Patent Application
20130154774
The present invention relates generally to hybrid direct current (DC) contactors and, more particularly, to a system and method for controlling operation of a hybrid DC contactor that improves performance of the hybrid contactor.
Electro-mechanical contactors are used in a variety of environments for turning on and off a power source to a load electrically. The contactors include movable contacts and fixed contacts. The movable contacts are connected to an electromagnet and are controlled to selectively turn on or off power from the source to the load. The contacts are typically maintained in an open position by way of a spring and are caused to translate to a closed position when power to the electromagnet's coil is applied.
When electro-mechanical contactors are used for interrupting AC currents, it is recognized that there is always a time when the current becomes zero. Electro-mechanical contactors can thus interrupt current at the zero current and when the contacts separated. However, when electro-mechanical contactors are used in a DC voltage system, an electric arc may form in the space between contacts during transition of the movable contacts between the closed and open positions. Without intervention, this arc will continue until the separation between the contacts is too large to sustain the arc. When interrupting DC current, the separation between the fixed and moving contacts has to be large (in air, under standard pressure conditions). Thus, it is known to experts in the field that, for interrupting DC currents, special magnets are required in DC contactors.
To address the issue of not being able to interrupt the current caused by arcing, hybrid DC contactors have been developed that incorporate a solid state device that is connected in parallel with the mechanical main contacts. The solid state device may, for example, include an IGBT switch, a snubber capacitor, and a snubber resistor. In operation, when changing the mechanical main contact from the closed state to the open state, the solid state device that is connected in parallel to the mechanical main contact is turned on first. The current flowing through the mechanical main contact is thus caused to flow through the solid state device. Next, the mechanical main contact is allowed to open by removing the voltage applied to the electromagnet coil that controls positioning of the mechanical main contact. By turning on the solid state device prior to opening the mechanical main contact, the voltage on both ends of the turned-on solid state device and the mechanical main contact can be opened with only a minimal voltage not sufficient to form an arc.
While existing hybrid DC contactors do function to provide a bypass path to the mechanical contacts, there are drawbacks to the design and control of such hybrid DC contactors. One such drawback to existing hybrid DC contactors is that, when bypassing the main contacts, the separation between the moving and fixed contacts cannot be determined. Not knowing the separation, the sold state device is left closed for a fixed but long enough delay to ensure interruption of the current. As such, the full current value needs to flow through the solid state switch for several milliseconds, necessitating that the solid state switch be oversized to handle several milliseconds of current. This oversizing of the IGBT switch increases the production cost of existing hybrid DC contactors.
Another drawback to existing drawback hybrid DC contactors is that the switching time of the contactor is prolonged enough that the contacts may still be exposed to an undesirable “restrike” of arcing. That is, when interrupting DC currents due to the inductance in the circuit, the voltage across the main contacts rapidly rises, and this rapid rise in voltage can cause a breakdown of the air gap between the fixed and moving contacts called “restrike.” The fixed and moving contacts have to be separated by a sufficient gap to prevent such a restrike (that is based on contactor design and other conditions). Still another drawback of the prior art hybrid DC contactors is that, if there is restrike of the arc, there is no capability to know the condition and this could result in the burning out of the contactor. Still another drawback to existing drawback hybrid DC contactors is that they do not provide galvanic isolation, which is desirable in some implementations of hybrid DC contactors. Still another drawback is that the existing design of hybrid DC contactors is not suitable for bidirectional currents.
It would therefore be desirable to provide a hybrid DC contactor system circuit and method for controlling thereof that reduces the time the solid state device carries the current, provides the capability to determine if the gap between the fixed and moving contacts is enough not to cause a restrike, provides for detection of a strike and ensures to turn on the solid state switch once again to ensure that the current is interrupted, provides galvanic isolation, and is suitable for bidirectional currents. Such a circuit could advantageously be applied to a breaker that can trip due to an over current or by a shunt trip. When the arc is detected, the circuit automatically waits, pulses the IGBT, and interrupts the current. The circuit could also be configured as a bidirectional circuit that is applied to circuit breakers as well. This hybrid contactor coil can be opened to activate the circuit with a number of detection circuits such as the following commonly used: over-current detectors, over-voltage or under-voltage detectors, and ground fault detectors.
