Design of Uninterruptible AC Power Supply System for Motor Based on Computer and Various Application
Author: Kuang Lijuan; Shi Hongchang; Jin JianhangWith the development of science and technology and the wide application of computers, people put forward more and more strict requirements for the quality of power supply. Computers or other sensitive equipment require the power supply system to have continuous and reliable performance. In many important occasions, the power supply system is required to use multi-channel power supply or self-contained generator as standby power supply.At present, diesel (steam) oil alternator is a device that can provide AC for load in the environment of mains power failure or no mains power. At present, in the market, if you want to use generators to form an alternator uninterruptible power supply system, the first thing you want to think of is to buy an uninterruptible power supply, which tracks the phase of mains power under normal mains power conditions and charges the battery at the same time; When the mains power is regulated or abnormal, while the DC stored by the battery is converted into AC through the inverter to continue to supply power to the load, the AC digital generator is automatically started. When the generator is started successfully, the generator will supply power to the load to ensure the uninterrupted power supply.Although the above methods can form an AC generator uninterruptible power supply, the cost of the system increases greatly and causes a waste of resources. This is because the inverter already exists inside the digital alternator, so it is necessary to form the uninterruptible power supply of the alternator. There is no need to purchase the uninterruptible power supply separately. As long as the internal structure of the digital alternator is modified, the relevant functions can be completed. If the existing AC digital generator is transformed and its internal inverter is used to convert the DC stored in the battery into AC for load use in the case of mains power failure, the investment cost can be greatly saved, there is no need to purchase the power without interrupting the power supply, and avoid repeated investment and waste of resources.1 brief introduction to the structure of digital alternator in the current marketCompared with ordinary generators, the digital alternator is directly combined with the engine and eliminates the flywheel. Therefore, its size and weight are reduced by 50%. The digital generator set also automatically adjusts the speed according to the actual change of load, and can output a constant 50 Hz frequency within this range, which not only meets the demand for electrical equipment with stable frequency requirements, At the same time, it can effectively reduce the fuel consumption, which is 20% 40% lower than that of ordinary units, and the operation time is longer, which greatly prolongs the service life of the whole machine. It has the characteristics of small volume, light weight, high efficiency, constant voltage and frequency.Fig. 1 is a schematic diagram of the internal structure of digital generators on the market. When the AC power is off, start the generator module 1, control the size of the throttle 6 by controlling the stepping motor, and the control / drive module 5 controls the output voltage of the generator to make the output voltage of the rectifier module 2 meet the range of 380 V Â± 20 V, indicating that the generator is started successfully, and then the inverter module 3 performs inverter, Finally, the output provides 220 V Â± 2% AC voltage to the load through LC filter module 4. Even under normal conditions, the startup of the generator takes several seconds. Since there is no battery to supply power to the inverter, the power supply of the generator to the load is interrupted during the startup of the generator. Therefore, the digital generator on the market does not achieve the function of zero interruption of load power supply.2 uninterrupted AC power supply system transformed by digital alternatorThe design provides a scheme that can transform the AC digital generator into uninterruptible power supply. The existing digital alternator is transformed and redesigned. When the mains power is normal, the mains power supplies the load through the inverter and charges the battery at the same time; In case of mains power failure, start the generator while converting the DC power of the battery into AC power through the inverter for load use, so that the system can provide uninterrupted power supply to the load regardless of whether the mains power is normal or abnormal. At the same time, new functions such as voltage stabilization, frequency stabilization, output zero switching, battery charge and discharge management are designed, Realize the uninterrupted function of power supply to the load.2.1 basic working principle of the systemThe single chip microcomputer in the system detects the input voltage of the mains power. When the input voltage of the mains power is in the range of 220 V Â± 25%, it indicates that the mains power is normal, then the mains power is boosted through input EMI filtering and PFIC rectification, and finally converted into AC 220 v Â± 2% output sine wave voltage through inverter to supply power to the load. The stepping motor is connected with the input AC mains power through the full bridge rectifier through the optocoupler. When the optocoupler is in the "on" state, it indicates that the AC mains power is within the normal range. When the optocoupler is in the "off" state, it indicates that the AC mains power is abnormal. At the same time, the main controller detects the voltage of the battery. When the DC voltage provided by the battery is boosted by DC / DC, the voltage is 360 v, It means that the battery supplies power to the inverter and the system is in the DC input state. At the same time, the stepping motor controller sends a signal to start the generator. The stepping motor throttle controller controls the throttle of the generator. When it is detected that the output voltage of the generator is 380 V Â± 20 V, it indicates that the generator is started successfully, Then the system is switched to the AC generator to supply power to the load through the electronic transfer switch.2.2 overall design of the systemThe uninterruptible power supply of alternator includes CPU main control module, mains power input module, EMI filter module, PFC, DC boost module, battery charge and discharge management module, inverter module, output filter module, generator module, throttle control of stepping motor and control / drive module of its generator.Figure 2 is the circuit structure diagram of the reconstructed digital alternator uninterruptible power supply system.The uninterruptible power supply of alternator in Figure 2 is introduced in detail below. The system is composed of the following modules: CPU main module 7, mains power input module 1, EMI filter module 2, PFC power factor correction and DC boost module 3, output filter module 5, battery charge and discharge management module 6, inverter module 4, generator module 8, stepping motor, Throttle control 11 and its generator control and drive module 10. The main CPU module 7 is respectively connected with the battery charge and discharge module 6, the inverter module 4, the output filter module 5 and the PFC DC boost module 3.In Fig. 2, after EMI filtering, the input mains power is subjected to power factor correction and DC boost through PFC module 3. On the one hand, the PFC module charges the battery in the system through battery charging management module 6, on the other hand, the PFC module boosts the voltage to DC 360 V, inverts through inverter module 4, and finally outputs 220 V Â± 2% AC through LC filter module 5. When the input mains power is normal, the load is powered by the above process; When the mains power is abnormal, the system automatically starts the generator module 8. During the startup of the generator, the battery provides DC power to the inverter module, and continues to provide zero interrupted AC power to the load after passing through the inverter module. During the startup of the generator, the size of the throttle 11 is controlled by controlling the stepping motor, and the rectifier output voltage of the generator is controlled by the control drive module 10. When the voltage sent by the generator passes through the rectifier module 9 is greater than 360 V, it indicates that the generator is started successfully, and the generator provides AC power to the load to realize uninterrupted power supply to the load. After the main control module 7 detects that the mains power is normal, the generator power supply is switched to the mains power supply. When the power supply of the generator is switched to the commercial power supply, the phase detection and tracking shall be carried out, and the phase-shifting technology shall be adopted to ensure the phase synchronization at any time. In the whole process of power supply switching, that is, from mains power to battery, battery to generator and generator to mains power, the power supply of the system to the load is zero interruption.3 conclusionIn view of the interruption of load power supply during the starting process of the current digital generator, which can not reach the zero interruption capacity of load power supply, a scheme is proposed, which can be redesigned on the basis of the original digital alternator structure, change the original software and hardware structure of the digital generator, but retain the internal inverter to form the uninterrupted power supply system of the alternator, Realize the zero interruption function of load power supply. At the same time, the system also adds commercial power rectification, filtering, PFC, DC boost and battery charge and discharge management modules, which can not only provide uninterrupted AC to the load, but also stabilize the voltage and frequency of commercial power, and provide pure sinusoidal AC to the load. At the same time, the cost of the system has been greatly reduced, the volume and weight are smaller, and the battery pack can be easily maintained and replaced.