The invention relates to a transfer pick-up circuit for inductively picking up power from a cable carrying an alternating supply current, wherein the transfer pick-up circuit comprises a first circuit comprising the main secondary winding of a transformer for providing an inductive coupling to the cable and a first capacitive module connected in parallel to the main secondary winding. Furthermore, the invention relates to a node comprising a transfer pick-up circuit.

Such a transfer pick-up circuit, for example, is known from JP 2002-354711. Figure 2 of JP 2002-354711 shows a non-contact power feeder device having a high-frequency power supply 11, a primary power supply line 12 connected to the high-frequency power supply. Further, the non- contact power feeder device comprises a power supply transformer 13 having a secondary winding 13s, a series- parallel resonance circuit 18 connected to the power supply transformer 13, a rectification unit 15 for rectifying the transformed power, and a constant voltage control unit 16 for supplying a voltage to a load.

SUMMARY OF THE INVENTION

In the known transfer pick-up circuit, a high- frequency power carrier signal is provided by the high- frequency power supply. It is noted that the frequency of the power signal is considered high if the total cable length of a power transfer system becomes larger than a tenth part of the wavelength of the power signal. In this case, power transfer from the cable to the secondary winding of the power supply transformer is heavily affected because of impedance changes due to internal reflections within the cable. A disadvantage of the known power transfer system, thus, is that the power transfer system has a low system power throughput and efficiency.

Furthermore, the electrical components of such a power transfer system have tolerances. For example, the value of capacitors may vary up to 10%, and the inductance of coils may vary 5 to 10% due to productions tolerances. Furthermore, tolerances are caused among others by working temperature and aging of the components. As the electrical components of the transfer pick-up circuit determine the resonance frequency of the transfer pick-up circuit, such tolerances can lead to significant deviation of the intended resonance frequency. A large deviation of the intended resonance frequency results in a low system power throughput and efficiency.

It is an object of the present invention to ameliorate or to eliminate one or more disadvantages of the known power transfer system, to provide an improved power transfer system or to at least provide an alternative power transfer system.

According to a first aspect, the invention provides a transfer pick-up circuit for inductively picking up power from a cable carrying an alternating supply current having a cable current frequency, wherein the transfer pick-up circuit comprises:

- the main secondary winding of a transformer for providing an inductive coupling to the cable and a capacitive module connected in parallel to the main secondary winding; - a switch mode converter connected in series to the main secondary winding and configured for converting a picked up alternating current to a direct current (DC); and

- a sensor configured for sensing at least one property of the alternating supply current carried by the cable and/or for sensing at least one property of the picked up alternating current, wherein the sensor is in electrical communication with the switch mode converter, wherein the switch mode converter further is configured for regulating a reactance on the input thereof to a predetermined setpoint on basis of the sensed at least one property of the alternating supply current.

As mentioned above, power transfer from the cable, which is operatively coupled to a base station which is a power source, to the main secondary winding of the power supply transformer is heavily affected because of impedance changes due to internal reflections within the cable. The most significant impedance changes occur on positions where loads, such as nodes, are placed on the cable. The impedance of the cable and the impedance of the load together determine the efficiency of power transfer between them. Impedance comprises a resistive part and a reactive part. The resistive part of the load is usually solely defined by the power demand of the load and the amplitude of the alternating supply current, following the equation R= ^/ _j2 - In order to optimize power transfer between the cable and the transfer pick-up circuit, the reactive part of the impedance of the load needs to be optimized. The reactive part depends among others on the position of the transfer pick-up circuit on the cable, the cable characteristics, the power requirement of the load, and the cable current.

The inventors have surprisingly found that the cable current is the most significant for regulating the optimum reactive part. The transfer pick-up circuit according to the invention senses at least one property of the alternating supply current, for example the current thereof, by means of the sensor. The sensed current is supplied to the switch mode converter, which applies the sensed current to regulate a reactance, also known as the reactive part, to a desired setpoint resulting in an optimum reactive part of the load. The optimum reactive part of the load, together with the resistive part of the load, results in optimal power transfer from the base station to one or more transfer pick-up circuits. An advantage of the invention, therefore, is that power transfer between the base station/cable, and the transfer pick-up circuit(s) and thus the load is more efficient and in the ideal case optimized.

