Dynamics Of Power Converters Research Articles

State Feedback with Integral Control Circuit Design of DC-DC Buck-Boost Converter

The pulse-with modulated (PWM) dc-dc buck-boost converter is a non-minimum phase system, which requires a proper control scheme to improve the transient response and provide constant output voltage during line and load variations. The pole placement technique has been proposed in the literature to control this type of power converter and achieve the desired response. However, the systematic design procedure of such control law using a low-cost electronic circuit has not been discussed. In this paper, the pole placement via state-feedback with an integral control scheme of inverting the PWM dc-dc buck-boost converter is introduced. The control law is developed based on the linearized power converter model in continuous conduction mode. A detailed design procedure is given to represent the control equation using a simple electronic circuit that is suitable for low-cost commercial applications. The mathematical model of the closed-loop power converter circuit is built and simulated using SIMULINK and Simscape Electrical in MATLAB. The closed-loop dc-dc buck-boost converter is tested under various operating conditions. It is confirmed that the proposed control scheme improves the power converter dynamics, tracks the reference signal, and maintains regulated output voltage during abrupt changes in input voltage and load current. The simulation results show that the line variation of 5 V and load variation of 2 A around the nominal operating point are rejected with a maximum percentage overshoot of 3.5% and a settling time of 5.5 ms.

Set-based fast gradient projection algorithm for model predictive control of grid-tied power converters

Model Predictive Control (MPC) has attracted much attention and is widely used in power electronics. However, implementing the MPC algorithm is still a difficult task due to the fast dynamics of power converters and strict time constraints. In this paper, a computationally efficient MPC algorithm for grid-tied power converters based on the fast gradient projection method and invariant set theory is proposed. The algorithm is implemented and tested through hardware-in-the-loop simulations using Texas Instruments digital signal processors and Xilinx Field Programmable Gate Arrays platforms.

Hybrid Dynamic Phasor Modeling Approaches for Accurate Closed-Loop Simulation of Power Converters

Modelling the fast dynamics of power converters is of growing concern in power grids and Microgrids. Dynamic phasor (DP) concept has been widely applied to switched power converter for modelling fast transients efficiently due to the inherent frequency shift property of DPs. The dynamics introduced by the DC/AC power converters depend on the controllers, which are implemented either in the stationary frame or on the synchronous reference frame (SRF). Hybrid closed-loop modelling methods that consider DP-based power converter plant model are not established and the applicability and accuracy of such hybrid approaches are not fully understood. This paper attempts to address this gap by proposing two hybrid closed-loop modelling approaches: Hybrid DP-DQ and Hybrid DP-EMT and discusses the applicability and accuracy for various controller types. Furthermore, this paper presents a DP switched model of single and three phase two level power converter and discusses the selection of harmonics to reduce model complexity. The proposed hybrid approaches were validated against detailed switched power converter models and for a wide range of scenarios, the Hybrid DP-EMT method is found to be superior compared other methods. Finally, application dependent recommendations are made for the selection of suitable hybrid closed-loop model for the accurate simulation of single phase and three phase power converters.

Photovoltaic Energy Conversion Systems with Sliding Mode Control

A new sliding-mode-control-based power conversion scheme is proposed for photovoltaic energy conversion systems. The perturbation and observation (P&O) maximum power-point tracking (MPPT) approach is adopted for optimizing the power generation capabilities from solar panels. Due to the inherent nonlinear dynamics of power converters, we need to adopt a nonlinear control approach to optimize the energy conversion efficiency and tolerate the fluctuations and changes of load and sunlight irradiance. In this manuscript, novel first-and higher-order sliding mode control approaches are proposed, aiming to provide a systematic approach for the robust and optimal control of solar energy conversion, which guarantees Lyapunov stability and consistent performance in the face of external perturbations and disturbances. Moreover, to eliminate the chattering phenomenon inherent in the first-order approach, super-twisting second-order sliding mode control is developed for the buck-boost converter. Furthermore, the output of DC–DC converter supplies a voltage-oriented-control (VOC)-based space-vector pulse-width-modulated inverter to generate three-phase AC power to the grid. To demonstrate the robustness and effectiveness of the proposed scheme, computer simulations and dSPACE hardware-in-the-loop platform have been carried on for examining the proposed sliding-mode-control-based solar energy conversion system.

Control of islanded microgrids considering power converter dynamics

In this paper, the control problem of Islanded Microgrids is approached. A controller scheme that considers the necessity to assure the generation of grid-forming nodes as well as the proper operation of grid-following nodes is proposed. The main feature of the contribution is the explicit inclusion of the dynamic of the power converters existing in this kind of networks making possible the evaluation of the system performance under sudden and fast changes in the operating conditions typically found in these applications. The scheme uses only the measurement of local variables and guarantees that both voltages and currents of the network achieve the values required to satisfy a prescribed power balance imposed by the loads. The design of the proposed controller is carried out by exploiting a Port-Controlled Hamiltonian representation of the system and applying the Passivity-based Controller design methodology. The stability properties of the closed-loop system are formally proved and its usefulness is illustrated via numerical simulations.

