Grid Standards Research Articles

Control and Real-Time Validation for Convertible Static Transmission Controller Enabled Dual Active Power Filters and PV Integration

This paper proposes a versatile convertible static transmission controller, in shunt-shunt mode, with dual active filters and photovoltaic (PV) power integration. The combined system aims to back up and control the power of a transmission transformer, as well as, improve the transmitted power quality to meet the grid standards and codes, especially the recently revised IEEE 1547 standards. The filters are also designed to eliminate the current and voltage harmonics due to the fluctuation in the injected PV power and the use of the switching power converters. A new reference generation technique is proposed to inject the solar power into the grid and compensate the system reactive power and harmonics. Moreover, the varying nature of PV power, due to the intermittent solar radiation and temperature, is accounted with the online computation of the dc voltage and power references with the help of the system rectifier. A simulation study adopted by real-time digital simulator is used to validate the proposed system for the integration of an actual solar PV under normal and faulted conditions.

Economic assessment of membrane-based power-to-gas processes for the European biogas market

Four different power-to-gas process chains implementing catalytic methanation and membrane upgrading are presented. Their economics for synthetic natural gas production and hydrogen storage are assessed for the first time in the context of multiple different European gas grid standards by simulation. Influence of two different fermentation setups for biogas production as well as pressure levels from 6 to 15 bar and catalyst specific flow rates from 100 to 150 Nl/(h gCAT) were considered. Based on this simulation an economic analysis was done. Capital expenditures and operational expenditures for electrolysis, methanation, membrane gas upgrading, and compressors of each chain are presented.It is shown that the integration of a simple recycle of the off-gas stream can reduce the costs from up to 2.93 €/Nm³ produced synthetic natural gas to at least 1.63 €/Nm³. Hydrogen storage cost can be decreased from up to 1.81 €/Nm³ stored hydrogen to at least 0.95 €/Nm³. Variation of the fermentation setup only leads to savings in the range of 0.03–0.08 €/Nm³ synthetic natural gas if off-gas recycling is included. Catalyst specific gas flow rate is shown to be of neglectable influence, contributing less than 0.01 €/Nm³ produced synthetic natural gas or stored hydrogen. Pressure influence is more pronounced at up to 0.10 €/Nm³ produced synthetic natural gas and up to 0.05 €/Nm³ stored hydrogen. Optimal operation pressure for simple off-gas recycling is shown to be below 10 bar.

Roles of IEC in supporting effective Smart City standards

The International Electrotechnical Commission is using its systems approach, honed in the development of international smart grid standards, to identify the requirements of cities and smart city solution providers for tried and tested solutions to common challenges and is working with the wider international standards development community to develop the coherent and interoperable packages of standards needed. This study discusses such developments and provides insights into the current state-of-the-art.

Critical Review of PV Grid-Tied Inverters

Solar Photovoltaic (PV) systems have been in use predominantly since the last decade. Inverter fed PV grid topologies are being used prominently to meet power requirements and to insert renewable forms of energy into power grids. At present, coping with growing electricity demands is a major challenge. This paper presents a detailed review of topological advancements in PV-Grid Tied Inverters along with the advantages, disadvantages and main features of each. The different types of inverters used in the literature in this context are presented. Reactive power is one of the ancillary services provided by PV. It is recommended that reactive power from the inverter to grid be injected for reactive power compensation in localized networks. This practice is being implemented in many countries, and researchers have been trying to find an optimal way of injecting reactive power into grids considering grid codes and requirements. Keeping in mind the importance of grid codes and standards, a review of grid integration, the popular configurations available in literature, Synchronization methods and standards is presented, citing the key features of each kind. For successful integration with a grid, coordination between the support devices used for reactive power compensation and their optimal reactive power capacity is important for stability in grid power. Hence, the most important and recommended intelligent algorithms for the optimization and proper coordination are peer reviewed and presented. Thus, an overview of Solar PV energy-fed inverters connected to the grid is presented in this paper, which can serve as a guide for researchers and policymakers.

