Method and system for improving low-speed operation performance of frequency converter driving motor

Abstract

The invention relates to a method and a system for improving low-speed operation performance of a frequency converter driving motor, and the method comprises the steps: employing a photoelectric pulse speed measurement sensor to measure speed through a T method, obtaining a motor rotating speed pulse signal of a current motor, obtaining a motor rotating speed through the measurement of a rotating speed observer, and transmitting the motor rotating speed to a sliding window processor; the current rotating speed of the motor is calculated and obtained through the sliding window speed measurement technology, rotating speed fluctuation generated when the photoelectric pulse speed measurement sensor rotates by one circle is extracted in a band-pass filtering mode to obtain the disturbance rotating speed, then the disturbance rotating speed is removed from the current rotating speed of the motor, and the real-time rotating speed used for driving the motor of the frequency converter control system is obtained. According to the invention, interval errors of grating signals of the photoelectric pulse speed measurement sensor caused by low-speed operation of the motor are eliminated through a sliding window speed measurement technology, and installation errors of the photoelectric pulse speed measurement sensor are eliminated through a band-pass filtering processing mode, so that a frequency converter control system obtains more accurate motor rotating speed signals; and the accurate control performance of low-speed operation of the frequency converter driving motor is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of motor control, and particularly discloses a method for improving the low-speed operation performance of a motor driven by a frequency converter and a system thereof. BACKGROUND

[0002] Motors are widely used in many fields such as industrial production, transportation and energy systems. The speed of a motor can be regulated by driving the motor with a frequency converter. The control accuracy of the motor speed by the frequency converter control system is an important physical index of the operation performance of the motor driven by the frequency converter. For some occasions requiring stable operation at a low speed, a speed sensor needs to be configured. The speed sensor plays an important role in the frequency converter control system as a feedback of the motor speed. The photoelectric pulse speed sensor is the most commonly used motor speed measuring device, which characterizes the speed by a grating signal. The photoelectric pulse speed sensor is widely used for measuring the speed of a motor rotor. Common speed measuring methods include the M method, the T method and the M / T method. The T method records the time interval between adjacent grating signals by sending a number of pulses from a high-frequency clock pulse with a known frequency to a counter to determine the measured speed. When the speed of the motor is low, the T method has high measurement accuracy, but it takes a long time to receive the grating signal, and there is a certain blind time during this period. If the blind time is long, the speed signal cannot be updated in time. The low speed leads to a long time for the pulse feedback of the photoelectric pulse speed sensor, and the pulse interval time of the photoelectric pulse speed sensor is greater than the sampling period of the speed, so that the speed cannot be calculated and updated before the pulse signal is received, and only the historical speed of the previous beat can be used, resulting in a constant value of the speed during this period. The speed observation is stagnant at a certain speed value, which cannot reflect the true speed, and affects the control performance of the frequency converter when the motor is running at a low speed, resulting in speed out of control, low-speed oscillation, poor low-speed performance and other problems.

[0003] Chinese patent CN1300590C discloses a speed measuring method using a pulse encoder when a motor is running at a low speed. The average speed C / T of the motor shaft during a time interval T between one or two encoder pulses is calculated, where C is a constant. When the speed of the motor slows down, the third pulse does not arrive at 2T+ t, the computer estimates the maximum possible value of the current speed as Vimax=C / (T+ ti), according to the experience of speed change, the value N is selected, N≥1, V=Vimax / N is taken as the measurement result estimation value, and is sent to control the motor rotating speed. The selection of N is related to the moment of inertia of the motor rotating part, the resistance condition of the rotating system, and the torque for driving rotation. The patent solves the problem of the speed measurement error of the pulse encoder when the motor runs at low speed, the highest possible speed extension curve calculated according to the patent is combined with the experience estimation method, to obtain a more accurate speed estimation value, and the motor can be more accurately controlled. Actually, the process of the patent is as follows: first, the average rotating speed C / T of the last beat is calculated according to the current pulse and the last pulse, and then the next pulse is waited for feedback for a time T. If the pulse is fed back in advance due to acceleration of the motor, the previous step is repeated; if the motor is decelerated and the pulse still cannot be received, the rotating speed C / T calculated before is taken as a calculation factor, and the estimated rotating speed C / (T ti). The defects of the patent are as follows: first, the estimated rotating speed is always based on the speed calculated according to the existing pulse and the last pulse as a reference, and once noise is introduced, the estimated rotating speed will also be wrong; second, the system keeps the historical rotating speed for one beat to wait for a new pulse to update, and at this time, the measured speed lags behind the actual speed, affecting the control performance.