Review of Small-Signal Modeling Methods Including Frequency-Coupling Dynamics of Power Converters

Over the past years, the linearized modeling techniques for power converters have been continuously developed to capture the small-signal dynamics beyond half the switching frequency. This paper reviews and compares the small-signal modeling approaches based on a buck converter with voltage-mode control. The study includes the small-signal averaged modeling approach, the describing function method, and the harmonic state-space modeling approach, in order to be able to better select the correct method when modeling and analyzing a power electronic circuit as well as a power-electronic-based power system. The model comparison points out that the describing-function-based models do improve the modeling accuracy beyond the half-switching frequency of the converter, yet they fail to predict the frequency-coupling interactions (e.g., beat frequency oscillations) among multiple converters, and instead, harmonic state-space models in the multiple-input multiple-output form are required.

Adaptive pulse width modulation design for power converters based on affine switched systems

In this work we propose a novel adaptive switching strategy for the design of pulse width modulation signals in power converters. Instead of an uncertain averaged model of the power converter, an uncertain switched model is considered, which can better represent the actual power converter dynamics. Uncertainties in the power converters parameters are handled via an adaptive control approach, and all circuit parameters of the switched model are assumed to be unknown (including the load and parasitic effects). After defining the pulse width modulation in terms of a reverse mode-dependent dwell time, an elementary-time-unit Lyapunov function is used to derive a set of linear matrix inequalities (LMIs) based on global uniformly ultimately boundedness of the switched system. The LMIs are solved in an adaptive fashion using an exploitation–exploration mechanism: exploitation is achieved by solving the LMIs based on the estimated switched model, while exploration is achieved by a persistently exciting input voltage source, which guarantees convergence of the estimated parameters to the true system parameters.

Identification of DC–DC buck converter dynamics using relay feedback method with experimental validation

Accurate dynamics of power converters are necessary to achieve good control performance. In this study, the dynamical model of the DC-DC buck converter is identified by the relay feedback method. The relay is connected in the closed loop to produce a limit cycle output. The important information of the oscillatory output is used for the identification. The relay is approximated using dual-input describing function (DIDF) in the mathematical modelling. DIDF can handle symmetric and asymmetric limit cycle outputs. The converter is modelled as a second-order plus dead-time system. Using the gain and phase angle criteria, analytical expressions are derived to estimate the dynamics. The converter dynamics obtained from the proposed method are compared with that estimated using the state-space averaging method. The model is also identified from the real-time experiment. To check the efficacy of the identified model, a model validation test is performed.

ESTIMATING THE UNCERTAINTY OF THE BEHAVIOR OF A PWM POWER CONVERTER BY ANALYZING A SET OF EXPERIMENTAL BIFURCATION DIAGRAMS

One of the main faults of a PWM power converter is linked to losing the operating process stability because of bifurcations. A bifurcation diagram contains information on the evolution of the behavior of a PWM power converter that could be theoretically used to prevent the bifurcations. Surprisingly, applying the bifurcation analysis is not yet typical in engineering practice. One of the reasons seems to be in the fundamental properties of the PWM power converter dynamics caused by the unavoidable uncertainty of its behavior near a bifurcation point. We propose a new approach to estimating this uncertainty. By analyzing a set of experimental bifurcation diagrams, our approach allows to determine both the location of the uncertainty zone and the quantitative regularities of the behavior within this zone. The proposed approach can be applied to design and maintenance, including fault diagnosis, and also to scientific research of the nonlinear dynamics regularities. Our results are experimentally verified by using the "PWM DC drive" setup.

Preventive diagnosis of pulse power converter dynamics

For the pulse power converters, consideration was given to the preventive diagnosis of their anomalous modes caused by the nonlinear evolutionary processes of multiple period variations. Proposed was a variant of solution based on the symbolic models of periodic and transient processes generated by the geometric treatment of the invariants of the phase images. Developed was a procedure of continuous transformation of the time series enabling estimation of the direction of convergence of the transient process before its completion.

Double-Frequency Buck Converter

Improving the efficiency and dynamics of power converters is a concerned tradeoff in power electronics. The increase of switching frequency can improve the dynamics of power converters, but the efficiency may be degraded. A double-frequency (DF) buck converter is proposed to address this concern. This converter is comprised of two buck cells: one works at high frequency, and another works at low frequency. It operates in a way that current in the high-frequency switch is diverted through the low-frequency switch. Thus, the converter can operate at very high frequency without adding extra control circuits. Moreover, the switching loss of the converter remains small. The proposed converter exhibits improved steady state and transient responses with low switching loss. An ac small-signal model of the DF buck converter is also given to show that the dynamics of output voltage depends only on the high-frequency buck cell parameters, and is independent of the low-frequency buck cell parameters. Simulation and experimental results demonstrate that the proposed converter greatly improves the efficiency and exhibits nearly the same dynamics as the conventional high-frequency buck converter. Furthermore, the proposed topology can be extended to other dc-dc converters by the DF switch-inductor three-terminal network structure.

Modeling, analysis, and design of the quasi-charge control

A current-mode control technique, quasi-charge control (QCC), is studied. A small-signal model is developed for QCC. The model is derived for converters operating in the continuous conduction mode. The model is accurate up to half of the switching frequency. The proposed small-signal model is used to assess the dynamics of pulse-width-modulated (PWM) power converters with QCC, and to compare their performance to the current-injected control (CIC) and charge control (CC) schemes. As in CC, the QCC converges to CIC at light loads close to the boundary between continuous and discontinuous conduction modes. The dynamics of power converters with QCC or CC are more sensitive to load change and less sensitive to line change than those of power converters with CIC, especially the current loop dynamics. However, unlike in the case of CC, the dependency on the load/line can be controlled when the QCC is designed. Control design guidelines for DC-DC power converters and power factor correction rectifiers are presented, and experimental measurements are performed to verify the proposed model. >