Showing papers on "Automatic frequency control published in 1994"

Vehicle accessory trainable transmitter

Abstract: A vehicle accessory includes a trainable transmitter for duplicating the signal of an existing remote control. In one embodiment, the system includes a variable frequency generator having a frequency control input and an output. In one embodiment, also, the transmitter includes a switch for selectively disabling the variable frequency generator. According to another embodiment, the transmitter is trained by adjusting the frequency of the signal output by the variable frequency generator until it matches a signal transmitted by an existing remote control for a garage door opening mechanism. According to another embodiment, a variable attenuator is controlled to adjust the magnitude of the output signal of the variable frequency generator in inverse relationship to the duty cycle of output signals therefrom.

A Self-Tuning Piezoelectric Vibration Absorber

Abstract: A self-tuning piezoelectric vibration absorber is presented. A piezoelectric absorber, similar to a mechanical vibration absorber, has to be tuned to a particular structural vibration mode in order to be effective. The absorber presented here will tune itself to a particular mode and track that mode if it varies in frequency. Design of the aborber consists of a pair of lead zirconate titanate (PZT) tiles attached to the structure and shunted by an inductor-resistor circuit. This produces an electrical resonance that can be tuned to the desired structural mode by a simple control system. The absorber is experimentally demonstrated on a cantilevered beam. The experiments include an ex amination of the response of the absorber to an abrupt change in system parameters.

Self-tuning load frequency control: multilevel adaptive approach

Abstract: A multilevel adaptive load frequency control (LFC) based on the self-tuning regulator (STR) is investigated. The technique identifies each subarea separately as an autoregressive moving average submodel and parameters are identified by using the recursive least-squares method. The parameters of the predicted submodel are used to ensure the subarea control error calculation. The application of the proposed algorithm is suggested as a suitable alternative to the integral control used normally for the LFC. This work differs from previous work in that the proposed technique permits optimality at all levels while providing a decomposed solution. The effectiveness of the control algorithm has been verified through numerical studies on the 20-machine, 118 bus IEEE test system.

Improvement of induction motor drive systems supplied by photovoltaic arrays with frequency control

Abstract: The overall efficiency of an induction motor drive system, powered by a PV array, drops significantly when the insolation condition varies away from its nominal level. This problem can be overcame using a control method in which the frequency of the inverter's PWM control signal is adjusted according to the insolation and temperature conditions. The motor speed, and therefore, the power delivered to the load, are adjusted by controlling the inverter's frequency. This eliminates the mismatch between the maximum power that is available from the source and the power that is required by the load. Simulation results presented in this paper show that using the proposed control system allows the induction motor drive system to maintain its optimum efficiency and deliver consistently more power to the load when insolation and temperature vary from the nominal level. This method also offers an improvement in the system stability. >

AFC circuit for QPSK demodulator

Abstract: AFC circuit for QPSK demodulator including, a circuit for obtaining quadrature related detection signals by multiplying a modulated input signal with quadrature related local oscillation frequency signals from a quadrature phase local oscillator, digital converter for converting the detection signals into corresponding digital signals by sampling them with quadrature related clocks which have a frequency two times higher than a symbol rate of the input signal, frequency error detecter for detecting a frequency error between the quadrature related digital signals using a symbol timing sample value and a symbol intermediate timing sample value in the converted digital signals, first validity determinator for determining whether the frequency error signal is valid or not through a detection of the pattern of the modulated input signal from sample values before and after the symbol timing so as to result a first validity signal, second validity determinator for deetermining whether the frequency error signal is valid or not through a detection of an absolute sample value of the symbol intermediate timing so as to result a second validity signal, and valid frequency error extractor for extracting the frequency error signal as a frequency control signal for controlling the oscillation frequency of the local oscillator when the frequency error signal has been proved to be valid by the first and the second validity signals.

