Electricity: electrical systems and devices – Safety and protection of systems and devices – Arc suppression at switching point
Patent
1984-04-17
1986-01-21
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Arc suppression at switching point
361 18, 361 91, 363 55, 363 56, H02H 7122
Patent
active
045660514
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention is directed to a single-phase or multi-phase inverter protected with respect to surges or the rates of increase of current and voltage. The inverter comprises a filter capacitor and a choke for protecting with respect to the current, increase rate connected at the DC-side of the inverter. Also provided, for each phase, are at least two controlled semiconductor switches and, connected in parallel with these, members protecting with respect to the voltage increase rate and a separate storage capacitor whose first terminal is connected to either terminal of the filter capacitor, whereas the other terminal is connected to means by which energy is transferred from the storage capacitor to the filter capacitor, as well as to means for transferring energy from the members protecting in respect of the rates of increase of current and voltage to the storage capacitor. The inverter in accordance with the invention is suitable for use as an inverter component of a pulse-width-modulated frequency transformer, by means of which an AC-voltage of desired frequency is formed out of a fixed DC-voltage, or as a step-down transformer of DC-voltage. The controlled semiconductor switch of the inverter may consist of any semiconductor component whatsoever that can be controlled conductive and nonconductive from a control electrode and which requires external limitation of the rate of increase of current and voltage. Such components are, e.g., a bipolar transistor, a power-FET, and a GTO-thyristor.
BACKGROUND OF THE INVENTION
An inverter in accordance with the conventional technology, which is provided with connections limiting the current-increase rate (di/dt) and the voltage-increase rate (du/dt), is illustrated with respect to one phase in FIG. 1. Therein, U.sub.DC is the supplying DC-voltage, C.sub.DC is the filter capacitor of the DC-voltage, S.sub.1 and S.sub.2 are semiconductor switches, D.sub.1 and D.sub.2 are so-called zero diodes, L is the choke limiting the rate of increase of the current, whereas the diode D.sub.5 and the resistor R.sub.3 constitute an alternative route for the current of the choke, and C.sub.1 and C.sub.2 are the capacitors limiting the rate of increase of the voltage, whereat diodes D.sub.3 and D.sub.4 as well as resistors R.sub.1 and R.sub.2, together with C.sub.1 and C.sub.2, form so-called polarized RC-shields.
The arrangement of FIG. 1 constitutes a change-over switch by which the poles of the input voltage can be alternately connected to the output pole. The change-over of the switch, e.g., from the lower branch to the upper branch takes place by opening S.sub.2, which had been conductive, and by closing S.sub.1. Thus, C.sub.1, which had been charged to a voltage U.sub.DC, is discharged through the resistor R.sub.1. C.sub.2, whose voltage has been zero, is charged along the path U.sub.DC -L-S.sub.1 -D.sub.4 -C.sub.2. After C.sub.2 has been charged, excess current of the choke L is turned so as to pass vid D.sub.5 and R.sub.3, being gradually reduced to zero, at which time a stable condition has been reached. The change-over of the switch in the opposite direction takes place in a corresponding way.
The operation of the inverter in accordance with FIG. 1, however, involves the drawback that the energy 1/2CU.sup.2 of the capacitor protecting with respect to the voltage increase rate, discharged on each change-over of the switch, as well as the energy 1/2LI.sup.2 .sub.max charged in the choke protecting with respect to the current increase rate on swinging of the resonance circuit are converted to heat in the resistors R.sub.1, R.sub.2 and R.sub.3. The power loss is proportional to the number of change-overs of the switches per unit of time, which makes the efficiency of the inverter poor at high (higher than 1 kHz) frequencies.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an inverter in which the energies of the di/dt protective choke and of the du/dt protective capacitor are not dissipated as heat, but they are re
REFERENCES:
patent: 4286314 (1981-08-01), Molyneux-Berry
patent: 4378586 (1983-03-01), Bete
patent: 4403269 (1983-09-01), Carroll
Kymi-Stromberg Oy
Moose Jr. Harry E.
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