Abstract: One or more solar cells are connected to a flex circuit, wherein: the flex circuit is single sheet; the flex circuit is comprised of a flexible substrate having one or more conducting layers for making electrical connections to the solar cells; and the flex circuit includes one or more flat sections where the solar cells are attached to the flex circuit that remain flat when the flex circuit is folded and one or more folding sections between the flat sections where the flex circuit is folded.

Abstract: This charging control device 50 controls charging of electricity storage elements B1-B4 and is provided with: a plurality of charging paths 61A, 61B leading to the electricity storage elements and connected in parallel with each other; voltage drop elements 64A, 64B and switches 65A, 65B which are connected in series on the charging paths; and a control unit 100. The control unit 100 controls the switches 65A, 65B and thereby switches a charging path not to be energized among the plurality of charging paths 61A, 61B during charging.

Abstract: A method, circuit and system arrangement is described for providing rapid de-energization for safety reasons of conductors having a DC power source at both ends. The invention is particularly envisaged for use in solar energy systems in which a battery is charged by solar power from a photovoltaic array, the invention comprising controlling the array to interrupt charge current flow and then isolating the battery from the conductors to be de-energized in a fail-safe manner.

Abstract: A system and method for combining power from DC power sources. Each power source is coupled to a converter. Each converter converts input power to output power by monitoring and maintaining the input power at a maximum power point. Substantially all input power is converted to the output power, and the controlling is performed by allowing output voltage of the converter to vary. The converters are coupled in series. An inverter is connected in parallel with the series connection of the converters and inverts a DC input to the inverter from the converters into an AC output. The inverter maintains the voltage at the inverter input at a desirable voltage by varying the amount of the series current drawn from the converters. The series current and the output power of the converters, determine the output voltage at each converter.

Abstract: Reconfiguration of a rechargeable energy storage system into two or more new capacitor or battery or fuel cell packs arranged in “connections”, e.g. series or parallel strings. Each pack of rechargeable energy storage devices includes rechargeable energy storage modules. In each rechargeable energy storage module, which can include one or more capacitors or fuel cells or battery cells, there is arranged a network of banks of switches. A first bank of switches is arranged to connect a rechargeable energy storage module in a first series connection string with other rechargeable energy storage modules. A second bank of switches is arranged to connect a rechargeable energy storage module in a second connection string with other rechargeable energy storage modules. A first bypass switch is arranged to exclude a rechargeable energy storage module from the first series connection string when the first bypass switch is activated.

Abstract: In one embodiment, a photovoltaic (PV) power generation system includes a plurality of PV arrays coupled to an automatic switchbox that connects the one or more PV arrays in series or in parallel with each other based at least in part on output voltage of the switchbox. In this embodiment, the automatic switchbox monitors the output voltage and ensures that the output voltage is within a predetermined operational range. If the output voltage exceeds a first predetermined voltage, then the array switchbox electrically couples one or more PV arrays in parallel with each other, which reduces the output voltage within the predetermined operational range. If the output voltage falls below a second predetermined voltage, the switchbox connects one or more PV arrays in series with each other, which increases the output voltage to within the predetermined range.

Abstract: A distribution transformer power flow controller apparatus includes at least one external source terminal configured to be coupled to a distribution transformer, at least one external load terminal configured to be coupled to a load, and a converter circuit configured to be coupled between the at least one external source terminal and the at least one external load terminal to provide series connection of the converter circuit with the load and to control a power transfer of the distribution transformer. The converter circuit may be configured to control a reactive power transfer of the distribution transformer. The converter circuit may also be configured to control a reactive power transfer and a real power transfer. In some embodiments, the converter circuit may be configured to be coupled to at least one energy storage capacitor, at least one battery and/or at least one power generation device.

Abstract: A photosensitive detection module is provided, comprising a photosensitive circuit, wherein the photosensitive circuit comprises a first resistive element, a second resistive element, a third resistive element, a fourth resistive element to form a resistor bridge, a first input terminal connected to a node between the first resistive element and the third resistive element, a second input terminal connected to a node between the second resistive element and the fourth resistive element, a first output terminal connected to a node between the first resistive element and the second resistive element, and a second output terminal connected to a node between the third resistive element and the fourth resistive element. All four resistive elements have an identical initial resistance value. The first resistive element and the fourth resistive element are photosensitive resistive elements.

