CN111600284A - Excitation inrush current suppression method applied to power frequency transformer in controllable inversion - Google Patents
Excitation inrush current suppression method applied to power frequency transformer in controllable inversion Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/02—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
- H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
- H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
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Abstract
The invention discloses a magnetizing inrush current suppression method applied to an industrial frequency transformer in controllable inversion, which comprises the steps that a singlechip microcomputer is arranged on the power supply side of the industrial frequency transformer to control an H-bridge circuit, so that the H-bridge circuit can output industrial frequency voltage; soft starting; cutting off the transformer when the primary side voltage of the power frequency transformer is at a specific zero crossing point, recording and storing the direction of the zero crossing point, wherein the transformer is also at the specific voltage zero crossing point when being put into; detecting the power supply state of the power grid based on the AD sampling unit, and executing corresponding actions according to the power supply state of the power grid; when the power grid recovers power supply, based on the AD sampling unit, when the power grid is judged to be stably operated, the load is put into the power grid. The invention actively controls the zero crossing point of the cut-off transformer and the input transformer to change the remanence along the remanence curve to the attenuation direction, obviously reduces the excitation inrush current when the transformer is input, controls the H-bridge circuit to output the primary side voltage of the transformer through the singlechip, and has more flexible operation and higher control precision.
Description
Technical Field
The invention relates to the field of safety guarantee of distribution network automation systems, in particular to a magnetizing inrush current suppression method applied to an industrial frequency transformer in controllable inversion.
Background
Terminal power supply: when the master station issues a test calling instruction, the power grid acquisition terminal must be capable of ensuring that the current meter reading data is uploaded. The terminal power supply can continuously and stably supply power to the acquisition terminal when the power grid is powered off so as to ensure that the acquisition terminal can continuously receive meter reading instructions and realize real-time uploading of meter reading data. However, residual magnetism is left in the magnetic core due to the hysteresis characteristic of the magnetic core material of the transformer, and the magnetic flux density in the magnetic core cannot change suddenly when the power frequency transformer is switched on, so that the magnetizing inrush current phenomenon is generated in the winding on the power supply side of the transformer.
Excitation inrush current: the magnetizing inrush current is a transient current generated in a winding of a transformer due to the nonlinear saturation characteristics of the core of the transformer and the influence of residual magnetic flux in the core before the transformer is put into operation when the transformer is charged at a full voltage. The current can reach 8-10 times of rated current at most, contains large harmonic components (mainly second harmonic and third harmonic), can generate great harm to the mechanical stability and the insulation strength of a transformer winding, and often causes differential protection action.
Differential protection: differential protection is the primary protection of a transformer, and provides quick-break protection against excessive currents, such as short-circuit currents, to prevent high currents from deforming the transformer windings. At the moment of closing the no-load transformer, a high current is randomly generated, and the normal range can be returned within a period of time. This high current is not a short-circuit current, but is sufficient to cause differential protection of the transformer, which results in that the transformer is protected from starting at the moment of starting.
Phase selection and switching-on: the core idea is to perform switching on at the zero crossing point of the magnetic flux, namely two peak points (pi/2 or 3 pi/2) of the sinusoidal voltage, so as to prevent the generation of transient magnetic flux and avoid the generation of no-load switching-on impact current. However, due to the inherent mechanical characteristics of the breaker switch, closing delay is often caused, so that the optimal closing time is missed and bias is generated. And the closing time of the phase selection closing technology is related to the residual magnetism in the magnetic core, but the residual magnetism in the transformer is difficult to measure, so that the application is still inconvenient.
