Search

In this paper, an exact solution of a circuit model for a three-phase rectifier with constant-voltage load and ac-side reactance that operates in the continuous conduction mode is presented. Obtained results are compared to the results provided applying sinusoidal approximation, published previously. It is shown that the sinnsoidal approximation provides acceptable re. suits at low output voltages, with the accuracy being decreased for the output voltages approaching to the discontinuous conduction mode boundary. Computational complexity of the exact solution is about the same as for the solution obtained applying sinusoidal approximation. Index Terms--Alternator, commutation, converter, generator, load matching, load regulation.

A corona discharge generator for surface treatment without the use of a step-up transformer with a high-voltage secondary is presented. The oil bath for high-voltage components is eliminated and still a reasonable volume, efficiency, and reliability of the generator are obtained. The voltage multiplication is achieved by an LC series resonant circuit. The resonant circuit is driven by a bridge type voltage-source resonant inverter. First, feasibility of the proposed method is proved by calculations. Closed form design expressions for key components of the electronic generator are provided. Second, a prototype of the electronic generator is built and efficiency measurements are performed. For power measurement, Lissajous figures and direct averaging of the instantaneous voltage-current product are used. The overall efficiency achieved is in the range between 80% and 90%. Index Terms--Surface treatment, corona, gas discharges, highvoltage technique, resonant power conversion.

Application of the third harmonic current injection in three-phase full-bridge thyristor rectifiers is analyzed. Spectra of the rectifier output terminal voltages are derived. Results of the optimal current injection for diode bridge rectifiers are generalized for the thyristor rectifiers, and the waveform of the optimal injected current is derived. It is shown that for the optimal third harmonic current injection, the current injection network takes 8.571% of the rectifier input power from the thyristor bridge output terminals, regardless the thyristor firing angle. A current injection network with a passive resistance emulator that provides recovery of the power taken from the thyristor bridge output terminals is proposed. Volt-ampere ratings of the magnetic components are derived. An algorithm to control the switches in the resistance emulator is presented. Analytically obtained results are experimentally verified.

A novel three-phase low-harmonic rectifier is proposed. The rectifier consists of a diode bridge, three bi-directional switches that are switched at the double of the line frequency, and a current shaping network. Two current shaping networks are proposed, the first one consisting of two capacitors and three resistors or switching resistance emulators, and the second one consisting of two capacitors, two resistors and a transformer. The power processed by the resistors or resistance emulators is shown to be equal 8.81% of the input power. The rectifier is suitable for application at medium and high power levels, since only the small amount of the input power is processed by high-frequency switching converters, and as a retrofit upgrade of existing rectifiers, requiring connection at only five points. Design guidelines are presented. Switching resistance emulation is discussed, and its feasibility is demonstrated. Analytical results are experimentally verified on a 2 kW rectifier. Index Terms--AC-DC power conversion, converters, harmonic distortion, power conversion harmonics, rectifiers.

A class of current injection based three-phase high power factor rectifiers is proposed. Low distortion of the input currents and high power factor are obtained applying near optimal current injection. The optimal current injection is discussed, and requirements it imposes to the current injection network are derived. A class of simple current injection networks that provide near optimal current injection, consisting of a transformer, two capacitors, and a number of resistors or resistance emulators is proposed. The power processed by the resistors or resistance emulators is shown to be 8.81% of the input power. Design of the current injection network is discussed, and dependence of the input current distortion on capacitance of the applied capacitors is analyzed. Volt-ampere rating of the transformer is shown to be only 0.16% of the input power. Effects caused by the output current ripple are studied, and a method for their compensation is proposed. Analytical results are experimentally verified. Switching resistance emulation is discussed and its feasibility is experimentally demonstrated.

A simple circuit for direct current (dc) measurement using a transformer is proposed. The circuit is based on nonlinear effects in the transformer ferromagnetic core, and it provides information about the current magnitude and polarity. The circuit is analyzed applying piecewise-linear model of the core magnetization curve. An averaged-circuit model and the circuit transfer function are presented. Good linearity and wide measurement range are obtained. Design guides for reduction of the output voltage ripple are given. Measurement error within 0.25% of the full scale is achieved.

