A method for voltage regulation and energy saving of three-phase asynchronous motor

Abstract

The present invention claims a method for voltage regulation and energy saving of a three-phase asynchronous motor, which includes the following steps: establishing a voltage regulation and energy saving model, using the efficiency of the motor to characterize the energy consumption, and using the power factor to represent the motor efficiency; building two soft start models respectively: a ramp soft start model and a current limiting soft start model to control the voltage, which is used to reduce the starting current, reduce the starting torque, and extend the time for the speed to reach the rated speed; using dynamic matrix control technology, taking a given power factor as a reference value as an input quantity, and outputting the trigger angle adjusted by the dynamic matrix control to control the switch of the thyristor, so that the power factor is always maintained near the ideal value, achieving voltage regulation and energy saving. After simulation, the soft start method has a good improvement effect on the starting current, torque size, and starting time when the motor starts, and the dynamic matrix control constant power factor control method can keep the power factor of the motor near the rated value and improve work efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of energy saving, in particular to a method for voltage regulation and energy saving of a three-phase asynchronous motor. Background Art

[0002] Because asynchronous motors have simple structures, are easy to operate, and are relatively mature, they still dominate the current power market. However, asynchronous motors are not without disadvantages. For example, when driving a large load, a starting current that may be more than ten times greater than the stable current will be generated during the startup process, which will have a huge impact on the power grid. In severe cases, the motor will burn and cause great damage. During the startup process, the motor rotor speed fluctuates greatly, which can easily cause instability in the startup process and excessive output torque. When driving a relatively small load or light load, due to the small output power, compared with the power lost by the asynchronous motor, the output power of the asynchronous motor when lightly loaded can be almost ignored, so it will cause the asynchronous motor to be inefficient and waste electric energy in vain. Therefore, how to reduce the starting current of the asynchronous motor during the startup process and how to improve the efficiency of the asynchronous motor are issues that today's society should think about.

[0003] After searching, the application publication number CN107659212A, a soft start control method for an asynchronous motor, characterized in that, wherein, the relationship between the load torque and the rotor speed of the asynchronous motor satisfies that when the asynchronous motor drives the load, the power factor angle of the asynchronous motor does not change; including: obtaining the power factor angle of the asynchronous motor; obtaining the trigger angle adjustment amount Δα according to the power factor angle; obtaining the trigger law of the preset initial trigger angle α; calculating the trigger law of the final trigger angle α'. The above-mentioned soft start control method for the asynchronous motor, for the special relationship between the load torque and the rotor speed of the asynchronous motor, the power factor angle is constant, the present application does not need to monitor the change of the power factor angle, so there is no need to correct the trigger angle of the thyristor in real time, only one correction is needed, the soft start control method for the asynchronous motor is optimized, the detection of the power factor angle is omitted, thereby omitting the related hardware, simplifying the hardware, and reducing the cost. The shortcomings of this invention patent: the soft start control method can only be used for the case where the power factor angle does not change. In fact, due to various working conditions, the power factor angle changes in real time; and due to different motor parameters, the target value of the power factor angle is also different, so this soft start method is not very applicable.

[0004] The dynamic matrix control algorithm proposed in the patent of this invention calculates the control quantity corresponding to the changing target value in each control cycle, and has a good tracking effect on the changing power factor angle, and is also suitable for asynchronous motors under different working conditions.

[0005] CN103762927A, a three-phase asynchronous motor energy-saving controller, is composed of a motor and a measuring device, a soft start module, a power factor module, a digital filter module, and a fuzzy control module. It is characterized in that the fuzzy energy-saving control is mainly divided into two energy-saving controls: voltage regulation and frequency modulation; the fuzzy voltage regulation energy-saving control only involves frequency modulation control at the time of starting. In the fuzzy voltage regulation energy-saving control, the trigger angle α is adjusted according to the change of the power factor and the stator terminal voltage to achieve the purpose of voltage regulation. The main circuit of the controller adopts anti-parallel thyristor phase-controlled voltage regulation, and the control circuit is composed of a closed loop composed of the detected power factor angle and the stator terminal voltage. The shortcomings of this invention patent: how to obtain fuzzy rules and membership functions, that is, the design method of the system, is completely based on experience; simple fuzzy processing of information will lead to reduced control accuracy and poor dynamic quality of the system. If the accuracy is to be improved, the quantization level will inevitably increase, resulting in an expansion of the rule search range, a reduction in decision-making speed, and even inability to perform real-time control. If the control rules are complex, it will lead to excessive calculation.

