Search Results (30)

This paper proposes an anti-disturbance model predictive fault-tolerance control strategy for open-circuit faults of five-phase flux intensifying fault-tolerant interior permanent magnet (FIFT-IPM) motors. This strategy is applicable to electric agricultural equipment that has an open winding failure. Due to the rich third-harmonic back electromotive force (EMF) content of five-phase FIFT-IPM motors, the existing model predictive current fault-tolerant control algorithms fail to effectively track fundamental and third-harmonic currents. This results in high harmonic distortion in the phase current. Hence, this paper innovatively proposes a multi-plane virtual vector model predictive fault-tolerant control strategy that can achieve rapid and effective control of both the fundamental and harmonic planes while ensuring good dynamic stability performance. Additionally, considering that electric agricultural equipment is usually in a multi-disturbance working environment, this paper introduces an adaptive gain sliding-mode disturbance observer. This observer estimates complex disturbances and feeds them back into the control system, which possesses good resistance to complex disturbances. Finally, the feasibility and effectiveness of the proposed control strategy are verified by experimental results. Full article

A grid-connected converter is the interface between renewable energy power generation systems, such as solar power generation, wind power, hydropower, etc., and the power grid, responsible for the stable and efficient transmission of electric energy generated by renewable energy power generation systems to the grid. In order to realize local access for distributed photovoltaic power generation devices and energy storage devices, a composite three-port converter has the advantages of small size, low cost and high power density compared with a combined three-port converter. In view of the current problems of the existing compound three-port (AC/DC/DC) converters, such as DC and AC circulating current in current composite three-port converters and the harmonic control problem, the proposed compound three-port topology consists of a full-bridge inverter with six switching tubes, a zigzag transformer, two sets of filter inductors and two filter capacitors. Among them, the power frequency transformer adopts the zigzag connection method, which can effectively restrain the AC circulation and eliminate the DC magnetic flux of the iron core while introducing the third port. Firstly, the principle of AC/DC and DC/DC power conversion in the composite three-port topology is analyzed, which has higher efficiency than other topologies. Secondly, the topology control strategy is analyzed, and a two-loop hybrid current control method with improved current loop is proposed. When the DC-side voltage fluctuates, the DC offset of the battery can effectively improve the stability of the network side. Through the MATLAB/Simulink simulation experiment platform, the high efficiency of energy conversion and stable grid-connected operation characteristics are verified. Finally, the experiment of integrating into the power grid was carried out. Experiments were used to verify the effectiveness and feasibility of the proposed topology and strategy. The experimental results show that Total Harmonic Distortion (THD) can be controlled below 3%. Full article

Hybrid-excited generators have a wide voltage regulation capability or a wide range of variable-speed constant-voltage output capability, providing a significant advantage in the new energy power generation field. To achieve the optimal design of brushless hybrid excitation synchronous generators with third harmonic excitation, it is necessary to grasp the influence of design parameters on excitation power accurately. Firstly, this paper elaborates on the structure and principle of the hybrid excitation synchronous generator. From the perspective of excitation power generation, the expression for excitation power in hybrid excitation generators has been derived, identifying the primary factors influencing excitation power, which include winding parameters, structural parameters, and magnetic circuit saturation. Secondly, qualitatively calculate the influence of the number of turns and arrangement, turns in rotor harmonic, air gap length, and thickness of the permanent magnet on the excitation power, which is verified by the electromagnetic field finite element method. The results showed that the use of full pitch and a moderate increase in turns, a decrease in air gap length, and an increase in the thickness of the permanent magnet can all increase the rotor excitation power. A brushless hybrid excitation synchronous generator prototype based on third harmonic excitation was developed, the correctness of theoretical analysis and calculation were verified by test results. Full article

