Method for positioning a vehicle over a base plate for inductive charging of a vehicle battery

Abstract

Method for positioning a vehicle (10) having a secondary resonant circuit over a base plate (3) having a primary resonant circuit for inductively charging a vehicle battery (13), wherein the primary coil (4) of the primary resonant circuit and the secondary coil (11) of the secondary resonant circuit are to be positioned on top of each other within a predetermined deviation, wherein several transmitting antennas (S1, S2, S3, S4) are installed in the base plate (3), the extent of which along one axis is greater than along an axis perpendicular to it, and wherein at least one receiving antenna is arranged in the vehicle (10), wherein each transmitting antenna (S1, S2, S3, S4) is connected to a signal generation unit and generates a magnetic field with a predetermined frequency, which is received by the receiving antenna, and an evaluation unit connected to the receiving antenna is designed to evaluate the voltage and / or the current flowing at the receiving antenna with respect to magnitude and phase and, by comparing its course as the vehicle (10) approaches the base plate (3) with predetermined values, to generate signals that indicate the deviation of the actual position of the vehicle (10) from a target position, wherein each transmitting antenna (S1, S2, S3, S4) is formed with a resonant circuit and to deactivate a transmitting antenna (S1, S2, S3, S4) the resonant circuit is detuned.

Description

[0001] The invention relates to a method for positioning a vehicle over a base plate for inductively charging a vehicle battery. A device for inductively charging a vehicle battery and a method for positioning the vehicle over the base plate are known from US 2015 / 0 260 835 A1.

[0002] Fig. Figure 1 shows such a device, known from US 2015 / 0 260 835 A1, for the inductive charging of a vehicle battery. It comprises a power supply unit 1 with a typically stationary charging station 2, often also called a "wallbox," which is connected to the public AC power grid, for example, via a power cable 16. The charging station 2 transmits the energy drawn from the grid, after appropriate conversion, as a high-frequency voltage via a power supply line 5 to a primary resonator unit comprising a primary coil 4, which is installed in a base unit 3.

[0003] The ground unit 3 is connected to the charging station 2 not only via the power supply line 5 but also via a communication line 6. In principle, communication between the ground unit 3 and the charging station 2 can also take place wirelessly.

[0004] The Fig. Figure 1 also shows a vehicle 10 which has a secondary resonant circuit with a secondary coil 11 which, in the optimally positioned state, forms a well-coupled transformer with the primary coil 4 of the ground unit 3 for the inductive transfer of energy to the vehicle 10.

[0005] The energy absorbed by the secondary resonant circuit 11 is transferred via an energy converter 12, which in particular has a rectifier, to an energy storage device 13, usually in the form of an accumulator and hereinafter referred to as a vehicle battery, and stored there to be available for the drive of electric motors.

[0006] The vehicle 10 shown also has a parking assistant 14, which enables the vehicle 10 to independently find a designated parking space and position itself there using sensors and actuators.

[0007] In such a system for the inductive charging of a vehicle battery 13, the primary coil 4 in the base unit 3 and the secondary coil 11 in the vehicle must be positioned spatially relative to each other to achieve the best possible coupling factor. The base unit 3 can communicate with the vehicle 10, if necessary, via the charging station 2 and a wireless communication device 15 implemented therein, so that the vehicle 10 knows the coil position and autonomously drives itself to the corresponding parking position, as is known from automated driving, and attempts to align the vehicle's secondary coil 11 with the primary coil 4 in the base unit 3. However, this is often not possible with the required positional accuracy.

[0008] The Fig. Figure 2 shows the dependence of the coupling efficiency on the horizontal offset of the two coils. It shows that the efficiency decreases significantly from an offset of approximately 10 cm.

[0009] Current standardization bodies are prescribing a "catch zone" between the primary and secondary coils of 7.5 cm in the direction of travel and 10 cm in the direction of lateral offset. According to the current state of discussion, the vehicle's task is to determine, in absolute terms, whether this "catch zone" is met. In standards terminology, this is called an "initial alignment check," as this function must take place before power transmission.