Abstract: An apparatus includes a shelf having a front edge, a solar cell circuit disposed at the front edge, a display screen, and a controller operatively coupled to the solar cell circuit and the display screen. The controller monitors the period of a waveform of a charging voltage of a storage capacitor of the solar cell circuit, displays an image on the display screen in response to a change in the waveform timing. A system includes a plurality of shelves each having a front edge, a solar cell circuit disposed at the front edge of each of the plurality of shelves, and a controller operatively coupled to the solar cell circuits. The controller monitors the frequency at which a power transfer of each solar cell circuit occurs, and signals a device in response to a change in the frequency at which the power transfer occurs.

Abstract: A common mode reference circuit comprises a divider stage and an output stage. The divider stage includes a first n-channel field effect transistor and p-channel filed effect transistor (NFET/PFET) pair connected in series to a high supply voltage circuit node; and a second NFET/PFET pair connected in series to a low supply voltage circuit node. The output stage includes a first FET connected as a current mirror to a transistor of the first NFET/PFET pair; a second FET connected as a current mirror to a transistor of the second NFET/PFET pair; and a common mode reference output at a series connection from the first FET to the second FET.

Abstract: A controller (10) of an electronic book reader selects, as a power source for operating the electronic book reader, a capacitor (6) configured to accumulate power from a solar cell (5) upon performing a page turning operation, and a storage cell (7) upon performing an operation of downloading an electronic book.

Abstract: A solar drive system, having: at least one photovoltaic array generating a DC current; at least one inverter electrically connected to the photovoltaic array for inverting the DC current into an AC current; at least one electric motor electrically connected to the inverter for supplying the electric motor with the AC current; and at least one device for determining a present rotational frequency of the electric motor; wherein the inverter is configured to track a maximum power point of the photovoltaic array by performing a Perturb and Observe Maximum Power Point Tracking method and to determine a step direction of the Perturb and Observe Maximum Power Point Tracking method using the determined present rotational frequency of the electric motor.

Abstract: An electric power converter includes a plurality of branches of switch units. A first stage, a second stage and a third stage of the converter are connected in series. The first stage includes first positive and negative branches, which are connected between a first output node and two first input nodes. The second stage includes three input nodes and positive and negative cells, each connected between a first input node and two second input nodes. The third stage includes third positive intermediate and negative branches, connected between the three second input nodes and three third input nodes. Capacitors are connected between the three second input nodes and between the three third input nodes.

Abstract: A description is given of an apparatus for disconnecting an electrical connection between solar modules of a photovoltaic string, the apparatus including a first and a second terminal for a respectively assigned solar module of the photovoltaic string, also a circuit breaker, a band-stop filter and a supply circuit for supplying energy to the apparatus, which are arranged in a series circuit with respect to one another between the first and second terminals. A bandpass filter for coupling out a high-frequency control signal from the electrical connection bridges the circuit breaker and the band-stop filter in parallel. In this case, a reverse current diode that is oppositely polarized relative to an operating current flow direction is connected in parallel with the circuit breaker or the partial series circuit comprising the circuit breaker and the band-stop filter.

Abstract: A solar power generation system includes an inverter configured to convert DC power inputted from a solar battery to AC power, a MPPT control section configured to perform maximum power point tracking control on the inverter, an input power measurement section configured to measure the DC power inputted to the inverter at a time of avoiding a transient state due to variation in DC voltage of the inverter by the maximum power point tracking control, an output power measurement section configured to measure the AC power outputted from the inverter at the time of avoiding the transient state, and a conversion efficiency computation section configured to compute conversion efficiency of the inverter based on the DC power measured by the input power measurement section and the AC power measured by the output power measurement section.

Abstract: A regulator control circuit includes a regulator configured to provide an output voltage by regulation using one of an input voltage and a dropped input voltage, to a load; and a heat dissipation circuit configured to sense a change in the input voltage, and provide the dropped input voltage to the regulator when the input voltage is sensed to be equal to or higher than a preset level.

