Amir Arzande

An Energy-Based Controller for HVDC Modular Multilevel Converter in Decoupled Double Synchronous Reference Frame for Voltage Oscillation Reduction

This paper consists of the presentation of a regulation strategy capable of controlling the energy stored in the modular multilevel converter (MMC) in an HVDC configuration. This is achieved by regulating the positive, negative, and zero sequences in dqo coordinates of the differential current using two rotating reference frames: at once and at twice the fundamental grid frequency value. The active and reactive negative sequence components of the differential current at twice the fundamental frequency are used to eliminate the oscillations of the three-phased leg energy, reducing significantly the capacitor voltage oscillations, while the zero-sequence component is used to regulate the total energy stored at a given reference. Meanwhile, active and reactive positive sequence components of the circulating current are used for eliminating the average energy difference between the upper and lower arms in a three-phase MMC. In order to decouple efficiently the differential current components, the decoupled-double-synchronous-reference-frame current control strategy is used. Finally, simulation results validate the performance of the MMC in an HVDC configuration with the proposed control. Control equations are demonstrated, and cross-coupled leg-energy terms are introduced.

An Online Simplified Rotor Resistance Estimator for Induction Motors

This brief presents an adaptive variable structure identifier that provides finite time convergent estimate of the induction motor rotor resistance under feasible persistent of excitation condition. The proposed rotor resistance scheme is based on the standard dynamic model of induction motor expressed in a fixed reference frame attached to the stator. The available variables are the rotor speed, the stator currents and voltages. Experiments show that the proposed method achieved very good estimation of the rotor resistance which is subjected to online large variation during operation of the induction motor. Also, the proposed online simplified rotor resistance estimator is robust with respect to the variation of the stator resistance, measurement noise, modeling errors, discretization effects and parameter uncertainties. Important advantages of the proposed algorithm include that it is an online method (the value of Rr can be continuously updated) and it is very simple to implement in real-time (this feature distinguishes the proposed identifier from the known ones).

A Generalized Power Control Approach in ABC Frame for Modular Multilevel Converter HVDC Links Based on Mathematical Optimization

This paper presents a generalized and versatile control approach using Lagrange multipliers in the ABC frame for a modular multilevel converter-based HVDC system. The methodology is capable of analytically obtaining desired operative conditions by calculating the differential current references previously established by the constraints in the optimization formulation, while obtaining the result with minimum: 1) differential current oscillations (Δi_diffk) or 2) capacitive phase-energy oscillations (Δω_Σk). Furthermore, the energy distribution inside the MMC (i.e., the capacitive phase average energy sum (ω̅_Σk) and difference (ω̅_Δk)) is being regulated by means of the constraint definitions. The optimization yields a differential current reference in “abc” coordinates with a similar structure to instantaneous power theories: as the addition of the product between varying conductances and the MMC internal dynamics input voltages (i.e., the dc bus voltage (v_dc) and the MMC load electromotice force (emf) (e_vk) on the one hand; and a contribution proportional to the ac load power (e_vki_vk) on the other. Both the objective function minimization and the energy constraints are achieved with one single current reference resulting from the optimization process, without the application of linear superposition techniques.

Real-Time Speed and Flux Adaptive Control of Induction Motors Using Unknown Time-Varying Rotor Resistance and Load Torque

In this paper, an algorithm for direct speed and flux adaptive control of induction motors using unknown time-varying rotor resistance and load torque is described and validated with experimental results. This method is based on the variable structure theories and is potentially useful for adjusting online the induction motor controller unknown parameters (load torque and rotor resistance). The presented nonlinear compensator provides voltage inputs on the basis of rotor speed and stator current measurements, and generates estimates for both the unknown parameters and the nonmeasurable state variables (rotor flux and derivatives of the stator current and voltage) that converge to the corresponding true values. Experiments show that the proposed method achieved very good tracking performance within a wide range of the operation of the induction motor with online variation of the rotor resistance: up to (87%). This high tracking performance of the rotor resistance variation demonstrates that the proposed adaptive control is beneficial for motor efficiency. The proposed algorithm also presented high decoupling performance and very interesting robustness properties with respect to the variation of the stator resistance (up to 100%), measurement noise, modeling errors, discretization effects, and parameter uncertainties (e.g., inaccuracies on motor inductance values). The other interesting feature of the proposed method is that it is simple and easily implementable in real time. Comparative results have shown that the proposed adaptive control decouples speed and flux tracking while standard field-oriented control does not.

