Asynchronous Pulse Width Modulation Research Articles

Formation of the Spectral Composition of the Output Voltage of Converters for Nuclear Magnetic Resonance

In this paper, we consider the construction of an asynchronous control system for semiconductor converters for nuclear magnetic resonance. The relevance of research in this direction, main problems that arise during the construction of these systems are shown. Derived the mathematical model of the inverter, on the basis of which a control system with asynchronous pulse-width modulation is constructed. Proposed an equivalent converter circuit with a constant structure, constant parameters, and an equivalent EMF generator. Established correspondence between the equivalent circuit of the converter and its mathematical model in the form of differential equations. On the basis of mathematical equations, a structural diagram of the converter with a control system was developed and the principle of operation of the device was described according to it. To develop an algorithm for the control system, the dependence of the frequency change relative to the resonant frequency on the phase shift between the current through the filter and the voltage on the antenna circuit is determined. For which the model was built in Simulink and the corresponding simulation was carried out. Numerical dependences of reference signal frequency change and phase shift were obtained. The increase in efficiency of device for nuclear magnetic resonance is considered due to the use of multilevel inverters with tuning the frequency of operation to the frequency of the resonant circuit. Simulation of a three-level diode-clamped inverter showed that when the capacitance of the resonant circuit changes and, therefore, the resonant frequency of the circuit, the input current increases. The work obtained specific numerical dependencies. Time diagrams of voltages and currents on the main elements of the converter are given, which illustrate the implementation asynchronous pulse-width modulation in the control system. After working out the automatic frequency control algorithm, the increase in current consumption can be leveled off. The simulation results also show that it is possible to reduce the amplitude of the third harmonic. The disadvantages of the proposed system include the fact that the frequency of the converter is adjusted at each subsequent period of its operation. At the same time, the parameters of the filter can change again, which leads us to believe that adjusting the frequency will never give a 100% result, but will only allow to get as close as possible to the set parameters of the sounding signal. The work also indicates that it is possible to improve the spectral composition of the probing voltage generated by the converter by using more levels of a diode-clamped multi-level inverter. However, increasing the number of levels reduces the action speed of the system and complicates the control system itself. Therefore, the need to maintain a balance between the number of levels of the inverter and the complexity of the system is indicated.

СТІЙКІСТЬ ЗАМКНЕНИХ СИСТЕМ ЕЛЕКТРОЖИВЛЕННЯ З ВИКОРИСТАННЯМ ШИРОТНО-ІМПУЛЬСНОЇ МОДУЛЯЦІЇ ПІД ЧАС ВРАХУВАННЯ ФАКТОРУ ПУЛЬСАЦІЙ

The vast majority of low- and medium power supply systems are based on pulse converters using pulse-width modulation, which provides flexible regulation of electricity parameters, which is especially important in systems with renewable energy sources. When synthesizing control systems based on pulse-width modulation, it is necessary to take into account the level of pulsation of the output voltage, which significantly affects stability and, accordingly, the value of the control system gain. The effect of pulsation on stability is described on the basis of the pulsation factor, which takes into account the component that precedes the switching moment. The paper suggests also taking into account the component that follows the moment of switching. Using the example of asynchronous pulse-width modulation, the transfer function of the closed loop system was obtained taking into account the proposed pulsation factor after switching, and the region of stability of the closed system was analyzed. References 12, figures 2.

ПОИСК НОВЫХ ВАРИАНТОВ КОНСТРУКЦИИ ТЯГОВОГО ПРИВОДА НИЗКОПОЛЬНЫХ ЭКИПАЖЕЙ

The possibility of increasing locomotive traction properties without using drives with asynchronous traction electric motors (TED) and pulse width modulation is considered. It is proved that collector TED allows realizing the traction force in a continuous mode of 63.75 kN per axle with a wheel diameter of 1250 mm, while it is advisable to use a drive with a support frame suspension of TED and an axial gearbox. Due to the significant mass of collector TED, it is proposed to make a promising diesel locomotive in the form of two sections on three two-axle bogies and a booster on two two-axle bogies. Taking into account that electric arc asynchronous motors (EAAM) simplify the converter part of the drive by eliminating pulse width modulation, a design of a traction drive for EAAM with a hollow shaft in the recess formed by arc-shaped inductors is proposed, which makes it possible to realize EAAM torque and locomotive traction force by increasing the diameter of EAAM rotor.