Abstract: A power storage apparatus including a battery and a control circuit controlling charging/discharging of the battery, wherein the control circuit determines, when a predetermined time period that has elapsed after the charging/discharging of the battery was ended is shorter than a polarization elimination time period extending from a time at which the charging/discharging of the battery was ended to a time at which polarization of the battery was judged to have been eliminated, an estimated open-circuit voltage for the battery after the elimination of the polarization of the battery; determines the difference between a first estimated charge state and a charge state determined by a time at which the estimated open-circuit voltage was estimated; and determines a second estimated charge state by summing the state of charge determined by the time at which the estimated open-circuit voltage was estimated and the product of the difference and the reflection coefficient.

Abstract: The present disclosure introduces a charger for inductively charging a mobile device inside a motor vehicle. The charger includes a power source configured to supply electrical energy in the form of DC voltage, a transmitter coil for inductively transferring power to the mobile device, a signal generator configured to generate a sinusoidal signal, and an output stage that is coupled to the power source, the transmitter coil and the signal generator. The output stage is configured to receive the sinusoidal signal as a control signal and to supply to the transmitter coil a current flow, corresponding to the control signal, of the energy provided by the power source.

Abstract: A data collection device for photovoltaic power generation is provided. The data collection device according to an embodiment includes a receiver that receives data on an amount of photovoltaic power generation, a storage unit that stores a representative pattern of a graph for monitoring the amount of photovoltaic power generation, a control unit that extracts a graph for a first piece of data on the amount of photovoltaic power generation received by the receiver and compares the extracted graph with the representative pattern stored in the storage unit to extract a pattern comparison value, and a transmitter that transmits the first piece of data compared by the system control unit to an external device.

Abstract: A solar panel assembly includes a solar panel and a module releasably coupled to the solar panel. The solar panel includes a front surface, a rear surface, and a plurality of solar cells provided along the front surface. The plurality of solar cells are configured to absorb light energy from a light source to generate electrical power. The module includes a support that is selectively repositionable between a first orientation and a second orientation and a load device attached to the support and electrically coupled to the plurality of solar cells such that the module stores electrical energy produced by the plurality of solar cells.

Abstract: A switching device for stabilizing an electric output of a solar panel is provided, and includes a voltage converter circuit, a switch circuit connected between the solar panel and the voltage converter circuit, and a control unit. The voltage converter circuit converts input voltage and current received from the solar panel through the switch circuit into output voltage and current. The control unit calculates an input electric power and an output electric power based on values of the input voltage and current and values of the output voltage and current, and controls the switch circuit to switch between a closed state and an open state according to the input electric power and the output electric power.

Abstract: A PV module is described with an array of PV cells whereby the module is reconfigurable, allowing different configurations to be applied after installation and during operation, i.e. at run-time. The run time configuration of the module has controllable devices. The main controllable devices are any of (individually or in combination): a) switches which determine the parallel/series connections of the cells as well as hybrid cases also. b) switches between the cells and local dc/dc converters and/or among the DC/DC converters; c) actively controlled bypass diodes placed in order to allow excess current to flow in the occurrence of a mismatch.

Abstract: Disclosed is a charging state indicating circuit, including a indicating circuit, having: a first operational amplifier, having a non-inverting input end inputted with a first sampled voltage and an inverting input end inputted with a first reference voltage; a first triode, having a base coupled to an output end of the first operational amplifier through a first resistor, an emitter coupled to a second reference voltage through a second resistor and a collector coupled to an anode of a first light emitting diode; a second triode, having a base coupled to the output end of the first operational amplifier through a third resistor, an emitter coupled to an anode of a second light emitting diode and a collector coupled to the second reference voltage; a cathode of the first light emitting diode and a cathode of the second light emitting diode are grounded and light colors are different.

Abstract: Provided herein are improved apparatuses and methods for protecting polarity sensitive loads in DC power circuits that include a power source, a relay coupled to the power source, and a polarity sensitive load coupled to the relay. A diode can be coupled between the power source and the relay. When the power source provides a DC voltage of a desired polarity, the diode can block a current from flowing to a coil of the relay. Consequently, the relay can provide a current path to the polarity sensitive load. When the power source provides a DC voltage of an incorrect or reverse polarity, the diode can allow a current to flow to the coil of the relay. In turn, the coil of the relay can be energized, causing the relay to disrupt the current path provided to the load, thereby protecting the polarity sensitive load from the reverse polarity condition.