[0010] From EP 3 103 674 A1, a system for the mutual relative position determination of two transformer elements of an inductive power transfer arrangement is known. The system comprises at least one first transformer element with a preferably planar first coil and at least one second transformer element with a preferably planar second coil. Several measuring coils are connected to an evaluation unit in which currents or voltages induced in the measuring coils are evaluated and a signal characteristic of the distance between the first and second coils is generated. At least four measuring coils are mounted on the first transformer element, their axes being parallel to the plane of the first coil. Two measuring coils are arranged parallel to each other and on opposite sides of the center of the first coil.In this case, the axes of one group of parallel measuring coils form a non-zero angle with the axes of the second group of parallel measuring coils.

[0011] From EP 2 584 665 A2, a battery charging system for a vehicle is known. Primary and secondary coils are located in such a way that the vehicle can draw power from the primary coil, for example, by parking in a parking space. The parking space can have a coil embedded in the ground or an array of coils embedded in the ground. The secondary coil in the vehicle can also be raised or lowered to improve the coupling. A guidance system and fine positioning are used to position the vehicle in the parking space.

[0012] From DE 10 2016 220 725 A1, a method for determining the actual relative position of a vehicle's secondary coil relative to a charging station's primary coil is known. The method comprises determining the actual field strength value of a magnetic field at a receiver, wherein the magnetic field was generated by a transmitter. The transmitter is located on the vehicle and the receiver on the charging station, or vice versa. The actual field strength value indicates the magnetic field strength at the position where the receiver is located. The method also includes determining position data with respect to the actual relative position by comparing the actual field strength value with reference field strength values ​​from a characteristic map, wherein the characteristic map displays reference field strength values ​​as a function of the relative position of the secondary coil relative to the primary coil, and wherein the characteristic map was determined beforehand for the vehicle and the charging station.

[0013] From WO 2013 / 045 999 A2, an energy transmission device is known which comprises: an energy transmission section that transmits electrical energy contactlessly to an energy receiving section that is spaced apart from the energy transmission section; a first coil unit that is spaced apart from the energy transmission section and that supplies the energy transmission section with electrical energy; and a supply cable that is connected to the first coil unit and that supplies the first coil unit with electrical energy from a power source. The first coil unit comprises a first coil that is connected to the supply cable and a second coil that is connected to the first coil, the first coil being arranged around the energy transmission section, converting the unbalanced current supplied by the power supply into balanced current, and supplying the balanced current to the second coil.

[0014] It is therefore the object of the invention to provide a method for positioning a vehicle over a base plate for inductive charging of a vehicle battery that fulfills this function.

[0015] The problem is solved by a method according to claim 1. Advantageous further developments are specified in the dependent claims.

[0016] Accordingly, in a method for positioning a vehicle having a secondary resonant circuit above a base plate having a primary resonant circuit for inductively charging a vehicle battery, - wherein the primary coil of the primary resonant circuit and the secondary coil of the secondary resonant circuit are to be aligned within a predetermined deviation, wherein several transmitting antennas are installed in the base plate, the extent of which along one axis is greater than along an axis perpendicular to it, and wherein at least one receiving antenna is arranged in the vehicle, - each transmitting antenna is connected to a signal generation unit and generates a magnetic field with a predetermined frequency, which is received by the receiving antenna, and an evaluation unit connected to the receiving antenna is provided.The system evaluates the voltage and / or current generated at the receiving antenna with respect to magnitude and phase, and, by comparing its behavior as the vehicle approaches the base plate with predefined values, generates signals indicating the deviation of the vehicle's actual position from a target position. Each transmitting antenna is formed with a resonant circuit, and to deactivate a transmitting antenna, the resonant circuit is detuned.

[0017] Advantageously, not only the magnitude of the magnetic field measured as the vehicle approaches the base plate is evaluated, but also its phase. The magnetic field lines run almost parallel to the plane of the secondary coil in the region of the primary coil windings, so that only a small voltage is induced in the secondary coil when it is in the region of the primary coil windings. In contrast, the phase changes direction at this point, which can be readily evaluated, allowing conclusions to be drawn about the vehicle's position.

[0018] In a further development of the method according to the invention, four transmitting antennas are installed in the base plate, wherein the transmitting antennas are arranged along the outer line of a square or rectangle and overlap, with only one transmitting antenna being controlled by the signal generation unit at any given time.

[0019] With such elongated antennas, the field strength profile can be advantageously adjusted to allow for unambiguous positioning.

