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The on–off controlled very-high-frequency Class E dc–dc converter has been extensively investigated for achieving high power density and fast dynamic response. However, the basic on–off control cannot limit the output current at overload or short-circuit condition. In this letter, we propose an on–off control with a current limitation function by adding an output current closed loop for reducing the output voltage reference when overload or short circuit occurs. The design considerations for the output current regulator are given. A prototype of a 30-MHz, 10-W Class E dc–dc converter is fabricated and tested in the lab, and the experimental results are provided to verify the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Permanent emergency lighting is a safety device whose lamp is always on and continues to operate when a mains failure occurs. The circuit has to charge the battery and drive the lamp while the grid is present and keep the lamp running from the battery in case of mains failure. This might require up to three different converters: front-end converter, electronic ballast, and battery charger. Since an emergency lamp must be on for as long as the local regulations require during a grid failure, efficiency is key. This article presents a permanent emergency lamp based on a series resonant current regulator that operates both as a ballast and as a battery charger. In this circuit, the power converter is placed in series with the LED array, operating as a controllable nondissipative impedance. A methodology based on the study of energy balances during resonant operation intervals is presented, aiming to design and build a laboratory prototype with low component count and high efficiency. [ABSTRACT FROM AUTHOR]

This article proposes an improved multiple synchronous reference frame (MSRF) current harmonic regulation strategy for dual three phase permanent magnet synchronous machine drive system. A new vector space decomposition transformation combined with auxiliary currents is designed to decouple the current fundamental with current harmonics, and the auxiliary currents can be established by the π/9 phase shifting of the physical currents in ABC set and the π/18 phase shifting of the physical currents in XYZ set. By employing the proposed current decomposition, it is easy to detect them using low pass filters in MSRFs. A generic complex vector proportional integral regulator is then employed to control the detected current harmonics to track the current harmonic references. Compared with the existing MSRF-based methods, the proposed method provides a new current harmonic detection with reduced delay effect, which contributes to enhancing the dynamic performance of current harmonic regulation, and also stabilizing the control system. Comprehensive experimental results are given to validate the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The control plant model of multiple grid-connected converters is a multivariable coupling model. There is complex coupling interaction between the control loops of the multiple converters, resulting in poor current control quality or interaction oscillation issues when the grid impedance is high or the number of converters is large. This article proposes a novel multivariable decoupling control method based on a summation difference coordinate for eliminating the current control interaction between multiple converters. With a summation difference coordinate transformation matrix, the multivariable model of multiple converters can be transformed to be multiple single-variable models. By designing specific current regulators for the summation current and the difference current loops in the summation difference coordinate, the summation current and each difference current can be regulated independently. Compared with the conventional methods, the proposed method can improve the current control bandwidth and stability without introducing any high-frequency oscillation especially when the grid impedance is high or the number of converters is large. Moreover, based on the proposed approach, the classical single variable control theory is enough to designthe regulator parameters for any number of converters under the new coordinate system. Experimental results of four three-phase 2 kW two-level converters have been presented, which validates the proposed approach. [ABSTRACT FROM AUTHOR]

Dual three-phase (DTP) permanent magnet synchronous machine (PMSM) systems exhibit high current harmonics due to low impedance to voltage disturbance such as inverter voltage errors and back-EMF harmonics. This article proposes a concept of virtual multi three-phase systems to achieve independent regulation of the current harmonics in a DTP PMSM system. The virtual multi three-phase currents are first reconstructed by appropriately shifting the phase of original physical DTP currents, and then decomposed with the help of vector space decomposition techniques. As a result, the fundamental and the major current harmonics, i.e., the 5th, 7th, 11th, and 13th, can be completely separated in several isolated subspaces, where the independent current control loops can be easily designed and implemented. Compared with existing methods, the steady-state and dynamic-state performance of current harmonic regulation are enhanced by the proposed virtual multi three-phase systems and the effectiveness is validated by experimental. [ABSTRACT FROM AUTHOR]

Regulator stations are widely used in gas transmission and distribution systems. Their state monitoring is of great significance to the safe operation of gas pipe networks. Due to the complexity of the working environment and the limitation of sensors, the acquired information is uncertain, which makes the state monitoring result prone to errors. The evidence theory has the ability to solve the uncertainty problem effectively. Most of the improvement methods of the evidence theory are in the spatial domain. These methods are not applicable to the fusion of the time-domain information. In this article, an improved method of the evidence theory is proposed for the state monitoring of a gas regulator station. It can meet the requirement of the dynamic fusion of the time-domain information. First, the back-propagation neural network is used to judge whether the evidence conflicts with each other. The simulation results demonstrate that it can judge the conflicts well. On this basis, the relative conflict factor is proposed to modify the evidence, and the calculation method of the adaptive time attenuation factor is proposed to reduce the accumulated error. The dynamic fusion of the time-domain information is realized by combining the time attenuation factor and the relative conflict factor. Finally, the proposed method is applied to the state monitoring of the gas regulator station. The feasibility and effectiveness of the method are verified by experiments. It verifies that the variation of the support degree of the proposed method for the correct proposition is 0.1478 higher than that of the temporal evidence combination based on relative reliability factor when the evidence is strongly conflicting. [ABSTRACT FROM AUTHOR]

