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This paper presents a model-predictive sliding-mode control (MPSMC) scheme for a three-phase ac/dc converter to achieve better stability and dynamic performances. In the conventional model-predictive control method, a proportional–integral (PI) controller is used to generate the active power reference. This traditional model-predictive PI control (MPPIC) scheme, however, produces a large overshoot/undershoot, a long settling time, and a large steady-state error under disturbances. To overcome these deficiencies, a sliding-mode controller is employed to replace the PI controller. Since the control law and the controller are designed based on the system model, the proposed MPSMC scheme can reduce the effects of unexpected disturbances, such as the output voltage demand and the resistance load variations. Both methods have been simulated in MATLAB/Simulink during various disturbances. Compared with the performances of MPPIC, the results obtained from MPSMC show that the settling time of the dc voltage can be minimized by about 91%, and the overshoot can be eliminated from 9.13% during the steady-state progress. The active and reactive power from MPSMC can also be controlled to the desired values, respectively, with a much smaller overshoot/undershoot and a faster response speed. Similar dynamic improvements can be achieved with MPSMC when the dc voltage demand varies. The simulation results are validated by experimental results. [ABSTRACT FROM AUTHOR]

State of charge (SoC) imbalance among batteries in a battery energy storage system (BESS) degrades the system performance and may lead to safety issue. A bidirectional multiple-input Ćuk converter for the BESS is proposed to prevent batteries from SoC imbalance issue. Compared to the traditional BESS, the battery balancing and voltage/current regulation subsystems are combined into one. As a result, the overall system complexity is significantly reduced. Moreover, the current flow of each battery is self-adjusted according to its terminal voltage. Therefore, the system does not require sophisticated control algorithm for battery balancing. Moreover, the proposed system has no energy dumping and energy transferring between batteries, which avoids unnecessary energy lose. Due to the nature of multiple-input converter structure, the proposed system can handle certain component failure. The proposed approach of designing the BESS has been investigated through simulation and validated experimentally. [ABSTRACT FROM PUBLISHER]

Finite-state predictive torque control (FS-PTC) of an induction motor (IM) drive has been widely investigated for two-level voltage source inverter recently. This control method suffers from high and variable switching frequencies in a wide range, due to the limited number of available voltage vectors of the power converter. In order to take advantage of multilevel inverter drives which offer the benefits of low harmonic distortion of the stator currents, torque ripple, and low switching frequency, this paper proposes the integration of the FS-PTC with a three-level neutral-point clamped (3L-NPC) inverter driven IM drive. The drawback inherited from the topology of 3L-NPC voltage source inverter (VSI), such as neutral-point voltage, is easily handled by treating it as a variable to the cost function. Similarly, apart from the inverter topology itself, the average switching frequency is reduced further, and is maintained almost constant over a wide speed range. The effectiveness of the proposed FS-PTC in terms of torque and flux responses, capacitor voltage balancing, and low average switching frequency is validated through experimental results. [ABSTRACT FROM AUTHOR]

Unbalanced load currents not only give rise to unbalanced voltages but also adversely affect the performance of the conventional current-limiting mechanisms. The latter might result in overcurrent stress on the distributed energy resources (DERs) or current harmonics. In this paper, a novel decentralized control method is proposed to improve the power quality and protect DERs from overload. The proposed controller makes use of the model predictive control (MPC) technique to minimize the voltage unbalance, improve current limiting, and prevent active power overload. The MPC is combined with the V-I droop method to realize coordinated operation with fast dynamic response. The proposed method is tested on the CIGRE benchmark microgrid. Simulation results demonstrate that the proposed method improves power quality but also allows for operation close to the maximum load capacity without imposing DERs to overload. [ABSTRACT FROM PUBLISHER]

