Showing papers on "Power optimizer published in 2017"

Wind Energy Systems

Abstract: Wind power now represents a major and growing source of renewable energy Large wind turbines (with capacities of up to 6–8 MW) are widely installed in power distribution networks Increasing numbers of onshore and offshore wind farms, acting as power plants, are connected directly to power transmission networks at the scale of hundreds of megawatts As its level of grid penetration has begun to increase dramatically, wind power is starting to have a significant impact on the operation of the modern grid system Advanced power electronics technologies are being introduced to improve the characteristics of the wind turbines, and make them more suitable for integration into the power grid Meanwhile, there are some emerging challenges that still need to be addressed This paper provides an overview and discusses some trends in the power electronics technologies used for wind power generation First, the state-of-the-art technology and global market are generally discussed Several important wind turbine concepts are discussed, along with power electronics solutions either for individual wind turbines or for entire wind farms Some technology challenges and future solutions for power electronics in wind turbine systems are also addressed

Fast-Frequency Response Provided by DFIG-Wind Turbines and its Impact on the Grid

Abstract: This paper presents a methodology for the analysis of frequency dynamics in large-scale power systems with high level of wind energy penetration by means of a simplified model for DFIG-based wind turbines. In addition, a virtual inertia controller version of the optimized power point tracking (OPPT) method is implemented for this kind of wind turbines, where the maximum power point tracking curve is shifted to drive variations in the active power injection as a function of both the grid frequency deviation and its time derivative. The proposed methodology integrates the model in a primary frequency control scheme to analyze the interaction with the rest of the plants in the power system. It is also proven that, under real wind conditions, the proposed version of the OPPT method allows us to smooth the wind power injected into the grid, thereby reducing frequency fluctuations.

A Modified Firefly Algorithm for Photovoltaic Maximum Power Point Tracking Control Under Partial Shading

Abstract: Photovoltaic modules subjected to partial shading conditions (PSC) can drastically decrease their power output. Hence, there have been various maximum power point tracking (MPPT) control algorithms developed to reduce or counteract the shading effects. Recently, a new metaheuristic algorithm known as firefly algorithm (FA) was developed, which, under PSC, has been shown to successfully track the global maximum point (GMP). Nevertheless, the FA still has some inherent problems that may hinder the performance of the MPPT. This paper modifies the existing FA to counteract these problems. As will be demonstrated in this paper, the proposed modified FA method can reduce the number of computation operations and the time for converging to the GMP that the existing FA requires. Experimental results show that the proposed method can track the global point under various PSC, has a faster convergence time compared with the FA, and can effectively suppress power and voltage fluctuations.

Virtual Synchronous Generator Control of Full Converter Wind Turbines With Short-Term Energy Storage

Abstract: One way to incorporate the increasing amount of wind penetration is to control wind turbines to emulate the behavior of conventional synchronous generators. However, the energy balance is the main issue for the wind turbines to be truly dispatchable by the power system operator such as the generators. This paper presents a comprehensive virtual generator control method for the full converter wind turbine, with a minute-level energy storage in the dc link as the energy buffer. The voltage closed-loop virtual synchronous generator control of the wind turbine allows it to work under both grid-connected and stand-alone condition. Power balance of the wind turbine system is achieved by controlling the rotor speed of the turbine according to the loading condition. With the proposed control, the wind turbine system can enhance the dynamic response, and can be dispatched and regulated by the system operator. The sizing design of the short term energy storage is also discussed in this paper. Experimental results are presented to demonstrate the feasibility and effectiveness of the proposed control method.

Constant power loads and their effects in DC distributed power systems: A review

Abstract: The penetration of dc distributed power systems is increasing rapidly in electric power grids and other isolated systems to cater demand for cheap, clean, high quality, and uninterrupted power demand of modern society. DC systems are more efficient and suite better to integrate some of the renewable energy sources, storage units, and dc loads. A dc distributed power system usually consists of large number of power electronic converters connected in cascad0ed configuration to satisfy the power quality and voltage magnitude requirements of the sources and loads. Tightly-regulated power converters in the aforementioned settings exhibit negative incremental impedance and behave as constant power loads (CPLs), and tend to destabilize their feeder systems and upstream converters. The presence of CPLs reduces effective damping of the system leading to instability of the whole system and present significant challenge in the system operation and control. In-depth knowledge of the instability effects of constant power loads (CPLs), available stabilizing techniques and stability analysis methods, is imperious to the young researchers, system designers, system integrators, and practicing engineers working in the field of dc power systems and emerging applications of dc power. This paper is intended to fill this gape by documenting present state of the art and research needs in one article. Modeling, behaviour and effects of typical CPL are discussed and a review of stability criteria used to study the stability of dc power systems are reviewed with their merits and limitations. Furthermore, available literature is reviewed to summarize the techniques to compensate the CPL effect. Finally, discussion and recent challenges in the dc distribution systems.

