This paper proposes a generalization of the fast parallel circuit simulation method for a power electric system by applying an explicit integration formula to selected energy storage elements such as inductors and capacitors. The forward Euler (FE) formula is applied to selected series inductors and parallel capacitors. Then an implicit formula such as the backward Euler (BE) formula is applied for stable numerical integration, and the optimum step size is selected for each subcircuit. A parallel processing method that utilizes thread processing techniques based on OpenMP application program interfaces with a multicore CPU and shared-memory system reduces its processing time. A new general algorithm based on a thread processing technique, a subcircuit memory processing technique, and a binary variable step size method is proposed to utilize numerical processing at each time step synchronously and efficiently.
An unbalanced input voltage three-level inverter can be applied to boost the input voltage by employing energy storage devices, such as the electric double layer capacitor (EDLC), in order to enhance the motor output performance. However, the unbalanced input DC voltage limits the output power and generates particular voltage harmonics. In this paper, the harmonic characteristics, a method to change the power distribution and the limit of the power distribution when the ratio of the DC source voltage to the EDLC voltage is changed are discussed.
This paper describes the performance of a power-leveling system with a 3.0-MJ, 9500-r/min flywheel energy storage. For the purpose of cost reduction, this system uses low-cost structures for the flywheel and the components used in the general-purpose products. Time delay of the measurement circuit limits the power control performance. To overcome this problem, a time delay compensation scheme based on the Smith predictor is used in the power control to improve the control performance of power regeneration. Consequently, the setting time is reduced by 40% as compared to the case when the compensator is not used. In addition, the effectiveness of power-leveling control in a prototype is evaluated experimentally. From the harmonics analysis, it was confirmed that power fluctuation was suppressed up to 84.6%. Furthermore, analysis of the vibrations during the power-leveling operation is carried out using an acceleration sensor. From the results, it was confirmed that the vibration levels of the prototype are sufficiently low.
A novel zero voltage soft-switching (ZVS) high-frequency resonant (HF-R) inverter using a reverse-conducting insulated gate bipolar transistor (RC-IGBT) for induction heating (IH) applications is presented in this paper. By utilizing the newly developed fixed-frequency phase angle difference (θ) control of two resonant currents, the IH load power can be continuously regulated in the proposed HF-R inverter over a wide range of output power setting under the conditions of ZVS while maintaining high efficiency. Its operating principle is described with theoretical analysis and simulation results, after which the wide-range power regulation and full-range ZVS operations are clarified by theory and analysis. Furthermore, the essential characteristics on the output power regulations, ZVS operations, and actual conversion efficiency are demonstrated in an experiment with a 1kW-60kHz laboratory prototype of the proposed HF-R inverter. Finally, its feasibility is evaluated from a practical point of view.
This paper discusses pulse density modulation (PDM) control methods for a single-phase to three-phase matrix converter (MC) in high-frequency applications. The proposed circuit is used as an interface converter for a wireless power transfer system. This converter can input a frequency of several hundred kilohertz and output a low frequency, i.e., 50Hz or 60Hz, for a commercial power grid. The proposed circuit implements a zero voltage switching (ZVS) operation by using PDM control methods and obtains high efficiency. In this paper, two PDM control strategies are compared: delta-sigma conversion and the PDM pattern generation method based on space vector modulation (SVM), which is proposed here. Also, the experimental results obtained with the proposed system will be presented and discussed. The total harmonic distortions (THDs) of the output voltage with delta-sigma conversion and the PDM pattern generation method based on SVM are found to be 5.96% and 2.15%, respectively. In addition, the maximum efficiencies with delta-sigma conversion and the PDM control based on SVM are 93.4% and 97.3%, respectively. From the results, the validity of the PDM control based on SVM has been confirmed for improvement of the output waveforms and reduction of the switching loss.
This paper presents the visualization of the PWM strategy of a matrix converter during input and output voltage periods. General relations for the duty cycles based on the input current references and the output voltage references are derived. Because the input current references and the output voltage references are treated as continuous values in the time domain, the PWM strategy can be extended to the input and output voltage periods from the control period treated as constant values. Under a low carrier frequency compared with the actual frequency, the PWM patterns that reduce the number of commutations for switching loss reduction can be visualized. The PWM strategy can be directly evaluated by using the waveforms of the input current and the output voltage. In the transient state with the change of the output voltage reference, the output voltage and input current can be visualized. The effectiveness of the visualization of the PWM strategy has been verified by comparison with the experimental waveforms.
