Direct AC/AC converters have been studied due to their potential use in power converters with no DC-link capacitor, which can contribute to the miniaturization of power converters. However, the absence of a DC-link capacitor makes it difficult to control the AC motor during power interruption. First, this paper proposes a system that realizes AC motor control during power interruption by utilizing a clamp capacitor. In general, direct AC/AC converters have a clamp circuit consisting of a rectifier diode(s) and a clamp capacitor in order to avoid over-voltages. In the proposed system, there is an additional semiconductor switch reverse-parallel to the rectifier diode(s), and the clamp capacitor voltage can be utilized for AC motor control by turning on the additional switch. Second, this paper discusses an operation method for AC motor control and clamp capacitor voltage control during power interruption. In the proposed method “DC-link voltage control”, the kinetic energy in the AC motor is transformed into electrical energy and stored in the clamp capacitor; the clamp capacitor is therefore charged and the capacitor voltage is controlled to remain constant at an instruction value. Third, this paper discusses a switching operation during power interruption. A dead-time is introduced between the operation of turning off all switches on the rectifier side and the operation of turning on the additional switch, which prevents the occurrence of a short circuit between the interrupted power source and the clamp capacitor. Finally, experimental results are presented. During power interruptions, an output current was continuously obtained and the clamp capacitor voltage was maintained to be equal to the instruction value of the capacitor voltage. These results indicate that both AC motor control and capacitor voltage control were successfully achieved by using the proposed system.
This paper presents a modular photovoltaic system (MPVS) that uses a chain-link-type multilevel converter (CLMC). In large-scale PV generating systems, the DC power supply is generally composed of a large number of PV panels. Hence, losses are caused by differences in the maximum power point at each PV panel. An MPVS has been proposed to address the above mentioned problem. It helps improve the photoelectric conversion efficiency by applying maximum power point tracking (MPPT) control to each group of PV panels. In addition, if a CLMC is used in an MPVS, a high voltage can be output from the AC side and transmission losses can be decreased. However, with this circuit configuration, the current output from the AC side may be unbalanced. Therefore, we propose a method to output balanced current from the AC side, even if the output of the DC power supply is unbalanced. The validity of the proposed method is examined by digital simulation.
This paper proposes a novel concept for non-isolated buck-boost DC/DC converter and control method. The proposed concept uses a series connection converter that only regulates the differential voltage between the input and output voltage. As a result, the power converter capacity is decreased. Moreover, the proposed circuit has advantages such as improved efficiency and losses reduction. The fundamental operation, control method, and design method of the proposed circuit are described in this paper. In addition, the validity of the proposed circuit is confirmed by carrying out simulations and experiments.
In PWM inverters, dead-time is necessary to prevent short-circuits in the power supply; the dead-time results in output quality deviations and hinders dc-link voltage utilization. In this paper, the dead-time mechanism of inverters with an LC filter is analyzed, and a mathematical model is presented. Using this model, we propose a new current control scheme involving the use of a PI controller and a sliding mode controller. Depending on the sliding mode controller output, the upper side switch or the lower side switch can be kept off, and the counter side switch can be controlled up to a PWM duty of 100%, with a smooth transition between different dead-time operation modes. The scheme maximizes the dc-link voltage utilization and improves the conversion efficiency. Experimental results show that harmonic distortion is decreased to 1/3-1/2 of that in the conventional PI control scheme, the dc-link voltage can be reduced by about 10%, and an improvement of 1.6% is achieved in the efficiency.
A high-frequency inverter is proposed and designed for high-power induction heating applications. It consists of a boost chopper, half bridge, and series load resonant circuit. High power is available without increasing the line voltage because the inverter consists of a boost chopper. The boost chopper also works as a part of the inverter circuit. Therefore, three IGBTs, which are included in the boost chopper, half bridge, and the output diode, operate as a full-bridge inverter. The switching operation which are classified into six modes, are illustrated. Soft switching operations of S1 and S2 are obtained by adopting a loss-less snubber capacitor. By using simple equations, the series resonant capacitor is designed for approximately tuning the resonant frequency. The maximum rated power can also be estimated by using these equations, and a simulation is carried out to verify its value. The experimental results using the scale models and the simulation results prove the equations. These experimental results show that the output power of the proposed inverter is higher than that of a conventional one.
This paper proposes a high efficiency isolated DC/DC converter using series compensation. The proposed converter consists of a high efficiency resonance half-bridge converter and a series converter. The proposed circuit regulates the output voltage by the series converter, which provides only differential voltage between the input voltage and output voltage. Therefore, the circuit achieves high efficiency when the input voltage is close to the output voltage, because only the resonance converter operates. In this paper, the approach used to obtain high efficiency with the proposed series compensation method is introduced. In addition, the fundamental operation and the design method of the proposed circuit are described. The validity of the proposed circuit was confirmed by experiment and loss analysis, with a maximum efficiency of 95.8%.