The overmodulation canimprove the utilization of dc-link voltage in the induction motor (IM) field-weakening (FW) control, thereby extending the maximum output torque. Nevertheless, the high modulation index (MI) will cause severe torque ripple. To figure out the relation between the torque ripple and MI, the amplitude of torque ripple with different MI is calculated quantitatively. Then, a torque quality evaluation function (TQEF) is designed to evaluate the torque quality in overmodulation-FW region by considering both fundamental torque extension and torque ripple suppression. On this basis, a modulation index optimization module is proposed for the maximum TQEF value realization. The analysis shows that the studied method could achieve the optimal trade-off between the fundamental torque extension and the torque ripple suppression. The TQEF value of the studied method is higher than that of the conventional six-step voltage method and the inscribed circle voltage method, meaning that the torque quality is optimized. Finally, the effectiveness of the studied method is verified experimentally on an advanced RISC machines (ARM)-based 3.7 kW IM platform. [ABSTRACT FROM AUTHOR]

Accurate set-point tracking across a broad operating region with minimum transients is a crucial requirement during the start-up and shutdown phases of a process plant operation. The emotional learning based controller, with its model-independent and nonlinear features, is extremely suitable for plant-based operations. However, the design of most of the existing emotional-learning strategies is based on narrow operating regions, and, hence, they may not yield satisfactory tracking performance when operated on a broader region. In this correspondence, a new design approach is adopted, which takes into consideration the specific requirements of multiple set-point tracking. This approach fuses a regression model with a constrained optimization problem to generate stimuli weights as well as the learning and inhibition parameters. Experimental validation of the proposed method on a quadruple tank system and comparison of its performance with an optimized second-order sliding mode controller illustrates its effectiveness. [ABSTRACT FROM AUTHOR]

The large-capacity electrically excited synchronous machines are widely applied in modern industrial production, and starting issues have become one of the most concerns of the synchronous motors in practical operation, such as the long starting time, large current shock, and poor adaption to a wide-ranging load. To deal with these starting problems, many starting methods have been proposed in previous studies. Regrettably, high-performance methods depend on specific motor parameters and complex sensorless technology, while simple and low-cost methods are low performance. In this article, a modified back-to-back starting method is proposed for large-capacity synchronous machines based on virtual synchronous generator (VSG) technology, where the cascaded H-bridge converter is controlled as a VSG to replace the prime mover and synchronous generator of the conventional back-to-back starting system. To reduce the current shock, an initial relative-angle regulator is designed. To improve the robustness in the presence of a wide-ranging load, a damping torque branch is adopted. Extra speed sensors are no longer required since the VSG speed is directly applied in the feedback control loop. To validate the effectiveness of the proposed approach, extensive simulation and experimental results are presented. Compared with conventional approaches, the proposed starting method achieves faster response, smaller starting current, and stronger robustness. [ABSTRACT FROM AUTHOR]

This article presents a robustness-improved control method combining super-twisting sliding mode control (ST-SMC) based control winding (CW) current controller and PI-based power regulator for cascaded brushless doubly fed induction generator (CBDFIG). To reduce the computation burden of the controller, the strong robustness and the fast dynamic response of the ST-SMC is extremely suitable for the inner CW current loop whose control period is smaller than that in the outer power loop. Therefore, the state-space model of CBDFIG is derived and a robust CW current controller is designed based on the ST-SMC with the stability analyzed. In addition, according to the relationship among the electrical variables of CBDFIG deduced, a PI-based power regulator is designed with the stability analyzed and the parameters selected to achieve a satisfying steady-state performance. Finally, the simulation and experimental results based on a 5-kW prototype CBDFIG demonstrate the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

Fuel cells (FCs) are an alternative source of energy whose by-products are heat, vapor, and water. For medium-power and standalone operation, an FC is integrated with a boost converter, as the required voltage level is higher than the supply. Control of such a converter with a slow dynamic source requires a fast-acting controller, since the demand executed by the controller affects the action taken by the hydrogen valve in FCs. In this article, a linear–quadratic regulator (LQR) is developed to control the power converter. In practical applications, the conventional LQR produces offset in output voltage due to effective series resistance (ESR) of the output capacitor. To make the LQR dynamic with load perturbation, information of inductor reference current is required, which changes with variation in load current. To solve these two problems, two modifications in the classical LQR have been proposed to minimize the impact of ESR (m-LQR) and incorporate control action based on the reference inductor current (M-LQR). The proposed methods are compared with the conventional average current-mode control technique. The M-LQR-based scheme is found to outperform the classical m-LQR technique in terms of improved transient dynamics and reduced offset at the steady state. In addition to numerical simulations, the proposed control techniques have been validated experimentally. [ABSTRACT FROM AUTHOR]

In the transition process from the base-speed region to the field-weakening region of induction motor (IM), the voltage margin would suddenly disappear due to the limited inverter voltage. This insufficient voltage margin would deteriorate the current control of IM, causing severe voltage saturation and current ripple. To address this problem, a circular arc voltage trajectory method is proposed with the smooth transition-combined field-weakening controller. The voltage and current behavior are analyzed quantitatively during the transition process. The theoretical analysis shows that the studied circular arc trajectory can suppress the sudden decrease of the voltage increasing rate in the transition region, leading to the reduced voltage saturation and current ripple. The sufficient voltage margin and smooth current can be realized at the cost of < 10% voltage utilization ratio. The effectiveness of the studied method is verified by contrast experiments on an ARM-based 3.7-kW IM platform. [ABSTRACT FROM AUTHOR]

The traditional direct toque control (TDTC) for induction motors (IM) is afflicted by large torque ripple, high current total harmonic distortion (THD), and variable switching frequency. Recently, some improved direct torque control (DTC) methods have been proposed to address the above problems, but they often suffer from obscure concept, intensive computation, and poor robustness. To further improve the performance, this article proposes a DTC method based on minimum voltage vector (VV) error. The proposed strategy effectively optimizes the duty ratio of fundamental VV to minimize the error between reference VV and final VV imposed on motor terminals. The optimization algorithm dose not increase the system's complexity much and can be intuitively understood by a graphical interpretation. Experiment comparisons between the proposed strategy and some existing DTC methods are conducted on a 0.55-kW IM platform. The proposed DTC method has proven to achieve better steady-state performance, while retaining fast dynamic response of TDTC. Furthermore, the proposed method can obtain almost constant average switching frequency in the entire speed range, especially with rated load, due to the utilization of proportional-integral type torque regulator. [ABSTRACT FROM AUTHOR]