Additionally, by regulating the reactive part of the load on the basis of the sensed cable current, it is possible to compensate for tolerances of the components of the transfer pick-up circuit.

In an embodiment, the sensor is configured for being operatively coupled to the cable. In an embodiment thereof, the sensor is configured for sensing the cable current of the alternating supply current carried by the cable. As mentioned above, the reactive part of the impedance of the load depends among others on the following parameters: position of the transfer pick-up circuit on the cable, the cable characteristics, the power requirement of the load, and the cable current. The inventors have surprisingly found that the cable current is the most significant for determining the optimum reactive part of the load, i.e. the transfer pick-up circuit. This embodiment has as an advantage, that only the most significant parameter that can be used for determining the optimum reactance is sensed at the side of the cable, therewith keeping the transfer pick-up circuit relatively simple.

Additionally, the sensed cable current can be used for determining a reactance setpoint, therewith maximizing power transfer.

In an embodiment the sensor, during use, applies a current sensing method selected from the group comprising resistance sensing, magnetic field sensing and inductance sensing. In an embodiment thereof, the sensor comprises a sensing secondary winding of a transformer inductively coupled to the cable.

In an embodiment, the sensor is configured for sensing the cable voltage of the alternating supply current carried by the cable and/or for sensing a voltage of the picked up alternating current. In an embodiment thereof, the transfer pick-up circuit is provided with a further sensor for sensing at least one property of the alternating supply current carried by the cable and/or for sensing at least one property of the picked up alternating current. According to this embodiment, the transfer pick-up circuit can be provided with the sensor for sensing the cable current of the alternating supply current and with a further sensor for sensing the voltage of the picked up alternating current. The presence of the sensor for sensing the cable current and of the further sensor for sensing the voltage of the picked up alternating current, advantageously provides the ability to optimize power transfer from the base station to the transfer pick-up circuit. In order to optimize the power transfer, the reactance on the side of primary winding of the transformer has to be controlled. The reactance can be controlled by regulating the reactive voltage of the transfer pick-up circuit, in particular the amplitude thereof. In order to regulate the reactance, both a sensed cable current and a sensed voltage of the picked up alternating current are required. By using the sensed cable current, the influence of the induction of the transformer is advantageously reduced or in the ideal case eliminated.

It is noted that the voltage at the secondary side is proportional to the voltage at the cable.

According to the invention, the transfer pick-up circuit comprises a controller configured for controlling the switch mode converter in order to regulate a reactance on the input thereof to a predetermined setpoint on basis of the sensed at least one property of the alternating supply current.

In an embodiment, the further sensor comprises a node voltage sensing circuit connected in parallel to the main secondary winding and configured for sensing the voltage of the power picked up from the cable, and/or an application voltage sensing circuit connected in parallel to an output of the transfer pick-up circuit and configured for sensing the application voltage. In an embodiment thereof, the further sensor, the node voltage sensing circuit and/or the application voltage sensing circuit are in data communication with the controller. During use, the reactance at the input of the switch mode convertor is regulated in order to regulate the reactance to a predetermined setpoint on basis of the sensed at least one property of the alternating supply current. Regulating the reactance on the input of the switch mode converter will affect the node voltage applied to the transfer pick-up circuit or the node, which is among others the transfer pick-up circuit in combination with a load, such as a switchable light bulb. By sensing the node voltage applied to the transfer pick-up circuit or the node and communicating the sensed node voltage to the controller, the controller receives a feedback about the effects of the regulated reactance. Therefore, the controller has the ability to control the switch mode converter among others in dependence of the sensed node voltage.

In respect of the application voltage sensing circuit, it is noted that regulating the reactance on the input of the switch mode converter will also affect the application voltage applied to a load, such as a switchable light bulb. By sensing the application voltage applied to the load and communicating the sensed application voltage to the controller, the controller receives a feedback about the effects of the regulated reactance. Therefore, the controller has the ability to control the switch mode converter among others in dependence of the sensed application voltage.

