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A Stable and highly reliable DC link voltage represents an important factor for efficient power transfer in high voltage direct current (HVDC) networks. In this framework, this paper investigates the control and stability analysis of voltage source converter (VSC) for DC link voltage regulation. To separately achieve the independent active and reactive power control, the system voltages and currents are represented in the synchronous reference frame. In order to optimally design the parameters of proportional-integral (PI) controller, the inner and outer loops’ transfer functions are thoroughly derived/developed. In addition,/moreover, in order to attain satisfactory/certain system performance, modulus optimum, symmetrical optimum pole placement control approaches are studied and implemented for the purpose of tuning the voltage/current controller gain parameters. In particular for the symmetrical optimum control method, the gain parameters of the DC-bus voltage are determined under different values of network impedance. Furthermore, the impact/influence of changing gain parameters on the DC-link voltage and poles/zeros movement are investigated. MATLAB/Simulink model is built and simulation studies are carried out to verify the introduced concepts.

A Stable and highly reliable DC link voltage represents an important factor for efficient power transfer in high voltage direct current (HVDC) networks. In this framework, this paper investigates the control and stability analysis of voltage source converter (VSC) for DC link voltage regulation. To separately achieve the independent active and reactive power control, the system voltages and currents are represented in the synchronous reference frame. In order to optimally design the parameters of proportional-integral (PI) controller, the inner and outer loops' transfer functions are thoroughly derived/developed. In addition,/moreover, in order to attain satisfactory/certain system performance, modulus optimum, symmetrical optimum pole placement control approaches are studied and implemented for the purpose of tuning the voltage/current controller gain parameters. In particular for the symmetrical optimum control method, the gain parameters of the DC-bus voltage are determined under different values of network impedance. Furthermore, the impact/influence of changing gain parameters on the DC-link voltage and poles/zeros movement are investigated. MATLAB/Simulink model is built and simulation studies are carried out to verify the introduced concepts. [ABSTRACT FROM AUTHOR]

This paper presents a systematic procedure to design a simple control for a three-phase VSC-based static synchronous compensator (STATCOM) in order to overcome the problems caused by the presence of the non-linear load at the point of common coupling (PCC). The proposed control method regulates the STATCOM in such a way that the source quadrature current component is forced to be zero so that only the active current component is drawn from the source and the harmonic and reactive current demands of the non-linear load are met by the STATCOM. The tuning of the inner and outer loop PI controllers is carried out with the help of the modulus optimum and symmetric optimum criteria, respectively. At last, a few case studies are presented using MATLAB simulation to exemplify the success of the proposed control method.

Multi-level rectifiers have low harmonic content and electromagnetic interference (EMI). In recent years, especially in medium and high-power applications are increasing use. As the voltage level per switch and switching frequency are low, the multi-level rectifiers have low losses and high efficiency. In this study, threelevel neutral point clamped (NPC) rectifier topology with pulse width modulation (PWM) is investigated and the decoupled equations in the d-q synchronous rotating axis of the rectifier are given and a space vector PWM (SVPWM) control algorithm based on the d-q synchronous rotating axis of three-level rectifier is proposed. The control of the whole system is provided by voltage oriented control (VOC) strategy, which enables the realization of control in cascade system with outer voltage and inner current control blocks. This paper is focused on explaining in detail modulus optimum and symmetrical optimum methods used in the design of the inner current and outer voltage PI controllers of the three-level rectifiers, respectively. PI voltage controller is used to keep the rectifier output voltage constant, and PI current controller is used to reduce the harmonic content of the grid current. In addition, a simplified method compared to conventional SVPWM is used to calculate switching times and switching sequences. In this study, three-level rectifier is simulated in Matlab / Simulink with the help of SVPWM. The performance of the circuit has been tested by changing both the load value and the load voltage suddenly and successful results have been achieved. [ABSTRACT FROM AUTHOR]

The modulus optimum (MO) criterion can be used for analytical design of the PID controller for linear systems with dominant dead time. However, although the method usually gives fast and non-oscillating closed-loop responses, in the case of large dead time the stability margin gets reduced and even non-stable behavior can be observed. In this case a correction of the settings is needed to preserve the stability margin. We describe and compare two methods of design of the PID controller based on the MO criterion that for the stable first-order systems with dead time preserve the stability margin, trying to keep maximum of the performance of the original MO settings.

The results of simulating the most widespread variants of dc electric drives with optimum adjustments of the parameters taking into account the natural and artificial constraints of variables in MATLAB and Simulink are presented. Particular attention is given to the modes of armature current constraints, the influence of constraints on electric drive parameters, and comparative analysis of transient processes when a drive is started. It is shown that the system with a PI speed controller and a P current controller, which is adjusted to the modulus optimum has the best indices of overshooting and speed of response taking into account the artificial constraint of the armature circuit current and the natural constraint of the converter output voltage. The one-loop control system with a PI controller, also adjusted to the modulus optimum, has similar indices. [ABSTRACT FROM AUTHOR]

A mathematical model of a two-loop control system of a dc drive with a control unit realized on the basis of the widely used P and PI controllers was obtained. The optimized parameters of the system are the gain coefficients of the current and speed closed loops and coefficients of the integral components of the corresponding controllers. Two variants of optimization of the system structure and parameters are considered: (1) standard consecutive adjustment of the current and speed loops to the modulus optimum, which leads to a static control system with a P speed controller and a PI current controller; and (2) system adjustment to the modulus optimum as a united whole, which leads to an astatic system with a PI speed controller and a P current controller or without a current controller with proportional current feedback to the power converter input. The formulas for optimal values of adjustable parameters for both variants are obtained. It was shown for instance by simulation in Matlab-Simulink that the system adjusted in accordance with the second variant has better performance indices, such as offset, transient time, and overshooting at a changing set point and disturbance variable. [ABSTRACT FROM AUTHOR]

The paper extends the popular modulus optimum with the original approach for the conventional digital controllers. The use of the D-transform allows obtaining the uniform computing formulas for the values of the digital and analog controller tuning parameters. The use is shown on an example.

Abstract: In this paper we analyze the properties of the design of PID controller based on the modulus-optimum criterion for an important class of non-oscillating linear plants with dead time and present some important properties of the settings not published so far. The results are used to design a suitable correction of the settings, which ensures that a sufficient stability margin is preserved. After inclusion of these enhancements a robust design method is obtained, which provides good performance even for systems with long dead time and is easy to implement. [Copyright &y& Elsevier]