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A hybrid modular multilevel converter (MMC) consists of both half-bridge submodule (HBSM) and full-bridge submodule (FBSM) in each arm. It has several advantages over other MMC topologies, such as low system loss, reduced cost of the system, but still maintains fault ride-through capability against a solid dc-side fault. However, the hybrid MMC may have a difficulty of submodule (SM) voltage balancing under variation of its dc-bus voltage. Since the voltage unbalance of SMs results in SM capacitor overvoltage and low reliability of the system, the voltage of SMs, which can be also represented as energy of SMs, should be balanced at all time. In this paper, to extend the narrow adjustable range of dc-bus voltage due to the voltage/energy unbalance, new feedback and feedforward energy balancing controllers with revised sorting algorithm are proposed. The feedback control ensures the zero steady-state error, while the feedforward control provides fast dynamic response in the energy balancing control. By applying the proposed control scheme, the hybrid MMC can keep the voltage balance between HBSMs and FBSMs in wider range of dc-bus voltage. The full-scale computer simulation results and down-scale experimental results demonstrate the validity of the proposed control scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a new and robust control strategy for distributed energy resource (DER) units operating in parallel with a three-phase ac grid that could have unbalance voltages. It is well known that the grid imbalance imposes double-frequency ripples on the dc-side capacitor and low-order harmonics on the ac side of a voltage source converter widely used to interface the DERs with the grid. The proposed controller is able to overcome both problems. This not only improves the power quality and stability aspects of the DER and overall system, but will also help reduce the size of the dc-side capacitor. The proposed controller belongs to the family of current controllers and can in principle be added as an upgrade to the existing current controllers. Mathematical analysis and optimal control design aspects are presented and then the performance of the proposed controller is evaluated by various simulation scenarios and hardware-in-the-loop experiments. [ABSTRACT FROM AUTHOR]

This paper proposes a novel pulsewidth modulation cell-level diffusion charge redistribution (DCR) converter based on a switched capacitor converter (SCC) utilizing diffusion capacitance of photovoltaic (PV) cells for PV modules under partial shading. Although a discrete inductor and capacitor are additionally necessary, Joule losses associated with switching operations can be reduced compared to the conventional capacitorless DCR converter. First, ac impedance measurement for a PV cell with 125 × 125 mm was performed, and the diffusion capacitance values were measured to be approximately 6.0 mF at its maximum power point voltage of 0.574 V. Second, the theoretical loss model was derived based on the detailed analysis, and it revealed that an optimal duty cycle achieving the lowest Joule loss was dependent on shading conditions. Third, a dual maximum power point tracking (MPPT) algorithm that controls duty cycles of not only the DCR converter, but a front-end boost converter is also proposed. With the dual MPPT control, the DPP converter operates at its optimal duty cycle to minimize the Joule loss while the boost converter seeks the MPP. The experimental results demonstrated that the maximum power significantly increased, thanks to the DCR converter, and that both the DCR and boost converters operated with respective optimal duty cycles. [ABSTRACT FROM AUTHOR]

In this paper, an integrated step-up inverter without transformer is investigated for photovoltaic (PV) power generation. The proposed topology can be derived by combining a traditional boost converter with a single-phase full bridge dc–ac converter. The main features of the integrated inverter are: First, the leakage current caused by the solar cell array-to-ground parasitic capacitance can be theoretically reduced to zero due to the characteristics of the converter configuration, which can improve the efficiency and the reliability of the PV generation system; second, the output ac voltage of the proposed inverter can be higher than the input dc voltage, which is capable of connecting low voltage PV panels to the grid; third, only five active switches are used in the presented inverter, and those switching devices can be synchronously driven by various sinusoidal pulsewidth modulation methods based on the carrier; therefore, the proposed inverter is compact and with curtailed cost. The working principle and analysis of the proposed integrated inverter are elaborated. Finally, simulation and experimental results are obtained in a lab prototype, which agree well with the theoretical analysis. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) is very popular in high power applications due to its attractive characteristics. The full bridge-based MMC featuring three-phase to single-phase direct ac/ac conversion is a potential solution for ac power supply (ACPS). In this paper, new modulated model predictive control (MMPC) methods are proposed for MMC-ACPS to improve the steady state multi-objective current tracking performance. In the proposed methods, modulated vectors sequence is employed, output voltage levels of upper and lower arms are combined and represented by vectors in the current increments plane first. Then, the plane is divided into eight sectors according to the predictive tracking errors of input current and circulating current. After determining sectors, a modulated vector sequence, consisting of one zero vector and two active vectors, is selected to eliminate these current tracking errors simultaneously at the end of each control period. Duty cycles of the three selected vectors are calculated based on the principle of multiple current tracking errors minimization. Optimized vector selection approaches are illustrated in detail for the proposed MMPC. Since only the adjacent nine vectors are utilized in the proposed methods, the calculation amount is suitable and the dv/dt of the output voltage is also limited. Finally, steady-state and dynamic performances of the proposed control methods are verified by experimental results. [ABSTRACT FROM AUTHOR]

A novel high step-down dc–dc converter with voltage demultiplier cell is proposed in this paper, which is widely used in the high step-down applications such as electric vehicle and digital circuits. The combination of switched-capacitor and coupled-inductor is employed to build extended voltage demultiplier in the proposed converter, which makes a quite higher voltage conversion ratio than that of the existing counterparts. Thus, the proposed converter can achieve extremely low output voltage with an appropriate duty ratio, and the extreme duty cycle is avoided. Accordingly, voltage stress on power switches is greatly reduced. Then, mosfets with low conduction resistance could be utilized to reduce conduction loss. Importantly, zero-voltage switching could be achieved for the main switch, which promotes the conversion efficiency further. In addition, the coupled inductor operates not only as a filter inductor, but also as a transformer when the main switch is in the off state, which reduces the volume of the magnetic core and improves the power density of the converter. The operation principle, performance analysis, design considerations of the proposed converter and performance comparison with recent counterparts are discussed in detail, and finally, an experimental prototype is built to verify the theoretical analysis and performance of the proposed converter. [ABSTRACT FROM AUTHOR]

