Circuit arrangement and method of operating a circuit arrangement

Abstract

The invention relates to a circuit arrangement of an electric vehicle, in particular a circuit arrangement of an electric vehicle for inductive power transfer to the vehicle, and a method of operating the named circuit arrangement. The circuit arrangement includes an impedance and at least one rectifier for rectifying an AC voltage. An AC part of the circuit arrangement includes the impedance. The rectifier connects the AC part to a DC part of the circuit arrangement. The circuit arrangement further includes at least one current control means for controlling a current flow in the AC part vehicle.

Claims

1. A circuit arrangement of an electric vehicle for inductive power transfer to the vehicle, wherein the circuit arrangement comprises an impedance and at least one rectifier for rectifying an AC voltage, wherein an AC part of the circuit arrangement comprises the impedance, wherein the rectifier connects the AC part to a DC part of the circuit arrangement, wherein the impedance is provided by an inductance and a capacitance, wherein the circuit arrangement comprises a voltage generator, wherein the voltage generator is arranged such that an output voltage of the voltage generator is fed into the AC part of the circuit arrangement, wherein the voltage generator is an inverter, wherein the inverter or an electric path comprising the inverter is connected in parallel to the rectifier or an electric path comprising the rectifier, wherein the capacitance is connected in series to the inductance, wherein the rectifier is connected in series to the capacitance, wherein the circuit arrangement further comprises at least one current control means for controlling a current flow in the AC part in order to achieve a desired power transfer, and wherein the voltage generator is used as the current control means.

2. The circuit arrangement according to claim 1, wherein the DC part of the circuit arrangement comprises a circuit capacitance, and wherein the inverter is connected in parallel to a series connection of the rectifier and the circuit capacitance.

3. The circuit arrangement according to claim 1, wherein the rectifier is a passive rectifier and/or the inverter is an active inverter.

4. The circuit arrangement according to claim 1, wherein the AC part of the circuit arrangement comprises three phases, wherein each of the phases comprises at least one inductance and at least one capacitance, and wherein the rectifier is a three-phase rectifier.

5. The circuit arrangement according to claim 4, wherein the inverter is a three-phase full-bridge inverter.

6. The circuit arrangement of claim 1, wherein the circuit arrangement further comprises a radio frequency interference filter.

7. The circuit arrangement of claim 1, wherein the circuit arrangement comprises a sensing means for sensing an output voltage of the rectifier and/or a sensing means for sensing an output voltage of the DC part of the circuit arrangement and/or a sensing means for sensing a phase current.

8. A method of operating a circuit arrangement of an electric vehicle for inductive power transfer to the vehicle, wherein the circuit arrangement comprises an impedance and at least one rectifier for rectifying an AC voltage, wherein an AC part of the circuit arrangement comprises the impedance, wherein the rectifier connects the AC part to a DC part of the circuit arrangement, wherein the impedance is provided by an inductance and a capacitance, wherein the circuit arrangement comprises a voltage generator, wherein the voltage generator is arranged such that an output voltage of the voltage generator is fed into the AC part of the circuit arrangement, wherein the voltage generator is an inverter, wherein the inverter or an electric path comprising the inverter is connected in parallel to the rectifier or an electric path comprising the rectifier, wherein the capacitance is connected in series to the inductance, wherein the rectifier is connected in series to the capacitance, wherein at least one current control means for controlling a current flow in the AC part is controlled such that a desired power transfer is achieved, and wherein the voltage generator is used as the current control means.

9. The method of claim 8, wherein the current flow in the AC part of the circuit arrangement is controlled depending on a period of an induced AC voltage and/or an output voltage of the DC part of the circuit arrangement.

10. The method of claim 9, wherein the period of the induced AC voltage is determined by a phase locked loop.

11. The method of claim 8, wherein the voltage generator is arranged such that an output voltage of the voltage generator is fed into the AC part of the circuit arrangement and wherein an output voltage of the voltage generator is controlled such that a desired voltage falling across the impedance is achieved.

12. The method of claim 11, wherein the circuit arrangement comprises an inverter, wherein the inverter or an electric path comprising the inverter is connected in parallel to the rectifier or an electric path comprising the rectifier and wherein an output voltage of the inverter is controlled such that a desired voltage falling across the impedance is achieved.

