Open-circuit Fault-tolerant Control Strategy Based on Five-level Power Converter for SRM System

Switched reluctance motor power converters are prone to open-circuit faults because it need to withstand large voltages and currents.Due to the small number of traditional asymmetrical half bridge topology switches,it is difficult to carry out fault tolerant control when power converters has an open-circuit fault,resulting in larger output torque ripple.This paper presents a five-level power converter based on the traditional asymmetric half-bridge power converter.The five-level topology has more switching states and can work in multi-level mode.Based on the topology,different excitation and demagnetization voltages can be choose at different speeds.A fault-tolerance strategy is developed to decrease the influence of the open-circuit fault.The five-level power converter has four switches per phase,and two of them will be used in one of the operating mode.So the remaining two of the switches can be used for safe backup,enabling fault-tolerant control when an open-circuit occur.Since each phase of the five-level power converter proposed in this paper is independent of each other,a reasonable control strategy can be used to avoid the unbalance of the midpoint potential.Finally,the topology and fault-tolerant strategy proposed in this paper are verified by simulation and experiment.

1064 nm InGaAsP multi-junction laser power converters

Laser photovoltaic devices converting 1064 nm light energy into electric energy present a promising prospect in wireless energy transmission due to the commercial availability of high power 1064 nm lasers with very small divergence. Besides their high conversion efficiency, a high output voltage is also expected in a laser energy transmission system. Meanwhile,1064 nm InGaAsP multi-junction laser power converters have been developed using p^+-InGaAs/n^+-InGaAs tunnel junctions to connect sub-cells in series to obtain a high output voltage. The triple-junction laser power converter structures are grown on p-type InP substrates by metal-organic chemical vapor deposition(MOCVD), and InGaAsP laser power converters are fabricated by conventional photovoltaic device processing. The room-temperature I–V measurements show that the 1 × 1 cm^2 triplejunction InGaAsP laser power converters demonstrate a conversion efficiency of 32.6% at a power density of 1.1 W/cm^2, with an open-circuit voltage of 2.16 V and a fill factor of 0.74. In this paper, the characteristics of the laser power converters are analyzed and ways to improve the conversion efficiency are discussed.

Finite Control Set Model Predictive Control with Feedback Correction for Power Converters

As an open-loop model predictive control algorithm,finite control set model predictive control(FCS-MPC)scheme in power converter system is based on assumption that responses of optimal control implemented on prediction model agree well with actual system.The influence of model parameter mismatches and environment disturbance on control performance of scheme is neglected.Then,based on feedback correction strategy in traditional model predictive control algorithm,we derive a finite control set model predictive control with feedback correction scheme(FCS-MPCFC)that allows us to adjust prediction model output at current instant by model prediction error at previous instant,and the closed-loop correction of prediction model output is achieved.Simulations comparison analyses on a two-level three-phase inverter with multi-type model parameter mismatches controlled by traditional and improved FCS-MPC scheme are presented.Experiments are carried out on DSP controller platform.

Energy band adjustment of 808 nm GaAs laser power converters via gradient doping

The gradient doping regions were employed in the emitter layer and the base layer of GaAs based laser power converters(LPCs).Silvaco TCAD was used to numerically simulate the linear gradient doping and exponential gradient doping structure,and analyze the transport process of photogenerated carriers.Energy band adjustment via gradient doping improved the separation and transport efficiency of photogenerated carriers and reduced the total recombination rate of GaAs LPCs.Compared with traditional structure of LPCs,the photoelectric conversion efficiency of LPCs with linear and exponential gradient doping structure were improved from 52.7%to 57.2%and 57.7%,respectively,under 808 nm laser light at the power density of 1 W/cm^(2).

