CN116154862B - Control method and system for accessing converter to power grid and readable storage medium - Google Patents
Control method and system for accessing converter to power grid and readable storage medium Download PDFInfo
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- CN116154862B CN116154862B CN202310427350.5A CN202310427350A CN116154862B CN 116154862 B CN116154862 B CN 116154862B CN 202310427350 A CN202310427350 A CN 202310427350A CN 116154862 B CN116154862 B CN 116154862B
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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
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/40—Synchronising a generator for connection to a network or to another generator
- H02J3/44—Synchronising a generator for connection to a network or to another generator with means for ensuring correct phase sequence
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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
- H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
- H02J13/00002—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by monitoring
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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
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
- H02M7/5395—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
Abstract
The invention provides a control method, a system and a readable storage medium for accessing a converter into a power grid, and relates to the technical field of solar energy, wherein the method comprises the steps of monitoring input voltage of the converter and instantaneous value of the power grid voltage; carrying out phase locking on the power grid voltage instantaneous value to obtain the phase of the power grid voltage instantaneous value; coordinate transformation is carried out on the instantaneous value of the power grid voltage, and transformed voltage is obtained; PWM modulation is carried out according to the phase, the conversion voltage and the input voltage, and a first driving wave of a converter switching device is generated; according to the first driving wave, the converter outputs following voltage and controls the access switch to be closed. Before the switch is closed, the output voltage of the converter is not required to be monitored, the cost of an acquisition circuit is reduced, a closed-loop control adjusting link is not required, the operation process is simplified, an alternating-current voltage waveform which is closer to the instantaneous value of the power grid voltage than the traditional method can be obtained, the converters at the two sides of the access switch can be stably connected with the power grid when the access switch is closed, and the unstable problem is avoided.
Description
Technical Field
The invention relates to the technical field of solar energy, in particular to a control method and system for accessing a converter to a power grid and a readable storage medium.
Background
The solar photovoltaic power generation system can be connected with a conventional power grid to jointly bear the power supply task. The converter inverts the direct current generated by the photovoltaic system into sinusoidal alternating current, the generated alternating current can be directly supplied to an alternating current load, and then the rest electric energy is input into a power grid, or all the generated electric energy is directly input into the power grid.
However, in order to ensure the stability of the switching-in process of the current transformer, the prior art mainly includes that three characteristic parameters of amplitude, frequency and phase of the voltage of the power grid are sampled before the switching-in switch acts, a sinusoidal PWM modulation wave synchronous with the power grid is generated, then the current transformer outputs the voltage identical to the fundamental wave of the power grid, the voltage containing harmonic content cannot be generated, although the problem of stable switching-in is relieved to a certain extent, for the power grid containing complex conditions such as high harmonic, the prior art cannot generate the voltage waveform identical to the power grid at the current transformer side of the switching-in switch, and therefore the problem of overlarge current peak and unstable switching-in caused by the voltage difference at the two ends of the switching-in switch cannot be effectively solved in the prior art.
Disclosure of Invention
The invention aims to solve the problem that the prior art cannot effectively solve the problem of unstable access at the moment of the actuation of an access switch for a power grid with complex conditions such as high harmonic content and the like.
In order to solve the above problems, in a first aspect, the present invention provides a method for controlling a converter to access to a power grid, including:
monitoring the input voltage of the converter and the instantaneous value of the grid voltage;
carrying out phase locking on the power grid voltage instantaneous value to obtain the phase of the power grid voltage instantaneous value;
coordinate transformation is carried out on the power grid voltage instantaneous value, and transformation voltage is obtained;
PWM modulation is carried out according to the phase, the conversion voltage and the input voltage, and a first driving wave of a switching device of the converter is generated;
and according to the first driving wave, the converter outputs a following voltage and controls the access switch to be closed.
Optionally, according to the driving wave, the converter outputs a following voltage, and controlling the access switch to close includes:
according to the driving wave, the current transformer outputs the following voltage and starts timing at the same time to obtain a first duration;
and when the first time length is larger than a first threshold value, controlling the access switch to be closed.
Optionally, after the converter outputs a following voltage and controls the access switch to be closed according to the driving wave, the control method for accessing the converter to the power grid further includes:
when the access switch is closed, starting timing to obtain a second duration;
and when the second time period is longer than a second threshold value, controlling a logic switch to switch, and switching an open-loop voltage output mode of the converter into a closed-loop current output mode.
