Abstract: A control device for a power factor correction device in forced switching power supplies is disclosed; the device for correcting the power factor comprises a converter and said control device is coupled with the converter to obtain from an input alternating line voltage a regulated output voltage. The converter comprises a power transistor and the control device comprises a driving circuit of said power transistor; the driving circuit comprises a timer suitable for setting the switch-off period of said power transistor. The timer is coupled with the alternating line voltage in input to the converter and is suitable for determining the switch-off period of the power transistor in function of the value of the alternating line voltage in input to the converter.

Abstract: The present invention relates to a power factor correction circuit for compensating distortion of an input current. According to the exemplary embodiment of the present invention, a turn-on interval length of a switch is controlled according to a voltage induced in a secondary winding wire of an inductor since the voltage induced in the secondary winding wire has information on an input voltage when the switch is turned on. The turn-on interval length of the switch is reduced when the input voltage is great and is increased when the input voltage is low. Therefore, distortion of the input current may be compensated by controlling the turn-on interval of the switch according to the voltage induced in the secondary winding wire without using an additional circuit for sensing the input voltage.

Abstract: A SVC control section detects a bus voltage from an instrument transformer, and adjusts reactive power generated by a SVC according to the detected bus voltage. A cooperative control section generates a control command for controlling the interconnection and parallel-off of a phase lead capacitor and a phase lag reactor on the basis of the amount of reactive power generated by the SVC and the bus voltage detected by the instrument transformer and a voltage sensor. A voltage comparator compares the bus voltage with a predetermined threshold voltage set to a voltage lower than a lower limit value of a steady state fluctuation range of the bus voltage and outputs the comparison result to a circuit breaker control section. When the bus voltage is lower than the threshold voltage, the circuit breaker control section locks the control command from the cooperative control section.

Abstract: A USB control system includes a first voltage controller, a control switch, a second voltage controller, and a PHY unit. The first voltage controller outputs a first internal voltage from an external voltage and a reference voltage, and the control switch regulates supplying and suspending the external voltage. The second voltage controller outputs a second internal voltage from the reference voltage and the external voltage applied through the control switch, and the PHY unit receives a request from a host using the first or second internal voltage as a voltage source. The power for certain internal blocks is suspended to reduce power consumption in the USB control system during a power-saving mode.

Abstract: A device, a system, and a method for preventing power-producing wind turbine generators from tripping due to the detection of a low-voltage condition on a power grid are disclosed. The disclosed device includes a resistor bank that absorbs real power and a control system that maintains the collector bus voltage above a threshold voltage level during the duration of low-voltage condition on the power grid. Collector bus voltage is maintained using gating signals that include phase delay angles to adjust the opening/closing of the switching devices.

Abstract: A reactive power compensation system includes a distributed energy resource situated at a local location configured to also receive power from a remote location by a distribution feeder line. The distributed energy resource includes an inverter including power semiconductor switching devices and an inverter controller configured for controlling the power semiconductor switching devices so as to provide reactive power support to the distribution feeder line.

Abstract: A power management device for enabling multiply power sources to supply power to a load. The power management device includes a plurality of switches and a control logic. The plurality of switches are coupled to a plurality of power sources respectively and each switch coupled to each power source. The control logic is capable of selecting a set of switches among the plurality of switches to cooperate in a time-divided fashion to allow the power sources to provide power to the load. The set of switches is selected based on an electrical requirement of the load and an electrical condition of each switch.

Abstract: This invention relates to a method of determining stability of unstable equilibrium point (UEP) computed by using BCU method, comprising selecting UEP computed by using BCU method, obtaining a test vector Xtest for the selected UEP, say XUEP using the following equation: Xtest=Xspost+0.99(XUEP?Xspost) where Xspost is the SEP, and checking boundary condition of XUEP by simulating system trajectory of post-fault original system starting from Xtest.

Abstract: An inductor for the excitation of polyharmonic rotating magnetic fields (RMF) for controlling the crystalline structure of continuous ingots and castings in metallurgy and other foundry applications. The inductor design makes it possible to use standard sources of sinusoidal currents for generating polyharmonic RMF, and significantly increase cos ? of the inductor.

