Design method of front passive filter for frequency converter driving motor

Abstract

The invention relates to a front passive filter design method for a frequency converter driving motor, which comprises the following steps of: aiming at a frequency converter driving alternating current servo motor system which is based on V-F control and has no special requirement on sine wave waveform distortion rate, connecting an electric reactor between a frequency converter and a motor in series to serve as a front passive filter; for a frequency converter driving alternating current servo motor system which is based on V-F control and requires a sine wave waveform distortion rate below 3%, a sine wave filter is connected in series between a frequency converter and a motor to serve as a front passive filter; for a vector control-based frequency converter driving alternating current servo motor system, a peak suppressor is connected in series between a frequency converter and a motor to serve as a front passive filter. The problem that when the frequency converter drives the motor through a long cable, overvoltage is generated at the motor end, so that insulation of a motor enameled wire is reduced, and the service life of the motor is short is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrical engineering and relates to a design method of a pre-passive filter for a frequency converter driven motor. Background Art

[0002] Inverter drive is a flexible motor control method. Inverters are widely used in various industrial scenarios due to their small size, light weight, high reliability, high power factor, and smooth startup process. In the aerospace field, inverter power supplies can also be used as ground medium-frequency power supplies to drive AC motors. Due to the layout characteristics of the usage scenario, the ground power supply to the servo motor is often connected through a power supply cable about 100 meters long. Due to the existence of cable distribution parameters, the transmission characteristics of PWM pulses on the cable are similar to the traveling wave transmission characteristics. According to transmission line theory, when the characteristic impedance of the cable does not match the motor impedance, the PWM pulse as the incident wave will generate a reflected wave at the motor end. The incident wave and the reflected wave are superimposed at the motor end, which will cause an overvoltage phenomenon at the motor end, causing the insulation of the motor enameled wire to decrease, resulting in a low motor service life. Summary of the invention

[0003] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and propose a pre-passive filter design method for a frequency converter driven motor, so as to solve the problem that when the frequency converter drives the motor through a long cable, an overvoltage is generated at the motor end, which causes the insulation of the motor enameled wire to decrease, resulting in a short service life of the motor.

[0004] The solution to the technical problem of the present invention is: the present invention installs a filter such as a reactor, a sine filter or a spike suppressor on one side of the inverter output end as a motor pre-filter device to achieve motor terminal voltage suppression, thereby eliminating overvoltage phenomenon, slowing down the aging of motor insulation, and thus extending the service life of the motor.

[0005] Specifically, a design method for a pre-passive filter for a frequency converter driven motor is proposed, and the design method includes:

[0006] For the inverter-driven AC servo motor system based on VF control and with no special requirements for the sine wave waveform distortion rate, a reactor is connected in series between the inverter and the motor as a pre-passive filter;

[0007] For the inverter-driven AC servo motor system based on VF control and requiring the sine wave waveform distortion rate to be less than 3%, a sine wave filter is connected in series between the inverter and the motor as a pre-passive filter;

[0008] For the inverter-driven AC servo motor system based on vector control, a spike suppressor is connected in series between the inverter and the motor as a pre-passive filter.

[0009] Furthermore, the reactor is composed of three equal-value inductors, and the inductance constraints of the designed reactor are as follows:

[0010] 2πf b L1I d ≤E d *k1%

[0011] Among them, f b is the fundamental frequency of the inverter, L1 is the inductance of the reactor winding, I d is the rated working current of the motor, E d is the rated working voltage of the motor, and k1 is the inductance voltage drop coefficient.

[0012] Furthermore, the sine wave filter is composed of an inductor and a parallel capacitor, and the inductance constraint of the sine wave filter is designed as follows:

[0013] 2πf b L2I d ≤E d *k1%

[0014] Among them, f b is the fundamental frequency of the inverter, L2 is the inductance of the sine wave filter winding, I d is the rated working current of the motor, E d is the rated working voltage of the motor, and k1 is the inductance voltage drop coefficient.

[0015] Furthermore, the capacitance constraints for designing the sine wave filter are as follows:

[0016]

[0017] Where α is the modulation depth and C is the capacitance value of the sine wave filter.

[0018] Furthermore, the cutoff frequency constraints of the designed sine wave filter are as follows:

[0019] k2*f b ≤f r ≤f s / k2

[0020]

[0021] Among them, f r is the cutoff frequency of the sine wave filter, f s is the carrier frequency of the inverter, and k2 is the proportional coefficient.

[0022] Furthermore, the center frequency constraints of the designed spike suppressor are as follows:

[0023]

[0024] Where f is the center frequency of the peak suppressor, t r is the peak rise time of the measured waveform.

