Electric power conversion systems – Current conversion – Using semiconductor-type converter
Patent
1993-06-14
1995-12-05
Sterrett, Jeffrey L.
Electric power conversion systems
Current conversion
Using semiconductor-type converter
363 8, 363134, H02M 7537
Patent
active
054735300
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention refers to a DC/AC converter, that is a device able to convert a DC generator into an AC one, in particular the type having galvanic insulation between input and output.
The subject of the invention can be employed in a wide range of applications, among which the one of ringing generator for telephone systems, as emergency supply for computer systems or as driving stage for AC motor.
To convert direct current, e.g. supplied by a battery, into alternate current (preferably sinusoidal) several topologies are known. Some topologies have several disadvantages, such as for instance considerable weight and overall dimensions, or a high output distortion.
In particular, the most advanced DC/AC converter includes a high frequency PWM converter stage with galvanic insulation which is controlled by a sinusoidal voltage. It also includes a compensation network and a transistorized full-bridge. In this converter, the first stage does not generate a direct voltage, but a rectified sinewave. The second stage (full-bridge) allows to extract the sinewave and working at low frequency it is able to get high efficiency. Unfortunately this converter requires in practice two stages and an additional compensation network to allow proper operation on reactive load.
Another DC/AC topology uses a full bridge PWM stage followed by a low frequency transformer, but the efficiency figure obtainable at relatively low input voltage is poor.
WO 82/02134 discloses a DC/AC converter suitable for producing an alternating output voltage on a load in accordance with the preamble of claim 1. However according to such prior art device a sinusoidal waveform is reconstructed in four time intervals under control of bidirectional switches that connect the converter branches one after the other in correspondence of the zero-current crossing. This device requires complex control means since a pair of precisely timed control signals is requested for each bidirectional switch to prevent discontinuities in the generated waveform, and moreover such timing is dependent from the load.
SUMMARY OF THE INVENTION
The purpose of this invention is to obtain a new converter that eliminates the disadvantages described above and in particular having reduced weight and volume, high efficiency, and low complexity.
These purposes are obtained with the invention which consists in a DC/AC converter suitable for producing an alternating output voltage on a load connected between two output terminals of an output circuit galvanically insulated from an input circuit having two input terminals connected to a direct current source, said input circuit comprising: input terminals; input terminals; filter means; filter means; second and fourth inductors being magnetically coupled together, the converter further including means to generate control signals for said switching means; switching means are connected to the output terminals in a differential manner, with a pair of capacitors connected between the common node of the differential connection, and one terminal of the load, semiconductor switch parallely connected with a diode, the control electrodes of said first and third semiconductor switches and those of said second and fourth semiconductor switches receiving from said control means signals that are out of phase by 180.degree., respectively.
The converter according to the invention is applied, preferably but not limited to, powers lower than 1 kVA.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention shall now be described more in detail making reference to preferred but not limiting realization forms, shown in the figures enclosed where:
FIG. 1 shows a general block diagram of a DC/AC converter according to the invention;
FIG. 2 gives the outline of the driving circuit;
FIG. 3 shows driving signals of Q1 and Q3 transistors;
FIG. 4 shows driving signals of Q2 and Q4 transistors;
FIGS. 5A and 5B show a variant of driving signals; and
FIG. 6 shows the application of the converter according to the invention to a call puls
REFERENCES:
patent: 3517300 (1970-06-01), McMurray
patent: 4213173 (1980-07-01), Link et al.
patent: 4479175 (1984-10-01), Gille et al.
patent: 4763237 (1988-08-01), Wieczorek
patent: 4772994 (1988-09-01), Harada et al.
Giuseppe Cimador
Paolo Prestifilippo
Italtel Societa Italiana Telecomunicazione S.p.A.
Sterrett Jeffrey L.
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