Steady-state Power Research Articles

Suppression of Power Angle Oscillation Among Synchronous Generators by Optimizing Steady–State Power of High-Voltage DC

Suppression of Power Angle Oscillation Among Synchronous Generators by Optimizing Steady–State Power of High-Voltage DC

An Adaptive Droop Scheme for Improving Transient and Steady-State Power Sharing among Distributed Generators in Islanded Microgrids

The droop control laws lack proportional power sharing in transient as well as steady-state conditions in AC microgrids. This paper proposes an adaptive droop coefficients based control strategy to address this issue. The droop coefficients are adaptively changed based on the output currents of the distributed generators. An appreciable improvement is achieved in the power sharing by using adaptive droop coefficients instead of fixed coefficients values. The proposed strategy can be used with conventional as well as inverse droop control laws in AC microgrids to enhance their performance. The proposed method does not require any type of additional communication or any extra hardware for its operation. The proposed scheme has been validated using extensive simulations and experiments for conventional and inverse droop laws using different type of loads (constant power, unbalanced, non-linear, dynamic). Further, the small signal eigenvalue analyses is used to find the stability limit of the variables used in the proposed scheme.

Steady-state power distribution in VSC-based MTDC systems and dc grids under mixed P/V and I/V droop control

This paper proposes a steady-state power distribution derivation method for voltage source converter (VSC)-based multi-terminal HVDC (MTDC) systems and dc grids under mixed power/voltage (P/V) and current/voltage (I/V) droop control. P/V and I/V droop control are two commonly used control schemes, which can be combined to achieve co-regulation of powers & currents in MTDC systems and dc grids. The proposed method can be used to estimate the power distributions under different scenarios for MTDC systems and dc grids based on VSCs with mixed P/V and I/V droop control. After determining the initial operating point based on an estimation-correction algorithm, redistributed power due to power disturbances, current changes or converter outages is analyzed in detail considering converter overload. An excess power reduction strategy is further proposed to avoid violation of power limits after converter outage. The accuracy of the proposed method is validated through multiple scenarios in a modular multilevel converter (MMC)-based four-terminal dc grid. The comparison between the proposed method and other approaches in the current literature further demonstrates the advantages of proposed power distribution derivation method. • Determination of initial operating point for mixed P/V and I/V droop control by proposed estimation-correction algorithm. • Derivation of power redistribution after dc power/ current reference changes and converter outages. • Consideration of possible converter overloads caused by different system disturbances.

Toward Models of Impact and Recovery of the US Western Grid from Earthquake Events

A Cascadia Subduction Zone (CSZ) earthquake will cause widespread damage to numerous lifelines and infrastructure along the northern US west coast. The goal of the presented research is to provide a bottom up estimate of the impact on and subsequent recovery of a Cascadia Subduction Zone earthquake on the US western grid to supplement and enhance the expert opinion estimates provided to date. The scope is limited to only consideration of shaking damage to utility substation equipment components of a power system model. The analysis utilizes probabilistic models of damage and recovery for substation power system assets, along with graph techniques for modeling connectivity, and Monte Carlo quasi steady state power flow solutions. The results show that a conservative estimate of the initial damage and loss of load is approximately 4000 MW, with a recovery estimate of 230 days.

Design of a cylindrical corrugated waveguide for a collinear wakefield accelerator

We present the design of a cylindrical corrugated waveguide for use in the A-STAR accelerator under development at Argonne National Laboratory. A-STAR is a high gradient, high bunch repetition rate collinear wakefield accelerator that uses a 1-mm inner radius corrugated waveguide to produce a $90\text{ }\text{ }\mathrm{MV}\text{ }{\mathrm{m}}^{\ensuremath{-}1}$, 180-GHz accelerating field when driven by a 10-nC drive bunch. To select a corrugation geometry for A-STAR, we analyze three types of corrugation profiles in the overmoded regime with $a/\ensuremath{\lambda}$ ranging from 0.53 to 0.67, where $a$ is the minor radius of the corrugated waveguide and $\ensuremath{\lambda}$ is the free-space wavelength. We find that the corrugation geometry that optimizes the accelerator performance is a rounded profile with vertical sidewalls and a corrugation period $p\ensuremath{\ll}a$. Trade-offs between the peak surface fields and thermal loading are presented along with calculations of pulse heating and steady-state power dissipation. In addition to the ${\mathrm{TM}}_{01}$ accelerating mode, properties of the ${\mathrm{HEM}}_{11}$ mode and contributions from higher order modes are discussed.

