GB2539863A - Active current protection and monitoring device (ACPMD) - Google Patents

Abstract

A circuit protection device which actively monitors and protects an electronic circuit from excess current, voltage transients and electromagnetic interference. The device comprises a high side current sensor, a high side load switch, processing means for monitoring and controlling operation of the device, means for recording, storing and communicating data relating to the operation of the device and the circuit in which it is installed, and means for generating or harvesting electric power to operate the device using only the power supply in the single positive wire which is being protected. The electric power may be harvested via a piezoelectric device, or may be induced. Data communication may be via radio transceiver, or via communication over the power line itself. The load switch preferably utilises MOSFETs. The device may be provided in different specific outlined shapes in order to directly replace standard passive over current protection devices, e.g. Automotive and Domestic Fuses.

Description

Active Circuit Protection and Current Monitoring Device (ACPCMD)

This invention relates to a device that allows the current passing through it to be monitored analysed, recorded and/or transmitted, whilst providing settable active circuit protection.

It is known that the current in a circuit can be measured in Amperes, using an instrument such as an ammeter and the product of current with time can be measured using apparatus such as an Ampere-hour meter. If the voltage in the circuit is at a relatively constant level then an ampere-hour meter can be calibrated as an energy or kilowatt-hour meter.

Such a meter is in all properties connected to an electricity supply to provide a reading of the supply of electricity to the property. The primary advancements made to these meters have been the addition of communications to make readings from the meter without having to inspect the meter, this could be over a wireless radio or through the power lines themselves. This has allowed the real time energy consumption of the property to be monitored within the range of the communications, typically 10 metres of the meter by both the supplier and the user. An external device with a built in microprocessor or computer can be used to store and average energy consumption and an estimated cost when compared to pre-configured or entered energy prices, along with displaying the reading in real-time.

However there are still problems with these devices, they are relatively large and statie devices and only provide an overall view of the energy consumed, at the point of entry for the electricity supply. They also rely on the communications for measurement whieh means that the readings are only made when an external device is in range and/or able to communicate with the meter. A primary problem is powering this additional equipment either through batteries or through the supply itself, which over time becomes counterproductive in trying to reduce costs and improve efficiency, especially if constantly transmitting and receiving date. This is without the hidden costs involved in installation, calibration and maintenance.

Some meters have become available that provide a more targeted approach in order to isolate a specific piece of equipment or electrical appliance, such as meters that plug in between the domestic plug socket and the plug of the deviee being monitored. Although this can allow a specific device to be measured the other problems highlighted above still apply, with the significant ones remaining of size, communications, installation, calibration and maintenance. The majority of these meters measure in Amperes and/or kilowatt-hours only, which can be too large a scale to sufficiently measure with the accuracy desired for most individual pieces of equipment. The problems highlighted with a plug-in device of this nature make it unworkable in the majority of applications and furthermore, impractical to implement a networked energy measurement solution.

Along-side the meters at the point of supply of electricity to the property, usually immediately after the meter in the power line, is a form of circuit protection protecting the individual circuits wired around the property. In modern properties this is usually in the form of a consumer unit containing a series of circuit breakers to protect against factory calibrated over-current conditions. This has replaced the fuse box and fuse wiring boards previously used in older properties. With improved safety, in particular with regards to fire from the arcing that occurs in fuse wire and the added benefit of being easily reset on a fault.

Further, domestic fuses are usually cylindrical fuses, that are commonly found in the equipment and appliances themselves. In the majority of cases and in particular in the United Kingdom these are found within the plug itself.

Similar meters and passive circuit protection devices are used in all vehicles and transport, including motor vehicles, trucks, air planes, buses, boats, tractors, diggers, trailers, caravans etc., both in the propulsion of the vehicle and the equipment in and on board the vehicle. The most common circuit protection device used in vehicles is the fuse, which has been formed over the years into standard packages, in order to allow ease of use and replacement within vehicles. The blade fuse is the most commonly used within both commercial and military vehicles, internationally.

Although the circuits in vehicles are Direct Current (DC) based systems in contrast to Alternating current (AC) systems found in properties, there is little difference in the characteristics of a vehicle and a domestic fuse and both have the same problems of use.