Abstract: A power factor correction method and the controller thereof, applied to a boost-type converter, are provided. First, the power factor correction method uses the input and output voltages to generate a reference switching signal. Next, a voltage control circuit uses the difference between the output voltage and a voltage command to get a duty phase. Then, the switching control signal is determined by shifting the phase of the reference switching signal according to the duty phase. Finally, a comparator compares the switching control signal with a triangle waveform signal to determine the switching signal. A power factor controller, which utilizes this method, uses only a single voltage control circuit to get the switching signal to regulate the output voltage and shape the current waveform without sensing current and a current control circuit, so that the complexity of the invented control circuit for the power factor correction is reduced dramatically.

Abstract: An apparatus for rapidly tracking fundamental frequency information in the signal of an electric grid is a cross-coupled phase-lock loop filter (CCPLL) that includes the use of a phase-lock-loop (PLL) apparatus having a plurality individual filters, wherein an input for a first filter in the plurality of individual filters comprises the signal of the electric grid and an output signal from at least a second filter in the plurality of individual filters. A method for using the CCPLL includes applying a signal to the CCPLL and monitoring the output of the CCPLL. Use of the CCPLL may be accomplished or modeled via computer instructions stored on machine readable media.

Abstract: A power supply system capable of supplying power from a power transmitter to a power receiver in an electrically non-contact manner, in which a power transmission module is attached to the power transmitter and a power reception module is attached to the power receiver. The power transmission module has a plurality of transmission-side coils for transmitting power and a plurality of transmission-side switches for turning on/off operation of the transmission-side coils. The power reception module has a plurality of reception-side coils for receiving power, a plurality of reception-side switches for turning on/off operation of the reception-side coils and, further, has a determination circuit for performing control so as to operate any of the transmission-side coils and any of the reception-side coils in a combination realizing highest power transmission efficiency.

Abstract: A power factor correction (PFC) controller and method uses a finite state machine to adjust the duty cycle of a pulse width modulation (PWM) switching control signal. The PFC controller has a target current generator that receives the link output voltage and generates a target current proportionate to the rectified line input voltage. The PFC controller further includes a comparator which outputs a two-level current comparison result signal. The finite state machine responsive to the two-level current comparison result signal, generates a switch control signal that has a duty cycle which is adjusted for controlling the switch so that the sensed current is approximately proportionate to the rectified line input voltage, such that power factor correction is performed.

Abstract: A power control system includes a switching power converter and a power factor correction (PFC) and output voltage controller. The switching power converter utilizes a nonlinear energy transfer process to provide power to a load. The PFC and output voltage controller generates a control signal to control power factor correction and voltage regulation of the switching power converter. The PFC and output voltage controller includes a nonlinear delta-sigma modulator that models the nonlinear energy transfer process of the switching power converter. The nonlinear delta-sigma modulator generates an output signal used to determine the control signal. By using the nonlinear delta-sigma modulator in a control signal generation process, the PFC and output voltage controller generates a spectrally noise shaped control signal. In at least one embodiment, noise shaping of the control signal improves power factor correction and output voltage regulation relative to conventional systems.

Abstract: A power control system includes a switching power converter and a power factor correction (PFC) and output voltage controller. The PFC and output voltage controller provides a control signal to a switch to control power factor correction and regulate output voltage of the switching power converter. During a single period of the control signal, the PFC and output voltage controller determines the line input voltage, the output voltage, or both using a single feedback signal received from the switching power converter. The feedback signal is received from a switch node located between an inductor and the switch. The PFC and output voltage controller determines either the line input voltage or the output voltage, whichever was not determined from the feedback signal, using a second feedback signal received from either a PFC stage or a driver stage of the switching power converter.

Abstract: A power control system includes a switching power converter and a programmable power factor correction (PFC) and output voltage controller. The programmable PFC and output voltage controller generates a control signal to control power factor correction and voltage regulation of the switching power converter. In at least one embodiment, the control signal is a pulse width modulated signal. The programmability of the PFC and output voltage controller provides the programmable PFC and output voltage controller flexibility to operate in accordance with programmable parameters, to adapt to various operating environments, and to respond to various operating exigencies. In at least one embodiment, the programmable PFC and output voltage controller includes a state machine to process one or more programmable, operational parameters to determine the period and pulse width states of the control signal.

