Switching Period Research Articles

Dynamic Freewheeling Control for SIDO Buck Converter With Fast Transient Performance, Minimized Cross-Regulation, and High Efficiency

Slow load transient performance, potential cross-regulation, and low efficiency are the major drawbacks for pseudocontinuous conduction mode single-inductor dual-output (SIDO) dc–dc converters. To overcome these drawbacks, this article proposes a voltage-ripple (VR)-based dynamic freewheeling (DF) control technique for hybrid conduction mode (HCM) SIDO buck converter. With the employment of VR controller, the proposed control technique improves the load transient performance significantly. As the fast recovery during load transition, the cross-regulation is minimized. Additionally, due to the DF controller, the freewheel current value automatically updates in each switching period, which can improve the efficiency of the HCM SIDO buck converter, especially under the light load conditions. Finally, the proposed converter has been verified through experimental results. The transient response time on 0.5 A load change takes only 1–2 switching periods. No observable cross- regulation is found and maximum efficiency of 92.03% is achieved. Finally, the experimental waveforms are presented to verify the theoretical research.

A Dual-Transformer-Based Three-Level DC–DC Converter With Wide ZVZCS Switching Range

In this letter, a dual-transformer-based three-level DC-DC converter (TLDC) with wide zero-voltage and zero-current switching (ZVZCS) switching range is proposed. Compared with traditional ZVZCS TLDCs, this converter can achieve zero-voltage switching (ZVS) for the leading switches and zero-current switching (ZCS) for the lagging switches without any extra auxiliary components. By introducing an additional transformer, the energy can be transmitted during the whole switching period, and the current ripple of the output filter inductor can be reduced, resulting in a reduction in output filter inductance. Besides, the control strategy is a traditional simple phase-shift control. The circuit, operation principle and some steady-state characteristics are discussed in this letter. Finally, a 1-kW 650–800 V input and 250 V output experimental prototype is designed to demonstrate the validity and features of the proposed converter.

A Modulation Method to Eliminate Leakage Current and Balance Neutral-Point Voltage for Three-Level Inverters in Photovoltaic Systems

In photovoltaic systems, common-mode voltage (CMV) generates leakage current, which shortens the insulation lifespan and causes safety problems. As for neutral-point-clamped (NPC) inverters, zero CMV PWM (ZCMV PWM) can be implemented to eliminate leakage current, but unable to balance neutral-point (NP) voltage in dc side. This article presents a novel modulation technique for NPC PV inverter. The strategy contains ZCMV PWM and another two modulation modes which keeps CMV constant in one switching period, so as to eliminate leakage current. In order to balance NP voltage, NP current is adjusted by selection of optimal modulation mode and the leakage current is still well eliminated during the process of balancing NP voltage. Compared with conventional ZCMV PWM, the proposed scheme can remove both leakage current and NP voltage deviation. The output performance and limitations of the proposed method are also introduced in the paper. Experiments are provided to verify the validity of the proposed method.

Clamping Modulation Technique for Balancing Power Losses of Dual Inverter With Isolated DC Bus

This paper proposes a clamping modulation technique to reduce and balance power losses in a dual inverter with an isolated DC bus. To drive an open-end winding permanent magnet synchronous motor (OEW-PMSM), dual inverter consisting of six legs has twelve switching actions, twice as many as a two-level voltage source inverter (VSI) per switching period. However, many switching actions cause power losses in switching devices, reducing the efficiency of the system. In this paper, a four-leg clamping modulation technique is presented to reduce the switching actions by analyzing the relationship between two reference voltage vectors of primary and secondary inverters on a space vector plane. To clamp four of the six legs overall, the switching states are determined by combining active and zero vectors during the switching period. The selected vector combinations differ according to 18 sectors divided by the magnitude and angle of the reference voltage vector. The zero vectors required for 18 sectors are then distributed to balance the power losses in upper and lower switching devices of each leg. This technique is implemented with carrier-based pulse width modulation (PWM) by calculating each three-phase reference voltage from two reference voltage vectors composed of the vector combinations. Balancing of the power loss between the upper and lower switching devices is achieved by adding offset voltages corresponding to the zero vector of each sector. The validity of the proposed technique is verified experimentally.

