Tatsuyoshi Kajikawa

A NEW DESIGN OF ROBUST DIGITAL CONTROLLER FOR DC-DC CONVERTERS

Abstract Robust DC-DC converters which can cover extensive load changes and also input voltage changes are needed. In this paper, we propose a new method for designing good approximate 2-degree-of freedom (2DOF) digital controller which makes the control bandwidth wider, and at the same time makes a variation of the output voltage very small at sudden changes of resistive load. The proposed approximate 2DOF digital controller is actually implemented on a DSP and is connected to a DC-DC converter. Experimental studies demonstrate that this type of digital controller can satisfy given specifications.

Robust control of PWM power amplifier by approximate 2-degree-of-freedom digital controller with bumpless mode switching

Robust PWM power amplifiers whose transient response characteristics do not deteriorate against extensive load changes and/or direct-current power-supply voltage changes are needed. In this paper, a digital robust controller with bumpless mode switching for PWM power amplifiers which can satisfy such demands and can extend the range of capacitive load wider is proposed. It is necessary to measure the value of load to implement this bumpless mode switching automatically according to the load range. Thus, the method of estimating capacitive load is shown. Although it is necessary to use current for estimating capacitive load, it is expensive if a current sensor is used. Therefore, an easy current estimating method which can be performed more cheaply is shown. The current estimated by this method is used for capacity estimation and current feedback. The bumpless mode switching is automatically performed by estimating a capacitive value, without specifying the value of capacitive load beforehand. That is, the value of capacitive load is estimated during DDC execution, and the control mode is automatically switched bumplessly according to this estimated value. The digital controller equipped with capacity estimation and the bumpless mode switching is realized by a DSP. An experiment shows that the digital controller with the proposed bumpless mode can satisfy larger specifications.

Robust digital control for boost DC-DC converter

If the duty ratio, load resistance and input voltage in boost DC-DC converter are changed, the dynamic characteristics is varied greatly, that is, boost DC-DC converter has non-linear characteristics. In many applications of DC-DC converters, the load cannot be specified in advance, and it will be changed suddenly from no load to full load. In the boost DC-DC converter system used a conventional single controller cannot be adapted to change dynamics and it occurs large output voltage variation. In this paper, the robust digital controller for suppress the change of step response characteristics and variation of output voltage in the load sudden changes is proposed. Experimental studies using micro-processor for controller demonstrate that this type of digital controller is effective to suppress variations.

Compact audio power supply using Approximate 2DOF robust digital control

A compact audio switching power supply for a car is needed. Since the output voltage change of an audio amplifier which is a load is large, the power supply voltage is changed largely. Usually, in order to suppress the change, a capacitor with large capacity is used at the output end. If the capacity is made small, the power supply can be compacted. In this paper, it is shown that the capacity can be made small using a robust digital control using an approximate 2DOF. The derived controller is actually implemented on a DSP. It is demonstrated from experiments that the power supply can be compacted by the robust controller.

Digital Robust Control for DC-DC Converter with Second-Order Differential Characteristics

Robust DC-DC converter which can cover extensive load changes and also input voltage changes with one controller is needed. Then the demand to suppressing output voltage change becomes still severer. We proposed an aproximate 2DOF digital controller which realizes the startup response and dynamic load response independently. The controller makes the control bandwidth wider, and at the same time makes a variation of the output voltage small at sudden changes of loads and the input voltages. In this paper, a new approximate 2DOF digital control system with additional zeros is proposed. Using additional zeros a second- order differential transfer characteristics between equivalent disturbances and an output voltage is realized. So the new controller makes a variation of the output voltage more small at sudden changes of loads and the input voltages. This controller is actually implemented on a DSP and is connected to a DC-DC converter. Experimental studies demonstrate that this type of digital controller can satisfy given severe specifications.

Current control of a PWM power amplifier by an approximate 2-degree-of-freedom digital controller

There is a need for robust current control of a pulse width modulation (PWM) power amplifier whose transient response characteristics do not deteriorate with extensive load changes and/or direct-current power supply voltage changes. In this article, we propose a digital robust controller with bumpless mode switching to control the current of a PWM power amplifier to satisfy the demands and extend the range of an inductive load width. It is necessary to measure the value of the load in order to implement this bumpless mode switching automatically depending on the load range. Therefore, a method of estimating the inductive load is shown. The bumpless mode switching is automatically performed by estimating an inductive value without specifying the value of the inductive load beforehand. That is, the value of the inductive load is estimated during the DDC execution, and the control mode is automatically switched bumplessly according to this estimated value. A digital controller equipped with inductance estimation and bumpless mode switching is realized by a DSP. Some experiments show that the digital controller with the proposed bumpless mode switching can satisfy larger specifications.

Automatic Multi-Stage Bumpless Mode Switching Type Digital Controller for PWM Power Amplifier using Load Estimation

In this paper a multi-stage switching type digital controller is proposed for spreading capacitance load range more and improving transient characteristics for inductance load. In the previous proposed controller, the configuration of the controller is the same to all loads. At inductive load, there is a possibility that the transient characteristics may become bad and the specification may not be satisfied. Therefore, a load current is estimated at inductive load, and the controller which also uses load current for feedback is configured. A inductance is estimated and a controller is switched to this controller bumplessly. In order to extend the range of capacitance load, a controller is increased from two stage to three stage, and these are switched to each other bumplessly. A DSP is implemented to this digital controller. It is demonstrated from experiments that the multi-stage switching type digital controller is realizable and the given specifications are satisfied

Robust digital control of a class-D amplifier with low switching frequency for vibration generator

In late years a class-D amplifier has been used for a vibration generator and IGBT is often used for the switching element of the class-D amplifier. However, since the switching frequency of IGBT is limited low, it is difficult to make the bandwidth of the class-D amplifier wide. The bandwidth 5 kHz is required by the amplifier for the vibration generator with load impedance 2∼8 Ω. In this paper, it is shown that the bandwidth 5 kHz of the class-D amplifier can be realized by applying A2DOF control with the switching frequency 50 kHz. Since the output PWM frequency of a bridge circuit increase twice as much as IGBT switching frequency by using a double carrier PWM generating system, the sampling frequency of a controller can be increased twice as much as the switching frequency, i.e. is 100 kHz. Then the bandwidth 5 kHz of the class-D amplifier for the vibration generator with load impedance 2∼8 Ω can be realized by devising how to design A2DOF control. The controller is implemented in a DSP and it is shown from experiment that the desired performance is attained enough.

Design method of a 1-bit digital filter using a new 2-Degree-of-Freedom control

To decrease the quantization noise, various 1-bit digital filters are shown. In this paper, we propose a design method of 1-bit digital filter using a new 2-Degree-of-Freedom control. This design method is applied to a high-pass filter, a low-pass filter and a equalizer. These filters are implemented on DSP, and the performance is verified by the experiment.

Design of digital robust controller for PWM power amplifier and bumpless mode switching

In this paper a multi-stage switching type digital controller is proposed for spreading capacitance load range more and improving transient characteristics for inductance load. In the previous proposed controller, the configuration of the controller is the same to all loads. At inductive load, there is a possibility that the transient characteristics may become bad and the specification may not be satisfied. Therefore, a load current is estimated at inductive load, and the controller which also uses load current for feedback is configured. A inductance is estimated and a controller is switched to this controller bumplessly. In order to extend the range of capacitance load, a controller is increased from two stage to three stage, and these are switched to each other bumplessly. A DSP is implemented to this digital controller. It is demonstrated from experiments that the multi-stage switching type digital controller is realizable and the given specifications are satisfied.