DE102012217424A1 - Energy transfer arrangement and method for operating the energy transfer arrangement - Google Patents

Abstract

The invention relates to a method (42) for operating a wireless energy transmission arrangement (10) having a primary element (18) and a secondary element (20) which can be inductively coupled to draw electrical energy from the primary element (18) to the secondary element (20) wherein an adjustable load impedance is coupled to the secondary link (20), wherein substitute electrical quantities for an electrical model (34) of the energy transfer assembly (10) are determined, the electrical model (34) comprising an electrically conductive object (32) in a transmission link (28) between the primary member (18) and the secondary member (20), wherein an impedance value of the load impedance is determined on the basis of the substitute electrical quantities and a determined electrical power dissipation of the arranged in the transmission path (28) object (32), and wherein the load impedance is set to the impedance value.

Description

The present invention relates to a method of operating a wireless power transmission arrangement having a primary member and a secondary member which are inductively coupled to transfer electrical energy from the primary member to the secondary member.

Furthermore, the present invention relates to a power transmission arrangement having a primary member and a secondary member, which are inductively coupled to transmit electrical energy from the primary member to the secondary member.

State of the art

In the field of motor vehicle drive technology, it is well known to use an electric machine as a sole drive or together with a drive motor of another type (hybrid drive). In such electric or hybrid vehicles electrical machines are typically used as a drive motor, which by an electrical energy storage such. As an accumulator to be supplied with electrical energy. The electrical energy storage of electric vehicles or plug-in hybrid vehicles must be regularly connected depending on the state of charge with an electrical power grid to load the energy storage with electrical energy.

For example, a cable can be used to transmit the electrical energy from a charging station to the vehicle. However, such a cable connection offers a very poor ease of use and also represents a potential danger to the user, as this could come in case of damage to the connector or the cable in contact with live parts.

As an alternative to a cable connection, it is possible to supply vehicles with electrical energy via a wireless energy transmission. In an inductive energy transfer, a magnetic alternating field is generated on a primary side by means of a coil. At least part of this alternating magnetic field penetrates a secondary side, which also has a coil. As a result, a voltage is induced in the coil of the secondary side and thus energy is transferred from the primary side to the secondary side. In this case, the coil system of the primary side and the secondary side can be modeled as a transformer with a large air gap. The air gap causes large stray inductances and relatively poor coupling between the primary and secondary coils. The stray inductances lead to high reactive currents in the system, which do not contribute to energy transfer, but produce ohmic losses. Therefore, the efficiency of the wireless power transmission is worse than in the wired transmission. However, such energy transfer is more comfortable due to the easier handling and thus offers greater acceptance by the user.

By utilizing primary and secondary capacitances, the energy transfer system can be resonated, effectively improving transferable performance and achievable efficiency. Therefore, in known wireless power transmission systems usually this resonant operating point is sought.

The transmittable power of a wireless power transmission system is limited by the security requirements to be met. Thus, during the energy transfer in a region between the primary coil and the secondary coil, a magnetic field of high field strength and flux density is built up. If humans or animals enter this area during the energy transfer, body currents can be induced. Electrically conductive objects are strongly heated in this area by the induced eddy currents. A protection goal is to reduce the heating of such objects and thus comply with the safety requirements set for it. If the wireless energy transmission system is set to the resonant operating point, then the maximum possible energy can not be transmitted in consideration of the safety requirements.

Disclosure of the invention

The present invention therefore provides a method of operating a wireless power transmission assembly having a primary member and a secondary member that are inductively coupled to transfer electrical energy from the primary member to the secondary member, wherein an adjustable load impedance is coupled to the secondary member, wherein first electrical Substitute sizes for an electrical model of the power transmission arrangement are determined, wherein the electrical model takes into account an electrically conductive object in a transmission path between the primary member and the secondary member, wherein an impedance value of the load impedance on the basis of the substitute electrical quantities and a determined electrical power dissipation arranged in the transmission line Object is determined and wherein the load impedance is set to the impedance value.

