Anticipating and Coordinating Voltage Control for Interconnected Power Systems

This paper deals with the application of an anticipating and coordinating feedback control scheme in order to mitigate the long-term voltage instability of multi-area power systems. Each local area is uniquely controlled by a control agent (CA) selecting control values based on model predictive control (MPC) and is possibly operated by an independent transmission system operator (TSO). Each MPC-based CA only knows a detailed local hybrid system model of its own area, employing reduced-order quasi steady-state (QSS) hybrid models of its neighboring areas and even simpler PV models for remote areas, to anticipate (and then optimize) the future behavior of its own area. Moreover, the neighboring CAs agree on communicating their planned future control input sequence in order to coordinate their own control actions. The feasibility of the proposed method for real-time applications is explained, and some practical implementation issues are also discussed. The performance of the method, using time-domain simulation of the Nordic32 test system, is compared with the uncoordinated decentralized MPC (no information exchange among CAs), demonstrating the improved behavior achieved by combining anticipation and coordination. The robustness of the control scheme against modeling uncertainties is also illustrated

Application of hybrid real-time simulation concept for modeling of HVDC back-to-back link

The application of new technologies considerably complicates the structure and the configuration of the electric grids, changes its dynamic proper-ties and creates new challenges to power system planning and operation for providing reliable and efficient use of intelligent electrical power systems. Considering of well-known specificity of electrical power systems operation, the modelling is the main way of effective solution of the problems. Hybrid simulation method is chosen as the one of the most appropriate approach. Adequate modeling of HVDC devices defines the inadmissible of separate simulation of different modes in equipment and electrical grids as a whole. It is proves by carried out research of hybrid simulation technique witch combine the different simulation approaches

Preventive countermeasures for transient stability-constrained power systems

peer reviewedA general transient stability control technique is applied to the design of preventive countermeasures consisting of rescheduling generators’ active power. The technique relies on SIME, a hybrid direct–time-domain method; and, like SIME, it preserves the accuracy of time-domain methods and their ability to handle any power system modeling, stability scenario and mode of instability. Its application to generation rescheduling may provide various patterns, able to comply with various operational specifics and strategies, as, for example, congestion management or available transfer capability calculations. The paper suggest how the technique may be shaped to choose automatically rescheduling patterns. A sample of such patterns are illustrated via simulations performed on an EPRI test system

Supervisory model predictive control of building integrated renewable and low carbon energy systems

To reduce fossil fuel consumption and carbon emission in the building sector, renewable and low carbon energy technologies are integrated in building energy systems to supply all or part of the building energy demand. In this research, an optimal supervisory controller is designed to optimize the operational cost and the CO2 emission of the integrated energy systems. For this purpose, the building energy system is defined and its boundary, components (subsystems), inputs and outputs are identified. Then a mathematical model of the components is obtained. For mathematical modelling of the energy system, a unified modelling method is used. With this method, many different building energy systems can be modelled uniformly. Two approaches are used; multi-period optimization and hybrid model predictive control. In both approaches the optimization problem is deterministic, so that at each time step the energy consumption of the building, and the available renewable energy are perfectly predicted for the prediction horizon. The controller is simulated in three different applications. In the first application the controller is used for a system consisting of a micro-combined heat and power system with an auxiliary boiler and a hot water storage tank. In this application the controller reduces the operational cost and CO2 emission by 7.31 percent and 5.19 percent respectively, with respect to the heat led operation. In the second application the controller is used to control a farm electrification system consisting of PV panels, a diesel generator and a battery bank. In this application the operational cost with respect to the common load following strategy is reduced by 3.8 percent. In the third application the controller is used to control a hybrid off-grid power system consisting of PV panels, a battery bank, an electrolyzer, a hydrogen storage tank and a fuel cell. In this application the controller maximizes the total stored energies in the battery bank and the hydrogen storage tank

A comparative study on improvement of image compression method using hybrid of DCT and DWT techniques with huffman encoding

