This paper proposes a method of improving the back-drivability of torque control according to the dynamic characteristic of forward-drivability based on the concept of proposed equivalent expression. The control strategy is composed of disturbance observer (DOB), a load-side DOB (LDOB) and the designed controller for torque control. The DOB realizes robust motion control by compensating for the friction and modeling error of the system, and the LDOB estimates the external torque input from the load-side. According to the designed controller, the proposed method constructs the back-drivability as forward-drivability via each transfer function of the equivalent expression. In addition, a scaling factor is introduced to quantitatively adjust the back-drivability to adapt to different application demands. Moreover, the decision basis of parameters in the proposed control is discussed and the effect on the control system is clarified. The experimental results are compared with the conventional torque control method, and show the consistency in the quantitative improvement of back-drivability effectively with the scaling factor.
We developed an integrated railway simulator that can simulate the collaboration each subsystem of a railroad, such as a train, signalling system, and power-supply system, and also train operation and energy usage on the basis of the collaboration of subsystems in all relevant railroads. The purpose of this simulator is to determine the change in energy consumption of trains and substations depending on the changes in the train characteristics, timetables, power-supply systems, and other such variables. This simulator's targets for calculation are the energy consumption of substations and trains restricted by the conditions of signalling and traffic-control systems. In this simulator, we modeled each subsystem on the basis of its physical characteristics, and we designed an electric circuit on the basis of the subsystem's characteristics. The characteristics of each subsystem are non-linear. Therefore, we used an iteration method to calculate the solution of the electric circuit. However, the iteration method may fail to calculate a solution. To prevent this, we developed a method to select an appropriate model of the subsystem using the convergence history of the iteration method. By applying the proposed method to our simulator, we could eliminate convergence failure and reduce the average number of iterations required for convergence.
The construction industry, which faces an aging workforce and shortages of skilled labor, presents attractive opportunities for autonomous heavy construction machinery. To achieve this goal, many difficulties must be overcome. Most of the problems are nonlinear and cannot be solved through convex optimization. Bulldozer operation presents especially difficult challenges, as it is a skilled trade and obtaining an operational method for bulldozers analytically is difficult. In this study, we optimized the route planning of a simulated bulldozer by using a genetic algorithm. To properly evaluate the solution candidates, we developed a simulator that emulates the dynamics of a sand mound. This paper describes the developed simulator and discusses the optimization of bulldozer paths on construction sites.
The robots used in our daily lives come in contact with the environment not only directly, but also through grasped objects and tools. In such cases, the shape of the grasped objects could be unknown or uncertain; thus, the shape must be estimated using information about the contact. However, previous studies could not estimate the shape of the grasped objects without knowledge about the contact environment. In this study, unscented particle filters were used to estimate the contact positions, contact forces, and shape of the tools, simultaneously. In addition, we verified that the proposed method can estimate these characteristics by measuring the force and torque in the robots.
This paper proposes a new synchronous rectification (SR) scheme for frequency-modulated bi-directional CLLC resonant converters. By introducing a small-phase-shift between the two full-bridges and utilizing the switching transient, the proposed scheme effectively avoids the magnetizing current being provided from the low voltage side. This leads to considerable reduction in the conduction losses and current stress of the switches in a high-step-down design. Furthermore, the output voltage characteristic is analyzed using a novel mathematical model, which, comparing to the fundamental harmonic approximation method, can not only acquire a more accurate result of steady-state characteristic, but also calculate an accurate set of initial values for the passive components, which is crucial to determine the proper dead-time and phase-shift. Based on the new model, the boundaries of dead-time and phase-shift are discussed in detail. Finally, a prototype is built, and experiments are conducted to verify the principles of the proposed scheme.
Conventional digital controllers have limited switching-frequency resolution and computational speed. This results in a large output voltage ripple and poor dynamic performance with a low control bandwidth in high switching frequency resonant converters using an inductor-inductor-capacitor (LLC)-type resonant tank. This paper proposed a controller design based on a field programmable gate array (FPGA) for an LLC resonant converter to improve the switching-frequency resolution and dynamic performance. The improved performance is analyzed using theoretical methods compared with that of a general-purpose digital signal processor (DSP). The performance improvement is verified through circuit simulations and signal-level tests using a hardware-in-the-loop (HIL) test system.