Application of multi-variable control for automatic frequency controller of HVDC transmission system

Abstract: In an HVDC transmission system that links two AC power systems, the automatic frequency controller (AFC) calculates power to be interchanged between the two AC systems according to their frequencies thereby improving the frequency characteristics of the two power systems. This paper introduces a newly developed DC AFC system, which applies a multi-variable control to the DC system-based frequency control. It is capable of controlling the frequencies of the two AC systems optimumly while maintaining their stability. This system was developed for one of Japan's HVDC transmission facilities and produced good results in a combined test using a power system simulator. The field installation will be completed in March 1993, when the AFC system will enter service. >

On-line search based pulsating torque compensation of a fault mode single phase variable frequency induction motor drive

Abstract: Improved reliability and fault tolerant operation of inverter-fed variable frequency AC drives are very important for critical industrial applications, The paper describes variable frequency variable voltage operation of a three-phase induction motor drive in single phase mode for inverter fault conditions, such as open base drive and device short circuit. The detailed mathematical analysis of the machine in single phase mode indicates that odd harmonic voltages of appropriate magnitude and phase can be injected at the machine terminal to neutralize the large low frequency pulsating torques so it permits smooth drive operation. The magnitude and phase angle of the desired harmonic voltages have been derived theoretically. However, to eliminate the parameter variation effect and operating point dependencies, a general purpose search algorithm has been proposed in the paper which fabricates the desired harmonic voltages on real time basis. The search algorithm was initially exercised manually on a simulated drive system to prove its validity, and then tested extensively on a volts/Hz controlled 3 hp drive system in the laboratory. The on-line search algorithm along with estimation and control related to the project was implemented with C language on a TMS320C30 digital signal processor board. The extensive laboratory investigation shows that the proposed search algorithm performs well and successfully eliminates low frequency pulsating torques not only in steady state condition but also during slow acceleration and deceleration of the drive. >

Radio scanner and display system

Abstract: A method is described for operating a radio receiver (4, 12) in such a manner as to accurately and rapidly identify unlistenable, very listenable and marginally listenable channels, and display the listenable and very listenable channels along with an indication of their signal strength, noise and quality on a screen (44). A reference value of automatic fine tuning voltage is found for the particular receiver. Capacitors (24, 26) that are charged in accordance with the levels of signal strength, noise and automatic fine tuning voltages are sampled before being fully charged at each channel change, and averages of the respective samples are computed as well as the offset between the average of the automatic fine tuning samples and the reference value of automatic fine tuning voltage. A channel having sample averages not meeting certain criteria is rejected as unlistenable, and, of the others, a channel having a very low average on its noise capacitor is identified as very listenable. Those of the remaining channels that are at least marginally listenable are identified by similar analysis of a second group of samples. The criteria for signal strengths and noise may be varied with ambient temperature, and the criteria for noise can be adjusted on the basis of the noisiest channel or the noise produced when the antenna (2) is grounded. Those channels having the greatest signal strength are associated with tuning buttons (42), and indications of these associations are made on the screen.

An enhanced neural network load frequency control technique

Abstract: We investigate the use of neural networks (NN) to act as the control intelligence in conjunction with a standard adaptive load frequency control scheme. In this approach a NN is operated in parallel with a full load frequency adaptive control scheme. The NNs are able to monitor the system frequency as the controller issues its control commands. If there is a condition where the frequency values are corrupted, or the system is not sufficiently exciting, then the NNs will be able to provide the power set points that may be directly communicated to those gensets that are providing system frequency control. This neural control approach is shown to have several advantages over the basic fixed parameter schemes and the more advanced adaptive control techniques that have been recently developed. The results of a number of real-time power system simulations are presented. >

Digital temperature compensated crystal oscillator

Abstract: A digital control system such as a digital temperature compensated crystal oscillator (DTCXO) system is arranged to offer superior oscillating performance with reduced size and cost. For example, to reduce the memory capacity, a memory 31 receives upper 6 bits of temperature data, and a decoder 32 calculates temperature compensation data from lower 4 bits and output data from the memory (FIGS. 1-11). For a one-chip configuration and low power consumption, a MOS type Colpitts oscillator (FIG. 16) is provided with a circuit for adjusting the source resistance of the MOS. For size reduction and fine frequency adjustment, a DTCXO is provided with sections such as an adder 341, an up-down counter 342 and an auxiliary frequency control section (AFC) 332 (FIGS. 20, 21, 24 and 25). An adding section 415 is provided between a D/A converting section 414 and a capacitance varying section 416 to obtain superior linearity with respect to a control voltage and quality of offset.

Frequency synthesizer for use in radio transmitter and receiver

Abstract: A phase comparator (91) makes a phase comparison between a frequency-divided signal from a frequency divider (98) and a reference oscillation signal from a reference signal oscillator (90). The phase error signal obtained from the comparison is passed through an LPF (92) to yield a frequency control signal, which is applied to a VCO (94). An oscillated signal from is frequency-multiplied by a frequency multiplier (96). The multiplied output oscillation signal SO is frequency-divided by the frequency divider (98) and output to the phase comparator (91). The multiplied output oscillation signal SO is sent out to a receiver circuit (43) and a transmitter circuit (45).

