GB2519653A

GB2519653A - Split voltage control and isolation system

Info

Publication number: GB2519653A
Application number: GB1415904.0A
Authority: GB
Inventors: Wayne Maddison
Original assignee: Controlled Power Technologies Ltd
Current assignee: Valeo Air Management UK Ltd
Priority date: 2013-09-09
Filing date: 2014-09-09
Publication date: 2015-04-29
Anticipated expiration: 2034-09-09
Also published as: GB2519653B; GB201415904D0; GB201315988D0

Abstract

A vehicle electrical system comprises a first low voltage electrical circuit 101 and a second high voltage electrical circuit 102, both receiving power simultaneously from a mechanically driveable switched reluctance generator 122. The circuits each have separate grounds 107, 108 that are electrically isolated from each other, but the low voltage and high voltage circuits are still able to communicate data through an isolation unit 120 comprising optoisolators and galvanic barriers. The generator 122 may be operated as either a motor or a generator and when generating produces high voltage power. A step down voltage converter 131 allows this power to be used by low voltage devices 105. The first electrical ground 107 may be the vehicle body and the second electrical ground 108 may be a terminal insulated from the casing of the mechanically driveable generator 122.

Description

Split Voltage Control and Isolation System This invention relates to a split voltage automotive electrical system having two electrical circuits, each requiring a different supply voltage which are supplied with electrical power using a single mechanically driveable electrical generator.

Under current industry standards, electrical systems for use in small to medium sized automotive vehicles operate using a supply voltage of 12 volts provided by a single 12 volt power source. For large automotive vehicles, industry standards specify the use of a 24 volt power supply. These standards have been in place for some time and as a result vehicular electrical devices, which require a supply voltage of 12 or 24 volts are commonplace.

In conventional internal combustion engine powered vehicles, propulsive power is provided solely by the internal combustion engine. Electrical power is used to power supplementary, ancillary devices such as engine control units, HVAC systems, headlights, starter motors, in car entertainment systems and so on. Some automotive electrical devices, have been created that require a supply voltage of more than 12 or 24 volts. This helps to reduce the current demands of high power devices with consequent advantages such as reductions in vehicle wiring loom weight.

48 volts has been proposed as a suitable value for the supply voltage for such high voltage devices. Situations therefore exist where it is necessary to simultaneously provide both 12 or 24 and 48 volts to different devices operating in the same vehicle.

The problem therefore exists of how to achieve this whilst maintaining system reliability and electrical safety.

US 2011/0140512 describes a high voltage (300-400Vdc) rechargeable battery charged from a conventional utility domestic, non-vehicle, mains supply. The high voltage circuit is used to drive an ac motor via a dc/ac inverter. A dc-dc converter is used to provide a lower voltage (typically l2Vdc) for other loads in a data network power system. The three systems; charger and high and low voltage power systems, are electrically isolated from one another with no electric current flowing directly between them and with communications via rf connections.

In a first aspect, the invention provides a vehicle electrical system comprising first and second electrical circuits; wherein the first electrical circuit includes a first electrical ground and requires electrical power at a first voltage level; wherein the second electrical circuit includes a second electrical ground and requires electrical power at a second voltage level; wherein the first and second electrical grounds are electrically isolated from one another; and wherein the first voltage level is lower than the second voltage level; the first and second electrical circuits being further arranged to send and receive control and/or other data signals between each other whilst still maintaining electrical isolation between the first and second electrical grounds; the vehicle electrical system further comprising a mechanically driven electrical generator arranged to provide the first and second electrical circuits with electrical power simultaneously.

It is preferable that the first electrical ground is the vehicle body and the second electrical ground is brought out as an insulated terminal on the casing of the mechanically driven generator. It is common practice for the vehicle body to be used as an electrical ground for automotive electrical systems. Whilst this practice is acceptable for use with low voltage devices, it is undesirable for the high voltage second circuit to use the vehicle body as an electrical ground, as the vehicle body is exposed and can be easily touched by a person during maintenance; the higher voltages potentially being hazardous.