An Efficient Zero-Voltage Switching Resonant Pole Inverter With High Reliability

To improve the transmission efficiency of the inverter, this brief proposes a novel efficient resonant pole inverter. The main switching devices will be capable of achieving zero-voltage switching when auxiliary circuits of each phase work in the commutation process of the novel inverter, which makes for the reliable efficiency improvement. Besides, the maximum voltage and maximum current which the main switching devices sustain under full load operation are respectively limited to the input DC voltage and maximum load current, avoiding the damage of main switching devices caused by over-voltage and over-current. Thus, main switching devices can work reliably. Moreover, the duration of the conducting state of the auxiliary switching devices in each switching period can be constant, making for the control reliability of auxiliary circuits. This brief illustrates each working state in a switching period. The relative experimental waveform indicates that switching devices attain soft-switching. Furthermore, the efficiency of the novel inverter achieves 98.8% at rated output power. Hence, the novel inverter can have higher reliability than other similar inverters.

Capacity and Volume Balance of Buffering Converters for the Marine Pulsed Power System

In marine integrated power systems (IPS), dc/dc converters have been widely used to buffer the power of pulsed loads. However, limited by ship space and safety, its buffering capacity and volume are conflicting and need to be balanced. Existing methods usually oversimplify the switching dynamic process caused by the different switching periods between the pulsed loads and converters, leading to oversizing or underpowering issues of the converts. To overcome this hurdle, this article proposes a millisecond-time-scale-based state-space averaging mode (MTS-SSAM) to analyze the dynamic process by taking pulsed loads period instead of the traditional converter period as the averaging operator. Based on MTS-SSAM, taking the system allowable voltage and current fluctuation rate and converter volume as the objective function, the converters’ parameters are optimized considering the balance between buffering capacity and volume. The proposed parameters optimization method can save 49% converter volume compared with existing methods. The simulation and experimental results are presented to verify the proposed SSAM and optimization method.

A Four-Capacitor Model for Interprimary-Winding Capacitances Analysis in the Input-Series Transformer-Integration Converters

The input-series transformer-integration (ISTI) converters are suitable for the high-input voltage multiple-output applications. In these converters, interprimary-winding capacitances are the unique stray capacitances of the integrated transformer, and energy influences of these capacitances cannot be ignored in the high-voltage applications. In order to analyze energy influences of the interprimary-winding capacitances, in this article, a four-capacitor model is proposed to represent these capacitances within arbitrary two primary windings of the integrated transformer. Based on the proposed model, energy varying of the interprimary-winding capacitances is analyzed in detail during each switching period. Furthermore, estimation of the four lumped capacitors is discussed. Finally, three different integrated transformers are designed for a 1-kV/60-W laboratory-made flyback ISTI converter, and validity of the proposed model is verified through the simulating and the experimental comparisons of these integrated transformers.

Pension System for the Rural Areas in Actual Social and Economic Conditions in China

The article first describes and analyzes China's social support measures for rural population from 1950s to nowadays. It depicts the indistinct stages of pension system institutionalization from the time it appeared and up to the present. The major Chinese society peculiarity lies in a huge gap between standards of living in the city and in the country. It has its present characteristics due to the historical environment of official employment in Chinese villages and the previous absence of social and pension governmental support as its circumstances. In the study latent periods of switching from one pension form to the others are revealed. The fact is that China's social support measures for rural population has only history of one hundred years. However different pension forms replace each other dramatically during this time while special aspects of moral issues, family relations and social structures of Chinese society complicate the situation. Various aspects of rural pension policy in China are underexplored for that moment. The paper fills this important gap and gives much attention to its social, cultural and economical aspects. Evolution of Chinese rural pension policy starts from the "Five Guarantees" system, continues with the "Baoji model" and concludes with the "New Pension System" development. This system is to equalize rural and urban pension rights in China. In conclusion due to the National Social Policy only from 2014 every Chinese rural citizen aged 60 and older has pension entitlements. This fact can indicate that the primary maturity of China’s state pension system for old-age rural population has been reached.

Control of PMSM Drive Using Lookup Table Based Compensated Duty Ratio Optimized Direct Torque Control (DTC)

There are several ways to reduce the ripple magnitude for direct torque-controlled permanent magnet synchronous motor (PMSM) drives. In this work, the compensated duty ratio optimized direct torque control (DDTC-TC) method was proposed to reduce the ripple for three-phase PMSM. The proposed control strategy employs the simplicity of conventional DTC (CDTC) and compensation of the reference torque to enforce the developed torque to oscillate around the required value. A torque error square minimization technique is employed to determine the duty ratio. The magnitude of the developed torque by the PMSM depends on the torque slope during the active and null voltage periods. The slope of the torque during each period is computed online. Based on the online computed slopes, the magnitude of the switching period and compensation torque were calculated. The ripple reduction capability of the proposed control scheme is tested using Matlab Simulink and a hardware in loop system. Results indicate that the control scheme is effective. Specifically, the torque and speed ripples are very small. The torque ripple during speed fluctuation is less for open-end winding PMSM. In addition, the proposed scheme is tested for four-quadrant operation, and the scheme is effective for four quadrant operation. Finally, verification of the effectiveness of the proposed scheme is performed using OPAL-RT-RT (OP4500). Verification indicates that the proposed scheme is effective.

