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A Method of Reducing Switch Count in Three-Level NPC Inverter – Analysis in Steady States

Abstract

The proof of a concept for a new method of modulation has been presented which reduce switch count in a three-level neutral point clamped (3L-NPC) inverter. The method is an implementation of space vector modulation (SVM) by means of a prediction algorithm and sequences of transistors, which are not common in use. Those sequences make active use of clamping diodes of the inverter. The prediction algorithm analyzes possible sequences of transistors’ states and choose those which offers smaller switch count. Measurements of steady states were taken on prototype 3L-NPC.

Open access
Modified Scheme of Predictive Torque Control for Three-Phase Four-Switch Inverter-Fed Motor Drive with Adaptive DC-Link Voltage Imbalance Suppression

Abstract

Classical voltage space vector modulation techniques cannot be efficiently applied in four-switch three-phase voltage inverter-fed electrical drives due to a voltage offset in DC-link capacitors. The capacitor voltages imbalance is a result of a bidirectional current which flows in a phase of an electric motor that is connected to a DC-link capacitor midpoint. To overcome this problem which leads to an incorrect inverter voltage modulation or even can affect the DC-link capacitors, predictive control algorithms considering the voltage offset in DC-link capacitors have been developed. Despite the predictive methods are highly effective, they require to adjust the cost function weighting factors which is normally an inexplicit task. In this paper, an on-line tuning method of the weighting factor related to the capacitor voltages imbalance incorporated in the cost function of the predictive algorithm has been proposed. According to the proposed approach, the weighting factor is self-adjusted so that the DC-link capacitor voltages are stabilized as well as a high quality of the drive control is remained simultaneously, regardless of its operating point. The proposed strategy has been validated by using simulation model of the induction motor drive system.

Open access
An Overview of Design, Control, Power Management, System Stability and Reliability in Electric Ships

Abstract

With the fast development of power electronics techniques, electrification of shipboard power systems (SPS) is an unstoppable trend, and the concepts of electric ships (ESs) and all-electric ships (AESs) emerge. In order to meet the constantly increasing electricity demand in SPS, the medium voltage direct current (MVDC) SPS becomes a promising shipboard electrical network architecture. This paper aims to present a comprehensive review of the design, control, power management, system stability and reliability in ESs. The most recent technologies and academic achievements in these fields are discussed. In the near future, it is possible that the electric propulsion technology will be widely applied to various types of ships.

Open access
Problems of Designing State Feedback Controllers for Objects with Transfer Function Zeros

Abstract

The analysis of the influence of transfer function zeros on the parameters of state feedback controllers has been conducted. If a transfer function of a control object has zeros which are located closely to poles, the control object tends to singularity, and the influence of the input control signal to the states of the control object becomes weaker. The problem of the state feedback controller synthesis becomes ill-conditioned, which leads to the appearance of extremely large state feedback coefficients. In this case, the state feedback coefficients are sensitive to the parameters of the control object. As a result, the parametric robustness of the control system is reduced. Known methods of structural analysis of control object models are included amongst different methods of the numerical evaluation of the controllability and the observability, as well as methods of the model order reduction. These methods have some disadvantages, such as dependence on the state space representation form of the control object, ignoring a part of the control object model. In this paper, some ways of the preliminary structural analysis of the state space models of control objects have been proposed. The singular (Hankel) matrix is proposed for analyzing the properties of control object models. The singular matrix is the invariant characteristic of the control object in various state space forms and it characterizes the property of the control object completeness. As a result of the research, it was found that the coefficients of the state feedback controller are inversely proportional to the determinant of the singular matrix, and the determinant of the singular matrix is equal to the resultant of the transfer function polynomials. Thus the value of the determinant of the singular matrix depends on the location of the zeros of the transfer function. The method of the structural transformation (decomposition) of the control object for the defining the need of the reducing the order of the control object model is proposed.

Open access
State Observer for Doubly-Fed Induction Generator

Abstract

The purpose of this paper is to show a new state observer for doubly-fed generator. A proposed z-type observer algorithm based on mathematical model of doubly fed generator with additional variables treated as a disturbances has been used. A nonlinear multiscalar control method has been proposed to control active and reactive power of the generator. All analyses were verified by simulations and experiments tests.