Preferably the mechanically driven electrical generator produces electrical power at the second voltage level and the mechanically driven electrical generator receives control and/or other data signals from the first electrical circuit. Also preferably the second electrical circuit includes multiple switching elements, control of which is provided by logical control devices included in the first electrical circuit.

With the use of a single generator, this electrical isolation therefore presents the problem of how to transfer control signals between the first circuit which will typically be powering most of the vehicle control systems and the second circuit which will necessarily power at least part of the generator control systems.

According to a second aspect, the invention provides a method for simultaneously providing first and second electrical circuits with electrical power using a single mechanically driven electrical generator; wherein the first electrical circuit includes a first electrical ground and requires electrical power at a first voltage level; and the second electrical circuit includes a second electrical ground and requires electrical power at a second voltage level; wherein the first voltage level is lower than the second voltage level; the first and second electrical circuits being further arranged to send and receive control and/or other data signals between each other; the method involving generating electrical power at the second voltage level; the method further involving performing a voltage conversion operation to step down the generated electrical power to the first voltage level; the method further involving electrically isolating the two electrical grounds.

Through this method, it is possible to provide both the first and second electrical circuits with electrical power at two desired voltage levels simultaneously, and preferably involves providing the mechanically driven electrical generator with control and/or other control signals from the first electrical circuit. The method also preferably involves controlling multiple switching elements in the second electrical circuit using logical control devices in the first electrical circuit.

According to a third aspect, the invention provides a vehicle including a vehicle electrical system comprising first and second electrical circuits; wherein the first electrical circuit includes a first electrical ground and requires electrical power at a first voltage level; wherein the second electrical circuit includes a second electrical ground and requires electrical power at a second voltage level; wherein the first and second electrical grounds are electrically isolated from one another; and wherein the first voltage level is lower than the second voltage level; the first and second electrical circuits being further arranged to send and receive control and/or other data signals between each other whilst still maintaining electrical isolation between the first and second electrical grounds; and the vehicle electrical system further comprising a mechanically driven electrical generator arranged to provide the first and second electrical circuits with electrical power simultaneously.

Preferably the first electrical ground is the vehicle body and the second electrical ground is an insulated terminal on the casing of the mechanically driven generator.

Embodiments of the invention will now be described by way of non-limiting example, and with reference to the drawings in which:-Figure 1 is a schematic diagram showing an overview of the invention; Figure 2 is a schematic diagram of an alternative embodiment of the invention, focusing particularly on the control and isolation aspects of the invention; and Figure 3 is schematic diagram of another alternative embodiment of the invention integrated into a starter/generator motor device.

As noted above, it may be necessary to operate low voltage electrical devices, requiring a supply voltage such as 12 volts, and high voltage electric devices, requiring a supply voltage such as 48 volts with electrical power simultaneously within an automotive vehicle.

The present invention proposes a design of vehicle electrical system to address this issue, embodiments of which will be discussed.

With reference to Figure 1, an automotive vehicle electrical system includes a first electrical circuit 101 and a second electrical circuit 102. Each electrical circuit includes a power rail at different voltages which may be derived directly from a voltage generated by a mechanically driven generator 122, or by a voltage conversion from another system voltage. In this embodiment the first power supply 103 is a low voltage supply, which outputs electrical power at a low voltage level, such as 12 volts. The second power supply 104 is a high voltage supply, which outputs electrical power at a high voltage level, such as 48 volts. The first circuit 101 is therefore the low voltage circuit, whilst the second circuit 102 is the high voltage circuit.

Also included in the low voltage circuit 101 are a group of low voltage electrical devices 105 such as vehicle computers and instrument packs, that require a supply voltage equal to that output by the low voltage power supply 103 to operate.

Similarly, connected to the high voltage circuit 102 are a group of high voltage electrical devices 106 such as high current motors, which require a supply voltage equal to that output by the high voltage power supply 104 to operate.

Electrical power is fed into the low voltage power supply 103 and high voltage power supply 104 from a mechanically driven electrical generator 122, which may be a starter/generator motor operating in generator mode. This electrical power can charge power storage devices (not shown), such as batteries in the low voltage power supply 103 and/or and high voltage power supply 104. These power storage devices can be discharged at later time to satisfy a supply power demand shortfall.

