Design of Induced Wind Turbine Control System Based on Power Line Carrier Communication

　　introduction

　　Induced ventilation uses an induced fan to eject high-speed gas to induce and drive the surrounding gas to move forward, thereby achieving the purpose of air circulation and ventilation. At present, most intelligent control systems are used, which have complex wiring, high costs, and inconvenient system debugging and maintenance. Power line carrier communication has the advantages of low cost and easy debugging and maintenance, and is very suitable for induced ventilation control systems.

　　1 Overall design of power line communication induced ventilation control system

　　The overall block diagram of the power line communication induced ventilation control system is shown in Figure 1. The system consists of multiple induced fan controllers . Power line communication is used between the controllers. Each controller has the function of detecting the surrounding air quality (smoke detection, CO detection) and can control an induced fan to work according to the detection results. The controller is divided into master/slave controllers. While completing the control of the induced fan it carries, the master controller must obtain the working status of each slave control node and control the slave controller. The slave controller controls the operation of the induced fan it carries according to the detection results, and reports the current working status to the master controller and is controlled by the master controller. When the self-control conflicts with the control command of the master controller, the control command of the master controller shall prevail. For example, if the self-control needs to turn on the fan, and the control command needs to turn off the fan, then the control turns off the fan.

　　2 Hardware Design of Power Line Communication Induced Ventilation Controller

　　2.1 Induced ventilation controller hardware structure diagram

　　The hardware structure of the power line communication induction controller is divided into functional units such as smoke detection, CO detection, power line carrier communication, induction fan control, power supply unit, clock unit, storage unit, watchdog reset and keyboard display, as shown in Figure 2. The keyboard is mainly used to set system control parameters (such as CO concentration threshold, master/slave node identification, fan start/stop delay, etc.) and calibrate the clock. The display unit can instruct the user on the parameter setting process and display the current status of the system, which is convenient for system installation, debugging and maintenance. After the parameters are set, the parameters are written into the memory, and the controller starts to perform smoke detection, CO detection, induction fan control and other tasks; the master controller needs to query the working status of each slave controller regularly and control the slave controller to work.

　　Due to insufficient oxygen supply in the working environment (such as a garage) of the induced ventilation control system, if a fire is discovered, it will be in a smoldering state at the beginning of the fire. If the induced fan is turned on at this time, it will help to burn into an open flame. Therefore, it is necessary for the controller to perform smoke detection (detect the smoldering state) to avoid major losses caused by the induced fan malfunction. When a fire hazard is detected, an audible and visual alarm will be issued and all fans will be stopped. C0 detection is used to measure the air quality in the area. When CO is detected to be excessive, the induced fan will be turned on to ensure ventilation. The controller realizes data transmission and information exchange with other controllers through the power line carrier communication unit. Due to the complex working environment of the controller and the unattended working process, the watchdog reset unit can effectively avoid system crashes and program runaway during the working process.

　　2.2 Induced ventilation controller hardware circuit diagram

　　The induced ventilation control processor uses a 32-bit ARM microcontroller LPC2200, which is based on the ARM7TDMI-S architecture. The processor clock frequency is as high as 60 MHz. It integrates high-speed Flash memory and rich peripheral components (such as external interrupts, A/D conversion, LCD controller, etc.); the processor's built-in 10-bit A/D conversion can ensure the needs of data collection in C0 detection and smoke detection; the processor has its own watchdog register. If there is no periodic reload during operation, an internal reset will be generated when the register overflows. The clock unit uses the clock chip SD2405AP, which has a built-in crystal oscillator, a rechargeable battery, and a standard I2C interface. It can be easily connected to the I2C interface of LPC2200. The chip has year, month, day, hour, minute, and second registers inside, which can meet the requirements of induced fan timing, delayed start/stop control, CO and smoke timing detection. The circuit diagram of the power line communication induced ventilation controller is shown in Figure 3. Among them, CAT24WC02 is a serial EEPRO-M, and SP708S is a microprocessor monitoring device.

　　Power line carrier communication uses a power line dedicated half-duplex asynchronous modem PL2102. As shown in Figure 3, the chip needs to add necessary peripheral circuits when in use. The peripheral circuits mainly include a transmit power amplifier circuit, a filter shaping circuit, a carrier coupling circuit, and a filter receiving circuit. The power amplifier circuit amplifies the carrier modulation signal output by PL2102 and filters out the noise and pseudo signals in the signal. The receiving filter and power amplifier circuit are shown in Figure 4. The output signal PSK_OUT is filtered and shaped by C1 and L2 after passing through the power amplifier circuit composed of Q1, Q2, Q3, and Q4, and then added to the coupling coil and sent to the power line through the coupling coil. In the receiving circuit, D1 is used for clamping to prevent excessive surge current. C2, C3 and L1 form a parallel resonance, which has the function of selecting the frequency of the 120 kHz signal and improving the sensitivity of the received signal.