The ATLAZUL project is an Interreg effort among 18 partners from Spain and Portugal along the Atlantic Iberian coasts. One of its objectives is the development of new methods and data processing for oceanic information to produce useful products for private and public stakeholders. This study proposes a new insight on the sea surface dynamic of the ATLAZUL area based on almost two years of multiscale high resolution sea surface temperature imagery. The use of techniques such as the Karhunen–Loève transform (Empirical Orthogonal Function) and the Maximum Entropy Spectral Analysis were applied to study long- and short-term features in the sea surface temperature imagery. Mathematical Morphology and the Geometrical Theory of Measure are utilized to compute the Medial Axis Transform and the Hausdorff dimension. The results can be summarized as follows: (i) the tow upwelling areas are identified along the Galician–Portugal coast as indicated in the second and third modes of KLT/EOF analysis, and they are partially affected by wind; (ii) the tow warm water outflows from the Bay of Cádiz to the Gulf of Cádiz are identified as the second and third modes of KLT/EOF analysis, which are also influenced by wind; (iii) the skeletons of the surface signature of the upwelling and of the warmer water outflow, along with their fractal dimensions, indicate a chaotic pattern of spatial distribution and (iv) the harmonic prediction model should be combined with the wind prediction. Full article

This article comprehensively compares the short circuits and irreversible demagnetization in star, delta, and hybrid winding connections for surface-mounted permanent magnet (SPM) machines, including the three-phase short circuit (3PSC) and two-phase short circuit (2PSC). The analytical and finite element (FE) methods are adopted. It is found that when 3PSC or 2PSC happens, the peak current is the largest in the hybrid connection, which further results in the severest demagnetization. In addition, the delta connection always results in a larger 2PSC peak current than the star connection. Under relatively low permanent magnet (PM) temperature, the delta connection leads to more severe demagnetization than the star connection. However, when PM temperature increases, the opposite condition can occur. As for 3PSC, whether the peak current of the delta connection exceeds that of the star connection is determined by the phase of the third back-EMF harmonic. The delta connection shows higher 3PSC peak current when the third harmonic is in phase with the fundamental back EMF, and conversely, the star connection shows higher peak current. The comparison of demagnetization also heavily depends on PM temperature. Finally, the experiments are conducted to verify the theoretical analysis. Full article

High torque ripple can be observed with a 6/4 variable flux reluctance machine (VFRM). In order to minimize the torque ripple in VFRMs, this paper presents a harmonic injection method for 6/4 VFRMs with an open-winding configuration. By analyzing the impact of harmonics on VFRMs, the method involves detecting the third harmonic using a first-order low-pass filter (FLPF). Subsequently, the extracted harmonics are controlled and shifted to counteract the voltage harmonics in both inverters without inducing phase imbalance or overvoltage. With the proposed method, the torque ripple can be significantly reduced by about 50% under load conditions. The effectiveness of the harmonic injection method is validated through a prototype VFRM. Full article

This article aims to realize the brushless operation of a wound rotor vernier machine (WRVM) by a third-harmonic field produced through stator auxiliary winding (X). In the conventional model, a third-harmonic current is generated by connecting a 4-pole armature and 12-pole excitation windings serially with a three-phase diode rectifier to develop a pulsating field in the airgap of a machine. However, in the proposed model, the ABC winding is supplied by a three-phase current source inverter, whereas the auxiliary winding (X) carries no current due to an open circuit. The fundamental MMF component developed in the machine airgap creates a four-pole stator field, while the third-harmonic MMF induces the harmonic current in the specialized rotor harmonic winding. The rotor on the other side contains the harmonic and the field windings connected through a full-bridge rectifier. The electromagnetic interaction of the stator and rotor fields generates torque. Due to the open-circuited winding pattern, the proposed machine results in a low torque ripple. A 2D model is designed using JMAG-Designer, and 2D field element analysis (FEA) is carried out to determine the output torque and machine’s efficiency. A comparative performance analysis of both the conventional and proposed topologies is discussed graphically. The quantitative analysis of the proposed topology shows better performance as compared to the recently developed third-harmonic-based brushless WRVM topology in terms of output torque and torque ripples. Full article

