Stefan Lundberg

Input-Admittance Calculation and Shaping for Controlled Voltage-Source Converters

A controlled power electronic converter can cause local instabilities when interacting with other dynamic subsystems in a power system. Oscillations at a certain frequency cannot, however, build up if the converter differential input admittance has a positive conductance (real part) at that frequency, since power is then dissipated. In this paper, input-admittance expressions for a voltage-source converter are derived. It is seen how the admittance can be shaped in order to get a positive real part in the desired frequency regions by adjusting the controller parameters.

Flicker contribution from wind turbine installations

In this paper, the flicker emission from a wind park connected to a grid with a high wind energy penetration is evaluated. The influence of wind speed, turbulence intensity, grid voltage quality, grid types, and number of turbines operating in the same group is measured and analyzed. The investigated wind turbines are of constant-speed stall-regulated type. It is found that the voltage quality of the grid to which the turbines are connected strongly influences the flicker emission of the turbines. Moreover, it is found that the formula used in IEC-61400-21 for determining the flicker contribution from a whole wind park gives too low total flicker value.

Low voltage DC distribution system compared with 230 V AC

In this work low voltage DC distribution systems for a home are investigated by evaluating the advantages and disadvantages to 230V systems. The aim of the work is to connect the systems with local generation such as solar cell, micro turbine and energy storages at the end user level. Data obtained from measurements of power consumption for different household appliances such as refrigerator, microwave oven, rice cooker, dish washer etc. have been used to evaluate the systems. The performance of the 230V AC system and the proposed low voltage DC system is analyzed by considering factors such as losses in the wire, internal loss of the device itself, investment cost for new wiring, energy consumption cost

Input Admittance Expressions for Field-Oriented Controlled Salient PMSM Drives

This paper presents analytical expressions for the converter input admittance in field-oriented controlled permanent-magnet synchronous motor (PMSM) drives. The effect of rotor saliency is taken into consideration and the derived admittance expressions are valid for maximum-torque-per-ampere as well as high-speed (field weakening) operation. Experimental results illustrate the validity of the derived admittance expressions. The presented work can be used to predict dc-link voltage instabilities in PMSM drives in, e.g., railway traction, aerospace and automotive applications.

Evaluation of Wind Farm Layouts

Abstract In this paper, layouts of various large-scale wind farms, using either AC or DC to transfer the generated power, are investigated. The criterion used to evaluate the different layouts is the energy production cost, which is defined as the total investment divided with the total energy production of the wind farm. To determine the energy production and the total investment, loss and cost models for the components in the wind farm are used and the most important ones are presented in this paper. The investigation shows that a wind farm with series connected DC wind turbines seems to have the best potential to give the lowest energy production cost, if the transmission distance is longer than 10–20 km.

Stability analysis of converter-grid interaction using the converter input admittance

A grid-connected power electronic converter can cause local instabilities when interacting other subsystems-particularly poorly damped resonances-that are electrically nearby. However, oscillations at a certain frequency cannot build up due to the converter if its differential input admittance has positive conductance (real part) at that frequency, since power is then dissipated. Input-admittance expressions for a voltage-source converter are derived in this paper. By adjusting the controller parameters, the admittance can be shaped in order to get positive conductance in desired frequency regions.

An efficient appliance for low voltage DC house

Kitchen appliances consume large amount of energy in residential houses. By using efficient appliances energy losses can be reduced. Most of the household appliances use DC internally except some appliances such as stove, refrigerator, dishwasher and microwave oven. The refrigerator and stove is one of the high power consuming kitchen appliances and it consumes large amount of energy. This work investigated on energy efficient home appliance design to run on low DC voltage and the purpose is to reduce energy consumption and losses. A combined refrigerator stove unit is designed to run on low voltage DC. The system is simulated with Matlab / Simulink and finally a prototype is built to analyze the performance.

Integration of wind power by DC-power systems

The world climate changing is driving the electric power production towards renewable energy sources. The development of wind turbines has reached the power level of 5 MW and wind farms up to 1000 MW are planned. Investigations have shown that the cost for production of wind energy is in the same level as coal and gas. The large amount of hydro power in the Nordic countries can be used to compensate for the irregularity of producing wind power in Europe. High voltage direct current connections between Sweden and Germany, with a wind farm between can be a solution in the future.

Sensorless control of a PMSM with a transmission system including shunt branches

In oil and gas applications, permanent magnet synchronous motors (PMSM) are becoming a preferred choice to drive subsea and submersible pumps to achieve higher efficiency than induction motors. In the drive system, a submersible PMSM is fed through a transmission system by a top-side variable speed drive. Previous studies have included the series impedance of the transmission system but excluded the transformer magnetizing branch and the cable capacitive branches. In this work, both the series impedance and the shunt admittance of the transmission system are considered. The PMSM current controller is restructured to be an inverter current controller. A static estimator is implemented to estimate the PMSM stator voltage and current. Sensorless control is realized by combining the statically compensated voltage model method and the high frequency injection method. The developed controller can successfully start and accelerate the PMSM from standing still up to 6000 rev/min within 5 s.