467 results about "Capacitive current" patented technology

The invention discloses an intelligent dynamic power distribution network neutral-point grounding method and a complete device. The complete device comprises a grounding transformer (1), an arc suppression loop switch (2), a resistance loop switch (3), an adjustable reactor (4), a damping resistor (5), a damping resistor short-circuit switch (6), a resistor (7), a neutral-point voltage transformer (8) and a computer testing and control system (9). The intelligent dynamic power distribution network neutral-point grounding method and the complete device is technically characterized in that a power distribution network neutral-point grounding mode is dynamically converted from an arc suppression coil grounding mode into a small-resistance grounding mode. When the device is connected to a power grid or a power grid operation mode changes, the device firstly works in the arc suppression coil grounding mode. The device measures capacitive current, adjusts inductive current and enables IL-IC to be smaller than or equal to I delta, wherein the I delta is a preset residual current control value. When a single-phase grounding fault of the power grid occurs, the device outputs the inductive current to perform compensation and arc suppression to grounding fault current. If the fault is an instantaneous fault, the fault is eliminated through the compensation and the arc suppression. If the fault is a permanent fault and the grounding fault is still not eliminated after certain time T, the arc suppression coil grounding is converted into the resistance grounding mode, and a fault line is judged and disconnected by detecting zero-sequence current of feeder lines.

The invention provides an online monitoring method for a DC-link capacitor of a three-phase system. The method comprises that voltage of the DC-link capacitor is collected, and a voltage drop curve of the DC-link capacitor is obtained; three-phase output current is collected, and capacitive current is reconstructed according to the three-phase output current; and the capacitance (C) and equivalent serial resistance (ESR) of the DC-link capacitor are obtained according to the voltage drop curve and the capacitive current of the DC-link capacitor. The voltage drop curve and the three-phase output current of the DC-link capacitor as well as control signals of a semiconductor switch are monitored in the process that power equipment as a three-phase frequency converter is switched off, so that the C and ESR of the DC-link capacitor are calculated accurately, and non-invasive online monitoring for the DC-link capacitor of the AC/DC/AC system is realized. The method can be applied to online monitoring for an aluminum electrolytic capacitor, other capacitors as a film capacitor as well as other three-phase systems including a wind power converter, a photovoltaic AC/DC/AC system and a three-phase aviation power system.

A method to optimize the amperometric detection in a microsystem consists in limiting the detection to times when the diffusion layer (18-20) of the analyte to detect remains smaller than the microchannel (7) height. The charge detected during the second part of the amperometric measurement (which corresponds to the integral of the measured current over the corresponding time period) can also be considered so as to remove the contribution of the capacitive current and, when applicable, of the current resulting from the reduction or oxidation of the analyte molecules present in a recess above the electrode at the beginning of the detection. A microfluidic amperometric sensor for performing the method comprises at least one microchannel (7) having at least one electrode (15-17), integrated in one wall of the microchannel, and having a characteristic length or radius which is smaller than half the microchannel height.

The invention provides a method for extracting the resistive current of a metal oxide arrester (MOA). The technical scheme comprises the following steps of: acquiring a voltage signal applied to the arrester and leakage current flowing through the MOA and performing fast Fourier transform on the voltage signal to acquire the amplitude and phase of each subharmonic; acquiring a capacitive current signal of which the waveform is the same as that of capacitive current of the arrester and the amplitude is in proportion to that of the capacitive current of the arrester according to a phase relationship between a voltage signal and a current signal on a capacitor and the acquired amplitude and phase of each subharmonic of voltage; and acquiring the resistive current of the arrester according to the principle that the resistive current is orthogonal to the capacitive current of the arrester. The method has a rigorous principle and is convenient to implement; a digital signal has high anti-jamming capability; phase shift is processed by the fast Fourier transform, so even if each subharmonic exists theoretically, errors cannot be generated; and the measurement accuracy of the resistive current can be effectively improved in practical application.

