Santanu Kapat - Profile on Academia.edu (original) (raw)

Papers by Santanu Kapat

Near time optimal recovery in a digitally current mode controlled buck converter driving a CPL

Stability of a distributed power architecture (DPA) still remains a major concern, even though in... more Stability of a distributed power architecture (DPA) still remains a major concern, even though individual stand-alone DC-DC converters are designed with sufficient (small-signal) stability margins. In such architectures, a tightly regulated point-of-load (PoL) converter resembles a constant power load (CPL) which introduces a negative-impedance effect to the source converter. This effect may introduce limit cycle oscillation (LCO) and may eventually destabilize the overall DPA. In this paper, a source buck converter is considered under digital current-mode control (DCMC) with a proportional-integral (PI) voltage controller, which is driving a CPL buck converter. During a power step-transient in the CPL, stable controller gain ranges under DCMC are computed for the source converter for individual operating conditions. Thereafter, a phase-plane based geometric framework is proposed to compute the optimal proportional gain for the source converter to achieve near time optimal recovery....

Bifurcation behavior of a boost converter under voltage controlled pulse skipping modulation in the light of 1-D discontinuous map model

Circuits and Systems (ISCAS), …, 2010

In our earlier work, we showed that the discrete-time model of a dc-dc converter governed by a pu... more In our earlier work, we showed that the discrete-time model of a dc-dc converter governed by a pulse skipping modulation (PSM), could be modeled as a discontinuous map, comprising either 1-D functions only or a combination of 1-D and 2-D functions. In this paper, we show that the entire map can be restricted to one dimension for a wide range

Improving load regulation in current mode control through inductor current filtering

International Journal of Power …, 2012

ABSTRACT

Near-Null Response to Large-Signal Transients in an Augmented Buck Converter: A Geometric Approach

IEEE Transactions on Power Electronics, 2012

The maximum closed-loop bandwidth of a dc–dc converter is restricted to a fraction of its switchi... more The maximum closed-loop bandwidth of a dc–dc converter is restricted to a fraction of its switching frequency when governed by a conventional average-based pulsewidth modulation (PWM) controller. Even an advanced geometric control is limited by internal slew rates. The bandwidth can reach or exceed the switching frequency through converter augmentation; however, this requires a nonlinear control algorithm and circuit arrangements.

Power and Energy …, 2012

This paper explores fundamental performance challenges inherent to the dc-dc boost converter topo... more This paper explores fundamental performance challenges inherent to the dc-dc boost converter topology and presents an augmentation method as a solution. Augmentation techniques provide additional energy paths to support the load during transients. In addition, the non-minimum phase nature of boost converters is overcome with augmentation. A small signal analysis for an augmented boost converter topology is developed. Experimental results show success in decreasing transient response time and output voltage droop.

ONE-DIMENSIONAL DISCONTINUOUS MAP ANALYSIS OF DC–DC CONVERTERS UNDER VOLTAGE CONTROLLED PULSE SKIPPING MODULATION

International Journal of Bifurcation …, 2012

Augmented boost converter for near null-load transient response

Power and Energy …, 2011

This paper describes a dc-dc boost converter which shows near null load transient response. The b... more This paper describes a dc-dc boost converter which shows near null load transient response. The boost converter is augmented with extra energy paths that sink or supply charge during load steps. The output voltage deviation and inductor current overshoot during load transients are substantially reduced or eliminated. A charge-balance based analysis is utilized in this paper to describe the control

RHP zero elimination with near optimum regulation in a current controlled tri-state boost converter through inductor current filtering

Power and Energy Conference …, 2010

This paper demonstrates how load regulation can be improved in a current controlled tri-state boo... more This paper demonstrates how load regulation can be improved in a current controlled tri-state boost converter along with the elimination of the right-half-plane (RHP) zero. Although use of a PI controller improves regulation, it degrades the dynamic performance, and a higher integral gain results in a considerably reduced phase margin. The objective of this paper is to investigate an alternative

PID controller tuning in a DC-DC converter: A geometric approach for minimum transient recovery time