Power management unit (PMU) is commonly used to manage power modules to achieve high efficient performance for integrated circuits. Inside the PMU, controllers that belong to different power modules could be pretty much similar. If the discrete feature of the digital control can be gainfully arranged, we can use only one controller to operate all the power modules inside the PMU, which can reduce circuit area and save cost. This article proposes a pipeline concept to realize this idea. To achieve high performance, this article also introduces a phase sequence interchange technique to reduce the cross regulation problem of the single inductor dual outputs converter and an autotuning charge balance algorithm (AT-CBA) to enhance the transient response. The PMU is fabricated in Taiwan Semiconductor Manufacturing Company (TSMC) 0.18 μm CMOS manufacturing process for functional validation. Experimental results show that the pipeline controlled PMU can simultaneously output six voltages with extremely low cross regulation. The proposed AT-CBA also successfully make both buck converter and low-dropout achieve near-optimal transient response in 40 mV/5 μs and 120 mV/1 μs, respectively. [ABSTRACT FROM AUTHOR]

Frequency shift islanding detection methods have been widely used in inverter-based distributed generations. Two representatives of such methods, Sandia frequency shift (SFS) and reactive current perturbation (RCP) methods, are investigated in this article. The investigation reveals two main issues with these two methods, i.e., parameter selection scheme for positive feedback gain and current static error. The current parameter selection scheme, in particular, is considered unreliable and inconvenient in this article, for it has not considered the weakening effect of PI regulators on positive feedback and the positive feedback gain is actually obtained by trial and error, which makes it difficult to use such methods well in field environments. In view of these issues, this article proposes a solution that contains an improved method to eliminate current static error and a reliable and convenient parameter selection scheme based on system stability analyses. The final simulations and experiments verify the good performance of the improved method and the parameter selection scheme. [ABSTRACT FROM AUTHOR]

Input-series-output-parallel (ISOP) converter system is suitable for high-input voltage applications owing to the reduced voltage stress of power switches. This article proposes an ISOP converter system with two-stage dc–dc converter as the basic module, which is composed by a non-isolated dc–dc converter and an isolated dc–dc converter. The isolated dc–dc converter functions as a dc transformer (DCX), and the non-isolated dc–dc converter serves as the pre- or post-regulator to regulate the output voltage. With this arrangement, a common duty ratio is applied to all the pre-or postregulators, and natural input-voltage sharing (IVS) and output-current sharing (OCS) can be achieved. The LLC resonant converter is adopted as the DCX, and the design considerations are given for achieving a nearly constant voltage gain even if there is parameters drift. Meanwhile, the non-isolated converter has simple topology and the parameters are easy to be identical. Thus, the proposed ISOP converter system realizes excellent IVS and OCS even the constituent modules are not well matched. Furthermore, the improved ISOP converter system employing boost+LLC resonant converter is proposed. Two 12-kW ISOP converter systems have been fabricated and tested in the lab, and the experimental results are provided to verify the natural voltage sharing of the proposed ISOP converter system. [ABSTRACT FROM AUTHOR]

In this article, a composite torque regulator is proposed for optimizing the torque tracking performance in direct torque-controlled permanent-magnet synchronous motor drives. In the proposed composite torque regulator, two new variable hysteresis bands are designed and combined with two constant hysteresis bands. In the conventional direct torque control (DTC) scheme, the torque increasing rate and decreasing rate are changed with different speeds and loads. Thus, the average torque will deviate the reference torque seriously under some operation states. With torque deviation, the reference torque can hardly reflect the actual electromagnetic torque, and the torque tracking becomes more difficult and unsatisfactory in dynamic process. On the other hand, the time delay of one sampling period further deteriorates the precision of torque tracking. By introducing the proposed composite torque regulator, both torque deviation and the impact of time delay on the torque ripple can be eliminated. In addition, the advantages of the conventional DTC scheme, namely low switching frequency, fast dynamic response, simple structure, and independence of motor parameters, can be reserved in the proposed DTC scheme with a composite torque regulator. Experimental results are presented to verify the effectiveness of the proposed scheme and compare its performance with the conventional DTC scheme. [ABSTRACT FROM AUTHOR]

This article presents the design and experimental tests of a modified braking control for induction machines using the scalar control method. The proposed method is able to brake the machine with improved performance without using a dissipation resistor in the dc link. For this, two supplementary control loops inside the scalar control structure are used. The first loop controls the dc voltage and the second one controls the stator current during the braking process. The proposed method is implemented in an industrial voltage-source inverter and evaluated in two different induction motor dynamometers. [ABSTRACT FROM AUTHOR]

Sequential switching shunt regulators (S3Rs) are widely used in the satellites owing to their simple structure and high reliability. The high-power communication satellites require a power supply with a high bus voltage and large solar array section current. However, a large solar array capacitance and new time-division multiple access operations complicate the design of a lightweight and cost-effective power supply by increasing the difficulty in dissipation and thermal control. On the basis of passive current limitation, in this article, we propose a novel shunt regulator with only one output diode and a protection strategy to achieve high efficiency, appropriate shunt current limitation, and low turn-off delay. In addition, to reduce the dissipation of an S3R cell when feeding the solar array current to the main bus and to satisfy the single point failure-free requirement, an innovative self-retriggerable diode short-circuit fault detector circuit is proposed, which includes a protection switch for a safe thermal or electrical operation. Finally, simulation and experimental results are presented to validate the proposed shunt regulator and the corresponding control method or protection strategy. [ABSTRACT FROM AUTHOR]

