Average-value Model Research Articles

A Universal Blocking-Module-Based Average Value Model of Modular Multilevel Converters With Different Types of Submodules

The large amount of power electronic submodules and semiconductor switching events in the Modular Multilevel Converter (MMC) introduces several challenges for efficient and accurate Electro-Magnetic Transient (EMT) simulation. Research efforts have focused on developing Average Value Models (AVMs) of MMC that enable fast and accurate dynamic simulation of the converter. This paper proposes a universal blocking-module-based AVM, which can simulate the MMC of different submodule types and provide accurate results for the MMC operating in both blocking and de-blocking modes. An analytical approach is included in the model to calculate the semiconductor losses of different submodule types in the MMC. The proposed model is validated against a detailed switching-based model and the state-of-the-art AVMs in a 41-level two-terminal MMC-HVDC system.

Combining Detailed Equivalent Model With Switching-Function-Based Average Value Model for Fast and Accurate Simulation of MMCs

Modeling and simulation play a vital role in the design and testing of modular multilevel converter (MMC) high voltage direct current (HVDC) systems. Detailed equivalent model (DEM) and switching-function-based average value model (SFB-AVM) are two major types of accurate and efficient models to represent the dynamic response of the MMCs. However, the DEM and the SFB-AVM possess unique benefits depending on the purpose of the simulation studies. The DEM provides a detailed representation of submodule (SM) switching events and individual capacitor ripples. The SFB-AVM provides faster simulation speed by using arm equivalent capacitance. Combining both models in a universal arm equivalent circuit gives the users the choice of selecting the most appropriate modeling method during dynamic simulation. This paper proposes a universal modeling framework combining the DEM with the SFB-AVM which allows the DEM and the SFB-AVM smoothly switch from one to the other during dynamic simulation. The proposed SFB-AVM can accurately represent the MMCs with different SM types. The proposed models are validated in offline and real-time simulation studies which demonstrate the improved simulation speeds of the proposed SFB-AVM over the DEM especially for large numbers of SMs.

Unified Reduced Model for a Dual-Control Scheme of the High-Speed Response Brushless Excitation System of Synchronous Generators

Developments of the high-speed response brushless excitation systems (HSRBESs) are ongoing in the power industry. This is because the transient response of the excitation system (ES) is a key performance indicator for the grid owner. In dealing with this problem, accurate prediction and control of the ES ceiling voltage are desirable. However, the brushless exciters’ nonlinear armature reaction causes the ceiling voltage to be unknown under varying operating conditions. This article proposes a numerical average-value model (AVM) that captures all the main dynamics of the HSRBES. It is shown that the AVM relationships can be utilized for online prediction of the ceiling voltage and employed in a dual-control scheme. The proposed model is validated against a dynamic voltage build-up test. Moreover, it is derived from a detailed model, which is verified from instantaneous field measurements and further from finite-element analysis. Finally, the accuracy and effectiveness of the AVMs’ transient relationships prove the feasibility of the proposed dual-control scheme and shows that it can be easily implemented in existing systems.

Diesel Mean Value Engine Modeling Based on Thermodynamic Cycle Simulation Using Artificial Neural Network

This study aims to construct a reduced thermodynamic cycle model with high accuracy and high model execution speed based on artificial neural network training for real-time numerical analysis. This paper proposes a method of constructing a fast average-value model by combining a 1D plant model and exhaust gas recirculation (EGR) control logic. The combustion model of the detailed model uses a direct-injection diesel multi-pulse (DI-pulse) method similar to diesel combustion characteristics. The DI-pulse combustion method divides the volume of the cylinder into three zones, predicting combustion- and emission-related variables, and each combustion step comprises different correction variables. This detailed model is estimated to be within 5% of the reference engine test results. To reduce the analysis time while maintaining the accuracy of engine performance prediction, the cylinder volumetric efficiency and the exhaust gas temperature were predicted using an artificial neural network. Owing to the lack of input variables in the training of artificial neural networks, it was not possible to predict the 0.6–0.7 range for volumetric efficiency and the 1000–1200 K range for exhaust gas temperature. This is because the mean value model changes the fuel injection method from the common rail fuel injection mode to the single injection mode in the model reduction process and changes the in-cylinder combustion according to the injection timing of the fuel amount injected. In addition, the mean value model combined with EGR logic, i.e., the single-input single-output (SISO) coupled mean value model, verifies the accuracy and responsiveness of the EGR control logic model through a step-transient process. By comparing the engine performance results of the SISO coupled mean value model with those of the mean value model, it is observed that the SISO coupled mean value model achieves the desired target EGR rate within 10 s. The EGR rate is predicted to be similar to the response of volumetric efficiency. This process intuitively predicted the main performance parameters of the engine model through artificial neural networks.