The present invention provides a system and method for controlling operation of a hybrid DC contactor.
In accordance with one aspect of the present invention, a hybrid direct current (DC) contactor includes a plurality of main contacts configured to provide a first current path between a DC power source and a load, an electromagnetic coil configured to position the plurality of main contacts in a closed position when power is supplied thereto, with the plurality of main contacts moving from the closed position to an open position when power to the electromagnetic coil is terminated. The hybrid DC contactor also includes a solid state device positioned in parallel with of the plurality of main contacts, the solid state device including a semiconductor switch that, when turned on, provides a second, parallel current path that diverts current away from the plurality of main contacts when the main contacts are being opened in either direction. The hybrid DC contactor further includes a controller configured to terminate a supply of power to the electromagnetic coil so as to cause the plurality of main contacts to begin to open, detect an arc voltage across the main contacts as the main contacts are opening, provide a gate signal to the semiconductor switch to cause the semiconductor switch to pulse on for a pre-determined period of time so as to route current to the semiconductor switch, measure a current through the main contacts and, if current is still present through the main contacts, then provide another gate signal to the semiconductor switch to cause the semiconductor switch to again pulse on for another pre-determined period of time so as to route current to the semiconductor switch.
In accordance with another aspect of the invention, a method for controlling current flow in a hybrid DC contactor includes providing a hybrid DC contactor on a circuit between a DC power source and a DC load, the hybrid DC contactor comprising a multi-pole arrangement and a solid state switch positioned in parallel with the multi-pole arrangement such that current is diverted away from the multi-pole arrangement and to the solid state device when the solid state device is turned on. The method also includes causing poles of the multi-pole arrangement to translate from a closed position to an open position and, during translation of the poles of the multi-pole arrangement from the closed position to the open position, the method further includes detecting a contact arcing across the poles of the multi-pole arrangement when all poles of the multi-pole arrangement are open and intermittently providing a pulsed gate signal to the solid state switch so as to selectively divert current to the solid state switch, wherein each gate signal causes the solid state switch to turn on for a pre-determined duration to divert current thereto and wherein the pulsed gate signal is intermittently provided to the solid state switch until it is determined that current through the poles of the multi-pole arrangement has been interrupted.
In accordance with yet another aspect of the invention, a hybrid direct current (DC) switching device includes an electromechanical switch comprising contacts movable between an open position and a closed position so as selectively provide a first current path between a DC power source and a load when the contacts are in the closed position and a solid state device positioned in parallel with the contacts of the electromechanical switch, the solid state device including a semiconductor switch that, when turned on, provides a second, parallel current path that diverts current away from the main contacts when the contacts are being opened. The hybrid DC switching device also includes a controller configured to detect an arc voltage through the contacts as the contacts begin to open from the closed position, institute a delay period configured to prevent a re-strike voltage across the contacts upon detecting the arc voltage, provide a gate signal to the semiconductor switch to cause the semiconductor switch to pulse on for a pre-determined period of time so as to route current to the semiconductor switch, measure a current through the contacts, and if current is still present through the contacts, then provide another gate signal to the semiconductor switch to cause the semiconductor switch to again pulse on for another pre-determined period of time so as to route current to the semiconductor switch.
Various other features and advantages of the present invention will be made apparent from the following detailed description and the drawings.
The drawings illustrate preferred embodiments presently contemplated for carrying out the invention.
In the drawings:
The embodiments of the invention set forth herein relate to a system and method for controlling operation of a hybrid DC contactor. A hybrid DC contactor is provided that includes a semiconductor switch connected in parallel to the plurality of contacts, so as to provide a parallel current path that diverts current away from the plurality of main contacts when the semiconductor switch is turned on and the power to the coil is de-energized (the current will not go through the IGBT when the contacts are closed). When the main contacts are desired to be opened, and start to open, a controller associated with the hybrid DC contactor detects an arc voltage across the main contacts. After the arc voltage is detected, the controller institutes a delay period before then providing a gate signal to the semiconductor switch to cause the semiconductor switch to pulse on for a pre-determined period of time so as to route all the current to the semiconductor switch. Upon pulsing the semiconductor switch on for the pre-determined period of time, a current through the main contacts is measured and, if current is still present, the controller continues to provide additional intermittent gate signals to the semiconductor switch as needed to cause the semiconductor switch to again pulse on for additional periods of time so as to route current to the semiconductor switch, until the current through the main contacts is interrupted.
