Soft start control method and system of asynchronous motor

Abstract

The invention discloses a soft start control method and system for an asynchronous motor, and belongs to the technical field of motor control. According to the method, the slope of the limiting current is adaptively changed by adopting the fuzzy control algorithm for loads with square torque characteristics, such as fans and pumps, so that the control accuracy and the response speed of the system are improved, an electromagnetic torque curve of an asynchronous motor can be adaptively fitted with a load torque curve in the starting process of the loads such as the fans and the pumps, and the starting speed of the system is improved. Approximate constant acceleration starting is realized, current impact, torque impact and energy loss during starting of the motor can be remarkably reduced, the overall efficiency of the system can be improved, and the starting process is accelerated; appropriate quantization factors can ensure that an input variable is converted from its actual object theory domain to a fuzzy set theory domain so as to facilitate fuzzy reasoning.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and in particular to a soft start control method and system for an asynchronous motor. Background Art

[0002] With the accelerated advancement of UHV power grid construction, phase-shifting devices have received more and more attention due to their outstanding reactive power response capability, and their role in improving UHV DC transmission power and strengthening regional power grid voltage support has become increasingly significant. Phase-shifting device auxiliary equipment is widely distributed in phase-shifting device lubricating oil system, external cooling water system, internal cooling water system, desalted water system and other parts. Phase-shifting device auxiliary equipment system includes many devices. Its operating reliability has a direct impact on the safe and stable operation of the phase-shifting device host.

[0003] Most of these auxiliary machines are asynchronous motors. In the asynchronous motor starting method, the direct starting method of putting the motor into the rated voltage is called full-voltage starting. The advantages of this starting method are simple equipment and relatively fast starting speed, but the starting current is usually large when directly starting a three-phase asynchronous motor. In particular, the direct starting of large-capacity asynchronous motors has a greater impact on the power grid, causing other electrical equipment to not operate normally. In serious cases, it will also damage the equipment and cause significant losses. On the other hand, the full-voltage starting of asynchronous motors will also produce a high electromagnetic torque impact, which will damage the transmission machinery, such as causing damage to the pipelines and valves of the pump system, shortening the service life, etc.

[0004] Most of the loads driven by the auxiliary machines of the phase regulator are fans and pumps with square torque characteristics. For this type of load, if the voltage ramp control method is used, because it is an open-loop control, the slope rise cannot be automatically adjusted during the starting process, which often causes the current to exceed the expected current. Therefore, current closed-loop soft start control technologies such as current limiting starting and current ramp soft starting are produced. However, the current limiting starting method is suitable for constant torque loads. Although the current ramp soft start is an effective method for soft starting of fans and pumps, it is difficult to make the electromagnetic torque curve of the motor during the starting process completely fit the load torque curve by using the current ramp soft start method with a fixed slope. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a soft starting control method and system for an asynchronous motor, which can adaptively change the slope of the set limiting current, achieve effective current limitation during the starting process of the asynchronous motor, reduce the starting time and torque impact, and speed up the starting process.

[0006] To achieve the above object, the present invention is implemented by adopting the following technical solutions: In one aspect, the present invention provides a soft start control method for an asynchronous motor, comprising: Acquire a pulse signal output by a synchronous pulse generating circuit; wherein the synchronous pulse generating circuit inputs an input voltage of the asynchronous motor and a preset starting trigger angle; According to the electromagnetic torque and load torque fed back by the asynchronous motor, the slope of the limiting current curve is obtained by using a fuzzy control algorithm; according to the slope of the limiting current curve, the limiting current is obtained; The obtained asynchronous motor feedback current is compared and converted with the limiting current in sequence to obtain a control signal variation; Using the pulse signal as a trigger signal of the thyristor, and calculating the trigger angle of the thyristor according to the change of the control signal; The start and stop of the asynchronous motor is controlled by the trigger signal of the thyristor, and the starting current of the asynchronous motor is controlled by the trigger angle of the thyristor.

[0007] Optionally, the processing steps of the synchronization pulse generating circuit include: The input voltage of the asynchronous motor is subjected to delay processing and speed limiting processing in sequence to obtain a voltage sinusoidal signal; Converting the voltage sinusoidal signal into a voltage triangular wave signal; The voltage triangle wave signal and the preset starting trigger angle are sequentially superimposed and delayed to obtain a pulse signal.

