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Power converters and electric motor drives when tightly regulated behave as constant power loads. These loads are different from resistive loads and have destabilizing negative impedance characteristics, which impact a system's stability. A boost converter is intrinsically nonlinear and is a nonminimum phase system at the output voltage with respect to the control input. The linear approximation of this boost converter loaded with a constant power load has a zero and poles in the right half of the $s$ -plane, making the system unstable and very difficult to control. Control techniques that employ some form of system inversion cannot be implemented for a nonminimum phase system. This paper describes a technique to modify the nonminimum phase boost converter to a minimum phase for a constant power load, further implementing the input–output linearization technique to stabilize the system. This paper also provides a methodological analysis of the problem followed by the proposed solution. Furthermore, it verifies the analysis of the proposed solution through simulation and experimental results. [ABSTRACT FROM AUTHOR]

The three-phase four-wire inverter with split dc-link capacitors can supply unbalanced loads. For the purpose of reducing the filter inductors, a neutral inductor could be introduced into the neutral line. This paper analyzes the operation principle of the three-phase four-wire inverter with split dc-link capacitors when a neutral inductor is introduced. It is illustrated that the neutral inductor can reduce the zero-sequence switching harmonics in the voltages between the phase-leg midpoints and the output neutral point, thus the filter inductors can be reduced. The optimized design of the neutral inductor and filter inductors is proposed with the considerations of the inductor current ripple, the ability of supplying unbalanced loads, and the total energy stored in the inductors. The equivalent circuits of the three-phase four-wire inverter with split dc-link capacitors and neutral inductor is derived in the α–β–0 frame, and the zero-axis voltage regulator is modified to suppress the third-order harmonic in the zero-sequence current caused by the deadtime of the drive signals for the power switches. Finally, the experimental results from a 9-kW prototype are provided to prove the effectiveness of the proposed optimized design of the neutral inductor and filter inductors and the control strategy of the inverter. [ABSTRACT FROM AUTHOR]

Single-phase ac light-emitting diode (LED) lamps require long-lifespan and high-efficiency ac–dc power converters for power factor correction (PFC) and current regulation. In such converters, the inherent double-line-frequency ripple power from the ac source is isolated from the load by large electrolytic capacitors (E-caps) or E-cap-less active circuits to improve reliability and lifespan. This paper presents an ac–dc LED driver with an additional active rectifier and a unidirectional auxiliary circuit for ripple power isolation. As compared with other similar designs, the proposed LED driver operates with reduced redundant power processing and a lower voltage on the storage capacitor, and the additional active circuits include fewer power components. The prototype with small polymer-hybrid capacitors and ceramic capacitors is separately tested in the experiment. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid pulsewidth modulation (PWM) scheme is proposed to suppress the LC resonance for the high-power current-source inverter (CSI) fed drives with low switching frequency. In CSI drive systems, the selective harmonic elimination (SHE) is selected due to the better performance of harmonics, but the LC resonance cannot be effectively damped due to the lack of control flexibility of SHE. In this paper, SHE is only used for the steady-state operation. The modulation scheme is then switched to space vector modulation with dynamic capacitor voltage control when the transient event occurs. The smoothed transitions between different modulation schemes are proposed. The proposed hybrid method effectively solves the resonant issues in CSI drives, while maintaining the power quality. Both simulation and experiments verify the performance of the proposed hybrid PWM scheme. [ABSTRACT FROM AUTHOR]

In this paper, a high step-up quasi-Z Source (QZS) dc–dc converter is proposed. This converter uses a hybrid switched-capacitors switched-inductor method in order to achieve high voltage gains. The proposed converter have resolved the voltage gain limitation of the basic QZS dc–dc converter while keeping its main advantages, such as continuous input current and low voltage stress on capacitors. Compared to the basic converter, the duty cycle is not limited, and the voltage stress on the diodes and switch is not increased. In addition to these features, the proposed converter has a flexible structure, and extra stages could be added to it in order to achieve even higher voltage gains without increasing the voltage stress on devices or limiting the duty cycle. The operation principle of the converter and related relationships and waveforms are presented in the paper. Also, a comprehensive comparison between the proposed and other QZS based dc–dc converters is provided which confirms the superiority of the proposed converter. Simulations are done in power systems computer aided design (PSCAD) in order to investigate the maximum power point tracking (MPPT) capability of the converter. In addition, the valid performance and practicality of the converter are studied through the results obtained from the laboratory built prototype. [ABSTRACT FROM AUTHOR]

Most of the two-stage converters for electric bike battery charging comprise of a boost converter for power factor correction (PFC) followed by a dc–dc converter with universal input voltage. These two-stage conversions suffer from poor efficiency and increased component count. In this paper, a single-stage switched inductor Cuk converter based PFC converter is proposed, which offers high step-down gain, low current stress, high efficiency, and reduced component count. The operational analysis and design equations for various components of the proposed converter are carried out in continuous current mode. This paper presents mathematical modeling, analysis, simulation, and experimentation on the proposed converter rated for 500 W, 48 V/10.4 A. The performance investigation of the proposed converter with respect to power quality indices like voltage total harmonic distortion (THD), current THD, and total power factor is carried out with various types of loads such as resistive load and battery load in both constant voltage (CV) and constant current (CC) mode. Furthermore, the dynamic performance of the proposed converter with battery charging is investigated in CV mode and CC mode with respect to the wide range of supply variations. [ABSTRACT FROM AUTHOR]