Alternatively, the power can be routed directly through the power supplies themselves to satisfy an immediate supply power demand.

In this embodiment, the generator 122 generates electrical power at the high voltage level. Consequently a voltage conversion operation, using a suitable voltage supply conversion device 131, is performed to step down the voltage of the generated electrical power to the low voltage level prior to it being received by the low voltage power supply 103. Since the generator 122 generates electrical power at the high voltage level, this electrical power can be fed into the high voltage power supply 104 without the need for a voltage conversion operation.

The low voltage circuit 101 also contains a low voltage interface/control unit 109, which exchanges data between the low voltage devices 105 and the low voltage interface/control unit 109 via the low voltage data connection 111. The low voltage interface/control unit 109 receives power from the low voltage power supply Similarly the high voltage circuit 102 contains a high voltage interface/control unit, which exchanges data between the high voltage devices 106 and the high voltage interface/control unit via the high voltage data connection 112.

The high voltage interface/control unit 110 receives power from the high voltage power supply via the high voltage interface/control power/data connection 114.

Should the high voltage interface/control unit 110 require a supply voltage other than the output voltage from the high voltage power supply 104, a high voltage interface/control unit voltage conversion device 118, such as a Switched-Mode Power Supply Unit (SMPSU), may be used to ensure that that the second interface/control device 110 receives electrical power from the second power supply 104 with the correct voltage The behaviour of high voltage devices 106 in the high voltage circuit 102 may require synchronisation with devices in the low voltage circuit 101. To allow this, the low voltage interface/control device 109 and high voltage interface/control device 110 can intercommunicate with each other.

The low voltage data connection 111, and the high voltage data connection 112 may, although depicted as unitary connections, may in reality comprise a multiplicity of data connections. The signals transmitted may conform to various signal standards, such as the CAN signal standard.

The low voltage circuit 101 and high voltage circuit 102 are electrically isolated from one another. This isolation is performed by the inclusion of an isolation unit 120, which is interposed between the high voltage interface/control unit 109 and low voltage interface/control unit 110. The isolation unit 120 may include isolation components such as opto-isolators and/or other galvanic barriers. The supply voltage conversion device 131 also includes electrical isolation features. By virtue of the isolation features of the voltage conversion device 131, the mechanically driven generator 122 is electrically isolated from the low voltage circuit 101 despite the fact that the mechanically driven generator 122 supplies the low voltage circuit 101 with electrical power.

The mechanically driven electrical generator 122, , is directly connected to the high voltage interface/control 110 via the generator data connection 124 and can exchange data directly with this device. Due to the requirement for electrical isolation, it is not possible for the mechanically driven electrical generator 122 to be directly connected to the low voltage interface/control unit 109 as to do so would mean connecting a high voltage component to the low voltage circuit 109. Instead the mechanically driven generator 122 communicates with the low voltage interface/control unit indirectly via the high voltage interface/control unit 110, which is in communication with the low voltage interface/control unit 109 via the isolation unit 120. The isolation unit 120 permits communication between the two devices whilst also isolating the two devices from one another. The low voltage interface/control unit 109 can therefore communicate with the mechanically driven generator 122, whilst being electrically isolated from it.

Isolating the electrical system in this way also provides for an electrical safety method, which aims to reduce the risk of a person receiving a high voltage electric shock, should they touch a live, high voltage component in the vehicle. It is currently common practice for automotive electrical systems to use the vehicle body as an electrical ground. Instances may arise, when a person is exposed to live, electrical components within the vehicle, for example when performing maintenance.

Thus if a person touches a live, electrical component whilst simultaneously touching the vehicle body, the person will receive an electric shock. If the component touched by the person is supplied with 12 volt electrical power, the electric shock is unlikely to cause significant harm to the person. If the device is supplied with electrical power with a greater voltage, such as 48 volts, the electric shock is more likely to cause significant harm to the person. In an attempt to protect a person from receiving a high voltage electrical shock, the present invention proposes a new grounding strategy involving two electrical grounds. Accordingly, the low voltage circuit 101 includes a low voltage ground 107 and the high voltage electrical circuit 102 includes a high voltage ground 108.

