Design of a new type of electric load control and monitoring system

0 Preface

This paper focuses on a new design method of electric load control and monitoring system. Based on reliable performance, high accuracy, low power consumption, and small size, this method can better meet the needs of functions such as load management, power analysis, power collection, multiple control methods, and optimized power analysis. It can meet the power load side. Various application requirements for management.

l System working principle

Figure 1 shows the block diagram of the working principle of this system. This system uses LPC2132FBD64 suitable for embedded system design as the main processor; the interface circuit mainly completes the collection of pulse, switch and analog, and the main processing circuit is responsible for computing it to form various power, power, and electricity meters Reading, demand, current, voltage and other real-time data. Then, the main processing circuit performs closed-loop management according to these real-time data and the working parameters issued by the master station, and sends these real-time data to the display drive circuit through the I2C bus, and then displays through the LCD liquid crystal module. When the main station calls for information, the system sends these data back to the main station via GPRS. At the same time, the main processing board controls the corresponding relays to achieve the purpose of closed-loop control and remote control. This system highlights the modular design, the functions of each part are relatively independent, and try to avoid the cross-connection between the program of each module. Therefore, it has good scalability, which can reduce the workload of modifying and maintaining the program in the future, and at the same time can improve the readability, reliability and stability of the program, making remote upgrade and maintenance possible.

2 Main module functions

2.1 Data collection

The data collection of this system is the collection of state quantity first. That is, the position status and other status information are collected in real time, and are recorded in the memory when the displacement occurs, and it is set to wait for the master station to query or actively report to the master station in two modes as needed.

The second is the energy meter data collection. Usually, the terminal can collect and store the data of the electric meter through the RS-485 communication interface and according to the set terminal meter reading day. Each power management terminal can read multiple energy meters at the same time. The data storage can store the electricity of two meter reading cycles (the zero point data at the end of the month or the meter reading day), and can be sent to the main station when the main station calls for measurement, or it can be sent to the main station regularly.

AC analog quantity acquisition refers to the terminal using the ATT7022B measurement chip to measure the three-phase voltage, current, active power, reactive power, power factor, active energy, reactive energy and other instantaneous values ​​of the user side in real time, with an accuracy of usually 0.5%.

2.2 Negative control function

(1) Power setting control

The power setting control can be divided into four control methods, and the priority is from low to high as time period control, factory shutdown control, business report stop control, and current power down control. The terminal can modify the corresponding control mode and control parameters according to the power control period, power setting value, fixed value floating coefficient, alarm time, control rounds and other instructions issued by the master station, and can notify the customer through an audio alarm. During the automatic execution of the terminal, the fixed value, control object, execution result, etc. can be displayed on the liquid crystal.

(2) Electric energy setting control

Electric energy fixed value closed-loop control can be divided into three control types: monthly electricity energy control, electricity purchase energy (fee) control, and reminder alert.

(3) Remote control function

After the terminal receives the trip control command of the master station, it will control the controlled load switch according to the set alarm delay time and power limit time; at the same time, the terminal shall notify the customer with an audible alarm and record the trip time, trip rounds, and before Power, power 2 min after tripping, etc. At the same time, the terminal display should show the execution result. When the terminal receives the closing control command of the master station, the customer will be notified by an audible alarm to allow the customer to close. When the terminal receives the permission / prohibition call and permission / prohibition initiative report command of the master station, the terminal will control the call according to the master station command and actively report the system.

2.3 Wireless communication function

This system adopts the built-in GSM / GPRS module communication mode (the communication mode of the external radio station can also be used, and the user can choose it by himself). As a new communication method, GPRS has many advantages in the application of distribution automation. The distribution transformer integrated management system based on GPRS communication is a relatively promising implementation scheme.

2.4 Harmonic analysis and alarm function

The terminal can analyze the voltage harmonics and current harmonics of the monitoring point according to the voltage and current harmonic thresholds, and record the daily maximum value and occurrence time of the phase separation 2-19 harmonic voltage content rate and total distortion rate, and statistics Split-phase harmonic limit data. The data includes the cumulative time of the phase-separated total distortion voltage content rate exceeding the limit, the cumulative time of the split-phase 2-19th harmonic voltage content rate exceeding the limit, the cumulative time of the split-phase total distortion current exceeding the limit day, the phase splitting 2-19 Accumulative time of harmonic current over limit day, etc. When the user's harmonic exceeds the standard, the system will automatically alarm.

