The utilization of powder cores for many power electronic applications has drawn a significant amount of attention owing to their attractive magnetic properties. However, because of their low relative permeability characteristics, a precise measurement of the core loss is very difficult to obtain. Imprecise estimation of the core loss may lead to an inaccurate thermal design of power converters. Measuring and calculating the accurate value of the core loss allows the circuit designer to design a more efficient system. This paper discusses the revalidation of electrical measurement by comparing the electrical method with the calorimetric method in powder cores. The calorimetric method is one of the most promising methods to accurately measure the core loss; however, it is time consuming. A difference less than 10% has been reported for the core loss measurement error while comparing the electrical method and the calorimetric method in various conditions. These results indicate that the electrical method using the B-H analyzer is effective for measuring the core losses in some conditions for powder cores. Along with the theoretical discussion, simulation and experimental tests are also conducted.
This paper proposes a method for direct predictive control of DC-link current using the interior permanent magnet synchronous motor (IPMSM) discrete equation for electrolytic capacitorless inverters. Electrolytic capacitorless inverters do not have any electrolytic capacitors or power factor correction circuits. Therefore, direct DC-link current control is proposed as a method for controlling the the DC-link current of the inverter to improve the input power factor. However, in the direct DC-link current-control method, an error occurs in the DC-link current due to the one-sample delay in the voltage output. Because of this error, a current harmonic is generated in the input current. The direct predictive DC-link current control proposed in this paper reduces this error, thus satisfying the input-current-harmonics regulation value of IEC 61000-3-2.
To reduce the cost of an AC-DC-AC system, a single-phase-to-three-phase electrolytic capacitor-less inverter has been proposed. In particular, to satisfy the requirements of a harmonic source current, it is necessary to control the source current under sinusoidal waveform conditions. However, the DC-link voltage becomes an absolute value of the source voltage, and the output voltage is almost zero near the zero-crossing region of the source voltage. In the zero-output-voltage region, the motor current response deteriorates while controlling the sinusoidal source current. When the motor speed is high, the copper loss is always large because the motor current in the zero-output-voltage region depends on the back-electromotive force of the motor. To suppress the copper loss in the zero-output-voltage region, this paper proposes a copper-loss reduction control method that utilizes the initial-condition response of the motor current.
The proposed method reduces the motor copper loss while controlling the source current sinusoidally, and improves motor efficiency while satisfying the requirements of a harmonic source current. This paper analyzes the motor current in the zero-output-voltage region and focuses on the initial-condition response of the d-axis current. In addition, an optimal initial value that reduces the copper loss in the zero-output-voltage region is calculated.
In this study, an inductive power transfer system (IPT) was designed and developed for an excavator, which will be operated under high air pressure. In the conventional excavator systems, power is supplied through trolley wires. The contact between the trolley wires and a pantagraph may be a reason of fire due to a spark because the excavator works under high air pressure. In the proposed system, a series resonance capacitor on a primary side and a parallel resonance capacitor in a secondary side is used to cancel out the leakage inductance. By using the series-parallel compensation, the load voltage is ideally constant regardless of load fluctuation. However, the constant-voltage characteristic may degrades when a winding resistance and an error of the resonant parameter cannot be ignored. Thus, the resonant parameters must be designed considering the error. This paper proposes the design method of the resonant parameter with the voltage ratio maps considering the error of the parameter including the winding resistance. The experimental results confirmed that the voltage fluctuation is smaller than 4.3% with a developed 15-kW IPT system. Furthermore, the constant-voltage characteristic is maintained even when the output power of an induction motor changes from 5 to 15kW and vice versa.
A control method of a starter generator, which are for a jet engine for an unmanned aerial vehicle (UAV) system is proposed in this paper. Both the jet engine and the propellers that are powered by the jet engine via a starter generator generates the thrust power. Using the jet engine for obtaining the thrust, it is possible to extend a flight range since the energy density of the jet engine of the developed system is higher than the energy density of the battery in the conventional system. The miniaturization is also achieved by connecting the starter generator to the jet engine because high-frequency operation makes the starter generator compact. The proposed control strategy achieves the starting, powering, and cooling operations using the starter generator. Each operation is demonstrated with a 3-kW prototype. As the results, the maximum conversion efficiency of 92.7% is observed. Moreover, the minimum total harmonic distortion of the generator current is 16.5% at the rated operation speed (70000r/min). Further, the exhaust nozzle temperature is stabilized within the maximum deviation of 2% of the command in a steady state.
