To implement the voltage control in this VSC system, the symmetrical optimum met

Question

To implement the voltage control in this VSC system, the symmetrical optimum method is used. i) Draw the simplified control block diagram in d-axis and q axis, including PI controller, dynamic models of VSC, and dynamic models of C_f; ii) List the open-loop transfer functions for d-axis and q-axis; iii) If C_f = 2400 mu F, L = 100 mu H, R = 1.19m Ohm, r_on = 0.88m Ohm, V_DC = 1500V, and f_s = 1800H_z, the load voltage is regulated at (V_sqref, V_sqref) = (400, 0)V and a frequency of omega_0 = 377 rad/s, the current-control time-constant T_i = 0.5ms), and the desired phase margin is 53 degree, design the PI controllers for d-axis and q-axis. A controlled-frequency VSC system to serve a three-phase RL load

Explanation / Answer

Autonomous Load Sharing of Voltage Source Converters

Abstract—An autonomous load-sharing technique for parallel connected three-phase voltage source converters is presented. An improved power-frequency droop scheme computes and sets the phase angle of the voltage source converter (VSC) directly to yield more rapid real power sharing without sacrificing frequency regulation. Reactive power sharing in the presence of a mismatch between the VSC output interface inductors is achieved by having each VSC regulate the high side voltage with a drooped voltage reference. Dynamics of the reactive power control can be tuned without interfering with steady-state reactive power sharing. Simulation results that validate the proposed technique are also provided.

VSC principle of operation

In contrast to the line-commutated converters, the VSC belongs to the self-commutated converter category, being able to switch its power electronic valves at any desired current flowing through them. This feature allows the VSC to generate a desired alternating voltage at its acside and produce a bi-directional power flow. This section describes how the VSC operates and provides a brief introduction to the application of the Pulse-Width Modulation (PWM) method. Observe that other modulation strategies can be applied in actual installations in order to reduce the system losses, but most of them share common traits with the (PWM) method. Finally, the operational limitations of the VSC are analyzed and a number of existing and future VSCHVDC converter topologies are presented.

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