This paper introduces a new bidirectional single-phase inverter topology. The proposed topology has three ports: a dc port, an ac port, and a ripple port. The ac and dc ports are bidirectional to support rectifier or inverter operation. A small inductor, which is of alternating current, exchanges power between different ports of the single-phase system. The proposed topology is capable of accomplishing voltage step-up or step-down, suppressing the ripple power, and performing inversion or rectification operation in one stage of power conversion. The proposed configuration offers an active decoupling function, which not only eliminates the double-frequency ripple power at the dc port but also achieves minimum capacitance requirements to minimize the size of the decoupling capacitor. This facilitates the use of a very small thin-film capacitor, which offers a much longer life-cycle and higher reliability compared with a bulky electrolytic capacitor. A control approach is also developed to regulate the dc-port and ac-port currents and manage the ripple power through proper distribution of power between each port. Moreover, a very small capacitor can be placed in parallel with the inductor to reinforce the proposed configuration with soft-switching operation, which enhances the overall efficiency and minimizes the voltage stress over the semiconductor devices. This converter is capable of accommodating an arbitrary number of dc or single-phase ac sources and/or loads configuring a multiple-input multiple-output inverter without introducing any additional passive elements or sacrificing the performance of the inverter. The primary focus of this paper is dc-to-ac conversion mode of operation, in spite of the fact that it can easily be configured to serve as a rectifier. Experimental and simulation results are presented to validate the operation of the proposed topology and its control strategy. [ABSTRACT FROM AUTHOR]

The double-sided LCC topology provides a highly efficient compensation method for electric vehicle (EV) wireless charging systems. However, the two compensated coils occupy a large volume. In order to address the volume increase as well as to be compatible with unipolar coil structures, which are widely applied in EV wireless charging systems, an integration method is introduced in this paper. Aspect ratios of the compensated coils are studied to minimize the respective coupling effect. With the proposed integration method, the extra coupling coefficients are either eliminated or decreased to a negligible level. A wireless charging system with the proposed integration method is built and the experimental results show that the system resonates at 85 kHz and delivers 3.09 kW with a dc–dc efficiency of 95.49% at an air gap of 150 mm. Furthermore, a comparison with the integration method into bipolar coil structures is presented and the results demonstrate that the system with the proposed integration method is more immune to front-to-rear and vertical misalignments. [ABSTRACT FROM AUTHOR]

An important feature of an inductive power transfer (IPT) system is its power transfer efficiency and capability can be significantly affected by the load and the magnetic coupling variations. Therefore, identifying the load and the mutual inductance is essential to improve the system performance. This paper proposes a load and mutual inductance identification method for IPT systems with parallel-compensated power pickups based only on the information detected from the primary side. The proposed method can be implemented for primary resonant circuits whether they are series or parallel tuned, or with a hybrid compensation, such as an LCL configuration. An identification model is established according to the steady-state characteristics of the system. Identification results are obtained based on mathematical derivations and analyses. The proposed identification method is realized without any extra communication or control, and both the simulation and experimental results have verified its feasibility. [ABSTRACT FROM AUTHOR]

For implantable devices, miniaturization is a key design consideration, which facilitates keyhole surgery and relieves the surgical pain. Wireless power transfer is a commonly used way for implants, and a high power transfer efficiency (PTE) could help to minimize or even remove the battery inside the human body. Conventionally, the required power is delivered transcutaneously to a medical implant by inductive coupling or capacitive coupling, but the PTE is extremely low when targeting at a very small implant through a thick tissue layer. In this paper, we propose a new technique by utilizing the body tissue as the power transfer channel, where a pair of medical electrodes are attached on the body surface to supply power to a miniaturized implant with a differential input. The PTE is remarkably improved by the current loop through the body tissue without violating the IEEE specific absorption rate standard. Measurement results show that the tissue-channel technique achieves 0.39% PTE for a 1-mm-sized implant locating 5 cm deep inside the tissue. [ABSTRACT FROM AUTHOR]

In this paper, a new pulse width modulation (PWM) scheme and commutation method is presented for one phase loss operation of three-phase isolated buck matrix-type rectifier. With the proposed PWM scheme, the maximum allowable voltage gain for one phase loss operation can be achieved, which permits the continuous operation of the converter to deliver two-third of the rated power and regulate the output voltage with maximum output voltage drop less than 5% of nominal output voltage. In addition, with the proposed commutation method, a safe transition from one phase loss operation to normal operation and vice versa can occur with minimum commutation steps (two-step) under zero-voltage switching condition. The performance of the proposed PWM scheme and commutation schemes with one phase loss operation is evaluated and verified by simulations and experiments on a 5 kW prototype. [ABSTRACT FROM AUTHOR]

A single-inductor multiple-output (SIMO) dc–dc converter with output-voltage-aware charge control (OVACC) is presented in this paper. The OVACC scheme reduces the cross regulation by computing the total energy required by all outputs to extract exactly the same amount of energy from the input. Moreover, the proposed design also extends the load capability range of the SIMO converter by supporting the operation in both continuous conduction mode and discontinuous conduction mode while boosting the overall power efficiency. The proposed SIMO (five outputs) dc–dc converter has been implemented in a 0.18 μm 1P6M CMOS process. Measurement results show that the best cross regulation is 0.016 mV/mA when the output current of 250 mA abruptly changes. And no cross regulation is observed when the first output current changes 150 mA, the second output current changes 160 mA, the third and fourth output currents change 180 mA, and the last output current changes 250 mA. Also, the measured peak power efficiency is 86%. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) for battery charging applications has significant advantages over the traditional plug-in system. Since misalignment between the primary and secondary windings is inevitable, it is of significance to improve the misalignment tolerance of IPT systems with constant-current (CC) and constant-voltage (CV) outputs for battery charging. In this paper, the load-independent output characteristic of the hybrid topology and the function switching between CC and CV of the reconfigurable topology are analyzed. Besides, a hybrid and reconfigurable IPT system with 3-D misalignment tolerance for CC and CV outputs is proposed, simplifying or even canceling control schemes. Moreover, a novel parametric design method is given for the IPT system, which can suppress the fluctuation of the output voltage/current within a certain range of misalignment. In order to validate the performance of the proposed topology, a 1-kW prototype is built, and the corresponding experiments are carried out. In the CC/CV mode, the system can operate with the longitudinal misalignment to 50% when the load varies from 36 to 480 Ω, and the fluctuation of the output current/voltage is within 5%. Similarly, the misalignment in Y- and Z-axis is 12.5% and 33.3%, respectively. [ABSTRACT FROM AUTHOR]

