Method of operating a three phase primary winding structure and a primary unit

Abstract

The invention relates to a method of operating a three phase primary winding structure of a system for inductive power transfer, wherein the primary winding structure includes a first phase line, a second phase line and a third phase line, wherein in a standard operational mode a first phase input voltage, a second phase input voltage and a third phase input voltage are controlled such that a predetermined phase shift between all three phase input voltages is provided, wherein in a modified operational mode the first phase input voltage, the second phase input voltage and the third phase input voltage are controlled such that the set of phase shift values includes at most two non-zero values and all non-zero phase shift values are equal. Furthermore, the invention relates to a primary unit of a system for inductive power transfer.

Claims

1. A method of operating a three phase primary winding structure of a system for inductive power transfer, the method comprising: providing a primary winding structure comprising a first phase line, a second phase line and a third phase line; controlling, with a control unit and in a standard operational mode, a first phase input voltage, a second phase input voltage and a third phase input voltage such that a predetermined phase shift value between all three phase input voltages is provided; and controlling, with the control unit and in a modified operational mode, the first phase input voltage, the second phase input voltage and the third phase input voltage such that a set of phase shift values comprises at most two non-zero values and all non-zero phase shift values are equal, wherein controlling the first phase input voltage, the second phase input voltage, and the third phase input voltage in the modified operational mode comprises: reducing one of the first phase input voltage, the second phase input voltage, or the third phase input voltage to zero; and adjusting a phase shift value between the phase input voltages that are not reduced to zero; generating a current in the primary winding structure that is greater than a current in the primary winding structure during the standard operational mode.

2. The method according to claim 1, wherein reducing one of the first phase input voltage, the second phase input voltage, or the third phase input voltage to zero comprises: switching off one of the first phase input voltage, the second phase input voltage, or the third phase input voltage to zero.

3. The method according to claim 2, further comprising controlling the phase input voltages that are not reduced to zero such that the non-zero phase shift value is 180 phase angle.

4. The method according to claim 1, further comprising controlling two of the three phase input voltages such that their respective voltage curves are equal.

5. The method according to claim 4, further comprising shifting a phase angle of at least one of the two phase input voltages that are not reduced to zero by a multiple of +/60 phase angle.

6. The method of claim 1, further comprising varying a frequency of at least one phase input voltage.

7. The method of claim 1, further comprising controlling the phase input voltages such that a predetermined secondary output power is provided.

8. The method of claim 1, further comprising controlling the phase input voltages such that a current-voltage-curve of each of the phase lines is of non-capacitive character.

9. The method of claim 1, further comprising controlling the phase input voltages such that a maximal DC primary-sided input voltage is smaller than or equal to a predefined threshold value.

10. The method of claim 1, further comprising controlling the phase input voltages such that phase currents are minimized.

11. The method of claim 1, further comprising controlling the first, the second and the third phase input voltage by a three-phase inverter; and controlling switching states of the switching elements of the inverter such that the desired first phase input voltage, the desired second phase input voltage and the desired third phase input voltage is provided.

12. The method of claim 1, further comprising adapting the control of the first, the second and the third phase input voltage to a geometric alignment of the primary winding structure and a secondary winding structure.

13. A primary unit of a system for inductive power transfer, wherein the primary unit comprises a three phase primary winding structure with a first phase line, a second phase line and a third phase line, wherein the primary unit further comprises: at least one control unit for controlling a first phase input voltage, a second phase input voltage and a third phase input voltage; and wherein in a standard operational mode the first phase input voltage, the second phase input voltage and the third phase input voltage are controllable such that a predetermined phase shift between all three phase input voltages is provided; and wherein in a modified operational mode the first phase input voltage, the second phase input voltage and the third phase input voltage are controllable such that the set of phase shift values comprises at most two non-zero values and all non-zero phase shift values are equal; wherein in the modified operational mode, the control unit reduces one of the first phase input voltage, the second phase input voltage, or the third phase input voltage to zero, adjusts a phase shift value between the phase input voltages that are not reduced to zero, and causes a current to be generated in the primary winding structure that is greater than a current in the primary winding structure during the standard operational mode.

14. The primary unit according to claim 13, wherein the primary unit comprises a three-phase inverter, wherein the first, the second and the third phase input voltage are providable by the three-phase inverter, wherein switching states of the switching elements of the inverter are controllable such that the desired first phase input voltage, the desired second phase input voltage and the desired third phase input voltage is provided.

