CN102856884B - Heat accumulation based frequency converter overload method - Google Patents
Heat accumulation based frequency converter overload method Download PDFInfo
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- CN102856884B CN102856884B CN201210343512.9A CN201210343512A CN102856884B CN 102856884 B CN102856884 B CN 102856884B CN 201210343512 A CN201210343512 A CN 201210343512A CN 102856884 B CN102856884 B CN 102856884B
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Abstract
The invention discloses a heat accumulation based frequency converter overload method including the steps: (1) computing data including heat dissipation potential, heat balance periods and overload capacity and conforming to actual hardware conditions according to hardware design; (2) performing integral computation for heat accumulation of all current in each latest heat balance period based on power consumption and temperature increase by a sliding window method; (3) making correction computation for an overload threshold according to the overload capacity obtained by actual testing; and (4) comparing a heat accumulation value in a heat balance period obtained by computing with a corrected overload threshold, and deeming as overload if the heat accumulation value exceeds the corrected overload threshold. Protective control of frequency converter overload is achieved by the steps. By means of computing heating and heat dissipation of hardware and current heat effect accumulation values within one heat balance period, the overload capacity of a specific frequency converter can be reflected accurately, and the hardware of the frequency converter is effectively protected from being damaged due to overload.
Description
Technical Field
The invention relates to an overload protection technology of a frequency converter, in particular to a frequency converter overload method based on heat accumulation.
Background
With the rapid development of modern power electronic technology and computer control technology, frequency converters have been widely used for stepless speed regulation of ac motors. The variable frequency speed regulation of the alternating current motor is a main means for saving electric energy, improving the production process flow, improving the product quality and improving the operation environment at present. The variable frequency speed regulation is regarded as the most promising speed regulation mode at home and abroad by virtue of a plurality of advantages such as high frequency, high power factor, excellent speed regulation and starting and braking performances, and the like, and is widely used in various industries such as steel, chemical engineering, textile, mechanical power, paper making and the like.
Generally, frequency converters have a certain overload capacity, because the current has a certain fluctuation range in the using process, the situation that the current exceeds the rated current is more or less occurred, if the frequency converters or load equipment are operated under the overload situation for a short time, the frequency converters or the load equipment cannot be damaged immediately, but if the system is left to operate under the condition that the rated current exceeds the rated current for a long time, the mechanical strength of insulation and parts can be reduced rapidly, the aging of the system is accelerated, and the reduction of the mechanical performance and the electrical contact performance provides possibility for other types of faults, and great damage is brought to the equipment. Overload protection is an important protection function of frequency converters. However, the load types are different, the load change modes are various, and the overload protection algorithm is difficult to effectively solve.
At present, the overload algorithms of domestic and Japanese frequency converters basically define an inverse time limit curve according to heat, and the larger the overload multiple is, the shorter the overload time is. In the control flow, whether the current meets the overload condition is judged firstly, then timing processing is carried out according to the overload time, and if the current is reduced before the overload fault is reported, the overload time is reduced. The method is only an overload mathematical model, only describes the inverse time limit relation between the current and the action time under the overload condition, does not consider the heat dissipation period, does not consider the difference of heat dissipation under different currents and conditions, cannot correctly reflect the influence of the thermal effect of non-overload and critical overload current on the inverse time limit action time, and can cause that hardware is burnt out but overload faults are not reported.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method for overloading the frequency converter based on heat accumulation is provided to overcome the defects in the prior art.
The invention adopts the following technical scheme for solving the technical problems:
the invention provides a frequency converter overload method based on heat accumulation, which comprises the following steps:
(1) calculating data including heat dissipation capacity, heat balance period and overload capacity according with actual hardware conditions according to hardware design;
(2) calculating the heat accumulation of all current based on power consumption and temperature rise in each latest heat balance period by integration by using a sliding window method;
(3) correcting and calculating the overload threshold value according to the overload capacity result obtained by actual test;
(4) comparing the calculated heat accumulation value in a heat balance period with the corrected overload threshold value, and if the heat accumulation value exceeds the corrected overload threshold value, determining that the heat accumulation value is overloaded;
through the steps, the overload protection control of the frequency converter is realized.
The method for realizing the step (1) can be as follows: calculating the thermal loss values at rated and different overload according to the characteristics of the power module and the structural appearance size; and under the condition of ensuring that the temperature of the power module does not exceed 40 ℃, combining CAE simulation and calculation values to formulate the overload capacity and the thermal balance period.
The method for realizing the step (2) can be as follows: sampling the current effective value in real time, performing average filtering processing on the data within 1s, storing the data into an array, and calculating I of the data2t value and calculating the accumulated I in the current heat balance period2Comparing and judging the value t with an overload threshold value; when the accumulated running time exceeds a thermal equilibrium period, acquiring and calculating a new current value every second, then replacing the current value at the earliest time with the new current value, and calculating I of the current value2t value, thereby ensuring accumulated I2the value t is always the latest value in the current thermal balance period, and the instantaneity of overload protection is ensured.
