4450 results about "Three-phase electric power" patented technology

An electronic electric meter for use in a networked automatic meter reading environment. The electric meter retrofits into existing meter sockets and is available for new meter installations for both single phase and three phase electric power connections. The meter utilizes an all electronic design including a meter microcontroller, a measurement microcontroller, a communication microcontroller and spread spectrum processor, and a plurality of other communication interface modules for communicating commodity utilization and power quality data to a utility. The electric meter utilizes a modular design which allows the interface modules to be changed depending upon the desired communication network interface. The meter measures electricity usage and monitors power quality parameters for transmission to the utility over a two-way 900 MHz spread spectrum local area network (LAN) to a remotely located gateway node. The gateway node transmits this data to the utility over a commercially available fixed wide area network (WAN). The meter also provides direct communication to the utility over a commercially available network interface that plugs into the meter's backplane or bus system bypassing the local area network communication link and gateway node.

An area electric power system includes a number of direct current power sources, and a number of inverters operatively associated with the number of direct current power sources. Each of the number of inverters is structured to provide real power and controlled reactive power injection to detect islanding. An output is powered by the number of inverters. A number of electrical switching apparatus are structured to electrically connect the number of inverters to and electrically disconnect the number of inverters from a utility grid. A number of devices are structured to detect islanding with respect to the utility grid responsive to a number of changes of alternating current frequency or voltage of the output.

This invention deals with an advanced Real-time Grid Monitoring System (RTGMS) suitable for both single-phase and three-phase electric power systems. This invention provides an essential signal processing block to be used as a part of complex systems either focused on supervising and diagnosing power systems or devoted to control power processors interacting with the grid. This invention is based on a new algorithm very suitable for real-time characterization of the grid variables under distorted and unbalanced grid conditions. The main characteristic of this invention is the usage of a frequency-locked loop, based on detecting the grid frequency, for synchronizing to the grid variables. It results in a very robust system response in relation to existing technique based on the phase-angle detection since grid frequency is much more stable variable than the grid voltage/current phase-angle, mainly during grid faults. Moreover, the algorithm supporting this invention is very efficient and can be implemented in regular industrial microprocessors. These features make the RTGMS object of this invention ideal to be applied in the control of distributed generation systems (DGS), flexible AC transmission systems (FACTS), power quality conditioners (PQC) and uninterruptible power supplies (UPS). In all these systems, the fast and precise real time detection of the voltage and/or current sequence components under grid fault conditions is a crucial matter.

Each of three-phase arm of an inverter has first and second switching elements connected in series together at a connection point to the corresponding phase coil of the three-phase motor. Control device turns on the first switching element of the i-th (i is a natural number smaller than four) for a predetermined time period, and determines that the second switching element of the i-th arm has a short fault, when an overcurrent exceeding a predetermined threshold is detected within the predetermined time period. The predetermined time period is shorter than a time period from a time point of turning on the first switching element of the i-th arm to a time point of attaining the predetermined threshold by a current flowing through a path extending from a power supply line through the second switching element of the remaining arm other than the i-th arm to a ground line.

The invention discloses a distributing net single phase earth fault type and a distinguishing method of phase identification, relating to a distributing net single phase earth fault distinguishing method in the field of AC distributing net testing and relaying protection technology. According to the invention, through collecting three-phase voltage of the distributing net system and neutral point voltage of the distributing net system, phase angle of each eigenvector is computed through a special relation, the type of the fault and the phase identification can be fast distinguished through the phase angle distinguishing logic. The inventive working system is that a three-phase bus (000), a grounding transformer (100), a linear side of an arc suppression coil (200) are connected in turn with the earth; a controller (400), a thyristor (300) and a secondary side of an arc suppression coil (200) are connected in turn. The invention is simple in criterion, small in collection quantity, fast in distinguishing speed, high in accuracy, reliable in security, which is suitable for 3-66 KV distributing net based on an aerial line or a power cable.