All forms of current protection presently available are passive and rely on the physical attributes of the component, whether one of the numerous varieties of fuses available, a circuit breaker or PTC (Positive Temperature Coefficient) thermistor devices more commonly found inside sensitive equipment, for instance computers.

The physical property that all these protection devices utilise to measure the current flowing and prevent excess flow is temperature, more specifically the temperature coefficient. This means that they are closely linked to the temperature coefficient for operation and therefore they are both limited in their control and accuracy, in particular with varying ambient temperatures.

These passive circuit protection devices, in particular fuses, require careful matching to the current required by the equipment and are often over rated. The current rating of a fuse can typically be de-rated by 25% for operation under “normal test” conditions of 25°C to avoid nuisance blowing. For instance a blade fuse with a current rating a lOA is not usually recommended for operation at more than 7.5A in an ambient operating temperature of 25°C.

Further a fuse’s time-current characteristics determine how fast a fuse responds to different overcurrent conditions. All fuses have inverse time-current characteristics, so opening times decreases as overcurrent increases.

Under any operating conditions, a standard fuse will never open before it has passed 110% of its rating. Even at 135% of its rating a fuse can take between 350 milliseconds to 600 seconds (10 minutes) before opening. At 200% or doubling the rated value, for instance 20 Amps in a 10 Amp rated fuse, a fuse can take between a 100 milliseconds to 5 seconds to open.

This becomes more critical the higher the current rating, where there is a great amount of energy involved, for example; a 40 amp rated fuse will take 1 second to open when 110 Amps is flowing through the circuit, alternatively in a 60 Amp fuse it could take 10 second to open with the same current flowing.

These variances are presently tolerated commercially in vehicles (partly as the majority of high powered equipment such as air conditioning and heaters can cope with these higher currents) and are often overlooked or relatively unknown. However this is rapidly changing with more high powered equipment being incorporated into vehicles in particular with the introduction of hybrid and electric vehicles.

As vehicles and the equipment incorporated in them become more sophisticated they also become more sensitive to excess currents and voltage transients.

Even at lower currents where the majority of sensitive equipment is currently found; a 1 Amp rated fuse will allow 2 Amps to flow for 1 Second or 4 Amps for 100ms before the fuse opens.

When the circuitry being protected requires operation within a wide operation temperature range, this matching becomes even more difficult or even impossible in some instances and significantly undermines the initial requirement of the passive protection device.

The current carrying capacity tests of fuses are performed at 25°C and will be affected by changes in ambient temperature. At higher ambient temperatures, a fuse will respond faster to a given overload. Conversely, at lower ambient temperatures, a fuse will respond slower to a given overload. In addition, the temperature of the fuse increases as the normal operating current approaches or exceeds the rating of the fuse. A blade fuse operating at 25”C and 110% of rated current has an estimated life of 100 hours. However, if that same fuse was operating at a very high ambient temperature, for example near an engine, re-rating would be necessary.

This highlights that the ‘simple’ process of protecting equipment from excess current using a fuse is not as simple as it first appears and is reliant on a number of physical properties. As highlighted previously the selection of the fuse rating is not as straight forward as one might expect and often implemented through a trial and error process, leading to far greater risks than intended or expected from a correctly rated fuse.

During emergency repairs of a frequently opening fuse or ‘Nuisance blowing’, the engineer or person servicing the fuse may unassumingly replace the fuse with the larger value. This could result in the loss of adequate protection and catastrophic damage to the vehicle or vehicles equipment.

For instance a piece of equipment protected by a 5 Amp fuse which keeps opening, requires replacement each time under normal conditions. If this is replaced with the next available size fuse, a 7.5A fuse then the excess current allowed to flow has increased from 8A / second to 13.5A / second.

Fast acting or slow blow fuses are often used to overcome this scenario, however they are impractical and not common practice in automotive applications, largely due to the vehicle environment and voltage transients.

The voltage transients on a vehicle power supply have an extreme range, from the severe - high energy transients generated by the alternator /regulator systems to the low-level ‘noise’ generated by the ignition system, equipment and various accessories. Electrical pulses produce thermal cycling and mechanical fatigue that affects the life of passive circuit protection such as a fuse.

