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C u r t i n & P U C R S. Fernando Soares dos Reis, Pontifical Catholic University of Rio Grande do Sul Syed Islam and Kelvin Tan, Curtin University of Technology. Table of Contents. Introduction Objectives Power Quality Harmonic Characterization
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C u r t i n & P U C R S Fernando Soares dos Reis, Pontifical Catholic University of Rio Grande do Sul Syed Islam and Kelvin Tan, Curtin University of Technology
Table of Contents • Introduction • Objectives • Power Quality • Harmonic Characterization • The Harmonic Mitigation Schemes • Power Losses • Conclusions
INTRODUCTION • Permanent magnet synchronous generators (PMSG) wind energy conversion system (WECS) using variable speed operation is being used more frequently in wind turbine application. Variable speed systems have several advantages over the traditional method of operating wind turbines, such as the reduction of mechanical stress and an increase in energy capture. To allow the variable speed operation of the PMSG WECS a conventional three-phase bridge rectifier (BR) with a bulky capacitor associated with voltage source current controlled inverter (VS-CCI) is used.
INTRODUCTION • This simple scheme introduces a high intensity low frequency current harmonic content into the PMSG and consequently increases the total loses in it. Subsequently, decreases the power capability of the system. This work presents a comparative simulation study between three different approaches applied to harmonic mitigation on PMSG WECS. The studied techniques are: a) harmonic trap filters (HTF), b) single-switch three-phase boost rectifier (PFC) and c) PWM Boost Rectifier.
AC-DC Conversion Loss Reduction The Bridge Rectifier increases the losses.
Power Quality • The power quality concepts are well established and Widely applied in the relationship between utility and consumer; • Because it allows the maximization of the energy resources; • But these concepts were not normally applied to WECS once there are studies showing that the system efficiency is practically the some with or without harmonics in the PMSG.
Harmonic Characterization It seems O.K.
The Harmonic Mitigation Schemes • Passive Harmonic Trap Filters (HTF) • Single-Switch Three-Phase Boost Rectifier • Three-Phase Boost type PWM Rectifier (AC-DC converter) • Active Power Filter
Using HTF for the 5th and 7th harmonic PMSG output current
Using HTF for the 5th and 7th harmonic PMSG output voltage
Power Losses • PMSG losses • Bridge Rectifier Losses • Harmonic Trap Filter Losses • Semiconductor Losses • Mechanical losses
Conclusions • In this work three well-known harmonic mitigation solutions were applied to PMSG WECS AC to DC conversion. They were the HTF, the PFC and the PWM Boost Rectifier. Harmonic trap filters are easily implemented by passive components but they are normally implemented with bulk components.
Conclusions • Notwithstanding the HTF had presented the good THD results they are not the best solution once they are a matched solution for a specific operation point (wind speed and output power). The losses study also has demonstrated that the PMSG efficiency (η) remains practically constant and the system η is the lowest when the HTF are used.
Conclusions • For these reasons, it is not a recommended way out to obtain harmonic mitigation on PMSG WECS. On the other hand, the single-switch three-phase boost rectifier has presented encouraged results. Such as: low current and voltage THD, simple power topology and control circuit, can work in all wind conditions and presents a real reduction of the PMSG total losses.
Conclusions • Which allow expecting an increasing in the PMSG lifetime without reduction of the power capability. The main drawbacks of this topology are a) the conduction losses in the BR diodes and switch Q1 since the high RMS current value caused by the DCM operation and b) the high output voltage 1 kV. Both problems could be minimized using proper diodes and switch like IGBT.
Conclusions • The PWM rectifier was studied once with this complex converter is possible to obtain ideal PF and THD. But the losses study has show results very closed to that obtained with the Single Switch Boost Converter. The main advantage is that with this converter is possible to work with output voltages around 600V in spite of 1000V.