Multi-level inverters have very attractive features such as lower harmonics in the output, lower EMI, and reduction of the required voltage rating of power semiconductor devices. Among them, lower harmonics in the output can reduce the volume of the output harmonic filter and additional losses caused by the harmonics. Therefore, multi-level inverters are expected to realize higher power density and higher efficiency. In this paper, as a basis of the quantitative investigation of these features, the harmonics in the PWM output voltage of multi-level inverters are analyzed theoretically. As an application of the theoretical results, the usefulness of the theoretical results is verified by the prediction of the harmonic contents of the load current.
Performance evaluations of a secondary-side phase shift (SPS) pulse-width-modulation (PWM)-controlled zero voltage soft-switching (ZVS) DC-DC converter with a zero current soft-switching (ZCS) active rectifier are presented in this paper. In the proposed DC-DC converter, the soft-switching operations are achievable from full to null loads by utilizing the parasitic inductances of the high-frequency (HF) transformer. In addition, no circulating current emerges in either the primary- or secondary-side full-bridge circuits, and thus the related idling power losses can be minimized. In this paper, the soft-switching operations over the wide-range load variations are verified, and the characteristics of output power and voltage versus phase shift angle regulations are demonstrated in an experiment based on a 1kW-50kHz laboratory prototype of the proposed DC-DC converter. Furthermore, the converter power losses, which include the switching and conduction power losses, are analyzed, after which the effectiveness of the proposed DC-DC converter is evaluated from a practical point of view.
A problem with an energy storage system with a flywheel is the larger power consumption during standby as compared with that of a battery or an EDLC. In order to reduce power consumption, a direct transmission mode of a matrix converter, in which the power grid is directly connected to an induction motor, is applied. However, a rush output current will occur in the matrix converter when the mode of the matrix converter is changed from the PWM mode to the direct transmission mode. In order to solve this problem, in this paper, a transition control using an AC chopper mode is proposed. In addition, the validity of the proposed control is experimentally demonstrated. Finally, the power loss of the matrix converter is analyzed for both a vector control and the direct transmission mode.
Short-circuit faults in windings due to the deterioration of insulation are one of the most common faults in motor drive systems. An easy and effective fault diagnostic method is urgently required to ensure the highly reliable operation. This paper proposes a novel online diagnosis method for short-circuit faults in the stator winding inside a low-voltage induction motor running under variable load conditions. In this study, first, several motor operations are carried out under various load conditions, and the features that represent the characteristics corresponding to the condition of the motor winding are extracted. From this experiment, it is observed that these features are linearly distributed in three-dimensional space. Second, some straight lines approximating this feature distribution obtained from healthy motors are derived, and the distances between the straight lines and the features obtained from a target motor are calculated. Then, we introduce a fault probability that can be used to diagnose the condition of the winding. On the basis of this probability, the quality of the stator winding is determined. The effectiveness of the proposed diagnosis method is experimentally verified.
There are techniques for detecting the motor current with a sensor that is placed in the DC portion of the inverter. Also, when using a DC current sensor, there is a case that current cannot be reproduced. These PWM techniques have been modified so that the detection rate of the motor current is improved. However, these PWM methods distort the motor current. In addition the acoustic noise of the motor is increased. In this paper, we theoretically explain the cause of the current distortion. The change of PWM generation causes distortion of current. We propose a PWM generation method using the three carriers. In addition, we also propose a method to reproduce the three-phase current from the DC current. We thus show that the proposed method improves the current detection rate without current distortion.
In recent years, the demand for position sensorless drives in motor drives has been increasing, and various methods to implement them have been studied. For sensorless driving at a low speed, a method using a saliency PMSM has been proposed. However, applying conventional techniques is difficult for SPMSM. In this paper, we propose a low speed sensorless drive for SPMSM without saliency in general. Then, we demonstrate the principle of anisotropy of the inductance of the SPMSM generated by the d-axis current and magnetic saturation by the magnet flux. In addition, we verify that the position can be detected with an error of 15°. In addition, we show experimentally that the rated load operation can be at a low speed.