The instantaneous input and output power of two-stage single-phase converter are imbalanced, resulting in the second harmonic current (SHC) in the dc–dc converter, dc source, or dc load. This paper revisits the SHC reduction control schemes from the dc-bus port-impedance perspective. The dc–dc converters in two-stage single-phase converters are categorized into two types, namely, bus-voltage-controlled converter (BVCC) and bus-current-controlled converter (BCCC). The dc-bus port impedance of the BVCC is revealed to be approximately inversely proportional to the voltage loop gain. Thus, for reducing the SHC in the BVCC, advanced control schemes are required for increasing the dc-bus port impedance. The dc-bus port impedance of the BCCC is proved to be a negative resistor within the control bandwidth. Hence, for reducing the SHC in the BCCC, the dc-bus voltage ripple should be limited. From the dc-bus port-impedance perspective, the SHC reduction control schemes are reclassified into closed-loop-design-based, virtual-impedance-based, and power-decoupling-based approaches, based on which, different SHC reduction control schemes are carefully reviewed and compared. Finally, potential challenges and issues are discussed. [ABSTRACT FROM AUTHOR]

This paper presents a single-stage single-switch soft-switching (S6) power factor correction (PFC) converter to enhance the current shaping performance and reduce the total harmonic distortion. This improvement is achieved by the aid of an auxiliary winding which is used to lower the input current harmonics and also achieve soft-switching condition. As a result, the switching losses are reduced and harmonic content of the input current is improved noticeably in comparison to the conventional S6 PFC converter. Also, the total number of semiconductor elements is reduced in the proposed topology which results in lower cost and higher efficiency. The operating modes of the proposed converter are discussed in detail and the design procedure is presented. A 200-kHz prototype of the proposed converter is implemented and the obtained results are provided to verify the converter theoretical analysis and operation. [ABSTRACT FROM AUTHOR]

When providing ac output, modular multilevel converters (MMCs) experience power fluctuation in the phase arms. The power fluctuation causes voltage ripple on the module capacitors, which grows with the output power and inversely to the output frequency. Thus, low-frequency operations of MMCs, e.g., for motor drives, require injecting common-mode voltages and circulating currents, and strict dc voltage output relative to ground is impossible. To address this problem, this paper introduces a novel module topology that allows parallel module connectivity in addition to the series and bypass states. The parallel state directly transfers power across the modules and arms to cancel the power fluctuations and hence suppresses the capacitor voltage ripple. The proposed series/parallel converter can operate at a wide frequency range down to dc without common-mode voltages or circulating currents; it also allows sensorless operation and full utilization of the components at higher output frequencies. We present detailed simulation and experiment results to characterize the advantages and limitations of the proposed solution. [ABSTRACT FROM AUTHOR]

A two-terminal active capacitor concept has been proposed recently based on an active power electronic circuit with a voltage control method and self-power scheme. It retains the convenience of use as a passive capacitor with two power terminals only without any additional required connections and has the potential to either increase power density or reduce design cost depending on the applications. Based on the previously proof-of-concept study, this paper addresses the design constraints, impedance modeling, and start-up solutions of two-terminal active capacitors. A design method for functionality, efficiency, lifetime, and cost-constraint applications is applied to size the active components and passive elements. A voltage feedforward control scheme is implemented to improve its dynamic response. Two start-up solutions are proposed to overcome the issues brought by the self-power scheme. A case study of an active capacitor for the dc link of a single-phase full-bridge rectifier is presented to demonstrate the theoretical analyses. [ABSTRACT FROM AUTHOR]

With the development of portable electronic products, the requirement for chargers is also getting higher. In this paper, a high-accuracy constant output current/constant output voltage (CC/CV) ac–dc flyback converter is proposed and a novel cable compensation method without external capacitor is put forward. The converter adopts primary-side regulation (PSR) scheme, detecting the output voltage through the auxiliary winding, and adjusting switching frequency to achieve output voltage constant in CV mode. Compared to conventional cable compensation module, the proposed circuit applies a method of pre-filtering, averaging, and re-filtering, to obtain the compensation voltage. This method eliminates the need of external capacitor, reducing cost and increasing reliability of the converter. In CC mode, the switching period is adjusted to be fixed multiple of the demagnetization time, thereby realizing the constant current output. The control chip was implemented in NEC 1 μm HVCMOS process, and a 5-V/1-A prototype has been built to verify its feasibility. Experimental results show that the deviations of output voltage and current are within ±0.9% and ±3% under different inputs and loads, while maximum conversion efficiency can reach a level of 78.2%. [ABSTRACT FROM AUTHOR]

Generating dense multilevel voltage space structure using polygons of higher sides is one of the novel and elegant method to suppress low-order harmonics and to obtain refined sinusoidal voltages using voltage source inverters for variable frequency drive application without passive filters. Apart from the advantages of conventional multilevel inverter topologies, schemes generating polygonal voltage space vector structure can equip full dc-bus utilization, low switching frequency strategies to eliminate low-order harmonics, and increased linear modulation range. In this paper, an induction motor drive scheme generating a highly dense multilevel 24-sided polygonal voltage space vector structure using a single dc source, which can eliminate harmonics till 23rd order from phase voltages, is presented. Cascaded power circuit topology with a flying capacitor inverter fed with a dc source and two low voltage floating capacitor fed H-bridge inverters is used. Detailed experimentally validated results, under scalar as well as indirect rotor field oriented control of induction motor are provided. Studies on voltage ripple and reactive energy in various floating capacitors, harmonic performance of output voltage for wide range of speed operation, are also included. [ABSTRACT FROM AUTHOR]

