A High-Power, Medium-Voltage, Series-Resonant Converter for DC Wind Turbines

Abstract

A new modulation scheme is introduced for a single-phase series-resonant converter, which permits continuous regulation of power from nominal level to zero, in presence of variable input and output dc voltage levels. Rearranging the circuit to locate the resonant LC tank on the rectifier side of the high turns-ratio transformer combined with frequency control and phase-shifted inverter modulation keep transformer flux constant from nominal frequency down to DC, always in sub-resonant continuous or discontinuous conduction mode. This overcomes the principal deficit of series-resonant converters, and the resulting compact and efficient transformer, and softcommutated inverter, present particular advantages in highpower, high-voltage applications, like DC offshore wind turbines. With transformer excitation frequency in hundreds of Hz range, line-frequency diodes can be employed in the high-voltage rectifier valve. Circuit operation and conduction modes, governing equations and sample waveforms are presented, together with experiments from a scaled demonstrator.

Harmonic Susceptibility Study of DC Collection Network Based on Frequency Scan and Discrete Time-Domain Modelling Approach

“…Considering the switching losses with IGTB applications, the subresonant mode is preferred in SRC# which allows ZCS or a low current at turnoff ( Figure 5(a)); regardless of switching frequency, a full-resonant current pulse is delivered to the load [12]. e control law of SRC# is also allowed ZVS at turnon and ZCS at turnoff for the diode rectifier, as shown in Figure 5(b).…”

“…(1) Control of the LVDC bus (2) High-voltage transformation from the LVDC to MVDC (3) Galvanic isolation (4) Roust and compact design Large amount of possible topology of converter topologies for a DC turbine is investigated. However, all of existing converter designs are immature technology, thus selecting an optimal topology is not a straightforward solution for converter design [12]. e turbine converter is designed to deliver the captured wind energy produced by the generator to the MVDC gird and then control the LVDC bus.…”

“…Operation waveform of SRC#: (a) inverter output voltage V g ; (b) resonant tank current i r ; (c) rectifier output current i o,Rec and output averaged current i average ; (d) transformer magnetizing current i m ;(e) switching patterns (T 1 , T 2 , T 3 , and T 4 )[12]…”

Model-Based Control Design of Series Resonant Converter Based on the Discrete Time Domain Modelling Approach for DC Wind Turbine

“…Traditional closed-loop control of SRC for the DC distribution system is easily implemented by detecting the zerocrossing of the resonant inductor current 푟 and controlling the length of transistor and diode conduction angle without considering circuit parameters of SRC [7]. Additionally, the output power flow control of SRC for DC network is achieved by controlling the phase-shift angle and frequency between the two arms of H-bridge inverter [6,8,9].…”

“…Based on the discrete time domain modelling approach, the small-signal model of an improved SRC (named SRC#) is proposed [9,10]. This paper continues with the smallsignal plant model addressed in Section 3 and the Appendix and mainly focuses on the closed-loop control design for the system.…”