Further, the present invention provides an energy transfer assembly having a primary member and a secondary member which are inductively coupled to transfer electrical energy from the primary member to the secondary member, wherein an adjustable load impedance is coupled to the secondary member, and with a control unit adapted thereto is to carry out the method of the type mentioned above.

Advantages of the invention

In the method according to the invention, the power loss of an object located in the transmission path is minimized or the transmittable power of the energy transmission arrangement is maximized by means of the adjustable load impedance. It is irrelevant which concrete electrically conductive object is used to set the load impedance of the energy transmission arrangement, since the optimization of the energy transmission arrangement is equally valid for all electrically conductive objects.

To analyze the operating behavior of the energy transmission arrangement, an electrical model or an equivalent electrical circuit diagram of the energy transmission arrangement is used in which the energy transmission arrangement and the object located in the transmission path (eg air gap between the primary element and the secondary element) are represented as substitute electrical quantities.

It is particularly preferred if the impedance value is determined such that the electrical power loss of the object is minimized at a predefined value of an active electrical power of the load impedance.

In this embodiment, the load impedance is adjusted so that heating of the object located in a region between the primary member and the secondary member is minimized for the same transmitted power. Thus, hazards due to an overheated object (eg a fire) can be avoided.

In another embodiment, the impedance value is determined such that the effective electrical power of the load impedance is maximized at a predefined value of the electrical power dissipation of the object.

With the load impedance adjustment in accordance with the present invention, in this embodiment, the transmittable power is maximized for given safety requirements (particularly with respect to heating of objects in the region between the primary member and the secondary member) and increased over known wireless energy transmission systems.

According to a further embodiment, the impedance value is determined by means of a numerical method.

According to the invention, an optimized impedance value of the load impedance is calculated on the basis of a numerical optimization method. For this purpose, in each operating point of the energy transmission arrangement, which is determined essentially by the current value of the load impedance, all necessary electrical currents and electrical voltages of the electrical equivalent circuit diagram are calculated in order to determine the power loss of the object. The one impedance value at which, for example, the lowest power loss occurs at a given power to be transmitted characterizes the optimized impedance value.

In a further embodiment, the impedance value is determined for a position of the object in the transmission path at which the electrical power loss of the object is maximum.

The impedance impedance value to be set depends, in particular, on the position of the object between the primary element and the secondary element. Does the primary link z. B. a primary coil for transmitting the electrical energy, the power dissipation of the object is relatively high when it is arranged in the vicinity of the windings of the primary coil. Accordingly, the object is heated particularly strongly at this position.

If the impedance value is determined for that position of the object at which the power loss / heating of the object is at a maximum, it can be ensured that the safety requirements for other arbitrary positions of the object between the primary element and the secondary element are observed.

In a further embodiment, the determining of the electrical substitute quantities comprises determining first electrical substitute quantities, wherein the object is arranged outside the transmission path, arranging the object in the transmission path, determining second electrical substitute quantities and determining the electrical substitute quantities on the basis of first and second electrical replacement sizes.

By this measure, first the electrical equivalent sizes of the electrical equivalent circuit diagram are identified, which characterize the wireless power transmission arrangement. Subsequently, the object is positioned in the transmission path. By re-determining the electrical Replacement sizes and a comparison with the previously determined replacement sizes and the electrical equivalent sizes of the object can be determined. This makes it possible to calculate the power loss of the object.

According to a further embodiment, the first and / or the second electrical substitute quantities are determined on the basis of measured physical quantities.

In this embodiment, the parameters or the electrical equivalent quantities of the equivalent electrical circuit diagram are determined by means of measurements on the energy transmission arrangement. For example, electrical currents and / or electrical voltages of the energy transmission arrangement can be measured.

Advantageously, the parameters of the equivalent electrical circuit diagram can thus be detected under real conditions.

In a further embodiment, the first and / or the second electrical substitute quantities are determined on the basis of a simulation.