[0004] Chinese patent CN1026937C discloses a system and method for controlling the speed of a motor, which is a system and method for controlling a motor in an extremely low speed range with a rotating pulse encoder. The pulse encoder outputs a pulse every time the rotating shaft of the motor rotates through a predetermined angle, the extremely low speed range is defined, the pulse interval of the output pulse is longer than the system control period, a lowest-order disturbance and load torque estimation value observer is provided, and the average value of the motor speed of each pulse interval is calculated according to the following formula. nM'(j): nM'(j)=[∑nM'(i)]j / n(j), where i represents the speed control period, and j represents the pulse interval of the pulse encoder. According to the torque instruction and the estimated load torque, the patent obtains an acceleration compensation estimation value. However, the defect is that it is based on the observer system of the system torque instruction and the load estimation obtained by the frequency converter, and the calculation process is relatively complex, and it does not have good implementation. SUMMARY

[0005] The purpose of the present application is to solve the defects existing in the prior art, disclose a method and system for improving the low-speed operation performance of a frequency converter driven motor, improve the low-speed operation performance of the frequency converter driven motor by improving the speed measurement performance of the photoelectric pulse speed measurement sensor, especially for the speed measurement blind area of the photoelectric pulse speed measurement sensor at a low speed when using the T method for speed measurement, eliminate the interval error of the grating signal of the photoelectric pulse speed measurement sensor caused by the low-speed operation of the motor by using the sliding window speed measurement technology, eliminate the installation error of the photoelectric pulse speed measurement sensor by using the band-pass filtering processing mode, and eliminate the process error of the photoelectric pulse speed measurement sensor by using the two methods in combination, and the method does not depend on the frequency converter driving link parameters, and the dynamic performance and implementability are considered, and the low-speed control performance of the frequency converter driven motor is further improved.

[0006] The present application is implemented as follows: a method and system for improving the low-speed operation performance of a frequency converter driven motor, the method uses a system for improving the low-speed operation performance of a frequency converter driven motor, which comprises a frequency converter control system and a band-pass filter, a sliding window processor, a speed observer and a photoelectric pulse speed measurement sensor arranged at the extension end of the motor shaft which are connected in sequence in the circuit with the frequency converter control system, the photoelectric pulse speed measurement sensor rotates synchronously with the rotor of the motor, uses the T method for speed measurement, obtains N motor speed pulse signals of the current motor and outputs them to the speed observer, the speed observer obtains the motor speed by measuring the motor speed pulse signals, and obtains the current motor speed by calculating the motor speed pulse signals using the sliding window speed measurement technology, wherein N is a positive integer and N is greater than or equal to 2, then the band-pass filtering mode is used to extract the speed fluctuation of one revolution of the photoelectric pulse speed measurement sensor to obtain the disturbance speed, and then the disturbance speed is removed from the current motor speed to obtain the real-time speed of the motor driven by the frequency converter control system, and the frequency converter control system drives the motor to operate at a low speed according to the real-time speed.

[0007] In the sliding window speed measurement technology, the N motor speed pulse signals obtained by the sliding window processor using the T method for speed measurement are stored one by one in a circular queue with a storage space corresponding to N, and the first-in-first-out method is used for circular storage after a new motor speed pulse signal is obtained.