Thermal welding systems are widely used in industrial applications such as packaging machinery, food manufacturing machinery, injection molding machinery, and chemical plants. In these machines, the modeling of the thermal welding system is important to control the temperature with high accuracy. The actual thermal welding system is a distributed parameter system. When implementing the actual machine, it is generally used to approximate a lumped parameter system. However, the optimal approximation such as the selection of necessary and sufficient order to a lumped parameter system is difficult. This paper proposes an abstraction method for the thermal welding system based on an element-description method. The proposed method can abstract the necessary and sufficient model. Therefore, it is possible to design a highly accurate control system according to requirements.
This study investigates a single-phase common-ground transformerless inverter topology for grid-connected photovoltaic (PV) systems. The inverter shares a common ground with the grid and utilizes minimal components for power conversion, making it suitable for use as an integrated microinverter for solar PV modules. The peak of the ac output voltage is the same as the input DC voltage, and a virtual DC bus capacitor is used to provide power during the negative cycle of the inverter. A simple unipolar sinusoidal pulse-width modulation technique is used to modulate the inverter minimizing switching loss, output filter requirements, and output current ripple. Moreover, a double-charging process is employed to minimize the inrush charging current of the virtual DC bus capacitor. Various operating states along with the design guidelines for choosing the constituent components are presented. Finally, some simulation and experimental results are presented for a 1kW prototype to validate the proposed topology.
This paper proposes an approximation model of the AC resistance for windings with partial layers. It introduces the concept of the number of layers for the partial winding without theoretical support. It is simpler compared to the original partial layer equation and and has a good accuracy. The error between the approximation and the original equation is derived and compared analytically. The approximation method is verified in two case studies with simulation results of the finite element method and experimental results. Based on the approximation equation, an optimization method is proposed for the winding with partial layers. This can provide a minimum AC resistance within the design restrictions and can be applied to inductors and transformers. Finally, the optimization method is verified in a case study of a 20kHz transformer winding design.
In this study, the impact of negative gate voltage (VG(off)) on the turn-off performance of Si-IGBT device is investigated. In general, the switching energies of the IGBT devices are given at specific VG(off) =-15V. When estimating the power dissipation of the inverter system at different VG(off), a correction factor of the switching energies from the given values is required. Although it is known that the value of VG(off) affects the turn-off switching characteristic, it has not been investigated in detail. Hence, it is difficult to theoretically estimate the correction factor for the turn-off energy (Eoff) for different VG(off) and gate resistance (RG). The effect of VGE(off) on the behavior of collector-emitter voltage (VCE) during the turn-off operation of the IGBT is investigated. The estimation method of Eoff at different VG(off) and RG is derived from the investigation and theoretical formula confirmed by the experimental results. Then, a novel procedure to estimate the Eoff correction factor under different gate drive conditions is proposed.
This work is concerned with a technique to alleviate thermal concentration on specific switching devices that drive a permanent magnet synchronous motor (PMSM) under zero-speed and high-torque condition. In this condition, e. g., start or stop of an elevator or hill-start of an electric vehicle, a large DC current flows in the PMSM, and the heat generated in the specific switching devices is locally concentrated. The proposed technique uses a zero-sequence voltage in a three-level inverter, and the polarity of the zero-sequence voltage is switched according to the magnetic pole position of the PMSM. The proposed technique can change the current paths in the inverter, and the loss concentrations in specific devices can be alleviated. The simulation results show that the amplitude and the time ratio of the zero-sequence voltage that depend on the magnetic pole position of the PMSM affect the temperature rise of the power device with the maximum temperature. In the experiment, the effectiveness of the proposed technique is evaluated using a small power inverter. This three-level inverter consists of discrete power devices so that the surface temperature of each device can be observed with a thermal camera. The experimental results show that the temperature rise of the device with the maximum temperature is reduced by about 31%.