Single-Phase Two-Stage Seven-Level Power Conditioner for Photovoltaic Power Generation System

This paper presents a new power conditioner with the inherent benefits of boosting, generation of seven-level output voltage with minimum leakage current in a grid-connected photovoltaic (PV) power generation system. The proposed power conditioner is an upgrade of a front-end multioutput dc–dc boost converter and an asymmetrical seven-level inverter. A high-frequency transformer (HFT) employed in front-end converter produces balanced dc-link voltages to generate the seven-level output voltage. The leakage current caused by the parasitic capacitance of the PV panel is minimized by providing a common-mode conducting path to the inverter. This results in a reduction of the leakage current well below the VDE0126-1-1 grid standards. Furthermore, the proposed configuration utilizes a minimum number of devices for every level generation, which reduces the control complexity and also improves the system efficiency. The dynamic performance of the system is tested for intermittent changes in the PV characteristics for grid-connected operation. The proposed power conditioner is simulated using MATLAB software, and a laboratory prototype of 750 W is developed to validate its feasibility. Finally, a comparison is made with other recently proposed seven-level inverters to highlight the benefits of this power conditioner over others.

Inductance-Independent Nonlinearity Compensation for Single-Phase Grid-Tied Inverter Operating in Both Continuous and Discontinuous Current Mode

This paper proposes a control for a single-phase grid-tied inverter operating in both continuous current mode (CCM) and discontinuous current mode (DCM) to minimize inductors without worsening a current total harmonic distortion (THD). In a conventional CCM/DCM control, an inductance is required in a DCM nonlinearity compensation; consequently, the control becomes inductance-dependent. In the proposed control, a duty ratio at a previous calculation period is utilized to compensate for the DCM nonlinearity and detect current modes independently from the inductance. A 4-kW 100-kHz prototype of the inverter with two designs of the inductor is realized to confirm the effectiveness of the proposed control. When the inductor impedance, which is normalized by an inverter impedance, is reduced from 1.8% to 0.5%, volume and material cost of the inductor are reduced by 51% and 62%, respectively, whereas the loss at a light load of 0.1 p.u. is reduced by 35%. However, due to this inductor minimization, the current THD at a rated load increases from 2.3% to 8.7% with the conventional control, violating the grid current harmonic constraint regulated by standard IEEE-1547. The proposed CCM/DCM control reduces the current THD from 8.7% to 2.1%, enabling the inductor minimization and satisfies the grid standard.

Comprehensive Review and Comparison of Single-Phase Grid-Tied Photovoltaic Microinverters

The power processing and the presence of the electrical isolation between the PV module and the grid is a very crucial aspect in determining the performance requirement, as well as the utility operator’s specifications for the PV microinverter design. The grid-connected PV microinverter design can be classified into four categories: 1) nonisolated single-stage topologies; 2) isolated single-stage topologies; 3) nonisolated double-stage topologies; and 4) isolated double-stage topologies. Typically, a microinverter’s performance can be enhanced by the use of nonisolated topologies to be more efficient, more compact, less bulky, and less costly than the isolated topologies. Whereas, the use of a transformer in microinverter topologies provides high-power quality as well as galvanic isolation to eliminate the safety issues, which in return meet the grid standards. The power processing (boosting the dc voltage of PV panel, extracting the maximum power and converting it to ac power), which can be achieved either via single stage or double stage, has a significant impact on the microinverter performance. This paper reviews and compares experimentally verified microinverter topologies in terms of their corresponding efficiency, power density, reliability, and cost. The most efficient topology in each category is designed and simulated in comparison with a benchmark. The topologies are then compared in terms of their component count, input voltage range, modular structure, soft-switching implementation, and battery integration.

