Traditional low-voltage circuit breakers are protected by electromagnetic components, but the anti-interference ability of electromagnetic components is poor and the protection effect is poor, so it is easy to bury potential safety hazards.
Once the electromagnetic components are damaged, it is possible to cause erroneous actions, affecting the normal use of electricity.
Intelligent controller is based on the traditional low-voltage circuit breaker, using the current advanced digital measurement and control protection technology to improve the protection accuracy and anti-interference of low-voltage circuit breaker, and then enhance the safety, intelligence and automation of low-voltage circuit breaker, in order to ensure the normal power security. Low-voltage circuit breaker is one of the most important switchgear in low-voltage distribution system. It plays a key role in the normal operation and safe power supply of power supply system and distribution system. The controller of low-voltage circuit breaker cooperates with it to complete the control, protection and monitoring of the power system, so as to ensure that when the system fails, it can quickly cut off the fault part of the system or interrupt the power supply of the whole system, so as to ensure the safety of the power system. The control system of intelligent controller should have the following functions: protection function, timely measurement, monitoring and display function, fault information storage function, communication networking function and low voltage circuit breaker maintenance function. Therefore, the control system of intelligent controller can be realized in three aspects: (1) building station communication module through intelligent controller and PROFIBUS-DP; (2) building monitoring system of low-voltage circuit breaker based on MODBUS and PROFIBUS-DP bus; (3) establishing effective maintenance system of low-voltage circuit breaker [1]. This design can achieve the following points: (1) low-voltage circuit breaker can communicate with third-party PROFIBUS-DP slave station communication module or other third-party communication module by RS485 and RS232 interface; (2) when network communication fails or temporarily fails to be used, RS232 interface can be used to continue monitoring the power network; and in the system, it can be used to monitor the power network. In the process of debugging, the RS232 interface can also be used to debug and monitor the related intelligent control, which eliminates the work of the conversion interface, reduces the workload and the complexity of the conversion information, and improves the reliability of the system operation [2,3].
There are three main purposes to optimize the interface board of intelligent controller: one is to provide the required power supply voltage for various circuits; the other is to complete the acquisition of signals from current transformer and voltage sensor, and to make appropriate pre-conditioning; the third is to connect the driving power of fast-switching input and output such as forecasting alarm, disconnection, unloading, closing and closing. Road, so that it can become a complete system and normal operation [4]. The main power supply mode of general intelligent controller is DC auxiliary power supply and voltage rectifier power supply. These two power supply modes can be used separately or cooperate with each other.
When the protection circuit of the intelligent controller is interrupted by the protection of the upper circuit breaker, the intelligent controller can not continue to work.
At this time, it is necessary to complete the parameter setting and function experiment of circuit breaker by adding auxiliary power supply, and to prepare and maintain the communication between computer and circuit breaker at any time. Signal pre-conditioning circuit is another important part of intelligent controller. Signal pre-conditioning circuit is operated by low-pass filter and over-voltage processing.
Another function of signal pre-conditioning is to convert the output voltage signal of current transformer and voltage transformer into the voltage type that can be accepted and processed by the main board, namely – 10-10V voltage signal.
After signal pre-conditioning, the signal can be calculated even when the current is low, and when the current is high, the signal can also be calculated. In this way, the measurement accuracy of current range is greatly improved [5]. The driving circuit of switching input and output is the key to improve the reliability of intelligent controller. The input and output of all switching signals are accomplished by complex programmable logic device (CPLD). Its working order is that all the output signals of switching variables need to be sent to CPLD by MCU, then processed by CPLD, and sent out final signals such as tripping, closing and unloading, at the same time, photoelectric will isolate CPLD and output circuit, thereby enhancing the anti-interference ability of intelligent controller.
It should be noted that if manual switch-off is required, the CPLD switch-off should be twisted down to ensure the validity of the switch-off signal when manual switch-off is needed. When the switch-off signal is valid, it will be fed back to CPLD to prevent the damage of the shunt coil due to long-term power-on, and help it realize the function of automatic protection well. The main board of intelligent controller should be composed of microcontroller, power supply circuit, signal conditioning circuit, clock circuit, storage circuit, man-machine interface and communication interface circuit. The MCU template can be built by MCU or CPLD.
MCU has a good advantage in computer measurement and measurement, and its power consumption is very low. It can be used as MCU with excellent performance and has been widely used in China. The general intelligent controller will choose the model of MSP430F149 single-chip computer, which has good storage function, has six eight-bit bidirectional multi-function ports and pin multiplexing, so that each port can be set as a module mode [6]. Because of its inherent chip with automatic scanning function, the A/D converter can work independently without relying on the CPU, which greatly reduces the workload of the central processing and improves the efficiency of the system.
At the same time, the MCU has a hardware generator, which can complete four kinds of operations, greatly reducing the working time of multiplication instructions; and its two UART interfaces enable it to communicate with the computer without expansion.
Low-voltage circuit breaker is a kind of device which needs to deal with short circuit, over current, insulation supervisor, undervoltage and other faults of distribution system, so that it can cut off the fault circuit in time, and notify maintenance personnel to check the faults in time, so as to prevent further deterioration of the accident. This is a relatively complex processing process, which requires the intelligent controller to have enough reliability to make the correct response in time when the fault occurs; when there is no fault, thermostatic element there will be no wrong action. When the circuit breaker is applied inductively, the arcing of the switch contacts will produce strong electromagnetic signals, which will cause strong interference to the intelligent control system. If the intelligent control system is in this kind of electromagnetic signal for a long time, it will certainly affect the reliability of its work. When CPLD constructs the internal hardware, it takes the above situation into account.
By using the methods of closing, opening and tripping to output the execution signal, it can effectively solve the situation that electromagnetic interference can not work properly, and greatly improve the security and reliability of the intelligent controller. At the same time, CPLD can also prevent the phenomenon that the shunt coil is burned out. It provides the greatest security guarantee for the normal operation of intelligent controller. Nowadays, intelligent controller has become the central control part of intelligent circuit breaker in power supply line, which is of great significance to ensure the normal operation of low-voltage circuit breaker and improve the normal operation of distribution system. The optimization of intelligent controller should be carried out from two aspects, one is to optimize its internal control system, the other is to optimize its external control hardware. The optimization of internal control system should pay attention to the realization of protection function, timely measurement, monitoring and display function, fault information storage function, communication networking function and low-voltage circuit breaker maintenance function. The optimization of external hardware should focus on the optimization of interface board and mainboard. Enhancing the anti-interference ability of intelligent controller and improving the ability of fault diagnosis and treatment of controller system in time are all required to be realized by both internal system and external hardware.