Shin-ichi Hamasaki

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.

A new simplified V/f control of induction motor for precise speed operation

This paper presents a new simplified V/f control system of induction motor (IM) for precise speed operation, which is based on the vector control theory. A linear model is derived for analyzing the system stability, including the influences of motor operating states in motoring and regenerating operations, and parameter variation of low pass filter. A stator resistance identification is proposed by using d-axis current. The effectiveness of proposed system has been demonstrated by simulations and experiments.

Characteristics of MRAS based induction motor sensorless vector control system taking into account iron loss

We have proposed a current observer-based speed sensorless vector control system taking into account both iron loss and stator resistance identification. The method is constructed in a synchronously rotating reference frame. The effectiveness of the proposed system has been investigated by digital simulation and experimentation. Furthermore important control parameters such as stator resistance, observer gain and filter of speed estimation are studied by comparing the computed result with experimental one.

A precise torque and high efficiency control for Q-axis flux-based induction motor sensorless vector control system

This paper presents a sensorless vector control system for induction motors by taking into account iron loss, in which a flux-observer-based method is applied. Since the flux observer is constructed in a synchronously rotating reference frame with respect to the rotor flux of a current model and the iron loss resistance of parallel exiting circuit is used, the proposed system is very simple and the compensation of iron loss related to the operating frequency is directly realized while calculating rotor fluxes and slip frequency. The accuracies of estimated torque and speed are improved. Furthermore, a high efficiency control method that minimizes the loss is proposed. The effectiveness of the proposed system has been verified by digital simulation and experimentation

Experimental verification of hexagonal modular multilevel converter for 3-phase system

The modular multilevel converter (MMC) with cascaded full bridge cells is available for a utility interactive inverter and AC/AC transmission system without transformers in high voltage line. When it is interconnected with power line, it is possible to control the active power flow in order to supply or charge the power in the line. This research applied a Hexagonal type MMC (H-MMC) to 3-phase AC-AC conversion system. The H-MMC has six arm modules with floating capacitors, which are connected in a shape of hexagon. It is required to regulate input power, output power and floating capacitor voltages by controlling currents in arm modules. These currents can be controlled by internal model principle and H-MMC can operate reliably. Theory of H-MMC control is explained and the operation is performed in simulation and experiment. Effectiveness of the proposed control method in some typical conditions is verified in experiment.

Transient characteristics of a new simplified speed sensorless vector control for induction motors

This paper presents a new simplified sensorless speed control method of induction motors (IM). The output voltage of d-axis PI current controller is used to compute the flux angle and to control the speed in correspondence with its reference. The effectiveness of the proposed method has been demonstrated by root loci and experiments. Especially the proposed method can stabilize the system at low speed regenerating operations.

Control of Modular Multilevel Converter based on bridge cells for 3-phase AC/AC converter

The Modular Multilevel Converter (MMC) with full bridge cells is available for a utility interactive inverter in high voltage line. When it is interconnected with power line, it is possible to control the active power flow in order to supply or charge the power in the line. This research applied a Hexagonal MMC to 3-phase AC-AC conversion system. The system is controlled by internal model principle and MMC can operate reliably. Theory of the power flow control of MMC and effectiveness of the proposed control method in the simulation are presented.