Since the electrical equivalent quantities are determined in this embodiment in a simulation, can be dispensed with expensive measurements. The parameters can thus be determined very quickly and in a simple manner.

According to a further embodiment, a plurality of ohmic resistors are determined as electrical equivalent quantities of the object.

During the positioning of the object in the alternating magnetic field of the energy transmission arrangement so-called eddy currents are induced in the object. The resulting eddy current losses can be represented as equivalent ohmic resistors in the electrical equivalent circuit diagram.

In a further embodiment, an ohmic component and a capacitive component of the load impedance are determined.

In determining the impedance value of the load impedance, both the real part (the resistive part) and the imaginary part of the load impedance are optimized. The imaginary part has a capacitive component in order to at least partially compensate for the large stray inductance of the energy transmission arrangement (caused by the large air gap between the primary element and the secondary element).

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the invention

In addition, it is understood that the features, properties and advantages of the method according to the invention also apply correspondingly to the device according to the invention or are applicable.

Brief description of the drawings:

1 shows in schematic view a power transmission arrangement for exchanging electrical energy between an electric vehicle and a charging station;

2 shows an electrical equivalent circuit diagram of the power transmission arrangement;

3 shows another electrical equivalent circuit diagram of the power transmission arrangement, which takes into account an electrically conductive object in a transmission path of the power transmission arrangement;

4 shows a diagram illustrating a temperature profile of the electrically conductive object at different load impedances; and

5 shows a diagram for explaining an embodiment of a method according to the invention.

Embodiments of the invention

1 shows a wireless power transmission arrangement 10 for transmitting electrical energy from a power grid 12 to an electric vehicle 14 , The electric vehicle 14 typically has an in 1 unspecified electric induction machine, which is used as a drive motor. In addition, the electric vehicle points 14 a traction battery 16 which provides electrical energy for operating the electric induction machine. After a certain period of operation of the electric vehicle 14 needs the traction battery 16 be recharged. For this purpose, electrical energy from the power grid 12 with the help of the power transmission arrangement 10 to the traction battery 16 transfer.

The energy transfer arrangement 10 has a primary link 18 and a secondary link 20 on. The primary link 18 has a primary coil for transmitting electrical energy 22 on and is electric with the power grid 12 coupled. In the present case, the primary member forms 18 a part one in 1 Unspecified ground station for charging electric vehicles in a road surface 24 is admitted. The secondary link 20 has a secondary coil for transmitting electrical energy 26 on and is electric with the traction battery 16 coupled. The secondary link 20 forms part of an in 1 Unspecified vehicle-mounted charging device for charging the traction battery 16 ,

To charge the traction battery 16 is using the primary coil 22 generates a magnetic alternating field. At least part of this alternating magnetic field penetrates the secondary coil 26 , thereby inducing a voltage and thus energy from the primary element 18 on the secondary link 20 and thus the traction battery 16 is transmitted.

Between the primary link 18 and the secondary member 20 is a transmission link 28 formed, for example, has a larger air gap. This air gap causes large stray inductances and leads to poor coupling between the primary element 18 and the secondary member 20 , For this reason, the vehicle-side charging device has an adjustment member 30 on, with which the transferable power and the efficiency of the energy transfer arrangement 10 can be influenced. The adaptation element 30 and the traction battery 16 together form one to the secondary link 20 coupled load impedance Z _L , for setting an operating point of the power transmission arrangement 10 is used.

Conventional wireless power transmission systems typically set a resonant operating point to improve the transferable power and energy transfer efficiency.

However, the reliability of wireless energy transmission systems is an important issue. Thus, when operating the power transmission arrangement 10 between the primary link 18 and the secondary member 20 a high-frequency alternating magnetic field formed. For example, is there an electrically conductive object 32 in this magnetic field, so eddy currents are induced, which leads to a heating of the object 32 to lead. Particularly problematic are materials which have both a good electrical and a good magnetic conductivity (eg iron). To an inadmissibly strong heating of the object 32 To avoid this, certain safety requirements must be met by the power transmission system 10 be respected.