In an embodiment according to the invention, the controller is provided with: - an application voltage controller configured for regulating the resistance of the transfer pick-up circuit on the cable to a predetermined application voltage value, preferably wherein the application voltage controller receives an application voltage setpoint; and - a reactive power controller configured for regulating the reactance of the transfer pick-up circuit to a predetermined reactive power value, preferably wherein the reactive power controller receives a reactive power setpoint. In a further embodiment thereof, the controller is configured for multiplying the predetermined application voltage value with a cable current, which is preferably delayed by one period of the cable current frequency, resulting in an active transfer pick-up circuit voltage component, wherein the controller further is configured for multiplying the predetermined reactive power value with an inverted cable current, which is preferably delayed by one quarter of one period of the cable current frequency, resulting in an reactive voltage component, and wherein the controller is configured for summing the active transfer pick-up circuit voltage component and the reactive voltage component, resulting in an predetermined output voltage.

The predetermined output voltage, according to this embodiment, is calculated by summing the active transfer pick-up circuit voltage component and the reactive voltage component, which both are sine waves. Both of the components are generated by multiplying correspondingly delayed, i.e. phase-shifted, cable currents with two controlled multiplicands, which are the predetermined application voltage value and the predetermined reactive power value. The predetermined application voltage value represents the resistance part of the impedance and the predetermined reactive power value represents the reactive part of the impedance. Both values are controlled separately by the application voltage controller and the reactive power controller. This is advantageous, as it results in a stable node/transfer pick-up circuit impedance during transients.

In an embodiment, the controller is further configured for dividing the predetermined output voltage by the application voltage determined by the application voltage sensing circuit, resulting in a DTC (duty cycle) signal, and wherein the controller comprises a PWM (Pulse Width Modulation) generator configured for generating one or more PWM switching signals on basis of the DTC signal, which one or more PWM switching signals are provided for telling the switch mode convertor which average voltage it should produce.

The controller of the transfer pick-up circuit, according to this embodiment, has as output one or more PWM switching signals for the switch mode convertor. Thus, the controller advantageously provides control signals which are suitable for controlling the switch mode converter.

In an embodiment, the controller comprises a power analyzer and a setpoint generator, wherein the power analyzer is configured for measuring active power by integrating the product of the sensed voltage of the power picked up from the cable, and the sensed cable current, and for measuring the reactive power by integrating the product of the voltage of the power picked up from the cable, and a sensed cable current shifted by 90 degrees, wherein the measured active power is transmitted from the power analyzer to a setpoint generator configured for generating a setpoint as a function of the measured active power, wherein the generated setpoint is provided to the reactive power controller, and the measured reactive power is transmitted from the power analyzer to the reactive power controller.

The output voltage of the switch mode convertor is not always equal to the transfer pick-up circuit voltage or the node voltage in both amplitude and phase. Production tolerances of the components to the transfer pick-up circuit cause an undesired uncertainty in the reactance of the transfer pick-up circuit or of the node. In order to compensate for these production tolerances of the components, feedback of either the reactive power, the reactive voltage or the reactance is required. The power analyzer measures the active power and the reactive power as described above and the feedback from the analyzer is used to compensate for errors between the reactive voltage component from the reactive power controller and the actual reactive voltage. An advantage of this embodiment, therefore, is production tolerances of the components of the transfer pick-up circuit are compensated.

In an embodiment, the switch mode converter is selected from a group comprising, a four quadrant power converter, a H-bridge topology and a Half bridge topology.

In an embodiment, the switch mode converter comprises a switching coil which together with the capacitive module forms a low-pass filter, allowing frequency components corresponding substantially to the frequency of the alternating supply current to pass, while damping higher switching frequency components.

In an embodiment, the transfer pick-up circuit comprises a transformer induction compensation component configured for compensating for the transformer induction. In an embodiment thereof, the capacitive module has a value which is chosen, such that the capacitive module compensates for the typical inductance of the main secondary winding for the frequency of the alternating supply current. Alternatively, an inductance measurement circuit is implemented for continuously measuring the transformer induction. The inductance measurement circuit can measure the inductance by inducing a small current through the transformer of a frequency different from the cable current frequency. By measuring the current/voltage relationship for this frequency only, the induction can determined and compensated for by adjusting the setpoint.

In an embodiment, the transfer pick-up circuit comprises an additional capacitive module connected in parallel to the switch mode converter.

