Commutation Overlap Research Articles

Online Current Spikes Suppression Strategy Research of Switched Reluctance Motors Based on Hybrid Torque Sharing Function

In this paper, an online compensation predictive control method based on hybrid torque sharing function (HTSF) is proposed to reduce current spikes in the torque sharing control of switched reluctance motor (SRM). First, predictive control is introduced to the torque sharing function (TSF) and a new cost function is designed with Laplace multiplier method by predicting the current and torque of the next cycle of SRM. Then the optimal current control amount is carried out. Second, the ratio of the torque error to the desired torque and its derivative are compensated online to the current phase at the beginning of the commutation overlap period to accurately track the torque, and the torque distribution is optimized by a HTSF at the end of the phase change to further reduce the current spikes and suppress the torque ripple. Finally, the experiment on 8/6 four‐phase SRM is achieved to verify the feasibility and effectiveness of the proposed control strategy, and the results show that the current spikes and the torque ripple are reduced by 25% and 14.5% respectively. Therefore, compared with traditional TSF control, this method can effectively reduce the SRM torque ripple and excessive current spikes. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Dynamic Phasor-Based Modeling and Simulation of a Single-Phase Diode-Bridge Rectifier

This paper presents dynamic phasor (DP) models of a single-phase diode-bridge rectifier (DBR). Single-phase DBRs serve as a primary building block of consumer electronics, whether with a simple filter or coupled with additional circuitry to produce unity power factor rectification. Four DP models are proposed, two models (DP-SF and DP-AW) suitable for systems with negligible line inductance and two models (DP-Full and DP-Fund) which can be used when the line inductance causes significant commutation overlap. The proposed models are implemented in MATLAB and simulation results are compared against a detailed switching model simulation. A significant reduction in simulation time is demonstrated by the proposed DP models. The simulation results are validated against experimental data, confirming the accuracy of the proposed modeling approaches.

Retracted: Research on Output Waveform of Generator with Rectifier Load considering Commutation Overlap Angle

Retracted: Research on Output Waveform of Generator with Rectifier Load considering Commutation Overlap Angle

Study on Calculation Method for Steady-State Short-Circuit Current of MMC During a DC Pole-to-Pole Fault

The modular multilevel converter based high-voltage direct current (MMC-HVDC) has drawn great attention in the field of HVDC transmission. Research on short-circuit fault current calculation method is of great significance for equipment protection and key MMC components selection. In common cases, IGBT will be blocked within a short period of time after the occurrence of a bipolar fault, and the short-circuit current will be suppressed. However, there are also cases where the fault progresses to stable stage. Therefore, research on the steady-state short-circuit current calculation method is of high importance for protection design and failure analysis. Taking AC-side reactance and DC-side short-circuit impedance into consideration, a steady-state short-circuit current calculation method based on solving the circuit initial value is proposed. Current calculation is discussed in three situations divided based on different fault parameters after defining the commutation overlap angle are respectively analyzed. The short-circuit current can be solved by formulating the equations based on the conduction state of the diode in the converter, and then solving the electrical quantities through the current boundary conditions of each state. Finally, a fault circuit model is built in PSCAD/EMTDC for simulation, and the accuracy of the calculation method is verified under different fault parameters.

Commutation Overlap Characteristic Modeling and Stability Analysis of LCC-HVDC in Sending AC Grid

In recent years, the doubly fed induction generator (DFIG)-based wind power generation and high-voltage direct-current (HVDC) transmission are widely utilized in practice. The stability issues of sending AC grid, which is composed of line-commutated converter (LCC)-based HVDC and DFIG system, is worthy of attention. Commutation is an important factor in the impedance model of LCC-HVDC rectifier, due to the nonnegligible leakage inductance of transformer. However, it was overlooked in previous studies because there are many difficulties in modeling commutation overlap characteristic. In this paper, the spectral models of voltage and current mapping functions are proposed by 3-D Fourier series method, in which the commutation overlap angle is considered. Then, based on the concept of harmonic linearization, an analytical model that describes the commutation process is established and validated by simulations. The mechanism that the commutation overlap characteristic affects the impedance model of LCC-HVDC is investigated, and the simplified modeling method in different frequency bands is studied. The stability of sending AC grid is analyzed applying the Generalized Nyquist Criterion (GNC). The results of stability analysis show that the effect of commutation overlap cannot be ignored. The simulation results confirm the correctness of the obtained conclusion.

