Procedures and devices for the connection and disconnection of electrical loads

Abstract

 A procedure for connecting a capacitive load (17) or disconnecting an inductive load (19) to/from a power supply line (10) using a contactor (13) and an SSPC (15) in parallel where the connection or the disconnection is performed in at least two steps having in one of them the contactor (13) switched OFF and the SSPC (15) switched ON, and having in the other step the contactor (13) switched ON and the SSPC (15) switched ON; and where the current (i_SSPC) through the SSPC (15) is actively controlled the during the connection or disconnection times (t_c, t_d) so that the current (i_CON) or the voltage (v_CON) through the contactor (13) when is switched ON is maintained under the maximum values (i_MAX-C, v_MAX-C) endured by the contactor (13). The invention also refers to a single switching device (18) comprising a contactor (13) and an SSPC (15) in parallel.

Description

FIELD OF THE INVENTION

[0001] This invention refers to procedures and devices for the connection and disconnection of electrical loads and more in particular for the connection of capacitive loads and to the disconnection of inductive loads using contactors.

BACKGROUND OF THE INVENTION

[0002] There is a strong trend in the aeronautical industry towards the More Electric Aircraft (MEA) concept as a consequence of substitutions of conventional equipments which depend on pneumatic, mechanic and hydraulic power by equipments that depend on electrical power. These new equipments provide an improved operational capacity thanks to an increased reliability, a lower maintenance, an efficient energy conversion and, therefore, a greater efficiency of the aircraft in general.

[0003] A similar trend can also be observed in the automotive industry, the space industry and other industries.

[0004] To cope with this increase in electrical energy, in the new distribution architectures high voltage levels are used in order to reduce the current levels and, consequently, the cable sections and its weight. On the other hand, more important electric loads can be directly fed with direct current in place of three-phase alternate current, which also means a decrease in the number of cables used to connect the different electrical loads.

[0005] In this context the prior art teaches the use of capacitor switching contactors for the connection of capacitive loads to the power supply lines. As it is well known a capacitor switching contactor combines a main contactor with a parallel circuit having an auxiliary contactor plus a resistor for limiting the overcurrents during the connection of a capacitive load such as a DC/DC converter or a DC/AC inverter. A detailed description of one capacitor switching contactor can be found for example in US 6,285,271.

[0006] However the capacitor switching contactors required by certain capacitive loads may have a physical size and a weight not compatible with, particularly, the needs of the aircraft and space industries. In this respect the paper "Electrical distribution of high power: impacts, technologies". Pierre Ravel. © 2009 MOET Project Consortium" concludes that weight and volume reduction remain a challenge in connection with Primary Electrical Power Distribution Centers (PEPDC) designed for aircrafts that include a pre-charge system for limiting the inrush current at the closure of a main contactor used for connecting a very capacitive load by means of an auxiliary contactor and resistor connected in parallel to the main contactor.

[0007] A similar problem of overvoltages can be found in the disconnection of inductive loads which is solved in the known switching devices with additional protection elements such as snubbers.

[0008] The present invention is focused to the solution of these problems.

SUMMARY OF THE INVENTION

[0009] An object of the present invention is to provide procedures and devices for switching capacitive loads and inductive loads to a power supply line using low weight components.

[0010] Another object of the present invention is to provide efficient procedures and devices for switching capacitive loads and inductive loads to a power supply line in aircrafts and space vehicles.

[0011] In one aspect, these and other objects are met by a procedure for switching a load in an electrical circuit fed by a power supply line, said load generating an overcurrent during the connection transient being a capacitive load or an overvoltage during the disconnection transient being an inductive load using a contactor and a Solid State Power Controller (hereinafter SSPC) in parallel with said contactor wherein the connection of the capacitive load to the power supply line or the disconnection of the inductive load from the power supply line is performed in at least two steps having in one of them the contactor switched OFF and the SSPC switched ON, and having in the other step the contactor switched ON and the SSPC switched ON and wherein the current i_SSPC through the SSPC during the connection or disconnection times t_c, t_d is actively controlled maintaining its magnitude equal to or less than the maximum value i_MAX-S endured by the SSPC so that the current i_CON or the voltage v_CON through the contactor when is switched ON is maintained under the maximum values i_MAX-C, v_MAX-C endured by the contactor.