The invention relates to a method for locating a single-phase disconnection non-ground fault of a power distribution network. After the single-phase disconnection non-ground fault occurs, the positive sequence voltage of the high-voltage side of each distribution transformer after a fault point is far lower than the positive sequence voltage of the high-voltage side of each distribution transformer before the fault point and the positive sequence voltage of the high-voltage side of each distribution transformer of a non-faulty line, and the positive sequence voltage of the low-voltage side of each distribution transformer after the fault point also correspondingly becomes about 50 percent of the positive sequence voltage before the fault point. For three-phase voltage information acquired by different types of measuring devices installed at load points, the positive-sequence component of the voltage of each load point is calculated in real time; and if the positive sequence voltage of a certain load point and the positive sequence voltages of all downstream load points of the load point are obviously reduced at one point, and the positive sequence voltages of upstream load points of the load point are constant, the single-phase disconnection non-ground fault can be determined in an upstream adjacent line connected with the load point. According to the method for locating the single-phase disconnection non-ground fault of the power distribution network disclosed by the invention, new equipment does not need to be equipped; the calculation is simple; and the fault can be located between two load points to realize the diagnosis and the location of the single-phase disconnection non-ground fault.

An electronic electric meter for use in a networked automatic meter reading environment. The electric meter retrofits into existing meter sockets and is available for new meter installations for both single phase and three phase electric power connections. The electric meter utilizes a modular design which allows the interface modules to be changed depending upon the desired communication network interface. The meter measures electricity usage and monitors power quality parameters for transmission to the utility. The gateway node transmits this data to the utility over a commercially available fixed wide area network (WAN). The meter also provides direct communication to the utility over a commercially available network interface that plugs into the meter's backplane or bus system bypassing the local area network communication link and gateway node.

A motor control apparatus comprises a fundamental wave current control system that controls a fundamental wave component of a motor current in an orthogonal coordinate system which rotates in synchronization with a rotation of a 3-phase AC motor, a higher harmonic current control system that controls a higher harmonic component contained in the motor current in an orthogonal coordinate system rotating with a frequency which is an integral multiple of the frequency of the fundamental wave component of the motor current, a voltage command value generating device that generates 3-phase AC voltage command values by adding an output from the fundamental wave current control system and an output from the higher harmonic current control system, a power conversion device that converts a DC source voltage to a 3-phase AC voltage corresponding to the 3-phase AC voltage command values and outputs the 3-phase AC voltage to the 3-phase AC motor, a voltage saturation detection device which detects that an output voltage from the power conversion device is in a saturated state and a gain adjustment device that reduces a current control gain for the higher harmonic current control system if the voltage saturation detection device detects that an output voltage is in a saturated state.

Solar photovoltaic power is collected in a multiple nodal arrangement where the DC output voltage of each node is held constant while the DC current is allowed to vary based upon the maximum power point of the solar cells making up the solar power collectors in each node. The output of each solar power collection node is regulated by a node-isolated step-down current regulator that maintains a constant DC current output while the DC output voltage is allowed to vary. The outputs of all node-isolated step-down current regulators are connected together in series and fed to a plurality of regulated current source inverters that each convert input DC power into a three phase AC output. The AC outputs of the regulated current source inverters are connected to a phase shifting transformation network that supplies three phase electric power to a conventional AC electrical transmission system.

The invention discloses a frequency conversion driving control system and method based on an electrolysis-free capacitive inverter. The method comprises the following steps: detecting system input voltage current, bus voltage, motor phase current and rotating speed; carrying out Clark and Park conversion on three-phase current to obtain d and q axis current; carrying out error adjustment on a given rotating speed and an actual rotating speed; calculating q axis given current according to input voltage current, speed ring output and capacitance; calculating d axis given current according to voltage; calculating d and q axis error current and carrying out PI adjustment to obtain d and q axis actual voltage; limiting amplitude of actual voltage to obtain d and q axis calculated voltage; carrying out error adjustment on the actual voltage and the calculated voltage and taking the result as current ring feedback; carrying out Park inverse conversion on the d and q axis calculated voltage to obtain alpha and beta axis voltage; and modulating the inverter to control a motor. By the frequency conversion driving control system and method based on the electrolysis-free capacitive inverter, the motor can run at high speed in a flux weakening region, a network side high power factor is obtained, a control structure is simplified, and the reliability of the system is improved.

