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Power electronics plays a key role in electric vehicle technology in areas such as the battery charging and managing, dc distribution and motor drive systems, among others. There are, however, significant challenges to be addressed in terms of cost, performance, reliability and power density. This paper aims at proposing an improved on-board charger architecture taking advantage of a power pulsating buffer topology. The proposed architecture will enable to significantly reduce the dc-link capacitor size, enabling a change in its technology, and leading to a higher power density and higher reliability implementation. The proposed architecture is analyzed, its main design considerations are discussed and, finally, a 3.6-kW experimental prototype is designed and implemented to prove the feasibility of this proposal. As a conclusion, the proposed topology is recommended as a high-performance high-power-density OBC implementation for future EVs.

Distributed energy resources (DERs), such as photovoltaic (PV) sources, together with storage systems, such as battery energy storage systems (BESS), are increasingly present and necessary in our electricity distribution networks. Furthermore, the need for efficient use of energy from DERs, especially in developing countries and remote communities, must be addressed with the development of nanogrids (NGs), particularly DC NGs, and standalone PV systems with adequate control strategies. This paper investigates the control and dynamic operation of a standalone PV system. It consists mainly of three DC–DC power converters for the PV source interface, battery management, and load voltage control. A two-level modulation scheme is applied to each of these converters to switch them ON and OFF. A maximum power point tracking (MPPT) closed-loop voltage control system is implemented to make sure that the PV operates at optimum power regardless of the irradiance level or temperature, while battery voltage and load-side voltage control are also implemented to indirectly provide the required load power. The control of each of the converters is achieved by deriving their small-signal models using a state-space approach from which various control objectives are implemented. The DC-link is clamped by a BESS which acts as a backup source to provide power to the DC load in the absence of sufficient power from the PV panel. The dynamic operation of the whole system is enhanced by proposing a robust feedforward scheme that improves the response of the system in the presence of disturbances. The models are analyzed and implemented using PLECS, and numerical simulations are performed to validate the developed models and control schemes. [ABSTRACT FROM AUTHOR]

Multistage inverters containing DC-DC converters are more common in grid-tied photovoltaic (PV) systems, because of the low DC voltage value provided by the PV generator, which requires a two-stage topology. The challenge in the latter case is to control the DC-link voltage with an accurate estimation of the current injected into the grid by PV system. In this paper, a two-stage grid-tied PV design based on a high-gain DC-DC converter and a 7 level packed U cells (7L-PUC) inverter, controlled by Finite-Control-Set Model Predictive Control (FCS-MPC) is presented, with the proposal of a novel model for controlling the DC-link voltage by considering system losses. The simulation and experimental results demonstrate the high effectiveness of the proposed control strategy in terms of power quality as well as response time and accuracy under changes in weather conditions and demonstrate the feasibility of the proposed system. [ABSTRACT FROM AUTHOR]

There is currently a growing interest in replacing the internal combustion engine with electric motors in transportation applications. However, there are different problems related to electric motors for this application. One of them is the oversizing of the energy decoupling system since to ensure that the decoupling capacitor can store the power fluctuations, the capacitance required by the system is usually oversized. This leads to preference for the use of capacitors with construction technologies that have a lower lifetime than the remaining elements of the propulsion system, directly affecting the reliability of the system. In this article, the energy flow handled by the decoupling capacitor is analyzed considering the critical case of operation of an induction motor to minimize the capacitance required by the propulsion system; emphasizing the conditions that generate a higher energy return, from the motor mode of the electric machine to the decoupling capacitor. From the energy analysis, an equation for the capacitor calculation is obtained, involving proportionality factors that relate to the different operating powers, reducing up to 62.2% of the capacitance value required by the decoupling system, under conditions of maximum energy return in motor mode, compared to existing equations in the literature. [ABSTRACT FROM AUTHOR]

