Akihiro Odaka

A novel approach to practical matrix converter motor drive system with reverse blocking IGBT

This paper proposes a novel control strategy and a protection circuit and shows the advantage of utilizing a newly developed reverse blocking insulated gate bipolar transistor (RB-IGBT), to solve several practical problems of the matrix converter. The proposed control strategy is based on a virtual indirect control method with a virtual rectifier and a virtual inverter. Pulse-width modulated (PWM) pulses for the matrix converter are obtained by combining PWM pulses for the virtual rectifier and inverter. As a result, the control part of the input current and output voltage can be clearly separated. Thus, the conventional inverter control algorithms can be applied to the virtual inverter control. The advantage of this method is confirmed by experimental results with a 22-kW induction motor drive system. Good sinusoidal waveforms are obtained for the input and output currents, and the total harmonic distortion (THD) of the input and output current are 5.1% and 1.4%, respectively. The conduction loss of the RB-IGBT is decreased to about two-thirds of the conventional ac switch with series connection diode. Thus, the converter loss is about a half to the conventional PWM rectifier-inverter system with the same capacity. Furthermore, the protection problem is solved by a dynamic clamp method without an electrolytic capacitor. This protection circuit directly dissipates reactive load energy by dynamic clamp operation of an IGBT.

An Improvement Method of Matrix Converter Drives Under Input Voltage Disturbances

While the matrix converter has many advantages that include bidirectional power flow, a size reduction, a long lifetime, and sinusoidal input currents, it is vulnerable to the input voltage disturbances, because it directly exchanges the input voltage to the output voltage. The instantaneous effective power control (IEPC) method has been proposed to compensate the input voltage disturbances, in which the instantaneous effective power is kept constant by controlling input current. However, to date, no method has been proposed to maintain the stability of the system with the IEPC. The purpose of this paper is to propose a method to control the stability of the system with IEPC. First, this paper explains the IEPC theoretically. Next, a model of the system with the IEPC is developed, and stability analyses are conducted. Then, based on the results of the analyses, a stability control method for the system with the IEPC is proposed. Furthermore, the validities of the proposed method are demonstrated by simulation and experiments. Finally, a restart performance of the system after momentary power interruption is discussed. Because the IEPC does not need phase-locked-loop to detect the phase angle of the input voltage, fast restart is expected

Realization of High Efficiency AC link Converter System based on AC/AC Direct Conversion Techniques with RB-IGBT

This paper proposes how to realize high efficiency of 95% for the high frequency AC link converter of three-phase input and output. The proposed control method is based on virtual converter system control method without resonant. Two novel approaches are proposed in this paper. First, reducing method of a switching loss is proposed. The proposed method realizes zero voltage switching for generator side converter without auxiliary circuit. Second, this experimental converter uses a reverse blocking IGBT (RB-IGBT) instead of a series connection diode to realize the AC switches. The effects of the RB-IGBT is mentioned by the loss analysis using PSIM and experimental results. At last, the benefit of adopting the RB-IGBT to the AC/AC direct converter is verified through experiments. The efficient of the proposed approach are confirmed through 1.5 kW experimental system with the RB-IGBT. The clean sinusoidal waveforms for power line side current and generator side voltage, and the maximum efficiency of 94.7% are obtained. The RB-IGBT improves the efficiency of 1.9 point. The efficiency of around 95 % is very high in case of AC/AC converter with transformer system at 1 kW class. In addition, the motor drive characteristics with 1.5 kW induction motor are also shown in this paper

A Novel Control Strategy for Matrix Converters in Over-modulation Range.

This paper proposes a control strategy for matrix converters to reduce the torque ripple in the over-modulation range. In the over-modulation range, motor drive performance of matrix converters is deteriorated because of the output voltage saturation. Especially, the torque ripple which has lower frequency components than the input voltage frequency is remarkable. In this paper, the theoretical analysis about the causes of the torque ripple and the effect of the proposed control strategy are shown. Experimental results verify the validity of the theoretical analysis and confirm the effectiveness of the proposed control strategy. Furthermore, the harmonic distortion of the output current is also reduced compared with another control strategy.

A novel control strategy for high-frequency AC-link AC/AC direct converter based on virtual converter system

This paper proposes a simple control strategy for a high-frequency AC-link AC/AC direct converter. The proposed control strategy is based on the virtual converter system that consists of a PWM rectifier part, a high-frequency AC-link part and an inverter part. The proposed method realizes wide control range, high performances and low snubber loss. The validity of the proposed method is confirmed through the simulation and experimental results

Performance analysis of shaft generator systems

A shaft generator system supplies electrical power required in a ship by using a part of the power produced by the main engine. Since the speed of the main engine can vary over a wide range, an externally commutated thyristor inverter, which has high reliability, is generally used to produce ac power with constant voltage and frequency. In this paper, a set of system equations, by which the total harmonic distortion of the output voltage, for example, can be estimated, is derived first. The effects of leading angle of the inverter and the reactance of ac reactor located in the output side of the inverter on the system performances and the operation limit of the system are then clarified. Moreover, a way of taking the system losses into account is proposed to obtain precise calculation results. Finally, the apparent power for the synchronous condenser to provide reactive power in the system is discussed.

Steady-state performance analysis of shaft generator systems

Steady-state performance of main-engine-driven shaft generator system, which is used in a ship to feed sufficient power to the electric apparatus, is discussed. A set of system equations, by which the total harmonic distortion of the output voltage, for example, can be estimated, is derived first, and the steady-state performance is analyzed in some detail. It is shown that if the reactance of an AC reactor located in the output-side of the inverter is small, a wide operating range is obtained. The effects of the leading angle of commutation of the inverter on the system performance are also clarified.

Reduction of input current harmonics based on space vector modulation for three-phase VSI with varied power factor

This paper proposes space vector modulation (SVM) which reduces the current harmonics flowing through the DC-link capacitor of three-phase motor drive systems. In a conventional SVM, the selection of the space vectors results in the long zero vector period, which increases the inverter input current harmonics. On the other hand, in the proposed SVM, the space vectors are selected in order to actively shorten the zero vector period. Furthermore, by applying the proposed SVM only in the regions where the instantaneous value of the input current is positive, the input current harmonics are reduced even when the load power factor becomes low. Through the experiment applying the proposed SVM, it is confirmed that input current harmonics is reduced by up to 33.9% of that of the conventional method. Moreover, it is confirmed that the input current harmonics with the proposed SVM are reduced in all range of the load power factor compared to that of the conventional SVM.