Concept Of Voltage Control Research Articles

Enhanced Predictive Torque Control for Three-Level NPC Inverter-Fed PMSM Drives Based on Optimal Voltage Magnitude Control Method

The major drawback of conventional predictive torque control (PTC) is that it fixes the magnitude of the reference voltage vector (VV) to 70%. This limitation results in large torque and flux ripples and slow dynamic response, especially when the permanent magnet synchronous motor operates in low-speed regions. A promising approach for reducing torque and flux ripples is by replacing the two-level inverter with a three-level neutral-point-clamped (NPC) inverter. Nevertheless, because of the elimination of zero VV during torque decrement in a conventional PTC, a large torque ripple appears in the low-speed region. In addition, high-speed operation is not applicable unless more dc-link is injected. To solve these problems, an effective, creative, and low-complex PTC based on a reference voltage vector magnitude control method (RVVCM) is proposed in this article. The proposed PTC effectively minimizes torque and flux ripples by utilizing only the required magnitude of reference VV of the three-level NPC inverter based on the variable voltage control concept. Furthermore, the dynamic response of the torque is improved by applying the full magnitude of applied VV. Simulation and experimental results are presented to validate the effectiveness of the proposed RVVCM-based PTC algorithm.

Analysis and systematic comparison of concepts for voltage control with inverted-based prosumer devices

The German energy transition resulting in increased penetration of renewable energy generation and electrification raises the load on the electrical power grid. Especially the low voltage grid with rising shares of prosumer devices like photovoltaic systems and electric vehicles is affected by severe deviations of the bus voltage from nominal values potentially violating the limits of the voltage band. In this paper several voltage control concepts are analysed with a focus on supply quality, additional grid load, and losses. The concepts presented are implemented and analysed within simulative investigations. Main results are a positive effect of all concepts on bus voltages with no concept being superior in all key figures. The reactive power feed-in based on the current grid status using the Q(U) method presents the best trade-off for photovoltaic systems with regard to impact on critical voltage values and negative effect on the grid and prosumer devices. While a combination of Q(U) and P(U) is the most appropriate option for consumption devices, voltage control concepts for battery storage systems do not seem to have any significant impact. Adjusting the installation specifications of grid operators based on these results could mitigate critical grid situations in congested grids.

Optimal Voltage Control in MV Network with Distributed Generation

The article presents the concept of voltage control in a medium-voltage network, using the classical control of a HV/MV (High Voltage/Medium Voltage) transformer and active participation of distributed generation sources. The proposed solution is based on the results of the optimization process. The objective function is considered as a single-criterion—the voltage quality indicator or value of power losses in the network, and optionally as two-criteria (voltage quality and losses combined, with appropriately selected weight factors). The analysis carried out for random selection of independent variables, using the original heuristic algorithm, indicated a very high efficiency of the proposed control process, compared to the traditional approach. A significant improvement in the voltage quality index and reduction of losses was found, which justifies the advisability of looking for new solutions in the field of voltage control in MV networks, taking into account active participation of distributed generation.

Towards modular composition of agent-based voltage control concepts

In the last years, diverse agent-based concepts for voltage control in distribution grids were presented in literature. All these approaches are developed manually. Up to now, no tailoring approach has been presented to adapt these concepts to different – likewise specific – grid situations. As the effectiveness of voltage control schemes is highly dependent on the specific grid situation, this can result in multiple problems with regard to performance, applicability and expandability of the proposed agent-based control. The ideal case would be a customizable agent system that is automatically tailored to the grid it shall be applied to, considering its specific characteristics. To address that complex task, this paper proposes an approach for the modular composition of voltage control agents by recombining existing concepts from literature to new fully functional agent systems. This approach makes the first move to an optimized and scenario-specific creation of agent-based control systems that are specifically designed and automatically tailored to a given power system.

On the Classification of Low Voltage Feeders for Network Planning and Hosting Capacity Studies

The integration of large amounts of generation into distribution networks faces some limitations. By deploying reactive power-based voltage control concepts (e.g., volt/var control with distributed generators), the voltage rise caused by generators can be partly mitigated. As a result, the network hosting capacity can be accordingly increased, and costly network reinforcement might be avoided or postponed. This works however only for voltage-constrained feeders (opposed to current-constrained feeders). Due to the low level of monitoring in low voltage networks, it is important to be able to classify feeders according to the expected constraint in order to avoid the overloading risk. The main purpose of this paper is to investigate to which extent it is possible to predict the hosting capacity constraint (voltage or current) of low voltage feeders on the basis of a large network data set. Two machine-learning techniques have been implemented and compared: clustering (unsupervised) and classification (supervised). The results show that the general performance of the classification or clustering algorithms might be considered as rather poor at a first glance, reflecting the diversity of real low voltage feeders. However, a detailed analysis shows that the benefit of the classification is significant.

New challenges to wind energy voltage control. Survey of recent practice and literature review

Implementing sophisticated voltage controls of wind farms may provide manifold benefits such as reducing losses of the distribution network (DNET) and harvesting network (HNET), increasing the wind hosting capacity of transmission networks (TNETs) and reducing wind curtailments. However, it represents an enormous challenge since wind energy is dispersed increasing the complexity of the required centralised control systems. This study contains a comprehensive state-of-the-art review of the huge research that is available in the literature in order to foster the participation of on-shore wind energy in voltage control. The current situation is described by the actual technological developments of control devices and the regulatory framework of a set of European countries with high wind penetration figures. A classification of key wind voltage control concepts will be proposed in order to understand and organise the available literature references. The state-of-the-art review covers the integration of wind energy through DNETs, smart grids and dedicated HNETs into the TNET, covering research from a steady state and also dynamic perspective. The new requirements of theTransmission system operators tend to suggest that wind farms should have a similar performance compared with conventional plants. Thus, in this study, special attention will be given to the literature review of HNETs since it has been the most promising alternative of integrating wind voltage control into the existing transmission grid hierarchical control schemes. A set of relevant field experiences and international projects will be described, showing some effort to implement academic research into practice.