Renewable energy sources (RESs), e.g., wind and solar photovoltaics, have been increasingly used to meet worldwide growing energy demands and reduce greenhouse gas emissions. However, RESs are normally coupled to the power grid through fast-response power converters without any inertia, leading to decreased power system inertia. As a result, the grid frequency may easily go beyond the acceptable range under severe frequency events, resulting in undesirable load-shedding, cascading failures, or even large-scale blackouts. To address the ever-decreasing inertia issue, this paper proposes the concept of distributed power system virtual inertia, which can be implemented by grid-connected power converters. Without modifications of system hardware, power system inertia can be emulated by the energy stored in the dc-link capacitors of grid-connected power converters. By regulating the dc-link voltages in proportional to the grid frequency, the dc-link capacitors are aggregated into an extremely large equivalent capacitor serving as an energy buffer for frequency support. Furthermore, the limitation of virtual inertia, together with its design parameters, is identified. Finally, the feasibility of the proposed concept is validated through simulation and experimental results, which indicate that 12.5% and 50% improvements of the frequency nadir and rate of change of frequency can be achieved. [ABSTRACT FROM AUTHOR]

Single-loop current control is an attractive scheme for the LCL-type grid-connected inverter due to its simplicity and low cost. However, conventional single-loop control schemes, which command either the inverter current or the grid current, are subject to the specific resonance frequency regions. The weighted average current control, which splits the filter capacitor into two parts (in form of an LCCL filter) and commands the current flowing between these two parts, is independent of the resonance frequency, but on the other hand, it is limited by the poor sensitivity to the grid impedance variation and weak stability in the grid current. These limitations are comprehensively explained in this paper and then addressed by identifying that the single-loop weighted average current control is equivalent to the dual-loop grid current control with an inherent capacitor current active damping. By tuning the capacitor split proportion as a second degree of freedom, an optimal damping performance that is robust to the grid impedance variation can be naturally achieved using only the inherent damping. Thus, no extra damping is required, and the single-loop structure with only one current sensing turns to be adequate. Moreover, for convenience of practical implementation, an improved LCCL filter configuration is proposed to allow the use of two equal nominal capacitances for the split capacitors. Finally, experiments are performed to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

High-frequency (HF) switching and ac-side unbalanced loads challenge smart transformer (ST)-fed hybrid grids (both ac and dc), causing common-mode (CM) voltage variations and dc-link oscillation. The HF switching introduces an HF CM voltage and the ac grid unbalanced loads introduce a fundamental frequency CM voltage in hybrid grids. The CM voltage in ST-fed distributed grids degrades the power quality, threatens the safety of the connected devices, and potentially constitutes a health risk for the operators of such devices. Therefore, this paper systematically analyzes the root causes of the ST CM voltage variations and the impacts on hybrid grids. Based on the two typical configurations (three- and four-leg converters), the performance and requirements of CM inductor filter and bypass CM filter on HF CM voltage suppression are studied in detail. By considering the CM voltage suppression and dc capacitor lifetime, a four-leg converter with improved modulation strategy and small dc bypass film capacitor is proposed. The simulation and experimental results clearly verify the feasibility and correctness of the proposed strategies. [ABSTRACT FROM AUTHOR]

Switched-capacitor (SC) converters have drawn more and more attention in recent years due to their unique advantages. The accurate analysis methods will fully determine an SC converter's steady-state and dynamical performance. Proper design of SC converters requires full understanding of all impacts on circuit operation including steady-state and dynamical performance. Some previous modeling methods for SC converters have established a popular static model for SC converters which is composed of an ideal transformer and equivalent output resistance. This paper presents a dynamic capacitor ampere-second balance transient calculation modeling method. The instantaneous state of input voltage, instantaneous state of output voltage, instantaneous state of voltage of flying capacitor, “on time” and “off time,” as well as switching period are all included in the proposed model. The proposed modeling method was applied in both the dual-phase SC converters and the two-switch boosting SC converters. This modeling method was validated by the simulation and experimental results. The proposed model can be used to accurately predict and optimize the performance in the design phase for the low and high power SC converters. Based on the proposed modeling method, the SC converters could be controlled by a variable frequency control method. [ABSTRACT FROM AUTHOR]

This paper investigates the open-circuit faults of switching devices in the three-level T-Type inverter and proposes a new tolerant control method. The three-phase current and variation of the neutral-point voltage are detected to determine the fault switch. A carrier-based pulse width modulation is developed to tolerate switch fault by transiting from three-level to two-level switching. This makes the modulation scheme easier to be implemented compared to space vector modulation. For the neutral-point fault, the fault phase is operated by two-level modulation to produce the same rating voltage. On the other hand, the inverter is able to produce balanced voltage with reduced rating by keeping the phase of half-bridge fault to the neutral-point voltage. The neutral-point voltage is also able to be balanced by using two-level modulation since it does not contribute the neutral-point current. The performance and effectiveness of the proposed tolerant control are verified by a laboratory build. [ABSTRACT FROM AUTHOR]

In order to incorporate the advantage of the $V^{2}$ control scheme and the benefits of digital implementation, this paper proposes a digital $V^{2}$ control with hybrid capacitor current ramp compensation, which includes the estimated output capacitor current ramp and the external ramp. Since capacitor current responds to the load change immediately, the proposed method has faster transient response than either digital inductor current compensation or external ramp compensation. The proposed estimator does not require high sampling rate and avoids the current ramp distortion due to the parasitic resistance and inductance. The small-signal model is derived by describing function to understand the dynamic characteristics of the proposed control scheme. The model provides design criteria of the current feedback gain and the external ramp slope. The effectiveness of the proposed control architecture and the current ramp estimator is verified by simulation and experimental results. Compared with the benchmark, the proposed control has 70% reduction on settling time and 20% reduction on undershoot deviation. [ABSTRACT FROM AUTHOR]