15. A method of operating a three phase primary winding structure of a system for inductive power transfer, the method comprising: providing a primary winding structure comprising a first phase line, a second phase line, and a third phase line; controlling, with a control unit and in a standard operational mode, a first phase input voltage, a second phase input voltage, and a third phase input voltage such that a predetermined phase shift between all three phase input voltages is provided; controlling, with the control unit and in a modified operational mode, the first phase input voltage, the second phase input voltage, and the third phase input voltage such that the set of phase shift values comprises at most two non-zero values and all non-zero phase shift values are equal; varying a frequency of at least one phase input voltage; adapting the frequency/frequencies of the phase input voltage(s) to a resonant frequency of a virtual single phase line; and providing the virtual single phase line between the input terminals of the phase input voltages which provide the non-zero phase shift value(s).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 a schematic circuit diagram of a primary unit of a system for inductive power transfer,

(3) FIG. 2 an exemplary side view of a vehicle located above a primary unit,

(4) FIG. 3 an exemplary time course of gate signals and currents in the standard operational mode,

(5) FIG. 4 an exemplary time course of gate signals and currents in a first control scenario of the modified operational mode and

(6) FIG. 5 an exemplary time course of gate signals and currents in another control scenario of the modified operational mode.

DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a schematic circuit diagram of a primary unit 1 (see FIG. 2). The primary unit 1 comprises a DC voltage source 2 which provides a DC input voltage to an inverter 3. The inverter comprises three legs 4a, 4b, 4c.

(8) The first leg 4a comprises a first switching element G.sub.1 and a second switching element G.sub.2. An input terminal of the first switching element G.sub.1 is connected to a high potential provided by the DC voltage source 2. A second terminal of the first switching element G.sub.1 is connected to a first terminal of the second switching element G.sub.2. A second terminal of the second switching element G.sub.2 is electrically connected to a low potential provided by the DC voltage source 2. A common connection point of the first and the second switching element G.sub.1, G.sub.2 also provides an input terminal IT1 of a first phase line P1.

(9) The remaining two legs 4b, 4c of the inverter 3 are designed correspondingly. In particular, the second leg 4b of the inverter 3 comprises a first switching element G.sub.3 and a second switching element G.sub.4 which are connected in the same way as the switching elements G.sub.1, G.sub.2 of the first leg 4a. A common connection point of the first switching element G.sub.3 and the second switching element G.sub.4 of the second leg 4b provides an input terminal IT2 of a second phase line P2.

(10) The third leg 4c comprises a first switching element G.sub.5 and a second switching element G.sub.6 which are designed and arranged correspondingly to the switching elements G.sub.1, G.sub.2 of the first leg 4a. A common connection point of the first switching element G.sub.5 and the second switching element G.sub.6 of the third leg 4c provides an input terminal IT3 of a third phase line P3.

(11) To each switching element G.sub.1, G.sub.2, G.sub.3, G.sub.4, G.sub.5, G.sub.6, a freewheeling diode D and a switch capacitor CG is connected in parallel.

(12) The primary unit 1 further comprises a current-shaping filter 5. The current-shaping filter 5 comprises inductive filter elements FL1, FL2, FL3 and capacitive filter elements FC1, FC2, FC3, one per phase line. Within each phase line P1, P2, P3, the inductive filter elements FL1, FL2, FL3 of the current-shaping filter 5 are connected in series to the respective input terminal IT1, IT2, IT3 of each phase line P1, P2, P3. Further, within each phase line, the respective capacitive filter elements FC1, FC2, FC3 are connected to the inductive filter elements FL1, FL2, FL3 and to a series connection of an inductive element L1, L2, L3 of a primary winding structure 6 and a resistive element R1, R2, R3 of a resistive structure 7.

(13) The current-shaping filter 5 is used to tune the primary unit 1.

(14) The primary unit 1 further comprises the primary winding structure 6. The primary winding structure 6 comprises one inductive element L1, L2, L3 per phase line P1, P2, P3. These inductive elements L1, L2, L3 are connected in series to the current-shaping filter 5, in particular to the inductive filter elements FL1, FL2, FL3. An inductive element L1, L2, L3 represents an inductance of a winding structure of the corresponding phase line P1, P2, P3 for generating the alternating electromagnetic field for inductive power transfer.

(15) Further shown is a resistive structure 7 of the primary unit 1 which comprises resistive elements R1, R2, R3. These resistive elements R1, R2, R3 represent a resistance of each phase line P1, P2, P3.