[0012] In embodiments of the present invention for switching capacitive loads the connection of the load is performed from an initial state where the contactor is switched OFF and the SSPC is switched OFF in the following steps:

a) in a first step keeping the contactor switched OFF and switching ON the SSPC during a first time period;

b) in a second step switching ON the contactor and keeping the SSPC switched ON during a second time period;

c) in a third step initiating the normal connection state keeping the contactor switched ON and switching OFF the SSPC;
and wherein the current i_SSPC through the SSPC 15 is actively controlled during the connection time t_c elapsed in said first and second steps maintaining its magnitude equal to or less than the maximum value i_MAX-S endured by the SSPC so that the current i_CON through the contactor in said second step is maintained under the maximum value i_MAX-C endured by the contactor. Hereby it is achieved an efficient procedure for switching capacitive loads using contactors avoiding overcurrents on the contactors during the connection of the load to a power supply line.

[0013] In embodiments of the present invention for switching capacitive loads, said active control of the current i_SSPC through the SSPC is carried out optimizing its value inside the semiconductor safe operation curve (SOA) of the SSPC until it reaches an objective absolute value equal to or less than the maximum value i_MAX-S endured by the SSPC and maintaining constant the magnitude of the current i_SSPC at said objective value during a final time stretch. This procedure optimizes the use of the SSPC and therefore provides a reliable connection of large capacitors.

[0014] In embodiments of the present invention for switching capacitive loads, the capacitive load is a capacitor bank of a vehicle (particularly an aircraft) and the power supply line is a DC power supply line (particularly having a voltage of 270v or ± 270v). Therefore it is provided a procedure particularly applicable to the so-called "More Electric Aircrafts".

[0015] In embodiments of the present invention for switching inductive loads the disconnection of an inductive load is performed from an initial state where the contactor is switched ON and the SSPC is switched OFF in the following steps:

a) in a first step keeping the contactor switched ON and switching ON the SSPC during a first time period;

b) in a second step switching OFF the contactor and keeping the SSPC switched ON during a second time period;

c) in a third step initiating the normal disconnection state keeping the contactor switched OFF and switching OFF the SSPC;
and wherein the current i_SSPC through the SSPC is actively controlled during the disconnection time t_d elapsed in said first and second steps maintaining its magnitude equal to or less than the maximum value i_MAX-S endured by the SSPC so that the voltage v_CON through the contactor in said first step is maintained under the maximum value v_MAX-C endured by the contactor. Hereby it is achieved an efficient procedure for switching inductive loads using contactors avoiding overvoltages on the contactors during the disconnection of the load from a power supply line.

[0016] In embodiments of the present invention for switching inductive loads said active control of the current i_SSPC through the SSPC is carried out optimizing its value inside the semiconductor safe operation curve SOA of the SSPC until the voltage v_SSPC reaches an objective absolute value equal to or less than the maximum value v_MAX-S endured by the SSPC. This procedure optimizes the use of the SSPC and therefore provides a reliable disconnection of inductive loads.

[0017] In embodiments of the present invention for switching inductive loads, the inductive load is a long cable/wire of one electrical load or other inductive loads such as magnetic transformers, valves, induction motors or inductive lighting loads of a vehicle (particularly an aircraft), and the power supply line is a DC power supply line (particularly having a voltage of 270v or ± 270v). Therefore it is provided a procedure particularly applicable to the so-called "More Electric Aircrafts".

[0018] In another aspect, the above-mentioned objects are met by a switching device comprising a contactor for switching a load in an electrical circuit fed by a power supply line, said load generating an overcurrent during the connection transient being a capacitive load or an overvoltage during the disconnection transient being an inductive load that also comprises an SSPC in parallel with said contactor comprising means for controlling actively the current on the SSPC and detecting means for detecting if the load generates an overcurrent during the connection transient or an overvoltage during the disconnection transient (measuring the load voltage and the load current and comparing its evolutions) and that is arranged for avoiding said overcurrent or said overvoltage on said contactor during the connection or disconnection time t_c, t_d of the load.

[0019] In embodiments of the present invention, said arrangement comprise means for switching capacitive or inductive loads according to the above mentioned methods. Therefore it is provided a single switching device for capacitive loads or inductive loads integrating a contactor and an SSPC of low weight and reduced volume.

[0020] Other characteristics and advantages of the present invention will be clear from the following detailed description of embodiments illustrative of its object in relation to the attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 

Figure 1 a shows schematically the connection of a capacitive load to the electrical power system of an aircraft and Figure 1b shows a time graph of the overcurrent during the connection transient of the capacitive load without any kind of control.

Figures 2a, 2b, 2c show schematically the connection of a capacitive load to the electrical power system of an aircraft using a capacitor switching contactor known in the art.

Figures 3a, 3b, 3c show schematically the connection of a capacitive load to the electrical power system of an aircraft using a switching device according to the present invention.