Open access
Compensation Methods of Current and Speed Sensor Faults for a Vector Controlled Induction Motor Drive System

Abstract

Chosen speed and current sensor fault detectors for a vector controlled induction motor drive system have been presented. Systems based on the artificial intelligence (neural network) and simple algorithmic systems were analyzed and tested in various drive conditions. The influence of chosen sensor faults on performance of the drive system has been presented. The compensation strategy was proposed and tested. A fault tolerant drive, based on hardware redundancy, has been developed and presented. Simulation and experimental results are obtained in direct field oriented control algorithm (DFOC) on the laboratory set-up with rapid prototyping card Micro Lab Box DS1202 by dSpace.

Open access
DC Link Condition Monitoring Method for Two-Level AC/DC/AC Converters

Abstract

Power electronics is one of the most important elements of today’s industry. Many of converters applications are being considered as critical for plant production process. Offering enhanced functionality in modern AC drives is a way to gain a competitive advantage in power converters market. One of the values to the customers comes from low cost condition monitoring of critical equipment and from optimized maintenance costs. DC bus is one of the elements of power converters. Although the designers pay a lot of attention when designing DC-link circuit, breakdowns and failures of the DC circuit components can still happen. Unfortunately this means that the whole converter must be shut down in emergency mode to be repaired. Nowadays, monitoring of the bus capacitor is becoming one of the desired features from customer side, as well as from the converter manufacturer. Proposed approach presents a method which assures the online evaluation of the equivalent series resistance (ESR) of a DC-link capacitor. The ESR increase trend is an important indicator of accelerated aging process or incoming failure of the capacitor. The important feature of the proposed condition monitoring method is that it does not require any additional sensors. For estimation purposes already installed sensors and other internal converter’s signals are used. Particularly the method employs the DC-link voltage measurement with the DC-link current reconstruction.

Open access
Filtered Integral Sliding Mode Control in a Two-Mass Drive System

Abstract

The paper presents issues related to the application of filtered integral sliding mode control to a two-mass drive system. A classical control structure has been presented and its design procedure is shown in detail. The properties of the classical structure, in which the chattering phenomenon seems to be a big drawback, have been summarized. In order to eliminate this phenomenon, an output low- -pass filter has been proposed and the performance of this system has been tested. In order to improve its characteristics, an adaptive low-pass filter has been proposed. The bandwidth of the filter was changed on-line by the fuzzy system according to the current state of the plant. During the steady-states, the bandwidth is low to eliminate chattering effect, and during transients higher in order to ensure the fast dynamics of the plant.

Open access
Finite-Element Analysis of Accidental Energizing of an Off-Line Turbogenerator

Abstract

The computation of accidental energizing of an off-line turbogenerator has been conducted. Inadvertent energizing of a turbogenerator has become a particular issue in a power plant. The investigated case is three phase energizing. Great emphasis is placed on physical phenomena occurring in the rotor. The results of computations allow one to indicate the risks of damages of construction elements and can confirm the limits of the values set in dedicated protection devices.

Open access
Frequency Based Islanding Detection Methods in Power Electronic Converters

Abstract

Frequency based methods developed to detect an islanding condition in modern power grid structures have been discussed. The condition may occur in power grid lines to which additional energy sources with power electronic converters have been connected such as solar panels or wind turbines. It is a hazardous operating state for grid workers and devices connected to the islanded part of the grid. Such a state results from the inability to control amplitude and frequency of basic harmonic of the grid voltage. An islanding problem in a power grid with additional small energy sources has been discussed. A basic passive and active islanding detection method have been presented and compared with known frequency based algorithms, namely active frequency drift and active frequency drift with a positive feedback algorithm. Finally, a laboratory test of the proposed islanding detection methods in a three- -phase grid with an AC-DC converter has been conducted. To demonstrate differences between the tested methods, total harmonic distortion injected into the output converter current and detection time of islanding state have been measured.

Open access