13. The method of claim 12, wherein the inverter is an active inverter comprising at least one leg, wherein the leg comprises a first switching element and a second switching element, and wherein duty cycles of the first and second switching elements are controlled such that a desired output voltage of the inverter is achieved.

14. The method of claim 12, wherein the inverter is an active three-phase full-bridge inverter comprising three legs, wherein each of the legs comprises a first switching element and a second switching element, and wherein duty cycles of the first and second switching elements are controlled such that a desired output voltage of the inverter is achieved.

15. The method of claim 12, wherein a duty cycle is determined depending on an output voltage of the DC part of the circuit arrangement and/or a phase current of the alternating part of the circuit arrangement.

16. The method of claim 8, wherein the AC part of the circuit arrangement comprises three phases, wherein each of the phases comprises an impedance, wherein at least one current control means controls a current flow in each phase, and wherein the at least one control means is controlled such that a desired power transfer is achieved.

17. A method of manufacturing a circuit arrangement, in particular a circuit arrangement of an electric vehicle for an inductive power transfer to the vehicle, wherein the circuit arrangement comprises an impedance and at least one rectifier for rectifying an AC voltage, wherein an AC part of the circuit arrangement comprises the impedance, wherein the rectifier connects the AC part to a DC part of the circuit arrangement, wherein the impedance is provided by an inductance and a capacitance, wherein the circuit arrangement comprises a voltage generator, wherein the voltage generator is arranged such that an output voltage of the voltage generator is fed into the AC part of the circuit arrangement, wherein the voltage generator is an inverter, wherein the inverter or an electric path comprising the inverter is connected in parallel to the rectifier or an electric path comprising the rectifier, wherein the capacitance is connected in series to the inductance, wherein the rectifier is connected in series to the capacitance, wherein at least one current control means is provided and arranged such that a current flow in the AC part is controllable, and wherein the voltage generator is used as the current control means.

18. The method of claim 17, wherein a voltage generator is provided, and wherein the voltage generator is arranged such that an output voltage of the voltage generator is fed into the AC part of the circuit arrangement.

19. The method of claim 18, wherein an inverter is provided as a voltage generator, and wherein the inverter or an electric path comprising the inverter is connected in parallel to the rectifier or an electric path comprising the rectifier.

20. An electric vehicle, wherein the electric vehicle comprises a circuit arrangement according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will be described with reference to the attached figures in the following:

(2) FIG. 1 a schematic circuit diagram of a vehicle-sided circuit arrangement of a system for inductive power transfer to the vehicle according to the state of the art,

(3) FIG. 2 a schematic circuit diagram of a wayside circuit arrangement and a vehicle-sided circuit arrangement according to the invention,

(4) FIG. 3 an exemplary time course of switching times of a switching element,

(5) FIG. 4 an exemplary course of a DC output voltage of a DC part of the proposed circuit arrangement versus a duty cycle of switching elements and

(6) FIG. 5 an exemplary course of a phase current of an AC part of the proposed circuit arrangement versus a duty cycle of the switching elements.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a schematic circuit diagram of a vehicle-sided circuit arrangement 1 of a system for inductive power transfer to a vehicle according to the state of the art. The circuit arrangement 1 comprises a so-called pick-up-arrangement 2 which comprises a magnetic part 3. The circuit arrangement 1 comprises an AC part 4 and a DC part 5. The AC part 4 is connected to the DC part 5 via a diode rectifier 6. The AC part 4 comprises three-phases. A first phase comprises a leakage inductance L.sub.S1 and a compensating capacitance C.sub.S1. Correspondingly, the other phases comprise leakage inductances L.sub.S2, L.sub.S3 and compensating capacitances C.sub.S2, C.sub.S3. For a better understanding, source elements V.sub.ph1, V.sub.ph2, V.sub.ph3 are shown which are considered according to a Thevenin equivalent circuit model. Within the real circuit arrangement, there are no such source elements V.sub.ph1, V.sub.ph2, V.sub.ph3. The source elements V.sub.ph1, V.sub.ph2, V.sub.ph3 generate the induced AC voltages.

