Variable Frequency Pulse Width Modulation Research Articles

A control method for acoustic radiation force of ultrahigh frequency ultrasound based on variable frequency pulse width modulation

Ultrahigh frequency ultrasound (>60 MHz) has emerged as a crucial actuating mechanism for non-contact manipulation, owing to its unique acoustic field properties. The acoustic field traps microparticles mainly via the gradient force of acoustic radiation force (ARF) on the transverse plane, which is up to hundreds of nanonewtons. In theory, directly using ARF can strengthen the manipulation force. Currently, the direct implementation of ARF is restricted to a specific frequency and magnitude range, which lacks a comprehensive and versatile control method. Additionally, it lacks an ARF calibration method that accommodates a wide magnitude and frequency range. We propose a variable frequency pulse width modulation-based control method for ARF, which uses an atomic force microscope microcantilever as a mechanical sensor to calibrate the magnitude and frequency. The precise control of ARF emitted by an 85 MHz transducer was achieved with a resolution of hundreds of piconewtons, magnitude range spanning from nanonewtons to micronewtons, and frequency range of 1 kHz to hundreds of kilohertz. This control method breakthrough holds great promise for expanding the application of ultrahigh frequency ultrasound in noncontact manipulation.

A Novel, Software-Defined Control Method Using Sparsely Activated Microcontroller for Low-Power, Multiple-Input, Single-Inductor, Multiple-Output DC–DC Converters to Increase Efficiency

This article proposes a novel control for the multiple-input, single-inductor, multiple-output dc–dc converters. It is digitally and discretely implemented, which can have an outstanding performance in low-power applications so that at the power of 10 mW, it has an efficiency of 92.5%. Conventionally, in this power range, an attempt is made to take advantage of an analog design that is flexible. Thus, a fully programmable (software designed) converter with digital design using a microcontroller is in great demand. This converter design basis is to deploy the microcontroller's central processing unit (CPU) as little as possible. Also, it only turns <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> the CPU when necessary to be employed in low-power, portable systems, e.g., energy-harvesting technologies. Therefore, construction costs are significantly reduced. Depending on the energy level of the inputs, they can simultaneously be utilized to charge the outputs. This article uses stability analysis, time-multiplexing control method, and variable-frequency pulsewidth modulation in the proposed control design. Each output can be charged with different frequencies according to its load, and the maximum switching frequency is equal to 10 kHz. Also, the proposed technique for zero-current switching has been digitally implemented; it can be utilized to determine the optimal value of the inductor discharge duty cycle based on the inductor's left-side voltage. Comparative simulations and experimental results reveal the superiority and practicality of the proposed approach.

A Step-Up Reconfigurable Multimode LLC Converter Module With Extended High-Efficiency Range for Wide Voltage Gain Application in Medium Voltage DC Grid Systems

In this article, a newmodular multimode reconfigurable step-up resonant converter that is capable of extending very high efficiency from full load to reduced load conditions is proposed for wide voltage gain application in medium voltage dc (MVdc) grid system. The proposed converter module is able to switch from a hybrid control scheme that consists of variable frequency and phase shift control to pulsewidth modulation (PWM) control in the auxiliary switch of the output voltage quadrupler (VQ). In addition, the input bridge can also be reconfigured to a half-bridge mode to suit high input voltage range while utilizing a hybrid control technique that consists of variable frequency and asymmetrical PWM control. With the proposed approach, the converter module is able to achieve constant output voltage regulation without requiring a wide spectrum of switching frequency or phase shift control. Hence, close-to resonance operation with very high efficiency can be maintained for a wide range of input voltage and loading conditions. Soft switching operations are always guaranteed for all the primary side switches, the output diodes and the auxiliary switch in the VQ. The steady-state and dynamic performance of the proposed modular multimode step-up converter are validated through simulation results on a silicon carbide (SiC) based 360 V–1 kV/16 kV, 80-kW system and experimental results on a proof-of-concept 150–400 V/6.6 kV, 10-kW SiC laboratory prototype. Results confirmed that the efficiency is maintained between 97.8% and 99.1% from full load to at least 20% load condition for the specified input voltage range.

Variable-Frequency Pulse Width Modulation Circuits for Resonant Wireless Power Transfer

In this paper, we develop a variable-frequency pulse width modulation (VFPWM) circuit for input control of 6.78-MHz resonant wireless power transfer (WPT) systems. The zero-voltage switching control relies on the adjustments of both duty cycle and switching frequency for the class-E amplifier used in the WPT as the power transmission unit. High-frequency pulse wave modulation integrated circuits exist, but some have insufficiently high frequency or unfavorable resolution for duty cycle tuning. The novelty of this work is the VFPWM circuit design that we put together. A voltage-controlled oscillator (VCO) of radio frequency and capacitor-coupled difference amplifiers are used to simultaneously perform the frequency and duty cycle tuning required in resonant WPT applications. Different circuit topologies of VFPWM are compared analytically and numerically. The most favorable circuit topology, enabling independent control of the frequency and duty cycle, is employed in experiments. The experimental results demonstrate the validity of the novel VFPWM, which is capable of operating at 6.78-MHz and has a duty ratio adjustable from 20% to 45% of the range applicable in the resonant WPT applications.