Figure 4 shows the variation over time of the current and the voltage in the SSPC during the connection of a capacitive load, being the SSPC controlled by an optimum trajectory current procedure.

Figure 5 shows a time graph of the overvoltage on the contactor during the disconnection transient of an inductive load without any kind of control.

Figures 6a, 6b, 6c show schematically the disconnection of an inductive load to the electrical power system of an aircraft using a switching device according to the present invention.

Figure 7 shows the variation over time of the current and the voltage in the SSPC during the disconnection of an inductive load, being the SSPC controlled by an optimum trajectory current procedure.

Figure 8 is a simplified block diagram of the SSPC used in the present invention.

Figure 9 is a block diagram of a switching device according to this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Figure 1 a shows schematically a DC power supply line 10 of the electrical power system of an aircraft, which is fed by the power provided by a generator 1 and transformed by the rectifier 3 and/or by the power provided by the battery 5, to which a very capacitive load 17 is connected through a contactor 13. As shown in Figure 1b, the current i_CONT during the connection transient may reach high values (i.e. thousands of amps) that can damage the contactor 13.

[0023] A similar problem can be found in the disconnection of a large inductive load from a power supply line using a contactor where the voltage v_CONT during the disconnection transient may also reach high values (see Figure 5).

[0024] As said before and illustrated in Figures 2a, 2b, 2c, in the known solution for limiting overcurrents on the contactor 13 during the connection transient of a large capacitive load 17 an auxiliary contactor 14 and a resistor 16 are added in parallel, so that in a first period of the connection (Figure 2a) the main contactor 13 is opened and the auxiliary contactor 14 is closed, in a second period of the connection (Figure 2b) the main contactor 13 is closed, and in a third period of the connection (Figure 2c) the auxiliary contactor 14 is opened.

[0025] The basic idea of the present invention is substituting the auxiliary contactor 14 and the resistor 16 used in the known capacitor switching devices or the additional protection used in the switching devices for inductive load by an SSPC 15 provided with control means for an active control of the current during the connection transient of a capacitive load and for an active control of the current during the disconnection transient of an inductive load.

[0026] The substitution of the auxiliary contactor 14 and the resistor 16 by the SSPC 15 allows an important reduction of the physical size and weight of the switching device with respect to said known solutions of great relevance for, particularly, aircrafts and space vehicle.

[0027] The switching procedure for the connection of a capacitive load 17 to the power supply line 10 will be therefore the following:

• Initially the contactor 13 is opened and the SSPC 15 is switched OFF;
• in a first period of the connection (see Figure 3a) the contactor 13 remains opened and the SSPC 15 is switched ON;
• in a second period of the connection (see Figure 3b) the contactor 13 is closed and the SSPC 15 remains switched ON;
• in a third period (Figure 3c) the SSPC 15 is switched OFF.

[0028] Being actively controlled the current i_SSPC through the SSPC 15 in said first and second periods, maintaining its magnitude equal to or less than the maximum value i_MAX-S endured by the SSPC 15, it can be assured that the current i_CON through the contactor 13 in said second and third periods is maintained under the maximum value i_MAX-C endured by the contactor 13.

[0029] The disconnection of the capacitive load 17 does not involve overcurrents on the contactor 13 and therefore will be performed simply opening the contactor 13.

[0030] Spanish patent application No. ES201031921 co-owned by the applicant discloses active control procedures for the connection of capacitive loads using SSPCs as single switching devices. Some of them are suitable active control procedures for the SSPC 15 used in this invention in combination with the contactor 13.

[0031] One embodiment of said active control procedures is illustrated in Figure 4. The connection of the capacitive load 17 is carried out optimizing its value inside the semiconductor safe operation curve (SOA) of the SSPC 15 until it reaches an objective absolute value equal to or less than the maximum value i_MAX-S endured by the SSPC 15. This active control by optimum trajectory current procedure allows the connection of big capacitors in small connection times, optimizing the SSPC 15 dissipated powers. On the other hand, the connection times of the loads can be configured and no hardware modifications of the device are required to implement other connection times. The main advantage is that it allows a reduction in the number of semiconductor elements needed for the commutation of a very capacitive load because, by means of this procedure, the SSPC 15 adjusts the connection times depending on the load, regardless of its value. It also improves the connection times of the load as it uses 100% of the functioning regions of the semiconductor and adjusts itself to the SOA of the main semiconductor.

[0032] The switching procedure for the disconnection of an inductive load 19 from the power supply line 10 will be the following:

• Initially the contactor 13 is closed and the SSPC 15 is switched OFF;
• in a first period of the disconnection (see Figure 6a) the contactor 13 remains closed and the SSPC 15 is switched ON;
• in a second period of the disconnection (see Figure 6b) the contactor 13 is opened and the SSPC 15 remains switched ON;
• in a third period (Figure 6c) the SSPC 15 is switched OFF.