Modular Multilevel Converter leg-energy controller in rotating reference frame for voltage oscillations reduction

This work consists of the presentation of a regulation strategy capable of controlling the energy stored in the DC capacitors of the upper and lower arms of a Modular Multilevel Converter (MMC) for each phase. This is achieved by regulating the positive, negative and zero sequences in dqo coordinates of the differential current using a rotating reference frame at twice the fundamental value. Active and reactive components of the differential current are used to eliminate the oscillations of the three-phased leg-energy which reduces significantly the capacitor voltage oscillations, while the zero sequence component is used to regulate the whole system energy at a given value. All feed-forwards equations are demonstrated, and cross-coupled leg-energy terms are introduced.

Modular Multilevel Converter-energy difference controller in rotating reference frame

This paper presents a control strategy capable of eliminating the mean value of the energy differences between the upper and lower arms in a three-phase Modular Multilevel Converter (MMC) in Park Coordinates for HVDC applications. This is achieved by controlling the active and reactive differential currents using a rotating reference frame at fundamental frequency in order to eliminate the zero sequence energy difference components by means of an inner and outer control loops. All feed-forward equations are demonstrated, with specific attention being paid to the cross-coupled terms.

An optimization-based control strategy for modular multilevel converters: Design and implementation

In this paper we present an optimization-based procedure for designing a reference circulating current which stabilizes the internal dynamics of a modular multilevel converter. This procedure relies on unconstrained convex optimization and it takes into account conflicting performance requirements such as reducing the oscillating components of circulating current and arm voltages. Tracking of such a reference signal is ensured by a robust tracking controller with gains chosen in order to attenuate the measurement noise. Since we were interested in implementation of the control algorithm by using a digital simulator, the design procedure is carried out in the discrete-time domain. Effectiveness of the proposed strategy is confirmed on a prototype of three-phase modular multilevel converter with five sub-modules per arm and RL load.

Improving the dynamics of lagrange-based MMC controllers by means of adaptive filters for single-phase voltage, power and energy estimation

A generalized and versatile approach for control of the circulating currents of Modular Multilevel Converters (MMC) has been recently proposed by using Lagrange Multipliers in the ABC frame. This approach is capable of analytically obtaining the differential current references associated with the desired operating conditions imposed to the optimization procedure. Previous implementations of this control approach have been sensitive to harmonic distortion of the control signals when applied to systems with a low number of levels, and have depended on average value calculations of sinusoidal variables, slowing down the dynamics of the control and making the tuning of the control system difficult under certain conditions. This work demonstrates that the performance of the versatile Lagrange-based control can be improved by introducing adaptive filtering based on Second Order Generalized Integrators (SOGIs) for processing the system variables needed for calculating the circulating current references. In addition to improved control dynamics and easier tuning of system controllers, the use of the adaptive filters provides inherent capability for operation under frequency variations, and is therefore suitable for control of MMCs operating in weak grids as well as for high- or medium-voltage motor drives.

CONTROL OF A NEW HYDRAZINE PUMP GENERATION IN PROPULSION SYSTEM

Abstract The aim of this paper is to emphasize the studies carried out for the new generation of hydrazine pump s, in terms of modeling, control and experiments in order to optimize the use of gas. It consists of an actuator conception for which it is possible to move the hydrazine pump leading to very short required displacements. It may be shown that the main advantage in using these new devices is the volume gain with respect to the existing satellites systems besides this will allow the system operates even if the gas reservoir pressure level is low, thus bringing great benefits.

An HVDC experimental platform with MMC and two-level VSC in the back-to-back configuration

In this paper we present the realisation of an HVDC experimental platform with modular multilevel converter and two-level voltage source converter. Local control strategies for both converters are outlined in detail. The experimental platform is configured in such a way that the power-flow is controlled by the modular multilevel converter, while the DC voltage is regulated by the two-level voltage source converter. Local control algorithms are implemented by using OPAL-RT and dSpace platforms for rapid control prototyping. Experimental verification is provided.