In this article, a novel method is proposed to reduce the dc-link capacitance of the brushless dc motor (BLDCM) system. In the proposed strategy, the charging mode of dc-link capacitor is designed to improve the energy stored by dc-link capacitor in the charging process instead of reducing the discharge time of dc-link capacitor used in previous article. The new modulation strategy and controller is designed to pump the dc-link capacitor voltage and ensure that it exceeds the ac voltage peak. The proposed modulation strategy has three vectors. The charging vector is used to improve the dc-link capacitor voltage, and the effective vector and zero vector are used to adjust the motor speed. For practical application, we provide an engineering calculation method to get the dc-link capacitance, and prove that the dc-link voltage can exceed the average voltage of the BLDCM. The experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a project method of the direct-current link necessary to decouple the rectification and inversion stages present in power electronics converters applied at Subsea Power System. The proposed methodology considers different aspects, such as topologies in the front-end and the back-end converters, its characteristic harmonics, the control strategies for both converters and the dynamical behavior of the load. The calculation memories of each capacitor, designed to be used in Variable Speed Drives that drive the subsea loads, are presented. The subsea power system was modeled with the PSCAD/EMTDC electromagnetic transient software to observe the influence of harmonics on the subsea power system and the voltage of the direct-current link. The results show that the proposed method is effective in filtering harmonics and even enhances the dc-link voltage-ripple compensation. [ABSTRACT FROM AUTHOR]

There is currently a growing interest in replacing the internal combustion engine with electric motors in transportation applications. However, there are different problems related to electric motors for this application. One of them is the oversizing of the energy decoupling system since to ensure that the decoupling capacitor can store the power fluctuations, the capacitance required by the system is usually oversized. This leads to preference for the use of capacitors with construction technologies that have a lower lifetime than the remaining elements of the propulsion system, directly affecting the reliability of the system. In this article, the energy flow handled by the decoupling capacitor is analyzed considering the critical case of operation of an induction motor to minimize the capacitance required by the propulsion system; emphasizing the conditions that generate a higher energy return, from the motor mode of the electric machine to the decoupling capacitor. From the energy analysis, an equation for the capacitor calculation is obtained, involving proportionality factors that relate to the different operating powers, reducing up to 62.2% of the capacitance value required by the decoupling system, under conditions of maximum energy return in motor mode, compared to existing equations in the literature.

This letter proposes a safe operating area (SOA) concept for film capacitors in dc-link applications. The SOA is presented by capacitor voltage and ripple current, considering the impact of ambient temperature, degradation, and parameter variance. The theoretical derivations and proof-of-concept experimental verifications are given. [ABSTRACT FROM AUTHOR]

In this article, authors implemented the hybrid system for continuous power distribution to fluctuating load demands. It contains a photovoltaic solar panel and wind turbine as renewable energy source, supercapacitor with a power convertor and a three-phase variation load. The combination of battery storage unit with super capacitor in hybrid system is proposed to solve many problems by its different technical features based on the system energy storage unit. Supercapacitor overcome the demerits of cells (batteries) such as charging and discharging cycles, critical charging current, reduced temperature coefficient and helps in extension of the electrical grid. Direct adjustment or indirect methods, such as to separate the energy storage unit output power adjustment, protect the hybrid energy storage components of the system. The optimal performance and desired control strategy is presented by MATLAB Simulink. [ABSTRACT FROM AUTHOR]

A novel three-phase resonant dc-link inverter with low energy consumption is presented to achieve efficient operation of the inverter. When the auxiliary resonant circuit is used to make the input voltage across bridge-arms become zero during every switching period, the main switching devices could achieve zero-voltage switching turn-on and zero-current switching turn-off. When the metal oxide semiconductor field effect transistor (MOSFET) or the insulated gate bipolar transistor (IGBT) is used as the main switching device, the lossless switching could be completed, and the capacitive turn-on loss caused by the internal junction capacitance of MOSFET and the turn-off loss caused by the tail current of IGBT are eliminated. The working process of the circuit and the realization condition of the soft-switching are analyzed. The experimental results on the three-phase prototype of 2.5 kW show that the switching devices achieve the soft-switching and the performance of the inverter is improved. Therefore, the novel topology is of great significance for improving the efficiency of the inverter. [ABSTRACT FROM AUTHOR]

Based on the brushless DC motor system with DC-link small capacitance powered by a single-phase AC power source, a boosting DC-link voltage strategy to reduce the commutation torque ripple of brushless DC motors is proposed in this paper. The control strategy utilizes the special topology of the motor system to boost the DC-link capacitor voltage in a specific zone during the non-commutation period. During the commutation period, the high voltage of the DC-link capacitor is released to meet the voltage requirement of the brushless DC motor during commutation. In order to reduce the commutation torque ripple and ensure the normal operation of the brushless DC motor, each rectifier cycle is divided into three zones according to the characteristics of the periodic change of the rectifier output voltage. Different operation modes are proposed for different zones. In DC-link capacitor boost voltage mode, the DC-link capacitor boosts the voltage to meet the voltage of the motor demand during the commutation period for achieving the purpose of reducing the commutation torque ripple. In this paper, the controller of the brushless DC motor system is designed and the experimental platform is built. The experimental results verified the correctness of the theoretical analysis and the feasibility of the proposed method.