[0008] Optionally, according to the electromagnetic torque and load torque fed back by the asynchronous motor, a fuzzy control algorithm is used to obtain the slope of the limiting current curve, including: The deviation and the deviation change rate are multiplied by the corresponding quantization factors respectively, and the product is mapped to the fuzzy set domain to obtain the deviation and the deviation change rate on the fuzzy set domain; wherein the deviation is the deviation between the electromagnetic torque of the asynchronous motor and the load torque, and the deviation change rate is the deviation change rate between the electromagnetic torque of the asynchronous motor and the load torque; The deviation and the deviation change rate on the fuzzy set domain are input into the fuzzy controller, and the slope of the limiting current curve is outputted by using the preset fuzzy control principle.

[0009] Optionally, the quantization factor corresponding to the deviation and the deviation change rate is expressed as: ; in, is the quantification factor of the deviation; is the quantitative factor of the deviation change rate; is the fuzzy input domain of the deviation; is the fuzzy input domain of the deviation change rate; is the actual domain of the deviation; is the actual domain of the deviation change rate.

[0010] Optionally, the fuzzy input domain of the deviation and the fuzzy output domain of the slope of the limiting current curve both adopt asymmetric domains.

[0011] Optionally, the preset fuzzy control principle includes: If the deviation on the fuzzy set domain is less than zero, the slope of the limiting current curve is increased; otherwise, the slope of the limiting current curve is reduced.

[0012] Optionally, the acquired asynchronous motor feedback current and the limiting current are sequentially compared and converted to obtain a control signal variation, including: The obtained asynchronous motor feedback current is compared with the limit current to obtain the deviation current; The deviation current is input into a PI controller for conversion to obtain a control signal variation.

[0013] Optionally, calculating the trigger angle of the thyristor according to the change in the control signal includes: The control signal change amount is subtracted from the preset starting trigger angle to obtain the trigger angle of the thyristor.

[0014] In a second aspect, the present invention provides a soft start control system for an asynchronous motor, comprising: The pulse signal acquisition module is used to: acquire the pulse signal output by the synchronous pulse generating circuit; wherein the synchronous pulse generating circuit inputs the input voltage of the asynchronous motor and the preset starting trigger angle; The limiting current acquisition module is used to: obtain the slope of the limiting current curve according to the electromagnetic torque and load torque fed back by the asynchronous motor using a fuzzy control algorithm; and obtain the limiting current according to the slope of the limiting current curve; A control signal acquisition module is used to compare and convert the acquired asynchronous motor feedback current and the limiting current in sequence to obtain a control signal variation; A starting current acquisition module is used to: use the pulse signal as a trigger signal of the thyristor and calculate the trigger angle of the thyristor according to the change amount of the control signal; The start and stop of the asynchronous motor is controlled by the trigger signal of the thyristor, and the starting current of the asynchronous motor is controlled by the trigger angle of the thyristor.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention aims at loads with square torque characteristics such as fans and pumps, and adopts a fuzzy control algorithm to adaptively change the slope of the limiting current, thereby improving the control accuracy and the response speed of the system, and can ensure that the electromagnetic torque curve of the asynchronous motor during the starting process of the fan and pump loads adaptively fits the load torque curve to achieve approximate constant acceleration starting, which can not only significantly reduce the current impact, torque impact and energy loss during motor starting, but also improve the overall efficiency of the system and speed up the starting process; the appropriate quantization factor can ensure that the input variable is converted from its actual physical domain to the fuzzy set domain for fuzzy reasoning. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. 1 is a flow chart of a soft start control method for an asynchronous motor according to an embodiment of the present invention; Figure 2 Shown is a schematic diagram of a membership function of a deviation between electromagnetic torque and load torque in an embodiment of the present invention; Figure 3 It is a schematic diagram of the membership function of the deviation change rate between the electromagnetic torque and the load torque in one embodiment of the present invention; Figure 4 Shown is a schematic diagram of a membership function of the slope of the current limiting curve in an embodiment of the present invention; Figure 5 Shown is a schematic structural diagram of a simulation model of the present invention in one embodiment; Figure 6 Shown is a schematic diagram of a curve of limiting current in an embodiment of the present invention; Figure 7 Shown is a curve diagram of the load torque of the present invention in one embodiment; Figure 8 Shown is a schematic diagram of a curve of the feedback current of an asynchronous motor of the present invention in one embodiment; Fig. 9 Shown is a schematic diagram of a curve of the speed of an asynchronous motor of the present invention in one embodiment; Fig.10 Shown is a schematic diagram of a curve of the electromagnetic torque of the present invention in one embodiment. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. The embodiments of the present invention and the technical features in the embodiments may be combined with each other unless there is a conflict.