Control and Modeling for Power Electronics …, 2010

A high performance proportional-integral-derivative (PID) controller in a dc-dc converter require... more A high performance proportional-integral-derivative (PID) controller in a dc-dc converter requires a time optimal tuning rule. A suitable auto-tuning rule needs to perform large-signal minimum-time transient recovery, while maintaining a sufficient small-signal stability margin and closed-loop bandwidth. This paper applies a geometric approach to analytically formulate a time optimal PID controller tuning rule for a buck converter. It is shown

Voltage controlled pulse skipping modulation: Extension towards the ultra light load

Circuits and Systems, 2009. …, 2009

Abstract—This paper presents the concept of a voltage controlled pulse skipping modulation (VCPSM... more Abstract—This paper presents the concept of a voltage controlled pulse skipping modulation (VCPSM) in a dc-dc converter, which improves the efficiency, ripple magnitude, and transient response over a wide range of light load condition. The duty ratio of VCPSM, instead of ...

International Journal of Bifurcation and Chaos, 2003

We present a classification of border-collision bifurcations in one-dimensional discontinuous map... more We present a classification of border-collision bifurcations in one-dimensional discontinuous maps depending on the parameters of the piecewise linear approximation in the neighborhood of the point of discontinuity. For each range of parameter values we derive the condition of existence and stability of various periodic orbits and of chaos. This knowledge will help in understanding the bifurcation phenomena in a large number of practical systems which can be modeled by discontinuous maps in discrete domain.

Achieving monotonic variation of spectral composition in DC–DC converters using pulse skipping modulation

IEEE Transactions on Circuits and Systems I-regular Papers, 2011

Abstract This paper presents a new type of pulse skipping modulation (PSM) in a dc–dc converter, ... more Abstract This paper presents a new type of pulse skipping modulation (PSM) in a dc–dc converter, which is controlled by a voltage mode scheme. The duty ratio of the pulses, instead of being constant as in the conventional PSM, is controlled using a voltage mode ...

Null response to a large signal transient in an augmented dc-dc converter: A geometric approach

Control and Modeling for Power Electronics …, 2010

The maximum closed-loop bandwidth of a dc-dc converter is restricted to a fraction of its switchi... more The maximum closed-loop bandwidth of a dc-dc converter is restricted to a fraction of its switching frequency, while governed by a conventional pulse-width-modulation (PWM) technique. Even an advanced geometric control is limited by its internal slew rate. The bandwidth can be made close to (even higher than) the switching frequency through converter augmentation; however, it requires a proper control algorithm

Improved time optimal control of a buck converter based on capacitor current

IEEE Transactions on Power Electronics, 2012

Time optimal control (TOC) is a technique to provide fast transient recovery in dc–dc converters.... more Time optimal control (TOC) is a technique to provide fast transient recovery in dc–dc converters. Prior published approaches are incomplete in the formulation of TOC because they ignore voltage-deviation effects on inductor-current and load-current dynamics during a large-signal recovery. An accurate TOC algorithm based on capacitor current is presented. This method achieves minimum transient recovery time for load transients and tracking in a buck converter. The minimum recovery time is preserved even with a transient-detection delay. This control configuration ensures large-signal stability in a sense similar to that of sliding-mode control. The results are demonstrated in an experimental buck converter that uses a digital control algorithm.

Formulation of PID Control for DC–DC Converters Based on Capacitor Current: A Geometric Context

IEEE Transactions on Power Electronics, 2012

The output-voltage-derivative term of a proportional-integral-derivative (PID) controller injects... more The output-voltage-derivative term of a proportional-integral-derivative (PID) controller injects significant noise in a dc-dc converter. This is mainly due to the presence of parasitic resistance and inductance of the output capacitor. Particularly during a large-signal transient, noise injection significantly degrades phase margin. Although noise characteristics can be improved by reducing the cut-off frequency of the low-pass filter associated with the voltage derivative, it degrades the closed-loop bandwidth. A new formulation of a PID controller is introduced to replace the output-voltage-derivative with information about the capacitor current, thus reducing noise injection. It is shown this new formulation preserves the fundamental principle of a PID controller and incorporates a load current feed-forward as well as inductor current dynamics. This can be helpful to further improve bandwidth and phase margin. The proposed method is shown to be equivalent to a voltage-mode controlled buck converter and a current-mode controlled boost converter with a PID controller in the voltage feedback loop.