Exact Dynamic Modeling of PWM DC-to-DC Power Converters—Part I: Continuous Conduction Mode

A general approach is presented by which the exact frequency response of any transfer function of switched linear networks can be determined. This is achieved with a describing function approach using a state space equation formulation. This work presents a somewhat simplified set of equations to one previously given by one of the authors. To demonstrate application of the general formulation, the frequency responses of switched networks used as PWM DC-to-DC converters operating in continuous conduction mode (CCM) under voltage mode control are derived. (The accompanying paper, Part II, will present results for converters operating in discontinuous conduction mode (DCM)). From the general sets of equations developed here, both the control to output and input source variation to output frequency responses are derived. The describing function approach enables exact frequency response determination, even at high frequencies where the accuracy using average models may be compromised. Confirmation of the accuracy of the derived models is provided by comparing the responses with those obtained using the commercial simulator PSIM on a PWM boost converter. The magnitude and phase responses are shown to match perfectly over the full range of frequencies up to close to half the switching frequency. Matlab code that implements the models is given such that the user can easily adapt for use with other PWM converter topologies.

Exact Dynamic Modeling of PWM DC-to-DC Power Converters—Part II: Discontinuous Conduction Mode

This paper follows on from the first paper, Part I, where a general formulation of a describing function approach to frequency response determination of switched linear networks, such as PWM converters, was simplified and updated. The models assume a piecewise linear state space equation description of the system and results in a closed form solution for the sought after frequency response. In Part I, model derivation was demonstrated for the case of PWM converters operating in the continuous conduction mode (CCM). This operating mode does not feature any state dependent switching times. In this paper, Part II, frequency response models for any transfer function for PWM converters operating in discontinuous conduction mode (DCM) are derived based on the theory presented in Part I. This operating model features state dependent switching times. The describing function models developed are exact and therefore, in terms of accuracy, are to be preferred over averaged models which are widely used. The example of a boost dc-to-dc converter operating in DCM is simulated to obtain the control to output and input to output frequency responses and are compared with the models derived here. Excellent agreement between the simulated and model responses was found. Matlab code implementing the analytical models is also presented which the user can adapt for any other PWM converter topology. The models derived here may be used as a basis from which simplified models may be derived while still preserving required accuracy.

Loop-Shaping Based Control for Switch Mode DC-DC Power Converters

Renewable energy sources require switching regulators as an interface to a load with high efficiency, small size, proper output regulation, and fast transient response. Moreover, due to the nonlinear behavior and switching nature of DC-DC power electronic converters, there is a need for high-performance control strategies. This work summarized the dynamic behavior for the three basic switch-mode DC-DC power converters operating in continuous conduction mode, i.e. buck, boost, and buck-boost. A controller was designed using loop-shaping based on current-mode control that consists of two feedback loops. A high-gain compensator with wide bandwidth was used in the inner current loop for fast transient response. A proportional-integral controller was used in the outer voltage loop for regulation purposes. A procedure was proposed for the parameters of the controller that ensures closed-loop stability and output voltage regulation. The design-oriented analysis was applied to the three basic switch-mode DC-DC power converters. Experimental results were obtained for a switching regulator with a boost converter of 150 W, which exhibits non-minimum phase behavior. The performance of the controller was tested for voltage regulation by applying large load changes.

Generic Modeling and Control Framework for Power Systems Dominated by Power Converters Connected Through a Passive Transmission and Distribution Grid

In this paper,a compact mathematical model having an elegant structure,together with a generic control framework,are proposed for generic power systems dominated by power converters that are interconnected through a passive transmission and distribution(T&D)grid,by adopting the port-Hamiltonian(pH)systems theory and the fundamental circuit theory.The models of generic T&D lines are developed and then the model of a generic T&D grid is established.With the proposed control framework,the controlled converters are proven to be passive and Input-to-State Stable(ISS).The compact mathematical model is scalable and can be applied to power systems with multiple power electronic converters with generic passive controllers,passive local loads,and different types of passive T&D lines connected in a meshed configuration without self-loops,so it is very generic.Moreover,the resulting power system is proven to be ISS as well.The analysis is carried out without assumptions on constant frequency/voltage,constant loads,and/or lossless networks,except the need of passivity for all parts involved,and without using the Clarke/Park transformations or the graph theory.To simplify the presentation,three-phase balanced systems are adopted but the results can be easily adapted for single-phase or unbalanced three-phase systems.

