Dynamic modeling of DC-DC converters with peak current control in double-stage photovoltaic grid-connected inverters

In photovoltaic (PV) double-stage grid-connected inverters a high-frequency DC-DC isolation and voltage step-up stage is commonly used between the panel and the grid-connected inverter. This paper is focused on the modeling and control design of DC-DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. In the proposed overall control structure the output voltage of the DC-DC converter is regulated by the grid-connected inverter. Therefore, the inverter may be considered as a constant voltage load for the development of the small-signal model of the DC-DC converter, whereas the PV panel is considered as a negative resistance. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. The theoretical analysis is corroborated by frequency response measurements on a 230 W experimental inverter working from a single PV panel. The inverter is based on a Flyback DC-DC converter operating in discontinuous conduction mode (DCM) followed by a PWM full-bridge single-phase inverter. The time response of the whole system (DC-DC + inverter) is also shown to validate the concept. Copyright © 2011 John Wiley & Sons, Ltd. In photovoltaic (PV) double-stage gridconnected inverters a high-frequency DC-DC isolation and voltage step-up stage is commonly used between the panel and the grid-connected inverter. This paper is focused on the modeling and control design of DC-DC converters with Peak Current mode Control (PCC) and an external control loop of the PV panel voltage, which works following a voltage reference provided by a maximum power point tracking (MPPT) algorithm. The sensitivity of the control loops to variations of the power extracted from the PV panel and of its voltage is studied. Copyright © 2011 John Wiley & Sons, Ltd. Copyright © 2011 John Wiley & Sons, Ltd.This work was supported by the Spanish Ministry of Science and Innovation (MICINN) under grant ENE2009-13998-C02-02. The company AUSTRIAMICROSYSTEMS co-financed this project.Garcerá Sanfeliú, G.; González Medina, R.; Figueres Amorós, E.; Sandía Paredes, J. (2012). Dynamic modeling of DC-DC converters with peak current control in double-stage photovoltaic grid-connected inverters. International Journal of Circuit Theory and Applications. 40(8):793-813. https://doi.org/10.1002/cta.756S793813408Carrasco, J. M., Franquelo, L. G., Bialasiewicz, J. T., Galvan, E., PortilloGuisado, R. C., Prats, M. A. M., … Moreno-Alfonso, N. (2006). Power-Electronic Systems for the Grid Integration of Renewable Energy Sources: A Survey. 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IEEE Transactions on Energy Conversion, 19(4), 748-755. doi:10.1109/tec.2004.827707Femia, N., Petrone, G., Spagnuolo, G., & Vitelli, M. (2009). A Technique for Improving P&O MPPT Performances of Double-Stage Grid-Connected Photovoltaic Systems. IEEE Transactions on Industrial Electronics, 56(11), 4473-4482. doi:10.1109/tie.2009.2029589Chiu, H.-J., Huang, H.-M., Yang, H.-T., & Cheng, S.-J. (2008). An improved single-stage Flyback PFC converter for high-luminance lighting LED lamps. International Journal of Circuit Theory and Applications, 36(2), 205-210. doi:10.1002/cta.404Chiu, H.-J., Yao, C.-J., & Lo, Y.-K. (2009). A DC/DC converter topology for renewable energy systems. International Journal of Circuit Theory and Applications, 37(3), 485-495. doi:10.1002/cta.475Martins DC Demonti R Photovoltaic Energy Processing for Utility Connected System 1292 1296 10.1109/IECON.2001.975968www.focus.ti.com/lit/ml/slup127/slup127.pdf2003 http://www.fairchildsemi.comEsram, T., & Chapman, P. L. (2007). Comparison of Photovoltaic Array Maximum Power Point Tracking Techniques. IEEE Transactions on Energy Conversion, 22(2), 439-449. doi:10.1109/tec.2006.874230Liserre, M., Blaabjerg, F., & Hansen, S. (2005). Design and Control of an LCL-Filter-Based Three-Phase Active Rectifier. IEEE Transactions on Industry Applications, 41(5), 1281-1291. doi:10.1109/tia.2005.853373Liserre, M., Teodorescu, R., & Blaabjerg, F. (2006). Stability of photovoltaic and wind turbine grid-connected inverters for a large set of grid impedance values. IEEE Transactions on Power Electronics, 21(1), 263-272. doi:10.1109/tpel.2005.861185Figueres, E., Garcera, G., Sandia, J., Gonzalez-Espin, F., & Rubio, J. C. (2009). Sensitivity Study of the Dynamics of Three-Phase Photovoltaic Inverters With an LCL Grid Filter. IEEE Transactions on Industrial Electronics, 56(3), 706-717. doi:10.1109/tie.2008.2010175Ciobotaru M Teodorescu R Blaabjerg F Control of single-stage single-phase PV inverter P.1 P.10 10.1109/EPE.2005.219501Zmood, D. N., & Holmes, D. G. (2003). Stationary frame current regulation of PWM inverters with zero steady-state error. IEEE Transactions on Power Electronics, 18(3), 814-822. doi:10.1109/tpel.2003.810852Castilla, M., Miret, J., Matas, J., Garcia de Vicuna, L., & Guerrero, J. M. (2009). Control Design Guidelines for Single-Phase Grid-Connected Photovoltaic Inverters With Damped Resonant Harmonic Compensators. IEEE Transactions on Industrial Electronics, 56(11), 4492-4501. doi:10.1109/tie.2009.2017820Timbus A Teodorescu R Blaabjerg F Liserre M Synchronization methods for three phase distributed power generation systems 2474 2481 10.1109/PESC.2005.1581980Vorperian, V. (1990). Simplified analysis of PWM converters using model of PWM switch. II. Discontinuous conduction mode. 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Distributed control of a fault tolerant modular multilevel inverter for direct-drive wind turbine grid interfacing