In this paper, a new control method is proposed for the utility interactive inverter based on the deadbeat control with the FPGA-based hardware controller to improve the control response of an utility current. Deadbeat control is one method to ensure the output voltage or current matches with the references at the sampling instant; therefore, by adopting this control law to the utility interactive inverter, the response of the system is much improved compared with the conventional PI control. The utility interactive inverter is linked to the commercial source via the interactive inductor, and so the inverter controls the output voltage based on the deadbeat control to regulate the output current through the interactive inductor. As a result, a very fast transient response of the utility current can be achieved. The current control method using voltage deadbeat control and PLL control with quasi dq transformation with multisampling parallel processing method are implemented in the FPGA-based hardware controller for the single phase utility interactive inverter.
DC machine has been used in steel industries and paper industries, Owing to their advantages for adjustable speed drive. The design objective for DC machines is to increase their output power and decrease their size and weight, though DC machines have more than 100 years of application history. Commutation is one of the most important for phenomenon which determines machine reliability, when the design objective is required in design stage. In other words, the commutation is an armature coil current reversing process, in commutation circuit where the coil is short circuited by brush. In this paper the “Equivalent commutation circuit" which is well known is applied to analyze the commutation process in this field. If the reversing process is retarded commutation spark may accrue at leaving edge of the brush and commutation failure may be caused.
We carried out FEM simulations for modeling ultra-high-speed universal motors by using the state function method and analyzed the phenomenon of commutator sparking, the characteristics of the air gap surface, and the contact condition or contact resistance of the brushes and commutator bars. Thus, we could quantitatively analyze commutator sparking and investigate the configuration of the iron core. The results of FEM analysis were used to develop a model for predicting the configuration of the iron core and for estimating the electromotive force generated by the transformer, armature reaction field, spark voltage, contact resistance between the rotating brushes, and changes in the gap permeance. The results of our simulation were experimental results. This confirmed the validity of our analysis method. Thus, an ultra-high-speed, high-capacity of 1.5kw motor rotating at 30,000rpm can be designed for use in vacuum cleaners.
This paper proposes a novel way for achieving wireless power transfer from a transmitting antenna to a receiving antenna. This technique is suitable for charging electric vehicles (EVs) because the proposed antennas can transfer power wirelessly with high efficiencies when the antennas are displaced and have large air gaps. This technique utilizes near-field antennas at resonance; however, this technique is still being perfected. This paper describes this techniques' analysis, its results, as well as the possible antennas that are suitable for EVs.
This paper proposes a novel method of contactless power transfer from a transmitting antenna to a receiving antenna. This method involves electromagnetic coupling of near-field antennas at resonance. However, the exact manner in which method this method can be used to design antennas and circuits has not been clarified. Therefore, this study focuses on defining the exact frequency and efficiency required fore electromagnetic coupling on the basis of the antenna theory, circuit theory, experimental observations, and electromagnetic computations and experiments.
This paper proposes sensorless sinusoidal driving methods of permanent magnet synchronous motors for fans and pumps by V/f control. The proposed methods are simple methods that control the motor peak current constant by voltage or frequency control, and are characterized by DC link current detection using a single shunt resistor at carrier wave signal bottom timing. As a result of the dumping factor from square torque load characteristics of fan and pump motors, it is possible to control stable starting and stable steady state by V/f control. In general, pressure losses as a result of the fluid pass of fan and pump systems are nearly constant; therefore, the flow rate and motor torque are determined by revolutions. Accordingly, high efficiency driving is possible by setting corresponding currents to q-axis currents (torque currents) at target revolutions. Because of the simple current detection and motor control methods, the proposed methods are optimum for fan and pump motor driving systems of home appliances.
An image sensor that can accurately measure the position and height of a crane spreader has been proposed for suppressing the sway motion generated in the process of manually operating a crane. The image sensor consists of a pair of landmarks attached to the upper surface of the spreader, a CCD camera installed in the trolley on the top of the crane, and a PC, and has the following several advantages. (1) The image sensor is safe for the operators handling cranes due to the passive measurement method. (2) It employs a specific landmark. (3) It uses a robust template matching method “Vector Code Correlation method”, which is suitable for the landmark detection under outdoor light conditions. We verified these features through the fundamental experiments such as the position change of a crane spreader using a moving stage and the illumination condition change. As in the results, we estimated that the absolute error of the image sensor is within 3.3mm in sway motion and within 0.5% while moving from 5m to 20m in height. In addition, we also confirmed the usefulness of the image sensor by applying the measured data to an anti-sway controller on a model crane.
A current source converter between single-phase and three-phase are presented. The converter circuit consists of four legs with eight switching devices. The PWM strategies with the sinusoidal modulating wave and the triangular carrier wave are employed for sinusoidal waves in ac sides. The selection of the device to obtain the sinusoidal PWM controlled current is shown and the switching patterns are given.
Single-phase half-controlled buck rectifier using a simple snubber energy recovery bridge leg is studied. When the active power devices assembled into this bridge leg are simultaneously turned on, the snubber capacitor is discharged and its stored energy is transferred to the load circuit. The experimental results confirm that the input current can be waveshaped sinusoidally with the higher efficiency than that of the conventional one.