Reduction of Circulating Current Flow in Parallel Operation of APF Based on Hysteresis Current Control

Capacity enhancement and operation flexibility are two of the important limitations of the centralized Shunt Active Power Filter (APFsh) unit. This can be overcome by multiple and parallel APFsh units (in distributed mode) with a common DC link. In that case, a circulating current (CC) can flow. In the case of a hysteresis current controller based multiple APFsh units in load sharing mode, this CC control is not yet achieved. One of the difficulties of this CC flow control or reduction is the variable switching frequency of the APFsh units. In this paper, the model for CC flow is derived by the switching dynamics study of the APFsh units. Detailed simulation and real time study show that the reduction of CC flow can be achieved at an acceptable level by proper selection of design parameters

A New Placement and Integration Method of UPQC to Improve the Power Quality in DG Network

A new proposal for the placement and integration of UPQC in DG connected microgrid/micro generation (μG) system has been presented here. DG converters (with storage), the load and shunt part of the UPQC will be placed at or after the PCC. The series part of the UPQC will be placed before the PCC and in series with the grid. DC link can be connected to the storage system also. Hence, it is termed UPQCμG. The advantages of the proposed UPQCμG over the normal UPQC are to compensate voltage interruptions in addition to voltage sags / swells, harmonic and reactive power compensation in the interconnected mode. The DG Converter with storage will supply the active power only and the shunt part of the UPQC will compensate the reactive and harmonic power of the load in the islanding mode. Therefore, the system can work both in interconnected and islanded mode. DG Converter does not require to be disconnected during the voltage disturbance. In all conditions, DG Converter will only provide the active power to the load and grid. Thus it will reduce the control complexity of the DG converter as well as improve the PQ of the network

Reduction of Circulating Current Flow in Parallel Operation of APF Based on Hysteresis Current Control

Capacity enhancement and operation flexibility are two of the important limitations of the centralized Shunt Active Power Filter (APFsh) unit. This can be overcome by multiple and parallel APFsh units (in distributed mode) with a common DC link. In that case, a circulating current (CC) can flow. In the case of a hysteresis current controller based multiple APFsh units in load sharing mode, this CC control is not yet achieved. One of the difficulties of this CC flow control or reduction is the variable switching frequency of the APFsh units. In this paper, the model for CC flow is derived by the switching dynamics study of the APFsh units. Detailed simulation and real time study show that the reduction of CC flow can be achieved at an acceptable level by proper selection of design parameters

Impact of power sharing method on battery life extension in HESS for grid ancillary services

Hybrid energy storage system (HESS) based on Li-ion and supercapacitor (SC) can play a potential role to stabilise the grid by providing the fast frequency ancillary services. The SC helps to reduce the battery charge/discharge stress and hence assists to extend the battery lifespan. The power sharing method (PSM) is the heart in control part to improve the HESS performance and reduce the battery stress. This paper proposes a hybrid PSM and investigates its impact on battery life extension along with its relation to the system design and regulation signal. The performance of hybrid PSM is compared with three other PSMs (low pass filter, first and second rule based) in a 10 MW / 10 MWh full-active parallel HESS for frequency regulation service in two networks: UK (national grid) and USA (PJM). Considering maximum possible battery lifetime up to 25 years, result shows that the hybrid PSM approach allows a degree of better performance for both grid while the sharing of SC is kept maximum 2.0% and 2.5% (for US and UK grid respectively) of the HESS capacity. This study also analyses the impact of PSM on shared capacity and design of HESS for different grid regulation signals

A Study on the Power Quality of DG Integrated Building Energy System in Virtual Environment

In this paper, the electrical energy demand of a typical residential building has been extracted from a Virtual Environment (VE) simulation. The extracted energy demand is generated by input load demand and hourly operating information. Based on the electrical energy demand for a typical day, a building integrated photovoltaic (PV) system is then simulated in MATLAB to extract the current/voltage disturbance information into the network. Outcome of this simulation shows the voltage/current waveform along with the disturbances at different locations in the building. The city of Dublin, Ireland has been chosen as a geographical location and VE-Pro software has been used to develop the virtual environment simulation for the building energy system. The simulation based on VE-Pro and MATLAB indicates the scope for possible placement of Custom Power Devices (CPDs) to improve the power quality of the DG integrated building energy system

