Design of intelligent battery inspection system for electric power supply

　　The power operation power supply monitoring system is generated with the automatic operation of the power system. The system can perform parameter monitoring, fault alarm and other operations on the AC power supply, DC control power supply, backup operation power supply and switch status in the substation. In this way, abnormal conditions of the power system can be discovered in time, and precautions can be taken in advance to ensure the continuous and reliable operation of the power system. At the same time, when a fault occurs in the power system, backup operation power is provided for secondary equipment such as relays and circuit breakers to protect the equipment.

　　The battery inspection instrument is a detection device for backup power supply. Its main function is to detect the voltage, temperature, capacity and other parameters of the single battery, and provide charging control and fault alarm functions, so as to reasonably control the battery, extend the battery life and improve the reliability of the system.

　　The power supply monitoring system started in the late 1980s. At that time, it could only monitor an independent DC power supply system or a bureau (station), and the power supply monitoring level was not high and the reliability was low. After the 1990s, especially in recent years, with the rapid development of computer and communication technology and the improvement of power supply equipment level, power supply monitoring has gradually matured and developed to monitor multiple circuits or even multiple systems.

　　The electric power operation power supply monitoring system cooperates with a reasonable controller and can fully realize the safe operation and automatic dispatching of the power system by controlling high-voltage circuit breakers and other relay equipment, thereby meeting the needs of modern power dispatching.

　　2 Overall system design

　　This power management instrument is mainly used for monitoring and management of operating power and backup power in small and medium-sized substations. In order to better save the energy of the backup battery, the low-power MSP430F149 microcontroller is selected as the processor of the device.

　　2.1 Sampling Module

　　The AC module uses the ATT7022B AC three-phase energy metering device to process the parameters of the AC part such as active power, reactive power, harmonics, voltage, current, etc. ATT7022B is relatively cheap and has an SPI (serial peripheral interface) interface, which can easily communicate with the MSP430F149 microcontroller.

　　Switch quantity monitoring, including the opening and closing status of AC circuit breaker (two main and backup power supplies), 8 AC control power supplies, and the opening and closing status of DC circuit breaker.

　　DC quantity monitoring, including ambient temperature, battery temperature, MCU temperature, single cell battery voltage, 2-way DC switching power supply, operating voltage and switching current.

　　2.2 Human-machine interface module

　　The keyboard is the main input source. In order to save costs, the system adopts scanning mode to realize the matrix keyboard and adopts Chinese LCD display.

　　2.3 Communication Module

　　Since the microcontroller has UART, RS-232 serial communication is used to communicate with the host computer. In order to match the level with the host computer, SP3220E is used as the interface level converter. The process flow of the equipment is shown in Figure 1.

　　
       According to FIG1 , the process of the system is introduced in sequence from AC voltage to DC voltage.

　　Battery pack management. The rectified voltage is generally higher than the battery pack voltage for charging the battery pack. When it is used as a working power source, it can be stepped down by a diode. Switches such as K1 and K2 are used to select the step-down value. The on and off of switches are controlled by the processor. The processor conducts a patrol inspection of the status of individual batteries in the battery pack, and reflects the battery usage status in real time, so as to facilitate timely understanding of the battery status.

　　AC parameter detection. The system uses a dedicated power metering device ATT7022B to detect the voltage, current, active power, power factor, harmonics and other parameters of the AC power grid, and connects to the microcontroller through the device's built-in SPI interface.

　　The management system communicates with the host computer in serial mode. The host computer can detect the system and modify the control parameters to achieve four remote control functions: remote measurement, remote communication, remote control, and remote adjustment.

　　The hardware principle structure of the device is shown in Figure 2. Its main functional modules include:

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       (1) Monitor the AC bus voltage, current, harmonics and other parameters, sample the AC circuit, process discrete data (sample 20 to 0 times in one cycle), and calculate the active power, reactive power and power factor of the line. These functions can be achieved using an ATT7022B.