Cascade Control With Adaptive Voltage Controller Applied to Photovoltaic Boost Converters

DC–DC boost converters have been widely employed at the dc input of grid-tied photovoltaic (PV) inverters. In order to comply with grid standards, their control systems must usually work in two operation modes: Maximum power point tracking (MPPT) mode and limited power tracking (LPT) mode. MPPT algorithms reach high dynamic and static efficiencies when they operate with high-speed PV voltage control, because PV voltage is not significantly dependent on solar irradiance variations. On another hand, high-speed LPT mode can be obtained by controlling inductor current, which is proportional to the power injected into the dc bus. Both modes can be integrated in a cascade control scheme with an inner and fast current loop and an outer voltage loop. The main challenge is that both voltage and current small-signal models are highly dependent on the operation point of the PV array, temperature, and solar irradiance. This may cause control interactions between both loops and instability, especially when small film capacitors are used in parallel with the PV array. A common approach is to increase the input capacitance and design a low-speed PV voltage controller, which is not the best solution when high MPPT dynamic efficiency is necessary. To overcome these challenges, this paper proposes a cascade control structure based on an inner non-linear current controller and an outer adaptive voltage controller with fast detection of the PV array's model without requiring extra current sensor. A control design methodology and a MATLAB stability analysis tool are presented to support application engineers. The proposed control system has been experimentally validated using a PV array and a boost converter switched at 40 kHz. PV voltage settling time lower than 8 ms has been achieved for low and high solar irradiance, demonstrating the efficacy of the proposed technique.

A new structure of single‐phase two‐stage hybrid transformerless multilevel PV inverter

SummaryTransformerless inverters are becoming popular for grid‐connected photovoltaic applications due to their simplicity, reduced size, weight, cost, and higher efficiency. In this paper, a two‐stage hybrid transformerless multilevel inverter (MLI) for single‐phase grid‐connected photovoltaic power generation system (PVPGS) is presented. The proposed topology comprises a multilevel boost converter (MLBC) and a symmetrical hybrid MLI. MLBC combines the boosting and switched capacitor voltage functions to produce self‐balanced multiple voltage levels. The proposed MLI is derived from a combination of bidirectional switches, a half bridge, and a diode‐clamped branch, which can produce only two variations in the total common mode voltage and is capable of suppressing leakage current as per DIN VDE 0126‐1‐1 grid standards. It offers the advantages of scalability, reactive power capability, reduced total harmonic distortion, and filter size. The proposed hybrid transformerless seven‐level inverter is simulated in MATLAB, and experimental setup is built to validate the effectiveness of the proposed configuration. Finally, a comprehensive comparison is made with other seven‐level inverter topologies.

Stability Analysis and Optimization of Wind Energy Conversion System Using Extremum Seeking Output Feedback Controller for Dynamic Wind Speed Variations

Stability of power systems is an important aspect for interconnecting different renewable energy sources into the existing electrical network. The concern over environmental effects due to conventional power plant made the researchers to implement many solutions for introducing renewable energy due to their intermittent nature. When the wind energy conversion system is introduced into the grid there’s need of voltage and frequency control for maintaining reactive power demand and also many issues from the consumer end and also it must satisfy the grid standards. As the wind is dynamic in nature there are issues like stability, load imbalance, power quality and other issues. In this paper, a non-linear feedback controller is introduced based on field-oriented control (FOC) approach and simulated in MATLAB environment. The designed controller is tested for wind data for examining the stability and power coefficient for the wind turbine. This controller also achieves fast transient response for rapid changes in the wind profile.

Fault Ride-Through Capability of Voltage-Controlled Inverters

An auxiliary voltage controller is proposed for the fault ride-through (FRT) control of voltage-controlled inverters used in distributed energy resources. The proposed auxiliary controller can be added to different existing voltage control strategies with minimum or no need to alter the original structure of the voltage controller. The proposed controller prevents the transient overcurrent during grid faults and controls the exchange of real and reactive powers according to the governing grid standard. A fault detection algorithm is also implemented to detect the fault instant and determine the interval of fault during which the real and reactive power references are adjusted accordingly. Complete stability analysis of the proposed controller is performed through a new model. Successful performance of the proposed controller in achieving FRT requirements of German and Danish codes are illustrated by simulations. Extensive real-time and experimental results are also presented and discussed.