[0020] To prevent the transmitting antennas from interfering with each other, according to the invention each transmitting antenna is formed with a resonant circuit, wherein the resonant circuit is detuned to inactivate a transmitting antenna.

[0021] If multiple resonant antennas are present on the transmitting side (and possibly also on the receiving side), and only one antenna may be active at any given time, effective suppression of the receiving characteristics of the otherwise inactive antennas is necessary. Without this suppression, an inactive transmitting antenna, which is not being driven, can pick up and re-emit the field of an active transmitting antenna. This massively disrupts the magnetic field pattern of the active transmitting antenna, rendering it unusable for precise positioning.

[0022] The same principle applies to potentially multiple receiving antennas. An inactive receiving antenna extracts energy from the field being measured, which is then lacking for the active receiving antenna. Consequently, the active receiving antenna absorbs less energy, and the induced voltage does not represent the true field strength being measured.

[0023] In an active antenna, its resonant frequency is tuned to the frequency of the excitation signal (e.g., 13.56 MHz). Conversely, this means that an inactive antenna is not resonant at this frequency, or may not be resonant at all. Resonance can be eliminated, for example, by using a switchable short circuit. The capacitor in the resonant circuit can be bypassed by a switch. Another possible solution is to detune the antenna using a PIN diode. Since the PIN diode can change its capacitive component via a controlled DC current, it acts as a controllable capacitor. By changing the capacitance of the diode, which is connected in parallel to the capacitor, the antenna can be detuned.

[0024] In a further embodiment of the method according to the invention, the evaluation unit is designed to evaluate the amplitude profile according to secondary and main maxima and to determine the distance to the target position from this.

[0025] Since the secondary maxima occur before a main maximum, the relative position can be determined early on.

[0026] In a further embodiment of the method according to the invention, the evaluation unit is configured to compare the signals from parallel transmitting antennas and to determine the distance to the target position. This increases the positioning accuracy.

[0027] In an advantageous further development of the method according to the invention, the evaluation unit is designed to evaluate the amplitude and / or phase profile of the signal received by a receiving coil as a function of the vehicle height.

[0028] Due to the mostly metallic underside of a vehicle, the vehicle height influences the magnetic field of the transmitting antenna, so that by taking the vehicle height into account, a more precise positioning can be achieved.

[0029] In another embodiment of the invention, the base plate also features a FOD (Foreign Object Detection) mat for detecting foreign objects, in which the transmitting antennas are integrated. This allows for considerable space savings.

[0030] In a training course, antennas of the FOD mat are used as transmitting antennas.

[0031] In a further development, the transmitting and / or receiving antennas are connected to the signal generation unit or the evaluation unit via coaxial cables or twisted lines.

[0032] The transmitting and / or receiving antennas can be connected to the signal generation unit or the evaluation unit via a common-mode filter.

[0033] The invention is explained in more detail below using an exemplary embodiment and the accompanying figures. These figures show... Fig. 1 an arrangement comprising a charging station for inductively charging the battery of a vehicle and a vehicle according to the state of the art, Fig. 2. the course of the efficiency of the magnetic coupling of the coil of a base plate with a vehicle coil as a function of the offset of the two coils, Fig. 3 an arrangement with four elongated, overlapping transmitting coils, Fig. 4 the magnitude of the magnetic field of a rectangular coil, Fig. 5 the phase of the magnetic field of a rectangular coil and Fig. 6. A representation of only one transmitting coil and the target window to be reached. Fig. 7. The representation of vehicle height for different vehicle types.

[0034] In the Fig. Figure 3 schematically depicts a base plate 3 in which four rectangular transmitting coils S1, S2, S3, S4 are indicated, overlapping each other. The transmitting coils S1, S2, S3, S4 are not located directly in the main field of energy transfer, but rather at the edge of a primary coil of the energy transformer, thus preventing them from being excessively heated by induced power. Combinations of elongated and round coils are also possible to simplify positioning. The coil of the receiving antenna on the secondary side, i.e., in the vehicle, is usually round to utilize the radial symmetry of the secondary coil.

[0035] The transmitting coils S1, S2, S3, S4, as well as (not shown) receiving coils, are connected with capacitors to form resonant circuits, thus forming the primary and secondary resonant circuits.