Optionally, when the second time period is longer than a second threshold, the logic switch is controlled to switch, and after the open-loop voltage output mode of the converter is switched to the closed-loop current output mode, the control method for the converter to be connected to the power grid includes:
monitoring the output current of the converter;
and obtaining the regulating current according to the output current and the reference current after the coordinate transformation.
Optionally, the control method for accessing the converter to the power grid after obtaining the regulating current according to the output current and the reference current after the coordinate transformation includes:
PWM modulation is carried out according to the regulating current, the phase, the conversion voltage and the input voltage, and a second driving wave of the switching device of the converter is generated;
and controlling the converter to output stable current according to the second driving wave.
Optionally, the coordinate transforming the power grid voltage instantaneous value to obtain a transformed voltage includes:
when the power grid voltage is three-phase voltage, carrying out coordinate transformation on the three-phase voltage instantaneous value of the power grid for a plurality of times to obtain transformed voltage;
when the power grid voltage is single-phase voltage, delaying the phase of the single-phase voltage instantaneous value of the power grid for a specified duration to obtain a delayed instantaneous value;
and carrying out coordinate transformation according to the single-phase voltage instantaneous value and the delay instantaneous value to obtain a transformation voltage.
Optionally, the generating the first driving wave of the switching device of the converter according to the phase, the conversion voltage and the input voltage includes:
performing reverse coordinate transformation according to the phase, the transformation voltage and the input voltage to obtain a voltage modulation wave;
the first driving wave of the switching device of the converter is generated according to the voltage modulation wave and carrier wave.
Optionally, after monitoring the input voltage of the converter and the instantaneous value of the grid voltage, the method further comprises:
judging whether the power grid voltage instantaneous value is in a normal range or not, and judging whether the input voltage is larger than the product of the power grid voltage instantaneous value and a preset proportion or not;
and when the power grid voltage instantaneous value is in the normal range and the input voltage is larger than the product of the power grid voltage instantaneous value and the preset proportion, controlling the converter to start working.
In a second aspect, the invention provides a control system for accessing a converter to a power grid, which comprises a monitoring unit, a phase-locked loop, a coordinate transformation unit, a PWM (pulse-Width modulation) unit and a converter control unit;
the monitoring unit is used for monitoring the input voltage of the converter and the instantaneous value of the grid voltage;
the phase-locked loop is used for phase-locking the power grid voltage instantaneous value to obtain the phase of the power grid voltage instantaneous value;
the coordinate transformation unit is used for carrying out coordinate transformation on the power grid voltage instantaneous value to obtain transformation voltage;
the PWM modulation unit is used for PWM modulation according to the phase, the conversion voltage and the input voltage, and generating a first driving wave of a switching device of the converter;
the converter control unit is used for outputting follow voltage according to the first driving wave and controlling the access switch to be closed.
In a third aspect, the present invention provides a computer readable storage medium having stored thereon a computer program which, when executed by a processor, implements a method for controlling access of a converter to a power grid as described above.
Compared with the prior art, the invention has the following beneficial effects:
according to the control method, the system and the readable storage medium for accessing the converter into the power grid, provided by the invention, only the input voltage and the instantaneous value of the power grid voltage are acquired, the output voltage of the converter is not required to be monitored, the acquired data quantity is reduced to the minimum, and the cost of an acquisition circuit is reduced; coordinate transformation is carried out on the power grid voltage instantaneous value to obtain transformation voltage, and harmonic characteristics in the power grid voltage instantaneous value are reserved; PWM modulation is carried out according to the phase, the conversion voltage and the input voltage, so that a first driving wave of a switching device of the converter is generated, a closed-loop control adjusting link is not needed, the operation process is simplified, the operation speed is improved, and the complexity of system control and the system cost are reduced; according to the first driving wave, the converter outputs the following voltage and controls the access switch to be closed, so that the converter outputs the voltage faster, the output following voltage can immediately follow the power grid voltage instantaneous value, the time difference between the following voltage and the power grid voltage instantaneous value is shortened, the dynamic response speed of the system is accelerated, a voltage waveform which is closer to the power grid voltage instantaneous value than the traditional method can be obtained, the power grid voltage instantaneous value at the output moment is basically consistent when the following voltage is output, and then circuits at two sides of the access switch can be stably connected when the access switch is closed, and the unstable problem is avoided.