Parton distribution functions and constraints on the intrinsic charm content of the proton using the Brodsky-Hoyer-Peterson-Saka approach

In this work, a new set of parton distribution functions taking into account the intrinsic charm (IC) contribution is presented. We focus on the impact of the EMC measurements on the large $x$ charm structure function as the strongest evidence for the intrinsic charm when combined with the HERA, SLAC and BCDMS data. The main goal of this paper is the simultaneous determination of the intrinsic charm probability ${P}_{c{\bar c/p}}$ and strong coupling $\alpha_s$. This allows us to study the interaction of these two quantities as well as the influence on the PDFs in the presence of IC contributions. By considering $\alpha_s$ which can be fix or free parameter from our QCD analysis, we find that although there is not a significant change in the extracted central value of PDFs and their uncertainties, the obtained value of ${P}_{c{\bar c/p}}$ change by factor 7.8\%. The extracted value of ${P}_{c{\bar c/p}}$ in the present QCD analysis is consistent with the recent reported upper limit of $1.93\%$, which is obtained for the first time from LHC measurements. We show the intrinsic charm probability is sensitive to the strong coupling constant and also the charm mass. The extracted value of the strong coupling constant $\alpha_s(M_Z^2) = 0.1191 \pm 0.0008$ at NLO is in good agreement with world average value and available theoretical models.

Formulation of Rectifier Numerical Average-Value Model for Direct Interface With Inductive Circuitry

The computational cost for the simulation of detailed models of machine-rectifier systems is expensive because of repetitive diodes switching. Average-value models (AVMs) of machine-rectifier systems have been developed that can alleviate the computational burden by neglecting the details of the switching of each individual diode while retaining the average characteristics. This paper proposes an alternative formulation of numerical AVMs of machine-rectifier systems, which makes direct use of the natural dynamic impedance of the rectifier without introducing low-frequency approximations or algebraic loops. By using this formulation, direct interface of the AVM is achieved with inductive circuitry on both the ac and dc sides allowing traditional voltage-in, current-out formulations of the circuitry on these sides to be used with the proposed formulation directly. This numerical AVM formulation is validated against an experimentally validated detailed model and compared with previous AVM formulations. It is demonstrated that the proposed AVM formulation accurately predicts the system's low-frequency behavior during both steady and transient states, including the cases where previous AVM formulations cannot predict accurate results. Both run times and numbers of time steps needed by the proposed AVM formulation are comparable to those of existing AVM formulations and significantly decreased compared with the detailed model.

Average value model of modular multilevel converters for switching overvoltage simulation in VSC‐HVDC grids

The first ±500 kV voltage source converter based high voltage direct current (VSC‐HVDC) grid in the world is being built in China. The half‐bridge submodule‐based modular multilevel converter (MMC), the direct current (DC) circuit breaker (DCCB), and the overhead line are used in the project. Switching overvoltage will occur after the DCCB turns off the short circuit current (SCC) in the VSC‐HVDC grid. The existing average value models (AVMs) of MMC still have some limitations in simulating such a kind of overvoltage. The main reason is that these AVMs cannot accurately simulate the working states of MMC in the VSC‐HVDC grid with DCCB. This article summarizes the possible cases of the action strategies between the DCCB and MMC in the VSC‐HVDC grid. Then, the working states of MMC in the different cases are analyzed. Corresponding to different working states, the limitations of existing AVMs are analyzed. The existing AVMs cannot simulate the alternating current or DC components in the arm current before being blocked and the charging process of the submodule capacitor after being blocked. An enhanced AVM is proposed in this article, which can fully simulate the MMC's working states. Simulation results show that the accuracy of the proposed AVM is highly improved over the existing AVMs. Meanwhile, the simulation efficiency of the proposed model is improved over the detailed equivalent model that is highly accurate but relatively low efficient for VSC‐HVDC grid simulations. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A Novel Critical Analysis Method of Homopolar Inductor Alternator for Preliminary Design in Capacitor Charge Power Supply

In order to realize quick preliminary design for capacitor charge power supply (CCPS), a novel critical analysis method of homopolar inductor alternator (HIA) is proposed in this paper. First, a specific base value system of CCPS is proposed for making the critical analysis method universally applied for different machine and charge parameters. Second, under the equivalent average-value phase model of HIA, a critical curve and a maximum power analysis method based on the curve are proposed. After that, an outline of the preliminary machine design under the critical analysis method is presented. Third, considering the salient rotor structure of HIA, under the equivalent average-value direct- and quadrature-axis (DQ) model of HIA, a critical map as well as its maximum power analysis method is proposed. In the end, for these two types of critical analysis method under different average-value models, each of their advantages and applications are discussed.

