Toshiji Kato

Sequential homotopy-based computation of multiple solutions for selected harmonic elimination in PWM inverters

The selected harmonic-elimination (HE) method, which is widely used for efficient inverter control, forms the basis of off-line digital PWM modulation techniques in the power electronics field. The method is based on numerical solutions of a set of selected HE equations which are often considered to be impractical to solve. Up to now, any effective method for this subject has not been reported. This paper proposes a systematic method which makes it possible to solve and analyze the equations sequentially by applying a homotopy method and a mathematical induction algorithm even if there are multiple solutions. According to the proposed method, unique HE solutions for single-phase cases and multiple solutions for three-phase cases are computed and reported.

Modified hysteresis control with minor loops for single-phase full-bridge inverters

An efficient online PWM (pulsewidth modulation) control method for single-phase full-bridge inverters is proposed. The conventional hysteresis control method has good dynamic responses, but the switching frequencies are high because it does not optimize switching patterns. Full-bridge inverters can generate +E, -E, and 0 (zero) levels where E is an input DC voltage level. The hysteresis control method does not utilize maximum freedom and it selects the output only among two levels (+E and -E). The method selects the optimum output among the three levels (+E, -E, and 0) instantaneously. The control circuit of the proposed method is very simple. Whereas the conventional hysteresis control has only one hysteresis comparator, the proposed method has two hysteresis comparators (wide and narrow loops). When a reference signal goes up, the wide-loop output becomes high and the inverter output is +E, or 0 according to the narrow-loop output. When a reference signal goes down, the wide-loop output becomes low and the inverter output is -E or 0. The method is validated to optimize the output level instantaneously and to reduce the switching times.<<ETX>>

A Study on an Optimal Torque for Power Regeneration of an Induction Motor

This paper proposes a design methodology of a regenerating braking torque for an induction motor in order to regenerate power as much as possible. At first, models of dissipation power in rotation and the copper losses in both a stator and a rotor are given. Then, a function of a regenerative power is derived from these losses, regenerating torque for the function of the regenerative power. A vector control method is employed in order to control the torque instantaneously in the case of acceleration and regeneration. The effectiveness of the proposed design method of the regenerative torque is illustrated by simulations.

An effcient induction motor drive method with a regenerative power storage system driven by an optimal torque

When the motor speed is reduced by using a regenerative brake, the mechanical energy of rotation can be converted to the regenerative electric energy. In order to improve the efficiency of the motor drive systems, the regenerative power is charged and discharged by power storage systems (PSS). Moreover, optimal regenerative and acceleration torque of the motor should be discussed in order to maximize the regenerative electric energy and to minimize the required energy for acceleration. This paper presents an effective robust control method of a regenerative power storage system (PSS) and a design methodology of an optimal acceleration torque in order to achieve an efficient induction motor drive system. The PSS, treated in this paper, consists of an electrolytic capacitor and a bi-directional DC-DC chopper. At first, it will be shown that the PSS can be represented by a quite general second order differential equation. For this model, a robust control method will be proposed. Secondary, an optimal acceleration torque will be derived by means of variational method. The effectiveness of the proposed methods are illustrated by some simulations and experiments.

Evaluation procedures for lightning impulse parameters in case of waveforms with oscillations and/or an overshoot

Definitions of standards IEC 60 and IEEE Std 4 are insufficient for the evaluation of lightning impulse parameters of waveforms with oscillations and/or overshoot. This has brought about different interpretations in the estimation of these parameters, especially when using digital recorders. Large discrepancies have resulted from the different interpretations. The working group 33.03 of CIGRE has collected various opinions about this problem. These are presented, analysed and discussed in this paper. Different ways of determining mean curves of impulses with oscillations and/or overshoot are proposed. In addition, different alternatives for the definitions of overshoot amplitude and duration are suggested for impulses with overshoot. The problems and alternative solutions are discussed in the light of analyzing three impulses of the IEC Test Data Generator. This illustrates clearly the need to change the above mentioned standards. Simple, easily applicable, reproducible and technically justified definitions are required in order to take advantage of the accuracy and facilities of digital recorders in impulse measurements. This paper offers the basis for further discussion on the subject before WG 33.03 of CIGRE makes its final proposal. Further studies with practical test impulses are still needed.

Multi-rate transient analysis of power electronic circuits by the envelope-following method with sensitivities of switch timings

Extension of the envelope-following method, which is an efficient transient analysis method of clocked power electronic circuits, is proposed by taking into account sensitivities of switch timings. This modification is necessary especially for analysis of closed-loop controlled converters to make the numerical process stabler. A general algorithm is derived and validated.<<ETX>>

Efficient steady-state analysis method with sensitivities of switch timings by the shooting method

An efficient steady-state analysis method of power converters is proposed. The method finds initial values which satisfy a steady-state boundary condition by solving a sensitivity matrix equation. For this matrix computation, consideration of switch timing variations reported by some papers is checked to be important especially for closed-loop controlled circuits to improve the stability of the algorithm. This paper derives a general principle of the method and proposes a new computation algorithm, which is validated through two application examples.<<ETX>>

Fast current-tracking control for grid-connected inverter with an LCL filter by sinusoidal compensation

A voltage source inverter with an LCL filter is often used for a utility interface to control its output current to a grid side because of its harmonic reduction advantages. The integral compensator is often used to reduce the steady-state errors. However, there is always a control delay due to sinusoidal variations. This paper proposes a digital sinusoidal compensator which is based on the internal model principle to realize a response with no deviation for a periodic sinusoidal reference input. It has a simple numerator and a denominator z2 − 2zcosωT + 1 of a transfer function which is equal to the z function of a sinusoidal waveform of the angular frequency ω and the sample time T. Compensator and feedback gains of the inverter are determined by the dead-beat or the optimal control principle. For an utility interface inverter, it is necessary to detect the sinusoidal phase of the source voltage. A new digital technique is proposed and it is based on the least-mean-square (LMS) method. The proposed method is investigated for performances and it is validated through simulation and experimental results by a DSP control system.

Optimal torque trajectories minimizing loss of induction motor under given condition of rotational angle

In order to improve the efficiency of the motor drive systems, the optimal torque should be discussed in order to minimize the total loss energy during the operation. The optimal torque trajectory for a squirrel-cage induction motor under the given two constraint conditions with respect to the operation time period and the rotating speed range have already reported. In these reports, however, the rotational angle is not taken into account as one of constraint conditions. In applications, such as electric trains, elevators, conveyer, and cranes, the rotational angle should be considered. This paper proposes a design methodology of an optimal torque trajectory to minimize the energy loss for IM drive by means of the variational method when the operation time period, rotating speed range, and total rotational angle are given as constraint conditions.

Computer-aided analysis of a power electronic circuit by a new multirate method

This paper proposes a new multirate analysis method which selects a proper numerical integration stepsize for each variable in analyzing a power electronic system which has a subcircuit with different rates. First a formulation technique of multirate circuit equations is derived. Then a rate classification technique is derived from the error estimation formula of the backward differentiation formulas (BDF). Further a stepsize adjustment technique at a break point is explained. Finally the proposed method is applied to a DC chopper, a DC-DC converter and a PWM inverter circuit which showed efficiency of the method.