Armature Current Research Articles

Accurate Condition Monitoring of Semiconductor Devices in Cascaded H-Bridge Modular Multilevel Converters

This article presents an online condition monitoring (CM) scheme for semiconductors used in modular multilevel converters (MMCs) that comprise cascaded H-bridge submodules. The CM algorithm is based on detecting changes in the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance of the semiconductors over time. The proposed method is shown to successfully perform a curve tracing of semiconductors in MMCs while the semiconductor junction remains at a temperature that is readily measurable and undergoes minute changes during the measurement process. The <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance value is estimated from the measured <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state voltage drop of the semiconductors and the measured arm current. Measuring the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance at known temperatures allows for separating temperature-dependent variations of the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance from age-dependent variations of this parameter. Suitable methods for reducing the effect of noise on the curve-traced data are proposed, and a recursive least square estimator is used to extract the optimum <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance from the traced <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$v_{CE}-i_{C}$</tex-math></inline-formula> curve. Simulation results show that the proposed scheme can accurately determine the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state resistance of semiconductors at a known temperature and under various levels of measurement noise. Moreover, experimental results on a low-power prototype show that the proposed scheme is applicable in practice, and provides similar online curves to what a commercial curve tracer can produce offline. The experimental verification has been conducted under constant load conditions; however, the proposed methods can be used under any variable load condition as well.

MMC 기반 HVDC 전력변환기의 밸브 성능 시험회로

A new test circuit for an MMC-based valve HVDC power converter is proposed. The proposed scheme satisfies the required clauses from IEC-62501. The valve test current contains second harmonic component and DC offset as well as a fundamental component that is quite similar to the real operating arm current of MMC based HVDC power system. The structure of the proposed test circuit is simple compared to conventional test circuits. Furthermore, the power supply voltage rating of the proposed test circuit is reduced dramatically around 20% of the conventional scheme with the same current rating. The validity of the proposed test circuit is verified through simulation and experimental results.

Adaptive Fuzzy-Based SMC for Controlling Torque Ripples in Brushless DC Motor Drive Applications

The use of Brushless-DC (BLDC) motor drives in many industrial settings has grown in recent years. In an ideal situation, the torque generated via BLDC motors with a trapezoidal back electromotive force (BEMF) remains unchanged. But, in actuality, the generated torque is distorted by torque ripples (TRs). These TRs make it essential that variable-speed drives operate smoothly. Power electronic switches are used by BLDC motors during commutation, which causes harmonics within the armature current. Sliding-mode control (SMC) is parameter-resistant and dynamic. SMC design involves reaching and sliding. SMC flaws include chattering. A reduced discontinuous gain control policy may strengthen this problem. The controller’s dynamic responsiveness will degrade. The standard SMC strategy’s indefinite converging rate for error to zero lowers dynamic reaction time. For the SMC to converge indefinitely, an adaptive strategy in fuzzy-based SMC (hybrid control technique) is developed to control the TRs in BLDC motor drives. In a BLDC motor, the recommended controller is used to regulate the harmonics as well as the speed. Based on modeling with MATLAB and observations on an operational 3 kW BLDC motor, the suggested approach is beneficial in the lowering of torque waves and current harmonics. The findings reported here support the efficiency of the suggested approach.

Magnetic stability of low corrective force PM in series hybrid magnet memory machine under inverter open-circuit fault

Variable flux memory machine (VFMM) can dynamically adjust its air-gap magnetic field by changing the magnetization states of the employed low corrective force (LCF) permanent magnets (PMs). Due to the demagnetization risk of LCF PMs under armature current, it is necessary to analyze their magnetic stability in various operation states. The magnetic stability of LCF PMs in series hybrid magnet VFMM (SHM-VFMM) under inverter open-circuit (IOC) fault is studied in this article. Firstly, the topology of the investigated SHM-VFMM is introduced, and the field-circuit coupled model of the machine under IOC fault is established. Then, the magnetic stabilities of LCF PMs during the normal and fault operations are analyzed and compared by using the finite element method. The effects of LCF PM demagnetization and fault current on torque are also studied. Afterward, the influence mechanism of the fault armature magnetomotive force (MMF) on LCF PM demagnetization is revealed by using the synthetic MMF graphic method. Finally, the main factor affecting the LCF PM demagnetization under IOC fault is highlighted and an effective method for recovering the magnetic stability of LCF PM is proposed.

