Water chilling unit coolant liquid level control method based on MFAC-PID algorithm

Abstract

The invention belongs to the technical field of water chilling units, and discloses a water chilling unit coolant liquid level control method based on an MFAC-PID algorithm, and relates to a water chilling unit liquid level control system based on the MFAC-PID algorithm, which comprises a PID controller and a frequency converter connected with a water chilling unit, and an expansion valve connected between a condenser and an evaporator in the water chilling unit, the expansion valve is connected with a model-free self-adaptive algorithm controller, the opening degree of the expansion valve is controlled by using the water chilling unit liquid level control system based on the MFAC-PID algorithm, and the flow of a coolant entering an evaporator is controlled in real time; according to the MFAC-PID algorithm, through online estimation and adjustment of control parameters, the change of the liquid level value can be quickly tracked, the control quantity can be adjusted in time, and the accuracy and robustness of liquid level control are improved.

Description

Technical Field

[0001] The invention relates to the technical field of chillers, and in particular to a chiller coolant level control method based on MFAC-PID algorithm. Background Art

[0002] The chiller is mainly composed of four parts: compressor, condenser, expansion valve and evaporator. These four parts are connected by pipes to form a closed circulation system. Its working process includes compression, condensation, expansion and evaporation.

[0003] Among them, the expansion valve can adjust the state and flow of the coolant in the entire chiller. The expansion valve is installed at the inlet of the evaporator. Its main function is to throttle and reduce the pressure of the high-pressure liquid refrigerant from the condenser, so that it is converted into a low-temperature and low-pressure gas-liquid mixed state and then enters the evaporator. Therefore, by adjusting the opening of the expansion valve, the coolant flow entering the evaporator can be controlled.

[0004] The control of the coolant level of the chiller is one of the key links to ensure the normal and efficient operation of the chiller. The appropriate coolant level is crucial to the performance and reliability of the chiller. If the level is too high, the coolant may overflow and enter the compressor and other components, causing liquid hammer and damaging the internal structure of the compressor; if the level is too low, the coolant in the evaporator will be insufficient, reducing the cooling effect, and may even cause local overheating of the evaporator, affecting the overall operating efficiency and service life of the unit.

[0005] At present, the expansion valve opening is generally adjusted manually or by PID algorithm. Although PID control is simple and easy, the adjustment of parameters is cumbersome. In addition, due to the time-varying nature of the chiller, PID control is difficult to ensure the control accuracy of the coolant flow. Summary of the invention

[0006] The main technical problem to be solved by the present invention is to provide a chiller coolant level control method based on the MFAC-PID algorithm. The MFAC-PID algorithm estimates and adjusts control parameters online, and can quickly track changes in liquid level values ​​and adjust control quantities in a timely manner, thereby improving the accuracy and robustness of liquid level control.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] A chiller coolant level control method based on an MFAC-PID algorithm, the chiller level control system based on the MFAC-PID algorithm comprising a PID controller (1) and a frequency converter (2) connected to the chiller, and an expansion valve (5) connected between a condenser (3) and an evaporator (4) in the chiller, wherein the expansion valve (5) is connected to a model-free adaptive algorithm controller (6), and the chiller level control system based on the MFAC-PID algorithm is used to control the opening of the expansion valve (5) to control the coolant flow entering the evaporator (4) in real time, the steps are as follows:

[0009] S1. Set initialization parameters and input the set liquid level value;

[0010] S2, taking the error between the set liquid level value and the current liquid level value and the opening of the expansion valve (5) at the previous moment as input, and using the pseudo partial derivative model formula to estimate the value of the pseudo partial derivative online;

[0011] In step S2, the pseudo partial derivative model formula is:

[0012] ;

[0013] in, is the pseudo partial derivative at the current moment, is a pseudo partial derivative The estimated value of is the estimate of the pseudo partial derivative at the previous moment, is the difference between the opening degree of the expansion valve (5) at the last moment and the opening degree of the expansion valve (5) at the moment before, is the difference between the current level error and the previous level error. is the weighting coefficient;

[0014] S3, the model-free adaptive algorithm controller (6) calculates the opening increment of the expansion valve (5) and the opening of the expansion valve (5) according to the control rate calculation formula;

[0015] In step S3, the control rate calculation formula is:

[0016] ;

[0017] in, is the difference between the opening degree of the expansion valve (5) at the current moment and the opening degree of the expansion valve (5) at the previous moment, is the weighting coefficient; is the proportional coefficient of PID control, is the integral coefficient of PID control, is the differential coefficient of PID control, is the opening degree of the expansion valve (5) at the current moment, is the opening degree of the expansion valve (5) at the previous moment, is the error between the set liquid level value and the actual liquid level value at the current moment. is the error between the set liquid level value and the actual liquid level value at the previous moment. It is the error between the set liquid level value and the actual liquid level value at the previous moment;

[0018] S4, the sensor in the evaporator (4) reads the current liquid level value;

[0019] S5. Determine whether the error between the current liquid level value and the set liquid level value is within the dead zone. If the error between the current liquid level value and the set liquid level value is within the dead zone, the opening of the expansion valve (5) meets the expected flow rate and the loop is exited. Otherwise, S2-S5 are executed again.