Circulating Current Suppression Method with Adaptive Virtual Impedance for Multi-bidirectional Power Converters Under Unbalanced Conditions

Multi-paralleled bidirectional power converters(BPCs)are commonly used to improve the power capacity and reliability in an AC/DC hybrid microgrid.However,circulating current through multi-BPCs has been one of the challenges and it can be aggravated in the presence of non-ideal operating conditions,such as unbalanced AC voltages,and the mismatch of hardware parameters.In order to suppress the circulating current,this paper proposes a distributed method based on adaptive virtual impedance,which also employs positive sequence power droop control and voltage deviation compensation control.The traditional positive sequence power droop control is adopted to only regulate the positive components of the BPCs output voltage.The negative sequence power term is fed to an adaptive virtual impedance generator to modify the damping characteristics of the BPCs.Also,an adaptive virtual impedance-based voltage deviation compensation method is proposed to recover the fluctuated output voltage of the BPCs due to droop action and the power fluctuations.The fully distributed regulation of adaptive virtual impedance enables the load power to be shared accurately among BPC modules and thus the circulating current can be effectively suppressed.The proposed control strategy does not require an additional communication system and the precise parameters of hardware equipment and line impedance.Furthermore,the effectiveness of the proposed method is verified by the experimental results.

Reliability Evaluation of Wind Power Converter Under Fault-tolerant Control Scheme with Quantification of Temperature and Humidity Effects

Wind power converter(WPC)is a key part of a wind power unit which delivers electric energy to power grid.Because of a large number of semiconductors,WPC has a high failure rate.This paper proposes a method to accurately evaluate the reliability of WPC,which is crucial for the design and maintenance of wind turbines.Firstly,the index of effective temperature(ET)is presented to quantify the effects of temperature and humidity on the semiconductor operation.A novel method is proposed to evaluate the lifetime and calculate the aging failure rates of the semiconductors considering the fluctuations of ET.Secondly,the failure mode and effect analysis(FMEA)of WPC is investigated based on the topology and control scheme.The conventional two-state reliability model of the WPC is extended to the multi-state reliability model where the partial working state under the fault-tolerant control scheme is allowed.Finally,a reliability evaluation framework is established to calculate the parameters of the WPC reliability model considering the variable failure rates and repair activities of semiconductors.Case studies are designed to verfify the proposed method using a practical wind turbine.

Fast SHEPWM Solution Method for Wind Power Converter Based on State Equations

Selective harmonic elimination pulse width modula-tion(SHEPWM)is a modulation strategy widely used for three-level wind power grid-connected converters.Its purpose is to eliminate specified sub-low frequency harmonics by controlling switching angle.Furthermore,it can reduce fluctuation of the microgrid system and improve system stability.Intelligent al-gorithms have been applied to the SHEPWM solution process to mitigate calculation complexity associated with the algebraic method,as well as the need to set the initial value.However,disorder of the optimization result causes difficulty in satisfying incremental constraint of the three-level NPC switching angles,and affects the success rate of the algorithm.To overcome this limitation,this paper proposes a fast SHEPWM strategy to optimize the result obtained by the intelligent algorithm.The SHEPWM can be realized by solving switching angles through a state equations-based mathematical model,which is constructed by using the initial variables randomly generated by the intelligent algorithm as the disturbance.This mathematical model improves the success rate of calculation by simplifying constraint representation of switching angles and solving the disorder problem of the optimization result.At the same time,a method based on the circle equation and the trigonometric function is applied to the initial variable assignment of the state equation,which further improves the speed and accuracy of the solution,realizes a more thorough filtering effect,and further reduces the impact of sub-low frequency harmonics on a wind power integrated system.Finally,simulation and experiment results have been used to prove the effectiveness of the proposed SHEPWM strategy when combined with intelligent algorithms.Index Terms-Wind power converter,adaptive genetic algorithm,selective harmonic elimination pulse-width modulation(SHEPWM),state equation,success rate.

