Method and System For Determining a Phase Shift Between a Phase Current and a Phase Voltage

Abstract

A method and a system for determining a phase shift between a phase current and a phase voltage in an AC phase line of a converter. A method and a system for determining a phase shift between a phase current (I.sub.u, I.sub.v, I.sub.w) and a phase voltage (U.sub.u, U.sub.v, U.sub.w) in an AC phase line (U, V, W) of a converter (5), in particular a converter (5) of a system for inductive power transfer, wherein a phase current change dependent quantity is determined, wherein a voltage-specific reference time point is determined depending on the phase current change dependent quantity, wherein the phase current (I.sub.u, I.sub.v, I.sub.w) is determined, wherein a current-specific reference time point is determined depending on the phase current (I.sub.u, I.sub.v, I.sub.w), wherein the phase shift is determined depending on the time difference between the voltage-specific reference time point and the current-specific reference time point.

Claims

1. A method for determining a phase shift between a phase current and a phase voltage in an AC phase line of a converter, in particular a converter of a system for inductive power transfer, wherein a phase current change dependent quantity is determined, wherein a voltage-specific reference time point is determined depending on the phase current change dependent quantity, wherein the phase current is determined, wherein a current-specific reference time point is determined depending on the phase current, wherein the phase shift is determined depending on the time difference between the voltage-specific reference time point and the current-specific reference time point.

2. The method of claim 1, characterized in that the voltage-specific reference time point is determined as the time point of a zero crossing of the phase current change dependent quantity.

3. The method of claim 1, characterized in that a derivative of the phase current change dependent quantity is determined by differentiating the phase current change dependent quantity at least once, wherein the voltage-specific reference time point is determined as the time point of a zero crossing of the derivative.

4. The method of claim 1, characterized in that the phase current is determined by integrating the phase current change dependent quantity over time.

5. The method of claim 1, characterized in that the phase current change dependent quantity is determined by a Rogowski coil-based determining means.

6. The method of claim 1, characterized in that the phase current change dependent quantity is compared to a first predetermined reference value by a first comparing means, wherein the phase current is compared to a further predetermined reference value by a further comparing means, wherein the voltage-specific reference time point is determined depending on an output signal of the first comparing means, wherein the current-specific reference time point is determined depending on an output signal of the further comparing means.

7. The method of claim 1, characterized in that a trigger signal is generated, wherein the voltage-specific reference time point and the current-specific reference time point are determined as time points within a time interval of predetermined duration after the time point of generating the trigger signal.

8. The method of claim 7, characterized in that the time point of generating the trigger signal is determined depending on a time point of a switch signal generation.

9. A system for determining a phase shift between a phase current and a phase voltage in an AC phase line of a converter, in particular a converter of a system for inductive power transfer, wherein the system comprises at least one means for determining a phase current change dependent quantity, at least one means for determining a voltage-specific reference time point depending on the phase current change dependent quantity, at least one means for determining a phase current, at least one means for determining a current-specific reference time point depending on the phase current and at least one means for determining the phase shift depending on the time difference between the voltage-specific reference time point and the current-specific reference time point.

10. The system of claim 9, characterized in that the means for determining a phase current change dependent quantity comprises a Rogowski coil-based determining means.

Description

[0075] The invention described with reference to the attached figures. The figures show:

[0076] FIG. 1: A schematic circuit diagram of a primary unit system for inductive power transfer,

[0077] FIG. 2: A schematic block diagram of a system for determining a phase shift and

[0078] FIG. 3: A schematic flow diagram of a method for determining a phase shift according to the invention.

[0079] In the following, the same reference numerals denote elements with the same or similar technical features.

[0080] FIG. 1 shows a schematic circuit diagram of a primary unit 1 of a system for inductive power transfer 2 (not shown). The primary unit 1 comprises and inverter 5 which is designed with a B6 bridge topology. The inverter 5 comprises switching elements 6, wherein a bypass diode 7 is connected antiparallel to each switching element 6. The inverter 5 has three legs, wherein each leg comprises a series connection of two switching elements 6 and one phase line U, V, W is connected to a connecting section of the two switching elements 6.

[0081] In particular, a first switching element 6 is connected to a high potential phase line, wherein the second switching element 6 is connected to a low potential phase line.

[0082] The switching element 6 of the inverter can e.g. be provided by a MOSFET or an IBGT.