Development of community grid: review of technical issues and challenges

The concept of a community grid is presented here. It involves the distribution grid and an increased use of renewable energy coming from distributed resources along with the consumers/prosumers engagement in energy trading mechanism. The possible operation and management with energy trading flexibility are briefly outlined. Under such scenario, the classical operation of the distribution grid is challenged by the issues brought by the large penetration level of the new energy resources. This paper presents a status review of the technical issues that may appear under the community grid scenario. Building upon those surveyed issues, this work also reviews and discusses approaches to solutions, which are required in order to make the community grid highly renewable and sustainable

Reduction of circulating current flow in parallel operation of APF based on hysteresis current control

Capacity enhancement and operation flexibility are two of the important limitations of the centralized Shunt Active Power Filter (APFsh) unit. This can be overcome by multiple and parallel APFsh units (in distributed mode) with a common DC link. In that case, a circulating current (CC) can flow. In the case of a hysteresis current controller based multiple APFsh units in load sharing mode, this CC control is not yet achieved. One of the difficulties of this CC flow control or reduction is the variable switching frequency of the APFsh units. In this paper, the model for CC flow is derived by the switching dynamics study of the APFsh units. Detailed simulation and real time study show that the reduction of CC flow can be achieved at an acceptable level by proper selection of design parameters

Real-Time Control of Shunt Active Power Filter under Distorted Grid Voltage and Unbalanced Load Condition Using Self Tuning Filter

In this paper, an alternative control method is proposed to improve the harmonic suppression efficiency of the active power filter in a distorted and an unbalanced power system to compensate for the perturbations caused by the unbalanced non-linear loads. The proposed method uses a self-tuning filter (STF) to process the grid voltage in order to provide a uniform reference voltage to obtain the correct angular position of the phase locked loop. Moreover, the required compensation currents are obtained by implementing another STF in the transformed set of currents in order to separate the fundamental and the harmonic currents. This allows the calculation of a precise reference current for the unbalanced, the non-linear and the variable load conditions. The proposed control method gives an adequate compensating current reference even for a non-ideal voltage and unbalanced current conditions. The real-time control of the filter under the distorted and the unbalanced power system is developed in an RT-LAB real-time platform. The results obtained in the software-in-the-loop configuration are presented to verify the effectiveness of the proposed control technique

A study on the power quality of DG integrated building energy system in Virtual Environment

In this paper, the electrical energy demand of a typical residential building has been extracted from a Virtual Environment (VE) simulation. The extracted energy demand is generated by input load demand and hourly operating information. Based on the electrical energy demand for a typical day, a building integrated photovoltaic (PV) system is then simulated in MATLAB to extract the current/voltage disturbance information into the network. Outcome of this simulation shows the voltage/current waveform along with the disturbances at different locations in the building. The city of Dublin, Ireland has been chosen as a geographical location and VE-Pro software has been used to develop the virtual environment simulation for the building energy system. The simulation based on VE-Pro and MATLAB indicates the scope for possible placement of Custom Power Devices (CPDs) to improve the power quality of the DG integrated building energy system

Fast frequency response from energy storage systems - A review of grid standards, projects and technical issues

Electric power systems foresee challenges in stability due to the high penetration of power electronics interfaced renewable energy sources. The value of energy storage systems (ESS) to provide fast frequency response has been more and more recognized. Although the development of energy storage technologies has made ESSs technically feasible to be integrated in larger scale with required performance, the policies, grid codes and economic issues are still presenting barriers for wider application and investment. Recent years, a few regions and countries have designed new services to meet the upcoming grid challenges. A number of grid-scale ESS projects are also implemented aiming to trial performance, demonstrate values, and gain experience. This paper makes a review on the above mentioned aspects, including the emerging frequency regulation services, updated grid codes and grid-scale ESS projects. Some key technical issues are also discussed and prospects are outlined