A synchronous reluctance motor (SynRM) is an inexpensive variable-speed motor that is receiving increased attention as a rare-earth-free motor. However, a concern regarding such motors is them having a high torque ripple, which generates undesirable noise and vibration. The focus of this study is to minimize the torque ripple of a SynRM by combining different flux barrier structures in the rotor. The effects of various flux barrier configurations on the motor's torque performance were examined, and two different flux barrier structures were combined by lamination in an asymmetric rotor structure. Further, the rotor was constructed by stacking two different rotor laminations with different flux barrier structures. The torque performance of the proposed SynRMs was evaluated using the two-dimensional finite element method.
Electric vehicles are equipped with an isolated DC-DC converter for controlling the bidirectional DC power flow. In this case, a current sensor was installed inside the circuit. This paper proposes a current sensor using current transformers for bidirectional DC-DC converters. The current sensor comprises a current transformer (CT), diode rectifier, and MOSFET. The current sensor can detect a pulse current containing a DC component without any magnetic saturation. This paper shows a circuit configuration of the bidirectional current sensor, and the principle of the bidirectional current detection of the sensor is analyzed. The validity of this analysis is verified through an experiment with the DC-DC converter rated at 150V and 1.4kW.
Industrial applications, such as semiconductor manufacturing equipment, require power amplifiers that provide high power with high precision and bandwidth. The Flying Capacitor Resonant Pole Inverter (FC RPI) provides a multilevel configuration with high switching frequencies and Zero-Voltage Switching (ZVS) across the entire operating range. However, the charge-based modulation scheme that is applied to ensure ZVS depends heavily on correct measurement of the zero-crossings of the filter inductor current. The delay incorporated in the measurement chain results in significant distortion of the output current, which deteriorates the performance of the end application. This research proposes to apply direct current feedback of the per-period average filter inductor current, measured using a high bandwidth Anisotropic Magneto-Resistive (AMR) sensor, to correct the distortion introduced in the output current. The simulation results of the complete converter and control configuration indicate a significant improvement in performance: 9dB increase in Spurious Free Dynamic Range (SFDR) and 16dB decrease in Total Harmonic Distortion (THD).
The quantification of stray load losses such as circulating-current loss in armature windings and in-plane eddy-current loss in electrical steel sheets is important for developing rotating machines with high efficiency. The circulating-current loss in parallel-connected armature windings is analyzed by using the two-dimensional finite element method. We investigate the losses caused by the in-plane eddy-current in the stator cores of permanent-magnet synchronous machines by using the three-dimensional finite element method. The influences of the coil-end structure, skew structure, and carrier harmonics of a pulse-width-modulated inverter on the in-plane eddy-current loss in the stator core are described. The accuracy of the analyses is confirmed through comparison with experimental results.
Interior permanent magnet synchronous motors (IPMSMs) are widely used because of their high efficiency and high power. However, since their design has a high degree of freedom, application-specific design of IPMSMs is difficult. In this study, we investigate the structural characteristics of the models obtained by an automatic design system using a genetic algorithm (GA), and examine the structural factors useful in the design of IPMSMs that reduce eddy current loss in the stator and have high efficiency at high speeds. In addition, we confirm that by using this design method for the general shape of concentrated winding IPMSM, the eddy current loss is reduced and the efficiency is improved in the high-speed range.
To improve the performance of light electric vehicles (LEVs), we propose a current sharing control system for series-parallel changeover, whose hybrid energy storage system (HESS) comprises an electric double-layer capacitor (EDLC) bank and a main battery. In the proposed system, the series or parallel connection between the EDLC bank and the main battery is decided depending on the bank voltage for managing the energy stored in the HESS. Moreover, we propose a simple output current control method for the parallel connection of the EDLC bank. This method allows for the ratio of output current in both storage components to be controlled by introducing a share command parameter. Experimental results from field tests demonstrate the parallel operation with adjustable current sharing control. Finally, we discuss the combination of series-parallel operations to provide power assistance for LEVs.