Electromagnetic interference (EMI) filters are inevitable parts of power electronic systems. A novel EMI filter for single‐phase grid‐inverter is proposed in this study, to suppress the common‐mode (CM) EMI noise. The noise source and propagation path impedances are analysed, and the interaction between AC and DC side is studied. By connecting the ground terminal of the CM capacitors to the midpoint of the DC‐link, the noise coupling between AC and DC side is reduced. When compared with the state‐of‐the‐art of EMI filter, the proposed topology has advantages: the AC and DC filters can be designed independently; the impedance of the CM loop is improved; there is a remarkable CM EMI noise suppression effect on both AC and DC sides. Simulation and experimental results verify the theoretical analysis and proposed EMI filter structure. [ABSTRACT FROM AUTHOR]

Grid-tied inverters, used in renewable energy sources, are exposed to distortions emitted by various sources including the reference signal, external power grid, and DC-link along with harmonics created by the pulse width modulation unit. However, the effect of these sources on grid-tied inverter output, especially near the resonant frequency of the inverter's filter, is unknown. In this study, a comprehensive harmonic model of the grid-tied inverter is presented by considering all three types of external sources. The proposed model can be utilised for low and high-frequency harmonic emission of grid-connected inverters. A new analytical expression is introduced as an indicator of the maximum possible individual grid current harmonic in the case of harmonic injection of multiple external sources. The impact of series damping resistor on harmonic rejection ability of the inverter is analysed at the range of frequencies around resonance. The simulation and experimental results fulfil the proposed harmonic model of the inverter. [ABSTRACT FROM AUTHOR]

The reliability of a motor control based on a variable speed drive is an important issue for industrial applications. Most of these machines are inverter based induction motors and are used in specific and complex industrial installations. Unlike the induction motor, the feeding part is very delicate and sensitive to faults. In order to improve system performance, it is therefore very important for a researcher to know the impact of a fault on the whole of his drive system. This paper discusses the short-circuit fault of the DC-link capacitor of an inverter fed induction motor. The simulation results of this type of faults are presented and its impact on the behavior of the rectifier, the inverter as well as the induction motor analyzed and interpreted. [ABSTRACT FROM AUTHOR]

This paper proposes a power electronic module that uses a switched capacitor for retaining the integrity of the dc-link voltage of a variable speed drive (VSD) during a 0.2 s short-term power interruption (STPI). Ride-through was achieved through switched capacitor onto the dc bus. However, this technique presents a challenge of the high inrush currents during a ride through compensation. In this work both analytical and experimental investigations were conducted in order to reduce the in-rush currents and its impact on the performance of the VSD during the STPI. Inrush peak currents were reduced by approximately 90%. Experimental results showed torque pulsations of 12.8% and 14.3% at the start and end of dc-link voltage compensation, respectively. A method for sizing the switched capacitor and the inrush limiting resistors is proposed. This methodology is based on the use of readily available nameplate information of the VSD and the electric motor. The proposed module can be retrofitted to existing VSDs that are based on v/f control.

Nowadays, energy storage systems, such as batteries, are spreading in many applications. Among the kinds of batteries, the lithium-ion technology is one of the most promising solutions. Considering the photovoltaic (PV) plants, it is very important to perform a correct sizing of the battery pack to both maximise the self-consumption and minimise the total costs. In general, PV plants need a dc–dc converter to maximise the electric power that can be extracted from PV panels and a dc–ac converter to connect them to the ac grid. The battery pack can be connected in three different ways: dc coupled and ac coupled using a dedicated converter or through a direct connection on the dc-link between the dc–dc and dc–ac converters. In the present study, the last solution, without any dedicated converters, is used and a simple control strategy to both maximise the power extracted from the PV panel and regulate the charging/discharging of the battery is proposed.

