ISMC for Boost-Derived DC–DC–AC Converter: Mitigation of $2\omega$ -Ripple and Uncertainty, and Improvement in Dynamic Performance

Abstract: This paper provides a comprehensive review of the control approaches and the power-decoupling topologies to mitigate 2ω-ripple problem in the single-phase inverters, its solutions, and discusses open challenges yet to be addressed. The cause and effects of 2ω-ripple problem and its solution based on the passive and active power-decoupling techniques are discussed. A subcategory of the active power-decoupling technique nominated as the control-oriented compensation technique is reviewed in detail, this technique can achieve the ripple-mitigation at the source through the control but not necessarily adds extra circuit or active filter to the system. The control-oriented compensation techniques can be applied in the two-stage DC-DC-AC converters and the single-stage inverters having a front-end control capability with the H-bridge such as in the quasi-switched-boost inverters. The merits and associated challenges of these techniques are listed and summarized in a tabular form. Finally, a conclusive discussion with open challenges is presented.

Abstract: Single-phase ac to three-phase ac converters are needed in numerous applications, including motor drives used for residential applications. These converters, however, suffer from an inherent problem of mismatch between instantaneous input and output powers. Specifically, the instantaneous input power has a dc component along with an alternating component with double-line frequency, while the three-phase instantaneous output power is only dc. Conventional single-phase ac to three-phase ac converters use large electrolytic capacitors to handle this mismatch of power. However, these electrolytic capacitors may have high failure rates, which contribute to reduced lifetime of the converters. Moreover, these capacitors can be bulky and heavy. This article introduces a new single-phase ac to three-phase ac converter that uses a small film capacitor instead of large electrolytic capacitors. Despite using a small film capacitor, the double-line frequency harmonic does not appear at the input or output currents/voltages. The principles of the operation of the proposed topology are presented in this article, and its performance is evaluated through both simulations and experiments.

Abstract: High-voltage dc power supplies (HVDCPSs) have been widely adopted for the vacuum tubes. In this application field, the low ripple voltage cannot be easily achieved by increasing the size of the output capacitance of the HVDCPS due to the limited permissible level of the stored energy. To obtain a low level of the output ripple as well as the limited value of the stored energy, the previously published literature proposed switching frequency increment. This approach has several shortcomings such as switching power loss increment, a limited level of the achievable ripple, and low value of the insulators’ lifetime. To improve the mentioned deficiencies, this article hybridizes the series linear regulator and a high-frequency high-power dc interleaved converter. Using the proposed method, at the first stage, the level of the ripple decreases to a rational margin with increasing the ripple frequency. At the second stage, the level of the ripple reduces using the linear regulator to reach the expected precision. In order to validate the performance of the proposed structure, simulation and experimental results are provided for a 15-kV and 22.5-kW converter with the output voltage precision of 0.02%.

Abstract: The paper generalized a new sliding mode design concept, namely integral sliding mode (ISM). The order of the motion equation in ISM is equal to the order of the original system, rather than reduced by the number of dimension of the control input. As the result, robustness of the system can be guaranteed throughout an entire response of the system starting from the initial time instance. Uniform formulations of the ISM design principle are developed in the paper. It is shown through examples that our generalized ISM scheme enables a wide scope of application areas. In the case that the given control matrix can not be used directly for generating the sliding mode, the associated decoupling problem was also discussed based on the concept of sliding mode transformation. To alleviate chattering, we remove the discontinuous control action from the real control path and insert it to an internal dynamic process for generating the sliding mode.

Abstract: The robustness properties of integral sliding-mode controllers are studied. This note shows how to select the projection matrix in such a way that the euclidean norm of the resulting perturbation is minimal. It is also shown that when the minimum is attained, the resulting perturbation is not amplified. This selection is particularly useful if integral sliding-mode control is to be combined with other methods to further robustify against unmatched perturbations. H/sub /spl infin// is taken as a special case. Simulations support the general analysis and show the effectiveness of this particular combination.

Abstract: A fuel cell power system that contains a single-phase dc-ac inverter tends to draw an ac ripple current at twice the output frequency. Such a ripple current may shorten fuel cell life span and worsen the fuel efficiency due to the hystersis effect. The most obvious impact is it tends to reduce the fuel cell output capacity because the fuel cell controller trips under instantaneous over-current condition. In this paper, the ripple current propagation path is analyzed, and its linearized ac model is derived. The equivalent circuit model and ripple current reduction with passive energy storage component are simulated and verified with experiments. An advanced active control technique is then proposed to incorporate a current control loop in the dc-dc converter for ripple reduction. The proposed active ripple reduction method has been verified with computer simulation and hardware experiment with a proton exchange membrane type fuel cell using a multiphase dc-dc converter along with a full-bridge dc-ac inverter. Test results with open loop, single voltage loop, and the proposed active current-loop control are provided for comparison.

Abstract: The effect of inverter ripple current on fuel cell stack performance and stack lifetime remains uncertain. This paper provides a first attempt to examine the impact of inverter load dynamics on the fuel cell. Since reactant utilization is known to impact the mechanical nature of a fuel cell, it is suggested that the varying reactant conditions surrounding the cell govern. at least in part the lifetime of the cells. This paper investigates these conditions through the use of a dynamic model for the bulk conditions within the stack, as well as a one-dimensional model for the detailed mass transport occurring within the electrode of a cell. These two independent modeling approaches are used to verify their respective numerical procedures. in this work, the inverter load is imposed as a boundary condition to the models. Results show the transient behavior of the reactant concentrations within the stack, and of the mass diffusion within the electrode under inverter loads with frequencies between 30 Hz and 1250 Hz.

Abstract: We describe an energy-efficient, fuel-cell power-conditioning system (PCS) for stationary application, which reduces the variations in the current drawn from the fuel-cell stack and can potentially meet the $40/kW cost target. The PCS consists of a zero-ripple boost converter (ZRBC) followed by a soft-switched and multilevel high-frequency (HF) inverter and a single-phase cycloconverter. The ZRBC comprises a new zero-ripple filter (ZRF), which significantly reduces the input low- and high-frequency current ripples, thereby potentially enhancing the durability of the stack. A new phase-shifted sinewave modulation of the multilevel HF inverter is proposed, which results in the zero-voltage switching (ZVS) of all four switches without the use of any auxiliary circuit components. For such a sine wave modulation technique, >90% ZVS range is obtained per line cycle for about 70% of the rated load. Further, the line-frequency switching of the cycloconverter (at close to unity power factor) results in extremely low switching losses. The intermediate dc bus facilitates the inclusion of power systems based on other forms of alternative-energy techniques (e.g., photovoltaic/high-voltage stack). A 5 kW prototype of the proposed PCS is built, which currently achieves a peak efficiency of 92.4%. We present a detailed description of the operation of the PCS along with its key features and advantages. Finally, experimental results showing the satisfactory performance and the operation of the PCS are demonstrated.