In this paper, we propose a novel machine that transfers electrical energy between the stator and the rotor via magnetic resonance coupling (MRC). As the energy conversion in an MRC does not require any magnetic core, its mechanism realizes an ultra-lightweight motor for potential use in an energy-efficient electric aircraft. The MRC-based motor, its design, operating principles, starting characteristics, and resonance conditions are discussed in detail herein. Through magnetic analysis, we clarify the essential characteristics of the proposed MRC motor and verify the resonance conditions calculated from the equivalent circuit. Our results confirm that the proposed MRC motor transfers electrical energy between the stator and the rotor, thereby generating torque. We further verify that the resonance conditions derived from the equivalent circuit achieve a resonant state.
This paper presents a condition-monitoring method of dc-link capacitors used in a high-power three-phase PWM inverter with an evaluation circuit intended for ageing tests. Although its power rating is 1/25 of the inverter, the evaluation circuit provides the equivalent ripple current waveform and dc-bias voltage to the high-power inverter. The monitoring method independently extracts the capacitance and ESR of the dc-link capacitor, where the fast Fourier transform is introduced to the ripple current waveform and the dc-link voltage of the evaluation circuit. Experimental results verify that the monitoring method obtains both the ESR and capacitance changes of a capacitor under test.
Power quality problems caused by grid-connected renewable energy inverters have been reported increasingly in recent literature. Excessive harmonics and interharmonics arise when the inverter starts to interact with the grid impedance. Small-signal impedance models have been proven to be useful tools to analyze the stability margins. However, in presented dq-domain models the grid voltage feedforward loop employed by the inverter is not included. To fill this gap, this paper presents a new impedance model, which includes the effect of feedforward, to analyze impedance-based stability in the presence of large grid impedance. The model was verified by impedance measurements from a laboratory prototype. The model gave accurate predictions of small-signal stability when the Nyquist stability-criterion was applied. Thus, the model can be used to re-shape the inverter impedance to avoid stability problems. The developed impedance model also provides a useful tool to monitor stability margins online, which necessitates adaptive impedance-shaping of grid-connected inverters.
In this study, we examine how to increase the operating speed of a consequent pole axial gap motor to achieve higher output density. Our research group has been developing a consequent pole axial gap motor with field windings as the traction motor for electric vehicles. A smaller and lighter traction motor is required for better fuel economy and layout of such vehicles, and it is profitable to manufacture a smaller motor with an increased operating speed. To achieve high-speed operation, it is necessary to suppress the line-to-line voltage, and to that end, we examine the slot/pole combination. Moreover, because the rotor outer diameter of an axial gap motor is larger than that of a radial gap motor, the rotor strength should also be considered. We study the use of non-magnetic high-tensile-strength steel for the component that supports the rotor. We present the motor design and the results of spin burst tests, and we confirm that the motor can operate at the target maximum speed and output power density.
Silicon carbide (SiC) devices are considered as key enablers for the development of highly efficient and compact dc-dc converters for low- and medium-voltage applications. Besides their high temperature capability and low conduction losses, they provide superior switching characteristics. This paper emphasizes the design challenges of SiC devices in the low- and medium-voltage ranges arising from their fast switching speeds. First, detailed measurement results on the switching characteristics of 1200 V SiC devices and the different leakage inductances are presented. The results are assessed with regard to the switching losses as well as the transient voltage and current overshoots. The impact on the switching behavior as a function of leakage inductances is shown. The leakage inductances also influence the resonance frequency of the power module and dc-dc converters. The determination of the size of the EMI filters is a crucial design aspect. Its significance is demonstrated using an 800 V dc-dc converter with commercially available SiC MOSFETs. In addition, zero-voltage switching is emphasized to reduce the impact of the parasitic elements of the module on the switching behavior. However, the performance of 10 kSiC SiC MOSFETs in a medium-voltage dc-dc converter shows that a significant amount of commutation energy is required to ensure a successful soft-switching transition.
This paper presents a disturbance modeling method for a semicircular linear motor called circular shaft motor (CSM). The CSM is a direct-drive motor that moves along the circumference of a circle, and is expected to realize multiple-degree-of-freedom (MDOF) haptic applications. To control the contact force in a CSM system, an observer is implemented to estimate the reaction force instead of using a force sensor. However, the estimated reaction force includes an estimation error caused by forces other than the reaction force. Therefore, a disturbance modeling method for the CSM is proposed to exclude the estimation error. In the proposed method, the variation in characteristics that depend on the velocity is approximated by a Fourier series. To evaluate the adequacy of the model, Akaike's information criterion (AIC) is introduced. To validate the effectiveness of the proposed method, a force control test is performed with the proposed disturbance model on a CSM. In addition, a bilateral control test is conducted to demonstrate the usefulness of the proposed method for force transmission.
