Abstract
This article studies a new hybrid converter that utilizes thyristors and full-bridge (FB) arms for achieving high-power capability with reduced semiconductor power rating compared to the FB modular multilevel converter. The study covers the theoretical analysis of the energy balancing, the dimensioning principles, the maximum power capability, and the limitations imposed by the discontinuous operation of the converter. Based on the analysis of these aspects, the theoretical analysis is concluded by identifying the operational constraints that need to be fulfilled for maximizing the power capability of the converter. It is concluded that the maximum power capability can be achieved for a certain range of modulation indices and is limited by both the commutation time of the thyristors and the power angle. Moreover, the P – Q capability of the hybrid converter is presented and discussed. Finally, simulation and experimental results that confirm the theoretical analysis and the feasibility of the studied converter are presented and discussed.
Highlights
T HE thyristor-based line-commutated converter (LCC) has been employed since the 1960s for enabling high-voltage dc (HVDC) transmission
For verifying that the power ratio of the hybrid alternate-common arm converter (HACC) is maximized for the range of modulation indices defined in Fig. 11, the three-phase HACC was connected to a passive load at the ac side
The comparison of the HACC, the two parallel FB-modular multilevel converter (MMC), and the two parallel HBMMCs is summarized in Table IV, which includes the ratings and number of the main semiconductor devices, the total semiconductor power rating, and the apparent power supplied to the grid for different grid power angles φg corresponding to inverter mode
Summary
T HE thyristor-based line-commutated converter (LCC) has been employed since the 1960s for enabling high-voltage dc (HVDC) transmission. The main advantages of the LCC is high efficiency, high surge-current capability, and dc-fault ridethrough capability. The LCC suffers from sensitivity to ac-grid disturbances, lack of independent active-reactive power control, high reactive-power consumption, and loworder harmonics in the ac-side currents [1]. The two-level VSC solves many of the shortcomings of the LCC, but suffers from relatively low efficiency, high cost, and lack of dc-fault blocking capability. The modular multilevel converter (MMC) [7] is a recently proposed VSC technology that remedies some of the shortcomings of the two-level VSC and opens new possibilities for the combination of the LCC and VSC technologies.
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