Modeling and analysis of DC-DC converters under pulse skipping modulation

TENCON 2008-2008 IEEE …, 2008

Abstract—The technique to model dc-dc converters governed by Pulse Skipping Modulation (PSM), whi... more Abstract—The technique to model dc-dc converters governed by Pulse Skipping Modulation (PSM), which is based on energy balance principle, is not accurate enough. In this paper, an attempt has been made to model them accurately using the discrete-time modeling ...

Beyond time-optimality: Energy-based control of augmented buck converters for near ideal load transient response

Applied Power Electronics …, 2011

This paper presents a buck converter augmented with additional energy paths that enable a near nu... more This paper presents a buck converter augmented with additional energy paths that enable a near null response to load transients. Fundamental performance limits, such as slew-rate limits, are overcome resulting in increased bandwidth with a response that is faster than previously established "minimum time" or "time optimal" control of conventional buck converters. An energy-based method is presented that allows simplified

A novel current controlled tri-state boost converter with superior dynamic performance

Circuits and Systems, 2008. …, 2008

Abstract—A novel current mode control of tri-state boost converter is proposed, which eliminates ... more Abstract—A novel current mode control of tri-state boost converter is proposed, which eliminates the zero in the right-half plane and improves the dynamic performance. The tri-state boost converter contains an additional switch across the inductor. Within a clock cycle, the inductor ...

Discontinuous map analysis of a DC-DC converter governed by pulse skipping modulation

IEEE Transactions on Circuits and Systems I-regular Papers, 2010

Abstract—This paper reports the bifurcation phenomena in a dc-dc converter governed by a pulse sk... more Abstract—This paper reports the bifurcation phenomena in a dc-dc converter governed by a pulse skipping modulation (PSM) scheme, which is normally used to improve efficiency under light load condition. It is shown that the discrete-time model of the system takes the form of ...

A current-controlled tristate boost converter with improved performance through RHP zero elimination

IEEE Transactions on Power Electronics, 2009

Abstract—A novel current mode control scheme for the tristate boost converter circuit is proposed... more Abstract—A novel current mode control scheme for the tristate boost converter circuit is proposed, which eliminates the zero in the right-half plane (RHP), and improves the dynamic performance. The tristate boost converter contains an additional switch across the ...

Near time optimal recovery in a digitally current mode controlled buck converter driving a CPL

Stability of a distributed power architecture (DPA) still remains a major concern, even though in... more Stability of a distributed power architecture (DPA) still remains a major concern, even though individual stand-alone DC-DC converters are designed with sufficient (small-signal) stability margins. In such architectures, a tightly regulated point-of-load (PoL) converter resembles a constant power load (CPL) which introduces a negative-impedance effect to the source converter. This effect may introduce limit cycle oscillation (LCO) and may eventually destabilize the overall DPA. In this paper, a source buck converter is considered under digital current-mode control (DCMC) with a proportional-integral (PI) voltage controller, which is driving a CPL buck converter. During a power step-transient in the CPL, stable controller gain ranges under DCMC are computed for the source converter for individual operating conditions. Thereafter, a phase-plane based geometric framework is proposed to compute the optimal proportional gain for the source converter to achieve near time optimal recovery....

Bifurcation behavior of a boost converter under voltage controlled pulse skipping modulation in the light of 1-D discontinuous map model

Circuits and Systems (ISCAS), …, 2010

In our earlier work, we showed that the discrete-time model of a dc-dc converter governed by a pu... more In our earlier work, we showed that the discrete-time model of a dc-dc converter governed by a pulse skipping modulation (PSM), could be modeled as a discontinuous map, comprising either 1-D functions only or a combination of 1-D and 2-D functions. In this paper, we show that the entire map can be restricted to one dimension for a wide range

Improving load regulation in current mode control through inductor current filtering

International Journal of Power …, 2012

ABSTRACT

Near-Null Response to Large-Signal Transients in an Augmented Buck Converter: A Geometric Approach

IEEE Transactions on Power Electronics, 2012

The maximum closed-loop bandwidth of a dc–dc converter is restricted to a fraction of its switchi... more The maximum closed-loop bandwidth of a dc–dc converter is restricted to a fraction of its switching frequency when governed by a conventional average-based pulsewidth modulation (PWM) controller. Even an advanced geometric control is limited by internal slew rates. The bandwidth can reach or exceed the switching frequency through converter augmentation; however, this requires a nonlinear control algorithm and circuit arrangements.

