In recent years, with the rapid development of the social economy, people’s quality of life has also been continuously improving. With the development of the tourism industry, more portable products that are close to life and improve life have been developed, such as handheld GPS, digital cameras, mobile phones, laptops, etc. Due to the continuous development of various functions in electronic devices, a large amount of energy consumption has also been generated. However, the battery capacity of these devices is not very large, which often leads to the dilemma of outdoor devices being unable to work properly due to insufficient power. Therefore, in order to improve the endurance of mobile devices for continuous outdoor operation, portable mobile power supplies that are convenient to carry and have good energy storage and power supply capabilities are gradually entering the public’s vision.
Portable mobile power supplies use lithium-ion batteries as their energy storage core, utilizing their excellent charging and discharging performance, as well as excellent environmental friendliness and service life, to perfectly apply their practical characteristics of secondary charging. Portable mobile power supplies, with their advantages of being green, pollution-free, safe, portable, easy to operate, diverse charging methods, noiseless, high-capacity, high-power, and equipped with various types of output interfaces, have almost solved the energy supply problem required by all commonly used electronic and electrical equipment. They are widely used in emergency electrical equipment and outdoor tourism, and other fields. With the continuous development and research of control technology, The performance of the system is increasingly close to people’s daily needs, therefore, the portable mobile power supply system studied in this article is of great significance.
1. Development status of portable mobile power supply systems
The concept of mobile power first appeared at the CES exhibition in 2001. A student used a control circuit to piece together several dry batteries to create an electronic product. Many manufacturers expressed interest in this and initially defined the core concept of mobile power. However, at that time, the cycle life of battery cells was not enough, and the volume of battery cells was too large, so an effective market was not formed. By 2004, with the improvement of battery management circuits and various chip research technologies, mobile power had gradually formed a basic structural framework. The magnificent debut of Apple’s iPhone in 2007 not only quickly captured the mobile phone market, but also made mobile power a complete independent product entering people’s daily lives due to its non replaceable battery. Since 2012, the concept of “mobile power supply” has gradually been accepted by the public, leading to an extremely considerable sales volume. Many mobile power supply manufacturers have started to not only research DC output, but also gradually configure corresponding mobile power supplies for AC load mobile devices. The concept of portable mobile power supply systems with sufficient energy storage, strong load capacity, and wide applications has emerged in people’s vision. In recent years, with the continuous development of microelectronics technology, the control technology of portable mobile power systems has also been constantly improving. The research on system charging and discharging control technology is related to whether the system performance can achieve a huge leap. At present, well-established companies in the portable mobile power market, such as Huabao Xinneng and Zhenghao Outdoor, are constantly improving their control technology and innovating their products. For example, Zhenghao Outdoor’s latest product, the Pro model of the DELTA series, can already drive appliances with a rated power of 7200W. By using hybrid fast charging technology, the charging time can be reduced to one seventh of the original, further meeting people’s daily needs.
1.1 Current Development Status of Wide Range Voltage Input Technology
For the system charging module, due to the portability of mobile devices, the charging methods need to meet diverse requirements. Generally, the charging of the system lithium battery pack is divided into three charging methods: mains, photovoltaic panel, and vehicle charging. Due to the different input voltages of the charging module in the three methods, it is necessary to meet a wide range of input voltage requirements when designing the charging module control strategy. Common up and down topologies include Sepic, Zeta, Cuk, and Buck Boost converters. It is proposed to use V2 control technology in a fourth-order Cuk converter to improve the slow transient response speed of current controlled Cuk converters and further enhance the transient performance of the system. The experimental results show that the improved output transfer function of the system has a wider bandwidth and lower low-frequency gain output impedance, achieving good transient characteristics. In reference [11], a scalable voltage gain unit circuit was proposed for the basic Sepic converter. By adjusting the number of voltage gain units, the converter achieved wide range and high gain ratio adjustment. The experimental results showed that the improved system converter has advantages such as wide input voltage range, small input current ripple, and easy topology expansion. Cascaded Buck Boost and Cuk topologies have opposite input-output polarities, while Zeta and Sepic topologies have more passive components and are not conducive to achieving high power density. Therefore, the market often focuses on the improved Buck Boost topology as the main research object. Compared to the aforementioned topology, the advantage of a dual transistor Buck Boost converter is that it achieves the same input and output polarity and also has the function of raising and lowering voltage. The traditional dual switch Buck Boost adopts the Buck Boost control mode, which simultaneously controls two switch tubes for state switching to achieve the up and down states. The control method is simple, but due to the fact that both switch tubes are changing their states during operation, the switch loss is greater compared to single mode, and the control efficiency is lower. In reference [12], a three mode control mode of dual transistor Buck Boost is proposed for the traditional dual transistor Buck Boost control mode. The original single Buck Boost mode is divided into Buck mode and Boost mode, and the transition mode is added to prevent large output ripple, reduce the switching loss of the system, and improve the conversion efficiency.