Design of the inverter in high accuracy and development of work therein by using compound ligation

A ligation (CL) system with a very high frequency in an inverter was used, it is a novelty in this study. We also employed a three-phase dynamic load (positive sequence voltage) to correct the power factor and account for active and reactive power in the output system this work is a novelty. The technique through compound ligation (CL) can improve inverter output waveform by reducing losses caused by ingrained agents in voltage source inverters (VSI), such as dead time caused by overload or voltage drop in an inverter's output, or abnormal load current conditions such as a short circuit current occur in the output stage of the inverter, and so on. The invention relates to the conversion of D.C. to A.C. power inverters, it is preferable to use compound ligation to achieve high efficiency, the device is lightweight, and has low losses and good precision. In addition, the present invention relates to improving an inverter load request sensation circuit, smoothing operational current, inverter response, and inverter spontaneous power factor improvement, as well as correction of the reactive power of passive components. In addition, an inverter with high active power (P) equal to (2.6×106 Watt), reactive power (Q) (5.4×107 VAR), was designed, and used positive sequence voltage (1.6×108 Watt ), as well as the switching period (10µs), The system's total harmonic distortion (THD) in voltage and current was 0.11 percent, while the system's accuracy was 99 percent. This is developed by using FPGA and oscillator circuit and programmable peripheral interface 8255 A as well as, ultrasonic PWM with a high-frequency range of (20–500 kHz) as demonstrated evidenced by the results obtained

Time‐modulated multi‐tone antenna array for wireless information and power transfer

SummaryThis paper aims to design a multi‐tone radiator exploiting harmonic radiation characteristic of time‐modulated antenna array for wireless information and power transmission (WIPT) and multi‐operational WIPT receiver. The time‐modulated linear antenna array (TMLAA) radiating simultaneously at modulating and harmonic frequencies separated in multiple switching periods is utilized as a multi‐tone radiating system. TMLAA with suitable power in harmonic bands generates multi‐tone radiation by employing an optimized switching sequence. The ON and OFF time instants of the TMLAA are optimized to suppress sidelobe level and enhance sideband level. A population‐based optimization algorithm, teaching learning based optimization (TLBO), is employed to optimize the ON and OFF instants of the TMLAA to suppress sidelobe level and enhance sideband level. TLBO is utilized for a 16‐element TMLAA with minimizing cost function to achieve the above objectives. The 16‐element TMLAA with optimized switching radiates multi‐tone beams with a minimum of 5 dB peak power difference exploited as WIPT. The purpose of multi‐operation is accomplished by utilizing the Wilkinson power divider in the receiver system; its power dividing capability is analyzed using applied wave research (AWR). A voltage doubler type rectifier is modeled for DC generation and is tested using AWR. The DC generating capability is tested for fixed power available at various frequencies, and the fixed desired frequency with various available power levels is tested. The results show that the designed circuitry provides a maximum of 80% power conversion efficiency (PCE).

Reciprocating Oscillation of a Floating Ferrofluid Marble Triggered by Magnetic Fields.

Liquid marbles have the potential for microfluidic transport, medical diagnostics, and chemical analysis due to their negligible stickiness, environmental independence, and excellent mobility. Here, we report a non-contact manipulation strategy to arouse a reciprocating oscillation of ferrofluid marbles floating on the water surface, which can be used as microreactors. We experimentally investigated the quantitative relationship between the oscillation behavior, the applied magnetic field parameters, and the field regulation mechanism. The variables, including the magnetic field strength, marble volume, and switching period, are vital in determining the final state. The oscillation can be separated into three stages: transitional movement, compressive deformation, and rebound, before entering the next cycle. Accordingly, we created a manipulation technique for improving the mixing of inner reactants inside this marble container by remote-controlled shaking after optimizing with an oscillation model.

