GB2561591A

GB2561591A - A method and system for determining a relative position or range of relative positions between a primary winding structure and a secondary winding structure

Info

Publication number: GB2561591A
Application number: GB1706274.6A
Authority: GB
Inventors: Lindt Rudolf; Garcia Federico
Original assignee: Bombardier Primove GmbH
Current assignee: Bombardier Primove GmbH
Priority date: 2017-04-20
Filing date: 2017-04-20
Publication date: 2018-10-24
Also published as: GB201706274D0

Abstract

A relative position, or range of relative positions, between a primary winding structure 3 and a secondary winding structure 4 of an inductive power transfer system 2 is determined, based a power-mode reactive phase current of at least one phase line (U, V, W) of the primary winding structure in a power transfer mode. At least one current-dependent parameter is determined, depending on the power-mode reactive phase current. At least one position parameter is determined, depending on the current-dependent parameter(s). The relative position, or range of relative positions, is determined, depending on the position parameter(s). The current-dependent parameter may be based on a phase switching current or at least one characteristic of the reactive phase current. The characteristic of the reactive phase current may be: an RMS value; a value at a switching time point; a peak value (or square value of the peak value); a duty cycle in one switching period; a voltage value at the time point of the current crossing zero; or a current value at the time point of the voltage crossing zero. A current-dependent parameter for each of the three phases may be determined and the position parameter(s) based on the ratios of the three current-dependent parameters.

Description

(71) Applicant(s):

Bombardier Primove GmbH (Incorporated in the Federal Republic of Germany)

Schoneberger Ufer 1, Berlin 10785, Germany (72) Inventor(s):

Rudolf Lindt Federico Garcia (56) Documents Cited:

EP 3203602 A1 WO 2015/112381 A1

EP 2800239 A1 WO 2014/014615 A1 (58) Field of Search:

INT CL B60L, H01F, H02J

Other: ONLINE: WPI, EPODOC, Patent FulIText (74) Agent and/or Address for Service:

German and European Patent Attorneys Bressel und Partner mbB

Potsdamer Platz 10, Berlin 10785, Germany (54) Title ofthe Invention: A method and system for determining a relative position or range of relative positions between a primary winding structure and a secondary winding structure

Abstract Title: Determining a relative position, or range of relative positions, between primary and second winding structures of an inductive power transfer system (57) A relative position, or range of relative positions, between a primary winding structure 3 and a secondary winding structure 4 of an inductive power transfer system 2 is determined, based a power-mode reactive phase current of at least one phase line (U, V, W) of the primary winding structure in a power transfer mode. At least one currentdependent parameter is determined, depending on the power-mode reactive phase current. At least one position parameter is determined, depending on the current-dependent parameter(s). The relative position, or range of relative positions, is determined, depending on the position parameter(s). The current-dependent parameter may be based on a phase switching current or at least one characteristic ofthe reactive phase current. The characteristic ofthe reactive phase current may be: an RMS value; a value at a switching time point; a peak value (or square value of the peak value); a duty cycle in one switching period; a voltage value at the time point of the current crossing zero; or a current value at the time point of the voltage crossing zero. A current-dependent parameter for each ofthe three phases may be determined and the position parameter(s) based on the ratios ofthe three current-dependent parameters.

A method and system for determining a relative position or range of relative positions between a primary winding structure and a secondary winding structure of a system for inductive power transfer

The invention relates to a method and a system for determining a relative position or range of relative positions between a primary winding structure and a secondary winding structure of a system for inductive power transfer, in particular to a vehicle.

Electric vehicles, in particular a track-bound vehicle, and/or a road automobile, can be operated by electric energy which is transferred by means of an inductive power transfer. Such a vehicle may comprise a so-called receiving device adapted to receive an alternating electromagnetic field and to produce an alternating electric current by electromagnetic induction. Such a receiving device can comprise or provide a so-called secondary winding structure. Furthermore, such a vehicle can comprise a rectifier adapted to convert an alternating current (AC) to a direct current (DC). The DC can be used to charge a traction battery or to operate an electric machine. The rectifier converts the AC provided by the receiving device into the DC.

The inductive power transfer is usually performed using a primary unit which generates the alternating electromagnetic field by a primary winding structure and a secondary unit which comprises the receiving device for receiving said electromagnetic field. The primary unit and the secondary unit can e.g. each comprise a set of three-phase windings providing the aforementioned primary and secondary winding structure. A set of windings of the primary unit can be installed on the ground (primary windings) and can be fed by a wayside power converter (WPC). A set of windings of the secondary unit is installed on the vehicle. For example, the second set of windings can be attached underneath the vehicle, in the case of trams under some of its wagons. The first and the secondary side can be part of a high frequency transformer to transfer electric energy to the vehicle. This transfer can be done in a static state (when there is no movement of the vehicle) and in a dynamic state (when the vehicle moves).

Inductive power transfer usually requires a correct positioning of a vehicle-sided secondary winding structure relative to a primary winding structure in order to maximize the amount of transfer power but also in order to meet safety requirements and ensure an electromagnetic compatibility.

US 7,454,170 B2 discloses an inductive transmission system for inductive transmission of power and full duplex data signals between first and second devices. The transmission system includes a bi-directional inductive channel between the two devices, a transmitter for transmitting a power signal at a first frequency from the first device to the second device over the inductive channel, a first modulating device for modulating a first data signal at a first modulation frequency, and a second modulating device for modulating a second data signal at a second modulation frequency. Further, the transmitters transmit the modulated first data signals from the first device to the second device over the inductive channel and transmit the modulated second data signals from the second device to the first device over the inductive channel. The first modulation frequency and the second modulation frequency are at least a factor two apart.

WO 2011/127455 A2 describes a wireless charging and wireless power alignment of wireless power antennas associated with a vehicle.

WO 2014/023595 Α2 discloses a vehicle and an induction charging unit, wherein the induction charging unit comprises a primary coil and the vehicle comprises a secondary coil. Further, in the charging position, the secondary coil is located in a preferred spatial position range with respect to the primary coil with the result that, in order to set the charging position, the system determines, by means of an electromagnetic distance and angle measurement using triangulation, a location which describes a time-dependent spatial position of the secondary coil with respect to the primary coil. The system detects, by means of the location and the charging position, at least one partial driving direction along which the location of a charging position can be approached.

