Inductive power transfer control

1. Method of detecting an operating condition of a secondary side of an inductive power transfer system, comprising the steps:

measuring at least one electric variable at a primary side of the inductive power transfer system which is dynamically coupled to the operating condition at the secondary side of the inductive power transfer system;

executing a first analysis of the at least one electric variable over time at the primary side of the inductive power transfer system for detection of the operating condition at the secondary side of the inductive power transfer system without use of measurement data measurable at the secondary side of the inductive power transfer system;

determining a rate of change of the at least one electric variable at the primary side of the inductive power transfer system; and

executing the first analysis by analyzing the rate of change of the at least one variable at the primary side of the inductive power transfer system using at least one threshold which is a fixed threshold.

2. Method according to claim 1 , wherein the at least one threshold is a fixed threshold.

3. Method according to claim 2 , wherein a rising edge crossing of a first threshold of a sampled electric variable at the primary side of the inductive power transfer system serves for detection of an open circuit condition at the secondary side of the inductive power transfer system.

4. Method according to claim 3 , wherein the sampled electric variable at the primary side of the inductive power transfer system is a primary side high frequency current.

5. Method according to claim 2 , wherein a falling edge crossing of a second threshold of a sampled electric variable at the primary side of the inductive power transfer system serves for detection of a short circuit condition at the secondary side of the inductive power transfer system.

6. Method according to claim 2 , wherein the sampled electric variable at the primary side of the inductive power transfer system is a primary side high frequency current.

7. Method according to claim 1 , wherein the rate of change of the at least one electric variable at the primary side of the inductive power transfer system is selected as a single value or combination of

a rate of change of the primary side current and/or at least one value based on the rate of change of the primary side current;

a rate of change of an electric power supplied to the primary side of the inductive power transfer system and/or at least one value based on the rate of change of the electric power supplied to the primary side of the inductive power transfer system; and

a rate of change of the phase difference between the primary side current and the primary side voltage and/or at least one value based on the rate of change of the phase difference between the primary side current and the primary side voltage.

8. Method according to claim 1 , comprising the steps:

measuring at least one electric variable at the secondary side of the inductive power transfer system for generation of measurement data in relation to the operating condition at the secondary side of the inductive power transfer system;

communicating the generated measurement data from the secondary side of the inductive power transfer system to the primary side of the inductive power transfer system;

executing a second analysis of the communicated measurement data over time at the primary side of the inductive power transfer system in combination with the first analysis for detection of the operating condition at the secondary side of the inductive power transfer system.

9. Method according to claim 1 , wherein the operating condition at the secondary side of the inductive power transfer system is related to a change from a regular operating condition to a non-regular operating condition.

10. Method according to claim 9 , wherein the second non-regular operating condition is an open circuit condition or a short circuit condition at the secondary side of the inductive power transfer system.

11. Method according to claim 1 , wherein the step of measuring at least one electric variable over time at the primary side of the inductive power transfer system comprises:

determining sample values of the at least one electric variable and/or a value being based on the at least one electric variable; and

analyzing the at least one electric variable and/or the value being based on the at least one electric variable using the sample values and a predetermined threshold scheme;

wherein the threshold scheme comprises at least one threshold which is an adaptive threshold or a combination of a fixed threshold and an adaptive threshold.

12. Method according to claim 11 , wherein the value being based on the at least one electric variable is the rate of change of the at least one electric variable.

13. Method according to claim 11 , wherein the at least one electric variable is the primary side current and the step of measuring at least electric variable over time comprises:

a step of sampling the primary side current; and

a step of analyzing absolute values I 1hf_abs (k) of sample values of the primary side current using a threshold scheme dividing into a first lower threshold I 1low (k) and a second higher threshold I 1high (k) according to

I 1low ( k )< I 1hf_abs ( k )< I 1high ( k )

I 1low ( k )= g m U 2,hf ( k )− a ( k )

I 1high ( k )= g m U 2,hf ( k )+ b ( k )

wherein

g

m

=

1

2

⁢

⁢

π

⁢

⁢

f

0

⁢

L

12

 is the trans-conductance, f 0 is the resonant frequency at the primary side of the inductive power transfer system, and L 12 is the mutual inductance or a representative value for the trans-conductance; and

U 2,hf (k) is the secondary side high frequency voltage of the inductive power transfer system ( 10 ; 34 );

a(k) is a lower bound for observing regular operation at the secondary side of the inductive power transfer system ( 10 ; 34 ) in relation to g m U 2,hf (k); and

b(k) is a upper bound for observing regular operation at the secondary side of the inductive power transfer system ( 10 ; 34 ) in relation to g m U 2,hf (k).