Abstract: A power distribution system configured to supply electric power from a power supply to at least one load, includes at least two solid state power controllers connected in parallel, each solid state power controller includes: a solid state switching device having a first terminal (D) connected to the power supply, and a second terminal (S) connected to the load, and is configured to switch between an OFF operation mode in which the second terminal (S) is electrically disconnected from the power supply, and an ON operation mode in which the second terminal (S) is electrically connected to the power supply. The system also includes a load current detection unit configured to detect a load current through the solid state switching device.

Abstract: A power control apparatus comprises a conversion unit which is capable of collectively converting DC power output by each of the plurality of power supply apparatuses to AC; and a communication unit which communicates with an external equipment control apparatus in accordance with a predetermined communication protocol. The communication unit notifies the equipment control apparatus of an equipment class of the power control apparatus in addition to notifying the equipment control apparatus of an equipment class of each of the plurality of power supply apparatuses.

Abstract: Exemplary embodiments provide a solar cell device, and method for forming the solar cell device by integrating a switch component into a solar cell element. The solar cell element can include a solar cell, a solar cell array and/or a solar cell panel. The integrated solar cell element can be used for a solar sensor, while the solar sensor can also use discrete switches for each solar cell area of the sensor. Exemplary embodiments also provide a connection system for the solar cell elements and a method for super-connecting the solar cell elements to provide a desired connection path or a desired power output through switch settings. The disclosed connection systems and methods can allow for by-passing underperforming solar cell elements from a plurality of solar cell elements. In embodiments, the solar cell element can be extended to include a battery or a capacitor.

Abstract: A current detecting apparatus measures an input current or an output current of an electronic apparatus. The current detecting apparatus includes a current detecting module, a direct-current measurement module and a current detecting module. The current detecting module includes a coil configured to electromagnetically couple to a path of an input or a path of an output of the electronic apparatus to obtain a first voltage signal. The direct-current measurement module measures the path of the input or the path of the output to obtain a second voltage signal. The current detecting module converts the first voltage signal into a first current command, and converts the second voltage signal into a second current command. The first current command is an alternating-current component of the input current or the output current. The second current command is a direct-current component of the input current or the output current.

Abstract: A power supply apparatus and an electronic apparatus are provided. The power supply apparatus includes: a plurality of power supplies arranged as a single array; a switch disposed between the plurality of power supplies configured to control connection states of the plurality of power supplies; and a controller configured to control the switch to connect the plurality of power supplies in parallel when a first event requiring a voltage less than a predetermined reference voltage occurs, and configured control the switch to connect the plurality of power supplies in series when a second event requiring a voltage exceeding the predetermined reference voltage occurs.

Abstract: A device includes a body and a rechargeable battery positioned within the body. A solar cell is coupled to the body and in communication with the battery. A connector is coupled to the body and configured to engage a corresponding connector of a fiber optic cable.

Abstract: An apparatus and method that controls the power produced by a string of solar cells, enabling the string to operate at its maximum power point when connected to a bus that operates at an externally controlled voltage. The apparatus and method can also be used to increase or decrease the output power of a string to any desired operating point.

Abstract: A system for simultaneously charging an energy storage device from multiple energy input devices includes energy input devices in the form of solar and non-solar modules and an energy storage device in the form of a rechargeable battery, which is part of an energy storage module. A first solar module is able to generate solar power and delivers this power to the energy storage module, while the non-solar module delivers, for example, electrochemically generated electricity to the energy storage module via the first solar module, which acts as a backplane. The system may also include additional solar modules that can be connected to the first solar module in collapsed or expanded states to adjust the amount of electricity generated from solar power.

Abstract: This invention relates to a method of controlling the light output of a solar-powered lighting device. The lighting device comprises a light source, a battery connected to the light source, a solar-power generator including a charger connected to the battery, and a control unit for performing the light output control.

Abstract: One or more techniques and/or systems are provided for facilitating shutdown of output power from an energy panel arrangement to a power converter. A shutdown implementation module is coupled between an energy panel arrangement and a power converter that converts DC power from the energy panel arrangement to AC power for an AC power grid. Responsive to identifying a power shutdown condition, the shutdown implementation module shuts down output power from the energy panel arrangement to the power converter. A power dissipating device is invoked to dissipate power associated with the shutdown of the output power (e.g., residual power within energy storage devices, such as capacitors, associated with the power converter). The shutdown implementation module may be located within a threshold distance from the energy panel arrangement (e.g., within about 10 feet) so that the output power may be shut off within a threshold timespan (e.g., within about 10 seconds).