[0006] The dynamic matrix algorithm proposed in the patent of this invention is an optimal control algorithm. By finding the minimum value of the performance index, the error has been minimized. Since an incremental algorithm is adopted, it is very effective in eliminating steady-state residuals. And for the calculation of the output, only simple matrix operations are required, so the calculation amount is small and the calculation speed is fast. Summary of the invention

[0007] A method for voltage regulation and energy saving of a three-phase asynchronous motor, comprising the following steps:

[0008] Establish a voltage regulation energy-saving model, use the efficiency of the motor to characterize the energy consumption, and use the power factor to represent the motor efficiency;

[0009] Three soft start models are built respectively: ramp soft start model and current limiting soft start model to control the voltage, which is used to reduce the starting current, reduce the starting torque, and prolong the time for the speed to reach the rated speed;

[0010] The third model uses dynamic matrix control (DMC) technology, takes a given power factor as a reference value as input, and outputs the trigger angle adjusted by dynamic matrix control to control the switching of thyristors, so that the power factor is always maintained near the ideal value, achieving voltage regulation and energy saving.

[0011] Furthermore, the ramp soft start model consists of a step module, an integral module, a conversion module, and a gain module, wherein the step module is used to generate a step signal, the integral module is used to convert the step signal into a ramp signal, the conversion module is used to convert the voltage and the trigger angle, and the gain module is used to amplify the signal.

[0012] Furthermore, the current limiting soft start model is composed of an absolute value module, a delay module, a product module, a gain module, an integral module, and a conversion module. The absolute value module is used to collect the absolute value of the stator current, and the delay module is used to form a hysteresis ratio after subtracting the collected absolute value of the stator current from the given current value; when the collected stator current feedback value is greater than the given value, the delay module outputs 0; when the collected stator current feedback value is less than the given value, the delay module outputs 1; the product module is used to multiply two input signals, the gain module is used to amplify the signal, the integral module is used to convert the step signal into a ramp signal, and the conversion module is used to convert the voltage and the trigger angle.

[0013] Furthermore, the dynamic matrix controller includes three modules: rolling implementation, feedback correction, and state update. The function of the rolling implementation module is that the controller only takes the instantaneous Δu(k) to form u(k), that is, u(k) = u(k-1) + Δu(k), and at the next moment, a similar optimization problem is proposed to solve Δu(k+1). The function of the feedback correction module is that due to model mismatch, environmental interference, errors, etc., the actual y(k+1) will not be equal to the predicted value after the implementation of Δu(k). Therefore, the output value needs to be corrected. The function of the state update module is to use the output value at k+1 as the starting point, and use the same method as before to calculate Δu(k+1), and so on, which is the process of state update.

[0014] The advantages and beneficial effects of the present invention are as follows:

[0015] The innovation of the present invention is mainly step 5. The traditional method of tracking power factor in industry is PID control, but the PID signal processing is too simple and fails to give full play to its advantages. It has the following main disadvantages: (1) The initial error is large, which is easy to cause overshoot, which is not only unreasonable, but also easy to cause a large impact on the motor. (2) It is easy to produce oscillation and control quantity saturation caused by integral saturation.

[0016] Advantages: The dynamic matrix algorithm proposed in step 5 is an optimal control algorithm. By minimizing the performance index, the error has been minimized. Since the incremental algorithm is used, it is very effective in eliminating steady-state residuals. And for the calculation of the output, only simple matrix operations are required, so the calculation amount is small and the calculation speed is fast.

[0017] Beneficial effects: fast calculation speed due to small amount of calculation; low requirements on hardware equipment; better tracking effect on motor power factor than traditional PID. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The preferred embodiment provided by the present invention is a constant power factor dynamic matrix control simulation diagram.

[0019] Figure 2 This is the simulation diagram of the ramp signal.

[0020] Figure 3 This is the simulation diagram of the current limiting soft start control signal;

[0021] Figure 4 It is a schematic diagram of the process of voltage regulation and energy saving of a three-phase asynchronous motor according to the present invention. DETAILED DESCRIPTION

[0022] The following will describe the technical solutions in the embodiments of the present invention in detail in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention.

[0023] The technical solution of the present invention to solve the above technical problems is:

[0024] The three models built by this method, the first ramp boost soft start and the second current limiting soft start focus on reducing the starting current and starting torque, so that the process of the motor speed rising to the rated speed is smoother. The third dynamic matrix control constant power factor simulation is to maintain the power factor of the motor near the power factor under the rated load when the motor load changes, so as to achieve energy saving effect.

[0025] Figure 1 This is a simulation diagram of constant power factor dynamic matrix control. The power factor is collected from the power acquisition module and then sent to the dynamic matrix controller to track the power factor under rated load. Because in MATLAB, the angle is expressed in radians, the function f(u) converts the value after the dynamic matrix algorithm into an angle. So f(u) = 180 / pi*acos(u(1)).