[0008] The band-pass filtering mode is to obtain the periodic speed fluctuation of one revolution of the photoelectric pulse speed measurement sensor with the motor rotor by using the band-pass filter to obtain the disturbance speed, and the center point frequency of the band-pass filter is the rotation frequency of the current motor rotor.

[0009] The motor speed obtained by the speed observer is the motor speed obtained by taking the average of the N motor speed pulse signals obtained by the photoelectric pulse speed measurement sensor.

[0010] The band-pass filter adopts filter circuit hardware or a software processor for filtering digital signals through a program.

[0011] The system for improving the low-speed operation performance of the motor driven by the frequency converter comprises a frequency converter control system, a band-pass filter, a sliding window processor, a rotating speed observer and an optical pulse type speed sensor arranged at the shaft extension end of the motor, which are sequentially connected in circuit, the optical pulse type speed sensor is used for converting a rotating signal into a pulse signal proportional to the rotating speed, the T method is used for measuring the speed, the motor rotating speed pulse signal of the current motor is obtained and transmitted to the rotating speed observer, the rotating speed observer is used for transmitting the motor rotating speed obtained by measuring the motor rotating speed pulse signal to the sliding window processor, the sliding window processor is used for calculating the current motor rotating speed according to the motor rotating speed, the band-pass filter is used for filtering the current motor rotating speed to obtain the disturbance rotating speed caused by the installation process of the optical pulse type speed sensor, and the frequency converter control system drives the motor to operate at low speed according to the real-time rotating speed of the motor obtained by subtracting the disturbance rotating speed from the current motor rotating speed.

[0012] The frequency converter control system is provided with a calculation and processing module, comprising a storage unit and one or more calculation units connected with the storage unit, the storage unit is used for storing instructions, the instructions are instructions for obtaining the real-time rotating speed of the motor driven by the frequency converter control system to operate at low speed, the one or more calculation units are arranged to execute the instructions, and the calculation unit is provided with a timer for the optical pulse type speed sensor and is used for timing and calculation in the T method speed measurement process.

[0013] The beneficial effects of the present application are that the sliding window speed measurement technology is used to eliminate the interval error of the grating signal of the optical pulse type speed sensor caused by the low-speed operation of the motor, especially solves the speed measurement blind area problem of the optical pulse type speed sensor at a low rotating speed when the T method is used, the band-pass filter processing method is used to eliminate the installation error of the optical pulse type speed sensor, solves the interval error problem of the grating signal of the optical pulse type speed sensor at low speed and the process error problem caused by the manufacturing process and installation process of the optical pulse type speed sensor when the rotating speed is obtained during the operation of the motor driven by the frequency converter, the process error of the optical pulse type speed sensor itself is eliminated by the cooperation of the two methods, the frequency converter control system can obtain more accurate motor rotating speed signals, the interference of the process error of the optical pulse type speed sensor itself on the frequency converter control system is reduced, the control with higher precision is realized without depending on the parameters of the frequency converter driving link, dynamic performance and implementability are also considered, and the low-speed control performance of the motor driven by the frequency converter is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1Fig. 1 is a schematic diagram of the signal of the photoelectric pulse speed sensor and four times frequency.

[0015] Figure 2 Fig. 2 is a schematic diagram of the sliding window speed measurement technology.

[0016] Figure 3 Fig. 3 is a schematic diagram of the ideal installation of the photoelectric pulse speed sensor in the system.

[0017] Figure 4 Fig. 4 is a schematic diagram of the actual installation of the photoelectric pulse speed sensor in the system.

[0018] Figure 5 Fig. 5 is a schematic diagram of the signal of the photoelectric pulse speed sensor.

[0019] Figure 6 Fig. 6 is a schematic diagram of the band-pass filtering process.

[0020] Figure 7 Fig. 7 is a schematic diagram of the connection relationship between the components for processing the motor speed signal.

