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In this paper, a model predictive scheme is proposed to control the grid-connected high-power four-level diode-clamped inverter. To predict the future behavior of active and reactive grid power values and dc link capacitor voltages, a discrete-time model of the inverter is developed in synchronous reference frame. The controller uses all the possible switching states of the inverter for the prediction and evaluates them using a cost function. The switching state, which minimizes the cost function, is then chosen and applied at the next sampling interval. The switching frequency minimization is also achieved by including an extra constraint in the cost function. A simplified extrapolation method with reduced computational burden is proposed to safeguard the semiconductor devices during the dynamic changes in reference power values. The performance of the proposed method is investigated with the perturbations in the grid filter and dc link parameters. The feasibility of the proposed method is verified through simulation and experimental results, showing good dynamic and steady-state performance. [ABSTRACT FROM PUBLISHER]

A grid-tied cascaded H-bridge (CHB) converter with low frequency modulation techniques needs to meet power quality standards. At the same time, the effects of grid voltage harmonics on CHB converter's current harmonics must be considered in the modulation techniques. Furthermore, the dc link voltages of grid-tied converters need to be regulated. In this paper, an asymmetric selective harmonic current mitigation-pulse width modulation (PWM) (ASHCM-PWM) technique is used to meet the current harmonic limits of a power quality standard with the effects of grid voltage harmonics considered in the equation set of its optimization process. A voltage balancing technique based on the average power of each cell is derived to regulate the dc link voltages of the CHB converters without using dc voltage sensors. By using the proposed voltage balancing technique, the CHB converters do not need complicated dc link voltage controllers. As a result, the cost and complexity of the grid-tied converters can be significantly reduced. Simulations and experiments were conducted on a 7-level grid-tied CHB converter to validate the proposed voltage balancing technique with ASHCM-PWM modulation technique. [ABSTRACT FROM AUTHOR]

Grid-connected power conversion systems for renewable energy sources must fulfill several requirements, e.g., the high efficiency, the reduced cost and complexity, and, quite often, the boost capabilities that is usually achieved using a front-end dc–dc boost converter before the inversion stage, leading to a two-stage architecture. Meanwhile, single-stage power conversion systems, which perform the boosting operation within the inversion one, offer some potential advantages, in terms of reducing the complexity and the volume of the whole system. Among several proposed options, the split-source inverter (SSI) has been recently proposed by Abdelhakim et al. as an alternative option with some interesting features to the commonly used Z-source inverter. Taking into account that the SSI is controlled by a single parameter, i.e., its dc and ac sides are controlled by the modulation index, it is of paramount importance to investigate its control scheme in grid-connected mode, which has never been studied yet. Hence, this paper models the SSI dc side and proposes a modified modulation scheme combined with the commonly used synchronous reference frame control technique to achieve a decoupled control scheme of the SSI in grid-connected mode, i.e., the dc and the ac sides of the SSI can be controlled independently, which is convenient for many applications. The introduced control scheme is analyzed and simulated using a MATLAB/Simulink model, where a reduced scale 1-kVA grid-connected SSI is designed and simulated for the sake of experimental validation. Finally, the designed system is implemented experimentally to validate and verify the reported analysis and simulations. [ABSTRACT FROM PUBLISHER]

This paper proposes a new single-phase dc/ac converter topology with soft-switching operation. The proposed converter achieves soft-switching by using DCM (discontinuous current mode) operation and a common turn-off snubber capacitor connected to the dc terminals of a full-bridge configuration. One additional semiconductor switch is used to disconnect the snubber capacitor from the dc side, and allows the snubber capacitor to be discharged. The DCM operation realizes zero-current turn-on and the snubber capacitor achieves zero-voltage turn-off. The proposed converter can be applied to a grid-connected converter for domestic renewable energy and energy storage, including Photovoltaic and battery energy storage devices. This paper describes operation principles, control and modulation techniques as a grid-connecting converter. Experimental verification including loss analysis with a 1-kW pilot device is provided. [ABSTRACT FROM AUTHOR]