Referring now to
As shown in the hybrid DC contactor 10 of
The hybrid DC contactor 10 further includes a solid state device 22 that is connected/positioned in parallel with the electro-mechanical contactor 17, such that the solid state device 22 provides a second, parallel current path that diverts current away from the electro-mechanical contactor 17 when the switching unit is turned on. Specifically, the solid state device 22 includes a semiconductor switch 24, such as an insulated-gate bipolar transistor (IGBT) switch or other suitable switch, that can be selectively turned on and off to divert current away from the main contacts 18 of electro-mechanical contactor 17. The solid state device 22 also includes a snubber circuit 26 in parallel with the IGBT 24, with the snubber circuit 26 having a capacitor 28 and a resistor 30 in series that function to suppress voltage transients in the solid state device 22, so as to protect the IGBT 24. According to one embodiment of the invention, a free-wheeling diode 32 is also included in hybrid DC contactor 10 to circulate inductive load currents, such that the source circuit is quickly isolated.
In operation, when it is desired to actuate the movable contacts 18 from a closed position to an open position, a supply power provided to electromagnetic coil 20 is terminated and the IGBT 24 is turned on, such that the current flowing through the main contacts 18 is caused to flow through the IGBT 24 and the main contacts 18 can be opened with minimal arcing occurring across the main contacts. For controlling operation of the electromagnetic coil 20 and the solid state device 22, one or more controllers 34 (shown as a single controller in
While the hybrid DC contactor 10 in
Referring now to
After the delay period has passed, the technique 40 continues with the controller 34 transmitting a gate signal to the IGBT 24 to turn the IGBT on, as indicated at 50. As shown in
After the pulsed gate signal to the IGBT 24 is terminated, the controller 34 then measures a current through the main contacts 18, as indicated at 54, and determines whether current is still present or has been interrupted, as indicated at 55 (
The intermittent pulsing of the gate signal to the IGBT 24 while the main contacts 18 are transitioning from the closed position to the open position provides/ensures that the IGBT 24 carries current for only very short durations, thus reducing losses and reducing the size of the IGBT 24 that is required. That is, by implementing the technique/control scheme 40, the size of the IGBT 24 can be reduced by approximately 30% on average. The wear experienced by main contacts 18 is also minimized by way of the pulsing of the IGBT 24, as the contacts arc for only a short time. Additionally, the technique/control scheme 40 for controlling hybrid DC contactor 10 reduces the time needed to open the main contacts 18 and circuit 12, with time reductions of 1-3 milliseconds being achievable. That is, by implementing the technique/control scheme 40, the delay for commuting the current with the IGBT 24 will be approximately 200 microseconds, with the current interrupting then occurring within an additional 50 microseconds.
Referring now to
While embodiments of the invention set forth above are shown and described with respect to a hybrid DC contactor 10 that includes an electro-mechanical contactor 17 therein, it is recognized that a relay, breaker, or other electro-mechanical switch could be substituted for the electro-mechanical contactor. In one such embodiment, a shunt trip would be provided for switching the breaker between an open and closed state for selectively conducting current therethrough. A control scheme as illustrated in
Embodiments of the invention thus provide a hybrid DC contactor, and method of controlling thereof, that reduces the amount of time that the IGBT carries current (so as to allow for a reduction in size thereof), reduces switching time, and provides galvanic isolation. The hybrid DC contactor provides the capability to determine if the gap between the fixed and moving contacts is enough not to cause a restrike, provides for detection of a strike, and ensures to turn on the solid state switch once again to ensure that the current is interrupted. The hybrid DC contactor also provides galvanic isolation and is suitable for bidirectional currents. Such a circuit would advantageously provide for the circuit to be applied to a breaker that can trip due to an over current or by a shunt trip. When the arc is detected, the circuit automatically waits, pulses the IGBT, and interrupts the current. The circuit could also be configured as a bidirectional circuit that is applied to circuit breakers as well. This hybrid contactor coil can be opened to activate the circuit with a number of detection circuits such as the following commonly used circuits: over-current detectors, over-voltage or under-voltage detectors, and ground fault detectors.