The documents disclose communication antennas of an inductive power transfer (IPT) unit, namely the primary unit or the secondary unit.

There is the technical problem of providing a method and a system for determining a relative position or range of relative positions between a primary winding structure and a secondary winding structure of a system for inductive power transfer, in particular to a vehicle, which allow a simple and accurate determination of the relative position or range of relative positions.

It is a main idea of the invention to determine a a relative position or range of relative positions between a primary winding structure and a secondary winding structure of a system for inductive power transfer based on a reactive current in each phase line of the primary winding structure.

A method for determining a relative position or range of relative positions between a primary winding structure and a secondary winding structure of a system for inductive power transfer, in particular to a vehicle, is proposed.

The system for inductive power transfer can comprise a primary unit with the primary winding structure and the secondary unit with a secondary winding structure.

The vehicle can comprise a secondary unit with the secondary winding structure for receiving an alternating electromagnetic field which is generated by the primary winding structure of a primary unit.

The primary winding structure generates the alternating electromagnetic field if the primary winding structure is energized or supplied with (an) operating current(s). The primary unit can comprise a totality or a subset of components by which an alternating electromagnetic field for inductive power transfer is generated. In particular, (an) operating current(s) for the primary winding structure can be provided by an inverter. If the primary winding structure comprises three phase lines, the inverter can be a 3-phase inverter. In particular, the inverter can have a so-called B6 bridge topology.

The primary winding structure can comprise at least one phase line. Preferably, the primary winding structure comprises three phase lines. Each phase line can be connected to an AC output terminal of the inverter. It is possible that each phase line is connected to the AC output terminal via a filter element, in particular a capacitive filter element. A capacitance of the capacitive filter element can be chosen such that the resonant frequency of the resonant circuit provided by the phase line and the capacitive filter element matches the desired operating frequency of the primary winding structure or does not deviate more than a predetermined amount from said operating frequency. The operating frequency can denote the frequency of the electromagnetic power transfer field. Preferably, the operating frequency is in the range of 60 kHz to 110 kHz, more particular in the range of 80 kHz to 90 kHz . In another preferred embodiment, the frequency may be in the range of 15 kHz to 25 kHz.

Correspondingly, the secondary unit can comprise a totality or a subset of components by which the alternating electromagnetic field for inductive power transfer is received and a corresponding output voltage is provided.

The primary unit can be provided by an inductive power transfer pad. An inductive power transfer pad can be installed on the surface of a route or a parking space or it can be integrated within such a surface. The invention is, however, not limited to a primary unit provided by a power transfer pad.

The present invention can be applied in particular to the field of inductive energy transfer to any vehicle, for example track bound vehicles, such as rail vehicles (e.g. trams), or watercrafts, e.g. marine vessels such as boats or amphibious vehicles. Further, the invention relates to the field of inductive energy transfer to road automobiles, such as individual (private) passenger cars or public transport vehicles (e.g. busses).

In the following, reference can be made to a primary-sided coordinate system and a secondary-sided coordinate system. The primary-sided coordinate system can be a coordinate system of the primary winding structure, wherein the secondary-sided coordinate system can be a coordinate system of the secondary winding structure.

The primary-sided coordinate system can comprise a first axis, which can also be referred to as longitudinal axis or x-axis, wherein the first axis can be a longitudinal axis of the primary winding structure or extend parallel to said axis. A second axis, which can also be referred to as lateral axis or y-axis can be a lateral axis of the primary winding structure or extend parallel to said axis. A third axis, which can also be referred to as a vertical axis or z-axis, can be oriented perpendicular to the first and the second axes. The third axis can be oriented parallel to a desired direction of power transfer, i.e. from the primary unit to the secondary unit. The vertical axis can be oriented from bottom to top if pointing from the primary unit to the secondary unit.

The longitudinal axis of the primary-sided coordinate system can also be oriented parallel to a desired driving direction of a vehicle driving straight ahead over the primary unit in order to position the secondary winding structure above the primary winding structure.

The secondary-sided coordinate system can also comprise a first axis, which can be referred to as longitudinal axis or x-axis, wherein the first axis can be a longitudinal axis of the secondary winding structure or extend parallel to said axis. A second axis of the secondary winding structure can be referred to as lateral axis or y-axis, wherein the second axis can be a lateral axis of the secondary winding structure or can extend parallel to said axis. A third axis can be referred to as a vertical axis or z-axis of the secondary winding structure and can be oriented perpendicular to the first and the second axes of the secondary winding structures. The third axis of the secondary winding structure can be oriented parallel to the desired direction of power transfer. It is further possible that the longitudinal axis is oriented parallel to a roll axis of the vehicle, the lateral axis is oriented parallel to a pitch axis of the vehicle and the vertical axis is oriented parallel to a yaw axis of the vehicle.

In the following, a length can be measured along the first axis, a width can be measured along the second axis and a height can be measured along the third axis. Directional terms referring to a direction such as “above”, “under”, “ahead”, “beside” can relate to the aforementioned longitudinal, lateral and vertical axes of the respective coordinate system.

An origin of the primary-sided coordinate system can correspond to any reference point fixed in the primary-sided coordinate system, in particular to a geometric center of the primary winding structure. Correspondingly, an origin of the secondary-sided coordinate system can correspond to any reference point fixed in the secondary-sided coordinate system, in particular to a geometric center of the secondary winding structure.

The primary and/or secondary winding structure can (each) comprise at least one phase line. In particular, the primary and/or secondary winding structure can (each) comprise three phase lines.

Further, the primary and/or secondary winding structure can comprise or provide at least one subwinding structure. A subwinding structure can be provided by at least one section of the winding structure. In particular, a subwinding structure can provide a loop or a coil, wherein the loop or coil is provided by one or multiple sections of the winding structure. A loop or coil can be circular-shaped, oval-shaped or rectangular-shaped. The windingstructure can extend along the longitudinal axis of the corresponding coordinate system.

Preferably, a winding structure comprises multiple subwinding structures which extend along the longitudinal axis. In this case, successive subwinding structures of the winding structure can be arranged adjacent to one another along said longitudinal axis. Adjacent to each other can mean that central axes of the subwindings, in particular the axes of symmetry, are spaced apart from another, e.g. with a predetermined distance along the longitudinal axis.

