A fixed frequency LCL-Type series resonant converter

A fixed frequency LCL-type series resonant converter (SRC) which uses an inductive output filter is proposed. Steady-state analysis of the converter is presented using complex ac circuit analysis. Based on the analysis, a simple design procedure is given. Detailed space integrated control experiment (SPICE) simulation results are presented to evaluate the performance of the designed converter under varying load and supply voltage conditions. Also, detailed experimental results obtained from a metal-oxide-semiconductor field-effect transistor (MOSFET) based 500 W converter are presented to verify the analysis and SPICE simulation results. The results obtained from the analysis, SPICE simulation and the experimental converter are compared. The proposed converter requires a narrow variation in pulsewidth while maintaining lagging power factor mode of operation for a very wide variation in the load as well as supply voltage     

Analysis of series-parallel resonant converter

A frequency-domain steady-state analysis is given for a series-parallel resonant converter (SPRC) operating in the continuous conduction mode (CCM) using Fourier series techniques. Equations for performance parameters are derived under steady-state conditions to provide simple design tools. The topology of the SPRC combines the advantageous properties of both the series resonant converter (SRC) and the parallel resonant converter (PRC). The key results of the work are: a novel half-wave rectifier SPRC, conditions for obtaining high part-load efficiency; and several boundary frequencies and limiting conditions such as the capacitive/inductive load boundary and open-circuit and short-circuit cases. Experimental results measured for an 80-W converter above the resonance at different load resistances and input voltages show excellent agreement with the theoretical performance predicted by the equations     

Bidirectional DC-to-AC inverter with improved performance

Switch-mode DC-to-AC inverters using DC-to-DC converter topology have many advantages over the traditional bridge-type inverter. A bidirectional power circuit combined with a nonlinear robust control is proposed to form a high performance inverter. The output voltage of the inverter can be stabilized regardless of large changes in input voltage and output current. The distortion near the zero crossing point can be minimized. The load of the inverter can be resistive, inductive, or capacitive. Simulation results and experimental verification are provided     

Self-oscillating DC-to-DC switching converters with transformer characteristics

Fourth-order converters with both input and output filters are analyzed in self-oscillating sliding mode. The boost converter with output filter and the Cuk converter are shown to have stable dynamics and an equilibrium point with transformer characteristics. The analytical predictions are verified by experimental results.     

AC/DC converter topologies for the Space Station

A new class of AC/DC converter topologies (Type-1 converters) is described, suitable for use in an advanced single-phase sine-wave voltage, high-frequency power distribution system, of the type that was proposed for a 20 kHz Space Station primary electrical power distribution system. The converter comprises a transformer, a resonant network, a current controller, a diode rectifier, and an output filter. The input AC voltage source is converted into a sinusoidal current source using the resonant network. The output of this current source is rectified by the diode rectifier and is controlled by the current controller. The controlled rectified current is then filtered by the output filter to obtain a constant voltage across the load. Three distinct converter topologies, Type-1A, Type-1B, and Type 1-C, are described, and their performance characteristics are presented. All three types have a close-to-unity rated power factor (greater than 0.98), low total harmonic distortion in input current (less than 5%), and high conversion efficiency (greater than 96%)     

An efficient active ripple filter for use in DC-DC conversion

When low ripple is required from a switched mode dc-dc converter, dissipative active filters offer an alternative to passive LC and coupled inductor filters. Analytical and experimental results are presented for a simple active ripple filter. The filter employs a pair of current transformers as sensors for feedforward and feedback control and two metal-oxide-semiconductor field-effect transistors (MOSFETs) as cancellation current drivers. Measurements demonstrate good ripple attenuation up to 5 MHz, more than 70 dB being obtained at 100 kHz, the switching frequency of a test converter. The overall efficiency was measured as 95%, with room for further improvement. The filter is suitable for input and output smoothing in dc-dc converters for aerospace and other critical applications     

Poly-phase codes and optimal filters for multiple user ranging

A technique is introduced to select poly-phase codes and optimal filters of a pulse compression system that have specific temporal and frequency characteristics. In the particular problem under study, multiple vehicles are assigned unique codes and receiver filters that have nearly orthogonal signatures. Narrowband users, that act as interference, are also present within the system. A code selection algorithm is used to select codes which have low autocorrelation sidelobes and low cross correlation peaks. Optimal mismatched filters are designed for these codes which minimize the peak values in the autocorrelation and the cross correlation functions. An adjustment to the filter design technique produces filters with nulls in their frequency response, in addition to having low correlation peaks. The method produces good codes and filters for a four-user system with length 34 four-phase codes. There is considerable improvement in cross and autocorrelation sidelobe levels over the matched filter case with only a slight decrease in the signal-to-noise ratio (SNR) of the system. The mismatched filter design also allows the design of frequency nulls at any frequency with arbitrary null attenuation, null width, and sidelobe level, at the cost of a slight decrease in processing gain     

Surge and Noise Generation in a Forward DC-to-DC Converter

Switching surge and noise voltages are analyzed under the common-mode condition in a forward dc-to-dc converter. The analysis is performed by partitioning the switching time into several states and introducing the high-frequency equivalent circuits. The equivalent circuits include not only inductive and capacitive parameters, but also the parameters related to the switching speed of the transistor and the recovery characteristics of the diode. As a result, the effects of these various parameters on the surge and noise generation are made clear quantitatively.     

