CN115347762B - Frequency converter cable length calculation method and system, and motor driving method and mechanism - Google Patents

Frequency converter cable length calculation method and system, and motor driving method and mechanism Download PDF

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Publication number
CN115347762B
CN115347762B CN202211273627.5A CN202211273627A CN115347762B CN 115347762 B CN115347762 B CN 115347762B CN 202211273627 A CN202211273627 A CN 202211273627A CN 115347762 B CN115347762 B CN 115347762B
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cable
frequency converter
motor
frequency
calculating
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CN115347762A (en
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谈源
蒋国中
王加飞
蒋驭城
张军
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Newtech Group Co Ltd
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Newtech Group Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
    • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
    • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
    • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P2207/00—Indexing scheme relating to controlling arrangements characterised by the type of motor
    • H02P2207/01—Asynchronous machines

Abstract

The invention relates to the technical field of carbon fiber production, in particular to a method for calculating the length of a cable of a frequency converter, which comprises the steps of determining the limit values of instant surge current and instant peak voltage; calculating a capacitive reactance reference value of the total length range of the cable between the output end of the frequency converter and the motor; determining a limit frequency value of high-frequency harmonics generated in PWM modulation of a frequency converter; calculating a distributed capacitance reference value of the total length range of the cable between the output end of the frequency converter and the motor; and calculating the maximum length of the cable between the output end of the frequency converter and the motor. The invention provides a new way for calculating the length of the cable between the output end of the frequency converter and the input end of the motor, and a new way for prolonging the length of the cable can be obtained through analysis by the way, namely, the condition that the motor is still effectively driven by the more distributed capacitance of the cable is met by reducing the limit frequency value, so that the length of the cable can be effectively improved. Meanwhile, the invention also discloses a system for calculating the cable length of the frequency converter, a motor driving method and a mechanism.

Description

Frequency converter cable length calculation method and system, and motor driving method and mechanism
Technical Field
The invention relates to the technical field of carbon fiber production, in particular to a method and a system for calculating the length of a cable of a frequency converter, and a method and a mechanism for driving a motor.
Background
The carbon fiber is a novel fiber material of high-strength and high-modulus fiber with the carbon content of more than 95 percent; it is made up by stacking organic fibres of flake graphite microcrystals along the axial direction of fibre, and making carbonization and graphitization treatment so as to obtain the invented microcrystal graphite material. The carbon fiber is flexible outside and rigid inside, has lighter weight than metal aluminum, higher strength than steel, corrosion resistance and high modulus, and is an important material in national defense, military industry and civil use.
In a carbon fiber production line, power is output in a mode of a frequency converter and an asynchronous motor in consideration of cost and control precision. Under normal circumstances, the control and the drive cabinet of motor often install by the production line near the motor, but in the production line of carbon fiber, because the carbon fiber silk has electric conductivity, in case electrically conductive carbon fiber silk gets into the electric cabinet and can make the circuit short circuit, exposes to the air even and explodes.
Therefore, for the production line of carbon fiber, the control and drive cabinets of the motor are often installed in the control room in a centralized manner, so that the transmission length of the cable is prolonged; for example, in actual production, when two carbon fiber production lines with a distance of 30 meters are adopted, each production line has a length of 350 meters, and a control room is arranged on at least two layers of a place where the production line is located for ensuring safety, the maximum distance from the control room to a control motor often reaches more than 200 meters, and the long-distance control of the motor can cause the following problems in an actual working process:
the output of the frequency converter is produced by modulating a high-power transistor by a settable carrier (i.e. a reference frequency, generally set by a user between 4K and 16K to configure different motors) to generate a PWM pulse sequence with a constant amplitude, a constant period and unequal width, and the PWM waveform contains a large amount of high-frequency high-voltage and even ultrahigh-frequency harmonic components according to the analysis of a pulse wave frequency spectrum, wherein the harmonic components generally consist of a plurality of sine wave series from hundreds of K to hundreds of MHZ.
In addition, because a high-power switching device IGBT in the frequency converter works in an on-off state, the high-speed switching action of the device enables the voltage and the current to jump in a short time, and therefore, a large amount of high-frequency harmonic components are contained in the voltage and current waveforms.