This paper proposes a voltage-source parallel resonant Class E inverter. The proposed circuit has a shunt capacitor including parasitic capacitance of a switching device and achieves zero-voltage switching and zero-voltage derivative switching at turning-on like a classical Class E inverter. Therefore, high power conversion efficiency is achieved under high operating frequency. Unlike the other Class E inverters, the proposed circuit has no choke inductor or dc blocking capacitor. Moreover, it has a parallel resonant tank unlike the classical Class E inverter. Thus, a circuit protection is not required in a wireless power transfer system. Circuit analysis, circuit simulations, and circuit experiments were carried out. The experimental circuit performed the desired operation and the power conversion efficiency was 93.2% with the output power 4.76 W at the operating frequency 1 MHz. [ABSTRACT FROM AUTHOR]

In this paper, a two-stage transformerless multiple-output converter is proposed for applications requiring a high voltage step-down ratio. The proposed circuit transfers power via a current interface and the use of current-source-mode (CSM) converters, resulting in low voltage stress and drastically simplified control. The first stage of this configuration is regulated to provide a constant current to the second stage. The second stage consists of series-connected CSM boost converters. The high step-down ratio of the proposed configuration reduces the voltage stress in the switches of the second stage. The series-connected CSM converters are inherently independent of each other, leading to a very simple control scheme without the need for decoupling of the input voltage of the interconnected converters. Input voltage variation to the system will not affect the input voltage of the second stage. Load variation in one output will not affect the other outputs. If one or more CSM converters are shorted, there is no impact on other converters. These advantages enable a high scalability. Besides, the first stage of the proposed configuration can operate both in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) with the same control strategy. This feature leads to a low control complexity and elimination of inductors. The performance of the proposed converter is illustrated with a laboratory prototype driving light emitting diodes (LEDs). [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are coming strongly into the lighting market due to their advantages over conventional lighting solutions: energy efficient, controllable in both light and color, long lifetime, lack of a warm-up period, and high power density. Some of these advantages will make LED light sources to be more than just a light bulb, being able to transmit data, control light color, hue, and intensity or even detect people in indoor environments. Nevertheless, these advantages attributed to LED capabilities are, in reality, achieved thanks to the LED driver. This paper reviews the current state-of-the-art strategies to drive LEDs from ac power grids with special emphasis into removing the most limiting component from the point of view of the lifetime, which is the electrolytic capacitor, while achieving a flicker-free performance of the light output of the LED driver. Moreover, it focuses on analyzing the required regulations, challenges, and applicability of LED drivers in both single-phase and three-phase ac power grids. [ABSTRACT FROM AUTHOR]

In this paper, a new class of dc–dc converter topologies based on capacitive link dc–dc converters—Ćuk, SEPIC, and Zeta converters—that operate under the critical conduction mode has been proposed. The proposed converters are the extensions of quasi-square-wave zero-current-switching converters, which use an auxiliary circuit to provide zero-current and zero-voltage switching for all semiconductor switches at both turn on and turn off transitions and eliminate voltage ringing across the output switch. Using the proposed auxiliary circuit, the value of dv/dt has been diminished; hence, the EMI of the proposed topology is significantly reduced compared to the conventional quasi-square-wave zero-current-switching converters. To verify the operation of the proposed converter and confirm its advantages, an experimental prototype has been implemented, and the experimental results and the efficiency of the proposed converter have been compared with the conventional quasi-square-wave zero-current-switching converters. [ABSTRACT FROM AUTHOR]

This paper introduces a novel H-bridge structured ac–ac pulsewidth modulation (PWM) converter topology based on two-level non-differential ac chopper legs, which can work at the non-inverting and inverting modes for the utility voltage compensation. Compared to the traditional bipolar-type H-bridge ac–ac converter, no bidirectional switches are switched in a complementary manner to overcome the commutation problem due to the delayed response of electronic circuits and semiconductor switching devices. The detailed PWM control signals and operational principles are presented to regulate the output voltage in a bipolar manner. Especially the main advantage is that the proposed ac–ac converter has the same buck/boost operation process for non-inverting and inverting modes, which ensures the continuously average current supply to the low-voltage output side without a high-value capacitor to support power. Additionally, due to the common sharing ground of the input and output, the feature that output can reverse or maintain phase angle with input is supported well. Then, the detailed analysis, design conditions, and experimental verification based on a 1 kW experimental prototype are presented. [ABSTRACT FROM AUTHOR]

This paper proposes a method for fault-tolerant operation of medium voltage modular multilevel converters (MMCs) with phase-shifted carrier (PSC) modulation. The existing methods need to recalculate and reconfigure all the carriers every time a submodule (SM) fails. However, the proposed method combines the sorting voltage balancing control and the PSC modulation to avoid breaking the symmetry and balance of the carriers. Therefore, the modulation stage in the proposed method can be kept the same and the output voltage of the MMC can remain unchanged without causing voltage mismatch. Moreover, considering the modulation margin and the physical redundancy configuration, two fault SM replacing strategies, i.e., optimal dynamic performance and optimal electrical stress are proposed as well as their respective control structures. Compared with the normal operation of the MMC, the proposed fault-tolerant operation method has only slightly changed the control system and thus the added calculation burden and control complexity can be ignored, which is extremely beneficial for the practical implementation. The effectiveness and performance of the proposed operation method are carefully verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes a new 7-level inverter topology for induction motor drives. It is a hybrid topology formed by cascading a 5-level active neutral-point-clamped inverter with a 3-level T-type converter. It is obtained using low-voltage semiconductor devices with voltage blocking capability of Vdc/3 and Vdc/6. The topology uses three floating capacitors per phase, which are balanced within a pulsewidth modulation (PWM) switching duration using switching-state redundancies for each pole-voltage level. Topology forms two stacks at the front-end, which requires individual symmetrical dc source. The analysis of switching loss and conduction loss is performed and compared with some of the existing 7-level multi-level inverters reported in various literatures to show the advantages of the proposed topology. Furthermore, the single dc source operation with two stacked capacitors and closed-loop control of neutral-point voltage using symmetrical six-phase induction motor is proposed. The voltage-control algorithms for floating capacitors and dc-link stacked capacitors are proposed, which are independent of load power factor and modulation index. Open-loop V/f and closed-loop rotor field oriented control are performed, and various results at steady and transient states are presented to validate the aforementioned claims. [ABSTRACT FROM AUTHOR]