A Review of Variable-inductor-based Power Converters for Eco-friendly Applications:Fundamentals,Configurations,and Applications

Modern eco-friendly industries such as renewable energy systems,electric vehicles(EVs),and light-emitting diodes(LEDs)have led to technological advancements in power electronics.Switching-based power converters have limited working ranges and can cause significant harmonics and oscillations in the output voltage and current.Introducing variable inductors can help solve this problem by changing the inductance without resorting to extreme switch duty cycles.Despite their advantages,there is still a lack of comprehensive reviews of variable inductor applications in power converter design.A thorough and in-depth review of variable inductance control in power conversion is presented,including its significance,working principle,core structure,modeling method,and typical applications.Traditionally,an inductor works in its linear magnetic region;its inductance in a power converter is considered constant,and the converter operates under fixed working conditions.However,a broad range of working conditions is required for power converters in practical applications.This is typically realized by changing the duty cycles of the switches.The working principle of variable inductance is reviewed,and the application of variable inductance control in power converters is presented,which will further help power electronics researchers and engineers design flexible and resilient power converters.

Inertia response from full-power converter-based permanent magnet wind generators

With a high penetration of wind turbines,the proportion of synchronous generation in the power system will be reduced at times,thus creating operating difficulties especially during frequency events.Therefore,it is anticipated that many grid operators will demand inertia response from wind turbines.In this article,different ways for emulating inertia response in full-rated power converter-based wind turbines equipped with permanent magnet synchronous generators are considered.Supplementary control signals are added to the controller of the wind turbine to extract stored energy from the rotating mass and DC-link capacitors.Simulations in MATLAB/Simulink show that the inertia response is improved by adding a term proportional to the rate of change of frequency and by extracting the stored energy in the DC-link capacitors.

Stability of interacting grid-connected power converters

The power grid in a typical micro distribution system is non-ideal,presenting itself as a voltage source with significant impedance.Thus,grid-connected converters interact with each other via the non-ideal grid.In this study,we consider the practical scenario of voltage-source converters connected to a three-phase voltage source with significant impedance.We show that stability can be compromised in the interacting converters.Specifically,the stable operating regions in selected parameter space may be reduced when grid-connected converters interact under certain conditions.In this paper,we develop bifurcation boundaries in the parameter space with respect to Hopftype instability.A small-signal model in the dq-frame is adopted to analyze the system using an impedance-based approach.Moreover,results are presented in design-oriented forms so as to facilitate the identification of variation trends of the parameter ranges that guarantee stable operation.

A six-junction GaAs laser power converter with different sizes of active aperture

We investigate a novel Ga As-based laser power converters(LPCs) grown by metal-organic chemical vapor deposition(MOCVD),which uses a single monolithic structure with six junctions connected by tunnel junctions to obtain a high output voltage. The LPCs with diameters of active aperture of 2 mm and 4 mm were fabricated and tested. The test results show that under an 808 nm laser,two LPCs both show an open circuit voltage of above 6.5 V. A maximum power conversion efficiency of 50.2% is obtained by 2 mm sample with laser power of 0.256 W,and an output electric power of 1.9 W with laser power of 4.85 W is obtained by 4 mm sample. The performances of the LPCs are deteriorated under illumination of high flux,and the 4 mm sample shows a higher laser power tolerance.

Analysis and control of wind-driven self-excited induction generators connected to the grid through power converters

The analysis of the wind-driven self-excited induction generators （SEIGs） connected to the grid through power converters has been developed in this paper. For this analysis, a method of representing the grid power as equivalent load resistance in the steady-state equivalent circuit of SEIG has been formulated. The technique of genetic algorithm （GA） has been adopted for making the analysis of the proposed system simple and straightfor- ward. The control of SEIG is attempted by connecting an uncontrolled diode bridge rectifier （DBR） and a line commutated inverter （LCI） between the generator term- inals and three-phase utility grid. A simple control technique for maximum power point tracking （MPPT） in wind energy conversion systems （WECS）, in which the firing angle of the LCI alone needs to be controlled by sensing the rotor speed of the generator has been proposed. The effectiveness of the proposed method of MPPT and method of analysis of this wind-driven SEIG-converter system connected to the grid through power converters has been demonstrated by experiments and simulation. These experimental and simulated results confirm the usefulness and successful working of the proposed system and its analysis.