The severest transients result from either a Load dump condition or a jump start over voltage condition. Other transients may also result from circuit breakers, relays and solenoids switching on and off, and from fuses opening. With the extensive use of more and more electronic modules and equipment being utilised in vehicles, the need for protection from transients has never been more essential to ensure reliable operation.

The load dump over voltage is the most formidable transient encountered in the automotive environment. It is an exponentially decaying positive voltage, which occurs in the event of a battery disconnect while the alternator is still generating charging current, with other loads remaining on the alternator circuit at the time of battery disconnect. The load dump amplitude depends on the alternator speed and the level of the alternator field excitation of the moment of battery disconnection. A load dump may result from a battery disconnect resulting from cable corrosion, poor connection or an international battery disconnect while the car is still running.

The jump start transient results from the temporary application of an overvoltage in excess of the rated battery voltage. The circuit power supply may be subjected to a temporary over-voltage condition due to the voltage regulator falling or it may be deliberately generated when it becomes necessary to boost start the car. Unfortunately, under such an application, the majority of repair vehicles use a 24V “battery” to jump start the car. Automotive specifications for call out services, state the extreme condition of jump starting, should be applied to up to 5 minutes, if necessary.

As more equipment is used on vehicles more than one vehicle battery can be used, thereby doubling the voltage used in some instances to 48V DC. This increases problems in circuit operation and protection, requiring specialist battery protection units to be developed.

Further to this, bright light emitting diodes (LEDs) for lighting and head lamps have been introduced on new vehicles, which are designed for higher voltage operation to reduce current and typically operate at 56V DC, placing further strain on vehicle circuit protection.

There have been many developments within the automotive industry and vehicles, which will increase and accelerate progress further in the future. In particular with the emphasis being placed on efficiency and low carbon vehicles, with international and European targets being introduced to reduce emissions and reliance on fossil fuels.

With more and more alternative power sources available in vehicles such as hybrid hydrogen, hybrid electric vehicles (HEV) and fully electric vehicles (EV); vehicle power systems and their protection are becoming more and more complex and are required to handle higher power levels, with higher voltages and larger currents; for instance electric vehicles can incorporate motors which typically operate at 370V DC and can be charged as high as 750V DC.

The strain this places on the physical properties or passive circuit protection devices is becoming very great and to the point where they are struggling to remain effective. The result is that this method of circuit protection can only increase in size and weight, which becomes counterproductive as it is clear that weight reduction is key to efficiency and optimisation of vehicles.

With this added complexity comes more complex management, control and protection systems, for instance battery management, engine control units and power nodes. These can be multiple large units within a vehicle that can add several kilograms in weight, which can be further difficult to distribute over the vehicle due to the size and shapes of these systems and devices. This is aside from the increase in cabling and interconnectivity required.

It can prove difficult to gain access to a circuit within a vehicle or property in order to attach a meter, in particular without altering the circuit with additional equipment or removal of equipment. It can be normal practice that a qualified person may use the circuit protection device such as a fuse in order to gain access to the circuit. When the fuse is removed the power line of the circuit is broken and thereby allows a meter such as an ammeter to be placed in line with the circuit.

Various adaptors and in fact some hand held meters have been adapted to safely allow a meter to be inserted into a fuse socket in particular an automotive fuse and allow the meter to be in line with the circuit as well. However these can only be used for troubleshooting offline and not in real time and with multiple circuits as once, which is often required. It further does not address the inherent problems of the fuse or allow access under all conditions of operation.

It is the object of the present invention to provide improvement on such systems, along with enhancements over the passive circuit protection and also to mitigate against some of the above mentioned problems and difficulties experienced.

This invention is not reliant on the temperature coefficient, as in passive circuit protection. Instead it actively monitors the current flowing through a known resistance in line with the circuit, therefore limiting the effects of temperature and the temperature coefficient.

As this invention is an active control system, it will be possible to compensate or adjust the levels of current to profile the protection response to various conditions in the system, load and environment, including the ambient and/or system temperature. Whilst further providing protection against reverse currents / polarity issues, surges and voltage transients in the power supply.

This invention’s active circuit protection approach allows controlled and repeatable protection against excess current whilst providing additional protection against voltage transients and electromagnetic interferences and allowing the current passing through the device to be accurately monitored, stored, recorded and transmitted.

