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Grid-forming converters (GFCs) offering sinusoidal voltage supply have been widely employed in a lot of applications. In this work, the dual-loop voltage-current control for GFCs is comprehensively approached. Firstly, optimum tuning of the current loop is addressed to achieve the maximum enhanced active damping from the prospect of the developed equivalent plant, instead of the current loop which has been the focus of the existing literatures. Then, effectiveness of the resonant controllers (RCs), i.e. proportional resonant and vector proportional integral, which are very popular for voltage regulation of GFCs, is addressed. It is found that for GFCs with reasonably designed output filter, specially for high-power applications with a low switching frequency, weakly-damped region exists in the close-loop frequency response with either of the two RCs employed, which can further result in constrained bandwidth and slow transient response. To solve this issue, a discrete resonant controller is developed which avoids the weakly-damped region and a fast response of the output voltage can be achieved. Experimental results have verified the effectiveness of the proposed controller for voltage regulation of GFCs.

Effective sinusoidal voltage regulation is of permanent importance for grid-forming converters. Usually, the following two types of schemes are employed to achieve a high level of performance: 1) single-loop voltage and 2) dual-loop voltage-current control. The performance of both schemes has comprehensively been evaluated in this work, based on the developed discrete-time model of the LC-filtered grid-forming converter. The challenges of insufficient stability margin, constraint bandwidth, and high sensitivity to parameter variation faced by the single-loop control scheme have been addressed, if the high-performance resonant controllers are employed for voltage regulation. Alternatively, the dual-loop control does not experience such issues with the inclusion of inner-current loop which provides active damping for the overall system. The essence of the inner-current loop is identified based on the discrete root locus analysis. Also, to obtain the highest damping and most enhanced stability, the criterion for current loop design has been addressed and a method for optimal tuning of the inner-current loop is developed, where the original plant with the one-sampling delay and the current gain are considered as the equivalent plant for the voltage controller. Experimental results have verified the effectiveness of the developed method for regulation of grid-forming converters.

In this paper, a single-stage full-bridge inverter with energy storage capacitor is proposed. The high-frequency transformer is used to achieve boosting voltage and electrical isolation. The energy storage capacitor is introduced in the secondary side and the stored energy is fed back into the bus capacitor through the body diode when energy is fed back reversely. Accordingly when energy flows forward, the energy stored in the bus capacitor is released to reach the energy balance of bus capacitor in each power frequency cycle, and thereby achieve the four-quadrant operation of inverter. Thus, problems of energy being fed back into the DC bus directly and increasing complexity of circuit are avoided. When the inverter is connected to the grid, the bus capacitor can be disconnected from the circuit and a single-phase single-stage grid-connected inverter is achieved. The operating principle and control strategy of the topology are analyzed in detail and the feasibility is proved by experiments.

Switching-linear hybrid envelope tracking (SLH ET) power supplies can achieve both high efficiency and high bandwidth. However, the switching frequency is often required to be far higher than or at least equal to the envelope bandwidth. With the modulation methods advance, the increasing envelope bandwidth may lead to a too high switching frequency to implement. This paper proposes an SLH ET power supply, consisting of a multilevel converter and a linear amplifier connected in series. Based on the multicell configuration of the multilevel converter, a pulse edge independent distribution method is proposed, which can break the control pulses for the multilevel converter into independent rising and falling edges, and rebuild them with new sequences. It can not only reduce the switching frequency to 1/ n ( n ∊ N ) of the envelope bandwidth but also extend the pulsewidths to provide a more reliable and effective driving for high bandwidth applications. A prototype for 2 MHz sine-wave tracking, with 7–27-V output voltage and 90-W peak output power, is fabricated and tested. It is also verified by a 5- and a 10-MHz bandwidth communication envelope. The experimental results validate the proposed method.