Моделирование процесса определения технического состояния тяговых электродвигателей электровозов 2ЭС6

Or positive results in reducing the number of failures of electric traction engines, predictive diagnostics in operation is proposed. The development of malfunctions in electric traction engines directly affects the registration of analog signal values by on-board equipment. Some distinctive criteria have been identified by which the technical condition of electric traction engines can be assessed. The previously developed algorithm for searching for electrical damage has been improved. The presence of a difference in armature current between adjacent bogies and pairs of the same type of electric traction engines is pointed out, the dependence between a serviceable and faulty electric traction engine in the form of discrepancy in correlation coefficients is revealed. All the revealed conditions are added to the algorithm for determining the technical condition, the processes of which are built on the KNIME intelligent analysis platform. The process of determining the technical condition with the output of the result on the serviceability / malfunction of the electric traction engine is modeled. A pair of electric traction motors with a potential malfunction is also identified. The relative modeling error, which is at an average level, allows us to partially solve the problem of occurrence of failures of electric traction engines during operation. The application of the model along with the existing methods improves the quality of predictive diagnostics of modern locomotive equipment.

An Asymmetrical Power Module Design for Modular Multilevel Converter With Unidirectional Power Flow

Modular multilevel converters (MMCs) are widely used in grid scale power electronics. Due to the presence of a dc component in the arm current, the MMC submodules (SMs) show an unbalanced current loading profile. This may lead to some semiconductor chips being more stressed than others, significantly affecting the overall reliability. To level the junction temperatures and improve the SM reliability, this article proposes an asymmetrical power module design in line with the loading profile, allocating more chips to higher current parts. This is shown to be realistic if the power flow is unidirectional. The concept is investigated using simulation backed by experiment. It is shown that the designed power module can significantly reduce the maximum temperature and the total power loss can be reduced by 5%–8%. The chip utilization rate is also improved. The proposed module is applicable in a certain range of power factor and modulation index adjustment. This article provides a guidance for optimum design of the power module for the SMs in an MMC.

Multifractal Spectrum and Complex Cepstrum Analysis of Armature Currents and Stray Flux Signals for Sparking Detection in DC Motors

Multifractal Spectrum and Complex Cepstrum Analysis of Armature Currents and Stray Flux Signals for Sparking Detection in DC Motors

Overvoltage Suppression for Modular Multilevel Converter With Switch Open-Circuit Fault

To enhance reliability and exploit advantages, modular multilevel converters (MMCs) are mostly desired with uninterrupted operational capability during submodule (SM) open-circuit fault. Once an SM fault is located, the closing signal will be delivered to the corresponding bypass switch. However, due to the response delay of mechanical switches, capacitor voltage of the SM with lower switch fault will continue increasing, thus resulting in severe overvoltage and threatening the safety of MMC. In view of this, this article proposes an arm current reshaping-based method to suppress capacitor overvoltage under SM failure. During the period of overvoltage suppression, all the arm currents are reshaped to decrease capacitor charging of the faulty SM and maintain the terminal currents of MMC. Besides, since the capacitor voltage variations are also reshaped by the reshaped arm current, common-mode voltage is injected to satisfy the requirements of arm voltages. Consequently, the degree of SM overvoltage can be alleviated by over 50% without extra hardware investment. Simulation and experimental results confirm the feasibility and validity of the proposed method.