According to the invention, therefore, the load impedance Z _L is proposed by means of the adaptation element 30 adjust so that either the heating of in the transmission line 28 located objects 32 is reduced with the same transmitted power or the transmittable power is increased while maintaining the same safety requirements.

In order to determine an optimized impedance value of the load impedance Z _L , first the operating behavior of the energy transmission arrangement is determined 10 with the help of an electric model 34 or a conventional electrical equivalent circuit diagram 34 a transformer that is in 2 is shown described.

It will be in 2 the following sizes are referenced:
u = w1 / w2: gear ratio formed by the ratio of the number of turns w1 of the primary coil 22 and winding number w2 of the secondary coil 26 ;
U ₁ : input voltage;
U ₂ : output voltage;
U ₂ '= u * U ₂ : transformed output voltage;
I ₁ : input current;
I ₂ : output current;
I ₂ '= 1 / u · I ₂ : transformed output current;
L _1σ : leakage inductance of the primary coil 22 ;
L _2σ ': transformed leakage inductance of the secondary coil 26 ;
R1: Winding resistance of the primary coil 22 ;
R2: transformed winding resistance of the secondary coil 26 ;
L _h : main inductance;
R _h : Resistance for modeling the iron losses of the energy transfer device 10 ;
Z _L : load impedance.

All parameters of the electrical equivalent circuit diagram 34 out 2 can be determined by measurements or simulations. The values measured on the secondary side are related to the transmission ratio u on the primary side. It should be noted that when determining the parameters / electrical equivalent quantities of the power transmission arrangement 10 initially no electrically conductive object in the transmission path 28 between the primary link 18 and the secondary member 20 is arranged. Since that in 2 illustrated equivalent circuit diagram 34 represents a conventional equivalent circuit diagram of a transformer, the determination of the electrical equivalent quantities contained therein is assumed to be known.

Subsequently, the electrically conductive object 32 in the transmission line 28 between the primary link 18 and the secondary member 20 positioned. Due to the high-frequency alternating magnetic field are in the object 32 Eddy currents induced, leading to heating of the object 32 and lead to corresponding eddy current losses.

To the losses in the object 32 To model, again the parameters / electrical equivalent sizes of the equivalent circuit diagram 34 measured or simulated. The resulting electrical equivalent circuit diagram 34 ' that is the electrically conductive object 32 in the transmission line 28 is considered in 3 shown. The additional eddy current losses in the object 32 can be measured as equivalent ohmic resistances R _FO1 , R _FO2 and R _FOh . In this case, the substitute electric variable R _FO2 'again _denotes the transformed resistor R _FO2 . The substitute quantity Z _L 'likewise identifies the load impedance Z _L related to the transmission ratio u to the primary side and is calculated according to the following formula: Z _L '= u ² .Z _L

The operating point of the power transmission arrangement 10 is significantly determined by the load impedance Z _L '. Advantageously, the load impedance Z _L 'should have a capacitive component in order to compensate for the large stray inductance L _2σ '. According to the invention, an impedance value of the load impedance Z _L 'is calculated by means of a numerical optimization method, in which the eddy current losses in the object 32 are minimal for the same secondary-side active power. For this purpose, in each operating point of the power transmission arrangement 10 the required electrical currents and voltages from the equivalent circuit diagram 34 ' calculated to the power loss P _{FO of} the object 32 to investigate: P _FO = | I ₁ | ² · R _FO1 + | I ₂ '| ² · R _FO2 '+ | I _h | ² · R _FOh

It can be adjusted with the help of the input voltage U _1, the transmitted power. The value of the load impedance at which the power loss P _{FO of} the object 32 becomes minimal, is called the optimized impedance value. By adjusting the load impedance Z _L to the optimized impedance value, the heating of the object 32 be reduced at the same transmitted power. This ultimately leads to increased reliability of the power transmission arrangement 10 ,