A transmission line single-phase grounding fault single-end ranging method belongs to the field of power system protection and control. According to the method of the invention, positive, negative and zero sequence voltage and current phasors of a line during the time section between the occurrence of a single phase grounding fault and single phase tripping and the time section between single phase tripping and reclosing are measured at a substation protection installation site and are used as input. The initial value of fault distance is set from 0 to the overall length of the line with delta1 as the step length, and the initial value of transition resistance starts from 1 ohm and increases to 1000 ohms with 1 ohm as the step length. For each combination of the values of fault distance and transition resistance, the equivalent electromotive force values of a system at the opposite end of the line during the time section between the occurrence of the single phase grounding fault and single phase tripping and the time section after single phase tripping are respectively calculated, the sum of absolute errors of the equivalent electromotive force values is calculated, and the fault distance value corresponding to the minimum value of the sum of absolute errors is selected as the fault ranging distance. The method is high in precision, is not affected by distributed capacitive current, transition resistance, load and system impedance and has very high practical values.

An ungrounded or floating DC electrical power distribution system may experience a single line to ground fault. Such a fault may not disrupt operation of the system, but its presence may raise a risk of additional problems if left uncorrected. A system for progressively grounding the ungrounded system may be initiated when a line to ground fault is suspected based on the voltage difference measured to a common chassis point. As grounding through successively lower impedance proceeds, fault current may increase and detection of severity of the line to ground fault may be more readily achieved, thus facilitating localization of the fault. Localization may be achieved through an analysis of direction of capacitive currents in isolatable zones of the system.

The invention discloses a virtual-capacitor-based power sharing control method for micro-grid inverter parallel connection. The method is characterized in that a voltage amplitude value and a phase angle value are obtained by using a power outer ring of a power outer ring control algorithm; and a virtual capacitor algorithm is added to obtain an output voltage amplitude value and a phase angle instruction, and dual-closed-ring control of the output voltage and the capacitive current is carried out. According to the virtual capacitor algorithm, parallel capacitor characteristics of output terminals of inverters are simulated by a control algorithm and the output voltages and reactive powers of the inverters are adjusted; and a virtual capacitance value is obtained by calculation based on outputted reactive powers of all inverters and a capacitance sagging formula. According to the invention, interconnection communication among inverters and connecting impedance detection are not required; the line impedance voltage drop can be compensated in a self-adaption mode; and reactive power sharing capabilities and output voltage precision of all inverters can be improved.

The invention provides a current full compensation method and a system based on single-phase earth fault. When zero sequence voltage is not in a preset voltage value range, namely, the happened single-phase earth fault is instant ground connection, an arc extinction coil device with high flexibility in high-resistance ground connection can compensate ground connection capacitive current. When thezero sequence voltage is in the preset voltage value range, namely, the happened single-phase earth fault is not instant ground connection, a breaker in a fault phase transfer ground connection deviceconnected with a fault phase is turned off, fault current is converted into earth current, and a compensable compensation device is further utilized to output full compensation fault residual current. The fault current is converted into the earth current, the earth current can serve as tracking compensation signals of the compensable compensation device, and judgment reference is provided for a compensation effect of the compensable compensation device. In addition, the earth current can be determined by measurement; furthermore, measurement is convenient, and complex calculation is avoided;thus, compensation quickness and accuracy are ensured, compensation precision is improved, and fault points are shielded.

The invention relates to a DC distribution system energy storage device adaptive virtual impedance droop control method, which is applied to multi-converter parallel control in a DC distribution system. The method comprises the steps of 1) acquiring electric power parameters of the DC distribution system, establishing a double closed-loop controller which consists a voltage outer loop and a capacitive current inner loop, and establishing a DC distribution system droop control model; 2) introducing virtual impedance ZD(s) into a part between converter output current and converter reference voltage signals of the double closed-loop controller in the DC distribution system droop control model so as to act as negative feedback, and acquiring equivalent output impedance Zov(s); and 3) enabling the equivalent output impedances Zov(s) corresponding to a plurality of lines to be equal through setting values of different virtual impedances ZD(s), and thus averaging output power and power distribution of the plurality of lines in the DC distribution system. Compared with the prior art, the method provided by the invention has the advantages of shock suppression, simple algorithm, low cost and the like.