Preferably, the primary and/or secondary winding structure can comprise one subwinding structure or multiple subwinding structures per phase line. In this case, the phase line can provide the at least one subwinding structure or multiple subwinding structures extending along the longitudinal axis. In particular, the primary and/or secondary winding structure can comprise three phase lines, wherein each phase line provides at least one subwinding structure. If multiple subwinding structures are provided by each of the three phase lines, the adjacent subwinding structures of each phase line can extend along the longitudinal axis.

It is possible that the winding structure or a subwinding structure comprises at least one winding section which extends along the longitudinal axis and at least one winding section which extends along the lateral axis of the corresponding coordinate system. The winding structure, in particular each subwinding structure, can thus be provided by sections extending substantially or completely parallel to the longitudinal axis and sections extending substantially or completely parallel to the lateral axis. In particular, each subwinding can be provided by two sections each extending substantially or completely parallel to the longitudinal and two sections each extending substantially or completely parallel to the lateral axis.

A reactive phase current can denote the phase current provided at the AC output terminal of the inverter to which the respective phase line is connected or a current flowing through a switching element of the inverter into the respective phase line.

Further, a power-mode reactive phase current of at least one phase line of the primary winding structure is determined in a power transfer mode. A phase line can also be referred to as a phase of the primary winding structure.

The power-mode reactive phase current denotes the reactive phase current determined in the power transfer mode. In the power transfer mode, power is transferred inductively from the primary winding structure to the secondary winding structure. In this case, the secondary winding structure is positioned such that at least a portion of the electromagnetic field generated by the primary winding structure is received/receivable by the secondary winding structure. In other words, the secondary winding structure can be arranged in an active volume assigned to the primary winding structure.

It is possible that the primary winding structure can be operated with different sets of phase shift values between the phase voltages and/or the phase currents in the power transfer mode as well as in an idle-mode, which will be explained in the following. In particular, the primary winding structure can be operated such that the phase shift between phase voltages/phase currents of one phase line and one of the two remaining phase lines equals to 120° and the phase shift between phase voltages/phase currents of said phase line and the other one of the two remaining phase lines equals to 240°. This mode of operation can also be referred to as symmetrical phase shift operation.

Alternatively, the primary winding structure can be operated such that the phase shift between phase voltages/phase currents of one phase line and one of the two remaining phase lines equals to 180° and the phase shift between phase voltages/phase currents of said phase line and the other one of the two remaining phase lines equals to 0°. This mode of operation can also be referred to as unsymmetrical phase shift operation.

That a reactive phase current of at least one phase line of the primary winding structure is determined can mean that at least one characteristic of the reactive phase current is determined. As will be explained later, a characteristic can e.g. be a root mean square value (RMS value) or a peak value of the reactive phase current.

The reactive phase current or the at least one characteristic of the at least one reactive phase current can be measured, e.g. by adequate measuring means such as a current sensor. It is, however, also possible to calculate reactive phase current depending on other electrical parameters, e.g. a phase voltage.

Further, at least one current-dependent parameter is determined depending on the powermode reactive phase current. A current-dependent parameter can denote a parameter which represents the reactive phase current, e.g. at least one characteristic of the reactive phase current. The current-dependent parameter can e.g. be equal to or proportional to the at least one characteristic of the reactive phase current. Further, the current-dependent parameter can e.g. be equal to or proportional to at least one corrected characteristic of the reactive phase current. This will be explained later.

Further, at least one position parameter is determined depending on the at least one currentdependent parameter. Such a position parameter can denote a parameter which represents the current-dependent parameter. The position parameter can e.g. be equal to or proportional to the at least current-dependent parameter.

It is also possible that a set of multiple position parameters is determined, wherein at least one position parameter of said set is determined depending on the at least one currentdependent parameter. A set of multiple position parameters can also comprise at least one parameter which is not a parameter depending on or related to the current-dependent parameter.

Further, the relative position or the range of relative positions is determined depending on the at least one position parameter. It is, of course, also possible to determine the relative position or the range of relative positions depending on the set of multiple position parameters.

A range of relative positions can have predetermined size, e.g. a size of 1 mm, 2 mm, 5 mm, 10 mm or 20 mm. The predetermined size can correspond to an inaccuracy of the position determination. If a certain range of relative positions is determined, a relative position between the primary winding structure and the secondary winding structure can e.g. correspond to a center value of said range plus minus half of the size of said range.

Preferably, a predetermined assignment of one, preferably more, position parameter(s) to a relative position or a range of relative position or vice versa can be provided. It is also possible to provide a predetermined assignment of one, preferably more, set(s) of multiple position parameters to a relative position or a range of relative position or vice versa.

The relative position or the range of relative positions can then be determined depending on the at least one position parameter and the predetermined assignment.

The predetermined assignment can e.g. be determined by calibration procedure or by numerical simulations. The predetermined assignment can e.g. be provided by a look-up table. The predetermined assignment can e.g. be stored in a memory unit.

The relative position can preferably be determined within the primary-sided coordinate system, alternatively within the secondary-sided coordinate system.

In the case that the relative position is determined in the primary-sided coordinate system, the relative position can e.g. be determined as the position of the origin of the secondarysided coordinate system, e.g. as the position of the geometric center of the secondary winding structure, within the primary-sided coordinate system. If the relative position is determined in the secondary-sided coordinate system, the relative position can be determined as the position of the origin of the primary-sided coordinate system, e.g. the position of the geometric center of the primary winding structure, within the secondary-sided coordinate system.

The relative position can e.g. be determined as position along the longitudinal axis and/or along the lateral axis and/or along the vertical axis. In this case, the relative position can be provided by a position vector with one or more entries. Preferably, the relative position is determined as the position along the longitudinal axis. In this case, the position vector can have only one entry.

It is further possible to additionally determine a relative orientation or a range of relative orientations between the primary and the secondary winding structure. The relative orientation can be determined as the orientation of the secondary-sided coordinate system relative to the primary-sided coordinate system or the orientation of the primary-sided coordinate system relative to the secondary-sided coordinate system. The orientation can e.g. be determined according to the yaw-pitch-role convention.

It is possible to determine the relative position and orientation in a two dimensional coordinate system provided by the longitudinal axes and lateral axis of the primary- or secondary-sided coordinate system. In this case, the vertical distance can be neglected.

The relative position and/or orientation can e.g. be determined in a two-dimensional Cartesian coordinate system or in a polar coordinate system.