[0026] Figure 2 This is a simulation diagram of the ramp control signal. When starting, the stator voltage first quickly rises to U s , U s is the voltage value when the motor starts. At this time, the starting torque is the minimum torque required for the motor to start, and then it rises linearly according to the set slope until it reaches the full voltage. The ramp soft start model consists of a step module, an integral module, a conversion module, a gain module, etc., among which the step module is used to generate a step signal, the integral module is used to convert the step signal into a ramp signal, the conversion module is used for the conversion of voltage and trigger angle, and the gain module is used to amplify the signal. The gain module K is set to 1000.

[0027] Figure 3This is a simulation diagram of the current-limiting soft-start control signal. The current-limiting soft-start model consists of an absolute value module, a delay module, a product module, a gain module, an integral module, and a conversion module. The absolute value module is used to collect the absolute value of the stator current. The delay module is used to form a hysteresis ratio after subtracting the absolute value of the stator current collected from the given current value. When the collected stator current feedback value is greater than the given value, the delay module outputs 0; when the collected stator current feedback value is less than the given value, the delay module outputs 1. The product module is used to multiply the two input signals. The signal coming out of the delay module is input together with the given acceleration voltage value (given by the reference value module) into the multiplication module for multiplication, and then input into the adder through the gain module and the integral module to sum with the given initial voltage value. The sum is taken as U c Input trigger pulse module, and make difference with synchronous voltage signal. Gain module is used to amplify the signal, integration module is used to convert step signal into ramp signal, conversion module is used to convert voltage and trigger angle.

[0028] It can be seen that when the collected stator current feedback value is greater than the given value, the PI link loses its effect, and we only need to wait for the starting current to decrease. When the starting current is smaller than the value we set, PI begins to work. Therefore, in the whole process, the two states are alternately converted during the startup process to ensure constant current startup.

[0029] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0030] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0031] The above embodiments should be understood to be only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the contents of the present invention, technicians can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A method for voltage regulation and energy saving of a three-phase asynchronous motor, characterized in that: The following steps are involved: Establish a voltage regulation energy-saving model, use the efficiency of the motor to characterize the energy consumption, and use the power factor to represent the motor efficiency; Three soft start models are built respectively: ramp soft start model and current limiting soft start model to control the voltage, which is used to reduce the starting current, reduce the starting torque, and prolong the time for the speed to reach the rated speed; The third model uses dynamic matrix control technology, takes a given power factor as a reference value as input, and outputs the trigger angle adjusted by dynamic matrix control to control the switching of thyristors, so that the power factor is always maintained near the ideal value, achieving voltage regulation and energy saving; The current limiting soft start model is composed of an absolute value module, a delay module, a product module, a gain module, an integration module, and a conversion module. The absolute value module is used to collect the absolute value of the stator current. The delay module is used to form a hysteresis ratio by subtracting the collected absolute value of the stator current from the given current value. When the collected stator current feedback value is greater than the given value, the delay module outputs 0; when the collected stator current feedback value is less than the given value, the delay module outputs 1; The product module is used to multiply two input signals. The signal coming out of the delay module is input into the multiplication module together with the given acceleration voltage value for multiplication, and then input into the adder through the gain module and the integration module to be summed with the given initial voltage value. The gain module is used to amplify the signal, the integration module is used to convert the step signal into a ramp signal, and the conversion module is used for the conversion of voltage and trigger angle.

2. The method for voltage regulation and energy saving of a three-phase asynchronous motor according to claim 1, characterized in that: The ramp soft start model consists of a step module, an integral module, a conversion module, and a gain module, wherein the step module is used to generate a step signal, the integral module is used to convert the step signal into a ramp signal, the conversion module is used to convert the voltage and the trigger angle, and the gain module is used to amplify the signal.

3. The method for voltage regulation and energy saving of a three-phase asynchronous motor according to claim 1, characterized in that: The dynamic matrix controller includes three modules: rolling implementation, feedback correction, and state update. The function of the rolling implementation module is that the controller only takes the instantaneous Δu(k) to form u(k), Δu(k) is the control increment at time k, and u(k) is the control amount at time k, that is, u(k)=u(k-1)+Δu(k). At the next moment, a similar optimization problem is proposed to solve Δu(k+1). The role of the feedback correction module is that due to model mismatch, environmental interference, and errors, the actual y(k+1), that is, the output at the next moment, will not be equal to the predicted output after Δu(k). That is, the output is predicted at time k+1, so the output value needs to be corrected; the function of the state update module is to take the output value at k+1 as the starting point, and use the same method as before to calculate Δu(k+1), and so on, that is, the state update process. The above three modules can achieve the tracking target of a given power factor.

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