Wide Frequency PWM Rectifier Control System Based on Improved Deadbeat Direct Power Control

The precision of deadbeat direct power control depends on the parameters of the system model. In wide frequency applications, such as multi- electric aircraft and electric vehicles, variations in frequency and resistive parameters will affect the control effect. The AC side voltage frequency of the generator rectifier varies widely, which will lead to a steady-state reactive power error in the deadbeat direct power control. In addition, the large temperature variation range during the operation of the multi-electric aircraft and electric vehicles leads to large changes in the filter inductance and line resistance of the AC side, and the model parameters do not match the actual parameters, which will further deteriorate the control accuracy. In this paper, a PWM rectifier control method is proposed for the occasions when the frequency and temperature change are in a wide range. Using repetitive control and power compensation, it solves the problems of steady-state reactive power error and control accuracy degradation caused by the mismatch of model parameters under severe operating conditions. The control method can precisely adjust the output DC voltage of PWM rectifier, and it also can maintain unity power factor and reduce the total harmonic distortion rate of the input current. The effectiveness of the proposed control method is verified by the experimental results.

Dynamic Aggregation Method of Wind Farms with Virtual Synchronous Generator-Controlled Wind Turbines

The frequency and voltage dynamic processes of each wind turbine in the existing wind farm are different, and the available aggregation model of wind farms mainly focuses on the steady-state output power, lacking an effective dynamic aggregation mechanism. Wind turbines usually adopt the virtual synchronous generator method (VSG) to simulate the external characteristics of the traditional synchronous generator. Its frequency dynamic response is mainly affected by the virtual inertia and damping parameters, and the excitation regulator parameters determine the voltage dynamic response. Therefore, the aggregation method of the traditional synchronous generator is also applicable to such wind turbines. Firstly, the dynamic characteristics of the points of wind farms’ point of common coupling (PCC) are discussed. Then, the dynamic aggregation method of the VSG-wind farms is proposed based on the Kuramoto (KM) model and the small signal analysis of the wind turbines. Finally, a wind farm consisting of multiple VSG-wind turbines under disturbances is simulated in PSCAD/EMTDC to verify the effectiveness of the proposed dynamic aggregation method.

Security constrained optimal placement of renewable energy sources distributed generation for modern grid operations

In modern distribution network planning and operation, optimal distribution generation (DG) placement has become increasingly important. Consequently, extending the optimal DG placement objectives beyond the commonly used deterministic indices to include probabilistic security indices is essential. This paper proposes a decision tree (DT) classification approach for multiple photovoltaic DG (PVDG) units’ placements using specific indices in an unbalanced distribution network. The security indices considered in this paper are the branches’ risk index (RI) and power loss (PL). The optimal branch(es) for PVDG units’ placements are determined through the branches’ RI and PL, and the optimal nodes are determined using the nodal hosting capacity (HC) and zero-point ( ). The proposed technique was tested on the IEEE 33 and 69 node radial distribution networks considering three common PV voltage control modes, namely, constant voltage (CV) mode, reactive power-voltage (QV) mode, and reactive power-power factor (Q-PF) mode. After the optimal placement of the PVDG units under the constant voltage control technique, the worst case of the average probabilistic voltage was improved from 0.798 and 0.941 to 0.94 and 0.975 for IEEE 33 and 69 node distribution networks, respectively. The steady-state power loss was also reduced by 78% and 32.72% for the IEEE 33 and 69 node distribution networks, respectively. The proposed technique was also compared with recent and existing methods in the literature. The proposed technique performs better in terms of power loss reduction and voltage enhancement.

Intermediate-phase engineering via dimethylammonium cation additive for stable perovskite solar cells.

Achieving the long-term stability of perovskite solar cells is arguably the most important challenge required to enable widespread commercialization. Understanding the perovskite crystallization process and its direct impact on device stability is critical to achieving this goal. The commonly employed dimethyl-formamide/dimethyl-sulfoxide solvent preparation method results in a poor crystal quality and microstructure of the polycrystalline perovskite films. In this work, we introduce a high-temperature dimethyl-sulfoxide-free processing method that utilizes dimethylammonium chloride as an additive to control the perovskite intermediate precursor phases. By controlling the crystallization sequence, we tune the grain size, texturing, orientation (corner-up versus face-up) and crystallinity of the formamidinium (FA)/caesium (FA)yCs1-yPb(IxBr1-x)3 perovskite system. A population of encapsulated devices showed improved operational stability, with a median T80 lifetime (the time over which the device power conversion efficiency decreases to 80% of its initial value) for the steady-state power conversion efficiency of 1,190 hours, and a champion device showed a T80 of 1,410 hours, under simulated sunlight at 65 °C in air, under open-circuit conditions. This work highlights the importance of material quality in achieving the long-term operational stability of perovskite optoelectronic devices.

