Grid integration and a power quality assessment of a wave-energy park

Abstract

This study presents a step toward the grid connection of a wave-energy park through an electric power conversion system (EPCS) developed and installed for the wave-energy harvesting in Lysekil, Sweden. The EPCS comprises a rectifier, a DC bus, and an inverter followed by a harmonic filter (HF). The higher- and lower-order harmonics injected by the inverter in a power quality context are investigated. The lower-order voltage harmonics partially distort the voltage-source inverter output grid current. A phase-locked loop-based (PLL) grid-phase tracking is used to attenuate the lower-order harmonics by reflecting the grid harmonics in the inverter output. An expression for the grid-current harmonics as a function of the grid-voltage harmonics has been derived and implemented. A mathematical model is derived to obtain a transfer function for the PLL, and finally, proportional–integral gains are tuned for stable system operation. An HF for mitigating the higher-order harmonics has been implemented. The total harmonic distortion is evaluated experimentally, and the results fulfil the grid-code requirements at various frequencies and harmonic orders.

Keywords

• power supply quality
• invertors
• power grids
• phase locked loops
• pi control
• power system harmonics
• harmonic distortion
• voltage-source convertors
• wave power generation
• power quality assessment
• wave-energy park
• grid connection
• electric power conversion system
• epcs
• wave-energy harvesting
• harmonic filter
• lower-order harmonics
• power quality context
• lower-order voltage harmonics
• grid-current harmonics
• grid-voltage harmonics
• proportional–integral gains
• higher-order harmonics
• total harmonic distortion
• grid-code requirements
• harmonic orders
• grid integration
• voltage-source inverter
• phase-locked loop
• pll transfer function
• grid-phase tracking
• lysekil
• sweden
• rectifier
• dc bus