Drawings
Fig. 1 is a schematic flow chart of a control method for accessing a converter to a power grid in an embodiment of the invention;
fig. 2 is a schematic flow chart of another control method for accessing a converter to a power grid in an embodiment of the invention;
fig. 3 shows a schematic structural diagram of a converter control system according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a three-phase voltage coordinate transformation process according to an embodiment of the invention;
fig. 5 shows a schematic diagram of a single-phase voltage coordinate transformation process in an embodiment of the invention.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. While the invention is susceptible of embodiment in the drawings, it is to be understood that the invention may be embodied in various forms and should not be construed as limited to the embodiments set forth herein, but rather are provided to provide a more thorough and complete understanding of the invention. It should be understood that the drawings and embodiments of the invention are for illustration purposes only and are not intended to limit the scope of the present invention.
It should be understood that the various steps recited in the method embodiments of the present invention may be performed in a different order and/or performed in parallel. Furthermore, method embodiments may include additional steps and/or omit performing the illustrated steps. The scope of the invention is not limited in this respect.
The term "including" and variations thereof as used herein are intended to be open-ended, i.e., including, but not limited to. The term "based on" is based at least in part on. The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "alternative embodiments". Related definitions of other terms will be given in the description below. It should be noted that the terms "first," "second," and the like herein are merely used for distinguishing between different devices, modules, or units and not for limiting the order or interdependence of the functions performed by such devices, modules, or units.
It should be noted that references to "one", "a plurality" and "a plurality" in this disclosure are intended to be illustrative rather than limiting, and those skilled in the art will appreciate that "one or more" is intended to be construed as "one or more" unless the context clearly indicates otherwise.
When the direct current is connected to an alternating current power grid, the direct current is converted into alternating current to be connected with the power grid smoothly, if the running state of the power grid is stable and unchanged, the direct current is converted into alternating current with fixed waveform, and the conversion is easy to realize. However, in the running process of the power grid, the power grid is affected due to the real-time change of the load, the change of the surrounding environment and the running of surrounding equipment, the voltage in the power grid becomes unstable, and the unstable factor is uncontrollable, so that direct current is converted into alternating current, and the converted alternating current voltage and the power grid voltage are kept consistent and are difficult to maintain.
The method is characterized in that the power grid voltage at the time T is collected, the output voltage of the converter is regulated according to the value of the power grid voltage at the time T, so that the output voltage of the converter is consistent with the power grid voltage at the time T, but because the converter needs time T for converting the voltage and the power grid voltage fluctuates in real time, when the converter outputs the output voltage which follows the power grid voltage at the time T, the power grid is at the time T+t, and the power grid voltage at the time T+t is different from the power grid voltage at the time T, so that the output voltage of the converter is inconsistent with the power grid voltage, the power grid voltage is continuously changed, the change of the power grid voltage is limited in the time T, and the power grid voltage of the converter is basically consistent with the power grid voltage as close to the time T as possible, so that the time T is shortened as much as possible is important.
Fig. 1 is a schematic flow chart of a control method for accessing a converter to a power grid in an embodiment of the present invention, where the control method for accessing the converter to the power grid includes:
s1: the input voltage of the converter and the instantaneous value of the grid voltage are monitored.
As shown in fig. 2, the PV array (photovoltaic array) outputs the generated voltage to the DC/DC device, and then the voltage is stabilized by filtering through a capacitor C1 to form an input voltageInput voltage into DA/AC converter, output follow voltage via the converter, and output current measured at inductor L>The following voltage is connected to the power grid via a capacitor C2, < + >>The instantaneous value of the power grid voltage is obtained.
Specifically, when the converter is not communicated with the power grid, the instantaneous value of the power grid voltage and the input voltage value of the converter are collected in real time, the input voltage and the instantaneous value of the power grid voltage also need to be simply judged before voltage conversion, and when the input voltage of the converter is larger than the power grid voltage by a certain proportion, the output of the alternating voltage which is the same as the power grid voltage is possible; in addition, the power grid voltage instantaneous value is collected to judge whether the current power grid operates normally, and when the power grid voltage instantaneous value is abnormal, the photovoltaic power generation system is not required to be connected into the power grid through the converter.
S2: and carrying out phase locking on the power grid voltage instantaneous value to obtain the phase of the power grid voltage instantaneous value. The phase of the power grid voltage instantaneous value is extracted by sending the power grid voltage instantaneous value to the phase-locked loop, so that the output voltage of the converter and the power grid voltage instantaneous value keep the same phase, and the phase difference conflict between the output voltage of the converter and the power grid voltage instantaneous value during the butt joint is avoided.
S3: and carrying out coordinate transformation on the power grid voltage instantaneous value to obtain transformed voltage.