Abstract: A system for extracting energy from an energy storage device configured to supply direct current (DC) energy at a nominal voltage rating comprises a first node dimensioned and arranged to receive direct current energy from the energy storage device. Embodiments include a self-oscillating circuit having primary and secondary windings wound around a ferrite core, wherein a positive terminal of the primary winding is tied to the negative terminal of the secondary winding at the first node, and wherein a positive terminal of the secondary winding is coupled to a second node, the second node being coupled to a load requiring power to be supplied at one of a voltage less than, equal to, or higher than the nominal voltage. Some embodiments further include a transistor having a base resistively coupled to a negative terminal of the primary winding and a collector coupled to the second node.

Abstract: Systems, methods, and devices relating to the control of power conditioning systems. For a micro-inverter, a controller block controls the DC/DC converter while a separate controller block controls the DC/AC inverter. A dynamic maximum efficiency tracker (DMET) control block receives state variable outputs from the converter and the inverter. The control block then perturbs specific control input parameters for the converter and the inverter and determines the effect of the perturbation on the converter and inverter efficiencies and on micro-inverter efficiency as a whole. If the efficiency decreases, then the direction of the perturbation is reversed. Other system control tasks, such as maximum power point tracking and DC-bus voltage regulation can be performed concurrently by adjusting other control input parameters.

Abstract: Switching control devices and related operating methods are provided. An exemplary electronic device includes a semiconductor die, a driver arrangement on the semiconductor die to generate a switch control output signal based on an input switching command signal, and a timer arrangement on the semiconductor die and coupled to the driver arrangement to measure a time difference between a first change in the command signal and an exhibited response in the switch control signal, which can then be utilized to achieve a desired dead time.

Abstract: A power distribution system and a method thereof regulate power distribution in a small form factor satellite flight system. The power distribution system may include a power source and a plurality of power channels. The power channels may distribute power from the power source to a plurality of systems in the small form factor satellite flight system. A processor may monitor power availability of the power source. The processor may also collect housekeeping information of the plurality of systems in the small form factor satellite flight system. The processor may regulate the power channels based on the power availability and the housekeeping information.

Abstract: Communicating across a power transformer is provided. Processes can include outputting a cyclical voltage at an alternating frequency across a multiple winding transformer and modulating the frequency of the alternating voltage to provide communication across the transformer. Devices and systems can also be employed with applicable features and designs.

Abstract: A solar electric system comprises photovoltaic elements having integrated energy storage and control, ideally on each PV-panel. The energy storage media may be primary or secondary cylindrical cells interconnected into a battery and/or an array of capacitors (or super-capacitors) and are accompanied by an electronic control circuit which may perform a variety of functions, including but not limited to power quality control, load following, pulse powering, active line transient suppression, local sensing, remote reporting, wireless or wired communications allowing two way programmable control through local or remote operation. The operation of the system may yield direct current or with the integration of bidirectional micro-inverters create distributed alternating current generation enhanced with energy storage and control two way energy flows between the solar system and the grid.

Abstract: An improved micro-inverter apparatus is disclosed for intelligently controlling energy harvest from photovoltaic solar panels based on one or more adjustable, user-defined variables. The improved micro-inverter apparatus may include a microcontroller configured to monitor the operating temperature of its micro-inverter and control the power harvested from associated solar panels in order to ensure the operating temperature of the micro-inverter does not approach a level that would damage the micro-inverter's circuitry or other components. Similarly, the micro-inverter apparatuses' microcontroller may be configured to monitor the total harmonic distortion of the micro-inverter's AC power output and control the power harvested from associated solar panels in order to ensure the total harmonic distortion of the AC power output does not exceed a threshold level.

Abstract: A method and apparatus is disclosed relating to smart microgrids supported by dual-output off-grid power inverters with DC source flexibility that can (1) intelligently and selectively pull power from one or multiple DC sources including solar panels, wind generators, and batteries based on certain criteria; (2) invert DC power to AC power; (3) supply the AC power to two off-grid circuits individually to power various types of AC loads that require different AC voltages, power quality, and power levels; (4) supply DC power through one or multiple DC output ports to power DC loads; and (5) charge batteries. Two or multiple dual-output off-grid power inverters can daisy-chain to form a group to support a larger microgrid which is ideal for off-grid AC Level 1 and Level 2 EV charging.