This paper proposes a generalized design framework for three-phase Vienna rectifiers to handle the neutral point voltage balance issue. On the basis of the design framework, it is convenient to construct various neutral point voltage balancing methods with the guarantee of stability. As demonstration, three representative neutral point voltage balance approaches are presented by choosing different zero-sequence voltages. A comprehensive comparison among the three approaches is given in the aspects of input current quality, capacitor voltage fluctuation, and system efficiency. The comparison results provide guidance for constructing the most appropriate approach based on the specific requirement. Finally, simulation and experimental results verify the correctness and effectiveness of the presented approaches and the related performance analysis. [ABSTRACT FROM AUTHOR]

Aluminum electrolytic capacitor (AEC) is one of the most age-affected components in power electronic converters and its reliability has been a major concern. As the growth of service life, the equivalent series resistance (ESR) of AEC increases due to the loss of electrolyte. Therefore, online ESR estimation is critical for condition monitoring of AEC. This paper proposes an online ESR estimation method for output capacitor of boost converter. By analyzing the output voltage ripple, an ESR calculation model is derived. Based on the model, only output voltage and inductor current need to be measured, which can be obtained directly from double closed-loops converter. To implement this proposed method, a detailed extraction scheme based on wavelet transform denoising is presented. Non-ideal factors (noise and voltage spikes) are analyzed and the superiority of the proposed parameter identification scheme is verified. The proposed estimation method can obtain ESR for the converter operating at different working conditions such as resistive loads and converter loads. Effect of temperature on ESR is incorporated for accurate determination of the health of capacitor. Simulation and experimental results are provided to verify the effectiveness of the method. [ABSTRACT FROM AUTHOR]

A conventional phase-shifted full-bridge (PSFB) converter is one of the most promising topologies in high-efficiency and high-power applications because of its small RMS current, inherent zero-voltage switching capability, and clamped voltage stress of the primary switches. However, when the PSFB converter operates with a small duty ratio, a large freewheeling current of an output inductor flows in the primary side, and it causes a large circulating current. In addition, it has a large voltage stress in the rectifier diodes due to a voltage ringing between parasitic components. To solve these problems, a new PSFB converter with a coupled inductor rectifier (CIR) is proposed in this paper. By adopting the CIR structure in the PSFB converter instead of the full-bridge rectifier, the proposed converter eliminates the freewheeling current in the primary side, which significantly reduces the primary circulating current. In addition, the two rectifier diodes of the CIR do not have voltage ringing. As a result, the proposed converter not only reduces the conduction loss in the primary side, but can also use two diodes in the rectifier with a low voltage rating. The effectiveness and feasibility were verified with a 320–400 V input and 56-V/12.8-A output prototype. [ABSTRACT FROM AUTHOR]

This paper presents a modified negator-based switched-capacitor (NSC) dc–dc converter to achieve fine-grained voltage conversion ratios. Based on a concept of reconfiguring several 2:1 switched-capacitor (SC) converters in series and parallel at the last stage, the proposed asymmetrical shunt SC (ASSC) converter provides more controllable variables of forward gain and feedback gain to decide different power path interconnections and increase the available conversion ratios, with a little sacrifice of its slow switching limit output impedance. The switching loss of the bottom-plate parasitic capacitance in the ASSC converter is less than the switching loss of the NSC topology because the two moderate voltages instead of the power rail are fed to the last stage 2:1 SC unit and reduce the voltage swing. The bottom-plate swapping prototype further reduces the parasitic loss at high conversion ratios. To handle a large number of conversion ratios in closed-loop regulation, the ASSC converter uses the fast optimum ratio searching (FORS) technique, which evaluates the transient voltage drop to quickly search for target ratios and reduce the transient recovery time. A three-stage ASSC converter achieving 187 conversion ratios is fully integrated in the test chip, which is fabricated in 0.25-μm CMOS process with an active area of 7.14 mm2. Furthermore, 2389 conversion ratios can be derived in theory for a four-stage ASSC converter. The proposed reconfigurable SC converter provides an output voltage range of 0.4 to 2.8 V under no load conditions, and greater than 80% power efficiency at an output voltage level of 0.9 to 1.5 V over a load range of 3 to 9.5 mA. Due to the FORS technique, the measured transient recovery time is reduced from 7 to 1.5 μs in case of load current step of 7 mA. [ABSTRACT FROM AUTHOR]

In the applications such as mixed-color light emitting diode (LED) lighting system, LED drivers are always required to provide constant current for each LED string and each current should be controlled independently. For this purpose, a single-stage series-type LED driver with independent control of N-channel output currents is proposed in this paper. The function of power factor correction can be realized inherently to obtain high power factor. N active output units, each one made up of a power switch, a diode, and an output filter capacitor, are series-connected to form the series-type N-channel outputs structure. According to different current reference values, N-channel output currents can be independently regulated just by sampling each output current to adjust the duty cycle of each secondary output-switch automatically. The operating principle and independent closed-loop control strategy of the proposed LED driver with N = 3 are analyzed as an example in detail. Finally, the quantitative parameter design method for a 120 W prototype is elaborated. And, the experimental results are presented to verify the effectiveness of the LED driver and the correctness of parameter design method. [ABSTRACT FROM AUTHOR]