[0018] The term "and / or" is only a description of the association relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " generally indicates that the related objects are in an "or" relationship.

[0019] Example 1

[0020] like Figure 1 As shown, this embodiment introduces a soft start control method for an asynchronous motor. For loads with square torque characteristics such as fans and pumps, a fuzzy control algorithm is used to adaptively change the slope of the limiting current, thereby effectively limiting the current during the starting process of the asynchronous motor driving the fan, pump and other loads, reducing the starting time and torque impact, and speeding up the starting process; the method specifically includes the following steps: Step 1: Construct a three-phase thyristor soft start main circuit, where each phase consists of a pair of anti-parallel thyristor circuits.

[0021] Step 2: Input the acquired input voltage of the asynchronous motor and the preset starting trigger angle into the synchronous pulse generating circuit to output a pulse signal, specifically: The synchronous pulse generating circuit is a six-pulse generating circuit, and the six-pulse generating circuit includes three double-pulse generators.

[0022] First, the double pulse generator sequentially performs delay processing and speed limiting processing on the input voltage of the asynchronous motor to obtain a voltage sinusoidal signal; Then, the voltage sine wave signal is converted into a voltage triangular wave signal, which is superimposed with the preset starting trigger angle, and a high and low level pulse signal is output after a delay module. The output pulse signal is connected to the gate of the thyristor as a trigger signal of the thyristor gate.

[0023] Step 3: According to the electromagnetic torque and load torque fed back by the asynchronous motor, the slope of the limiting current curve is obtained by using the fuzzy control algorithm, which is: The deviation and the deviation change rate are multiplied by the corresponding quantization factors respectively, and the product is mapped to the fuzzy set domain to obtain the deviation and the deviation change rate on the fuzzy set domain; wherein the deviation is the deviation between the electromagnetic torque of the asynchronous motor and the load torque, and the deviation change rate is the deviation change rate between the electromagnetic torque of the asynchronous motor and the load torque; The quantization factor corresponding to the deviation and the deviation change rate is expressed as: ; in, is the quantification factor of the deviation; is the quantitative factor of the deviation change rate; is the fuzzy input domain of the deviation; is the fuzzy input domain of the deviation change rate; is the actual domain of the deviation; is the actual domain of the deviation change rate.

[0024] The quantization factor is selected according to the preset range of deviation. In this embodiment, , , in the domain of three fuzzy variables, set the deviation e The fuzzy input domain is an asymmetric domain, and its domain range is [-20, 10]; the deviation change rate ec The fuzzy input domain is [-100, 100]; set the output variable, that is, the slope of the limiting current curve k The fuzzy output domain of is also an asymmetric domain, and its domain range is [0.5, 1.5], in order to expand the scope of each membership function and improve the response speed of the system. Figure 2-Figure 4 The following are shown: e , ec , k Schematic diagram of the corresponding membership function.

[0025] In the domain of three fuzzy variables, seven fuzzy subsets are selected, namely: negative big (NB), negative middle (NM), negative small (NS), zero (ZO), positive small (PS), positive middle (PM), positive big (PB). The triangle is selected as the shape of the membership function. When the domain is asymmetric, it is also designed to be an asymmetric structure.

[0026] The deviation and the deviation change rate on the fuzzy set domain are input into the fuzzy controller, and the slope of the limiting current curve is outputted by using the preset fuzzy control principle; The preset fuzzy control principles include: If the deviation on the fuzzy set domain is less than zero, the slope of the limiting current curve is increased; otherwise, the slope of the limiting current curve is reduced.