(8) It is shown that the leakage inductances L.sub.S1, L.sub.S2, L.sub.S3 and the compensating capacitances C.sub.S1, C.sub.S2, C.sub.S3 of each phase are connected in series. Also shown are phase currents I.sub.L1, I.sub.L2, I.sub.L3 of each phase. The rectifier 6 connects the three-phase AC part 4 of the circuit arrangement 1 to the DC part 5 and therefore rectifies an AC voltage of the AC part 4. The DC part 5 comprises a circuit capacitance 7 and a radio frequency interference filter 8. An output voltage of the DC part 5 of the circuit arrangement 1 is denoted by V.sub.out. Also shown is a load 9 which is connected to an output of the DC part 5.

(9) In each phase of the AC part 4, a series connection of the leakage inductances L.sub.S1, L.sub.S2, L.sub.S3 and the respective compensating capacitances C.sub.S1, C.sub.S2, C.sub.S3 provides an impedance IM1, IM2, IM3, respectively. The compensating capacitance C.sub.S1, C.sub.S2, C.sub.S3 can e.g. be provided by a compensating capacitor. The impedance IM1, IM2, IM3 of each phase is a sum of impedances of the respective leakage inductance L.sub.S1, L.sub.S2, L.sub.S3 and the respective compensating capacitance C.sub.S1, C.sub.S2, C.sub.S3. These impedances IM1, IM2, IM3 may have unwanted variations. For example, an impedance of each of the compensating capacitances C.sub.S1, C.sub.S2, C.sub.S3 can vary by age and temperature under various operational and ambient conditions. The phase currents I.sub.L1, I.sub.L2, I.sub.L3, and the DC output voltage V.sub.out are determined by the induced voltages and the impedances IM1, IM2, IM3 of the respective phase and the load 9. Therefore, even when induced voltages and the load 9 are constant, any variation in the phase impedances IM1, IM2, IM3 can change a power flow. This is called detuning.

(10) In FIG. 2 a schematic circuit diagram of a wayside circuit arrangement 10 and a vehicle-sided circuit arrangement 11 according to the invention are shown. The wayside circuit arrangement 10 comprises different segments N, N+1 which are arranged along a path of travel of a vehicle traveling on a driving surface of a route. Each segment N, N+1 comprises an inverter 12, a filter circuit 13 and primary windings 14. The inverters 12 are connected via a capacitance 15 to a power line 16 which is fed by a voltage source 17 via a rectifier 18.

(11) As the circuit arrangement 1 in FIG. 1, the circuit arrangement 11 in FIG. 2 comprises an AC part 4, a DC part 5 and a rectifier 6. In FIG. 2, only leakage inductances L.sub.S1, L.sub.S2, L.sub.S3 and compensating capacitances C.sub.S1, C.sub.S2, C.sub.S3 are shown. The circuit arrangement 11 comprises a three-phase full-bridge inverter 19. The inverter 19 is connected in parallel to a connection of the rectifier 6 and a circuit capacitance 7, which is part of the DC part 5 of the circuit arrangement 11. The inverter 19 comprises a first leg 20, a second leg 21 and a third leg 23. Each leg 20, 21, 23 comprises a first switching element Q1, Q3, Q5 which can be referred to as high-side switching element. Furthermore, each leg 20, 21, 23 comprises a second switching element Q2, Q4, Q6 which can be referred to as low-side switching element. A parallel connection of a diode and a capacitor is connected in parallel to each of the switching elements Q1, . . . , Q6. If the switching element has a conducting direction, the diode of said parallel connection is arranged such that it is connected anti-parallel to the respective switching element Q1, . . . , Q6. A connection point of the first switching element Q1 and the second switching element Q2 of the first leg 20 is connected to a first phase of the AC part 4 of the circuit arrangement 11. Correspondingly, connection points of the first switching elements Q3, Q5 and the second switching elements Q4, Q6 of the remaining legs 21, 23 are connected to a second and a third phase of the AC part 4 respectively. A high power line 22 of the inverter 19 is connected via a diode D1 to a high power line of the DC part 5 of the circuit arrangement 11. Correspondingly, a low power line 24 of the inverter 19 is connected via a diode D2 to a low power line of the DC part 5 of the circuit arrangement 11. Because two diodes D1, D2 are used to connect the inverter 19 to the DC part 5 of the circuit arrangement 11, the added inverter 19 does not process the whole power of the system. The added inverter 19 generates a controlled voltage out of an energy stored in the circuit capacitance 7. This (alternating output) voltage is added to an induced voltage of each phase. Therefore, phase currents I.sub.L1, I.sub.L2, I.sub.L3 through the impedances IM1, IM2, IM3 (see FIG. 1) can be controlled. By proper controlling of this additional voltage, it is possible to compensate a power drop and keep the system performance at the level of a perfectly tuned system. A conducting direction of the diode D1 connecting the high power line 22 of the inverter 19 to the DC part 5 is oriented from the inverter 19 towards the DC part 5. A conducting direction of the diode D2 connecting the low power line 24 of the inverter 19 to the DC part 5 is oriented from the DC part 5 towards the inverter 19. Due to the presence of the diodes D1, D2, if any short circuit happens in the inverter 19, the diodes D1, D2 will block a reverse current and a DC output voltage V.sub.out of the DC part 5 of the circuit arrangement 11 will still be available. If the forward voltage drop of diodes D1 and D2 is small, it is possible to use two or more diodes in series in order to provide the diode D1 and two or more diodes in series in order to provide the diode D2.

