Gert Karmisholt Andersen

A new green power inverter for fuel cells

This paper presents a new grid connected inverter for fuel cells. It consists of a two stage power conversion topology. Since the fuel cell operates with a low voltage in a wide voltage range (25 V-45 V) this voltage must be transformed to around 350-400 V in order to invert this DC power into AC power to the grid. The proposed converter consists of an isolated DC-DC converter cascaded with a single phase H-bridge inverter. The DC-DC converter is a current-fed push-pull converter. A new dedicated voltage mode startup procedure has been developed in order to limit the inrush current during startup. The inverter is controlled as a power factor controller with resistor emulation. Experimental results of converter efficiency, grid performance and fuel cell response are shown for a 1 kW prototype. The proposed converter exhibits a high efficiency in a wide power range (higher than 92%) and the inverter operates with a near unity power factor and a low current THD.

Current programmed control of a single-phase two-switch buck-boost power factor correction circuit

This paper presents a new current programmed control (CPC) technique for a cascaded two-switch buck-boost converter suitable as a low-cost power factor correction (PFC) rectifier in a variable speed motor drive. This new CPC technique, which is an extension of the conventional CPC method, enables the variable output dc voltage, and is therefore suitable in a pulse amplitude modulated (PAM) motor drive or as a universal input-power supply. The CPC method is very simple and requires only a constant-current reference without any changes in the transition between boost and buck operating mode, and the line current is practically unaffected by the topology-mode shift. Simulations and experimental results verify the presented control technique. Compliance with IEC-61000-3-2 class A is achieved. The experimental setup is based on a commercial CPC integrated circuit (IC) for dc-dc converters. This new control technique enables a simple low-cost control circuit for the two-switch buck-boost converter, which complies with IEC-61000-3-2, and the PFC circuit has inherent in-rush and overcurrent protection.

A basic IGBT model with easy parameter extraction

Simple parameter extraction is the goal of a new basic IGBT model designed for use by application engineers. The model has good accuracy yet its parameters can be quickly extracted from three standard measurements or from data sheets.

Low-cost digital implementation of proportional-resonant current controllers for PV inverter applications using delta operator

The performances of the P+Resonant controller in case of current control for a single phase grid connected inverter have been proved to be superior to the PI controller, since it is able to remove the phase error of the control at the fundamental frequency of the grid. It offers also the possibility of selective harmonic compensation. However, in case of digital implementation on a low-cost fixed-point DSP, the limited computational power and the limited numerical representation precision can restrict the utilization of it. The present paper proposes a different way of digital implementation of the P+Resonant controller with selective harmonic compensation on a low-cost fixed-point DSP. The resonant part of the P+R has been implemented as a second order filter based on delta operator. The current controller, together with harmonic compensation for the 3/sup rd/, 5/sup th/, and 7/sup th/ harmonics has been successfully tested in practice with a 1.5 KW PV inverter, achieving a 1.2% total harmonic distortion (THD) of the grid current.

A new power converter for fuel cells with high system efficiency

This paper presents a new high-efficiency grid-connected single-phase converter for fuel cells. It consists of a two-stage power conversion topology. Since the fuel cell operates with a low voltage in a wide voltage range (25 V–45 V) this voltage must be transformed to around 350–400 V in order to be able to invert this dc power into ac power to the grid. The proposed converter consists of an isolated dc–dc converter cascaded with a single-phase H-bridge inverter. The dc–dc converter is a current-fed push-pull converter. The inverter is controlled as a standard single-phase power factor controller with resistor emulation at the output. Experimental results of converter efficiency, grid performance and fuel cell dynamic response are shown for a 1 kW prototype. The proposed converter exhibits a high efficiency in a wide power range (higher than 92%) and the inverter operates with a near-unity power factor and a low current THD.

Current programmed control of a single phase two-switch buck-boost power factor correction circuit

This paper presents a new current programmed control (CPC) technique for the cascaded two switch buck-boost converter suitable as a low-cost power factor correction (PFC) rectifier in a variable speed motor drive. This new CPC technique, which is an extension of the conventional CPC method, enables variable output DC-voltage and is therefore suitable in a pulse amplitude modulated (PAM) motor drive or as a universal input power supply. The CPC method is very simple and requires only a constant current reference without any changes at the transition between boost and buck operating mode and the line current is practically unaffected by the topology mode shift. The presented control technique is verified by simulations and experimental results and compliance with IEC 61000-3-2 class A is achieved. The experimental setup is based on a commercial CPC IC for DC-DC converters.

An asymmetrical space vector method for single phase induction motor

Single phase induction motors are the workhorses in low-power applications in the world, and also where variable speed is necessary. Normally it is achieved either by the mechanical method or by controlling the capacitor connected with the auxiliary winding. Any of the above methods have some drawback for which the motor torque performance is not good enough. This paper addresses a new control method, an asymmetrical space vector method with PWM modulation, also a three-phase inverter is used for the main winding and the auxiliary winding. This method with PWM modulation is implemented to control the motor speed and to improve the torque performance. The control theory and simulation results are presented. This control method is verified by experimental results.

A performance oriented wind turbine model for grid stability studies

A generic model of a wind turbine with a double fed generator for grid stability studies is presented. The model takes-off in the required model performance rather than the physical structure and components of the wind turbine. Analysis shows that substantial reductions in model complexity can be achieved by extending some of the basic assumptions for a grid stability model into model simplifications. In spite of large variation in model complexity, a case study in PowerFactory reveals no significant performance variations when the performance oriented model is compared to a far more complex component-oriented model.

Utilizing the free running current programmed control as a power factor correction technique for the two switch buck-boost converter

This paper presents a new power factor correction technique based on the free running current programmed control (FRCPC) technique. The FRCPC technique is adapted to the two switch cascaded buck-boost converter which provides variable output voltage and it can be used for universal input voltage. The converter has two operating modes: boost and buck. Boost mode occurs when the output voltage is higher than the input voltage and buck mode occurs when the output voltage is lower than the input voltage. Peak current control is used in boost mode and valley current control is used in buck mode. This new control technique exhibits high quality input current and its based on a simple control structure.

Online variation of wind turbine controller parameter for mitigation of SSR in DFIG based wind farms

The aim of this paper is to investigate the risk for Subsynchronous Resonance (SSR) conditions in Doubly Fed Induction Generator (DFIG) based wind farms connected to series-compensated transmission lines. The well-known IEEE First Benchmark Model for SSR studies is adopted and the impact of the turbine controller parameters on the risk for unstable conditions is analyzed. In particular, it is shown through frequency domain studies that a reduction of the closed-loop bandwidth of the current controller that regulates the rotor current effectively reduces the risk for SSR. Simulation results are presented to validate the theoretical findings.