Disclosure of Invention
Aiming at the problems, the invention overcomes the defects of the prior art and provides a magnetizing inrush current suppression method applied to an operating frequency transformer in controllable inversion. According to the method, the working state of the power grid is detected by sampling the voltage of the power grid, and the relay of the load power supply circuit is controlled and switched by adopting the single chip microcomputer, so that the continuous power supply of the load is realized. The single chip microcomputer is adopted to control the H-bridge circuit to output the primary side alternating voltage of the transformer, the switching point of the alternating voltage is actively controlled, the input and the cut-off of the alternating voltage of the transformer are ensured to be at the specific zero crossing point, and the magnetic flux of the magnetic core of the transformer when the standby voltage is input is reduced, so that the excitation inrush current of the transformer is inhibited, the differential protection action is avoided, and the working stability and the reliability of the industrial frequency transformer in the controllable inversion can be ensured.
The invention adopts the following technical scheme to solve the technical problems:
a strategy for reducing the magnetizing inrush current of a power frequency transformer applied to controllable inversion comprises the following steps,
step one, arranging a single chip microcomputer on a power supply side of a power frequency transformer to control an H-bridge circuit so that the H-bridge circuit can output power frequency voltage;
step two, soft starting, namely, boosting the primary side voltage of the power frequency transformer to a rated voltage and stably operating for a period of time in a no-load mode;
cutting off the transformer when the primary side voltage of the power frequency transformer crosses a specific zero point, and recording and storing the direction of the zero point;
and step four, detecting the power supply state of the power grid based on the AD sampling unit, and executing corresponding actions according to the power supply state of the power grid.
Step five, when the power grid recovers power supply, based on the AD sampling unit, when the power grid is judged to be stably operated, the load is put into the power grid, and after the load is put into the power grid, the step four is executed in a circulating mode;
in the first step, PWM is modulated through singlechip control, so that an H-bridge circuit outputs power frequency voltage and harmonic compensation is carried out by adopting an LC filter, namely, the high frequency to be cut off is not passed through by using a method of capacitance absorption and inductance obstruction, and the low frequency to be cut off is passed through by using the characteristics of high resistance of a capacitor and low resistance of an inductor;
in the second step, the transformer soft start is to reduce the initial voltage of the transformer when the transformer is put into operation by controlling the H-bridge circuit through the single chip microcomputer, and gradually increase the voltage to the rated voltage according to a set curve.
In the third step, because the switching of the transformer is controlled by adopting PWM conversion, in order to ensure the stable output of the H-bridge circuit, the invention selects a specific zero crossing point of the primary side voltage of the power frequency transformer to switch the alternating current power supply of the transformer; the specific zero crossing point is the primary side voltage zero crossing point of the power frequency transformer, the direction of the voltage zero crossing point can be from negative to positive zero crossing point, or from positive to negative zero crossing point, but the directions of the voltage zero crossing points of the transformer which is cut off and put into the transformer are ensured to be consistent.
In the fourth step, the AD sampling is to sample the voltage of the power grid by designing a differential sampling circuit, and a sampling value is input to an AD conversion unit of the single chip microcomputer; the corresponding operations performed are:
if the power grid normally supplies power, the PWM wave is output by the H-bridge circuit every hour under the control of the single chip microcomputer, whether the H-bridge is short-circuited or not is self-detected, and wave sending is stopped at a specific zero crossing point of output voltage;
if the power grid is powered off, after the power grid is powered off for n periods, the transformer is put into a specific voltage zero-crossing point which is the same as the primary side alternating voltage of the cut-off transformer, and a load is put into the standby power unit;
the transformer is switched on by selecting a voltage zero-crossing point which is the same as the cut-off of the primary side alternating voltage of the transformer, so as to inhibit transient magnetic flux generated at the moment of switching on the transformer; the alternating voltage output by the H bridge is selected to be input at a specific alternating voltage zero crossing point, because the voltage at two ends of the filter capacitor cannot be suddenly changed at the switching moment, and the current in the inductor cannot be suddenly changed.