[0027] That is, when the electromagnetic torque is smaller than the load torque, the limiting current should be increased in a quick response; when the electromagnetic torque is smaller than the load torque, the greater the difference, the faster the response should be; when the electromagnetic torque is larger than the load torque, the speed of increasing the limiting current should be reduced in a quick response.

[0028] The fuzzy control principle can be represented by the fuzzy control rule table shown in Table 1.

[0029] Table 1 Fuzzy control rules table

[0030] The limiting current is obtained according to the slope of the limiting current curve.

[0031] Step 4: Compare and convert the acquired asynchronous motor feedback current and the limiting current in sequence to obtain the control signal variation, specifically: The obtained asynchronous motor feedback current is compared with the limit current to obtain the deviation current; The deviation current is input into a PI controller for conversion to obtain a control signal variation.

[0032] Step 5: Using the pulse signal as a trigger signal of the thyristor, and calculating the trigger angle of the thyristor according to the change in the control signal; that is, subtracting the change in the control signal from the preset starting trigger angle to obtain the trigger angle of the thyristor.

[0033] Step six: controlling the start and stop of the asynchronous motor by the trigger signal of the thyristor, and controlling the starting current of the asynchronous motor by the trigger angle of the thyristor.

[0034] Example 2

[0035] Based on the same inventive concept as that of Embodiment 1, this embodiment introduces an experimental example of a soft start control method for an asynchronous motor, which specifically includes: Establish as Figure 5 The ramp current limiting soft start simulation model shown in the figure includes a three-phase power supply, a thyristor voltage regulation circuit, a synchronous pulse circuit, a trigger angle calculation circuit, a current limiting curve circuit, a 75kW asynchronous motor, and current, torque, and speed measurement circuits. The main parameters of the 75kW asynchronous motor model are shown in Table 2: Table 2 Main parameters of 75kW asynchronous motor model

[0036] In this simulation case, the three-phase power supply supplies power to the asynchronous motor through the thyristor voltage regulation circuit. The synchronous pulse circuit collects the phase of the power supply voltage and receives the given trigger angle. The trigger angle calculation circuit compares the feedback current value with the limiting current curve value, and then calculates the thyristor trigger angle through the PI controller. The limiting current line compares the feedback electromagnetic torque with the load torque, and then obtains the slope of the limiting current curve through the fuzzy algorithm.

[0037] based on Figure 5 The simulation model of Figure 6 and Figure 7 They are the limiting current curve and load torque curve obtained by simulation calculation respectively. It can be seen that the load torque change curve is consistent with the changing law of the limiting current curve. Figure 8 , Fig. 9 , Fig.10 They are the effective value of motor current, speed and electromagnetic torque curves respectively. It can be seen from the figure that the current during the startup process is small, the startup process is smooth, and the speed does not fluctuate greatly.

[0038] Example 3

[0039] Based on the same inventive concept as that of Embodiment 1, this embodiment introduces a soft start control system for an asynchronous motor, comprising: The pulse signal acquisition module is used to: acquire the pulse signal output by the synchronous pulse generating circuit; wherein the synchronous pulse generating circuit inputs the input voltage of the asynchronous motor and the preset starting trigger angle; The limiting current acquisition module is used to: obtain the slope of the limiting current curve according to the electromagnetic torque and load torque fed back by the asynchronous motor using a fuzzy control algorithm; and obtain the limiting current according to the slope of the limiting current curve; A control signal acquisition module is used to compare and convert the acquired asynchronous motor feedback current and the limiting current in sequence to obtain a control signal variation; A starting current acquisition module is used to: use the pulse signal as a trigger signal of the thyristor and calculate the trigger angle of the thyristor according to the change amount of the control signal; The start and stop of the asynchronous motor is controlled by the trigger signal of the thyristor, and the starting current of the asynchronous motor is controlled by the trigger angle of the thyristor.

[0040] The specific functional implementation of each of the above modules can be found in the relevant contents of the method in Example 1 and will not be elaborated here.

