Commutation Method Research Articles

Analysis of Hybrid Modular Multilevel Rectifier Operated at Nonunity Power Factor for HVDC Applications

Hybrid modular multilevel rectifier (HMMR) is a type of unidirectional modular voltage source converter (VSC) that has been proposed for the high-voltage (HV) dc transmission applications. Compared to the modular multilevel converter (MMC), up to 50% of the submodules (SMs) and capacitors can be replaced by the simple HV line-frequency diode stacks at unity power factor (PF). The nonunity PF operation is also favored for the rectifier station to support the grid. Therefore, this article proposes two new current commutation methods for HMMR to reduce the SM number at nonunity PF. In addition, an average model is given to reveal the inherent power flow relationship of HMMR. It is found that part of the active power is delivered from ac to dc side through the diode directly, which reduces the energy storage requirement. The performance of HMMR is also evaluated and compared with MMC. Both methods can successfully decrease the 30% low voltage devices. Method 1 can reduce 32% capacitor and method 2 achieves 52% reduction. The feasibility of the proposed converter is verified by the simulation results from a 200-kV 200 MVA HVdc model. Finally, a scale-down 400-V HMMR prototype is developed to validate the effectiveness of the proposed control scheme.

A soliton solution of the DD-Equation of the Murnaghan’s rod via the commutative hyper complex analysis

In this study, we apply the commutative hyper complex algebraic method to solve analytically the Doubly Dispersive Equation (DDE) in (1+1)-D, for the strain waves propagating in a cylindrical circular rod in complex polymer systems, within the framework of analytical mechanics. Relying on the stability of the solutions via phase portrait analysis, the resulting solitary waves obtained by applying the complex Jacobi elliptic function method, show the compression characters in the non-linearly elastic materials tackled in our article. The estimated Lagrangian density confirms the potential well criterion of the physical situation. Some comparisons are made with recent models conducted by several authors.

Decay Estimates for Unitary Representations with Applications to Continuous- and Discrete-Time Models

We present a new technique to obtain polynomial decay estimates for the matrix coefficients of unitary operators. Our approach, based on commutator methods, applies to nets of unitary operators, unitary representations of topological groups, and unitary operators given by the evolution group of a self-adjoint operator or by powers of a unitary operator. Our results are illustrated with a wide range of examples in quantum mechanics and dynamical systems, as for instance Schrödinger operators, Dirac operators, quantum waveguides, horocycle flows, adjacency matrices, Jacobi matrices, quantum walks or skew products.

A comparison between six-step and sine-wave commutation methods for brushless direct current motors

<p>This research is focused on the design and implementation of an electronic circuit for commuting a brushless direct current (BLDC) motor and its data acquisition system, as well as conducting experiments on them. We propose a drive circuit using two modules, each consist of a dual H-bridge, that are cheap and can be easily obtained. Two different commutation methods, namely six-step and sine-wave commutations, are applied. Each of these implements a different way for its open-loop speed control, i.e., a voltage-controlled-current-source is implemented along with the six-step commutation and the step duration approach is implemented along with the sine-wave commutation. The experiment data are acquired using a developed desktop application. Some experiment results lead us to find that, on its own, both commutation methods have a narrow range of speed. Nevertheless, if both methods are used together, this range can be increased. Also, the relation between speed and its controlling signals for both methods are shown.</p>

A new commutator method for averaging lemmas

A new commutator method for averaging lemmas

ВЕКТОРНОЕ УПРАВЛЕНИЕ ЭЛЕКТРОПРИВОДОМ НА ОСНОВЕ ВЕНТИЛЬНОГО ДВИГАТЕЛЯ С ДИСКРЕТНОЙ КОММУТАЦИЕЙ ОБМОТКИ

The article considers the possibility of implementing phase vector control (FVU) of a synchronous motor with permanent magnets in the thyratron motor mode. The characteristics of the FVU with three methods of discrete commutation of the three-phase winding are considered: six-stroke 120- and 180-degree and twelve-stroke 150-degree. A comparative assessment of the efficiency of the PVF is carried out in terms of expanding the range of implemented mechanical coordinates and energy indicators, both with different methods of discrete switching and with respect to sinusoidal power supply. It is shown that 120-degree switching is the most advantageous in terms of energy indicators. However, with it, the values of the maximum achievable speeds and moments weakly depend on the angle of commutation θ, therefore, operation is recommended at a constant θ = 0, corresponding to the efficiency value close to the maxi­mum in a wide range of speeds. With 180-degree commutation, the FVU allows you to adjust both the maximum speed and the maximum torque. However, with small values of the relative inductance of the winding, which refers to the ratio of inductive resistance to active, this method of regulation is ineffective due to low efficiency and is inferior in this indicator to both 120-degree commutation and the case of sinusoidal power supply. As the relative inductance increases, the difference between the case of sinusoidal power supply and 180-degree switching decreases. The use of 150-degree commutation allows, on the one hand, to increase efficiency while maintaining the ability to adjust coordinates, on the other hand, reduces the pulsation of the motor torque, expanding the possible scope of the drive.