The ever-increasing utilization of sensitive loads in the industrial, commercial, and residential areas in distribution networks requires enhanced reliability and quality of supply. This can be achieved, thanks to self-healing features of smart grids that already include the control technologies necessary for the restoration strategy in case of a fault. In this paper, an analytical and global optimization model is proposed for the restoration problem. A novel mathematical formulation is presented for the reconfiguration problem reducing the number of required binary variables while covering more practical scenarios compared to the existing models. The considered self-healing actions besides the network reconfiguration are the nodal load-rejection, the tap setting modification of voltage regulation devices (incl. OLTCs, SVR, and CBs), and the active/reactive power dispatch of DGs. The voltage dependency of loads is also considered. Thus, the proposed optimization problem determines the most efficient restoration plan minimizing the number of de-energized nodes with the minimum number of self-healing actions. The problem is formulated as a Mixed-Integer Second Order Cone Programming (MISOCP) and solved using the Gurobi solver via the MATLAB interface YALMIP. A real 83–node distribution network is used to test and verify the presented methodology. [ABSTRACT FROM AUTHOR]

Single-phase universal-input ac–dc converters are needed in a wide range of applications. This paper presents a novel power factor correction (PFC) architecture that can achieve high-power density and high efficiency for grid-interface power electronics. The multitrack PFC architecture reduces the internal device voltage stress of the power converter subsystems, allowing PFC circuits to maintain zero-voltage-switching at high frequency (1 MHz–4 MHz) across universal input voltage range (85  $\rm V_{\text{ac}}$ –265  $\rm V_{\text{ac}}$). The high performance of the power converter is enabled by delivering power in multiple stacked voltage domains and reconfiguring the power processing paths depending on the input voltage. This multitrack concept can be used together with many other design techniques for PFC systems to create mutual advantages in many function blocks. A prototype 150 W, universal ac input, 12  $\rm V_{\text{dc}}$ output, isolated multitrack PFC system with a power density of 50 W/in $^3$ , and a peak end-to-end efficiency of 92% has been built and tested to verify the effectiveness of the multitrack PFC architecture. [ABSTRACT FROM AUTHOR]

A 1-φ hybrid nine-level inverter (H9LI) topology has been proposed in this paper. The proposed H9LI topology uses a simple phase disposition pulsewidth modulation strategy to generate nine-voltage levels in the output. The main advantage of this topology is that it has a low switch count (ten switches) compared to the existing nine-level inverter topologies. To regulate the voltage across auxiliary capacitor, two innovative control techniques are proposed, which are integrated with the inverter modulation technique itself. Hence, it does not require any extra voltage balancing circuits to maintain the voltage across the auxiliary capacitor and input dc capacitors. A major advantage of these control techniques is that they eliminate the sensing of the coupled inductor current. Another significant advantage of H9LI is that loss distribution among all the power switches is more uniform compared to existing nine-level inverters. Due to low part count and absence of extra voltage balancing circuits, the H9LI achieves higher efficiency (η ≍ 94.5%) and lower cost. Furthermore, the requirement of filter size reduces due to the presence of coupled inductor in H9LI. The proposed 1-φ grid connected H9LI is verified through MATLAB/Simulink simulations and validated through experiments on a laboratory prototype of 400-VA rating. [ABSTRACT FROM AUTHOR]

Grid-connected current control plays an important role in the renewable grid-connected system. This paper investigates the grid-connected current hysteresis control of the asymmetry three-level inverter. In order to effectively utilize asymmetry three-level inverter and conquer the disadvantages of traditional hysteresis control, the multistage hysteresis control and current predict hysteresis control are developed. In the multistage hysteresis control method, the switching times of main switches can be declined by regularly adjusting the bus voltage without altering the inductor and bandwidth. In addition, the current predict hysteresis control is developed, which adapts to proper bus voltage without dividing bus switching time. In order to overcome the invalidation issue of the bandwidth in hysteresis control, virtual sample technology is used without increasing real sample frequency. Both simulation and experimental tests have been conducted to verify the efficacy of the proposed methods. [ABSTRACT FROM AUTHOR]

Unbalanced grids introduce performance deterioration for Vienna rectifier topology by producing twice fundamental frequency ripples in dc-link voltage and input active/reactive power. A common current reference generation for the purpose of eliminating the input power ripple, such as dual-frame hybrid vector control, can maintain constant input power and eliminate ripples in dc-link voltage under light voltage unbalanced grids. Under severe unbalanced grids, this type of a control method will fail to work. This paper first analyzes the theoretical operation area of a constant power control method under unbalanced grids, and then a novel control method is proposed. The proposed control method can work under severe unbalanced grids by injecting a small amount of input power ripple and balance the performance of working area and output dc voltage ripples. Finally, the experiment results using the constant power control method are given and validate the performance of the proposed control method. [ABSTRACT FROM PUBLISHER]