Multifunctional Megawatt-Scale Medium Voltage DC Test Bed Based on Modular Multilevel Converter Technology

Recent developments in modular multilevel converters (MMCs) provide new opportunities for medium-voltage dc (MVDC) systems for all-electric ship design and offshore wind farms. The Center for Advanced Power Systems at Florida State University has recently commissioned a new MVDC power hardware-in-the-loop laboratory rated at 5 MW at dc voltages from 6 to 24 kV. The new lab features four individual MMCs, each composed of 36 full-bridge cells, capable of delivering 210 A at any voltage in the range of 0–6 kV. This paper describes the entire system in detail, including the advanced current and voltage control concepts along with the state-of-the-art digital control hardware. Selected commissioning results are shown, which demonstrate the performance of the system under dynamic conditions and provide comparison with simulations obtained from a corresponding controller hardware-in-the-loop setup. The results indicate that an MMC-based MVDC system is a strong candidate for the ship power system because of its excellent fault management capability. The setup can be used for the understanding and design of fast fault management schemes in a breakerless MVDC system in the future all-electric ship.

Investigation on the reproducibility of optical constants of TiO_2, SiO_2, and Al_2O_3 films, prepared by plasma ion assisted deposition

Titanium dioxide, aluminum oxide, and silicon dioxide layers have been prepared by plasma ion assisted electron beam evaporation employing the Advanced Plasma Source (APS). The refractive indices have been determined by spectrophotometry in order to quantify their reproducibility. Standard deviations in the refractive index turned out to be highest for titanium dioxide, and lowest for silicon dioxide. The refractive index reproducibility of titanium dioxide could be improved by replacing the commonly used BIAS voltage control concept by a novel alternative approach concerning ion beam power, termed JE. All these findings are discussed in terms of a model that considers the real oxide film as a binary mixture of a solid fraction with a small amount of pores, within the limits provided by the Wiener bounds.

Design and Analysis of a Slope Voltage Control for a DFIG Wind Power Plant

This paper addresses a detailed design of a wind power plant and turbine slope voltage control in the presence of communication delays for a wide short-circuit ratio range operation. The implemented voltage control scheme is based upon the secondary voltage control concept, which offers fast response to grid disturbances, despite the communication delays, i.e., this concept is based on a primary voltage control, located in the wind turbine, which follows an external voltage reference sent by a central controller, called secondary voltage control, which is controlling the voltage at the point of connection with the grid. The performance has been tested using PSCAD/EMTDC program. The plant layout used in the simulations is based on an installed wind power plant, composed of 23 doubly fed generator wind turbines. The resulting performance is evaluated using a compilation of grid code voltage control requirements. The results show that fast response to grid disturbances can be achieved using the secondary voltage control scheme, and the fulfillment of the design requirements can be extended for a wide range of short-circuit ratios.

PFC Bridge Converter for Voltage-controlled Adjustable-speed PMBLDCM Drive

In this paper, a buck DC-DC bridge converter is used as a power factor correction (PFC) converter for feeding a voltage source inverter (VSI) based permanent magnet brushless DC motor (PMBLDCM) drive. The front end of the PFC converter is a diode bridge rectifier (DBR) fed from single phase AC mains. The PMBLDCM is used to drive the compressor of an air conditioner through a three-phase voltage source inverter (VSI) fed from a variable voltage DC link. The speed of the air conditioner is controlled to conserve energy using a new concept of voltage control at a DC link proportional to the desired speed of the PMBLDC motor. Therefore, VSI operates only as an electronic commutator of the PMBLDCM. The current of the PMBLDCM is controlled by setting the reference voltage at the DC link as a ramp. The proposed PMBLDCM drive with voltage control-based PFC converter was designed and modeled. The performance is simulated in Matlab-Simulink environment for an air conditioner compressor load driven through a 3.75 ㎾, 1500 rpm PMBLDC motor. To validate the effectiveness of the proposed speed control scheme, the evaluation results demonstrate improved efficiency of the complete drive with the PFC feature in a wide range of speed and input AC voltage.

Three-Phase Y-Rectifier Cyclic 2 Out of 3 DC Output Voltage Balancing Control Method

A three-phase Y-rectifier is formed by the star connection of single-phase unity-power-factor rectifier systems and represents a highly interesting concept for the realization of the input stage of high-power telecommunications power supply modules using established single-phase technology. However, for stable operation, control and balancing of the independent DC output voltages of the phase rectifier systems is required. A novel, easy-to-implement DC output voltage control concept is proposed in this paper. Here, the mean value of all three DC output voltages is controlled, and, in addition, always two out of the three DC voltages are compared and balanced. The basic operating principle of the control is described, the theoretical limit for the admissible asymmetric loading of the DC voltages is calculated, and numeric results for a 10-kW system are given. Finally, the theoretical considerations are verified by measurements on a 3 times1 kW Y-rectifier prototype.