This paper develops a new field weakening method for an integrated permanent magnet synchronous machine vehicle drive. This method adopts both the DC-link and the rotor speed as a feedback signals to generate the demagnetising current reference. This eliminates the effect of the rotor speed on the FW controller dynamics and ensures stable operation across the whole range of speeds. Mathematical analysis of the system is used to design the controller gains to achieve the desired dynamic response. A maximum torque per ampere (MTPA) strategy is included in the control design, with a linearised function to reduce the computational demand. Experimental results show stable and satisfactory operation at different speeds and load conditions. They also illustrate smooth transition between the MTPA operation and the FW operation when the rotor speed crosses base speed.

Direct current microgrids are attaining attractiveness due to their simpler configuration and high-energy efficiency. Power transmission losses are also reduced since distributed energy resources (DERs) are located near the load. DERs such as solar panels and fuel cells produce the DC supply; hence, the system is more stable and reliable. DC microgrid has a higher power efficiency than AC microgrid. Energy storage systems that are easier to integrate may provide additional benefits. In this paper, the DC micro-grid consists of solar photovoltaic and fuel cell for power generation, proposes a hybrid energy storage system that includes a supercapacitor and lithium–ion battery for the better improvement of power capability in the energy storage system. The main objective of this research work has been done for the enhanced settling point and voltage stability with the help of different maximum power point tracking (MPPT) methods. Different control techniques such as fuzzy logic controller, neural network, and particle swarm optimization are used to evaluate PV and FC through DC–DC boost converters for this enhanced settling point. When the test results are perceived, it is evidently attained that the fuzzy MPPT method provides an increase in the tracking capability of maximum power point and at the same time reduces steady-state oscillations. In addition, the time to capture the maximum power point is 0.035 s. It is about nearly two times faster than neural network controllers and eighteen times faster than for PSO, and it has also been discovered that the preferred approach is faster compared to other control methods.

Mitigation of commutation current ripple (CCR) in the brushless direct current (BLDC) motor drive using DC-DC converter based topologies are achieving widespread popularity. However, undesired alternating current (AC) components are presented in the DC-link voltage across the capacitor of the DC-DC converter which leads to a destabilization of the power supply during the commutation interval. In addition, undesired speed regulation and audible noise occur which deteriorates the motor performance. In order to encounter this problem, different conventional compensation techniques based on the low-pass filter (LPF) has been proposed. However, LPF requires a close relation between dynamic coupling and active compensation. In view of the limitation, this paper proposes a proportional-resonant (PR) compensator to stabilize the DC-link voltage. Performance of the PR compensator is tested on a combination of modified single-ended primary inductor converter (MSEPIC), DC-link voltage selector circuit is used in the proposed current ripple mitigation technique for BLDC motor drive. The PR compensator is utilized to stabilize the DC-link voltage whereas the DC-link voltage selector circuit is employed to achieve a regulated DC voltage from the MSEPIC converter for efficient current ripple suppression during the commutation interval. Simulation and experimental results verify the effectiveness of the proposed compensation scheme for current ripple mitigation technique of BLDC motor drive. The simulation and experimental results clearly reveal that the PR compensator effectively stabilized the DC-link voltage, which alleviates the CCR. [ABSTRACT FROM AUTHOR]

The non-conventional energy sources possess a major problem of power reliability due to their dependencies on the environment. Advance research and development in solar, wind and other renewable energy sources are needed to solve the problem of power demand and reliability. The proposed hybrid system incorporates three renewable energy systems consisting of photo-voltaic (PV), wind turbine (WT) and fuel cell (FC) systems working together to provide maximum power at DC-link. A vast deal of novel research is done for improving the efficiency of an overall system using maximum power point tracking (MPPT) method. In this paper, the developed fuzzy logic controller (FLC)-based MPPT method has been used to analyze PV, WT and FC with DC–DC converters. The FLC-based MPPT control method optimizes the output of the proposed hybrid system with variable inputs to extract maximum power. In order to fabricate a reliable hybrid system, there is a massive scope of research to develop multi-input renewable energy systems. [ABSTRACT FROM AUTHOR]