Linear Hall-effect sensors are integrated into permanent magnet motors and provide positional feedback with the advantages of compact size and low cost. Field-oriented control (FOC) is widely used in high-performance situations yet limited by its computational cost. This paper proposes a novel simplified FOC that uses the linear Hall outputs directly to obtain the coefficients required to perform coordinate transformations through linear combination; neither the computation of trigonometric functions nor the flux position estimations are required. The method is computationally efficient because it involves less latency and fewer hardware resources, when implemented on digital controllers. Furthermore, the method has been used for sensor delay compensation, which has been verified as important to eliminate direct current. The experimental results validate the feasibility and effectiveness of the proposed method with a 126 W motor under various speed and load conditions. [ABSTRACT FROM AUTHOR]

Droop-controlled distributed energy resource converters in dc microgrids usually show low output impedances. When coupled with ac systems, second-order harmonics typically appear on the dc-bus voltage, causing significant harmonic currents at the converters resource side. In this paper, we show how to reduce such undesired currents by means of notch filters and resonant regulators included in the converters control loops. The main characteristics of these techniques in terms of harmonic attenuation and stability are systematically investigated. In particular, it is shown that the voltage control-loop bandwidth is limited to be below twice the line frequency to avoid instability. Then, a modified notch filter and a modified resonant regulator are proposed, allowing to remove the constraint on the voltage loop bandwidth. The resulting methods (i.e., the notch filter, the resonant regulator, and their corresponding modified versions) are evaluated in terms of output impedance and stability. Experimental results from a dc microgrid prototype composed of three dc–dc converters and one dc–ac converter, all with a rated power of $\text{5 kW}$ , are reported. [ABSTRACT FROM AUTHOR]

Current imbalance in multistring light-emitting diodes (LEDs) is a critical issue. It may cause overcurrent in one or more LED strings, leading to rapid degradation. In this paper, a mixed high-order compensation networks-based wireless power transfer system is proposed to generate multiple constant current outputs. It is composed of an LCC resonant network in the transmitting side, a series resonant network, and multiple CLC resonant rectifiers in the receiving side. The CLC resonant rectifiers are connected in parallel to form multiple independent output channels, and each channel is then connected to an LED string. Based on the analysis of the T resonant circuit and the modeling of coupling coils, multiple constant output currents can be derived. As a result, current balance can be achieved, which is very suitable for driving multistring LEDs. The proposed system also offers a modular, scalable, and maintenance-free design, which can significantly reduce the construction cost and the control complexity. In addition, the inverter in the transmitting side can achieve zero phase angle. A laboratory prototype with dual independent output currents is built to verify the proposed method. The experimental results agree well with the theoretical analysis. [ABSTRACT FROM AUTHOR]

A current-mode hysteretic buck converter is described in which inductor current is sensed by a resistor-capacitor (RC) network. The inductor current sensing RC network is reset multiple times per switching clock period, which allows it to have time constant much smaller than switching clock period and therefore occupy small silicon area. A frequency regulator ensures the switching frequency to be constant regardless of the operating condition of the buck converter and also integrates comparator delay compensator as its loop filter. The current-mode hysteretic buck converter implemented in a 65 nm complementary metal-oxide-semiconductor (CMOS) process provides 0.6–2.0 V output from 3.3 V input with 1 MHz switching frequency. The maximum load current is 1.5 A and the measured peak power efficiency is 96.3%. [ABSTRACT FROM AUTHOR]

One promising solution for future large wind turbine power conversion is to use medium-voltage power conversion systems for high efficiency and high power-density, e.g., by using a cascaded structure presented in this paper. However, a medium-frequency (MF) oscillation issue was observed while testing the experimental prototype of the above system. Given the complex multivariable coupling models of the multiwinding transformer and multiple inverters, conventional single-variable theories are not suitable. Therefore, this paper presents a new decoupling analysis method. Using a proposed linear transformation matrix, the output currents of multiple inverters can be transformed to a summation (grid) current and difference currents, where the former is the summation of inverter currents and the latter are the differences between currents of any two inverters. This transformation has enabled the use of single-variable theories, e.g., Bode diagram to analyze the summation current and difference current separately. It was found that the MF oscillation issue is caused by the equivalent impedance of the summation current being much larger than that of the difference current. Specifically, using small controller parameters cannot ensure the grid current quality and using large parameters may cause oscillation in the difference current. The proposed method can provide guidelines to design the parameters of current regulators and filters in multiple-inverter systems. Experimental results of a downscaled wind energy conversion system are presented to verify the proposed method. [ABSTRACT FROM AUTHOR]

The offset voltage variation of current sensors is mainly due to the thermal drift, and it causes torque ripples in current vector-controlled surface permanent magnet synchronous motor (SPMSM) drives. This paper proposes a current offset error compensator for the current vector-controlled SPMSM drives used in robotic applications, wherein dynamic movements frequently occur. The current offset error compensator for this kind of applications should provide a stable performance in estimating current offset errors during dynamic movements. Especially, the current offset error compensator should be able to suppress interferences from outer-loop controllers. In this paper, analysis on a synchronous frame current regulator is performed to see the relation between current commands and measured currents under the current offset error existing condition. The analysis shows that pure current offset error components can be obtained by subtracting low-pass filtered current commands from measured currents in a synchronous reference frame. It means that the interference from current commands in correcting current offset errors can be easily decoupled by the simple subtraction process, and the dynamic control capability of a current offset error compensator could be significantly improved. The dynamic performance of the proposed current offset error compensator is proved through simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper exhibits a robust speed controller equipped with a self-tuner for permanent magnet synchronous motors (PMSMs), taking nonlinearity and model-plant mismatches into account. The first contribution of the proposed technique is designing a self-tuner for updating the cutoff frequency of target speed dynamics. The second one is rendering the closed-loop system to recover the target tracking performance and remove the offset errors in the absence of integrators. A 5-kW prototype interior PMSM is used to experimentally verify the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

