A robust servo system is important for the performance improvement of motion control systems in several industrial applications. An ideal position servo system should accelerate the rotor to its rated speed by applying maximum acceleration torque, and it should decelerate the rotor by applying the maximum deceleration torque. The position servo system should stop at the target position without overshoot. When the position reference profile of the conventional position servo system is not ideal, there are two problems in achieving the ideal high-speed positioning response. One is the windup phenomenon caused by the saturation of the PI speed regulator. The other problem is the slow deceleration response near the target position that is due to the error input of the position servo system becoming small. In order to overcome these problems, this paper proposes a new robust high-speed positioning servo system based on a disturbance observer. The proposed system corrects the integrator value of the PI speed regulator by using the torque current reference estimated by the disturbance observer. The experimental results show that the proposed robust high-speed positioning servo system has a quick and stable position response.
In this study, we investigate the torque response of a control system that is based on the direct torque control (DTC) principle for an interior permanent magnet synchronous motor (IPMSM). We also propose a gain-scheduling method for improving the torque response. Reference flux vector calculation (RFVC) DTC is used in this study. In RFVC DTC, a PI controller is used for torque control; this is in contrast to the use of the hysteresis comparator and switching table in basic DTC. In this paper, we present the relationship between the torque response and the gain of the PI controller. This relationship is derived by using the transfer function of the torque control loop. In this study, we also examine the difference between the torque responses of two motors that have different machine parameters. The proposed method can be used to realize a torque response that is independent of the operating torque. The simulation results and experimental results presented in this paper show the validity of the derived relationship as well as the effectiveness of the proposed method.
Series compensation in transmission systems is efficient for improved utilization of the grid. However, during faults, large over-currents will result and necessary protection must be installed. This increases the costs significantly. A power flow controller called the magnetic energy recovery switch (MERS) is investigated. The configuration consists of four active switches and a small dc capacitor. It is characterized by a large steady-state voltage-current operating range. A special capability of the configuration is the possibility to conduct current in two parallel arms when the voltage across the capacitor is zero. It can be found that this increases the over-current capability of the device to almost the double. A protection method utilizing the active switches is suggested. By applying simple control, parallel conduction mode can be reached quickly after fault occurs. Small scale experiments demonstrate simple implementation and successful operation. Additionally, large scale system investigations show that the influence of the protection method on the required semiconductor rating is low. This indicates the potential for significant protection cost reductions.
This paper presents input power factor control of three-phase to three-phase matrix converters. The authors propose the three kinds of switching patterns for the matrix converters that can realize arbitrary input-power-factor angle between 0 to 2π and reduce the number of commutations in all of the three phases to four times during the control period. Also, the control range of the output voltage reference in the proposed control scheme is derived. The improvement of the input power factor by using of the proposed control algorithm has been verified by experiments.
A new identity dimensional D-state observer whose state variables are the stator reaction flux and rotor flux is proposed for the sensorless drive of permanent-magnet synchronous motors. Furthermore, sufficient conditions are newly and analytically derived for the observer gains that guarantee stable convergence of state variable estimates. Additionally, two new methods for designing observer-gain are presented; these methods—the constant and speed-dependent gain-methods—satisfy the derived analytical conditions. The observer gain conditions used in these design methods are validated through extensive numerical experiments. In addition, typical design examples of the observer gains by using the proposed design methods are presented.
Permanent-magnet synchronous motors (PMSMs) with a sinusoidal back EMF are widely used in domestic appliances for reduction of acoustic noises and energy consumption. PMSMs are generally controlled with a sinusoidal waveform current. Typically, PMSMs are controlled by vector-controlled sinusoidal drives, which require powerful computational resources. Hence, simpler sinusoidal wave drives such as V/f drives, which control the phase difference between the voltage and the current (power factor of PM Motor) have been proposed for controlling PMSMs. This paper presents a new method that does not require current sensors but can be used to estimate the phase difference by sampling the voltage of the shunt register, which is used to detect the over current supplied to the inverter. This method enables detection of current and accurate estimation and appropriate control of the phase difference. Using this method, we could control the phase difference and achieve high efficiency, cost reduction, and high reliability.
This paper presents a new air flow controller for a thermal power plant. When an inverter power source is used for a forced draft fan (FDF) in order to save power, the conventional counter measures do not caver all in abnormal state. The proposed controller is evaluated by performing a simulation. It is clarified that the power source is changed from the inverter to a commercial power source within 0.5s in abnormal state. The changing time is decided 0.55s by a mechanical permission of design. When testing is carried out in an actual plant by using the proposed controller method, a transient response is compared with simulated and measured data. The errors are less than 3.4%. Furthermore, the FDF changes over smoothly and the plant condition keeps as same as normal state in the actual plant testing. This paper deals with the safe operation of a thermal power plant that employs the proposed air flow controller.
This paper proposes a method for calculating and analyzing the current waveforms of a permanent magnet synchronous machine (PMSM) that is controlled by a PWM inverter with harmonic distortion. This method is based on dq axis equations. Reactances are calculated by considering the saturation and cross-magnetization, and they are examined along with their frequency characteristics. These reactances are calculated by using the finite element method and the dq axis equations to satisfy the steady load condition. A comparison of the calculated and measured waveforms for a 5-kW PMSM shows that the two waveforms are in good agreement.