In order to match the long life span of light emitting diodes (LEDs), electrolytic capacitor-less off-line LED drivers have been intensely developed. However, the relatively low power efficiency is a common issue for many electrolytic capacitor-less designs. In this paper, a more efficient single-coupled-inductor multiple-output (SIMO) LED driver is proposed. The electrolytic capacitor-less design is targeted for lighting applications with color mixing and color temperature adjustment, where a small capacitance actively balances the power difference between the ac input and multiple dc outputs. Using energy-flow-path optimization, the proposed LED driver has some direct and efficient energy flow paths. In particular, additional energy flow paths are implemented, connecting directly from the small capacitance to multiple dc outputs. Thus, the overall power efficiency is improved. Furthermore, the proposed LED driver is designed with a carrier-based control without the high-precision current sensor for the single-coupled inductor, and thus simpler signal sampling and reduced control complexity can be achieved for independent regulations of multiple dc outputs. [ABSTRACT FROM AUTHOR]

Zero-voltage-switching (ZVS) mosfet grid inverter has distinct advantages such as higher efficiency and higher power density. However, the ZVS inverter may lose ZVS condition during startup stage if it does not start properly. It may increase the voltage stress on mosfets and even destroy the power semiconductor device. In order to achieve the ZVS condition for ZVS inverter during the startup stage, this paper proposes a safe startup method with an auxiliary clamping capacitor pre-charging circuit and designed ZVS pre-charging pulse sequence. The pre-charging circuit is enabled only at the startup stage. Theoretical analysis shows that the proposed method is capable of reducing the voltage stress during the startup stage for the ZVS inverter. Finally, the proposed safe startup method is verified on a 3 kW grid inverter. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive power management circuit, which maximizes the energy transfer from the energy harvester to wireless sensor nodes in real-world applications. Low power consumption techniques were adopted in the power management circuit to maximize the delivery of the harvested energy to the load instead of being consumed by the circuit. The presented circuit incorporates an analogue control circuit (ACC) for maximum power transfer from the energy harvester to the storage capacitor and an energy-aware interface (EAI) for controlling the energy flow from the storage capacitor to the load. To evaluate the performance of the presented circuit, piezoelectric energy harvesting was used as a studied case. The piezoelectric energy harvester (PEH) was mechanically excited at different strain loadings and frequencies. The experimental results show the circuit can self-start and powered directly by the PEH since the EAI and ACC have low power consumption in the range of microwatts. The circuit is adaptive to energy harvesters of varying output and various electrical loads, with a peak efficiency of 76.18% in transferring the harvested energy from the PEH to the storage capacitor. More than 96% of the energy released from the storage capacitor is effectively transferred to the electrical load. [ABSTRACT FROM AUTHOR]

Constant on-time control has been widely used due to its advantages of fast transient response and light load efficiency. However, the control scheme is intrinsically unstable if the output capacitor's equivalent series resistance (ESR) is not large enough, which needs ripple injection techniques to enhance loop stability. The traditional passive ripple compensation technique uses only passive component networks to realize this function, which exhibits some inherent shortcomings, including difficulties in high-speed current sensing amplifier design and large chip area consumption. This paper proposes an internal active ripple compensation strategy that senses the low-side power mosfet current and extracts relevant ac information for feedback-ripple enhancement. Output-voltage dc offset does not occur and subharmonic instability is significantly improved even with ceramic capacitors. The circuit architecture has been realized in a synchronous buck regulator with a 0.5 μm 40 V bipolar-CMOS-DMOS (BCD) process. The programmable switching frequency is up to 1 MHz and the maximum load current is 4 A. Simulation and experimental results are given to prove the proposed high performance. [ABSTRACT FROM AUTHOR]

Modules with series and parallel connectivity add new features and operation modes to modular multilevel converters (MMCs). Compared to full- and half-bridges, the series/parallel modules allow sensorless module balancing and reduce conduction loss with the same semiconductor area. However, in high-voltage applications with limited switching rates, the sensorless operation of the series/parallel modules suffers from large charge-balancing currents. This paper introduces a series/parallel module variant with a small port inductor. The port inductor suppresses the charge-balancing current despite low switching rates. We also propose a carrier-based modulation framework and show the importance of the carrier assignment in terms of efficiency and balancing. The proposed module and the modulation method are verified on a lab setup with module switching rates down to 200 Hz. The module voltages are kept within a narrow band with the charge-balancing currents below 5% of the arm current. The experimental results show practicality and advantages of the new series/parallel modules in high-voltage MMC applications. [ABSTRACT FROM AUTHOR]

This paper proposes a quasi-resonant boost half-bridge dc–dc converter with high power conversion efficiency and a wide input voltage range for a photovoltaic micro-inverter. The proposed converter has a combined structure of a boost-integrated half-bridge converter on the primary side of the transformer and a voltage doubler with a snubber capacitor on the secondary side. By using the quasi-resonance techniques, it achieves zero-voltage switching (ZVS) turn-on and low turn-off losses for the switches, as well as ZVS turn-on for the diodes. In addition, the proposed converter has no dc-magnetizing current for the transformer due to the dc-blocking capacitor, and it doubles the voltage gain with half the voltage stress of diodes through the voltage doubler. The effectiveness of the converter was verified with a 300-W prototype with an input voltage range of 13–50 V, an output voltage of 400 V, and a switching frequency of 50 kHz. The experimental results show that the converter had more than 90.0% power conversion efficiency for the output power range of ∼300 W, and its maximum power conversion efficiency was 97.5% for an output power of 160 W. [ABSTRACT FROM AUTHOR]

Energy harvesting has attracted increased attention recently. Energy sources are present all around us, such as, mechanical vibrations, stress, strain, waste heat, sunlight or room light, electromagnetic rays, and chemical or biological sources. Vibration generators based on piezoelectric elements have been highlighted as low-power sources; however, their output power is very low, around the milliwatt or microwatt level, and thus, improving their performance is necessary to make the generated power usable. This paper investigates the use of passive devices to improve output characteristics of the vibration generators. The proposed circuits are a resonator and a passive rectifier. The proposed resonator consists of a parallel inductor and capacitor for $LC$ resonance. The $LC$ resonance equivalently reduces the internal capacitor of the piezoelectric elements. As a result, the output voltage and power are increased compared with that of conventional circuits. In addition, a boost-type current-improving passive rectifier is applied as the passive rectifier. The validity of the proposed circuit is numerically and experimentally verified. [ABSTRACT FROM AUTHOR]