This paper develops a new field weakening method for an integrated permanent magnet synchronous machine vehicle drive. This method adopts both the DC-link and the rotor speed as a feedback signals to generate the demagnetising current reference. This eliminates the effect of the rotor speed on the FW controller dynamics and ensures stable operation across the whole range of speeds. Mathematical analysis of the system is used to design the controller gains to achieve the desired dynamic response. A maximum torque per ampere (MTPA) strategy is included in the control design, with a linearised function to reduce the computational demand. Experimental results show stable and satisfactory operation at different speeds and load conditions. They also illustrate smooth transition between the MTPA operation and the FW operation when the rotor speed crosses base speed. [ABSTRACT FROM AUTHOR]

This outcome of this research paper improves the quality and performance of the power system by using a four-quadrant chopper circuit in the DC -LINK of the variable speed drive systems (VSDS). In addition, the effects on reducing the ripple factor for both the current and voltage in DC-LINK are illustrated. In this study, a variable speed drive system is simulated and designed with the proposed chopper. Furthermore, the control system of pulses for the transistors is determined. Finally, a discussion of the results is introduced. The given results show the advantages of using the proposed chopper circuit with variable speed drive systems. Likewise, the superiority of the proposed method over other newly suggested techniques is verified by several simulation scenarios. [ABSTRACT FROM AUTHOR]

Shunt active power filters (SAPFs) have been widely used to improve power quality of the grid by mitigating harmonics injected from nonlinear loads. This paper presents a new method for improving the performance of SAPFs using neutral-point-clamped (NPC) three-level inverters. NPC three-level inverters often suffer excessive voltage fluctuations at the neutral-point of DC-link capacitors, which may damage switching devices and cause additional high harmonic distortion of the output voltage. In order to solve the problem, two compensating schemes are proposed to restrict voltage fluctuation in the inverters. The first is voltage dependent, adopting a voltage compensation method, while the second is current dependent, using a current compensation method. The paper describes the respective circuit architectures and principles of operation. Corresponding models are mathematically formulated and evaluated under typical balanced and unbalanced working load conditions. The results show that both schemes are able to alleviate considerably voltage oscillations and hence harmonic distortions, and the current-compensated NPC inverter outperforms the voltage-compensated NPC inverter. Consequently, it is shown that the proposed approaches are effective and feasible for improving power quality of the grid when connected to nonlinear loads. [ABSTRACT FROM AUTHOR]

Wind is one of the most develop renewable energy to help human meet the electricity needs as availability is abundant. Instrument which can be used to convert wind energy into electrical energy is an induction generator. In this final project will discuss about the operation of the wind turbine with induction generator controlled using back to back voltage source inverter with grid connected system low voltage 380 V. Switching of back to back voltage source inverter was designed in average model.In back to back voltage source inverter, there are two converters that are machine side converter and grid side converter. Machine side converter has function to regulate the voltage and frequency of generator and turbine speed in order to the wind turbine can generate maximum power at any wind speed with method volt / hetrz constant control. Grid side converter has function to adjust the DC voltage keep be contant by synchronizing the phase angle between the converter output and grid using current controlled voltage source inverter method.The simulation results showed that wind turbine always generated the maximum power at any wind speed. Voltage and frequency of Generator is stable and directly proportional to the wind speed and the dc link voltage is always constant so the power flow can bidirectional. Therefore, back-to-back voltage source inverter is suitable for controlling wind turbine using an induction generator.