This paper presents a droop-based distributed control strategy for multithree-phase machines that provides augmented controllability during power sharing transients. The proposed strategy is able to mitigate the mutual interactions among different sets of windings without controlling any subspace variable, also offering a modular and redundant design. On the contrary, in a centralized configuration, subspaces would be controlled using the vector space decomposition, but fault tolerance and reliability levels required by the stricter regulations and policies expected in future transportation systems would not be satisfied. The proposed method is analytically compared against the state-of-the-art power sharing technique and equivalent models and control design procedures have been derived and considered in the comparison. Uncontrolled power sharing transients and their effects on mutual couplings among isolated sets of windings have been compared against the proposed regulated ones. Experimental results on a 22-kW nine-phase multithree-phase synchronous machine rig validate the design procedures showing good agreement with the expected performances. [ABSTRACT FROM AUTHOR]

The presence of a neutral current is quite common in three-phase (3P) four-wire (4W) distribution systems due to an unequal distribution of linear and nonlinear single-phase (1P) loads and small distributed generators. However, a high neutral current can overload the neutral conductor and distribution transformer, which can cause electrical safety concerns and even fire. Among several existing neutral current compensators, the 3P four-leg (4L) voltage-source inverter (VSI) provides better control flexibility and more efficient performance than the passive compensators but requires a higher VSI capacity for the fourth-leg operation. To provide a solution to the aforementioned problem, this paper presents a novel control method to utilize the available capacity of a 3P-4L VSI after active and reactive power regulation to enhance the neutral-current compensation. A smart VSI (SVSI) is designed to operate with a solar photovoltaic unit, regulate the ac side voltage, and minimize the neutral current. Case studies are conducted with actual load data from a commercial building in the PSCAD/EMTDC software environment. The designed system with the proposed control method can provide a significant improvement in the neutral-current compensation, phase balancing, and unbalance factor compared to a fixed-capacity 3P-4L SVSI. Experimental results using a TMS320F28335 digital signal processor microcontroller and modified Semiteach 3P-4L inverter are presented to verify the robustness of the designed controller and the enhancement to the neutral-current compensation using the proposed dynamic capacity-control method. [ABSTRACT FROM AUTHOR]

Capacitorless (CL) low-dropout regulators (LDO) have gained significant research interest for point-of-load voltage regulation without off-chip capacitors. While analog CL-LDOs can deliver superior power supply rejection (PSR), digital CL-LDOs are more scalable and efficient. To achieve the advantages of both types, this paper presents a digital CL-LDO with an analog PSR enhancer, delivering strong PSR without compromising scalability and efficiency. Load regulation is performed by an asynchronous digital feedback controller for fast transient response and scalable load drivability. PSR is achieved by a load-insensitive wide-bandwidth analog controller. A prototype chip of the analog-assisted digital CL-LDO is fabricated in a 130-nm CMOS process with an active area of 0.0645 mm2 , supporting load current up to 50 mA at nominal 1-V input and 0.8-V output. The measured PSR is better than –20 dB for frequencies up to 10 MHz, and the measured current efficiency peaks at 99.3%, with average current efficiency of 96.7% across 50× load range. The measured transient response to a full load step, with two values of load capacitance (100 pF and 10 nF), demonstrates the LDO's stable operation over a wide range of load resistance and capacitance. [ABSTRACT FROM AUTHOR]

This paper presents a simple but effective overmodulation scheme for direct torque controlled reluctance synchronous motor (RSM) incorporating field-weakening (FW) operation. To overcome the problems of high torque ripples and variable switching frequency experienced by conventional direct torque control (DTC), constant-switching-frequency-based torque regulator is employed. By combining the proposed overmodulation scheme with this torque regulator, the dynamic torque response and constant power speed range of RSM drives are improved. Simultaneously, low torque ripples are obtained. Furthermore, an adaptive activation algorithm is proposed to activate overmodulation only when high torque output is demanded. This algorithm also contributes to ensure the stability of drives with overmodulation through effective flux regulation, which is essential for FW operations. The validity of the proposed method is verified by experimental results supplemented in this paper. [ABSTRACT FROM AUTHOR]

This paper presents a new topology based on a modified class-E resonant inverter used as an LED series current regulator. The proposed topology behaves as a controllable nondissipative impedance that adjusts the current flowing through the lamp. In this circuit, the LED is placed at the dc side of the class-E inverter, in series with the input filter inductance. The power handled by the ac side is sent back to the input by means of two diodes. Despite the addition of these two diodes, the converter maintains all the advantages of the class-E inverter: low component count, simple control, and extremely low switching losses. The LED current can be controlled with a small variation of the operating frequency. This way, the low-frequency current ripple of the lamp can be strongly reduced even when there is a considerably high input voltage excursion, such as the one expected in electrolyticless high-power-factor LED ballast. This paper proposes a simplified methodology based on the fundamental approach aiming to design and build a laboratory prototype. The prototype is designed in order to minimize the effect of LED voltage in the output current. This way, the input voltage ripple can be canceled using a simple feedforward control. [ABSTRACT FROM AUTHOR]

