Lars Norum

Design and implementation of an extended Kalman filter for the state estimation of a permanent magnet synchronous motor

Practical considerations for implementing the discrete extended Kalman filter in real time with a digital signal processor are discussed. The system considered is a permanent magnet synchronous motor (PMSM) without a position sensor, and the extended Kalman filter is designed for the online estimation of the speed and rotor position by only using measurements of the motor voltages and currents. The algorithms developed to allow efficient computation of the filter are presented. The computational techniques used to simplify the filter equations and their implementation in fixed-point arithmetic are discussed. Simulation and experimental results are presented to demonstrate the feasibility of this estimation process. >

Modeling and Simulation of All-Electric Ships With Low-Voltage DC Hybrid Power Systems

DC hybrid power systems are of interest for future low emission, fuel-efficient vessels. In spite of the advantages they offer onboard a ship, they result in a complex, interconnected system, which requires effective analysis tools to enable a full realization of the advantages. Modeling and simulation are essential tools to facilitate design, analysis, and optimization of the system. This paper reviews modeling of hybrid electric ship components including mechanical and electrical elements. Power electronic converters are modeled by nonlinear averaging methods to suit system-level studies. A unified model for bidirectional converters is proposed to avoid transitions between two separate models. A simulation platform using the derived models is developed for the system-level analysis of hybrid electric ships. Simulation results of power sharing among two diesel generators, a fuel cell module, and an energy storage system are presented for three modes of operation.

Active damping of resonance oscillations in LCL-filters based on virtual flux and virtual resistor

This paper presents several methods for active damping of resonance oscillations in LCL-filters. All the methods are implemented using only estimated values of the capacitor voltages and currents. The sensorless control strategy used in this paper is based on the virtual flux concept and all voltages and currents with the exception of the dc bus voltage and the converter output currents are derived from the virtual flux. The presented theory is then verified experimentally in the lab.

Overirradiance (Cloud Enhancement) Events at High Latitudes

Contrary to intuition, solar irradiance peaks at partially cloudy conditions. Clouds can boost sunlight by over 1.5 times, even at high latitudes. Depending on cloud velocity, the bursts last from seconds to minutes. Measuring irradiance on a tilted surface with 10-ms resolution allows for a detailed study of such events in Southern Norway, almost at sea level. All monthly maxima from April through September 2011 exceeded 1300 W/m2. The slow sensor registered an annual maximum of 1413 W/m2, while the fast sensors range was found insufficient. A burst reaching 1528 W/m2 was registered in June 2012. Near the Equator, bursts exceeding 1800 W/m2 have been observed. These numbers are striking since the extraterrestrial solar irradiance peaks in January at about 1400 W/m2. The phenomenon is attributed mainly to forward scattering of light in optically thin clouds (adjacent to the sun), which is much stronger for angles within 5° around the solar disk.

A method for charging and discharging capacitors in Modular Multilevel Converter

In this paper, a method for charging and discharging capacitors in Modular Multilevel Converter (MMC) is explained. The proposed method helps to start the converter from a de-energized condition and does not require any auxiliary voltage source. An additional resistance is inserted in the MMC arm and by appropriately switching this resistance, both charging and discharging of the MMC cells can be accomplished. A theoretical background is presented for drives applications and design examples are included. Simulation and experimental results are included at the end to validate the proposed concept.

Modular Multilevel Converter With an Adaptive Observer of Capacitor Voltages

A modular multilevel converter (MMC) is an attractive solution for power conversion without transformers. The MMC consists of cascade connections of floating dc capacitors. In this paper, an adaptive observer design has been proposed to estimate the capacitor voltages from the measurement of arm currents. This work introduces the capacitance value of the cell capacitors as a parameter uncertainty for making the system performance robust with unknown constant parameters. It may be used for predictive control, condition monitoring for capacitors, and diagnosis check for capacitor health. In addition, a pulsewidth modulation (PWM) technique for MMC has been explored. The PWM technique is performed using a carrier-based level-shifted PWM strategy. It does not necessitate the calculation of duty cycles, and can be easily implemented in a DSP. By using the PWM technique, harmonics in the phase voltage is shifted to twice the switching frequency. Theoretical analysis is included in this paper for showing stability and convergence of the proposed observer. Analytical expressions are verified by simulation and experimental results.

Recognition of electric arcing in the DC-wiring of photovoltaic systems

The paper presents an approach for protection of PV-systems against electric arcing in the DC-wiring. An intelligent protection device for integration into the PV-modules is developed. The main focus is on the methods that can be used for detection of a burning arc inside the system. The impacts of an arc on the voltages and currents in the system are shown and an algorithm for detection of arcing by a low-power low-cost DSP/microcontroller is proposed.

Effective use of film capacitors in single-phase PV-inverters by active power decoupling

The lifetime and reliability of PV-inverters can be increased by replacing electrolytic capacitors by film-capacitors. Film-capacitors have a lower capacitance per volume ratio; therefore a direct replacement leads to very large and expensive solutions, especially for single-phase applications. This paper presents an active circuit which acts as an interface between the DC-link of a PV-inverter and an additional storage capacitor. The voltage ripple in the storage capacitor can be increased compared to the DC-link capacitor, allowing a more efficient use of the stored energy and thus a massive reduction of the overall installed capacitance. An especially promising application can be found in module-integrated PV-inverters, because here the most efficient and cheapest topologies suffer from big electrolytic capacitors which deteriorate the lifetime. The paper focuses on different possible control schemes of the decoupling circuit. Results from simulations are used for discussing the proposed control methods. Also results from an experimental efficiency comparison between systems with electrolytic and film-capacitors are given. Finally a lab-prototype of the decoupling-circuit is presented which will be used for further experiments.

A Pulse Width Modulation technique for reducing switching frequency for modular multilevel converter

In this paper, a Pulse Width Modulation (PWM) technique for modular multilevel converter has been explored. The PWM technique is implemented using carrier based level shifted PWM strategy. It does not necessitate the calculation of duty cycles, and can be easily implemented in a DSP. With the proposed technique, harmonics in the phase voltage is shifted to twice the switching frequency. Thus, the devices of the converter can be switched at a reduced switching frequency to maintain the same output voltage quality. A detailed explanation of the carrier based level shifted PWM for implementing the proposed technique is included in the paper. This is verified by computer simulation on a 6.6kV, 6MW drive system.

Tuning of control loops for grid connected voltage source converters

Traditional tuning techniques like modulus optimum or symmetrical optimum can be applied to the design of control loops for many power electronic applications. When directly implemented in digital control systems, this will lead to reduced stability margins since the sampling effects are not taken into account for the controller design. This paper is investigating a method for obtaining discrete time equivalents to the traditional tuning techniques and shows the application of the obtained criteria to the control loops of a grid connected voltage source converter. A bilinear transform from the discrete time z-domain to a virtual frequency w-domain is utilized to obtain the discrete time tuning criteria. By this, similar derivations as for obtaining the traditional continuous time criteria can be carried out to obtain equivalent analytical criteria that are valid for design of discrete time controllers. The results are applied to both continuous time and discrete time controllers of the presented example, to discuss the influence of the sampling effects on the controller performance.