[0020] The following is a further optimization of the above technical solution by the present invention:

[0021] In the above step S2, a parameter reset mechanism is introduced:

[0022] ;

[0023] ;

[0024] ;

[0025] in, , yes The initial value of .

[0026] The present invention adopts the above technical solution and has the following beneficial effects:

[0027] 1. The MFAC-PID algorithm adopted in the present invention combines the advantages of model-free adaptive control and traditional PID control, can quickly track the changes in the coolant level value, and timely adjust the opening of the expansion valve so that the coolant level value quickly reaches the preset value, thereby improving the control accuracy of the coolant level control system.

[0028] 2. The MFAC-PID algorithm is data-driven and does not rely on precise mathematical models, so it can better adapt to the complex operating conditions of the chiller and maintain good coolant level control accuracy under different operating conditions.

[0029] 3. The MFAC-PID algorithm can respond quickly to the disturbances on the chiller and offset the impact of the disturbances by adjusting the opening of the expansion valve, so that the coolant level value returns to the set value as soon as possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0031] Figure 1 This is a schematic diagram of system connection in accordance with the first embodiment of the present invention;

[0032] Figure 2 This is a flow chart of Embodiment 2 of the present invention.

[0033] In the figure: 1. PID controller; 2. Frequency converter; 3. Condenser; 4. Evaporator; 5. Expansion valve; 6. Model-free adaptive algorithm controller; 7. Compressor. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Embodiment 1

[0036] like Figure 1 As shown, a chiller coolant level control method based on MFAC-PID algorithm, the chiller level control system based on MFAC-PID algorithm includes a PID controller 1 and a frequency converter 2 connected to the chiller, and an expansion valve 5 connected between a condenser 3 and an evaporator 4 in the chiller, and the expansion valve 5 is connected to a model-free adaptive control (MFAC) algorithm controller 6.

[0037] In this embodiment, the PID controller 1 and the frequency converter 2 may be ATV series frequency converters (including ATV320, ATV610, ATV630, ATV650 and other models) produced by Schneider Electric.

[0038] In this embodiment, the chiller may be a 30HXY / HXC screw chiller produced by Carrier Corporation, which mainly includes a compressor 7 , an evaporator 4 , a condenser 3 and an expansion valve 5 .

[0039] The chiller level control system based on MFAC-PID algorithm has the following advantages:

[0040] First, it has good adaptability: Since the operating conditions of the chiller may be affected by many factors, such as load changes, refrigerant flow fluctuations, external ambient temperature changes, etc., the chiller level control system based on the MFAC-PID algorithm has strong adaptability to complex working conditions and can adapt well to the complex characteristics of the chiller system such as nonlinearity, large inertia, and large delay, and can maintain good control effects under different working conditions.

[0041] Second, it has strong robustness, strong anti-interference ability, and high tolerance to model uncertainty: because the chiller is susceptible to various interferences, such as water supply pressure fluctuations, changes in the heat exchange efficiency of evaporator 4 and condenser 3, etc., the chiller level control system can respond quickly to these interferences under the operation of the MFAC-PID algorithm, and offset the impact of the interference by adjusting the flow rate of the coolant, so that the liquid level value can be restored to the set value as soon as possible.

[0042] Even in the presence of large interference, the chiller level control system can maintain good control performance and ensure the normal operation of the chiller.

[0043] Moreover, the structure of the chiller is very complex, and it is difficult to establish an accurate mathematical model, and some parameters in the model may be uncertain. The MFAC-PID algorithm in the chiller level control system does not rely on an accurate model, and therefore has a high tolerance for the uncertainty of the chiller mathematical model. It can achieve accurate and effective control of the coolant level under uncertain or partially unknown conditions.

[0044] Third, it has precise control performance, can respond quickly, and has small steady-state error: During the operation of the chiller, in order to ensure the normal operation of the chiller, the coolant level needs to be controlled in time. The MFAC-PID algorithm combines the advantages of model-free adaptive control and traditional PID control, and can quickly track changes in the coolant level value, so as to adjust its level value in time, so that the coolant level value quickly reaches the set value, improving the effect speed and control accuracy of the chiller level control system.

[0045] Embodiment 2

[0046] like Figure 2 As shown, the liquid level control system of the chiller based on the MFAC-PID algorithm is used to control the opening of the expansion valve 5 and control the coolant flow entering the evaporator 4 in real time.

[0047] The specific steps are as follows:

[0048] S1. Set the initialization parameters and input the set liquid level value.

[0049] In this embodiment, the initial value of the pseudo-partial derivative of the parameter in the system is , step factor , proportionality coefficient , integral coefficient , differential coefficient Initialize.