Diesel-driven generator sets (DGs) are widely utilized in distributed electrical power generation due to their high reliability. This paper presents a tenth-order nonlinear state-space DG model, for which a supervisory linear quadratic regulator is designed. The proposed model-based design reduces the time-consuming task of regulator tuning in comparison with current industry-standard solutions while demonstrating improved transient frequency and voltage performance, when subject to electrical load steps. These improvements are shown experimentally on two differently rated DGs. [ABSTRACT FROM AUTHOR]

An LED driver consisting of dimmable current balancing circuits (CBCs) and a boost converter with drain voltage balance (DVB) and phase-shifted pulsewidth modulation (PSPWM) control schemes is presented. To reduce the power loss on conventional linear current regulators, CBCs are employed. The DVB control scheme is proposed to maintain a desired constant voltage across the CBCs, so as to increase current balance and achieve high efficiency of the CBCs. Thus, the bus voltage of the boost converter is adaptively regulated based on the DVB control. The PSPWM control scheme can alleviate the variation of the bus current provided by the boost converter. As a result, the transient ripple of the bus voltage can be reduced when the light-emitting diode (LED) strings are turned on and off. Furthermore, the utilization of DVB control is increased when the PWM dimming duty cycle becomes lower. The experimental results demonstrate that the minimum voltage among the CBCs is always kept at the lowest constant level while maintaining the required current passing through the LED strings. The efficiency of the CBCs is kept almost the same for different LED currents and is over 95%. Thus, a high-efficient parallel-string dimmable LED driver with simple circuitry can be achieved. [ABSTRACT FROM PUBLISHER]

Aiming at effective power management in microgrids with high penetration of renewable energy sources (RESs), this paper proposes a simple power control for the so-called second-generation, single-phase electric springs (ES-2), which overcomes the shortcomings of the existing ES control methods. By the proposed control, the unpredictable power generated from RESs is divided into two parts, i.e., the one absorbed by the ES-2 that still varies and the other injected into the grid that is controllable by a simple and accurate signal manipulation that works both at steady-state and during RES transients. It is believed that such a control is suitable for the distributed power generation, especially at domestic homes. In this paper, the proposed control is supported by a theoretical background. Its effectiveness is at first validated by simulations and then by experiments. To this purpose, a typical RES application is considered, and an experimental setup is arranged, built up around an ES-2 implementing the proposed control. Testing of the setup is carried out in three steps and proves not only the smooth operation of the ES-2 itself, but also its capability in running the application properly. [ABSTRACT FROM PUBLISHER]

DC microgrids provide a coordinated paradigm to facilitate the penetration of photovoltaic (PV) sources due to their direct current essence. Along with the sustained growth of PV penetration, there is an increasing demand on PV sources to participate in dc bus voltage regulating, especially in small-sized or islanded dc microgrids. This paper develops a decentralized coordination control strategy that applies $V$ –$I$ droop concept to cooperate multiple PV sources in a dc microgrid. The proposed method enables PV sources to regulate the dc bus voltage and share their output power in an expected proportion. Furthermore, the maximum power point tracking (MPPT) function is unified in the suggested control method with a $dp/dv$ regulator, which means multiple PV sources can work in the MPPT mode when they are grid-connected or shift with load demands in an coordinated way while keeping the dc bus voltage without switching the control configuration. Hardware-in-loop tests for different scenarios are conducted to validate the feasibility and effectiveness of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

Tap changers are commonly used to maintain the limits in medium-voltage lines. Initially based on electromechanical switches, efforts have been made since the 1990's to reduce maintenance expenses with thyristor-based versions. Among the methods to limit the short-circuiting current in commutating taps, the multiwinding coil has demonstrated, during decades of use in the low-voltage field, to be reliable and cheap. Two previous papers showed that multiwinding changers can be applied to medium-voltage lines up to 34.5 kV, 15 MVA with no parallel or series thyristor association. This paper proposes a new topology, based on a double array of tap switches per phase, allowing for step-up the power from 15 to 36 MVA and insertion in any point of the line with no connection to the head transformer. A comparative cost analysis gives technical and economical results for a typical 10 MVA, 34.5 kV stabilizer demonstrating the advantages of the proposed circuit over the electronic single array topology and the classic mechanical solutions. [ABSTRACT FROM PUBLISHER]

A novel high-efficiency resonant light emitting diode (LED) backlight driver with passive current balancing and dimming is proposed and analyzed in this paper. The proposed LED driver achieves uniform brightness of each LED string by the charge balance of the resonant capacitor, which benefits from high efficiency. By controlling the output current of one LED string, the output currents of other LED strings can be controlled via current balancing of resonant capacitors, which makes its control simple. The proposed LED driver uses only one active switch, which decreases circuit volume and simplifies the control. Furthermore, a wide load range can be achieved by controlling the turn-on duty ratio of the single power switch of the LED driver with a fixed frequency. Finally, a prototype of a high-dimming-ratio small-size three-string LED driver is provided to verify the studied results. [ABSTRACT FROM PUBLISHER]

In order to reduce the cost and the size of a single-phase to three-phase power converter, an electrolytic capacitor-less single-phase to three-phase inverter is proposed. As the system does not have energy storage, such as an electrolytic capacitor, it results in source current harmonics due to the spatial harmonics of the motor. Adding an inductor for filtering the source current harmonics increases the cost and size of the system. In order to improve the source current waveform without adding passive components, it is necessary to reduce the source current harmonics via inverter control. However, when the inverter control reduces the source current harmonics, voltage saturation of the inverter causes source current distortion. At the rated speed and load, the voltage saturation region amounts to 40–50% of the source period, and the source current harmonics do not meet the guideline of IEC 61000-3-2. This paper proposes a direct dc-link current control (DDCCC) considering voltage saturation and the dq -axis current reference calculation for applying the DDCCC, which reduces the source current harmonics below the guideline. The effectiveness of the proposed method is verified through experiments. [ABSTRACT FROM PUBLISHER]