According to this strategy, the low voltage ground 107 is, as in accordance with current practice, the vehicle body. The high voltage ground 108 is a conductive component integrated into the high voltage circuit 102. The two grounds are electrically isolated from each other. According to this strategy, if a person touches a live clement of the high voltage circuit 102 whilst simultaneously touching the vehicle body (i.e. . the low voltage ground 107), the person will not receive an electric shock. A person will only receive a high voltage electrical shock, it a person touches a live element of the high voltage circuit 102 whilst simultaneously touching the high voltage ground 108. . To reduce the risk of this situation occurring, it may be desirable to locate the component forming the high voltage ground 108 in a location that is not easily accessible by a person, even when performing maintenance to the vehicle.

Figure 2 shows selected aspects of an embodiment of the invention! the structure of which is similar to that of the invention shown in Figure 1. For reasons of clarity the complete system is not shown in Figure 2, with system elements such as the single mechanically driven generator 122, the supply voltage conversion unit 131, the low and high voltage grounds 107 and 108 and so on, still present in this embodiment of the invention but omitted from Figure 2.

With reference to Figure 2, electrical power and data respectively are passed to the to the low voltage interface/control unit 109 via connection 113 and 111.

In the embodiment of the invention shown in Figure 2, the low voltage interface/control unit 109 contains two sections, an interlace section 109a and a

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CAN controller section 1 09b. The interface section 1 09a receives power and data from the low voltage interface/control unit power conversion device 117. The CAN controller 109b exchanges data with low voltage devices 105 (not shown) via the low voltage data connection 111.

In this embodiment, the high voltage interface/control unit 110 also contains two sections, a first interface section 1 ba and a second interface section 11 0b. The first interface section 11 0a receives power from the high voltage power supply 104 and also passes data to the high voltage devices 106 via connection 112a. The second interface device 11 Ob exchanges data with the high voltage devices 106 via connection 11 2b. Connections 11 2a and 11 2b are analogous to the high voltage data connection 112 shown in Figure 1.

In this embodiment, the high voltage devices 106 are diagnostic and system support devices, which are integrated in the high voltage power supply 104. These devices monitor and control the behaviour of the high voltage power supply 104. To function, these high voltage devices 106 exchange data with some low voltage devices 105. There therefore exists the necessity for the transfer of data between the high voltage circuit 102 and the low voltage circuit 101.

To allow this data transfer, whilst still electrically isolating the two circuits from one another, the isolation unit 120, in this embodiment of the invention, includes opto-isolators 120a and a galvanic barrier 120b. The opto-isolators 120a transfer data between interface units 1 09a and 11 Oa via optical means, whilst still providing electrical isolation. Similarly, the galvanic barrier 120b allows for data transfer between the CAN controller 109b and the second interface unit liOb whilst still providing electrical isolation.

Although not shown in Figure 2, this embodiment also includes the grounding strategy shown in Figure 1 With reference now to Figure 3, the high voltage power supply 104 is explicitly described as a mechanically driven generator, and in particular, a 3-phase switched reluctance machine which is operable as an integrated starter/generator. Other numbers of phases and/or generator-only modes may be used instead. For reasons of clarity, some aspects of the complete system, such as the low and high voltage grounds 107 and 108, have been omitted. The generator will typically be mechanically coupled to the vehicle prime mover, such as by a belt drive taken from the crankshaft of an internal combustion engine mounted on the vehicle.

The high voltage interface/control unit 110 is connected to and controls the behaviour of a three-phase switched reluctance machine 302. The switched reluctance machine 302 can operate as either as an electric motor or as an electrical generator. The switched reluctance machine 302 comprises, three phase windings 304, a mechanical interface 306 and a mechanical shaft 308. The mechanical shaft 308 is connected to an engine crankshaft (not shown), typically via a belt drive. The phase windings 304 are connected to the high voltage power supply 104 via high voltage power connections 310.

