Ruwan P.S. Chandrasena

Control, operation and power sharing among parallel converter-interfaced DERs in a microgrid in the presence of unbalanced and harmonic loads

This paper demonstrates power management and control of DERs in an autonomous MG. The paper focuses on the control and performance of converter-interfaced DERs in voltage controlled mode. Several case studies are considered for a MG based on the different types of loads supplied by the MG (i.e. balanced three-phase, unbalanced, single-phase and harmonic loads). DERs are controlled by adjusting the voltage magnitude and angle in their converter output through droop control, in a decentralized concept. Based on this control method, DERs can successfully share the total demand of the MG in the presence of any type of loads. This includes proper total power sharing, unbalanced power sharing as well as harmonic power sharing, depending on the load types. The efficacy of the proposed power control, sharing and management among DERs in a microgrid is validated through extensive simulation studies using PSCAD/EMTDC.

Secondary Control in Microgrids for Dynamic Power Sharing and Voltage/Frequency Adjustment

This paper discusses the operation of the central controller for a microgrid. The central controller is responsible to maintain the voltage and frequency of the microgrid within the acceptable ranges while the distributed energy resources supply the required power demand of the loads based on the droop control. The desired ratio among the output active power of the distributed energy resources is determined by the distribution network tertiary controller. To achieve a dynamic variation for the output active power ratios among the distributed energy resources, the central controller has to adjust the references of the rated active power and the droop control coefficients. As this may lead to unacceptable voltage and frequency in the microgr-id, the central controller has to adjust the references of the voltage and frequency consequently. The proposed central controller strategy for the microgrid is validated through PSCAD/EMTDC simulations.

Autonomous operation of multiple interconnected microgrids with self-healing capability

This paper shows how multiple interconnected microgrids can operate in autonomous mode in a self-healing medium voltage network. This is possible if based on network self-healing capability, the neighbour microgrids are interconnected and a surplus generation capacity is available in some of the Distributed Energy Resources (DERs) of the interconnected microgrids. This will reduce or prevent load shedding within the microgrids with less generation capacity. Therefore, DERs in a microgrid are controlled such that they share the local load within that microgrid as well as the loads in other interconnected microgrids. Different control algorithms are proposed to manage the DERs at different operating conditions. On the other hand, a Distribution Static Compensator (DSTATCOM) is employed to regulate the voltage. The efficacy of the proposed power control, sharing and management among DERs in multiple interconnected microgrids is validated through extensive simulation studies using PSCAD/EMTDC.

Grid side converter controller of DFIG for wind power generation

With the advancement of technology, electricity generation using wind has drawn an increased attention in the world. As the amount of wind power integrated into the system is increased, it causes power quality and stability problems. Therefore power utilities are developing stringent grid codes which are to be satisfied by the wind power producers. Voltage control capability, reactive range capability, frequency control ability and fault ride through capability are among the major requirements stipulated in the grid codes. Due to the variable speed operation capability of Doubly Fed Induction Generators (DFIGs), they are becoming popular in wind power generation. The voltage control of the DFIG wind farm has been identified as the latest challenge with the present grid code requirements. This paper presents the design methodology of a stator side controller of the DFIG, which produces the terminal voltage control in addition to the DC link voltage regulation. The developed controller is simulated using PSCAD/EMTDC software to verify the performance of the controller. Further, a 60 MW typical wind farm is modeled in both PSCAD/EMTDC and IPSA+ and applicability of the above controller is justified.

Operation and Control of a Hybrid AC-DC Nanogrid for Future Community Houses

A hybrid AC-DC nanogrid (NG) can be considered as the power supply system for future community houses. In this paper, the operation and control of a NG are presented. The NG consists of an AC bus and a DC bus, interconnected through a tie-converter. Each bus may have several loads and micro sources. The NG should have an adequate generation capacity to supply its loads in off-grid mode as well as the capability of exchanging power with the utility grid. The tie-converter exchanges the power between two buses and regulates bus voltage in both buses in the case of off-grid operation. Several case studies are presented using PSCAD/EMTDC to verify the NG dynamics.

Data communication network and its delay effect on the dynamic operation of distributed generation units in a microgrid

A three-level hierarchical control system is considered for microgrids. The microgrid central controller receives the desired ratio for the output power of the available distributed generation units (DG) from the network tertiary controller. It then passes this information to the primary controller of each DG in the form of setpoints. In addition, the central controller receives some information from the DGs or the network and considers them to adjust the setpoints for the DGs. In this paper, the effect of the data transfer delays in the communication system of future microgrids is investigated on the dynamic operation of the distributed energy resources.

Different power sharing techniques for converter-interfaced DERs in an autonomous microgrid

This paper discusses three different techniques which can be used for power sharing control and adjustment among parallel converter-interfaced distributed energy resources in an autonomous microgrid. This ratio is decided by the distribution network tertiary controller and passed by the microgrid central controller to the primary controllers of each energy resource. In this paper limitations of the first two methods are discussed in detail and the proposed (third) method is designed such that it overcomes the limitations of the other two methods. The studies and discussions are validated for an autonomous microgrid under consideration through PSCAD/EMTDC-based simulations studies.

Application notes and recommendations on using TMS320F28335 digital Signal Processor to control voltage source converters

This paper presents general recommendations on utilizing TMS320F28335 Digital Signal Controller (DSC) as the controller for Voltage Source Converters (VSC). First, a comparison is provided on different DSCs that can be used for such applications and the reasons for selecting this specific Texas Instrument device are discussed. Later, the strategy for realtime algorithm developed in the DSC, also referred to as digital Signal Processor (DSP) is explained and its main features that are used for VSC control are described. Some new functions are developed and their characteristics and specifications are summarized. The paper also presents a discussion on the most probable difficulties when programming the DSC/DSP for VSC control applications followed by some improvement methods proposed for tackling these difficulties.

Constraints for the development of wind power generation in Sri Lanka

The demand for the electricity of the country is increasing dramatically. Therefore, it requires more and more generating facilities connected to the national grid. Since, all most all the economically feasible hydro potentials are captured, the utilities are more concerned on other source of electricity generation. The fossil fuel based electricity generation does not provide a sustainable solution, since the worlds fossil fuel resources are depleting at a rapid pace. Another major problem with conventional fossil fuel based electricity generation is the emission of both air pollutants and green house gases. Therefore, in the recent past renewable energy based electricity generation has drawn an increased attention in worldwide. Among the renewable energy sources available in Sri Lanka, wind power has been identified as the most promising option for grid connected electricity generation. However, wind power development in Sri Lanka is not at a satisfactory level and it has some technical, logistical as well as policy constraints. This paper discusses about those constraints in detail and present a result of a case study carried out to investigate one such technical constraint

Developing the Guidelines for Fabrication of Laboratory Prototype Voltage Source Converters

This paper presents the general guidelines on developing a laboratory prototype Voltage Source Converter (VSC). One of the main possible reasons behind the limited hardware verification by postgraduate students, carrying out research in the area of power electronics and especially the VSCs, is the lack of knowledge and unavailability of proper tutorials and guidelines for developing hardware prototypes. In this paper, majority of the auxiliary circuits and modules which are required for building up a prototype VSC are introduced. Proper examples are provided at each stage to improve the effectiveness of the developed guideline. The main difficulties of the hardware experiments are mentioned and possible solutions and recommendations are presented throughout the paper. It is believed that this paper will highly benefit the postgraduate students at the early stages of their hardware experiments.