Circulating Current Reduction in MMC-HVDC System Using Average Model

Modular multilevel converters (MMCs) are quickly emerging as a suitable technology for a voltage-source converter-based high-voltage direct-current (VSC-HVDC) transmission systems due to its numerous advantages as reported in literature. However, for a large DC-network, MMCs require large numbers of sub-modules (SMs) and switches, which makes its modeling very challenging and computationally complex using electromagnetic transient (EMT) programs. Average Value Model (AVM) provides a relatively better solution to model MMCs by combining cells as an arm equivalent circuit. Circulating current is an important issue related to the performance and stability of MMCs. Due to circulating currents, power loss in a converter increases as root mean square (RMS) values of the arm current increases. The traditional method for inserting SMs in each arm is based on direct modulation, which does not compensate for the arm voltage oscillations, and generates circulating current in each leg of a three-phase MMC. This paper presents a new method for reducing the circulating current by adding 2nd and 4th harmonics in the upper and lower arm currents of an MMC. Less capacitor energy variations are obtained by the proposed method compared to traditional direct modulation methods. The proposed method is tested on a common symmetrical monopole (point-to-point) MMC-HVDC system using vector current control strategy in PSCAD/EMTDC software. Analytical and simulation results show the effectiveness of the new method in minimizing the circulating current and arm voltage oscillation reductions as compared to the direct modulation approach.

Parametric Average-Value Modeling of Thyristor-Controlled Rectifiers With Internal Faults and Asymmetrical Operation

Recently, a parametric average-value model (PAVM) has been presented for diode rectifiers with internal faults, which considers their asymmetrical operation by including the ac-side harmonics in both positive and negative sequences. In this letter, the PAVM methodology is extended and generalized for thyristor-controlled rectifiers with faults. The presented PAVM considers the firing angle of thyristors in its formulation. Using extensive computer studies, the proposed PAVM is verified to reconstruct the detailed model results even under dynamics of thyristor firing angle control under faulty conditions, while providing faster and more efficient simulations compared with the detailed model.

An improved averaged value model of MMC-HVDC for power system faults simulation

Detailed model (DM) of modular multilevel converter (MMC) brings about a high computational burden for electromagnetic transient (EMT) simulation. Therefore averaged value model (AVM) of MMC is proposed for fast simulation of large-scale multi-terminal HVDC system. No direct electrical contact exists between AC and DC system in conventional AVM and therefore the coupling relationship among electric quantities in fault analysis could not be accurately modelled. In order to solve the aforementioned problem, an improved AVM (IAVM) of half-bridge (SB) MMC topology is proposed. All capacitor voltages of AVM are constant and an arm is directly equivalent to a controlled voltage source. The proposed AVM can be applied for the DC faults and blocking conditions by introducing a group of switches connecting AC and DC sides. Two extra controlled voltage sources are introduced for correct DC voltage offset in AC voltages under DC line-to-ground (LTG) faults. Simulation results verify the accuracy and efficiency of the IAVM. IAVM could be implemented in commonly used software packages and is suitable for power system fault analysis.

An Averaged-Value Model of an Asymmetrical Hybrid Multi-Level Rectifier

The development and the validation of an averaged-value mathematical model of an asymmetrical hybrid multi-level rectifier is presented in this work. Such a rectifier is composed of a three-level T-type unidirectional rectifier and of a two-level inverter connected to an open-end winding electrical machine. The T-type rectifier, which supplies the load, operates at quite a low switching frequency in order to minimize inverter power losses. The two-level inverter is instead driven by a standard sinusoidal pulse width modulation (SPWM) technique to suitably shape the input current. The two-level inverter also plays a key role in actively balancing the voltage across the DC bus capacitors of the T-type rectifier, making unnecessary additional circuits. Such an asymmetrical structure achieves a higher efficiency compared to conventional PWM multilevel rectifiers, even considering extra power losses due to the auxiliary inverter. In spite of its advantageous features, the asymmetrical hybrid multi-level rectifier topology is a quite complex system, which requires suitable mathematical tools for control and optimization purposes. This paper intends to be a step in this direction by deriving an averaged-value mathematical model of the whole system, which is validated through comparison with other modeling approaches and experimental results. The paper is mainly focused on applications in the field of electrical power generation; however, the converter structure can be also exploited in a variety of grid-connected applications by replacing the generator with a transformer featuring an open-end secondary winding arrangement.

