Adam Milczarek

Reactive Power Management in Islanded Microgrid—Proportional Power Sharing in Hierarchical Droop Control

A microgrid (MG) is a local energy system consisting of a number of energy sources (e.g., wind turbine or solar panels among others), energy storage units, and loads that operate connected to the main electrical grid or autonomously. MGs provide flexibility, reduce the main electricity grid dependence, and contribute to changing large centralized production paradigm to local and distributed generation. However, such energy systems require complex management, advanced control, and optimization. Moreover, the power electronics converters have to be used to correct energy conversion and be interconnected through common control structure is necessary. Classical droop control system is often implemented in MG. It allows correct operation of parallel voltage source converters in grid connection, as well as islanded mode of operation. However, it requires complex power management algorithms, especially in islanded MGs, which balance the system and improves reliability. The novel reactive power sharing algorithm is developed, which takes into account the converters parameters as apparent power limit and maximum active power. The developed solution is verified in simulation and compared with other known reactive power control methods.

Optimized Energy-Conversion Systems for Small Wind Turbines: Renewable energy sources in modern distributed power generation systems

Renewable energy sources (RESs) play an increasingly important role in modern distributed power generation systems. Some RES technologies, e.g., photovoltaics and high power wind turbines (WTs), are already reaching a mature stage of development. However, there is another area that still needs further development and requires more attention: low-power small WT (SWT) systems. Many solutions with different features are being proposed with the aim of achieving the best efficiency while minimizing costs and improving performance. The goal of this article is to investigate the status of the SWT sector and its possible expansion. To evaluate future trends, it is essential to review and summarize current technology in the SWT sector, including the design and construction of wind rotors and generators, power electronics converter topologies, and their controls.

Grid integration issues of PMSG-based residential wind turbines

Residential generation of electricity from renewable sources has grown substantially owing to active governmental stimulation programs in many countries. Permanent magnet synchronous generators (PMSG) are a preferable solution for residential wind turbines (WTs) due to their high efficiency and reliability. In the design of grid integration equipment, PMSG-based WTs need special attention because of their variable-speed-variable-voltage nature. This paper reviews current trends in residential wind energy conversion systems based on the PMSG. Specific focus is on the design standards, PMSG-based WTs technology, typical power electronics building blocks, maximum power point tracking, and control systems for grid integration.

Implementation of Equal Reactive Power Sharing Algorithm in Droop-Controlled Islanded AC Microgrid

This paper presents the implementation of the hierarchical control algorithm with droop method and equal reactive power sharing algorithm (ERPS) for an islanded AC microgrid. In the typical applications of microgrid the reactive power flow remains uncontrolled, what may negatively impact the efficiency of the generation unit and cause various problems to power converters. The presented solution will provide an equal reactive power generation by each source, enhancing effectiveness of each generation unit and an overall microgrid reliability and performance. Streszczenie. Artykul omawia zagadnienia implementacji hierarchicznego systemu sterowania, zawierającego metode sterowania uchybem amplitudy i czestotliwości napiecia przeksztaltnika oraz algorytm rownomiernego podzialu mocy biernej w autonomicznej mikrosieci elektroenergetycznej AC. W klasycznej metodzie sterowania uchybem podzial mocy biernej zalezy od stosunku mocy czynnych poszczegolnych przeksztaltnikow. Nie ma mozliwości sterowania tym podzialem, co moze prowadzic do przeciązenia i wylączenia przeksztaltnika bądź cyrkulacji mocy biernej pomiedzy przeksztaltnikami. Przedstawione rozwiązanie zapewnia rowny podzial mocy biernej bez wzgledu na zmieniającą sie moc czynną, co eliminuje wspomniane problemy. (Implementacja algorytmu rownego podzialy mocy biernej ze sterowaniem uchybem napiecia w autonomicznej mikrosieci AC).

Proportional reactive power sharing algorithm in Islanded AC microgrid

A microgrid (MG) is a local energy system consisting a number of energy sources (e.g. wind turbine or solar panels), energy storage units and loads that operate connected to the main electrical grid or autonomously. MGs require complex management and advanced control. One of the most important parts in microgrid structure are power electronic converters (PEC). They provide correct energy conversion from every Renewable Energy Sources (RES) and common control structure for whole system. In islanded microgrid a Classical Droop Control is usually implemented, which allows for the correct operation of parallel voltage source converters (VSC). However, additional complex power management algorithm is required, which balances system and improves reliability. The novel reactive power sharing algorithm is described in this paper, which takes into account the converter parameters as apparent power limit and maximum active power. The developed solution is verified in experimental research and compared with other known reactive power control methods.