ПОИСК ПУТЕЙ ПОВЫШЕНИЯ ТЯГОВЫХ СВОЙСТВ ТЕПЛОВОЗОВ И КОНСТРУКЦИЯ ТЯГОВОГО ПРИВОДА

The work objective is to increase the traction properties of locomotives without the use of traction drives with asynchronous traction motors and pulse width modulation.
 Research methods: methods of physical and field experiments, analytical methods for calculating the dynamics of the rolling stock.
 Conclusion: based on the conducted research, it is proposed to perform a promising diesel locomotive in the form of two sections on three two-axle bogies and a booster on two two-axle bogies, as well as to carry out experimental design work to develop an arc-type stator asynchronous motor and traction drives of a diesel locomotive using it.

Multilevel Fixed Pulse Pattern Control for Medium-Voltage High-Frequency Inverter

To satisfy the demand for more compact medium-voltage motor drive systems, it is desirable to increase the frequency of the cascaded H-bridge inverters used in high-speed motor systems. However, in asynchronous pulse width modulation (PWM) systems, as the output frequency increases, the command voltage and triangular wave carrier frequencies get closer, making it impossible to accurately output the command voltage. This manifest itself as increased current harmonics, increased surge voltage at the motor terminals, and increased low-frequency ripple current due to the asynchronous nature of the system. In this study, we adopt a fixed pulse pattern modulation method to address these problems. In our method, a low-distortion output voltage is compiled in advance into a table, and subsequently output in synchronization with the fundamental voltage phase. We were able to confirm the effectiveness of the proposed method in simulations at fundamental wave frequencies of 700 Hz and 1000 Hz.

Parallel connected GaN E‐HEMT VSI‐based servo drives for PMSMs

The operation of parallel-connected servo drives has the advantages of increasing the torque (hence the power) capacity, reliability, redundancy and modularity. However, smaller discrepancies of the system clocks of the independent microcontrollers, asynchronous pulse width modulation (PWM) carrier signals and hardware differences can make the output voltages of the parallel modules non-identical, which results in circulating currents. These circulating currents limit the parallel operation, introduce additional power dissipation, cause unbalanced power distribution and degrade the control performance. To eliminate the circulating currents separated DC supplies, coupled inductors (CIs), PWM techniques, modified control techniques etc. are proposed in the literature. In this study, a fault-tolerant parallel-connected gallium nitride enhancement-mode high electron mobility transistor voltage source inverter-based servo drive scheme that eliminates the need for CIs and separate DC supplies and also enables the use of a standard proportional-integral current control and a standard space vector PWM approach is proposed and tested. To evaluate the performances of the proposed scheme, up to six servo drives (limit-6 × 7 Arms) are connected in parallel and tested under various conditions with a 24 V permanent magnet synchronous motor (nominal-61.9 Arms). The results show that the parallel operation not only increases the torque capacity of the system but also increases modularity, flexibility, reliability and also redundancy.

Analysis and Transition Techniques for a Bidirectional DC–DC Converter

This article proposes two new pulsewidth modulation (PWM) schemes, namely, asynchronous PWM scheme (APS) and synchronous PWM scheme (SPS), for a nonisolated fourth-order bidirectional dc-dc converter (FOBDC), which are implemented to achieve a smooth start-up operation and mode transition to reverse the direction of power flow. The presented FOBDC is reported already in the literature as a unidirectional boost converter, the functionality of which is modified in this work, to enable bidirectional power flow. The FOBDC can operate in either discharging (Mode-I) or charging (Mode-II) mode. The overshoot/undershoot of inductor currents in the FOBDC occur during converter start-up operation in either of the modes and while transitioning modes (from charging to discharging and vice-versa). To eliminate the overshoot/undershoot of inductor current, two effective transition techniques are developed for smooth start-up operation and mode transition, thereby reducing the delay time significantly. The FOBDC is modeled using the state-space modeling technique, and duty ratio-to-inductor current transfer function is derived, which is validated for resistive load and battery load. Two different compensators are designed for these two transfer functions to achieve an average current-mode control (ACMC) during the charging and discharging modes of operation. The performance of the compensators is evaluated by introducing perturbations. A 12-48-V FOBDC converter, controlled by these PWM techniques with the aforementioned features, is designed, analyzed, and experimentally verified for low-power applications.