Automatic frequency control apparatus for FSK receiver and FSK receiver including the same

Abstract: A first AFC apparatus receives and detects I and Q signals from a received first FSK signal with a local osc signal; demodulates the I and Q signals; F/V-converts I or/and Q signals into a voltage; compares it with a reference; and detects a frequency deviation direction of the local osc signal from the carrier signal according to the results of comparing and the demodulating. The local osc frequency is controlled by a given amount according to the result of the frequency deviation direction detection. A second AFC apparatus receives and detects I and Q signals using a first osc signal; FSK-modulates the I and Q signals with a second local osc signal having a lower frequency than the first local osc signal; and compares the frequency of the second FSK signal and the second local osc signal to supply a demodulation result. A frequency control for the first local osc signal is obtained by an averaging circuit averaging the modulation result. The F/V converter used in this apparatus has various modification and amplitude limiter may be provided as necessary. The averaging may be effected for a given data period of the first FSK signal. Power consumption can be reduced by selectively supplying a power with/without a holing circuit. FSK receivers use these automatic frequency control apparatus are also disclosed.

Tdma data receiver

Abstract: PURPOSE: To implement automatic frequency control by taking correlation between reception data after base band delay detection and a known synchronization word and using a complex correlation and a correlation power CONSTITUTION: A correlation arithmetic circuit 9 takes a base band signal corresponding to a known synchronization word from a synchronization word generating circuit 10 with received data for a block of synchronization words of I, Q signals and gives a complex correlation ψ as an estimated phase error θe due to a frequency offset to an averaging circuit 12 and a correlation power |ψ| to a correlation power discrimination circuit 11 When the correlation power |ψ| exceeds the threshold power, the discrimination circuit 11 gives its output to the averaging circuit 12 as a control signal, in which the complex correlation values ψ in preceding and current reception slots are averaged and a resulting signal is fed to a phase compensation circuit 13 On the other hand, when the correlation power |ψ| is less than the threshold power, the discrimination circuit 11 gives the complex correlation ψ obtained in the precedingly received slot to the phase compensation circuit 13 after calculation of averaging as an estimated phase error θe in a current reception slot Then an estimate offset is used to compensate the phase and its output is given to discrimination circuits 14, 15, in which the signal is discriminated in terms of binarization and the result is outputted from a decoder 16 COPYRIGHT: (C)1995,JPO

Reference frequency generating device

Abstract: PROBLEM TO BE SOLVED: To prevent frequency accuracy in an automatic running from being deteriorated when reception cannot be made, by accumulating phase difference data where an external reference signal is synchronously compared with an internal voltage controlled crystal oscillator(VCXO) in a normal reception state. SOLUTION: A reference frequency generating device for receiving a time signal with high accuracy from a satellite or the like is provided with, for example, an operation means 40 for calculating a steady frequency deviation, a part 45 for generating automatic run frequency correction data, and the like. Then, the part 45 for generating correction data stores frequency deviation D (n) data from the operation means 40 into a memory with time information in a normal reception state. On the other hand, when no signals can be received, the part 45 calculates the amount of transition regarding the aging of oscillation frequency focs of a VCXO 10 at each specific time based on the stored data. Automatic traveling correction data C (h) being calculated according to the operation are added to frequency control data C (n) being outputted by an operation means 23 for controlling steady frequency, and the fluctuation of the oscillation frequency focs of the VCXO 10 in an automatic traveling state is corrected. COPYRIGHT: (C)1999,JPO

Automatic frequency control apparatus

Abstract: The preferred embodiment of the present invention encompasses an automatic frequency control system implemented in a radiotelephone (101). The radiotelephone (101) includes a frequency synthesizer. The frequency synthesizer uses a division ratio varied with time by a multi accumulator fractional N synthesizer (140) such that the effective division ratio may be varied by non-integer steps. The division ratio is programmed to realize the desired channel frequency, the desired modulation waveform, and any automatic frequency correction offset. An accurate clock is provided to the control logic (104) and the user interface (105) sections of the radiotelephone (101) using a second multiple accumulator fractional N division system (139). This second fractional N division system (139) is programmed based on the automatic frequency control programming of the first fractional N synthesizer (140). This lower frequency may then be multiplied in a phase locked loop to provide an accurate reference at a second reference frequency.