In this paper, an algorithm for solving piecewise-linear networks that include elements with discontinuous characteristics is presented. The algorithm is based on modifications of the Katzenelson algorithm that traces the solution curve through regions where boundary conditions are satisfied. Jumps in the network output variables, caused by state changes of elements with discontinuous characteristics, may in turn result in additional state changes of piecewise-linear elements. To resolve these state changes, the network solution point is dragged over the line segment that connects the solution points at the discontinuity, and the network state is changed whenever boundary conditions are violated. Since the algorithm traces cause and effect sequence of state changes, it is well suited for application in time-domain simulations. The algorithm has been implemented in a simulator for piecewise linear networks, and extensively tested on networks encountered in power electronics. An example of such application is presented.

A method for fast time-domain simulation of piecewise-linear networks with switches is described in this paper. The method is based on a discrete-time switch model that consists of a constant conductance in parallel with a current source. In each simulation step, value of the current source is updated as a function of known network signals. The function takes one of two forms, depending on the state (on or off) of the switch. Since system matrix is constant, regardless of the states of the switches, simulation time is essentially the same as for linear, time-invariant network of the same complexity. The paper discusses selection of model and simulation parameters. Simulation algorithm is described and an example is included. It is shown that the method is not only efficient but also quite general and void of convergence problems. Its primary application is for long-term transient simulation of power electronic systems.

Two high power factor rectifiers that apply the third harmonic current injection principle and passive resistance emulation are presented in this paper. Two methods of current injection, simultaneous current injection in all three of the phases, and current injection to only one of the phases, are discussed. Conditions for the optimal third harmonic current injection are derived. Structures of the rectifiers that apply passive resistance emulation, enabling recovery of the power taken by the current injection network, are presented. Proposed resistance emulator consists of a transformer, two diodes and a capacitor. Choice of the passive components is discussed, and their values are proposed. Volt-ampere ratings of the magnetic components are derived. Influence of the higher order harmonics is discussed. Dependence of the input current total harmonic distortion on the load level is presented for both of the current injection methods. Analytically obtained results are verified on 1.5 kW experimental rectifiers. Index Terms--AC-DC power conversion, converters, harmonic distortion, power conversion harmonics, power quality, rectifiers.

A novel current injection network for low-harmonic rectifiers that apply the third harmonic current injection is proposed in this letter. The current injection network requires one inductor, two capacitors, and one 1:1 transformer with voltampere rating of only 0.16% of the input power. The transformer is introduced to provide complete rejection of harmonic components of the injected currents at even triples of the line frequency, resulting in significant reduction of the input current total harmonic distortion (THD). Dependence of the input current THD on the current injection network Q factor is computed. The THD is shown to be in the range 4% [is less than] THD [is less than] 5.125%. Analytically obtained results are experimentally verified on a 1.5-kW rectifier. Index Terms--AC-DC power conversion, converters, harmonic distortion, power conversion harmonics, rectifiers.

An analysis of the three-phase low-harmonic rectifiers applying passive third-harmonic current injection networks is presented in this paper. Optimal amplitude of the injected current to minimize the input current total-harmonic distortion (THD) is derived as a function of the injected current phase displacement. Power aspects of the third-harmonic current injection are analyzed, and it is shown that improvement in the input current THD could be obtained at the expense of the power taken by the current injection network. In the case of optimal current injection, the power taken by the current injection network is shown to be equal to 8.571% of the input power, resulting in the input current THD of 5.125%. Effects of unwanted higher order harmonics in the injected currents are studied for two previously proposed passive current injection networks. The current injection networks are compared under the constraint that volt-ampere ratings of applied components are the same. Analytically obtained results are experimentally verified. Index Terms - AC-DC power conversion, converters, harmonic distortion, power conversion harmonics, power quality, power system harmonics, rectifiers.

Current programming in a three-phase high-power-factor rectifier based on two boost converters is discussed in this paper. It is shown that the converter currents can be expressed in terms of two mutually related auxiliary functions. The auxiliary functions are related to the input current spectrum. Optimal auxiliary functions that eliminate harmonics of the input currents are derived. A method to generate reference signals for the optimal current programming is proposed. Experimental results confirming the proposed concepts are presented. Index Terms - AC-DC power conversion, converters, harmonic distortion, power conversion harmonics, power quality, power system harmonics, rectifiers.