Abstract : To address the complexity of electricity management in university student dormitories and the need for safe electricity use, an intelligent management terminal for safe electricity use in student dormitories was designed. Test results show that the intelligent management terminal can quickly identify malicious loads connected to dormitory circuits and, through combined control logic, monitor dormitory electricity use to meet the electricity management needs of the university's logistics department.
Keywords : dormitory electricity; intelligent management; logic control; load identification
0 Introduction
With the development of the social economy and the widespread adoption of student dormitories, the electricity usage in student dormitories has undergone tremendous changes. The scientific and rational management of electricity use in student dormitories has become a crucial issue for school logistics management departments. A comprehensive survey and comparison of electricity usage in school student dormitories reveals the following needs for school electricity management:
(1) Electricity commodification. The traditional time-limited and quantity-limited power supply method and the method of collecting electricity fees from accommodation fees are not suitable for the increasing demand of electrical equipment. Adopting the method of purchasing electricity on demand to implement electricity commodification is an inevitable management approach.
(2) Electrical safety. In order to prevent fires caused by students using unsafe electrical equipment, control measures such as automatic power cut-off based on overload and critical load identification should be considered.
(3) Control as needed. In order to cultivate good living habits and regulate students' daily routines, the power circuits in student dormitories should be controlled on a timed basis in accordance with the school's management needs.
This paper designs an intelligent management terminal for safe electricity use in student dormitories to meet the electricity management needs of the school's logistics management department.
1. Functional Design
In accordance with the requirements of metering and billing, intelligent monitoring and identification, and power outage control management, the dormitory safe electricity use intelligent management terminal is designed with the following functions:
(1) Accumulate the total electricity consumption and deduct the remaining electricity consumption;
(2) It can detect electrical parameters such as voltage, current, active power, reactive power and power factor in real time;
(3) Supports independent control of 3 output circuits (such as lighting, sockets, and air conditioning);
(4) Supports four types of logic control functions: prepaid control, load identification control, time control, and forced control;
(5) Various log records can be queried.
2 Hardware Components
The dormitory safety electricity management terminal adopts a dedicated microcontroller unit (MCU) design. The hardware system of the entire machine is implemented according to each functional module, including a microprocessor, voltage sampling via a resistor divider network, current sampling via a current transformer, control output of three magnetic latching relays, ferroelectric data storage, LCD display, key input, and active energy pulse indication output, etc. The hardware composition is shown in Figure 1.
Figure 1 Hardware Composition
3 Software Design
3.1 Main Program Flow
The main program manages the various functional modules by setting time slices and event triggering conditions. The main program software flow is shown in Figure 2.
Figure 2 Main Program Software Flow
3.2 Load Limiting and Load Identification Algorithm
When students use electrical appliances that are purely resistive loads (malicious loads), it can easily lead to electrical fires and other safety accidents, affecting the students' lives and property. Similarly, when students use too many regular electrical appliances, the accumulated electrical load can also cause safety accidents.
Therefore, the management terminal determines the load control result based on the requirements of both maximum power limitation and malicious load identification, so as to ensure the safety of dormitory electricity use.
The method for limiting maximum power is relatively simple: if the sum of the power of all loads exceeds the maximum total power, it is judged as power over-limit, and the dormitory power supply circuit must be cut off.
For identifying malicious loads, using the total power assessment method alone is insufficient for accurate identification. Testing the operating characteristics of low-power, purely resistive malicious loads reveals a high power factor. However, directly testing the power factor of the dormitory's main power supply circuit does not yield a high value. Therefore, this design employs an incremental assessment method, real-time monitoring of the power factor increment of the power supply circuit as the basis for identifying malicious loads. If the total power of the dormitory's main power supply circuit exceeds the limit, and the power factor increment exceeds the maximum set value, it is identified as a malicious load connection. The power factor increment is...
Where: PN—current active power;
PL—Active power at the previous moment;
ΔP—Increment in active power;
QN—Current reactive power;
QL—Previous reactive power;
ΔQ — Reactive power increment.
3.3 Logic control method.
3.3.1 Mandatory Control
Some university dormitories are allocated to management personnel and international students. These dormitories often have uninterrupted power supply and no load or time restrictions. In this case, if the forced control function is activated, other control functions will not function. Additionally, when universities organize large-scale events, they need to uniformly cut off and restore power to all dormitory circuits, which also requires the forced control function.
3.3.2 Time Control
Universities have a large number of students, and to ensure a unified schedule, power needs to be switched on and off at set times. For example, from 6:00 to 8:00 AM is the time when students get up and wash in the morning, so lighting and socket circuits should be kept powered on; from 8:00 to 11:00 AM is the time when students are in class and generally not in their dormitories, so all circuits should be switched off; from 11:00 PM to 6:00 AM is the time when students are resting, so lighting should be switched off, but sockets and air conditioning circuits should be kept powered on; on weekends, from 8:00 AM to 11:00 PM, students generally do not have classes and spend most of their time in their dormitories, so all relevant circuits should be kept powered on.
The terminal provides two independent control time schedules for lighting, sockets, and air conditioning circuits, which allows school management to control the power on/off of different circuits at different times according to actual conditions, thus meeting the requirements of timed control management.
3.3.3 Load Control
The terminal provides load control for the dormitory's main power circuit, and can identify malicious loads and respond quickly.
3.3.4 Prepaid Control
The terminal, in conjunction with a remote prepaid electricity management system, enables students to pay in advance before using electricity. Students can recharge their accounts based on their dormitory's electricity usage to ensure normal power supply. Once a student has used up their prepaid electricity, the terminal will automatically cut off power to the dormitory. Power will be restored promptly if the student recharges their account in a timely manner.
3.3.5 Combined Control
The above four logic control methods can be used individually or in combination. The terminal can determine whether the power supply output circuit is on or off based on the combined control logic and priority of forced control, time control, load control, and prepaid control.
The combinational control logic is shown in Figure 3.
Figure 3 Combinational Control Logic
4. Experimental Results
The results of the malicious load identification test are shown in Table 1.
As shown in Table 1, the management terminal can quickly identify malicious loads connected to the dormitory circuit by students and issue a trip command. The combined control logic, as shown in Table 2, can realize combined logic control such as time period control, load control, and prepaid control to jointly monitor the electricity consumption of the dormitory.
5 Conclusion
This student dormitory electricity management terminal has metering, monitoring, and control functions, which can reduce the difficulty of electricity fee collection for schools and other management departments, improve work efficiency, optimize operation, effectively save electricity, and provide data basis for users' reasonable management. It is a practical user-end electricity fee management system.
References:
Wen Tao. Application of Safe Electricity Management System in Student Dormitories [J]. Electronic Testing, 2013, 06(11): 64-65
Luo Hui, Qiao Lili, Zhong Donghua. Application of intelligent safe electricity consumption and energy-saving metering management system in energy management of universities [J]. Intelligent Building and Urban Information. 2012(5):68-71
Lai Xiaojun. Design and Implementation of Intelligent Power Management System for Logistics at Jinhua Polytechnic [D]. Chengdu: University of Electronic Science and Technology of China, 2010.
Hu Xinfeng, Zhou Lu, Sun Yiwen. A power management system for university student dormitories based on 51 microcontroller [J]. Electronic Production, 2013(11):36-38
Table 1. Malicious Load Identification Test Results
Table 2 Combinational Control Logic