The output torque of a three-phase interior permanent magnet synchronous motor (IPMSM) can be controlled within its allowable range using a pulse-width modulation (PWM) DC-AC inverter. In this paper, the effect of load torque on the iron losses of an IPMSM is studied by considering three different driving conditions, namely no-current, no-load, and load conditions. In order to perform a careful evaluation in the experiments, the motor is tested at various rotational speeds, namely 750min-1, 1500min-1, and 2250min-1; the voltage modulation index of the PWM inverter and the load torque are also varied. The experimental results in all the test cases show that the iron losses of the motor vary when the excitation condition is varied among the no-current, no-load, and load cases. Furthermore, a three-dimensional (3D) finite element analysis (FEA) is performed for the main test case when the motor is operated at the rated speed of 750min-1 for reference purpose. The harmonic components caused by the excitation inverter in the stator voltage, current, and magnetic flux density are found to be the main reasons for the increase in iron losses of the motor in the no-load and load conditions compared to the no-current condition; an increase in torque also causes a relatively significant increase in the iron losses.
In this paper, an artificial neural network (ANN), which estimates the power consumption of an electric vehicle (EV) during the deterioration process of power storage is described. This network provides important information for real-time battery diagnosis, such as state of charge of a Li-Ion battery for an EV or HEV. The data are retrieved from a scaled experiment, based on the JC08 test cycle. The network is presented as a practical alternative to analytical and empirical methods. It can predict the power consumption by an optimal solution and categorize the deterioration of the power storage with high estimation precision and within short time.
In a push-type electric tiller, the vehicle vibrates when the ground shoves the tilling claw during tilling motion. A torque is generated from the ground during tilling, and it is called reaction torque. Vehicle vibration degrades the operability of the vehicle and creates irregularity in the soil. Therefore, a tilling claw should maintain a constant speed, and should compensate for the reaction torque from tilling. The reaction torque from tilling has a periodicity. Therefore, repetitive control is suitable for the speed control of the tilling claw. In practical situations, the periodicity of the reaction torque from tilling changes when the speed of the tilling claw changes. Furthermore, there are variations in the condition of the soil surface. Repetitive control does not compensate for the variation in the periodicity and condition of the soil. This study proposes a method that combines two other methods. The first method compensates for the variation in the periodicity of the reaction torque from tilling. The second method estimates and compensates for the variation in the soil surface. The effectiveness of the proposed method is confirmed based on the experimental results.
This paper proposes a field-weakening control strategy to optimize the torque production and motor efficiency of a four-switch three-phase inverter-fed induction motor drive in the high-speed region. A method to control the torque component current (Iq) and the flux component current (Id) of the field-weakening region is proposed. The feasibility of the proposed control strategy is verified through a simulation and validated experimentally. The results show that the speed-torque characteristics and the motor efficiency are improved in the high-speed region.
This article proposes a dual active bridge (DAB) converter based wide dimming range LED driver with high-speed turn-off for high-brightness LED floodlight. In conventional LED drivers, the LED current does not turn off immediately due to the transient response of LED on-resistance and output smoothing capacitor. Furthermore, due to the constraint of minimum on-interval of MOSFET, the low LED current region is limited. DAB converter is a bidirectional DC-DC converter configured by two full-bridge converters and a transformer. The LED current feedback control is used for wide-range dimming control, and the LED voltage feedback control is used to achieve quick turn-off of the LED floodlight. Experimental results demonstrate that the proposed system is effective for LED drivers.
This paper describes the influence of rotor eccentricity on the vibration characteristics of a concentrated winding interior permanent magnet synchronous motor (IPMSM) by using a finite element method (FEM) and several measurements. The rotor eccentricity primarily caused an increase in radial electromagnetic force. In addition, an IPMSM with rotor eccentricity has higher vibration acceleration than an IPMSM without rotor eccentricity.
Real-time pricing is one of the primary features of demand response schemes for the future smart grids. From the demand side's point of view, coordination of load management conforming to the rapid power price changes is necessary. This study attempts to optimize a number of multi-unit-type air-conditioning facilities installed in an office building by using a complex evaluation function, which consists of power cost, room temperature comfort terms with priority, and total power consumption. Since an actual experiment lacks reproducibility, simulation experiments with different electricity pricing patterns are carried out. An original air-conditioner emulating model is developed and used to conduct the simulation experiments.