This paper presents an improved full-bridge three-level (IFBTL) dc/dc converter for a wind turbine in a dc grid by inserting a passive filter into the dc/dc converter to improve the performance of the converter. The passive filter can effectively reduce the voltage stress of the medium frequency transformer in the IFBTL dc/dc converter. A modulation strategy, including two operation modes, is proposed for the IFBTL dc/dc converter. Then, a voltage balancing control strategy is proposed for the IFBTL dc/dc converter. Furthermore, the control of the wind turbine based on the IFBTL dc/dc converter in a dc-grid system is presented. Finally, a small-scale IFBTL dc/dc converter prototype was built and tested in the laboratory, and the results verify the theoretical analysis. [ABSTRACT FROM AUTHOR]

Solid-state transformers (SSTs) are an emerging technology that has been developed to improve the stability, reliability, and economic operation of distribution systems. These new transformers are composed of a medium ac voltage (MV) stage, a dc stage, and a low ac voltage (LV) stage. Passive and active dc links are used to construct the dc stage in SSTs in order to offer new functionalities, including hybrid (ac and dc) distribution, reactive power compensation, voltage/frequency regulation, power quality improvement, and distributed generation utilization. On one hand, a distribution SST has its ac stage connected to an MV level, which mandates specific power electronic converter (PEC) topologies, switching element capabilities, and filtering circuits. On the other hand, the dc-link stage has to provide isolation between the MV and LV levels, which requires the employment of isolated dc PECs. Part I of this work provides a review of SST designs and constructions (for deployment in distribution systems), in terms of the required technology, supported functionalities, and construction features. [ABSTRACT FROM AUTHOR]

In this paper, a model-predictive control of medium voltage, grid-tied four-level diode-clamped inverter for use in high-power wind energy conversion systems is presented. The control objectives such as regulation of net dc-link voltage, reactive power generation to meet the grid operator request, dc-link capacitor voltages balancing, and switching frequency minimization are included in the cost function. The latter objective is an important requirement for high-power converters, and this has been achieved without any modifications to the software or hardware configuration. The future behavior of the grid currents and dc-link voltages is predicted for all the possible switching states using the discrete-time model of the inverter, dc-link, inductive filter, and grid. The switching state that minimizes the cost function has been chosen and applied to the inverter directly. During different operating conditions, the switching frequency is regulated between 750 and 850 Hz with the help of a lookup-table-based weighting factor, and thus, the proposed methodology appears as a promising tool to control the high-power grid-tied inverters. The results obtained through the MATLAB simulations on 4 MVA/4000 V system and dSPACE DS1103-based experiments on 5 kW/208 V prototype are in a close relationship and thus validate the proposed control strategy. [ABSTRACT FROM AUTHOR]

This paper presents a dead-beat predictive direct power control (DPC) strategy and its improved voltage-vector sequences for reversible three-phase grid-connected voltage-source converters (VSCs). The instantaneous variation rates of active and reactive powers, by applying each converter voltage vector in 12 different sectors, are deduced and analyzed. Based on the power variation rates, it is found that the values of the predicted duration times for the two conventional active converter voltage vectors are less than zero when the grid-connected VSC operates as either a rectifier or an inverter. In order to solve this issue, two new alternative vector sequences are proposed and compared. Experimental results on a 1.5 kW reversible grid-connected VSC system are presented to validate the feasibility of the proposed voltage-vector sequences on the dead-beat predictive DPC strategy. [ABSTRACT FROM AUTHOR]

A simple decentralized interleaving PWM approach is proposed for parallel grid-tied converters, in order to achieve significant reduction of switching current ripples at the point of common couplings (PCC). First, the remote PCC voltage phase angle information is calculated through only the local measurement of a distribution generation (DG) unit converter and the estimation of the corresponding feeder voltage drops. With simple interpolations, the discretized PCC voltage angle information at a DG local controller is used as a novel synchronizer to effectively identify the carrier angle of DG units at the exact time instant of the PCC voltage phase angle zero crossing. Then, the relative digital carrier phase angles of parallel DG units are adaptively adjusted in a high-resolution manner until they are properly interleaved. It has been validated that the proposed modulation approach is effective under adverse situations with mismatched feeder impedances, processor crystal oscillator frequency deviations, and notable grid voltage frequency/magnitude disturbances. [ABSTRACT FROM AUTHOR]