Simple theft deterrent for electronic control modules

Abstract: An electronic theft deterrent system for deterring theft of an electronic device, such as a radio associated with a vehicle, that takes advantage of already existing device parameters, controls and displays associated with the device. When used as a theft deterrent system for the vehicle radio, a radio operator will first activate a frequency control switch in order to set an arbitrary frequency in the display of the radio. Next, a predetermined set of theft key radio control buttons are activated for a predetermined time in order to cause the arbitrary frequency that is displayed to be stored in a non-volatile memory. When the frequency is stored, the radio volume is impaired, but the total operation of the radio is not disabled. When the operator wishes to restore the radio to its normal operating condition, the operator will reset the arbitrary frequency, and reactivate the theft key control buttons. If the currently displayed frequency setting matches the stored frequency setting in the memory, the radio will be removed from the theft guarded condition, and the audio portion of the radio will be restored. If successive attempts to restore the radio to its normal operating conditions fail, an attempts counter will cause the radio to remain in its impaired state until an authorized service agent is able to restore the operation of the radio.

Control conditions to improve conducted EMI by switching frequency modulation of basic discontinuous PWM preregulators

Abstract: In this paper the authors analyze the operation conditions to control basic discontinuous AC-DC preregulators with variable switching frequency. The correct use of variable switching frequency control can lead to a reduction of conducted EMI generated. The basic PWM converters (buck, boost, buck-boost, sepic, Cuk and zeta) are studied. The authors achieve results which allow them to operate the converters under the condition proposed maintaining a very small low-order harmonic-current content. Some simulation examples using a buck-boost as DCM-PFP show the amplitude reduction of the high order harmonic content. Experimental results using a sepic converter show the feasibility of the approach. >

Noise performance of two frequency-error detectors derived from maximum likelihood estimation methods

Abstract: Frequency tracking loops are used in digital links to control the carrier frequency of the received signals. A basic component in these loops is the frequency difference detector. This paper concentrates on two detectors that have previously been derived from maximum likelihood estimation criteria. Noise spectra of the detector outputs are computed and the results are used to assess the performance of frequency control loops operating in the tracking mode. Computer simulations are used to validate the theory. The detector implementation in digital form is also addressed and design criteria are provided that lead to structures with a limited computing complexity. Comparisons are made with other frequency detection schemes available in literature. >

EMI reduction of power supplies by Bi-Frequency modulation

Abstract: In this paper, a new control (modulation) technique, called Bi-Frequency control, is proposed By operating the converters at two fixed switching frequencies with a modulation frequency to adjust the duration ratio, the emission spectrum of the control signal is spread and the spectral power level is reduced The spectral analysis of the Bi-Frequency control signal is given, and the spectral comparison between PWM and Bi-Frequency control is presented A Bi-Frequency controlled buck ZVS converter is breadboarded to confirm the operation of the Bi-Frequency control >

Automatic frequency control apparatus and method therefor

Abstract: An automatic frequency control apparatus includes a local oscillator (13), a quadrature detector, a frequency offset value estimation circuit (17), a demodulation circuit (15), a synchronization determination circuit (16), a memory (19), and an AFC circuit (18). The synchronization determination circuit (16) determines reception synchronization on the basis of demodulated signals from the demodulation circuit to output a synchronization determination signal to the AFC circuit (18) when reception synchronization is established and outputs the value to the AFC circuit. The apparatus also includes a power-on state detection circuit (20) for outputting a detection signal to the AFC circuit (18). The AFC circuit (18) determines the oscillation frequency of the local oscillator on the basis of the outputs from the above components. An automatic frequency control method is also disclosed.

Computer controlled in situ radiolysis electron spin resonance spectrometer incorporating magnetic field-microwave frequency locking

Abstract: A lab‐built personal computer‐based electron spin resonance (ESR) spectrometer is described which incorporates a wide range magnetic field/microwave frequency lock as part of its magnetic field control subsystem. Instrument operation is accomplished by keyboard commands, with important experimental variables logged automatically for reference during subsequent data analysis. The spectrometer features both narrowband field modulation and direct‐detection time‐resolved ESR modes. The data acquisition system and field/frequency lock operate such that spectrum recordings consisting of multiple magnetic field sweeps are undistorted by long‐term klystron frequency drift. The spectrometer features low noise microwave preamplification, balanced mixer detection, automatic reference arm phase control, and a fast automatic frequency control system requiring no klystron frequency modulation. Natural abundance 13C and 33S studies of the terephthalic acid radical trianion and sulfite radical anion are presented as proo...