Single-stage power-factor-corrected (S2PFC) power supplies usually suffer from high voltage stress, due to lack of control on the intermediate bus capacitor voltage. In the past, analysis of such voltage stress was mostly based on steady-state condition without providing sufficient explanation during the transient circuit operation. This paper revisits the problem at circuit level and reports that the root cause is due to the inherent negative current feedback property of the output inductor or the transformer operating in continuous conduction mode (CCM). Based on the finding, this paper further proposes a new approach to reducing the voltage stress by adding an auxiliary circuit branch to existing S2PFC converters. The additional circuit branch limits the effect of negative current feedback by suppressing the change of output current slope due to change of load. This assists the pulsewidth modulation controller to track the change of load better such that the bus capacitor voltage range is reduced through duty cycle control. The auxiliary circuit branch also reduces reverse-recovery-related losses of the converter under CCM operation. A laboratory prototype using the popular boost PFC converter combined flyback dc/dc converter was built and tested to confirm the analysis and effectiveness of the approach. [ABSTRACT FROM AUTHOR]

In this paper, the two-input buck converter is proposed as the dc/dc stage for photovoltaic (PV) cascaded converters. This converter is attractive for this application because it is cost effective and reliable and can achieve dual maximum power point tracking (MPPT) with only one power transistor. However, due to the simplified and integrated structure, the nonlinear characteristics of the converter and the two PV arrays complicate the control. By means of a small-signal modeling, the control theme of the two PV voltages is formulated, and the effect of the nonlinearities is presented. It is shown that, while fast voltage dynamics are achieved for the first input, the second-input voltage response depends on the second-stage converter control. Simulation and experimental results are reported to validate the theoretical analysis, showing the dual MPPT capability. [ABSTRACT FROM PUBLISHER]

A single-switch nonisolated dc/dc converter for a stand-alone photovoltaic (PV)-battery-powered pump system is proposed in this paper. The converter is formed by combining a buck converter with a buck-boost converter. This integration also resulted in reduced repeated power processing, hence improving the conversion efficiency. With only a single transistor, the converter is able to perform three tasks simultaneously, namely, maximum-power-point tracking (MPPT), battery charging, and driving the pump at constant flow rate. To achieve these control objectives, the two inductors operate in different modes such that variable switching frequency control and duty cycle control can be used to manage MPPT and output voltage regulation, respectively. The battery in the converter provides a more steady dc-link voltage as compared to that of a conventional single-stage converter and hence mitigates the high voltage stress problem. Experimental results of a 14-W laboratory prototype converter with a maximum efficiency of 92% confirmed the performance of the proposed converter when used in a PV-battery pump system. [ABSTRACT FROM PUBLISHER]

This paper proposes a current control strategy with zero steady-state tracking error for grid-connected boost inverters. Two boost converters are controlled separately to achieve both output current tracking and balanced output voltages. Based on cascading control and feedback linearization, the inner- and outer-loop controllers are as the combination of the inversion of boost converter model and the output error compensation. After the boost converter model is linearized, proportional and resonant controllers are derived from the internal model principle to achieve zero tracking error. Experimental results confirm that the proposed control achieves good current tracking to meet stringent grid-connection harmonics standards. [ABSTRACT FROM AUTHOR]

A transformerless single-stage single-switch ac/dc converter is presented in this paper. The converter allows a portion of the input power to be processed once only, resulting in enhanced conversion efficiency. Additionally, due to the absence of a transformer, the size and manufacturing cost of the converter can be reduced. The intermediate bus voltage is well kept below 400 V while maintaining high power factor even at light load and high line-input conditions. Extended experimental results on a 100-W hardware prototype for universal input-voltage range (90–270 Vrms) are given to confirm the theoretical analysis and performance of the proposed converter. [ABSTRACT FROM PUBLISHER]

