Abstract: A vehicle includes a drive system ground fault determination unit configured to determine that, when the first magnetic contactor is in a conduction state, the drive system electrical system has a ground fault when a ground stray capacitance of the drive system electrical system measured by a drive system ground fault sensor included in the drive system electrical system exceeds a drive system conduction state threshold value, and to determine that, when the first magnetic contactor is in a non-conduction state, the drive system electrical system has a ground fault when the ground stray capacitance of the drive system electrical system measured by the drive system ground fault sensor exceeds a drive system non-conduction state threshold value, which is different from the drive system conduction state threshold value.

Abstract: An illustrative receiver includes: a decision element that derives symbol decisions from a slicer input signal; an equalizer that converts a receive signal into the slicer input signal; a summer that combines the symbol decisions with the slicer input signal to produce an error signal; and a level finder that operates on said signals to determine thresholds at which each signal has a given probability of exceeding the threshold. One illustrative level finder circuit includes: a gated comparator and an asymmetric accumulator. The gated comparator asserts a first or a second gated output signal to indicate when an input signal exceeds or falls below a threshold with a programmable condition being met. The asymmetric accumulator adapts the threshold using up steps for assertions of the first gated output signal and down steps for assertions of the second gated output signal, with the up-step size being different than the down-step size.

Abstract: To mitigate phase noise and amplitude noise in a 5G or 6G message, the transmitter can include an extremely compact demodulation reference with a predetermined format including a first branch and an orthogonal second branch. The first branch can exhibit the maximum positive amplitude level of the modulation scheme, and the second branch can exhibit either the minimum positive level or the maximum negative level, depending on implementation. The receiver can determine, from the received branch amplitudes, a phase correction and an amplitude correction. Upon receiving a message including noise, the receiver can calculate a sum-signal amplitude and sum-signal phase according to the branch amplitudes of each message element, subtract the amplitude correction and phase correction, derive corrected branch amplitudes, and compare them to the predetermined amplitude levels of the modulation scheme. The receiver can thereby demodulate the message element with the phase noise and amplitude noise largely negated.

Abstract: AC to DC power supplies are disclosed. One AC to DC power supply includes a transformer having a primary side and a secondary side and a passive rectifier coupled to the secondary side of the transformer. The passive rectifier is configured to rectify AC power at the secondary side to DC power at an output of the rectifier. An active rectifier is configured to control voltages applied to the primary side of the transformer to induce a non-sinusoidal voltage at the secondary side of the transformer and a sinusoidal current drawn by the passive rectifier. An isolating DC-to-DC converter is coupled between the active rectifier and the output of the passive rectifier to magnetically couple power from the active rectifier to the output of the passive rectifier while galvanically isolating the active rectifier from the output of the passive rectifier.

Abstract: Short-form pulse-amplitude demodulation references disclosed herein may enable low-cost receivers to demodulate wireless messages while avoiding complex 5G and 6G protocols, thereby enabling a multitude of cost-constrained applications. Despite their small footprint, the short-form pulse-amplitude demodulation references enable the receiver to determine all of the amplitude levels of the modulation scheme, including the effects of noise and interference. Mitigation of noise and interference can therefore be provided by embedding short-form pulse-amplitude demodulation references within longer messages, thereby providing an immediate refresh of the modulation calibrations, enhancing communication reliability, and avoiding costly message faults despite high background interference. Short-form pulse-amplitude demodulation references disclosed herein can be used as a default standard demodulation reference in 5G and 6G wireless messages.

Abstract: A method and apparatus for autonomous, automatic interleaving of cycled loads coupled to a grid. In one or more embodiments, the method comprises (i) determining, by a smart load coupled to a grid, a first grid stress value; (ii) comparing, by the smart load, the first grid stress value to an activation threshold; (iii) waiting, by the smart load, when the first grid stress value is less than the activation threshold, a delay period; (iv) determining, by the smart load and after the delay period ends, a second grid stress value; (v) comparing, by the smart load, the second grid stress value to the activation threshold; and (iv) activating, by the smart load, when the second grid stress value is less than the activation threshold.