[0025] Furthermore, the center frequency of the peak suppressor is selected to be 40 to 80 kHz.

[0026] Furthermore, the inductor voltage drop coefficient k1 is set to a value of 3-5.

[0027] Furthermore, the proportionality coefficient k2 is set to a value of 5-10.

[0028] The beneficial effects of the present invention compared with the prior art are:

[0029] (1) Compared with the solution of shortening the cable distance between the inverter and the load and installing a filter device on the load side, the present invention has the least impact on the system;

[0030] (2) The present invention provides a variety of solutions for different control modes and different system requirements, thereby solving the problem of a frequency converter driving an AC motor over a long distance;

[0031] (3) The pre-filter solution designed in the present invention has a low coupling degree with the original system, which facilitates the disassembly, inspection and maintenance of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of a reactor connected in series with a system according to Embodiment 1 of the present invention;

[0033] Figure 2 This is a schematic diagram of a sine filter connected in series with a system according to Embodiment 2 of the present invention;

[0034] Figure 3 This is a schematic diagram of a spike suppressor connected in series with a system in Example 3 of the present invention. DETAILED DESCRIPTION

[0035] The present invention uses a passive filter to filter out the high-order harmonics output by the inverter, reducing the peak voltage at the motor end to below the initial discharge voltage (Partial Discharge Inception Voltage, PDIV), and slowing down the rise rate of the peak voltage to avoid partial discharge. The type of filter required to be introduced depends on the filtering effect requirements and the AC motor control method.

[0036] At present, AC motors mostly use VF control and vector control. VF control is an open-loop control method without speed feedback based on the basic control method of variable voltage and frequency conversion. It has the advantages of simple structure, reliable operation and low control operation speed requirement. Vector control is based on the dynamic mathematical model of the motor and uses the vector transformation method to simulate the AC motor into a DC motor, which can realize the decoupled independent control of magnetic flux and torque.

[0037] The present invention provides three filter solutions suitable for different application scenarios: a reactor (L filter circuit), a sine wave filter (LC filter circuit), and a spike suppressor (LRC filter circuit).

[0038] For inverter-driven AC servo motor systems based on VF control and with no special requirements for the distortion rate of the sinusoidal waveform, a reactor solution can be used. Reactors are widely used in power transmission systems and consist of only three equal-value inductors with a simple structure. The electromagnetic induction generated can suppress rapid changes in current, thereby filtering out peak voltage at the load end.

[0039] For inverter-driven AC servo motor systems based on VF control and requiring a sine wave waveform distortion rate of less than 3%, a sine wave filter solution can be used. The sine wave filter is composed of an LC filter circuit consisting of an inductor and a parallel capacitor.

[0040] For the inverter-driven AC servo motor system based on vector control, if the output end is connected to a filter with too large capacitance, it is easy to cause the closed loop to lose control, resulting in the motor being unable to start or unstable operation. The use of a spike suppressor can effectively suppress the peak voltage and peak voltage rise rate at the load end. The spike suppressor is composed of an LRC filter circuit consisting of an inductor, parallel capacitors and resistors.

[0041] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0042] Example 1

[0043] In this embodiment, the reactor is used as the pre-passive filter. The schematic diagram of the reactor design is as follows: Figure 1 As shown in Figure 1, after the reactor is connected in series, a certain voltage drop will be generated at both ends. The fundamental voltage drop of the inverter should not exceed a certain range. Generally, the inductor voltage drop is required to be ≤ 3-5% of the fundamental voltage. As shown in formula (1), selecting a larger L value is beneficial to suppressing the peak voltage, but the waveform is prone to greater distortion, resulting in higher power loss.

[0044] 2πf b L1I d ≤E d *k1% (1)

[0045] Among them, f b is the fundamental frequency of the inverter, L1 is the inductance of the reactor winding, I d is the rated working current of the motor, E d is the rated working voltage of the motor, k1 is the inductance voltage drop coefficient, and its value ranges from 3 to 5.

[0046] Example 2

[0047] In this embodiment, a sine wave filter is used as a pre-passive filter. The design diagram of the sine wave filter is shown in FIG. Figure 2 As shown in Figure 1, capacitance, inductance, and cutoff frequency constraints must be considered when designing a sine wave filter.

[0048] The inductance constraints of a sine wave filter are the same as those of a reactor, which are:

[0049] 2πf b L2I d ≤E d *k1%

[0050] Wherein, L2 is the inductance of the sine wave filter winding.

[0051] In addition to the voltage drop at the inductor end, the sine wave filter in series will also generate AC current in the capacitor branch. The fundamental current in the capacitor branch should not be too large. The fundamental current in the capacitor branch is ≤ the inverter rated current * 20%. The modulation depth is generally selected as 1. The capacitor constraint of the sine wave filter is shown in formula (2).