Fault diagnosis is indispensable for the reliable operation of modular multilevel converters (MMCs). This paper presents a submodule voltage similarity-based, real-time, and fast open-circuit fault diagnosis method for MMCs. The proposed fault detection and location (FDL) method is derived based on the similarity analysis of capacitor voltages under both normal and fault conditions. Due to the absence of the discharging current path caused by the open-circuit fault, capacitor voltage of the submodule with the faulty switch will differ from those with healthy switches. This characteristic can be extracted by designing the correlation coefficients of the capacitor voltages at the same arm. With the help of correlation coefficients, the open-circuit fault can be located at the early stage before the capacitor voltage is charged very high. All the data required for the proposed FDL method can be obtained by the available sampled data for the control scheme of MMCs. No extra measurement or hardware is required. Experimental results validate that the proposed FDL method can detect and locate the open-circuit fault rapidly and accurately within one fundamental period. [ABSTRACT FROM AUTHOR]

In order to produce more voltage levels and meet the requirement of the motor drive in electric vehicles (EVs), a hybrid cascaded multilevel converter based on three-level (TL) cells is proposed in this paper. In each unit, there is a battery and two series-connected capacitors, which hold a half of the battery voltage, respectively. Each TL cell is controlled to be connected or bypassed by a converter unit because of the modular structure. Three voltage levels can be produced when the TL cell is connected. All TL cells are cascaded to produce a staircase dc voltage, and an H-bridge is utilized to alternate the direction of it to form the ac output voltage. Compared to similar converter based on half-bridge arms, the proposed topology is able to produce more voltage levels with same number of battery modules. Voltage balances among TL cells and between two capacitors in each TL cell are both realized by a proposed overall control strategy. Experiments are provided to show the validity of the analysis. [ABSTRACT FROM AUTHOR]

There have been several advanced topologies proposed by the community for micro-inverter applications. However, many such applications suffer from unwanted second-order harmonic current ripple at dc input. Moreover, in the absence of suitable passive filter or ripple compensator, the second-order harmonics ripple may propagate into the dc source. This results in several problems to the system, related to system efficiency, life, cost, size, reliability, and stability. This paper proposes an adaptive sliding-mode controller to shape the output impedance of the boost-circuit of quasi-switched boost inverter such that the propagation of the ripple from dc link to the dc-input source is resisted. The quasi-switched boost inverter is one of the advanced and suitable topologies for the micro-inverter applications. The adaptive nature of the proposed controller improves the transient performance of the system at the line–load transients unlike some existing solutions, which affects dynamics adversely to achieve ripple mitigation objective. The controller ensures voltage regulation within ${5\%}$ at dc link. The proposed control technique is verified using a lab-prototype of 500 W quasi-switched boost inverter. [ABSTRACT FROM AUTHOR]

It is considerable to reduce the computation load while keeping a good total harmonic distortion (THD) performance for the modular multilevel converter (MMC) with model predictive control (MPC). In this paper, the discrete-time mathematical model of the MMC is derived and the output voltage ripples of the cascaded submodules (SMs) are analyzed in detail. Accordingly, a modified increased-level MPC method A (IL-MPC-A) is proposed with 2N + 1 ac-side output voltage levels. The computation load is significantly reduced without losing the harmonic circulating currents suppression and capacitor voltage ripples compensation capabilities. In this method, the cost function minimization step and capacitor voltage sorting algorithm are combined to determine the optimal control option. In addition, to avoid the selection of weighting factors and further reduce the computation load as the increasing of the SM number, another modified IL-MPC-B is proposed by directly calculating the optimal ac-side output voltage level and arm summation voltage according to the discrete-time mathematical model. As a result, the ac-side output current and circulating current controls are decoupled. Furthermore, the capacitor voltages are balanced with a proposed control scheme by adjusting the circulating current reference. The effectiveness of the proposed MPC methods is verified by simulation and experimental results. [ABSTRACT FROM AUTHOR]

A multiphase-interleaved non-isolated high step-up dc/dc resonant converter for high-current applications with wide load range is proposed in this paper. The converter consists of an inverter stage with multiple resonant inverters in parallel interleaving operation that is cascaded to a common diode–capacitor rectifier stage. The topology of the inverter stage is a variation of class E inverter, which is designed for voltage boosting and of which the voltage gain is insensitive to load change. The rectifier stage comprises multiple pairs (correlated to the number of inverters in parallel) of diodes in parallel and a small output capacitor, which makes it simple to implement and of low cost. Together, the voltage gain variance of the converter can be confined within a small value and zero voltage switching operation can be maintained over a wide load range. A detailed mathematical analysis of the proposed converter is conducted for systematizing its design. A prototype of the proposed converter with an input voltage of 23.6 V, a rated output voltage of 190 V, and a rated output power of 80 W at 486 kHz is constructed for verification. A frequency controller is implemented to achieve fine regulation of the output voltage. [ABSTRACT FROM AUTHOR]

This paper proposes a modulation reference compensation method to completely eliminate the intercoupling between the output active and reactive powers of modular multilevel converters (MMCs). Different from the existing methods, it is realized not based on an accurate control model, but by directly amending the initial arm modulation references of MMCs. Therefore, the proposed method is essentially a compensation algorithm, which is extremely easy to implement in a microcontroller with low calculation burden. In addition, it does not need any additional closed-loop controllers or voltage/current sensors, which is very beneficial to practical projects. The proposed method finally realizes accurate and fully decoupled active and reactive power regulation, avoids overload operation and protection malfunction, and significantly improves the dynamic performance of MMCs. The effectiveness and accuracy of the proposed analysis and compensation method are carefully verified by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