In this paper, a technique of variable-turns-ratio high-frequency link inverter is proposed to provide a simple method to achieve multi-level outputs for the isolated single-stage high-frequency link inverters. By dynamically adjusting the turns ratio of transformer, five-level (±2, ±1, and 0) outputs can be achieved to improve the current quality. The single transformer, compared with the existing two-level high-frequency link inverter, is employed in the structure and only a few auxiliary devices are added, where the added circuit operates at low frequency and the power density is refined. Based on this technique, the single-stage active clamped forward grid-connected inverter with variable turns ratio is taken as an example to better illustrate the analysis process and a 1000-W prototype is designed and established to evaluate the output performance. The conducted simulation results and prototype tests verify the feasibility of the proposed single-stage variable-turns-ratio high-frequency link grid-connected inverter.

In this study, an integrated control strategy is proposed which can be widely used in two-stage boost inverters, and an improved two-stage boost inverter is taken as an example to present the proposed integrated control idea. The presented inverter can operate in four quadrants, which can realise grid-connected or stand-alone inverter. With improved control strategy, it not only can reduce the number of switching times and improve the efficiency but also can reduce the harmonic contents of bridge arm voltage and further decrease the volume and weight of the filter. Therefore, the presented inverter still has the advantages in efficiency and volume when compared with single-stage boost inverters. The operating principle, harmonic analysis, simulation and experiments are provided in this study. A 500 W prototype is established and tested, and the results of simulation and experiments verify the correctness of the theoretical analysis.

In the high-frequency AC (HFAC) power distribution system, problems such as high switching frequency, a complicated circuit configuration and difficult parameter design still exist in the traditional inverters. A multi-level high-frequency inverter topology based on a forward converter is proposed in this study, which implements the electrical isolation of input and output. With the introduction of variable turns ratio technology, the nine-level output is achieved, which is conductive to the decrease of output harmonics. The selected harmonic elimination method is also adopted to further reduce the output harmonic distortion through the Fourier analysis of output waveforms. Besides, the HFAC output can be achieved at a lower switching frequency for the maximum switching frequency is only double the output frequency. The detailed analysis on operating principles and parameter design of the proposed inverter are provided in this study. Finally, the feasibility of the inverter is verified by the simulations and experiments.

Transformerless photovoltaic (PV) inverters are more widely adopted due to high efficiency, low cost, and light weight, etc. Many novel topologies and their corresponding modulation methods have been proposed, verified, and put into use, solely focusing on active power injection without leakage current issues. However, some new grid codes require PV inverters to have the ability of injecting reactive power into the utility for grid support. In order to map the challenge, an improved hybrid modulation method is proposed and evaluated for one nonisolated H6 topology as an example. With only simple modification for switching patterns and phase shift for current reference, the variable reactive power generation ability with zero crossing distortion is achieved, while the common mode voltage is also eliminated. The operation modes with the improved hybrid modulation approach are presented in detail and some design considerations are also provided. Extensive results from a 4-kVA prototype along with the SMPLIS simulation verify the proposed hybrid modulation method.

A 1500 V three-level forward converter with phase-shifted control is proposed to meet the requirements on medium- and high-voltage DC bus of photovoltaic grid-connected system. The architecture of 1500 V DC bus is established by filtering the phase-shifted outputs in series centrally, in which the internal filters of each DC/DC converter are removed. The three-level voltage is superimposed by phase-shifting the rectified output voltages in series, which is beneficial to decrease the inductor current pulsation, diminish the ripple of output voltage and improve the system efficiency. The centralised filter contributes to downsizing the filter and reducing the system cost. With the introduction of parallel-series structure, the characteristics of low-voltage stress are retained and the power transmission is improved. Meanwhile, the minimum value of total harmonic distortion (THD) with phase-shifted control is obtained through the Fourier decomposition of three-level voltage waveform. By analysing the variation rule of THD with the change of conduction angle, the optimal steady-state operating point of the converter is achieved. The operating principle of the proposed system is presented minutely in this study and a prototype has been established. The experimental results verify the validity of the proposed converter.