Abstract: A power control system includes a feedback loop having a power factor correction (PFC) and output voltage controller and a switching power converter. The switching power converter includes an inductor to supply charge to an output capacitor and a switch to control inductor current ramp-up times. The PFC and output voltage controller provides a control signal to the switch to control PFC and regulate output voltage of the switching power converter. During a single period of the control signal, the PFC and output voltage controller obtains the line input voltage and output voltage of the switching power converter using a single feedback signal received from the switching power converter.

Abstract: Provided are a method and apparatus for improving the power factor of an input power. The apparatus includes an input unit receiving the input power, a power factor correction unit correcting the power factor of the input power applied to the input unit, and a saturation prevention unit controlling the power factor correction unit such that the corrected power does not exceed a set power limit.

Abstract: Disclosed is an actuating circuit and method for actuating a switch regulating the power consumption in a power factor correction circuit having input terminals for applying an input voltage and output terminals for providing an output voltage. The switch is cyclically turned on for an on-time and turned off for an off-time, the on-time having a first on-time period and a second on-time period directly adjacent to the first on-time period. A length for the first on-time period is dependent on the control signal, and a length for the second on-time period is proportional, at least for a prescribed range of values for an instantaneous value of the input voltage, to a quotient with a first first-degree function for the instantaneous value in the denominator and a second first-degree function for the instantaneous value in the numerator, with function values for the first function increasing as the instantaneous value rises.

Abstract: A power factor correction circuit (PFC) including a switch, a feedback signal generator for generating a feedback voltage corresponding to an output voltage, and a switching controller for receiving the feedback voltage and for controlling turn-on/turn-off of the switch. The feedback signal generator includes first and second resistors serially connected to first and second ends of an PFC output terminal; a first capacitor connected between a first node of the first and second resistors and the first end of the PFC output terminal; and a comparator for comparing a voltage of the first node and a reference voltage, and for generating a feedback voltage.

Abstract: In a power supply, a plasma display including the power supply, and a method of driving the plasma display, a DC voltage output by a power factor correction unit is converted into a voltage Vs supplied to a sustain or scan electrode during a sustain period, and the voltage Vs is converted into a voltage Va supplied to an address electrode during an address period. The voltage Vs is a less than the DC voltage of the power factor correction unit, and components with a low voltage rating can be used for the Va voltage generator.

Abstract: In a PFC (Power Factor Correction) converter control unit, a PWM (pulse width modulated) signal is produced by comparing a PFC converter output voltage error signal, produced by a transconductance amplifier, with a ramp signal, which may be from a control unit of a resonant mode converter in cascade with the PFC converter. Level shifting is used to match the amplitude ranges of the compared signals. A current, representing an input current of the PFC converter and produced by a current mirror, is switched by the PWM signal to a parallel resistance and capacitance to produce a smoothed voltage constituting a control signal for the PFC converter.

Abstract: A method and an apparatus for reducing energization transients in a three phase AC power system which includes an electrical device having legs A, B and C associated with corresponding phases of the power system. The method includes the steps of connecting the legs of the device with the power system in an order determined by an energization sequence, wherein the energization sequence is either ABC or ACB. The apparatus includes a three phase electrical device having legs A, B, and C associated with corresponding phases of a three phase AC power system and switches operable to connect the legs of the device with the power system, wherein the switches are configured to be actuated in an order determined by an energization sequence, and wherein the energization sequence is either ABC or ACB. The switches may be controlled by a switch controller.

Abstract: Bidirectional power conversion systems provide the ability to change power attributes to and from a component. Current bidirectional power conversion systems use a unidirectional power converter for each direction. The integration of the two normally independent power converters results in a bidirectional power converter with nearly half the size, weight, volume, cost and complexity. Described are embodiments of bidirectional power conversion systems that allow power transfer between two or more components without requiring the use of separate unidirectional power converters.

Abstract: A power factor correction apparatus is for correcting a power factor of transmission lines. The power factor correction apparatus includes a switch, a compensator, a detecting apparatus, a voltage processing circuit, a voltage comparison unit, and a time-delay unit. The switch is electrically connected to the transmission lines. The compensator is electrically connected to the switch for compensating the power factor. The detecting apparatus is electrically connected to the transmission lines for detecting voltages transmitted in the transmission lines. The voltage processing circuit electrically is connected to the detecting apparatus and the switch. The voltage processing circuit includes a voltage comparison unit and a time-delay unit. The voltage comparison unit is electrically connected to the detecting apparatus for comparing the voltages with each other to generate a voltage. The time-delay unit is electrically connected to the voltage comparison unit and the switch delaying the voltage.

