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Single-stage grid-connected photovoltaic (PV) systems have advantages such as simple topology, high efficiency, etc. However, since all the control objectives such as the maximum power point tracking (MPPT), synchronization with the utility voltage, and harmonics reduction for output current need to be considered simultaneously, the complexity of the control scheme is much increased. This paper presents the implementation of a single-stage three-phase grid-connected PV system. In addition to realize the aforementioned control objectives, the proposed control can also remarkably improve the stability of the MPPT method with a modified incremental conductance MPPT method. The reactive power compensation for local load is also realized, so as to alleviate grid burden. A DSP is employed to implement the proposed MPPT controller and reactive power compensation unit. Simulation and experimental results show the high stability and high efficiency of this single-stage three-phase grid-connected PV system.

Extended Kalman filter (EKF) is a typical method for state-of-charge (SOC) estimation of lithium batteries. An equivalent circuit model for the lithium battery is established, and model parameters are identified by experimental methods. Based on the battery model and model parameters, an EKF is proposed for SOC estimation. Analysis is conducted on the effect of the model coefficients of EKF to the stability and rapidity of SOC estimation. By calculating the sensitivity of SOC to EMF under different SOC stages and according to the needs of various operating conditions, the EKF process noise and measurement noise are adaptively adjusted to regulate the proportion of the measurement update to estimation result. The regulation contributes to tracking the SOC and improving the smoothness of the estimation result. It is validated by experiments on lithium iron phosphate (LiFeP04) battery that the performance of the EKF on SOC estimation in different situations is optimized by the noise adaptive algorithm.

The cascade H-bridge topology is novel for the battery energy storage system (BESS). A multi-level battery management system (BMS), which contains three subsystems, is introduced. The functions and communication of each subsystem are discussed. An algorithm based on extended Kaiman filter is used for the state-of-charge (SOC) estimation in battery modules. The pack SOC is derived from those of the modules according to the current direction. To keep all cells in a balanced SOC value, a four-level balance control method is proposed. The balance for cells and modules depends on extra circuits, while that for packs and phases are accomplished by the H-bridge converters.

Inconsistency is common in lithium-ion battery packs and it results in voltage differences. Data from a battery pack with 200 cells connected in serial in a battery energy storage system (BESS) are applied for study. According to the causes of the voltage difference, three cell inconsistencies can be categorized as state-of-charge (SOC), internal resistance and capacity. The divergences among the cell voltage curves present different trends due to different causes. Based on an equivalent circuit model and the characteristics of lithium-ion batteries, a simulation has been performed for a further study of the cell inconsistencies. The simulation result is similar to that of the 200-cell battery pack. Experiment results on an 8-cell battery pack show that internal resistance difference is the main cause for voltage difference and a low charge current helps to make full use of the pack capacity. Meanwhile, SOC difference can be easily detected at low SOC stage.

This paper presents an accurate flux observer used in distributed multi-processor (DMP) adjustable speed drive systems. The stator flux linkage is estimated with a full-order observer, while the rotor speed is identified by using Lyapunov theorem. In order to improve the system performance in a wide speed range, the stator resistance is estimated simultaneously. In this paper, the structure of the DMP system, the principle of the full-order observer and the method for identifying the rotor speed and state resistance are all described in details. Relevant simulation results based on MATLAB/SIMULINK are given to prove the performance of the method. Experiments of a real system also verify the feasibility of this scheme

Single-stage grid-connected photovoltaic (PV) system has advantages such as simple topology, low cost, etc. However, since this kind of system has only one stage of power conversion, all the control objectives need to be considered simultaneously, such as maximum power point tracking (MPPT), synchronization with the utility voltage and harmonics reduction for output current, so that the complexity of control scheme is much increased. This paper presents a modified MPPT strategy, which can remarkably improve the stability of the single-stage grid-connected PV system during rapidly changing process of light intensity, besides realizing the control objectives above. Comparing it with traditional constant-step MPPT strategy, this paper illustrates the improvement of the novel strategy based on PSIM simulation platform. A 300 Wp grid-connected PV system is also established in laboratory to verify the stability of this modified MPPT strategy, in which DSP (TMS320F2407) is employed to implement the proposed MPPT controller. Simulation and experimental results show the high stability and high efficiency of this modified strategy applied in single-stage grid-connected PV system

Sinusoidal pulse width modulation (SPWM) and space vector pulse width modulation (SVPWM) are the most popular modulation strategies applied to variable frequency and adjusting speed systems, and there are diverges in comparing the merits and demerits of their own. Also there is another modulation strategy called one-cycle control. This paper gathers the three strategies and does some comparisons through simulation based on a simulation tool-PSIM, and has drawn some profitable conclusions.

This paper presents a high-efficiency stand-alone photovoltaic (PV) lighting system which can provide functional illumination based on high-pressure sodium (HPS) lamp. HPS lamp in the system works at very high efficiency with specially designed ballast and ignitor. In order to provide a steady-state operating environment for HPS lamp, a DC-DC converter and a DC-AC inverter are also implemented. A high frequency also remarkably reduces the size and the operating noise of the ballast. Maximum power point tracking (MPPT) technique is also implemented in this system. Experimental results will show the performances of the photovoltaic lighting system.

This paper describes the first successful power system device with multifunctional directional transversal difference protection in China. It realized some protection action performances which are difficult for conventional relay protection. Especially, eliminating both the voltage dead-zone and increasing action sensitivity and selectability are important improvements over conventional relay protection. By using the advantages of microcomputers, this device has created some new functions which are impossible for conventional protection, and has progressed toward the direction of multifunctionality and automation. It has been successfully in field operation in a 66 kV substation in Liaoning Province since May of 1992. >