Power and Energy …, 2012

This paper explores fundamental performance challenges inherent to the dc-dc boost converter topo... more This paper explores fundamental performance challenges inherent to the dc-dc boost converter topology and presents an augmentation method as a solution. Augmentation techniques provide additional energy paths to support the load during transients. In addition, the non-minimum phase nature of boost converters is overcome with augmentation. A small signal analysis for an augmented boost converter topology is developed. Experimental results show success in decreasing transient response time and output voltage droop.

ONE-DIMENSIONAL DISCONTINUOUS MAP ANALYSIS OF DC–DC CONVERTERS UNDER VOLTAGE CONTROLLED PULSE SKIPPING MODULATION

International Journal of Bifurcation …, 2012

Augmented boost converter for near null-load transient response

Power and Energy …, 2011

This paper describes a dc-dc boost converter which shows near null load transient response. The b... more This paper describes a dc-dc boost converter which shows near null load transient response. The boost converter is augmented with extra energy paths that sink or supply charge during load steps. The output voltage deviation and inductor current overshoot during load transients are substantially reduced or eliminated. A charge-balance based analysis is utilized in this paper to describe the control

RHP zero elimination with near optimum regulation in a current controlled tri-state boost converter through inductor current filtering

Power and Energy Conference …, 2010

This paper demonstrates how load regulation can be improved in a current controlled tri-state boo... more This paper demonstrates how load regulation can be improved in a current controlled tri-state boost converter along with the elimination of the right-half-plane (RHP) zero. Although use of a PI controller improves regulation, it degrades the dynamic performance, and a higher integral gain results in a considerably reduced phase margin. The objective of this paper is to investigate an alternative

PID controller tuning in a DC-DC converter: A geometric approach for minimum transient recovery time

Control and Modeling for Power Electronics …, 2010

A high performance proportional-integral-derivative (PID) controller in a dc-dc converter require... more A high performance proportional-integral-derivative (PID) controller in a dc-dc converter requires a time optimal tuning rule. A suitable auto-tuning rule needs to perform large-signal minimum-time transient recovery, while maintaining a sufficient small-signal stability margin and closed-loop bandwidth. This paper applies a geometric approach to analytically formulate a time optimal PID controller tuning rule for a buck converter. It is shown

Voltage controlled pulse skipping modulation: Extension towards the ultra light load

Circuits and Systems, 2009. …, 2009

Abstract—This paper presents the concept of a voltage controlled pulse skipping modulation (VCPSM... more Abstract—This paper presents the concept of a voltage controlled pulse skipping modulation (VCPSM) in a dc-dc converter, which improves the efficiency, ripple magnitude, and transient response over a wide range of light load condition. The duty ratio of VCPSM, instead of ...

International Journal of Bifurcation and Chaos, 2003

We present a classification of border-collision bifurcations in one-dimensional discontinuous map... more We present a classification of border-collision bifurcations in one-dimensional discontinuous maps depending on the parameters of the piecewise linear approximation in the neighborhood of the point of discontinuity. For each range of parameter values we derive the condition of existence and stability of various periodic orbits and of chaos. This knowledge will help in understanding the bifurcation phenomena in a large number of practical systems which can be modeled by discontinuous maps in discrete domain.

Achieving monotonic variation of spectral composition in DC–DC converters using pulse skipping modulation

IEEE Transactions on Circuits and Systems I-regular Papers, 2011

Abstract This paper presents a new type of pulse skipping modulation (PSM) in a dc–dc converter, ... more Abstract This paper presents a new type of pulse skipping modulation (PSM) in a dc–dc converter, which is controlled by a voltage mode scheme. The duty ratio of the pulses, instead of being constant as in the conventional PSM, is controlled using a voltage mode ...