The relative position and/or orientation can e.g. be determined by a secondary-sided control unit or by a primary-sided control unit. This means that the relative position and/or orientation can either be determined on the primary side or on the secondary side.

Information on the relative position and/or orientation can e.g. be provided to a driver of the vehicle or driver assistance system. Thus, these information can be used to position the secondary winding structure relative to the primary winding structure such that an aligned state is provided. The aligned state can be provided if the relative position and/or orientation is within a desired interval of positions and/or orientations, e.g. if the secondary winding structure is arranged above the primary winding structure or within an active volume of the primary winding structure.

Further, these information can be used in order to control or enable the inductive power transfer. In particular, the inductive power transfer can only be enabled if the primary and secondary winding structure are in an aligned state.

When a secondary winding structure, e.g. with a battery load connected to said secondary winding structure, is located in the active volume of the primary winding structure, e.g. above the primary winding structure, and the power transfer process has been started, the constellation or amount of reactive power or power-mode reactive phase currents in a phase line of the primary winding structure or in the inverter changes with varying relative positions between the primary and the secondary winding structure, in particular with varying relative positions along the longitudinal axis.

The position dependency of the reactive phase current is due to the fact that the secondary winding structure represent an additional and not constant load (impedance) to the primarysided inverter. In particular, a variation of the relative position also varies the coupling coefficient between primary and secondary winding structure. This variation in the coupling coefficient is reflected in the change of an impedance of the electric circuit connected to the AC output terminals of the inverter which, in turn, leads to a change of the power-mode reactive current(s). This effect can also be referred to as reactive power circulation. Thus, the power-mode reactive current can represent a unique characteristic, e.g. a unique image, reflection, shadow or finger print that represents the magnetic configuration between the primary and the secondary unit.

The coupling coefficient and thus the reactive phase current which occurs can also depend on the specific design of the primary and secondary unit, in particular on the geometry of the primary and secondary winding structure. Thus, the relative position or the range of relative positions can also be determined depending on the design of the primary and secondary unit. It is, for instance, possible, that a parameter representing a certain design of the primary unit and/or a parameter representing a certain design of the secondary unit provide(s) a position parameter. It is further possible to transmit information on the design, e.g. one or both of said parameters, between the primary unit and the secondary unit, e.g. via primarysided and secondary-sided communication means.

The proposed method advantageously allows a reliable and computationally effective, in particular fast, determination of a relative position with a desired degree of tolerance.

In a preferred embodiment, an idle-mode reactive phase current of the at least one phase of the primary winding structure is determined in an idle mode.

The idle-mode reactive phase current denotes the reactive phase current determined in the idle mode. In the idle mode, no power is transferred inductively from the primary winding structure to a secondary winding structure. In particular, an operating current is supplied to the at least one phase line, wherein no secondary winding structure is positioned such that at least a portion of the electromagnetic field generated by the primary winding structure is received/receivable by the secondary winding structure. In other words, no secondary winding structure is arranged in the active volume assigned to the primary winding structure.

The idle-mode reactive phase current can be determined once, e.g. before putting the 10 primary unit into service. It is, of course, also possible to determine the idle-mode reactive phase currents in predetermined time intervals. It is, however, possible to use the determined idle-mode reactive phase current for multiple successive determinations of a relative position or range of relative positions.

Further, the at least one current-depending parameter is determined depending on the power-mode reactive phase current and the idle-mode reactive phase current of the at least one phase of the primary winding structure. In particular, the at least one current-depending parameter can be equal to or proportional to the difference between the power-mode reactive phase current and the idle-mode reactive phase current, in particular to the difference between corresponding characteristics of said reactive phase currents.

In the case that there is no secondary winding structure of a secondary unit arranged in an active volume of a primary unit, said primary winding structure represents a pure inductive load to the inverter that acts as a steady impedance to the inverter. When the inverter delivers energy to the primary winding structure, a magnetic field is generated by the primary winding structure, wherein the power required to generate said magnetic field provides a reactive power to the inverter.

This operation with a constant inductive impedance load and without a secondary winding structure arranged in the active volume can be referred to as “idle mode”. In this idle mode, the reactive phase currents can be determined, e.g. measured or calculated.

It is possible that the primary unit is designed such that in the idle mode, the reactive phase currents in each phase line of a multiple phase system are balanced. This can e.g. mean that the shape and amplitude of the reactive phase currents are periodically symmetrical. In particular for a three-phase system, the RMS value of each reactive phase current as well as the peak value of each reactive phase current can be equal if a phase shift between the phase voltages/phase currents equals to 120°. In this case, the primary unit can be referred to as well-tuned primary unit. The procedure to realize this balance of reactive power can be provided by a resonant tuning process.

Determining the at least one current-depending parameter depending on the power-mode reactive phase current and the idle-mode reactive phase current of the at least one phase line of the primary winding structure advantageously allows to normalize or correct the power-mode reactive phase current. Beside the relative position between the primary and secondary winding structure, the power-mode reactive phase current can also depend on the amount of power which is transferred to the secondary unit and/or on the operating frequency. Normalizing the power-mode reactive phase current advantageously reduces or eliminates the power-dependent portion and/or frequency-dependent portion of the reactive phase current. This, in turn, allows a more accurate and thus reliable determination of the relative position or range of relative position.

In another embodiment, the current-dependent parameter is determined depending on at least one characteristic of the reactive phase current. It is possible that the currentdependent parameter is determined as the at least one characteristic or as a value which is proportional to said characteristic. The at least one characteristic can denote a parameter or a set of multiple parameters which, preferably uniquely, characterizes the reactive phase current, in particular its value. It is e.g. possible that the at least one characteristic is a time course of the reactive phase current within a time period with a predetermined duration. It is also possible that the at least one characteristic characterizes the time course. The at least one characteristic can be determined in the power transfer mode and in the idle mode, i.e. as a characteristic of the power-mode reactive phase current or the idle-mode reactive phase current.

As the relative position between the primary and the secondary winding structure affects the reactive phase current, in particular a time course of the reactive phase current, the determination of such a characteristic advantageously allows a reliable determination of the relative position or range of relative positions.

In a preferred embodiment, the at least one characteristic is selected from the group comprising a RMS value of the reactive phase current, a value of the reactive phase current at a switching time point (phase switching current), a peak value of the reactive phase current, a square value of said peak value, a duty cycle of the reactive phase current in one switching period, a voltage value at the time point of the current zero crossing and a current value at the time point of the voltage zero crossing.