[0021] In the figure: 1, motor rotor; 2, photoelectric pulse speed sensor; 3, theoretical centering line; 4, photoelectric pulse speed sensor coupling; 5, actual speed of the photoelectric pulse speed sensor; 6, actual speed of the motor rotor. DETAILED DESCRIPTION

[0022] The application will be further described below in combination with the accompanying drawings and specific embodiments.

[0023] According to the accompanying Figures 1-7 , the application is a method and system for improving the low-speed running performance of a frequency converter driven motor. The system for improving the low-speed running performance of the frequency converter driven motor comprises a frequency converter control system, a band-pass filter, a sliding window processor, a speed observer and a photoelectric pulse speed sensor arranged at the extension end of the motor shaft, which are connected in sequence by circuits. The photoelectric pulse speed sensor rotates synchronously with the rotor of the motor, converts the rotating signal into a motor speed pulse signal proportional to the rotating speed and transmits the signal to the speed observer. The speed observer measures the motor speed pulse signal, obtains the motor speed and transmits the speed to the sliding window processor and the band-pass filter in sequence for further processing.

[0024] The photoelectric pulse speed sensor adopts T method to measure speed, obtains the motor speed pulse signal of the current motor and outputs the motor speed pulse signal to the speed observer, the speed observer transmits the motor speed obtained after measuring the motor speed pulse signal to the sliding window processor, the current motor speed is obtained through the sliding window processor, the disturbance speed caused by the installation process of the photoelectric pulse speed sensor is obtained after the current motor speed is filtered through the band-pass filter, and the real-time speed of the frequency converter control system for driving the motor is obtained after the current motor speed is subtracted by the disturbance speed.

[0025] The frequency converter control system is provided with a calculation and processing module, including a storage unit and one or more calculation units connected with the storage unit, the storage unit is used for storing instructions, the instructions are instructions for obtaining the real-time speed of the motor driven by the frequency converter control system at low speed, the one or more calculation units are executed, the calculation unit is provided with a timer for the photoelectric pulse speed sensor, and the timer is used for timing and calculation in the T method speed measurement process.

[0026] The method comprises that the photoelectric pulse speed sensor adopts T method to measure speed, obtains N motor speed pulse signals, and obtains the motor speed after the motor speed pulse signal is measured by the speed observer, then the current motor speed is calculated and obtained through the sliding window speed measurement technology, wherein N is a positive integer and N is greater than or equal to 2, the disturbance speed is obtained by extracting the speed fluctuation of one rotation of the photoelectric pulse speed sensor through the band-pass filtering mode, then the disturbance speed is removed from the current motor speed, and the real-time speed of the motor driven by the frequency converter control system is obtained. The motor speed obtained by the speed observer is obtained by accumulating the N motor speed pulse signals of the photoelectric pulse speed sensor and taking the average.

[0027] During the speed regulation process of the motor driven by the frequency converter, in order to achieve better control effect and low-speed operation performance, the angular velocity of the motor rotor needs to be obtained through the photoelectric pulse speed sensor, the photoelectric pulse speed sensor is mechanically connected with the rotor shaft at the extension end of the motor shaft, the photoelectric pulse speed sensor converts the mechanical displacement generated by the rotation of the rotor shaft into periodic electric signals through photoelectric conversion, generates pulse signals due to the periodic change of the received light caused by the blocking and light transmission of the grating, and represents the angular displacement through the pulse signals. Figure 1 and 2, the photoelectric pulse speed sensor often takes ABZ signal to represent the relevant motor speed pulse signal, wherein the A signal and the B signal are theoretically orthogonal differential signals, and the Z signal is the pulse signal of one rotation of the photoelectric pulse speed sensor. When the photoelectric pulse speed sensor rotates forward, the A signal leads the B signal by 90° in phase; when the photoelectric pulse speed sensor rotates reversely, the A signal lags behind the B signal by 90° in phase. In combination with the rising and falling pulses of the A signal and the B signal, a four-fold frequency signal speed is constructed to improve the precision. If one pulse of the A&B orthogonal signal is directly used at a lower speed, the manufacturing error of the photoelectric pulse speed sensor itself will be inevitably introduced. Therefore, the application adopts a sliding window method (i.e. a sliding window speed measurement technology) to obtain the motor speed feedback of the photoelectric pulse speed sensor, and the dynamic performance and the precision are considered. The specific principle and working process are as follows: Firstly, it is determined that the sliding window contains N motor speed pulse signals, and N is generally 4 at low speed to avoid the measurement error caused by the AB phase quadrature deviation of the photoelectric pulse speed sensor.