The method for realizing the step (3) can be as follows: a series of experimental data of the actual overload capacity of the frequency converter are obtained by adding loads of different multiples to the frequency converter to carry out overload experiments, and certain correction calculation is carried out on an overload threshold value according to experimental results, so that the final program execution result really meets the actual hardware condition.
In the step (4), under the condition of overload, an operator can select to do nothing, alarm or report a fault and stop the machine for locking according to the setting of a user.
Compared with the prior art, the invention has the following main advantages:
the method fully considers the heating and heat dissipation capacity of specific hardware, is suitable for any load current, and solves the problem that the commonly used inverse time limit characteristic curve only describes the inverse time limit relation between the current and the action time under the overload condition, and can not correctly reflect the influence of the thermal effect of non-overload and critical overload current on the inverse time limit action time, so that the hardware can not be effectively protected.
The overload capacity of a specific frequency converter can be accurately reflected by calculating the heating and heat dissipation of hardware and calculating the accumulated value of the heat effect of current in a heat balance period, the problem that the hardware cannot be effectively protected by a traditional inverse time limit overload algorithm when the load current of the frequency converter is frequently overloaded and not overloaded is solved, and meanwhile, the hardware of the frequency converter is effectively protected from being damaged due to overload.
After the design work is finished, loads of different multiples are added to frequency converters of each power section to carry out overload experiments, and the load current is frequently switched, because a certain margin is specially reserved in the design, when the temperature rise of a power module reaches about 38 ℃, the frequency converters report overload, the fact that an overload algorithm is suitable for any load current is fully proved, the actual heating and heat dissipation conditions of hardware are met, the overload capacity of the frequency converters can be accurately reflected, and the hardware is really and effectively protected from being damaged due to overload.
In a word, the invention can accurately reflect the overload capacity of the frequency converter, namely, the frequency converter has stronger overload capacity under the condition of hardware permission, and simultaneously, the hardware of the frequency converter is effectively protected from being damaged due to overload.
Drawings
Fig. 1 is a typical light load overload operation cycle of the present invention.
Fig. 2 is a typical heavy duty overload operation cycle of the present invention.
Fig. 3 is a program flow diagram of the present invention.
Detailed Description
The present invention will be further described with reference to the following specific examples.
The basic characteristic of overload is that the temperature rise exceeds the rated temperature rise, and the purpose of overload protection is to prevent the hardware from burning out due to overheating.
The theoretical basis of the invention is to carry out I on the output current2And (4) calculating t, wherein the value reflects the accumulation of the power consumption and the temperature rise of the frequency converter.
The theoretical formula is as follows:
wherein,
i (t) is a time function of the effective value of the output current of the frequency converter;
IRatedis the rated output current of the frequency converter;
KDis a current de-rating factor;
t is a thermal equilibrium period.
In the actual programming, in order to simplify the calculation, the above formula is discretized, and n constant-current stages are used as substitute values. The specific calculation formula is simplified as follows:
wherein,
I1-Inoutputting current for each time point in a heat dissipation period of the frequency converter;
IRatedrated output current of the frequency converter;
T1-Tnfor the duration of each output current;
t is a thermal balance period and is provided by a heat dissipation designer according to the calculation of hardware design conditions;
KDthe derating factor is also provided by the heat dissipation designer according to the calculation of the hardware design condition.
In this embodiment, a frequency converter EC550 series developed by southern china metallurgy (wuhan) automation limited is taken as an example, the rated temperature rise is defined as 40 ℃, and the temperature rise of the power module under the rated power is calculated through CAE simulation. The temperature rise at overload time t is then:
in the formula:is the thermal time constant of the power module.Is the thermal resistance of the heat sink and,is the heat capacity of the heat sink.
From transient thermal impedance ， ，，
Is the temperature rise at an overload time of t
Is the temperature rise at rated power
Is the difference of thermal loss at overload
And calculating the overload capacity and the thermal balance period T according to the function of the relation between the overload power consumption and the time.
KDThe set value is calculated by thermal simulation software and power consumption calculation software, and then certain correction is carried out by referring to final test data. This value is related to the ambient temperature, altitude and pulse frequency. The value is taken to be 1 in case of non-derated use.
In order to ensure the accuracy of overload protection and simultaneously consider the memory occupation amount of the dsp and the change curve of the current, the current effective value is sampled in real time in the program, the average value in 1s is taken and stored in an array, and I of the current effective value is calculated2t value and calculating the accumulated I in the current heat balance period2And comparing and judging the value t with the overload threshold value. Adopting a sliding window mode in the whole program, acquiring and calculating a new current value every second after the accumulated running time exceeds a thermal equilibrium period, then replacing the current value at the earliest time with the new current value, and calculating I of the new current value2t value, thereby ensuring accumulated I2the value t is always the latest value in the current thermal balance period, and the instantaneity of overload protection is ensured.