When operating as a motor, the switched reluctance machine 302 draws electrical power from the high voltage power supply 104, typically using energy stored in a battery. Operating in this mode, the switched reluctance machine 302 outputs mechanical power to the engine crankshaft via the mechanical shaft 308.

Conversely, when operating as an electrical generator, the switched reluctance machine 302 supplies electrical power to the high voltage power supply 104 and also the low voltage power supply 103 (not shown). The engine crankshaft supplies the switched reluctance machine 302 with mechanical power via the mechanical shaft 308. Electrical power is typically generated directly at the high voltage level, although dc-dc step up or down features may be included with power generated directly at the low or an intermediate voltage. When operating in generator mode, the switched reluctance machine 302 becomes the mechanically driven generator 122 of Figure 1.

The switched reluctance machine 302 includes three phase windings 304. The current in each phase winding is controlled by a set of field effect transistors (FET5), to give a total, typically, of twenty-four FET5 (not shown). The switching of the FETs controls the behaviour of the switched reluctance machine 302 and the switching of the FET5 is controlled by the high voltage interface/control unit 110.

The switched reluctance machine 302 exchanges data with an engine control unit (ECU) (not shown) or other vehicle processor in order to function efficiently. The ECU is low voltage device, which is part of the low voltage circuit 101. The switched reluctance machine 302, is a high voltage device and is part of the high voltage circuit 102. There therefore exists for the requirement for the exchange of data between the low voltage circuit 101 and the high voltage circuit 102.

The isolation unit 120 shown in Figure 2, will now be described in more detail. In the embodiment of the invention shown in Figure 3, the isolation unit 120 includes two opto-isolators and a galvanic barrier. The design of the isolation unit 120 and the positioning of this element within the system have been deliberately selected to reduce the physical size and cost of the overall system.

In this embodiment, the two opto-isolators and the galvanic barrier are used to form a bridge between the low voltage interface/control unit 109 and the high voltage interface/control unit 110. The high voltage interface control unit 110 is then connected to 24 FET5 in the phase windings 304 via 24 individual wired connections. This construction is compact and cheap to implement. The electrical isolation therefore occurs between the low voltage interface/control unit 109 and the high voltage interface/control unit 110 and uses a small number of communication channels (each of which requires electrical isolation).

An alternative solution would be to use a single interface/control unit to perform the functions of both the low voltage interface/control unit 109 and the high voltage interface/control unit 110 and to instead, interpose an isolation unit between the single control unit and the phase windings 304. The single interface/control unit could then communicate with the FET5 using opto-isolators located in the isolation unit. Since each of the 24 FET5 would require its own opto-isolator, this solution would require the use of 24 opto-isolators. This solution would therefore be less compact and more expensive to implement.

Data signals from the low voltage devices 105 are collected by the low voltage devices mechanical/electrical connector 301, before being passed to the low voltage interface/control unit 109. The low voltage connector 301 is also connected to the low voltage power supply 103.

To maintain electrical isolation, isolating grommets 314 made from electrically insulative material are placed around the conductors forming the motor/generator high voltage power connections 310 on the outside of the motor/generator case3o3.

This allows the motor/generator case 303 to be fixed to the vehicle engine/body using conventional, electrically conductive fixings.

Although not shown in Figure 3, this embodiment of the invention also includes the grounding strategy shown in Figure 1, whereby the low voltage ground 107 is the vehicle body and the high voltage ground 108 is one of the insulated terminals 314 and which is isolated from the vehicle body.

In the embodiments discussed thus far, it has been suggested that the low voltage power supply 103 should provide electrical power with a voltage of 12 or 24 volts and the high voltage power supply 104 should provide electrical power with a voltage of 48 volts. Whilst such voltages may satisfy current industry trends, a different combination of low voltage and high voltage values may be more suitable in the future. Accordingly the invention is not to be considered as being limited to applications in which 12 or 24 volts and 48 volts are used as the low and high voltage levels but instead the invention is to be considered to include all combinations of voltages.

By describing the invention through the use of the embodiments depicted in Figures 1 to 3, it is not intended that the scope of the invention be limited only to the embodiments hereby discussed. By describing the invention using multiple embodiments, it is intended to demonstrate that the invention can be implemented in different scenarios, be constructed of different constituent pads and be used in conjunction with a wide variety of high voltage and low voltage devices, without deviating from the invention.