　　(2) Monitor the rectified DC operating power supply line. Monitor its voltage, closing current, and whether the operating power supply has any faults. At the same time, the monitored voltage can be used as the basis for automatic voltage regulation of the diode to achieve automatic voltage regulation of the operating power supply.

　　(3) Conduct patrol inspections on the backup operating power supply equipment (battery) (inspection of single cells), understand the battery power and related parameters, replace the battery in time, and control the battery charging and discharging status. Keep the battery in the best condition and effectively extend the battery life.

　　(4) Since the device does not require a functional keyboard, a matrix keyboard expanded by the general I/O port of the microcontroller can be used, and the display part uses a Chinese LCD display module.

　　(5) Serial communication protocol is used to communicate with the host computer, which can be remotely controlled and monitored.

　　According to the process of the system, the system mainly implements three modules: AC data sampling module, battery pack management module and DC operating power signal analysis module. In addition, there are other small modules such as display, keyboard, communication module, etc. The first three modules run in parallel and sample in a roving manner. The sampling time is set by the timer. The system operation process is shown in Figure 3.

  The MSP430 series microcontroller has three low-power modes. In order to reduce energy consumption, the interrupt mode can be used. The system workflow is shown in Figure 4.

　　
       3 Detailed design of module subsystem

　　3.1 DC Sampling Hardware Design

　　The DC sampling part mainly includes battery charge and discharge control, monitoring, and monitoring of operating voltage and current after rectification. Battery management also includes its temperature, voltage, capacity, etc. In addition, the fault alarm circuit also belongs to the DC module. The DC sampling circuit can be divided into hardware design parts such as battery inspection circuit, rectifier DC power supply monitoring, switch input and control output.

　　The battery inspection circuit includes battery cell voltage monitoring, temperature detection, battery charging and discharging, and alarm circuits. Battery cell voltage monitoring includes sampling circuit design and inspection logic circuit. The temperature detection circuit is mainly divided into three channels, namely ambient temperature, battery pack temperature, and internal temperature of the single-chip microcomputer, and a total of three A/D converters are used. The battery charging circuit uses a high-frequency switching rectifier power supply to charge it, and some use a high-frequency switching charger as a charging power supply, and a relay is used to control the charging of the battery pack. When the power supply is normal, the high-frequency switching power supply directly supplies power to the secondary circuit relay. Once the main power supply fails, the backup power supply is immediately used to prevent accidents. The battery pack is in a constant standby state. The alarm circuit mainly drives a buzzer and an alarm light-emitting diode to realize the sound and light alarm function.

    Rectified DC power supply monitoring includes voltage and current monitoring and automatic voltage regulation control of operating power supply. DC voltage monitoring can adopt the same resistance voltage division method as single cell voltage sampling, and can be grounded with single cell voltage. The operating power supply includes all secondary measured action voltages, which are provided by a high-frequency switching power supply.

　　The switch quantity input and control quantity output are mainly composed of signal conditioning circuit, control logic circuit, drive circuit, address decoding circuit, isolation circuit, etc. The output circuit structure of the control quantity is basically the same.

　　3.2 AC sampling hardware design

　　The AC part is mainly used to monitor the voltage, current, power, harmonics and other parameters of the AC power supply circuit in real time to ensure the safe operation of the power supply circuit, and to understand the status of the three-phase AC power supply, the consumed power, reactive power, power factor and other parameters in real time. Once the power supply fails, fault handling measures can be taken in time. In this design, the sampling and calculation of the AC module are realized by the multifunctional three-phase power metering device ATT7022B. In order to ensure the safe and stable operation of the system, this design adopts the method of combining external power supply with battery pack for power supply at the same time.

　　3.3 Communication and human-machine interface circuit hardware design

　　The circuit design mainly includes two parts: human-machine interface circuit design and serial communication interface circuit design. The human-machine interface circuit design mainly includes keyboard matrix circuit and liquid crystal display circuit. The keyboard matrix circuit is mainly used to input data to realize human-machine interaction. The keyboard design of this system adopts scanning method to realize matrix keyboard. Liquid crystal display circuit is very important as an important human-machine interface component in intelligent devices. This design adopts LCM 12864ZK Chinese liquid crystal display. The communication interface circuit design belongs to the information exchange part between the system and the host and the operator. The communication between this system and the host computer adopts UART asynchronous communication method.

