April 05, 2020

The principle and exploration of fuzzy controller

The goal of air conditioning technology is to create a comfortable environment for people, but from an indoor environment, a constant temperature environment is not a standard environment for hygiene and comfort. Because in addition to temperature, there are many factors such as humidity and air flow rate that affect comfort. Conventional air conditioning systems mostly use a simple mechanical temperature control switch to set the control temperature, and the constant temperature control of the air conditioning system is achieved by stopping the compressor.

On the one hand, this temperature-variable operation mode ignores the multi-factors that affect the comfort of the human body; on the other hand, due to the frequent starting and stopping of the compressor, not only the compressor is easily damaged, but also causes a certain energy loss. The fully automatic fuzzy air conditioner with fuzzy control can automatically adjust the speed of the compressor according to the thermal environment of the room, creating a comfortable environment for people, and also conducive to saving energy and improving the service life of the compressor.

The fuzzy control relationship of the fully automatic fuzzy air conditioner is as shown. The input quantities are: indoor temperature difference and its rate of change with time; the temperature of the front wall of the indoor heat exchanger and its rate of change with time; the temperature of the front wall of the outdoor heat exchanger and its rate of change with time. The output includes intelligent control of functions such as cooling, heating, dehumidification, defrosting, wind direction, and air volume of the air conditioner.

Two fuzzy control principle 1 fuzzy inference block diagram. The main control target of the air conditioner is room temperature and keep the room temperature stable. The increase or decrease of indoor personnel, the opening and closing of the door, or the generation of other heat sources in the room will cause changes in the indoor air temperature, which are input variables that constitute the temperature control system. The output of the control system, ie the output variable, should be the speed of the compressor. The functional relationship between the input variable and the output variable is determined by fuzzy inference, and the reasoning block diagram is as shown.

The deviation of the ambient temperature from the set temperature; the other is the rate of change of the temperature difference, which reflects the strength of the driving factor causing the temperature difference change, such as the sudden increase of personnel, the introduction of hot air caused by opening the door, and the magnitude of the indoor and outdoor temperature difference.

Therefore, the rate of change of temperature contains many factors. The output variable f is the frequency of the frequency converter, which determines the speed of the compressor.

2 Fuzzy quantity definition (1) Input fuzzy quantity: temperature difference temperature difference change rate d/ dt ( / S) ( 2) Output fuzzy quantity: The frequency of the inverter f ( Hz) according to the actual working condition of the indoor air conditioner, taking into account the actual detection Condition and appropriate control accuracy, the input variable temperature difference domain is -3 + 3, take 5 fuzzy quantities: negative large % (NB), negative small % (NS), zero % (ZO), positive small (PS) Zhengda (PB).

The input temperature difference rate change rate d / dt is defined as ( - 0 03 / S) ( + 0 03 / S). Take 5 blurs: negative high (NH), negative low (NL), zero% (ZO), positive low (PL), positive high % (PH).

The output variable f is the frequency of the inverter corresponding to the speed n, which is defined as 15 125 Hz. Take 5 blurs: zero % ( ZO), low ( L ), medium ( M ), high % ( H), Highest (MH).

3 fuzzy control rules table. According to the actual operating experience, the experimental analysis and induction shall be carried out. The operating state of the air conditioner shall be in accordance with the following rules: IF is PB and d/ dt is PH then f is MH; IF is PS and d/ dt is PL then f is M IF is NB and d/ dt is NH then f is MH; in the heating condition IF is NS and d / dt is NL then f is M; there are 25 similar rules. The basic structure of the fuzzy controller is shown in the figure. It can be divided into three parts: fuzzy output interface, fuzzy inference decision making mechanism and fuzzy output interface.

The main function of the fuzzy input interface is to calculate the input variable of the selected system based on the output value of the system obtained by this sampling, and change the exact value of the input variable into a fuzzy amount. The exact value of the temperature difference and the rate of change of the temperature difference of the controlled system is converted into a fuzzy quantity for fuzzy reasoning and decision making.

The main function of the fuzzy decision-making mechanism is to infer the control decision based on the fuzzy inference rule table and the fuzzy quantity of the input variable. The main function of the fuzzy output interface is to convert the fuzzy control quantity obtained by the fuzzy inference decision into an accurate quantity to control the speed of the compressor.

Three air conditioner fuzzy control hardware system The frequency conversion speed control split type fuzzy control air conditioner hardware system is divided into two parts: indoor unit and outdoor unit.

1 The composition of the indoor control system. The schematic of the indoor control system is shown. The control core is an 8098 quasi 16-bit MCU, and its input includes two parts. The first input interface receives the input control information from the remote controller, and determines the given operation mode and temperature control index of the system of the indoor control system; The other input interface receives field detection information such as room temperature and humidity from the sensor. The output has three parts, one is the LED display and driving circuit in the running state, the other is the indoor fan operating parameter control, and the third is the serial communication interface connected with the outdoor control device.

The remote control is matched with the indoor control part to set the operation mode and temperature control indication of the air conditioner, and to transmit infrared remote control information, which is composed of a single 4-bit single-chip CPU.

2 The composition of the outdoor control system. The core of the outdoor unit is also a quasi-16-bit single-chip 8098 CPU, and the schematic diagram of its control system is shown. The input information includes outdoor air temperature, outdoor heat exchanger inlet and outlet temperature, and overcurrent and overvoltage protection information of the inverter circuit; the output part includes the drive circuit of the outdoor fan motor, the inverter IGBT module and its driving circuit, and the connection with the indoor device. Serial communication interface, etc.

The frequency converter adopts AC-DC voltage inverter circuit, capacitor filtering, self-shutdown power device bipolar insulated gate transistor (IGBT) constitutes single-phase inverter, the output frequency range is 15 125Hz, the power is about 15KW, with over-current Pressure and undervoltage protection.

The software design of the variable frequency fuzzy control split air conditioner is divided into three parts: indoor unit, outdoor unit and remote control. The control command is transmitted between the indoor unit and the remote controller through infrared signal coding, and information is transmitted between the indoor unit and the outdoor unit by a serial communication interface.

The indoor unit is the core of the control system and is mainly responsible for the control functions. The software adopts modular structure, mainly including main program, timing subroutine, A/D conversion subroutine, error weighting subroutine, error change subroutine, fuzzy inference subroutine, fuzzy decision subroutine, function subroutine, fuzzy relation R Forms, etc. The main block diagram is shown. First, the initialization is performed, and then the loop waits. When the timing is up, the data of the analog channel port is collected, and the A/D conversion subroutine is called to determine whether it is acquired twice. If it is collected twice, it will be processed by weighting, fuzzy, fuzzy reasoning, fuzzy decision, etc.; otherwise, the second acquisition will be performed. Finally, the results are quantified and stored in the corresponding unit.

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