DESCRIPTION

Technical field

The present invention is developed in the field of wireless recharging of electric or hybrid vehicles, while they are moving along a road path, by means of the technology called Dynamic Wireless Power Transfer (D-WPT), in accordance with the preamble of claim 1.

Background art

Electric vehicles notoriously run into autonomy issues, which are linked to the weight and to the cost of the batteries needed to drive the vehicle, and also to the prolonged time needed to recharge said batteries.

Dynamic wireless power transfer systems to be installed along a road path are known in the art. They allow to power the batteries of a vehicle while the vehicle is in motion, so that the batteries are recharged or do not get discharged, or in any case get discharged more slowly than in a travel on a traditional road path. This can clearly resolve or strongly mitigate the aforementioned autonomy issues.

The supply of the vehicle in motion, also with reference to the appended Figures 1 and 2 in which a system in accordance with the state of the art is shown, is based on transmission coils 2 embedded in the surface of the road path 100, and receiver coils installed on board the vehicle 200. The transmission coils are powered when a vehicle passes over them, and generate a suitable high-frequency electromagnetic field, established by current regulations equal to 85 kHz.

While the vehicle is moving forward, the receiver coils are temporarily inductively coupled to the transmission coils. The receiver coils are then powered by the electromagnetic field and transfer electric power to the batteries of the vehicle, after appropriate conversions inside the vehicle.

The known systems, illustrated schematically in Figures 1 and 2, comprise a plurality of management units 3 for controlling and powering the transmission coils 2. Each management unit 3 comprises a delivery point 33 for of a low-voltage alternating-current distribution network, typically the three-phase 400 V industrial distribution network, powered by an electrical substation 400.

Each management unit 3 further comprises a rectifier 34, for converting the power drawn from the distribution network into direct current, and a plurality of inverters 32. Each inverter 32 is powered by the direct current inside the management unit 3, and is connected to a single transmission coil 2, which supplies high-frequency alternating current at the appropriate time.

Since the high-frequency electric power transport is inefficient over long distances, a single management unit 3 is used to power transmission coils 2 with a maximum distance of about 50 m in both directions of the road path 100. Therefore, a management unit is required every 100 m approximately of the road path 100.

Other known examples of dynamic wireless power transfer system are described in the paper “charging infrastructure design for in-motion WPT based or sensorless vehicle detection system” (DOI 10.1109/WOW45936.2019.9030646), and in CN 103779971 and US 2013214591.

Problems of the prior art

The known wireless systems have so far made it possible to realize the dynamic power transfer only on experimental paths of short length, not more than 2 km. The cost for powering these systems is particularly significant, given that numerous delivery points from the industrial network must be available, i.e. one every 100 m of the path.

Each delivery point in fact needs to occupy a certain area of land along the road with electrical infrastructures. In addition to the cost of these works, the high number of close delivery points entails a high environmental impact and difficulty in having all the necessary space available along the path.

Also the systems in the paper “charging infrastructure design for in-motion WPT based or sensorless vehicle detection system” and of the documents CN 103779971 and US 2013214591 envisage supplies that involve problems of costs and occupied space.

Summary of the invention

The aim of the present invention is to provide a dynamic wireless power transfer system that solves the mentioned drawbacks of the prior art.

In particular, aim of the invention is to increase efficiency, reduce costs, and reduce the occupied surface of the dynamic wireless power transfer systems.

The aim of the invention is also to make economically sustainable the realization of dynamic wireless power transfer systems on road paths with significant lengths, for example interurban lengths of tens or hundreds of kilometres.

These and other aims are achieved by a dynamic wireless power transfer system according to any one of the appended claims.

The invention envisages providing conversion substations to be connected to a medium voltage alternating current distribution network. In the conversion substations, the electric power is converted centrally into direct current, in low voltage, and is distributed downstream of this conversion among the management units. The management units in turn no longer need their own delivery points or rectifiers, but their inverters are powered directly by the direct current distribution network.

The centralization of the electric power straightening increases efficiency and reduces the costs of the management units. In addition, thanks to the medium voltage connection, the number of delivery points from the alternating current distribution electricity network is drastically reduced.

The central conversion also makes the voltage more stable, both on the alternating current network and on the internal direct current network, and improves the quality of the power absorbed.

Thanks to the direct current distribution downstream of the conversion substations, the power of the individual transmission coils can be increased. With the same density of coils in the road surface, this increases the autonomy benefits of the batteries of the vehicle on the path since one can have greater power or, with the same power transmitted per coil, reduce the number of receiver coils installed on board the vehicles themselves. For example, a freight vehicle with a tractor and trailer can travel substantially without reducing the state of charge of the batteries, and this effect is achievable by installing receiver coils on the tractor alone, without the need to install additional coils on the trailer.