The switching period can denote a time interval in which the phase voltage changes from a high level to a low level and from the low level to the high level or in which the phase voltage changes from a low level to a high level and from the high level to the low level. In other words, the switching period can comprise an active time period in which the phase voltage signal has a high level and an inactive time period in which the phase voltage has a low level.

The duty cycle of the reactive phase current can be value proportional to the area under the positive reactive phase current sub-wave or proportional to the area under the negative reactive phase current sub-wave in the switching period or in the active time period or in the inactive time period.

Generally, the at least one characteristic can be chosen as a characteristic of the phase current which is proportional to an average value of the reactive phase current in one switching period of the phase voltage or to an average value in in the active time period or inactive time period of the switching period.

It is possible that the characteristic, e.g. the RMS value, the peak value, a square value of said peak value, is determined within or over a predetermined time period, e.g. the switching time period or the active time period or the inactive time period.

In another embodiment, the current-dependent parameter is determined depending on a phase switching current. The current-dependent parameter can be equal to or proportional to the phase switching current, in particular to an amplitude difference between the phase switching currents in the power transfer mode and in the idle mode.

The phase switching current can denote the current flowing through a switching element of the inverter into the respective phase line of the primary winding structure in the moment of the phase voltage switching, e.g. at the moment of zero crossing of the phase voltage. In this case, it is possible to operate the inverter in a zero voltage switching mode.

This advantageously allows a fast and reliable determination of the current-dependent parameter and thus a fast and reliable determination of the relative position or range of relative positions.

In another embodiment, a first current-dependent parameter for a first phase line of the primary winding structure and at least one further current-dependent parameter for a further phase line of the primary winding structure are determined. In this case, the primary winding structure comprises at least two phase lines, wherein the first current-dependent parameter and the further current-dependent parameter are phase-specific parameters.

Further, the at least one position parameter is determined depending on a ratio of the at least two current-dependent parameters. For different relative position, in particular for different ranges of relative positions, it is possible that either the first or the further current-dependent parameter is higher than the remaining current-dependent parameter, in particular more than a certain amount. It is thus possible to assign a relative position, in particular a range of relative positions, to a certain ratio between the current-dependent parameters. In this case, it is not absolutely necessary to provide an absolute value of a current-dependent parameter as a position parameter, wherein a relative position or range of relative positions is assigned to said absolute value or a set of parameters comprising said absolute value.

It is, of course possible, that a set of multiple position parameters comprises said ratio and the absolute value of the first current-dependent parameter and/or the absolute value of the at least one further current-dependent parameter.

Determining the relative position, in particular the range of relative position, depending on the at least one ratio advantageously allows a computationally fast and reliable determination.

In another embodiment, a first current-dependent parameter for a first phase line of the primary winding structure, a second current-dependent parameter for a second phase line of the primary winding structure and a third current-dependent parameter for a third phase line are determined, wherein the at least one position parameter is determined depending on the ratios of the three current-dependent parameters. In this case, the primary winding structure comprises three phase lines. For different relative position, in particular for different ranges of relative positions, it is possible that either the first, the second or the third current-dependent parameter is higher than the remaining current-dependent parameters, wherein one of the remaining current-dependent parameters is again higher than the other remaining currentdependent parameter. It is thus possible to assign a relative position, in particular a range of relative positions, to certain ratios between the current-dependent parameters.

In this case, a set of multiple position parameters can comprise at least two ratios between different current-dependent parameters. It is, of course, possible that set of multiple position parameters comprises at least the three ratios between the three current-dependent parameters.

Determining the relative position, in particular the range of relative position, depending on the at least two ratios advantageously allows a computationally fast, reliable and accurate determination.

In another embodiment, the at least one position parameter is additionally determined depending on the transferred power and/or the operating frequency and/or a duty cycle duration and/or a phase shift values between the phase currents.

In other words, the dependency between the at least one position parameter (which is determined as a function of the at least one current-dependent parameter) and the relative position or range of relative position can change for different levels of transferred power and/or for different operating frequencies and/or for different duty cycle durations and/or for different phase shift values. In further other words, the dependency between the at least one position parameter and the relative position or range of relative position can be a power14 specific and/or operating frequency-specific and/or duty cycle duration-specific and/or phase shift value-specific dependency.

It is e.g. possible that a set of multiple parameters can comprise a parameter which characterizes the transferred power and/or a parameter which characterizes the operating frequency. In particular, a set of multiple parameters can comprise a parameter which is equal to or proportional to the transferred power and/or a parameter which is equal to or proportional to the operating frequency.

It is possible that the reactive phase current, in particular the power-mode reactive phase current, and/or the relative position depends on the amount of transferred power. The reactive phase current, e.g. one characteristic of the reactive phase current, can be proportional to the amount of transferred power.

It is further possible that the reactive phase current, in particular the power-mode or the idlemode reactive phase current, and/or the relative position depends on the operating frequency. The reactive phase current, e.g. one characteristic of the reactive phase current, can be proportional to the operating frequency.

It is further possible that the reactive phase current, in particular the power-mode or the idlemode reactive phase current, and/or the relative position depends on the duty cycle duration. The reactive phase current, e.g. one characteristic of the reactive phase current, can be proportional to the duty cycle duration.

It is further possible that the reactive phase current, in particular the power-mode or the idlemode reactive phase current, and/or the relative position depends on the phase shift between the phase currents, in particular on the previously explained phase shift operation. It is in particular possible that in a certain relative position or in a certain range of relative positions, inductive power transfer is only possible in the symmetrical or unsymmetrical phase shift operation.

In this case, it is possible to provide a predetermined assignment of at least one position parameter to a relative position or range of relative position for multiple levels of transferred power and/or for multiple operating frequencies and/or for multiple duty cycle durations and/or for multiple phase shifts. In other words, the amount of transferred power and/or the operating frequency and/or the duty cycle duration and/or for the phase shift can provide position parameters to which certain relative positions or ranges of relative positions are assigned.

This advantageously allows a more precise and reliable determination of the relative position or range of relative positions.