Coordinated Distributed MPC for Load Frequency Control of Power System With Wind Farms

Abstract: Load frequency control (LFC) is crucial for the operation and design of modern electric power systems. This becomes quite challenging, as more wind power is included into the power system. This paper proposes a coordinated distributed model predictive control (DMPC) for the LFC of a power system that includes inherently variable wind-power generations. This DMPC communicates power system measurement and prediction data, and considers the information of other controllers for their local objective to realize effective coordination. The controllers solve the optimization problem while considering given constraints, e.g., generation rate constraints, wind speed, pitch angle, and load input constraints for each area. Since the wind-power output depends largely on the wind speed, different optimization modes for the DMPC were used. Both simulation and experimental tests of a four-area interconnected power system LFC, which consists of thermal plants, hydro units, and a wind farm, demonstrate the improved efficiency of the coordinated DMPC.

Active power filter (APF) for mitigation of power quality issues in grid integration of wind and photovoltaic energy conversion system

Abstract: The deep integration of renewable energy resources, including solar photovoltaic (PV) and wind turbine (WT) energy, mainly depend on the inexpensive technological improvement of global emissions and the precise techniques for power quality. Grid-connected inverters act as key components in distributed generation systems for cutting-edge technology. The inverter connects the renewable energy sources and power distribution network systems for the conversion of power. In grid-connected systems, several current and voltage harmonics affect the system performances. Likewise, highly unstable devices coupled with the growing demand for nonlinear loads and renewable energy resources influence the power networks and systems performance in terms of power quality. The effective solutions to these problems are passive filters (PFs), static var generators, and active power filters (APFs). However, the use of PFs in a high-power system increases its cost, size, and weight. This study aims to assess the most advanced APFs by reducing the number of power switches and focus on the reduction of cost, size, and weight of grid-connected inverters. Several studies compared and evaluated reduced-switch-count APF inverter topologies, such as AC–AC, back-to-back, and common leg, under the single-phase and three-phase systems. Recently, cost-effective solutions to reduce the number of components, transformerless inverters, multilevel and multifunctional inverters based on the APF in PV, and wind energy conversion systems have been greatly explored. The current techniques and their limitations for developing advanced inverter-based devices for renewable energy systems are discussed with justifications. Therefore, this review would potentially help industrial researchers improve power quality in PV and WT energies and power distribution network systems.

Control of a Hybrid AC/DC Microgrid Involving Energy Storage and Pulsed Loads

Abstract: This paper presents a real-time coordinated control of the hybrid ac/dc microgrids involving energy storage and pulsed loads. Grid-isolated hybrid microgrid applications require special considerations due to the intermittent generation, online energy storage control, and pulsed loads. In this study, we introduce a comprehensive frequency and voltage control scheme for a hybrid ac/dc microgrid consisting of a synchronous generator, solar generation emulator, and bidirectional (ac/dc and dc/dc) converters. A bidirectional controlled ac/dc converter with an active and reactive power decoupling technique is used to link the ac bus with the dc bus, while regulating the system voltage and frequency. A dc/dc boost converter with a maximum power point tracking function is implemented to maximize the intermittent energy generation from solar generators. Current-controlled bidirectional dc/dc converters are applied to connect each lithium-ion battery bank to the dc bus. Lithium-ion battery banks act as energy storage devices that serve to increase the system resiliency by absorbing or injecting power. Experimental results are presented for verification of the introduced hybrid ac/dc power flow control scheme.

Bidirectional Power Flow Control in a DC Microgrid Through a Switched-Capacitor Cell Hybrid DC–DC Converter

Abstract: This paper focuses on a bidirectional hybrid dc–dc converter suitable as an interface between two dc voltage buses in various applications including microgrids. The switched-capacitor cell, incorporated in the converter topology, gives the advantage of high voltage conversion ratio without using a transformer. This paper analyses the converter operation and the stability in the step-up and step-down operating modes through the state-space averaging method and through the pulse width modulation switch model method applied on an equivalent circuit model. The converter employs a current controller designed in frequency domain based on the Bode plot, using the K factor method. The simulation results obtained by means of an average and a detailed switching model prove, in good correspondence, that the controller is able to track the reference current waveform with good dynamic performance . Experimental results obtained from a 2 kW converter prototype confirm the theoretical considerations and the simulation results.

