CN116915035A - Current transformer and bus midpoint fluctuation compensation method thereof - Google Patents
Current transformer and bus midpoint fluctuation compensation method thereof Download PDFInfo
- Publication number
- CN116915035A CN116915035A CN202310903891.0A CN202310903891A CN116915035A CN 116915035 A CN116915035 A CN 116915035A CN 202310903891 A CN202310903891 A CN 202310903891A CN 116915035 A CN116915035 A CN 116915035A
- Authority
- CN
- China
- Prior art keywords
- bus
- fluctuation
- voltage
- inverter circuit
- current
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 238000000034 method Methods 0.000 title claims abstract description 62
- 230000007935 neutral effect Effects 0.000 claims abstract description 47
- 238000006243 chemical reaction Methods 0.000 claims description 24
- 238000004364 calculation method Methods 0.000 claims description 15
- 239000003990 capacitor Substances 0.000 claims description 6
- 238000012545 processing Methods 0.000 claims description 3
- 238000000605 extraction Methods 0.000 abstract description 6
- 238000010586 diagram Methods 0.000 description 4
- 238000013461 design Methods 0.000 description 3
- 230000001276 controlling effect Effects 0.000 description 2
- 238000013016 damping Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 238000010248 power generation Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000000452 restraining effect Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000013589 supplement Substances 0.000 description 1
Classifications
-
- 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
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
-
- 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
-
- 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
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
-
- 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
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/487—Neutral point clamped inverters
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Inverter Devices (AREA)
Abstract
The application provides a current transformer and a bus midpoint fluctuation compensation method thereof, wherein after the fluctuation quantity of the DC bus midpoint voltage of the current transformer is obtained, fluctuation components with preset frequency are extracted from the fluctuation quantity, and then bus modulation voltage of an inverter circuit in the current transformer is compensated by the fluctuation components; determining the duty ratio of PWM signals of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit, and further realizing control of the inverter circuit; meanwhile, by means of the compensation process, the influence of the midpoint voltage fluctuation on the output current harmonic wave of the converter can be eliminated. In addition, the neutral point voltage fluctuation of the direct current bus is obtained in real time, and the follow-up extraction and compensation processes are realized based on the real-time data, so that the dynamic stability under different conditions can be considered.
Description
Technical Field
The application relates to the technical field of power electronics, in particular to a converter and a bus midpoint fluctuation compensation method thereof.
Background
With the rapid development of new energy power generation, the working voltage and capacity of the converter are larger and larger, and most inverter circuits in the converter adopt a three-level conversion topological structure; due to the working characteristics of the three-level conversion topology, the midpoint voltage of the direct current side of the three-level conversion topology inevitably has inherent fluctuation; these fluctuations are superimposed on the output voltage on the ac side of the converter by PWM (Pulse Width Modulation) links, which results in harmonic content in the output current on the ac side of the converter, thereby affecting the power quality of the output current of the converter.
Aiming at the harmonic content of the output current of the converter, more in the prior art, the harmonic content in the output current is restrained by an output current harmonic restraining algorithm, generally in a closed-loop control mode, but the algorithm adopted in the prior art cannot solve the stability problem under the condition of weak current network while compensating the harmonic problem caused by midpoint disturbance.
Disclosure of Invention
In view of the above, the application provides a converter and a bus neutral point fluctuation compensation method thereof, so as to consider the harmonic problem caused by neutral point disturbance and the stability problem under the weak current network condition.
In order to achieve the above purpose, the present application provides the following technical solutions:
the application provides a bus midpoint fluctuation compensation method of a converter, which comprises the following steps:
acquiring the neutral point voltage fluctuation quantity of a direct current bus of the converter in real time;
extracting fluctuation components of preset frequency in the fluctuation quantity of the neutral point voltage of the direct current bus;
compensating bus modulation voltage of an inverter circuit in the converter by using the fluctuation component;
and determining the duty ratio of the Pulse Width Modulation (PWM) signal of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit.
Optionally, the preset frequency includes: the fundamental frequency, and/or, multiple of the fundamental frequency.
Optionally, extracting a fluctuation component of a preset frequency in the fluctuation amount of the midpoint voltage of the direct current bus includes:
if the AC side output current of the converter or the power grid voltage is unbalanced, extracting a fluctuation component of fundamental wave frequency in the fluctuation quantity of the neutral point voltage of the DC bus;
and if the inverter circuit works normally, extracting fluctuation components which are multiple times of the frequency of the fundamental wave in the fluctuation quantity of the midpoint voltage of the direct current bus.