Analysis and design of an asynchronous pulse‐width modulation technique for switch mode power supply

This paper presents a new mathematical approach to design an asynchronous pulse width modulation (APWM) for the switched mode power supply (SMPS). Unlike the conventional APWM that utilises a Hysteretic comparator based Asynchronous Pulse Width Modulation (HAPWM) to provide the self-oscillating property, the proposed APWM is based on a Binary comparator based Asynchronous Pulse Width Modulation (BAPWM) and a delay cell. This way, compared to the HAPWM, the mathematical analysis of the modulator is significantly simplified. This was achieved by replacing the describing function (DF) -based graphical method with a ?linearised mathematical model. The introduced mathematical approach is extended to study the behaviour of the higher order self-oscillating modulators in terms of the harmonic distortion. To confirm the effectiveness of the analytical derivations, the BAPWMs are employed in a classic DC-DC buck converter and the system-level simulation results are provided. It is concluded that there is an acceptable degree of similarity between the simulation results and the deployed analytical calculations for different orders of the modulators. Finally, to validate these analytical and simulation results and also to compare the BAPWM performance with its HAPWM counterpart, both modulators are implemented using off-the-shelf components and their measurement results are presented.

An asynchronous pulse width modulator for DC‐DC buck converter

SummaryThis paper presents an asynchronous pulse width modulation (APWM) approach for the analysis of a new class of the switched mode power supply (SMPS). The proposed APWM significantly simplified the mathematical analysis by utilizing a binary comparator (BAPWM) and a distinctive delay cell instead of hysteretic comparator. By this way, the mathematical analysis can be extended to study the behavior of high‐order self‐oscillating modulators in terms of key parameters such as the harmonic distortion and the stability. The performance of the proposed BAPWM is deeply analyzed for different orders of loop filters (here up to third order) in both time and frequency domain. To verify the effectiveness of the proposed analytical derivations, the BAPWMs are employed in a classic synchronous DC‐DC buck converter and its closed loop performance, in terms of stability, has been investigated. Then the converter is designed and simulated in 130‐nm CMOS technology to convert input voltage of 5 to 3.3 V with maximum load current of 1 A, using Spectre simulator. From the post‐layout simulation results, the peak efficiency conversion efficiency for 3.3 V output voltage is higher than 89%.

A buck converter based on dual mode asynchronous pulse width modulator

This paper presents a buck type DC-DC converter based on an asynchronous pulse width modulator (APWM). The proposed APWM is a self-oscillating circuitry which is composed of a binary comparator (BAPWM) and a distinctive digitally controlled delay cell. The oscillating frequency of the BAPWM can be tuned by the delay of the modulator loop. By increasing the delay of the modulator loop, the switching frequency decreases and the BAPWM can be reconfigured as a low frequency APWM (LFAPWM) modulator to meet the efficiency requirement at light loads. Also, to save the switching power consumption the high-side power switch size is scaled according to the load conditions. Since the carrier signal is internally generated by the APWM itself, there is no major concern about the ramp signal discontinuity which is make duty cycle disturbance. In addition to, from the point of view of the output spectrum, the proposed converter provides a better performance compared to the conventional PWM (CPWM) and PFM due to its noise shaping property. The proposed converter is designed and simulated in a 0.13-µm CMOS technology to convert an input voltage of 5 V to the output voltage of 2.5 V with the maximum load current of 1 A. The conversion efficiency with full loading range for the 2.5 V output voltage is higher than 85% whereas the peak efficiency is about 92%.

Time Domain Processing Techniques Using Ring Oscillator-Based Filter Structures

The ability to process time-encoded signals with high fidelity is becoming increasingly important for the time domain (TD) circuit techniques that are used at the advanced nanometer technology nodes. This paper proposes a compact oscillator-based subsystem that performs precise filtering of asynchronous pulse-width modulation encoded signals and makes extensive use of digital logic, enabling low-voltage operation. First- and second-order primitives are introduced that can be used as TD memory or to enable analogue filtering of TD signals. These structures can be modeled precisely to realize more advanced linear or nonlinear functionality using an ensemble of units. This paper presents the measured results of a prototype fabricated using a 65-nm CMOS technology to realize a fourth-order low-pass Butterworth filter. The system utilizes a 0.5-V supply voltage with asynchronous digital control for closed-loop operation to achieve a 73-nW power budget. The implemented filter achieves a maximum signal to noise and distortion ratio of 53 dB with a narrow 5-kHz bandwidth resulting in an figure-of-merit of 8.2 fJ/pole. With this circuit occupying a compact 0.004-mm2 silicon footprint, this technique promises a substantial reduction in size over conventional Gm-C filters, whilst additionally offering direct integration with digital systems.

