Method for operating an apparatus for wirelessly transferring energy in the direction of an electrical consumer by means of inductive coupling, apparatus and system

A method for operating an apparatus (100) for wirelessly transferring energy in a direction of an electrical consumer (200) by inductive coupling, the method comprising steps of:

• a) providing an apparatus (100) comprising:
• a rectifier (101) for generating a DC voltage (UG) from a power supply system voltage (UN), an inverter (102) fed from the DC voltage (UG) and configured to generate a pulse-width-modulated drive signal (AS),
• a coil (103) driven by the pulse-width-modulated drive signal (AS), via which an alternating magnetic field is generated to transfer the energy, and
• a control unit (105) configured to control the inverter (102) to output an electrical actual power output to a pre-defined electrical target power, wherein a frequency and a duty cycle of the pulse-width-modulated drive signal (AS) serve as manipulated control variables,
• b) setting a start frequency (f_0), c) setting a start duty cycle (DC_1) in such a way that the pre-defined electrical target power is undershot,
• d) measuring an electrical actual power output by the inverter (102) at the start frequency (f_0) and the start duty cycle (DC_1),
• e) choosing an adjustment target power which is less than or equal to the pre-defined electrical target power,
• f) calculating a duty cycle (DC_2) which computationally corresponds to the adjustment target power,
• g) setting the calculated duty cycle (DC_2),
• h) measuring an electrical actual power output by the inverter (102) in a case of the start frequency (f_0) and the calculated duty cycle (DC_2), and
• i) repeating steps e) to h) with increasing the adjustment target power until a deviation between the pre-defined electrical target power and the electrical actual power falls below a predefined threshold, wherein, during this repetition, in subsequent iterations of step f), a new duty cycle (DC_3) which computationally corresponds to the adjustment target power is calculated on a basis of a combination of (1) the duty cycle (DC_2) calculated in the preceding iteration of step f), (11) the electrical actual power measured in the preceding iteration of step h), and (iii) the adjustment target power,
• wherein:
• in step h), at least one switching current when switching off a semiconductor switch (106, 107) of the inverter (102) is determined in addition to the electrical actual power, and
• the frequency for the subsequent repetition of steps e) to h) is increased if the at least one switching current exceeds a capacitive limit value.