Further features and advantages of the invention will be recognisable by a person skilled in the art from the following detailed description of exemplary embodiments of the invention.

Brief Description of the Figures

For a better understanding of the following detailed description, some embodiments of the invention are illustrated in the accompanying drawings, wherein: - Figures 1 and 2 schematically show some details of a dynamic wireless power transfer system, according to the prior art,

- Figure 3 schematically shows a part of a dynamic wireless power transfer system according to an embodiment of the invention,

- Figure 4 schematically shows some details of the system of Figure 3,

- Figure 5 schematically shows some details of a conversion substation of the system of Figure 3,

- Figures 6 and 7 schematically show other exemplary embodiments of dynamic wireless power transfer systems.

DETAILED DESCRIPTION

A dynamic wireless power transfer system, denoted by numeral 1, which extends along a road path 100, is schematically illustrated in the figures.

The system 1 comprises a plurality of inductive transmission coils 2 embedded in the road surface of the path 100.

In a known manner, each transmission coil 2 is configured to transmit high frequency electromagnetic power above the road surface, in a predetermined transmission area, when traversed by high-frequency current.

For this purpose, the coil 2 comprises a winding of conductive material which is wound around a substantially vertical axis.

The high frequency intended for this application is currently regulated in some countries to be substantially equal to 85 kHz. In particular, the invention can be made with high frequencies in the range between 79 and 90 kHz, as required by the IEC 61980-3 standard.

Still in a known manner, vehicles 200 passing along the path 100 can be provided on board with receiver coils (not illustrated), configured to intercept the electromagnetic power transmitted by the transmission coils 2. Therefore, when a vehicle 200 of this type is in the transmission area of a transmission coil 2, its receiver coil is traversed by a high-frequency current.

Still in a known manner, the vehicle 200 further comprises a storage device (not illustrated), for example with batteries, and a rectifier configured to convert the current of the receiver coil into a direct current to be fed to the storage device or to be sent directly to the drive motor(s). The vehicles 200 provided with receiver coils may be electric or hybrid drive vehicles.

The system 1 comprises a plurality of management units 3, positioned along the road path 100, preferably next to the path 100.

Each management unit 3 is electrically connected to a respective group of transmission coils 2, for the purpose of their electrical supply. Each group of transmission coils 2 connected to the same management unit 3 comprises transmission coils 2 distributed at least along a travel direction of the road path 100, i.e. the direction along which the road path 100 is designed for traffic of vehicles.

Therefore, separate groups of transmission coils 2, distributed along the path 100, are powered by separate management units 3, also distributed along the path 100.

In the following, reference will be made to the case of a single lane of the path 100 which is provided with transmission coils 2 for powering electric vehicles. However, the invention can also be applied on several lanes of the same path 100, and in particular one or more lanes for each travel direction.

The transmission coils 2 positioned along different lanes can be powered by the same management unit 3 or by separate management units 3. Therefore, in each group of transmission coils 2 connected to the same management unit 3, in addition to coils spaced out in the travel direction of the road path 100, there may also be transmission coils 2 spaced out in a width direction of the road path 100, transverse to the driving direction.

Indicatively, two consecutive transmission coils 2 along a same lane of the path 100, if belonging to the same group of transmission coils 2 powered by a single management unit 3, can be spaced out by a distance of less than 1 m, for example between 0.5 and 1 m. More in detail, the transmission coils 2 have structures that are joined between consecutive transmission coils 2. The distance can instead be greater among transmission coils 2, although consecutive, but which are powered by two different management units 3, and which therefore belong to different groups of transmission coils 2.

It should be noted that the dimensions of a transmission coil 2 may be comparable to or even greater than the distance between consecutive transmission coils 2. For example, the dimensions of a transmission coil 2 along the direction of the road path 100 may be between 1 m and 2 m. Therefore, the distance between geometric centres of consecutive transmission coils 2 can be comprised between 1 and 3 m.

Instead, two consecutive management units 3 along the path 100 can be spaced out by a greater distance, for example up to 100 m. More in detail, all the transmission coils 2 of the same group powered by the same management unit 3 are spaced out from the management unit 3 up to 50 m, and are spaced out up to 100 m.

In one embodiment, each management unit 3 can power 60 transmission coils 2. Along an entire road path 100, separate management units 3 do not necessarily all power the same number of transmission coils 2. For example, management units 3 at positions of the road path 100 with space constraints due to the geography of the road path 100 might power a small number of transmission coils 2. Preferably, each management unit 3 is connected to at least ten transmission coils 2, more preferably at least twenty.

The 100 m limit is connected to the 85 kHz supply frequency for the transmission coils 2, which is not efficient over longer distances. However, the innovative features of the invention, presented below, can also be compatible with management units 3 located at greater distances, for example up to 200 m, in particular if the use of other frequencies, transportable at greater distances, is allowed at regulatory level, or if transmission lines 4 are developed for example using cables with different technologies.