Disclosed are an automatic three-phase unbalanced load compensation experimental device and its control method. The experimental device comprises an automatic compensation device, a load simulation part, and detection, display and control parts. The automatic compensation device comprises power capacitors and intelligent grouping compound switches; the detection, display and control part comprises current transformers, molded case circuit breakers, a three-phase digital display ammeter, a three-phase electric power monitoring instrument, a protocol conversion module, 485 buses, Ethernet cables and an upper computer; the load simulation part comprises phase A, B and C loads which are in star connection and are same in component and circuit connection, an analog output module and a relay output module. Power monitoring instrument and digital ammeter are connected to the grid by circuit breaker and current transformer. The automatic compensation device and load simulation part are connected to the grid in parallel.

The invention discloses a digital electric energy meter checking device based on an analog source tracing method, which is used for the accuracy testing of an electric energy meter based on an IEC61850 standard. The device comprises an AC signal conditioning board, a central control board, an industrial personal computer and a liner power panel which provides power to the device, wherein the AC signal conditioning board carries out front-end low-distortion conversion to three-phase voltage and three-phase current provided by a circumscribed standard power source, and the three-phase voltage and the three-phase current are converted into a voltage signal ranged by the AD analog to digital converter of the rear central control board; the central control board finishes the functions of AC signal sampling, electricity energy accumulation, IEC61850 standard communication, error calculation and data exchange with the industrial personal computer; the industrial personal computer is used for developing a human-computer interface, finishing the functions of giving an order, communicating data and displaying a result and exchanging the order and the data with the central control board via a serial port. The self precision of the checking device reaches 0.05 level, and the magnitude can be upwards traced to the source to higher level of the existing national standard.

A three-level inverter dead time compensation control method is used for compensating the decrease of system performance caused by dead time. According to the topological structure of a three-phase three-level PWM (pulse width modulation) inverter, the method first sets corresponding dead time and determines the on-off delays of power elements in the inverter; the method then considers the tube voltage drops of the power transistors of the inverter and the tube voltage drops of clamping diodes of the inverter and calculates the common voltage expression of the output neutral point of the inverter; afterwards, according to the sector with three-phase current value and a reference voltage vector, the method determines the relational coefficient between voltage error caused by the tube voltage drops of the power transistors, the tube voltage drops of the clamping diodes and the on-off delays of the power transistors and current, and thereby the total dead time compensation time of each phase of the three-level PWM inverter is worked out. The method takes the dead time, the on-off delays of the power elements and the tube voltage drops into full consideration, solves the problem of voltage and current distortion caused by the dead time effect in the three-level inverter, and enhances system performance.

Proposed is a parallel inverter drive system including includes a plurality of inverter drives connected in parallel with each other, in which each inverter drive includes a switch; a PWM controller connected to the switch for controlling switching operations of the switch device according to a duty cycle signal; and a circulating current suppressor for collecting current information associated with the current of each inverter drive and a summation current, and generating an index according to the collected current information and the desired circulating current quantity. A zero-sequence voltage is generated for each phase of a three-phase voltage command according to the index and the voltage command and the operating mode of the inverter drive, thereby injecting the zero-sequence voltage into the voltage command with a feed-forward configuration so as to fix the voltage command. The PWM controller can generate the duty cycle signal according to the fixed voltage command.

