Fast optimum-predictive control and capacitor voltage balancing strategy for bipolar back-to-back NPC converters in high-voltage direct current transmission systems

Abstract

Multilevel power converters have been introduced as the solution for high-power high-voltage switching applications where they have well-known advantages. Recently, full back-to-back connected multilevel neutral point diode clamped converters (NPC converter) have been used inhigh-voltage direct current (HVDC) transmission systems. Bipolar-connected back-to-back NPC converters have advantages in long-distance HVDCtransmission systems over the full back-to-back connection, but greater difficulty to balance the dc capacitor voltage divider on both sending and receiving end NPC converters. This study shows that power flow control and dc capacitor voltage balancing are feasible using fast optimumpredictive-based controllers in HVDC systems using bipolar back-to-back-connected five-level NPC multilevel converters. For both converter sides, the control strategytakes in account active and reactive power, which establishes ac grid currents in both ends, and guarantees the balancing of dc bus capacitor voltages inboth NPC converters. Additionally, the semiconductor switching frequency is minimised to reduce switching losses. The performance and robustness of the new fast predictive control strategy, and its capability to solve the DC capacitor voltage balancing problem of bipolar-connected back-to-back NPCconverters are evaluated.

Improved Model Predictive Control of Three-level Voltage Source Converter

“…When the system works in the full-load condition, the steadystate operations by both methods are shown in Figures 8,9,and 10. These figures show that a high amplitude jump U dc occurs to the line voltage when the traditional method is employed.…”

“…A multi-level voltage source converter generally adopts the system composed of an outer voltage loop and inner current loop. The main purpose of the current loop is to quickly track current instructions and to reduce as much transient tracking time as possible [9][10][11]. The outer voltage loop provides current instructions for the inner current loop.…”

Capacitor Voltage Balancing of Five Level Diode Clamped Converter based STATCOM

“…The sinusoidal PWM method for DCMC is given in [9]. Fast optimum predictive control for bipolar back to back converter can be seen in [2]. In [4] the capacitor voltage balancing is done with the help of current flow model.…”

A New Dual Lagrangian Model and Input/Output Feedback Linearization Control of 3-Phase/Level NPC Voltage-Source Rectifier

“…The converters are significantly used for medium-voltage and high-power applications [1][2][3][4]. Among these topologies, multilevel neutral-point-clamped (NPC) converters are the most widely used because of their advantages such as series connection of power switches and bi-directional power transfer capability.…”