Intelligent circuit breaker technology -Lithium - Ion Battery Equipment

Development and research of intelligent circuit breakers -Lithium - Ion Battery Equipment

Electrical switches (including circuit breakers, transfer switches and contactors) in the power supply network are usually used to close or disconnect the circuit that supplies electrical energy to achieve the purpose of power outage, power supply and conversion circuit.

When abnormal conditions occur in the power grid, such as overload, overvoltage, undervoltage, short circuit, etc., the load can be automatically disconnected from the power grid. Because these abnormal conditions will endanger the safety of operators and the normal operation of equipment, and even cause personal death or fire.

Distribution circuit breakers are mainly used for overload, short circuit, overvoltage and undervoltage protection in low-voltage distribution systems, and can also be used for infrequent operation of circuits. There are two types of circuit breakers for distribution: selective and non-selective. Non-selective protection features are relatively simple and are mostly used for branch circuit protection. The main circuit breaker is required to be of selective type to meet the selective disconnection of various protective appliances in the circuit and limit the accident area to the minimum range.(Lithium - Ion Battery Equipment)

The traditional circuit breaker protection function utilizes certain physical effects and is implemented through the action of the mechanical system. Therefore, the volume is larger and the effect is not ideal. In order to prevent the failure of electrical equipment from affecting the entire power supply line, and from damaging electrical equipment when abnormalities occur in the power supply network, circuit breakers that are more reliable and have more protective functions are gradually developed based on traditional circuit breakers.

For example, circuit breakers with functions such as short-circuit protection, overcurrent and overheating protection, leakage protection, and phase loss protection.

With the development of microelectronics technology, the emergence of integrated circuits has greatly reduced the size of ordinary electronic circuits, so multi-functional circuit breakers based on application-specific integrated circuits have emerged. This kind of circuit breaker is a big step forward than the original mechanical circuit breaker, but it still cannot be called intelligent.

The development of microcomputer technology provides conditions for the intelligentization of electrical switches. Intelligent electrical switches can not only provide various protection functions of ordinary circuit breakers, but also display various parameters in the circuit (current, voltage, power, power factor, etc.) in real time.

The action parameters of various protection functions can also be displayed, set and modified. The fault parameters when the protection circuit operates can be stored in the non-volatile memory for query. These functions can only be realized after using a microprocessor.

At present, foreign countries have developed a series of intelligent circuit breakers.

The performance of these intelligent circuit breakers is much better than traditional circuit breaker products. my country's product development in this area has just started. This article discusses the related technologies of intelligent electrical switches and gives an example of the design and development of an intelligent circuit breaker for low-voltage power grids.

2 Key Technologies of Intelligent Electrical Switches 2.1 Single-chip microcomputer and its application technology Single-chip microcomputer is widely used due to its compact structure and rich functions, and has become the core component of intelligent instrumentation. At present, when developing high-performance, high-precision, and multi-functional measurement and control instruments, microprocessors and microcontrollers are almost always considered. After using single-chip microcomputer technology in measurement and control instruments to make them smart instruments, it can solve many problems that traditional instruments cannot or are not easy to solve. It can also simplify the control instrument circuit, improve the reliability of the system, reduce the cost of the whole machine and accelerate new products. development speed. With the continuous improvement of integrated circuit manufacturing technology, the size of microcontrollers is getting smaller and smaller, and their functions are becoming more and more abundant. The new generation of microcontroller products has integrated program ROM, timer/counter, serial communication interface, A/D converter, PWM conversion output, waveform generator, WATCHDOG monitor, I2C bus interface, more I/O ports and Internal RAM registers are integrated to accommodate a wider range of uses. On the other hand, microcontrollers with simple functions are developing in the direction of low power consumption and miniaturization. A microcontroller using a serial bus has only 8 external pins. Listed in Table 1 are the performance parameters of some typical microcontroller products.

2.2 Application-specific integrated circuits Intelligent electrical switches often involve some special and complex functions. If these functions are completely completed by a computer, it will undoubtedly increase the burden on the CPU, and the effect may not be ideal. In fact, before the emergence of intelligent electrical switches, many effective ASICs have been developed, such as leakage protection ASICs. The use of application-specific integrated circuits can not only reduce the workload of the CPU, but also ensure reliable operation in the event of a CPU failure. It can also improve the response speed of the system to a certain extent.

2.3 Intelligent integrated sensors With the continuous improvement of power protection technology, the functions and technical requirements of various protection devices are also constantly improving. Generally speaking, low-voltage circuit breakers are required to have the following protection functions: ① Overvoltage and undervoltage protection function; ② Three-stage current protection function; ③ Leakage protection function; ④ Phase loss protection function; ⑤ Other abnormal protection functions (instantaneous spike pulse , instantaneous power outage, etc.).