In the context of reducing total CO $_2$ emissions as well as reducing the total copper cable length and weight on cars, automotive manufacturers propose to derive all the supply voltages from a single $\text{48 V}$ bus through high step-down ratio dc–dc converters. The series capacitor tapped inductor (SCTI) converter is a promising topology for efficient single-stage step-down conversion from the $\text{48 V}$ bus. In the synchronous version of the SCTI, however, turn-off of the synchronous rectifier at positive drain-to-source current leads to a voltage spike and to a potential catastrophic failure of the converter. In this paper, a simple control technique is proposed, which prevents the foregoing condition to occur. The approach enables a reliable operation of the synchronous SCTI topology without disrupting its main features and advantages, and eliminating the need for additional snubbers, voltage clamps or auxiliary windings. The approach is validated via computer simulations and experimental tests on a $\text{48}$ -to- $\text{1.5}\;\text{V}$ , $\text{4 A}$ SCTI converter prototype. [ABSTRACT FROM AUTHOR]

The derivation and implementation of the natural switching surfaces (NSS) considering certain parametric uncertainties for a flyback converter operating in the boundary conduction mode is the main focus of this paper. The NSS with nominal parameters presents many benefits for the control of nonlinear systems; for example, fast transient response under load-changing conditions. However, the performance worsens considerably when the converter actual parameters are different from the ones used in the design process. Therefore, a novel control strategy for NSS considering the effects of parameter uncertainties is proposed. This control law can estimate and adapt the control trajectories in a minimum number of switching cycles to obtain excellent performances even under extreme parameter uncertainties. The analytical derivation of the proposed adaptive switching surfaces is presented together with simulations and experimental results showing adequate performance under different tests, including comparisons with a standard PI controller. [ABSTRACT FROM AUTHOR]

Single-phase inverters and rectifiers require the use of an energy buffer to absorb twice-line-frequency power ripple. Historically, this challenge has been addressed by the use of large electrolytic capacitors. Lifetime constraints and the need for improved system performance have motivated designers to seek other capacitor technologies, such as ceramic and film, which are frequently used in conjunction with active filtering converters to reduce the capacitance required. Active filtering converters cycle the capacitor voltage over a wide voltage range while maintaining a constant dc bus voltage. This large-swing operation demands different capacitor qualities than most other filtering applications, and the data sheet parameters available for commercial capacitors may be ineffective or require special care for calculating characteristics, such as efficiency and energy storage capability. This work presents an experimental setup for evaluating capacitor performance under a large voltage swing along with detailed experimental results. Energy storage data for a number of capacitors in the 50–630 V range from several manufacturers are included. The approach and findings of this paper can serve as an aid to power electronics designers for the selection and evaluation of capacitors in energy buffering applications. [ABSTRACT FROM AUTHOR]

Reduced dc-link capacitance interior permanent magnet synchronous motor (IPMSM) drives have many advantages, such as longer lifetime, reduced cost, and higher power density. However, due to the dc-link voltage fluctuation, the dc-link voltage utilization rate and the torque ripples are two major issues in flux-weakening operation region. It is important to consider these two issues comprehensively when a flux-weakening control method is adopted. In this paper, the IPMSM torque ripples caused by the dc-link voltage fluctuation and the overmodulation are analyzed in depth. In order to reduce the torque ripples and increase the utilization rate of the dc-link voltage, a novel adjustable maximum voltage based voltage closed-loop flux-weakening method is proposed. By switching between the minimum dc-link voltage control mode and the extended dc-link voltage control mode, the torque ripples can be reduced effectively and a nearly maximum utilization of the dc-link voltage can be realized. The proposed flux-weakening control method only depends on the dc-link voltage and the stator current vector reference. Experimental results on a 2.2-kW IPMSM drive platform are provided to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In recent years, dc distribution grids have become increasingly popular because of the interest in the diffusion of distributed renewable energy. In this scenario, dc distribution grids are also favored because of the increased use of batteries and power electronic loads. The main limit to the spread of dc grids is their protection devices, which still present several problems. At present, protection devices are represented by traditional mechanical breakers or static electronic components. The first, which interrupt dc currents, have good reliability but need maintenance and have long intervention periods. In contrast, electronic switches are fast and reliable, but they reduce the efficiency because of their voltage drop. In this scenario, some hybrid breakers have been proposed to obtain the advantages of both devices. The previous solutions of hybrid breakers still suffer several critical issues and, usually, are not capable of protecting a system from short circuits without significantly reducing their lifetime. In this paper, a new low-voltage hybrid circuit breaker topology is proposed. The procedure to dimension all of the active and passive components in the device is analyzed, and the effectiveness of the proposed solution is proven by means of experimental results obtained using a prototype. [ABSTRACT FROM AUTHOR]

In high gain voltage conversion applications, the low-side switches usually suffer large current stress, resulting in dominate switching loss. In this paper, a general soft-switching method based on an advanced interleaved high-step-up converter, which features excellent performance but works in hard-switching, is presented to combat this issue by using a plug-play resonant circuit. Under this soft-switching method, the main switches reach zero-voltage switching (ZVS) turn-on and ZVS turn-off, and the soft-switching condition is derived. Meanwhile, the added auxiliary switches could be turned off under ZVS condition and turned on under zero-current switching condition as well. More importantly, due to its location out of the energy transferring path, the auxiliary circuit will never lead gain lost to the converter and maintain its other existing merits, such as current auto-balancing and diode inverse-recovery well. A 1-kW prototype is built and tested to verify the significant efficiency improvement and merits maintenance for the proposed converter considering active resonant soft switching. [ABSTRACT FROM AUTHOR]