Specifically, various coordinate transformations, such as park coordinate transformation and clark coordinate transformation, can be performed on the power grid voltage instantaneous value to generate a power grid voltage mathematical model containing various harmonic characteristics, after coordinate transformation, the variable number is reduced, so that the operation is more concise, and high-frequency harmonic information of the power grid voltage is not lost in the coordinate transformation process, so that follow-up voltage generated subsequently can also contain the harmonic information, and the follow-up voltage output by the converter is consistent with the power grid instantaneous voltage. In addition, when the acquired power grid voltage instantaneous value is three-phase voltage, the three-phase voltage is required to be subjected to coordinate transformation respectively; when the acquired power grid voltage instantaneous value is single-phase voltage, another voltage variable and the acquired power grid voltage instantaneous value are required to be constructed to form the input quantity of coordinate transformation.
S4: and performing PWM modulation according to the phase, the conversion voltage and the input voltage to generate a first driving wave of a switching device of the converter.
Specifically, the switching device is a power semiconductor device built in the converter, and the output voltage of the converter is controlled by controlling the on-off state of the semiconductor device. Knowing the following voltage required to be output by the converter according to the value and the phase of the converted voltage, and generating PWM modulation waves; and then calculating the amplitude, frequency and duty ratio of the driving wave according to the input voltage of the converter, a preset carrier wave and a PWM (pulse-width modulation) wave, and controlling the output time and the output size of the input voltage after passing through the converter by controlling the on-off of a switching device in the converter so as to ensure that the output following voltage is consistent with the power grid voltage instantaneous value. In addition, the steps S2 to S4 together constitute an open loop voltage output mode, i.e., the control mode 1 in fig. 2.
S5: and according to the first driving wave, the converter outputs a following voltage and controls the access switch to be closed. When the current transformer outputs the following voltage, the voltages at the two sides of the current transformer are basically consistent, and the access switch can be controlled to be closed at the moment, so that the current transformer is smoothly accessed into a power grid, and the voltage in the power grid cannot be opposite to the access point, so that the butt joint is smoothly completed.
Because in the process of collecting data, the precision of the collecting equipment and the loss of a collecting line and other factors can increase errors in the collecting process, the more the collected data is, the more complex the operation process is needed, the operand is increased, the time consumption of a plurality of links such as the speed of uploading the collected data is increased, the processing time of the converter is increased, in the embodiment, only the input voltage and the instantaneous value of the power grid voltage are collected, the output voltage of the converter is not required to be monitored, the collected data quantity is reduced to the minimum, the introduction amount of the collecting errors is reduced, the time of uploading the data is saved, and the circuit cost is reduced; coordinate transformation is carried out on the power grid voltage instantaneous value to obtain transformation voltage, and harmonic characteristics in the power grid voltage instantaneous value are reserved; PWM modulation is carried out according to the phase, the conversion voltage and the input voltage, so that a first driving wave of a switching device of the converter is generated, a closed-loop control adjusting link is not needed, the operation process is simplified, the operation speed is improved, and the complexity of system control and the system cost are reduced; according to the first driving wave, the converter outputs the following voltage and controls the access switch to be closed, so that the converter outputs the faster output voltage, the output following voltage can follow the power grid voltage instantaneous value immediately, the time difference between the output following voltage and the power grid voltage instantaneous value is shortened, the dynamic response speed of the system is accelerated, the voltage waveform which is closer to the power grid voltage instantaneous value than the traditional method can be obtained, the power grid voltage instantaneous value at the output moment is basically consistent when the following voltage is output, the circuits at the two sides of the access switch can be stably connected when the access switch is closed, the unstable problem is avoided, the operation speed of the system can be improved, the time t required by the converter for converting the voltage is reduced while the acquired data is simplified, the time difference between the following voltage output by the converter and the power grid instantaneous voltage is shortened, and the stable connection of the circuits at the two sides of the access switch in the system can be ensured.
In one embodiment of the present invention, as shown in fig. 3, the step of controlling the access switch to close according to the driving wave and the following voltage output by the converter includes:
s51: according to the driving wave, the converter outputs following voltage and starts timing at the same time to obtain a first duration;
s52: and when the first time length is larger than a first threshold value, controlling the access switch to be closed.
Specifically, when the current transformer just outputs the following voltage, there is a voltage difference between the following voltage just output and the voltage output by the previous current transformer, so that the access switch needs to be ensured to be stable at the current transformer side, and therefore, after the current transformer outputs the following voltage for a period of time, the access switch is closed, so that the current transformer outputs the stable following voltage.