Abstract: A system for controlling a microgrid includes microgrid assets and a tieline for coupling the microgrid to a bulk grid; and a tieline controller coupled to the tieline. At least one of the microgrid assets comprises a different type of asset than another one of the microgrid assets. The tieline controller is configured for providing tieline control signals to adjust active and reactive power in respective microgrid assets in response to commands from the bulk grid operating entity, microgrid system conditions, bulk grid conditions, or combinations thereof.

Abstract: A switching operation is performed on a switching element of a power-factor improving unit that includes a reactor. An output voltage of the power-factor improving unit is set to a load voltage by switching on and off the switching element based on a result of comparison between an input current and an input-current reference signal of a power-supply voltage waveform. A zero cross of an alternate-current power supply is detected, and the switching operation is performed on the switching element a predetermined number of times based on a detection of the zero cross.

Abstract: A method and apparatus are described for controlling the flow of power in each input line to a three phase AC inductive load in order to reduce the amount of VAR in the system, and thus increase the operational efficiency of the inductive load. Solid state relays are positioned in series in each of the three inductive load line inputs, and current allowed to flow to the inductive load only during the time during which the SSRs are in a conducting state. The calculation of VAR is achieved by processing data from each of the input lines using a separate controller boards each dedicated to each of the lines. The controller in turn, based on the calculated VAR, increments the time, either increasing or decreasing it from a predetermined value, during which the SSRs in that line remains in the non-conducting state.

Abstract: Present invention uses the main power source and auxiliary power source to supply power to a load, makes them take partial charge of power supply, and when the load current reaches its peak, detects a current and a voltage generated by the auxiliary power source, and when the detected values are larger than set values or lower than the set values, controls the output current of the main power source.

Abstract: A system and method is provided for generating DC power using a synchronous reluctance machine (12) or a salient-pole synchronous machine (102) and a power converter (110). The present invention can be used to achieve power production for a synchronous reluctance machine (12), or can be used to achieve partial production of power from a traditional salient-pole synchronous machine/starter (102) in the case where the salient-pole synchronous machine/starter has degenerated into a synchronous reluctance machine due to, for example, a loss of excitation. In a power generation system, a control system and method can include a power converter (110), controlled by a voltage command and at least one of a measured DC link (120) voltage or DC link (120) current, for use with a synchronous reluctance machine armature winding (102A) and a prime mover (116), such that movement of the synchronous reluctance machine rotor of the synchronous reluctance machine can be used to produce at least partial DC power generation.

Abstract: A power converter for a hybrid power filter includes a power electronic switch set and a DC capacitor. The power converter permits a power line of a power system to directly connect or connect through the passive power filter to a positive or a negative terminal of the DC capacitor of the power converter for free control of the power electronic switches. Consequently, the power converter has a structural configuration that reduces the number of power electronic switches, which can reduce manufacturing costs.

Abstract: The power factor improving circuit has a current detecting resistor Rsh for detecting current conducting through a set up reactor L1 or current conducting through a switch Q1, an output voltage detector 11 which amplifies a difference between output voltage Eo and reference voltage Vref to generate error voltage, a variable gain amplifier 15 which amplifies voltage which is proportional to current detected by the current detecting resistor Rsh by varying gain in accordance with a value of the error voltage of the output voltage detector 11, and a pulse width modulator 14 which generates a pulse signal whose pulse width is controlled in accordance with a value of output of the variable gain amplifier 15 and which applies the pulse signal to the switch Q1 to control the output voltage Eo to predetermined voltage.

Abstract: An analysis method for an electrical power system whereby the plurality of buses are grouped into agents, family lines of agents and families of agents based on the reactive reserves depleted when the buses are loaded. Contingencies are then applied to the electrical power system. The reactive reserves are monitored, and an exhaustion factor is determined for one or more family lines in one or more families. A boundary case solution is used to assess where, why, and how the contingency causes voltage instability, voltage collapse and/or local blackout. Based on this information, the design of voltage rescheduling, active rescheduling, unit commitment, load shedding, etc., is determined that can be used as preventive, corrective or emergency controls in applications such as system design and planning, operation planning, reactive and voltage management, real time control and Special Protection System Control. Based on this information, solutions can then be applied to the power system.