СРАВНИТЕЛЬНАЯ ОЦЕНКА СПОСОБОВ ПИТАНИЯ СДПМ В РЕЖИМЕ ВЕНТИЛЬНОГО ДВИГАТЕЛЯ

The article provides a comparative assessment of various ways of powering a synchronous motor with permanent magnets (PMSM) in the mode of a thyratron motor (TM). Numerically, on analytical and computer models, mechanical ω = f(M), the dependence of speed on electromagnetic torque, and energy ηэ = f(M), the dependence of elec-tromagnetic efficiency are calculated from the moment, the characteristics of the motor with sinusoidal power supply and discrete switching with different values of the relative inductance of the winding. Moment pulsations are investigated. The three most common methods of discrete degree commutation are considered – 120, 180 and 150. It is shown that discrete 120 degree commutation provides the highest value of ηэ in comparison with other methods, and the mechanical character-istics are approximately the same in appearance with different power supply methods. The study of moment pulsations has shown that discrete switching without additional measures cannot compete in this indicator with the case of sinusoidal power supply, which theoretically has zero moment pulsations. However, the use of 150 degree commutation makes it possible to significantly reduce them, bringing them closer to 2…3 %. Curves are given that allow an approximate estimate of the expected moment pulsations for all discrete switching methods. Practical recommendations on the choice of the method of powering the PMSM are given.

Approximate solutions to second-order parabolic equations: Evolution systems and discretization

<p style='text-indent:20px;'>We study the discretization of a linear evolution partial differential equation when its Green's function is known or well approximated. We provide error estimates both for the spatial approximation and for the time stepping approximation. We show that, in fact, an approximation of the Green function is almost as good as the Green function itself. For suitable time-dependent parabolic equations, we explain how to obtain good, explicit approximations of the Green function using the Dyson-Taylor commutator method that we developed in <i>J. Math. Phys.</i> <b>51</b> (2010), n. 10, 103502 (reference [<xref ref-type="bibr" rid="b15">15</xref>]). This approximation for short time, when combined with a bootstrap argument, gives an approximate solution on any fixed time interval within any prescribed tolerance.</p>

Development and Design of a Starter-Generator for a Turbofan Engine

The purpose of this article is to develop a starter-generator (STG) with reduced supply voltage of 27 V for a turbofan engine. The analysis has showed that the existing design schemes of the STG are mainly designed for high voltage, due to the complexity of the implementation of the power converter. As a result of the conducted research, a method for increasing efficiency has been proposed by modifying the phase commutation control method, and a power converter topology that allows all the operating modes of the designed STG has been developed. In addition, in this article, a comparison of two methods of phase commutation, traditional and with a modified angle has been presented and its result shows the difference and the prospects, as well as the effectiveness of the chosen solution. Thermal calculations have confirmed the possibility of providing all the necessary operating modes, in which the temperature of the active elements has not exceeded the permissible values. The resulting technical solution of the STG has a mass of the active part of no more than 6.09 kg, and it allows providing an output power of up to 40 kW in all the operating modes, at frequencies from 1000 rpm to 12367 rpm.

Congruence and geometric feature-based commutative encryption-watermarking method for vector maps

The commutative encryption-watermarking (CEW), in which the encryption and watermarking are distinct and commutative, has become a promising method for protecting data security. For vector maps, current methods combine encryption with watermarking directly, but cannot satisfy the CEW properties. For example, the watermark embedding and encryption are not commutative and lack flexibility. Considering the essential characteristics of vector maps, this paper proposes a CEW method based on the congruence relationship and geometric feature for vector maps. In the proposed CEW method, the angles and the distance ratios are selected as the geometric features which provide separate spaces for cryptography and watermarking operations. They are encrypted by making the original values and encrypted values congruent. At the same time, the watermark is embedded into their residue. As the residue keeps invariant under congruence operations, the watermark can be extracted from either the plaintext or the ciphertext. Experiments are conducted to verify the commutativity between encryption and watermarking. Besides, the superiority in terms of watermark robustness and capacity of the proposed method has been also compared with other encryption-combining-watermarking methods for vector maps.