Flexible control of DC interlinked multiple MGs cluster

A cluster with multiple AC or DC microgrids (MGs) based on flexible DC interlinking and distributed energy storage systems is studied in this paper, which has been identified to have the following issues in terms of its primary control scheme: coordinated power control among slack terminals in the MG cluster, seamless operation mode transition for the interlinking converters and the common DC bus voltage control. A novel flexible control scheme that unifies the control of all the MGs only using local measured signals without further communications is proposed in this paper, which aims to improve control stability, and operation reliability and flexibility. Theoretical introduction and analysis are presented to explain the proposed control. The detailed average value model and small-signal model of an MG cluster with two AC MGs and two DC MGs are simulated, respectively, with the proposed control in power systems computer-aided design/electro-magnetic transient design and control to verify the effectiveness in control stability and flexibility enhancement, and the impact of control parameters on the small-signal stability of the considered cluster is analysed through root locus.

SimPower-based analysis and design of a hybrid wind–diesel-superconducting magnetic energy storage system for simultaneous frequency and voltage control

Power quality control in a stand-alone power system is a demanding task. For satisfactory operation, such systems are being augmented with fast-acting energy storage devices. In this article, a stand-alone wind–diesel system augmented with a small-rating superconducting magnetic energy storage system is considered for both reactive and real power balance. Suitable controllers are proposed which force the superconducting magnetic energy storage system to exchange both reactive and real power with the system under various perturbations. A simulation platform is developed in SimPower to virtually validate the system model and control design aspects. Superconducting magnetic energy storage system and its power electronic interface are represented by average value models and the various controller parameters are tuned using Genetic Algorithm. Simulation results show that both voltage and frequency of the system are improved.

Basic Ideas of Information Thermodynamics

We apply a certain unifying physical description of the results of Information Theory. Assuming that heat entropy is a thermodynamic realization of information entropy, we construct a cyclical, thermodynamic, average-value model of an information transfer chain as a general heat engine, in particular a Carnot engine, reversible or irreversible. A working medium of the cycle (a thermodynamic system transforming input heat energy) can be considered as a thermodynamic, average-value model or, as such, as a realization of an information transfer channel. We show that for a model realized in this way the extended II. Principle of Thermodynamics is valid and we formulate its information form.In addition we solve the problem of a proof of II. Principle of Thermodynamics. We state the relation between the term of information entropy, introduced by C. Shannon (1948), and thermodynamic entropy, introduced by R. Clausius (1850) and, further, explain the Gibbs paradox. Our way to deal with the given topic is a connection of both the mathematical definitions of information entropies and their mutual relations within a system of stochastic quantities, especially with thermodynamic entropies defined on an isolated system in which a realization of our (repeatable) observation is performed [it is a (cyclic) transformation of heat energy of an observed, measured system].We use the information description to analyze the Gibbs paradox, reasoning it as a property of such observation, measuring an (equilibrium) thermodynamic system. We state a logical proof of the II. P.T. as a derivation of relations among the entropies of a system of stochastic variables, realized physically, and, the Equivalence Principle of the I., II. and III. Principle of Thermodynamics is formulated.

Novel Average Value Model for Faulty Three-Phase Diode Rectifier Bridges

Rectifiers are widely used in industrial applications. Although detailed models of rectifiers are usually used to evaluate their performance, they are complex and time-consuming. Therefore, the Average Value Model (AVM) has been introduced to meet the demand for a simple and accurate model. This type of rectifier modeling can be used to simplify the simulations of large systems. The AVM of diode rectifiers has been an area of interest for many electrical engineers. However, healthy diode rectifiers are only considered for average value modeling By contrast, faults occur frequently on diodes, which eventually cause the diodes to open-circuit. Therefore, it is essential to model bridge rectifiers under this faulty condition. Indeed, conventional AVMs are not appropriate or accurate for faulty rectifiers. In addition, they are significantly different in modeling In this paper, a novel application of the parametric average value of a three-phase line-commutated rectifier is proposed in which one diode of the rectifier is considered open-circuited. In order to evaluate the proposed AVM, it is compared with experimental and simulation results for the application of a brushless synchronous generator field. The results clearly demonstrate the accuracy of the proposed model.

