LCD Display Inverter

“The power operation power monitoring system is generated with the automatic operation of the power system. The system can perform parameter monitoring and fault alarm operations on the AC power supply, DC control power supply, standby operating power supply and switch status in the substation. Thereby, the abnormal situation of the power system can be detected 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 the power system fails, it provides backup operating power for secondary equipment such as relays and circuit breakers to protect the equipment.

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Author: Feng Wei, Su Mei

1 Introduction

The power operation power monitoring system is generated with the automatic operation of the power system. The system can perform parameter monitoring and fault alarm operations on the AC power supply, DC control power supply, standby operating power supply and switch status in the substation. Thereby, the abnormal situation of the power system can be detected 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 the power system fails, it provides backup operating power for secondary equipment such as relays and circuit breakers to protect the equipment.

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

The power 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 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, power monitoring has gradually matured, and it has developed to monitor multiple circuits or even multiple systems.

The power operation power monitoring system cooperates with a reasonable controller to fully realize the safe operation and automatic dispatch of the power system by controlling the high-voltage circuit breaker and other relay equipment, so as to meet the needs of modern power dispatch.

2 Overall design scheme of the system

This power management instrument is mainly used for the monitoring and management of operating power and backup power in small and medium-sized substations. In order to better save the energy of backup batteries, a 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 parameters such as active power, reactive power, harmonics, voltage, and current in the AC part. The price of ATT7022B is relatively cheap, and it has an SPI (serial peripheral interface, serial peripheral interface) interface, which can easily communicate with the MSP430F149 microcontroller.

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

DC quantity monitoring, including ambient temperature, battery temperature, microcontroller temperature, single battery voltage, 2-way DC closing power supply, operating voltage and closing current.

2.2 Human-machine interface module

The keyboard is the primary input source. In order to save costs, the system adopts the scanning method to realize the matrix keyboard, and adopts Chinese liquid crystal Display.

2.3 Communication module

Since the microcontroller has a UART, the RS-232 serial communication method is used to realize the communication with the upper computer. In order to achieve level matching 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 Fig. 1, the technological process of the system is introduced in the sequence from AC voltage to DC voltage.

Battery pack management. The rectified voltage is generally higher than the voltage of the battery pack for charging the battery pack. When it is used for the working power supply, it can be stepped down through a diode, and switches such as K1 and K2 are used to select the step-down value. Controlled by the controller, the processor conducts a round-robin inspection of the status of a single battery in the battery pack, and reflects the use status of the battery in real time, which is convenient for timely understanding of the battery status.

AC parameter detection. The system uses a special energy metering device ATT7022B to detect the voltage, current, active power, power factor, harmonics and other parameters of the AC grid, and is connected to the microcontroller through the SPI interface that comes with the device.

The management system communicates with the upper computer in serial mode. The host computer can detect the system and modify the control parameters, so as to realize four remote control functions such as telemetry, remote signaling, remote control, and remote adjustment.

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

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

(2) Monitor the rectified DC operating power supply lines. Monitor its voltage, closing current and whether the operating power supply fails. At the same time, the voltage obtained by monitoring can be used as the basis for automatic voltage regulation of the diode, so as to realize the automatic step-by-step voltage regulation of the operating power supply.

(3) Carry out patrol inspection (detection of single battery) for standby power supply equipment (battery), understand the battery power and related parameters, replace the battery in time, and control the state of battery charge and discharge. Keep the battery in the best condition and effectively extend the life of the battery.

(4) Since there is not much demand for functional keyboards of the equipment, a matrix keyboard extended by the general I/O port of the single-chip microcomputer can be used, and the Display part adopts a Chinese liquid crystal display module.

(5) The serial communication protocol is used to realize the communication with the upper computer, which can be controlled and monitored remotely.

According to the process of the system, it can be known that the main functions of the system have three modules: AC data sampling module, battery pack management module and DC operation power supply signal analysis module, in addition to other small modules such as: display, keyboard, communication module, etc. The first three modules run in parallel and are sampled in a round-robin fashion. The sampling time is set by the timer. The operation process of the system is shown in Figure 3.

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

3 Detailed design scheme 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. The management of the battery 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, rectified DC power monitoring, switching input and control output.