In this paper, a unified equivalent circuit model which can simplify the design and analysis of a family of high-voltage (HV) generation architectures based on the series–parallel (LCC) resonant converter is proposed. First, four HV generation architectures are reviewed in terms of the modularization level of HV transformers and rectifiers. Next, the steady-state, unified equivalent resistor and capacitor (RC) model that can be easily embedded into the resonant tank to replace the complex HV transformers and rectifiers is derived. The generic model can be applied to the HV generators with different architectures, different voltage multiplier topologies, stage, and polarities number. Further analysis of the power factor of the resonant tank, the voltage gain of HV generators, and electrical stresses of power components is achieved with the derived equivalent circuit model. The analysis reveals the inherent circuit properties among HV generators with different configurations. Subsequently, a comprehensive design methodology considering the power factor, conduction angle, and quality factor is presented, which leads to low electrical stresses on the components and high efficiency. Furthermore, the parameter selection constraint based on the power factor, conduction angle, and quality factor is derived, which can ensure the effective design outputs. Finally, the proposed unified equivalent model and comprehensive design methodology are validated by the experimental results of a 250 V input, 20 kV output 500 W HV generator hardware prototype with distributed transformers and voltage multipliers. [ABSTRACT FROM AUTHOR]

A photovoltaic (PV) microinverter converts the dc from a PV panel to ac directly, which has the advantages of improved energy harvesting, friendly “plug-and-play” operation, enhanced flexibility/expandability, excellent system redundancy, and no dc cabling/safety issue; therefore, it is an attractive solution for the grid-connected PV system. In ac PV module applications, the features such as power density, reliability, efficiency, and reactive power capability are essential for the microinverters. In order to overcome the drawbacks of the conventional microinverters, including the power density/reliability issues caused by the bulky input capacitors and the limited output reactive power capability, a three-phase microinverter without energy storage capacitors is proposed in this paper. The proposed microinverter consists of a flyback stage, a third-harmonic injection circuit, and a line-commutated current-source-type inverter. The flyback stage realizes maximum power point tracking, while the third-harmonic injection circuit is responsible for output power factor correction. In addition to having the potential of achieving compact structure, long lifetime, and high efficiency, the developed microinverter provides extended output reactive power control range and three-phase balanced output. Finally, the proposed topology and the method are verified by simulations and experimental results. [ABSTRACT FROM AUTHOR]

In high-power applications, parallel-operated T-type three-level pulse width modulation (PWM) rectifiers (T3LPRs) are widely employed to improve the power capacity and system reliability. For parallel-operated T3LPRs, there are two important issues need to be properly addressed: 1) the neutral-point potential (NPP) balancing, and 2) the zero sequence circulating current (ZSCC) between the common ac and dc bus. In this paper, the fluctuation of NPP in a T3LPR and the generative mechanism of ZSCC in parallel-operated T3LPRs are first investigated. The zero sequence voltage (ZSV) difference between the parallel-operated T3LPRs is identified as the main excitation source of the ZSCC problem. Meanwhile, the disconnection of the neutral point and the control effect difference of NPP balancing in each T3LPR also affect the ZSCCs within the parallel-operated T3LPRs. To adjust the ZSV of T3LPRs, the dwell time of the positive small voltage vector in each switching period of the converter, which is usually adjusted to balance the NPP, is also required to be controlled to suppress ZSCC. Therefore, in this paper, to avoid the possible conflict, an improved modulation mechanism is designed to guarantee simultaneous ZSCC suppression and NPP balancing. The neutral points of each T3LPR are connected. Then, by adjusting the dwell time of the positive small voltage vector, the charging time of two dc capacitors is adjusted to balance the NPP, and the ZSV differences between different T3LPRs are adjusted to suppress ZSCCs. To avoid the control effect difference of independent NPP balancing in different T3LPRs, all T3LPRs share the same value marking the difference between two dc capacitor voltages. Thus, a communication with a greatly reduced baud rate requirement is needed for NPP balancing to transfer the difference between the two dc capacitor voltages. Moreover, no extra circuit is needed for ZSCC suppression. These approaches make the proposed improved space vector PWM strategy much more practical and easy to employ. The proposed method is verified with experiments on two 3-kW T3LPR prototypes. [ABSTRACT FROM AUTHOR]

High-step-up dc/dc converters are widely required in grid-connected applications with renewable energy sources. An extremely high-ratio step-up nonisolated dc/dc converter, in the form of a harmonics-boosted resonant converter, is proposed in this paper. This proposed converter consists of a high-frequency dc/ac inverter stage that is followed by a passive ac/dc rectifier stage connected in cascade. Conventionally, such a dc/ac inverter is designed to output a pure sinusoidal ac voltage with an amplitude several times the amplitude of the input voltage. However, for the proposed converter, the harmonics-boosted inverter stage is designed to contain selected voltage harmonics that significantly boost the amplitude of its output voltage. This greatly increases the overall gain of the converter. The adopted ac/dc stage is a diode-capacitor rectifier, which is of high efficiency and easily extendable to increase the voltage gain. Importantly, the proposed converter involves only one active switch. With only one active switch, the driver's loss is minimized and the converter's control is simplified. Zero-voltage switching is applied to reduce the switching loss, which also allows the converter to operate efficiently at high frequency, and thus can be designed for high power density. The optimal design of the two converter stages and their combined voltage gain is investigated and reported. Besides, a design guideline of the proposed converter is provided. A prototype of a 57-time harmonics-boosted resonant converter with 3.3 V input voltage, 500 kHz switching frequency, and 21 W output power, is built. The experimental result shows that the achieved converter's efficiency is as high as 88.6%. [ABSTRACT FROM AUTHOR]

Reliability analysis is an important tool for assisting the design phase of a power electronic converter to fulfill its life-cycle specifications. Existing converter-level reliability analysis methods have two major limitations: 1) being based on constant failure rate models; and 2) lack of consideration of long-term operation conditions (i.e., mission profile). Although various studies have been presented on power electronic component-level lifetime prediction based on wear-out failure mechanisms and mission profile, it is still a challenge to apply the same method to the reliability analysis of converters with multiple components. Component lifetime prediction based on associated models provides only a $B_{X}$ lifetime information (i.e., the time when X% items fail), but the time-dependent reliability curve is still not available. In this paper, a converter-level reliability analysis approach is proposed based on time-dependent failure rate models and long-term mission profiles. Two different methods to obtain the component-level time-to-failure are illustrated by a case study of dc/dc converters for a 5 kW fuel cell-based backup power system. The reliability analysis of the converters with and without redundancy is also performed to assist the decision making in the design phase of the fuel cell power conditioning stage. [ABSTRACT FROM AUTHOR]