A Sensorless Power Reserve Control Strategy for Two-Stage Grid-Connected PV Systems

Abstract: Due to the still increasing penetration of grid-connected photovoltaic (PV) systems, advanced active power control functionalities have been introduced in grid regulations. A power reserve control, where namely the active power from the PV panels is reserved during operation, is required for grid support. In this paper, a cost-effective solution to realize the power reserve for two-stage grid-connected PV systems is proposed. The proposed solution routinely employs a maximum power point tracking control to estimate the available PV power and a constant power generation (CPG) control to achieve the power reserve. In this method, the solar irradiance and temperature measurements that have been used in conventional power reserve control schemes to estimate the available PV power are not required, and thereby, being a sensorless approach with reduced cost. Experimental tests have been performed on a 3-kW two-stage single-phase grid-connected PV system, where the power reserve control is achieved upon demands.

A New Three Input DC/DC Converter for Hybrid PV/FC/Battery Applications

Abstract: In this paper, a new three-port dc/dc converter is presented for hybrid photovoltaic (PV)/fuel cell (FC)/battery applications. The proposed structure comprises a conventional buck-boost and a boost converter. Four power switches and four diodes are employed in the proposed converter. The voltage gain of the presented converter is more than the conventional boost converter. This advantage and having two unidirectional and a bidirectional inputs make the structure a suitable power electronic interface for hybrid generation applications. In addition, there are no limitations in switching the modulation. Therefore, tracking the maximum power of the PV source, setting the FC power, controlling the battery power, and calibrating the output voltage can be equipped by controlling duty ratios of the switches. The input power sources can provide power to the load and either charge or discharge the battery individually or simultaneously. The steady-state analyses of the presented converter are discussed thoroughly in this paper. Finally, in order to validate the feasibility of the presented converter, experimental results are provided.

An Enhanced MPPT Method Combining Fractional-Order and Fuzzy Logic Control

Abstract: A fractional-order fuzzy logic control (FOFLC) method for maximum power point tracking (MPPT) in a photovoltaic (PV) system is presented. By combining the robustness of fuzzy logic with the accuracy of fractional order, the proposed method can improve the tracking accuracy in weather variations compared with the conventional fuzzy MPPT. First, the fractional-order factor is carefully selected according to the dynamic range of the fuzzy controller. It takes a bigger alpha factor in the first place to expand the fuzzy domain and shortens the time of searching for the MPP. When the maximum power point is approached, it uses a smaller the alpha factor to contract the fuzzy domain and eliminates the oscillations at the MPP. Therefore, the FOFLC in a PV system has rapid dynamic responses under environment variations and high tracking accuracy of the maximum power point. Second, MATLAB/Simulink software is employed to simulate a PV power system and verify the proposed algorithm by various simulations. The enhanced MPPT algorithm has been implemented on a field programmable gate array (FPGA) board. Finally, a boost dc–dc converter experiment has been carried out to evaluate the system performance. The simulation and experiment results show that this method can improve the transient and steady-state performance simultaneously.

Delta Power Control Strategy for Multistring Grid-Connected PV Inverters

Abstract: With a still increasing penetration level of grid-connected photovoltaic (PV) systems, more advanced active power control functionalities have been introduced in certain grid regulations. A delta power constraint, where a portion of the active power from the PV panels is reserved during operation, is required for grid support (e.g., during frequency deviation). In this paper, a cost-effective solution to realize delta power control (DPC) for grid-connected PV systems is presented, where the multistring PV inverter configuration is adopted. This control strategy is a combination of maximum power point tracking (MPPT) and constant power generation (CPG) modes. In this control scheme, one PV string operating in the MPPT mode estimates the available power, whereas the other PV strings regulate the total PV power by the CPG control strategy in such a way that the delta power constraint for the entire PV system is achieved. Simulations and experiments have been performed on a 3-kW single-phase grid-connected PV system. The results have confirmed the effectiveness of the proposed DPC strategy, where the power reserve according to the delta power constraint is achieved under several operating conditions.