14. Method according to claim 13 , comprising the steps:

detecting the short circuit condition at the secondary side of the inductive power transfer system when absolute values I 1hf_abs (k) of the sample values of the primary side current are lower than the first lower threshold I 1low (k) over a first pre-determined period of time; and/or

detecting the open circuit condition at the secondary side of the inductive power transfer system when the absolute values I 1hf_abs (k) of the sample values of the primary side current are higher than the second higher threshold I 1high (k) over a second predetermined period of time.

15. Method of controlling an inductive power transfer system, comprising the steps:

detecting operating conditions at a secondary side of an inductive power transfer system according to claim 1 ;

controlling an operation of the inductive power transfer system in response to detected operating conditions of the inductive power transfer system.

16. Method according to claim 15 , wherein the primary side of the inductive power transfer system comprises an inverter for converting a direct current input signal into a high frequency primary side current and a high frequency primary side voltage and wherein the at least one electric variable for detecting the operating state at the secondary side is the high frequency primary side current, comprising the step:

sampling the high frequency primary side current with a phase shift relative to the high frequency primary side voltage.

17. Method according to claim 16 , comprising the steps:

analyzing absolute values I 1hf_abs (k) of sample values of the high frequency primary side current by using a threshold scheme set up by a first lower threshold I 1low (k), a second higher threshold I 1high (k), and a third maximum threshold I 1max according to

I 1low ( k )< I 1hf_abs ( k )< I 1high ( k )< I 1max

I 1low ( k )= g m U 2,hf ( k )− c ( k )

I 1high ( k )= g m U 2,hf ( k )+ d ( k )

wherein

g

m

=

1

2

⁢

⁢

π

⁢

⁢

f

0

⁢

L

12

 is the trans-conductance, f 0 is the resonant frequency at the primary side of the inductive power transfer system, and L 12 is the mutual inductance or a representative value for the trans-conductance;

c(k) is a lower bound for observing regular operation at the secondary side of the inductive power transfer system in relation to g m U 2,hf (k); and

d(k) is a upper bound for observing regular operation at the secondary side of the inductive power transfer system in relation to g m U 2,hf (k);

the method further comprising the step:

detecting the short circuit condition at the secondary side of the inductive power transfer system when absolute values I 1hf_abs (k) of the sample values of the high frequency primary side current are lower than the first lower threshold I 1low (k) over a first predetermine period of time; and

limiting or decreasing the electric power supply at the primary side of the inductive power transfer system for protection of hardware circuitry in the inductive power transfer system.

18. Method according to claim 17 , further comprising the steps:

detecting the open circuit condition at the secondary side of the inductive power transfer system when absolute values I 1hf_abs (k) of the sample values of the high frequency primary side current are higher than the second higher threshold I 1high (k) over a second predetermined period of time; and

limiting or decreasing the electric power supply at the primary side of the inductive power transfer system peak value of the primary side current for protection of hardware circuitry in the inductive power transfer system upon detection of an open circuit condition or short circuit condition of the secondary side of the inductive power transfer system.

19. Method according to claim 17 , comprising the step:

interrupting the operation of the inductive power transfer system when the absolute values I 1hf_abs (k) of the sample values of the high frequency primary side current exceed the third the maximum threshold I 1max over a third predetermined period of time for protection of hardware circuitry in the inductive power transfer system.

20. Method according to claim 17 , comprising the step:

controlling the first lower threshold I 1low (k) and the second higher threshold I 1high (k) in an adaptive manner according to a time varying trans-conductance of the inductive power transfer system.

21. Controller apparatus for controlling an inductive power transfer system, the controller comprising at least one interface to establish input output functionality, at least one processor, and a memory storing instructions to be executed by the at least one processor, whereby the controller apparatus is adapted to:

detect operating conditions in the inductive power transfer system according to claim 1 ;

control an operation of the inductive power transfer system in response to detected operating conditions in the inductive power transfer system.