Claims

Claims 1. A vehicle electrical system comprising first and second electrical circuits; wherein the first electrical circuit includes a first electrical ground and requires electrical power at a first voltage level; wherein the second electrical circuit includes a second electrical ground and requires electrical power at a second voltage level; wherein the first and second electrical grounds are electrically isolated from one another; and wherein the first voltage level is lower than the second voltage level; the first and second electrical circuits being further arranged to send and receive control and/or other data signals between each other whilst still maintaining electrical isolation between the first and second electrical grounds; the vehicle electrical system further comprising a mechanically driveable switched reluctance generator mechanically coupled to the vehicle prime mover; the generator being arranged to provide the first and second electrical circuits with electrical power simultaneously.
2. A vehicle electrical system according to Claim 1 in which the first electrical ground is the vehicle body and the second electrical ground is a terminal insulated from the casing of the mechanically driveable generator.
3. A vehicle electrical system according to any preceding claim, in which the generator is arranged to generate electrical power directly at the second voltage level and in which the generator receives control and/or other data signals from the first electrical circuit.
4. A vehicle electrical system according to any preceding claim in which the electrical generator generates electrical power at the second voltage level and the second electrical circuit includes multiple switching elements, control of which is provided by logical control devices included in the first electrical circuit and operating at the first voltage level.
5. A vehicle electrical system according to claim 4 wherein the first and second electrical circuits include respective low voltage interface/control and high voltage interface/control units for controlling switching of the generator phases wherein the interface/control units include multiplex and de-multiplex functions so that the electrically isolated communication between them requires less electrical channels than the number of phase switching devices in the generator.
6. A method for simultaneously providing first and second electrical circuits with electrical power using a single mechanically drivable electrical generator; wherein the first electrical circuit includes a first electrical ground and requires electrical power at a first voltage level; and the second electrical circuit includes a second electrical ground and requires electrical power at a second voltage level; and wherein the first voltage level is lower than the second voltage level; the first and second electrical circuits being further arranged to send and receive control and/or other data signals between each other; the method involving generating electrical power directly at the second voltage level using a switched reluctance machine having logic phase switching controls operating at the first voltage level; the method further involving performing a voltage conversion operation to step down the generated electrical power to the first voltage level; the method further involving electrically isolating the two electrical grounds.
7. The method according to Claim 6 involving providing the electrical generator with control and/or other control signals from the first electrical circuit.
8. The method according to Claim 6 or 7 involving controlling multiple switching elements in the second electrical circuit using logical control devices in the first electrical circuit.
9. The method according to claim 8, wherein the number of channels communicating switching data from the logical control devices to the generator is less than the number of phase switching devices in the generator.
10. A vehicle including a vehicle electrical system comprising first and second electrical circuits; wherein the first electrical circuit includes a first electrical ground and requires electrical power at a first voltage level; wherein the second electrical circuit includes a second electrical ground and requires electrical power at a second voltage level; wherein the first and second electrical grounds are electrically isolated from one another; and wherein the first voltage level is lower than the second voltage level; the first and second electrical circuits being further arranged to send and receive control and/or other data signals between each other whilst still maintaining electrical isolation between the first and second electrical grounds; and the vehicle electrical system further comprising a mechanically driveable switched reluctance electrical generator mechanically coupled to the vehicle prime mover; the generator arranged to provide the first and second electrical circuits with electrical power simultaneously, and the switching logic for the generator being arranged to operate at the first voltage level.
11. A vehicle according to Claim 10 in which the first electrical ground is the vehicle body and the second electrical ground is an insulated terminal on the casing of the mechanically driven generator.
12. A vehicle electrical system substantially as hereinbefore described and with reference to the accompanying figures.
13. A method for simultaneously providing first and second electrical circuits with electrical power using a single mechanically driven electrical generator substantially as hereinbefore described and with reference to the accompanying figures.
14. A vehicle including the vehicle electrical system substantially as hereinbefore described and with reference to the accompanying figures.