Abstrak— Photovoltaic (PV) merupakan sumber energi terbarukan yang paling banyak dijumpai di alam serta merupakn energi alternatif yang sangat pesat perkembangannya. Untuk mengahasilkan daya, sebuah PV dipengaruhi sebuah nilai intensitas cahaya matahari yang mengenainya. Sebuah sistem PV membutuhkan sebuah kontrol yang bertujuan untuk meningkatkan efisien daya PV tersebut. Kontrol ini adalah Maximum Power Point Tracking (MPPT) yang dapat mengoptimalkan daya yang dihasilkan oleh PV. Sebuah PV hanya menghasilkan nilai tegangan yang rendah, untuk itu perlu menggunakan koverter DC-DC step up untuk menaikan rasio tegangan DC tadi. Untuk mengoptimalkan sistem ini, diperlukan sebuah konverter yang efisien dan dapat menghasilkan rasio konversi tegangan yang tinggi. Pada penelitian menggunakan firefly algoritm (FFA) dan modified perturb and observe (P&O) sebagai MPPT untuk mendapatkan nilai daya optimal pada keluaran PV. Konverter DC-DC yang digunakan adalah hybrid cuk converter boost mode yang memiliki rasio tegangan yang tinggi. Dari DC-link kemudian masuk ke inverter (VSI) yang diinterkoneksi dengan grid menggunakan current control. Hasil analisis simulasi menunjukan bahwa FFA dan P&O mampu menghasilkan daya PV yang optimum dengan riak yang kecil dan konverter hybrid cuk converter boost mode dapat menghasilkan rasio tegangan yang lebih besar dibandingkan konverter cuk biasa. Kata Kunci — PV, MPPT FFA, MPPT P&O, Hybrid Cuk Converter, DC-Link, Inverter Grid Connected

With the development of Microgrids (MG) in distribution networks, how to coordinate the reconfiguration of distribution networks with the energy sharing of Direct Current (DC)-linked multi-MG is an unsolved problem. In this paper, a multi-party optimization framework is proposed, the involving parties include the Distribution Network Operator (DNO), the Multi-MG Coalition Operator (MCO), and the MG operator. For the DC-linked MGs, the MCO is obligated to coordinate the energy sharing, a stochastic optimal scheduling model for the MG coalition is formulated, considering the uncertainties of Photovoltaic (PV), Wind Turbines (WT), and load power. Moreover, a billing mechanism is designed to distribute the cost of each MG participated in the energy sharing. For the distribution network, an event triggered dynamic reconfiguration model is proposed. Based on the scheduling results of MCO, the decisions of switch operations are finally co-decided by the expected exchanging power of the MGs and the real-time errors caused by uncertainty factors. Finally, a modified IEEE-33 nodes distribution system are used to test and verify the effectiveness of the method. [ABSTRACT FROM AUTHOR]

In this paper, neuronal direct power control (DPC) strategy is applied for a doubly fed induction generator (DFIG) based wind energy generation system. Used in three level neutral point clamped (NPC) rectifiers, to directly control the active and reactive power, switching vectors for rotor side converter were selected from the optimal switching table using the estimated stator flux position and the errors of the active and reactive power, also the grid side is controlled by direct power control based a grid voltage position to ensure a constant DC- link voltage. This approach is validated by using MATLAB/SIMULINK software and simulation results can prove the excellent performance of this control as improving power quality and stability of wind turbine. [ABSTRACT FROM AUTHOR]

A sensorless stand-alone control scheme of a doubly fed induction generator (DFIG)-DC system is investigated in this paper. In this layout, the stator voltage is rectified by a diode bridge that is directly connected to a dc bus. The rotor-side voltage source inverter is the only controlled converter required in this system and is directly powered by the same dc bus created by the stator-side rectifier. DC voltage and stator frequency are regulated by two independent proportional-integral regulators that give the references for inner current controllers implementing field-oriented control. As it is capable of creating a stable and regulated dc bus, this system can be conveniently adopted to supply dc loads or to form a dc grid. Due to the constraint imposed by the stator diode bridge, the DFIG has to operate under a constant stator voltage, and the conventional stator field-oriented control implemented in stand-alone ac DFIG must be modified. This paper presents the control structure and the theoretical framework for the controller synthesis. Simulation and experimental validations on a small-scale rig are included. [ABSTRACT FROM PUBLISHER]

This paper proposes a novel harmonic suppression scheme for two-level inverter fed three-terminal induction motor drives using switched capacitive filter. Capacitor fed H-bridges used as filters are cascaded to conventional two-level inverter to eliminate fifth- and seventh-order harmonics for the full modulation range including a six-step operation. For the first time, two-level dodecagonal voltage space vector is implemented with single dc supply for three-terminal induction motor drive. Enabling the switched capacitive filtering at low-voltage domain and shifting the high frequency switching to the switched capacitive filter is shown. A uniform pulse width modulation technique is shown which charges and maintains the capacitor voltages while eliminating the fifth- and seventh-order harmonics for the full speed range. [ABSTRACT FROM AUTHOR]

