Direct Multivariable Control for Modular Multilevel Converters

Abstract

Modular multilevel converters (MMC) have enabled new and demanding applications for power electronics in the high voltage/high power range. In these applications very fast and tight control of all variables of the MMC is of prime importance. This paper presents a new multivariable control (MVC) concept, which enables independent and extremely fast control of all essential variables. For each variable a tolerance band can be specified, which is strictly met even under unexpected severe transients and disturbances. The minimized dead times achieved by the control are more than one order of magnitude smaller than the state of the art. The MVC has been implemented based on FPGA-hardware and digital signal processing of the measured values. Experimental results of the control performance and the robustness against parameter variation are presented, using a down scaled MMC with 96 submodules. These results include the analysis of steady state operation, dynamic performance and fault scenarios.

An Energy Model-Based Controller for a Three-Phase Grid-Tied Modular Multilevel Converter

“…The regulation and balance of the individual capacitors voltages is left to the natural balancing capability of the modulation scheme PSC-PMW under certain conditions [23]. Furthermore, to facilitate the controller design, it is convenient to express (17) in terms of new variables defined as…”

“…In [8], the authors proposed a controller comprising proportional-plus-resonant (PR) and feedforward terms to solve the output current tracking, while the circulating current was regulated using a proportional action plus a feedforward term; [13] and [14] proposed a proportional plus integral (PI) controller for the regulation of circulating currents; [10] applied a linear extended state observer and a linear state error feedback to control circulating and output currents; [15] designed a proportional controller and a PI controller for the control of the arm differential energy and the arm-accumulated energy, respectively; [21] proposed a sorting algorithm and a level shifted modulation to guarantee capacitor voltage balance. In [9] and [16], feedforward and PR terms were applied to control output and circulating currents, while PI controllers were used in the energy regulation and balance loops; [17] proposed a direct multivariable control for output and circulating currents in combination with a sorting algorithm for capacitor voltages; and [18]- [20], [22] relied on model predictive control (MPC) combined with other technique to tackle all control issues on MMC; [18] used MPC for output and circulating currents, and the capacitor voltage balancing was left to the so-called nearest-level control; MPC in [19] was employed to control the arm currents, while a balancing control and the phaseshifted carrier-based pulse-width modulation (PSC-PWM) was applied to capacitor voltages; [20] also used MPC for circulating currents, and a voltage balancing algorithm for the capacitors, while a modulated MPC with bound-constrained quadratic programming (QP) is proposed in [22] to try to obtain an optimal solution.…”

An accelerated modelling method of full-bridge modular multilevel converter considering dead-time

“…Researches on dead time for power devices can be generally divided into two categories: compensation of dead-time effect and analysis modelling of switching with dead time. The compensation of dead-time effect category achieves dead-time compensation through control pulse width angle selection [5] , injection voltage error compensation [6] or multivariable control [7] , etc. However, since the existence of inductor current ripple and parasitic capacitance, it will add some difficulty to data detection, and the dead-time compensation effect is not ideal.…”

DC current flow controllers for meshed HVDC grids

“…As a result, researchers are also considering multi-port CFC structures that can be connected to a generic number n of lines. Some multi-port CFC devices can be found in [46,[51][52][53] For example, in [51,52] an extended version of the Dual H-bridge presented in [34] is proposed. For each HVDC line, a H-bridge is added and a single capacitor is connected to each H-bridge (see Fig.…”

“…A multi-port CFC concept based on MMC arms and called Multi-port polygon-shape is introduced in [53] and also illustrated in Fig. 2.12(b).…”