Masatoshi Nakahara

Analysis of ripple effects on frequency response characteristics of boost converter

In this paper we clarify for the boost converter that the ripple effect is not ignorable for the frequency response, and reveal that it causes the unexpected characteristics where either the phase lag or the phase lead appears depending on the shape of the ramp generator. Eventually the phase margin for the stability drastically changes depending on the slope direction (normal or reverse) of the ramp generator even in the same circuit configuration. For these ripple effects we propose the general analysis model and analyze them on the frequency response characteristics by applying the state-space averaging technique. As the result we identify that the ripple effects are caused mainly by the variation of the slope and average of the ripple, and reveal that the boost converter has the asymmetry characteristic for the slope direction of the ramp generator and there is more advantage for the stability in case of the reverse slope direction than in case of the normal slope direction. The proposed analysis method can also treat the compensation circuit in the control circuit and is validated by the experiments and simulations.

Cooperative control of power system with battery and solar cell for a satellite

In General, the dispersed power supply system is possible to be robust and small compare with centralized power system. In the satellite system, we aim to downsize the power supply system by using the dispersed power system and cooperative control, which is constructed by solar panel and some bi-directional DC-DC converters. In this paper, we describe the evaluation results for the behavior of the parallel connected bidirectional DC-DC converters, Power interchanging between these converters and result of the cooperative control.

Newton's method for fast speed MPPT of solar panel

Generally in order to achieve the fast MPPT the algorithm must have features of reduced number of repetition and stable operation with high sampling frequency. We propose the new algorithm employing Newton’s Method to satisfy requirements above for the fast MPPT. We also actually implement the proposed method in a MPPT circuit board by using the rapid-control-prototyping (RCP) tool dSPACE. And this paper shows results of the simulation and experiments.

Application of Model-based design in development of micro-grid system

The micro-grid system is not able to be realized just by assembling conventional DC/DC converters and DC/AC inverters. The efficient environment for the software development is mandatory because the sophisticated control software is required for each component to realize the micro-grid system. We have developed new software environment by integrating MATLAB/Simulink which is commonly used in Model-based design, and SCALE for circuit simulation engine. This software development environment enables us to develop software with drastically short time and low cost.

Analysis of ripple effects on frequency response characteristics of switching regulators

In this paper we clarify for the buck-boost converter that the ripple effect is not ignorable for the frequency response, and reveal that it causes the unexpected characteristics where either the phase lag or the phase lead appears depending on the shape of the ramp generator of the PWM circuit. Eventually the phase margin for the stability drastically changes depending on the slope direction (normal or reverse) of the ramp generator even in the same circuit configuration. For the ripple effects we propose the general analysis model and analyze them of the buck-boost converters. As the result we identify that the ripple effects are caused mainly by the variation of the slope and the average of the ripple, and reveal that the buck-boost converter has the asymmetric characteristics for the slope direction of the ramp generator and there is more advantage for the stability in case of the reverse slope direction than in case of the normal one. The proposed analysis method is validated by the experiments and simulations.

FPGA-based hardware-in-the-loop simulator of high switching frequency power converters

To take advantage of volatile renewable energy, implementation of digital control is effective since it supports the application of various advanced control theory and communication functions. However, it is usually difficult to use the actual plant to be controlled at the control software development stage, particularly in terms of cost and safety. Therefore, during the control software development phase, it is expected to substitute a Hardware-in-the-Loop (HIL-simulator) so that the controller hardware can be placed in the feedback control loop for the actual plant. The development of HIL-simulators for the switching converter has been recognized to be a challenge because of the high control frequencies involved. However, it is possible to realize a HIL-simulator using a partial variable step method that is able to compute switching behavior in a precise manner and with state space equations that help minimize the calculation time required for the execution of the aforementioned method. This technique can also be applied to slower computational devices such as microprocessors. However, using FPGA, it is possible to develop a more realistic simulator with minimal computational delay. This study describes a HIL-simulator that simulates the electrical circuit of the switching converter that is able to provide 0.1% duty ratio resolution at a 100 kHz switching frequency.

New development method of control software for smart energy applications dealing with multi-sample-rate controllers

In a smart energy system, power converters should be controlled by complex control software. However the efficient development of reliable control software is difficult. We have proposed to introduce a “model-based design” process using MATLAB/Simulink, established in the automotive and aerospace fields, to the development of power electronics systems. However, it was difficult in the past because calculating switching circuit as the plant model is difficult in MATLAB/Simulink due to the socalled stiff equation problem. Thus, in this study, we have developed a simulation environment in which the standard model-based design tool, MATLAB/Simulink, and the simulation engine for power switching circuits, SCALE, work cooperatively. SCALE was originally developed to solve stiff equation and efficiently simulate power switching circuits. This software environment enables us to design control algorithms with intuitive block diagram expression and test them in actual hardware, without writing a C program. Furthermore to improve this environment, a mechanism that handles the multiple sample rates was introduced. Smart energy systems that use several controllers with different sampling rates can be simulated in the proposed environment. Thus, we can develop control software for smart energy systems in a timely and cost effective manner.

Effect of ripple on frequency response characteristics of boost converter - Analysis in consideration of ESR of output capacitor -

The output voltage of DC-DC converter contains the ripple and it substantially affects the frequency response although the ripple is usually neglected in the control circuit as PWM control. The authors already have clarified that the effect of the ripple is not ignorable for the frequency response and it causes the unusual characteristics. In this paper, we analyze the effect of the ripple in consideration of ESR of the output capacitor of the boost converter. As a result it has been found that the effect of ESR in the stability is different according to the shape of the slope direction of the ramp generator in the PWM circuit.