1.2 Development status of inverter control technology
For the discharge module of the system, it is required that the AC power output be the same pure sine wave voltage as the mains power of the State Grid, ensuring compatibility with multiple devices without causing damage. The focus should be on considering its stability during operation and designing a reasonable inverter control technology strategy. With the continuous maturity of control technology, inverter power supplies often use a combination of analog and digital control systems to achieve control objectives. However, there are still shortcomings such as complex control circuits and low flexibility. Therefore, digitizing inverter power supply control technology is the mainstream trend of today’s development. It can not only achieve complex control strategies, but also optimize device structure, reduce volume, and improve reliability. Below, by consulting relevant references, we will introduce the commonly used digital control methods for inverter power supplies one by one.
PID control is often applied in the field of automatic control due to its simple algorithm, good robustness, and high reliability. However, when tracking sine commands, PID control often uses outer loop mean feedback to ensure steady-state accuracy. By adopting dual closed-loop control technology, a current inner loop is added to the commonly used voltage loop in inverter power supplies, which enhances system stability and improves load disturbance. However, analog circuits are also needed to achieve the fast tracking required by the current inner loop. The advantage of hysteresis control lies in the strong anti-interference ability and fast dynamic response of the system, but its disadvantage lies in the irregular operation mode and unfixed switching frequency, which increases the difficulty of the design process. Although various schemes such as constant frequency hysteresis control and adaptive hysteresis control have been designed to address the shortcomings, the complex circuit design and high-frequency switching requirements have resulted in less practical application.
Perform deadbeat digital control on the inverter power supply, and calculate the pulse width for the next sampling period based on the system’s state equation and the feedback of the output signal. The transient response speed is very fast, but the robustness of the system is poor. When subjected to interference fluctuations, it is easy to cause system instability and high hardware requirements. The advantage of state feedback control is that it allows for arbitrary pole configuration of the closed-loop system, greatly improving the dynamic quality of the system. Introduced the addition of state feedback control in the dual closed-loop control strategy of inverter power supply, which utilizes two feedback variables to change the dynamic characteristics of the object in the state space concept by selecting a reasonable feedback gain matrix, thereby improving the control effect. For dual frequency grid connected inverters, single cycle control technology is used for improvement. The improved inverter has good dynamic performance, but the total harmonic distortion rate is slightly higher. With the continuous innovation of technology, the intelligent control theory combining control theory and artificial intelligence has emerged. Fuzzy control is an important branch of intelligent control, which optimizes complex nonlinear control systems by simulating the reasoning process of human thinking. It plays a prominent role in dealing with complex systems with high uncertainty. The repetitive fuzzy control scheme is used to adjust the output voltage of the system cycle by cycle, enhancing the stability of the output voltage.
For photovoltaic grid inverter power generation, fuzzy control is added to sliding mode control to reduce the chattering of sliding mode control. The control system has strong robustness and good dynamic response, but requires a very high sampling frequency to have good control effects. Therefore, further research is needed to be applied in practical products. The control schemes mentioned in the above literature indicate that each control technology has its own advantages and disadvantages. Therefore, the integration, penetration, and complementarity of different control methods are a major research focus for improving control strategies today. If fuzzy control technology is incorporated into traditional control strategies, it can not only improve the dynamic performance of the system, but also enhance its steady-state performance, achieve complementary advantages, and enable the system to achieve good steady-state and dynamic characteristics simultaneously.
2. Summary
Through the background and significance of the research project, the importance of portable mobile power supply systems was explained. In response to the practical needs of outdoor sports or emergency work and the secondary charging characteristics of lithium batteries, FSBB transformation, push-pull boost, SPWM modulation, fuzzy control and other technologies were used to study the charging and discharging control processes of lithium batteries. Designed a portable mobile power supply system that can adapt to a wide range of voltage charging methods, with good power frequency voltage output and a simple and clear power management interface. The specific structure of the paper is as follows.
1) This article introduces the research background of portable mobile power supplies and the current development status of system control technology, and elaborates on the research significance and focus of this topic.
2) System scheme design: Firstly, conduct a requirement analysis of the entire system, elaborating on the key research areas of each module, including power management module, charging module, and discharging module. Secondly, based on the research focus of each module, build a brief functional description of each module’s research block diagram.
3) Research on Control Strategies for Portable Mobile Power Supply Systems: Corresponding control strategies have been proposed for the control technologies of charging and discharging modules in the system. In the charging module part, a single carrier three mode control strategy is proposed to smooth the transition of mode conversion, improve the stability of the system and realize the demand of wide range voltage input; The AC discharge module utilizes a dual closed-loop control strategy with a fuzzy PID controller to sample feedback signals and achieve stable AC output voltage.
4) System hardware design: Introduced the key hardware circuit design among the three major modules of the system, including the main circuit design and sampling circuit design of each module. After designing the hardware of each module separately, connect them through PCB hardware wiring to form the entire system.
5) System software design: Introduce the software program design of the key parts of the three major modules of the system, including the main circuit program of each module, AD sampling subroutine, display screen driver subroutine, FSBB working mode subroutine, and voltage fuzzy PID composite control subroutine. On the basis of the hardware wiring connection in the previous chapter, the combination communication of various modules of the system will be carried out from the software program.
6) System experiment and testing: On the basis of completing hardware circuit design and software program design, build the corresponding experimental platform. By testing the performance indicators of each module, the feasibility and accuracy of the control strategy in this article are verified, and the overall system equipment is assembled to test the performance of the entire machine.