The two aspects can directly influence the length of a cable output to the motor by the frequency converter, so that the control and the drive cabinet of the motor are difficult to realize the long-distance separation of the position from the motor.
Disclosure of Invention
The invention provides a method and a system for calculating the length of a cable of a frequency converter, a motor driving method and a motor driving mechanism, which effectively solve the problems pointed out in the background technology.
In order to achieve the purpose, the invention adopts the technical scheme that:
the method for calculating the cable length of the frequency converter is used for calculating the cable length from the output end of the frequency converter to the input end of a motor, and comprises the following steps:
determining the limit values of the instantaneous surge current and the instantaneous peak voltage generated by the cable;
calculating a capacitive reactance reference value of the total length range of the cable between the output end of the frequency converter and the motor according to the ratio of the instantaneous peak voltage to the limit value of the instantaneous surge current;
determining a limit frequency value of high-frequency harmonics generated in PWM modulation of a frequency converter;
calculating a distributed capacitance reference value of a cable total length range from the output end of the frequency converter to the motor according to the capacitive reactance reference value and the limit frequency value;
and calculating the maximum length of the cable between the output end of the frequency converter and the motor according to the distributed capacitance reference value and the capacitance value of the cable.
Further, the instantaneous peak voltage is 1~2 times of the working voltage of the motor.
Converter cable length calculation system includes:
the input module is used for inputting the limit values of the instantaneous surge current and the instantaneous peak voltage generated by the cable and the limit frequency value of the high-frequency harmonic generated in the PWM modulation;
and the calculating module is used for calculating a capacitive reactance reference value of the total length range of the cable between the output end of the frequency converter and the motor according to the ratio of the instantaneous peak voltage to the limit value of the instantaneous surge current, calculating a distributed capacitance reference value of the total length range of the cable between the output end of the frequency converter and the motor according to the capacitive reactance reference value and the limit frequency value, and calculating the maximum length of the cable between the output end of the frequency converter and the motor according to the distributed capacitance reference value and the capacitance value of the cable.
Further, the instantaneous peak voltage is 1~2 times of the working voltage of the motor.
A motor driving method comprising the steps of:
suppressing surge sharp pulse of high-frequency harmonic component generated in PWM modulation of the frequency converter;
isolating the residual high-frequency harmonic waves generated in the PWM of the frequency converter;
re-determining the PWM waveform of the frequency converter through the steps, and determining the limit frequency value of the high-frequency harmonic wave according to the new PWM waveform;
determining the maximum length of the cable between the output end of the frequency converter and the input end of the motor by adopting the frequency converter cable length calculation method according to the limit frequency value;
and connecting the output end of the frequency converter and the input end of the motor through a cable which is equal to or less than the maximum length set range, and executing the drive control of the motor.
Further, the derating rate of the frequency converter is 30% -50% for use.
Further, 30% -50% of the wire diameter of the cable is reserved for surplus use.
The motor driving mechanism comprises an alternating current input circuit, a PWM control circuit and a frequency converter IGBT output circuit which are sequentially connected;
the power supply is characterized by further comprising an output filter and an output reactor which are sequentially connected, wherein the output filter and the output reactor are arranged between the frequency converter IGBT output circuit and the motor;
the system also comprises a frequency converter cable length calculating system which is used for calculating the maximum length of the cable between the output end of the frequency converter IGBT output circuit and the input end of the motor.
Further, the distance between the output end of the frequency converter IGBT output circuit and the input end of the output filter is smaller than 0.1m.
Further, the distance between the output end of the output filter and the input end of the output reactor is less than 0.1m.
Through the technical scheme of the invention, the following technical effects can be realized:
1. according to the invention, a new way for calculating the length of the cable between the output end of the frequency converter and the input end of the motor is provided, and a new way for prolonging the length of the cable can be obtained through analysis by the way, namely, the condition that the motor is still effectively driven by the more distributed capacitance of the cable is met by reducing the limit frequency value, so that the length of the cable can be effectively improved.