Asymmetric Neutral Point Diode Clamped Topology with Reduced Component Count for Switched Reluctance Machine Drive

The Reduced Asymmetric Neutral Point Clamped converter topology for unipolar driven, multiphase switched reluctance machines is proposed in this paper. This topology shares similarities with the conventional NPC and Asymmetric-NPC topologies, however it is unique in that the components for the capacitor string and outer semiconductor switches are shared among all the phases for a reduced component count. Some switching state combinations are not possible during commutation overlap between motor phases, resulting in minor torque transients during regenerative braking. A custom modulation scheme is implemented with fixed frequency, phase-shifted carrier waveforms that allow for automatic balancing of the neutral point voltage and interleaved switching of the semiconductor switches. A simple torque observer control architecture is used with minor adjustments for arbitrating torque contribution priorities between phases during handover.

An Accurate Impedance Model of Line Commutated Converter With Variable Commutation Overlap

This paper proposes an accurate impedance model for line commutated converter (LCC) in the stationary frame. The commutation overlap process caused by the transformer leakage inductance complicates the modeling for LCC. Traditional impedance models are derived in positive sequence and negative sequence frame based on the simplified commutation overlap process, which degrades the modeling accuracy and limits the description of frequency coupling. This paper systematically analyzes the effects of the commutation overlap process on the impedance model, and the impedance model with the accurate commutation overlap process is established in the <i>dq</i>-frame. For clearly revealing the frequency coupling phenomenon of the LCC, the complex space vector is employed to extend the impedance model in the <i>dq</i>-frame to the complex <i>&#x03B1;&#x03B2;-</i>frame. A closed-loop model on PSCAD&#x002F;EMTDC is used to verify the proposed impedance model in the time-domain and the frequency-domain. The consistency between the simulation results and theoretical analysis effectively verifies the accuracy of the proposed model.

Research on Output Waveform of Generator with Rectifier Load considering Commutation Overlap Angle

The purpose of this paper is to study the influence of the uncontrolled rectifier circuit on the generator’s output waveform when considering the commutation overlap angle. Taking the nonsalient permanent magnet (PM) generator directly connected with the uncontrolled rectifier circuit as an example, the equivalent circuit of the generator with rectifier load is established, and the commutation process of the rectifier circuit is analyzed when the effect of the commutation overlap angle is considered. The output waveforms of generator’s output side are obtained by analytical method, circuit simulation method, field-circuit coupled simulation method, and experimental method. The validity of the analysis methods is demonstrated by comparison. According to the results of analytical analysis, we know the characteristics of the output waveform under the influence of the commutation overlap angle. The existence of the commutation overlap angle will cause the voltage waveform to concave or convex, prolong the conduction time of the winding, and result in phase difference between the voltage waveform and current waveform. The influence of synchronous inductance and extra inductance on the output waveforms and harmonic distortion rate is analyzed. The research of this paper provides a theoretical basis for improving the output waveform of the generator with rectifier load.

Research on Self-exciting Air-core Pulsed Alternator Considering Armature Reaction

Compared with the traditional synchronous generator with iron core structure, air-core pulse alternator usually adopts self-excitation to establish a higher field current to meet its demand for high flux density. In this paper, the topology of the self-exciting rectifier is determined to be the full bridge rectifier by discussing the respective application scope of the full bridge and the half wave rectifier. Considering the armature reaction, the self-excitation process and the coupling relationship between the field winding and the armature winding are analyzed. According to the commutation overlap angle, the equivalent circuits of different states are carried out, and the instantaneous expressions of field current and armature current are deduced, which lays a foundation for the following phase control research.