[0052]

[0053] Where α is the modulation depth and C is the capacitance value of the sine wave filter.

[0054] When designing the cutoff frequency constraint, select the proportional coefficient k2 = 5 ~ 10, that is, the cutoff frequency is 1 / 5 ~ 1 / 10 of the carrier frequency, which is more than 10 times higher than the fundamental frequency. This can achieve a good filtering effect. If the difference between the inverter carrier frequency and the fundamental frequency is within 100 times, a compromise coefficient can be selected based on the proportional relationship. The cutoff frequency constraint of the sine wave filter is shown in equations (3) ~ (4).

[0055] k2*f b ≤f r ≤f s / k2 (3)

[0056]

[0057] Among them, f r is the cutoff frequency of the sine wave filter, f s is the carrier frequency of the inverter.

[0058] Example 3

[0059] In this embodiment, a spike suppressor is used as a pre-passive filter. The schematic diagram of the spike suppressor design is shown in FIG. Figure 3 As shown, the center frequency constraint of the designed peak suppressor is shown in formula (5):

[0060]

[0061] Where f is the center frequency of the peak suppressor, t r It is the peak rise time of the measured waveform (the time required for the voltage to rise from 10% of the peak value to 90% of the peak value).

[0062] In order to achieve good filtering effect, the center frequency of the peak suppressor is selected in the range of 40 to 80 kHz.

[0063] The present invention solves the problem that when a frequency converter drives a motor through a long cable, an overvoltage is generated at the motor end, causing the insulation of the motor enameled wire to decrease, resulting in a short service life of the motor, by designing a pre-passive filter.

[0064] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

[0065] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for designing a pre-passive filter for a frequency converter driven motor, characterized in that: The design method comprises: For the inverter-driven AC servo motor system based on VF control and with no special requirements for the sine wave waveform distortion rate, a reactor is connected in series between the inverter and the motor as a pre-passive filter; For the inverter-driven AC servo motor system based on VF control and requiring the sine wave waveform distortion rate to be less than 3%, a sine wave filter is connected in series between the inverter and the motor as a pre-passive filter; For the inverter-driven AC servo motor system based on vector control, a spike suppressor is connected in series between the inverter and the motor as a pre-passive filter.

2. A method for designing a pre-passive filter for a frequency converter driven motor according to claim 1, characterized in that: The reactor is composed of three equal-value inductors, and the inductance constraints of the designed reactor are as follows: 2πf b L1I d ≤E d *k1% Among them, f b is the fundamental frequency of the inverter, L1 is the inductance of the reactor winding, I d is the rated working current of the motor, E d is the rated working voltage of the motor, and k1 is the inductance voltage drop coefficient.

3. The method for designing a pre-passive filter for a frequency converter driven motor according to claim 1, characterized in that: The sine wave filter is composed of an inductor and a parallel capacitor. The inductor constraints for designing the sine wave filter are as follows: 2πf b L2I d ≤E d *k1% Among them, f b is the fundamental frequency of the inverter, L2 is the inductance of the sine wave filter winding, I d is the rated working current of the motor, E d is the rated working voltage of the motor, and k1 is the inductance voltage drop coefficient.

4. A method for designing a pre-passive filter for a frequency converter driven motor according to claim 3, characterized in that: The capacitor constraints for designing a sine wave filter are as follows: Where α is the modulation depth and C is the capacitance value of the sine wave filter.

5. The method for designing a pre-passive filter for a frequency converter driven motor according to claim 3, characterized in that: The cutoff frequency constraints for designing a sine wave filter are as follows: k2*f b ≤f r ≤f s / k2 Among them, f r is the cutoff frequency of the sine wave filter, f s is the carrier frequency of the inverter, and k2 is the proportional coefficient.

6. The method for designing a pre-passive filter for a frequency converter driven motor according to claim 1, characterized in that: The center frequency constraints of the designed spike suppressor are as follows: Where f is the center frequency of the peak suppressor, t r is the peak rise time of the measured waveform.

7. A method for designing a pre-passive filter for a frequency converter driven motor according to claim 6, characterized in that: The center frequency of the peak suppressor is selected from 40 to 80kHz.

8. A method for designing a pre-passive filter for a frequency converter driven motor according to any one of claims 2 or 3, characterized in that: The inductance voltage drop coefficient k1 is 3 to 5.

9. The method for designing a pre-passive filter for a frequency converter driven motor according to claim 5, characterized in that: The proportionality coefficient k2 ranges from 5 to 10.

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