A new buck inverter without shoot-through problem is presented and analysed in this study. The traditional dual-buck inverter has been proposed to solve the shoot-through problem of bridge-type inverters, eliminate the dead-time effect and improve the reliability along with the conversion efficiency. However, the existing dual-buck inverter is prone to result in the problem of circulation and low utilisation rate of input voltage in half-bridge-type inverters. Besides, two or even four inductors are needed in the traditional dual-buck inverter configuration, which leads to a larger volume and weight. In this study, single inductor and single power are used in the proposed buck inverter topology. The operating circuit is equivalent to a buck circuit during each mode, and only one switch works in high-frequency condition at any time. A 1-kW prototype is established and tested in this study. The results of simulation and experiments verify the validity of the theoretical analysis, along with the good performance in situations where small size, high conversion efficiency and high stability are required.

On the basis of dual-buck half-bridge inverter, a three-bridge buck inverter is proposed, which not only remains the advantages of dual-buck half-bridge inverter, but also improves the inverter's performance such as avoids shoot-through problem, removes the reverse recovery losses of body diodes and so on. By adding a new bridge, the three-level modulation and the single power supply are realised, which increase the DC voltage utilisation rate. In addition, smaller volume and weight of the system and higher system integration can be achieved using only one filter inductor compared with other dual-buck-type inverters. The unipolar sinusoidal pulse width modulation scheme is adopted in the inverter system, so the switching frequency is fixed, which is beneficial to the design of filter. The operating principle and characteristics of the proposed inverter are analysed in detail. A 1 kW prototype is established and tested, and the results of simulation and experiment verify the good performance of the proposed inverter.

A novel interleaved dual buck full-bridge three-level inverter (IDBFTI) is proposed for the grid-connected system in this paper. It retains the advantages of interleaved parallel technology for inverter as follows: reducing the output ripple current and the total harmonic distortion of the output current, increasing the power density of system, and reducing the current stress and thermal stress of power devices. Besides, it can solve the problem of zero sequence circulation current (ZSCC) in interleaved inverter system by the circuit structure, and it also has the advantages of no shoot-through problem, no reverse recovery of the body diode, and three-level output. The interleaved inverter circuits share two power-frequency switches, which are resized for each specific application, and it is easier to extend the system by improving current capability of the two switches. The working principle of this system is introduced in detail, and a 2-kW experimental prototype has been established and tested. Test results verify the principle and the excellent performance of IDBFTI.

Continuous polishing technology is an important means to realize batch processing of large aperture and high precision planar optical components. However, traditional continuous polishing process largely depends on the operator's experience, with poor controllability of component surface figure and unstable processing efficiency. In order to solve this problem, the in-situ shape measurement technologies including measurement of pitch lap surface figure and workpiece surface figure have been proposed in this paper. The real-time states of the pitch lap flatness and the workpiece surface figure in polishing process are obtained by in-situ measurement technologies, which provide the quantitative informations for adjusting process parameters. In the experiment, a large aperture mirror (material as K9; size as 800mm×400mm×100mm) was polished. The results show that the surface figure of the component was improved from λ/2 (1λ=632.8nm) to λ/6 by using the in-situ measurement technologies during the continous polishing process.

A new single inductor dual buck full-bridge inverter is proposed in this paper. The inverter is improved on the basis of a dual buck inverter, and it retains the advantage of a no reverse recovery of body diode. The dc voltage utilization rate can be increased by adopting the voltage commutation bridge instead of the voltage-dividing capacitors in the inverter. In addition, comparing with other dual buck inverters, the inverter has just one filter inductor, which can make the volume and weight of the system decreased observably and improve the integration. The controlling method, combining the high- and low-frequency modulation, is adopted to weaken the complexity of control and improve the reliability and stability of the system. The operating principle, characteristic analysis, simulation and experiment are provided in this paper. A 1-kW prototype is established and tested, and the results of simulation and experiment verify the correctness of the theoretical analysis.