Double-layered model predictive optimization control strategy for temperature uniformity of microwave heating process

Based on the application requirements of the dynamic process analysis of heating materials using high-power microwave reactors with multiple microwave sources, a novel layered control framework is proposed for temperature uniformity during the process of heating heterogeneous materials using microwaves. The framework comprehensively considers the material temperature distribution, production process constraints and energy consumption elements. This double-layered model predictive optimization control framework is implemented through two layers. The upper layer is realized by a distributed data computation of the input electric power of microwave sources and temperature target tracking to find the real-time steady-state optimal input electric power based on the material temperature, process constraints, and energy consumption coefficients. In the lower layer, a dynamic predictive control method based on dynamical models of the heating process with multiple microwave sources is used to track the temperature targets and results calculated by the upper layer. A temperature target shifting strategy is used between the upper and lower layers to eliminate model prediction errors. The effectiveness of the proposed double-layered control framework was validated by heating alumina ceramic in a ducted microwave reactor with six microwave sources.

Soft Switching High Voltage Gain Quasi-Z-Source DC–DC Converter With Switched-Capacitor Technique

Nonisolated high-voltage gain soft-switching dc–dc converter is an ideal candidate for distributed generation system converters. This article proposes a high-voltage gain soft switching quasi-Z-source dc–dc converter. The converter integrates a coupled inductor and switched capacitor into a quasi-Z-source network. Soft switching is achieved for all active devices in the converter by controlling the auxiliary switch <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> . By inheriting the advantages of the quasi-Z-source network and coupled-inductor/switched-capacitor, the converter has high voltage gain, high efficiency, low input current ripple, low voltage spike of main switch, and common ground. In addition, the efficiency of the converter is improved by recycling the energy of leakage inductance, resulting from an inherent active clamp of the main switch. The steady-state operation, voltage relationship, current/voltage stress, and power dissipation of each component of the converter have been analyzed and derived in detail. The properties of the proposed converter are verified by designing a 200 W prototype in the laboratory. When the input voltage is 48 V and the output voltage is 380 V, the converter efficiency reaches 96.92%, while the efficiency is 93% in a hard switching. The key waveforms of the converter obtained from the experiment agree well with the theoretical analysis results.

Managing Power Flow in Hybrid Electric Vehicle with Auxiliary Hybrid Energy Source coupled with Bidirectional Converter Using PI Control

Background: The overall performance of the hybrid electric vehicle is mainly governed by the energy storage systems characteristics with respect to their power and energy density. The batteries have a good energy density, while the supercapacitor (SC) has a good power density. Method: This paper presents a hybrid auxiliary source combined with a battery and the supercapacitor to use both characteristics of auxiliary energy source for Hybrid Electric Vehicle (HEV) application. The PI control technique is used for managing the power flow so that the supercapacitor fulfills the transient power and the battery supplies the steady-state power. The parameters of controllers are tuned by Ziegler Nichols and frequency response-based method. Result: The performance of the controller is evaluated by error coefficients (IAE, ISE, ITAE and ITSE). The model with different tuning parameters is simulated for fixed and variable reference inputs. The speed, dc bus voltage, and error coefficients are evaluated for the battery alone and battery-SC combinations. Conclusion: The value of error-based parameters suggests that controller parameters tuned by the frequency response-based method provide better results. The error coefficients for battery-supercapacitor combination are lower as compared to battery-alone systems indicating the better performance of hybrid input.

Optimal Secondary Frequency Regulation With ON-OFF Loads in Power Networks

Load-side participation can provide support to the power network by appropriately adapting the demand when required. In addition, it enables an economically improved power allocation. In this study, we consider the problem of providing an optimal power allocation among generation and ON-OFF loads within the secondary frequency control timeframe. In particular, we consider a mixed-integer optimization problem, which ensures that the secondary frequency control objectives (i.e., generation–demand balance and the frequency attaining its nominal value at steady state) are satisfied. We present analytic conditions on the generation and ON-OFF load profiles such that an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\epsilon $ </tex-math></inline-formula> -optimality interpretation of the steady-state power allocation is obtained, providing a nonconservative value for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\epsilon $ </tex-math></inline-formula> . Moreover, we develop a hierarchical control scheme that provides ON-OFF load values that satisfy the proposed conditions. We study the interaction of the proposed control scheme with the physical dynamics of the power network and provide analytic stability guarantees. Our results are verified with numerical simulations on the Western System Coordinating Council (WSCC) 9-bus system and the Northeast Power Coordinating Council (NPCC) 140-bus system, where it is demonstrated that the proposed algorithm yields a close to optimal power allocation.