2. In the process of selecting the cable, after the actual calculation is finished, the cable can be directly selected according to the maximum length result of the calculation, and after the cable connection is finished, the frequency converter can stably and reliably drive a common three-phase asynchronous motor which is 250 meters away.
3. In the working process, the harmonic waves of various frequencies can emit radio interference of different frequencies to the space, possibly causing malfunction of other equipment, and the problem is solved by the system form of the invention.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a flow chart of a method for calculating a cable length of a frequency converter;
FIG. 2 is a flow chart of a motor drive method;
FIG. 3 is a diagram of the actual PWM waveform after switching by the high power switching device IGBT;
FIG. 4 is a diagram of a PWM waveform after suppression of surge spikes;
FIG. 5 is a PWM waveform diagram after the remaining high frequency harmonics are isolated;
FIG. 6 is a schematic diagram of distributed capacitance of a long cable of a current drive motor;
FIG. 7 is a frame diagram of the motor drive mechanism of the present invention;
reference numerals: 01. an AC input circuit; 02. a PWM control circuit; 03. a frequency converter IGBT output circuit; 04. distributing capacitance; 05. a motor; 06. a ground line PE; 07. an output filter; 08. and an output reactor.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
Example one
The method for calculating the cable length of the frequency converter is used for calculating the cable length from the output end of the frequency converter to the input end of the motor, and comprises the following steps as shown in figure 1:
s1: determining the limit values of the instantaneous surge current and the instantaneous peak voltage generated by the cable; in the implementation process, the instant surge current is generated by the capacitive reactance of the distributed capacitor of the cable, so that the motor winding generates heat, vibration and noise are generated, the insulation aging is accelerated, and the motor can be damaged; the resonance of the distributed capacitor and the distributed inductor on the cable can generate surge voltage which is superposed on the output voltage, and the instantaneous peak voltage which is twice of the direct-current voltage can be generated at the highest voltage, so that overvoltage and overcurrent protection can be easily caused, and even the module is burnt out; therefore, in the invention, the allowable instantaneous surge current and instantaneous peak voltage are determined according to the actual system condition as the limit condition of the overall stable operation of the system;
s2: calculating a capacitive reactance reference value of a total length range of a cable between the output end of the frequency converter and the motor according to the ratio of the instantaneous peak voltage to the limit value of the instantaneous surge current; the specific calculation formula is as follows: capacitive reactance reference = instantaneous peak voltage/instantaneous surge current, where the unit of the instantaneous peak voltage is U, the unit of the instantaneous surge current is a, and the unit of the capacitive reactance reference is Ω;
in this embodiment, taking the instantaneous peak voltage as 700V and the instantaneous surge current as 22A as an example, the capacitive reactance reference value Zc =700/22 ≈ 32 Ω;
because the voltage waveform output by the frequency converter is not a sine wave, but a PWM pulse sequence with the same amplitude and the same period but different widths; according to the pulse wave spectrum analysis, the PWM waveform contains a large number of harmonic components with high frequency, high voltage and even ultrahigh frequency, and the frequency of the harmonic generally consists of a plurality of sine wave series from hundreds of K to hundreds of MHZ; meanwhile, because a high-power switching device IGBT in the frequency converter works in an on-off state, voltage and current jump in a short time due to high-speed switching action of the device, so that voltage and current waveforms contain a large amount of high-frequency harmonic components; the high-frequency harmonics are all generated in the PWM modulation, and the frequency of the larger high-frequency harmonics can increase the instantaneous output current of the frequency converter, which causes the heating of the motor winding, the generation of vibration and noise, the accelerated insulation aging, and the possible damage to the motor, so that the present invention also uses the frequency converter as one of the limit conditions, and specifically executes the following steps:
s3, determining a limit frequency value of high-frequency harmonic waves generated in PWM of the frequency converter;
in the above steps, step S3 may be performed before step S2, or may be performed before step S1, and it is only necessary to ensure that the step is completed before the following steps are performed;
s4: calculating a distributed capacitance reference value of the total length range of the cable between the output end of the frequency converter and the motor according to the capacitive reactance reference value and the limit frequency value; the specific calculation formula is as follows: c =1/2 pi Zc F, where F is the above-mentioned limit frequency value and is expressed by HZ, and the unit of the reference value C of the distributed capacitance obtained by the final calculation is F;
in this embodiment, in combination with the above steps, the limiting frequency value f is further 10 6 HZ for example, C =1/2 x 3.14 x 32 x 10 6 ≈5*10 -9F ;
According to the calculation, when the limit frequency value of the high-frequency harmonic is reduced, the cable can bear larger distributed capacitance under the same condition;
and S5, calculating the maximum length of the cable between the output end of the frequency converter and the motor according to the reference value of the distributed capacitance and the capacitance value of the cable. Usually, the capacitance value of the output cable of the frequency converter is 1.5-3 × 10 -10F In this embodiment, a capacitance of 1.6 x 10 is used -10F (ii)/m; the maximum length L =5 x 10 of the cable available is calculated -9 /1.6*10 -10 ≈30m。
The reference value of the distributed capacitance obtained by the calculation is the distributed capacitance under the limit condition, and the corresponding length is the maximum length allowed under the limit condition.