This article addresses the design of reconfigurable single-inductor multiport converters with bidirectional power flow, no cross regulation, and simple control. The design uses both the voltage-source-mode and current-source-mode cells, thus allowing a full range of connectivity. The proposed single-inductor converters offer high modularity and scalability while offering bidirectional power flow and no cross regulation. The single-inductor structure reduces the overall size. The adoption of voltage-source-mode and current-source-mode cells leads to high modularity. High scalability is achieved due to arbitrary ports being allowed to the derived converters. Moreover, the topology inherently achieves no cross regulation among the output ports. The ports of the derived converters are reconfigurable, permitting transformation among single-input multi-output mode, multi-input multi-output mode, and multi-input single-output mode. Through the transformation of operating modes, bidirectional power flow is achieved. Thus, regenerative loads can be integrated seamlessly. In terms of control, the absence of cross regulation permits the adoption of very simple control design, leading to high flexibility. Thus, the derived converters can integrate multiple and various kinds of terminating sources and loads simultaneously with simple control methods. A reconfigurable single-inductor four-port converter is presented for illustration. Finally, experimental results are presented to verify the analytical findings. [ABSTRACT FROM AUTHOR]

This paper presents a new approach to controlling and optimizing a single-stage boost-integrated full-bridge dc–dc converter for a stand-alone photovoltaic-battery-powered dc motor system by combining pulse-frequency modulation (PFM), pulsewidth modulation (PWM), and phase angle shift (PAS). Unlike most of the existing multiport dc–dc converters, which aim at regulating the output voltage (first- or second-quadrant operation), the dc motor load requires both voltage and current reversals (four-quadrant operation). The converter is able to perform three tasks simultaneously: maximum power point tracking (MPPT), battery charging/discharging, and driving the dc motor at variable speeds including bidirectional and stall motions. To achieve these control objectives, the boost inductor and the motor inductance operate in different modes such that PFM and PWM can be used to achieve MPPT and a wide motor voltage range, respectively. By properly adjusting the PAS of the duty cycles, the capacitor and battery rms current value can be reduced, while the operation of the converter remains unchanged, hence improving the conversion efficiency. Experimental results of a 26-W laboratory prototype converter confirmed the proposed design and operation and the efficiency improvement by 2–6%. [ABSTRACT FROM AUTHOR]

This paper proposes a distributed control strategy for coordination of distributed energy resources (DERs) in low-voltage resistive microgrids. The proposed framework consists of two level structures; primary and secondary control. Unlike the existing distributed control solutions, the proposed method is based upon the practical assumption of network impedance being resistive. The primary control level consists of a V-I droop mechanism, where GPS timing is used to synchronize the control agents. A consensus-based distributed secondary control method is introduced to improve the voltage regulation and load sharing accuracy of the V-I droop method. In the proposed approach, the d-axis component of the voltage is altered so as to regulate the average microgrid voltage to the rated value while guarantying proper sharing of active power among the DERs. Additionally, the q-axis component of voltage is adjusted to perform proper current and, accordingly reactive power sharing. The proposed control methodology accounts for the distribution line impedances. It features a plug-and-play environment; prior system knowledge is not required, and an arbitrary DER can enter the microgrid without any need for additional synchronization. An ac microgrid is prototyped to experimentally demonstrate the efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

In this paper, a grid-tied residential smart microgrid topology is proposed, which integrates energies of a photo-voltaic (PV), a fuel cell, and a battery bank to supply the local loads through a combination of electric and magnetic buses. In contrast to multiple-converter-based microgrids with a common electric bus, using a multiport converter with a common magnetic bus can effectively reduce the number of voltage conversion stages, size, and cost of the renewable energy system and isolates the conversion ports. The resultant topology utilizes a centralized system level control that leads to a faster and more flexible energy management. The proposed microgrid is able to operate in multiple grid-connected and off-grid operation modes. A fuzzy controlled energy management unit (EMU) is designed to select the appropriate operation mode considering both real-time and long-term predicted data of the energy generation and consumption. A mode transition process is designed to smooth the mode variation by using a state transition diagram and bridging modes. To improve the microgrid operation performance, appropriate control techniques, such as synchronized bus-voltage balance, are used. A prototype of the proposed microgrid and the EMU are developed and experimentally tested for three different energy management scenarios. Energy distribution and energy cost analysis are performed for each scenario to validate the proposed control method. [ABSTRACT FROM AUTHOR]