Image is an important media used to visualize or represent a message in daily conversation between users device. Nowadays, there are many application that involve image processing such as security system, communication system and medical system where images are processed digitally. Image is mainly known for its large data capacity especially high resolution image. Thus, image compression is important to reduce storage size and achieve specific application goals. In this research, hybrid of Discrete Cosine Transform (DCT), Discrete Wavelet Transform (DWT) and Huffman compression technique is proposed. Stand-alone technique of DCT, DWT and Huffman are execute before hybrid all techniques together. Besides, the performance in determining the quality of image, compression ratio and computing time are carefully observed by evaluating the result of Mean Square Error (MSE), Power Signal to Noise Ratio (PSNR), Structural Similarity (SSIM), compression ratio and time of compression and decompression. It is found that the proposed hybrid technique able to reduce storage size with 3.72:1 compression ratio and short computing time with 5 second. The quality of image is slightly reduce compared to original image which are calculated based on MSE, PSNR and SSIM value with 52.74, 30.92 dB and 0.90, respectively. In conclusion, DWT technique has the ability in compressing image size within short time while DCT and Huffman are able to reduce data loss during compression and maintaining good quality of image. Therefore, DCT, DWT and Huffman method are combined together to support each other in producing good performance

A decision-making method for the operation flexibility enhancement of hybrid cascaded MTDC

To enable the integration of large-scale renewable energy, hybrid HVDC technology, which combines the technical advantages of LCC-HVDC and VSC-HVDC, is being gradually deployed in the power grid nowadays. The operation of the Wu-dong-de Hybrid DC Project and the Jian-su Hybrid cascaded MTDC Project has proved its advantages. However, for the simultaneous application of different converter station technologies in the system, the control strategies become complex. Issuing appropriate control instructions to ensure system stability according to operational requirements is an issue that cannot be ignored in decision-making. Even under abnormal conditions, when the topology changes due to various failure scenarios, reasonable decision-making and precise control instruction definitions are required. To achieve flexible planning of the MTDC system, this paper presents a decision-making method for control strategies of a hybrid cascaded MTDC system, which analyzes the control strategy combinations selected for normal and abnormal conditions of the MTDC system. In addition, a control instruction calculating method and decision-making process for precise control in normal and abnormal control conditions is proposed. Simulation results based on a five-terminal hybrid cascaded MTDC in PSCAD/EMTDC have verified the effectiveness of the proposed method

Energy dissipation of MMC-HVDC based onshore wind power integration system with FB-DBS and DCCB

With the development of high-voltage direct current (HVDC), modular multilevel converter (MMC) is seeking its application in onshore wind power integration. AC and DC faults are important issues for the wind power integration system, during which the wind generation system continuously provides wind power and the surplus power may cause overvoltage to sub-modules of MMC. This study focuses on the energy dissipation during AC and DC faults for the overhead-line MMC-HVDC system integrating large-scale wind power. A two-terminal MMC-HVDC system with permanent magnet synchronous generator based wind farm is studied. Hybrid DC circuit breakers (DCCBs) are employed to interrupt DC fault current and the method based on measuring the rate of change of DC line voltage is adopted to trip DCCBs. Also a full-bridge sub-module based dynamic braking system (FB-DBS) is implemented at the DC link to absorb the surplus wind power in case of AC or DC faults in the HVDC grid. To ride-through AC and DC faults without blocking IGBTs, the control of hybrid DCCB and the system fault ride-through strategies are properly designed. PSCAD/EMTDC simulations are shown to demonstrate theoretical analysis

Digital Solution of Power-flow Problems by Newton\u27s Method of Using a Hybrid Matrix