During use, the additional capacitive module functions as a buffer capacitive module for preventing or reducing filter surges of the direct current outputted by the switch mode converter. As a result, the output voltage of the switch mode converter is prevented advantageously from being a series or rises and falls and is brought to more of a straight line, like true DC, or the rises and falls are reduced.

According to a second aspect, the invention provides a node provided with a transfer pick-up circuit according to the first aspect of the invention.

The node according to the second aspect of the invention has at least the same advantages as described above in relation to the transfer pick-up circuit according to the first aspect of the invention.

The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings, in which:

Figure 1 shows a block diagram of a transfer pick-up circuit according to a first embodiment of the invention, inductively coupled to a cable; Figure 2 shows a block diagram of a transfer pick-up circuit having a controller, according to a further embodiment of the invention, inductively coupled to a cable; and

Figure 3 shows a DSP code block diagram of the controller of figure 2.

DETAILED DESCRIPTION OF THE INVENTION

A block diagram of a transfer pick-up circuit 1 is shown in figure 1. The transfer pick-up circuit 1 is configured for inductively picking up power from a cable 2. The cable 2 is connected to a non-shown base station configured for providing an alternating supply current, which alternating supply current is supplied to the cable 2. The cable 2 carries the alternating supply current to one or more locations where the alternating supply current can be inductively picked up from the cable by means of the transfer pick-up circuit 1.

The transfer pick-up circuit 1 includes the main secondary winding 3 of a transformer. The main secondary winding 3 is provided for inductive coupling of the transfer pick-up circuit 1 to the cable 2. For the sake of clarity, the first winding 4 of the transformer is schematically indicated in the cable 2. The transfer pick- up circuit 1 further comprises a capacitive module 5, which is connected in parallel to the main secondary winding 3. During use, the main secondary winding 3 picks up power inductively from the cable 2.

Although not shown, in an alternative embodiment, the transfer pick-up circuit is provided with a ferrite element which can be placed in proximity of the cable 2. The main secondary winding 3 of the transformer can be placed around the ferrite element at least partially, such that the ferrite element forms the core of a transformer.

A switch mode converter, specifically a four quadrant power converter 6 is connected in series to the main secondary winding 3. The four quadrant power converter 6 is configured for receiving the picked up power from the main secondary winding 3, which is an alternating current (AC), and for converting the picked up alternating current to a direct current (DC). From the four quadrant power convertor 6, the direct current can be supplied to a non- shown load, such as a switchable light bulb that can be switched on or off at demand.

As shown in figure 1, an additional capacitive module 7 is connected in parallel to the four quadrant power converter 6. The additional capacitive module 7 functions as a buffer capacitive module 7 in order to reduce filter surges of the direct current outputted by the four quadrant power converter 6. As a result, the rises and falls of the output voltage of the four quadrant power converter 6 are reduced, such that the output voltage is brought to more of a straight line, like true DC.

The transfer pick-up circuit 1 is further provided with a current clamp sensor 8 which is clamped to the cable 2, as shown in figure 1. The current clamp sensor 8 is configured for sensing the current of the alternating supply current carried by the cable 2. The current clamp sensor is in electrical communication with the four quadrant power converter 6, such that the sensed current of the alternating supply current can be communicated to the four quadrant power converter 6.

During use, the transfer pick-up circuit 1 is used for picking up inductively power from the cable 2 in order to supply power to a load, such as the switchable light bulb. The combination of among others the transfer pick-up circuit 1 and the switchable light bulb hereafter is referred to as a node. The efficiency of power transfer between the cable 2 and the node is inter alia dependent on the impedance of the node. Impedance of the node comprises a resistive part and a reactance part. The resistive part is defined by the power demand of the node and the amplitude of the alternating supply current, corresponding to the following equation:

«= . wherein R represents the resistance of the node, P represents the power demand of the node, and I represents the amplitude of the alternating supply current. The optimum value for the reactance part depends on the following parameters: power requirement of the node, the particular position of the node on the cable, the cable characteristics and the cable current. The cable current is the most significant parameter and can be used to determine the optimum value for the reactance part of the node. The current clamp sensor 8 senses the cable current and communicates the sensed cable current to the four quadrant power converter 6. The four quadrant power converter 6 regulates the reactance at the input thereof to a predetermined setpoint, which predetermined setpoint is determined to result in optimum power transfer of power from the base station to the transfer pick-up circuit 1, preferably to multiple transfer pick-up circuits 1 arranged in multiple nodes.