Current Prediction-Based Fast Diagnosis of Electrical Faults in PMSM Drives

Open-phase fault (OPF) and open-switch fault (OSF) are two common electrical faults in the permanent magnet synchronous machine (PMSM) drives. To locate the faults rapidly and relieve the fault damage, a current prediction-based diagnosis scheme is proposed for OPF and OSF in three-phase PMSM drives. The proposed diagnosis scheme consists of three steps, namely, determining fault occurrence, locating the faulty phase, and identifying the specific fault. The general current deviations between dq-axis predicted currents from the normal model and dq-axis feedback currents are used to determine the fault occurrence. The general current deviations between dq-axis feedback currents and dq-axis predicted currents from different faulty models are used to locate the faulty phase. Then, an intervention-based diagnosis is developed to identify the specific fault. In this way, the specific fault can be quickly located within several switching periods. Finally, the effectiveness of the proposed diagnosis scheme is verified by the experimental results.

Fast Quasi-Static Time-Series Simulation for Accurate PV Inverter Semiconductor Fatigue Analysis with a Long-Term Solar Profile

Power system simulations with long-term data typically have large time steps, varying from one second to a few minutes. However, for PV inverter semiconductors in grid-connected applications, the minimum thermal stress cycle occurs over the fundamental grid frequency (50 or 60 Hz). This requires the time step of the fatigue simulation to be approximately 100 μs. This small time step requires long computation times to process yearly power production profiles. In this paper, we propose a fast fatigue simulation for inverter semiconductors using the quasi-static time-series simulation concept. The proposed simulation calculates the steady state of the semiconductor junction temperature using a fast Fourier transform. The small thermal cycling during a switching period and even over the fundamental waveform is disregarded to further accelerate the simulation speed. The resulting time step of the fatigue simulation is 15 min, which is consistent with the solar dataset. The error of the proposed simulation is 0.16% compared to the fatigue simulation results using the complete thermal stress profile. The error of the proposed method is significantly less than the conventional averaged thermal profile. A PV inverter that responds to a transactive energy system is simulated to demonstrate the use of the proposed fatigue simulation. The proposed simulation has the potential to cosimulate with system-level simulation tools that also adopt the quasi-static time-series concept.

Analysis and Design of Zero-Voltage-Switching Multiphase AC/DC Converters

In this article, the generic analysis and design of zero-voltage-switching (ZVS) multiphase ac/dc converters are proposed. With the edge aligned pulsewidth modulation (PWM) (EA-PWM) scheme, all switches of ZVS multiphase ac/dc converters can realize ZVS operation. Besides, the switching frequency is fixed and the auxiliary switch only operates once in each switching period. Its operation stages in a switching cycle are analyzed and a generic ZVS condition is derived. Based on the proposed theory, a ZVS two-stage three-phase photovoltaic (PV) inverter is investigated, which is regarded as a five-phase converter. Its ZVS condition under different working conditions is discussed. Finally, a 10-kW prototype with 150 kHz switching frequency of the ZVS two-stage three-phase PV inverter is built and the experimental results are given to verify the analysis. In addition, the extension of the ZVS multiphase converter in different applications is introduced.

An Improved DPWM Method for Single-Phase Five-Level ANPC Converters With Switching Loss Reduction and Capacitor Voltage Balance

Neutral-point (NP) voltage and flying capacitor (FC) voltage balance, and power loss reduction are important guarantees for the stable and high-efficiency operation of single-phase five-level active neutral-point clamped (5L-ANPC) converters. However, little reports about capacitor voltage balancing with the power loss reduction have been proposed for single-phase 5L-ANPC converters. In order to obtain the above merits, an improved discontinuous pulsewidth modulation (DPWM) method with capacitor voltage balance and power loss reduction is proposed. First, an optimized common-mode voltage is injected into the modulation waves to decrease the switching loss in each switching period. In particular, the calculation of the injected common-mode voltage is based on the analysis of the deviation of the NP voltage. Hence, a fast-dynamic response of the real-time NP voltage controlling is acquired in the meantime. Besides, in order to balance the FC voltage, the weight factors of NP voltage deviation and FC voltage deviation are compared to generate the selecting signals of redundant switching states. As a result, the capacitor voltage balance and power loss reduction are realized simultaneously. Finally, the simulation and experimental results validate the correctness and feasibility of the proposed DPWM method.

