Abstract:
A converter that feeds an electric drive in an electric vehicle is used to transmit energy to the vehicle without contact using resonant operation for inductive transmission of energy. The leakage inductance of the transformer is resonantly adjusted by a serial capacitor. The load current is then switched at zero-crossing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. national stage of International Application Ser. No. PCT/EP2010/054496, filed Apr. 6, 2010 and claims the benefit thereof. The International Application claims the benefits of German Application No. 10 2009 016 823.0 filed on Apr. 9, 2009, both applications are incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    Electric vehicles are usually connected to the power supply system or to a stationary charging rectifier by plug connectors. If a battery is intended to be charged with 20 kWh within 15 minutes (what is known as 6 C charging), charging powers of approximately 87 kW can be expected, this corresponding to a current of 125 A on the 400 V power supply system. This requires the largest commercially available plug with a diameter of 126 mm and a length of 282 mm. The manual forces required for connection and disconnection amount to a few 100 N, this making operation considerably more difficult. Even higher charging powers cannot be transmitted with currently available plug systems. In addition, plug systems are susceptible to soiling and an increased contact resistance as a result of corrosion, together with a corresponding risk of overheating. An alternative which avoids these problems is the transmission of energy to the vehicle in a contact-free manner. 
       SUMMARY 
       [0003]    Described below is an apparatus for transmitting power for charging electric vehicles in a contact-free manner, the apparatus having a simplified design. In addition, an improved charging method for an energy storage device of an electrically operated vehicle is described. 
         [0004]    The operating arrangement described below for use in an electrically operated vehicle which has at least one electric drive and at least one energy storage device for feeding electrical energy to the electric drive includes: 
         [0005]    a converter which can be connected to the energy storage device at the input end and is designed to convert an input-end DC voltage into an output-end single- or polyphase AC voltage and to convert an output-end single- or polyphase AC voltage into an input-end DC voltage, 
         [0006]    a coil arrangement for the inductive transmission of electrical energy, 
         [0007]    a capacitance which is connected in series with the coil arrangement for resonance tuning. 
         [0008]    A first switching device may be provided at the output end of the converter, for connecting the converter to the electric drive and a second switching device may be provided at the output end of the converter, for connecting the converter to the coil arrangement. 
         [0009]    In this case, the converter which is present in the electrically operated vehicle in any case is therefore advantageously also used for the inductive transmission of electrical energy and for charging the battery. To this end, it is expedient to disconnect the converter from the vehicle motor using the first switching device and to connect the converter to the transmitter for inductive energy transmission using the second switching device when inductive transmission is intended to take place. At other times, the converter is connected to the vehicle motor by the first switching device and disconnected from the transmitter using the second switching device. 
         [0010]    Converters for actuating electrical machines are expediently designed as hard-switching power converter circuits which commutate the motor current within a half-bridge between the two semiconductor switches, for example insulated gate bipolar transistors (IGBTs), or the associated freewheeling diodes. In order to reduce the switching losses, the switching frequency of a drive power converter of this kind is set in the kHz range, in particular to approximately 8 to 10 kHz. The switching losses are therefore approximately equal to the losses caused by the conduction of power in the semiconductors. Since the power which can be transmitted in an inductive energy transmission operation is proportional to the frequency given a defined cross section of the flux-carrying components (iron circuit, ferrites etc.), the maximum possible transmission frequency should be selected. Frequencies of between 20 and 30 kHz are advantageously used for inductive energy transmission, with ferrites then being used for carrying flux. When the converter is intended to be hard-switched at approximately 3 times the switching frequency compared to operation of the electric motor with approximately the same current, approximately double the losses would then be produced overall, this leading to thermal overloading of the power semiconductors. 
         [0011]    Therefore, a resonant circuit is advantageously indicated for inductive energy transmission by the leakage inductance of the coil arrangement being resonantly adjusted by a capacitance which is connected in series. As a result, the load current can advantageously be switched at the zero crossing in each case. Only the magnetization current of the coil arrangement has to be subjected to hard-commutation. The resonant circuit which is formed by the leakage inductances and resonant capacitors is excited by the converter with a square-wave voltage with a frequency which corresponds to the resonant frequency. 
         [0012]    The resonant capacitors can alternatively be provided on both sides of the transmitter or only on one side of the transmitter. If only one resonant capacitor is used, it can be arranged on the vehicle or on the charging station. 
         [0013]    The transmitter, which performs contact-free transmission of the energy and includes the coil arrangement, can be designed in the form of a single-phase or a three-phase transmitter. 
         [0014]    The converter may have three half-bridges, two of the half-bridges being connected to the second switching device at the output end, while the third half-bridge can be connected to the energy storage device via a DC/DC converter. As an alternative, the converter has four half-bridges, three of the half-bridges being connected to the second switching device at the output end, while the fourth half-bridge can be connected to the energy storage device via a DC/DC converter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    These and other aspects and advantages will become more apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
           [0016]      FIG. 1  is a circuit diagram of a first variant embodiment with a single-phase transmitter, 
           [0017]      FIG. 2  is a circuit diagram of a second variant embodiment with a single-phase transmitter and a single-phase converter, 
           [0018]      FIG. 3  is a circuit diagram of a third variant embodiment with a single-phase transmitter and a DC/DC converter between the battery and the converter, and 
           [0019]      FIG. 4  is a circuit diagram of a fourth variant embodiment with a three-phase transmitter and a DC/DC converter between the battery and the converter. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
         [0021]      FIG. 1  shows a first complete system  10  which is made up of vehicle-side elements  12  and of stationary elements  11  and includes a first exemplary embodiment of the charging system. The stationary elements  11  are located outside the vehicle, for example beneath the vehicle, when the vehicle is in a charging station. 