Capacitive-loaded push-pull parallel-resonant converter

Results of a theoretical and experimental investigation of a capacitive-loaded push-pull parallel-resonant DC-DC converter (CL-PPRC) are presented and discussed. The push-pull parallel-resonant converter (PPRC) is driven by a lower-than-resonance frequency and the secondary voltage is rectified and smoothed by a capacitive filter. The CL-PPRC is shown to operate in the zero voltage switching (ZVS) mode with a boost-like DC transfer ratio that is approximately linear with the period of the switching frequency. Experimental results of a 180 W, high output voltage (1.8 KV) prototype are found to be in good agreement with the analysis, models, and simulation results presented. The basic characteristic of ZVS, the fact that the resonant current is passing through the switches only during a fraction of the period, the high-voltage transfer ratio, and the inherent input/output (I/O) isolation, make the proposed topology a viable design alternative in avionic and aerospace applications     

Charge equalization for an electric vehicle battery system

Charge equalization for series connected battery strings has important ramifications on battery life. It enhances the uniformity of the battery cells and hence improves the life of the battery as a whole. A new charge equalization technique for a series string of battery cells has been recently proposed by the authors. The basic technique utilizes a simple isolated dc-to-dc converter with a capacitive output filter along with a multiwinding transformer. The possibility of integrating the trickle charge function with the charge equalization function is potentially very attractive, as it can lead to an efficient and low cost implementation     

Maximum Power Transfer for Full-Wave Rectifier Circuits

An analysis is done to determine the maximum power transfer conditions for full-wave rectifier circuits. Potential applications noted are implanted medical instruments, inductive power transfer to weapons, power transfer using space reflectors, and power generation in space. Three types of series impedances are considered: resistive/inductive (RL), resistive/capacitive (RC), and resistive/inductive/capacitive (RLC). The optimum ratio of ac-to-dc voltage output is determined for each type. For the case that involves all three impedance types, the optimum turning condition is also determined. The differential equations describing the circuits are solved in nondimensional form. The solutions involve partial differential equations, closed-form relationships, and simultaneous equations that are solved by numerical methods. The optimum ratio of peak ac-to-dc voltage ranges from 2.0 to 2.8, depending upon the circuit. The optimum turning differs significantly from the usual resonant conditions, especially for low Q.     

Signal Resolution via Digital Inverse Filtering

Research in numerous areas is directed toward the resolution of multiple overlapping signals in a noisy environment. These areas include radar, sonar, speech, seismology, and electrophysiology. Sometimes matched filters are used; other times inverse filters are employed. This paper discusses one approach to the analysis of the resolution of inverse filters. Our method is to compromise the trade-off between signal resolution and the output signal-to-noise ratio (SNR). A performance measure for the inverse or deconvolution filter is defined as a quantity proportional to the harmonic mean of the resolution and the SNR. An optimum output pulse duration is obtained using this criterion, where the pulse shape has been previously selected and the input signal waveform is known. In addition, upper and lower bounds for the output pulse duration are presented. Graphs are given which allow the designer to select the optimum inverse filter output pulse duration for a desired signal resolution and an estimated SNR.     

A Computationally Efficient Approximation to a Discrete-Time Matched Filter

When the number of filter coefficients is large, the solution of the discrete-time matched filter equation can be computationally difficult. In this paper several techniques are presented for approximating the impulse response of a matched filter without actually solving the matched filter equation. The performance of these approximating filters is analyzed and compared with the performance of the matched filter. It is also shown that an approximation which is best in a mean-squared-error sense is not necessarily best in terms of output signal-to-noise ratio.     

The effect of the clutter-to-noise ratio on Doppler filterperformance

The effect of the clutter-to-noise ratio on the performance of a Doppler filter is considered. Clutter is assumed to have a power level which is unknown and varies in range. The assessment of the performance of a Doppler filter is based on the gain of the filter, which is the normalized output signal-to-interference ratio improvement at a given Doppler. The gain is generally a complex function of the statistics of the clutter. New upper and lower bounds on the gain differential between the expected design point clutter-to-noise ratio and the actual clutter-to-noise ratio are found. These bounds are independent of the clutter covariance matrix and are only a function of the unknown clutter-to-noise ratio. The bounds are valid for both Gaussian and non-Gaussian noise and for arbitrary linear filters. The upper and lower bounds differ by the theoretical coherent integration gain, 10 logN dB, where N is the number of pulses. A tighter lower bound is found for the case when the filters are matched filters. A simple exact expression is found for matched filters assuming a Gaussian Markov clutter model as the clutter spectral width approaches zero. An easily implementable adaptive procedure is given which improves performance due to the unknown clutter-to-noise ratio. This work extends a previous result, valid for the Emerson filter, that shows the effect of clutter-to-noise ratio on performance in terms of an average quantity, the improvement factor     