[0028] The rated speed of the motor is defined as n1, the speed regulation range is from n0 to n1, and the number of pulses per rotation of the photoelectric pulse speed sensor is P. The T method speed measurement, also known as the fixed angle speed measurement method, is a method for determining the measured speed by measuring the time interval between two adjacent pulses. A high-frequency clock pulse with a known frequency f c is sent to a counter, and the counter is controlled by the start and stop of two adjacent pulses of the speed measurement pulse. If the reading of the counter is m, then the number of revolutions per minute of the motor n M is .

[0029] The extremely low speed leads to a long time of the pulse feedback of the photoelectric pulse speed sensor, and the pulse interval time of the photoelectric pulse speed sensor is greater than the speed sampling period, so that the speed cannot be calculated and updated in time before the pulse signal is received, and the frequency converter control system can only use the historical speed of the previous beat, so that the speed of this section is a constant value of the historical speed of the previous beat. After the signal is processed by four times frequency, the sliding window containing N motor speed pulse signals is selected, and the motor speed of the current sliding window is measured by the T method speed measurement. The motor speed is updated in real time every time the sliding window advances by one rising edge, and the acceleration a of the two speed measurements is recorded at the same time. The arrival time of the next rising edge pulse is estimated. If the time arrives but the pulse of the photoelectric pulse speed sensor is still not coming, the estimated motor speed is used to replace the current motor speed.

[0030] The motor speed obtained by the previous speed measurement is denoted as ω2, the current motor speed is denoted as ω1, and the time of the two motor speeds is denoted as t1, so that the accelerationa is: .

[0031] estimated arrival time of the next rising edge pulse t is: .

[0032] then the next estimated motor speed ω next The calculation formula is: .

[0033] The N motor speed pulse signals obtained by the sliding window processor using the T method in the sliding window speed measurement technology are stored in the circular queue with a storage space corresponding to N in sequence. After a new motor speed pulse signal is obtained, the first-in-first-out method is used for circular storage.

[0034] Referring to Figure 3 and 4 , when the actual photoelectric pulse speed sensor is installed, there is inevitably a difference in installation precision, and the process and precision of the photoelectric pulse speed sensor installation need to be considered during measurement. Due to the limitations of installation process and other related factors during actual installation, the photoelectric pulse speed sensor 2 is installed on the motor rotor 1 through the photoelectric pulse speed sensor coupling 4, and there is a certain angle deviation from the theoretical center line 3, and the photoelectric pulse speed sensor 2 cannot achieve complete concentricity with the motor rotor 1. The speed of the photoelectric pulse speed sensor fluctuates within one rotation period. The time for one revolution of the photoelectric pulse speed sensor is consistent with the time for one revolution of the motor rotor, but the speed is slightly different at different positions within one revolution. The rotor angular frequency can be obtained by obtaining the motor rotor speed through the photoelectric pulse speed sensor. With the rotor angular frequency as the center frequency, the disturbance speed is obtained by extracting the speed fluctuation of the photoelectric pulse speed sensor rotating one revolution in a band-pass filtering manner, and the installation error of the photoelectric pulse speed sensor can be eliminated by removing the disturbance speed.

