M. Sippola

Tampere University of Technology, Tampere, Western Finland, Finland

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Publications (12)9.25 Total impact

  • M. Karppanen, M. Sippola, T. Suntio
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    ABSTRACT: The supply-voltage requirements of the modern integrated circuits necessitate the use of distributed power systems. There are concerns about the use of single intermediate bus voltage to power multiple point-of-load (POL) converters such as signal integrity due to the high frequency circulating currents and narrow duty ratios of POL converters. The paper investigates the possibility to implement the bus converter as multi-output semi-regulated converter to overcome the aforementioned concerns with insignificant additional costs. The concept was implemented by means of active-clamp forward converter with synchronous rectification and input-voltage-feedforward control. The main concerns have been the input-to-output noise attenuation and cross-regulation between the outputs. Frequency and time domain results are provided to support theoretical findings.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
  • M. Karppanen, T. Suntio, M. Sippola
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    ABSTRACT: The paper investigates the dynamics associated to the fourth-order converter known as two-inductor buck, current-sourced buck or superbuck converter under peak-current-mode control. In late 1970s, the optimality of a converter was considered based on the continuity of the input current and the output current supplying the output capacitor. As a consequence, the converter named as Cuk converter according to its inventor was qualified as an optimal converter. The continuity of input and output currents does not suffice anymore but the properties such as input and output invariance, nonexistence of control anomalies, and the order of control dynamics have to be considered. The paper investigates the dynamic properties of the superbuck converter under peak-current-mode control. The investigations show that the superbuck converter contains all the desired features but it may also incorporate resonant right-half-plane (RHP) zeros and poles, which can destroy the optimality. The appearance of the RHP zeros and poles can be controlled by careful power-stage design. Practical evidence is provided based on two high-frequency converters.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
  • T. Suntio, M. Karppanen, M. Sippola
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    ABSTRACT: The current-mode-controlled converters are current sources at open loop, and therefore, they cannot operate at a constant-current-type load required for measuring the transfer functions constituting the internal or unterminated set known as the G-parameters, which only describes the dynamics of the voltage-output converter. The paper investigates the methods by means of which the set can be determined by measurements and computationally. The methods are partly derived from the presently developed knowledge on characterizing the current-output converters.
    Power Electronics Specialists Conference, 2008. PESC 2008. IEEE; 07/2008
  • M. Karppanen, M. Sippola, T. Suntio
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    ABSTRACT: Output-voltage remote sensing is typically used to improve static voltage accuracy at the point of load as well as to improve the load transient response. Every switched-mode converter has its unique dynamical profile, which may definitively change due to adding of extra impedances into the converter, when the output-voltage remote sensing is applied. A typical effect of a pure cable connection is an increase in the capacitive-load sensitivity especially at high frequencies. Resonant- type impedances may have more profound effects making the converter more sensitive to other types of source and load interactions. The paper provides consistent methods to analyze the impact of remote sensing based on a general two-port model of an electrical voltage-output system. Buck converters are used to provide practical evidence.
    Power Electronics and Applications, 2007 European Conference on; 10/2007
  • M. Karppanen, M. Sippola, T. Suntio
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    ABSTRACT: The paper investigates the validity of the input-side minor-loop-gain-based design rules given usually as a certain forbidden region in a complex plane out of which the minor-loop gain should stay in order to ensure stability and sufficient transient dynamics of the converter. The prevailing forbidden-region-based design rules would ensure the stability but do not ensure the sufficient transient dynamics. The design rules developed by Middlebrook are usually considered too conservative but, as shown in this paper, those are the most appropriate but needing refinement. Experimental evidence is presented to support the theoretical predictions and findings.
    Power Electronics Specialists Conference, 2007. PESC 2007. IEEE; 07/2007
  • M. Karppanen, T. Suntio, M. Sippola
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    ABSTRACT: The use of input-voltage-feedforward (IVFF) control has become a popular method to implement a low-cost bus converter in the telecommunications distributed power architectures because the IVFF control can provide adequate output-voltage accuracy in respect to the variations in the input voltage even at open loop, when applied to a buck converter. The method in itself is well known from the 1980s, but the dynamical features that the method would provide have not been fully investigated and reported. The results of the investigations made in this paper show that the IVFF control would provide input-noise attenuation comparable to the peak-current-mode control, voltage-loop gain largely independent of input voltage, and highly reduced input-filter interactions as compared to the voltage-mode control. The main disadvantage is the reduced output-voltage-load-transient response due to the input-voltage-dependent maximum duty ratio. The observations are supported with comprehensive experimental measurements