Null response to a large signal transient in an augmented dc-dc converter: A geometric approach

Control and Modeling for Power Electronics …, 2010

The maximum closed-loop bandwidth of a dc-dc converter is restricted to a fraction of its switchi... more The maximum closed-loop bandwidth of a dc-dc converter is restricted to a fraction of its switching frequency, while governed by a conventional pulse-width-modulation (PWM) technique. Even an advanced geometric control is limited by its internal slew rate. The bandwidth can be made close to (even higher than) the switching frequency through converter augmentation; however, it requires a proper control algorithm

Improved time optimal control of a buck converter based on capacitor current

IEEE Transactions on Power Electronics, 2012

Time optimal control (TOC) is a technique to provide fast transient recovery in dc–dc converters.... more Time optimal control (TOC) is a technique to provide fast transient recovery in dc–dc converters. Prior published approaches are incomplete in the formulation of TOC because they ignore voltage-deviation effects on inductor-current and load-current dynamics during a large-signal recovery. An accurate TOC algorithm based on capacitor current is presented. This method achieves minimum transient recovery time for load transients and tracking in a buck converter. The minimum recovery time is preserved even with a transient-detection delay. This control configuration ensures large-signal stability in a sense similar to that of sliding-mode control. The results are demonstrated in an experimental buck converter that uses a digital control algorithm.

Formulation of PID Control for DC–DC Converters Based on Capacitor Current: A Geometric Context

IEEE Transactions on Power Electronics, 2012

The output-voltage-derivative term of a proportional-integral-derivative (PID) controller injects... more The output-voltage-derivative term of a proportional-integral-derivative (PID) controller injects significant noise in a dc-dc converter. This is mainly due to the presence of parasitic resistance and inductance of the output capacitor. Particularly during a large-signal transient, noise injection significantly degrades phase margin. Although noise characteristics can be improved by reducing the cut-off frequency of the low-pass filter associated with the voltage derivative, it degrades the closed-loop bandwidth. A new formulation of a PID controller is introduced to replace the output-voltage-derivative with information about the capacitor current, thus reducing noise injection. It is shown this new formulation preserves the fundamental principle of a PID controller and incorporates a load current feed-forward as well as inductor current dynamics. This can be helpful to further improve bandwidth and phase margin. The proposed method is shown to be equivalent to a voltage-mode controlled buck converter and a current-mode controlled boost converter with a PID controller in the voltage feedback loop.

Modeling and analysis of DC-DC converters under pulse skipping modulation

TENCON 2008-2008 IEEE …, 2008

Abstract—The technique to model dc-dc converters governed by Pulse Skipping Modulation (PSM), whi... more Abstract—The technique to model dc-dc converters governed by Pulse Skipping Modulation (PSM), which is based on energy balance principle, is not accurate enough. In this paper, an attempt has been made to model them accurately using the discrete-time modeling ...

Beyond time-optimality: Energy-based control of augmented buck converters for near ideal load transient response

Applied Power Electronics …, 2011

This paper presents a buck converter augmented with additional energy paths that enable a near nu... more This paper presents a buck converter augmented with additional energy paths that enable a near null response to load transients. Fundamental performance limits, such as slew-rate limits, are overcome resulting in increased bandwidth with a response that is faster than previously established "minimum time" or "time optimal" control of conventional buck converters. An energy-based method is presented that allows simplified

A novel current controlled tri-state boost converter with superior dynamic performance

Circuits and Systems, 2008. …, 2008

Abstract—A novel current mode control of tri-state boost converter is proposed, which eliminates ... more Abstract—A novel current mode control of tri-state boost converter is proposed, which eliminates the zero in the right-half plane and improves the dynamic performance. The tri-state boost converter contains an additional switch across the inductor. Within a clock cycle, the inductor ...

Discontinuous map analysis of a DC-DC converter governed by pulse skipping modulation

IEEE Transactions on Circuits and Systems I-regular Papers, 2010

Abstract—This paper reports the bifurcation phenomena in a dc-dc converter governed by a pulse sk... more Abstract—This paper reports the bifurcation phenomena in a dc-dc converter governed by a pulse skipping modulation (PSM) scheme, which is normally used to improve efficiency under light load condition. It is shown that the discrete-time model of the system takes the form of ...

A current-controlled tristate boost converter with improved performance through RHP zero elimination

IEEE Transactions on Power Electronics, 2009

Abstract—A novel current mode control scheme for the tristate boost converter circuit is proposed... more Abstract—A novel current mode control scheme for the tristate boost converter circuit is proposed, which eliminates the zero in the right-half plane (RHP), and improves the dynamic performance. The tristate boost converter contains an additional switch across the ...