2.5 Event recording and reporting of important events

The terminal can record power-on, power-off, programming, timing, demand reset, phase failure, overvoltage, voltage loss, current loss, reverse phase sequence, overload, three-phase current imbalance, CT short circuit, CT two The occurrence time, status, data, event type and related conditions of events such as secondary short circuit, CT secondary open circuit, metering box opening, etc. And according to the time sequence of occurrence, it is divided into two queues of general events and important events to record separately. The maximum length of each queue is 255 records, and the queue is refreshed in a first-in first-out manner.

For the important events set by the master station (such as power control trip, electronic control trip, remote control trip, important parameter change, etc.), when the event occurs, the terminal can refresh the content of the important event counter in real time, make a record, and set it through ACD Proactively report incident records directly.

2.6 Load curve and historical data storage and reporting function

Daily load curve data is collected every 15 minutes, 96 data per day, usually save the data of the last 10 days (including active, reactive, voltage, current and other data); and can report to the main station according to the settings. The system terminal has an active reporting function, which can report data or passively (waiting for the master station to recruit data), and can also query historical data.

2.7 Meter reading test function

In order to facilitate users to know whether the energy meter connected to the terminal can communicate successfully, manual meter reading can also be performed by setting different meter addresses and communication rates through the LCD screen and buttons.

3 Software and hardware implementation of AC analog quantity acquisition module

3.1 Hardware circuit of AC analog quantity acquisition module

After the system passes the voltage transformer and current transformer, it can process the three-phase AC voltage value and three-phase AC current value of the collected electrical equipment, and then send it to the ATT7022B chip for measurement and calculation. Figure 2 shows the voltage and current acquisition circuit of this system.

ATT7022B can measure the active power, reactive power, apparent power, active energy and inactive energy of each phase and combined phase, and can also measure the current, voltage effective value, power factor, phase angle, frequency and other parameters of each phase. The peripheral circuit of the ATT7022B chip is shown in Figure 3. ATT7022B integrates 7-channel 16-bit ADC on-chip and adopts double-ended differential signal input. The maximum input voltage is 1.5 V, and the maximum effective value of the sinusoidal signal that can be input is 1V. In practical applications, the input of the voltage channel Un corresponding to the ADC can be selected at about 0.5 V, while for the current channel, the ADC input at Ib is selected at about 0.1 V. The metering module mainly performs high-pass filtering, phase shift filtering or phase correction on the data collected by the voltage and current sampling channels to obtain the required parameters (including three phases such as voltage, current effective value, power, frequency, phase angle, etc.) Parameters), and store these parameters in the corresponding registers, and then transfer the parameters to the MC-U through the SPI port.

3.2 ATT7022B and microprocessor data transmission software process

Figure 4 shows the SPI communication process based on ATT7022B. This procedure is mainly to complete the initialization of ATT7022B. And according to the LPC2132FBD64 query command to send data or modify the parameters in the ATT7022B register. If an abnormal situation is encountered, the terminal will automatically send an alarm message to the monitoring center.

The data transmission between the ATT7022B and the microprocessor is initiated by the LPC2132FBD64 sending an 8-bit command word to the DIN end of the SPI interface. Commands are divided into read commands and write commands, which can be distinguished by the most significant bit of the command word. If the highest bit is 1. The command is a write command, if the highest bit is 0, it is a read command.

Through the read command, LPC2132FBD64 can read the active power, reactive power, apparent power, active energy and inactive energy of each phase and combined phase in ATT7022B, and at the same time can obtain the effective value of each phase current and voltage Power factor, phase angle, frequency and other parameters.

The corresponding program of the write command, that is, the calibration table command, mainly completes the correction of the parameter accuracy of ATT7022B. ATT7022B must be corrected for the accuracy of parameters to ensure that the acquisition results meet the accuracy requirements of the system.

4 System performance test

This product has now passed field tests and expert appraisal, and all properties are up to standard. The error between the data collection function test result and the measurement center test result is within 0.2%. The negative control function has passed 500 tests and no misoperation has occurred. In terms of reliability and stability, except for the operating temperature of the liquid crystal at -20 to 70 degrees, the operating temperature of all other devices is at -40 to 85 degrees, which can cope with a variety of harsh environments.

5 Conclusion

This system can measure the power quality data information of the power grid in real time and accurately, obtain real-time detailed power quality monitoring reports at any time, and directly manage and control the power consumption settings. Therefore, the shape of the power load curve can be effectively improved, the load curve tends to be flat, the peak-valley difference is reduced, and the optimal distribution of the power load in a certain time and space can be achieved. At the same time, the load rate of the user and the power grid can be increased, thereby increasing the power generation, The utilization rate of power supply and power consumption equipment can achieve the safe and economic operation of the power grid. Since the widespread application of load control and monitoring system is the trend of the development of automation technology in electric power companies, the system is of great significance to the development of electric power resources of electric power companies and the adjustment of the economic and power supply order of electric power companies.