[0036] In the Fig. 4 and Fig. Figure 5 shows the magnitude and phase of the alternating magnetic field of a transmitting coil S1, S2, S3, S4. It can be seen that in a region where the magnitude of the magnetic field is almost zero, the phase changes abruptly, which is easily detectable. Therefore, according to the invention, both the magnitude and phase are evaluated to enable precise positioning.

[0037] To perform the aforementioned "initial alignment check," it must be ensured that the vehicle is positioned unambiguously within the target window. Due to changes in the field strength at different vehicle heights and load conditions, position detection based solely on field strength cannot be guaranteed. As additional information, the phase relationship between current and voltage in the secondary coil on the secondary side, induced by the magnetic field generated by the primary coil, can be used.

[0038] In an antenna, according to Fig. 4 a forehill and a main hill.

[0039] Fig. Figure 5 shows the phase of the signal induced in the secondary coil. The phase in the two hills differs significantly, allowing identification of the relative positions of the primary and secondary coils. By using multiple transmitting antennas on the underside of the vehicle, the magnitude and phase of the magnetic field strengths during successive activation of these antennas can be used to calculate a unique geometric position of the vehicle, provided the relative positions of the multiple transmitting antennas are known.

[0040] Instead of multiple transmitting antennas as in Fig. 3. A single transmitting antenna can also be used, as in Fig. Figure 6 shows the procedure for performing the initial alignment check. For this, it must be ensured that the transmitting and receiving coils are positioned one above the other within a specific window. This window is located at + / - 10 cm in the Y direction and + / - 7.5 cm in the X direction. However, the exact geometric position of the coil within the target window cannot be determined. By using a suitably designed transmitting antenna where the phase shift corresponds to the edge of the target window, it can be clearly determined whether the vehicle's antenna is located within or outside the target window.

[0041] As an additional check, the magnitude of the field strength, i.e., the voltage measured at the receiving antenna, can be used to eliminate ambiguities. The phase is within the target window according to... Fig. 5 at approximately 120°. When the target window is exited, the phase should change drastically. The phase switches from +120° to -60°, which can be easily detected by a circuit. A phase detector can be used to enable simple evaluation. No complex algorithm is necessary to perform the initial alignment check.

[0042] The target window depends on the antenna size and shape, as well as the distance between the transmitting and receiving antennas. Increasing the distance decreases the size of the target window.

[0043] To enable positioning even when the vehicle is fully charged, several solutions exist. One option is to use fixed antennas on the secondary side, regardless of the vehicle's height. Depending on the vehicle type, the inductive charging standard defines three vehicle heights. A primary coil is used for each of these classes, and the secondary coil attached to the vehicle is selected according to class Z1-Z3. Fig. 7. The secondary receiver coil is adjusted to the vehicle height. This can also be used in the system presented here, allowing different sizes to be used for the initial alignment check for different vehicle classes. The higher the vehicle, the smaller the receiver coil must be.

[0044] Secondly, two receiving antennas can be used instead of one to cover the maximum vehicle heights. It makes no difference whether the antenna is mounted on the primary or secondary side. This allows for precise detection of the target window even with varying vehicle heights. The antennas are activated alternately, and the inactive one is deactivated to prevent interference. Charging can only begin when both antennas and their respective signal strengths indicate that the target window has been reached.

[0045] Another possibility is to use odometry (vehicle-side driving sensors such as wheel speed / circumference and steering angle), the gradient of the field strength and the phase change to calculate how high the vehicle is and whether the vehicle is reaching the target window during the approach.

[0046] Another possible solution involves integrating the antenna into the FOD (foreign object detection) sensor mat, which should already be present in the primary-side base plate, or integrating it into the plastic cover without any additional height. Generally, the positioning antennas used for approach and alignment are no longer needed for subsequent use, such as charging. These positioning antennas, possibly integrated into the FOD mat, can even physically function as a direct FOD measuring coil, but may then need to be switched between the two operating modes.

[0047] As in Fig.As shown in Figure 4, the main peak or saddle of the magnetic field strength is preceded by a so-called "forepeak" (a small elevation in front of it). Between the main peak and the forepeak, there is a zero crossing, the shape of which, viewed from above, roughly corresponds to the shape of the transmitting antenna. The distance of the forepeak to the crest of the main peak after driving through the trench indicates that the vehicle is inside the transmitting coil or within the dimensions of the main peak. Based on the known dimensions of the main peak, the "capture area" or the vehicle's position relative to the transmitting coil can be determined. If the vehicle or the ground coil registers that the forepeak has already been driven over, the next "elevation" must be the main peak, even if it appears very small in absolute terms due to, for example, a large vehicle height or a lateral offset of the car.By coupling this knowledge with the odometry of the vehicle and possibly with the help of a neural algorithm, the position of the vehicle in relation to the base plate can be calculated quite clearly.