Analysis and research on the influence of multiple factors on the steady operation area of large-capacity MMC-HVDC transmission system

Aiming at the MMC-HVDC (modular multilevel converter based high voltage direct current), this paper studies the influence of multiple factors such as the AC system and converter characteristic limits on the steady-state operating range of the MMC-HVDC transmission system. First, a mathematical model based on the steady-state operation of the MMC-HVDC transmission system is established, and the AC-side power quality requirements and stability limiting factors of the MMC-HVDC system are analyzed and summarized, as well as the constraints of multiple limiting factors on the converter side. Based on this, the power operation range of MMC-HVDC transmission project under different conditions is obtained. Finally, combined with the actual project, the effects of modulation ratio, equivalent reactance between the AC outlets of the converter and AC system equivalent impedance on the steady-state power operating range are analyzed and studied separately.

The steady state power model of two-level grid connected inverter with amplitude phase control

Because of its high efficiency and flexible control, inverters are widely used in renewable energy generation. The inverter’s mathematical model is critical in system design and analysis. It is necessary to establish an accurate grid connected inverter model to carry out a reliable load flow analysis calculation. The amplitude and phase of the reference control strategy can be used to perform power transformation and control analysis. This paper proposed a steady-state power model controlled by amplitude and phase based on a two-level inverter. Then, the mathematical derivation of the proposed model is presented in detail. Furthermore, the simulation model’s details are then built. The simulation results validate the model’s effectiveness.

Cold Load Pickup Model Adequacy for Power System Restoration Studies

When a grid section is re-energized after an interruption, the load behaviour can be significantly different from normal operation. In this manuscript, the impact of the phenomenon—known as cold load pickup—is investigated by evaluating 31 time series measured after network outages in Austria and Germany. Its impact on power system restoration and the adequacy of the most common type of simplified model for such investigations is assessed by the time domain simulation of a restoration setting involving the parallel operation of conventional and renewable generation. Parameter distributions are provided for the exponential decay and the delayed exponential decay model with the aim of facilitating meaningful consideration of the phenomenon in time domain simulations of power system restoration. The benefits and limitations of these models are assessed by comparison of time domain simulation results using either the normalized raw data, an exponential decay model or a step-wise active power chance to reflect load behaviour. It is shown that using an exponential decay model leads to higher fidelity of simulation results with respect to the resulting steady-state active power sharing among generators than just applying a step-wise power change in the simulation.

Double duty ratio PWM control method for a novel HSV actuator with low power consumption

This paper presents a novel high speed valve (HSV) actuator with low power consumption. The structure design of tapered armature and control method of double duty ratio pulse width modulation (PWM) are proposed in the HSV actuator to improve steady and transient characteristics. The electric-magneto-mechanical model of the HSV actuator is established and investigated by theoretical analysis. Parameters improvement of the HSV actuator is analyzed by the model, and optimized results for a prototype actuator have been obtained. The experimental and simulation curves agree well with the changing trend, and show that the opening time of the HSV actuator is 7.3 ms, the closing time is 20 ms, and power consumption in maintenance stage is 1.35 W, within the stroke of 2.5 mm. Compared with normal driving method, the proposed structure and method have the advantages of opening time reduced by 37%, closing time reduced by 29%, and steady-state power consumption reduced by 93.5%. The proposed structure and method in the HSV actuator are available to meet the driving requirements of both steady and transient performance in fluid control systems better, especially in power shortage or power supply inconvenient engineering.

Optimal Allocation of Renewable Energy Sources and Battery Storage Systems Considering Energy Management System Optimization Based on Fuzzy Inference

The main problem in planning the optimal operation of renewable energy sources and battery storage systems is the amount of data that must be considered to cover an entire observation period. If the observation period is one year, the characteristic days or averaged data (daily, weekly or monthly averages) are considered to reduce the number of data. Since the average values of the entered data differ from the actual values, it is better to work with hourly or 15-min data at the annual level. The study presents a framework for solving the problem of the optimal allocation and operation of renewable energy sources and battery storage systems. The proposed method simultaneously solves the optimal allocation and energy management problem considering hourly data at the annual level. The fuzzy inference-based system is proposed for scheduling optimal profiles of battery storage systems and renewable energy sources. The developed fuzzy inference system manages the power factors of the photovoltaic and wind power systems, the power factor and output of the biogas plant, and the operating status of the battery storage system. The presented method simultaneously finds the optimal parameters of the energy management system and the optimal allocation and operation of the renewable energy sources and the battery storage system. The developed method is based on the calculation of steady-state power flow. The proposed method is to be used in the design phase for the installation of various renewable energy sources and battery storage systems. In addition, the method is intended to be used to optimally control the power output of energy sources and the operation of energy storage systems during steady-state operation in order to operate the distribution network with minimum annual active energy losses. The developed method is applied to the test distribution system IEEE with 37 nodes. The reduction in annual energy losses in the tested distribution system is about 80% compared to the base case without renewable energy sources and battery storage system.