The aim of the invention is to be directly interchangeable with a standard passive fuse device, whilst providing a more sophistieated intelligent switching function: With the capability of autonomously and accurately responding to over current events to milliampere accuracy and within milliseconds, in contract to Amperes and hundreds of milliseconds to minutes. The device independently measures the current passing through, in order to gather vital information as to the eurrent and/or energy consumed in the circuit being protected.

This invention incorporates the functions of a meter or ammeter as described above with the intelligence of the external recording device and communication options, along with an electronic based switching system that protects against excess current and voltage transients, within a discrete self contained package. The ability this invention has, in directly replacing standards fuse devices, brings with it, design restrictions on the invention. For instance it immediately limits the allowable or feasible sizes and shapes of the invention. As an example, to replace the most common blade fuse found in vehicles, the invention must have outline dimensions that conform to the Society of Automotive Engineering (AES) standard J1284.

To be a true direct replacement it further means that there is only a single wire connection to the device; the positive power line eonnection being protected, switehed and monitored. Therefore the only connections to the invention is a positive power line into the device and one out of the device.

There are five main functional parts to the invention as illustrated in the block diagram at Figure. 1, with the additional sixth function being the communication transceivers.

The First function is the Single Wire energy Generator, this is to provide the power to the inventions circuitry and isolate it from the power line itself.

Due to the size constraints it is not practical to add power storage devices such as batteries or ultra-capacitors to the invention. This approach could potentially undermine the concept of the invention, as it is key that it does not add any unnecessary parts in particular consumable or serviced parts. It would further not be possible to charge such components from the power line supplied to a fuse as there is only a positive line with no ground or return path.

As there is only the single positive power ne it is also not feasible to simply regulate power from this power source, without a connection to ground or the systems power return line. Any extra connections made would also undermine the advantage of this invention, in directly replacing the fuse.

In order to overcome this, a proprietary method of generating energy from the positive rail has been implemented in this invention, based on energy harvesting techniques, such as using an element or component as a source of power. This could be a piezoelectric element that harvests energy from the heat generated in the power line and or system, and/or the vibrations and movements in the system in order to generate a current.

It could also be through an inductive element such as a coil, inductor, transformer or isolated track mnning in close proximity to the power line, in order to induce energy. Energy may also be harvested from the voltage drop across a component, such as a MOSFET or diode.

The energy harvested is then inverted which allows the creation of a virtual earth or ground.

This provides an isolated power source for the inventions circuitry that is referenced to the positive power line.

Sufficient power is generated in order to power an ultra low power micro-controller with sufficient features such as internal memory and interfaces to store, record and transmit the data. The communications transceivers could be internal to the micro-controller or as separate functions interfaced to the embedded micro-controller.

This invention can use either communication over the positive power line connected to the device, or through a radio transceiver, such as low power radio, for instance on the unlicensed sub-lGhz bands for Short Range devices or 2.4Ghz bands. This can then interoperate with the unlicensed frequency bands commonly used for external networks and home automation. This would further allow interaction and automation between devices, along with humans and devices.

This invention can allow remote control and switching of equipment as well as monitoring. A preferred method of communications in a majority of applications, may be to communicate over the single power line itself, in particular where radio communications are not suitable, such as safety and mission ciritical applications. This would still allow the devices in the circuit to communicate, although may require an adaptor or terminal transceiver.

The High Side Current Sensor of the invention, as shown in Figure 1, provides the measuring of the current through the invention, the equivalent of the ammeter of meter function described.

The measurement and reading are sent to the micro-controller which can then process the data, either through direct analysis, recording or transmitting of the data; in some instances this maybe carried out by the use of a processor or using Direct Memory Access (DMA) techniques.

There are a number of ways that these measurements can be made. The two main ways that apply to this invention are a hall-effect sensing device and a resistive/micro-power difference amplifier combination. At present the Hall-effect sensor is more challenging to implement due to the size of the devices, the sensors power requirements and the potential susceptibility to the affects of electromagnetism and interference.

The High Side Load Switch function in Figure 1. uses the latest developments in MOSFET or similar technology as part of a complex circuit that controls the forward voltage drop across the MOSFET to provide smoothed current delivery to the load. It is therefore immune from oscillation with light loads and has a fast turn off time in the event of reverse current transients and reverse input voltage.