         [0022]    The vehicle-side elements  12  include an electric motor  13  for driving the vehicle, a battery  14 , a converter  18 , an intermediate circuit capacitor  22 , a first switching arrangement  15 , a second switching arrangement  16 , a coil arrangement  17  as a vehicle-side part of a transmitter  21 , and a vehicle-side resonant capacitor  19 . 
         [0023]    The stationary elements  11  include a rectifier  23 , a stationary-side intermediate circuit capacitor  24  and a stationary-side converter  25 . The stationary elements  11  also include a stationary-side resonant capacitor  20  and the stationary-side part of the transmitter  21 . 
         [0024]    In order to charge the battery  14  of the vehicle, the rectifier  23  converts the three-phase voltage of the power supply system into a DC voltage which is converted by the stationary-side converter  25  into a suitable AC voltage. The transmitter  21  ensures that the AC voltage is forwarded to the vehicle-side circuit. To this end, the connection of the converter  18  to the transmitter  21  is established by the second switch arrangement  16 . At the same time, the connection between the converter  18  and the electric motor  13  is interrupted by the first switch arrangement  15 . 
         [0025]    In the first exemplary embodiment, the DC intermediate circuit, that is to say the intermediate circuit capacitor  22  of the converter  18 , is substantially directly connected to the battery  14  during the charging process. As a result, the intermediate circuit voltage level of the converter  18  is determined by the state of charge of the battery  14 . The vehicle transmits the desired charging power, which can also be negative, by radio or likewise by inductive or capacitive transmission to the stationary-side converter  25  or to the controller of the converter. The converter or controller then adjusts the flow of power to the desired value by tracking the setpoint value for its intermediate circuit voltage. 
         [0026]    In the first exemplary embodiment, the resonant capacitors  19 ,  20  are tuned to the transmitter  21  such that a resonant circuit frequency of 25 kHz is produced. In contrast, the switching frequency of the converter  18  for motor operation is 10 kHz in this example. 
         [0027]      FIG. 2  shows a second complete system  30  of a second exemplary embodiment of the charging system. In contrast to the first complete system  10 , the vehicle-side converter  31  includes two, rather than three, half-bridges. Furthermore, Schottky diodes  32  are connected in parallel to the semiconductor switches of the converter  31 . Finally, no resonant capacitor  19  is used on the vehicle side in the second exemplary embodiment. 
         [0028]    In the case of unidirectional energy transmission, the converter  31  can be passively switched and the parallel Schottky diodes  32  can be used as passive rectifiers. This reduces the conduction losses of the converter  31 . This ensures reliable charging of the battery  14  in the event of failure of the converters  31 ,  25  to synchronize. This variant can be realized both with a single-phase and with a three-phase transmitter  21 ,  73 . 
         [0029]    In order to ensure resonant operation in such a way that the power semiconductors always switch at the zero crossing of the load current, the two power converters expediently switch in a completely synchronized manner. This can be realized, for example, with an additional unloaded winding or a transformer. Phase-locked loop (PLL) or digital implementation ensures the synchronization of the two converters  18 ,  31 ,  71 ,  25 . 
         [0030]      FIG. 3  shows a third complete system  50  of a third exemplary embodiment of the charging system. In the third exemplary embodiment, the vehicle-side converter  18  has three half-bridges. However, in contrast to the first two exemplary embodiments, a DC/DC converter  51  is provided between a connection of the battery  14  and the converter  18 . In the third exemplary embodiment, the flow of power is controlled by adjusting the voltage of the DC intermediate circuits of the two power converters in the following manner: 
         [0031]    In the case of a single-phase transmitter  21 , only two half-bridges are required for actuation purposes on the vehicle-side and the stationary side in each case. In this case, the third half-bridge in the vehicle is used to connect the battery  14  to the intermediate circuit by a bidirectional buck-boost converter, the DC/DC converter  51 , with an additional controller inductor also being required. In this case, the intermediate circuit voltage of the vehicle-side converter  18  is increased to a level above the final charge voltage of the battery  14 . The flow of power is controlled by slightly changing the intermediate circuit voltage in the vehicle-side converter  18  by the outflow of power from the intermediate circuit to the battery  14  being correspondingly adjusted. If less power is output to the battery, the voltage in the intermediate circuit increases automatically, as a result of which the voltage ratio between the stationary side and the vehicle side changes, this once again reducing the transmitted power. 
         [0032]      FIG. 4  shows a fourth complete system  70  of a fourth exemplary embodiment of the charging system. In contrast to the first three exemplary embodiments, a three-phase transmitter  73  is used in the fourth exemplary embodiment. In this case, resonance tuning is also performed on the vehicle side using three vehicle-side resonant capacitors  74 . If a three-phase transmitter is used, three half-bridges are required both on the stationary side and on the vehicle side in each case. In this case, a fourth half-bridge is provided on the vehicle side, the fourth half-bridge taking on the functionality of the DC/DC converter  76  and connecting the battery  14  to the intermediate circuit of the vehicle-side converter  71 . As an alternative, this fourth half-bridge can be used as a protective module in the normal driving mode, that is to say when the converter  71  feeds a synchronous machine which exhibits permanent-magnet excitation 
         [0033]    A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in  Superguide v. DIRECTV , 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).