Optionally, extracting a fluctuation component of a preset frequency in the fluctuation amount of the midpoint voltage of the direct current bus includes:
and extracting the fluctuation component of the fundamental wave frequency and the fluctuation component of the frequency which is multiple times of the fundamental wave in the fluctuation quantity of the neutral voltage of the direct current bus.
Optionally, multiple times the frequency of the fundamental wave, including: 3 times or 2 times the frequency of the fundamental wave.
Optionally, acquiring the voltage fluctuation of the midpoint of the dc bus of the converter in real time includes:
acquiring at least two of three voltages of direct-current bus voltage and two half bus voltages of the converter in real time to determine the two half bus voltages;
and calculating the difference between the voltages of the two half buses as the fluctuation amount of the neutral point voltage of the direct current bus.
Optionally, the voltage fluctuation amount at the midpoint of the direct current bus is: the difference between the positive half bus voltage minus the negative half bus voltage.
Optionally, compensating the bus modulation voltage of the inverter circuit in the converter with the ripple component includes:
and respectively overlapping half of the fluctuation component to corresponding half bus modulation voltage in the bus modulation voltage in two directions to obtain the compensation result.
Optionally, overlapping half of the fluctuation component to corresponding half bus modulation voltage in the bus modulation voltages in two directions, respectively, including:
adding half of the ripple component to the positive half bus modulation voltage; the method comprises the steps of,
and inverting half of the fluctuation component and then adding the inverted half of the fluctuation component to the negative half bus modulation voltage.
Optionally, the two half bus modulation voltages are: half of the dc bus voltage.
Optionally, determining the duty ratio of the PWM signal of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit includes:
for the phase modulation voltage which is larger than zero in the inversion modulation voltage, taking the ratio of the phase modulation voltage to the positive half bus modulation voltage in the compensation result as the duty ratio of the corresponding phase bridge arm in the inversion circuit;
for the phase modulation voltage smaller than zero in the inversion modulation voltage, taking the ratio of the phase modulation voltage to the negative half bus modulation voltage in the compensation result as the duty ratio of the corresponding phase bridge arm in the inversion circuit;
and regarding zero phase modulation voltage in the inversion modulation voltage as the duty ratio of a corresponding phase bridge arm in the inversion circuit.
Optionally, before determining the duty ratio of the PWM signal of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit, the method further includes:
acquiring an alternating-current side output current of the inverter circuit and an alternating-current side output voltage of the converter in real time;
performing current loop control on the inverter circuit according to the two to obtain an inverter modulation voltage of the inverter circuit;
after determining the duty ratio of the PWM signal of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit, the method further comprises:
and generating the corresponding PWM signal according to the duty ratio.
A second aspect of the present application provides a current transformer, comprising: an inverter circuit, a filter and a controller; wherein,,
the alternating current side of the inverter circuit is connected with the alternating current side of the converter through the filter;
the direct-current side positive and negative poles of the inverter circuit are respectively connected with corresponding poles of a direct-current bus, a bus capacitor branch is arranged between the positive and negative poles of the direct-current bus, and the midpoint of the bus capacitor branch is used as the midpoint of the direct-current bus to be connected with the midpoint of the direct-current side of the inverter circuit;
the inverter circuit is controlled by the controller;
the controller is configured to perform the method for compensating for a bus bar midpoint fluctuation of the converter according to any one of the first aspect.
Optionally, the controller includes: the device comprises a duty ratio calculation unit, a current loop control unit and a PWM control unit; wherein,,
the current loop control unit is used for determining the inversion modulation voltage of the inverter circuit according to the alternating-current side output current of the inverter circuit and the alternating-current side output voltage of the converter;
the duty ratio calculation unit is used for generating a duty ratio according to the DC bus midpoint voltage fluctuation quantity of the converter obtained in real time and outputting the duty ratio to the PWM control unit;
the PWM control unit is used for generating PWM signals according to the duty ratio and controlling the inverter circuit.
Optionally, the duty ratio calculating unit includes: and the band-pass filter is used for extracting fluctuation components of preset frequency in the fluctuation quantity of the midpoint voltage of the direct current bus.
Optionally, the controller further includes: and the processing unit is used for judging whether unbalance occurs in the alternating-current side output current or the power grid voltage of the converter and whether the inverter circuit works normally.
Optionally, the inverter circuit is a neutral point clamped type conversion topology.