(16) A control unit (not shown) controls the switching elements G.sub.1, . . . , G.sub.6 of each leg 4a, 4b, 4c of the inverter 3, in particular switching times of each switching element G.sub.1, . . . , G.sub.6. By controlling the switching times, in particular the points in time at which a switching element G.sub.1, . . . , G.sub.6 is opened or closed, a desired voltage course of a phase input voltage U1, U2, U3 can be provided for each phase line P1, P2, P3. By controlling the switching times, also an amplitude and a frequency of the phase input voltages U1, U2, U3 and a phase shift between the phase input voltages U1, U2, U3 can be controlled.

(17) FIG. 2 shows a schematic side view of a vehicle 8 which travels along a surface 9 of a route 10. On the surface 9, a primary unit 1 is installed. The primary unit 1 can e.g. be designed as an elevated charging pad. Alternatively, the primary unit 1 can be integrated into the ground providing the route surface 9. The vehicle 8 comprises a secondary unit 11 which can be also referred to as receiving device or pick-up.

(18) Shown is a reference point RPP of the primary unit 1 which is stationary with respect to the primary unit 1. Further shown is a reference point RPS of the secondary unit 11 which is stationary with respect to the secondary unit 11. Further shown is a longitudinal axis x and a vertical axis z of a reference coordinate system which is originated in the reference point RPP in the primary unit 1. The longitudinal axis x is directed into a longitudinal direction. This longitudinal direction can e.g. be a direction of travel if the vehicle travels straight forward on the surface 9 of the route 10. The vertical axis z is oriented perpendicular to the surface 9 of the route 10. A lateral axis (not shown) is oriented perpendicular to the shown longitudinal and vertical axes x, z. With respect to the reference coordinate system, a longitudinal and a vertical displacement is provided between the reference points RPP, RPS of the primary and secondary unit 1, 11 respectively. Not shown is a lateral displacement.

(19) In a reference relative position and/or orientation of the primary unit 1 and the secondary unit 11, the transformer provided by the electric elements of the primary unit 1 and the secondary unit 11, in particular by the primary winding structure 6 (see FIG. 1) and a secondary winding structure (not shown), is tuned.

(20) This means that for a predetermined reference longitudinal, lateral and/or vertical displacement and, if applicable for a predetermined reference relative orientation, the inverter 3 can be operated at a predetermined operating frequency, wherein no reactive power has to be provided or compensated by the inverter 3. Operating the inverter 3 at the predetermined frequency can mean that a switching state of switching elements G.sub.1, . . . , G.sub.6 can be changed with said operating frequency. Thus, the phase input voltages U1, U2, U3 or at least a first harmonic of said phase input voltages U1, U2, U3 have said operating frequency.

(21) In other words, in this predetermined reference relative position and/or orientation, a resonant frequency of a circuit structure connected to the input terminals IT1, IT2, IT3 of each leg 4a, 4b, 4c matches the operating frequency. It is important to note that the aforementioned circuit structure connected to the input terminals IT1, IT2, IT3 does not only comprise the primary-sided elements shown in FIG. 1 but also secondary-sided elements, wherein inductances, capacitances and/or resistances of said secondary-sided elements are transferred to the primary side, wherein these transferred elements are also part of the circuit structure.

(22) FIG. 3 shows exemplary time courses of gate signals G1_S, G2_S, G3_S, G4_S, G5_S, G6_S of the switching element G.sub.1, . . . , G.sub.6 shown in FIG. 1. If the respective gate signal G1_S, . . . , G6_S corresponds to a value of 1, the respective switching element G.sub.1, . . . , G.sub.6 is closed. If the value of the respective gate signal G1_S, . . . , G6_S corresponds to a value of 0, the respective switching element G.sub.1, . . . , G.sub.6 is opened. At a first switching time instant t1, the second switching element G.sub.2 of the first leg 4a is switched off and the first switching element G.sub.1 of the first leg 4a is switched on. After the first switching time instant t1, the DC input voltage provided by the DC voltage source 2 is applied to the input terminal IT1 of the first phase line P1.

(23) At a second switching instant t2, the first switching element G.sub.5 of the third leg 4c is switched off. Within a predetermined time lag after this switching off time instant, the second switching element G.sub.6 of the third leg 4c is switched on.

(24) At a third switching time instant t3, the second switching element G.sub.4 of the second leg 4b is switched off. A predetermined time leg after that switching off instant, the first switching element G.sub.3 of the second leg 4b is switched on.

(25) At a fourth switching time instant t4, the first switching element G.sub.1 of the first leg 4a is switched off and the second switching element G.sub.2 of the first leg 4a is switched on. At a fifth switching time instant t5, the second switching element G.sub.6 of the third leg 4c is switched off and the first switching element G.sub.5 of the third leg 4c is switched on. At a sixth switching time instant t6, the first switching element G.sub.3 of the second leg 4b is switched off and the second switching element G.sub.4 of the second leg 4b is switched on. At a seventh switching time instant t7 one switching period of the first phase line P1 has passed.

