J. Van den Keybus

A Voltage and Frequency Droop Control Method for Parallel Inverters

In this paper, a new control method for the parallel operation of inverters operating in an island grid or connected to an infinite bus is described. Frequency and voltage control, including mitigation of voltage harmonics, are achieved without the need for any common control circuitry or communication between inverters. Each inverter supplies a current that is the result of the voltage difference between a reference ac voltage source and the grid voltage across a virtual complex impedance. The reference ac voltage source is synchronized with the grid, with a phase shift, depending on the difference between rated and actual grid frequency. A detailed analysis shows that this approach has a superior behavior compared to existing methods, regarding the mitigation of voltage harmonics, short-circuit behavior and the effectiveness of the frequency and voltage control, as it takes the R to X line impedance ratio into account. Experiments show the behavior of the method for an inverter feeding a highly nonlinear load and during the connection of two parallel inverters in operation.

DSP implementation of power measurements according to the IEEE trial-use standard 1459

A digital signal processor (DSP) based prototype platform used to support advanced power measuring algorithms is presented. For this study, the definitions proposed in the new IEEE Standard 1459-2000 are considered. The general structure of the system and the impact of the software implementation are discussed. Experimental measurement results from tests performed on a low voltage distribution grid are included.

Design and Operation of a Phase-Locked Loop with Kalman Estimator-Based Filter for Single-Phase Applications

This paper describes the design procedure of a phase-locked loop (PLL) preceded by a Kalman estimator-based filter. It provides a highly accurate and fast estimate of the grid frequency and phase angle in grid-connected power electronic applications. Moreover, it enables the transformation to the rotational dq frame for various control purposes. Closed-form equations allow for a performance driven design for both PLL and estimator. By using a variable sample frequency controlled by the PLL, the Kalman filter is always operated around its center frequency, which is the rated grid frequency. The new topology is compared to other published single-phase PLL designs and its operation is verified by both simulations and experiments. The PLL exhibits excellent performance even under severely distorted utility grid voltage conditions. This robustness makes it very suitable for use in systems connected to grids having an important share of non-linear loads

A 96% Efficient High-Frequency DC–DC Converter Using E-Mode GaN DHFETs on Si

III-Nitride materials are very promising to be used in next-generation high-frequency power switching applications. In this letter, we demonstrate the performance of normally off AlGaN/GaN/AlGaN double-heterostructure FETs (DHFETs) using a boost-converter circuit. The figures of merit of our large (57.6-mm gate width) GaN transistor are presented: RON * QG of 2.5 Ω·nC is obtained at VDS = 140 V. The switching performance of the GaN DHFET is studied in a dedicated high-frequency boost converter: both the switching times and power losses are characterized. We show converter efficiency values up to 96.1% at 500 kHz and 93.9% at 850 kHz at output power of 100 W.

Using a fully digital rapid prototype platform in grid-coupled power electronics applications

This paper describes a rapid development system that was used to speed up implementation and testing of a number of grid-coupled power electronic systems. The system uses a fully software reconfigurable processing core based on a powerful DSP and FPGA and a limited set of well-specified functional hardware blocks. Three examples using the same hardware in diverse areas of power electronic control demonstrate that this technique allows the implementation of demanding state-of-the-art power electronics systems, with the important benefit of a much reduced development time and increased reliability. It also proves to be an excellent tool in power electronics courses.

Power measurement using the wavelet transform of analytic signals

The wavelet transform of analytic signals is presented as a basis for instantaneous active and reactive power definitions. This is possible due to the instantaneous amplitude and phase information available from the proposed technique. The RMS values of these power quantities relate to the classical definitions of active and reactive power. It is argued that the property of orthonormality of the wavelet transform is important in order to obtain correct measurement of the power flow. The proposed method is verified by real measurements on the in-house developed rapid prototyping measuring platform.

Development of a measurement system for power quantities in electrical energy distribution systems

The design of an experimental flexible energy measurement system consisting of a DSP, sensor and communication units is treated. This system is intended to be used in modern electricity distribution networks, characterized by multiple suppliers in a deregulated market, bi-directional energy flows due to distributed generation and a diversified demand for the quality of electricity delivery. Various system aspects concerning signal processing, communication and dependability are discussed Examples of the use of such devices are included.

Model-based generation of low distortion currents in grid-coupled PWM-inverters using an LCL output filter

In this paper, a single phase inductance–capacitance– inductance (LCL) output stage for grid coupled inverters is designed and built. An accurate model and observer of the output filter and the distorted grid voltage are implemented. The paper deals with the construction of a 14-state model, and the feedback control loop to obtain adequate closed loop response. Simulations indicate a good performance of the controller, with a total harmonic current distortion (THD) below 1%. Experimental results confirm simulations, and illustrate the correct operation of the Kalman observer to estimate the distorted grid voltage (THD 3%). The observer only uses the inverter current measurement as input. The output filter effectively reduces the pulsewidth modulation harmonics in the grid current.

Distributed control of renewable generation units with integrated active filter

Due to the current concern about the environment, there is a growing interest in distributed generation from renewable energy sources. Usually a power electronic converter is required to interface renewable generation units with the utility grid. The power electronic converters can be designed to provide nonactive power in addition to active power supply in order to compensate distorted currents. This paper proposes a distributed control method for converter-interfaced renewable generation units with active filtering capability. Agent-based communication makes coordination between the generation units possible. Experimental results are included to demonstrate the validity of the proposed method.

DSP and FPGA based platform for rapid prototyping of power electronic converters and its application to a sampled-data three-phase dual-band hysteresis current controller

A platform for prototyping industry relevant power electronic converters and systems is presented. The use of a digital signal processor (DSP) and programmable logic (field programmable gate array-FPGA-and complex logic device-CPLD) shortens implementation time and reduces electromagnetic interference (EMI) susceptibility. The design concept is demonstrated with an implementation of a modified three-phase dual hysteresis band current controller.