A slowly rotating synchronous generator (ring generator) for a wind power installation, the generator having a rotor and a stator surrounding the rotor, and the stator having at least one three-phase current winding on which a capacitive current is impressed, and the generator having a part of the exciter power of the generator produced by the stator.

The invention discloses a method for designing a hybrid damping parameter of an LCL filter in a photovoltaic grid-connected inverter, and belongs to the technical fields of new energy sources and distributed grid-connected generation. The method is characterized in that: the resonance of the LCL filter is suppressed by adopting an active damping/passive damping cooperative working method, whereina filter capacitive current feedback control method is adopted for an active damping part and the method of connecting filtering capacitance in series with damping resistance is adopted for a passivedamping part. For the LCL filter, the damping resistance required by passive damping and a feedback coefficient of active damping are computed under the condition of ensuring a sufficient damping coefficient, and a designed cooperative damping control scheme is checked to make the loss of the damping resistance as low as possible, avoid the influence of system control delay on damping running; and the damping is adapted to strong power grid access and the weak power grid access of remote areas. The method is applied to photovoltaic grid-connected generation systems adopting the LCL filter, fuel cells and grid-connected wind power generation systems.

The invention discloses a UHV DC transmission line protection method utilizing current abrupt change characteristics based on a distributed parameter model. The UHV DC transmission line protection method comprises the steps of processing voltage and current signals measured by transformers at both ends of a DC line by means of an intelligent electronic device (IED), and identifying internal and external faults according to polarities of current abrupt variables. The UHV DC transmission line protection method adopts a distributed parameter model for carrying out distributed capacitive current compensation, eliminates the influence of asynchronization of the distributed capacitive current and data. A protection criterion selects components with the frequency band of [0,100] Hz in current information, avoids the electromagnetic coupling between DC side characteristic harmonics and a bipolar DC line and the influence of lightning interference. The polarities of current abrupt variables at both ends of the line are Boolean quantities, and the communication traffic of longitudinal channels is small. The UHV DC transmission line protection method utilizing the current abrupt change characteristics based on the distributed parameter model only utilizes polarities of the current abrupt variables for identifying the internal and external faults, is simple in principle and small in communication traffic, and is stable and reliable.

The invention discloses a bipolar parallel multi-terminal direct current power transmission system electric current modulus longitudinal differential protection method. The method comprises the steps that digital sampling and modulus decoupling are conducted in each converter station of the parallel system, and 1, 0-mode voltage and electric current are obtained; one point on the direct current main line is selected as the destination point of calculation, starting from each converter station, the line terminal voltage, the electric current up to the destination point are calculated segment-by-segment and the 1, 0-mode differential current is obtained through the overlay at the destination point. If the 1-mode differential current is greater than the fault threshold, the fault is an internal area fault, otherwise the fault is an external fault; if the 0-mode differential current is greater than the threshold, the fault is a positive pole grounding fault; if the 0-mode differential current is less than the threshold, the fault is a negative pole grounding fault; if the 0-mode differential current is between the positive and negative selection thresholds, the fault is an inter polar short-circuit fault. The differential protection method is fast in movement speed, high in transition resistance capability, and is not under the influence of capacitive current in distribution, and can be extended to arbitrary end parallel direct current systems, in principle can recognize the fault type and is strong in adaptability. According to the differential protection method, the required sampling rate is low, the method is easy to implement and has practical value.

An apparatus for detecting deterioration of a lightning arrester includes: a high-frequency power supply; a pair of detecting terminals 12 connected to the high-frequency power supply via a resistance for measurement and touched to the terminals of the arrester; a voltage detecting circuit for obtaining a terminal voltage of the resistance for measurement when the detecting terminals touch the terminals of the arrester; and a determining circuit for comparing the detected voltage with a reference value to determine whether the detected voltage is good or bad. A voltage having a frequency sufficiently higher than the operation frequency of a power line is generated by the high-frequency power supply and applied to the arrester, and change in electrical characteristics due to deterioration of zinc oxide elements is detected as change in current including capacitive current, and then it is determined whether the detected change is good or bad.

