At present, with the rapid development of electronic information technology, and the reliable operation of electronic information equipment, environmental temperature and humidity have higher requirements, so precision air conditioning came into being, and has been widely used and developed. Precision air-conditioning fan controller, as the energy driving equipment of the fan in the automobile air-conditioning control system, is a key part of the widely used automobile air-conditioning control system. Therefore, it has gradually become a focus of attention in the air-conditioning and refrigeration industry. The design and assembly of the new precise air conditioning fan controller introduced in this paper proceeds from the actual needs of customers, and adds a variety of system protection and protection functions on the basis of taking into account the functions of the common controller circuit. In this industry, similar products are at a more advanced level. The precise air conditioning controller is composed of two parts, the main circuit and the control circuit. The microcircuit processor chipset adopts the DSP chip MC56F8025, which is the most advanced and precise controller chipset produced by Freescale Company. With the rapid development of electronic information technology, people pay more and more attention to the stability of electronic equipment in operation. The stability of electronic equipment operation depends not only on the reliability of equipment design, but also on the surrounding environment to a large extent. If the environment changes rapidly, or the high and low are extremely unstable, it will affect the normal operation of electronic equipment and shorten its service life. The electronic circuit design of air conditioning fan controller seen in daily life is very simple, its function is very single, and it has no recoverability.
Obviously, it can not meet the rigorous requirements of the design. Therefore, we need a more high performance and precision air conditioning to meet this requirement, so precision air conditioning came into being and will soon be applied in reality. At present, three-phase asynchronous motor is widely used in precision air conditioning fan controller. It is well known that asynchronous motor has a variety of speed regulation methods, and now the most commonly used is variable frequency speed regulation. However, because of the high cost of variable frequency speed regulation, electromagnetic interference has a greater impact on accuracy, and control is more difficult, its use is limited in many cases. On this premise, the structure of the controller is very simple, and the relatively low cost of the regulator is widely used in the precision air conditioning fan speed control system. With the rapid development of electronic technology and the design and application of power electronic devices developed by computer microcontrollers, the high-speed development and technological improvement of precision air conditioning fan control system have been greatly promoted. Because the way of variable frequency speed regulation is to change the power supply frequency of the stator to change the synchronous speed, the accuracy of frequency modulation can be guaranteed. Therefore, the speed regulation performance of frequency conversion speed regulation has the characteristics of high accuracy, high efficiency and high range. Although frequency conversion speed regulation is the mainstream direction at present, there are still many problems, such as high cost, high requirements for components specifications, complex circuits, complex structure and control methods, high maintenance costs after damage.
The most important thing is that the high-order harmonic generated in the process of frequency conversion speed regulation will pollute the adjacent electrical equipment and endanger the healthy operation of the surrounding equipment. Air conditioning fan adopts three-phase asynchronous motor, and three-phase asynchronous motor stator winding adopts triangular connection mode. Each phase winding and one TRIAC are connected to three-phase power supply in series. The trigger pulse is generated by DSP.
The trigger pulse is isolated by optical coupling, and the controlled side of the optocoupler is turned on. The gate of TRIAC is connected with the input power side through the optocoupler. When the gate passes through enough current, the TRIAC is turned on and the effective value of the voltage is controlled by changing the trigger angle of TRIAC. Three-phase AC voltage regulating and speed regulating circuit adopts three-phase three-wire type. The voltage of each phase of the stator and the current of each phase in steady state are symmetrical. Trigger angle of TRIAC is controlled once every half cycle to adjust the effective value of output voltage and achieve the purpose of speed regulation. Asynchronous motor is a resistance-inductance load, and the current is not zero when the passing voltage is zero. Therefore, the conduction of thyristor is not only related to the trigger angle, but also to the power factor angle of the motor. The control circuit uses MC56F825 developed by Freescale Company to control the main circuit, and real-time detection of voltage zero-crossing point, current, environmental temperature and other information. The clock signal input is a 32 MHz system clock generated by 8 MHz external crystal oscillator through internal frequency doubling. Control chip MC56F825 collects pressure signal, current signal, voltage zero-crossing signal of condensate tube, and after software processing, outputs trigger pulse: There are three zero-crossing detection circuits in the control circuit, and zero-crossing detection of line voltage is carried out by using three interruptions of the control chip respectively. Then phase-missing, phase-sequence detection and abnormal frequency detection are realized by software, thermostatic element and working current of fan is also set up. The detection circuit detects the phase line current and calculates the power factor angle when the fan works with zero-crossing signal. The controller uses MAX3232 transceiver developed by MAXIM company for level conversion to realize serial communication between the controller and PC. In addition, the controller has a series of abnormal detection circuits, such as bidirectional thyristor temperature detection circuit, ambient temperature detection circuit, and simple and convenient man-machine interface such as keys and digital tubes. The controller uses DSP chip, which has the advantages of low cost and flexible configuration. It is widely used in many industrial control, motion control, power management and medical detection equipment. 56F8025 series DSP has abundant peripheral interfaces, each peripheral interface can be closed independently, which can save external forces. Precision air conditioning is usually used in places where there are many electronic information equipments. It is very easy to cause interference to the control chip of fan controller, which makes the system unable to work properly. Therefore, in order to improve the stability of the system, in addition to adding anti-interference measures in circuit design and PCB plate-making, the external watchdog module is added in the system, so that when the program error occurs, the control chip can be reset to ensure the stability of the system. Software program is the key to realize the control of voltage regulation and speed regulation by DSP. The control chip MC56F8025 obtains the zero-crossing signal of three-phase input voltage through interruption, and the pressure signal of condenser tube through AD. The angle of TRIAC trigger pulse is calculated, and then the trigger pulse is output by IO output. At the same time, the three zero-crossing signals of line voltage obtained by DSP are analyzed and processed, and the phase-out sequence detection and frequency anomaly detection are carried out. In addition, the temperature signal is analyzed by DSP, and the corresponding protective measures are taken when the controller is abnormal. At the same time, the abnormal reasons are displayed by digital tube. The main circuit adopts bidirectional thyristor trigger circuit. The circuit uses MOC3061 series photoelectric bidirectional thyristor driver. The output of this photoelectric coupler is sinusoidal wave. The waveform is not distorted and noiseless. It can control high voltage and high current with low DC voltage and low current. It has the advantages of low cost, simple structure design and high reliability. Bidirectional thyristor trigger circuit is a very critical part of the main circuit.
The damage of this part of the circuit will directly lead to the collapse of the whole system. Therefore, the protection circuit must be designed to protect it. The protection of bidirectional thyristor mainly includes the following two kinds: voltage protection and current protection. When the circuit works normally, we call the maximum pulse which exceeds the maximum peak voltage that the bidirectional thyristor can bear as overvoltage. There are many reasons for overvoltage, including the violent fluctuation or interference of grid voltage, lightning stroke, etc. In addition, when the bidirectional thyristor is turned off and the positive current drops to zero, there will be a lot of current interceptors in it. Under the action of the reverse current, there will also be a very high current spike. If this spike exceeds the maximum allowed peak current of the bidirectional thyristor, the components will be damaged. Nowadays, the speed control system of precision air-conditioning fan mostly adopts the way of frequency conversion, but there are various limitations in the practical application of frequency conversion.
Therefore, this paper introduces a relatively advanced controller of voltage regulation and speed control of air-conditioning fan based on DSP. It not only takes into account the functions of ordinary controllers, but also overcomes the weakness that ordinary fan controllers can not be restored after protection. Zero-crossing detection is fast and accurate, which can ensure the dynamic and static performance of voltage regulation and speed regulation.