In another embodiment, the relative position or the range of relative positions is determined depending on a predetermined assignment of the at least one position parameter to a relative position or to a range of relative positions. Further, the relative position or the range of relative positions can determined depending on a predetermined assignment of a set of multiple position parameters to a relative position or to a range of relative positions. The set of position parameters can comprise at least one of the following parameters: a currentdependent parameter for at least one phase line, at least one ratio between two currentdependent parameters for different phase lines, the amount of transferred power, the operating frequency, a parameter characterizing the design of the primary unit, e.g. the geometry of the primary winding structure, a parameter characterizing the design of the secondary unit, e.g. the geometry of the secondary winding structure. It is, of course possible that the set of position parameters comprises at least one further parameter which affects the reactive phase current. This and corresponding advantages have been explained before.

In another embodiment, the relative position or the range of relative positions is determined by determining an interpolated relative position or an interpolated range of relative positions.

It is, for instance possible, that an assignment of relative positions or ranges of relative positions to at least one position parameter is only provided for a limited amount of position parameters or limited amounts of sets of multiple position parameters. If a position parameter or a set of position parameters which are determined does not match one of said assignments, the relative position or range of relative positions can be determined by interpolation or extrapolation using at least one position parameter or at least one set of multiple position parameters from the limited amount of position parameters or sets of multiple position parameters.

It is possible that a linear interpolation is applied, in particular for determining a relative position or range of relative position for a certain amount of transferred power and/or for a certain operating frequency and/or for a certain duty cycle duration which cannot be matched to limited amount of predetermined assignments.

This advantageously allows a reliable and sufficiently precise determination for a large variety of position parameters.

Further proposed is a system for determining a relative position or range of relative positions between a primary winding structure and a secondary winding structure of a system for inductive power transfer, in particular to a vehicle.

The system comprises at least one means for determining a reactive phase current of at least one phase line of the primary winding structure and at least one evaluation means.

The means for determining a reactive phase current can e.g. be provided by a current sensor. The means for determining a reactive phase current can e.g. measure the reactive phase current, in particular at least one characteristic of the reactive phase current, e.g. an amplitude, a peak value or a RMS value. The means for determining the reactive phase current can also determine a shape of a time course of the reactive phase current or at least one parameter characterizing said shape.

The evaluation means can e.g. be provided by an evaluation unit. This evaluation unit can e.g. be provided by or comprise a microcontroller.

The system advantageously allows to perform a method according to one of the embodiments described in this disclosure. Thus, the system can be designed accordingly. Further, the method for determining a relative position or range of relative positions can be performed by the system according to one of the embodiments described in this disclosure.

In particular, a power-mode reactive phase current of at least one phase line of the primary winding structure is determinable in a power transfer mode, in particular by the means for determining the reactive phase current. Further, at least current-dependent parameter is determinable depending on the power-mode reactive phase current, in particular by the evaluation means. Further, at least one position parameter or at least one set of multiple position parameters is determinable depending on the at least one current-dependent parameter, in particular by the evaluation means. Further, the relative position or the range of relative positions is determinable depending on the at least one position parameter, in particular by the evaluation means.

The system can also comprise at least one memory unit for storing at least one assignment of at least one position parameter to a relative position or set of relative positions.

The system can also comprise at least one control unit for controlling an operation of the inverter. The system can also comprise the inverter. It is possible that the control unit controls the operation of the inverter depending on the relative position or range of relative positions. The system can also comprise at least one signal or data transmission means, in particular for transmitting information on the relative position and or the range of relative positions to an external system, e.g. a secondary unit or a vehicle.

The invention will be described with reference to the attached figures. The figures show:

Fig. 1 a schematic circuit diagram of a primary unit,

Fig. 2 a schematic side view of a system for inductive power transfer to a vehicle,

Fig. 3 a schematic design of a primary winding structure,

Fig. 4 a schematic relation between switching currents and a relative position along a longitudinal axis of a primary winding structure,

Fig. 5 a schematic relation between a switching current value and an operating frequency and

Fig. 6 a schematic look-up table for different ranges of relative positions along a longitudinal axis of a primary winding structure.

In the following, the same reference numerals denote elements with the same or similar technical features.

Fig. 1 shows a schematic circuit diagram of a primary unit 1 of a system for inductive power transfer 2 (see Fig. 2). Further shown are elements of a system for determining a relative position or range of relative positions between a primary winding structure 3 and a secondary winding structure 4. The primary unit 1 comprises and inverter 5 which is designed with a B6 bridge topology. The inverter 5 comprises switching elements 6, wherein a bypass diode 7 is connected antiparallel to each switching element 6. The inverter 5 has three legs, wherein each leg comprises a series connection of two switching elements 6 and one phase line U,

V, W is connected to a connecting section of the two switching elements 6. A switching element 6 of the inverter 5 can e.g. be provided by a MOSFET or IGBT. The inverter 5 generates AC (alternating current) phase voltages for phase lines U, V, W of the primary winding structure 3.

The primary winding structure 3 is a three-phase winding structure. Schematically shown is an inductance Lu, L_v, L_w provided by each phase line U, V, W. Further shown are compensating capacitances Cu, Cv, Cw in each phase line U, V, W wherein a capacitance value of said capacitances Cu, Cv, Cw is chosen such that the resonant frequency of the resonant circuit provided by the inductance Lu, L_v, L_w and the capacitance Cu, Cv, Cw of each phase line U, V, W matches an operating frequency f (see Fig. 5).

Further shown are phase currents lu, Iv, lw in each phase line U, V, W which can provide reactive phase currents.

The system for determining a relative position or range of relative positions between a primary winding structure 3 and a secondary winding structure 4 comprises current sensors 8 which measure the phase currents lu, Iv, lw in each phase line U, V, W. In particular, the current sensors 8 measures the phase currents lu, Iv, lw which flow through one switching element 6 of a leg of the inverter 5 into the respective phase line U, V, W.

Further, the system comprises an evaluation unit 9 which is connected to the current sensors 8 by a signal link (shown by dashed lines). Further, the system comprises a memory unit 10 which is also connected to the evaluation unit 9 by a signal or data link. Further shown is a control unit 11 for controlling an operation of the inverter 5, e.g. of the switching elements 6. The control unit 11 is connected to the evaluation unit 9 by a signal or data link.

