69 results about "Current decay" patented technology

A method of determining the impedance, inductance, and resistance of the network connecting an electrical power supply to an electric arc welding station including an electrode and a workpiece, wherein the method-comprises: shorting the electrode to the workpiece; creating at least one waveform including a first state operating the power supply at constant current of a selected value and a second state operating the power supply at a low value of current or open circuit voltage whereby the current decays from the selected value along a decay path indicative of di/dt; obtaining the average current Iavg and average resistance Ravg during the first state; selecting a portion of the decay path; sampling the instantaneous current for a number of times on the path during the second state to read the rate of the decay; and, using the average current and the average resistance with the rate of decay to obtain the inductance of the network.

A method for determining a concentration of an analyte is disclosed. The method includes applying a potential excitation to a fluid sample containing an analyte and determining if a current decay curve associated with the fluid sample has entered an analyte depletion stage. The method also includes measuring a plurality of current values associated with the fluid sample during the analyte depletion stage and calculating an analyte concentration based on at least one of the plurality of current values.

A synchronous DC-to-DC converter includes an inductor coupled to receive an input voltage, a first transistor having a source coupled to a first reference voltage and a drain coupled to the inductor, and a second transistor having a source coupled to an output conductor to produce an output voltage and a drain coupled to the inductor. A feedback signal representative of a value of the output voltage is generated, and a switch control signal is produced in response to the input voltage and a second reference voltage. The second transistor is turned off in response to the switch control signal each time the inductor current has decayed to zero to prevent reverse current flow through the inductor. A regulating signal indicates whether or not the feedback voltage exceeds the second reference voltage, to regulate the output voltage in a pulse-frequency modulation mode.

A method and associated stimulation device for ensuring firing of an action potential in an intended physiological target activated by a stimulus pulse generated by an electrode of a non-invasive surface based stimulation device irrespective of skin-to-electrode impedance by: (i) increasing internal impedance of the stimulation device so as to widen a Chronaxie time period thereby ensuring firing of the action potential of the intended physiological target irrespective of the skin-to-electrode impedance; and/or (ii) generating a stimulation waveform that optimizes a non-zero average current (e.g., non-zero slope of the envelope of the stimulation waveform) during preferably substantially the entire current decay of the stimulus pulse.

A wide gain range current digital-to-analog converter (DAC) is presented that includes a unit current cell having a current source module biased by a current source voltage bias, a differential switch module, a main cascode module biased by a first bias voltage and an attenuation cascode module biased by a second bias voltage, configured such that a particular current gain range is obtained at the main cascode module output when a unit current cell current is at or above a current threshold. The output current at the attenuation cascode module output can be input into a current attenuator when the unit current cell current is below the current threshold to obtain additional current gain range. The current attenuator can include a plurality of attenuator cells that can be programmed to a desired level of current gain in linear decibels or linear step intervals. Smaller step sizes can be obtained by programming a current source within the step intervals.

The invention is a testing method and testing circuit of motor, the motor includes a stator and a rotor, the stator possesses a winding, the winding generates a reversing electromotive force when rotor rotates, the testing circuit includes: a controller which is used to receive a activating signal to drive a current to the winding to make rotor rotate, when the rotor achieves definite speed, drive current is stopped to make current degenerated, and when the current in the winding is degenerated to zero, measuring the end voltage of the winding to be a uncompensated reversing electromotive force, and based on voltage of the winding, the value of the rotor can compensate the reversing electromotive force to obtain the reversing electromotive force; and a signal conditioning circuit is coupled to the motor and the controller and condition the voltage signal; thereinto, using the controller to analyze the reversing electromotive force and select at least one character values of the reversing electromotive force, and comparing the at least one character values with the corresponding character value of expected reversing electromotive force to decide whether the charge magnetism of motor is eligible.

The invention discloses a three level integration gate commutation SCR potential source converter bridge arm through protector, the bridge arm through protector is parallel-connected in the direct-current circuit of a three level integration gate commutation SCR potential source converter which is formed by the parallel connection of a rectifier, a direct-current filter electric capacity and a inverter in turn, and consists of a protection unit, a bridge arm through protection control unit which is connected with the protection unit, and a plurality of bridge arm through signal detection unit which is connected with the bridge arm through protection control unit. The invention can rapidly bypasses and reduces the short-circuit current of a through bridge arm; bypasses a reverse surge current produced by a direct-current circuit inductance; consumes the direct current bus energy and speeds up the decay process of surge current; after examining the bridge arm goes nonstop, can trigger the bypass thyristor to drain direct current energy through the bypass, and sends out the alarm to the system, causes the system interconnection protection. When occurring the breakdown that the bridge arm goes nonstop, the invention can protect the three-level IGCT potential source medium voltage frequency converter effectively.