Proposed Commutation Method for Performance Improvement of Brushless DC Motor

This study focused on the efficiency improvement and acoustic noise reduction of brushless DC (BLDC) motors by reducing current harmonics using a novel BLDC commutation method. To achieve these goals, we designed an improved 150° commutation method for a three-phase permanent magnet BLDC motor that can improve the current waveform. Although the 120° commutation method is generally employed for BLDC motors, an improved 150° commutation method is introduced to operate the BLDC with increased efficiency and acoustic noise similar to a brushless AC motor. This study investigated the attributes of various commutation methods, both theoretically and experimentally, to determine the optimal commutation method. The results of this study indicate that the improved 150° commutation method is optimal in terms of harmonic attributes and reduced torque ripple, allowing it to improve motor efficiency and reduce acoustic noise.

Current-Source Inverter Integrated Motor Drives Using Dual-Gate Four-Quadrant Wide-Bandgap Power Switches

Four-quadrant (FQ) switches that have both bidirectional current and reverse-voltage blocking (RVB) capabilities are appealing candidates for use in current-source inverters (CSI) to significantly reduce the switch conduction losses. However, the FQ characteristics of these switches can create problems during switching events by causing transient overcurrent pulses that damage the inverter. Commutation methods for FQ switches in CSI topologies that address these challenges are presented in this article. Several key aspects of the performance and implementation of these commutation methods are explored for a high-power density 3 kW integrated motor drive incorporating both a current-source active rectifier and inverter stage that has been developed using these FQ switch methods. Experimental results demonstrate the benefits of implementing these commutation methods in CSIs that use FQ switches. The benefits include substantial efficiency improvement compared to the conventional CSI implemented with series power diodes as well as reduced mass and volume of passive components due to the high switching frequency (100 kHz).

Bands of pure absolutely continuous spectrum for lattice Schrödinger operators with a more general long range condition

Commutator methods are applied to get limiting absorption principles for the discrete standard and Molchanov–Vainberg Schrödinger operators, Δ + V and D + V on ℓ2(Zd), with emphasis on d = 1, 2, 3. Considered are electric potentials V satisfying a long range condition of the following type: V−τjκV decays appropriately at infinity for some κ∈N and all 1 ≤ j ≤ d, where τjκV is the potential shifted by κ units on the jth coordinate. More comprehensive results are obtained for small values of κ, e.g., κ = 1, 2, 3, 4. We work in a simplified framework in which the main takeaway appears to be the existence of bands where a limiting absorption principle holds, and hence, pure absolutely continuous spectrum exists. Other decay conditions at infinity for V arise from an isomorphism between Δ and D in dimension 2. Oscillating potentials are examples in application.

The binary Darboux transformation revisited and KdV solitons on arbitrary short‐range backgrounds

AbstractIn the KdV context, we revisit the classical Darboux transformation in the framework of the vector Riemann–Hilbert problem. This readily yields a version of the binary Darboux transformation providing a short‐cut to explicit formulas for solitons traveling on a wide range of background solutions. Our approach also links the binary Darboux transformation and the double commutation method.

Оптимизация пульсаций момента двигателя в электроприводе с прямым управлением

The article discusses the features of the synthesis of a hybrid method for commutation of a three-phase inverter in a classic version of drives with direct torque control (DTC), which involves the use of relay characteristics in the flux- and torque control blocks. It is proved that the output voltage of a converter based on a B6-inverter formed by only six basic vectors (excluding the zero vector) limits further optimization of flux- and torque ripples in the electrical motors. It has also been proven that with the classical drives with direct torque control, the torque ripples on the motor shaft are indeed higher than in systems with pulse width modulation. An analysis of the method was carried out which could allow reducing the amplitude of the torque ripples when drives with direct torque control are applied for motors supplied with only basic vectors of the inverter due to the modified (hybrid) method of inverter commutation. The conditions under which the hybrid control method of the inverter is really capable of reducing the amplitude of the motor flux- and torque ripples are considered. Based on the analysis of the proposed solution, the law of hybrid control of the inverter is presented by means of the formation of additional vectors of its output voltage via basic vectors of the inverter. The advantages of the method include the simplicity of drive control under development or in the existing drive control system, the implementation of which is carried out exclusively by a software product. With the absence of iterative methods of mathematics, the resources of microprocessor control units are reduced, which makes this method even more attractive in low-budget electrical drives that do not claim to be "high-end" of control blocks. The oscillograms are shown of a flux and current of motor with direct torque control motor application only with six base vectors of the output voltage of a semiconductor inverter and a drive with direct torque control by the hybrid method with additional voltage vectors based on the basic vectors of the inverter.