The invention has the beneficial effects that: the invention provides a magnetizing inrush current suppression method applied to an operating frequency transformer in controllable inversion, residual magnetism of a magnetic core of the transformer is not required to be estimated, the transformer is cut off and put into the transformer and is selected at a specific zero crossing point of voltage, so that the residual magnetism changes along a residual magnetism curve to the attenuation direction, the magnetizing inrush current when the transformer is put into the transformer is obviously reduced, differential protection action is avoided, and the working stability and reliability of a standby power supply can be ensured; the PWM is adopted to convert and output the primary side voltage of the transformer, so that the closing time of the circuit breaker and the residual magnetism of an iron core in the traditional strategy are not considered, and the control precision is higher; in addition, the application environment of the invention is that when the power grid is cut off, the standby power supply supplies power to the power utilization acquisition terminal, the cutting point of the alternating voltage of the power frequency transformer can be actively controlled, the phase angle of the cutting point of the voltage can be obtained by monitoring the applied voltage in real time, and the operation is more flexible.
Drawings
FIG. 1 is a schematic diagram of an application environment of the present invention;
FIG. 2 is a general flow chart of the method for suppressing the magnetizing inrush current of the controllable power frequency transformer according to the present invention;
FIG. 3 is a graph of a soft start voltage waveform in the strategy of the present invention;
FIG. 4 is a schematic diagram of a backup power switching point selection strategy according to the present invention;
FIG. 5 is a schematic diagram of the primary side input voltage and the magnetizing inrush current of the transformer winding according to the present invention with the suppression strategy;
FIG. 6 shows the primary side input voltage of the transformer winding during the power grid operation, transformer no-load and load input,
The waveform diagram of the transformer output voltage and the magnetizing inrush current.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and examples to specifically illustrate the technical solutions of the present invention. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.
A magnetizing inrush current suppression method applied to an operating frequency transformer in controllable inversion is disclosed, an application scene schematic diagram is shown in fig. 1, a general scheme design flow diagram is shown in fig. 2, and scheme implementation steps are described in detail below.
Step one, arranging a single chip microcomputer on a power supply side of a power frequency transformer to control an H-bridge circuit to output power frequency voltage;
the PWM is controlled and modulated by a singlechip, so that the H-bridge circuit outputs power frequency voltage, and harmonic compensation is performed by adopting an LC filter, namely, the high frequency to be cut off is not passed by using a method of capacitance absorption and inductance obstruction, and the low frequency to be cut off is passed by using the characteristics of high resistance of a capacitor and low resistance of an inductor;
step two, soft starting, namely, boosting the primary side voltage of the power frequency transformer to a rated voltage and stably operating for a period of time in a no-load mode;
because the size and the direction of the residual magnetism of the magnetic core of the transformer can not be determined when the transformer is put into use for the first time, in order to inhibit the transformer from generating excitation inrush current when the transformer is started for the first time, a soft starting method is adopted to put into the transformer. The H-bridge circuit is controlled by the single chip microcomputer, the initial voltage of the transformer during the switching-in process is reduced, the voltage is gradually increased to the rated voltage according to a set curve, and a preset soft start voltage change curve is shown in figure 3.
Cutting off the transformer when the primary side voltage of the power frequency transformer crosses a specific zero point, and recording and storing the direction of the zero point;
the single chip microcomputer is adopted to control PWM output so as to control the switching of the transformer alternating current power supply, the H bridge output alternating current voltage is connected to the primary side of the transformer through the LC filter circuit, and the transformer alternating current power supply is switched at a specific zero crossing point of the primary side voltage of the power frequency transformer in order to ensure the stable output of the H bridge circuit;
the specific zero crossing point is the primary side alternating voltage zero crossing point of the power frequency transformer, the direction of the specific zero crossing point can be from negative to positive zero crossing point, and also can be from positive to negative zero crossing point, but the directions of the voltage zero crossing points of the transformer cut-off and input are ensured to be consistent, as shown in fig. 4, the primary side alternating voltage of the transformer is cut off by adopting the voltage zero crossing point from negative to positive in case implementation.