Abstract: An energy blending device has a first input for alternating current, a second input for connection to a solar array, and an output, the energy blending device receiving energy from the first input, both inputs coupled to power an energy blending node. The device is in a configuration either with the solar array matching a voltage of the energy blending node, the blending node providing power through a DC-DC converter to a load interface device, and the solar array coupled through a DC-DC converter to the energy blending node, the energy blending node providing power to a load interface device. A microcontroller controls the DC-DC converter and a load interface device. The energy blending device has an energy storage system having a battery coupled either directly to the energy blending node or through a bidirectional energy storage interface to the energy blending node.

Abstract: The switching power supply device is provided with: a plurality of power supply circuits corresponding to phases of a multi-phase AC power supply; a switching circuit that is capable of switching a phase connected to a power supply circuit not corresponding to one discretionary phase of the multi-phase AC power supply between the one discretionary phase and a phase to which the power supply circuit corresponds; an inrush current prevention circuit for preventing inrush current that is provided on a negative-electrode-side power supply line of the multi-phase AC power supply and at a position further toward the multi-phase AC power supply than is a connection point to which each of the plurality of power supply circuits are connected; and a filter circuit that is provided between the multi-phase AC power supply and the inrush current prevention circuit and has all lines of the plurality of phases magnetically coupled thereto.

Abstract: The switching power supply device is provided with: a plurality of power supply circuits corresponding to phases of a multi-phase AC power supply; a switching circuit that is capable of switching a phase connected to a power supply circuit not corresponding to one discretionary phase of the multi-phase AC power supply between the one discretionary phase and a phase to which the power supply circuit corresponds; an inrush current prevention circuit for preventing inrush current that is provided on a negative-electrode-side power supply line of the multi-phase AC power supply and at a position further toward the multi-phase AC power supply than is a connection point to which each of the plurality of power supply circuits are connected; and a filter circuit that is provided between the multi-phase AC power supply and the inrush current prevention circuit and has all lines of the plurality of phases magnetically coupled thereto.

Abstract: The present invention relates to a millimeter or terahertz wave sensor for providing inline inspection, preferably including but not limited to continuous monitoring of objects, for example thin sheet dielectric material.

Abstract: A control system for providing electrical power to an electronic flight bag device on an aircraft. The control system including a power switching component coupled to a plurality of power sources and at least one electronic flight bag device. The power switching component is operative and configured to selectively apply electrical power from at least one of the plurality of power sources to the at least one electronic flight bag device based upon a condition of the aircraft.

Abstract: A generator system may include two or more generators electrically connected through a generator bus. A controller receives operation data from a first generator. The operation data may describe a power flow from a second generator to the first generator. From the operation data, either a loss of speed control or a loss of voltage control may be identified at the second generator. The controller may generate a command for the second generator based on the loss of speed control or the loss of voltage control.

Abstract: Embodiments of a ground power unit are disclosed for providing power to a grounded vehicle, such as an aircraft. In accordance with certain embodiments, the ground power unit (GPU) accepts a wide range of AC input voltages and is capable of providing a range of DC output voltages. The GPU may include a switched rectifier that converts an AC input signal to a DC link signal. The DC link signal is then converted to a switched DC signal that simulates an AC-like sine wave using a high frequency DC-to-DC switching converter. A single-phase transformer modulates and isolates the switched DC signal, which is subsequently converted to a DC output signal using diode rectifiers coupled to the secondary winding of the transformer. The disclosed GPU may be controlled using a software-based control algorithm that controls the AC input parameters independently of the DC voltage parameters.

Abstract: A control system for providing electrical power to an electronic flight bag device on an aircraft. The control system including a power switching component coupled to a plurality of power sources and at least one electronic flight bag device. The power switching component is operative and configured to selectively apply electrical power from at least one of the plurality of power sources to the at least one electronic flight bag device based upon a condition of the aircraft.

Abstract: An auto-synchronous isolated inlet power converter is disclosed that can be daisy-chained with other power converters and/or an alternating current (AC) power source. The power converter automatically generates output AC power that is in parallel with external input AC power coming into the power converter when the power converter senses the external input AC power so that the power converter operates as a slave in this state. The power converter automatically generates output AC power when the power converter fails to detect the external input AC power coming into the power converter where the power converter operates as a master in this state. The power converter generates the output AC power without any reliance on the external input AC power generated by a utility grid and/or other AC power sources external to the power converter.

