Next Generation Inverters Equipped with Virtual Synchronous Compensators for Grid Services and Grid Support

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Optimal Design of Grid-Side LCL Filters for Electric Vehicle Ultra-Fast Battery Chargers

This paper proposes a complete design procedure for LCL filters intended for electric vehicle (EV) ultra-fast battery chargers. The basic modeling of LCL filters is reported and the optimal ratio between grid-side and converter-side inductance is discussed. The design methodology is based on the identification of all parameter constraints, which allow to graphically determine the filter design space. Once the available space is identified, the feasible design which minimizes the total required inductance is selected, since inductors dominate the overall LCL filter volume, loss and cost. The proposed design procedure is directly applied to a 50 kW, 20 kHz 3-level unidirectional rectifier for a modular EV ultra-fast charger. The performances of the selected design, in terms of harmonic filtering and current control dynamics, are verified by means of simulation in PLECS environment, proving the validity of the proposed design methodology

Optimal Design of Grid-Side LCL Filters for Electric Vehicle Ultra-Fast Battery Chargers

This paper proposes a complete design procedure for LCL filters intended for electric vehicle (EV) ultra-fast battery chargers. The basic modeling of LCL filters is reported and the optimal ratio between grid-side and converter-side inductance is discussed. The design methodology is based on the identification of all parameter constraints, which allow to graphically determine the filter design space. Once the available space is identified, the feasible design which minimizes the total required inductance is selected, since inductors dominate the overall LCL filter volume, loss and cost. The proposed design procedure is directly applied to a 50 kW, 20 kHz 3-level unidirectional rectifier for a modular EV ultra-fast charger. The performances of the selected design, in terms of harmonic filtering and current control dynamics, are verified by means of simulation in PLECS environment, proving the validity of the proposed design methodology

Battery Sources and Power Converters Interface in Waterborne Transport Applications

In recent years the electrification in the waterborne transport application is in noticeable development. To face the high battery cost, a proper design of the energy storage system is required. For battery sources, the solution worthy of investigation is the use of a hybrid energy storage system (HESS). HESS is composed of a power-dense battery and an energy-dense battery. The use of a HESS allows better optimization of the energy and power levels of the energy storage system. In the paper, the battery source requirements in the waterborne transport application are evaluated to achieve the best trade-off among energy, maximum power, and life cycle. Furthermore, the power converters selection, to balance the power flow among the batteries and the vessel electrical network is described

Simple Tuning Method of Virtual Synchronous Generators Reactive Control

The integration of renewable energy sources requires new control strategies to make static converters able to provide ancillary grid services, such as virtual inertia and grid support during faults. To address this issue, the idea of making inverters behave as synchronous machines is well known in the literature as the concept of Virtual Synchronous Generator. Thanks to this solution, inverters can provide both inertia and reactive grid support as traditional synchronous machines. However, the tuning of the excitation control of Virtual Synchronous Generator for proper reactive power management has not been properly analyzed in the literature. Therefore, the goal of this paper is to provide a simple tuning criterion for the VSM excitation control with improved dynamic behavior using a feed-forward term. This way, the VSM is able to provide the desired reactive support during faults and quickly track the desired reactive power setpoints. Both a theoretical analysis and experimental tests are provided for a 15 kVA system

A Lead-Lag Filter for Virtual Synchronous Machines with Improved Electromechanical Damping

Traditional power systems based on synchronous generators often feature low frequency electromechanical oscillations. However, the integration of renewable energy sources through power converters can help tackling this issue. In fact, thanks to the concept of Virtual Synchronous Machine (VSM), it is possible to make the inverters behave as real synchronous machines (SMs). This way, the inverters can be integrated into the grid as traditional SMs and can even outperform them when it comes to damping low frequency oscillations in the power system. In order to do that, proper damping algorithms must be adopted in the VSM model. Therefore, this paper presents a simple and straighforward damping method for VSMs based on a single lead-lag filter acting on the VSM active power feedback. The proposed method and its integration in the VSM model are described. Then, the proposed solution has been experimentally compared to conventional methods, along with comparison metrics, to highlight its benefits

Modular Stator Flux and Torque Control of Multi-Three-Phase Induction Motor Drives

direct flux vector control, induction motor drives, modular torque control, multiphase electrical machine

General Method to Foresee the Behavior of Virtual Synchronous Machines working with Distorted and Unbalanced Voltage Conditions

To make photovoltaic and wind power plants able to provide grid services (i.e., inertial behavior, grid support and harmonic compensation), several control algorithms have been proposed in the literature during the last years. The most promising ones make the power electronic converters behave as conventional alternators, using the concept of Virtual Synchronous Machine (VSM). Several VSM models are available in the literature, some of which can improve the voltage quality at the point of connection with the grid behaving as harmonic and unbalance sinks under non–ideal grid voltage conditions. However, the literature lacks a general method to foresee the behavior of a generic VSM configuration in such conditions along with a well–established definition of the needed features to make VSMs able to work as harmonic or unbalance sinks. Therefore, this paper proposes a simple and general method to foresee the behavior of different VSM configurations under non–ideal grid voltage conditions before any experimental verification. The proposed method accurately foresees the VSMs behavior, as experimentally demonstrated on five VSM models available in the literature, working with fifth harmonic and inverse sequence voltage distortions. Moreover, the method identifies which VSM configuration can feature a beneficial harmonic and unbalance compensation

Power Decoupling Method for Grid Inertial Support Provided by Ultra-Fast Bidirectional Chargers

The Active Front-End (AFE) converter unit of ultra-fast battery chargers can contribute to the inertial frequency response by embedding the Virtual Synchronous Machine (VSM) control algorithm. However, the injection of inertial active power involves a non-negligible reactive power contribution due to the active-reactive power coupling, thus increasing the current output of the converter. Therefore, this paper proposes an active-reactive power decoupling solution to minimize the AFE current rating for frequency support

Design Space Optimization of a Three-Phase LCL Filter for Electric Vehicle Ultra-Fast Battery Charging

State-of-the-art ultra-fast battery chargers for electric vehicles simultaneously require high efficiency and high power density, leading to a challenging power converter design. In particular, the grid-side filter, which ensures sinusoidal current absorption with low pulse-width modulation (PWM) harmonic content, can be a major contributor to the overall converter size and losses. Therefore, this paper proposes a complete analysis, design and optimization procedure of a three-phase LCL filter for a modular DC fast charger. First, an overview of the basic LCL filter modeling is provided and the most significant system transfer functions are identified. Then, the optimal ratio between grid-side and converter-side inductance is discussed, aiming for the maximum filtering performance. A novel design methodology, based on a graphical representation of the filter design space, is thus proposed. Specifically, several constraints on the LCL filtering elements are enforced, such that all feasible design parameter combinations are identified. Therefore, since in low-voltage high-power applications the inductive components typically dominate the overall filter volume, loss and cost, the viable LCL filter design that minimizes the total required inductance is selected. The proposed design procedure is applied to a 30 kW, 20 kHz 3-level unidirectional rectifier, employed in a modular DC fast charger. The performance of the selected optimal design, featuring equal grid-side and converter-side 175 µH inductors and 15 µF capacitors, is verified experimentally on an active front-end prototype, both in terms of harmonic attenuation capability and current control dynamics. A current total harmonic distortion (THD) of 1.2% is achieved at full load and all generated current harmonics comply with the applicable harmonic standard. Moreover, separate tests are performed with different values of grid inner impedance, verifying the converter control stability in various operating conditions and supporting the general validity of the proposed design methodology