Optionally, the dc bus is connected to a dc side of the converter, and the dc side of the converter is used for connecting a dc power supply;
alternatively, the current transformer further includes: and one side of the front-stage conversion circuit is connected with the direct current bus, the other side of the front-stage conversion circuit is connected with an external power supply through the other side of the converter, and the front-stage conversion circuit is controlled by the controller.
According to the bus midpoint fluctuation compensation method of the converter, after the fluctuation quantity of the direct-current bus midpoint voltage of the converter is obtained, fluctuation components with preset frequency are extracted from the fluctuation quantity, and then bus modulation voltage of an inverter circuit in the converter is compensated by the fluctuation components; determining the duty ratio of PWM signals of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit, and further realizing control of the inverter circuit; meanwhile, by means of the compensation process, the influence of the midpoint voltage fluctuation on the output current harmonic wave of the converter can be eliminated. In addition, the neutral point voltage fluctuation of the direct current bus is obtained in real time, and the follow-up extraction and compensation processes are realized based on the real-time data, so that the dynamic stability under different conditions can be considered.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following description will briefly explain the embodiments or the drawings to be used in the description of the prior art, and it is obvious that the drawings in the following description are only embodiments of the present application, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of a method for compensating for a fluctuation in a bus midpoint of a current transformer according to an embodiment of the present application;
fig. 2 is a schematic structural diagram of a current transformer according to an embodiment of the present application;
fig. 3 is another flowchart of a method for compensating for a fluctuation in a bus midpoint of a current transformer according to an embodiment of the present application;
fig. 4 is a circuit diagram of an inverter circuit in a converter according to an embodiment of the present application;
fig. 5 is another circuit diagram of an inverter circuit in a converter according to an embodiment of the present application;
fig. 6 is another circuit diagram of an inverter circuit in a converter according to an embodiment of the present application.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In the present disclosure, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises an element.
The application provides a bus neutral point fluctuation compensation method of a converter, which aims at solving the harmonic problem caused by neutral point disturbance and the stability problem under the condition of weak current network.
Referring to fig. 1, the bus midpoint fluctuation compensation method of the converter comprises the following steps:
s101, acquiring the neutral point voltage fluctuation quantity of a direct current bus of the converter in real time.
Referring to fig. 2, it is assumed that the converter mainly includes an inverter circuit 10, and the positive and negative electrodes and the middle point of the dc side of the inverter circuit 10 are respectively connected with the positive and negative electrodes and the middle point of the dc bus; v in FIG. 2 dc Is the voltage of a direct current bus, V p Is the positive half bus voltage, V n Is the negative half bus voltage. Normally, V p ＝V n When the midpoint of the direct current bus fluctuates, the voltage V of the two half buses p And V is equal to n The difference value is the neutral point voltage fluctuation of the DC bus.
Thus, the S101 may specifically include:
(1) And acquiring at least two of three voltages, namely the direct current bus voltage and the two half bus voltages, of the converter in real time so as to determine the two half bus voltages.
That is, in practical application, two half bus voltages V can be directly collected p And V is equal to n Two half bus voltages V can also be collected p And V is equal to n One of the DC bus voltages V dc Based on V again dc ＝V p +V n Determining two half bus voltages V p And V is equal to n Another of which is a member of the group. In this case, the dc bus voltage V may be determined and obtained dc For implementing other control or monitoring protection. Of course, the simultaneous acquisition of the three parameters V mentioned above is not excluded either dc 、V p V (V) n According to the specific application environment, the scheme is within the protection scope of the application.
(2) And calculating the difference between the voltages of the two half buses as the fluctuation amount of the neutral point voltage of the direct current bus.
Specifically, the neutral point voltage fluctuation of the dc bus may be: positive half bus voltage V p Minus half-bus voltage V n The difference, i.e. the amount of fluctuation V of the neutral point voltage of the DC bus mid The calculation formula of (C) can be V mid ＝V p -V n The method comprises the steps of carrying out a first treatment on the surface of the In practical application, the calculation formula can also be V mid ＝V n -V p Depending on the specific application environment, the method is not limited herein.
S102, extracting fluctuation components of preset frequency in the fluctuation quantity of the neutral point voltage of the direct current bus.
In practical application, when the inverter circuit works normally, the converter mainly has 3-frequency or 2-frequency fluctuation components due to the relation between the output current and the duty ratio. Wherein, 3 times frequency refers to 3 times frequency of fundamental wave, 2 times frequency refers to 2 times frequency of fundamental wave, and the fundamental wave can be fluctuation of 50Hz power frequency. When the output current of the alternating current side of the converter or the voltage of the power grid is unbalanced, a larger fundamental component, namely a fluctuation component of fundamental frequency exists in the neutral point voltage fluctuation quantity of the direct current bus due to the action of negative sequence power.