(26) Correspondingly, one switching period of the third phase line P3 has passed at an eighth switching time instant t8 and a switching period of the second phase line P2 has passed at a ninth switching time instant t9.

(27) It is shown that the predetermined time lag is arranged in between all switching-off and the switching-on time instants shown in FIG. 3.

(28) Thus, the phase input voltages U1, U2, U3 have a square-wave form.

(29) A phase angle between the first phase input voltage U1 and a second phase input voltage U2 is shown by the time lag between the third switching time instant t3 and the first switching time instant t1. The phase shift between the first phase input voltage U1 and the third phase input voltage U3 is provided by the time lag between the first switching time instant t1 and the fifth switching time instant t5. The phase shift between the second phase input voltage U2 and the third phase input voltage U3 is provided by the time lag between the third switching time instant t3 and the fifth switching time instant t3.

(30) It can be seen that the phase shift between the first and the second phase input voltages U1, U2 is equal to the phase shift between the second and the third phase input voltages U2, U3 and non-zero, in particular 120. Further, the phase shift between the first and the third phase input voltage U1, U3 corresponds to the double value of the phase shift between the first and the second phase input voltage U1, U2, e.g. to 240. Thus, the set of phase shift values comprises three non-zero values.

(31) FIG. 3 shows the time courses for standard operational mode. Further shown are currents I_FL1, I_FL2, I_FL3 which flow through the inductive filter elements FL1, FL2, FL3 of the current-shaping filter 5. Further shown is a time course of winding currents I_L1, I_L2, I_L3 which flow through the inductive elements L1, L2, L3, e.g. the winding structures, of

(32) primary winding structure 6.

(33) In the standard operational mode, the currents I_L1, I_L2, I_L3 have a sinusoidal form and have phase shifts of 120 or 240.

(34) FIG. 4 shows exemplary time courses of gate signals G1_S, G2_S, G3_S, G4_S, G5_S, G6_S. The time course of the gate signals G1_S, G2_S of the first leg 4a (see FIG. 1) equals to the time course shown in FIG. 3.

(35) However, the time courses of the gate signals G3_S, G4_S for the switching elements G.sub.3, G.sub.4 of the second leg 4b are shifted by 60 with respect to the time course of the gate signals G3_S, G4_S shown in FIG. 3. This means that the second switching element G.sub.4 of the second leg 4b is switched off at fourth time instant t4 and not at the third time instant t3 as shown in FIG. 3.

(36) Also, time courses of the gate signals G5_S, G6_S of the switching elements G.sub.5, G.sub.6 of the third leg 4c are shifted by +60 with respect to the time course of the gate signals G5_S, G6_S shown in FIG. 3. This means that the time course of the gate signals G5_S, G6_S of the switching elements G.sub.5, G.sub.6 of the third leg 4c equals to the time course of the gate signals G3_S, G4_S of the switching elements G.sub.3, G.sub.4 of the second leg 4b. This, in turn, means that voltage curves of the second and the third input voltage U2, U3 are equal.

(37) The switching pattern shown in FIG. 4 can be applied in particular if there is a misalignment between the primary unit 1 and the secondary unit 11 shown in FIG. 2. A misalignment can be provided if the relative position and/or orientation between the primary unit 1 and the secondary unit 11 deviates from the reference relative position and/orientation.

(38) Further shown are the filter currents I_FL1, I_FL2, I_FL3 and the winding currents I_L1, I_L2, I_L3. As stated before, the filter and winding currents I_FL2, I_FL3, I_L2, I_L3 of the second and the third phase are equal to each other.

(39) Compared to the time course of the winding currents I_L1, I_L2, I_L3 shown in FIG. 3, it

(40) can be seen that a maximal amplitude of the winding current I_L1 through the inductive element L1 of the winding structure 6 in the first phase line P1 has increased. In contrast, the winding currents I_L2, I_L3, e.g. a maximal amplitude, have decreased. Illustratively, a higher amount of power is transferred by the inductive element L1 of the winding structure 6 in the first phase line P1, wherein less power is transferred by the inductive elements L2, L3 of the winding structure 6 in the remaining phase lines P2, P3. This can e.g. be the case if the section of the primary side winding structure 6 provided by the inductive element L3 in the third phase line P3 is only partially covered by the secondary winding structure of the secondary unit 11.

