Xiaoling Xiong

Bifurcation Analysis of Standalone Photovoltaic-Battery Hybrid Power System

Standalone photovoltaic-battery hybrid power systems are attractive renewable power generation systems, a popular form of which is based on a photovoltaic system and a battery connected to an output dc bus via a buck converter and a bidirectional buck/boost converter, respectively. Due to variation of the available sunlight intensity, the battery voltage and load condition, the systems structures and operating modes are switched from time to time. The dynamic behavior is thus quite complex, and the design for stable operation of the system requires consideration of the stability conditions for all possible operating modes. This paper studies the dynamic behavior of this system and reveals the smooth and non-smooth bifurcation phenomena. Under certain conditions, when the system switches its operating mode, a non-smooth bifurcation, manifested as a jump from stable to unstable behavior, has been observed and verified with full-circuit simulations. Moreover, a detailed analysis based on averaged modes is performed to identify the two types of bifurcation and evaluate the stability boundaries of the system. The results provide useful insights and information about the behavior of the system and the interacting effects of control parameters on the design of the control loops.

Full Feedforward of the Output Voltage to Improve Efficiency for Envelope-Tracking Power Supply Using Switch-Linear Hybrid Configuration

A synchronous rectification buck converter in parallel with a Class AB linear amplifier is presented in this paper to construct an envelope-tracking (ET) power supply. To eliminate the influences of the output voltage on the linear amplifier output current, a full feedforward of the output-voltage scheme with two feedforward terms is proposed in this paper, which can counteract all the two load admittances of the linear amplifier, respectively, consequently decreasing the linear amplifier output current substantially. An ET power supply prototype with 100-kHz sine-wave tracking, 5-15 V output voltage, and 75-W-peak output power is fabricated and tested in the lab. The experimental results are well in agreement with the theoretical analyses, and the system efficiency is improved significantly.

Bifurcation Analysis and Experimental Study of a Multi-Operating-Mode Photovoltaic-Battery Hybrid Power System

Stand-alone hybrid renewable power generation systems have gained popularity in recent years. However, due to the intermittent nature of the renewable resources, hybrid renewable power generation systems are often designed to operate with multiple structures and multiple operating modes. The design for stable operation of such systems requires consideration of the stability conditions for all possible structures and operating modes. A stand-alone photovoltaic-battery hybrid power system is studied for illustrating the possible complex behavior in this paper. We reveal smooth bifurcation, including slow-scale Neimark-Sacker bifurcation, fast-scale period-doubling bifurcation as well as coexisting bifurcation. Under certain conditions, when the system switches its operating mode, a nonsmooth bifurcation, manifested as a jump between stable and unstable behavior, can also be observed. Moreover, a detailed analysis based on a discrete-time mapping model is performed to evaluate the stability boundaries of the system. Extensive experiments verify the analysis and simulated results.

SMOOTH AND NONSMOOTH BIFURCATIONS IN MULTI-STRUCTURE MULTI-OPERATING-MODE HYBRID POWER SYSTEMS

Hybrid renewable power generation systems have been developed rapidly in recent years. Due to the inherent fluctuation of availability of energy from renewable sources, systems that are designed to capture energy from such sources and deliver it in loads have to cope with the difficult challenges of maintaining stability under all possible operating conditions. As a result, the structures and operating modes of such hybrid systems are inherently time-varying. Due to their multiple structures and operating-modes, hybrid systems have rather complex dynamic behavior and the design for stable operation requires thorough consideration of the effects of variation in parameters on the operating modes and corresponding stability statuses. This paper presents a formal system description for such systems and a general procedure for analyzing the change of dynamical behavior under parameter variations (i.e. bifurcation) of this kind of systems. A hybrid power system consisting of dual-input buck converters is taken as an example for illustrating the possible complex behavior. We reveal smooth and nonsmooth bifurcation phenomena in this system. Under certain conditions, nonsmooth bifurcations have been observed and verified with full-circuit simulations. Moreover, a detailed analysis based on an averaged model is performed to identify two specific types of bifurcation and evaluate the stability boundaries of the system.

Feed-Forwarding the Output Voltage to Improve Efficiency for Envelope-Tracking Power Supply Based on a Switch-Linear Hybrid Scheme

Envelope-tracking (ET) technique is one of the most promising methods to improve the efficiency of the modern wireless communication transmitters, which is based on using a high-efficient power supply to provide varying voltage to the RF power amplifier. For this application, this letter adopts an AB-type linear amplifier and a synchronous rectification buck converter connected in parallel at the output to construct the ET power supply. The linear amplifier features of wide bandwidth and makes the output voltage follow the envelope of the transmitted signal; the buck converter features of high efficiency provides most of the load current. An average current control strategy with constant switching frequency is proposed, and it is further improved by feed-forwarding the output voltage to reduce the current of the linear amplifier, leading to higher efficiency. A prototype is built and shown to perform very well, achieving high efficiency and track bandwidth of about 100 kHz.

Bifurcation analysis in dual-input buck converter in hybrid power system

Multiple-input dc/dc converters are widely used in hybrid power systems which normally derive power simultaneously from several renewable energy sources and deliver power continuously to the load. Due to intermittent features of the available energy from the renewable sources, such multiple-input conversion systems are often designed with multiple structures and multiple operating modes, and their dynamic behavior is thus quite complex. We consider a hybrid power system with the dual-input buck converter as its constituent system. We study the dynamic behavior of this system and reveal the smooth and non-smooth bifurcation phenomena with low-frequency oscillation. Moreover, a detailed analysis based on an averaged model is performed to identify the two types of bifurcation and evaluate the stability boundaries of the system.

Bifurcation in standalone photovoltaic-battery hybrid power systems

Standalone photovoltaic-battery hybrid power systems are attractive renewable power generation systems, a particular form of which is based on a photovoltaic system and a battery connected to an output dc bus via a buck converter and a bidirectional buck-boost converter, respectively. To operate this system, a specific control strategy is required. In this paper we consider one such system and control strategy, and study the effects of variations of the load current and sunlight intensity on the stability of the system. A Neimark-Sacker bifurcation is identified in this system. Moreover, a detailed analysis based on discrete-time mapping is performed to evaluate the effect of variations in sunlight intensity and load current on the stability boundary of the system.

Smooth and Non-smooth Bifurcations in Multi-structure Multi-operating-mode Systems: Case Study of a Power Conversion System with Two Energy Sources

Renewable power generation systems are gaining popularity and have developed quickly in recent years. However, due to the intermittent features of the renewable energy sources, conversion systems involving more than one energy sources are usually designed with multiple structures and multiple operating modes. The dynamic behavior is thus quite complex, and the design for stable operation of such systems requires consideration of the stability conditions for all possible structures and operation modes. This paper describes such conversion systems, and uses a standalone photovoltaic-battery hybrid power system as an example for illustrating the possible complex behavior. We reveal smooth and non-smooth bifurcation phenomena in this system. Under certain conditions, when the system switches its operation mode, a non-smooth bifurcation has been observed and verified with full-circuit simulations. Moreover, a detailed analysis based on an averaged model is performed to identify the two types of bifurcation.