Compared with the conventional high voltage DC power supply, the high voltage pulse power supply can significantly improve the dust removal efficiency of electrostatic precipitator and reduce the energy consumption. This paper presents a new type of high voltage pulse electrostatic precipitator power supply topology, the symmetric cascaded structure of the low voltage side which can significantly reduce the voltage stress of switching device, rectifier circuit, clamp circuit and resonant capacitor, thereby significantly reducing the cost. This paper analyzes the steady-state operating principle of the high voltage pulse power supply and the working conditions during flashover while the expressions of the output voltage and current of the transformer primary side are both deduced and verified by simulations. Finally, the experimental verification is carried out by a pulse power supply with a peak voltage of 100kV.

A hybrid resonant zero-voltage zero-current switching three-level converter is proposed in this paper, which undergoes half of the input voltage for switches. The proposed converter, utilizing two transformers, adopts IGBTs for all six power switches and operates in discontinuous current mode and can achieve zero-current switching for the four main switches and rectifier diodes over the whole load range. Hence, the switching loss is reduced. The influence of the turns ratio of auxiliary transformer and the resonant capacitance on the peak and turn-off currents is discussed in detail. The operation principles of the proposed converter are analyzed and verified by the simulation and experimental results.

Due to nonlinear time-varying characteristic of a single-phase dc/ac inverter, its front-end dc/dc converter tends to draw an alternate current ripple current at twice the output frequency, which may cause interaction issues, e.g., stability problem and input ripple current limit in distributed generation systems. A novel method is proposed to evaluate the behavior of low-frequency input current ripple. This approach is based on back current gain Ai (s) (input current to output current) model of the dc/dc converter. The theoretic model with different control schemes is verified in Saber environment. It is indicated and proved that the average current mode control strategy is more effective as compared with linear voltage mode control and open-loop control schemes. Design principles are presented based on Ai (s) as guidelines. Dynamic response with bandwidth limitation is also discussed and improved with proposed proportional-resonant (PR) filter placed based on Ai (s) model. Detail simulation and experiment results for different linear control and nonlinear control strategies, 50 and 400 Hz, buck-type stand-alone two-stage single-phase systems are provided to verify the proposed back current gain model and PR-filter solutions.

The main contribution of this paper is the derivation rules summarized from existing high-performance inverters with H6-type configuration, which makes novel topologies possible. In addition, a novel high-efficiency single-phase transformerless photovoltaic inverter with hybrid modulation method is also proposed and evaluated as an example. Without input split capacitors, common-mode voltage and leakage current issues in a nonisolated system with H6-type configuration are eliminated, and the feature of a three-level output voltage in the inverter bridge's middle point helps inductors and power quality optimization. The detailed operation principles with hybrid modulation strategy combined with unipolar and bipolar pulsewidth modulation schemes are presented. Experimental results of a 2200VA prototype verify the proposed topology with hybrid modulation method.

This paper describes an investigation of a high-strength concrete frame reinforced with high-strength rebars that was tested in the structure engineering laboratory at Shenyang Jianzhu University. The frame specimen was pseudodynamically loaded to indicate three earthquake ground motions of different hazard levels, after which the test specimen was subjected to a pseudo-static loading. This paper focuses on the design, construction and experiment of the test frame and validation of the simulation models. Research shows that a high-strength concrete frame reinforced with high-strength rebars is more efficient and economical than a traditional reinforced concrete frame structure. In addition to the economies achieved by effective use of materials, research shows that the frame can provide enough strength to exceed conventional reinforced concrete frames and provide acceptable ductility. The test study provides evidence to validate the performance of a high-strength concrete frame designed according to current seismic code provisions. Based on previous test research, a nonlinear FEM analysis is completed by using OpenSees software. The dynamic responses of the frame structure are numerically analyzed. The results of the numerical simulation show that the model can calculate the seismic responses of the frame by OpenSees. At the same time, the test provides additional opportunities to validate the performance of the simulation models.