The enhanced High Side Load switch in this invention, acts independently of the microprocessor allowing turn on detection, energy harvesting and switching and turning off times that are 300 nanoseconds or faster, to ‘instantly’ respond to a fault if required and provide a significant improvement on passive based circuit protection as previously described.

The control of the MOSFET technology in the High Side Load Switch has been configured to withstand high negative voltages without damage and continue to operate through severe voltage transients such as load dumping, cold cranking (starting) cycles and Jump starting (two-battery jumps). Whilst also protecting the load or vehicle equipment attached from these voltage transients.

Through the implementation of two back to back MOSEETs, this invention allows power flow control in the forward direction whilst retaining an ideal-diode behaviour in the reverse direction and without the penalty of a changeable high forward voltage drop as experienced with a standard Schottky diode.

This invention mitigates against voltage transients and reverse currents, which are a significant disadvantage in the passive circuit protection as described previously.

This invention contains all the required components to provide an Active Circuit Protection and Current Monitoring Device.

The embodiments of this invention will now be described, by way of example only, with references to the accompanying drawings.

The circuitry of this invention can be delivered using standard manufacturing processes. One such method can be seen in Figure 2 using discrete components surface mounted on a substrate or Printed Circuit Board (PCB) which is formed in the shape of the fuse outline as seen in the example in Figure 2.

This invention can be sealed through various methods, for instance using potting compound with a containing structure such as a plastic enclosure, that maybe treated or coated to enhance difference electrical properties such as enhanced electromagnetic conformance properties or a metal can structure. It is also possible to seal the potting compound using vacuum forming techniques.

Other methods of sealing the invention could involve resins similar to potting compound that do not require a containing structure and form a blob shaped mound covering the circuitry.

The terminals of the invention are formed to replace the terminals of the fuse or passive protection device, these can be pads formed on the PCB or substrate. Allowing the devices backplane or mounting surface to be in one piece.

Alternatively there could be terminal connections mounted into or into the substrate/PCB, although this would be likely to hinder the performance of the invention, in particular with regard to its strength and integrity.

At present the inventions circuitry is implemented through discrete components on a substrate or layered PCB construction. However it is envisaged that as the invention develops and is adopted this circuitry can be embodied within a single silicon device with two terminals embodied in the device as illustrated in Figure 3.

There will also be many construction possibilities in between these two methods, for instance the invention can be delivered as a hybrid component mounted on the board, incorporating key aspects or all the circuitry of the invention within a single die of silicon as a surface mount component.

Other methods of mounting the circuitry are also feasible, such as etching the circuit onto a substrate formed, moulded or printed using 3D printing technology into the shape of the passive circuit protection being replaced.

Figures 4, 5, 6, 7 and 8 illustrate some of the passive element shapes and forms that this invention will adopt and replace. The first four Figures 4,5,6,7 are examples of the outline and packaging of fuses and Figure 8 shows an outline of a circuit breaker. All of which are intended to be replaceable by this invention.

Claims (31)

Active Circuit Protecoon and Current Monitoring Device (ACPCMD) Claims

1. A circuit protection device ("ACPCMD") which actively monitors and protects an electric circuit from over-current events comprising: • a high-side current sensor; • a high-side load - switch; • processing means configured to monitor and control the operation of the ACPCMD; • means for recording, storing and communicating data relating to the operation of the ACPCMD and of the circuit in which it is installed characterised in that to drive its own circuit load the ACPCMD is equipped with means of generating or harvesting electric power using only the power supply in the single positive wire that is being protected.

2. An ACPCMD according to any preceding claim providing a means whereby the voltage component of the electric power acquired or harvested may be inverted and increased by a factor of at least 2 times so as to create a virtual earth for the isolated single line power supply to the ACPCMD.

3. An ACPCMD according to any preceding claim wherein the single wire energy/power generator provides all the power required to drive the ACPCMD circuitry.

4. An ACPCMD according to any preceding claim wherein the isolated power generated is referenced to the single positive power line into and out of the ACPCMD.

5. An ACPCMD according to any preceding claim in which the ACPCMD circuitry is isolated from the single positive power line being protected.