Abstract: A power supply arrangement for producing polysilicon with a central control unit and a basic supply unit, which are regulated and controlled by control means. The basic supply unit supplies the supply module with electric energy, an output for connecting to loads which are supplied with electric energy from the mains via basic supply unit, and controllable switches, which are connected to the input and to the output and which are configured for adjusting the energy to be supplied to the loads. The switches are controllable. The control unit is supplied with electric energy. The power supply includes a communication bus. The control module and the basic supply module are connectable to the control module and the basic supply module to the communication bus. The control module and the basic supply module provide connections to the control module and the basic supply module to the communication bus.

Abstract: At least one embodiment of the invention generally relates to a drive system for a facility having an alternating-current isolated network, in particular for a ship or an offshore platform, including a three-phase drive machine, which can be operated both as a motor and as a generator, and including a converter having a direct-current intermediate circuit having an intermediate circuit voltage. At least one embodiment of the invention aims to provide a way of avoiding undesired and/or impermissible voltage and/or frequency increases in the alternating-current isolated network.

Abstract: Aspects of the invention are directed to power distribution systems and methods for distributing power from a primary power source and a backup power source to a load. In one particular aspect, a power distribution system includes a first input to receive input power from the primary power source, a second input to receive input power from the backup power source, an output that provides output power from at least one of the primary power source and the backup power source, a first switch operatively coupled to the first input and the output and operative to selectively couple the first input to the output, a second switch operatively coupled to the second input and the output and operative to selectively couple the second input to the output, and a controller operatively coupled to the first switch and to the second switch and configured to control the first switch and the second switch to provide an electrical interlock.

Abstract: A system for combining electrical power from two or more power sources includes first and second conversion stages (120) which receive input power from two or more power sources (110), and produce different output voltages, including DC outputs. The input power sources (110) may have different voltage, frequency, and phase characteristics, and may be DC voltages. Various embodiments are disclosed for converting and combining the input power sources (110) to provide at least a DC output voltage and an optional AC output voltage which may have different voltage, frequency, and phase characteristics than the input power sources (110). In another embodiment, a method of power conversion is disclosed.

Abstract: A photovoltaic inverter having an inverter bridge section, a first output, a second output, and a power switch. The inverter bridge section is operable for converting DC electrical energy into AC electrical energy. The inverter bridge section has an output for outputting the AC electrical energy. The power switch is connected to the output of the inverter bridge section, the first output, and the second output. The power switch is selectively switchable between a first state in which the output of the inverter bridge section is connected to the first output via the power switch and a second state in which the output of the inverter bridge section is connected to the second output via the power switch.

Abstract: Disclosed is a hybrid wind-solar energy device comprising: a) a wind-capture assembly comprising: i) one or more wind sails evenly distributed circumferentially around a central axis thereof; and ii) a solar-energy capture means on an outer surface of the wind-capture assembly; and c) a turbine assembly comprising an anchoring base, an electrical generator and an output shaft; the wind-capture assembly rotatably mounted on the output shaft and coupled thereto; the hybrid wind-solar energy device configured to convert energy harnessed by the wind capture assembly to electrical energy, wherein: interaction of the one or more wind sails with wind induces rotation of the wind-capture assembly and turbine assembly around the central axis; and the outer surface of the wind capture assembly is directly exposed to sunlight throughout daylight hours.

Abstract: An airplane ground support system includes a multi-voltage power supply. A control system within the power conversion module receives measurements to regulate the power module's output to a predetermined preset voltage level as mandated by the power output selection signal. In an alternate embodiment a multi-voltage or upgradable power supply has A.C. and D.C. capability, A.C. only capability with an upgrade kit available to add D.C. capability in addition to the A.C. capability, D.C. only capability with an upgrade kit available to add A.C. capability in addition to the D.C. capability.

Abstract: A solar power generation system includes a control system and a DC to AC converter coupled to a photovoltaic (PV) module and for supplying power to a power network. The control system includes a power point tracker to extract either maximum power available from the PV module or less than maximum power available from the PV module, a frequency monitor to obtain a network frequency from the power network, an internal reference frame element to provide an internal reference frequency of the solar power generation system, a frequency comparator to compare the network frequency and the internal reference frequency, and a command signal generator to use the frequency comparison to determine whether a transient increase or decrease in commanded output power is warranted and to provide a command signal.

Abstract: An HVAC/R system is configured with a variable frequency drive power supply which provides power to each of a compressor, a condenser fan, and a blower. In some embodiments, the compressor has a three-phase motor and the condenser fan has a single-phase motor.