Characterizations of high-voltage vertically-stacked GaAs laser power converter

Six-junction vertically-stacked Ga As laser power converters（LPCs） with n^＋-Ga As/p^＋-Al0.37 Ga0.63 As tunnel junctions have been designed and grown by metal-organic chemical vapor deposition for converting the power of 808 nm lasers. The LPC chips are characterized by measuring current–voltage（I–V） characteristics under 808 nm laser illumination, and a maximum conversion efficiency ηc of 53.1% is obtained for LPCs with an aperture diameter of 2 mm at an input laser power of 0.5 W. In addition, the characteristics of the LPCs are analyzed by a standard equivalent-circuit model, and the reverse saturation current, ideality factor, series resistance and shunt resistance are extracted by fitting of the I–V curves.

Evolution of Single-Phase Power Converter Topologies Underlining Power Decoupling

Single-phase power converters are widely used in electric distribution systems under 10 kilowatts,where the second-order power imbalance between the AC side and DC side is an inherent issue.The pulsating power is decoupled from the desired constant DC power,through an auxiliary circuit using energy storage components.This paper provides a comprehensive overview of the evolution of single-phase converter topologies underlining power decoupling techniques.Passive power decoupling techniques were commonly used in single-phase power converters before active power decoupling techniques were developed.Since then,active power decoupling topologies have generally evolved based on three streams of concepts:1)current-reference active power decoupling;2)DC voltage-reference active power decoupling;and 3)AC voltage-reference active power decoupling.The benefits and drawbacks of each topology have been presented and compared with its predecessor,revealing underlying logic in the evolution of the topologies.In addition,a general comparison has also been made in terms of decoupling capacitance/inductance,additional cost,efficiency and complexity of control,providing a benchmark for future power decoupling topologies.

A review of high frequency resonant DC-DC power converters:Topologies and planar magnetic technologies

With the development of high frequency resonant DC-DC power converters,the system efficiency,power density and dynamic characteristics have been significantly improved.High frequency resonant DC-DC converters have been applied in DC grid,renewable energy,transportation,aerospace,point-of-load(POL)power supply and many other fields.Under high switching frequencies,switching loss and magnetic loss are the main concerns;thus,the resonant topology and planar magnetic are two key technologies to reduce loss.This review compares different resonant topologies and analyzes the advantages and disadvantages respectively,such as LLC circuit,dual active bridge(DAB)circuit,and other high order resonant circuits.For planar magnetic components,optimal winding structures,modeling methods and integration methods are thoroughly surveyed.With corresponding topics,the opportunities and challenges in the future development are summarized,which mainly focus on the characteristics of wide bandgap devices,such as the dynamic resistance,output capacitance loss and also the integrated module.This review can be a helpful guidance when designing high frequency resonant DC-DC converters.

Four-junction AlGaAs/GaAs laser power converter

Four-junction A1GaAs/GaAs laser power converters （LPCs） with n＋-GaAs/p＋-A10.37Ga0.63As hetero- structure tunnel junctions （TJs） have been designed and grown by metal-organic chemical vapor deposition （MOCVD） for converting the power of 808 nm lasers. A maximum conversion efficiency ηc of 56.9% ＋ 4% is obtained for cells with an aperture of 3.14 mm2 at an input laser power of 0.2 W, while dropping to 43.3% at 1.5 W. Measured current-voltage （I-V） characteristics indicate that the performance of the LPC can be further improved by increasing the tunneling current density of TJs and optimizing the thicknesses of sub-cells to achieve current matching in LPC.