[0041] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. A soft start control method for an asynchronous motor, characterized in that: include: Acquire a pulse signal output by a synchronous pulse generating circuit; wherein the synchronous pulse generating circuit inputs an input voltage of the asynchronous motor and a preset starting trigger angle; According to the electromagnetic torque and load torque fed back by the asynchronous motor, the slope of the limiting current curve is obtained by using a fuzzy control algorithm; according to the slope of the limiting current curve, the limiting current is obtained; The obtained asynchronous motor feedback current is compared and converted with the limiting current in sequence to obtain a control signal variation; Using the pulse signal as a trigger signal of the thyristor, and calculating the trigger angle of the thyristor according to the change of the control signal; The start and stop of the asynchronous motor is controlled by the trigger signal of the thyristor, and the starting current of the asynchronous motor is controlled by the trigger angle of the thyristor.

2. The soft start control method of an asynchronous motor according to claim 1, characterized in that: The processing steps of the synchronization pulse generating circuit include: The input voltage of the asynchronous motor is subjected to delay processing and speed limiting processing in sequence to obtain a voltage sinusoidal signal; Converting the voltage sinusoidal signal into a voltage triangular wave signal; The voltage triangle wave signal and the preset starting trigger angle are sequentially superimposed and delayed to obtain a pulse signal.

3. The soft start control method of an asynchronous motor according to claim 1, characterized in that: According to the electromagnetic torque and load torque fed back by the asynchronous motor, the slope of the limiting current curve is obtained by using the fuzzy control algorithm, including: The deviation and the deviation change rate are multiplied by the corresponding quantization factors respectively, and the product is mapped to the fuzzy set domain to obtain the deviation and the deviation change rate on the fuzzy set domain; wherein the deviation is the deviation between the electromagnetic torque of the asynchronous motor and the load torque, and the deviation change rate is the deviation change rate between the electromagnetic torque of the asynchronous motor and the load torque; The deviation and the deviation change rate on the fuzzy set domain are input into the fuzzy controller, and the slope of the limiting current curve is outputted by using the preset fuzzy control principle.

4. The soft start control method for an asynchronous motor according to claim 3, characterized in that: The quantization factor corresponding to the deviation and the deviation change rate is expressed as: ； in, is the quantification factor of the deviation; is the quantitative factor of the deviation change rate; is the fuzzy input domain of the deviation; is the fuzzy input domain of the deviation change rate; is the actual domain of the deviation; is the actual domain of the deviation change rate.

5. The soft start control method of an asynchronous motor according to claim 4, characterized in that: The fuzzy input domain of the deviation and the fuzzy output domain of the slope of the limiting current curve both adopt asymmetric domains.

6. The soft start control method of an asynchronous motor according to claim 3, characterized in that: The preset fuzzy control principles include: If the deviation on the fuzzy set domain is less than zero, the slope of the limiting current curve is increased; otherwise, the slope of the limiting current curve is reduced.

7. The soft start control method of an asynchronous motor according to claim 1, characterized in that: The obtained asynchronous motor feedback current is compared and converted with the limiting current in sequence to obtain a control signal variation, including: The obtained asynchronous motor feedback current is compared with the limit current to obtain the deviation current; The deviation current is input into a PI controller for conversion to obtain a control signal variation.

8. The soft start control method for an asynchronous motor according to claim 1, characterized in that: Calculating the trigger angle of the thyristor according to the change amount of the control signal includes: The control signal change amount is subtracted from the preset starting trigger angle to obtain the trigger angle of the thyristor.

9. A soft start control system for an asynchronous motor, characterized in that: include: The pulse signal acquisition module is used to: acquire the pulse signal output by the synchronous pulse generating circuit; wherein the synchronous pulse generating circuit inputs the input voltage of the asynchronous motor and the preset starting trigger angle; The limiting current acquisition module is used to: obtain the slope of the limiting current curve according to the electromagnetic torque and load torque fed back by the asynchronous motor using a fuzzy control algorithm; and obtain the limiting current according to the slope of the limiting current curve; A control signal acquisition module is used to compare and convert the acquired asynchronous motor feedback current and the limiting current in sequence to obtain a control signal variation; A starting current acquisition module is used to: use the pulse signal as a trigger signal of the thyristor and calculate the trigger angle of the thyristor according to the change amount of the control signal; The start and stop of the asynchronous motor is controlled by the trigger signal of the thyristor, and the starting current of the asynchronous motor is controlled by the trigger angle of the thyristor.

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