Abstract: An electric power generating system includes a plurality of variable power sources including at least one source of DC power and at least one source of AC power. Converters convert power supplied by the plurality of power sources to a common source of power to be communicated to a collector bus. A power grid supplies three-phase power to components requiring three-phase power downstream of the collector bus. Converters provide three phases of power to the power bus from the collector bus.

Abstract: The present invention relates to a motor control device of an air conditioner using a distributed power supply, comprising: a DC/DC converter which level-converts a DC power supply supplied from the outside to output the level-converted DC power supply to a DC bus terminal; a bidirectional DC/AC converter which converts the DC power supply of the DC bus terminal into an AC power supply to transfer the converted AC power supply to a system, or which converts the AC power supply from the system into the DC/power supply to supply the converted DC power supply to the DC bus terminal; and an inverter which converts the DC power supply of the DC bus terminal into the AC power supply by a switching operation, and drives a compression motor by the converted AC power supply.

Abstract: At least one embodiment of the invention generally relates to a drive system for a facility having an alternating-current isolated network, in particular for a ship or an offshore platform, including a three-phase drive machine, which can be operated both as a motor and as a generator, and including a converter having a direct-current intermediate circuit having an intermediate circuit voltage. At least one embodiment of the invention aims to provide a way of avoiding undesired and/or impermissible voltage and/or frequency increases in the alternating-current isolated network.

Abstract: A power converter having an aircraft power source detector configured to limit the amount of power that can be drawn by the power converter when utilized in an aircraft. The power converter may detect an artifact of the aircraft power source, such as the 400 Hz ripple noise on an aircraft power line, or existing in the aircraft cabin, such EMI or aircraft lighting.

Abstract: An airplane ground support system includes a multi-voltage power supply. This system includes an air conditioning module and a control module having a display and a processor, the display and processor presenting an airplane type or class selection menu to airplane support technicians and responding to the selection of a type or class of airplane by generating a power output selection signal designating the type of power needed by the selected type or class of airplane. The system also includes a power supply module which has an A.C. power input, at least one power output, and which receives the power output selection signal as an incoming signal. A power conversion system within the power supply module connects to the A.C. power input and supplies converted and voltage regulated power to the at least one power output. This power conversion system also receives the power conversion control signal as an input signal.

Abstract: An uninterruptible power supply has first and second input terminals, first and second inductors, first and second AC switch units, first and second storing devices and a control unit. The first and the second inductors are electrically connected to the first and the second input terminals. The first and the second AC switch units are electrically connected to the first and the second inductors for conducting input currents. The control unit is electrically connected to the first and the second AC switch units which may be turned on and off thereby to control the first and the second inductors which charge the input currents and discharge the input currents to the first and the second storing devices.

Abstract: A system for combining electrical power from two or more power sources includes first and second conversion stages (120) which receive input power from two or more power sources (110), and produce different output voltages, including DC outputs. The input power sources (110) may have different voltage, frequency, and phase characteristics, and may be DC voltages. Various embodiments are disclosed for converting and combining the input power sources (110) to provide at least a DC output voltage and an optional AC output voltage which may have different voltage, frequency, and phase characteristics than the input power sources (110). In another embodiment, a method of power conversion is disclosed.

Abstract: There is provided an electricity grid, system having a substation connecting two grid parts, preferably at different levels in the grid hierarchy, wherein flow control means is provided for controlling the flow of electricity between the two parts in dependence on the level of stress of the respective grid part of the network.

Abstract: A power station comprises a power-consuming shaft run on which a motor and a compressor are arranged, as well as a power-emitting shaft run on which a generator and an expansion machine are arranged. The compressor feeds a compressed fluid into a storage volume. The compressed storage fluid is expanded in the expansion machine, producing work. The generator and the motor are connected to the electrical grid system via frequency converters. This makes it possible to operate the electrical machines at a rotation speed which is asynchronous with respect to the grid system. A method and apparatus is disclosed that allows the net power output of the power station to be matched to the demands of the electrical grid system by varying the rotation speed of at least one of the shaft runs.

Abstract: A method of operating a power system is provided. The power system has a plurality of generator sets and a bus. The method monitors the bus and generator sets disconnected from the bus. The method supplies to a control device information associated with the operating state of each of the generator sets and the bus. The method determines a relative frequency mismatch and a relative phase mismatch between the frequency and phase of the bus and a generator, and generates a frequency speed bias and a phase speed bias for the generator. The method adds the frequency and phase speed biases to form a total speed bias, tunes the total speed bias to make the frequency and phase speed biases combine in a complementary manner, and connects the generator to the bus when the voltage, frequency, and phase of the generator are within a permissible range of the bus.