In one embodiment of the invention, as shown in fig. 3, after the converter outputs a following voltage according to the driving wave and controls the access switch to be closed, the control method for accessing the converter to the power grid further includes:
s6: when the access switch is closed, starting timing to obtain a second duration;
s7: and when the second time period is longer than a second threshold value, controlling a logic switch to switch, and switching an open-loop voltage output mode of the converter into a closed-loop current output mode.
Specifically, before the access switch is closed, the converter works in an open-loop voltage output mode, so that the voltage at two sides of the access switch is basically consistent at the moment of the access of the converter, and the problem of unstable access caused by current peak generated at the moment of the closing is avoided. In addition, when the access switch is closed, the current output by the converter needs to be regulated to avoid uncontrollable current output, so that the control mode of the inverter needs to be changed into a closed-loop current output mode after the access switch is closed, so that the converter outputs the required current. However, since the access switch needs a certain time from receiving the closing control signal to completely closing, in order to make the circuit stably run, the switching of the control model cannot be performed under the condition that the access switch is not completely closed, so that the problem that the access switch is caused to swing in the switching process is avoided, and the stable running of the access point is not good. It should be noted that, as shown in fig. 2, the closed loop current output mode is a control mode 2, and when the logic switch contacts the connection point 3, the control mode of the current transformer is an open loop voltage output mode; when the logic switch is in contact with the connection point 4, the control mode of the current transformer is a closed loop current output mode.
In one embodiment of the invention, when the second time period is longer than a second threshold value, the logic switch is controlled to switch, and after the open-loop voltage output mode of the converter is switched to the closed-loop current output mode, the control method for the converter to be connected to the power grid includes:
monitoring the output current of the converterThe method comprises the steps of carrying out a first treatment on the surface of the After the control mode is changed, the output current of the converter needs to be monitored so as to know the output condition of the converter in real time.
And obtaining the regulating current according to the output current and the reference current after the coordinate transformation. The reference current is the current required by the system, and the current can be fixed and can be adjusted at any time according to the requirement. Specifically, as shown in the figure2, because the current regulator is needed to be used when analyzing the output current and the reference currentAnd->) While the current regulator is suitable for analysis of the direct current in order to facilitate the exchange of the output current of the alternating current with a reference current (">And->) For analysis, it is necessary to coordinate-transform the output current so that the alternating output current is converted into a relatively stationary current (+)>And->) At this time, the current after coordinate transformation can be regarded as direct current, and then adjustment analysis is performed to obtain adjustment current.
In this embodiment, the control method for accessing the converter to the power grid after obtaining the adjustment current according to the output current and the reference current after the coordinate transformation includes:
and performing PWM modulation according to the regulating current, the phase, the conversion voltage and the input voltage to generate a second driving wave of the switching device of the converter.
Specifically, after the control mode is switched, the converter is in a constant power working state, so that after the regulating current is obtained, the voltage value required to be output by the converter can be known according to the regulating current, and then PWM modulation is carried out according to the voltage value required to be output by the converter, the instantaneous value of the power grid voltage and the input voltage of the transformer, so as to obtain the second driving wave.
And controlling the converter to output stable current according to the second driving wave.
In the embodiment, the output current of the converter is collected and fed back to the converter, and compared with the reference current, so that the output current of the converter is corrected, closed loop feedback is formed, the stability of the output current is ensured, uncontrollable current after being connected to a power grid is avoided, and the reliability of the system is improved.
In one embodiment of the invention, the coordinate transforming the grid voltage transient to obtain a transformed voltage includes:
when the power grid voltage is three-phase voltage, carrying out coordinate transformation on the three-phase voltage instantaneous value of the power grid for a plurality of times to obtain transformed voltage.
Specifically, as shown in fig. 4, when the grid voltage is a three-phase voltage, three ac variables of the three-phase voltage are changed #、/>And->) Conversion to two relative DC variables (+)>And->) For example, by Clark coordinate transformation>And->Then, the park coordinate transformation is performed to obtain a transformation voltage +.>And->After coordinate transformation, the system operation is moreIs simple and convenient.
When the power grid voltage is single-phase voltage, delaying the phase of the single-phase voltage instantaneous value of the power grid for a specified duration to obtain a delayed instantaneous value; and carrying out coordinate transformation according to the single-phase voltage instantaneous value and the delay instantaneous value to obtain a transformation voltage.