Since the reactance part of the node is regulated to a desired setpoint, the transfer pick-up circuit 1 is enabled to regulate the reactance part of the node to the optimum value for optimum power transfer. Additionally, the transfer pick-up circuit 1 is enabled to compensate for production tolerances of the electrical components of the transfer pick-up circuit 1.

A block diagram of a transfer pick-up circuit 101 according to a further embodiment of the invention is shown in figure 2. The transfer pick-up circuit 101 also comprises the main secondary winding 103 of a transformer. The main secondary winding 103 is provided for inductive coupling of the transfer pick-up circuit 101 to the cable 102. For the sake of clarity, the first winding 104 of the transformer is schematically indicated in the cable 102. The transfer pick-up circuit 101 further comprises a capacitive module 105, which is connected in parallel to the main secondary winding 103. During use, the main secondary winding 103 picks up power inductively from the cable 102.

The value of the capacitive module 105 is chosen, such that it compensates the typical inductance of the main secondary winding 103 for the frequency of the alternating supply current, such as 20 kHz.

The transfer pick-up circuit 101 also comprises a four quadrant power converter, in this embodiment formed by a H-bridge topology 106 and connected in series to the main secondary winding 103. The H-bridge topology 106 is configured for receiving the picked up power from the main secondary winding 103, which is an alternating current (AC), and for converting the picked up alternating current to a direct current (DC). From the H-bridge topology 106, the direct current can be supplied to a load 110, such as a switchable light bulb that can be switched on or off at demand. During use, the H-bridge topology is working at a switching frequency, which is at a least a factor 10 higher than the frequency of the alternating supply current. For example, the switching frequency is 500 kHz, while the frequency of the alternating supply current is 20 kHz.

As shown in figure 2, the H-bridge topology 106 comprises a switching coil 111 which together with the capacitive module 105 forms a low-pass filter, allowing frequency components corresponding substantially to the frequency of the alternating supply current to pass, while damping higher switching frequency components. The H-bridge topology 106 further comprises four switching elements Ql, Q2, Q3 and Q4 configured to be switched in order to set the desired voltage. As shown in figure 2, the H-bridge topology 106 is provided with a H-bridge driver 112, schematically indicated by two blocks, for driving the four switching elements Ql, Q2, Q3 and Q4 on basis of a PWM (pulse width modulation) duty cycle signal, and a overvoltage protection 113 for protecting the H-bridge driver 112 against overvoltage.

As indicated in figure 2, the transfer pick-up circuit 101 comprises a controller 109, in particular a digital signal processor (DSP). The controller 109 is configured for generating the PWM duty cycle signal and for providing the generated PWM duty cycle signal to the H- bridge topology 106, as is elucidated in detail below.

The transfer pick-up circuit 101 also comprises a current clamp sensor 108 for sensing the current of the alternating supply current. The current clamp sensor 108 comprises a sensing secondary winding 120 of a sensing transformer, wherein the first sensing winding 121 is schematically indicated in the cable 102. A sensing capacitive module 122 and a sensing resistance 123 are connected in parallel to the sensing secondary winding 120. Furthermore, a node primary current sense circuit 124 is connected in in series to the sensing secondary winding 120. The node primary current sense circuit 124 comprises a node current sense comparator 125 having a positive input and a negative input, as indicated in figure 2. The node current sense comparator 125 can be configured for amplifying the difference between the positive input and the negative input, and providing as a cable current sensing output signal 126 the amplified difference to the controller 109.

As indicated in figure 2, the main secondary winding 103 and the sensing secondary winding 120 can be provided in a single inductive clamp 127, such that the main secondary winding 103 and the sensing secondary winding 120 can be clamped to the cable 102 at once.

The transfer pick-up circuit 101 further comprises a node voltage sense circuit 130 connected in parallel to the main secondary winding 103. The node voltage sense circuit 130 has a voltage sense comparator 132 having a positive input and a negative input. The voltage sense comparator 131 can be configured for amplifying the difference between the positive input and the negative input, and providing as a node voltage sensing output signal 132 the amplified difference to the controller 109.