(41) FIG. 5 shows exemplary time courses of gate signals G1_S, . . . , G6_S. In the switching pattern shown in FIG. 5, the time course of the gate signals G1_S, G2_S of the first and the second switching element G.sub.1, G.sub.2 of the first leg 4a corresponds to the time course shown in FIG. 3. Also, the time course of the gate signals G3_S, G4_S of the switching elements G.sub.3, G.sub.4 of the second leg 4b corresponds to the time course shown in FIG. 4. This means that the time course is shifted by 60 with respect to the time course of the gate signals G3_S, G4_S shown in FIG. 3.

(42) The switching elements G.sub.5, G.sub.6 of the third leg 4c are turned off. This means that the third phase input voltage U3 is reduced to zero.

(43) Also shown are filter currents I FL1, I FL2, I FL3 and winding currents I_L1, I_L2, I_L3. The filter current I_FL3 and the winding current I _L3 of the third phase line P3 are zero. It is shown that the winding currents I_L1, I_L2 have a phase shift of 180 and their maximal amplitude is increased if compared to the maximal amplitude of the corresponding winding currents I_L1, I_L2 shown in FIG. 3. Illustratively, a larger amount of power is transferred by the inductive elements L1, L2 of the winding structure 6 in the first and the second phase line P1, P2, wherein no power is transferred by the inductive element L3 of the winding structure 6 in the third phase line P3. Such a switching pattern can e.g. be applied if there is a vertical misalignment of the primary and the secondary unit 1, 11, in particular if the vertical distance of the difference relative position is decreased.

(44) Simulations have been performed for different misalignment scenarios. Within all misalignment scenarios, different criteria of the inductive power transfer have been analyzed. A first criteria has been fulfilled if a secondary output power has been equal to 7.2 kW. A second criteria has been fulfilled if non-capacitive switching has been provided at the switching time instances t1, . . . , t9 (see FIG. 3, FIG. 4, FIG. 5).

(45) The proposed method can advantageously be implemented without changing a hardware configuration of an existing system of inductive power transfer, e.g. by a software update. There is no need to add any passive or active components to the wayside or the vehicle. Also, there is no need to change the ratings of existing components. In fact, it is even possible to select the smaller ratings or use the same components with lower stress.

(46) The aforementioned non-capacitive switching can be essential for minimizing the ratings of the components and also reduces a required cooling effort. In order to obtain the non-capacitive switching, the phase current in a phase line P1, P2, P3 corresponding to a positive gate signal of a switching element G.sub.1, . . . , G.sub.6 assigned to the phase line P1, P2, P3 can be less than predetermined value.

(47) Simulations have shown that there always exists a switching pattern that fulfills the requirements for non-capacitive switching, i.e. switching with non-capacitive character, for any alignment scenario. It has also been shown that an adapted switching pattern exists, wherein a RMS-value of phase currents on the primary side are significantly lower when compared to a symmetrical three-phase switching. These lower phase currents are obtained with no compromise in the power transfer capability. This, in turn, helps to minimize the primary losses toward higher efficiencies.

(48) Simulations have further shown that currents passing via the current-shaping filter 5 can be considerably lower using an adapted switching pattern compared to the currents in a symmetrical three-phase switching. This means that the loss in the equivalent series resistor of said capacitors is reduced considerably. Also, voltages falling across the capacitors of the current-shaping filter 5 can be considerable lower using an adapted switching pattern compared to the voltages in a symmetrical three-phase switching.

(49) Simulations have further shown that the required range for the DC input voltage can be reduced using an adapted switching patterns compared to the symmetrical three-phase switching. This means that for every position and/or orientation of the secondary winding structure relative to the primary winding structure, there is a possibility to choose an adapted switching pattern to gain adequate power transfer with an acceptable value of DC input voltage. This provides a high controllability (especially in the case when the DC input voltage is not close to the limits) while the zero voltage switching features and higher efficiency are maintained.

(50) Also shown is that electromagnetic emissions are not increased considerably by changing a switching pattern.

(51) A large ratio of an air gap to a pole pitch can cause the coupling between the primary winding structure and secondary winding structure to change as a function of vertical and horizontal displacement in a very high degree, especially in the case of a geometrical short primary winding structure. Thus, even if voltages and currents can be brought to symmetry using additional means, any displacement between the primary and secondary winding structure can lead to detuning. By adapting the switching pattern, a most favorable pattern can be found, for example by examining one switching pattern after the other. The resulting switching pattern can allow achieving desirable features for the inductive power transfer system while fulfilling demanded requirements. Losses can be reduced by using an adapted switching pattern. In total, the system can be designed lighter, less expensive and more reliable.