When a drive signal that is a PWM input signal is small (when the drive duty component of the PWM drive signal is small), shoot-through (through state) between the upper transistor and lower transistor can occur when there is variation in the drive circuit or transistors. An upper switching device and lower switching device control current supply to a load, and an upper drive circuit and lower drive circuit respectively drive the upper switching device and lower switching device. The upper drive circuit has an input terminal that receives a control signal that turns the upper switching device on or off; an upper source circuit that SOURCE outputs a drive current to the control terminal of the upper switching device according to a first level or second level signal applied to the input terminal; an upper sink circuit that SINK outputs drive current to the control terminal of the upper switching device according to a second level or first level signal applied to the input terminal; an upper sink transistor that sinks capacitive current through the control terminal when the upper switching device is off; an upper interface circuit that generates a first input drive signal to the upper source circuit according to the input terminal signal, and a second input drive signal to the upper sink circuit or the upper sink transistor; and a selector that selectively supplies the second input drive signal to the upper sink circuit or the upper sink transistor based on a signal from the inverter. The lower drive circuit is identically configured.

The invention discloses a method for restraining a voltage background harmonic wave of a grid-connected inverter. The method adopts a direct-current source, an IGBT (Insulated Gate Bipolar Transistor) intelligent power module and an LCL (Lower Control Limit) type filter, wherein the direct-current source is subjected to a single-phase inversion output through the IGBT intelligent power module; and the single-phase inversion output is accessed to a power grid after being accessed with the LCL type filter. The method disclosed by the invention is characterized by comprising the following steps of: multiplying a sampling voltage signal of the power grid with a reference current amplitude I* after carrying out PLL (Phase Locking Loop) phase locking, so as to obtain a reference current signal; carrying out closed-loop adjustment on the reference current signal and a feedback current iL2 so as to obtain a first path of signals; multiplying the sampling voltage signal of the power grid with a feed-forward function so as to obtain a second path of signals; multiplying a capacitive current signal led by a capacitive branch of the LCL type filter with a virtual resistance function so as to obtain a third path of signals; and combining the first path of the signals, the second path of the signals and the third paths of the signals and then sending the combined signals to Ginv(s) for modulation so as to generate a PWM (Pulse Width Modulation) gate pole drive signal; and triggering a switching tube of the IGBT intelligent power module to be switched on or off by the PWM gate pole drive signal. With the adoption of the method disclosed by the invention, the influence of the background harmonic wave of the power grid can be effectively removed.

The invention discloses a characteristic-harmonic-based protection method and a characteristic-harmonic-based protection system for a high-voltage direct current transmission line. The characteristic-harmonic-based protection method for the high-voltage direct current transmission line comprises the following steps of: synchronously sampling direct currents on the two sides of the high-voltage direct current transmission line to obtain real-time current data, and performing discrete Fourier transform to obtain current characteristic harmonics at the two ends of the line; and counting the number Nn.m of characteristic current harmonics, calculating a weighted index IH.M, and performing logic judgment on the weighted index IH.M, the number Nn.m of the characteristic current harmonics and set values IH.set and Nn.set to obtain a failure type. The influence of distributed capacitive current can be avoided, and the shortcomings of the conventional differential protection for the high-voltage direct current transmission line are overcome; and moreover, the method and the system are high in resistance to transition resistance, simple in operation, easy to implement and high in working speed and reliability, and special requirements on sampling frequency are avoided.

A device for preventing bearing damage from currents through a three-phase motor is provided, including a shield for winding and copper wire within each stator slot of a motor. The shield includes an electrically conductive layer which is insulated from the winding and from the laminated stator core of the three-phase motor. The conductive layer is grounded or conductively connected to the laminated stator core of the three-phase motor on only that side on which the three-phase current is fed to the winding of the motor.