Global Maximum Power Point Tracking Method for Photovoltaic Arrays Under Partial Shading Conditions

Abstract: The power–voltage characteristic of photovoltaic (PV) arrays displays multiple local maximum power points when all the modules do not receive uniform solar irradiance, i.e., under partial shading conditions (PSCs). Conventional maximum power point tracking (MPPT) methods are shown to be effective under uniform solar irradiance conditions. However, they may fail to track the global peak under PSCs. This paper proposes a new method for MPPT of PV arrays under both PSCs and uniform conditions. By analyzing the solar irradiance pattern and using the popular Hill Climbing method, the proposed method tracks all local maximum power points. The performance of the proposed method is evaluated through simulations in MATLAB/SIMULINK environment. Besides, the accuracy of the proposed method is proved using experimental results.

Security-Constrained Unit Commitment With Flexible Uncertainty Set for Variable Wind Power

Abstract: Power system operation has recently witnessed major challenges, which are often due to large-scale integrations of wind power generation. In this paper, a two-stage robust security-constrained unit commitment (SCUC) model is proposed for managing the wind power uncertainty in the hourly scheduling of power system generation. Different from previous studies on robust SCUC, which considered a predefined uncertainty set, the proposed method applies a flexible uncertainty set for managing the variable wind power generation. The proposed method seeks a feasible and economic dispatch in the flexible uncertainty set, takes into account wind spillage and load curtailment risks, and makes a tradeoff between the optimal wind power absorption and the economic grid operation. Several case studies are applied to the proposed method and the corresponding solutions are analyzed in the paper. The impacts of major factors, including flexible generation resources and power transmission capacity, on the proposed solution are also discussed. The numerical results demonstrate the merits of the proposed method for managing large variations in the hourly wind power generation and lowering the power system operation cost in uncertain conditions.

Stochastic Scheduling of Battery-Based Energy Storage Transportation System With the Penetration of Wind Power

Abstract: Battery-Based Energy Storage Transportation (BEST) is a potential solution for optimizing the power system operations with a high penetration of wind energy. In this paper, we propose a scenario-based stochastic model for the BEST-integrated power system scheduling. In this model, load and wind energy forecasting inaccuracies and random disturbances are modeled in scenario trees using the Monte Carlo simulation method. Random disturbances represent forced outages of both power system and railway system components, including generation units, transmission lines, railway stations, and railway lines. Benders decomposition is adopted to solve the stochastic model. Two BEST-integrated power systems are used to illustrate the proposed model and the performance of the proposed solution algorithm. The first one is a 6-bus power system integrated with a 3-station and 3-line railway network. The second one is the modified IEEE 118-bus power system integrated with a railway network composed of 8 railway stations and 10 rail lines. Simulation results show that the BEST system implementation is a viable option for managing the large-scale integration of wind power which can reduce the curtailment of wind power and accordingly lower the operation cost of power systems.

Least Power Point Tracking Method for Photovoltaic Differential Power Processing Systems

Abstract: Differential power processing (DPP) systems are a promising architecture for future photovoltaic (PV) power systems that achieve high system efficiency through processing a faction of the full PV power, while achieving distributed local maximum power point tracking (MPPT). In the PV-to-bus DPP architecture, the power processed through the DPP converters depends on the string current, which must be controlled to minimize the power processed through the DPP converters. A real-time least power point tracking (LPPT) method is proposed to minimize power stress on PV DPP converters. Mathematical analysis shows the uniqueness of the least power point for the total power processed through the system. The perturb-and-observe LPPT method is presented that enables the DPP converters to maintain optimal operating conditions, while reducing the total power loss and converter stress. This work validates through simulation and experimentation that LPPT in the string-level converter successfully operates with MPPT in the DPP converters to maximize output power for the PV-to-bus architecture. Hardware prototypes were developed and tested at 140 and 300 W, and the LPPT control algorithm showed effective operation under steady-state operation and an irradiance step change. Peak system efficiency achieved with a 140-W prototype DPP system employing LPPT is 95.7%.

Real-Time Power-Hardware-in-the-Loop Implementation of Variable-Speed Wind Turbines

Abstract: This paper presents the real-time (RT) power-hardware-in-the-loop (PHIL) emulation of the two most popular variable-speed wind turbines (WT): the doubly-fed induction generator WT with partial-scale power converter and the permanent-magnet synchronous machine WT with full-scale power converter. RT-PHIL emulation offers a realistic, controlled, and easily reconfigurable test environment for analyzing grid integration problems, in which classic tools frequently show a lack of capacity. The proposed discrete-time models and implementation methodology result in creation of platform-independent models suitable for application on any RT platform. A voltage-source converter is used as PHIL power interface between the RT simulation and a microgrid testbed. This test environment is of interest for verification of high-level control strategies for wind farms and for evaluation of the response of hardware systems, such as active filters or static synchronous compensators (STATCOMs) connected to a grid (or microgrid) in presence of wind power generation. The RT discrete models of both WTs are demonstrated in a grid-connection experiment.