This paper investigates basic stability properties of the three-level flying-capacitor Buck converter when operated under current-mode control (CMC). The proposed analysis is developed for both peak CMC (P-CMC) and valley CMC (V-CMC), and addresses both the static instability of the inductor current and the flying capacitor (FC) voltage runaway phenomenon. Conditions for avoiding current subharmonic oscillations are derived first, along with the expressions of the minimal compensation ramp, which guarantee current stability throughout the entire operating range. As for the stability of the FC voltage, P-CMC results to be inherently unstable unless the converter operates with a relatively large peak-to-peak inductor-current ripple, a feature not yet recognized in the literature. However, V-CMC results to be inherently stable once the static instability of the current is eliminated with an external compensating ramp—a property that has been highlighted in the literature but never formally proven. The proposed analysis is verified both using a simulation model and experimentally using a 3.3-V, 500-mA, 500-kHz prototype. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) inverters form the backbone of PV generation. This paper proposes an all-film-capacitor, transformerless single-phase inverter for PV application. The topology is a combination of a front-end boost stage, a half-bridge (HB) inverter stage, and a buck–boost power decoupling stage. The grid ripple power is decoupled by a large swing of the HB capacitors along with a limited ripple on the dc link, thus reducing the capacitance requirement and converter volume. Being an HB-derived inverter, the high-frequency common mode leakage current through the PV parasitic capacitance is mitigated. Furthermore, the dc-link average is optimally controlled to ensure a higher efficiency over wide operating load and power factor range. To validate its operation, a Silicon Carbide based 1-kVA laboratory prototype is built and closed-loop experimental results are provided at 100/75 kHz switching frequency over wide operating conditions. [ABSTRACT FROM AUTHOR]

This paper presents, initially, a systematic derivation of extended first harmonic approximation (FHA) analysis and, later, a comprehensive time-domain (T-D) analysis to study series–series compensated inductive power transfer (IPT) systems with a diode bridge rectifier. Further, the paper shows that both FHA and T-D methods predict four mutually exclusive and collectively exhaustive modes of operation. Explicit criteria for each operation mode and formulae for mode boundaries are derived and it is concluded that FHA can explain three of four modes. The proposed T-D analysis is capable of describing the quantitative behavior of the system in all four operation modes with closed-form equations for all the mode boundaries. This analysis provides an objective basis to assess the accuracy of FHA predictions under the entire operating conditions. Quantitative comparison of key variables revealed that the FHA results can be unacceptably inaccurate for certain operating points. It is shown that the T-D approach provides a comprehensive design base for series–series compensated IPT without a need to know the load value. The T-D predictions are validated by experiment. A mathematical design calculator tool is also provided to the reader to visualize the mode boundaries, all the waveforms and the numerical results from both methods. [ABSTRACT FROM AUTHOR]

In this paper, a new space vector pulse width modulation method to extend the linear modulation range of a cascaded five level inverter topology with a single dc supply is presented. Using this method, the inverter can be controlled linearly and the peak phase fundamental output voltage of the inverter can be increased from 0.577 to 0.637 V\text{dc} without increasing the dc bus voltage and without exceeding the induction motor voltage rating. This new technique makes use of cascaded inverter pole voltage redundancy and property of the space vector structure for its operation. Using this, the induction motor drive can be operated till the full speed range (0–50 Hz) with the elimination of lower order harmonics in the phase voltage and phase current. The five-level topology presented in this paper is realized by cascading a two-level inverter and two full bridge modules with floating capacitors. The inverter topology and its operation for extending the modulation range is analyzed extensively. Simulation and experimental results for both steady-state and dynamic operating conditions are presented in this paper. [ABSTRACT FROM AUTHOR]

This paper analyzes the possibility of controlling the output voltage of a standalone single-phase inverter by directly controlling the output filter capacitor current without using a dedicated output voltage sensor. The plant modeling and controller design are presented. The proposed method depends on having the value of the output filter capacitance. A method to estimate the output filter capacitance is also presented. Rigorous analysis is done to show that the proposed sensorless scheme is largely insensitive to parameter variations and ensure that the output voltage is within specified regulations at utility level. It is also demonstrated in this paper that compared to the conventional voltage control scheme the proposed control scheme ensures an improved total harmonic distortion of the output voltage waveform. Experimental results presented validate the proposed scheme. [ABSTRACT FROM AUTHOR]

This paper proposed a new half-bridge (HB) LLC resonant converter family with pulse-width modulated (PWM) auxiliary switch (sLLC converter) for hold-up mode operation. The proposed sLLC converters could operate with synchronous rectifier, which is suitable for low-output voltage applications. In the proposed converters, an auxiliary switch is added at the primary side to provide charging path for the series resonant inductor. For nominal 400-V input, sLLC achieves same performance as conventional LLC converter, and all the good features such as soft switching are naturally retained. For slight input voltage fluctuation, frequency modulation is used to regulate the output voltage. When the input voltage reduces further, HB switches will operate at constant minimum frequency, and the auxiliary switch will operate in the PWM mode to energize the resonant inductor with the bus voltage directly during hold-up period. Thus, the converter achieves higher voltage gain, and the output voltage can be maintained at desired level. To verify the effectiveness of the proposed sLLC converter, operational principle and equivalent circuits will be carefully explained and analyzed in this paper. A 300-W prototype is built for 250–400-V input 12-V output application. [ABSTRACT FROM AUTHOR]

In high-voltage applications, the magnitude of total semiconductor losses (on-state and switching) determines the viability of modular-type multilevel converters. Therefore, this paper presents a new cell arrangement that aims to lower total semiconductor loss of the modular multilevel converter (MMC) to less than that of the half-bridge modular multilevel converter (HB-MMC). Additional attributes of the proposed cell are: it eliminates the protective thyristors used in conventional half-bridge cells that deviate part of the dc-fault current away from the antiparallel diode of the main switch when the converter is blocked during a dc short-circuit fault, and it can facilitate continued operation of the MMC during cell failures without the need for a mechanical bypass switch. Thus, the MMC that uses the proposed cell retains all advantages of the HB-MMC such as full modularity of the power circuit and internal fault management. The claimed attributes of the proposed cell are verified using illustrative simulations and reduced scale experimentations. Additionally, this paper provides brief and critical discussions that highlight the attributes and limitations of popular MMC control methods and different MMC cells structures proposed in the literature, considering the power electronic system perspective. [ABSTRACT FROM AUTHOR]