency of the rotation difference; omega₁Is the synchronous rotational speed angular frequency; i.e. i_sdIs the d-axis stator current; i.e. i_sqIs the d-axis rotor current; u. of_sd、u_sqThe dq-axis stator voltages, respectively; n is_PIs the number of pole pairs of the motor; l is_s、L_r、L_mThe self inductance and mutual inductance of the stator and the rotor are respectively.

Technical Field

The invention belongs to the technical field of alternating current induction motors and control thereof, and particularly relates to an energy efficiency optimization method of a constant-voltage frequency ratio speed regulation system of an induction motor under the limitation of multiple conditions.

Background

The variable-frequency speed regulation method of the alternating current motor mainly comprises a constant-voltage frequency ratio and a variable-voltage variable-frequency, and the variable-voltage variable-frequency speed regulation method is divided into vector control and direct torque control. The speed regulating system adopting the constant-voltage frequency ratio is widely applied due to the simple principle, easy realization of software and hardware, convenient maintenance and capability of meeting the performance requirement of dragging loads.

The principle of constant voltage frequency ratio control of induction motors is that the ratio of stator voltage to current frequency needs to be kept constant when the motor is operated below fundamental frequency. When speed is required to be adjusted, the voltage amplitude input by the stator is adjusted according to the angular frequency and the specific value corresponding to the rotating speed, and then the alternating current speed adjustment of the induction motor can be realized through PWM modulation according to the frequency and the voltage amplitude.

The induction motor operating range is generally divided into two parts: a constant torque zone and a constant power zone. The constant torque area means that the running frequency of the motor is below the fundamental frequency, the exciting current of the motor keeps constant when the motor runs in the area, and the motor can output constant electromagnetic torque; when the motor operates above the fundamental frequency, the voltage can not be increased any more due to the limitation of the motor design and the input voltage, and the product of the torque and the rotating speed, namely the power, is kept constant.

The constant voltage frequency ratio control speed regulating system of induction motor usually adopts the slip control system of rotational speed closed loop to control the motor. In the control system, the operation of the motor can be adjusted by adjusting the control quantity of the slip, so that the energy efficiency level of the motor is improved. The literature provides an energy efficiency optimization control strategy for optimal slip by analyzing the relationship between the motor rotation speed, slip and motor efficiency based on a mathematical model of an induction motor. However, this method does not consider the iron loss parameter of the motor, only takes the efficiency of the motor as an optimization target, neglects the loss of excitation heating of the motor, and these problems make the actual energy efficiency optimization effect not ideal.

Disclosure of Invention

Aiming at the existing problems, the invention provides an energy efficiency optimization method of a constant voltage frequency ratio speed regulating system of an induction motor by combining a mathematical model of the induction motor considering iron loss, which is characterized in that on the basis of the mathematical model of the induction motor considering iron loss, an expression of the relation between the torque input power ratio and the rotating speed and slip in an induction motor control system is analyzed, the optimal slip frequency corresponding to the maximum torque input power ratio is solved, the operation of the motor is regulated by using the optimal slip frequency, and the aim of improving the operation energy efficiency level of the motor is fulfilled.

In order to realize the energy efficiency optimization effect of the induction motor, the invention provides an energy efficiency optimization method of a constant voltage-frequency ratio speed regulation system of the induction motor, which comprises the following steps:

the motor is started at a constant voltage-frequency ratio K and at a given rotating speedWith the actual speed omega_rAfter passing through the PI regulator, the difference is added with the actual rotation speed to obtain the synchronous rotation speed omega₁At this time, the voltage amplitude is: u shape_s＝K×ω₁，U_sAnd omega₁The value of the voltage is sent to a PWM module, the PWM module modulates pulse voltage meeting the control requirement and inputs the pulse voltage to the motor, and when the motor reaches steady state operation for a period of time, an optimal slip energy efficiency optimization module is started.

Wherein the value of the pressure-frequency ratioU_sNIs the rated voltage, omega, of the motor_1NIs the nominal synchronous speed of the motor.

The optimal slip energy efficiency optimization module has the functions of calculating the optimal slip angular frequency according to the operation parameters of the motor, and outputting compensation voltage U through a PI regulator after the optimal slip angular frequency is differed from the actual slip angular frequency_sAfter the compensation voltage is input into the PWM module, the calculation formula of the optimal slip is as follows:

the specific technical effects of the invention are embodied as follows:

1) the energy efficiency level of the induction motor during the operation of the constant voltage-frequency ratio speed regulating system is improved, the optimal slip angular frequency is calculated in a mode of inputting the power ratio through the maximum torque, and the optimal slip angular frequency is converted into the compensation voltage, so that the energy efficiency optimization of the induction motor during the operation is realized.

2) The stability and the anti-interference capability of the constant voltage frequency ratio control system of the induction motor are enhanced, the control system is easy to realize in software and hardware, the cost is low, and the effect is obvious.

In general, compared with the traditional optimal slip calculation method, the method has more comprehensive consideration, not only considers the influence of iron loss in the induction motor, but also achieves the purpose of reducing the loss of the motor by minimizing the input power of the motor under certain load torque. The energy efficiency level of the motor is improved, the stability and the anti-interference capability of the system are enhanced, and the system is easy to realize.

Drawings

FIG. 1 is a schematic diagram of a constant voltage frequency ratio speed control system for an induction motor based on a maximum torque input power ratio;

FIG. 2 is a flow chart of the operation of the constant voltage to frequency ratio governor system of the induction motor based on the maximum torque to input power ratio;

fig. 3 is an experimental waveform diagram of the method.