Specifically, as shown in fig. 5, at least two variable factors are required to perform coordinate transformation when performing coordinate transformation, but the single-phase voltage has only one voltage variableTherefore, a second voltage transformation is required, so that the phase of the single-phase voltage is delayed by pi/2, and two voltage variables are respectively constructed as +.>And->Then performing park transformation to obtain transformation voltage +.>And->。
In one embodiment of the invention, the generating the first driving wave of the switching device of the converter according to the phase, the converted voltage and the input voltage includes:
performing reverse coordinate transformation according to the phase, the transformation voltage and the input voltage to obtain a voltage modulation wave;
as shown in fig. 4 and 5, the phase-locked loop PLL performs phase locking on the instantaneous value of the power grid voltage to obtain the phase of the instantaneous value of the power grid voltage, and if the instantaneous value is three-phase voltage, the voltage phase of each phase is obtained respectively，/>And->) If the single-phase voltage is the single-phase voltage, the phase theta of the single-phase voltage is directly obtained. In the open-loop voltage output mode, the voltage after transformation according to the coordinates +.>And->Input voltage +.>And a phase, performing reverse coordinate transformation to obtain a regulated voltage, wherein when the grid voltage is a three-phase voltage, the regulated voltage is obtained through reverse Peak transformation>And->Then obtaining the regulating voltage by anti-Clark conversion>、/>And->The method comprises the steps of carrying out a first treatment on the surface of the When the acquired voltage is single-phase voltage, the adjusting voltage is obtained through inverse Peak conversion>The method comprises the steps of carrying out a first treatment on the surface of the In the closed loop current output mode, the regulating current is required to be increased, and the regulating voltage is limited in the working state of constant power of the converter. And then generating a voltage modulation wave according to the regulated voltage and the phase, wherein the voltage modulation wave represents the outline of an alternating voltage waveform which needs to be output by the converter.
The first driving wave of the switching device of the converter is generated according to the voltage modulation wave and carrier wave. Specifically, the carrier wave can be a triangular carrier wave or a zigzag carrier wave, and the carrier wave is compared with the voltage modulation wave to generate a driving wave for driving the on-off of a semiconductor switching device in the converter, so that the magnitude and the phase of the voltage value output by the converter are controlled to obtain a required voltage waveform, and the output voltage of the converter follows the instantaneous value of the power grid voltage. In the closed loop current output mode, the PWM modulation principle is the same, and the magnitude of the regulating voltage input into the PWM modulation unit is changed under the limiting action of the regulating current, so that the driving wave generated by the PWM modulation unit is changed.
In one embodiment of the invention, after the monitoring of the input voltage of the converter and the instantaneous value of the grid voltage, the method further comprises:
judging whether the power grid voltage instantaneous value is in a normal range or not, and judging whether the input voltage is larger than the product of the power grid voltage instantaneous value and a preset proportion or not;
and when the power grid voltage instantaneous value is in the normal range and the input voltage is larger than the product of the power grid voltage instantaneous value and the preset proportion, controlling the converter to start working.
Specifically, before the converter starts to work, whether the current power grid environment and the solar photovoltaic power generation amount are normal or not needs to be judged, the basic conditions for connecting the photovoltaic power generation to the power grid are not satisfied, and if the basic conditions cannot be satisfied, the converter does not work much. The basic conditions include: the instantaneous value of the grid voltage is in a normal range; the input voltage is greater than the product of the instantaneous value of the grid voltage and a preset proportion, the preset proportion can be 105% or 103%, and the like, and the input voltage of the converter is required to be higher than the output voltage of the converter because the converter generates certain loss when carrying out voltage-current conversion, and the output voltage is the instantaneous value of the grid voltage which is required to be followed.
In another embodiment of the present invention, as shown in fig. 2, the present invention further provides a control system for accessing a converter to a power grid, including a monitoring unit, a phase-locked loop, a coordinate transformation unit, a PWM modulation unit, and a converter control unit;
the monitoring unit is used for monitoring the input voltage of the converter and the instantaneous value of the grid voltage;
the phase-locked loop is used for phase-locking the power grid voltage instantaneous value to obtain the phase of the power grid voltage instantaneous value;
the coordinate transformation unit is used for carrying out coordinate transformation on the power grid voltage instantaneous value to obtain transformation voltage;
the PWM modulation unit is used for PWM modulation according to the phase, the conversion voltage and the input voltage, and generating a first driving wave of a switching device of the converter;
the converter control unit is used for outputting follow voltage according to the first driving wave and controlling the access switch to be closed.