Additionally, the transfer pick-up circuit 101 further comprises a H-bridge current sense circuit 135 connected in series to the main secondary winding 103 via a further sensing resistance 138. The H-bridge voltage sense circuit 135 has a H-bridge current sense comparator

136 having a positive input and a negative input. The H- bridge current sense comparator 136 may be configured for amplifying the difference between the positive input and the negative input, and providing as a H-bridge current sensing output signal 137 the amplified difference to the controller 109.

As shown in figure 2, the controller 109 also receives the application voltage V _app , being the voltage over the load 110, as signal 140.

A DSP (digital signal processor) code block diagram of the controller 109 is shown in figure 3. The controller 109 receives as inputs the cable current sensing output signal 126, the voltage sensing output signal 132 and the application voltage V _app signal 140. In the shown block diagram, the H-bridge current sensing output signal

137 is not received by the controller 109.

As shown in figure 3, the application voltage V _app signal 140 is received by a first ADC (AD-convertor) 150 for converting the application voltage V _app signal 140. While converting the application voltage V _app signal 140, the application voltage V _app signal 140 is sampled at a first sampling frequency which is lower than the switching frequency of the H-bridge topology 106. For example, the first sampling frequency is around 50 kHz. Subsequently, the sampled application voltage V _app signal 140 is sent to an application voltage controller 151 and to a divider 152 resulting in a DTC (duty cycle) signal indicating the mean voltage to be generated by the H-bridge topology 106 expressed in V _app (VHB_in_V _app ), which is the output between the source of switching element Q1 and the source of switching element Q2. The application voltage controller 151, in short, regulates the resistance of the node on the cable 102 to a value that achieves the desired application voltage.

The application voltage controller 151, also known as a PI (Proportional Integral) controller, has a second input an application voltage setpoint 152, for example of 25V. The sampled application voltage V _app signal and the application voltage setpoint 152 are fed to a first substractor 153, which subtracts the application voltage setpoint from the sampled application voltage V _app signal, resulting in an application voltage difference signal. The application voltage difference signal is split and fed to a first amplifier 154 and a second amplifier 155. The first amplifier 154 amplifies the application voltage difference signal with a first gain parameter Kp _x , and the second amplifier 155 amplifies the application voltage difference signal with a second gain parameter Ki _x . The first and second gain parameters Kp _x and Ki _x are tuned to provide a desired step response. The output of the first amplifier 154, subsequently, is sent to a first adder 158.

The output of the second amplifier 155 is input to a second adder 156 having a second adder output. The second adder output is sent to a first unit delay 157 for holding and delaying the second adder output, in this case by 1 iteration. The first unit delay output downstream of the first unit delay 157 is fed to the first adder 158 and to the second adder 156 as a further input thereof. The second adder 156 and the first unit delay 157 form an integrator. The output of the first adder 158 and therewith of the application voltage controller 151 indicates the resistance formed by the transfer pick-up circuit 1 or the node on the cable 2. The indicated resistance is fed to a first multiplier 159.

The node current sensing output signal 126 is received by a second ADC (AD-convertor) 160 for converting the cable current sensing output signal 126. While converting the cable current sensing output signal 126, the cable current sensing output signal 126 is sampled at a second sampling frequency which is equal or substantially equal to the switching frequency of the H- bridge topology 106. For example, the second sampling frequency is around 500 kHz. Subsequently, the sampled cable current sensing output signal is sent to a power analyzer 161, to a second unit delay 162 and a third unit delay 163.

The second unit delay 162 inverts and delays the sampled cable current sensing output signal with approximately one quarter of the cable current frequency and transmits the delayed sampled cable current sensing output signal to a second multiplier 164. Correspondingly, the third unit delay 163 delays the sampled cable current sensing output signal with one period of the cable current frequency, and transmits the delayed sampled cable current sensing output signal to the first multiplier 159, wherein the delayed sampled cable current sensing output signal is multiplied with the determined cable resistance. The output of the first multiplier 159 is transmitted to a final adder 165.