In the above process, it is known from a reverse derivation that the distributed capacitance inevitably increases in the process of increasing the length of the cable, but in the process of actual use, the output load of the frequency converter is composed of two parts, namely, a motor load Lm and a capacitive reactance Zc load, and the smaller the capacitive reactance Zc, the larger the load is, which may cause the frequency converter to overcurrent and even burn out a high-power transistor, so it is known from the formula C =1/2 x pi Zc f that, in order to ensure stable operation of the system, when the distributed capacitance increases due to the extension of the cable, the large capacitive reactance Zc needs to be ensured to reduce the load, and then reducing the limit frequency value f becomes a key for extending the length of the cable.
According to the embodiment of the invention, a new way for calculating the length of the cable between the output end of the frequency converter and the input end of the motor is provided, and a new way for prolonging the length of the cable can be obtained through analysis by the way, namely, the condition that the motor is still effectively driven by the larger distributed capacitance obtained by the cable is met by reducing the limit frequency value, so that the length of the cable can be effectively improved.
Preferably, the instantaneous peak voltage is 1~2 times the motor operating voltage. The current operating voltage of the motor is 380V, and in the above embodiment, the voltage of 700V is in the above range.
In summary, since the distributed capacitance is the capacitance formed between the cable and the ground, it exists objectively and cannot be eliminated, and the only thing that can be suppressed is the high frequency harmonic generated in the PWM modulation.
Example two
Converter cable length calculation system includes:
the input module is used for inputting the limit values of the instantaneous surge current and the instantaneous peak voltage generated by the cable and the limit frequency values of the high-frequency harmonic waves generated in the PWM modulation;
the calculation module calculates a capacitive reactance reference value of a cable total length range from the output end of the frequency converter to the motor according to the ratio of the instantaneous peak voltage to the limit value of the instantaneous surge current, calculates a distributed capacitance reference value of the cable total length range from the output end of the frequency converter to the motor according to the capacitive reactance reference value and the limit frequency value, and calculates the maximum length of the cable from the output end of the frequency converter to the motor according to the distributed capacitance reference value and the capacitance value of the cable.
As described in the above embodiments, the input module inputs the limit values of the instantaneous surge current and the instantaneous peak voltage determined according to the actual system conditions, and the limit frequency value of the high-frequency harmonic, and by setting the limit values, the finally determined cable length can ensure the stable operation of the system, thereby effectively avoiding the above problems. In the specific implementation process, the computing system may adopt the computing method as described in the first embodiment, and details are not described here.
In the present embodiment, the instantaneous peak voltage is 1~2 times the motor operating voltage in the same manner.
