Hirohito Funato

Fuel-cell parameter estimation and diagnostics

In the future, a major role of fuel cells in combined heat and power generation systems is envisaged. It is well known that a fuel cells efficiency is highly dependent on the operating conditions, such as temperature, humidity, and air flow. In the aim to assure optimal operating conditions as well as to minimize the losses, parameter identification, diagnostics, and control are going to play an important role. The paper deals with parameter identification and diagnostics of a low-power proton-exchange membrane fuel cell considering a system identification approach. This multi-input multi-output electrochemical system can be tested or monitored by identifying its parameters, which has real importance in the manufacturing, exploitation, and maintenance phase. Therefore, parameter identification represents the core of any diagnostics or online monitoring procedure. Furthermore, online parameter estimation might be used for control purposes to maintain the fuel cell in an optimal operating point with minimal losses. The proposed parameter identification method is simple, cost-effective, and can be extended easily for fuel-cell stacks too.

Realization of negative inductance using variable active-passive reactance (VAPAR)

The concept of the variable active-passive reactance (VAPAR) has been proposed previously. VAPAR consists of an inverter and a few passive elements with a control system, which behaves like a two-terminal reactive element, and the produced active reactance works as a passive reactive component, including in transient state. The main purpose of this paper is to analyze the characteristics of negative inductance and to show how to produce negative inductance by VAPAR. First, the principle and realization of VAPAR and complete two-terminal VAPAR (CTT-VAPAR) are explained. Second, the characteristics of negative inductance are analyzed from the point of view of frequency characteristics of impedance and transient response, using capacitance as a reference. Finally, through simulations and experiments, it is verified that VAPAR can generate negative inductance, and it is demonstrated that the actual inductance is cancelled.

Proposal of variable active-passive reactance

The concept of a variable active-passive reactance (VAPAR) which consists of an inverter and a passive element is proposed. The VAPAR behaves like a two-port reactive element and the produced active reactance works as a passive reactive component, including in the transient state. The authors present the principle of the VAPAR and two possible control schemes to realize the VAPAR. Through simulations and experiments, it is verified that the VAPAR shows two-port reactive characteristics not only in steady state but also in the transient state.<<ETX>>

Stability analysis of nonlinear power electronic systems utilizing periodicity and introducing auxiliary state vector

Variable-structure piecewise-linear nonlinear dynamic feedback systems emerge frequently in power electronics. This paper is concerned with the stability analysis of these systems. Although it applies the usual well-known and widely used approach, namely, the eigenvalues of the Jacobian matrix of the Poincare/spl acute/ map function belonging to a fixed point of the system to ascertain the stability, this paper offers two contributions for simplification as well that utilize the periodicity of the structure or configuration sequence and apply an alternative simpler and faster method for the determination of the Jacobian matrix. The new method works with differences of state variables rather than derivatives of the Poincare/spl acute/ map function (PMF) and offers geometric interpretations for each step. The determination of the derivates of PMF is not needed. A key element is the introduction of the so-called auxiliary state vector for preserving the switching instant belonging to the periodic steady-state unchanged even after the small deviations of the system orbit around the fixed point. In addition, the application of the method is illustrated on a resonant dc-dc buck converter.

AR-based identification and control approach in vibration suppression

In vibration suppression control with a wide bandwidth for a resonant plant, it is a requisite to identify the plant with high accuracy. However, the more complicated the plant is, the more difficult its system identification becomes. This paper proposes the identification of a modified plant instead of the original plant. The modified plant is a minor control loop (MCL), considering the original plant, when one of the output values is the control feedback. The MCL is designed in order to obtain an optimal damping factor of the modified plant. Moreover, the modified plant is identified based on the autoregressive exogenous (ARX) model and the least-squares method. Based on these techniques, it is possible to specify an exact uncertainty between the nominal and identified parameters of the ARX model. Therefore, a robust vibration suppression control system, which has a wide frequency band, can be systematically designed. The advantages of the proposed design method for a two-mass resonant system are demonstrated through simulations and experiments in the cases of the position and speed control.