[0083] The inverter 5 generates or provides AC (alternating current) phase voltages U.sub.U, U.sub.V, U.sub.W for the phase lines U, V, W of the primary winding structure 3. AC output terminals of the inverter 5 are connected to the phase lines U, V, W, respectively. In the shown embodiment, these phase lines U, V, W of primary winding structure 3 are electrically connected to AC phase lines of the inverter 5. Thus, phase lines U, V, W also denote AC phase lines of the inverter 5.

[0084] The primary winding structure 3 is a three-phase winding structure. Schematically shown is an inductance L.sub.U, L.sub.V, L.sub.W provided by each phase line U, V, W. Further shown are compensating capacitances C.sub.U, C.sub.V, C.sub.W in each phase line U, V, W wherein a capacitance value of said capacitances C.sub.U, C.sub.V, C.sub.W is chosen such that the resonant frequency of the resonant circuit provided by the inductance L.sub.U, L.sub.V, L.sub.W and the capacitance C.sub.U, C.sub.V, C.sub.W of each phase line U, V, W matches an operating frequency f (see FIG. 5).

[0085] Further shown are AC phase currents I.sub.U, I.sub.V, I.sub.W in each phase line U, V, W which correspond to phase currents in AC phase lines of the inverter 5. In arrowhead of each phase current I.sub.U, I.sub.V, I.sub.W indicates a positive direction of the phase current I.sub.U, I.sub.V, I.sub.W. A positive value of the phase current I.sub.U, I.sub.V, I.sub.W indicates a current flow with the indicated direction. AC phase voltages of the AC phase lines U, V, W are referenced by U.sub.U, U.sub.V, U.sub.W.

[0086] A system 12 (see FIG. 2) for determining a phase shift between the phase currents I.sub.U, I.sub.V, I.sub.W and the phase voltages U.sub.U, U.sub.V, U.sub.W in each AC phase line U, V, W comprises a phase current change sensor 8 which provides a sensor for measuring a phase current change depending quantity and which measures the phase current change of phase currents I.sub.U, I.sub.V, I.sub.W in each phase U, V, W, wherein the phase current change provides the phase current change depending quantity. In particular, the phase current change sensors 8 measure the phase current change of the phase I.sub.U, I.sub.V, I.sub.W which flow through one switching element 6 of a leg of the inverter 5 into the respective phase line U, V, W. The phase current change sensor 8 can comprise a Rogowski coil 13 (see FIG. 2).

[0087] It is, however, also possible that the system 12 comprises a phase current sensor and at least one means for determining a derivative of the measured phase current I.sub.U, I.sub.V, I.sub.W.

[0088] Further, the system 12 comprises an evaluation unit 9 which is connected to the phase current change sensors 8 by a signal link (shown by dash lines). The phase current change sensors 8 can provide samples of the measured phase current I.sub.U, I.sub.V, I.sub.W. Further, the system comprises a memory unit 10 which is also connected to the evaluation unit 9 by a signal or data link. Further shown is a control unit 11 for controlling an operation of the inverter 5, e.g. of the switching elements 6. The control unit 11 is connected to the evaluation unit 9 by a signal or data link.

[0089] It is possible that the evaluation 9 determines a voltage-specific reference time point depending on the phase current change, in particular as the time point of a zero crossing of the phase current change provided by the phase current change sensor 8. Further, a phase current I.sub.U, I.sub.V, I.sub.W can be determined, in particular by integrating the phase current change over time. This can also be performed by the evaluation unit 9. Further, a current-specific reference time point can be determined depending on the phase current I.sub.U, I.sub.V, I.sub.W, in particular a time point of zero crossing of the phase current I.sub.U, I.sub.V, I.sub.W.

[0090] In addition or alternatively, it is possible that the evaluation 9 determines the voltage-specific reference time point depending on a first derivative or a derivative with a higher order of the phase current change.

[0091] Further, in particular by means of the evaluation 9, the phase shift can be determined depending on, in particular as, the time difference between the voltage-specific reference time point and the current-specific reference time point.

[0092] It is further possible that the evaluation unit determines a first derivative of the phase current change provided by the phase current change sensor 8. Then, the voltage-specific reference time point can be determined as the time point of a zero crossing of this first derivative.