The invention discloses a primary cut-out state monitoring method, which comprises following steps: using existing fault recording apparatus and digital protective-relay device in converting station automatic system to record normal divided brake current decay process; using recorded data to calculate circuit breaker opening time; then estimating circuit breaker state according to opening time of circuit breaker and opening time trend in some time.

A method of detecting a rotor condition of a dc motor is provided. The motor 14 is part of a motor control circuit 10 having a free-wheeling diode 20 in parallel with the motor 14. The method establishes a threshold voltage for back emf voltage evaluation. The motor is energized to operate at a certain speed. Current is cut-off to the motor via a switch 16 for a time sufficient for current through the free-wheeling diode to decay to zero. The back emf voltage detected at leads of the motor is then compared via a comparator 21 to the threshold voltage.

The present invention discloses a direct-current power transmission protection device, including a resistor unit and a bidirectional circulation current switch unit, and the resistor unit and the bidirectional circulation current switch unit being connected in parallel to form the protection device, where at least one resistor is cascaded to form the resistor unit, and at least one bidirectional circulation current switch is cascaded to form the bidirectional circulation current switch unit. In addition, the present invention also provides a converter including the protection device, and at least one protection device is connected in series in each phase unit. The present invention provides the protection device, the converter and a protection method for flexible direct-current power transmission, which can rapidly and effectively suppress direct-current short circuit current and damp current oscillation, and not only can better protect equipment safety, but also can greatly shorten fault current attenuation time, thus shortening direct-current shutdown time and further decreasing economic loss and system destabilization risk caused by shutdown to the max. Moreover, the protection device is structurally simple and low in cost, and has good implementability and economic efficiency.

A motor driving apparatus for constant-current control of a current of a coil of a motor, including: a detector detecting the current; and a controller for controlling every first cycle to feed the coil until the current reaches a target value, and to decay the current after the current reaches the target value, wherein the controller selects, every second cycle shorter than the first cycle, between decaying the current in a first mode, and decaying the current in a second mode of which a decay rate is lower than the first mode, and wherein the controller decays the current in the first mode when the current is equal to or higher than a predetermined threshold, and decays the current in the second mode when the current is lower than the predetermined threshold.

The invention discloses an improved MMC (modular multi-level converter) structure with direct current fault clearing capacity. The improved MMC structure is characterized in that on the basis of a double-thyristor method, an accelerating current-limiting module is connected in series into each arm of an MMC; during normal operation of a system, all thyristors are in a disconnected state, an IGBT (insulated gate bipolar transistor) in each accelerating current-limiting module is in a connected state, and a current-limiting resistor Rc is in a bypass state all along; when a fault occurs on the direct current side of the system, all the IGBTs Ta and Tb in each MMC sub-module are disconnected and all the thyristors are connected, fault current is prevented from being fed into the direct current fault point by a direct current side power supply, meanwhile, all the IGBTs in the accelerating current-limiting modules of six arms are disconnected simultaneously, the accelerating current-limiting resistor Rc is added, and the fault isolation speed is increased and overcurrent on the direct current side is prevented. The improved MMC structure is applicable to all the direct current fault types, and the protection range is enlarged; meanwhile, the fault current attenuation speed is increased, and time for fault isolation is shortened greatly; overcurrent on the direct current side is reduced, and overcurrent harm on the direct current side is reduced greatly.

A control circuit (10) for controlling the residual or tail current decay in a single phase or polyphase SRM winding when a phase is switched from active to inactive. A Hall-effect type sensor (30) senses rotor position of the SRM. Current flows through a winding (W) of the motor when the motor phase winding is active; and, current flow into the winding decays to zero when the phase becomes inactive. Semiconductor switches (22) direct current flow into the winding when the phase is active and then redirect residual energy in the winding between an energy recovery circuit and an energy dissipation circuit when the phase becomes inactive. A PWM signal generator (44) provides PWM operating signals to the switches to control current flow first into the winding and then between the recovery and dissipation circuits. A control module (42), or microprocessor (52) with a PWM output, is responsive to rotor position information for controlling operation of the PWM signal generator. The signal generator provides PWM signals having one set of signal characteristics when there is current flow to the winding and a different set of characteristics when there is not. This produces alternate intervals of zero voltage and forced commutation residual current decay while the phase is inactive. During the decay interval, both the PWM frequency and pulse duty cycle are variable to produce a current decay scheme which eliminates ringing and motor noise.

Stepper motor winding current regulation methods and apparatus continuously and bi-directionally sense winding current to determine both the magnitude of the winding current and the slope of a waveform representing the winding current. The magnitude and slope information is used to more precisely control periods of current rise and characteristics of fast and slow current decay during pulse-width modulation (“PWM”) regulation cycles. Winding current rise and decay shaping is based upon the sensed magnitude of the winding current, the magnitude of the winding current regulation set-point ITRIP, whether the sensed winding current is greater than or less than ITRIP at a selected sampling time, whether the sensed winding current is increasing or decreasing when a waveform of the sensed winding current crosses over ITRIP, and whether or not the magnitude of ITRIP changes during a PWM cycle in response to a receipt of a subsequent DAC code.