EXAMPLE III
The motor driving method, as shown in fig. 2, includes the steps of:
a1: suppressing surge sharp pulse of high-frequency harmonic component generated in PWM modulation of the frequency converter; the result of the suppression can be known by comparing fig. 3 and fig. 4, in fig. 3, the actual PWM waveform after switching through the high-power switching device IGBT, where the rising edge kickback indicates that high-voltage high-frequency harmonics are contained; after the suppression of the surge spike, the waveform is shown in fig. 4, and obviously, many high-frequency and high-voltage harmonics are filtered by the rising edge;
a2: isolating the residual high-frequency harmonic waves generated in the PWM of the frequency converter; as can be seen from a comparison between fig. 4 and fig. 5, fig. 5 shows the PWM waveform with the isolated remaining high-frequency harmonics, wherein the rising edge is smoother;
after the above operation, the PWM waveform outputted from the inverter is changed, and thus, the following steps are performed:
and A3, re-determining the PWM waveform of the frequency converter through the steps, determining the limit frequency value of the high-frequency harmonic wave according to the new PWM waveform, wherein the result participates in the length calculation method in the embodiment I so as to obtain the maximum cable length allowed by the currently designed and optimized system, and the specific steps are as follows:
a4, determining the maximum length of a cable between the output end of the frequency converter and the input end of the motor by adopting the method for calculating the length of the cable of the frequency converter in the first embodiment;
and A5, connecting the output end of the frequency converter and the input end of the motor through a cable equal to or less than the maximum length set range, and executing the drive control of the motor.
In the process of selecting the cable, after the calculation is actually finished, the cable can be directly selected according to the calculated maximum length result, and in order to ensure the safety, the cable can be appropriately shortened, wherein the specific shortening degree is preferably less than or equal to 20% of the calculated length; after the cable connection is finished, the frequency converter can stably and reliably drive a common three-phase asynchronous motor which is 250 meters away.
The main measures for reliably driving the motor by the frequency converter in a long distance are adopted, and in addition to the measures, the frequency converter can be derated by 30% -50% in a preferable mode; reserving 30% -50% of allowance for the wire diameter of the cable; after the measures are combined, the motor can be driven by the frequency converter in a long-distance and reliable manner.
Besides the above measures, the carrier frequency can be adjusted to reduce harmonic interference. The carrier frequency of the frequency converter is the frequency which determines the switching frequency of the PWM high-power switching device and the on-off frequency of the high-frequency harmonic. (1) The influence of the carrier frequency on the frequency converter per se on the power loss of the IGBT (insulated gate bipolar transistor) of the high-power switching device is related to the carrier frequency, the larger the carrier frequency is, the larger the loss of the frequency converter is, the smaller the output power is, and the heat generation of a power module is increased; if the environmental temperature is high, the dead zone of the upper inverter tube and the lower inverter tube of the inverter bridge in the alternate conduction process becomes small, and the bridge arm can be short-circuited to damage the frequency converter in serious conditions.
(2) When the carrier frequency is too low, the effective torque of the motor is reduced, the loss is increased, the temperature is increased, and meanwhile, the change rate dv/dt of the output voltage is increased, so that the insulation effect on the motor is large; when the carrier frequency is too high, the vibration of the motor is reduced, the running noise is reduced, the heating of the motor is also reduced, but the frequency of harmonic current is increased, the skin effect of a motor stator is more serious, the loss of the motor is increased, and the output power is reduced.
Motors with different power grades have different carrier frequency ranges, generally between 4 and 16K; the larger the motor power, the smaller the carrier frequency is generally selected. (3) The higher the carrier frequency is, the more serious the interference of the high-frequency voltage to the electronic device through electrostatic induction, electromagnetic radiation, and the like.
In practical use, the carrier frequency is selected to avoid the inherent resonant frequency of the motor firstly, and then the carrier frequency is selected to be smaller, such as less than or equal to 6Khz, according to the heating condition of the motor under the condition of meeting the two conditions, which is favorable for long-line transmission.
Example four
The motor driving mechanism, as shown in fig. 7, includes an ac input circuit 01, a PWM control circuit 02, and a frequency converter IGBT output circuit 03 connected in sequence; the power supply also comprises an output filter 07 and an output reactor 08 which are connected in sequence and arranged between the IGBT output circuit 03 and the motor 05 of the frequency converter; and the system also comprises a system for calculating the length of the cable of the frequency converter as described in the second embodiment, and the system is used for calculating the maximum length of the cable between the output end of the frequency converter IGBT output circuit 03 and the input end of the motor 05.