By means of the currents sensors 8, a power-mode reactive phase current lu, Iv, lw can be measured in a power transfer mode. In the power transfer mode, power is transferred from the primary unit 1 to a secondary unit 12 (see Fig. 2), wherein a secondary winding structure 4 is arranged within an active volume 13 of the primary unit 12. A phase shift between the first and the second phase current lu, Iv can be equal to120°, wherein a phase shift between the first and the third phase current lu, lw can be equal to 240°.

Further, in particular by means of the evaluation units, a phase-specific current-dependent parameter for each phase line U, V, W can be determined depending on the measured power-mode reactive phase currents. In particular, the phase-specific current currentdependent parameter can be determined as an amplitude of a switching current lu,s, lv,s, lw,s (see Fig. 3), wherein the switching current lu,s, lv,s, lw,s denotes the phase current lu, Iv, lw at the moment at which the corresponding phase voltage has a zero crossing .

Alternatively, the phase-specific current-dependent parameter can be determined as RMS or peak value within a time course of the phase current lu, Iv, lw with a predetermined duration.

Further, in particular by means of the evaluation unit 9, at least one position parameter or a set of multiple position parameters is determined depending on the at least one currentdependent parameter. In particular, a set of multiple position parameters can e.g. comprise each of the three phase-specific current-dependent parameters.

Further, in particular by means of the evaluation unit 9, the relative position or the range of relative positions is determined depending on the set of multiple position parameters.

In the memory unit 10, assignments of different sets of multiple position parameters to a relative position or range of relative positions can be stored. Each set can differ from the remaining sets by at least one position parameter. Based on the stored assignments, a position or range of relative positions is determined for the actual set of position parameters.

It is also possible to determine an interpolated relative position or an interpolated range of relative positions based on the stored assignments.

Information on the relative position or range of relative position can be transmitted to the control unit 11 which can control an operation of the inverter 5 based on the relative position or range of relative positions. It is e.g. possible to enable an operation if a secondary unit 12 with a secondary winding structure 4 is arranged within a predetermined enabling interval of relative positions. It is further possible to disable an operation if a secondary unit 12 with a secondary winding structure 4 is arranged outside the predetermined enabling interval.

Fig. 2 shows a schematic side view of a system 2 for inductive power transfer. The system 2 comprises a primary unit 1 which is provided by a charging pad installed on the surface of a route for a vehicle 14. The primary unit 1 comprises a primary winding structure 3. Not shown is an inverter 5 (see Fig. 1) of the primary unit 1. A secondary unit 12 with a secondary winding structure 4 is attached to a bottom of the vehicle 14. Further indicated is an active volume 13 of the primary unit 1. The active volume 13 can denote a volume in which an inductive power transfer from the primary unit 1 to the secondary unit 4 can be performed with a desired amount of power. In other words, a secondary winding structure 4 arranged in the active volume 13 can receive a desired power inductively. If arranged outside the active volume 13, the secondary winding structure cannot receive sufficient power inductively.

Further indicated is a primary-sided coordinate system. The primary-sided coordinate system comprises a longitudinal axis x, a lateral axis y (see Fig. 3) and a vertical axis z. The axes x, y, z provide a Cartesian coordinate system. An arrow 15 indicates a travel direction of the vehicle 14 if the vehicle 14 travels straight forward above the primary unit 1. The longitudinal axis x is oriented parallel to said travel direction. The vertical axis z is oriented from the primary unit 1 towards the secondary unit 12. The vertical axis can be oriented parallel to a direction of a gravitational force. Further indicated is an origin O of the primary-sided coordinate system which can correspond to a geometric center of the primary winding structure 3.

Further indicated is a secondary-sided coordinate system. The secondary-sided coordinate system comprises a longitudinal axis xs, a lateral axis ys (not shown) and a vertical axis z_s. The axes xs, ys, z_s provide a Cartesian coordinate system. The longitudinal axis xs is oriented parallel to a roll axis of the vehicle 14. The lateral axis ys is oriented parallel to a pitch axis of the vehicle 14. The vertical axis z_s is oriented parallel to a yaw axis of the vehicle 14. Further indicated is an origin Os of the secondary-sided coordinate system which can correspond to a geometric center of the secondary winding structure 4.

In an aligned state of the primary and the secondary unit 1,12, corresponding axes x, y, z, xs, ys, z_s can be oriented parallel. Alternatively, an angle between corresponding axes x, xs, y, y_s,z, z_s can be smaller than a predetermined value.

The relative position between the primary and the secondary winding structure 3, 4 can correspond to a position of the origin Os of the secondary-sided coordinate system in the primary-sided coordinate system. Preferably, the relative position between the primary and the secondary winding structure 3, 4 can correspond to a position of the origin Os of the secondary-sided coordinate system along the longitudinal axis x in the primary-sided coordinate system.

Fig. 3 shows a schematic top view on a primary winding structures 3 of a system 2 for inductive power transfer (see Fig. 2). The primary winding structure 3 comprises a first phase line U, wherein the first phase line U provides three subwinding structures U1, U2, U3.

Further, the primary winding structure 1 comprises a second phase line V and a third phase line W, wherein each phase line V, W provides three subwinding structure V1, V2, V3, W1, W2, W3. In the example shown in Fig. 3, the subwindings U1, .., W3 each have the shape of a rectangular loop.

Further shown is a primary-sided coordinate system with a primary-sided longitudinal axis x and a primary-sided lateral axis y. Directions of these axes x, y are indicated by arrows. These axes x, y span a plane, wherein the subwinding structures U1,..., W3 are substantially arranged in planes parallel to said plane.

A primary-sided vertical axis z (see Fig. 2) is oriented perpendicular to said plane. It is possible that the subwinding structures U1,...,W3 of different phase lines U, V, W are arranged in different planes in order to overlap each other.

The subwinding structures U1, ..., W3 of each phase line U, V, W extend along the longitudinal axis x. This means that the subwinding structures U1, ..., W3 of each phase line U, V, W are arranged adjacent to one another along the longitudinal axis x. The subwinding structures U1, ..., W3 of one phase line U, V, W do not overlap. That the subwinding structures U1,..., W3 extend along the longitudinal axis x can mean that geometrical centres of each subwinding U1,..., W3 are arranged along a straight line parallel to the longitudinal axis x.

Fig. 4 shows a schematic relation between switching currents lu,s, lv,s, lw,s and a relative position along a longitudinal axis x of a primary winding structure 3. In this example, the operating frequency f can be equal to 85.5 kHz and the amount of transferred power can be equal to 2.8 kW. Switching currents lu,s, lv,s, lw,s can be determined in a power transfer mode.