    IEEE Transactions on Industrial Electronics 05/2007; · 5.17 Impact Factor
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    ABSTRACT: The paper investigates the effect of unity-gain output-current-feedforward in a peak-current-mode-controlled (PCMC) buck converter. A consistent theoretical basis is provided showing that the unity-gain feedforward can improve significantly the load invariance and transient performance of a PCMC buck converter. The nonidealities associated to the scheme would, however, deteriorate the obtainable level of invariance. The nonidealities can be maintained at acceptable level, and therefore, the scheme would provide a viable method to reduce significantly the load interactions as well as improve the load-transient response. The theoretical predictions are supported with comprehensive experimental evidence both at frequency and time domain as well as comparisons between three different buck converters
    IEEE Transactions on Power Electronics 04/2007; · 4.08 Impact Factor
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    ABSTRACT: An electrical device such as a switched-mode converter has unique internal dynamical profile, which mainly dictates, how the device as a subsystem in an interconnected system would behave and how it will affect the other subsystems within the constellation. The paper defines the vital representative parameters by means of which the stability and dynamics of the individual electrical device as well as the overall interconnected system can be analyzed and predicted. The very existence of such a dynamical priflle is proved based on extensive experimental evidence.
    Telecommunications Energy Conference, 2007. INTELEC 2007. 29th International; 01/2007
  • M. Hankaniemi, T. Suntio, M. Sippola
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    ABSTRACT: The paper investigates the load interactions in constant-current-controlled buck converters. The nominal transfer functions and the load interaction formalism are derived from the voltage-output-converter model by applying duality. It is observed that the constant-current control makes the converter very sensitive to load interactions implying that a proper controller design is a necessity. The high crossover frequency in the nominal control-to-output transfer function may lead to performance degradation if the initial control design is done with resistive load, because the typical load for constant-current controlled converters is a low impedance storage-battery recovering the nominal feature. It is shown that electronic loads, typically used in prototype testing and verification, might have unexpected characteristics. This may lead to wrong deductions of the converter stability and performance
    Telecommunications Energy Conference, 2006. INTELEC '06. 28th Annual International; 10/2006
  • Matti Karppanen, Mika Sippola, Teuvo Suntio
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    ABSTRACT: The use of input-voltage-feedforward (IVFF) control has become a popular method to implement a reduced-cost bus converter in the DC power systems known as intermediate bus architecture (IBA), because the IVFF control can provide adequate output voltage accuracy in respect to the variations in the input voltage even at open loop, when applied to a buck converter. The method in itself is well known from 1980's but the dynamical features the method would provide have not been fully investigated and reported. This paper provides the theory behind the IVFF control according to which the dynamical properties of the associated converter are studied and experimentally verified. According to the investigations, the properly implemented IVFF control would provide input-to-output noise attenuation comparable to the peak-current-mode controlled converter, the voltage-loop gain largely independent of input voltage, highly reduced input-filter interactions but also increased sensitivity to negative-resistor-oscillation (NRO) phenomenon even at open loop
    Telecommunications Energy Conference, 2006. INTELEC '06. 28th Annual International; 10/2006
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    ABSTRACT: The characterization of regulated converters is investigated in order to establish a set of dynamical parameters defining the interactions arising in the interconnected systems such as telecom distributed power supply (DPS) systems. The commercially available converters are usually vaguely specified in respect to those interactions. Provided information do not suffice for predicting the stability and performance. It is noticed that there are certain double reflections, which are not previously recognized but may increase the load sensitivity if not properly considered. The defined parameter set can be also used to design the converters to be more insensitive to different interactions
    01/2005;
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    ABSTRACT: The effect of load impedance on the dynamics and performance of a regulated converter is investigated. Theoretical formulation is derived utilizing two-port modelling technique. It is definitively shown that the load interactions are reflected into the converter dynamics via the internal open-loop output impedance. At the frequencies, where the loop gain is much higher than unity, the internal closed-loop output impedances acts as a boundary for the control-bandwidth reduction. The loop gain is always affected, whenever the internal open-loop output impedance is equal or greater than the load impedance. The converters are sensitive especially to the capacitive and resonant-type loads. The sensitivity is dependent on control mode, and cannot be much reduced by means of basic controller design
    01/2005;