6. An ACPCMD according to any preceding claim equipped with a means of regulating the voltage derived from the single wire power supply by means of a voltage regulator circuit.

7. An ACPCMD according to any preceding claim wherein the single wire electric power supply harvests energy from a known voltage drop.

8. An ACPCMD according to any of the preceding claims wherein the single wire electric power supply harvests energy through an inductive element located proximately to the protected power line.

9. An ACPCMD according to any preceding claim wherein the single wire electric power supply harvests power by means of the Peltier effect in an element using heat generated from the power line and adjacent system.

10. An ACPCMD according to any preceding claim wherein the single wire electric power supply harvests power by means of the piezoelectric effect in an element using energy generated from vibrations and movements in the system.

11. An ACPCMD according to claim 1 wherein a preferred method of detecting the current flow in the high side current sensing circuit is by measuring the potential across a resistor.

12. An ACPCMD according to claim 11 wherein an alternative method of detecting current flow in the high side current sensing circuit is by means of a Hall-effect sensing device.

13. An ACPCMD according to any preceding claim wherein the high side load switch is in an open circuit or off state by default and is switched closed to operate.

14. An ACPCMD according to any preceding claim wherein the high side load switch provides power flow control in the forward direction whilst retaining an ideal-diode behaviour in the reverse direction.

15. An ACPCMD according to any preceding claim wherein the high side load switch provides power flow control through back to back metal-oxide-silicon field-effect transistors, behaving as an ideal diode.

16. An ACPCMD according to any preceding claim wherein the power flow control allows automated reset functions whilst ensuring continuing power flow sufficient to detect any fault or over current event that may still be present providing that in such a case the switch remains open circuit.

17. An ACPCMD according to any preceding claim having a low power microprocessor configured to enable a user to vary the operating parameters of the device including (but without limitation): • the over-current threshold level • the profile of the device's response to an over-current event, for example (but without limitation); ♦ the speed of response to an over-current event ♦ the number of times the CPD automatically resets after a trip

18. An ACPCMD according to any preceding claim equipped with means for recording and storing data relating to the operation of the ACPCMD circuitry or surrounding environment.

19. An ACPCMD according to any preceding claim equipped with means of communicating to an external receiver any data generated, recorded or stored by the device.

20. An ACPCMD according to any preceding claim protecting a direct current circuit wherein a bleed circuit is added in parallel with the high side switch in order to allow the continuous operation of the single positive wire power generator whilst the high side switch is open circuit and a load is applied.

21. An ACPCMD according to claim 20 wherein the bleed circuit is created using a small load power resistor.

22. An ACPCMD according to claim 20 and 21 wherein the efficiency and operation of the bleed circuit is improved using a depletion mode metal-oxide-silicon field-effect transistor circuit.

23. An ACPCMD according to any preceding claim wherein a secondary voltage generating circuit is implemented in place of a Bleed circuit, to allow operation whilst the high side switch is in an open circuit state.

24. An ACPCMD according to claim 13 where the High Side switch consists of a bi-directional gate-controlled thyristor for full wave control of Alternating Current power or dual back to back silicon controlled rectifiers, instead of Back to Back Metal-oxide-silicon field-effect transistors.

25. An ACPCMD according to any preceding claim protecting an alternating current circuit wherein the power regulation circuits provide a regulated and isolated Direct Current power supply to the ACPCMD.

26. An ACPCMD according to claim 17 and 19 with means to add additional application specific sensors, transducers or other devices to measure particular properties.

27. An ACPCMD according to any preceding claim wherein any communication transceiver communicates over the single positive power line that is the only operational input and output of the ACPCMD.

28. An ACPCMD according to any preceding claim wherein any communications transceivers and related circuitry are equipped to permit the configuration control and operation, of the ACPCMD by a user operating.

29. An ACPCMD according to any preceding claim wherein two communication transceivers are implemented to allow communications in both directions through the input end output of the ACPCMD, even when the high side switch is open circuit, for instance with one transceiver on the input and one on the output.

30. An ACPCMD according to any preceding claim wherein any communication transceiver is a Radio Frequency (RF) transceiver.

31. An ACPCMD according to any of claims 28,29,30 and 31 wherein the data may be accessed by means of a terminal interface, network or adaptor.