Low power brushless direct current (BLDC) motors are used in many consumer appliances. These motors have a relatively high winding resistance and therefore current control loop can be avoided in some cases, but fast and accurate speed regulation can be still needed. To minimize harmonics and generated sound noise, improved sinusoidal pulse width modulation (PWM) has been tested in the paper. As the most suitable commutation type, the sine wave with the third harmonic component has been selected. This type of communication reduced the torque ripple of the motor. This paper analyses the possibility to improve traditional proportional-integral-derivative (PID) speed regulator with Fuzzy logic block. A simulation model of BLDC motor, inverter, speed detection circuit and controller have been created. Simulation results showed that by applying the Fuzzy-based PID controller, the transient time can be reduced from 0.2 s to 0.05 s and overshoot can be avoided in comparison with traditional PID controller. Experimental results show a significant improvement in the motor dynamics—the overshoot and transient time were reduced twice. The difference with simulation results and experimental ones can be explained by delays introduced by the microcontroller. Full article

Off-shore wind power plants can be connected to the on-shore grid using diode rectifier HVdc links. As diode rectifiers are passive converters, off-shore WPPs require grid-forming capability. This paper shows how to improve the WTG dynamic response and the voltage and current harmonic rejection by using ${\mathcal{H}}_{\infty }$-based controllers. The paper explains how to synthesise three different ${\mathcal{H}}_{\infty }$ voltage controllers: the first is a single-loop ${\mathcal{H}}_{\infty }$ controller, the second is a cascaded ${\mathcal{H}}_{\infty }$ controller and the third is a proportional–resonant controller that is optimised using ${\mathcal{H}}_{\infty }$ synthesis. The three ${\mathcal{H}}_{\infty }$-based controllers improve the performance and the robustness obtained with a benchmark case PR controller tuned using the root locus technique. All the controllers are designed in continuous time and implemented in discrete time, applying bilinear discretisation with a sampling rate of 0.25 ms. Detailed PSCAD simulations validate the improvement of the performance and robustness, as well as an improvement in the harmonic rejection. The single ${\mathcal{H}}_{\infty }$ controller shows the best combined characteristics of all tried controllers, at the expense of losing the separation between voltage and current control loops. Full article

Accurate calculation of the electromagnetic force distribution of transformer windings under different loads and fault conditions is of great significance for transformer maintenance, condition evaluation and life prediction. Due to the influence of offshore wind power systems, offshore wind power transformers have high harmonic content and large changes in load rates, which can easily cause the coil destabilization, winding deformation or even damage because of the uneven distribution of the electromagnetic force. To improve the accuracy of electromagnetic force calculation, this paper proposes a fractional order numerical method. First, a three-dimensional axisymmetric transformer model and a symmetrical lumped parameter equivalent circuit model are established, respectively, based on field-circuit coupling. Second, the fractional order approximation of circuit components is realized by using the improved Oustaloup filter. In the fractional order model, the transformer is replaced by the lumped parameter equivalent circuit model. Third, as in the calculation process for integer order electromagnetic force, the integer order current has a large error, and the current waveform does not match the actual power frequency. The fractional order current and electromagnetic force at the 0.9 order are closer to the rated value. Finally, the effects of different load rates, three-phase short circuits and harmonic conditions are studied with the fractional order model. Compared with the traditional integer order finite element electromagnetic model, the fractional order equivalent circuit model established in this paper is more accurate and suitable for electromagnetic force calculation. The proposed method is significant for the structural design and state detection of transformers and also could be applied in the analysis of other dry-type transformers. Full article

This paper presents a new winding with a low higher spatial harmonics content. This winding enables the elimination of the fifth harmonic, as the most significant, in three-phase winding and the third harmonic in two-phase symmetrical winding. The suppression of higher spatial harmonics is particularly evident with the number of slots per pole per phase q_s = 2. The winding factors for the higher spatial harmonics of the order ν = 6 k ± 1 in the case of three-phase winding, and ν = 4 k ± 1 in the case of two-phase winding, for k = 1, 3, 5, …, will be equal to zero. A two-phase measurement winding, with the number of slots per pole per phase q_s = 1, was used to evaluate the higher spatial harmonics content in the magnetic field in the air gap of the machine. Experimental verification of the designed winding was carried out. Full article