Detecting the power supply state of the power grid based on the AD sampling unit, and executing corresponding actions according to the power supply state of the power grid;
sampling the voltage of the power grid by using a designed differential sampling circuit, and inputting a sampling value to an AD conversion unit of the single chip microcomputer;
the corresponding operations performed are:
if the power grid normally supplies power, the PWM wave is output by the H-bridge circuit every hour under the control of the single chip microcomputer, whether the H-bridge is short-circuited or not is self-detected, and wave sending is stopped at a specific zero crossing point of output voltage;
if the power grid is powered off, after the power grid is powered off for n periods, the transformer is put into a specific voltage zero-crossing point which is the same as the primary side alternating voltage of the cut-off transformer, and a load is put into the standby power unit;
because the voltage at the two ends of the filter capacitor can not change suddenly at the switching moment and the current in the inductor can not change suddenly, the alternating voltage output by the H bridge is switched at a specific voltage zero crossing point. On the other hand, in order to suppress transient magnetic flux generated at the moment of transformer input and minimize magnetic flux of the transformer core during switching, the specific calculation formula is as follows:
where Φ is the magnetic flux of the transformer core, ΦmAt the maximum value of the steady-state magnetic flux,
is a transient magnetic flux of phirRemanence of magnetic core, related to the moment of cutting off the AC power supply of transformermsin α is a dc bias, which is a magnetic flux necessary for ensuring that the magnetic flux of the transformer core does not abruptly change, and is related to the closing timing, ω is the frequency of the ac power supply, α is the closing angle of the transformer, R1 is the resistance of the primary winding, L1 is the inductance of the primary winding, and-R1/L1 is the attenuation constant of the bias.
By the formula, when the transformer is put into the transformer at the specific voltage zero-crossing point which is the same as the primary side alternating voltage of the cut-off transformer, the residual magnetism and the direct current magnetic bias can be mutually counteracted, and the magnetic flux of the magnetic core of the transformer is stable magnetic flux.
FIG. 5 is a schematic diagram of the primary-side input voltage and the magnetizing inrush current of the transformer winding according to the suppression strategy of the present invention; in the figure, when the power grid is cut off and the standby circuit is started and the load is put into the standby circuit, the magnetizing inrush current is slightly increased, but the next period is recovered to be the state of the exciting current in the stable operation.
Step five, when the power grid recovers power supply, based on the AD sampling unit, when the power grid is judged to be stably operated, the load is put into the power grid, and after the load is put into the power grid, the step four is executed in a circulating mode;
fig. 6 is a waveform diagram showing the primary side input voltage, the transformer output voltage and the magnetizing inrush current of the transformer winding during the power grid operating state, the transformer no-load and the load input of the present invention.
In summary, the present invention provides a method for suppressing inrush current of an rf transformer in a controllable inverter, in which a single chip is used to control an H-bridge circuit to output an ac voltage at a power frequency, so as to ensure that the amplitude and phase angle of the ac voltage at the primary side of the transformer are controllable; when the standby power is started for the first time, the primary side voltage of the power frequency transformer is raised to a rated voltage by using a soft start technology and stably operates for a period of time in a no-load mode; by actively controlling the switching point of the primary side voltage of the transformer, the input and the cut-off of the alternating voltage of the transformer are ensured to be both at the specific zero crossing point, so that the excitation inrush current of the power frequency transformer is reduced, the differential protection action is avoided, and the working stability and the reliability of the standby power supply can be ensured; and detecting the working state of the power grid according to the voltage sampling of the power grid, and controlling a relay of a switching load power supply circuit by adopting a single chip microcomputer to realize continuous power supply of the load.
The above embodiments are illustrative of specific embodiments of the present invention, and are not restrictive of the present invention, and those skilled in the relevant art can make various changes and modifications without departing from the spirit and scope of the present invention to obtain corresponding equivalent technical solutions, and therefore all equivalent technical solutions should be included in the scope of the present invention.
