Voltage Direct Current Power System Research Articles

Investigation of the Behavior of Output Variables for Arbitrary Inputs to high Voltage Direct Current Power System Modeling Using Lyapunov Function Nonlinear Control Model

Background: Until now, a variety of proportional integral controllers and local controllers and predictive controller models have been used to stabilize VSC-HVDC transmission lines. One of the disadvantages of a linear model predictive control is that it is difficult and time consuming to adjust it for times when the disturbance entering the system is sudden. the goal is to monitor and take appropriate action to balance power and eliminate voltage or current that has exceeded the allowable limit. Methods: The way it works is that first, the DC current and the measured voltage of converter power source (VSC) is supplied based on various factors, and then the converters slowly begin to track the desired reference value, and this continues until the power sources adjusted according to current and voltage limits. Results: To achieve this goal, this paper examines recent articles on the modeling of VSC-HVDC power transmission systems and a comprehensive model has been chosen that has not been published for several months since its publication. Next, to control the se-lected model, the combined control strategy of nonlinear predictive based on the Lyapunov function is used to ensure the stability of the system. Conclusion: The results of the implementation of this control strategy on the HVDC power transmission system model in MATLAB soft-ware express the ability of this controller to track the reference input values.

Modeling and Control of the Isolated DC–DC Modular Multilevel Converter for Electric Ship Medium Voltage Direct Current Power System

The dc–dc modular multilevel converter (dc–dc MMC) with a medium-frequency ac-link transformer is a promising candidate for the modern electric ship medium voltage dc power system to provide galvanic isolation, flexible voltage regulation, and fault ride through ability. However, the steady states and dynamics of such an isolated dc–dc MMC are rather complicated because it contains many state variables. Moreover, the on-ship requirements further complicate the system design. This paper thus proposes the modeling and control of such a dc–dc MMC. Based on the fact that such a dc–dc MMC is controlled by the phase-shifted operation, the fundamental period averaging (FPA) method is applied to obtain the steady-state and small-signal models, and based on the on-ship requirements, the modulation index control as well as the simple but efficient competitive dual closed loops (a voltage loop for normal condition and a current loop for overload condition) are designed. It is proved that the FPA method can preserve the necessary model information about the dc–dc MMC, and the proposed controllers can be well designed based on the steady-state and small-signal FPA models by compromising the on-ship requirements. The analysis and design results are verified by the simulations and experiments.

Notional all-electric ship systems integration thermal simulation and visualization

This work presents a simplified mathematical model for fast visualization and thermal simulation of complex and integrated energy systems that is capable of providing quick responses during system design. The tool allows for the determination of the resulting whole system temperature and relative humidity distribution. For that, the simplified physical model combines principles of classical thermodynamics and heat transfer, resulting in a system of three-dimensional (3D) differential equations that are discretized in space using a 3D cell-centered finite volume scheme. As an example of a complex and integrated system analysis, 3D simulations are performed in order to determine the temperature and relative humidity distributions inside an all-electric ship for a baseline medium voltage direct current power system architecture, under different operating conditions. A relatively coarse mesh was used (9410 volume elements) to obtain converged results for a large computational domain (185m×24m×34m) containing diverse equipment. The largest computational time required for obtaining results was 560 s, that is, less than 10 min. Therefore, after experimental validation for a particular system, it is reasonable to state that the model could be used as an efficient tool for complex and integrated systems thermal design, control and optimization.

Design Sensitivity Analysis Applied to High Temperature/High Voltage Direct Current Power Systems

In this paper, the finite element algorithm is implemented to calculate field and temperature variation in high voltage direct current cylindrical cables. Such cables contain joins and interconnects which result in physical discontinuities where strong fields may be present, resulting in dielectric breakdown during power switching events. To minimize the possibility of catastrophic failure, design sensitivity analysis is applied to determine a geometry that minimizes the field variation within the region of interest. Since the material properties in these systems demonstrate both temperature and field dependencies, the resulting nonlinearities are considered in the formulation.