Study on AC Copper Losses in an Air-Cored Axial Flux Permanent Magnet Electrical Machine With Flat Wires

In this article, we propose the calculation method of ac copper losses of air-cored axial flux permanent magnet (AFPM) electrical machine with flat wires fed by pulsewidth modulation (PWM) inverters. The ac copper loss due to armature currents in air-cored electrical machines is significant when these machines are driven by PWM inverters. Besides, the exposure of windings to the inhomogeneous alternating rotor magnetic field causes ac copper loss. Analytical formulas are efficient tools to evaluate these losses but few pieces of literature have reported the derivation in such machines. To address this issue, the formulas of aforementioned ac copper losses are derived based on Maxwell's equations and Poynting theorem. As for end windings, the ac copper loss caused by armature current is calculated analytically, while the rotor-induced ac copper loss is calculated by aid of static three-dimensional finite-element analysis (FEA). The interaction of load current and rotor-induced eddy current is also studied. A 12-slot-16-pole air-cored AFPM machine is analyzed with the proposed method, and the analysis is validated by time-transient FEA simulations and prototype experiments. The influence of modulation ratio on ac copper loss due to armature current of the AFPM machine is also discussed.

Component-Level Semiconductor Loss Balancing for IGBT Based High Power MMC Through Insertion Index Modification

Modular multilevel converter (MMC) is the state-of-the-art converter topology in HVdc transmission applications. The reliability and lifetime of MMCs are strongly dependent on the health of the internal power semiconductors. The operating loss of power semiconductors, which is one of the dominant factors affecting component aging, is not uniformly distributed between the top and bottom switches in the same submodule (SM) due to the dc bias in the arm current. Such loss imbalance leads to differences in lifetime of semiconductors and reduces the reliability of SM. Especially under inverter conditions, the bottom insulated gate bipolar transistor (IGBT) in SM is subjected to a severe thermal stress and has a relatively high failure rate for the thermal vulnerability of IGBT. To extend the lifetime and improve the reliability, this article proposes a component-level loss balancing method. It is achieved by insertion index modification based on a feed-forward gain controller. The proposed method can improve the loss distribution among the top and bottom semiconductors without side effects on ac and dc outputs. Its effectiveness and feasibility are validated through simulation and experimental results.

A Robust Capacitor Voltage Balancing Method for CPS-PWM-Based Modular Multilevel Converters Accommodating Wide Power Range

Capacitor voltage balancing is one of the most important issues for the safe, reliable, and economical operation of the modular multilevel converter (MMC). This article proposes a modified individual capacitor voltage balancing method for MMCs with phase-shifted carrier pulsewidth modulation (PWM) (CPS-PWM) to solve the problem of the poor dynamic performance that the conventional individual voltage balancing methods suffer at low output power. In the proposed method, the information of arm current is incorporated into the balancing algorithm to cancel out the coupling effect of the output power on balancing control. Compared with conventional balancing methods, the proposed method shows better robustness against varying output power and maintains a good dynamic performance in a wider power range. The complete modeling process and parameter design are presented and considered for system stability. The effectiveness of the proposed method is verified with both MATLAB/Simulink simulation and experimental results.

Comparison of Two DC Motor Speed Observers on Sensorless Speed Control Systems

In a sensorless motor speed control system, the motor speed is not directly measured using a speed sensor, but it is estimated using an observer. The sensorless speed control systems are mostly applied to AC motors, while they have not been widely applied to DC motors. Therefore, this paper presents simple observers to estimate the DC motor speed. The observers used were based on the DC motor electric equation. Two methods were used in this research. The first method was the observer estimating the speed based on the resistance inductance values (L-R method), while the second was the observer estimating the motor’s speed only based on the motor’s resistance value (R method). The speed was estimated using armature current (ia) and voltage (va). Therefore, a current and voltage sensor was used. Not only was the observer estimated, but it was also implemented on a real DC motor. An Arduino microcontroller was used to calculate the speed. The LN298 was used as a DC motor drive. Even though the R method is simpler, the test result showed that its speed estimation was less precise than the L-R method. By manual calculation, the motor speed estimation result in the L-R method had an error of 0.14%, while the motor speed estimation results in the R method had an error of 5.03%. The estimation results of motor speed implemented on a real DC motor and microcontroller system in the L-R method had an error of 3.98%, while the result of the estimation of motor speed in the R method had an error of 4.87%.