Fig. 6 shows a schematic diagram of a distributed capacitance 04 of a long cable of the present driving motor 05, where the distributed capacitance 04 is a distributed parameter, and the value of the distributed capacitance 04 varies with different manufacturers of the cable and varies with the laying mode, working condition and external environment factors of the cable, but the longer the cable, the larger the distributed capacitance 04, which is substantially proportional to the length of the cable, and in the case that it is difficult to change the distributed capacitance, the capacitive reactance of the cable is increased by shortening the length of the cable in the original mode, so as to reduce the load.
In the present invention, the driving action of the motor 05 is executed in the form of a system as shown in fig. 7, and in the implementation process, a driving method as in the third embodiment may be adopted, specifically:
(1) An output filter 07 suppresses a surge spike of a high-frequency harmonic component generated in the PWM modulation of the frequency converter; the output filter 07 selects the working voltage to be three-phase alternating current 380V, namely, one output filter 07 is installed on each phase, and the working current is selected to be larger than the rated current of the motor 05; specifically, different output filters 07 can be selected according to the power of the motor 05.
(2) The output reactor 08 isolates the remaining high-frequency harmonic waves generated in the PWM modulation of the frequency converter; the output reactor 08 is characterized in that: when the frequency of the high-frequency harmonic is smaller, the inductive reactance of the output reactor 08 is smaller, and the output reactor 08 is equivalent to a channel for a low-frequency signal; when the frequency of the high-frequency harmonic is higher, namely the inductive reactance is higher, the high-frequency harmonic which can pass through the output reactor 08 is smaller; for high-frequency harmonic waves, an output reactor 08 plays an isolation role between the output filter 07 and the motor 05; therefore, the output reactor 08 can effectively suppress instantaneous high voltage and high frequency harmonic generated when the high-power switching device IGBT of the frequency converter is switched on and off, isolate the direct damage of the distributed capacitor 04 of the long cable to the high-power switching device IGBT output module of the frequency converter, and greatly prolong the effective transmission distance of the frequency converter.
During the operation, the harmonics of various frequencies can transmit radio interference of different frequencies to the space, which may cause other devices to malfunction.
The motor 05 driving mechanism in the present embodiment performs the calculation of the cable length by using the calculation system as in the second embodiment, but it should be noted that the calculation result is the maximum length of the cable between the output terminal of the inverter IGBT output circuit 03 and the input terminal of the motor 05, but actually, the calculation of the cable length is performed after the remaining high frequency harmonics generated in the inverter PWM modulation are isolated and the PWM waveform is newly determined, and therefore, as a preference of the above-mentioned embodiment, the distance between the output terminal of the inverter IGBT output circuit 03 and the input terminal of the output filter 07 is less than 0.1m; and the distance between the output end of the output filter 07 and the input end of the output reactor 08 is less than 0.1m.
Through the mode, the connecting lines among the IGBT output circuit 03, the output filter 07 and the output reactor 08 of the frequency converter are all shortened as much as possible, the influence of the cable length among the devices is reduced, and the cable length among the modules can be ignored as a final result in a final calculation result.
In the implementation process, a double-shielded cable is required to be adopted as a long-distance output cable of the output reactor 08 so as to reduce electromagnetic radiation; and a good grounding system is also one of the keys for realizing long-line transmission of the frequency converter and meeting EMC, so that a special frequency converter driving cable shielding ground wire PE06 is preferably buried in a factory building area, and the output cable shielding layer of the output reactor 08 adopts a source end grounding wire PE06 technology, wherein the PE ground wire must be strictly separated from a power supply 0 line. By adopting a series of hard and soft control schemes, the frequency converter can stably and reliably drive a common three-phase asynchronous motor which is 250 meters away.
The foregoing illustrates and describes the principles, general features, and advantages of the present invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims (10)

1. The method for calculating the cable length of the frequency converter is used for calculating the cable length between the output end of the frequency converter and the input end of a motor, and is characterized by comprising the following steps of:
determining the limit values of the instantaneous surge current and the instantaneous peak voltage generated by the cable;
calculating a capacitive reactance reference value of a total length range of a cable between the output end of the frequency converter and the motor according to the ratio of the instantaneous peak voltage to the limit value of the instantaneous surge current;
determining a limit frequency value of high-frequency harmonics generated in PWM modulation of a frequency converter;
calculating a distributed capacitance reference value of a cable total length range from the output end of the frequency converter to the motor according to the capacitive reactance reference value and the limit frequency value;
and calculating the maximum length of the cable between the output end of the frequency converter and the motor according to the distributed capacitance reference value and the capacitance value of the cable.
