Mineo Tsuji

A sensorless vector control system for induction motors using q-axis flux with stator resistance identification

This paper presents a sensorless vector control system for general-purpose induction motors, which is based on the observer theory and the adaptive control theories. The proposed system includes a rotor speed estimator using a q-axis flux and stator resistance identifier using the d-axis flux. The advantages of the proposed system are simplicity and avoidance of problems caused by using only a voltage model. Since the mathematical model of this system is constructed in a synchronously rotating reference frame, a linear model is easily derived for analyzing the system stability, including the influence of the observer gain, motor operating state, and parameter variations. In order to obtain stable low-speed operation and speed control accuracy, an algorithm for compensating for the deadtime of the inverter and correcting the nonideal features of an insulated gate bipolar transistor was developed. The effectiveness of the proposed system has been verified by digital simulation and experimentation.

A novel V/f control of induction motors for wide and precise speed operation

The V/f control method is one of speed control methods for induction motors. We have proposed an auto-boost voltage method to compensate the voltage drop of stator impedance and a slip frequency compensation method to decrease the speed error caused by the change of load. Stability of the proposed V/f control system is analyzed by root locus. Steady-state torque-speed characteristics and transient responses of proposed system are presented by experimental system. Compared with the constant V/f control method, speed accuracy of proposed method is improved in various speeds and loads.

A wavelet approach to real time estimation of power system frequency

Frequency is an important parameter of electric power system, also a key index of power quality. A new approach to the estimation of power system frequency using wavelet transform is proposed in this paper. This approach adopts a complex wavelet function as band pass FIR filters to estimate the instantaneous average frequency in its pass frequency band. Besides this, a recursive algorithm of continuous wavelet transform (CWT) based on polynomial type wavelet function is also presented, by which this wavelet approach is very suitable for real time implementation. The performance evaluation exhibits a high robustness and estimation accuracy of the proposed technique over a wide range of frequency deviation. It is further shown that this approach is capable of tracking power system frequency under dynamic conditions, and is immune to the effects of harmonics and decaying DC component.

Wavelet approach to power quality monitoring

Power quality issues have become more concerned with the extensive use of power electronic devices and nonlinear loads in the electric power system, the sensitive detection and accurate classification of power disturbances attracts more attention from both utilities and industrial customers. A wavelet transform based new approach to the detection of power disturbance and measurement of power quality is proposed in this paper. This approach adopts a series of complex wavelet functions as multi-channel band pass FIR filters to detect the occurrence of disturbance, and precisely estimate the instantaneous average magnitudes and frequencies in their respective frequency bands as time varies, which are essential to power quality assessment. The performance evaluation of the proposed approach has been conducted under a variety of disturbances including momentary interruption, sag, swell, flicker, harmonics, frequency deviation, transients etc., on the basis of simulations in MATLAB environment. The evaluation results demonstrate the effectiveness and advantages of the proposed approach.

A simplified MRAS based sensorless vector control method of induction motor

This paper presents a new sensorless vector control system that is based on the model reference adaptive system (MRAS) theory. The estimation of stator currents and rotor flux is constructed in a synchronously rotating reference frame, a simple slip frequency control is obtained and a linear model is easily derived. By a constant flux control and estimation of q-axis current only, a very simple sensorless scheme is proposed too. By computing the poles and zeros of the speed transfer function, the system stability is discussed. The effectiveness of the proposed system has been investigated by digital simulation and experimentation.

A mechanical sensorless vector-controlled induction motor system with parameter identification by the aid of image processor

This paper presents a mechanical sensorless vector-controlled system for induction motors with the assistance of an image processor. Based on the observer theory and the adaptive control theory, the proposed system includes a rotor speed estimator and stator resistance identifier using the flux errors and rotor resistance identifier using the speed error between the estimated speed and the calculated speed by the aid of image sensor. The effectiveness of the proposed system has been verified by digital simulation and experimentation.

A study on power flow control for distributed generator with EDLC

Power flow control for the distributed generator (DG) with Electric Double Layer Capacitor (EDLC) is studied. The DG system consists of a voltage type inverter for connection to the AC-line and a two-quadrant DC chopper for connection to the DC-bus. The inverter and the DC chopper can be controlled cooperatively to regulate active power flow. The active power from DG to AC line is regulated by the control method. And considering the power flow in DC-bus, the EDLC current is regulated to obtain proper balance of the power and DC-bus voltage by the control method. The control theory and considerations of effectiveness of the proposed control method in simulation are presented.

Steady-state and transient characteristics of a novel V/f controlled induction motor

This paper presents a novel V/f controlled induction motor for improvement of speed characteristics. The proposed method is an auto-boost voltage method to compensate the voltage drop of stator impedance and a slip frequency compensation method to decrease the speed error caused by the change of load. The operating region of proposed method is discussed by using vector locus. The stability of the proposed system is analyzed by using root locus. In motoring mode and regenerating mode, steady-state characteristics and transient responses of V/f control method are investigated by experimental system.

Control of hexagonal Modular Multilevel Converter for 3-phase BTB system

The Modular Multilevel Converter (MMC) with cascaded full bridge cells is available for AC/AC transmission system without transformers in high voltage line. This research applied a Hexagonal MMC (H-MMC) to 3-phase AC-AC back-to-back (BTB) system. The H-MMC has six arm modules with floating capacitors and is required to regulate the input-output power and capacitor voltages by controlling currents in arm modules. Theory of the power flow of H-MMC is analyzed and the control scheme of the power flow and capacitor voltage regulation is proposed. Currents in the arm modules are controlled by the internal model principle and H-MMC can operate appropriately. Effectiveness of the proposed control method is presented in simulation and experiment.

Control of power leveling unit with super capacitor using bidirectional buck/boost DC/DC converter

As a distributed generation system increases, a stable power supply becomes difficult. Thus control of power leveling (PL) unit is required to maintain the balance of power flow for irregular power generation. The unit is required to respond to change of voltage and bidirectional power flow. So the bidirectional buck/boost DC/DC converter is applied for the control of PL unit in this research. The PL unit with Super Capacitor (SC) is able to absorb change of power, and it is examined whether the stable power supply is possible. The output current of PL unit is controlled so as to keep power balance and DC bus voltage. The effectiveness of the proposed control is proved in simulation.