This paper proposes a new method to reduce the ripple current of the DC-link capacitor in a two-level voltage source inverter (VSI), with a discontinuous pulse-width modulation (DPWM). In real applications, a capacitor block is very bulky, due to the parallel connection of several capacitors that share the value of the ripple current. Hence, it contributes significantly to the volume and weight of the whole system. Conventional DPWM is used to minimize the amount of switching for the power transistors, therefore, reducing stress and power loss. This leads to increased efficiency and reliability of the system. Nevertheless, the reduction of the DC link ripple current is still not optimal. Therefore, the proposed method introduces a PWM phase-shift technique to provide further reduction of the DC-link ripple current in a DPWM-based VSI. The efficacy of the proposed method is confirmed by simulation and experimental results.

This paper describes an alternative to connect power converters to a direct-current network with an inductor circuit. The circuit allows the connection of converters through a coil and avoids short-circuit currents with different instantaneous values of voltage output. A description of the calculation and the choice of components together with a real implemented example in a dc network within Smart City project (Endesa Utility) is presented. [ABSTRACT FROM PUBLISHER]

The field-weakening operation of a doubly fed induction generator (DFIG) connected to a dc-link is analyzed in this paper, in order to optimize the efficiency. In the considered DFIG-dc system, the stator feeds a constant-voltage dc link by a diode bridge, and the rotor current is controlled using a voltage-source inverter connected to the same dc link. Since the stator voltage amplitude is imposed by the dc-link, a variation in stator flux magnitude results in a frequency change. However, in this system, a stator frequency variation over a wide range can be accepted, if the rated flux is not exceeded. Thus, the stator flux amplitude can be adjusted through the magnetization current component by the voltage-source inverter and according to the load level, in order to reduce losses in the machine and in the inverter. This paper presents an optimization analysis and simplified formulae determining the optimal reference magnetization current in the control of the system. Conversely to field weakening in conventional drives, in this case, the enabling of field weakening control is not dependent on rotor speed, but depends on the reference torque. The proposed optimal control is validated through simulation and experimental results. [ABSTRACT FROM PUBLISHER]

The integration of renewable power sources with power grids presents many challenges, such as synchronization with the grid, power quality problems and so on. The shunt active power filter (SAPF) can be a solution to address the issue while suppressing the grid-end current harmonics and distortions. Nonetheless, available SAPFs work somewhat unpredictably in practice. This is attributed to the dependency of the SAPF controller on nonlinear complicated equations and two distorted variables, such as load current and voltage, to produce the current reference. This condition will worsen when the plant includes wind turbines which inherently produce 3rd, 5th, 7th and 11th voltage harmonics. Moreover, the inability of the typical phase locked loop (PLL) used to synchronize the SAPF reference with the power grid also disrupts SAPF operation. This paper proposes an improved synchronous reference frame (SRF) which is equipped with a wavelet-based PLL to control the SAPF, using one variable such as load current. Firstly the fundamental positive sequence of the source voltage, obtained using a wavelet, is used as the input signal of the PLL through an orthogonal signal generator process. Then, the generated orthogonal signals are applied through the SRF-based compensation algorithm to synchronize the SAPF's reference with power grid. To further force the remained uncompensated grid current harmonics to pass through the SAPF, an improved series filter (SF) equipped with a current harmonic suppression loop is proposed. Concurrent operation of the improved SAPF and SF is coordinated through a unified power quality conditioner (UPQC). The DC-link capacitor of the proposed UPQC, used to interconnect a photovoltaic (PV) system to the power grid, is regulated by an adaptive controller. Matlab/Simulink results confirm that the proposed wavelet-based UPQC results in purely sinusoidal grid-end currents with total harmonic distortion (THD) = 1.29%, which leads to high electrical efficiency of a grid-connected PV system. [ABSTRACT FROM AUTHOR]

In this paper, an improved direct power control with space vector modulation for a 3-phase 3-level neutral point clamped converter supplied by unbalanced and/or distorted grid voltage is proposed. The main objective of the control scheme is to obtain balanced and sinusoidal input current with unity power factor under nonideal voltage supply. To achieve the control objectives, compensated active and reactive powers are calculated and added to the referencing one. A theoretical analysis of active and reactive power under a nonideal source is clearly demonstrated. In order to calculate the compensated powers, the extraction of positive, negative, and harmonic sequences of voltage and current is needed and a multiple-complex coefficient filter-based method is used for rapid and accurate extraction. The proposed controller also ensures voltage balance in DC-link capacitors using redundant vectors in the space vector modulation block without the need for additional components. Simulation results verified the effectiveness of the modified control strategy. [ABSTRACT FROM AUTHOR]