Due to the rapid development of wind power, the stable operation of doubly fed induction generators (DFIGs) has attracted much attention. This paper focuses on the finite frequency (FF) H_∞ control for the DFIG with input delay, aiming to reduce the effects of current harmonic interferences and gain disturbances on the DFIG and improve the stability of the system. First, a DFIG state–space model with input delay under current harmonics was constructed. Second, based on the DFIG state–space model, an FF H_∞ state-feedback controller was designed from the frequency domain perspective, which makes the DFIG stable and robust against harmonic interferences and gain disturbances. Third, via the generalized Kalman–Yakubovich–Popov (GKYP) lemma and the Lyapunov theory, the FF H_∞ performance was evaluated in the form of linear matrix inequalities (LMIs), and then the state feedback FF H_∞ controller was designed. Finally, the simulation results showed the efficiency of the proposed approach. Full article

This paper analyzes the field performance of two cup anemometers installed in Zaragoza (Spain). Data acquired over almost three years, from January 2015 to December 2017, were analyzed. The effect of the different variables (wind speed, temperature, harmonics, wind speed variations, etc.) on two cup anemometers was studied. Data analysis was performed with ROOT, an open-source scientific software toolkit developed by CERN (Conseil Européen pour la Recherche Nucléaire) for the study of particle physics. The effects of temperature, wind speed, and wind dispersion (as a first approximation to atmospheric turbulence) on the first and third harmonics of the anemometers’ rotation speed (i.e., the anemometers’ output signature) were studied together with their evolution throughout the measurement period. The results are consistent with previous studies on the influence of velocity, turbulence, and temperature on the anemometer performance. Although more research is needed to assess the effect of the anemometer wear and tear degradation on the harmonic response of the rotor’s angular speed, the results show the impact of a recalibration on the performance of an anemometer by comparing this performance with that of a second anemometer. Full article

This paper proposes a dual-harmonic pole-changing (PC) motor with split permanent magnet (PM) poles (DHPCM-SPMPs). By adopting a split PM pole structure, the amplitude of the third PM flux density is increased greatly. Therefore, when a PC winding is adopted to couple with the fundamental and third PM flux density components, respectively, the proposed motor can work as a PC PM motor to satisfy operating demands of electric tractors. The design and effect of the proposed split PM pole structure is introduced first. The winding topology is then designed according to the slot vector diagrams of the two PM flux density components, and the PC operation can be realized by electric switches. Aiming at a torque ratio design objective, the PM structure parameters can be determined based on mathematical derivation, and the speed-widening capability is proved based on the operation characteristic analysis. Finally, the electromagnetic performance of the DHPCM-SPMPs is investigated and compared by finite element analysis, which shows the high torque capability in eight-pole mode and the wide speed range in twenty-four-pole mode benefiting from the PC operation. Full article

The difficulty of open-switch fault detection in an open-winding inverter is that the fault at the diagonally opposite position within the H-bridge power cell has the same fault characteristics. To solve this problem, this paper proposes an open-switch fault detection method based on open-winding (OW) five-phase fault-tolerant permanent-magnet (FPFTPM) motor drives. The detection method includes three steps: first, the drives open-switch fault is detected by monitoring the component of the third harmonic residual in the stationary reference frame; second, the least squares iterative method based on the forgetting factor is used to identify the relationship between the residual components, which determines the faulty phase and the faulty phase current type; third, an online current injection test method is proposed to accurately identify the open-switch within the H-bridge power cell. Based on the above steps, the open-switch fault at the diagonally opposite position within the H-bridge power cell could be accurately identified. The novelty of the proposed method lies in the possibility that the open-switch fault detection of any switches within the one H-bridge power cell could be accurately achieved by an online current injection test and does not require hardware changes. The experimental results demonstrate the effectiveness of the proposed detection method. Full article