Solid State Power electronic transformer (PET) is an emerging new type of power converter in recent years. It has not only the basic functions of power transformation and isolation, but also the extra functions of power quality control. This paper presents the key control strategies of solid state PET for electrical distribution system application, especially under voltage disturbance conditions. Several critical grid voltage disturbances are generated by a disturbance voltage source based on a three phase PWM inverter. And the solid state PET prototype is tested and passed voltage disturbance ride through function. The experimental results verify the PET power quality control abilities.

This paper proposed a generalized modeling methodology based on the PWM Switch Model for steady-state analysis and dynamic performance investigation of the single phase inverter. The motivation, algorithm and modeling methodology are presented. The developed models are verified against the switching models of both a half bridge dual buck inverter and a half bridge inverter in time domain to demonstrate the effectiveness of the modeling methodology. Input impedance of the half bridge inverter is also obtained for stability investigation of the cascaded two-stage power system.

The SOC and SoH of Li-ion batteries are of prime importance in EVs and their condition monitoring techniques have been extensively studied. This paper proposes a grey system theory for predicting the battery capacity and healthy conditions in relation to their discharge cycles. Numerical results via grey system theory-based models are obtained based on the aging data from NASA prognostics data repository. Therefore, the accuracy for the SOC estimation can be examined and improved. In this paper, the accuracy of different grey models including GM (1,1), segmental GM (1,1), Verhulst model, sliding window Verhulst model are investigated and the sliding window Verhulst model is found to be effective for EV batteries.

In multilevel inverter, it is a key problem that how to balance voltages of input capacitors. Because of the coupling of multilevel modulation and input voltage balance, no matter hardware circuit or control method of multilevel inverters are always complex, and speed of voltage balance is low. Dual Buck circuit which composed by two Buck DC/DC converter bridges, works in current half-period mode. A novel diode-clamped multilevel dual Buck inverter is presented, which inherits those features. At any moment, one Buck bridge works for inverter, another works as a reverse Boost circuit and charges up input capacitors. So inverter and voltage balance control are completely decoupled. If multilevel number is not small, this method is conducive to reduce the number of devices and the system complexity, and improve reliability of the system. Simulation and experiment of a diode-clamped three-level inverter verifies these analyses.

Due to power time-varying characteristic of a single phase photovoltaic (PV) grid-connected inverter in grid side, its front-end dc/dc converter tends to draw a large ac ripple current with double grid frequency, which would decrease maxim power point tracking performance of PV side. A novel method is proposed for the low frequency input current ripple analysis of a boost converter in a non-isolated single phase PV inverter, based on back current gain A i (s) (input current to output current) model. Mathematical models with different control schemes are built and derived, which are verified in SABER environment. It is indicated and proved that average current mode control strategy is more effective than voltage mode control and open loop control methods. Design principles are also presented. Simulation and experimental results are provided for model verification. Bandwidth limitation is also discussed and improved with proposed PR controller with A i (s) model.

Leakage current (common mode current) appears through the stray capacitance between the PV array and the grid in transformer-less grid-connected photovoltaic (PV) inverters. The seriousness of the effect has been an area of concern over the past years. Detailed review, investigation, classification and evaluation of full-bridge (H4) single phase PV inverter topologies without this problem are presented in this paper, such as H4, H5 and H6 circuits. Based on the analysis and comparison, some novel H6 topologies with high efficiency and ground leakage current issue eliminated are also proposed, which are also selected as candidate topologies for the standardized inverter topology. Simulation and experimental results are provided for the topology verification, 98.5%maximum efficiency of the prototype is achieved.

Isolated dc/dc converters' reliability suffers from forward/reverse recovery current issue of secondary rectifying diodes. In this paper, resonant double voltage rectifying technique is employed to eliminate this problem without any additional components added like that in variable frequency LLC circuits. And it still maintains fixed frequency features. Novel high step-up gain active clamp forward/flyback converter with voltage-doubler-rectifier (ACFF-VDR), interleaved ACFF-VDR, and push-pull-forward converter with voltage-doubler-rectifier (PPF-VDR) are proposed and evaluated. Design principles are also presented. Simulation and experimental results are provided for verification.