Operation of a single-phase grid connected inverter with large DC bus voltage ripple for distributed generation

Distributed generation (DG) looks promising for meeting the increasing energy demand with reduced environmental impact. Traditionally, the electric power plants are located far from load centers. DG units based on Photovoltaic (PV), wind, fuel cell etc. can be installed at the distribution level close to the loads, thus reducing investments in the utility's infrastructure. Distributed energy resources, DG plus storage, are connected to the grid by means of power electronic converters. Normally, a single-phase voltage source inverter (VSI) is used as a power interface for low power (< 10 kVA) consumer owned DG units. Its main function is to transfer active power to the grid, but it can also provide reactive power compensation adding value to the DG unit. The reliability of single-phase VSI is relatively low due to the large electrolytic capacitors required at the dc bus for attenuating the 2 nd order voltage ripple. This Thesis discusses a control scheme suitable for the VSI operating with large dc bus ripple, when a small and high reliability thin film capacitor can be used. It is based on a dc bus voltage ripple estimator and a voltage control loop with higher bandwidth. Different types of current controllers were tested for the inner loop but did not affect much the system's performance. An experimental set-up was implemented to show that a variable power factor inverter with a small dc capacitor can perform better than a conventional inverter regarding the transient response and the low frequency harmonic distortion in the ac side current

Control Strategies for Power Electronic Interfaces in Unbalanced Diesel Hybrid Mini-Grids with Renewable Sources and Storage

Traditionally, remote communities worldwide consist of autonomous power systems (mini-grids) supplied almost exclusively by diesel-engine generator sets (gensets) at relatively high costs. Integration of renewable energy sources (RESs), such as, photovoltaic (PV) and wind, can substantially reduce the cost of electricity generation and emissions in these remote communities. However, the highly variable load profile typical of mini-grids and the fluctuating characteristics of the RESs, cause frequent operation of the diesel genset at low loading condition, at low efficiency points and subject to carbon build up, which can significantly affect the maintenance costs and even the life time of the genset. Another important issue that is frequently overlooked in small (< 100 kVA) mini-grids, which usually present a low number of loads thus reducing the averaging effect, is load unbalance. Diesel gensets supplying unbalanced loads experience overheating in the synchronous generator and vibration in the shaft. For efficient operation, the genset should be operated near its full capacity and also in balanced mode. In order to address the above mentioned issues, a fast and reliable multi-mode battery energy storage system (BESS) employing voltage source inverter (VSI), is proposed in this thesis. In the genset support mode, as a basic feature, it can provide minimum loading for the genset and supplement it under peak load conditions. In addition, it can also provide load balancing and reactive power compensation for the mini-grid system. Therefore, the genset operates in balanced condition and within its ideal power range. In cases when the power demand from the genset is low, due to high supply of RESs and/or low load consumption, the genset can be shut-down and the BESS forms the grid, regulating voltage and frequency of the mini-grid system in the grid forming mode. Besides, the logic for defining the operating mode of the BESS and for achieving smooth transitions between modes are also presented in this thesis. The conventional approach for the control of three-phase VSI with unbalanced loads uses three-phase vector (dq) control and symmetrical components calculator which usually results in slow dynamic responses. Besides, the common power (P) vs. frequency (f) droop characteristic of the genset results in the mini-grid operating with variable frequency what further complicates the design of the controller for the VSI. Therefore, a new frequency adaptive per-phase dq-control scheme for three-wire and four-wire three-phase VSI based on the concept of fictive axis emulation is presented. It enables the control of current/voltage of each phase separately to achieve better dynamic performance in the variable frequency diesel hybrid mini-grid system. The effectiveness of the proposed techniques is demonstrated by means of simulation and experimental results

The smart grid international research facility network - SIRFN

SIRFN's vision is to accelerate progress and pave the way for the global deployment of renewable energy and smart grids, in conjunction with joint global activities of research facilities, application & standardization

Development of benchmark system for charging control Investigation

To address the emerging threat of climate change, consumers must transition to sustainable transportation. The electrification of the transport sector through e-mobility poses new challenges and uncertainties for grid operators. Without efficient prior measures, grid development problems will inevitably arise, causing a need for costly grid expansions. To ensure a technically and economically successful transition to electric vehicles, grid operators need modern, digital tools that enable the investigation of a variety of future scenarios. At present, these tools only exist in a simulation environment, where multiple assumptions are made to obtain feasible results. This poses a high risk, as operators must design and maintain distribution grids in advance and based on clear-cut scenarios

Advanced laboratory testing methods using real-time simulation and hardware-in-the-loop techniques : a survey of smart grid international research facility network activities

The integration of smart grid technologies in interconnected power system networks presents multiple challenges for the power industry and the scientific community. To address these challenges, researchers are creating new methods for the validation of: control, interoperability, reliability of Internet of Things systems, distributed energy resources, modern power equipment for applications covering power system stability, operation, control, and cybersecurity. Novel methods for laboratory testing of electrical power systems incorporate novel simulation techniques spanning real-time simulation, Power Hardware-in-the-Loop, Controller Hardware-in-the-Loop, Power System-in-the-Loop, and co-simulation technologies. These methods directly support the acceleration of electrical systems and power electronics component research by validating technological solutions in high-fidelity environments. In this paper, members of the Survey of Smart Grid International Research Facility Network task on Advanced Laboratory Testing Methods present a review of methods, test procedures, studies, and experiences employing advanced laboratory techniques for validation of range of research and development prototypes and novel power system solutions

Development and evaluation of open-source IEEE 1547.1 test scripts for improved solar integration

Distributed Energy Resources (DERs) equipped with standardized, interoperable, grid-support functionality have the capability to provide a range of services for power system operators. These requirements have been recently codified in the 2018 revision of the American DER interconnection and interoperability standard, IEEE Std. 1547, as well as the revised Canadian interconnection standard, CSA C22.3 No. 9. Currently, the IEEE standards committee is drafting a new revision of the IEEE Std. 1547.1 test standard, which outlines the test procedures for certifying equipment compliant to IEEE Std. 1547. In addition, it is often referenced as a test standard in CSA C22.3 No. 9. This draft test standard has not been fully exercised yet to identify mistakes, redundancies, and/or implementation challenges. In this work, an international community of research laboratories developed open-source IEEE Std. 1547.1 test scripts. The scripts are used to evaluate grid-support functions – such as constant-power-factor, volt-var, volt-watt, and frequency-watt functions – of several DER devices to the draft standard, EEE1547.1. Sample test results are presented and discussed, and recommendations are offered to improve the draft standard during the balloting process