The voltage sensing output signal 132 is received by a third ADC (AD-convertor) 166 for converting the voltage sensing output signal 132. While converting the voltage sensing output signal 132, the voltage sensing output signal 132 is sampled at the second sampling frequency. Subsequently, the sampled voltage sensing output signal is sent to the power analyzer 161. The power analyzer 161 is configured for measuring active power P by integrating the product of the sampled node voltage sensing output signal and the sampled cable current sensing output signal, and for measuring the reactive power Q by integrating the product of the sampled node voltage sensing output signal and a 90 degrees shifted sampled cable current sensing output signal. The measured active power P is transmitted from the power analyzer 161 to a setpoint generator 167, and the measured reactive power Q is transmitted from the power analyzer 161 to a reactive power controller 168.

The setpoint generator 167 is configured for generating a reactive power setpoint, which reactive power setpoint is a function of the measured active power P. The generated reactive power setpoint is transmitted to the reactive power controller 168.

The reactive power controller 168, also known as a PI (Proportional Integral) controller, corresponds to the application voltage controller 151. In short, the reactive power controller 168 controls the reactance of the node on the cable 102 to a value that achieves optimum node reactive power. As input, the reactive power controller 168 receives as input the measured reactive power Q and the generated reactive power setpoint, which are received by a second substractor 153, which subtracts the generated reactive power setpoint from the measured reactive power Q, resulting in an reactive power difference signal. The reactive power difference signal is split and fed to a third amplifier 170 and a fourth amplifier 171. The third amplifier 170 also amplifies the reactive power difference signal with the first gain parameter Kp _x , and the fourth amplifier 171 also amplifies the reactive power difference signal with the second gain parameter Ki _x . The first and second gain parameters Kp _x and Ki _x are tuned to provide a desired step response. The output of the third amplifier 170, subsequently, is sent to a third adder 172. The output of the fourth amplifier 171 is sent to a fourth adder 173 having a fourth adder output. The fourth adder output is sent to a fourth unit delay 174 for holding and delaying the fourth adder output, in this case by 1 iteration. The fourth unit delay output downstream of the fourth unit delay 174 is fed to the third adder 172 and to the fourth adder 173 as a further input thereof. The fourth adder and the fourth unit delay 174 form an integrator. The output of the third adder 172 and therewith of the reactive power controller 168 is a compensation value for compensating for production tolerances of transfer pick-up circuit 1 or the node. The determined compensation value is transmitted to the second multiplier 164, where the determined compensation value is multiplied with the sampled cable current sensing signal.

The output of the first multiplier 159 is a first sine wave U _R , also known as the active node voltage component, which is in phase with the cable current, and the output of the second multiplier 164 is a second sine wave Ux, also known as the reactive voltage component, running 90 degrees ahead of the cable current. The first and second sine wave U _R and U _x are transmitted to the final adder 165 where the first and second sine wave U _R and U _x are summed up, resulting in a sum signal U _out representing the desired mean voltage to be generated by the H-bridge topology 106 in Volts (VHB_in_V). The sum signal U _out is transmitted to the divider 152, where the sum signal U _out is divided by the application voltage V _app , resulting in a DTC signal having a value between -1 and 1. The DTC signal is transmitted to a PWM (pulse width modulation) generator 175, wherein the PWM generator 175 generates PWM switching signals on basis of the received DTC signal. For example, the DTC signal having a value of 1 tells the PWM generator 175 that the H-bridge topology 106 should produce an average voltage equal to the application voltage V _app , and a value of -1 tells the PWM generator 175 that the H-bridge topology 106 should produce an average voltage equal to the negative application voltage -V _app . -The PWM generator 175 may use different modulation schemes to generate any average voltage between V _app and -V _app , such as an unipolar modulation scheme. The PWM generator 175 generator generates a PWM schedule on basis of the DTC signal, which PWM schedule is transmitted to the H-bridge driver 112. The H-bridge driver 112 drives the H-bridge topology on basis of the received PWM schedule, therewith controlling the voltage and thus the impedance, or at least the reactive part thereof, of the node. By controlling the voltage of the node, the power transfer of power from the base station through the cable 102 to the transfer pick-up circuit 101 can be optimized.

It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the scope of the present invention.