To support the development of high-frequency ac microgrids in terms of compact design, high-voltage gain and low total harmonic distortion (THD), a buck–boost dual-leg-integrated step-up inverter is proposed in this paper. The inverter is formed by integrating a buck–boost converter into a conventional single-phase full-bridge inverter by sharing the upper switch and the body diode of the lower switch in both bridge-legs. Consequently, the component count is significantly reduced over the step-up inverter counterparts. In addition, to address the drawbacks of hybrid modulation methods adopted by existing dual-leg-integrated inverters, such as double-variable control, and high THD of output voltage/current at high input voltage and heavy load conditions, unipolar frequency doubling sinusoidal pulse width modulation scheme is adopted in this inverter. As a result, the modulation ratio M becomes the only control variable to regulate the output voltage/current and the control is simplified. The THD of the proposed inverter output can remain low throughout the entire input voltage range and load power range. This paper presents the topology derivation procedure, operation principle, and steady-state characteristics of the proposed inverter. To validate the effectiveness of theory, experimental results of a 400 W hardware prototype, where the output voltage frequency is at 500 Hz, are reported. [ABSTRACT FROM PUBLISHER]

In this article, a low computational burden model predictive control (MPC) strategy without weighting factor is proposed for the single-phase cascaded H-bridge CHB converters. To reduce the switching state candidates, a hierarchy control algorithm is proposed. The grid current is controlled by selecting a subregion from the designed 2-D control plane, instead of the entire area. Two vectors are chosen in one sampling period for more accurate tracking. Then, the voltage balancing is achieved by selecting the optimal switching state from the subregion candidates to form the above two vectors. The cost function can be constructed of one variable: load voltage. Therefore, the weighting factor can be eliminated. No tuning or retuning processes are required in the proposed method. To reduce the computational time further, the principle of eliminating the switching state candidates operating the same voltage balancing performance is proposed. Conventional and proposed MPC methods are verified by experimental tests via a laboratory setup of a three-cell connected CHB converter. Steady-state and transient operations demonstrate that the proposed method guarantees less distortion grid current and shorter execution time (reduced from 15 to 3 $\mu s$). Fast response speed to variations in voltage reference and load resistance can be achieved t. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hierarchical control strategy for improvement of load sharing and power quality in ac microgrids. This control framework is composed of a droop-based controller at the primary level, and a combination of distributed power sharing and voltage conditioning schemes at the secondary level. The controllers in the primary level use GPS timing technology to synchronize the local reference angles. The voltage reference of each distributed generation is adjusted according to a voltage–current (V–I) droop characteristic to enable proper current and power sharing with a fast dynamic response. The droop coefficient, which acts as a virtual resistance, is adaptively changed as a function of the peak current. This strategy not only simplifies the control design but also improves the current sharing accuracy at high loading conditions. The distributed power sharing scheme uses consensus protocol to ensure proportional sharing of average power. The voltage conditioning scheme produces compensation signals at fundamental and dominant harmonics to improve the voltage quality at a sensitive load bus. Experimental results are presented to validate the efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a new single-source three-phase seven-level inverter with an inherent three-time voltage boosting capability for medium-voltage applications. The proposed topology is comprised of series connection of two switched-capacitor (SC) networks with an added half-bridge module per phase. Each of such integrated SC networks requires a single capacitor associated with three active power switches. The three-time voltage boosting feature of the proposed topology can reduce the dc-link voltage requirements by 50% in comparison to the traditional neutral point clamped (NPC), flying capacitors, active NPC (ANPC), hybrid clamped ANPC, and cascaded H-bridge topologies, and 75% to advanced ANPC topologies. It can also reduce the number of required switches and capacitors as well as their voltage stresses compared to those state-of-the-art topologies reported in the literature. By integrating “n” number of added SC networks in the proposed seven-level basic topology, the number of output voltage levels can be extended to 2n+3 per phase. A finite control set model predictive control algorithm is also derived to control the converter in both the active and reactive power exchanges modes without distorting the generated grid current quality. The capacitor voltage balancing is inherent in the proposed topology, and thus, there is no need for any additional voltage balancing circuit, which further reduces the control complexity. The performance of the proposed topology and its control algorithm are validated by several measurement results. [ABSTRACT FROM AUTHOR]