Routing Architecture of Software Defined Energy Internet

Energy Internet is a new and constantly evolving technology, of which the most critical part is how the energy flows. The concept of software customization used in the field of information will decouple the control plane from the data plane. It adopts a logical centralized control model. The control part of the device is implemented by a centralized programmable controller. Referring to the basic concept of computer network, the energy internet can be divided into energy resource subnet and energy transmission subnet. Energy micro-network, wide area energy internet and global energy internet are introduced. The concept of software-defined is applied to the field of smart grid which is the foundation and critical part of energy internet. This paper describes a software defined wide area energy internet routing architecture and implementation approach, which not only takes into account the compatibility of power devices with smart grid standards such as IEC61850 but also provides flexible software defined innovative application deployment.

Grid emulator for small scale distributed energy generation laboratory

This paper presents the design of a grid emulator dedicated to test small scale distributed energy generation. laboratory The proposed emulator aims to test its performances under different power quality conditions considering grid codes and standards. The developed emulator can generate common grid faults and line impedance variations. This last point is an additional feature versus common grid emulators. The paper discusses design and implementation aspects. Emulator performance analysis are investigated under special operating conditions. Simulation results are carried out to illustrate theoretical developments and a set of experimental results are provided to demonstrate the effectiveness of the proposed emulator.

Primary frequency optimization control method of thermal power unit based on safe and stable operation

With the rapid development of energy-saving and clean new energy, power fluctuations bring great challenges to frequency control of power grid. The main ways of dealing with the instantaneous power gap depends on primary frequency compensation(PFC) of thermal power units. The characteristics and questions of automatic generation control (AGC) and PFC were analyzed, and the optimization of unit control were offered. It can ensure that the frequency modulation and peak shaving capacity of the thermal power unit meets the requirements of power grid standards, and effectively ensure the priority of the PFC action when the grid frequency fluctuates, improve the coordinated operation of the AGC and PFC.

A Study of Inverter Drives and Its Ride Through Capabilities in Industrial Applications

In modern industry, majority of the mechanical elements are driven by either induction motors or special motors like servo motors, synchronous motors, BLDC motors. In order to drive the motors and to vary the speed of the motors, electronics drives are required. Since the drives are powered with three phase AC, if the power grid has power quality issue, which directly reflects on to the power electronics drives. As per Indian grid standards, power quality is defined as harmonics, surge, sag, swell, which was formulated in the year of 2003 and further revision was done in 2010. But in the recent day’s majority of the industries are constructed in same place (special economic zone), unpredicted industrial loads are increased and inserted in to existing running load, so eventually the power quality definition also changes and even sometimes connections are made as temporary for certain loads. Although these motors typically tolerate variations in utilization voltage, power quality professionals continue to spend a great deal of time answering questions about proper utilization voltage for a given motor. The voltage quality factors that create the most serious problems and confusion in the field include nominal utilization voltage that does not match the motor nameplate, proper voltage sag ride-through protection for the motor control circuitry, and phase-to-phase voltage imbalance. In review article, modern industry premises failure of components list and condition of power quality will be surveyed in various segments. Various failure of inverter drives namely, switching failure, commutation failure, common mode voltage problem, bearing current issues, harmonics etc., are discussed in details from various research article and presented in this review.

Standards on cyber security assessment of smart grid

Security evaluation of communication systems in smart grid poses a great challenge to the developers and operators. In recent years, many new smart grid standards were proposed, which paradoxically results in the difficulty in finding a relevant publication in this plethora of literature. This paper presents the results of a systematic analysis which aimed at addressing this issue by identifying standards that present sound security assessment guidance. This should help practitioners in choosing the standards that are applicable to their area. Additionally the contents extracted from the standards can serve as a useful guidance on security assessments of smart grid components.

Analytical Design of Passive LCL Filter for Three-Phase Two-Level Power Factor Correction Rectifiers

This paper proposes a comprehensive analytical LCL filter design method for three-phase two-level power factor correction rectifiers (PFCs). The high-frequency converter current ripple generates the high-frequency current harmonics that need to be attenuated with respect to the grid standards. Studying the high-frequency current of each element proposes a noniterative solution for designing an LCL filter. In this paper, the converter current ripple is thoroughly analyzed to generalize the current ripple behavior and find the maximum current ripple for sinusoidal pulse width modulation (PWM) and third-harmonic injection PWM. Consequently, the current ripple is used to accurately determine the required filter capacitance based on the maximum charge of the filter capacitor. To choose the grid-side inductance, two methods are investigated. First method uses the structure of the damping to express the grid-side filter inductance as a function of the converter current ripple. Reducing the power loss in the filter and optimizing the grid-side filter inductance is the main focus of the second method which is achieved by employing line impedance stabilization network (LISN). Accordingly, two LCL filters are designed for a 5 kW silicon-carbide-based three-phase PFC. Various experimental scenarios are performed to verify the filters attenuation and performance.