　　4 Software Design

　　4.1 DC module software design

　　Since the system adopts modular design, each module can be programmed independently. The software design of the DC module mainly includes sampling of parameters such as single battery voltage, temperature, and system switch input and output control. It involves sampling patrol time interval, temperature patrol time interval, data processing method, etc. [page]

　　(1) The monitoring of the battery inspection circuit mainly includes the measurement of battery cell voltage, battery temperature, ambient temperature, and battery charge and discharge status. The temperature detection includes three subroutines, which use interrupt mode to enter the temperature acquisition submodule to realize temperature acquisition.

　　(2) The monitoring of the rectifier DC bus power supply includes voltage and current monitoring and operating the power supply automatic voltage regulation device. The functions implemented by this software module mainly include voltage detection, closing current detection and operating the power supply automatic voltage regulation device.

　　4.2 AC sampling software design

　　The AC sampling part is used to sample the voltage and current of the AC power supply circuit in real time and process the data to obtain the active power, reactive power, harmonics and other parameters of the power grid. These functions can be realized by a dedicated power metering device ATT7022B.

　　4.3 Communication and human-machine interface software design

　　The human-machine interface is the medium for interaction and information exchange between the system and the user. It realizes the conversion between the internal form of information and the form acceptable to humans. The human-machine interface is an indispensable part of intelligent devices. It is the key to understand and control intelligent devices. This design mainly includes two parts: keyboard design and LCD Chinese display.

　　The keyboard input part is a matrix scanning keyboard, which has 10 function keys, including: system reset, battery parameter display, AC parameter display, DC parameter display, switch status display, temperature display, up page, down page, alarm status reset. In addition, there is a keyboard for expansion.

　　Combined with the design of the keyboard circuit, the LCD display mode adopts two methods: default and interrupt processing. In the absence of any key input, the LCD module displays the AC sampling data: once there is a key input, such as the battery inspection parameter display, the display module immediately enters the battery parameter display state.

　　Serial port communication realizes the communication between the microcontroller and the host computer, thereby transmitting the collected data to the host computer for processing and control.

      4.4 Main program processing module

　　The main program processing module is the framework of the system and is mainly responsible for the coordination and data interaction between various modules. The main program processing module is first initialized, which mainly includes the definition of the functions of each pin of the microcontroller and the assignment of the corresponding registers, which also includes the assignment of the control registers of each functional module and the setting of parameters. Then it enters the processing process of the main program, which includes the SPI communication and LCD display modules. The main program processing flow is shown in Figure 5. The entire program basically adopts the interrupt service structure. In order to realize the data interaction between the interrupt program and the main program, the system can appropriately define some global variables and global buffer areas to realize data interaction.

　　After the main program has been parameterized, it immediately enters the SPI communication, stores the AC data value in the MCU register, saves and sets the parameters, and then immediately scans the switch status (scans the I/O status).

　　As can be seen from Figure 5, the main program only has two simple functional modules, and then it is responsible for flag judgment and flag setting. The other is to read data from the specified buffer or temporarily store data in the specified buffer. All other functional modules are completed by interrupt processing, and the main program only interacts with these modules.

　　
   5 Conclusion

　　The system is a multi-task processing system based on the MSP430F149 single-chip microcomputer, mainly for the integrated management of the automated operation of small and medium-sized substations, with the characteristics of strong specialization, high reliability and low cost. The system includes 9 main modules, including battery pack single voltage measurement, battery and ambient temperature detection, operating power supply voltage and current detection, AC voltage (current, power factor) detection (SPI communication part), switch state detection, operating power supply automatic voltage regulation control, battery low voltage automatic charging control, keyboard and display, communication, etc., and there is still a certain amount of expansion space, which can basically meet the detection and control needs of small and medium-sized substations. In addition. Since the processor of the system has reliable operation and multiple low-power operation modes, it is particularly suitable for use in energy control units such as substations.