Modular generator and converter topologies are being pursued for large offshore wind turbines to achieve fault tolerance and high reliability. A centralized controller presents a single critical point of failure which has prevented a truly modular and fault tolerant system from being obtained. This study analyses the inverter circuit control requirements during normal operation and grid fault ride-through, and proposes a distributed controller design to allow inverter modules to operate independently of each other. All the modules independently estimate the grid voltage magnitude and position, and the modules are synchronised together over a CAN bus. The CAN bus is also used to interleave the PWM switching of the modules and synchronise the ADC sampling. The controller structure and algorithms are tested by laboratory experiments with respect to normal operation, initial synchronization to the grid, module fault tolerance and grid fault ride-through

Nonlinear Analysis and Control of Interleaved Boost Converter Using Real-Time Cycle to Cycle Variable Slope Compensation

Switched-mode power converters are inherently nonlinear and piecewise smooth systems that may exhibit a series of undesirable operations that can greatly reduce the converter's efficiency and lifetime. This paper presents a nonlinear analysis technique to investigate the influence of system parameters on the stability of interleaved boost converters. In this approach, Monodromy matrix that contains all the comprehensive information of converter parameters and control loop can be employed to fully reveal and understand the inherent nonlinear dynamics of interleaved boost converters, including the interaction effect of switching operation. Thereby not only the boundary conditions but also the relationship between stability margin and the parameters given can be intuitively studied by the eigenvalues of this matrix. Furthermore, by employing the knowledge gained from this analysis, a real-Time cycle to cycle variable slope compensation method is proposed to guarantee a satisfactory performance of the converter with an extended range of stable operation. Outcomes show that systems can regain stability by applying the proposed method within a few time periods of switching cycles. The numerical and analytical results validate the theoretical analysis, and experimental results verify the effectiveness of the proposed approach

Unified model of voltage/current mode control to predict saddle-node bifurcation

A unified model of voltage mode control (VMC) and current mode control (CMC) is proposed to predict the saddle-node bifurcation (SNB). Exact SNB boundary conditions are derived, and can be further simplified in various forms for design purpose. Many approaches, including steady-state, sampled-data, average, harmonic balance, and loop gain analyses are applied to predict SNB. Each approach has its own merits and complement the other approaches.Comment: Submitted to International Journal of Circuit Theory and Applications on December 23, 2010; Manuscript ID: CTA-10-025

A general approach to synthesis and analysis of quasi-resonant converters

A method for systematic synthesis of quasi-resonant (QR) topologies by addition of resonant elements to a parent pulse-width modulation (PWM) converter network is proposed. It is found that there are six QR classes with two resonant elements, including two novel classes. More complex QR converters can be generated by a recursive application of the synthesis method. Topological definitions of all known and novel QR classes follow directly from the synthesis method and topological properties of PWM parents. The synthesis of QR converters is augmented by a study of possible switch realizations and operating modes. In particular, it is demonstrated that a controllable rectifier can be used to accomplish the constant-frequency control in all QR classes. Links between the QR converters and the underlying PWM networks are extended to general DC and small-signal AC models in which the model of the PWM parent is explicitly exposed. Results of steady-state analyses of selected QR classes and operating modes include boundaries of operating regions, DC characteristics, a comparison of switching transitions and switch stresses, and a discussion of relevant design trade-offs

