Dual threshold overcurrent reset

Abstract

A method of operating a power conversion system including converting variable frequency AC voltage to constant frequency AC voltage by a power converter, setting a first peak current reset threshold above operating currents previously observed during steady state short circuit current regulation in by a controller of the power converter, setting a second peak current reset threshold at a current lower than the previously observed steady state short-circuit regulation point observed during previous operation during steady state short circuit current regulation by the controllers of the power converter, resetting inverter converter AC output regulating voltage to 0 volts, and ramping AC output regulating voltage back up into steady-state operation when the second a peak current reset threshold is exceeded.

Claims

1. A method of operating a power conversion system comprising the steps of: converting variable frequency AC voltage to constant frequency AC voltage by a power converter; setting a first peak current reset threshold above operating currents previously observed during steady state short circuit current regulation by a controller of the power converter; setting a second peak current reset threshold at a current lower than the previously observed steady state short-circuit regulation point during steady state short circuit current regulation by the controllers of the power converter; resetting converter AC output regulating voltage to 0 volts; and ramping AC output regulating voltage back up into steady-state operation when the second peak current reset threshold is exceeded; wherein if a short circuit is present, the AC output regulating voltage and current output ramp up at a controlled rate; and increasing an inverter operating duty cycle up to a value where a controller is limiting and regulating short circuit currents.

2. The method of claim 1, further comprising raising the second peak current reset threshold to the first peak current reset threshold in order to allow for the converter to deliver short circuit currents levels.

3. The method of claim 1, wherein the inverter operating duty cycle is increased to a preset short circuit rms current reference value of 1.5 to 2.5 times rated load current.

4. The method of claim 1, wherein if the AC output voltage is overloaded but no short circuit is present, the AC output voltage ramps up to a value set by a pre-determined fold-back curve.

5. The method of claim 4, wherein the foldback curve, represents a relationship between output voltage and load current produced by a variable speed constant frequency (VSCF).

6. The method of claim 4, wherein when the power converter has ramped up to the value determined by the pre-determined fold-back curve or short-circuit current reference value, a higher reset detection threshold is set by the controller to be used for any subsequent resets of the output voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:

(2) FIG. 1 is a block diagram of showing the steps of the method of the disclosure; and

(3) FIG. 2 shows a foldback curve diagram.

DETAILED DESCRIPTION

(4) Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of the method in accordance with the invention is shown in FIG. 1. The methods of the disclosure can be used to reduce the peak operating currents in converter thereby reducing the size of the switching devices and filter inductors.

(5) This disclosure deals with events where the variable speed constant frequency (VSCF) converter is operating in the normal voltage regulating range, currents at or below 1.5 pu when subsequently a load fault, short circuit is applied to the point of regulation load bus. The current increases rapidly and must be detected quickly to immediately decrease the VSCF voltage output from rated to zero volts and cease the build-up of current.

(6) FIG. 1 shows the method 100 of operating a power conversion system including converting 102 variable frequency AC voltage to constant frequency AC voltage by a power converter, setting a first peak current reset threshold above operating currents previously observed during steady state short circuit current regulation by a controller of the power converter 104, setting a second peak current reset threshold at a current lower than the previously observed steady state short-circuit regulation point during steady state short circuit current regulation by the controllers of the power converter 106, resetting converter AC output regulating voltage to 0 volts 108, and ramping AC output regulating voltage back up into steady-state operation when the second peak current reset threshold is exceeded 110. The method also includes raising the second peak current reset threshold to the first peak current reset threshold in order to allow for the converter to deliver short circuit currents levels 112.

(7) If a short circuit is present, the AC output regulating voltage and current output can be ramped up at a controlled rate 114. An inverter operating duty cycle up can be ramped up to a value where a controller is limiting and regulating short circuit currents, wherein the inverter operating duty cycle can be increased to a preset short circuit RMS current reference value of 1.5 to 2.5 times rated load current.

(8) If the AC output voltage is overloaded but no short circuit is present, the AC output voltage can be ramped up to a value set by a pre-determined by a fold-back curve, e.g., as shown in FIG. 2. The foldback curve, represents relationship between output voltage and load current produced by the VSCF at the POR. The first key point in the curve is the maximum current at rated voltage, v,i point 1, this is the maximum power that is allowed to be extracted from the variable frequency generator, beyond this point the voltage must be reduced as a function of current to limit the power to the load to a level equal or less than the power extracted at point 1. The second key point in the foldback curve is the maximum output current delivered during short circuits when the output voltage is zero point 3. The controller will adjust the inverter voltage to limit and regulate POR current delivered to the fault per the preset current limit previously mentioned. Prior to ramping up the voltage the reset threshold must be raised to a level that is above the peak short circuit regulating currents point 4. This allows the VSCF to source short circuit current for a continuous steady state period of time to clear circuit breakers in series with the fault and downstream of the POR.

(9) When the power converter has ramped up to the value determined by the pre-determined by a fold-back curve or short-circuit current reference value, a higher reset detection threshold can be set by the controller to be used for any subsequent resets of the output voltage. If the fault is no longer present as the voltage is ramped up, the voltage will return to its normal predetermined level and after a preset amount of time if the current is below line 5 the over current reset threshold will be reset from threshold 2, line 4 to threshold 1, line 2. This last transition will prepare the VSCF for the next potential fault.

(10) The methods and systems of the present disclosure, as described above and shown in the drawings, provide for a method for short-circuit control. While the apparatus and methods of the subject disclosure have been showing and described with reference to embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and score of the subject disclosure.