Christian Klumpner

Evaluation of three-phase transformerless photovoltaic inverter topologies

This paper analyzes and compares three transformerless photovoltaic inverter topologies for three-phase grid connection with the main focus on the safety issues that result from the lack of galvanic isolation. A common-mode model, valid at frequencies lower than 50 kHz, is adopted to study the leakage current paths. The model is validated by both simulation and experimental results. These will be used to compare the selected topologies, and to explain the influence of system unbalance and the neutral conductor inductance on the leakage current. It will be demonstrated that the later has a crucial influence. Finally, a comparison of the selected topologies is carried out, based on the adopted modulation, connection of the neutral and its inductance, effects of unbalance conditions, component ratings, output voltage levels, and filter size.

A new matrix converter motor (MCM) for industry applications

The trend in electrical drives is to integrate the frequency converter, the electrical motor, and even the gear or the pump into a single unit, in order to reduce the costs, to increase the overall efficiency and the equipment reliability. This paper presents the first integrated regenerative frequency converter motor for industry applications, based on a matrix converter topology. The low volume, the sinusoidal input current, the bidirectional power flow, and the lack of the bulky and limited-lifetime electrolytic capacitors recommend this topology for this application. This paper shows how the matrix converter disadvantages-the lack of bidirectional power devices, the lower voltage transfer ratio, and the overvoltages caused by the input filter during power-up-that have delayed the industrial implementation have been overcome. In order to demonstrate the validity of the solution, a 4-kW matrix converter motor prototype is built using a standard frequency converter motor enclosure for testing the requirements for an industrial drive. The tests demonstrate the good performance of the drive.

Space-Vector Modulated Multilevel Matrix Converter

A matrix converter is an ac-ac power converter topology that has received extensive research attention as an alternative to traditional ac-dc-ac converter. A matrix converter is able to convert energy from an ac source to an ac load without the need of a bulky and limited-lifetime energy-storage elements. The indirect three-level sparse matrix converter (I3SMC) is a new topology from this family that can synthesize three-level voltage in order to improve the output performance in terms of reduced harmonic content. This paper discusses the operating principles and a space-vector-modulation scheme for this topology. Simulation and experimental results are shown to prove the ability of this topology to generate multilevel output voltages as well as to maintain a set of sinusoidal balanced input currents. The performance of the converter is compared with the conventional matrix converter and an alternative multilevel matrix-converter topology in order to demonstrate the advantages and disadvantages of the I3SMC.

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.

A new modulation method for matrix converters

This paper presents a new modulation method for matrix converters based on the indirect modulation model. During the switching period, the proposed modulation method uses a combination of only one active vector and a zero vector in the inversion stage to achieve minimum flux error, while in the rectification stage a single current vector is selected, according to the error of the input current vector angle. This reduces the number of switching sequences in the switching period, improving the accuracy of generating the output voltage vector especially in the low modulation index range. Supplementary, the direct control of the input current vector is implemented. The estimation of the angle of the input current vector is done by applying the inverse transformation, that corresponds to the applied active vector, to the output currents.

A new matrix converter-motor (MCM) for industry applications

The trend in electrical drives is to integrate the frequency converter, the electrical motor and even the gear or the pump into a single unit, in order to reduce the costs and to increase the overall efficiency and the equipment reliability. This paper presents the first integrated regenerative frequency converter-motor for industry applications, based on a matrix converter topology. The low volume, the sinusoidal input current, the bi-directional power flow and the lack of the bulky and limited-lifetime electrolytic capacitors recommend this topology for this application. This paper shows how the matrix converter disadvantages-the lack of bi-directional power devices, the lower voltage transfer ratio, the lack of ride-through capability and the overvoltages caused by the input filter during power-up-which have delayed the industrial implementation, have been overcome. In order to demonstrate the validity of the solution, a 4 kW matrix converter-motor (MCM) prototype is built using a standard frequency converter-motor enclosure and tested to meet the requirements for an industrial drive.

Implementation of a hybrid AC/AC direct power converter with unity voltage transfer ratio

A novel hybrid approach for direct power conversion (DPC) based on two-stage matrix converter (2-stage MC) topology is proposed, which has practically proven advantages of improved voltage transfer ratio and higher robustness against supply voltage unbalances over the conventional matrix converters (CMC). The hybrid approach also has inherent advantages of the CMC such as: controllable supply power factor, sinusoidal supply currents and no bulky energy storage elements which reduce the life time of the converter. The proposed converter can theoretically have more than unity voltage transfer ratios; even in the case the supply voltage is highly unbalanced. Important aspects of design and implementation of the new hybrid direct power converter (HDPC) are presented with theoretical analysis and simulations. Experimental waveforms using a laboratory prototype is presented to confirm the viability of the proposed idea in practice

Using reverse-blocking IGBTs in power converters for adjustable-speed drives

A new semiconductor power device that is urgently needed particularly in power converter topologies, the reverse blocking insulated gate bipolar transistor (RB-IGBT), has been realized by adding minor changes to the structure of a standard IGBT to make it capable of withstanding reverse voltage. However, the switching behavior of the devices intrinsic diode during reverse recovery is not as good as a discrete IGBT and series diode implementation. This paper analyzes the use of this device in three power converter topologies that may benefit from it, namely: 1) the matrix converter, 2) the two-stage direct power converter (DPC), and 3) the three-level voltage source rectifier. A commutation method to override the poor reverse-recovery characteristic of the RB-IGBT intrinsic diode in a two-stage DPC is proposed. A loss analysis shows that by using RB-IGBTs the efficiency of the two-stage DPC becomes similar to a two-level voltage source converter.

Repetitive and Resonant Control for a Single-Phase Grid-Connected Hybrid Cascaded Multilevel Converter

This paper investigates the use of adaptive repetitive and resonant control approaches for the control of a single-phase hybrid cascaded multilevel converter designed to interface with power grids of highly distorted voltage waveform. The proposed repetitive/resonant control (RPC/RSC) is used for the extraction of clean phase angle, frequency, and magnitude information of the fundamental grid voltage together with the control of the converter current and mitigation of current harmonics under distorted grid voltage and variable frequency. The RPC time period and the RSC resonant frequency are updated adaptively using the estimated grid frequency while interpolation is used to preserve the RPC rejection capability under noninteger number of time steps per period. Detailed modeling and experimental investigation of the proposed control scheme are carried out.

Experimental evaluation of ride-through capabilities for a matrix converter under short power interruptions

The matrix converters, which are direct power electronic converters, are able to provide important benefits such as bidirectional power flow, sinusoidal input currents with adjustable displacement angle, and a great potential for size reduction. Still, two major disadvantages exist: a lower than unity voltage transfer ratio and high sensitivity to power grid disturbances. Many solutions to provide continuous operation of adjustable speed drives (ASDs) during power grid disturbances have been proposed, but they are all applied to DC-link ASD. In this paper, a new solution to provide limited ride-through operation is presented with a matrix converter using a scalar controlled induction motor for a duration of hundreds of milliseconds, without any hardware modification. During the ride-through operation, the drive is not able to develop torque or to control the motor flux. By recovering the necessary power to feed the control hardware of the matrix converter, it is able to keep the ASD operating. When normal grid conditions are reestablished, the matrix converter is able to accelerate the motor from nonzero speed and flux by initializing the modulator with the estimated frequency and the initial angle of the reference output voltage vector. The maximum duration of the ride-through operation depends on the initial motor flux, speed level, rotor time constant, load torque, and inertia. This method is verified on a laboratory setup with a matrix converter.