This paper describes a single-phase full-bridge inverter that possesses limited current ripple at the dc link while providing a sinusoidal square power at the ac output. This is achieved through the addition of an extra pair of switches and complementary control for the full-bridge inverter. The extra switches operate to prevent the double-line frequency ripple current from flowing into the input of the inverter. In doing so, the pulsation component of the sinusoidal square output power is confined to flow between the output capacitors and the load. Thus, the dc link input only supplies the dc component of the output power. Simulation and experimental results validating the proposed solution are presented. [ABSTRACT FROM PUBLISHER]

This paper presents a self-sensing technique for the field-oriented control and frequency regulation of a doubly fed induction generator connected to a dc-link. In this system, the stator circuits are connected to a dc-link through a diode bridge and the rotor circuits are controlled by a voltage source inverter connected to the same dc-link. As the diode bridge maintains the fundamental harmonics of the stator current and voltage approximately in phase, an almost zero average d\mbox-axis stator current results in the stator flux reference frame. This property is used to estimate the slip angle, required to implement the field orientation in the self-sensing technique in loaded conditions. At no load the system is controlled using a different methodology. The analysis and synthesis of the control chains are presented by analytic relations. The sensitivity study shows that the method exhibits reduced sensitivity to the parameter mismatch, resulting in a small orientation error. Experimental results confirm the good performance of the proposed method. [ABSTRACT FROM PUBLISHER]

This paper proposes a technique to suppress low-order harmonics for an open-end winding induction motor drive for a full modulation range. One side of the machine is connected to a main inverter with a dc power supply, whereas the other inverter is connected to a capacitor from the other side. Harmonic suppression (with complete elimination of fifth- and seventh-order harmonics) is achieved by realizing dodecagonal space vectors using a combined pulsewidth modulation (PWM) control for the two inverters. The floating capacitor voltage is inherently controlled during the PWM operation. The proposed PWM technique is shown to be valid for the entire modulation range, including overmodulation and six-step mode of operation of the main inverter. Experimental results have been presented to validate the proposed technique. [ABSTRACT FROM PUBLISHER]

With the development of wind power generation system and requirement of large‐scale and long‐distance power transmission, it is greatly important for wind farm to achieve the high effective DC grid connection technology. This study presents a novel grid connection topology for doubly‐fed induction generator (DFIG) connected to a DC‐link, in which a stator side converter and rotor side converter fed by a common DC bus are employed. Coordinated control method for the converters is proposed to regulate the electromagnetic torque directly based on the air‐gap flux orientation technique. Compared with the traditional grid connection system, the proposed system has a lot of advantages such as simpler structure, lower requirement for the converter capacity and higher power transmission efficiency. The power distribution between stator side converter and rotor side converter is analysed based on the proposed grid connection topology. Finally, DFIG‐based experimental system is developed to validate the correctness and availability of the proposed DC grid connection topology and control strategy. [ABSTRACT FROM AUTHOR]

This paper deals with a new conversion topology for doubly-fed induction generators (DFIGs) suitable for wind energy conversion systems integrated in microgrids. It consists of a DFIG which is fed by a pulse width modulation converter on the rotor and with the stator connected to a dc grid through a diode rectifier. In this configuration, the stator diode rectifier and the rotor-side inverter share the same dc bus, so that the conventional grid-side inverter is avoided. Since only a diode rectifier designed for the full power and a reduced power inverter are required, this layout allows a cheap and effective integration of the DFIG with other generating and storage systems connected to the same dc bus. A simple control technique suitable to regulate the power delivered to the dc grid is proposed. The scheme is based on the regulation of the amplitude of a suited fraction of the rotor flux linkage: the optimal value of this fraction is theoretically deduced in order to minimize the DFIG derating due to the current harmonics. The effectiveness of the proposed control is proven by simulations and experimental tests. [ABSTRACT FROM AUTHOR]