This article presents a novel dual-mode five-level common grounded type (5L-DM-CGT) transformerless inverter topology for a medium-power application with a wide input voltage range (200–400 V). It consists of nine semiconductor switches, two inner flying-capacitors, and a small LC filter at the output side. Due to the direct connection of the negative terminal of the photovoltaic to the neutral point of the grid, there is no leakage current in the 5L-DM-CGT. Depending on the magnitude of the input voltage, the converter can operate in both buck and boost mode to produce the same ac output voltage. The theoretical analysis shows the advantages of the dual-mode inverter for various industrial applications. Finally, the laboratory test results are presented to verify the theoretical analysis. Measurement results show that the proposed inverter rated at 1 kW has around 97±1% efficiency over a wide range of load with a peak efficiency of 98.96% at 130 VA in buck mode and peak efficiency of 99% at 122 VA in boost mode. [ABSTRACT FROM AUTHOR]

A model predictive control (MPC) strategy based on optimal switching sequence concepts is presented for direct power control of grid-connected three-level neutral-point clamped converters. The proposed control strategy explicitly considers the modulator in its formulation along with the model of the system. Through two well-formulated optimal control problems, the proposed strategy is shown to optimally achieve control of the average trajectory of the active and reactive powers as well as the dc-link capacitor voltages without using weighting factors to tradeoff both control targets. Experimental results demonstrate this strategy produces improved steady-state performance with a well-defined output voltage spectrum and fixed-switching frequency while maintaining the inherent fast dynamic responses of MPC strategies. [ABSTRACT FROM AUTHOR]

Multi-input multi-output (MIMO) dc–dc converters can integrate multiple input sources and output loads simultaneously. This article proposes a new single-inductor MIMO dc–dc converter with a wide conversion ratio. The proposed converter allows input sources to be added or removed seamlessly with no cross-regulation problem. Meanwhile, the outputs are independently controlled, i.e., the load change at one output cell will not affect the other interconnected output cells. Constant current control is the main control requirement. When constant current control is applied to all input cells, the power provided by each input source is proportional to the voltage magnitude of the source. When the constant current control is applied to some of the input cells, the input sources with direct duty-cycle controlled input cells can provide specific power through controlling the duty cycles of the switches of the corresponding input cells. Moreover, the switching time of switches is irrelevant. Therefore, it is easy to realize the high extension capability for arbitrary inputs/outputs. A dual-input dual-output prototype is constructed to illustrate the performance of the proposed converter. The corresponding component design is presented. [ABSTRACT FROM AUTHOR]

This article proposes a robust control strategy for five-level T-type (5L-T) hybrid power converters to achieve superior dynamic performance for effectively regulating the dc-bus voltage under external disturbances and generating high-quality grid current at the same time. A new filter-less dc-bus ripple voltage estimation method and a simple technique to remove this ripple component from the measured dc-bus voltage of a single-phase converter are developed. A sliding-mode control (SMC) incorporated with an extended-state observer (ESO) is employed for the outer voltage control loop, and to dynamically calculate the input (i.e., the active power reference) for the inner current-tracking controller. The proposed SMC-ESO approach presents a high disturbance rejection capability and robustness against the dc-bus load variation, and thus, significantly improves the dynamic and steady-state performance during system uncertainties. Moreover, a finite control set-model predictive control algorithm is derived as the inner current controller to track their references while balancing the dc-bus capacitor voltages. The effectiveness of the proposed controller is demonstrated and verified through measurement results. [ABSTRACT FROM AUTHOR]