Shinzo Tamai

Secondary Resistance Identification of an Induction-Motor Applied Model Reference Adaptive System and Its Characteristics

Induction-motor torque is not accurately controlled when the estimated secondary resistance of an induction-motor model in a vector controller differs from the true secondary resistance. An algorithm which identifies the secondary resistance on-line is developed. The motor operating condition for secondary resistance identification, the stable identifier organization, and the experimental investigation confirming the identification algorithm performance are presented. The algorithm is based on the theory of model reference adaptive systems (MRAS). The proposed algorithm stably identifies the secondary resistance under any load and any speed when a sinusoidal signal is injected into the flux axis primary current. The vector controller adopting this algorithm controls motor torque accurately under any load and any speed.

Static starting device for the start-up of the gas turbine using position sensorless control method

Static starting devices, also called static frequency converters (SFCs), have been utilized to start gas turbines in gas turbine combined cycle (GTCC) power plants, etc. In general, a gas turbine is started using a generator as a synchronous motor with a single-shaft arrangement that is rotated by the electric power fed from the SFC. Because the rotor position signal of the generator is indispensable for controlling the SFC, a mechanical position sensor is installed beside the rotor shaft. However, such mechanical position sensors require considerable time for installation and adjustment at the site. Therefore, a sensorless control method called the advanced position sensor (APS) has been developed and applied to an SFC. In this paper, we describe an SFC that employs this position sensorless control method. Further, we investigate the applicability of the APS by comparing the pulses of the two systems — APS and the traditional position sensor — observed during start-up.

Immunity test results of a quick power failure detector of uninterruptible secondary battery system

An uninterruptible secondary battery system (USBS) consists of secondary batteries and a multi-functional power converter having plural operational modes including local load leveling and uninterruptible power supply (UPS). For the USBS, a quick power failure detector is essential for the smooth operational mode changes. However, commercial AC line voltage harmonic distortion or voltage unbalance may cause misoperation of the quick power failure detector. In this paper we present immunity test results of the USBS. The test results proved that the proposed detector has sufficient immunity to harmonic distortion and unbalance of the commercial AC line voltage.

Disturbance ride through of SVC stabilizing AC voltage at remote Renewable generations

The Renewable power generations are sometimes located in remote area from the load centers and connected through the long transmission lines. In such case, the AC voltage likely varies along with the renewable power variation. The static Var compensator (SVC) is required to stabilize the AC voltage for stable power transmission [1]. In long transmission lines, the geomagnetic disturbance possibly makes problems [2], which may stop the SVC operation. Without the SVC, the renewable generations are sometimes required to limit its output power. This paper, firstly, discusses the mechanism of the problem which is related to the DC current component induced by the geomagnetic disturbance in the current of the Thyristor Controlled Reactor, TCR, a type of Static Var Compensator, SVC. Without any mitigation, the magnetizing condition of the transformer connected to the TCR may be worsened and may result in stopping SVC operation. Then, secondly, the paper discusses suppression of the DC current component. In the discussion, the paper proposes the practical algorithm for the DC current component estimation for the three phases considering asymmetrical even-order voltage harmonics. Finally, the paper verifies the DC current suppression control through the simulations.

Development of a novel power apparatus to make up for voltage dips and interruptions based on quick reversible operation of a PWM converter

Along with wide and deep penetration of electronics application into our modern society, voltage dips and momentary interruptions, mainly due to lightning and snow damage on overhead transmission lines, have become a disturbance to normal operation of loads. A UPS, which is mostly employed to protect sensitive loads from disturbances, has such limitations that it dissipates no less energy in running operation because currents flow through two converters in series, it is poor in feeding electric motors which occupy the main loads in industrial plants and that its costs are high to be commonly applied. UPS can be regarded not as omnipotent against voltage dips and short interruptions. We have developed a novel power apparatus termed QBS (quick backup system) to supplement the above drawbacks in UPS, employing one reversible AC/DC converter and one high-speed switch. Normally QBS supplies power directly from a commercial network to critical loads while the reversible converter interconnects with it to charge the battery. When the critical bus voltage deviates from the tolerance range QBS disconnects the high-speed switch and continues to feed the critical loads in UPS mode. The whole power transition is completed within 2 ms. QBS of several thousands kVA has already been put to commercial use in telecommunication centers, electronics manufacturers and others.