Therefore, when the inverter circuit works normally, the preset frequency may be multiple frequency, i.e. multiple frequency than the fundamental wave, such as 3 times frequency or 2 times frequency, and only the fluctuation component of the frequency needs to be extracted. When the ac side output current of the converter or the grid voltage is unbalanced, the preset frequency may be referred to as the fundamental frequency, that is, only the fluctuation component of the frequency is extracted. That is, the S102 specifically may include: if the inverter circuit works normally, extracting the frequency multiplication fluctuation component in the neutral point voltage fluctuation quantity of the direct current bus; if the AC side output current of the converter or the voltage of the power grid is unbalanced, the fluctuation component of the fundamental wave frequency in the fluctuation quantity of the neutral point voltage of the DC bus is extracted.
Or, in practical application, the preset frequency may be set to include: the fundamental frequency, and, multiple times; furthermore, if the inverter circuit works normally at the current moment, the fluctuation component of the multiple frequency can be extracted; if the output current of the alternating current side of the current transformer or the voltage of the power grid is unbalanced at the current moment, the fundamental wave can be extracted; if the above fluctuation components are present at the same time, they can be extracted at the same time. That is, the S102 specifically may include: and extracting the fluctuation component of the fundamental wave frequency and the frequency-multiplied fluctuation component in the fluctuation quantity of the neutral point voltage of the direct current bus.
In practical applications, the multiple frequency may include only one frequency, such as 3 or 2 frequency, or 5 or 7 frequency; or, the multiple frequency may also include at least two frequencies, for example, including the 3-frequency multiplication and the 2-frequency multiplication, and may further include at least one of other frequencies such as the 5-frequency multiplication or the 7-frequency multiplication; depending on the specific application environment, the method is within the protection scope of the application.
The specific implementation process of S102 may depend on the specific application environment, and is within the protection scope of the present application.
In practical application, a filter can be used to obtain a main fluctuation component in the fluctuation amount of the neutral point voltage of the direct current bus. For example, a bandpass filter Bf can be provided to couple the DC bus midpoint voltage fluctuation amount V mid After the band-pass filter Bf is processed, 3 times frequency or fundamental frequency components are extracted.
The bandpass filter Bf is used for extracting the fluctuation quantity V of the midpoint voltage of the direct current bus mid For example, the 3-frequency multiplied ripple component can be used to design the bandpass filter Bf as follows:where τ is the damping coefficient of the band-pass filter, and τ=0.707 is generally preferable; for the case of 50Hz fundamental frequency, the frequency multiplication of 3 is 150Hz, at which time w 3 =2pi×150; s is the Laplace operator. By the design, the fluctuation component V of 3 times frequency can be extracted mid_3th The calculation formula is V mid_3th ＝Bf3*V mid 。
And S103, compensating bus modulation voltage of an inverter circuit in the converter by using a fluctuation component.
In practical applications, the bus modulation voltage includes two half bus modulation voltages, which can be half of the DC bus voltage, i.e. V dc /2. Therefore, in executing the S101, the DC bus voltage V can be obtained in real time dc Two half bus voltages V p And V is equal to n To determine two half bus voltages V p And V is equal to n At the same time of determining the DC bus voltage V dc And further for determining two half-bus modulation voltages V dc /2。
Then, the ripple component extracted in S102 may be added to the bus modulation voltage to compensate for the influence of the midpoint voltage ripple on the output current harmonic.
S104, determining the duty ratio of the PWM signal of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit.
In the embodiment, the compensation result of S103 is used to replace the bus modulation voltage to obtain the duty ratio, so as to eliminate the influence of the midpoint voltage fluctuation on the output current harmonic wave and solve the harmonic wave problem caused by the midpoint disturbance in the prior art.
According to the bus neutral point fluctuation compensation method of the converter, through the principle, the control of the inverter circuit is achieved, and meanwhile, the influence of neutral point voltage fluctuation on the output current harmonic wave of the converter can be eliminated by means of the compensation process. In addition, the neutral point voltage fluctuation of the direct current bus is obtained in real time, and the follow-up extraction and compensation processes are realized based on the real-time data, so that the dynamic stability under different conditions can be considered.