In this paper, a coordinated adaptive droop control is addressed for DC microgrid to optimize its power distribution. The optimal solution for economical dispatch problem (EDP) of the microgrid is found through a fully distributed hierarchical control. The consensus-based economical regulator calculating the optimal solution for the generator is fully distributed. Thus, it eliminates the requirement of centralized coordinator. The droop controller receives the reference from the economical regulator and ensures the output power converging to the reference while maintaining the power balance of the system. Moreover, the economical regulator can estimate the load information of the system based on the characteristics of droop control. Thus, the information from load or renewable energy source is no longer required to solve the EDP that consequently decreases the number of communication nodes. This will reduce infrastructure cost, enhance the reliability, and fasten the converging speed of algorithm. The dynamic model is established and parameter selection guideline are given in this paper. A low-voltage dc-microgrid prototype platform is utilized to validate the effectiveness of the proposed control. [ABSTRACT FROM PUBLISHER]

A low-power ac–dc light-emitting diode (LED) driver with adaptive driving bus voltage (ADBV) and energy recycling (ER) control schemes is proposed to drive red, green, and blue LEDs in series to achieve high efficiency. The bus voltage of the power factor correction flyback converter with the ADBV control is always adjusted, so as to reduce power loss on current regulators. However, since the small bandwidth of the flyback converter and large bus capacitor limit the transient response of the flyback converter, it is difficult to maintain the voltage across current regulators at the minimum value. The ER control is proposed to accelerate the transient response of the bus voltage, making the voltage across current regulators as close to the minimum voltage as possible. Furthermore, extra energy is stored and restored on the recycling capacitor when the bus voltage is switched between different supplying levels without consuming much power due to the ER control. The experimental waveforms of the laboratory prototype are shown to confirm the validity of the proposed schemes. [ABSTRACT FROM PUBLISHER]

For the purpose of improving the performances of T-type neutral point clamped (T-NPC) photovoltaic (PV) grid-connected inverter under large grid, a passivity-based decoupling control scheme is proposed in this paper. First, the Euler–Lagrange (EL) mathematical model of a T-NPC PV grid-connected inverter with an LC filter is built based on the power circuit and operating principles. Second, with this EL mathematical model and passivity of the inverter, the passivity-based controller is designed by the damping injecting method. Third, by adopting a proportional integral regulator to directly control direct current (dc) voltage, together with passivity-based indirect control, better performances of the dc voltage control can be further obtained. With the proposed passivity-based controller, the PV grid-connected inverter can achieve both dynamic current decoupling under the synchronous rotating dq coordinate and dc side voltage dynamic decoupling, which can improve the quality of the current connected into the power grid. The passivity-based PV grid-connected inverter is with strong robustness against parameters perturbations of resistors and attenuating the influence of delay in the inverter. Moreover, the passivity-based decoupling control scheme proposed in this paper for the T-NPC PV grid-connected inverter has a simple structure, and is easily debugged and realized in engineering. Experimental results under 10-kW prototype show that the proposed control scheme is effective. [ABSTRACT FROM PUBLISHER]

Safe and reliable automatic pressure regulation for the oxygen mask is a primary consideration in an oxygen supply system (OSS). In order to enhance comfort of users, it is of significance to improve performance of the oxygen regulator. Based on analyses of the operation principle of electronic oxygen regulator (EOR), a new EOR is designed, where a proportional flow valve is adopted as the throttle valve, and an active disturbance rejection control (ADRC) strategy is applied to control the throttle valve. The external disturbances and the internal dynamics are estimated using an extended state observer. The dynamic compensation using a state error feedback in each sampling period reduces the plant approximately to an integrator tandem structure. Mathematical simulations are performed for the OSS to evaluate the control method compared with the proportional integral derivative (PID) control approach. The simulation and experimental results demonstrate that the ADRC can achieve precise pressure regulation with superior lower inspiratory resistance than the PID method, considering some environmental disturbances including the user's changing pulmonary ventilation. The work in this paper may be a reference for the EOR design. [ABSTRACT FROM PUBLISHER]

This paper presents a self-powered interface enabling battery-like operation with a regulated 3 V output from ac signals as low as 0.4 Vpeak, generated by electromagnetic energy harvesters under low frequency vibrations. As the first stage of the 180 nm standard CMOS circuit, harvested signal is rectified through an ac/dc doubler with active diodes powered internally by a passive ac/dc quadrupler. The voltage is boosted in the second stage through a low voltage charge pump stimulated by an on-chip ring oscillator. The output is finally regulated to 3 V at the last stage. The voltage doubling rectification stage deviates by less than 40 mV from ideal expectation for the validated 0.15–1 V input voltage range. The full system delivers 3 V output to 4.4 MΩ load for input voltage of 0.4 V peak, which is the lowest operable input voltage in the literature. The demonstrated system generates 9 μW of dc power with 3 V stable output for 32 μW input, whereas the circuit is able to supply even more output power for higher input power levels. The maximum efficiency of the rectification stage is 86%, while the full system efficiency is 37% and 28% for unregulated and regulated operation, respectively, when interfaced to an in-house electromagnetic energy harvester under 8 Hz 0.1 g vibration. [ABSTRACT FROM PUBLISHER]