Grid-Interfaced DFIG-Based Variable Speed Wind Energy Conversion System With Power Smoothening

Abstract: This paper deals with the analysis, design, and control of grid-interfaced doubly fed induction generator (DFIG) based variable speed wind energy conversion system (WECS) for power smoothening with maximum power point tracking (MPPT) capability. This DFIG uses rotor position computation algorithm for the sensorless control through rotor position estimation. Power fluctuations due to the unpredictable nature of the wind are eliminated by introducing battery energy storage system (BESS) in the dc link between two back-to-back connected voltage source converters. The design of BESS is presented for feeding regulated power to the grid irrespective of the wind speeds. The control algorithm of the grid-side converter is modified for feeding regulated power to the grid. Rotor-side converter is controlled for achieving MPPT and unity power factor operation at the stator terminals. A prototype of the proposed DFIG-based wind energy conversion system is developed using a digital signal processor (DSP-dSPACE DS1103). This developed DFIG is tested extensively at different wind speeds and also presented some of the steady-state test results. Dynamic performance of this DFIG is also demonstrated for the variable wind speed operation.

DC Electric Springs—A Technology for Stabilizing DC Power Distribution Systems

Abstract: There is a growing interest in using dc power systems and microgrids for our electricity transmission and distribution, particularly with the increasing penetration of photovoltaic power systems. This paper presents an electric active suspension technology known as the dc electric springs (DC-ES) for voltage stabilization and power quality improvement. The basic operating modes and characteristic of a DC-ES with different types of serially connected non-critical loads will first be introduced. Then, the various power delivery issues of the dc power systems, namely bus voltage variation, voltage droop, system fault, and harmonics, are briefly described. The operating limits of a DC-ES in a dc power grid is studied. It is demonstrated that the aforementioned issues can be mitigated using the proposed DC-ES technology. Experiment results are provided to verify the feasibility of the proposed technology.

Output Predictor-Based Active Disturbance Rejection Control for a Wind Energy Conversion System With PMSG

Abstract: Considering the internal and external disturbances in wind energy conversion systems, a predictive active disturbance rejection control (PADRC) strategy for a direct-driven permanent magnet synchronous generator (PMSG)-based wind energy conversion system, is proposed to maximize the wind power extraction in this paper. First, the proposed PADRC method can successfully deal with the effects of the uncertainties in the internal dynamics, modeling error, external forces and the variety of wind speeds, since it inherits the merits of active disturbance rejection control (ADRC). Second, the introduction of Smith Predictor can overcome the time delay in wind turbine system to guarantee the maximum power tracking performance for different wind speeds. Finally, simulation studies are conducted to evaluate power tracking performances of the proposed control strategy. It is shown that the proposed PADRC strategy exhibits significant improvements in both maximum power tracking performance and anti-disturbance ability compared with the traditional ADRC approach.

Stability improvement of a multimachine power system connected with a large-scale hybrid wind-photovoltaic farm using a supercapacitor

Abstract: This paper presents the stability improvement of a multimachine power system connected with a large-scale hybrid wind-photovoltaic (PV) farm using an energy-storage unit based on supercapacitor (SC). The operating characteristics of the hybrid wind-PV farm are simulated by an equivalent aggregated 300-MW wind-turbine generator (WTG) based on permanent-magnet synchronous generator and an equivalent aggregated 75-MW PV array. The WTG and the PV array are connected to a common dc link through a voltage-source converter and a dc/dc boost converter, respectively. The power of the common dc link is transferred to the multimachine power system through a voltage-source inverter, step-up transformers, and a connection line. The SC-based energy-storage unit, which is integrated into the common dc link through a bidirectional dc/dc converter, is employed for smoothing out the power fluctuations due to variations of wind speed and/or solar irradiance. A proportional-integral-derivative (PID)-supplementary damping controller (PID-SDC) is designed for the bidirectional dc/dc converter of the SC to enhance the damping characteristics of the low-frequency oscillations associated with the studied multimachine power system. The root loci of the studied system are examined under wide ranges of wind speed and solar irradiance. The effectiveness of the proposed SC joined with the PID-SDC on improving the performance of the studied system under different disturbance conditions is also demonstrated using time-domain simulations.