A technical contribution for the disclosed method and apparatus is that it provides for a controller-implemented technique for controlling operation of a hybrid DC contactor. The technique detects an arc voltage across main contacts of the contactor and provides a pulsed gate signal to the semiconductor switch in parallel with the main contacts to cause the switch to pulse on for a pre-determined period of time and route current to the semiconductor switch. Upon pulsing the semiconductor switch on for the pre-determined period of time, a current through the main contacts is measured and, if current is still present, the controller continues to provide additional intermittent gate signals to the semiconductor switch as needed to cause the semiconductor switch to again pulse on for additional periods of time so as to route current to the semiconductor switch, until the current through the main contacts is interrupted.
Therefore, according to one embodiment of the present invention, a hybrid direct current (DC) contactor includes a plurality of main contacts configured to provide a first current path between a DC power source and a load, an electromagnetic coil configured to position the plurality of main contacts in a closed position when power is supplied thereto, with the plurality of main contacts moving from the closed position to an open position when power to the electromagnetic coil is terminated. The hybrid DC contactor also includes a solid state device positioned in parallel with the plurality of main contacts, the solid state device including a semiconductor switch that, when turned on, provides a second, parallel current path that diverts current away from the plurality of main contacts when the main contacts are being opened in either direction. The hybrid DC contactor further includes a controller configured to terminate a supply of power to the electromagnetic coil so as to cause the plurality of main contacts to begin to open, detect an arc voltage across the main contacts as the main contacts are opening, provide a gate signal to the semiconductor switch to cause the semiconductor switch to pulse on for a pre-determined period of time so as to route current to the semiconductor switch, measure a current through the main contacts and, if current is still present through the main contacts, then provide another gate signal to the semiconductor switch to cause the semiconductor switch to again pulse on for another pre-determined period of time so as to route current to the semiconductor switch.
According to another embodiment of the present invention, a method for controlling current flow in a hybrid DC contactor includes providing a hybrid DC contactor on a circuit between a DC power source and a DC load, the hybrid DC contactor comprising a multi-pole arrangement and a solid state switch positioned in parallel with the multi-pole arrangement such that current is diverted away from the multi-pole arrangement and to the solid state device when the solid state device is turned on. The method also includes causing poles of the multi-pole arrangement to translate from a closed position to an open position and, during translation of the poles of the multi-pole arrangement from the closed position to the open position, the method further includes detecting a contact arcing across the poles of the multi-pole arrangement when all poles of the multi-pole arrangement are open and intermittently providing a pulsed gate signal to the solid state switch so as to selectively divert current to the solid state switch, wherein each gate signal causes the solid state switch to turn on for a pre-determined duration to divert current thereto and wherein the pulsed gate signal is intermittently provided to the solid state switch until it is determined that current through the poles of the multi-pole arrangement has been interrupted.
According to yet another embodiment of the present invention, a hybrid direct current (DC) switching device includes an electromechanical switch comprising contacts movable between an open position and a closed position so as selectively provide a first current path between a DC power source and a load when the contacts are in the closed position and a solid state device positioned in parallel with the contacts of the electromechanical switch, the solid state device including a semiconductor switch that, when turned on, provides a second, parallel current path that diverts current away from the main contacts when the contacts are being opened. The hybrid DC switching device also includes a controller configured to detect an arc voltage through the contacts as the contacts begin to open from the closed position, institute a delay period configured to prevent a re-strike voltage across the contacts upon detecting the arc voltage, provide a gate signal to the semiconductor switch to cause the semiconductor switch to pulse on for a pre-determined period of time so as to route current to the semiconductor switch, measure a current through the contacts, and if current is still present through the contacts, then provide another gate signal to the semiconductor switch to cause the semiconductor switch to again pulse on for another pre-determined period of time so as to route current to the semiconductor switch.
The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.