A Comparative Review on Energy Storage Systems and Their Application in Deregulated Systems

Electrical energy is critical to the advancement of both social and economic growth. Because of its importance, the electricity industry has historically been controlled and operated by governmental entities. The power market is being deregulated, and it has been modified throughout time. Both regulated and deregulated electricity markets have benefits and pitfalls in terms of energy costs, efficiency, and environmental repercussions. In regulated markets, policy-based strategies are often used to deal with the costs of fossil fuel resources and increase the feasibility of renewable energy sources. Renewables may be incorporated into deregulated markets by a mix of regulatory and market-based approaches, as described in this paper, to increase the systems economic stability. As the demand for energy has increased substantially in recent decades, particularly in developing nations, the quantity of greenhouse gas emissions has increased fast, as have fuel prices, which are the primary motivators for programmers to use renewable energy sources more effectively. Despite its obvious benefits, renewable energy has considerable drawbacks, such as irregularity in generation, because most renewable energy supplies are climate-dependent, demanding complex design, planning, and control optimization approaches. Several optimization solutions have been used in the renewable-integrated deregulated power system. Energy storage technology has risen in relevance as the usage of renewable energy has expanded, since these devices may absorb electricity generated by renewables during off-peak demand hours and feed it back into the grid during peak demand hours. Using renewable energy and storing it for future use instead of expanding fossil fuel power can assist in reducing greenhouse gas emissions. There is a desire to maximize the societal benefit of a deregulated system by better using existing power system capacity through the implementation of an energy storage system (ESS). As a result, good ESS device placement offers innovative control capabilities in steady-state power flow regulation as well as dynamic stability management. This paper examines numerous elements of renewable integrated deregulated power systems and gives a comprehensive overview of the most current research breakthroughs in this field. The main objectives of the reviews are the maximization of system profit, maximization of social welfare and minimization of system generation cost and loss by optimal placement of energy storage devices and renewable energy systems. This study will be very helpful for the power production companies who want to build new renewable-based power plant by sighted the present status of renewable energy sources along with the details of several EES systems. The incorporation of storage devices in the renewable-incorporated deregulated system will provide maximum social benefit by supplying additional power to the thermal power plant with minimum cost.

A Comparative Study on System Profit Maximization of a Renewable Combined Deregulated Power System

Electrical energy plays a key role in the development of the social as well as the economic front. The power sector has historically been owned and operated by state agencies due to its tremendous importance. It has been restructured over time, and the power market is being deregulated. In terms of consumer prices, efficiency, and environmental implications, both regulated and deregulated electricity markets offer advantages and disadvantages. Policy-based techniques are typically used in regulated markets to address the costs of fossil-fuel resources and boost the viability of renewable energy sources. Renewables can be integrated into deregulated markets through a combination of regulatory and market-based measures to extend the system’s economic stability which has been deployed in this paper. As the need for energy has expanded dramatically over the last few decades, particularly in developing countries, the amount of greenhouse gas emissions has climbed rapidly, as have fuel prices, which are the key driving forces behind initiatives to use renewable energy sources more effectively. Despite the apparent benefits of renewable energy, it has significant downsides, such as generation of optimization methods applied to renewable consistency, because most renewable energy supplies are climate-dependent, necessitating complicated design, planning, and control optimization methods. There have been numerous optimization strategies applied to the renewable integrated deregulated electricity system. With the increased use of renewable energy, energy storage technology has grown in importance, as these devices can capture electricity generated by renewables during off-peak demand hours and put it back into the grid during peak demand periods. Using stored renewable energy instead of adding generation based on fossil fuel can help to minimize greenhouse gas emissions. There is an interest in better utilizing available power system capacity by implementing FACTS to maximize the social benefit in a deregulated system. As a result, effective FACTS device placement provides novel control capabilities in both steady-state power flow regulation and dynamic stability control. This study reviews several aspects of renewable integrated deregulated power systems and provides a clear picture of the most recent research developments on this subject. The main objectives of the reviews are the maximization of system profit, maximization of social welfare, and minimization of system generation cost and loss by optimal placement of energy storage devices and FACTS controllers.