Control of simplified multilevel AC-DC-AC converter for small power generation systems

This paper describes control and modulation algorithm of a simplified multilevel AC-DC-AC converter for small power generation system which is based on well known Neutral Point Clamped (NPC) topology. Main advantage of this approach allows single 3-phase, 3-level converter to be utilized as a full interface between Permanent Magnet Synchronous Generator (PMSG) and the single-phase grid. Study of control and modulation for simplified converter are supported by simulation and experimental results. The three-phase AC-DC converter is controlled with regard of Field Oriented Control (FOC) principle. The current control of the single-phase DC-AC converter is based on the P+Multi-Resonant controller and Second Order Generalized Integrator Phase Locked Loop (SOGI-PLL). The multi resonant structure in single-phase converter allows a proper operation under non-ideal grid voltage.

Control algorithm of a DC/AC converter applied in a small wind turbine

Paper in detail presents control algorithm of a DC/AC converter applied in a small wind turbine (SWT), which has grid connected and a stand-alone operation mode. Common problems encountered SWTs transient between modes are described. Algorithm was implemented using a digital signal processor (DSP) control platform and tested using a lab setup with a 2.2 kW permanent magnet synchronous generator (PMSG). That type of generator is popular among SWTs. Results obtained from experimental verification are included.

Harmonic power sharing between power electronics converters in islanded AC microgrid

The dynamic evolution of renewable energy sources (RESs) with utilization of power electronics converters (PECs) caused the situation, where many energy generation units works parallel in local systems named microgrids (MGs). This distributed generation systems with many few kW micro-sources have to provide energy for linear and non-linear loads in grid connected mode of operation, but also in islanded mode of operation, which requires more advanced monitoring and energy management algorithms to ensure power balance and good voltage quality. The issues of power management in islanded AC microgrids are studied by many research centres and novel solutions are necessary to improve the reliability of MGs. In literature, there is still a gap for development of harmonic power sharing method in MG with most often used non-linear loads. Together with active and reactive power management algorithms the harmonic power sharing algorithm need to be implemented in control system to obtain complete solutions. The most often used approach in MG is hierarchical control structure, which includes the basic control loops at primary level, independent for each of PECs and outer control loops at secondary level, which allow to improve voltage amplitude and frequency in point of common coupling, as well as power sharing between PECs. Moreover, the hierarchical control structure is a great opportunity to implement a distributed control algorithm, which is able to execute many operations in the same time. Based on this idea, the novel proportional harmonic power sharing algorithm has been developed. It causes the harmonic power sharing between PECs proportionally to active powers, improving the output current waveforms of converters by decreasing the amplitude of selected current harmonics. The principles of hierarchical droop control and reactive power management has been presented in this paper. The developed solution has been implemented in simulation research together with proportional reactive power sharing algorithm. In order to present the advantage of harmonic power sharing, the results have been compared with non-controlled harmonic power.

Simulation and experimental research of reactive power management methods in islanded AC microgrid

The microgrids (MGs) integrates renewable energy sources (RESs), energy storages (ESs) and local loads to a one self-control energy system. In 2nd quarter of 2015 the global microgrids capacity reached the 12 GW. That result is a near triple more than in 2nd quarter of 2014 [1]. The MGs are capable to manage energy generation, storage and demand, making the user less dependent of the main grid, but more responsible for energy utilization and generation. It means the advanced control technics have to be applied in MGs. One of the important control issues in MG is related to reactive power sharing. The classical droop control does not provide the appropriate reactive power sharing, what may cause the reactive power circulation. This problem can be easily solved by equal reactive power sharing algorithm, however the limitation of active power resulted from keeping equal reactive power may occur and the converter will not be working with maximum available active powers. In order to provides better exploitation of RESs and to avoid reactive power circulation, the novel proportional reactive power sharing has been developed. The simulation and experimental verification have been performed and the results have been compared.

Supervisory Control for Real Time Reactive Power Flow Optimization in Islanded Microgrids

A microgrid (MG) is a local energy system consisting of a number of energy sources, energy storage units and loads that operate connected to the main electrical grid or autonomously. MGs include wind, solar or other renewable energy sources. MGs provide flexibility, reduce the main electricity grid dependence and contribute to change the large centralized production paradigm to local and distributed generation. However, such energy systems require complex management, advanced control and optimization. Interest on MGs hierarchical control has increased due to the availability of cheap online measurements. Similarly to any process system, MG hierarchical control is divided into three levels. However, an additional control algorithm is required to manage power transmission between sources and loads, maximizing efficiency and minimizing transmission losses. This real-time optimization problem is addressed to locally readjust converters operation to attain global efficiency. An algorithm is presented by formulating and solving the power sharing optimization problem in a two-level approach. The objective function is the sum of the apparent power transferred, whose minimization reduces total power losses and energy costs. The performance of the approach proposed is validated on a simulated case study. Different scenarios are tested and the performance of the algorithm is compared and discussed. The power losses reduction obtained with the proposed approach are compared with those obtained by standard procedures (Equal Power Sharing - EPS), showing enhanced performance.