Fast convergence delayed signal cancellation method for sequence component separation

Delayed Signal Cancellation (DSC) is one of the methods used to separate the negative and positive sequence components in unbalanced 34 systems. In this paper a DSC methodology with a fast convergence time is proposed and is shown that an improved separation of the positive and negative sequences is feasible. Experimental results are presented to demonstrate the performance of the proposed methodology

An enhanced dq-based vector control system for modular multilevel converters feeding variable speed drives

Modular multilevel converters (M2C) are considered an attractive solution for high power drive applications. However, energy balancing within the converter is complex to achieve, particularly when the machine is operating at low rotational speeds. In this paper, a new control system, based on cascaded control loops and a vector-power-voltage (vPV) model of the M2C, is proposed. The control system is implemented in a dq-synchronous frame rotating at ωe rad/s with the external loop regulating the capacitor voltages using proportional-integral (PI) controllers. The internal loop controls the converter currents using PI and resonant controllers. In addition, the control systems required to operate the machine at other points, i.e., at medium and high rotational speeds, are also discussed in this paper. Experimental results obtained with an M2C-based drive laboratory prototype with 18 power cells are presented in this paper

A simplified space-vector modulation algorithm for four-leg NPC converters

To interface generation sources and loads to four-wire distribution networks is important to use power converters and modulation methods which provide high performance, flexi¬bility and reliability. To achieve these goals, this paper proposes a simple and efficient Space Vector Modulation (SVM) algorithm in α3-y coordinates for Neutral Point Clamped (NPC) converters. The proposed SVM method reduces a three-dimensional (α3-y) search of the modulating vectors into a simple two-dimensional (α3) problem. Moreover, the algorithm provides full utilisation of the dc-link voltage, full utilisation of the redundant vectors and it can be applied to any other four-leg converter topology. The proposed SVM has been successfully validated using a 6kW three-level four-leg NPC converter, achieving control over the voltages of the dc-link capacitors and simple definition of switching pattern for shaping frequency spectrum

A new space-vector-modulation algorithm for a three-level four-leg NPC inverter

For power conversion systems interfaced to 4-wire supplies, four-leg converters have become a standard solution. A four-leg converter allows good compensation of zero-sequence harmonics and full utilization of the dc-link voltage. These are very important features when unbalanced and/or non-linear loads are connected to the system. This paper proposes a 3D-SVM algorithm and provides a comprehensive analysis of the algorithm implemented on a three-level, four-leg NPC converter. The algorithm allows a simple definition of the different switching patterns and enables balancing of the dc-link capacitor voltages using the redundancies of the converter states. A resonant controller is selected as the control strategy to validate the proposed SVM algorithm in a 6kW experimental rig

Control of wind energy conversion systems based on the Modular Multilevel Matrix converter

The nominal power of single Wind Energy Conversion Systems (WECS) has been steadily growing, reaching power ratings close to 10MW. In the power conversion stage, medium-voltage power converters are replacing the conventional low-voltage back-to-back topology. Modular Multilevel Converters have appeared as a promising solution for Multi-MW WECSs, due to their modularity, and the capability to reach high nominal voltages. This paper discusses the application of the Modular Multilevel Matrix Converter (M3C) to drive MultiMW WECSs. The modelling and control systems required for this application are extensively analysed and discussed in this paper. The proposed control strategies enable decoupled operation of the converter, providing maximum power point tracking (MPPT) capability at the generator-side, grid code compliance at the grid-side [including Low Voltage Ride Through Control (LVRT)], and good steady state and dynamic performance for balancing the capacitor voltages in all the clusters. Finally, the effectiveness of the proposed control strategy is validated through simulations and experimental results conducted with a 27 power-cell prototype

An integrated converter and machine control system for MMC-based high power drives