• 1. Erfindungsgemäß optimierter Impedanzwert der Lastimpedanz Z_L zur Minimierung der Verlustleistung in dem Objekt 32: R_L = 5 Ω, C_L = 195 nF (Serienschaltung); Temperaturverlauf dargestellt als durchgezogene Kurve 36
• 2. Ohmsche Last: R_L = 5 Ω; Temperaturverlauf dargestellt als gepunktete Kurve 38
• 3. Resonante Last zur Kompensierung der Streuinduktivität L_2σ: R_L = 5 Ω, C_L = 466 nF (Serienschaltung); Temperaturverlauf dargestellt als gestrichelte Kurve 40.

4 shows a diagram illustrating a temperature profile of the in the transmission path 28 arranged electrically conductive object 32 at different load impedances Z _L. The abscissa of the diagram shows the time in seconds and the ordinate the temperature in ° C. This will be the temperature of the object 32 each with the same output power of the power transmission arrangement 10 and an operating frequency of f = 100 kHz detected. In the 4 shown temperature curves arise when setting the following load impedances Z _L :

• 1. According to the invention optimized impedance value of the load impedance Z _L to minimize the power loss in the object 32 : R _L = 5 Ω, C _L = 195 nF (series connection); Temperature profile shown as a solid curve 36
• 2. Ohmic load: R _L = 5 Ω; Temperature profile shown as a dotted curve 38
• 3. Resonant load to compensate the stray inductance L _2σ : R _L = 5 Ω, C _L = 466 nF (series connection); Temperature profile shown as a dashed curve 40 ,

• 1. P_FO = 0,26 W
• 2. P_FO = 0,61 W
• 3. P_FO = 0,39 W

With the electrical equivalent circuit diagram 34 ' out 3 the power loss is calculated in the object 32 for the above-mentioned load impedances Z _L to:

• 1. P _FO = 0.26 W
• 2. P _FO = 0.61 W
• 3. P _FO = 0.39 W

From these calculated values of power dissipation in the object 32 and the different temperature gradients 36 . 38 . 40 from the 4 It can be seen that with the aid of the inventively optimized impedance value, the power loss of the object 32 (see P _FO under 1.) and associated with the heating of the object 32 (see curve 36 ) is reduced.

The determination of the optimized impedance value must advantageously only once with the aid of any electrically conductive object 32 (eg with a metallic tube). Get other electrically conductive objects in the transmission path 28 So is the optimization of the power transmission arrangement 10 by means of the load impedance Z _L equally valid for these objects. In other words, the eddy current losses and thus the heating are also reduced in any other electrically conductive objects.

5 shows a diagram for explaining an embodiment of a method according to the invention 42 , The procedure 42 is directed to the wireless power transmission arrangement 10 to operate and in particular to determine an optimized impedance value of the load impedance Z _L , which leads to a minimal heating of one in the transmission path 28 arranged object 32 leads.

This will be done in one step 44 first electrical equivalent quantities of the equivalent circuit diagram 34 determined. At first, there is no electrically conductive foreign object in the transmission path 28 arranged. The substitute quantities are determined via a measuring process or via a simulation.

Subsequently, in one step 46 the electrically conductive object 32 in the transmission line 28 or in the air gap between the primary member 18 and the secondary member 20 brought in. The electrically conductive object 32 is advantageously positioned in the air gap that in the object 32 the highest possible power loss due to induced eddy currents occurs. This can be z. B. a position near the windings of the primary coil 22 be. As the eddy current losses of the object 32 from the positioning of the object 32 between the primary link 18 and the secondary member 20 it is particularly preferable if the object 32 is arranged so that the maximum power loss is generated at this position. This ensures that the safety requirements for any positioning of the electrically conductive object 32 in the transmission line 28 be respected.