One-Quadrant Switched-Mode Power Converters

This article presents the main topics related to one-quadrant power converters. The basic topologies are analysed and a simple methodology to obtain the steady-state output-input voltage ratio is set out. A short discussion of different methods to control one-quadrant power converters is presented. Some of the reported derived topologies of one-quadrant power converters are also considered. Some topics related to one-quadrant power converters such as synchronous rectification, hard and soft commutation, and interleaved converters are discussed. Finally, a brief introduction to resonant converters is given.Comment: 25 pages, contribution to the 2014 CAS - CERN Accelerator School: Power Converters, Baden, Switzerland, 7-14 May 201

Relative Stability of the Inner-Current Loop of Peak Current-Mode Controlled PWM DC-DC Converters in CCM

Current-mode control is a commonly adopted method of regulation for pulse-width modulated (PWM) dc-dc power converters in industry, but is not well understood. The advantages of current-mode control over the voltage-mode control include inherent overload and short circuit protection, faster response, line-noise rejection, and multiple converter paralleling. Current-mode controlled system consists of (1) an inner-current loop and (2) an outer-voltage loop, which sets the reference voltage to the inner loop. To ensure stable operation of the multi-loop converter, all the sequential loops in the circuit should be stable with sufficient degree of stability. The research in this dissertation is focused on the relative stability of the inner-current loop in peak current-mode (PCM) controlled PWM dc-dc converters operating in CCM. The operating principle of peak current-mode control is presented. The inner-current loop dynamics of a peak current-mode controlled dc-dc converter is investigated using perturbation theory. Considering its mixed-signal (analog and digital) behavior, the current loop is modeled using sample-and-hold theory. Taking the discrete nature of the inner-current loop into account, a closed-loop transfer function for the current loop is derived in z-domain and an equivalent-hold approximation is used to derive an approximate closed-loop transfer function in the continuous s-domain using modified Pad´e approximation. A general expression for the loop gain of the inner-loop, independent of the converter topology, is derived. Using the loop gain, a measure of relative stability of the inner loop is developed. Expressions for amount of slope compensation required at maximum duty cycle, for the inner loop to be marginally stable and to achieve a specified margin of stability, are derived. Also, expressions for maximum duty cycle at a given amount of slope compensation, for the inner loop to be marginally stable and to obtain a specified margin of stability, are derived. The control current expressions for the inner loop of peak current-mode controlled converters without and with slope compensation are derived. A procedure to design the inner-current loop is developed. Saber Sketch simulation and experimental results are presented to validate the presented theory. The dynamic behavior of the inner-current loop of peak current-mode controlled PWM dc-dc buck converter operating in CCM is analyzed. The critical path power stage transfer functions, the relevant inner-current loop transfer functions, and the control-to-output transfer function of peak current-mode controlled PWM dc-dc buck converter operating in CCM are derived. The presented model is validated using experimental Bode plots

Design and analysis of feedback controllers for a DC buck-boost converter

In Murdoch University, students majoring in Electrical Power Engineering have the opportunity to learn about the basics of power electronic systems. ENG349 Power Electronic Converters and Systems is a unit where students are exposed to a range of industrial electronics. The power pole board provided by the University of Minnesota is used for laboratory teaching on how DC converters operate [1, 2]. This thesis topic gives an opportunity for Electrical Power students to further expand their basic knowledge on power electronics. Additionally, Instrumentation and Control System Engineering students will have a better understanding of dynamic control systems, which are essential in designing and analysing feedback control on DC converters. Industrial computer systems students are able to design and implement external hardware to enhance power board components. Renewable Energy students will be interested in how DC converters are applied to renewable energy systems. This thesis provides project expansion for all types of electrical engineering majors taught at Murdoch University. The main focus of this thesis is to design and analyse different feedback controllers for the converter system. The literature review and steps into designing feedback controllers are adapted from Ned Mohan’s approach in designing feedback controllers for DC converters [3]. The results presented are based on the author’s knowledge learnt from Electrical Power and Instrumentation and Control Systems Engineering. Computer simulations from Pspice and MATLAB are used for testing the feedback responses of implementing different feedback compensators. The most difficult task in this thesis is to produce accurate results from the power pole board, especially with the peak current controller circuit. Although the simulated results are successful, it is hard to compare these to the experimental results due to the ways of how the power board components are connected. This thesis will further explain the process in exploring these feedback controllers

A comparative study of electric power distribution systems for spacecraft

The electric power distribution systems for spacecraft are compared concentrating on two interrelated issues: the choice between dc and high frequency ac, and the converter/inverter topology to be used at the power source. The relative merits of dc and ac distribution are discussed. Specific converter and inverter topologies are identified and analyzed in detail for the purpose of detailed comparison. Finally, specific topologies are recommended for use in dc and ac systems