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The Gaussian noise distribution is typically used in dynamic state estimation (DSE) but it is not always true in practice because of abnormal system inputs, impulsive noise and measurement outliers. In this paper, a new robust DSE approach based on a new robust Lp norm based estimator and the cubature Kalman filter (CKF) is developed for power systems with non-Gaussian noise statistics. The Lp norm based estimator is derived from the Lp norm formula and the quadratic formula in order to alleviate the impacts from bad data and outliers. The proposed Lp-CKF DSE approach exhibits good accuracy because a new estimation error covariance is obtained by using the influence function. The robustness of the proposed Lp-CKF DSE approach is verified by performing simulations on a generator in the IEEE 39-bus system.

To sustain operation and maintenance of an active distribution network (ADN), a network fee should be charged by the distribution network service provider (DNSP) for facilitating the P2P energy trading service. To this end, this paper models the interaction among the DNSP and multiple prosumers as a Stackelberg game, and then develops a non-iterative and decentralized transactive mechanism to simultaneously achieve optimal network utilization pricing and peer-to-peer (P2P) trading. Simulation results in an ADN with four prosumers connected to a common substation bus validate the effectiveness and efficiency of the proposed scheme.

Transactive energy is an effective way to share and trade energy among peers. A transactive energy framework is composed of several integrated blocks such as an energy market, service providers, generation companies, transmission and distribution networks, prosumers, etc. The success of such a framework can be measured by analyzing the effectiveness of its major building blocks. This paper provides a basic definition of transactive energy which helps in identifying its primary building blocks. Based on the identified building blocks, each block of the transactive energy system is discussed briefly to highlight its significant role and effectiveness. Some enabling technologies for such systems are then reviewed along with pilot projects. In the end, some policy guidelines are presented to speed up their implementation.

The isolated dual active bridge (DAB)-based two-stage AC-DC-DC converters have been widely applied in grid-connected power electronics systems. However, the impedance interactions between the DAB converter and the AC-DC rectifier can cause instability problems to the two-stage converter systems. The accurate terminal impedance characteristics of the DAB converters are still not clear due to the high frequency ac conversion stage. This makes it difficult to assess the impacts of the DAB circuit parameters on the stability of the two-stage converters. To address these issues, the impedance models of the DAB converters are originally derived in this paper. Based on the developed impedance models, the stability of the DAB-based two-stage AC-DC-DC converters is analyzed. The impacts of the DAB converter circuit parameters on the stability of the two-stage AC-DC-DC converters are comprehensively revealed by the Bode and Nyquist plots. The analysis results offer instructive implications to finetune the design rules of the DAB converters. The conclusions are validated by comprehensive simulation and experimental results.

The impedance-based criterion has turned out to be a very effective tool for the stability analysis of the dual active bridge (DAB) converter with its input LC filter. While the input impedance of the DAB converter is highly dependent on the modulation methods, the influences of the modulation methods on the input impedances of the DAB converters are still not clear. To close this gap, three typical modulation methods of DAB converters, traditional single-phase-shift (SPS), dual-phase-shift (DPS) and the emerging cooperative triple-phase-shift (CTPS) modulation, are studied in this paper. First, the full-order input impedance models of the DAB converter with these modulation methods are derived for the first time. Second, based on the developed models, the impacts of these modulation schemes on the DAB input impedances are revealed. An interesting phenomenon is found that the open-loop impedances of SPS-DAB and DPS-DAB converters present the characteristics of the parallel-connected inductor and capacitor, while the open-loop impedance of CTPS-DAB converter presents the resistor characteristics. Third, the optimal modulation scheme for system stability is investigated. Finally, the theoretical analysis has been validated by the experimental results.

This paper investigates the ability of correcting the power factor at the point of common coupling (PCC) of the source side using dynamic voltage restorer (DVR). By applying the phase angle control (PAC) method, the DVR compensating voltage will be injected with a specific phase angle and magnitude in series with the transmission line, which leads to a power factor angle shift of the resultant load voltage. As a result, the source voltage is always in phase with the source current under different load conditions, which means that the power factor correction is achieved at the PCC of the source side. A laboratorial prototype of the DVR is utilized to verify the proposed control algorithm. The experimental results validate that an approximate unity power factor can be maintained at the source side.

The isolated two-stage ac-dc-dc converter containing an isolated dual-active-bridge (DAB) dc-dc converter and an ac-dc rectifier has been widely used for connecting the dc sources to the ac utility grid. However, the impedance interaction between the DAB converter and the ac-dc rectifier may cause the instability problem. To address this issue, this paper proposes two control methods to reshape the impedances of the isolated two-stage ac-dc-dc converter by building a virtual impedance connected in parallel or series with the input impedance of the DAB converter. The magnitude of the input impedance of the DAB converter is increased to satisfy the Middlebrook criterion without changing its negative resistance characteristics by the proposed control methods. Furthermore, the design requirements for the proposed controllers are also given to ensure the stable operation of the two-stage converter. The comparison of these two proposed methods is also discussed in terms of stabilizing ability, dynamic performance, and cost. The comprehensive experimental results are provided to validate the proposed methods.

This paper proposes a simplified four-level (S4L) inverter based dynamic voltage restorer (DVR). In the proposed configuration, the dual buck stage can output full, two thirds, and one third of dc link voltage. Including the zero voltage provided by the two-level inverter, the output of the proposed inverter can be four levels. With the same switching frequency, the S4L inverter based DVR achieves better performance than the existing two-level and three-level inverters based DVRs. Moreover, compared with the existing four-level inverter based DVRs, it requires less active switches/diodes and only requires a single DC power source. The experimental results are provided for the validation of the proposed system.

The dual active bridge (DAB) converter is gaining more and more attention in various applications such as energy storage systems, electric vehicles and smart grids. To improve the quality of the input current, a LC filter is often cascaded at the input side of the DAB converter. However, there are instable problems of this cascaded system due to the impedance interactions of the DAB converter and the LC filter, although the DAB converter is stable at the individual operation mode. To assess the stability of the cascaded system of the DAB converter and the LC filter, the impedance model of the DAB converter is firstly developed based on generalized state-space averaging method. The developed impedance model can be used to accurately predict the stability of the DAB converter with its LC input filter. Based on the stability analysis, the optimum filter parameter design guideline is determined. The impedance model and stability analysis are validated by the simulation and experimental results.