In one step 48 Second electrical equivalent sizes are measured or simulated to the equivalent electric sizes of the equivalent circuit diagram 34 ' to determine. By comparing the first and the second electrical equivalent quantities, the eddy current losses in the object 32 be determined as equivalent ohmic resistances.

In one step 50 is calculated by means of a numerical optimization method, an optimized impedance value of the load impedance Z _L , in which the eddy current losses in the object 32 are minimal for the same secondary-side active power. The power loss of the object 32 is determined by at each operating point of the power transmission arrangement 10 , which is essentially set by the load impedance Z _L , all the required electrical currents and voltages of the equivalent circuit diagram 34 ' be calculated.

In one step 52 the load impedance Z _{L is set} to the determined optimized impedance value. Thus, the heating of the object 32 be minimized for the same transmitted power. The operational safety of the power transmission arrangement 10 is increased because of hazards from overheated objects in the air gap between the primary member 18 and the secondary member 20 be significantly reduced.

Although thus preferred embodiments of the method according to the invention 42 It is understood that various modifications and changes can be made without departing from the scope of the invention.

For example, the impedance value of the load impedance determined according to the invention can also be used such that the transmittable power of the energy transmission arrangement 10 is increased in compliance with the same safety requirements.

Furthermore, the inventive method 42 be used for the design / adjustment of any power transmission systems with inductive power transmission (eg charging systems for e-bikes or battery-powered tools).

Claims (11)

Procedure ( 42 ) for operating a wireless power transmission arrangement ( 10 ) with a primary link ( 18 ) and a secondary member ( 20 ) which are inductively coupled to receive electrical energy from the primary member ( 18 ) to the secondary member ( 20 ), wherein an adjustable load impedance to the secondary link ( 20 ), comprising the steps of: determining electrical replacement quantities for an electrical model ( 34 ) of the energy transfer arrangement ( 10 ), where the electric model ( 34 ) an electrically conductive object ( 32 ) in a transmission path ( 28 ) between the primary member ( 18 ) and the secondary member ( 20 ), determining an impedance value of the load impedance on the basis of the electrical equivalent quantities and a determined electrical power loss of the in the transmission path ( 28 ) arranged object ( 32 ), and - setting the load impedance to the impedance value. The method of claim 1, wherein the impedance value is determined such that the electrical power loss of the object ( 32 ) is minimized at a predefined value of an active electrical power of the load impedance. The method of claim 1, wherein the impedance value is determined such that the active electrical power of the load impedance at a predefined value of the electrical power loss of the object ( 32 ) is maximized. Method according to one of claims 1 to 3, wherein the impedance value is determined by means of a numerical method. Method according to one of claims 1 to 4, wherein the impedance value for a position of the object ( 32 ) in the transmission path ( 28 ) is determined at which the electrical power loss of the object ( 32 ) is maximum. Method according to one of claims 1 to 5, wherein the determination of the electrical equivalent quantities comprises the following steps: - determining first electrical equivalent quantities, wherein the object ( 32 ) outside the transmission link ( 28 ), - arranging the object ( 32 ) in the transmission path ( 28 ) Determining second substitute electrical quantities; and determining the substitute electrical quantities based on the first and second substitute electrical quantities. The method of claim 6, wherein the first and / or the second electrical substitute quantities are determined on the basis of measured physical quantities. The method of claim 6 or 7, wherein the first and / or the second electrical equivalent quantities are determined on the basis of a simulation. Method according to one of claims 1 to 8, wherein a plurality of ohmic resistances as electrical equivalent quantities of the object ( 32 ) be determined. Method according to one of claims 1 to 9, wherein an ohmic portion and a capacitive portion of the load impedance is determined. Energy transfer arrangement ( 10 ) with a primary link ( 18 ) and a secondary member ( 20 ) which are inductively coupled to receive electrical energy from the primary member ( 18 ) to the secondary member ( 20 ), wherein an adjustable load impedance to the secondary link ( 20 ) and a control unit adapted to carry out the method according to one of claims 1 to 10.

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