Digital data receiver

Abstract: PURPOSE: To simplify the configuration by generating a 1st local oscillation signal with a variable oscillation means employing a PLL and generating a 2nd local oscillating signal with an oscillation means controlled by a frequency control signal generated by a quadrature demodulation means. CONSTITUTION: An I axis phase comparator circuit 24 and a Q axis phase comparator circuit 25 compare a phase of a 2nd IF signal with a phase of a 3rd local oscillation signal to apply synchronization detection processing or quasi-synchronization detection processing to the 2nd IF signal thereby demodulating I, Q signals. A frequency error in the I, Q signals caused by a 1st local oscillation circuit 16 and a 3rd local oscillation circuit 26 configured to be a highly stable oscillation circuit such as a VCXO is corrected by a 2nd local oscillation signal from a 2nd high frequency oscillation circuit 20 controlled by a phase control voltage received from a phase control voltage generating circuit 28 via an LPF 31. Through the constitution above, since one system of PLL is enough for the purpose, the receiver is manufactured economically. COPYRIGHT: (C)1995,JPO

Automatic frequency control in a radio communication receiver

Abstract: A selective call radio frequency (RF) communication device (105) includes a receiver (203) for receiving and converting an RF signal into a converted signal. A controller (206) generates binary message information, a synchronization command signal and an address detection signal. An alert device (207) indicates the receipt of the message information. A frequency counter (427) measures the frequency of the converted signal and also determines the associated binary state of the binary message information. A measurement memory (439) stores the converted signal frequency measurements. The frequency control generator (440) generates a frequency control signal in response to the synchronization command signal being generated. The frequency control signal is a function of the stored converted signal frequency measurements and the associated binary states. The controllable local oscillator (215) supplies a local oscillator signal to the receiver, the local oscillator signal having a frequency controlled by the frequency control signal.

Phase lock loop circuit using a sample and hold switch circuit

Abstract: A phase lock loop circuit that can be formed into a full monolithic integrated circuit without an external component part, and that can maintain the phase locked state even for a consecutive identical bit state of input data including more than several tens of consecutive identical bits. The input data applied to a data input terminal is doubled in frequency by a doubler. A phase difference between the output of the doubler and that of a VCO is detected by a phase comparator, and is supplied to a low-pass filter through a sample and hold switch circuit. The low-pass filter produces a DC output corresponding to the phase difference, and supplies it to the frequency control terminal of the VCO. The output frequency of the VCO is controlled so that the phase difference becomes zero. The sample and hold switch circuit is maintained at the off state (holding mode) during the consecutive identical bit state to hold the output of the low-pass filter, so that the VCO continues that frequency at the beginning of the consecutive identical bit state.

Method and apparatus for digital automatic frequency control

Abstract: A method and apparatus for digital automatic frequency control includes circuitry for frequency controlling a first information portion of a digital input signal, correlating the output with a known characteristic of the first information portion, and outputting a timing signal and channel estimation signal. The digital input signal is also decimated using the timing signal and frequency controlled into a frequency controlled output signal. This signal is used, along with a signal quality estimate derived from the channel estimation signal and first information portion, to determine an estimated frequency correction signal. The estimated frequency correction signal is used to control the frequency correction steps.

Radio equipment based on AFC system with temperature detection and method of automatic frequency control

Abstract: Radio equipment based on an AFC system comprising a local oscillator, a reference frequency oscillator, a receiver, a frequency comparator, an AFC controller, a temperature detection sensor, and a memory. The AFC controller inputting, when starting AFC, reads out a control frequency corresponding to the detected temperature inputted thereinto to control the reference frequency for the reference frequency oscillator. When a lock signal is inputted thereinto, the detected temperature and control frequency are stored in a memory.

DSP-based real-time harmonic elimination of PWM inverters

Abstract: Pulsewidth modulation (PWM) using a harmonic elimination technique necessitates the solution of systems of nonlinear transcendental equations. Conventionally, due to their high complexity, these equations have to be solved off-line and the calculated optimal switching angles are stored in look-up tables or interpolated by simple functions for real-time operation. System flexibility is very limited, especially for applications which require both amplitude and frequency control. A new implementation scheme based on real-time solution of nonlinear harmonic elimination equation using a digital signal processor DSP56001 is reported in this paper. Real-time generation of switching patterns that have 15 notches to be determined in each quarter fundamental period has been accomplished within 2.15 ms. >