Each management unit 3 comprises its own low-voltage direct current bus 31. Furthermore, each management unit 3 comprises a plurality of inverters 32 connected to the bus 31.

More in detail, each inverter 32 has a direct current side connected to the bus

31, and a high frequency alternating current (HF) side.

A plurality of high frequency alternating current lines 4 connect each transmission coil 2 to a respective inverter 32, on its alternating current side (these lines 4 are only schematically represented in Figures 2 and 4, without taking into account their length and the spacing between management units 3 and transmission coils 2).

In a known manner, each management unit comprises one or more controllers (not illustrated) connected to the inverters 32, and configured to control the inverters

32, such that each inverter 32 powers the respective transmission coil 2 when a vehicle passes over the transmission coil 2.

Furthermore, the system 1 may comprise in a known manner a sensor or telecommunications infrastructure (not illustrated) configured to detect and signal to the controllers the presence of vehicles 200 in the transmission areas of the transmission coils 2.

According to one aspect of the invention, the system 1 comprises one or more conversion substations 5, along the path 100. The conversion substation 5 is distanced from the management units 3. In particular, each management unit 3 can be contained in a box, arranged spaced from the conversion substation 5.

The conversion substations 5 are fewer in number than the management units 3, for example, consecutive conversion substations 5 along the path 100 may be spaced out by a distance of at least 1 km, preferably at least 2 km, more preferably about 4 km.

Each conversion substation 5 comprises a delivery point 51 for connection to a medium voltage alternating current distribution network 300. The network 300 may be the common industrial network, for example with a frequency of 50 or 60 Hz. In this description, terms such as low voltage, medium voltage, high voltage and very high voltage are to be understood in accordance with the IEC 60038, 1983 standard.

The substation 5 further comprises a step-down transformer 52 having a primary side, connected to the delivery point 51, and at least one secondary side.

In addition, the substation 5 comprises a rectifier 53 having an alternating current side, connected to the at least one secondary side of the transformer 52, and a direct current side. The transformer 52 and the rectifier 53 are therefore in series with each other. The substation 5 also comprises a low-voltage de bus 54, connected to the direct current side of the rectifier 53. The transformer 52 and the rectifier 53 are configured together to supply power from the delivery point 51 to the bus 54, and to maintain on the bus 54 a voltage comprised between 600 and 1500 V, for example equal to 800 V. It should be noted that 1500 V represents the limit recognized by the regulations to distinguish the low voltage from the medium voltage, in direct current.

In the preferred embodiment, the rectifier 53 of the conversion substation 5 is a twelve-pulse rectifier, preferably diode rectifier.

As is known, the twelve-pulse rectifiers generate a continuous voltage with low undesired harmonic components.

In order to obtain the twelve-pulse reaction, the transformer 52 of the conversion substation 5 is a transformer with two sets of secondary windings 521, 522. Preferably, one of the two sets of secondary windings 521 comprises three star- connected phase conductors, while the other set of secondary windings 522 comprises three triangle-connected phase conductors. Further, the rectifier 53 comprises two interconnected conversion modules 531, 532 each configured to be powered by a separate set of secondary windings 521, 522 of the transformer 52. In a known manner, the two conversion modules 531, 532 may be interconnected in series or in parallel.

According to one aspect of the invention, the system 1 comprises a direct current distribution network 6, which comprises at least one positive pole conductor 61 and one negative pole conductor 62. The direct current distribution network 6 extends from the conversion substation 5 to the management units 3, and in particular connects the de bus 54 of the conversion substation 5 to the de buses 31 of the management units 3, and thus to the inverters 32 of the management units 3, on the direct-current side of the inverters 32.

The buses 31 of the management units 3 are therefore powered by the conversion substations 5 through the direct current distribution network 6, without providing rectifiers or individual delivery points for the management units 3.

The choice to realize the distribution network 6 in direct current, instead of alternating current, also entails a number of other advantages for the system 1. This distribution, although in low voltage in order to be subject to less regulatory constraints, can be managed at a nominal voltage higher than that in alternating current, which is normally 400 V.

Therefore, smaller currents are sufficient, resulting in lower voltage losses and drops in the distribution network 6. In addition, a smaller number of conductors is sufficient, which without reducing performance can be made with smaller sections, and therefore less active material required, and with cheaper materials, for example aluminium instead of copper. In addition, the electromagnetic emissions along the distribution network 6 are reduced.

A further advantage is that the direct current distribution allows to supply transmission coils 2 of higher power. Thus, with an equal number of transmission coils 2 buried in the road surface, each receiver coil on a vehicle receives more power. This is particularly useful for vehicles 200 consuming high powers, but with little room to install receiver coils. For example, in a trailer vehicle the receiver coils are usually installed in the tractor only, where the batteries and the drive motors are also present. Instead, the trailer can be connected to different types of vehicles 200, even vehicles without electric traction, and thus the trailer manufacturers do not equip them with receiver coils. Clearly, the increase in power of the transmission coils 2 facilitates the travel with reduced or zero battery consumption for these types of vehicles 200 (depending on the speed of the vehicle 200), compared to the prior art.