Abstract: Equipment for exchanging power, in shunt connection, with an electric power network. A reactive impedance element and a voltage source converter provide mutual connection in series. The power network has a nominal voltage of a fundamental frequency and a given phase position. The converter is intended for generating a fundamental-tone voltage within a control range which limits the amplitude of the fundamental-tone voltage. The control range limits the amplitude of the fundamental-tone voltage to a value that is lower than the nominal voltage of the power network and comprises generation of a reactive component of the fundamental-tone voltage with a phase position that either coincides with the phase position for the voltage of the power network, or that deviates by 180° electrically form the phase position for the voltage of the power network.

Abstract: A digitally controlled hybrid power module is controlled by a programmable controller. The hybrid power module includes a digitally controlled switching supply with an output coupled to an input of a digitally controlled linear voltage regulator. Independent control of switching supply and the linear regulator is provided by the programmable controller, which may be a field programmable gate array (FPGA), microcontroller, or digital signal processor (DSP). The programmable controller may independently control one or more power modules. Each power module may also include enable switching and an associated current clamp for capacitive loads. An output voltage transient suppressor may also be used to control transients, such as those produced under fast switching conditions.

Abstract: A power flow controller responsive to power circulation demand for optimizing power transfer is disclosed. When a power flow controller operates at its rated capacity, it can no longer regulate from-bus voltage set-points, line power flow set-points, or both. In such cases, the power flow controller switches to power circulation set-point control without exceeding the rated capacities of the voltage-sourced converters in the power flow controller. Power-voltage (PV) curves associated with voltage stability analysis for maximizing power transfer can be generated and stored for use with a power flow controller operating in automatic power flow control mode.

Abstract: A power factor correcting converter includes a control circuit that modulates on and off intervals of a power switch so that a momentary input current of the converter is directly proportional to both a momentary value of an input voltage of the converter and to a momentary value of a current absorbed by a load coupled to an output of the converter.

Abstract: The present invention provides an apparatus for controlling power factor compensation and method thereof, in which a turn-on timing point of a power factor compensation switch is delayed by a prescribed time from a zero crossing timing point to enhance a power factor. The present invention includes periodically detecting a zero crossing time point of an inputted voltage, turning on the power factor compensation switch if a turn-on time point of the power factor compensation switch set to a time point delayed by a prescribed time from the detected zero crossing time of the inputted voltage is reached, and turning off the power factor compensation switch if a prescribed time passes after turning on the power factor compensation switch.

Abstract: EMI noise in a system using a power converter with switching control is reduced in a simple configuration. The power converter 3 includes a converter 31, a smoothing capacitor 32, and an inverter 33, and receives the power from an AC power supply 1 via an AC reactor 2 and converts it into a power of an optional frequency and voltage to supply to a motor 4. Damping impedance elements 6, 7, 8 are inserted between the frame of the motor 4 and the ground 5, between the cooling fin 34 of the power converter 3 and the ground 5, and between the AC reactor 2 and the ground 5, respectively. Further, paths between the AC reactor 2 and ground 5, between the power converter 3 and ground 5, and between the motor 4 and ground 5 are insulated except that the damping impedance elements 6, 7, 8 are inserted.

Abstract: A hybrid reactive power compensation device comprises a passive type reactive power compensator and an active type reactive power compensator serially connected thereto. The passive type reactive power compensator is an AC power capacitor adapted to provide the reactive power that reduces capacity of the active type reactive power compensator. The active type reactive power compensator comprises a power converter, a DC capacitor, a high-frequency ripple filter and a controller. The hybrid reactive power compensation device can supply a linearly adjustable reactive power within a predetermined range, and is adapted to supply a current with a nearly sinusoidal waveform. Therefore, it can avoid the destruction of AC power capacitor caused by the power resonance.

Abstract: A power flow controller for controlling the flow of active and reactive power on an AC transmission line between an input and output includes first and second power converters, coupled to each other to exchange active power and coupled to the input and output. A controller is coupled to the power converters and controls the converters to provide a controlled quantity of active power to the output, and draw this controlled quantity of active power from the input of the power flow converter. Electric current is diverted at a node between the input and the output, allowing independent control of currents at the input and output. In a preferred embodiment, the two power converters are interconnected in series. A controllable susceptance is connected in shunt at a node between the converters to divert the current.