2. The method for calculating the cable length of the frequency converter according to claim 1, wherein the instantaneous peak voltage is 1~2 times of the working voltage of the motor.
3. Converter cable length calculation system, its characterized in that includes:
the input module is used for inputting the limit values of the instantaneous surge current and the instantaneous peak voltage generated by the cable and the limit frequency value of the high-frequency harmonic generated in the PWM modulation;
and the calculating module is used for calculating a capacitive reactance reference value of the total length range of the cable between the output end of the frequency converter and the motor according to the ratio of the instantaneous peak voltage to the limit value of the instantaneous surge current, calculating a distributed capacitance reference value of the total length range of the cable between the output end of the frequency converter and the motor according to the capacitive reactance reference value and the limit frequency value, and calculating the maximum length of the cable between the output end of the frequency converter and the motor according to the distributed capacitance reference value and the capacitance value of the cable.
4. The system of claim 3, wherein the instantaneous peak voltage is 1~2 times the motor operating voltage.
5. A motor driving method characterized by comprising the steps of:
suppressing surge sharp pulse of high-frequency harmonic component generated in PWM modulation of the frequency converter;
isolating the residual high-frequency harmonic generated in the PWM of the frequency converter;
re-determining the PWM waveform of the frequency converter through the steps, and determining the limit frequency value of the high-frequency harmonic wave according to the new PWM waveform;
determining the maximum length of the cable between the output end of the frequency converter and the input end of the motor by adopting the frequency converter cable length calculation method according to the limit frequency value;
and connecting the output end of the frequency converter and the input end of the motor through a cable which is equal to or less than the maximum length set range, and executing the drive control of the motor.
6. The motor driving method according to claim 5, wherein the frequency converter is derated by 30% to 50%.
7. The motor driving method according to claim 5 or 6, wherein a margin of 30% to 50% of the wire diameter of the cable is reserved for use.
8. The motor driving mechanism is characterized by comprising an alternating current input circuit, a PWM control circuit and a frequency converter IGBT output circuit which are sequentially connected;
the power supply is characterized by further comprising an output filter and an output reactor which are sequentially connected, wherein the output filter and the output reactor are arranged between the frequency converter IGBT output circuit and the motor;
further comprising a frequency converter cable length calculation system as claimed in claim 3, calculating the maximum length of cable between the output of the frequency converter IGBT output circuit and the motor input.
9. The motor drive of claim 8, wherein the distance between the output of the inverter IGBT output circuit and the input of the output filter is less than 0.1m.
10. The motor drive according to claim 8, wherein a distance between an output end of the output filter and an input end of the output reactor is less than 0.1m.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102694457A (en) * 2011-03-21 2012-09-26 季平 Frequency converter output DVDT filter
CN104281736A (en) * 2014-08-01 2015-01-14 国家电网公司 Power supply cable type selecting method for urban track traffic traction power supply and distribution system
CN106788118A (en) * 2017-02-28 2017-05-31 广东工业大学 A kind of suppression circuit of Inverter Drive System motor side common-mode voltage
CN113420398A (en) * 2021-06-22 2021-09-21 杭州和昶电子科技有限公司 Comprehensive high-frequency modeling method for cable in variable-frequency motor long-line driving system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102694457A (en) * 2011-03-21 2012-09-26 季平 Frequency converter output DVDT filter
CN104281736A (en) * 2014-08-01 2015-01-14 国家电网公司 Power supply cable type selecting method for urban track traffic traction power supply and distribution system
CN106788118A (en) * 2017-02-28 2017-05-31 广东工业大学 A kind of suppression circuit of Inverter Drive System motor side common-mode voltage
CN113420398A (en) * 2021-06-22 2021-09-21 杭州和昶电子科技有限公司 Comprehensive high-frequency modeling method for cable in variable-frequency motor long-line driving system

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