Abstract: There is provided a power supply for AC/DC and DC/DC conversion which receives the DC power supplied from airplanes, vehicles and vessels as well as normal AC power, and converts the power to DC power and supplies it to portable electronic products. The power supply for AC/DC and DC/DC conversion includes an AC input 10, a DC input 20, a switch 30 for selecting AC input power or DC input power, a DC output 40, and a circuit used for AC/DC and DC/DC conversion 100 which converts the power input from the AC input or the DC input to DC power having predetermined values of current and voltage, and a secondary side of a transformer (TL) for AC/DC conversion inside the circuit for conversion serves as an inductor for performing DC/DC conversion.

Abstract: An external transformation socket without a power cord is disclosed, which includes an AC or DC power input, a transformer and an AC or DC power output. The functions of inputting, transforming and outputting include AC/AC, AC/DC, DC/DC, and DC/AC. The circuit board of the socket thereon includes an AC/DC power input, transformation coils, a capacitor, a constant voltage regulator, and many groups of AC/DC outputs with different voltages and currents after being transformed. Thereby, power may be supplied and output via various AC/DC outputs, depending on DC or AC requirements for users.

Abstract: An improved method and system for facilitating no-break power transfer between an APU and a main engine includes determining a required APU speed for conducting power transfer based on various APU operating parameters, such as engine speed, fuel, environmental temperature, etc. The APU controller then adjusts the APU speed up or down to the required APU speed. Communication between an aircraft computer and the APU controller may also be provided so that operational data can be exchanged to adjust the electrical load of the aircraft below a maximum load threshold set by the APU, avoiding overloading of the APU during power transfer. By exchanging operational data between the APU controller and the aircraft computer, both the APU and the electrical load can be adjusted to optimize no-break power transfer despite varying APU operating conditions and main engine generator frequencies.

Abstract: Aspects of the invention are directed to power distribution systems and methods for distributing power from a primary power source and a backup power source to a load. In one particular aspect, a power distribution system includes a first input to receive input power from the primary power source, a second input to receive input power from the backup power source, an output that provides output power from at least one of the primary power source and the backup power source, a first switch operatively coupled to the first input and the output and operative to selectively couple the first input to the output, a second switch operatively coupled to the second input and the output and operative to selectively couple the second input to the output, and a controller operatively coupled to the first switch and to the second switch and configured to control the first switch and the second switch to provide an electrical interlock.

Abstract: In various embodiments, various systems and methods are provided for power distribution. In one embodiment, power distribution apparatus is provided comprising a power multiplier comprising a multiply-connected electrical structure, and a plurality of power network couplings in the multiply-connected electrical structure. The multiply-connected electrical structure is a resonant circuit tuned to a nominal frequency of a power network.

Abstract: Multiple sources are provided for a transmitter cable for use in electromagnetic surveying. The transmitter cable includes a dipole antenna comprising a pair of spaced apart electrodes mounted on their respective cables. Two antennas may be powered from each source. Alternatively, the outputs of each source are connected to a common antenna pair. A single large power supply may be mounted on a vessel to supply power through the tow cable. Alternatively, a number of power supplies may be provided aboard the vessel, with each power supply having dedicated conductors through the tow cable to power the plurality of current sources.

Abstract: An apparatus, system, and method for supplying an uninterruptible power source to a dual power device capable of being alternately powered through either a primary power input connected to a primary power source or a secondary power input connected to a secondary power source is provided. One implementation includes a power input for receiving AC from the primary power source, one or more converter elements operative to receive the AC from the power source, to convert the AC to DC, and to deliver the DC to a power storage element. The apparatus also includes a power storage element that stores at least a portion of the DC delivered from the converter elements. The power stored in the power storage elements is delivered to the secondary power input of the dual power device when the primary power source is disconnected from the dual power device.

Abstract: A method and apparatus are provided in which control data for a generator system is multiplexed onto a synchronization signal.