Abstract: A power harvesting system including multiple parallel-connected photovoltaic strings, each photovoltaic string includes a series-connection of photovoltaic panels. Multiple voltage-compensation circuits may be connected in series respectively with the photovoltaic strings. The voltage-compensation circuits may be configured to provide respective compensation voltages to the photovoltaic strings to maximize power harvested from the photovoltaic strings. The voltage-compensation circuits may be include respective inputs which may be connected to a source of power and respective outputs which may be connected in series with the photovoltaic strings.

Abstract: Methods and systems are described for using detection coils to detect metallic or conductive foreign objects that can interfere with the wireless transfer of power from a power transmitter to a power receiver. In particular, the detection coils are targeted to foreign objects that are smaller than a power transmitter coil in the power transmitter.

Abstract: Apparatus and techniques for controlling measurement of an electrical parameter of an energy source can be used to obtain information for use in enhancing a power transfer efficiency between the energy source and a load. For example, during a first measurement cycle, information indicative of the electrical parameter of the energy source can be obtained using a measurement circuit during a first sampling duration in which the load is decoupled from the energy source. The information indicative of the obtained electrical parameter can be compared to a threshold. In response to the comparing, a different second sampling duration can be determined for use in obtaining information indicative of the electrical parameter during a subsequent measurement cycle. The information indicative of the electrical parameter of the energy source includes information for use in enhancing the power transfer efficiency between the energy source and the load.

Abstract: A power harvesting system including multiple parallel-connected photovoltaic strings, each photovoltaic string includes a series-connection of photovoltaic panels. Multiple voltage-compensation circuits may be connected in series respectively with the photovoltaic strings. The voltage-compensation circuits may be configured to provide respective compensation voltages to the photovoltaic strings to maximize power harvested from the photovoltaic strings. The voltage-compensation circuits may be include respective inputs which may be connected to a source of power and respective outputs which may be connected in series with the photovoltaic strings.

Abstract: A digital voltage regulator controller includes control logic, an interface and configuration logic. The control logic is operable to control power stages of a voltage regulator so that groups of one or more of the power stages individually regulate one or more output voltages of the voltage regulator. An external electrical parameter that indicates a location of the controller on a board or a version of the board is measured via the interface. The configuration logic is operable to determine a set of configuration parameters for the voltage regulator based on the location of the controller on the board or the version of the board as indicated by the external electrical parameter, and configure the control logic in accordance with the set of configuration parameters so that each output voltage is regulated based on the location of the controller on the board or the version of the board.

Abstract: The present invention relates to an energy converter for converting energy received from at least one energy source, wherein the at least one energy source includes a first photovoltaic generator, wherein the energy converter is configured to be connected to a second photovoltaic generator; the energy converter further includes a sensing unit configured to sense an open circuit voltage (VPVSS) of the second photovoltaic generator; and the energy converter is configured to convert energy received from the first photovoltaic generator based on the open voltage circuit sensed by the sensing unit. Moreover, the present invention relates to an energy conversion and storage system including the energy converter and least one energy storage element.

Abstract: A circuit that operates as a low-power ideal diode is disclosed, as well as an IC chip that contains the ideal diode circuit. The circuit includes a first P-channel transistor connected to receive an input voltage on a first terminal and to provide an output voltage on a second terminal, a first amplifier connected to receive the input voltage and the output voltage and to provide a first signal that dynamically biases a gate of the first P-channel transistor as a function of the voltage across the first P-channel transistor, and a second amplifier connected to receive the input voltage and the output voltage and to provide a second signal that acts to turn off the gate of the first P-channel transistor responsive to the input voltage being less than the output voltage.

Abstract: There is provided a control apparatus for a photovoltaic inverter. The control apparatus includes a system voltage detector, a DC voltage detector that detects a DC voltage applied to the inverter, an output voltage deficiency detector that detects an output voltage deficiency of the inverter based on the system voltage and the DC voltage, an output-current detector, an output-current distortion detector that detects distortion of the output current based on a harmonic included in the output current, a MPPT controller, and an output-current distortion controller that performs control to set the DC voltage applied to the inverter to a voltage at a power point less than a maximum power point when the output voltage deficiency is detected and the distortion of the output current is detected.