An optimum filter for direct A/D conversion

The author describes a design procedure to find the optimum finite-impulse-response (FIR) filter coefficients when the characteristics of the bandpass filter preceding the analog-to-digital (A/D) converter are known. A simulation of direct A/D conversion performance shows the improvement over the filter coefficients designed to minimize the maximum error over a specified band of frequencies. DC cancellation may be added to the process with very little change in the coefficients of the optimum FIR filter or its performance.<>     

Improved Range Resolution Filters for Rectangular-Pulse Radar Systems

The performance of several new clutter-reduction filters suitable for rectangular-pulse radar systems is investigated. The new filters consist of various approximations and modifications of two filters known to be optimal for certain criteria: the well-known Urkowitz filter which optiizes the clutter improvement ratio, and the newer sidelobe reduction filter which minimizes output noise power subject to peak sidelobe constaints. The new filters are compared usig five basic criteria: clutter improvement ratio, signal-to-noise ratio, sidelobe peak ratio, pulse compression ratio, and filter complexity. The results are summarized in tabular and graphical form.     

Adaptive Tracking Filter for Maneuvering Targets

A general method of continually restructuring an optimum Bayes-Kalman tracking filter is proposed by conceptualizing a growing tree of filters to maintain optimality on a target exhibiting maneuver variables. This tree concept is then constrained from growth by quantizing the continuously sensed maneuver variables and restricting these to a small value from which an average maneuver is calculated. Kalman filters are calculated and carried in parallel for each quantized variable. This constrained tree of several parallel Kalman filters demands only modest om; puter time, yet provides very good performance. This concept is implemented for a Doppler tracking system and the performance is compared to an extended Kalman filter. Simulation results are presented which show dramatic tracking improvement when using the adaptive tracking filter.     

The effects of IF bandpass mismatch errors on adaptive cancellation

The effects of IF bandpass mismatch errors on adaptive cancellers are investigated. Frequency mismatch errors occur because of errors in the synthesis process of the bandpass filters which are designed to be identical and are in each input channel. Tapped-delay line transversal filters can be used to compensate for these frequency mismatches and thus improve cancellation performance. A pole/zero error model of the filters is developed whereby closed-form solutions of the maximum achievable average cancellation are obtained. This cancellation is a function of the order of the ideally matched frequency filters, the number of time-delay taps in the compensating transversal filter, the bandwidth-tapped time-delay product, and the constraints on these parameters. A design procedure is outlined for optimizing the canceller with respect to these parameters and their constraints; specifically, results are presented for Butterworth-type input filters. It is shown that an arbitrarily low output noise residue cannot be achieved by arbitrarily increasing the number of time-delay taps     

Analysis of upgraded GPS internal Kalman filter

GPS receivers with provisions for inertial navigation system (INS) aiding are designed with internal Kalman filters that model generic INSs and process the basic GPS pseudorange and deltarange (range-rate) data to produce an output of inertially-smoothed, “GPS-derived” position and velocity. These Kalman filters model only the basic nine INS errors (position, velocity, and tilt) and do not model any INS gyro or accelerometer errors. It was found that a significant performance improvement could be achieved under conditions of degraded GPS satellite availability by augmenting this type of filter with the six INS gyro and accelerometer bias errors. It is, therefore, recommended that serious consideration be given to incorporating these states into the design of the GPS internal Kalman filter     

A Closely Regulated TWT Converter

The design concept for the traveling wave tube amplifier converter for possible use in the Thermoelectric Outer Planet Spacecraft (TOPS) is presented. An unusual combination of semiconductors and magnetics were utilized to achieve very stable voltage regulation on a number of separate outputs to satisfy the requirements of a high-power traveling wave tube (TWT), and at the same time operate at an efficiency of better than 90 percent from a 30-volt source. The circuitry consists of an output filter, an auxiliary Jensen oscillator driving a high-reactance transformer to provide current limiting to the heater, a variable time delay, a main Jensen oscillator driving the power transformer with a maximum step-up ratio of 120 to 1, and series transistorized post regulators to provide precise voltage adjustment and low output impedance. This paper discusses the design of the high-reactance transformer and the high step-up ratio transformer, as well as the high-voltage series regulators that are limited in range and operate at the top of the unregulated output voltage. Test data is presented, and details of current transients caused by charging the filter circuits, input current ripple, and output voltage ripples are considered. The circuit provides better than 0.5 percent regulation against load change, input voltage change, and over-operating temperature range of from -20 to + 80°C, with output ripple voltage of less than 2 volts peak-to-peak on top of the 3600-Vdc output. The measured efficiency was typically 87 percent. and recommendations are included to improve this to in excess of 90 percent.