Claims (5)
1. A magnetizing inrush current suppression method applied to an operating frequency transformer in controllable inversion is characterized by comprising the following steps: comprises the following steps of (a) carrying out,
step one, arranging a single chip microcomputer on a power supply side of a power frequency transformer to control an H-bridge circuit to output power frequency voltage;
step two, soft starting, namely, boosting the primary side voltage of the power frequency transformer to a rated voltage and stably operating for a period of time in a no-load mode;
cutting off the transformer when the primary side voltage of the power frequency transformer crosses a specific zero point, and recording and storing the direction of the zero point;
and step four, detecting the power supply state of the power grid based on the AD sampling unit, and executing corresponding actions according to the power supply state of the power grid.
And step five, when the power grid recovers power supply, based on the AD sampling unit, when the power grid is judged to be stably operated, putting the load into the power grid, and after putting the load into the power grid, circularly executing the step four.
2. The method for suppressing the magnetizing inrush current of the medium frequency transformer applied to the controllable inverter as claimed in claim 1, wherein: in the first step, PWM is modulated through singlechip control, so that the H-bridge circuit outputs power frequency voltage and harmonic compensation is carried out by adopting an LC filter, namely, the high frequency to be cut off is not passed through by using a method of capacitance absorption and inductance obstruction, and the low frequency to be cut off is passed through by using the characteristics of high resistance of a capacitor and low resistance of an inductor.
3. The method for suppressing the magnetizing inrush current of the medium frequency transformer applied to the controllable inverter as claimed in claim 1, wherein: in the second step, the transformer soft start is to reduce the initial voltage of the transformer when the transformer is put into operation by controlling the H-bridge circuit through the single chip microcomputer, and gradually increase the voltage to the rated voltage according to a set curve.
4. The method for suppressing the magnetizing inrush current of the medium frequency transformer applied to the controllable inverter as claimed in claim 1, wherein: in the third step, because the switching of the transformer is controlled by adopting PWM conversion, in order to ensure the stable output of the H-bridge circuit, the invention selects a specific zero crossing point of the primary side voltage of the power frequency transformer to switch the alternating current power supply of the transformer; the specific zero crossing point is the primary side voltage zero crossing point of the power frequency transformer, the direction of the voltage zero crossing point can be from negative to positive zero crossing point, or from positive to negative zero crossing point, but the directions of the voltage zero crossing points of the transformer which is cut off and put into the transformer are ensured to be consistent.
5. The method for suppressing the magnetizing inrush current of the medium frequency transformer applied to the controllable inverter as claimed in claim 1, wherein: in the fourth step, the AD sampling is to sample the voltage of the power grid by designing a differential sampling circuit, and a sampling value is input to an AD conversion unit of the single chip microcomputer; the corresponding operations performed are:
if the power grid normally supplies power, the PWM wave is output by the H-bridge circuit every hour under the control of the single chip microcomputer, whether the H-bridge is short-circuited or not is self-detected, and wave sending is stopped at a specific zero crossing point of output voltage;
if the power grid is powered off, after the power grid is powered off for n periods, the transformer is put into a specific voltage zero-crossing point which is the same as the primary side alternating voltage of the cut-off transformer, and a load is put into the standby power unit;
the transformer is switched on by selecting a voltage zero-crossing point which is the same as the cut-off of the primary side alternating voltage of the transformer, so as to inhibit transient magnetic flux generated at the moment of switching on the transformer; the alternating voltage output by the H bridge is selected to be input at a specific alternating voltage zero crossing point, because the voltage at two ends of the filter capacitor cannot be suddenly changed at the switching moment, and the current in the inductor cannot be suddenly changed.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116094297A (en) * | 2022-12-23 | 2023-05-09 | 华为数字能源技术有限公司 | Inverter, power grid power supply system and excitation surge current control method |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116094297A (en) * | 2022-12-23 | 2023-05-09 | 华为数字能源技术有限公司 | Inverter, power grid power supply system and excitation surge current control method |
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