When compared to plugged-in chargers, inductive power transfer (IPT) methods for electric vehicle (EV) battery chargers have several benefits, such as greater convenience and higher safety. In an EV, the battery is an indispensable component, and lithium-ion batteries are identified as the most competitive candidate to be used in EVs due to their high power density, long cycle life, and better safety. In order to charge lithium-ion batteries, constant current/constant voltage (CC/CV) is often adopted for high-efficiency charging and sufficient protection. However, it is not easy to design an IPT battery charger that can charge the batteries with a CC/CV charge due to the wide range of load variations, because it requires a wide range of variation in its operating frequency, duty, or phase-shift. Furthermore, zero phase angle (ZPA) condition for the primary inverter cannot be achieved over the entire charge process without the help of additional switches and related driver circuits to transform the topology. This paper proposes a design method that makes it possible to implement the CC/CV mode charge with minimum frequency variation during the entire charge process by using the load-independent characteristics of an IPT system under the ZPA condition without any additional switches. A theoretical analysis is presented to provide the appropriate procedure to design the double-sided LCC compensation tank which can achieve both CC and CV mode charge under ZPA condition at two different resonant frequencies. As a consequence, the proposed method is advantageous in that the efficiency of compensation tank is very high due to achieving the perfect resonant operation during the entire charge process. A 6.6-kW prototype charger has been implemented to demonstrate the feasibility and validity of the proposed method. A maximum efficiency of 96.1% has been achieved with a 200-mm airgap at 6.6 kW during the CC mode charge. [ABSTRACT FROM AUTHOR]

A coupled-inductor dc–dc converter has several modes of operation in continuous-conduction mode (CCM) and discontinuous-conduction mode (DCM), and is quite complex. This paper presents the derivation of the complete small-signal model of a two-phase interleaved dc–dc boost converter utilizing a single-core coupled-inductor operating in both CCM and DCM. Several small-signal models are required to fully model the converter due to the complexity of the converter operating in DCM. The transfer functions are then derived from these small-signal models. The theoretical analysis is validated experimentally using frequency sweeps from a 1-kW prototype. [ABSTRACT FROM AUTHOR]

This paper proposes generation of a 15-level (14 concentric) dodecagonal voltage space vector structure (DVSVS) for a star connected induction motor drive. The proposed multilevel DVSVS is obtained by cascading two inverters, namely a primary and secondary inverter. The primary inverter is a five-level (5L) structure formed by stacking two three-level flying capacitors with individual reduced dc sources and the secondary inverter is also a 5L structure formed by cascading two capacitor-fed cascaded H-bridges (CHB). The active power is supplied by the primary inverter, while the secondary inverter acts as switched capacitor harmonics filter, and capacitors in the secondary inverter are balanced naturally irrespective of load power factor for entire modulation index. The high-voltage dc supply fed primary inverter is operated in quasi-square wave mode, while the high frequency switching is applied to low voltage CHBs, thus, reducing the overall switching loss. The proposed scheme gives the advantages of both DVSVS and multilevel structure, thus, making it one of the solutions for battery or stacked dc-fed applications. The paper also presents the experimental results as well as comparison study with the existing topologies to support the advantages of proposed scheme. [ABSTRACT FROM AUTHOR]

This paper presents a new solution for filtering current harmonics in three-phase four-wire networks. The original four-branch star (FBS) filter topology presented in this paper is characterized by a particular layout of single-phase inductances and capacitors, without using any transformer or special electromagnetic device. Via this layout, a power filter, with two different and simultaneous resonance frequencies and sequences, is achieved-one frequency for positive-/negative-sequence and another one for zero-sequence components. This filter topology can work either as a passive filter, when only passive components are employed, or as a hybrid filter, when its behavior is improved by integrating a power converter into the filter structure. The paper analyzes the proposed topology, and derives fundamental concepts about the control of the resulting hybrid power filter. From this analysis, a specific implementation of a three-phase four-wire hybrid power filter is presented as an illustrative application of the filtering topology. An extensive evaluation using simulation and experimental results from a DSP-based laboratory prototype is conducted in order to verify and validate the good performance achieved by the proposed FBS passive/hybrid power filter. [ABSTRACT FROM AUTHOR]

A bidirectional dc-dc converter typically consists of a buck and a boost converters. In order to have high-power density, the converter can be designed to operate in discontinuous conducting mode (DCM) such that the passive inductor can be minimized. The DCM operation associated current ripple can be alleviated by interleaving multiphase currents. However, DCM operation tends to increase turnoff loss because of a high peak current and its associated parasitic ringing due to the oscillation between the inductor and the device output capacitance. Thus, the efficiency is suffered with the conventional DCM operation. Although to reduce the turnoff loss a lossless capacitor snubber can be added across the switch, the energy stored in the capacitor needs to be discharged before device is turned on. This paper adopts a gate signal complimentary control scheme to turn on the nonactive switch and to divert the current into the antiparalleled diode of the active switch so that the main switch can be turned on under zero-voltage condition. This diverted current also eliminates the parasitic ringing in inductor current. For capacitor value selection, there is a tradeoff between turnon and turnoff losses. This paper suggests the optimization of capacitance selection through a series of hardware experiments to ensure the overall power loss minimization under complimentary DCM operating condition. According to the suggested design optimization, a 100-kW hardware prototype is constructed and tested. The experimental results are provided to verify the proposed design approach. [ABSTRACT FROM AUTHOR]