An Enhanced Short-Horizon Integration Actual Voltage Reconstruction Method Based on Inverter Nonlinear Error Inverse-Compensation

In this article, an enhanced short-horizon integration actual voltage reconstruction method based on nonlinear error inverse-compensation (NEIC-SHIVR) is proposed for voltage source inverters. The NEIC-SHIVR method takes into account not only the influence of nonlinear errors in modulation such as dead time addition and narrow pulses elimination on voltage reconstruction but also considers the influence of nonlinear errors in PWM transfer links such as power switch delay and switch voltage drop on voltage reconstruction. First, the real-state driving signal is computed by the output driving signal and the power switch delay time. The auxiliary driving signal is reconstructed to get the auxiliary switching state according to the phase current direction. Second, referring to the auxiliary switching states and the phase-current directions, the instantaneous equivalent bus voltage within each clock pulse is computed by the dc-bus voltage and the switch voltage drop. Finally, the output voltage within each switching period is integrated by the reconstructed instantaneous equivalent bus voltage in each clock pulse. Compared with SHIVR, NEIC-SHIVR provides a more accurate reconstructed voltage. Compared with other methods, NEIC-SHIVR inherits many advantages of SHIVR. For example, it can apply to any PWM method and does not use high-cost high-frequency voltage sensors, which improves system reliability and reduces system complexity. Simulations and experiments verify the effectiveness of the proposed method.

Carrier Redistribution Pulsewidth Modulation for Five-Level Stacked Multicell Converter

This article presents a modified carrier redistribution pulsewidth modulation (CRPWM) method for the five-level stacked multicell converter (SMC). The proposed CRPWM method is modified by exchanging the arrangement of the carriers of phase disposition pulsewidth modulation (PDPWM). With the ingenious carrier arrangement, the proposed PWM technique equalizes the utilization of phase leg voltage redundancies corresponding to the charging and the discharging state of each floating capacitor during one switching period of all the switches. The proposed modulation strategy has the same harmonic performance of line-to-line voltage with PDPWM, while the switch utilization is the same as phase-shifted pulsewidth modulation (PSPWM). Therefore, the voltage balancing of floating capacitors is achieved during a minimum switching period even with the influence of load current change and inappropriate carrier ratio is considered. The modified CRPWM is analyzed in theory and the voltage balancing ability and output harmonics performance are compared with PSPWM and traditional CRPWM. Simulation and experimental results on the laboratory prototype five-level SMC confirm the validity of the proposed CRPWM technique.

A Single-Phase Switched-Capacitor Nine-Level Inverter With Reduced Capacitance

A novel nine-level switched-capacitor multilevel inverter (SCMLI) with reduced capacitance and balanced capacitor voltage is proposed in this article. Utilizing only two capacitors, the proposed SCMLI can boost the input voltage and realize nine output voltage levels under different kinds of load conditions. The controllable capacitor charging speed in the proposed SCMLI depends on the charging resonant inductor rather than the equivalent resistance of the devices in conventional topologies. The two capacitors can be charged or discharged independently by a dc source when their voltages deviate from the rated voltage. This makes the proposed SCMLI free of the capacitor voltage imbalance. The longest discharging time (LDT) of capacitors is reduced to twice the switching period, which contributes to reduced capacitance in the proposed SCMLI. With the required capacitor voltage ripple, the quality of output waveforms is also very high. A comprehensive comparison with previous SCMLIs in terms of capacitance, the voltage imbalance problem, the output voltage level, and so on is conducted to validate the merits mentioned above. The theoretical analysis, the simulation, and experiment results are accordant, confirming the feasibility of the proposed SCMLI.

Characterization and Selection of Probability Density Function in a Discrete Random Switching Period SVPWM Strategy

Aiming at suppressing the switching frequency harmonics in the integrated permanent magnet synchronous motor (PMSM) systems, a discrete random switching period (DRSP) space vector pulse width modulation (SVPWM) technique is proposed in the present study. In the proposed DRSP-SVPWM technique, the switching period is randomized according to a predefined frequency sequence. Accordingly, the narrow-band harmonics of the switching frequency are extended to a wider range. Then, a mathematical correlation between the probability density function and the harmonic distribution is established. Moreover, the effects of discrete uniform and beta distributions on the harmonic spreading are studied. Based on the proposed DRSP-SVPWM technique, the mathematical expression of the harmonic power spectrum is derived, demonstrating the intrinsic dependency between the discrete random factor and the harmonic energy distribution. Finally, a series of simulations and experimental results are compared to evaluate the performance of the proposed technique. The present study is expected to provide a theoretical basis for the design and selection of discrete frequency sequences. Meanwhile, it provides a reference to investigate the random SVPWM and improve noise and electromagnetic interference in power converters.