The Modular Multilevel Converter (MMC) is a promising topology for high power drive applications. However, large voltage fluctuations are produced in the floating capacitors when the machine is operating with high stator currents at low rotational speed. To compensate these oscillations, relatively large mitigation currents are required to keep the capacitor voltages within an acceptable range. In this paper, a new integrated control scheme is discussed to regulate the voltage fluctuations. The strategy is based on closed-loop vector-control of the voltage fluctuations, maintaining them inside a pre-defined threshold. The proposed control system is also augmented using flux weakening operation of the machine at low rotational speeds. An experimental prototype composed of eighteen power cells, feeding a vector-controlled induction machine in the whole speed range, is used to validate the effectiveness and feasibility of the proposed control strategies

Resonant control system for low-voltage ride-through in wind energy conversion systems

Owing to the high penetration of electrical energy from wind energy conversion systems (WECSs), some countries are enforcing stringent grid codes to regulate low-voltage-ride-through (LVRT) operation of WECSs. This study presents a self-tuning resonant control (RC) system which can be used for LVRT control of the grid interface in the presence of symmetrical or asymmetrical faults. Only two RCs are required to fully control the four degrees of freedom of the converter output current. Sequence component separation is achieved using a new fast-convergence delayed signal cancellation method which is also discussed in this work. The mathematical analysis and design procedure of the control system are presented. Simulation and experimental results obtained from a 3 kW prototype are discussed in this study

Continuous Set Model Predictive Control for Energy Management of Modular Multilevel Matrix Converters

The Modular Multilevel Matrix Converter is an AC-AC power converter proposed for high power applications such as motor drive and wind energy conversion systems. The M 3C has 9 clusters, allowing 4 circulating currents for converter energy management. Control of the M 3C is frequently divided into Different Frequency Mode (DFM) and Equal Frequency Mode (EFM). EFM is more challenging, because of the larger capacitor voltage oscillations that can be produced. Conventional energy management control strategies for EFM/DFM are usually based on 8 energy control loops used to define four circulating current references composed of several predefined frequencies and positive/negative sequences. The control schemes are typically different for EFM/DFM operation increasing the complexity. In this paper, a Continuous-Control-Set Model Predictive Control (CCS-MPC) for energy management of the M 3C is proposed. The control scheme is based on solving an equality constrained quadratic programming problem, using a state variable model of the M3C, where the optimal solution is analytically obtained. The result is a single and simple control law to obtain circulating current references during EFM/DFM, ensuring a good performance with optimal current specifications. The proposed strategy is experimentally validated using a down-scaled M3C prototype composed of 27 power cells

A design methodology of multi-resonant controllers for high performance 400Hz ground power units

In aerospace applications, a Ground Power Unit (GPU) has to provide balanced and sinusoidal 400 Hz phase-to-neutral voltages to unbalanced and non-linear single-phase loads. Compensation of high-order harmonics is complex, as the ratio between sampling frequency and compensated harmonics can be very small. Thus multiple superimposed resonant controllers or PI nested controllers in multiple dq frames are not good alternatives. The first approach cannot ensure stability, while the second cannot track sinusoidal zero-sequence components, typically present in unbalanced system, and unachievable high bandwidth at the inner current control loop is typically required. In this paper, a simple methodology for designing a single-loop, multiple resonant controller for simultaneous mitigation of several high-order harmonics, ensuring stability, is presented. Experimental results, based on a 6kW four-leg NPC converter, validates the proposed controller design, showing excellent steady state and transient performance

Vector control of a modular multilevel matrix converter operating over the full output-frequency range

The Modular Multilevel Matrix Converter ( M 3 C ) is an ac-to-ac converter topology suitable for the control of high-power variable-speed drives. The control of this converter is complex, particularly when the two ac system frequencies are similar or identical because large voltage oscillations can be produced in the floating capacitors within the M 3 C . This paper proposes a new Vector Control System based on nested controllers to regulate the M 3 C over the full-range of frequencies. The proposed control scheme is especially useful to mitigate or eliminate the oscillations that arise when the frequencies are similar. An extensive discussion of the model and control of the M 3 C is presented in this work. The effectiveness of the proposed Vector Control System is demonstrated through simulation studies and experimental validation tests conducted with a 27-cell-5kW M 3 C prototype