The invention discloses a PMSM rotary transformer zero position initial angle calibration method and calibration system. The PMSM rotary transformer zero position initial angle calibration method comprises steps of connecting an PMSM, on which a rotary transformer is installed, to a driving motor, enabling a motor stator of the PMSM to perform three-phase short circuit, using the driving motor to drive the PMSM to rotate forward and maintain at a preset rotation speed, using an electronic control unit to perform sampling on three phase current Ia, Ib and I c and a rotary transformer reading phi read at a same moment, using the rotary transformer reading phi read to perform Park conversion on three phase current Ia, Ib and Ic to obtain current vectors Is,p, calculating a vector angle theta p corresponding the current vector Is,p, using the driving motor to drive the PMSM to rotate backwards and maintaining the rotation at a preset rotation speed, using the electronic control unit to record a vector angle theta n corresponding to a current vector Is,n when the motor is rotated backwards, and calculating that a practical electric rotation angle theta 0 corresponding to the rotary transformer reading zero point angle is a zero position initial angle according to a formula theta 0=(thetap+thetan)/2-180 degree.

The invention discloses a photovoltaic grid-connected inverter low voltage ride through (LVRT) control method, and relates to the field of grid-connected photovoltaic power generation. The method is characterized by comprising a distribution procedure of active power and reactive power in the LVRT process, and procedures about elimination of current peak and protection to an inverter. The procedure of protection to the inverter includes that when a grid is in a grid voltage drop stage or in a grid voltage recovery stage, if an average current value of any phase of three-phase current outputted by the inverter is detected to exceed an average threshold value, a pulse-width modulation (PWM) control signal of the inverter is switched off, and the PWM control signal of the inverter can be recovered after duration of half PWM control signal cycle time; and if an instantaneous value of any phase of the three-phase current of an output end of the inverter is detected to exceed an instantaneous threshold value, the connection between the inverter and the grid can be switched off. The instantaneous threshold value is higher than the average threshold value and the like.

The invention discloses a field failure on-line diagnostic method and system for a permanent magnet synchronous motor. The field failure on-line diagnostic method comprises the steps of (1) sampling a stator three-phase current signal of the motor to be detected, (2) determining a field failure characteristic frequency according to the number of poles of the permanent magnet synchronous motor to be detected, using the field failure characteristic frequency as a field failure characteristic quantity, (3) estimating the frequencies of frequency components in the stator three-phase current signal to be detected, judging whether a field failure happens or not according to whether the field failure characteristic quantity appears or not, and (4) after estimating the amplitudes of the frequency components in the stator three-phase current signal to be detected, calculating the ratios of the amplitudes of the frequency components to the amplitudes of same-frequency components within a same-current range of a motor in the normal state so as to judge the degree of severity of a field failure. The field failure on-line diagnostic system comprises the permanent magnet synchronous motor, a Hall current sensor, a signal conditioning circuit, a data acquisition circuit, a diagnosis control circuit and a display circuit. The field failure on-line diagnostic system is short in sampling time and high in anti-jamming capability, can judge field failures at different rotating speeds and under different load conditions, and is applicable to dynamic on-line monitoring.

A current sampling circuit used for frequency converter comprises six switch pipes, and a sampling resistance is connected in serious at a lower bridge arm output end of at least two phases of direct current bus negative end or frequency converter of the current sampling circuit; a current sampling method of the current sampling circuit includes step of collecting information of current passing through the sampling resistance by the sampling resistance connected in series in the sampling circuit. The invention further provides two schemes, in one scheme, only a sampling resistance is connected in serious at a negative end of the direct current bus of the current sampling circuit, direct current bus current information is collected by the sampling resistance connected in serious at the negative end of the direct current bus, furthermore three-phase current information of a motor is reconstructed; in the other scheme, a sampling resistance is connected in serious at each output end of the three-phase lower bridge arm of the frequency converter, and three-phase load current information is obtained by directly sampling. The invention has simple sampling method, is easy to realize in engineering, and can be applied in any AC motor-driven system of three-phase balance current.