The battery inspection circuit includes battery cell voltage monitoring, temperature detection, battery charge and discharge 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, which are the ambient temperature, the temperature of the battery pack, and the internal temperature of the single-chip microcomputer. A total of three channels of A/D converters are used. The battery charging circuit uses a high-frequency switching rectifier power supply to charge it, some use a high-frequency switching charger as the charging power source, and use a relay to control the battery pack charging. 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, and the battery pack is in a constant standby state. The alarm circuit mainly drives a buzzer and an alarm LED, so as to realize the function of sound and light alarm.

Rectified DC power monitoring includes voltage and current monitoring and automatic voltage regulation control of operating power. The DC voltage monitoring can use the same resistance voltage division method as the single battery voltage sampling, and can share the ground with the single battery voltage. The operating power supply includes all the operating voltages of the secondary measurement, which are provided by the high-frequency switching power supply.

Switch input and control output are mainly composed of signal conditioning circuit, control logic circuit, drive circuit, address decoding circuit, isolation circuit, etc. The structure of control output circuit 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 power consumption and reactive power, Power factor and other parameters, 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 electric energy metering device ATT7022B. In order to ensure the safe and stable operation of the system, this design adopts an external power supply combined with a battery pack to supply power at the same time.

3.3 Communication and HMI Circuit Hardware Design

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

4 Software Design

4.1 DC Module Software Design

Due to the modular design of the system, each module can be programmed independently. The software design of the DC module mainly includes sampling parameters such as the voltage and temperature of the single battery and the digital input and output control of the system. It involves the sampling tour time interval, temperature inspection time interval, data processing method, etc.

(1) The monitoring of the battery inspection circuit mainly includes the measurement of parameters such as battery cell voltage, battery temperature, ambient temperature, and battery charge and discharge status. The temperature detection includes three subroutines in total, and the temperature acquisition sub-module is entered in an interrupt mode to realize temperature acquisition.

(2) The monitoring of the rectified DC bus power supply includes voltage and current monitoring and operation of the automatic voltage regulation device of the power supply. The functions realized by this software module mainly include three parts: voltage detection, closing current detection and operation power supply automatic voltage regulation device.

4.2 Design of AC Sampling Software

The AC sampling part is used to sample the voltage and current of the AC power supply circuit in real time, and perform relevant processing on the data to obtain parameters such as active power, reactive power, and harmonics of the power grid. These functions can be realized with a dedicated energy metering device ATT7022B.

4.3 Communication and Human-Machine Interface Software Design

Human-machine interface is the medium of interaction and information exchange between the system and users, which realizes the conversion between the internal form of information and the form acceptable to human beings. Human-machine interface is an indispensable part of intelligent equipment. It is the key to understand and control smart devices. This design mainly includes two parts: keyboard design and LCD Chinese display.

The keyboard input part consists of a matrix scanning keyboard and a total of 10 function keys, including: system reset, battery parameter display, AC parameter display, DC parameter display, switch status display, temperature display, turn up, turn down, and reset the alarm state. In addition, there is a keyboard for expansion.

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

Serial communication realizes the communication between the single-chip microcomputer and the upper computer, so that the collected data is transmitted to the upper computer for processing and control.

4.4 Main program processing module

As the framework of the system, the main program processing module is mainly responsible for the coordination processing and data interaction between the various modules. The main program processing module is initialized first, which mainly includes the definition of each pin function of the single-chip microcomputer and the assignment of the corresponding registers, which also includes the assignment of the control registers of each function module and the setting of parameters. Then enter the processing process of the main program, which includes two modules of SPI communication and liquid crystal display. The main program processing flow is shown in Figure 5. The whole 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 the data interaction.

The main program enters the SPI communication immediately after parameter setting, stores the value of the AC data in the microcontroller register, saves and adjusts the parameters, and then immediately scans the switching state (scanning the I/O state).

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

5 Conclusion

The system is a multi-task processing system based on MSP430F149 single-chip microcomputer. It is mainly oriented to the comprehensive management of automatic operation of small and medium-sized substations. It has the characteristics of strong specificity, high reliability and low cost. The system includes battery cell voltage measurement, battery and ambient temperature detection, operating power supply voltage and current detection, AC voltage (current, power factor) detection (SPI communication part), switching state detection, and automatic voltage regulation control of operating power supply , battery low-voltage automatic charging control, keyboard and display, communication, etc., a total of 9 main modules, and also retains a certain expansion space, which can basically meet the detection and control needs of small and medium-sized substations. in addition. Because the processor of the system has reliable operation and multiple low-power operation modes, it is especially suitable for the use of energy control units such as substations.