Flatness Based Optimal Control for Induction Machine Drives

Aim of this study is to derive an efficient method and problem formulation for optimal control of induction machines in variable speed drives, as used for example in electric vehicles. Induction machine dynamics are thus represented as a differential flat system and voltage source inverter losses are considered as an average value model. Based on the canonical form of the equivalent flat system, a nonlinear discrete finite horizon optimal control problem with a predefined torque and speed profile is introduced. If it is required to find a global solution, this problem can be efficiently solved by discrete dynamic programming or, when time is of essence, by means of sequential quadratic programming. The former is applied to a practical electric vehicle load cycle with limiting voltage constraints. The solution demonstrates how optimal control methods may be beneficial to drive design.

Temporal and spatial variation in the predictability of building occupancy

It has been widely acknowledged that occupants are one of the major contributors to account for the performance gap between predicted vs. actual building energy consumption. So far, occupancy has been represented as an average value model (deterministic), Markov chain model, survival model, or data mining model. Recent studies by Ahn et al. and Ahn & Park [1, 2] suggest a concept — the “random walk” occupancy model — that in random-walk driven buildings, occupancy is unpredictable. In this study, the authors investigate whether such predictability of occupancy is influenced by temporal and spatial measurement resolutions. For this purpose, occupancy data were recorded in six rooms in a library building for 16 days. Normalized Cumulative Periodograms and the Bartlett test were used to examine the predictability of occupancy. It was found that the occupancy of a small group (in this study, occupants numbering 18 or fewer) is unpredictable and can be regarded as a random-walk driven space. In contrast, when the number of occupants is equal to or more than a certain number (in this study, 27 people) either in a single large space or aggregated over multiple spaces (up to the whole-building level), occupancy becomes predictable. Additionally, it is shown that the predictability of the time-series occupancy data is not significantly influenced by varying the temporal resolution (sampling interval) between 5 and 60 min, but is dominantly driven by the number of occupants.

Average-Value Modeling of Diode Rectifier Systems Under Asymmetrical Operation and Internal Faults

Line-commutated rectifiers (LCRs) are extensively utilized in exciters of large electrical machines, ac–dc power systems of ships, vehicles, aircraft, and many other industrial applications. Efficient and accurate computer simulations are necessary to analyze various aspects of such systems under both normal and unbalanced/faulty operating conditions. The so-called parametric average-value modeling (PAVM) technique has been recently developed and shown to provide accurate and computationally efficient models of power-electronic converters for system-level simulations. In this paper, the PAVM methodology is extended to LCRs with internal faults. The new formulation considers the asymmetrical operation of rectifiers by including the ac-side characteristic (i.e., 5th, 7th, etc.) and non-characteristic (i.e., 2nd, 3rd, 4th, etc.) harmonics in both positive and negative sequences as well as dc components that may be present on ac variables. The proposed PAVM is verified by experimental measurements and detailed model and is demonstrated to have excellent accuracy under various operating modes and fault configurations.

Analytical Model of Small Hydropower Plant Working at Variable Speed

In this paper, a small hydropower plant working at variable speeds is analyzed. The energy conversion system contains a propeller turbine, which is coupled directly with a permanent magnet synchronous generator that is connected with a power system through a power electronic converter (PEC). The PEC that consists of a diode bridge rectifier and a DPC-SVM controlled inverter is described using the average value modeling method. The presented analysis considers only the fundamental harmonic component of ac currents and voltages. The system components are structured in the form of equivalent circuits that also include the power losses. The turbine model consists of the discharge and torque characteristics, which are approximated by analytical formulas based on the turbine hill diagram. The dynamic features represent the speed limiter of the guide vane governor and the mass of water, which fills the turbine chamber and the inlet and outlet pipes. The model is verified on a prototype hydropower plant with nominal power of 150 kW by the steady-state characteristic and a transient performance comparison. Such approach is found to minimize the necessary measurement, simplify the description, and provide satisfactory accuracy of the hydroset model.