The last decade and a half has witnessed dramatic developments in the application of digital computers for solving power-flow problems. Previously these problems were analyzed on the direct analog computers called a-c calculating boards. With the enormous growth of the interconnected power systems during this period of time, digital computers established a distinct advantage over the analog computers for such reasons as: (a) Their ability to analyze large-size systems (with such features as automatic tap setting, automatic area interchange control, and control of reactive constraints of generators). (b) Elimination of human error in reading data and recording information on the system diagram. (c) Accessibility and economy in making only a few changes from the base case. (d) Availability of additional information such as the total transmission loss by easy extension of the power-flow program. The power-flow problem can be solved by both direct and iterative methods. In fact, all the methods are iterative in the sense that the load flow problem involves the solution of a system of nonlinear equations. However, the so-called direct methods employ the direct solution of a related linear system in the iterative algorithm, whereas the iterative methods use a scheme of successive displacements such as Gauss-Seidel. Newton\u27s method has an advantage over an iterative method because of its much faster (quadratic) convergence to a solution, thus saving computer time. The usual approach has been to use the bus admittance matrix for the network-defining equations. The purpose of this investigation has been to apply. Newton \u27s method for the solution of power-flow problems employing a hybrid matrix for the network-defining equations in order to confirm the possibility of affecting further saving in computer time. A sample 6-bus problem was solved on an. IBM 360 Model 40 computer with 1 28 K core memory with single precision programming for the precision indices of 1 x 10-3 and 1 x 10-S for real and reactive power mismatches at the busses. A double precision program was written for the precision index of 5 x l0-7. The hybrid matrix was formed by considering generator busses (1 and 2) as voltage-corrected and load busses (3 to 6) as current-corrected. Bus 1 is considered the swing bus

Investigation and control of a hybrid asymmetric multi-level inverter for medium-voltage applications

Power-electronic inverters are becoming popular for various industrial drives applications. In recent years also high-power and medium-voltage drive applications have been installed. However, the existing solutions suffer from some important drawbacks. Hybrid asymmetric multi-level inverters promise significant improvements for medium-voltage applications. This dissertation investigates such a hybrid inverter. To simplify the topology, some inverter parts are deprived of their feeding from the net and can only supply reactive power. The non-supplied intermediate-circuit capacitor voltages are inherently unstable and require a suitable control method for converter operation, preferably without influence on the load. Apart from normal operation, also converter start-up is an issue to consider, for which it is desirable to limit additional equipment. In this dissertation, we investigate the behaviour of this new inverter, and develop methods to obtain its reliable operation for the considered applications. These methods include modulation, voltage stabilization and start-up. We establish suitable models for their foundation. The principle achievement of this work is the development of a control method to stabilize a multitude of capacitor voltages which have no equilibrium state. Power balancing is performed by varying the common-mode output voltage, using a non-linear model-predictive controller. This method, which is new to power electronics, is applied to our hybrid asymmetric nine-level inverter driving an asynchronous motor. Computer simulations and measurements on an experimental drive system demonstrate stable behaviour in steady-state and during transients over the whole operating range. The obtained results prove the possible implementation of such a complex control algorithm for fast real-time operation. As second important accomplishment, this thesis proposes a start-up method that charges the non-supplied intermediate-circuit capacitors in parallel with the supplied ones, without additional equipment. Measurements show its successful application in the investigated drive system

Review of latent thermal energy storage systems for solar air-conditioning systems

Solar air-conditioning is an important approach to satisfy the high demand for cooling given the global energy situation. The application of phase-change materials (PCMs) in a thermal storage system is a way to address temporary power problems of solar air-conditioning systems. This paper reviews the selection, strengthening, and application of PCMs and containers in latent thermal storage system for solar air-conditioning systems. The optimization of PCM container geometry is summarized and analyzed. The hybrid enhancement methods for PCMs and containers, and the cost assessment of latent thermal storage system are discussed. The more effective heat transfer enhancement using PCMs was found to mainly involve micro-nano additives. Combinations of fins and nanoadditives, nanoparticles and metal foam are the main hybrid strengthening method. However, the thermal storage effect of hybrid strengthening is not necessarily better than single strengthening. At the same time, the latent thermal storage unit has less application in the field of solar air-conditioning systems, especially regarding heat recovery, because of its cost and thermal storage time. The integration of latent thermal storage units and solar air-conditioning components, economic analysis of improvement technology, and quantitative studies on hybrid improvement are potential research directions in the future