Optimal Arm Current Reallocation of Modular Multilevel Matrix Converter Dedicated for Power Grid Interconnection

The modular multilevel matrix converter (M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C) is the high-power three-phase to three-phase AC/AC converter of the next generation. However, when the M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C is applied for power grid interconnection, with equal or close input and output frequency, the current distribution in its nine arms becomes significantly uneven. Furthermore, the current distribution pattern is directly influenced by the randomly changing input-output angle-difference, forcing each arm to be designed based on the highest-possible current, which significantly increases the required semiconductor rating and converter cost. To address this issue, a novel current reallocation is proposed to attenuate the highest-possible arm current of M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C. The equal-frequency operation of M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C is first modeled and analyzed, and the operation sweet-spot where each arm stays in natural energy balance is located. Then, the current reallocation is analytically derived for sweet-spot operation. By injecting proper circulating current, the highest-possible arm current is reduced by 13.4%, and the required circulating current component is analytically derived. The implementation method into the classic control structure of M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> C is provided. Performance of the proposed strategy is validated by a simulation benchmark established in MATLAB/Simulink environment in the context of interconnection between two 220 kV/50 Hz power grids.

A Novel Field Current Estimation Method for Brushless Wound-Field Synchronous Machine

Compared with other electric machines, wound-field synchronous machines (WFSMs) have the advantage of having three control variables (stator <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$d$ </tex-math></inline-formula> - and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$q$ </tex-math></inline-formula> -axis currents and rotor current). Determining the optimum combination of field and armature currents is necessary for ensuring the high-performance control of the WFSM. Two methods are usually employed to supply the field winding of the WFSM. The first one uses brushes and slip rings, while the second one uses a brushless excitation system. Concerning the WFSM with a brushless excitation system, a dc field current is provided by a rotating diode bridge rectifier fed by an exciter machine. Therefore, direct measurement of the field current is not possible. As a solution, field current needs to be accurately estimated. Previously, field current estimation methods proposed in the literature have been based on modeling the brushless exciter machine and the rotating rectifier. Using the brushless exciter machine model, these methods estimate electric quantities of the exciter rotor (currents and voltages); then, through the rotating rectifier model, the rectified field current is estimated. Accordingly, any inaccuracy in the models leads to estimation errors. The effectiveness of the techniques relying on the brushless excitation system model is not clearly justified, especially because the nonlinearity of the brushless system has been intensified by the existence of the rotating uncontrolled diode bridge rectifier. This article proposes an accurate online field current estimation method for WFSMs without the need neither to estimate exciter rotor voltages or currents nor to use a rotating rectifier model. The accuracy and effectiveness of the proposed field current estimation method are demonstrated by experimental validation tests.

3-D Electromagnetic Force Characteristics and Modeling of Double-Sided Air-Cored Superconducting Linear Synchronous Motor for EDS Train

Double-sided air-cored superconducting linear synchronous motors (DSAC-SLSMs) play an important role in electrodynamic suspension trains. For this type of motor, the existing magnetic field modeling method is improved in this study, and a new 3-D electromagnetic force (EMF) analysis method is proposed to analyze the influence on the 3-D EMFs when the onboard superconducting coils (SCs) have multiple degrees of freedom motions such as deviation and deflection. First, based on Biot–Savart law and Poisson’s equation of magnetic vector potential, the analytical prediction of superconducting air-gap flux density is conducted. Thus, the relationship between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -axis armature current and 3-D EMFs is determined. Second, the equivalent circuit of DSAC-SLSM is established, and the effects of lateral and vertical displacements of the onboard SCs on armature current are analyzed. Finally, the validity of the proposed model is verified by using the finite-element model, two static experiments, and publicly available data on the Yamanashi maglev test line, while the 3-D EMF characteristics of the motor under various conditions are analyzed in detail.

A data-driven method for IGBT open-circuit fault diagnosis for the modular multilevel converter based on a modified Elman neural network

Modular multilevel converter is widely used in electrical energy with many advantages, its safety and reliability has become a research hotspot. Since the structure of MMC is composed of multiple cascaded sub-modules, including a large number of IGBTs and capacitors. Therefore, fault diagnosis measures must be taken to quickly eliminate the faults. In order to solve this problem, a data-driven method is proposed based on a modified Elman neural network. By comparing the distance Ek between the predicted and true value of bridge arm current, this method can quickly realize fault detection. The original contribution of this paper is using the modified cuckoo search (MCS) to optimize the parameters of Elman model, so as to achieve the optimal balance between fault diagnosis accuracy and diagnosis speed. The simulation results proved that it can quickly detect the open-circuit fault of IGBT by data-driven, and the detection time is about 20 ms.