It should be noted that, in order to timely feed back the fluctuation of the dc bus voltage on the duty ratio of the PWM signal, if the bus modulation voltage is directly used as the decoupling link to be put on the duty ratio generating link, the calculation formula of the duty ratio of each phase bridge arm in the inverter circuit is specifically as follows:wherein D is mi Is the duty ratio of an i-phase bridge arm in the inverter circuit, V mi I=a, b, c when the inverter circuit ac side outputs three-phase ac for the i-phase modulation voltage of the inverter circuit among the inverter modulation voltages; v (V) dcp For positive half of the bus modulation voltage, V dcn The negative half bus of the bus modulation voltages is used for modulating the voltages.
If the real-time value of the half bus voltage (i.e. V as above is directly adopted p And V is equal to n ) Respectively as two half-bus modulating voltages, i.e. let V dcp ＝V p ，V dcn ＝V n At this time, although the harmonic problem caused by the bus fluctuation can be compensated, the system stability problem is easy to occur under the working condition of power fluctuation or weak current network, so that the system is crashed.
Therefore, considering system stability issues, the voltage of the DC bus can be half (i.e., V dc Respectively as two half-bus modulating voltages, i.e. commandAt the moment, the stability problem caused by half bus modulation can be solved; however, since the fluctuation disturbance amount of the neutral point voltage of the bus will cause the increase of the output current harmonic of the converter, the bus neutral point fluctuation compensation method provided in this embodiment supplements the bus modulation voltage of the inverter circuit in the converter with the fluctuation component through S103And then, replacing bus modulation voltage with compensation results to generate a duty ratio, so as to eliminate the influence of midpoint voltage fluctuation on output current harmonic waves.
Specifically, the S103 may include: and respectively overlapping half of the fluctuation component to corresponding half bus modulation voltage in the bus modulation voltage in two directions to obtain a compensation result. With the neutral point voltage fluctuation quantity V of the DC bus mid Is V mid ＝V p -V n For illustration, the stacking process specifically includes: adding half of the ripple component to the positive half bus modulation voltage; and, inverting half of the ripple component, and then adding the inverted half to the negative half bus modulation voltage. Wave component V multiplied by 3 mid_3th For illustration, the compensation results include:wherein V is dcp ' is the alignment half bus modulation voltage V dcp V is as a result of compensation of dcn ' is the modulating voltage V of the negative half bus dcn Is a result of the compensation of (a).
At this time, in S104 of the bus midpoint fluctuation compensation method, the duty ratio of the PWM signal of the inverter circuit is determined according to the compensation result and the inverter modulation voltage of the inverter circuit, specifically including: for the phase modulation voltage which is larger than zero in the inversion modulation voltage, the ratio of the phase modulation voltage to the positive half bus modulation voltage in the compensation result is used as the duty ratio of the corresponding phase bridge arm in the inversion circuit; for the phase modulation voltage smaller than zero in the inversion modulation voltage, taking the ratio of the phase modulation voltage to the negative half bus modulation voltage in the compensation result as the duty ratio of the corresponding phase bridge arm in the inversion circuit; and regarding the phase modulation voltage with zero in the inversion modulation voltage, taking zero as the duty ratio of a corresponding phase bridge arm in the inversion circuit. That is, at this time, the calculation formula of the duty ratio of each phase arm in the inverter circuit is specifically:
in practical application, the method for compensating the midpoint fluctuation of the bus, before S104, further includes the steps shown in fig. 3:
s201, acquiring an alternating-current side output current of an inverter circuit and an alternating-current side output voltage of a converter in real time.
The ac side of the inverter circuit outputs current, i.e., ibabc shown in fig. 2; the ac side of the converter outputs a voltage, namely Uabc as shown in fig. 2.
S202, performing current loop control on the inverter circuit according to the two to obtain the inverter modulation voltage of the inverter circuit.
The inverter modulation voltage V of the inverter circuit is obtained by internal calculation of a controller according to the AC side output current Iabc of the inverter circuit and the AC side output voltage Uabc of the converter mi When the inverter circuit employs a three-phase conversion circuit (such as a three-level neutral point clamped type conversion topology shown in a dotted line frame of fig. 4 to 6), i=a, b, c.
Referring to fig. 2, after the ac side output current ibabc of the inverter circuit is subjected to abc/dq conversion, a reactive current feedback Idq is obtained; subtracting the difference between the reactive current feedback Idq from the reactive current command Idq_ref, and obtaining a reactive current regulation quantity Idqout after passing through the PI regulator; the alternating-current side output voltage Uabc of the converter is subjected to phase-locked loop PLL to obtain a power grid phase angle theta, and simultaneously is subjected to abc/dq conversion to obtain reactive voltage feedback Udq; the sum um_dq of the reactive current regulating quantity Idqout and the reactive voltage feedback Udq is converted by dq/abc to obtain the inverter modulation voltage V mi 。
Further, the bus bar midpoint fluctuation compensation method further includes, after S104, as shown in fig. 3:
and S203, generating a corresponding PWM signal according to the duty ratio.