[0048] The invention describes a near-field positioning system (< 1 m) in the MHz range (e.g., 13.56 MHz, although other frequencies are also possible). Elongated coils are used to enable absolute positioning for the initial alignment check. Overlapping these coils, which act as antennas, allows for improved positioning. The antenna size, shape, and position can be adapted to the magnetically active area of ​​the ground coil or to the accuracy requirements for the final position (for example, the smaller the detection range, the smaller or narrower the coils).

[0049] Common-mode filters with common-mode choke are used to ensure undisturbed measurement signals, along with a twisted (possibly shielded) feed line. Individual antennas are switched sequentially using PIN diodes or relays. During this process, the resonant circuit of uninvolved antennas is either interrupted (switching, see above) or detuned to prevent interference with the respective pair of transmitting and receiving antennas.

[0050] In addition to the amplitude, the phase is also evaluated (e.g., between voltage and current of the secondary or receiving coil).

[0051] The transmitting antenna(s) can be integrated into the FOD film or the base plate lid. FOD measuring coils (sensors) can also be used as positioning antennas if simultaneous use is not required.

[0052] Pre-hill analysis, elevation analysis, and odometry can be performed, for example, using a neural network.

Claims

[1] Method for positioning a vehicle (10) having a secondary resonant circuit over a base plate (3) having a primary resonant circuit for inductively charging a vehicle battery (13), wherein the primary coil (4) of the primary resonant circuit and the secondary coil (11) of the secondary resonant circuit are to be positioned on top of each other within a predetermined deviation, wherein several transmitting antennas (S1, S2, S3, S4) are installed in the base plate (3), the extent of which along one axis is greater than along an axis perpendicular to it, and wherein at least one receiving antenna is arranged in the vehicle (10), wherein each transmitting antenna (S1, S2, S3, S4) is connected to a signal generation unit and generates a magnetic field with a predetermined frequency, which is received by the receiving antenna, and an evaluation unit connected to the receiving antenna is designed to evaluate the voltage and / or the current flowing at the receiving antenna with respect to magnitude and phase and, by comparing its course as the vehicle (10) approaches the base plate (3) with predetermined values, to generate signals that indicate the deviation of the actual position of the vehicle (10) from a target position, wherein each transmitting antenna (S1, S2, S3, S4) is formed with a resonant circuit and to deactivate a transmitting antenna (S1, S2, S3, S4) the resonant circuit is detuned. [2] Method according to claim 1, wherein four transmitting antennas (S1, S2, S3, S4) are installed in the base plate (3), wherein the transmitting antennas (S1, S2, S3, S4) are arranged along the outer line of a square or rectangle and overlap, wherein only one transmitting antenna (S1, S2, S3, S4) is controlled by the signal generation unit at any given time. [3] Method according to one of the preceding claims, wherein the evaluation unit is configured to evaluate the amplitude profile according to secondary and main maxima and to determine the distance to the target position from it. [4] Method according to one of the preceding claims, wherein the evaluation unit is configured to compare the signals of parallel transmitting antennas (S1, S2, S3, S4) and to determine the distance to the target position. [5] Method according to one of the preceding claims, wherein the evaluation unit is configured to evaluate the amplitude and / or phase response of the signal received by a receiving coil as a function of the vehicle height. [6] Method according to one of the preceding claims, wherein the base plate (3) also has a FOD mat and the transmitting antennas (S1, S2, S3, S4) are integrated therein. [7] Method according to claim 6, wherein antennas of the FOD mat are used as transmitting antennas (S1, S2, S3, S4). [8] Method according to any of the preceding claims, wherein the transmitting (S1, S2, S3, S4) and / or receiving antennas are connected to the signal generation unit or the evaluation unit via coaxial cables or twisted pairs. [9] Method according to one of the preceding claims, wherein the transmitting and / or receiving antennas are connected to the signal generation unit or the evaluation unit via a common-mode filter.

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