A Method for the Evaluation of Power-Generating Sets Based on the Assessment of Power Quality Parameters

This article presents a new method for the classification of machine failures using an example of selected generating sets. Measurements and an analysis of the electrical parameters, such as the phase-to-phase voltages at the terminals of a synchronous generator, armature current, and voltage and excitation current of a synchronous generator, are the basis for determining the failure symptoms. The existing energy quality coefficients are adopted as symptoms for the assessment of failures in the monitored generating set. We assume in this method that the description of the input–output relationship is in the form of a black box and use the binary diagnostics matrix (BDM) to investigate the failure–symptom relationships between the inputs (intentional failures) and outputs (failures symptoms = fault-sensitive power quality (PQ) coefficients). The method presented in this article enables the detection and classification of both electrical damage in a synchronous generator and mechanical damage in a diesel engine. It is anticipated that further work and development of the method will focus on the implementation of the algorithm in the form of software into a miniature IoT module for the automatic classification of failures.

Non-characteristic harmonics in modular multilevel converters—An analytical approach

This paper analyzes the harmonic content of the arm currents and voltages of the modular multilevel converter (MMC) by using the dynamic phasor (DP) theory. DP modeling of the MMC facilitates a study without relying on simplifying assumptions on the harmonic content of the currents and voltages. In doing so, the DP-MMC model used in this paper reveals generalized conditions under which non-characteristic harmonics can exist. These conditions offer a detailed insight into the transient behavior of harmonics in the MMC. An open-loop DP model of the MMC is developed, which has the harmonics of the arm currents and voltages as independent state variables. The linearized state-space matrices of the DP model are assessed under different grounding options at the ac side of the MMC, and the relationship between characteristic and non-characteristic harmonics of the MMC voltages and currents is discussed.

Operation Principle and Influence of the Sub‐Harmonic Component Utilized in the Brushless Hybrid Excited Machine with PM in Rotor

Hybrid excited machine (HEM) is a novel type of machine which has attracted much attention as it is able to adjust the flux linkage flexibly and ensure the wide speed range operation. In this paper, a novel brushless HEM with permanent magnet (PM) located in rotor is further researched. By supplying specific armature currents, the sub-harmonic component magnetomotive force (MMF) in stator MMF would be generated and utilized to realize the brushless hybrid excited operation. Firstly, the generation principle of the sub-harmonic component is derived analytically. Secondly, during the brushless hybrid excited operation, the influence of the stator current amplitude ratio m $$ m $$ is quantitatively studied. Thirdly, based on 2D finite element analysis (FEA), the electromagnetic performance of the brushless HEM is analyzed under different operation statuses over a wide speed range. At last, the experiment is performed based on a 6 kW brushless HEM prototype machine, and the correctness of the theoretical analysis and FEA results are validated by the test. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Steady-State Performance Characteristics of a DC Motor fed by Quadratic DC-DC Boost Converter

This paper presents the analysis of steady-state performance of a DC motor fed by a non-isolated quadratic DC-DC boost converter. The proposed quadratic configuration based non-isolated high voltage gain DC-DC converter operating in continuous conduction mode employs one power switch and reduced number of diodes and passive components. Due to single power switch, the switching and conduction losses are reduced thereby improving the converter efficiency. A DC shunt motor of 5 HP power rating is used as load to the proposed converter. The proposed cost-effective converter-fed DC motor operating under no-load is simulated using MATLAB / SIMULINK tool. The steady-state performance characteristics, such as speed, torque, and armature current of the DC motor, are obtained for one particular value of duty ratio of the power switch. The results validate the superior performance of the suggested DC-DC converter-fed DC motor at moderate duty ratio.