In this correspondence, it is shown that there are some problems when an inductive load is considered in Figs. 2–5 of the original paper [1]. The objective of this correspondence is to point out these problems using analysis and detailed computer simulation. [ABSTRACT FROM AUTHOR]

In this paper, the control of an ac-dc-ac converter with a front-end diode rectifier and reduced dc-link capacitor based on the space vector modulation strategy is investigated. The modulation index is time-varying and determined by the instantaneous value of the dc voltage measured by a voltage sensor. Using a small bipolar capacitor, instead of a large electrolytic capacitor on the dc-link, increases the lifetime of the converter and reduces its size. The input current quality of this converter has been shown to be superior to that of the conventional ac-dc-ac converter with front-end diode rectifier. The perfectly sinusoidal local average output voltage can still be achieved under unbalanced input voltage condition by implementing a time-varying modulation index. The rule for determining the dc capacitance has also been studied in this paper. The simulation results obtained from PSIM simulation software and experimental results obtained from the lab prototype are used to verify the theoretical expectations. [ABSTRACT FROM AUTHOR]

This paper presents a fully-digital-controlled shunt hybrid filter for damping of harmonic propagation in power distribution systems. The harmonic propagation is caused by resonance between line inductances and power capacitors installed for power factor correction. possible solution to damping out harmonic propagation is based on installation of a shunt pure active filter at the end of a feeder. This paper proposes a shunt hybrid active filter characterized by series connection of a seventh-tuned LC filter per phase and a small-rated three-phase active filter. Like the pure filter, the hybrid filter is connected to the end bus of a feeder. The capacitor of the LC filter imposes a high impedance to the fundamental frequency, so that the fundamental voltage appears across the capacitor. This unique feature allows us to directly connect the hybrid filter to the 6.6-kV power line without step-down transformers. Furthermore, the capacitor used in this hybrid filter is lighter, cheaper and smaller than the transformer used in the pure filter. Theoretical analysis, along with experimental results obtained from a 200-V, 20-kW laboratory system, verifies the viability and effectiveness of the proposed hybrid filter. [ABSTRACT FROM AUTHOR]

This paper presents a new design for an integrated, multilayer dielectric ceramic device that is suitable for isolated high frequency ($>$100 kHz) power transfer. The multilayer capacitive isolation device (MLCID) is a four terminal multilayer ceramic structure consisting of barium strontium titanate and alumina layers. Some key advantages of the MLCID are a reduction in the losses achieved in comparison with conventional decoupling techniques and the ease of manufacturing due to the planar design. The paper focuses on the MLCID design details, its characterization, and its performance. [ABSTRACT FROM AUTHOR]

Stability analysis of average value models (AVMs) of vector-controlled modular multilevel converters (MMCs) is the subject matter of this paper. Stability analysis of fundamental frequency phasor-based AVMs of MMCs can be conducted in a traditional linear time-invariant framework through eigenvalue computation. This class of models does not consider circulating current control loop and hence fails to capture system instability that occurs in a certain range of gains of the circulating current controller. We propose stability analysis in a linear time-periodic (LTP) framework to solve this issue. To that end, a nonlinear AVM is presented that considers the submodule capacitor insertion dynamics and takes into account the output and the circulating current control schemes in the vector control approach. Upon linearization, an LTP model is derived from this averaged model. It is shown that the Poincar \acutee multipliers are indicative of system instability corresponding to a certain range of gains of the circulating current controller. [ABSTRACT FROM AUTHOR]

This paper provides theoretical and experimental discussions on an optimal carrier frequency for a phase-shifted pulsewidth modulation modular multilevel cascade converter for grid connections. The theoretical discussion concludes that a ratio of the optimal carrier frequency with respect to the supply (ac) frequency is 5/2. A three-phase downscaled front-to-front system is designed, constructed, and tested to confirm validity of the theoretical discussion. It consists of a pair of three-phase modular multilevel cascade converters rated at 400 Vdc and 10 kW, where the carrier frequency is set to 450 Hz and the ac frequency to 180 Hz, that is, their ratio is equal to 5/2. Moreover, simulated waveforms are compared to experimental ones under the same operating conditions. Both experimental and simulated waveforms agree well with each other not only in steady states but also in transient states. [ABSTRACT FROM AUTHOR]

In this paper, an alternative method to achieve more efficient dc power distribution and voltage regulation for future data centers is presented. This paper describes a series-stacked power delivery architecture, where servers are connected electrically in series, thereby, providing inherent step down of voltage. Server voltage regulation is performed by differential power converters, which only process the mismatch power between servers. The bulk power flows with no power processing, yielding greatly increased system efficiency compared to conventional architectures. We demonstrate the series-connected architecture with an experimental proof of concept and compare the proposed architecture with a conventional dc power delivery architecture employing a best-in-class power supply unit for servers. The proposed power delivery architecture is validated with a series-stacked server rack consisting of four 12 V servers, powered from a 48 V dc bus, performing two different real-world operations: web traffic management and computation. Through experimental measurements, we demonstrate up to a 40x reduction in power conversion losses compared to state-of-the-art hardware, and an overall best-case system conversion efficiency of 99.89%. [ABSTRACT FROM AUTHOR]