To complete these protection functions, it is necessary to have various corresponding sensors. The performance of these sensors is directly related to the performance of intelligent electrical switches. On the other hand, the sensor must have higher accuracy, wider dynamic range and detection range, and at the same time be smaller in size, and the output signal must be easy to interface with the intelligent control circuit. This is still difficult to do at present. Influenced by microelectronics technology, sensors are developing in the direction of small, solid-state, multi-functional and integrated. If the latest technology can be used to develop an integrated sensor, that is, integrating various power sensors together, its performance will be greatly improved. Going a step further, the microprocessor and sensor can also be integrated into one. This can improve the overall performance of intelligent electrical switches to a higher level.

2.4 Power supply technology The circuit of an intelligent electrical switch can have three power supply methods: dedicated power supply, battery power supply and current transformer power supply. The latter is also called self-power supply. These three power supply methods can be used alone or in combination to form a redundant power supply system. The first two power supply methods are technically no different from general microcomputer application systems. Current transformer power supply is a unique power supply method for circuit breakers. When used alone, other power supply circuits can be omitted, and it can automatically start working when the power grid is connected. It is an ideal power supply method. However, the current transformer power supply has the following problems that need to be properly handled: ① Since the power energy comes from the current transformer, the power supply is insufficient when the current in the grid circuit is small. ② When the current of the grid circuit rises slowly, the voltage of the self-powered power supply also rises slowly. This won't be a problem for analog circuits, but for microprocessors and digital circuits, there should be a reliable reset circuit to get them up and running properly. ③Since the current transformer must not only serve as a current signal but also provide power energy, there will inevitably be a cross-influence between the two. That is, the operating current of the intelligent circuit will affect the detection results of the power grid circuit current. Therefore, there must be a method of compensation and correction.

Using redundant power supply from multiple power supply methods can increase the power supply reliability of the system. However, the redundant power supply method requires a switching device. Since the operating current of intelligent circuits is usually small, switching circuits are technically not difficult to implement. Switching control can be directly performed by a microprocessor in conjunction with a dedicated power detection circuit.

2.5 System Integration Technology Intelligent electrical switches are mechatronics products with microprocessors as the core. It includes the power supply part (conventional power supply, battery power supply, current transformer self-power supply), special sensor, control part, adjustment part, actuator and switch body. Each component is interrelated and affects each other. How to coordinate and handle the relationship between the various components so that it can meet all functional requirements without exceeding the scope allowed by existing technical conditions (volume, power consumption, reliability, electromagnetic compatibility, etc.) is the system The main content of integrated technology.

Intelligent electrical switches are a type of product with high technical content. Practice shows that the higher the technical content of a product, the greater the impact and role of system integration technology on it. Especially in production practice, due to the large area involved, problems with one component often affect the performance and quality of the entire machine. In modern industry, system integration technology embodies the overall level of basic industry.

It is worth mentioning that the currently rapidly developing CAD/CAM technology has an important impact on system integration technology. CAD/CAM technology has been widely used in machinery, electronics, electrical engineering, architecture, art, clothing and other fields. CAD technology has not only functioned as a drawing tool, but also can perform calculation, analysis, verification and simulation. These functions can not only improve design efficiency and reduce design errors, but also enable designers to see the realistic appearance of the product during the design stage and simulate the actual operation of the product. This enables participating designers to have an overall grasp of all aspects of the product.

3. Development of intelligent full-function low-voltage release. The CM1-Z intelligent trip controller is a full-function low-voltage distribution protection device developed by the author. It is used in distribution switch cabinets to match a variety of releases. use.

3.1 Main technical requirements and conditions of use. Three-phase four-wire circuit. Working voltage protection function. Three-stage current protection; over-voltage, under-voltage protection; leakage protection; phase loss protection.

Display function. Display of voltage, current, power and power factor; setting parameter display; test current display; 10 fault memory and parameter display; fault pre-alarm display; closing and opening status display.

The accuracy is 3% within the range of ~1.3 times the rated current. The power display is kW. The power factor display resolution is 0.01; the fault time display resolution is 0.001s. 3.2 Overall structure CM1-Z intelligent trip controller consists of switching power supply, 87C552 microcontroller and its peripheral circuits, signal sampling and filtering amplification circuit, automatic range switching circuit, phase-locked loop frequency tracking circuit, leakage protection circuit, display and operation panel, function selection switch, RS-485 serial communication interface and E2PROM memory composition. The system composition and structural block diagram are as listed.

Due to the use of the high-performance 87C552 microcontroller, the three-phase four-wire circuit parameters can be independently detected in real time, and the relevant circuit parameters (voltage, current, power and power factor, etc.) can be displayed according to the user's needs. The device has conventional three-stage current thermal analog protection functions, as well as overvoltage, undervoltage, leakage and phase loss protection functions. It can effectively and reliably protect electrical appliances such as distribution lines or motors.



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