Performance analysis of three-phase hybrid fault current limiter with one commutation circuit

This paper describes the development of a hybrid fault current limiter and interrupting device (HCLID) suitable for low and medium voltage AC or DC industrial installations. By substituting the three-commutation circuit on each phase in HCLID with one controlled commutation circuit, the commutation capacitance, let-through current, volume, and weight can be reduced. Reducing the number of commutations circuit aims at decreasing the initial cost of the (HCLID), which is mainly the focus of the commutation capacitors. The fault current commutation method is introduced as a new current limiting means. This technique is based on the injection of counter-current to the main contacts of the circuit breaker for very fast-breaking of fault currents. The HCLID consists of two electric circuits, one to force the fault current down to zero (commutation circuit) and the other to establish the electro-dynamic force to separate the main contacts. The proposed control method is easy to implement and has a low initial cost. The simulated results presented in the research confirm the validity of the new HCLID over traditional methods. Experimental tests were carried out to validate the proposed method. Simulations and experimental results prove the feasibility of the new HCLID.

Spectral and scattering theory of one-dimensional coupled photonic crystals

We study the spectral and scattering theory of light transmission in a system consisting of two asymptotically periodic waveguides, also known as one-dimensional photonic crystals, coupled by a junction. Using analyticity techniques and commutator methods in a two-Hilbert spaces setting, we determine the nature of the spectrum and prove the existence and completeness of the wave operators of the system.

New Explicitly Diagonalizable Hankel Matrices Related to the Stieltjes–Carlitz Polynomials

Four new examples of explicitly diagonalizable Hankel matrices depending on a parameter \(k\in (0,1)\) are presented. The Hankel matrices are regarded as matrix operators on the Hilbert space \(\ell ^{2}(\mathbb {N}_{0})\) and the solution of the spectral problem is based on an application of the commutator method. Each of the Hankel matrices commutes with a Jacobi matrix which is related to a particular family of the Stieltjes–Carlitz polynomials. More examples of explicitly diagonalizable structured matrix operators are obtained when taking into account also weighted Hankel matrices.

Current-Fed Isolated Three-Phase Matrix-Type Grid Inverter With Soft-Switching Capability

The grid inverters play an important role in renewable energy systems, transferring the dc power to the ac grid. Galvanic isolation is usually needed between the dc source and the grid due to safety reasons and grounding leakage current mitigation. In this article, a soft-switching isolated grid inverter is proposed based on the current-fed matrix-type configuration. The topology of this converter is composed of a current-fed H-bridge on the side of dc source and a direct matrix converter on the grid side, which are linked by a high-frequency transformer. The current-fed H-bridge on the primary-side can smooth the dc-source current and control the dc-source current directly. The avoidance of dc-link energy-storage element in the single-stage matrix converter can prolong the system's life. A space-vector-modulation-based soft-switching scheme is proposed for the matrix converter on the grid side and a model-based commutation method is adopted in the current-fed H-bridge on the dc side. With the proposed modulation methods, the soft switching can be realized for all devices in the converter. Finally, a laboratory prototype of the proposed converter has been built to verify the effectiveness of the proposed method experimentally.

Capacitor Commutation Method for MVDC Hybrid Circuit Breakers

The medium voltage DC (MVDC) type system can connect multiple terminals to a common MVDC bus, so it is possible to connect several renewable DC power sources to the common MVDC bus, but a DC circuit breaker is needed to isolate short circuit accidents that may occur in the MVDC bus. For this purpose, the concept of a hybrid DC circuit breaker that takes advantage of a low conduction loss contact type switch and an arcless-breaking semiconductor switch has been proposed. During break the hybrid switch, a dedicated current commutation device is required to temporarily bypass the load current flowing through the main switch into a semiconductor switch branch. Existing current commutation methods include a proactive method and a reverse current injection method by a LC (Inductor-capacitor) resonant circuit. This paper proposes a power circuit of a new MVDC hybrid circuit breaker using a low withstanding voltage capacitor branch for commutation and a sequence controller according to it, and verifies its operation through an experiment.