Xiaobo Dou

Optimal configuration of hybrid solar-wind distributed generation capacity in a grid-connected microgrid

Reasonably selecting the capacity of different types of DGs is the key element to guarantee that microgrid system can operate economically and reliably. Firstly a grid-connected hybrid wind/solar/storage micro-grid system is constructed and the output models of various distributed generations are built. On the basis of correction of wind speed and atmospheric density, the power of wind turbine is predicted by linear interpolation. The output of the photovoltaic generation system is calculated by using the Hay, Davies, Klucher and Reindl model(HDKR model). In order to determine the amount of energy that can be absorbed by or withdrawn from the battery bank each time step, this paper uses the Kinetic battery model. Then considering tax collection of greenhouse gas emission and reliability of the system, an optimal configuration design method is proposed, taking minimizing the whole life cycle cost of the system as the optimization objective. Finally, based on the weather conditions in Yantai city, a simulation analysis is performed, the optimal configuration scheme meeting the load is given. According to Chinese meteorological conditions, a sensitivity analysis of the wind speed and solar resource is given and optimal results are obtained on different conditions. The results are conducive to Chinese planning and design work of the micro-grid.

Design and realization of regional power quality monitoring system

Power quality monitoring is the necessary condition that makes power supply in good working order. This paper presents a kind of new system that can monitor regional power quality. The system adopts the standard of PQDIF as the power quality data norm, expert system to analyse the status of regional power quality and the communication way of GPRS to transmit data. First of all, through this system the power quality manager can check the power quality status of each monitoring station by network from time to time, so we can analyse in time and reflect overall power quality level. Secondly, through the monitoring track record and statistic of power quality accident, the power supply and consumers both can define respective power quality administration obligation, so this system can also provide evidence which effectively settles the dissension because of power quality. Also it can monitor actual power quality of customers and is useful to establish a green electric power system.

Discrete consensus-based distributed secondary control scheme with considering time-delays for DC microgrid

To ensure stable and optimal operation of DC microgrid, a three-level based hierarchical control strategy is proposed which consists of primary, secondary and tertiary controls. Usually, the primary control is performed locally without communication, the higher levels, however, can be either centralized or distributed. Considering the risks brought by centralized control, such as surviving central node or link failures, this paper proposes a distributed secondary control strategy for DC microgrid which is designed by Discrete Average Consensus Algorithm (DACA). In this paper, the controller embedded the distributed strategy will communicate with their neighbors through Low Bandwidth Communication to obtain average voltage of the whole system or power flow of grid-connected converter. Through the proposed novel strategy, the secondary control objectives such as reference power control, equal load sharing, voltage regulation will be realized in distributed means. Furthermore, the influence of communication delay to the strategy is studied at length, and the effectiveness and robustness of the proposed strategy are verified through detailed simulations.

A Concise Discrete Adaptive Filter for Frequency Estimation Under Distorted Three-Phase Voltage

To improve the control performance for grid-tied power converters, the fundamental frequency and harmonics of the grid voltage should be quickly and accurately estimated even under distorted voltage condition. This paper introduces a straightforward discrete adaptive filter to observe fundamental and harmonic sequence components of the grid voltage. The proposed filter possesses a simple and straightforward implementation. Based on the newly developed filter, frequency error transmission was analyzed when the frequency of the input voltage was unequal to the center frequency of the filter. Consequently, a frequency estimation loop was designed to adapt to the frequency variation for the filter. Compared to previous algorithms, the proposed algorithm has a better dynamic performance rating for frequency estimation, robust stability, and a simpler implementation. The effectiveness of the algorithm is verified by simulations and laboratory experiments.

Self-synchronized voltage control algorithm for microgrid inverter

The wide application of distributed generations (DGs) and microgrids (MGs) infuses new vitality into the voltage control of the inverter, which represents a traditional power electronic research area. In this paper, a self-synchronized resonance voltage control algorithm is proposed to satisfy the requirement of an inverters seamless switching from grid-connected (GC) mode to stand-alone (SA) mode, limiting switching over-voltage and improving switching dynamic performance. Meanwhile, a frequency closed-loop control method is proposed to get rid of the frequency static errors introduced by the self-synchronized feedback voltage control. The effectiveness of the proposed algorithm was confirmed by an experimental MG system.

Discrete time optimal design for voltage prefilter in grid synchronization system from control perspective

The grid synchronization system, which plays an important role in the control of grid-connected power converters, often needs to manipulate the grid voltage to extract the fundamental and harmonic sequence components. Generally a prefilter can achieve this function. In this paper, a systematic and general approach to design the multiple block based prefilter is introduced. First a complex variable discrete resonantor is adopted in the prefilter. Furthermore, the multiple coefficients of the prefilter are tuned by means of minimum energy method with variance constraint from control perspective. The proposed approach is described as an optimal solution in form of linear matrix inequality (LMI). Moreover, the approach is allowed to customize the settling time of the prefilter by designer. In addition, the prefilter yielded from the approach also performs good dynamic performance such as the fast settling time and smooth transient waveforms. The effectiveness and superiority of the proposed approach is verified by the numerical results.

An integrated nine-switch power conditioner parallel with transformer for power quality enhancement

In this paper, a configuration with a dual-port power converter bridging two sides of the transformer is proposed for power quality enhancement in distribution systems. The proposed configuration employs a nine-switch power converter instead of the traditional back-to-back power converter with 12 switches. The high voltage side port works as a double resonance injection hybrid active power filter to enhance the injection ability of harmonic currents, while the low voltage side port works as a traditional shunt active filter, thus the harmonic and reactive currents to the transformer can be reduced while the stability of DC-link voltage is enhanced. The simulation shows the validity of the proposed configuration.

A composite space vector hysteresis current controller based on duration allocation strategy

A composite space vector hysteresis current controller (CSVHCC) is proposed in this paper to control the three phase power converter. The duration of the modulation period is divided into two parts. One part for the carrier comparison controllers is to minimize errors at low frequency and provide a basic switching sequence. The other part for space vector hysteresis current controller (SVHCC) is to minimize errors at high frequency and its switching sequence is added to the basic switching sequence. Thus the proposed CSVHCC can make coordination between accuracy and dynamic response. The simulation and experiment shows the validity of the proposed CSVHCC.

Design of a Microgrid with Low-Voltage Ride-Through Capability and Simulation Experiment

A microgrid with low-voltage ride-through capability is designed. The designed microgrid avoids operating in unplanned islanded mode during an asymmetric ground fault which occurs in the low voltage distribution network and supports fault recovery for distribution network. Furthermore, compared with the traditional microgrid topology, the proposed microgrid topology also saves a lot of power electronic devices. The simulation results with PSCAD/EMTDC show that the microgrid can keep the distributed generations and loads operate normally when an asymmetric ground fault occurs in the low voltage distribution grid. It can also increase the active power output according to the requirement of the distribution network to support the distribution network fault recovery.