In the embodiment, the monitoring unit only collects the input voltage and the power grid voltage instantaneous value, the output voltage of the converter is not required to be monitored, the collected data quantity is reduced to the minimum, the introduction quantity of the collection error is reduced, the time for uploading the data is saved, and the circuit cost is reduced; the coordinate transformation unit performs coordinate transformation on the power grid voltage instantaneous value to obtain transformation voltage, and the harmonic characteristic in the power grid voltage instantaneous value is reserved; the PWM modulation unit carries out PWM modulation according to the phase, the conversion voltage and the input voltage to generate a first driving wave of a switching device of the converter, a closed-loop control adjustment link is not needed, the operation process is simplified, the operation speed is improved, and the complexity of system control and the system cost are reduced; the converter control unit outputs following voltage according to the first driving wave and controls the access switch to be closed, so that the converter outputs voltage quickly, the output following voltage can immediately follow the power grid voltage instantaneous value, the time difference between the following voltage and the power grid voltage instantaneous value is shortened, the dynamic response speed of the system is accelerated, a voltage waveform which is closer to the power grid voltage instantaneous value than the traditional method can be obtained, the power grid voltage instantaneous value basically keeps consistent with the output moment when the following voltage is output, and circuits on two sides of the access switch can be stably connected when the access switch is closed, so that the unstable problem is avoided.
In another embodiment of the invention, the control system for the converter to access the power grid further comprises a current regulator;
the converter control unit is further used for controlling the logic switch to switch when the second time length is larger than a second threshold value;
the monitoring unit is also used for monitoring the output current of the converter;
the current regulator is used for obtaining a regulating current according to the output current and the reference current after coordinate transformation, and inputting the regulating current to the coordinate transformation unit;
the PWM modulation unit is further used for PWM modulation according to the regulating current, the phase, the conversion voltage and the input voltage, and generating a second driving wave of the switching device of the converter;
the converter control unit is further configured to control the converter to output a stable current according to the second driving wave.
In this embodiment, after the control mode is switched, the converter is in a constant power working state at this time, so after the current regulator sends the regulating current to the PWM modulation unit, the PWM modulation unit can learn the voltage value that the converter needs to output according to the regulating current, and then PWM modulate according to the voltage value that the converter needs to output, the instantaneous value of the grid voltage and the input voltage of the transformer, so as to obtain the second driving wave. The monitoring unit collects output current of the current transformer and feeds the output current back to the current transformer, the current regulator compares the output current with reference current, and then the output current of the current transformer is corrected, closed loop feedback is formed, stability of the output current is guaranteed, uncontrollable current after the power grid is connected is avoided, and reliability of the system is improved.
The computing device comprises a memory, a processor and a computer program stored on the memory and capable of running on the processor, and when the processor executes the computer program, the control method for accessing the converter to the power grid is realized.
The technical effects of the computing device in the embodiment of the invention are similar to those of the control method for the converter to access the power grid, and are not described in detail herein.
In one embodiment of the present invention, there is further provided a computer readable storage medium having a computer program stored thereon, which when executed by a processor, implements the above-mentioned method for controlling the converter to access a power grid.
The computer readable storage medium of the invention has similar technical effects to the control method of the converter accessing to the power grid, and will not be described in detail herein.
In general, computer instructions for implementing the methods of the invention may be carried in any combination of one or more computer-readable storage media. The non-transitory computer-readable storage medium may include any computer-readable medium, except the signal itself in temporary propagation.
The computer readable storage medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or a combination of any of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
Program code for carrying out operations of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, smalltalk, C ++ and conventional procedural programming languages, such as the "C" language or similar programming languages, and in particular, the Python language suitable for neural network computing and TensorFlow, pyTorch-based platform frameworks may be used. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any kind of network, including a Local Area Network (LAN) or a Wide Area Network (WAN), or may be connected to an external computer (for example, through the Internet using an Internet service provider).
Although the invention is disclosed above, the scope of the invention is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications will fall within the scope of the invention.
