There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

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Solid-state switch-mode rectification converters have reached a matured level for improving power quality in terms of power-factor correction (PFC), reduced total harmonic distortion at input AC mains and precisely regulated DC output in buck, boost, buck-boost and multilevel modes with unidirectional and bidirectional power flow. This paper deals with a comprehensive review of improved power quality converters (IPQCs) configurations, control approaches, design features, selection of components, other related considerations, and their suitability and selection for specific applications. It is targeted to provide a wide spectrum on the status of IPQC technology to researchers, designers and application engineers working on switched-mode AC-DC converters. A classified list of more than 450 research publications on the state of art of IPQC is also given for a quick reference.

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A review of single-phase improved power quality AC-DC converters

The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

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Power Electronics Converters Applications And Design

An isolated three-port bidirectional dc-dc converter composed of three full-bridge cells and a high-frequency transformer is proposed in this paper. Besides the phase shift control managing the power flow between the ports, utilization of the duty cycle control for optimizing the system behavior is discussed and the control laws ensuring the minimum overall system losses are studied. Furthermore, the dynamic analysis and associated control design are presented. A control-oriented converter model is developed and the Bode plots of the control-output transfer functions are given. A control strategy with the decoupled power flow management is implemented to obtain fast dynamic response. Finally, a 1.5 kW prototype has been built to verify all theoretical considerations. The proposed topology and control is particularly relevant to multiple voltage electrical systems in hybrid electric vehicles and renewable energy generation systems.

An Isolated Three-Port Bidirectional DC-DC Converter With Decoupled Power Flow Management

This paper describes the design and implementation of a discrete controller for grid-connected voltage-source inverters with an LCL filter usually found in wind power generation systems. First, a theorem that relates the controllability of the discrete dynamic equation of the inverter with LCL filter and the sampling frequency is derived. Then, a condition to obtain a partial state feedback controller robust to grid impedance uncertainties and based on linear matrix inequalities is proposed. This controller guarantees the stability and damping of the LCL filter resonance for a large set of grid conditions without requiring self-tuning procedures. Finally, an internal model controller is added to ensure asymptotic reference tracking and disturbance rejection, significantly reducing the impact of grid background voltage distortion on the output currents. Experimental results are presented to support the theoretical analysis and to demonstrate the system performance.

Design and Implementation of a Robust Current Controller for VSI Connected to the Grid Through an LCL Filter

This paper proposes a sensorless vector control that combines two discrete-time observers to estimate the rotor speed and position of permanent magnet synchronous machines (PMSM). The first one is a sliding mode (DSM) current observer and the second one is an adaptive electromotive force (EMF) observer. Initially, the sliding conditions that assure the sliding motion around the sliding surface are derived and a design procedure to the DSM current observer is developed. Moreover, using discrete-time adaptive Lyapunov based EMF observer the rotor speed and position are obtained. Experimental results validate the theoretical analysis and demonstrate the very good performance of the proposed discrete-time sensorless vector control.

Discrete-Time Sliding Mode Observer for Sensorless Vector Control of Permanent Magnet Synchronous Machine

This paper proposes a new robust controller in a stationary reference frame for doubly fed induction generators (DFIGs) of grid-connected wind turbines. Initially, a DFIG dynamic model is derived from the voltage and flux equations in αβ coordinates, where uncertainties and disturbances intrinsic to the system are accounted for as perturbation terms are added to the nominal model. Then, a controller design procedure that guarantees the DFIG stability under uncertainties and disturbances at the grid side is presented in detail. It is demonstrated that a very fast dynamic behavior can be obtained with the proposed controller, which improves the transient response of the grid-connected DFIG, particularly under conditions of unbalanced voltage dips resulting from asymmetrical network faults. In order to conform with the fault ride-through capability requirements, this paper proposes a new reference strategy, which is divided into normal and fault operation modes. Experimental results are given to support the theoretical analysis and to illustrate the performance of the grid-connected DFIG with the proposed controller.

Robust Controller for DFIGs of Grid-Connected Wind Turbines

This paper presents a discrete-time adaptive current controller for grid-connected pulse width modulation voltage source converters with LCL filter. The main attribute of the proposed current controller is that, in steady state, the damping of the LCL resonance does not depend on the grid characteristic since the adaptive feedback gains ensure a predefined behavior for the closed-loop current control. An overview of model reference adaptive state feedback theory is presented aiming to give the reader the required background for the adaptive current control design. The digital implementation delay is included in the model, and the stability concerning the variation of the grid parameters is analyzed in detail. Furthermore, current distortions due to the grid background voltage are rejected without using the conventional stationary resonant controllers or the synchronous proportional-plus-integral controllers. Simulation and experimental results are presented to validate the analysis and to demonstrate the good performance of the proposed controller for grid-connected converters subjected to large grid impedance variation and grid voltage disturbances.

Adaptive current control for grid-connected converters with LCL-filter

This paper presents a linear matrix inequality-based procedure for the design of state feedback current controllers that are robust to uncertainties on grid inductance for grid-connected converters with LCL filters. The state feedback control law includes the filter state variables, the states of resonant controllers, and considers also the delay from digital control implementation. As the main contribution here, the proposed strategy allows to deal with resonant controllers of arbitrary dimension, and provides results complying with IEEE Standard 1547 requirements. The control synthesis condition takes into account the assignment of the closed-loop eigenvalues in a circular region with radius r, located inside the unit circle, and the control design relies only on the choice of the value of the radius in the interval 0 <; r ≤ 1, providing all the state feedback gains in a simple and efficient procedure.

Humberto Pinheiro

Papers

Design and Implementation of a Robust Current Controller for VSI Connected to the Grid Through an LCL Filter

Discrete-Time Sliding Mode Observer for Sensorless Vector Control of Permanent Magnet Synchronous Machine

Robust Controller for DFIGs of Grid-Connected Wind Turbines

Adaptive current control for grid-connected converters with LCL-filter

LMI-Based Control for Grid-Connected Converters With LCL Filters Under Uncertain Parameters