Pulse-frequency modulation

About: Pulse-frequency modulation is a research topic. Over the lifetime, 4151 publications have been published within this topic receiving 53039 citations. The topic is also known as: PFM.

Harmonic reduction in single-phase inverter using a parallel operation technique

Abstract: A technique is presented for harmonic reduction in inverters using sinusoidal pulse-width modulation (PWM). A modified circuit based on parallel operation of MOS-based inverter sets using interphase reactors as harmonic reducing elements and making use of a specific phase shift between the modulating and carrier waveforms is investigated as a means to economically and efficiently reduce the harmonic contents in the output waveform. The output waveform of a single-phase PWM inverter is investigated both theoretically and experimentally. Detailed analysis shows that the harmonics lower than the 15th are all less than 1% of the fundamental component when the frequency ratio is relatively low, i.e. about nine and similarly for the 29th harmonic when the ratio is about 15. This is done without noticeable reduction in the fundamental component. The results show the feasibility of obtaining practically sinusoidal output waveforms. >

Random carrier frequency modulation of PWM waveforms to ease EMC problems in switched mode power supplies

Abstract: Electromagnetic compatibility (EMC) remains an issue which can present many problems to designers of high frequency power converter circuits. Usual techniques for alleviating the problems of interference generation by power converters involve the use of screening materials and filters. However, the effectiveness of such measures depends on the frequency of the interference and the power density at each frequency of interest. As pulse width modulation (PWM) generates high frequency harmonics at multiples of the switching frequency, modulation of the switching frequency may be used to spread the spectral power density present at these harmonic frequencies. This paper presents a technique of frequency-hopping spread-spectrum modulation which may be applied to switched-mode power converters to reduce the spectral power density at harmonics of the switching frequency. The influence of the peak frequency deviation and the modulation sequence length on the resultant spectrum are discussed. These predictions have been broadly confirmed in practice. >

Optimum Pulse Shaping in Digital Angle Modulation

Abstract: This paper presents a technique for optimizing the baseband pulse shapes in digital angle modulated signals to minimize the fraction of out-of-band power for a given channel bandwidth. As examples of practical interest, the optimization is carried out for channel bandwidths up to three times the bit rate and for the range of modulation indices usually encountered in digital transmission. Results for MSK-type signals appear as a special case.

Pulse-width modulation for microcontroller servo control

Abstract: 27 0278-6648/06/$20.00 © 2006 IEEE ANIMATRONICS ARE USED in the movie industry to bring aliens, dinosaurs, and man-eating sharks to life. Many mechanical devices are used to impart realism to these puppets. Large motors and hydraulics are employed to control limbs, necks, and other areas requiring high torque. Small motors are used to create facial expressions, control eyes, and provide fluidity of movement to add life to these robots. A common motor used in animatronics is a servo motor. Instead of providing constant rotation, like most motors, servos are used for precise angular positioning but are often limited to only 180◦ of maximum rotation. Dozens of servos are used to control the facial expressions of a robotic puppet. Even a simple android might have five servos controlling just the eyes. The latex skin or muscles of an android’s face are connected to the servo’s shaft so that the servo can contort the face into different expressions. Servos are also common in devices such as radio-controlled cars to control steering, radio-controlled airplanes to control rudders, or even in the cruise control systems of cars. Servos are ideal for applications requiring absolute positioning of a motor shaft. Microcontrollers are an excellent and inexpensive device for controlling servos. In order to properly control a servo with a microcontroller, it is necessary to learn a few techniques, such as properly generating a control signal for a servo, which the rest of this article will cover. Servos may be purchased in a prepackaged form, or you can create your own servo with a few common components. Internally, a servo can be thought of as a direct current (dc) motor (which rotates an external motor shaft but provides no way to determine the amount of rotation) with a built-in controller. The control circuitry compares an angular position, determined by a control signal, to the current position of the motor shaft (as shown in Fig. 1). The motor shaft’s angular position is often determined by a potentiometer, which is rotated by the motor shaft. A potentiometer is a three-terminal resistor whose center connection has variable resistance, usually controlled by a slider or dial. The potentiometer acts as a variable voltage divider. The voltage from the center connection of the potentiometer represents the angular position the motor shaft is in. Other methods to determine angular position and rotation exist for bigger servos, but a potentiometer is the most common for small servos. The built-in controller generates an internal signal from the voltage controlled by the potentiometer, compares it to the control signal, and then provides power to the dc motor to rotate the shaft in the appropriate direction to match the two. Servos usually require a pulse-width modulated control signal.

Frequency modulation signal receiving system

Abstract: This invention relates to frequency modulation Signal receiving systems of the type in which frequency variations of the carrier wave or mean frequency of the signal are employed for the reProduction of transmitted signals. ' An important object of the inventioni is to prdoVide an improved...