(12) In FIG. 3 an exemplary time course of an induced voltage V.sub.in1 in a first phase of an AC part 4 (see FIG. 2) and of gate signals G.sub.Q1, G.sub.Q2 of switching elements Q1, Q2 of a first leg 20 of an inverter 19 are shown (see FIG. 2). The induced voltage V.sub.in1 has a period T. This period T is equal for all three-phases. At a first zero crossing moment t0 of the induced voltage V.sub.in1, the second switching element Q2 is switched on for a predetermined on-time DT2 of the second switching element Q2. At the end of this on-time Q2 is switched off. Correspondingly, the first switching element Q1 is switched on at a second zero crossing moment t1 within the period T for a predetermined on-time DT1. A duty cycle of the first switching element Q1 is defined as the ratio between the on-time DT1 and the time period T. Correspondingly, a duty cycle of the second switching element Q2 is defined as the ratio between the on-time DT2 and the time period T. By controlling the duty cycles of the gating signals G.sub.Q2, G.sub.Q1 of the switching elements Q1, Q2, Q3, Q4, Q5, Q6 shown in FIG. 2, it is possible to increase the DC output voltage V.sub.out of the DC part 5 or equivalently the phase currents I.sub.L1, I.sub.L2, I.sub.L3. Increasing the phase currents I.sub.L1, I.sub.L2, I.sub.L3 means that RMS-values of the phase currents I.sub.L1, I.sub.L2, I.sub.L3 are increased. A control means or a control circuit for controlling the duty cycles of the switching elements Q1, . . . , Q6 can therefore be operated depending on a DC output voltage V.sub.out and a current (RMS) value of the phase currents I.sub.L1, I.sub.L2, I.sub.L3. Hence, such a control means needs samples of the output voltage V.sub.out and the phase currents I.sub.D, I.sub.L2, I.sub.L3.

(13) In FIG. 4, a course of a DC output voltage V.sub.out vs. different values of a duty cycle is shown. The duty cycle shown in FIG. 4 can be a duty cycle of all switching elements Q1, . . . , Q6 shown in FIG. 2. It is shown that a value of the output voltage V.sub.out does not change significantly for duty cycles ranging from 0.00 to approx. 0.08. This shows that a variation in the duty cycle within the interval from 0.00 to 0.08 will not affect the output voltage V.sub.out significantly. Thus, a very robust control of the duty cycles is provided which is e.g. insensitive against an incorrect determination of zero crossing moments t0, t1 of an induced voltage V.sub.in1 (see FIG. 3). For values of the duty cycle higher than 0.08, the output voltage V.sub.out increases with an increasing duty cycle in a linear fashion which is highly desirable.

(14) In FIG. 5, an exemplary course of a RMS-value of a phase current I.sub.L1,RMS vs. a value of the duty cycle is shown. The behavior of the RMS-value of the phase current I.sub.L1,RMS is equivalent to the behavior of an output voltage V.sub.out vs. a value of the duty cycle shown in FIG. 4. It is also shown that the RMS-value of the phase current I.sub.L1,RMS does not change significantly for duty cycle values ranging from 0.00 to 0.08. For values of the duty cycle larger than 0.08, the RMS-value of the phase current I.sub.L1,RMS increases with an increasing value of the duty cycle in a linear fashion which is highly desirable.