Claims (8)
1. The control method for the converter to access the power grid is characterized by comprising the following steps of:
monitoring the input voltage of the converter and the instantaneous value of the grid voltage;
carrying out phase locking on the power grid voltage instantaneous value to obtain the phase of the power grid voltage instantaneous value;
coordinate transformation is carried out on the power grid voltage instantaneous value, and transformation voltage is obtained;
PWM modulation is carried out according to the phase, the conversion voltage and the input voltage, and a first driving wave of a switching device of the converter is generated;
according to the first driving wave, the converter outputs following voltage and controls the access switch to be closed;
wherein, according to the driving wave, the converter outputs a following voltage, and controlling the access switch to be closed includes:
according to the driving wave, the current transformer outputs the following voltage and starts timing at the same time to obtain a first duration;
when the first time length is larger than a first threshold value, the access switch is controlled to be closed;
wherein, according to the driving wave, the converter outputs a following voltage and controls the access switch to be closed, and then the method further comprises:
when the access switch is closed, starting timing to obtain a second duration;
and when the second time period is longer than a second threshold value, controlling a logic switch to switch, and switching an open-loop voltage output mode of the converter into a closed-loop current output mode.
2. The method for controlling the converter to access the power grid according to claim 1, wherein when the second time period is longer than a second threshold value, the logic switch is controlled to switch, and after the open-loop voltage output mode of the converter is switched to the closed-loop current output mode, the method further comprises:
monitoring the output current of the converter;
and obtaining the regulating current according to the output current and the reference current after the coordinate transformation.
3. The method for controlling the converter to access the power grid according to claim 2, wherein after obtaining the regulated current according to the output current and the reference current after the coordinate transformation, the method further comprises:
PWM modulation is carried out according to the regulating current, the phase, the conversion voltage and the input voltage, and a second driving wave of the switching device of the converter is generated;
and controlling the converter to output stable current according to the second driving wave.
4. The method for controlling the converter to access the power grid according to claim 1, wherein the performing coordinate transformation on the power grid voltage instantaneous value to obtain a transformed voltage includes:
when the power grid voltage is three-phase voltage, carrying out coordinate transformation on the three-phase voltage instantaneous value of the power grid for a plurality of times to obtain the transformation voltage;
when the power grid voltage is single-phase voltage, delaying the phase of the single-phase voltage instantaneous value of the power grid for a specified duration to obtain a delayed instantaneous value; and carrying out coordinate transformation according to the single-phase voltage instantaneous value and the delay instantaneous value to obtain the transformation voltage.
5. The method for controlling the converter to access the power grid according to claim 1, wherein the generating the first driving wave of the switching device of the converter by PWM modulating according to the phase, the converted voltage and the input voltage includes:
performing reverse coordinate transformation according to the phase, the transformation voltage and the input voltage to obtain a voltage modulation wave;
the first driving wave of the switching device of the converter is generated according to the voltage modulation wave and carrier wave.
6. The method for controlling the converter to access the power grid according to any one of claims 1 to 5, wherein after monitoring the input voltage of the converter and the instantaneous value of the power grid voltage, the method further comprises:
judging whether the power grid voltage instantaneous value is in a normal range or not, and judging whether the input voltage is larger than the product of the power grid voltage instantaneous value and a preset proportion or not;
and when the power grid voltage instantaneous value is in the normal range and the input voltage is larger than the product of the power grid voltage instantaneous value and the preset proportion, controlling the converter to start working.
7. The control system for accessing the converter into the power grid is characterized by comprising a monitoring unit, a phase-locked loop, a coordinate transformation unit, a PWM (pulse-width modulation) unit and a converter control unit;
the monitoring unit is used for monitoring the input voltage of the converter and the instantaneous value of the grid voltage;
the phase-locked loop is used for phase-locking the power grid voltage instantaneous value to obtain the phase of the power grid voltage instantaneous value;
the coordinate transformation unit is used for carrying out coordinate transformation on the power grid voltage instantaneous value to obtain transformation voltage;
the PWM modulation unit is used for PWM modulation according to the phase, the conversion voltage and the input voltage, and generating a first driving wave of a switching device of the converter;
the converter control unit is used for outputting following voltage according to the first driving wave and controlling the access switch to be closed;
wherein, according to the driving wave, the converter outputs a following voltage, and controlling the access switch to be closed includes:
according to the driving wave, the current transformer outputs the following voltage and starts timing at the same time to obtain a first duration;
when the first time length is larger than a first threshold value, the access switch is controlled to be closed;
wherein, according to the driving wave, the converter outputs a following voltage and controls the access switch to be closed, and then the method further comprises:
when the access switch is closed, starting timing to obtain a second duration;
and when the second time period is longer than a second threshold value, controlling a logic switch to switch, and switching an open-loop voltage output mode of the converter into a closed-loop current output mode.
8. A computer readable storage medium, on which a computer program is stored, characterized in that the control method of the converter according to any one of claims 1-6 for accessing a power grid is implemented, when the computer program is executed by a processor.
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