Damped-SOGI-Based Control Algorithm for Solar PV Power Generating System

Abstract: This paper deals with two-stage solar photovoltaic (PV) system with a damped-second-order generalized integrator (SOGI) algorithm. Proposed topology not only integrates the PV energy to the grid, in addition, it provides the load compensation, power factor correction, and harmonics elimination. Therefore, a double stage system is proposed where the first stage is a dc–dc boost converter, which performs the maximum power point tracking by regulating its duty ratio. For extracting maximum power from the PV array, an incremental conductance-based approach is utilized. Moreover, in the next stage, a voltage source converter (VSC) is utilized. To control the VSC, a damped-SOGI algorithm is used. By using a damped-SOGI-based control algorithm, fundamental active components of load currents are extracted for evaluating the reference grid currents. After comparing reference grid currents with sensed grid currents, switching pulses for the grid tied VSC are produced. A prototype of the proposed system is developed in the laboratory and test results are presented for verification of control of solar photovoltaic system.

Power Quality Enhancement for a Grid Connected Wind Turbine Energy System

Abstract: A comprehensive control of a wind turbine system connected to an industrial plant is discussed in this paper, where an algorithm has been developed allowing a control structure that utilizes a four-leg inverter connected to the grid side to inject the available energy, as well as to work as an active power filter mitigating load current disturbances and enhancing power quality. A four-wire system is considered with three-phase and single-phase linear and nonlinear loads. During the connection of the wind turbine, the utility-side controller is designed to compensate the disturbances caused in presence of reactive, nonlinear, and/or unbalanced single- and intra-phase loads, in addition to providing active and reactive power as required. When there is no wind power available, the controller is intended to improve the power quality using the dc-link capacitor with the power converter attached to the grid. The main difference of the proposed methodology with respect to others in the literature is that the proposed control structure is based on the conservative power theory decompositions. This choice provides decoupled power and current references for the inverter control, offering very flexible, selective, and powerful functionalities. Real-time software benchmarking has been conducted in order to evaluate the performance of the proposed control algorithm for full real-time implementation. The control methodology is implemented and validated in hardware-in-the-loop based on the real time simulator “Opal-RT” and a TMSF28335 DSP microcontroller. The results corroborated our power quality enhancement control and allowed to exclude passive filters, contributing to a more compact, flexible, and reliable electronic implementation of a smart-grid based control.

Replacing the Grid Interface Transformer in Wind Energy Conversion System With Solid-State Transformer

Abstract: In wind energy conversion systems, the fundamental frequency step-up transformer acts as a key interface between the wind turbine and the grid. Recently, there have been efforts to replace this transformer by an advanced power-electronics-based solid-state transformer (SST). This paper proposes a configuration that combines the doubly fed induction generator-based wind turbine and SST operation. The main objective of the proposed configuration is to interface the turbine with the grid while providing enhanced operation and performance. In this paper, SST controls the active power to/from the rotor side converter, thus, eliminating the grid side converter. The proposed system meets the recent grid code requirements of wind turbine operation under fault conditions. Additionally, it has the ability to supply reactive power to the grid when the wind generation is not up to its rated value. A detailed simulation study is conducted to validate the performance of the proposed configuration.

A Medium-Frequency Transformer-Based Wind Energy Conversion System Used for Current-Source Converter-Based Offshore Wind Farm

Abstract: Offshore wind farms with series-interconnected structures are promising configurations because bulky and costly offshore substations can be eliminated. In this paper, a medium-frequency transformer (MFT)-based wind energy conversion system is proposed for such wind farms based on current source converters. The presented configuration consists of a medium-voltage permanent magnet synchronous generator that is connected to a low-cost passive rectifier, an MFT-based cascaded converter, and an onshore current source inverter. Apart from fulfilling traditional control objectives (maximum power point tracking, dc-link current control, and reactive power regulation), this study endeavors to ensure evenly distributed power and voltage sharing among the constituent modules given the cascaded structure of the MFT-based converter. In addition, this paper thoroughly discusses the characteristic of decoupling between the voltage/power balancing of the modular converter and the other control objectives. Finally, both simulation and experimental results are provided to reflect the performance of the proposed system.