[0050] S2. Taking the error between the set liquid level value and the current liquid level value and the opening degree of the expansion valve 5 at the previous moment as input, the pseudo partial derivative model formula is used to estimate the value of the pseudo partial derivative online.

[0051] In this embodiment, the MFAC-PID algorithm continuously reduces the steady-state error of the coolant level value by online estimating and adjusting the control parameter value, so that the coolant level value fluctuates within a small range near the set value, thereby improving the stability and reliability of the chiller level control system.

[0052] In step S2, the pseudo partial derivative model formula is:

[0053] ;

[0054] in, is the pseudo partial derivative at the current moment, is a pseudo partial derivative The estimated value of is the estimate of the pseudo partial derivative at the previous moment, is the difference between the opening degree of the expansion valve (5) at the last moment and the opening degree of the expansion valve (5) at the moment before, is the difference between the current level error and the previous level error. is the weighting coefficient.

[0055] At the same time, a parameter reset mechanism is introduced:

[0056] ;

[0057] ;

[0058] ;

[0059] in, , yes The initial value of .

[0060] S3, the model-free adaptive algorithm controller 6 calculates the opening increment of the expansion valve 5 and the opening of the expansion valve 5 according to the control rate calculation formula;

[0061] In step S3, the control rate calculation formula is:

[0062] ;

[0063] in, is the difference between the opening degree of the expansion valve (5) at the current moment and the opening degree of the expansion valve (5) at the previous moment, is the weighting coefficient; is the proportional coefficient of PID control, is the integral coefficient of PID control, is the differential coefficient of PID control, is the opening degree of the expansion valve (5) at the current moment, is the opening degree of the expansion valve (5) at the previous moment, is the error between the set liquid level value and the actual liquid level value at the current moment. is the error between the set liquid level value and the actual liquid level value at the previous moment. It is the error between the set liquid level value and the actual liquid level value at the previous moment.

[0064] It can be seen from the above control rate calculation formula that when When it is equal to 1, the control mode degenerates into traditional incremental PID control. By introducing pseudo gradient, the robustness and control accuracy of the algorithm can be enhanced, as well as the tracking performance can be better.

[0065] S4. The sensor in the evaporator 4 reads the current liquid level value.

[0066] S5. Determine whether the error between the current liquid level value and the set liquid level value is within the dead zone. If the error between the current liquid level value and the set liquid level value is within the dead zone, the opening of the expansion valve 5 meets the expected flow rate and exits the cycle, otherwise re-execute S2-S5.

[0067] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A chiller coolant level control method based on MFAC-PID algorithm, characterized in that: The chiller liquid level control system based on the MFAC-PID algorithm involved comprises a PID controller (1) and a frequency converter (2) connected to the chiller, and an expansion valve (5) connected between a condenser (3) and an evaporator (4) in the chiller, wherein the expansion valve (5) is connected to a model-free adaptive algorithm controller (6). The chiller liquid level control system based on the MFAC-PID algorithm is used to control the opening of the expansion valve (5) and to control the flow of coolant entering the evaporator (4) in real time, and the steps are as follows: S1. Set initialization parameters and input the set liquid level value; S2, taking the error between the set liquid level value and the current liquid level value and the opening of the expansion valve (5) at the previous moment as input, and using the pseudo partial derivative model formula to estimate the value of the pseudo partial derivative online; In step S2, the pseudo partial derivative model formula is: ； in, is the pseudo partial derivative at the current moment, is a pseudo partial derivative The estimated value of is the estimate of the pseudo partial derivative at the previous moment, is the difference between the opening degree of the expansion valve (5) at the last moment and the opening degree of the expansion valve (5) at the moment before, is the difference between the current level error and the previous level error. is the weighting coefficient; S3, the model-free adaptive algorithm controller (6) calculates the opening increment of the expansion valve (5) and the opening of the expansion valve (5) according to the control rate calculation formula; In step S3, the control rate calculation formula is: ； in, is the difference between the opening degree of the expansion valve (5) at the current moment and the opening degree of the expansion valve (5) at the previous moment, is the weighting coefficient; is the proportional coefficient of PID control, is the integral coefficient of PID control, is the differential coefficient of PID control, is the opening degree of the expansion valve (5) at the current moment, is the opening degree of the expansion valve (5) at the previous moment, is the error between the set liquid level value and the actual liquid level value at the current moment. is the error between the set liquid level value and the actual liquid level value at the previous moment. It is the error between the set liquid level value and the actual liquid level value at the previous moment; S4, the sensor in the evaporator (4) reads the current liquid level value; S5. Determine whether the error between the current liquid level value and the set liquid level value is within the dead zone. If the error between the current liquid level value and the set liquid level value is within the dead zone, the opening of the expansion valve (5) meets the expected flow rate and the loop is exited. Otherwise, S2-S5 are executed again.

2. The chiller coolant level control method based on MFAC-PID algorithm according to claim 1, characterized in that: In the above step S2, a parameter reset mechanism is introduced: ； ； ； in, , yes The initial value of .

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