The five-level active neutral-point-clamped (5L-ANPC) converter is becoming an attractive topology of multilevel converter family. A novel SVPWM algorithm based on line voltage coordinate was studied in this paper to overcome shortcomings of the traditional algorithm. Through coordinate transformation, steps of determining the basic vectors and the solution about the basic vector corresponding action time are simplified. Combining with the characteristics of 5L-ANPC converter and the new control algorithm, a method of controlling the voltage balancing of dc-link capacitors and floating-capacitors is proposed. According to the voltage of dc-link capacitors, the suitable switching sequence which can balance the voltage of dc-link capacitors is chosen. The high common-mode voltage will affect the service life of motor and reduce the reliability of the system especially in high-voltage converter. The common-mode voltage is also reduced by choosing the right switching state in this paper. The validity of the proposed method was proved by the experimental results. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) are widely used in different applications. Due to low-loss operation, compactness, and high modularity, MMC is extremely attractive for high-voltage direct-current (HVDC) transmission systems. The HVDC station loss is highly related to the converter switching pulse pattern, which is generated by modulation algorithm and cell selection methods. This paper formulates the switching pulse pattern generation, as a versatile optimization problem. The problem constraints and objectives are formulated for HVDC applications and compared with similar problems in the field of computer science. To overcome the computational complexity in solving the introduced optimization problem, a heuristic method is proposed for cell selection algorithm. The method utilizes the current level in order to obtain lossless switching at zero-current crossings. The study of the proposed method, in a time-domain simulation platform, shows that the method can reduce the switching converter losses by 60% compared to carrier-based modulation, maintaining the same capacitor voltage ripple. Eventually, the practical functionality of the proposed method is verified in a real-time digital simulator, RTDS, for a 512-level converter in a point to point HVDC link. Although this paper focuses on HVDC, the mathematical model is applicable for any MMC application. [ABSTRACT FROM PUBLISHER]

Cascaded converter is formed by connecting two subconverters together, sharing a common intermediate dc-link voltage. Regulation of this dc-link voltage is frequently realized with a proportional-integral (PI) controller, whose high gain at dc helps to force a zero steady-state tracking error. Such precise tracking is, however, at the expense of increasing the system type, caused by the extra pole at the origin introduced by the PI controller. The overall system may, hence, be tougher to control. To reduce the system type while preserving precise dc-link voltage tracking, this paper proposes a coordinated control scheme for the cascaded converter, which uses only a proportional dc-link voltage regulator. The resulting converter is thus dynamically faster, and when compared with the conventional PI-controlled converter, it is less affected by impedance interaction between its two subconverters. The proposed scheme can be used with either unidirectional or bidirectional power flow, and has been verified by simulation and experimental results presented in this paper. [ABSTRACT FROM PUBLISHER]

Compared with conventional power transformer, the power electronic transformer (PET) or solid-state transformer has many attractive additional features. This paper focuses on an H-bridge-based three-phase three-stage modular PET, which consists of an input stage with series-connected H-bridge converters, an isolation stage with several independent dual-active-bridge converters, and an output stage with parallel-connected H-bridge converters. This PET suffers dc-link capacitor voltage unbalancing issue, and the parallel-connected module current unbalancing sharing issue. In this paper, a system control structure is proposed for the PET to deal with these issues. Different input-stage individual module dc-link voltage balancing control methods are analyzed and compared. It is found that the one implemented by directly trimming module output voltage amplitude is most suitable for PET. Moreover, a downscaled laboratory prototype is designed, built, and tested to verify the control strategy. [ABSTRACT FROM PUBLISHER]

This paper discusses an alternative approach to designing LED drivers based on high-voltage operation. Compared with the conventional approach of driving LEDs with low voltage and high current, the alternative approach aims to deliver the same power to LED load with high voltage and low current so that small and nonelectrolytic capacitor can be used. High-voltage operation also facilitates the use of simple PFC preregulators such as boost or SEPIC converters as single-stage LED drivers. This paper begins with the derivation of the relationship between the nominal output voltage and output capacitor's size of a PFC preregulator for achieving a given output voltage ripple's size, followed by a review of the recently emerged high-voltage LED packages suitable for the proposed application. This paper also discusses the flicker and colorimetric performances of LED light sources under the influence of large current ripple when nonelectrolytic capacitor is used. The method of third-harmonic current injection to the input current of LED drivers is also incorporated as an option for further reducing the output capacitor's size while meeting a specified flicker limit. Finally, a design example of high-voltage LED driver based on a boost PFC preregulator with third-harmonic current injection is presented and verified experimentally. [ABSTRACT FROM PUBLISHER]

In order to balance the light-emitting-diode (LED) current in each channel, many active and passive methods have been investigated. Among the various methods, the passive method using the LLC converter with a blocking capacitor or flyback converter with a current-sharing transformer (CST) in the secondary side is one of the simplest methods because it does not use any active component. However, the LLC driver requires two main switches and external resonant inductor to obtain a wide output voltage range. Also, flyback with a CST requires an additional magnetic component for CST and high-voltage rated diodes, resulting in the limitation of the cost and system volume. In this paper, a single-switch forward-flyback driver for a two-channel LED is proposed. The most powerful advantage of the proposed driver is the cost effectiveness, since it eliminates additional magnetic component. Furthermore, due to the reduced-voltage stress on rectifier diodes compared to the flyback driver, the proposed driver achieves a higher efficiency. The prototype of the 150–100-V/0.3-A two-channel LED verifies the effectiveness of this paper. [ABSTRACT FROM PUBLISHER]

In this paper, a modulation and control method for the new transformerless unified power flow controller (UPFC) is presented. As is well known, the conventional UPFC that consists of two back-to-back inverters requires bulky and often complicated zigzag transformers for isolation and reaching high power rating with desired voltage waveforms. To overcome this problem, a completely transformerless UPFC based on an innovative configuration of two cascade multilevel inverters has been proposed. The new UPFC offers several advantages over the traditional technology, such as transformerless, light weight, high efficiency, low cost and fast dynamic response. This paper focuses on the modulation and control for this new transformerless UPFC, including optimized fundamental frequency modulation for low total harmonic distortion and high efficiency, independent active and reactive power control over the transmission line, dc-link voltage balance control, etc. The new UPFC with proposed control method is verified by experiments based on 4160-V test setup. Both the steady-state and dynamic-response results will be shown in this paper. [ABSTRACT FROM PUBLISHER]

In order to obtain a high step-up voltage gain, high-efficiency converter, this paper proposed a dual switches dc/dc converter with three-winding-coupled inductor and charge pump. The proposed converter composed of dual switches structure, three-winding-coupled inductor, and charge pump. This combination facilitates realization of high step-up voltage gain with a low voltage/current stress on the power switches. Meanwhile, the voltage across the diodes is low and the diode reverse-recovery problem is alleviated by the leakage inductance of the three-winding-coupled inductor. Taking all these into consideration, the efficiency can be high. This paper illustrated the operation principle of the proposed converter; discussed the effect of leakage inductance on voltage gain; the conditions of zero current shutting off of the diodes are illustrated; the voltage and current stress of the power devices are shown; a comparison between the performance of the proposed converter and previous high step-up converters was conducted. Finally, a prototype rated at 500 W has been established, and the experimental results verify the correctness of the analysis. [ABSTRACT FROM AUTHOR]