　　The smoke detection signal amplifier circuit is shown in Figure 5. Smoke detection uses a pair of infrared transmitting/receiving tubes and is installed in a dark room. The two tubes are in a relative state at an obtuse angle. When smoke detection is required, the infrared transmitting tube is turned on through the PO.6 port. If there is no fire hazard (no smoke), the infrared light cannot reach the infrared receiving tube; when there is a fire hazard (smoke), the infrared light is diffusely reflected and refracted on the surface of the smoke particles and enters the infrared receiving tube. The greater the smoke, the stronger the infrared light diffuse reflection and refraction, and the stronger the infrared light receiving tube signal. The weak signal received by the infrared receiving tube is amplified by two stages of TLC27L2 and sent to LPC2200 for A/D conversion. The controller determines whether it is necessary to perform a fire sound and light alarm and shut down the fan operation based on the size of the A/D conversion value.

　　The CO detection uses the electrochemical element ME3-CO, which obtains a weak current signal proportional to the CO gas concentration. The signal must be amplified before A/D conversion can be performed. The signal conditioning circuit is shown in Figure 6. The operational amplifier of the conditioning circuit uses AD8572, in which UA, R5~R7, and C1 form a constant potential circuit, so that the potential between the C and R poles and the W pole remains constant; UB, R1~R4, and C2 form a signal amplification circuit, which is used to detect the current generated by gas electrolysis in the CO sensor, amplify the weak signal of the sensor, and have a low-pass filtering function to filter out high-frequency interference signals in the detection signal. The amplified detection signal is input to LPC2200 for A/D conversion. The controller determines the air quality circulation in the current area through the size of the A/D conversion value and controls the fan.

　　3 Power line communication induced ventilation controller software

　　3.1 Controller-induced fan control process

　　After the controller is powered on, it must first initialize the relevant software modules, including the clock chip, LCD display, A/D conversion, external interrupt, watchdog reset, etc.; after the initialization is completed, the relevant parameters are set and written to the I2C memory for storage. The parameters that need to be set are listed in Table 1.

　　The controller detects smoke and CO. If the smoke detection value exceeds the preset value (the smoke threshold is fixed in the program after experimental calibration), the controller will issue an audible and visual alarm and set the fire alarm flag. The main controller stops all fans. The delay time to recover from the "fire alarm state" is determined by the "system restart delay after fire alarm" parameter. The main controller queries the working status of each slave controller every 5 seconds. When a fire is detected in a certain area, it stops all fans and modifies the current working status of the slave controller. The program control flow of the controller for the induced fan is shown in Figure 7. The controller displays the current status of the fan, smoke and CO detection values, whether a fire occurs, whether CO exceeds the standard, and the system working status (working status of each main component, such as clock chip operation, A/D conversion, communication) and other information during operation.

　　3.2 Power Line Carrier Communication Program Flow

　　The master controller and the slave controller in the system use master/slave communication. The communication process is initiated by the master controller. The messages sent by the master controller are divided into "status query messages" and "control messages". After receiving the data message from the master controller, the slave controller needs to reply with a response message. Considering the convenience of software design, the sending message and the response message use the same message format. The message format is as follows:

　　In the message format, 40 "1"s are used to synchronize the pseudo-code random codes of the receiving end and the sending end, and the frame header sequence is fixed to 0x09AF; the source address is the node address of the sending datagram, and the destination address is the node address to which the datagram needs to be delivered; the data is the information to be transmitted by the datagram, occupying 1 byte, the upper 4 bits are the message type, and the lower 4 bits are the data information. The data field format is listed in Table 2; CRC16 is the CRC check value of the source address, destination address, and data.

　　The carrier communication program uses an interrupt mode and is divided into two parts: sending and receiving. The interrupt signal is generated by the PL2102 synchronous pulse output pin (HEAD). The carrier communication receiving and sending program is shown in Figure 8.

　　Conclusion

　　The induced ventilation control system based on power line communication uses a dedicated power line carrier communication chip in hardware design, and power amplification and receiving filter circuits are used for signal transmission and reception respectively. The software uses data check CRC16 to ensure the reliability of communication. This design has the advantages of simple system construction, low cost, and convenient debugging and maintenance.