Detailed Description

In order to clearly and clearly show the objects, technical solutions and effects of the present invention, the present invention will be further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, in the embodiments of the present invention described below, the technical features may be combined with each other as long as they do not conflict with each other.

In order to improve the energy efficiency level of a constant voltage frequency ratio control system of an induction motor, the invention provides an optimal slip calculation method based on a maximum torque input power ratio.

When the induction machine takes into account iron time, the mathematical model in the dq coordinate system is as follows:

voltage equation:

current equation:

the flux linkage equation:

the torque equation:

the motor input power equation: p_input＝u_sdi_sd+u_sqi_sq (5)

In the formulae (1) to (5), ω₁Is the synchronous rotational speed angular frequency; omega_rIs the rotor speed angular frequency; omega_sl＝ω₁-ω_rIs the angular frequency of the rotation difference; r_s、R_rAnd R_mRespectively a stator resistor, a rotor resistor and an iron loss equivalent resistor; l is_s、L_r、L_mThe self inductance and mutual inductance of the stator and the rotor are respectively; l is_ls、L_lrRespectively determining leakage inductance of the stator and the rotor; i.e. i_sd、i_sq、i_rd、i_rqStator and rotor currents of dq axes, respectively; i.e. i_Rmd、i_RmqThe dq axis iron loss equivalent currents are respectively; i.e. i_Lmd、i_LmqAre dq-axis excitation currents, respectively; u. of_sd、u_sqThe dq-axis stator voltages, respectively; psi_sd、ψ_sq、ψ_rd、ψ_rqRespectively a dq-axis stator-rotor magnetic chain, n_PIs the pole pair number of the motor.

When the coordinate system is rotor field oriented and in steady state operation:

the formula (6) can be substituted into the formulae (1) to (5):

u_sd＝R_si_sd (9)

T_e＝Aω_sli_sd ² (12)

wherein the content of the first and second substances,

according to equations (9) - (10), the input power of the motor can be expressed as:

wherein:

according to equations (12) and (13), the ratio of torque to input power is:

from equation (14), the ratio of torque to input power is a function of the motor speed and the slip angular frequency when the motor is operating steadily. When the torque and the speed of the motor are constant, namely the output power is constant, the lower the input power is, the lower the loss power is, and the higher the energy efficiency level of the motor is. It follows that an optimum slip angular frequency is determined so that the losses at the load torque are minimal, i.e. so that the torque-to-power ratio is maximal.

Order toThe following can be obtained:

by analyzing a mathematical model of the induction motor in a dq coordinate system based on the rotor magnetic field orientation and considering the iron loss, an expression of torque and input power considering the iron loss is obtained, and a partial derivative is obtained by comparing the torque and the input power and calculating the slip angular frequency, so that an expression of the optimal slip angular frequency corresponding to the maximum torque input power ratio is obtained. This optimum slip enables energy-efficient operation of the induction motor.

The method is combined with a constant-voltage frequency ratio speed regulating system of the induction motor, and a constant-voltage frequency ratio energy efficiency optimization control system of the induction motor based on the maximum torque input power ratio is designed.

A schematic block diagram of the system implementation is shown in fig. 1. The device comprises a slip PI regulator 1, an optimal slip calculation module 2, a compensation voltage PI regulator 3, a voltage-frequency ratio calculation module 4, a pulse modulation PWM module 5, a three-phase voltage source inverter 6, a photoelectric encoder 7 and an induction motor 8.

The rotation speed is given because of the constant pressure frequency ratio control mode and the direct proportion relation between the torque and the slipWith actual speed omega_rAfter being processed by the slip PI regulator 1, the difference is added with the actual rotating speed to obtain the synchronous rotating speed omega₁And the rotating speed closed loop is realized. Synchronous speed omega₁The voltage amplitude U at the moment is obtained through a voltage-frequency ratio calculation module 4_s. The real-time rotating speed of the motor is sent into an optimal slip calculation module 2, and the current optimal slip is calculated according to the formula (15)Making a difference with the real-time slip of the motor, sending the difference value into a compensation voltage PI regulator 3, and calculating a compensation voltage U_s′。U_sAfter compensating for the voltage, with omega₁Are sent to the pulse modulation PWM module 5. The pulse modulation PWM module 5 modulates six groups of pulses meeting the control requirement and sends the six groups of pulses to the three-phase voltage source inverter 6. The voltage inverted by the three-phase voltage source inverter 6 is input to the induction motor 8, so that the motor meets the control requirement and operates stably and efficiently. The photoelectric encoder 7 is responsible for detecting the rotating speed of the induction motor 8 in real time and feeding the rotating speed back to the control system.

FIG. 2 is a flow chart of the operation of the control system based on the combination of the maximum torque input power ratio energy efficiency optimization control strategy and the constant voltage frequency ratio.

FIG. 3 is a graph showing the results of the experiment of the present method. Fig. 3 is a comparison result graph of the method and the conventional constant voltage frequency ratio speed regulation method in the process of operating the induction motor from no load to 100n.m and rotating speed from 50rad/s to 140rad/s, in order to more vividly embody the effect of the present invention, the change curve of the loss power is taken as the comparison, wherein the dotted line represents the change curve of the loss power of the conventional constant voltage frequency ratio speed regulation system, and the solid line represents the change curve of the loss power of the present invention.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.