Due to the radiation, the resin in the radiograph undergoes a change in properties. Such property changes include light reflectance and light transmittance attenuation of the resin. One consequence of the change in resin properties is a reduction in the output current of the detector and affects the operating life of the detector. Provided is a radiation detector and a CT device, which have a small attenuation of the output current of the detector even under a large amount of radiation, and have a long working life. A cured mixture of rutile-type titanium oxide powder and polyester resin was used for the light reflective material covering the scintillator. Also, polyester resin is used to bond the scintillator and the semiconductor photodetection element.

The invention provides a method for turning on/off an electro-mechanical integrated high-voltage direct-current circuit breaker. The method comprises the following steps: when a short circuit failure occurs at a high-voltage direct-current side and current and a current rise gradient reach corresponding on/off set values, a super-fast mechanical switch is immediately activated to separate contacts in a super-high instantaneous separating speed, a physical clearance is formed, electric arcs are produced, and an on/off command is instantly sent to a power electronic switch; short circuit current is quickly disconnected by the power electronic switch so as to quickly extinguish the electric arcs between the contacts of the super-fast mechanical switch and form an isolation fracture; when the contacts of the super-fast mechanical switch are separated to a final breaking position and the current in a lightning arrester is attenuated to zero, the circuit breaker finishes the whole on/off process, and a high-voltage direct-current power transmission power grid is isolated from the failure circuit. Optimal matching can be carried out in the comprehensive consideration of the cost-to-performance ratios of different elements. The elements can be reduced as far as possible, the size is reduced, the weight is reduced, and the reliability is improved. A novel means is created for the research and development of future high-voltage switch products.

A power converter operable to draw an input current that is in phase with an input voltage of the power converter and proportional to a voltage of the input voltage of the power converter includes a drive switch, a waveform generator, and a current shaping circuit. The drive switch is connected between an input inductor and ground and draws current through the input inductor when turned on. The current shaping circuit provides an on-time of the drive switch for a next cycle of the drive switch as a function of an input current decay time, a switching period of the waveform generator, and an output voltage of the power converter. The waveform generator is responsive to the on-time provided by the current shaping circuit for selectively turning the drive switch on and off to cycle the drive switch as a function of the received on-time.

The method includes the following steps. The relation curve between the grid voltage and the attenuation rate of the reading current is decided. The actual grid voltage and its relevant attenuation rate of the reading current are predicted. The accelerated test grid voltage and the test time relevant to the actual grid voltage are solved from the said relation curve. The test is carried out continuously in the test time number the accelerated test grid voltage in order to measure the reading current related as well as determine whether the memory is in effect or not. Thus, the reliability testing for the non-volatile memory is completed.

A technique for de-gaussing the pole tips and yoke of a write transducer in a perpendicular magnetic recording system is provided. An oscillator in the read channel is configured to produce an adjustable signal pattern output to the preamplifier when a write operation ends for a given time and at a predetermined frequency, such that as the preamplifier write current decays, it decays with transitions (polarity reversals). This results in a decaying AC field being applied to the write transducer at the end of a media write operation, effectively de-gaussing it and reducing the effects of remanent magnetization remaining in the poles and yoke of the magnetic recording head after a write current is turned off. This defeats a potential pole tip lockup or yoke lockup circumstance in the magnetic recording media which can result in an inability to write further data or a possible erasure of valid data on the hard disk with which the write head is associated.

A current attenuation mode detection circuit of a motor drive chip comprises a current attenuation time control circuit, an external parallel connection circuit and a digital logic control circuit, wherein the current attenuation time control circuit comprises a plurality of NMOS (N-channel Metal Oxide Semiconductor) transistors, a plurality of PMOS (P-channel Metal Oxide Semiconductor) transistors, a core circuit and a current mirror structure, wherein the external parallel connection circuit includes a capacitor CT and a resistor RT, and is connected with the current attenuation time control circuit; the digital logic control circuit includes a comparer, a latch, and a logic gate circuit; the input signal of the digital logic control circuit is the output signals of both the current attenuation time control circuit and the external parallel connection circuit; the output switch signal of the digital logic control circuit is still fed back to the current attenuation time control circuit; the current attenuation time depends on the CT and the RT; the fast attenuation time and the slow attenuation time are controlled by the current attenuation time control circuit and the digital logic control circuit together. The current attenuation mode detection circuit provided by the invention realizes switching in intelligent control between current rise process and current attenuation process according to motor operating speed.