[0093] FIG. 2 shows a schematic circuit diagram of a system for determining a phase shift between a phase current I.sub.U, and a phase voltage U.sub.U (see FIG. 1) in an AC phase line U of an inverter 5 (see FIG. 1). FIG. 2 provides a schematic circuit diagram of said system for the first phase line U. A similar system can also be applied to the remaining phase lines V, W.

[0094] Schematically indicated is an AC input terminal 14 for the system 12 to which the AC phase current I.sub.U is provided. Further indicated is an AC output terminal 15, which can e.g. be connected to a phase line of the primary winding structure 3 (shown in FIG. 1).

[0095] Further shown is phase current sensor 8 with the Rogowski coil 13. The phase current change sensor 8 provides an output signal which is proportional to a change over time of the phase current I.sub.U, i.e. a time derivative of the phase current I.sub.U,

[0096] The system comprises an amplifier 16 for amplifying the output signal of the phase current change sensor 8. The amplifier output signal is compared to a first threshold value TH1 by a first comparator 17. It is indicated that the first threshold TH1 is amplified by an amplifier 18 before being provided to the first comparator 17. The first threshold value TH1 can be zero or have a value close to zero. Thus, output signal of the first comparator 17 changes from signal representing a logical “1” status to a signal representing a logical “0” status or vice versa if the amplified output signal of the phase current change sensor 8 has a zero crossing. The output signal of the first comparator 17 is amplified by an amplifier 19 and provided to an evaluation unit 24. The output of the first comparator 17 can have a square form.

[0097] Further, the amplified output signal of the phase current change sensor 8 is provided to an integrator 20 which integrates the output signal of the phase current change sensor 8 over time. The integrated phase current change which corresponds to the phase current I.sub.U is amplified by an amplifier 21 and provided to a second comparator 22. Further, a second threshold value TH2 is amplified by an amplifier 23 and also provided to second comparator 22. The second threshold value TH2 can be zero or have a value close to zero. An output signal of the second comparator 22 changes from first signal representing e.g. a logic “1” status to a signal representing a logic “0” status if the phase current has a zero crossing. Thus, the output signal of the second comparator 22 can also have a square wave form.

[0098] The output signals of the comparators 17, 22 are provided to the evaluation unit 24 which can be equal to the evaluation unit 9 shown in FIG. 1. By means of the evaluation unit 24, signal edges, e.g. rising or falling signal edges, of the output signals provided by the comparators 17, 22 can be detected. The time point of the detection of such a signal edge in the amplified output signal of the first comparator 17 can correspond to a voltage-specific reference time point, wherein the time point of detection of a signal edge in the amplified output signal of the second comparator 22 can correspond to a current-specific reference time point.

[0099] Then, the evaluation means 24 can determine the phase shift as the time difference between the said voltage-specific reference time point and the current-specific reference time point.

[0100] It is further possible that the control unit 11 (see FIG. 1) generates a trigger signal if a switching signal for a switching element 6 in one leg of the inverter 5 is generated by the control unit 11, wherein said leg is connected to the phase line U for which the phase shift is to be determined. The trigger signal can be transmitted to the evaluation unit 24. Then, the voltage-specific reference time point and the current-specific reference time point are determined as time points within a time interval of predetermined duration after the reception of said trigger signal.

[0101] FIG. 3 shows a schematic flow diagram of a method for determining the phase shift between the phase current I.sub.U, I.sub.V, I.sub.W and a phase voltage U.sub.U, U.sub.V, U.sub.W in one of the AC phase lines U, V, W of an inverter 5 is shown. In a first step S1, a phase current change is determined, e.g. by measuring the phase current change with a Rogowski coil-based sensor 8. Further, in a second step S2, a voltage-specific reference time point is determined depending on the phase current change, in particular as the time point of a zero crossing of the phase current change. In a third step S3 a phase I.sub.U, I.sub.V, I.sub.W is determined, in particular by integrating the phase current change over time. In a fourth step S4, a current-specific reference time point is determined depending on the phase current I.sub.U, I.sub.V, I.sub.W, in particular as the time point of a zero crossing of a phase current I.sub.U, I.sub.V, I.sub.W. In a fifth step S5, a phase shift is determined depending on the time difference between the voltage-specific reference time point and the current-specific reference time point.

[0102] The sequence shown in FIG. 3 is not a mandatory sequence. It is for instance possible that single steps, in particular the second, third and fourth step S2, S3, S4 are performed simultaneously or at least partially simultaneously.