Variable Frequency Average Current Mode Control for ZVS Symmetrical Dual-Buck H-Bridge All-GaN Inverter

The quasi-square-wave (QSW) zero-voltage-switching (ZVS) symmetrical dual-buck H-bridge (DBHB) all-GaN inverter has been proven to have high efficiency and high density in Google's Little Box Challenge. This variable frequency QSW ZVS inverter is drawing more and more interest in the industry and academia. However, the ac current control with cycle-by-cycle variable frequency ZVS operation is a basic challenge for this inverter. The conventional control methods for this QSW ZVS inverter, such as the hysteresis current mode control and the variable on-time control, require high-speed current sensing or zero-crossing detection (ZCD) circuits, which are very sensitive to noises. In this article, achieving variable frequency average current mode control with variable frequency pulsewidth modulation (VFPWM) is discussed and implemented for this QSW ZVS inverter to eliminate high-speed current sensing or ZCD circuits. For any synchronous half-bridge type converter, the voltage conversion ratio is dependent only on the duty-cycle in either continuous conduction mode (CCM) or QSW ZVS mode. The frequency of the PWM triangular carrier is another degree of freedom. In this control method, the averaged inductor current is sensed and regulated by the average current mode feedback controller and the duty-cycle is generated by the average current controller. The frequency of the PWM carrier is variable and directly calculated based on the duty-cycle signal and the sensed and filtered voltage and current signals. Since all the sensed signals for this current controller are low speed and filtered signals, this current control is highly immune to noises. The reliability of ZVS for this inverter is improved. The complexity of the controller is also reduced. A detailed analysis of the QSW ZVS conditions for the full range operation of the symmetrical DBHB inverter is done in this article. More negative currents can be introduced to reduce the switching frequency and increase the reliability of ZVS. A frequency limiter helps limit the frequency when the current is close to zero or under light load conditions. A frequency updating method with a constant and low interrupt frequency in a digital controller is also discussed. Finally, to verify this control method, a 1-kW all-GaN DBHB inverter prototype is developed and tested in this article.

Variable-Switching Frequency PWM Technique for Induction Motor Drive to Spread Acoustic Noise Spectrum With Reduced Current Ripple

Pulse-width modulation (PWM) of a motor drive at a fixed switching frequency leads to harmonic currents in narrow bands around integral multiples of the switching frequency resulting in tonal frequency acoustic noise components, which are irritating to the human ear. Random variation of carrier frequency to spread the spectrum poses challenges in device loss calculation, thermal design, and closed-loop controller design. Random pulse positioning is not quite effective at high speeds of the drive, where the problem of acoustic noise is most pronounced. This paper proposes a simple variable-frequency PWM and evaluates the performance of the same experimentally on a 6-kW induction motor drive. The experimental results show that the acoustic noise is spread uniformly over a range of frequencies without introducing low-frequency current harmonics. Compared with fixed-frequency PWM, the dominant acoustic noise is reduced significantly over a wide range of speeds. The variable-frequency PWM is further shown to reduce line current total harmonic distortion at high speeds of the drive. The computational effort required by the variable-frequency PWM is only marginally higher than that required by fixed-frequency PWM.

A single stage three-level full bridge resonant AC/DC converter

This article presents a new three-level full bridge resonant single stage AC/DC converter. The converter is operated with a variable frequency pulse width modulation controller (PWM). A PWM is used to provide the required input current shaping as well as regulating the DC-bus voltage, whereas variable frequency control is used to tightly regulate the output voltage. Zero voltage switching (ZVS) is achieved for all switches. The proposed topology can operate with either continuous or discontinuous input current while maintaining high power factor. Owing to ZVS operation, reduced component stresses and low circulating currents the proposed converter has high conversion efficiency making it suitable for higher power operations compared to existing single stage AC/DC topologies as well as operating with universal input voltage. Operation, analysis and performance of the converter will be presented in this article.

ロボットの定格外瞬発駆動のための可変周波数ＰＷＭ方式

The purpose of the study is to develop a method to control the armature current of the DC servo motors effectively and safely in the case of over-rated driving of the motors for realizing quick motion of robots. A method of variable frequency PWM (Pulse Width Modulation) has been developed both to suppress the rush current generated at the starting and to prevent the decrease of the effective value of the current. To apply the method to quick driving of a robot leg with three joints, the mathematical model with similar responses has been derived, and experiments on the model has been performed. The results have shown the effectiveness of the method.

Load-adaptive frequency tracking control implementation of two-phase resonant inverter for ultrasonic motor

The basic driving and control principles and the operating characteristics of a newly-developed ultrasonic motor (USM) are described. The two-phase resonant inverter for driving the USM, which includes a variable-frequency PWM (pulse width modulation) control scheme and a phasor control function between inverters, is discussed. A novel automatic resonant frequency tracking strategy using the PLL (phase-locked loop) technique is presented. It uses both sensor and sensorless interfaces to operate at a certain optimum point. The two-phase high-frequency inverter using parasitic resonant impedances incorporated in the ultrasonic motor, which is represented in terms of an electrical resonant tank circuit model, is proposed as a high-power density switching mode ultrasonic power amplifier. Experimental results obtained with this inverter-drive USM system with frequency timing control are illustrated. >