However, the transmission coils 2 currently on the market are sized for the power and the voltage level that the systems of the prior art were able to provide, indicatively up to 25 kW.

In view of a subsequent replacement of the transmission coils 2 with higher power models, for example up to 40 or 50 kW, as well as for better manageability of the system 1, it is preferable that the transformer 52 of the conversion substation 5 is a variable ratio transformer.

In the preferred embodiment, its transformation ratio is variable under no-load circuit conditions, and not under loaded circuit conditions, with steps of the output voltage (secondary side) of for example 50 V. Since the transmission coils 2 are powered only at the passage of a vehicle 200 prepared for recharging with this type of system 1, the no-load circuit conditions occur frequently enough to vary the voltage when desired.

In the presence of several conversion substations 5, the direct current distribution network 6 preferably comprises at least one or more network segments 63, each with two ends. Each network segment 63 connects two conversion substations 5 to each other, so that the segment 63 is powered from two sides. More in detail, the ends of each segment 63 are connected to the de buses 54 of respective separate conversion substations 5.

For each segment 63, various management units 3, belonging to both conversion substations 5 at the ends of the segment 63, are distributed along the network segment 63 and connected to it. The inverters 32 of the management units 3 connected to the segment 63 are powered in parallel by the conversion substations 5 located at both ends of the segment 63.

Since the management units 3 are more numerous than the conversion substations 5, preferably at least five management units 3, preferably at least twenty management units 3, for example about forty management units 3, are connected to each segment 63.

In alternative embodiments, as shown in Figure 7, the direct current distribution network 6 may be a loop network.

In some embodiments, the conversion substation 5 comprises an earthing system 55, preferably connected to a star centre point of a set of secondary windings 521 of the transformer 52. In addition, the direct current distribution network 6 comprises a protective conductor 64, which in use has an intermediate voltage between the positive pole conductor 61 and the negative pole conductor 62.

The protective conductor 64 is connected to the earthing system 55 of the conversion substation 5. Like the positive pole 61 and negative pole 62 conductors, also the protective conductor 64 extends from the conversion substation 5 to the management units 3. However, while the positive pole 61 and negative pole 62 conductors are necessarily connected to the inverters 32, in various embodiments the protective conductor 64 may also be connected to the inverters 32 and/or to boxes of the management units 3, and/or may simply extend in the vicinity of the management units 3.

Advantageously, the protective conductor 64 guarantees equipotential conditions of the soil along the direct current distribution network 6.

In addition, no problems of wandering currents occur as is the case for some types of railway supplies, which are in direct current and use the rails as a negative pole conductor. Furthermore, the presence of the protective conductor 64 promotes the recognition of bipolar faults between the positive and negative pole conductors 61, 62, and/or unipolar faults of one of such conductors 61, 62 towards the earth.

Regarding the electrical protections, preferably the direct current distribution network 6 comprises a plurality of direct current static circuit breakers 65, preferably at least one for each management unit 3.

Each static circuit breaker 65 is configured to connect and disconnect a respective management unit 3 from the conversion substation 5, when actuated by a suitable command or automatically upon the occurrence of predetermined voltage and/or current conditions.

The connection or disconnection occurs when the circuit breaker 65 switches between a conduction state and an interruption state.

In the illustrated embodiment, separate static circuit breakers 65 are connected to the positive pole conductor 61 and to the negative pole conductor 62.

It should be noted that unipolar and bipolar faults cause the passage of high currents in separate conductors 61, 62, 64, such as to cause the circuit breakers 65 to switch. In fact, in a known way, the circuit breakers 65 can be provided with relays or other detectors of electrical quantities, to command the automatic switching of the circuit breaker 65 upon the occurrence of predetermined conditions.

Thus, unipolar faults and bipolar faults result in the switching of different static circuit breakers 65 or groups of static circuit breakers 65 connected to several conductors 61, 62, 64, for example of a single circuit breaker 65 on the positive pole conductor 61, or a single circuit breaker 65 on the negative pole conductor 62, or both. This makes it easier to identify and resolve faults, keeping operative as much equipment as possible that is not involved in the fault operational.

In addition, the direct current distribution network 6 may comprise at least one circuit breaker 66 configured to connect and disconnect a respective conversion substation 5 to/from all the management units 3. Said circuit breaker 66 is preferably of the extrarapid, or static type.

Obviously, a person skilled in the art will be able to make numerous equivalent modifications to the variants set forth above, without thereby departing from the scope of protection as defined by the appended claims.