The relative position is indicated by a displacement Sx between the origin Os of the secondary-sided coordinate system and the origin O of the primary-sided coordinate system (see Fig. 2) along the longitudinal axis x of the primary-sided coordinate system. Indicated is a course of switching currents lu,s, lv,s, lw,s for each phase line U, V, W (see Fig. 1) for different displacements Sx. It can be seen that each course of switching currents lu,s, lv,s, lw,s for different displacements has a sinusoidal or quasi sinusoidal shape, wherein the courses are phase-shifted relative to each other.

In different ranges of relative positions, ratios between the switching currents lu,s, lv,s, lw,s are different. In the range of relative positions between -100 mm to -80 mm, the switching current lu,s of the first phase line U is higher than the switching current I_v,s of the second phase line V, wherein the switching current l_v,s of the second phase line is higher than the switching current l_w,s of the third phase line W. In the range of relative positions between -80 mm to -60 mm, the switching current lu,s of the first phase line U is higher than the switching current lw,s of the third phase line W, wherein the switching current lw,s of the third phase line is higher than the switching current I_v,s of the second phase line V.

Thus, a range of relative positions can be assigned to a specific combination or set of ratios of the switching currents lu,s, Iv.s, lw,s- In turn, determination of the ratios between the switching currents lu,s, Iv.s, lw,sallows to determine a range of relative positions.

Fig. 5 shows a schematic relation between switching currents lu,s, Iv.s, Iw.sand an operating frequency f. In this example, the amount of transferred power can be equal to 3.4 kW and the relative position between the primary and secondary winding structure 3, 4 (see Fig. 2) can be constant. Switching currents lu,s, lv,s, lw,s can be determined in a power transfer mode. It can be seen that the switching currents lu,s, lv,s, lw,s decrease linearly with an increasing operating frequency f. This advantageously allows a linear interpolation to determine a relative position or a range of relative positions for an operating frequency f which does not match exactly a position parameter, in particular of a set of multiple position parameters, of a predetermined assignment.

Fig. 6 shows a schematic look-up table for different ranges of relative positions along a longitudinal axis x of a primary winding structure 1 (see Fig. 2). Indicated is the highest switching current lu.s, lv,s, lw,s, (see second row of the table) the minimum switching current lu. s, Iv.s, Iw.s (see fourth row of the table) and the medium switching current lus, Iv.s, lw,s (see third row of the table) for different ranges of relative positions, wherein a relative position is again indicated by a displacement Sx between the origin Os of the secondary-sided coordinate system and the origin O of the primary-sided coordinate system (see Fig. 2) along the longitudinal axis x of the primary-sided coordinate system. It can be seen that the sequence of switching currents lu.s, lv,s, Iw.sfrom the highest to the lowest value is unique in a certain range of relative positions Sx. This, in turn, allows to reliably determine a range of relative positions Sx if the said sequence, i.e. the ratios between the switching currents lu.s, lv. s, lw,s, is determined.

Claims

1. A method for determining a relative position or range of relative positions between a primary winding structure (3) and a secondary winding structure (4) of a system (2) for inductive power transfer, wherein a power-mode reactive phase current of at least one phase line (u, v, w) of the primary winding structure (3) is determined in a power transfer mode, wherein at least a current-dependent parameter is determined depending on the power-mode reactive phase current, wherein at least one position parameter is determined depending on the at least one current-dependent parameter, wherein the relative position or the range of relative positions is determined depending on the at least one position parameter.

2. The method according to claim 1, characterized in that an idle-mode reactive phase current of the at least one phase line (U, V, W) of the primary winding structure (3) is determined in an idle mode, wherein the at least one current-depending parameter is determined depending on the power-mode reactive phase current and the idle-mode reactive phase current of the at least one phase line of the primary winding structure (3).

3. The method according to one of the preceding claims, characterized in that the currentdependent parameter is determined depending on at least one characteristic of the reactive phase current.

4. The method according to claim 3, characterized in that the at least one characteristic is selected from the group consisting of a RMS value of the reactive phase current, a value of the reactive phase current at a switching time point, a peak value of the reactive phase current, a square value of said peak value, a duty cycle of the reactive phase current in one switching period, a voltage value at the time point of the current zero crossing and a current value at the time point of the voltage zero crossing.

5. The method according to one of the preceding claims, characterized in that the currentdependent parameter is determined depending on a phase switching current (lu.s, lv,s, lw,s)·

6. The method according to one of the preceding claims, characterized in that a first currentdependent parameter for a first phase line (U) of the primary winding structure (3) and at least one further current-dependent parameter for a further phase line (V, W) of the primary winding structure (3) is determined, wherein the at least one position parameter is determined depending on a ratio of the at least two current-dependent parameters.

7. The method according to one of the preceding claims, characterized in that a first currentdependent parameter for a first phase line (U) of the primary winding structure (3), a second current-dependent parameter for a second phase line (V) of the primary winding structure (3) and a third current-dependent parameter for a third phase line (W) of the primary winding structure (3) is determined, wherein the at least one position parameter is determined depending on the ratios of the three current-dependent parameters.

8. The method according to one of the preceding claims, characterized in that the at least one position parameter is additionally determined depending on the transferred power and/or the operating frequency (f) and/or a duty cycle duration and/or phase shift values between the phase currents.

9. The method according to one of the preceding claims, characterized in that the relative position or the range of relative positions is determined depending on a predetermined assignment of the at least one position parameter to a relative position or to a range of relative positions.

10. The method according to claim 9, characterized in that the relative position or the range of relative positions is determined by determining an interpolated relative position or an interpolated range of relative positions.

11. A system for determining a relative position or range of relative positions between a primary winding structure (3) and a secondary winding structure (4) of a system (2) for inductive power transfer, wherein the system comprises at least one means for determining a reactive phase current of at least one phase line (U, V, W) of the primary winding structure (3) and at least one evaluation means, wherein a power-mode reactive phase current of at least one phase line of the primary winding structure is determinable in a power transfer mode, wherein at least current-dependent parameter is determinable depending on the power-mode reactive phase current, wherein at least one position parameter is determinable depending on the at least one current-dependent parameter, wherein the relative position or the range of relative positions is determinable depending on the at least one position parameter.

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Application No: GB1706274.6