[0035] The band-pass filtering manner is to obtain the periodic fluctuation of the photoelectric pulse speed sensor rotating one revolution with the motor rotor through a band-pass filter, and the center frequency of the band-pass filter is the current motor rotor rotation frequency. The band-pass filter is a filter circuit hardware or a software processor that filters digital signals through a program. Figure 6 , the band-pass filter center frequency is the motor mechanical rotation frequency, and the angular speed ω r is calculated based on the current motor speed obtained through the sliding window processor. r The disturbance speed ω hThe current motor speed minus the disturbance speed is the real-time speed ω, which can eliminate the installation error of the photoelectric pulse speed sensor.

[0036] The transfer function H(s) of the band-pass filter is formula (1): (1).

[0037] The three coefficients a, b, and c of the filter are determined by the three variables: the frequency point ω0, the notch bandwidth parameter k1, and the notch depth parameter k2. a is the numerator coefficient, b is the damping coefficient, c is the center frequency square, and s is the Laplace variable.

[0038] The Figure 5 The actual measured speed 5 of the motor through the photoelectric pulse speed sensor is a curved waveform, and the actual speed 6 of the motor rotor is a broken line waveform. It can be seen that the actual measured speed of the motor through the photoelectric pulse speed sensor contains the installation error factor of the photoelectric pulse speed sensor. Therefore, during the stable operation of the motor, the installation disturbance speed of the photoelectric pulse speed sensor can be filtered out through the band-pass filter matched with the motor rotor rotating frequency. Then, the actual measured speed of the motor minus the installation disturbance speed of the photoelectric pulse speed sensor can obtain the real-time speed which is closer to the actual speed of the motor rotor, which is convenient for the further control of the frequency converter control system, improves the control accuracy of the motor during stable operation, and especially improves the stability of the driving motor during low-speed operation. Embodiment

[0039] The application is applied to a high-performance vector control frequency converter example, in which a frequency converter control system adopts a DSP TMS320C6747 chip as a core control CPU, controls motor speed regulation operation through the frequency converter control system, and feeds back motor speed pulse signals of a motor speed to a speed observer through a photoelectric pulse speed sensor, transmits the motor speed obtained after the speed observer measures the motor speed pulse signals to a sliding window processor, obtains the current motor speed through the sliding window processor, obtains the disturbance speed caused by the photoelectric pulse speed sensor installation process through the current motor speed after the band-pass filter filtering, and obtains the real-time speed of the motor used by the frequency converter control system after the disturbance speed is subtracted from the current motor speed. In this example, the high-speed speed pulse frequency is 40MHz, the photoelectric pulse speed sensor adopts 4096PPR, the motor allows the highest speed to be ±200r / min, and needs to realize forward and reverse rotation in operation. The processing frequency of the frequency converter speed regulator is 640Hz, and when the speed is measured according to the conventional M method, the motor speed feedback by the photoelectric pulse speed sensor is 9.375 r / min, that is, the photoelectric pulse speed sensor outputs 640 pulses per second, which is just matched with the processing speed of the frequency converter speed regulator. However, if the motor speed continues to decrease, for example, to 1r / min, that is, the photoelectric pulse speed sensor outputs about 68 pulses per second, the motor speed pulse signal feedback by the photoelectric pulse speed sensor cannot be effectively updated within about 10 processing cycles of the frequency converter, which will cause disorder of the control link of the frequency converter. Figure 1 With Figure 2 , the speed control resolution of the frequency converter control system can be improved to 2.34r / min by using four times frequency and sliding window speed measurement technology.

[0040] It should be noted that the above specific embodiments are exemplary, and those skilled in the art should understand that the present application specification and its drawings are illustrative and do not constitute a limitation on the claims. Those skilled in the art can make various equivalent or equivalent changes under the inspiration of the disclosure of the present application, and these solutions should all belong to the disclosed range of the present application and fall within the protection scope of the present application, and the protection scope of the present application is defined by the claims of the present application and its equivalents.