[0033] Being actively controlled the current i_SSPC through the SSPC 15 in said first and second periods, maintaining its magnitude equal to or less than the maximum value i_MAX-S endured by the SSPC 15, it can be assured that the voltage v_CON through the contactor 13 in said first period is maintained under the maximum value v_MAX-C endured by the contactor 13.

[0034] Figure 7 show a similar embodiment of the active control procedure illustrated in Figure 4 for the disconnection of an inductive load 19.

[0035] The connection of the inductive load 19 does not involve overvoltages on the contactor 13 and therefore will be performed simply closing the contactor 13.

[0036] Figure 8 shows a block diagram of an SSPC 15 in which said active control procedures can be implemented, which includes a semiconductor 25, a detection unit 24 for detecting the type of load (capacitive or inductive), an active control unit 23 where said active control procedures (whether for the connection transient of a capacitive load or for the disconnection transient of an inductive load) are implemented and a microcontroller 21. The semiconductor 25 may be any semiconductor and preferably a MOSFET or a IGBT.

[0037] As illustrated in Figure 9 (where the thicker lines represent power lines and the thinner lines represent control lines) a switching device 18 according to the present invention is placed between an In bus 10 and an Out bus 12 and comprises a contactor 13, an SSPC 15 and a control unit 31. The SSPC 15 is parallel connected to the contactor 13. A fuse 27 is included in the parallel circuit as a protection device. The control unit 31 of the switching device 18 is connected with a contactor control unit 33 and with the SSPC 15 and uses signals from an input line 35 and voltage and current signals 37, 39 from the Out bus 12.

[0038] The load may be a capacitive load 17 or an inductive load 19. After its detection using the above mentioned means the active control of the SSPC 15 and the control unit 31 of the switching device 18 will be duly arranged for switching a capacitive load 17 or an inductive load 19 according to the above mentioned procedures.

[0039] Although the present invention has been described in relation to preferred embodiments, it is evident that modifications within its scope can be introduced, understanding that it is not limited to said embodiments, but to the content of the following claims.

Claims

1. A procedure for switching a load (17, 19) in an electrical circuit fed by a power supply line (10), said load generating an overcurrent during the connection transient being a capacitive load (17) or an overvoltage during the disconnection transient being an inductive load (19), characterized by:

- using a contactor (13) and an SSPC (15) in parallel with said contactor (13);

- performing the connection of the capacitive load (17) to the power supply line (10) or the disconnection of the inductive load (19) from the power supply line (10) in at least two steps having in one of them the contactor (13) switched OFF and the SSPC (15) switched ON, and having in the other step the contactor (13) switched ON and the SSPC (15) switched ON;

- actively controlling the current (i_SSPC) through the SSPC (15) during the connection or disconnection times (t_c, t_d) maintaining its magnitude equal to or less than the maximum value (_iMAX-S) endured by the SSPC (15) so that the current (i_CON) or the voltage (v_CON) through the contactor (13) when is switched ON is maintained under the maximum values (i_MAX-C, v_MAX-C) endured by the contactor (13).

2. A procedure according to claim 1, wherein:

- the connection of a capacitive load (17) is performed from an initial state where the contactor (13) is switched OFF and the SSPC (15) is switched OFF in the following steps:

a) in a first step keeping the contactor (13) switched OFF and switching ON the SSPC (15) during a first time period;

b) in a second step switching ON the contactor (13) and keeping the SSPC (15) switched ON during a second time period;

c) in a third step initiating the normal connection state keeping the contactor (13) switched ON and switching OFF the SSPC (15);

- the current (i_SSPC) through the SSPC (15) is actively controlled during the connection time (t_c) elapsed in said first and second steps maintaining its magnitude equal to or less than the maximum value (i_MAX-S) endured by the SSPC (15) so that the current (i_CON) through the contactor (13) in said second step is maintained under the maximum value (i_MAX-C) endured by the contactor (13).

3. A procedure according to claim 2, wherein said active control of the current (i_SSPC) through the SSPC (15) is carried out optimizing its value inside the semiconductor safe operation curve (SOA) of the SSPC (15) until it reaches an objective absolute value equal to or less than the maximum value (i_MAX-S) endured by the SSPC (15) and maintaining constant the magnitude of the current (i_SSPC) at said objective value during a final time stretch.

4. A procedure according to any of claims 2-3, wherein:

- the capacitive load (17) is a capacitor bank of a vehicle;

- the power supply line (10) is a DC power supply line.