Reliability Improvement Approach Based on Flatness Control of Parallel-Connected Inverters

In this paper, a global study in terms of control architecture is applied to parallel voltage-source inverters. Parallelism of inverters represents very interesting advantages for the industrial applications to meet the high-power requirements, and it is possible to apply maintenance during the operation without interruptible operation. The main objective of this paper is to guarantee a reliable operation of the parallel inverters system during healthy and faulty conditions due to full disconnection of any inverter. Special precautions are recommended to avoid the negative effects of the circulating currents, which are caused essentially by the asynchronous pulse width modulation or existence of dispersion of the system component characteristics. To deal with this crucial problem, one-loop flatness-based control is proposed to the control of N parallel inverters and allows obtaining low total harmonic distortion. The proposed control uses the advantages of the flatness to ensure high power quality at the point of common coupling and equal currents distribution between the parallel inverters and minimize the impact of a full disconnection of any inverter on the performance. The proposed algorithm is theoretically analyzed and validated experimentally.

Analysis of Turbine Generator Shaft Torsional Vibration Caused by Self‐Commutated Converters

SUMMARYThis paper presents a simple analysis tool for torsional vibration of the rotor shaft of a turbine generator which is interconnected with a power system with self‐commutated converters. The evaluation is based on analysis of measurement data in the field and instantaneous value‐based power system simulation. A number of power converters with large capacity are installed in industrial power systems. Especially, interharmonics originating from self‐commutated converters cause torsional vibration at the rotor shaft of rotating machines. The interaction between rotating machines and converters is known as sub‐synchronous torsional interaction. The resonance between interharmonics from converters and the natural frequency of the rotor shaft causes large torsional vibrations, leading to shaft damage. In this paper, the influence of interharmonics on turbine generators is investigated. If there were air gap torque fluctuations with a frequency near the natural frequency caused by interharmonics, which have frequencies below 100 Hz of the sideband wave caused by asynchronous pulse width modulation, the rotor shaft may be damaged by the torsional vibration. In this paper, the emerging condition of the torsional vibration and the impact on the generator are investigated.

A wideband time‐based continuous‐time sigma‐delta modulator with 2nd order noise‐coupling based on passive elements

SummaryEmbedding the time encoding approach inside the loop of the sigma‐delta modulators has been shown as a promising alternative to overcome the resolution problems of analog‐to‐digital converters in low‐voltage complementary metal‐oxide semiconductor (CMOS) circuits. In this paper, a wideband noise‐transfer‐function (NTF)‐enhanced time‐based continuous‐time sigma‐delta modulator (TCSDM) with a second‐order noise‐coupling is presented. The proposed structure benefits from the combination of an asynchronous pulse width modulator as the voltage‐to‐time converter and a time‐to‐digital converter as the sampler to realize the time quantization. By using a novel implementation of the analog‐based noise‐coupling technique, the modulator's noise‐shaping order is improved by two. The concept is elaborated for an NTF‐enhanced second‐order TCSDM, and the comparative analytical calculations and behavioral simulation results are presented to verify the performance of the proposed structure. To further confirm the effectiveness of the presented structure, the circuit‐level implementation of the modulator is provided in Taiwan Semiconductor Manufacturing Company (TSMC) 90 nm CMOS technology. The simulation results show that the proposed modulator achieves a dynamic range of 84 dB over 30 MHz bandwidth while consuming less than 25 mW power from a single 1 V power supply. With the proposed time‐based noise‐coupling structure, both the order and bandwidth requirements of the loop filter are relaxed, and as a result, the analog complexity of the modulator is significantly reduced. Copyright © 2015 John Wiley & Sons, Ltd.

An NTF-enhanced time-based continuous-time sigma-delta modulator

Translation of the amplitude axis to the time axis can be a promising approach to alleviate the analog-to-digital converter's resolution problems in low-voltage CMOS circuits. From this point of view, a noise-coupled time-based continuous-time sigma-delta modulator (TCSDM) based on the asynchronous pulse width modulator (APWM) and the time-to-digital converter (TDC) is presented. Noise-coupling is realized by extracting the time quantization error of the TDC and injecting its delayed version to the input of the APWM. By using a novel implementation of the noise-coupling technique in the proposed TCSDM, the modulator's noise-shaping order is improved by one. Unlike the conventional noise-coupled sigma-delta modulators, in the proposed structure, the need of an extra subtractor at the quantizer input is resolved through merging the excess loop delay compensation path with the proposed noise-coupling branch. Comparative analytical calculations and behavioral simulation results are presented to verify the performance of the proposed time-based modulator. To confirm the validity of the proposed structure, the effects of main circuit non-idealities in the modulator's performance are taken into consideration and the related simulation results are investigated. A digital-friendly implementation of the quantizer in the proposed modulator makes it suitable for low-voltage nanometer CMOS technologies.