Claims

1. A method for improving the low speed performance of a variable frequency drive motor, characterized by: The method adopts a system for improving the low-speed operation performance of a motor driven by a frequency converter, which comprises a frequency converter control system and a band-pass filter, a sliding window processor, a speed observer and a photoelectric pulse speed sensor arranged at the extending end of a motor shaft, which are connected in sequence by circuits, the photoelectric pulse speed sensor rotates synchronously with the rotor of the motor, the T method is used to measure the speed, N motor speed pulse signals of the current motor are obtained and output to the speed observer, the speed observer obtains the motor speed by measuring the motor speed pulse signals, the current motor speed is calculated by the sliding window processor using the sliding window speed measurement technology, wherein N is a positive integer and N is greater than or equal to 2, then the speed fluctuation of the photoelectric pulse speed sensor during one rotation is obtained by extracting the speed fluctuation of the photoelectric pulse speed sensor in a band-pass filtering manner to obtain the disturbance speed, then the disturbance speed is removed from the current motor speed to obtain the real-time speed of the motor driven by the frequency converter control system, and the frequency converter control system drives the motor to operate at low speed according to the real-time speed.

2. The method for improving the low speed performance of a motor driven by a frequency converter according to claim 1, characterized in that: In the sliding window speed measurement technology, the N motor speed pulse signals obtained by the T method through the sliding window processor are stored in a circular queue with a storage space corresponding to N one by one, and the new motor speed pulse signals are stored in the circular queue in a first-in-first-out manner.

3. The method of claim 1, wherein the variable frequency drive is configured to operate in a low speed mode when the motor is operating at a low speed. The band-pass filtering manner is to obtain the periodic speed fluctuation of the photoelectric pulse speed sensor during one rotation of the motor rotor by the band-pass filter to obtain the disturbance speed, and the center frequency of the band-pass filter is the rotation frequency of the current motor rotor.

4. The method of claim 1, wherein the variable frequency drive is configured to operate in a low speed mode when the motor is operating at a low speed. The motor speed obtained by the speed observer is obtained by accumulating the N motor speed pulse signals obtained by the photoelectric pulse speed sensor and taking the average.

5. The method of claim 3, wherein the variable frequency drive is configured to: The band-pass filter adopts a filter circuit hardware or a software processor for filtering digital signals through a program. ​ 6. A system for improving the low speed performance of a motor driven by a frequency converter, for the method of improving the low speed performance of a motor driven by a frequency converter as claimed in any one of claims 1 to 5, characterized in that: The system for improving the low-speed operation performance of a motor driven by a frequency converter comprises a frequency converter control system and a band-pass filter, a sliding window processor, a speed observer and a photoelectric pulse speed sensor arranged at the extending end of a motor shaft, which are connected in sequence by circuits, the photoelectric pulse speed sensor is used to convert the rotating signal into a pulse signal proportional to the rotating speed, the T method is used to measure the speed, the motor speed pulse signals of the current motor are obtained and transmitted to the speed observer, the speed observer is used to transmit the motor speed obtained by measuring the motor speed pulse signals to the sliding window processor, the sliding window processor is used to calculate the current motor speed according to the motor speed, the band-pass filter is used to filter the current motor speed to obtain the disturbance speed caused by the installation process of the photoelectric pulse speed sensor, and the frequency converter control system drives the motor to operate at low speed according to the real-time speed of the motor obtained by subtracting the disturbance speed from the current motor speed.

7. A system for improving the performance of a variable frequency drive motor at low speeds as recited in claim 6, wherein: The variable frequency converter control system is provided with a computing and processing module, including a storage unit and one or more computing units connected with the storage unit, the storage unit is used for storing instructions, the instructions are instructions for the real-time speed acquisition process of the variable frequency converter control system driving the motor to run at low speed, the one or more computing units are executed, the computing unit is provided with a timer for the photoelectric pulse speed sensor, and the timer is used for timing and calculation of the T method speed measurement process.

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