This paper first analyzes the current paths on a planar busbar based on insulated-gate bipolar transistor bridge switching states and dc-link capacitor configurations. The busbar's circuit models which include both self- and mutual inductances are developed based on the identified current paths. The inductance circuit models are analyzed and reduced for different switching states, transition states, and dc-link capacitor configurations. Inductance and current sharing is analyzed based on circuit theory. Both simulations and measurements are conducted to verify the developed technique. [ABSTRACT FROM AUTHOR]

In order to solve the neutral-point voltage unbalancing problem for three-level inverters, this paper proposes a method to balance the neutral-point voltage for three-level inverters with variable modulation wave offset sinusoidal pulse-width modulation (SPWM) control. Based on the mathematical expressions of neutral-point voltage unbalancing, the factors are studied, which affect the fluctuation of neutral-point voltage. Theoretically the mathematical expressions of the neutral-point voltage with the proposed method are derived, and the mathematical relationship between the fluctuation of neutral-point voltage and the adjusting offset of modulation wave is studied. This proposed method realizes controlling the neutral-point voltage balance by dynamically calculating the offset superimposed to the modulation wave based on SPWM (DCOSPWM). This DCOSPWM method is very simple, which has good steady-state performance and is easy for digital implementation. The simulation results verify the correctness of the theoretical analysis in this paper, and the feasibility and effectiveness of this method is verified by the experiments in the experimental platform of neutral point clamped three-level inverters based on digital signal processor (DSP)-complex programmable logic device (CPLD). [ABSTRACT FROM AUTHOR]

This paper proposes a new multilevel converter based on the cascade connection of double flying capacitor multicell (DFCM) converters, as multilevel modules, to decrease the voltage diversity of the flying capacitors. Furthermore, a new switching pattern based on the phase-shifted pulse-width modulation technique is proposed to reduce the voltage ripple across the flying capacitors. Moreover, the proposed modulation technique reduces the rms value of the current flowing through flying capacitors. This results in an increase in the life time of flying capacitors and a decrease in the capacitance of the flying capacitors, to keep the same amount of the ripple, meaning a reduction in the physical size of the converter. In addition, this paper presents an analytical approach to calculate the average and rms currents of the insulated gate bipolar transistors (IGBTs)/diodes in the DFCM converter in a closed-form expression. The derived closed-form equations to calculate the average and rms currents of the IGBTs/diodes are utilized to investigate the conduction power losses in a DFCM converter and the proposed multilevel converter. Numerical results of the derived closed-form equations match the simulation results well, which validates the derived equations. Furthermore, simulation results and experimental measurements of the proposed multilevel power converter, configured by cascading two two-cell five-level DFCM converters, are presented to validate the performance of the proposed converter as well as the suggested modulation technique. [ABSTRACT FROM AUTHOR]

Passive or active current balancing circuits are usually used to mitigate current imbalance in driving multiple light-emitting-diode (LED) strings. Passive current balancing schemes adopting capacitors with high reliability, small size and low cost are very popular in many applications. However, the high reactive power of the capacitive balancing scheme with variable frequency control will bring high power stress on the VA rating of the main switches which drive this passive current balancing circuit and decrease the overall efficiency. Fixed frequency control does not permit zero-voltage switching (ZVS) under load variations. Hence, this paper proposes a current-source-output LED driver based on LCLC resonant circuit to provide a constant output current regardless of variations in LED parameters. In the LCLC circuit, the number of additional capacitors is scalable with the number of LED strings for current balancing. Moreover, the input impedance of the improved LCLC circuit is designed to be resistive at the operating frequency to minimize reactive power. The conventional duty cycle control can easily incorporate ZVS. The analysis, implementation and verification are detailed in this paper. [ABSTRACT FROM AUTHOR]

This paper presents an integrated solution for a photovoltaic (PV)-fed water-pump drive system, which uses an open-end winding induction motor (OEWIM). The dual-inverter-fed OEWIM drive achieves the functionality of a three-level inverter and requires low value dc-bus voltage. This helps in an optimal arrangement of PV modules, which could avoid large strings and helps in improving the PV performance with wide bandwidth of operating voltage. It also reduces the voltage rating of the dc-link capacitors and switching devices used in the system. The proposed control strategy achieves an integration of both maximum power point tracking and V/f control for the efficient utilization of the PV panels and the motor. The proposed control scheme requires the sensing of PV voltage and current only. Thus, the system requires less number of sensors. All the analytical, simulation, and experimental results of this work under different environmental conditions are presented in this paper. [ABSTRACT FROM AUTHOR]

This paper has presented a stability analysis of a LCL-type grid-connected inverter in the discrete-time domain. It has been found that even though the system is stable when the resonance frequency fr is higher than one-sixth of the sampling frequency ( fs/6), an effective damping scheme is still required due to the potential influence of the grid impedance. With a conventional proportional capacitor-current-feedback active damping (AD), the valid damping region is only up to fs/6. This however is not sufficient in the design process for obtaining a high quality output current and the system can easily become unstable due to the resonance frequency shifting. Considering the resonance frequency design rules of the LCL filter, this paper proposes an improved capacitor-current-feedback AD method. With a detailed analysis and proper parameter design, the upper limit of the damping region is extended to fs/4, which can cover all the possible resonance frequencies. Then, the damping performance of the proposed AD method is studied. It shows that the optimal damping is obtained when the actual resonance frequency is (fr + fs/4)/2. Moreover, an approximate calculation for the optimal damping coefficient R is given. Finally, the experimental results have validated the effectiveness of the proposed AD method. [ABSTRACT FROM AUTHOR]