Research on LLCL Filtering Grid - Connected inverter under the Control of PFI

This passage puts forward a kind of LLCL inverter which is based on the proportional feedback integral(PFI) control so as so satisfy the request of the grid-current outputed by the renewable energy generation system. The passage builds the topological graph of grid-connected inverter and makes an analysis of principle of linear superposition aims to reveal the essence of the problem of steady-state error that exists in proportional integral control. We use LLCL filter and the method of passive damping to solve the problem of resonant peak. We make simulation of the grid system with the software named MATLAB/Simulink. The result shows that the grid current enters steady state quickly and in the same time, which has the identical phase and frequency of grid-voltage. The harmonic content in grid current satisfies the request of grid standard.

Grid-Interactive Cascaded H-Bridge Multilevel Converter PQ Plane Operating Region Analysis

Cascaded H-bridge (CHB) multilevel converters are being considered as a promising option for interfacing renewable energy resources with the grid due to their modularity, scalability, and increased efficiency when compared with traditionally used two-level inverters. When used as grid interfaces, CHB converters should be capable of controlling the injected active and reactive power while also satisfying operating criteria such as grid standards, e.g., IEEE 519. This paper aims to identify $PQ$ plane operating points available when using symmetric and asymmetric grid-interactive CHB converter topologies, and to determine the factors that prevent utilization of other converter output points. Notably, for asymmetric CHB converters, a technique is proposed to identify discordant output points where power is transferred between cells within a leg, e.g., one cell has a net regenerative power flow while the overall CHB leg does not. This work ( i ) provides distribution engineers with information regarding the active and reactive power that can feasibly be generated by grid-interactive CHB converter topologies, ( ii ) creates a framework for assessing operating point trajectories when altering the steady-state operation of grid-tied CHB converters, ( iii ) provides a basis for selecting and modifying steady-state pulse-width modulation generation techniques in order to meet desired performance criteria, and ( iv ) presents analytical techniques that can be built upon to facilitate analysis of grid-interactive CHB under conditions such as grid imbalance or during continued operation after CHB cell faults.

Novel dense skin hollow fiber membrane contactor based process for CO2 removal from raw biogas using water as absorbent

Abstract CO2 removal from raw biogas is required in order to meet standards for the gas grid or as a vehicle fuel. Among biogas upgrading available techniques, pressurized water absorption using packed column (PWA) is one of the most well-established technique. In this work, a novel absorption/desorption loop using dense based hollow fiber membrane contactor (HFMC) process and water as absorbent is proposed and investigated by simulation. Thanks to the ability of dense membranes to withstand a high transmembrane pressure, neither water depressurization before the desorber nor water recompression before the absorber is needed. 1D modeling based on a resistances in series approach is used for the modeling of both absorption and desorption units. HFMC process performances are compared to state of the art packed column (PWA) process reported in literature. Using commercially available dense based HFMC, the process is able to recover 96.6% of CO2 and reach biomethane purity of 98%. The corresponding energy requirement is of 0.17 kWh/Nm3 of raw biogas, which is 20 to 35% lower than that reported for packed column based process, under comparable gas inlet conditions and product specifications. HFMC process offers absorption intensification factor of about 1.68, corresponding to a volumetric reduction of about 68% of the absorption unit. Under the investigated operating conditions and due of the preponderant liquid side mass transfer resistance, process selectivity is mainly controlled by the absorbent selectivity. Without flash recovery, CH4 loss is of about 8%. No significant methane loss reduction is obtained from increasing membrane selectivity from 17 to 60 with membrane mass transfer coefficient of 5.10-4 and 5.10-5 m/s respectively. Perspectives for further process optimization are exposed.