Novel modulated equivalent model of point-to-point LCC-based high voltage AC/DC/AC system for geomagnetic storm-induced unbalanced harmonic studies

Geomagnetically induced currents have been recognized as significant factors in causing power transformer saturation and damage to other key components of the power system via the injection of a wide range of harmonics to the system. Non-characteristic harmonics owing to transformer saturation during geomagnetic storms generates a wide range of reflected harmonics in HVDC/HVAC grids which cannot be filtered using conventional passive filters. These harmonics depending characteristic impedance of adjacent grid can be damped or amplified. Due to the nonlinear nature of converters, assessing the impact of each injected harmonics on the generation of different frequency components requires complete circuit analysis on both AC and DC sides, the complexity of which often necessitates mitigation solutions beyond a simple converter filter design. This work aims to introduce a novel numerical model to represent the HVDC system’s reaction for all harmonic components from disturbances. Also, accurate calculations have been provided to obtain time-variant transferred impedance by the modulation process of 12-pulse bridge converters behind the converter transformer. With proper parametrization of the converter and grid, this model enables the analysis of the whole system without requiring further calculations on the HVDC side. The impact of the commutation overlap angle has been studied thoroughly in this work. The accuracy of proposed model was verified by comparing the results obtained from a direct impedance method and fully-controlled LCC model in Electromagnetic Transient Program (EMTP) for both single and multiple injected harmonic scenarios. Grid voltage and current values at different frequencies for similar harmonic injection scenarios using the proposed reflected equivalent circuit and EMTP model were obtained and compared.

Accurate Analysis of Harmonic Transmission of Line Commutated Converter Considering Firing Angle Fluctuation

Line commutated converter (LCC) has been widely applied in hybrid high voltage direct current (HVDC) transmission system, where the modular multilevel converter (MMC) is applied as receiving end and may induce low order harmonics in DC-link voltage. These low order harmonics will introduce the low frequency fluctuation into the control loop of LCC and complex the harmonics analysis. The traditional method to calculate LCC harmonics is derived by the switching function and modulation theory, which only obtains characteristic harmonics. The low-frequency fluctuation superimposed on the firing angle in the control system is ignored in the traditional method. In this paper, the interharmonics, which is introduced by firing angle fluctuation, is revealed by the double Fourier method. A fitting function method is applied for depicting the varied commutation overlap caused by firing angle fluctuation. Compared to the traditional method, the proposed method can effectively analyze both characteristic harmonics and interharmonics in the condition of low-frequency fluctuation of the firing angle. The accuracy and effectiveness of the theoretical analysis are verified with a three-phase LCC rectifier built in PSCAD/EMTDC and experimental test.

Comparative Research of a Wound-Field Doubly Salient Generator With Different Rectifiers

The wound-field doubly salient generator (WFDSG) is receiving consideration for the field of industrial and aerospace/aviation, since it has the advantages of high robustness with simple structure and adjustable output voltage. In this paper, upon the analysis of generator structures, the features of three rectifiers that are suitable for WFDSG are analyzed in detail. The comparative research of WFDSG with hybrid half-bridge rectifier (HHBR), full-bridge rectifier (FBR), and half-bridge rectifier is presented by the finite-element method (FEM). Then, the load and no-load characteristics of WFDSG under the three rectifiers mentioned above are researched comparatively. The commutation overlap angles and total commutation output voltage losses of three rectifiers are deduced. The experiments of a 12/8-pole single armature-winding WFDSG (SAW-WFDSG) with an FBR and a 12/8-pole dual-armature-winding WFDSG (DAW-WFDSG) with HHBR prototypes have been performed. The FEM and experiment results shows that the SAW-WFDSG with FBR and the DAW-WFDSG with HHBR both have a good application prospect.

High‐efficiency full‐range soft‐switching full‐bridge high‐frequency‐link inverter

A novel full-range soft-switching full-bridge (FSFB) cycloconverter-type high-frequency-link inverter (CHFLI) with active snubber network is proposed. By adding an auxiliary inductor in primary-side DC/AC converter and adopting centre-tapped transformer structure, the proposed FSFB-CHFLI achieves zero voltage switching (ZVS) for all switches under different operating conditions from light load to rated load, which benefits with high efficiency and high switching frequency. The secondary-side active snubber network is utilised to recycle leakage inductor energy and suppress voltage spikes caused by the resonance of the leakage inductor and the parasitic capacitance of switch. The commutation overlap strategy is adopted to guarantee complete ZVS turn-on and ZVS turn-off of bidirectional switches. Experimental results of a high efficient and high switching frequency (200 kHZ) prototype are presented to verify the analysis results of the proposed FSFB-CHFLI.