Abstract: Power supply apparatus and method based on parasitic power extraction is disclosed. Power is extracted from signals that are inbound and/or outbound from an equipment. The extracted power is converted to dc voltages for a device associated with the equipment. The positive portions of the extracted power are combined in an additive manner to provide a first potentially time-varying signal and negative portions of the extracted power are also combined in an additive manner to provide a second potentially time-varying signal. The two potentially time-varying signals are also combined in an additive manner and divided into the desired number of dc voltages and magnitudes. An optional dc voltage power source is provided should the extracted power be inadequate to provide the dc voltages.

Abstract: Aspects of the invention are directed to power distribution systems and methods for distributing power from a primary power source and a backup power source to a load. In one particular aspect, a power distribution system includes a first input to receive input power from the primary power source, a second input to receive input power from the backup power source, an output that provides output power from at least one of the primary power source and the backup power source, a first switch operatively coupled to the first input and the output and operative to selectively couple the first input to the output, a second switch operatively coupled to the second input and the output and operative to selectively couple the second input to the output, and a controller operatively coupled to the first switch and to the second switch and configured to control the first switch and the second switch to provide an electrical interlock.

Abstract: A charging contactor and charging resistor of a capacitor battery in a prior art intermediate circuit of a frequency converter are replaced with three semiconductor switches connected between a three-phase voltage supply and a capacitor battery. When the frequency converter is connected to a supply network, the three semiconductor switches are arranged to operate at first in a current regulating mode in order to charge the capacitor battery using a regulated charging current until the voltage of the capacitor battery reaches a predetermined level. After this, the three semiconductor switches are directed to operate in a diode bridge mode in parallel with an actual network inverter, thus providing a second rectification branch. In a preferred embodiment of the invention, each semiconductor switch comprises a diode and a series connection of a gate-triggered component, preferably a thyristor.

Abstract: A no break power transfer system that is particularly useful onboard an aircraft ensures that there is an appropriate frequency match between the outputs of different power supplies. A frequency adjuster between an auxiliary power unit and a load alters the frequency of power available from the auxiliary power unit before that power is supplied to the load. In one example, a controller determines when the frequency of output power from the main power supply does not match that from the auxiliary power unit. The controller controls the frequency adjuster to make an appropriate frequency change until there is a sufficient match. In one example, the frequency adjuster includes a rectifier that converts an alternating current output of the auxiliary power unit to a direct current output that is then converted by an inverter to provide an alternating current output having the appropriate frequency.

Abstract: A generator control system of a vehicle AC generator includes a field coil, a first polyphase armature winding, a second polyphase armature winding, a first rectifier connected to the first armature winding and a second rectifier connected to the second armature winding. The generation control system includes a power transistor connected with the field coil, a voltage regulator for controlling the power transistor, a voltage comparator for providing a pulse signal by comparing output voltage of one of phase-windings of the first armature winding with one of second phase-windings of the second armature winding and a counter circuit for driving the voltage regulator when the number of pulses of the pulse signal becomes larger than a predetermined value.

Abstract: An electrical control system for an induction motor for achieving optimum efficiency at both full and partial loads at markedly reduced electrical components costs while maximizing reliability over the range of load, and for achieving a two step motor power output in a greatly simplified manner, the circuit having an electrical induction motor adapted for connection to line electrical power at maximum motor operating frequency, and to a second source of electrical power at approximately one half of the maximum operating frequency, wherein an electrical switch is provided for selectively connecting each power source to the motor, wherein the second source is a generator for producing a reduced frequency sine wave form.

Abstract: An electrical power system for an aircraft includes an ac generator bus, an air conditioning system ("ACS") generator and a main engine generator. The ACS generator supplies primary ac power to the bus while the frequency of the ac power is within a frequency range. If the frequency of the ac power goes outside the frequency range, the main engine generator supplies backup ac power to the bus. The frequency of the ac power generated the ACS generator is maintained between upper and lower limits. Such ac power can be used directly by certain ac loads onboard the aircraft. Other ac loads onboard the aircraft are supplied with fixed frequency ac power by reduced-size inverters.

Abstract: A method for detecting islanding operation of a rotating-machine type dispersed generator. The dispersed generator is interconnected with a main electric source through a circuit breaker to constitute an electric power system. The estimating method is implemented as follows: (a) changing electric power of the electric power system; (b) detecting frequency component of the electric power; and (c) deciding that an islanding operation of the dispersed generator is executed if the change of the frequency component becomes greater than a predetermined value. With this method, it becomes possible to detect the islanding operation of the dispersed generator even if the power flow at the interconnecting circuit breaker is generally zero.