This paper deals with a resonant gate-drive circuit for fast and high-voltage power semiconductor devices, which is equipped with optical fibers for both control and power supply. A resonant inductor connected with the gate terminal of the power device makes it possible to charge or discharge the gate-to-source voltage by using parallel resonance between the inductor and the input capacitance. The optical fibers can be used to deliver the driving power to the circuit, because the circuit theoretically produce no power consumption for driving the power device. Moreover, the proposed circuit makes it possible to suppress fluctuations in the gate-to-source voltage caused by rapid charging or discharging of the drain-to-source terminals. Experimental results are shown to verify the viability of the proposed circuit.
Switched reluctance motors (SRMs) are widely employed as industrial drives because they are inexpensive, simple, and sturdy, further, they deliver a robust and reliable performance. SRMs are controlled with a rotor position sensor attached to the motor shaft. Normally, encoders, resolvers, or Hall sensors are used as position sensors. The use of these sensors, however, increases the size and cost of the machine and degrades its performance. Therefore, to overcome these difficulties, several sensorless drive techniques have been reported. In this paper, a method for estimating the position of a rotor in an SRM; this method is based on calculation of the space vector of phase inductance at standstill and low speeds. The position at standstill is obtained simply without making use of the magnetic characteristics of the motor or any additional hardware. Assuming the inductance waveform to be a sine wave, the position of rotor at standstill is obtained from the phase inductance vectors of all phases. At low speeds, position estimation is carried out by applying a DC link voltage to the unenergized phases. The validity of the proposed method is experimentally verified.
In this paper, a novel method for bandwidth compression and transmission of environmental information is proposed for bilateral teleoperation systems with multiple degrees of freedom (MDOF). In this method, environmental information, i.e., the position of end-effectors and the reaction force exerted on them, is converted into environmental modes by using discrete Fourier transform (DFT) matrices. The environmental modes to be transmitted are then selected on the basis of the communication bandwidth between master and slave robots. Bilateral control is achieved in low-frequency modal spaces, and local position control is achieved in high-frequency modal spaces. The validity of the proposed method is confirmed by performing an experiment.
It has been reported that the calculated values of field transient behavior in a synchronous machine differ considerably from the measured values. This discrepancy is caused by the use of equivalent circuit constants in standardized tests provied by JEC2130 and IEC60034-4, in which the mutual leakage reactance between the damper and field windings is not accounted for. The authors have been studying a method for calculating equivalent circuit constants for the accurate simulation of transient behavior including the field winding side, by means of a standstill test with a small-capacity DC power supply (DC decay testing method). The authors have previously presented a calculation method using operational impedances with the field windings opened, shorted, and inserted with an external resistance, obtained by the DC decay test. This paper presents a new method in which the external resistance used in our previous method is no longer needed. Instead, the field winding impedance is determined based on its invariability against slip. The validity of the new method is demonstrated by comparing the calculated and measured values of the armature and field currents during a sudden three-phase short-circuit using 10kVA-200V-31.9A-4P-50Hz test machines.
We present a three-degree-of-freedom planar actuator that can position a mover over a wide range of locations in the yaw and translational directions. In conventional planar actuators, which have multiple pairs of permanent magnets and armature coils, the mover cannot be displaced by large amounts unless the planar actuator has numerous armature coils. Furthermore, the movable area of conventional planar actuators in the yaw direction is quite narrow because of the interference between the different pairs of permanent magnets and armature currents that occurs due to the yaw displacements. The proposed planar actuator has only six stationary armature conductors for two sets of three-phase currents. The mover constantly faces all the armature conductors, and hence, it can be subjected to driving forces for three-degree-of-freedom movement anywhere on a plane parallel to the stator surface. Therefore, the movable area of the actuator can be easily expanded by increasing the length of the armature conductors. However, the driving forces depend on the yaw angle, and large yaw displacements impede the generation of sufficiently strong driving forces. In this paper, we present the results of experiments conducted to determine the movable area of our proposed planar actuator in the yaw direction. The experimental results indicate that sufficient torques in the yaw direction can be generated when the yaw displacement is less than 26deg. The driving force acting on the mover is a function of the yaw angle and is periodic with a 90-deg period due to the central symmetry of the actuator. The experimental results also indicate that the mover can travel over 90-deg displacements in the yaw direction. Thus, we successfully demonstrate the three-degree-of-freedom large movement of the planar actuator by controlling two sets of three-phase currents.
One type of braking system for railway vehicles is the eddy current brake. Because this type of brake has the problem of rail heating, it has not been used for practical applications in Japan. Therefore, we proposed the use of a linear induction motor (LIM) for dynamic braking in eddy current brake systems. The LIM reduces rail heating and uses an inverter for self excitation. In this paper, we estimated the performance of an LIM from experimental results of a fundamental test machine and confirmed that the LIM generates an approximately constant braking force under constant current excitation. At relatively low frequencies, this braking force remains unaffected by frequency changes. The reduction ratio of rail heating is also approximately proportional to the frequency. We also confirmed that dynamic braking resulting in no electrical output can be used for drive control of the LIM. These characteristics are convenient for the realization of the LIM rail brake system.
A soft-switched neutral-point-clamped single-phase boost rectifier capable of compensating the imbalance load voltage is studied. This is based on a single-phase rectifier, in which an inductor is placed in series with the AC supply to resonate with a capacitor connected across the DC output of a full-bridge rectifier and the switching transition is mainly governed by a series resonance. The experimental prototype using insulated-gate bipolar transistors is implemented to investigate the operation under the charge control. The experimental results confirm that the rectifier has a neutral-point-clamp feature providing a good quality AC current.