Converter-fed synchronous machine for pumped hydro storage plants

Abstract

Pumped hydropower is gaining importance as a key technology for the integration of large quantities of renewable electricity, in particular from wind and solar sources. With the progress in power electronics, it has recently become possible to build frequency converters with a rated power in excess of 100 MVA, paving the way for a new variable speed pumped hydropower solution based on synchronous machines whose stator is driven with a variable frequency. This solution, refered to as converter fed synchronous machine (CFSM), is offering even higher flexibility and efficiency than DFIM (doubly-fed induction machine). A first CFSM plant with a rated power of 100 MVA has been installed in Switzerland and has been in productive operation since late spring 2013. As a further step a new CFSM power converter type based on modular multi-level converter (MMC) technology is proposed. This topology, powered by advanced IGCT (integrated gatecommutated thyristor) power semiconductor devices, enables a total power conversion efficiency greater than 98.5%. Very smooth waveforms and special starting algorithms make it possible to use standard generator and transformer insulation schemes. Due to a modular converter construction, the accessible range of rated power spans from approximately 50 MVA up to 500 MVA. Built-in redundancy enables a very high availability.

A Variable Speed Pumped Storage System Based on Droop-Fed Vector Control Strategy for Grid Frequency and AC-Bus Voltage Stability

“…A study in [5] shows that the variable speed pumped storage (VSPS) system can improve the steady state operations and dynamic stability of the power system. Having dependable features, the VSPS plant can play a key role in stabilizing the dynamics and transients of the grid affected by wind power fluctuations and other contingencies [6][7][8][9][10][11].…”

Investigation of magnetic field and radial force harmonics in a hydrogenerator connected to a three-level NPC converter

“…Frequency spectrum of the time-varying amplitude (not presented here) shows that the largest additional frequency components in the main spatial harmonics are 850 Hz (for =1050 Hz) and 250 Hz ( =450 Hz). As mentioned before, these two component are the largest additional time harmonics in stator current ( 4 ) and are produced by the PWM converter.…”

“…To realize variablespeed operation, the following two configurations can be utilized: doubly fed induction machine (DFIM), and converterfed synchronous machine (CFSM). While CFSM has many advantages over DFIM [1,4], its drawback is the need for a fullrated converter. In DFIM configuration, the rating of the converter is reduced (around 30% of rated power).…”

Analysis of magnetic forces and vibration in a converter-fed synchronous hydrogenerator

“…To realize such a variable-speed system, two electrical configurations can be employed using either a doubly-fed induction machine (DFIM) or converter-fed synchronous machine (CFSM) [1,2]. CFSM system has distinct advantages over DFIM configuration [3], but the main drawback is the need for a full-power converter. On the other hand, the size of the converter in a DFIM system is up to 30% of the rated power.…”

“…Because of this, DFIM system has been the preferred configuration in high power applications (above 100 MW). However, with the advancements in the field of semiconductor devices and converter topologies, converters with higher power ratings will be available in future, making CFSM an interesting choice even for high power applications [1,3]. In addition to pumped-storage plants, a CFSM system can be used in HVDCconnected [4] and also small hydropower [5] plants.…”