Analysis of Turbine Generator Shaft Torsional Vibration Caused by Self-commutated Converters

SUMMARY This paper presents a simple analysis tool for torsional vibration of the rotor shaft of a turbine generator which is interconnected with a power system with self-commutated converters. The evaluation is based on analysis of measurement data in the field and instantaneous value-based power system simulation. A number of power converters with large capacity are installed in industrial power systems. Especially, interharmonics originating from self-commutated converters cause torsional vibration at the rotor shaft of rotating machines. The interaction between rotating machines and converters is known as sub-synchronous torsional interaction. The resonance between interharmonics from converters and the natural frequency of the rotor shaft causes large torsional vibrations, leading to shaft damage. In this paper, the influence of interharmonics on turbine generators is investigated. If there were air gap torque fluctuations with a frequency near the natural frequency caused by interharmonics, which have frequencies below 100 Hz of the sideband wave caused by asynchronous pulse width modulation, the rotor shaft may be damaged by the torsional vibration. In this paper, the emerging condition of the torsional vibration and the impact on the generator are investigated.

The Simulation Research and Modeling of Asynchronous Motor's Vector Control

Based on the analysis of the mathematical model of the three-phase asynchronous motor and sine pulse width modulation principle, According to the theory of asynchronous motors vector control , software is building simulation model of asynchronous motors vector control system according to the rotor flux in Matlab/Simulink, analysis dynamic characteristics of rotational speed, torque and stator current ,provided the simulation results of the control system, verify the vector control is effective and feasible.

A mm-Sized Wirelessly Powered and Remotely Controlled Locomotive Implant

A wirelessly powered and controlled implantable device capable of locomotion in a fluid medium is presented. Two scalable low-power propulsion methods are described that achieve roughly an order of magnitude better performance than existing methods in terms of thrust conversion efficiency. The wireless prototype occupies 0.6 mm × 1 mm in 65 nm CMOS with an external 2 mm × 2 mm receive antenna. The IC consists of a matching network, a rectifier, a bandgap reference, a regulator, a demodulator, a digital controller, and high-current drivers that interface directly with the propulsion system. It receives 500 μW from a 2 W 1.86 GHz power signal at a distance of 5 cm. Asynchronous pulse-width modulation on the carrier allows for data rates from 2.5-25 Mbps with energy efficiency of 0.5 pJ/b at 10 Mbps. The received data configures the propulsion system drivers, which are capable of driving up to 2 mA at 0.2 V and can achieve speed of 0.53 cm/sec in a 0.06 T magnetic field.

A Polar Modulator Using Self-Oscillating Amplifiers and an Injection-Locked Upconversion Mixer

A polar modulator for use with non-constant envelope signals is presented. Techniques for efficient behavior of both the amplitude (AM) and phase (PM) path are introduced. The amplitude modulation technique is based on asynchronous pulse-width modulation of a phase-modulated RF signal. The digital signal generated in this way is suited for amplification using a nonlinear, efficient type of PA, while preserving the AM modulation, since this information is present in the signal. The efficiency of the switching amplifier is less dependent of the output power, compared to class B operation. Using a self-oscillating, asynchronous type of pulse-width modulator, the spurs are concentrated in narrow bands well separated from the signal band. These switching spurs are filtered out by the filters already present in the transmitter. The feasibility of this RF-pulse-width-modulation is proven by measurements with amplitude modulated signals on a prototype in 0.18 mum CMOS. Unmodulated, the circuit is able to deliver a peak output power of 8.26 dBm with a drain efficiency of 35%. In the phase-modulation path of the polar modulator, injection locking of an oscillator is used as a single-stage high-gain amplifier. Avoiding multiple stages and related power loss improves the overall power efficiency.

High-Frequency and Precision Three-Phase Sine/PWM Controller With Near-Zero Frequency of MPU Intervention—Novel Design Supporting Distributed AC Drive Systems

Conventional pulsewidth-modulation (PWM) schemes fully depend on a microprocessor (MPU) for extensive real-time computation, intervention, and housekeeping, and are limited to applications at low fundamental frequencies and low precision. At 20-kHz switching, the overhead of a modern 16-bit CPU increases up to 90%, making virtually no time available for regular control tasks. It also has poor cycle-to-cycle accuracy of /spl plusmn/5-10 /spl mu/s. A novel self-managed high-frequency and precision PWM architecture and integrated circuit are developed for distributed drive control systems. This architecture permits near-zero interfacing rate with the coprocessor, thus eliminating the overhead of the MPU's intervention and housekeeping, while being capable of both asynchronous and synchronous PWM at a range of 0-1000 Hz of fundamental frequencies, expandable to several kilohertz. A cycle-to-cycle accuracy of 50 ns is achievable in precision open-loop control. Experimental results verify our new design. This effectively supports distributed ac drive systems with highly coordinated controls.