Abstract: One embodiment of the present invention is a method to control input to an alternating current (AC) induction motor from a power supply that includes steps of: (a) determining a measure of reactive power (VAR) in two input lines to the motor during a time period; and (b) maintaining an SSR (solid state relay) connected in series between the power supply and the motor in a non-conducting state for a subsequent time period, the length of which subsequent time period is determined by analyzing the measure of VAR.

Abstract: Bidirectional power conversion systems provide the ability to change power attributes to and from a component. Current bidirectional power conversion systems use a unidirectional power converter for each direction. The integration of the two normally independent power converters results in a bidirectional power converter with nearly half the size, weight, volume, cost and complexity. Described are embodiments of bidirectional power conversion systems that allow power transfer between two or more components without requiring the use of separate unidirectional power converters.

Abstract: A hybrid reactive power compensation device comprises a passive type reactive power compensator and an active type reactive power compensator serially connected thereto. The passive type reactive power compensator is an AC power capacitor adapted to provide the reactive power that reduces capacity of the active type reactive power compensator. The active type reactive power compensator is consisted of a power converter, a DC capacitor, a high-frequency ripple filter and a controller. The hybrid reactive power compensation device can supply a linearly adjustable reactive power within a predetermined range, and is adapted to provide with a serial-connected virtual harmonic damping. Therefore, it can avoid the destruction of AC power capacitor caused by the power resonance.

Abstract: The novel circuit arrangement is used for the static generation of a variable electric output, as is common in static reactive-power compensation systems. According to the invention, a voltage is applied to a consumer, i.e. to a capacitor and/or an inductor, and a transformer (T) has at least two power-control windings (W1, W2) in a secondary circuit, said windings being connected electrically in series via bridge circuits (B1, B2). In their branches, the bridge circuits contain static switches (BSS1 . . . 4) in an inverse-parallel connection, said switches can be selectively connected or disconnected.

Abstract: A system and method for using reluctance torque or a combination of both reluctance and reaction torque components of an attached synchronous machine (102) to accelerate a prime mover (116), such as a gas turbine engine, within a desired start time. The system selects a mode of starting operation, and thereafter applies reluctance torque through a synchronous machine (102) armature winding (102A) excitation as a single, sufficient starting force in a first mode, or staged reluctance and reaction torque through the additional excitation of the synchronous machine (102) field winding (102B) excitation in a second mode, using existing power electronics and controls.

Abstract: A variable speed drive control system operates a variable speed drive to power a first load from a power source simultaneously powering a second load. An AC reactive power is monitored which may comprise or consist of an AC reactive power of the second load. Responsive to the monitored AC reactive power, the variable speed drive is controlled to counter the AC reactive power of the second load.

Abstract: A method is specified for operating a transformer (1) from a drivable voltage source (2), in which the voltage source, (2) produces an output voltage (uA) for feeding active power and/or a reactive component via the transformer (1) into an electrical AC voltage supply network (3), and an output current (iA) from the voltage source (2) is monitored for a maximum permissible value (iAmax) in which the magnetic flux (&phgr;) of the transformer (1) is determined continuously, and, when the maximum permissible value (iAmax) of the output current (iA) is exceeded, the voltage source (2) is disconnected from the transformer (1).

Abstract: An oscillator for use in a preconditioner includes a rectifier, a converter receiving an input voltage and supplying an output voltage, and a control unit effecting peak current mode control. The oscillator has a switching frequency with a period dependent on the input voltage and the output voltage.

Abstract: A device (2) for control of a power flow in a three-phase ac transmission line (L2, La, Lb, Lc) has, for each of its phases (a, b, c), a transformer (12a, 12b, 12c) with a primary winding (121c) and a secondary winding (122c). The secondary winding is serially connected into the respective phase of the transmission line. A voltage dependent on a controllable part of the voltage between the other two phases of the transmission line is applied to the primary winding of the transformer. The device comprises, for each of the phases of the transmission line, a series circuit with a first (T1a, T1b, T1c) and a second (T2a, T2b, T2c) terminal and a connection point (Ja, Jb, Jc). The series circuit comprises a first reactive impedance element (21a, 21b, 21c) with a fixed reactance connected between the first terminal and the connection point, and a second reactive impedance element (22a, 22b, 22c, 23a, 23b, 23c) with a variable reactance connected between the connection point and the second terminal.