This paper presents a three-phase Modular Differential Inverter (MDI) utilizing DC-DC modules that provide AC power to the utility grid with step-up voltage capability. The construction of the MDI has many advantages such as flexibility and reliability, and can be designed, optimized and scaled to any power level. Moreover, Single-Ended Primary-Inductor Converter (SEPIC) modules have been proposed to incorporate in the MDI because it has many merits that enhance the overall performance of the differential inverter. SiC devices are also integrated into the SEPIC modules for efficient operation at a high switching frequency. An in-depth mathematical model discussing the practical issues of differential inverter such as variable duty cycle, low order harmonics and circulating power is also presented. The design steps of the proposed SEPIC modules are presented in detail considering the standard grid side requirements of total harmonic distortion (THD). The MDI, which implements three parallel modules in each phase, is investigated using PSIM simulation software. A mismatch of ±20% in the SEPIC module parameters of each phase is investigated to confirm the system performance. Moreover, a laboratory prototype of the system, considering only one SEPIC module in each phase with 200V grid-side voltage, 1.6kW, and 50kHz switching frequency, is carried out to verify the validity of the system.
Growth in the electric vehicle industry has resulted in considerable chemical battery waste, which requires special recycling processes. The power and recharging capacities of waste batteries are insufficient for the operation of traction motors. However, such batteries can be reused as power sources in residential renewable energy systems because household energy demands are much lower than those of electric vehicles. To enable this reuse, a battery pack should be equipped with an equalizer. Hence, in this study, we propose a battery module equalizer that adjusts the state of charge (SOC) of each battery module to the same point using a generation control circuit (GCC). By strategically changing the duty ratio of the GCC while detecting the overall voltage of the entire battery pack, the relative SOC of each battery module can be observed while the battery system is in operation. Although this approach uses only two sensors, it enables SOC observation for the entire battery pack, leading to reduced implementation costs and form factor. The equalization current is further regulated based on the observed relative SOC. The simulation and experimental results demonstrate the rapid equalization capability of the proposed GCC-type equalizer during the discharging process.
This paper focuses on the response deterioration of the force balance control system including the temperature control system due to the difference between heating and cooling speed. Our conventional method uses the limit error feedback method to suppress the windup of the temperature controller. The proposed method realizes the quick force balance control system using the equilibrium point movement controller. The experimental results show that the convergence time of the proposed method is faster than that of our conventional method, and the same response is obtained at different operating points.
This article deals with harmonics compensation with a four-leg structured active power-line conditioner (APLC) in three-phase four-wire distribution feeders (TPFWDFs). The instantaneous power flowing into the APLC shows that the constant DC-capacitor voltage-control (CDCVC) of the four-leg structured APLC obtains balanced and sinusoidal source currents with a unity power factor (PF) at the point of common coupling (PCC). A reduced-scale experimental model is constructed and tested. Experimental results demonstrate that balanced and sinusoidal source currents with a unity PF at the PCC are achieved with the CDCVC-based method of the four-leg structured APLC, compensating harmonic, unbalanced-active, and reactive currents in TPFWDFs.
The theory for three types of power conversion is established. In a controlled rectifier circuit, the input poly-phase AC sources are switched and connected to the load one by one; thus, AC-DC conversion is established. This mechanism is referred to as power conversion by change of sources. On the other hand, in a DC-DC step-up chopper circuit, there is an interval when the input source supplies energy to a reactor and this reactor energy possessing its own direction is defined as electromagnetic momentum. After a switching action, in the next interval, the circuit begins to enclose the load and forms a current loop circulating through the source, reactor and load. Then, the electromagnetic momentum will force the current to flow into the load which is at a higher voltage than the source. The switch action will be repeated on and off, and the current loop will be changed accordingly; then, power conversion will be established and this mechanism is named as power conversion by change of loops. In addition, by using a four-quadrant switching device to change the source polarity, DC-AC conversion can be achieved, and this mechanism is defined as combined power conversion. Extensive discussions on the technical terms have also been undertaken, such as classification naming for the diode and the thyristor.
Drive train bench, which is a type of dynamometer, is used to test the power train components of a vehicle such as transmission, torque converter, etc. The test system has to simulate the vibration torque of the engine by motor control. Conventionally, a sine wave is used to simulate the vibration torque of an engine. However, the actual vibration torque waveform contains harmonic distortion components inherent in the engine. Therefore, it is desirable to have a vibration control technique capable of simulating the waveform of the engine torque more accurately. This paper proposes a novel engine torque simulated vibration control for the drive train bench system. The proposed method can achieve a shaft torque detection value that follows the desired engine pulsation torque waveform by utilizing robust resonance suppression control and a generalized periodic disturbance observer. The validity and usefulness of this technology are indicated by the theoretical explanation, simulation, and experimental results.