5. A procedure according to claim 1, wherein:

- the disconnection of an inductive load (19) is performed from an initial state where the contactor (13) is switched ON and the SSPC (15) is switched OFF in the following steps:

a) in a first step keeping the contactor (13) switched ON and switching ON the SSPC (15) during a first time period;

b) in a second step switching OFF the contactor (13) and keeping the SSPC (15) switched ON during a second time period;

c) in a third step initiating the normal disconnection state keeping the contactor (13) switched OFF and switching OFF the SSPC (15);

- the current (i_SSPC) through the SSPC (15) being actively controlled during the disconnection time (t_d) elapsed in said first and second steps maintaining its magnitude equal to or less than the maximum value (i_MAX-S) endured by the SSPC (15) so that the voltage (v_CON) through the contactor (13) in said first step is maintained under the maximum value (v_MAX-C) endured by the contactor (13).

6. A procedure according to claim 5, wherein said active control of the current (i_SSPC) through the SSPC (15) is carried out optimizing its value inside the semiconductor safe operation curve (SOA) of the SSPC (15) until the voltage (v_SSPC) reaches an objective absolute value equal to or less than the maximum value (v_MAX-S) endured by the SSPC (15).

7. A procedure according to any of claims 5-6, wherein:

- the inductive load (19) is a long wire/cable of one electrical load of a vehicle;

- the power supply line (10) is a DC power supply line.

8. A procedure according to any of the preceeding claims, wherein:

- the electrical circuit is located in a vehicle, the vehicle being an aircraft;

- the power supply line (10) is a DC power supply line of 270v or ± 270v.

9. A switching device (18) comprising a contactor (13) for switching a load (17, 19) in an electrical circuit fed by a power supply line (10), said load generating an overcurrent during the connection transient being a capacitive load (17) or an overvoltage during the disconnection transient being an inductive load (19), characterized in that:

- also comprises an SSPC (15) in parallel with said contactor (13) comprising means (23) for controlling actively the current on the SSPC (15) and detecting means (24) for detecting if the load generates an overcurrent during the connection transient or an overvoltage during the disconnection transient;

- it is arranged for avoiding said overcurrent or said overvoltage on said contactor (13) during the connection or disconnection time (t_c, t_d) of the load (17, 19).

10. A switching device (18) according to claim 9, wherein said detecting means (24) comprise:

a) means for measuring the load voltage;

b) means for measuring the load current;

c) means for comparing the evolution between the load voltage and the load current, thereby detecting if the load generates an overcurrent during the connection transient or an overvoltage during the disconnection transient.

11. A switching device (18) according to any of claims 9-10, wherein:

- the load is a capacitive load (17);

- said arrangement comprise means for performing the connection from an initial state where the contactor (13) is switched OFF and the SSPC (15) is switched OFF in the following steps:

a) in a first step keeping the contactor (13) switched OFF and switching ON the SSPC (15) during a first time period;

b) in a second step switching ON the contactor (13) and keeping the SSPC (15) switched ON during a second time period;

c) in a third step initiating the normal connection state keeping the contactor (13) switched ON and switching OFF the SSPC (15).

12. A switching device (18) according to claim 11, wherein said means for controlling actively the current on the SSPC (15) are means that maintain an optimized value of the current (i_SSPC) inside the semiconductor safe operation curve (SOA) of the SSPC (15) until it reaches an objective absolute value equal to or less than the maximum value (i_MAX-S) endured by the SSPC (15) and that maintain constant the magnitude of the current (i_SSPC) at said objective value during a final time stretch.

13. A switching device (18) according to any of claims 9-10, wherein:

- the load is an inductive load (19);

- said arrangement comprise means for performing the disconnection of the load (19) from a connected state where the contactor (13) is switched ON and the SSPC (15) is switched OFF in the following steps:

a) in a first step keeping the contactor (13) switched ON and switching ON the SSPC (15) during a first time period;

b) in a second step switching OFF the contactor (13) and keeping the SSPC (15) switched ON during a second time period;

c) in a third step initiating the normal disconnection state keeping the contactor (13) switched OFF and switching OFF the SSPC (15).

14. A switching device (18) according to claim 13, wherein said means for controlling actively the current (i_SSPC) on the SSPC (15) are means that maintain an optimized value of the current (i_SSPC) inside the semiconductor safe operation curve (SOA) of the SSPC (15) until the voltage (v_SSPC) reaches an objective absolute value equal to or less than the maximum value (v_MAX-S) endured by the SSPC (15).

15. An aircraft comprising a switching device (18) according to any of claims 9-14.

Drawing