The embodiment of the invention discloses a resonance wave detecting and phase-locking method and a resonance wave detecting and phase-locking method for an active power filter. The method comprises the following steps of: carrying out phase shift filtering to a sampled three-phase voltage signal to obtain a first-grade processing signal; substituting the first-grade processing signal into an sequence-dividing formula to obtain a three-phase voltage fundamental positive sequence component; and adopting a dq synchronous coordinate system to lock phase of the three-phase voltage fundamental positive sequence component. The embodiment of the invention extracts the three-phase voltage fundamental positive sequence component in an unbalanced grid by using a way of dividing sequence first and locking phase consequently, locks phase of the positive sequence component by using a dq synchronous coordinate system phase-locking algorithm to obtain a positive sequence fundamental phase angle and eliminate the influence of grid imbalance on the phase locking link, so that the phase locking precision is wholly improved and the technical effect that the real-time and precise phase locking can also be carried out in the situation of unbalanced voltage in the grid is achieved.

The invention discloses a three-phase rectifier rapid model predictive control method. According to the technical scheme, the method is characterized by including the steps that an output voltage reference value needed by a next moment is acquired according to a three-phase voltage rectifier model and a current reference value, equivalent transformation is conducted on a value function in model prediction control to acquire a value function expression based on output voltage, and lastly an optimal output voltage vector is chosen through a vector zonal method. Specific to the control of a three-phase voltage rectifier, the model predictive control method can effectively simplify the steps of traditional model predictive control. Therefore, the control algorithm structure is simple, calculation amount is small, calculation time is remarkably shortened, response speed of a control system is guaranteed, stable operation of the control system is guaranteed, and conditions are provided for expanding other auxiliary control algorithms.

The invention belongs to the field of converter control, and relates to a simplified model forecasting control method of a network voltage unbalance three-level rectifier. The simplified model forecasting control method of the network voltage unbalance three-level rectifier comprises the steps that (1) positive and negative sequence separation is carried out on three-phase network voltage and current to obtain positive and negative sequence components; (2) coordinate transformation is carried out on three-phase positive sequence voltage and current to obtain positive sequence voltage and current under a two-phase static coordinate system; (3) according to the three-phase positive sequence voltage, three levels are changed into two levels in an order reduction mode through reference voltage; (4) an active power reference value and a current reference value are calculated; (5) a current forecasting value of the rectifier, a direct current side capacitance voltage forecasting value and the changing number of switching elements are calculated; (6) current control, neutral-point potential control and switching frequency control are forecast according to a model, and the best switching state is selected. The simplified model forecasting control method of the network voltage unbalance three-level rectifier can effectively suppress double-frequency fluctuation of input power of the rectifier, lower the switching frequency of the elements, shorten circulation calculation time, control neutral-point potential balance, and improve the operation efficiency of the system.

The invention discloses a method and a device for controlling three-phase unbalanced current of a virtual synchronous generator. The method comprises the following steps: establishing a rotor movement equation of the virtual synchronous generator (VSG) and a virtual excitation equation of the VSG; decomposing unbalanced voltage of a power grid into positive sequence voltage, negative sequence voltage, zero sequence voltage and corresponding phase-sequence current, and decomposing active power and reactive power output by the VSG to analyze an encountered imbalance problem; calculating a reference instruction of dq axis current according to the output three-phase voltage signal; and converting the reference instruction of the current into a pulse-width modulation (PWM) voltage modulation signal through a self-designed current inner ring, and controlling the virtual synchronous generator to run through the PWM voltage modulation signal, so as to enable the output three-phase current of the virtual synchronous generator to reach the balance. According to the control method disclosed by the embodiment of the invention, the VSG can still output three-phase balanced current when the three-phase voltage of the power grid is unbalanced, so that the operation safety of the power grid can be relatively well ensured; and the method and the device are safe, reliable, simple and convenient.