Because hardware designs of frequency converters with different powers are different more or less, in order to reflect the overload capacity of the frequency converter most practically, loads with different multiples are added to the frequency converters in each power section to carry out overload experiments, a series of experimental data of the actual overload capacity of the frequency converter are obtained, certain correction calculation is carried out on an overload threshold value according to the experimental results, the actual overload capacity of the frequency converter can be reflected most truly by the final program execution result, and hardware is protected effectively.
Well smelt south (wuhan) automation ltd independently research and development's EC550 series converter in south, its powerful, structural layout is reasonable. This converter mainly comprises power board, radiator, reactor and control box, wherein: the power board dispels the heat alone through the aluminium alloy radiator of customization, and the radiator is put in independent wind channel to 24V axial compressor double fan carries out direct heat dissipation of blowing to it, and the reactor is placed in the radiator front end simultaneously, can let the reactor keep lower temperature. The control panel is placed with the power board layering, and the control panel assembly has completely cut off external heat source in special control box, has independent exhaust system in the control box simultaneously, has stopped the possibility of heat accumulation in the control box, and effectual reduction control panel temperature has prolonged the device life-span, has improved system stability and reliability.
According to the embodiment, the heating and heat dissipation capacity of specific hardware is fully considered, the method is suitable for any load current, and the problem that the hardware cannot be effectively protected due to the fact that a common inverse time limit characteristic curve only describes the inverse time limit relation between the current and the action time under the overload condition and cannot correctly reflect the influence of the thermal effect of non-overload and critical overload current on the inverse time limit action time is solved.
Claims (4)
1. A frequency converter overload method based on heat accumulation is characterized by comprising the following steps:
(1) calculating data including heat dissipation capacity, heat balance period and overload capacity according with actual hardware conditions according to hardware design;
(2) the method of using a sliding window calculates the heat accumulation based on current in each latest heat balance period through integration, and the heat accumulation value reflects the accumulation of the power consumption and the temperature rise of the frequency converter, and the specific method is as follows: sampling the current effective value in real time and carrying out average filtering on data within 1sStoring the data into an array after the processing, and calculating I of the data2t value and calculating the accumulated I in the current heat balance period2Comparing and judging the value t with an overload threshold value; when the accumulated running time exceeds a thermal equilibrium period, acquiring and calculating a new current value every second, then replacing the current value at the earliest time with the new current value, and calculating I of the current value2t value, thereby ensuring accumulated I2the value t is always the latest value in the current thermal balance period, so that the instantaneity of overload protection is ensured;
(3) correcting and calculating the overload threshold value according to the overload capacity result obtained by actual test;
(4) comparing the calculated heat accumulation value in a heat balance period with the corrected overload threshold value, and if the heat accumulation value exceeds the corrected overload threshold value, determining that the heat accumulation value is overloaded;
through the steps, the overload protection control of the frequency converter is realized.
2. The heat accumulation based frequency converter overload method according to claim 1, wherein the method for implementing the step (1) is: calculating the thermal loss values at rated and different overload according to the characteristics of the power module and the structural appearance size; and under the condition of ensuring that the temperature of the power module does not exceed 40 ℃, combining CAE simulation and calculation values to formulate the overload capacity and the thermal balance period.
3. The heat accumulation based frequency converter overload method according to claim 1, wherein the method for implementing the step (3) is: a series of experimental data of the actual overload capacity of the frequency converter are obtained by adding loads of different multiples to the frequency converter to carry out overload experiments, and certain correction calculation is carried out on an overload threshold value according to experimental results, so that the final program execution result really meets the actual hardware condition.
4. The frequency converter overload method based on heat accumulation as claimed in claim 1, wherein in the step (4), in case of overload, an operator selects no action, alarm or fault-reporting shutdown lockout according to user's setting.
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| CN105790677A (en) * | 2016-04-15 | 2016-07-20 | 郑州宇通客车股份有限公司 | Motor controller overload protection method and system |
| CN110867820A (en) * | 2019-11-15 | 2020-03-06 | 陕西航空电气有限责任公司 | Alternating current intelligent contactor system adaptive to multi-specification load current |
| CN114083989A (en) * | 2021-12-24 | 2022-02-25 | 天津英捷利汽车技术有限责任公司 | Current inverse time limit protection method for pure electric vehicle |
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| CN101123348A (en) * | 2007-09-14 | 2008-02-13 | 西安理工大学 | AC motor unbalanced protection method based on unbalanced accumulation |
| US8054599B2 (en) * | 2008-07-14 | 2011-11-08 | International Business Machines Corporation | Apparatus, system, and method for detecting a power system component failure |
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