Control of variable active-passive reactance (VAPAR) and negative inductance

The concept of the variable active-passive reactance (VAPAR) which behaves like a two-terminal reactive element, and the produced active reactance works as a passive reactive component, including in transient state. In this paper, the authors propose the equivalent resistance control method for the capacitor DC voltage regulation when a capacitor is used as an energy storage element of the VAPAR. The series equivalent resistance is added to the produced virtual inductance, and the capacitor voltage is controlled by changing the series equivalent resistance. The proposed scheme is verified by simulations and experiments. The realization of the negative inductance is then proposed. Through simulations and experiments, it is verified that the VAPAR can generate negative inductance, which may be applied to FACTS. The effects of negative inductance are compared with that of series capacitance used in power systems.<<ETX>>

The power loss of the PWM voltage-fed inverter

The power loss of the valve devices in pulsewidth-modulated (PWM) inverters operated with relatively high carrier frequency is discussed. The devices covered are bipolar transistors, MOSFETs, and antiparalleled diodes. On-state loss and switching loss are treated separately, on the basis of the control method and the circuit conditions. The resultant allowable load current is discussed from the viewpoint of switching frequency.<<ETX>>

Transient response of three phase variable inductance realized by variable active-passive reactance (VAPAR)

Inductance has a particularly important role in power circuits. For example, the power flow is essentially restricted by a line inductance. The authors have proposed the variable active-passive reactance (VAPAR) which can produce a virtual variable inductance. They analyzed the transient power flow of a balanced three-phase variable inductance and obtained interesting results. In this paper, the transient power flow of a three-phase variable inductance connected to an external constant three-phase inductance is analyzed using instantaneous active and reactive power theorems. The analysis were performed not only about the case of a balanced three phase inductance but also about the case of unbalanced three-phase inductance. The transient power is analyzed theoretically, then the results as verified through simulations and some of them are verified through experiments.

Transmission power control using variable inductance with feedforward- and feedback-based power controllers

The transmission power is essentially restricted by a line inductance. The authors have previously proposed the transmission power control using a variable inductance which can be realized by variable active passive reactance (VAPAR). The transmission power controlled by this variable inductance with feedforward-based power controller showed quick transient response, although there were slight transient oscillations. This paper, at first, describes a basic theory of the power control method using a variable inductance. Second, the concept of the power control method using variable inductance with a feedforward-based power controller is expressed. Simulations and experiments were carried out using the feedfoward-based power controller to verify the ability of this method. Then, the characteristics of the power control were analyzed for different line impedance by simulations. The results show that the transmission power can be quickly controlled using variable inductance with the feedfoward-based power controller in the case with a small line resistance, while transient oscillation is observed in the transmission power when a line is rather large. Third, a new transmission power control using a variable inductance with a power feedback-based controller is proposed, which can be applied to a power system with large line resistance. The effectiveness of the proposed method was verified by simulations. The transient response of the transmission power can be greatly improved using the proposed method.

Hybrid sensor-less control of permanent magnet synchronous motor in low-speed region

This paper proposes a method of improving the stability in sensor-less control of permanent magnet synchronous motors. The control method for low-speed region is divided into two: One is a high frequency method, which involves a problem of reverse rotation once misdetection of the permanent magnet polarity should occur, and another one is a current drive method, which has a problem that phase and speed oscillations are caused by quick speed changes. Hence, authors propose adoption of the current drive method for the basic control system with added compensation of stabilization by means of the high frequency method. This combination secures stable control with no risk of reversal and less vibration. In addition, authors have also considered a frequency separation filter of a shorter delay time so that current control performance will not lower even when high frequencies are introduced. This filter has achieved simplified compensation using repetitive characteristic through the utilization of the periodicity of high frequency current. Simulation and experiment have been conducted to verify that the stable performance of this system is improved.