In this paper, a new active current balancing method for a light-emitting diode (LED) driver with multichannel outputs is proposed. In the proposed structure, a low-power nonisolated dc–dc converter in series with each LED string is used to regulate the LED string current. Different from conventional active current balancing methods, in the proposed method, the nonisolated dc–dc converters only process a small portion of the total output power. Thus, the cost and size can be greatly reduced. An adaptive bus voltage control method is also proposed to minimize the output power of the nonisolated dc–dc converters. The proposed method features good modularity, expandability, and individual current control capability. Performance of the proposed method is validated by the experimental results from an 80-W prototype with four channel outputs. [ABSTRACT FROM PUBLISHER]

Deadbeat control (DBC) is developed based on the system model, which is commonly used to achieve good control performance for a three-phase grid connected converter (GCC). Unbalanced grid voltage is a common phenomenon in power systems. In this study, an improved DBC based on current predictive correction (CPC_DBC) is used to control GCC under an unbalanced grid voltage. The main purposes of CPC_DBC are to reduce the adverse effects due to random sampling error to improve current control performance, and to enhance the interference rejection capability of the control system. Then, the characteristics of CPC_DBC and the conventional DBC (Con_DBC) are analyzed by transfer functions in the discrete time domain. Several common control objectives under an unbalanced grid voltage are used to demonstrate the superiority of CPC_DBC. Finally, the experimental results indicate that CPC_DBC can effectively reduce the adverse effects of random sampling error; the robustness of system due to the uncertain value of the filter inductance is improved as well. [ABSTRACT FROM PUBLISHER]

The shunt regulator is a key part of the power conditioning unit, which is becoming more and more important in the spacecrafts. Due to the nonlinear link, the switch operating with hysteresis control, the shunt regulator is a nonlinear system; however, the stability analysis method for the system is still grounded on the approximate linearization method, which neglects some of the ac and dc characteristics. In this paper, a novel stability analysis method for the nonlinear systems is proposed based on the describing function, which can be used to model the nonlinear link in the shunt regulator system. Further, the different conclusion of the shunt regulator system stability are drawn, by the approximate linearization method and the stability analysis method proposed in this paper, respectively. Finally, the simulation and experimental results prove the correctness of the stability analysis method with describing function and discover the incompletion of the approximate linearization methods on the stability analysis. Therefore, this paper provides a new way to analyze the stability of the nonlinear systems. [ABSTRACT FROM PUBLISHER]

Duty-ratio-control-aided LLC converter for current balancing of two-channel light-emitting diode (LED) driver is proposed and analyzed. Conventional current-balancing methods have the limitation on the power density and losses from additional components. With the aid of duty ratio control of an LLC converter, the proposed driver does not require any additional component. The total output current is controlled with the frequency modulation, and the duty ratio control is added to obtain current balancing of each LED channel. The advantage of the proposed method is the high power density and high efficiency. Also, it does not affect design procedure of a conventional LLC converter. The prototype of two-channel LED driver with 400-V input and 150–100-V/0.3-A output for each channel verifies the effectiveness of the proposed driver. [ABSTRACT FROM AUTHOR]

This paper is the continuation of Part I in which a quasi-Z-source modular cascaded converter (qZS-MCC), comprising front-end isolated qZS half-bridge dc–dc converter submodules (SMs), for dc integration of high-power photovoltaic (PV) systems is proposed. The qZS-MCC-based PV system features modular structure, high-voltage dc collection of PV power, simple control with a unified and constant duty cycle for the front-end isolation converter of all SMs, and low qZS impedance due to no double-line-frequency pulsating power. Here, control scheme of the qZS-MCC PV system integrated into the dc collection grid is investigated. Dynamic model of the system is established for controllers design and time-domain transient simulation. Experimental tests are carried out on the downscaled prototype as a proof-of-concept of the proposed control and modeling, demonstrating the validity of the proposed approaches. [ABSTRACT FROM PUBLISHER]

Reliability of the power distribution unit (PDU) is very important in electrical systems. Since any failure in this unit leads to system failure. A commonly used method for increasing the reliability of a dc PDU is using the redundant modules. If a fault occurs in a voltage regulator of PDU, it is replaced by its redundant module. In conventional redundancy, each dc voltage regulator has its exclusive redundant modules. Therefore, if both a regulator and its redundant modules fail, the system is stopped. It is an important drawback since the exclusive redundant modules of other voltage regulators may not be used, but, the PDU cannot use them instead of faulty regulators. In this paper, the application of the nonexclusive redundant regulators is presented for solving this problem. In the proposed method, dc power distribution unit consists of a number of redundant modules, which can be adjusted to a desired voltage and can be used instead of faulty regulators. An analysis based on Markov model is presented to compare reliability of the proposed structure with the conventional structure presuming a variable failure probability. Theoretical study indicates more reliable operation of the proposed PDU structure than the conventional structure. Experimental results are presented to show practical considerations of the proposed structure and its proper performance. [ABSTRACT FROM AUTHOR]

With the increase of the rated power, the sampling and switching frequencies of the high-power pulse-width-modulated (PWM) converter tend to be lower so that a challenging scenario is arising in current control system design. This strongly affects the stability and control performance of the current control system due to the undesirable dynamic coupling of the dq current components. From this perspective, this paper presents a systematic procedure for accurately evaluating the coupling of current control systems, which is based on static and dynamic relative gain array (static relative gain array and dynamic relative gain array). Unfortunately, the dynamic coupling of these systems is so serious at low-frequency band, and the parameter variation makes it easier for these systems to lose stability, when a classical proportional integral regulator with feed-forward decoupling or nondecoupling is employed. Hence, a novel output feedback decoupling control method is proposed, which is based on linear control for multiple-input-multiple-output system. Considering the amplification of the first-order differential, the decoupling unit is further improved by replacing the differential with high-pass filter. Experimental results in a small-power converter are presented to support the theoretical analysis and demonstrate the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]