Soft‐switching single‐stage three‐level power amplifier for high‐voltage audio distribution systems

An isolated fully soft-switching single-stage three-level power amplifier (SS3L) based on dual auxiliary networks (DAN) is proposed in this Letter. Compared with the conventional class-D power amplifier, the proposed DAN-SS3L achieves high level of integration without bulky dc link capacitor, and high-efficiency by single-stage conversion and zero voltage switching for all the switches under different operating conditions from light load to full load, which is suitable for high-voltage audio distribution systems. By adopting active auxiliary network, the energy stored in the leakage inductor can be recycled, which eliminates the pulse width modulation voltage spikes. The passive auxiliary network provides enough reactive current for primary-side switches, extending soft-switching range. In addition, commutation overlap strategy is employed to enable natural commutation of bidirectional switches. Experimental results of a 200 W prototype are presented to verify the analysis results.

A Commutation Overlap Period Reduction Method Expanding the Buck Operating Range for a Bidirectional Isolated DC–DC Converter

SUMMARYThis paper proposes a bidirectional isolated DC–DC converter with an active clamp circuit and two novel control methods in the buck mode. A circulating current reduction method decreases the conduction loss. A commutation overlap period reduction method maintains the output power by expanding the maximum actual duty cycle even if the input voltage decreases. The experimental results show that the proposed method increased the maximum output 1.5 times, without increasing the voltage applied to the low‐voltage side MOSFETs under the minimum input voltage condition. A 2‐kW class prototype showed a higher than 90% efficiency over a wide operating range for a greater than 20 input–output voltage ratio at 100‐kHz switching frequency.

A Commutation Overlap Period Reduction Method Expanding Buck Operating Range for a Bi-directional Isolated DC-DC Converter

A Commutation Overlap Period Reduction Method Expanding Buck Operating Range for a Bi-directional Isolated DC-DC Converter

A Study on Overlapping Commutation Time in Permanent Magnet Brushless DC Motor

To determine the control method using overlapping commutation overlap time, this article on the four-phase permanent magnet brushless DC motor torque ripple based on the analysis of the use of overlapping commutation torque ripple suppression in the overlap time were derived by Ansoft software calculated four-phase permanent magnet brushless DC motor parameters, using MATLAB/Simulink software and simulate the model, simulation results were derived.

A novel synchronism method for thyristor power converters using the space vector approach

Phase-controlled operation of thyristor power rectifiers requires instantaneous phase information of the fundamental component of the grid voltage in order to generate the proper gating sequence. In many high-power, high-precision applications, such as driving the bending magnets of large particle accelerators, the power converters are fed from a local grid, which produces significant frequency variations and large voltage notches superimposed to the sinusoidal AC voltage due to the commutation interval. These strong disturbances impose some difficulties in measuring the phase of the mains, affecting the precision of the converter. In this paper, we present a new method to generate a fast and precise synchronism signal based on the concept of space vectors. The proposed method allows to track line frequency changes within one cycle of the mains in spite of the large voltage notches produced by the commutation overlap angle. Simulation and experimental results are provided.

Direct method for calculation of AC side harmonics and interharmonics in an HVDC system

AC side current harmonics in an HVDC system are shown to be dependent on the commutation overlap and the DC side ripple. Interharmonics exist when the AC networks operate at different frequencies. An analytical method is proposed to represent such effects in the AC side harmonic calculation. The algorithm does not require iteration between the AC and DC sides. The result obtained using the analytical method is verified using time domain simulation.

Sequence impedance and equivalent circuit of HVDC systems

This paper considers the sequence impedance and equivalent circuit of an HVDC converter and system. The results can be used in the steady state analysis of power systems containing HVDC terminals with systems operating under balanced or unbalanced conditions. The effects of commutation overlap are considered. The method described provides a simple model for steady state studies for power systems containing converters and HVDC links.