I.e. based on the compensation result V dcp ' and V dcn ' and the inverter modulation voltage V mi Determining the duty ratio D of each phase of the inverter circuit mi Then, PWM signals corresponding to each phase can be generated according to the PWM signals, so that on-off control of switching tubes of each phase in the inverter circuit is realized; this process may be referred to in the prior art and will not be described in detail here.
The embodiment provides the bus midpoint fluctuation compensationCompensation method, wherein the neutral point voltage fluctuation V of the DC bus of the converter is obtained mid Then extracting main fluctuation components by a band-pass filter or other methods; and then, based on the extracted fluctuation component, compensating the bus modulation voltage, thereby eliminating the influence of the voltage fluctuation at the middle point of the converter on the output current harmonic wave. The method can be realized only by software, and any hardware cost is not required to be increased; moreover, the extraction and compensation can be performed based on the existing sampling data, and the harmonic content of the output current of the converter is greatly optimized; in addition, through real-time online calculation and compensation, the operation stability of the converter under harmonic compensation can be greatly improved.
Another embodiment of the present application provides a current transformer, referring to fig. 2, specifically including: an inverter circuit 10, a filter 20, and a controller 30; the ac side of the inverter circuit 10 is connected to the ac side of a converter through a filter 20, and the ac side of the converter is used for connecting to a power Grid (Grid as shown in the figure); the positive and negative poles of the direct current side of the inverter circuit 10 are respectively connected with the corresponding poles of the direct current bus, a bus capacitor branch 40 is arranged between the positive and negative poles of the direct current bus, and the midpoint of the bus capacitor branch 40 is used as the midpoint of the direct current bus to be connected with the midpoint of the direct current side of the inverter circuit 10; the inverter circuit 10 is controlled by the controller 30; the controller 30 is configured to perform the method for compensating for the fluctuation of the bus bar midpoint of the converter according to any of the embodiments described above. The process and principle of the bus midpoint fluctuation compensation method are just described in the above embodiments, and are not described in detail herein.
In practical applications, the inverter circuit 10 is a neutral point clamped type conversion topology, such as the three-level neutral point clamped type conversion topology shown in the dashed boxes of fig. 4 to 6, and may specifically be a T-type structure (as shown in fig. 4) or an I-type structure (as shown in fig. 5 or 6); or, it can be a neutral point clamped type conversion topology with more levels such as five levels, etc., which is within the protection scope of the present application according to the specific application environment.
In addition, the converter may be an inverter, in which case, the DC side thereof is used to connect to a DC power source such as a photovoltaic array or an energy storage battery, and the DC bus thereof may be directly connected to the DC side thereof (as shown in fig. 2), or a primary pre-stage conversion circuit, such as at least one DC/DC conversion circuit, may be added between the DC bus and the DC side thereof, where one side of each DC/DC conversion circuit is used as a set of interfaces on the DC side of the converter for connecting to a corresponding DC power source, and the other side of each DC/DC conversion circuit is connected to the DC bus. Alternatively, the converter may be a converter connected to an AC power source such as a wind turbine generator, and in this case, the front-stage conversion circuit between the DC bus and the AC power source is specifically an AC/DC conversion circuit, and the AC side is connected to the AC power source and the DC side is connected to the DC bus. Regardless of the configuration employed, the added pre-stage conversion circuitry is controlled by the controller 30.
Taking the structure shown in fig. 2 as an example, the controller 30 may include: a duty ratio calculation unit 302, a current loop control unit 301, and a PWM control unit 303; the current loop control unit 301 is configured to determine an inverter modulation voltage V of the inverter circuit 10 according to an ac side output current ibabc of the inverter circuit 10 and an ac side output voltage Uabc of the converter mi The method comprises the steps of carrying out a first treatment on the surface of the The duty ratio calculation unit 302 is configured to obtain the voltage fluctuation V at the midpoint of the dc bus of the converter according to real time mid Generating a duty cycle D mi And outputs to the PWM control unit 303; the PWM control unit 303 is used for controlling the duty ratio D mi A PWM signal is generated to realize control of the inverter circuit 10.
Specifically, the duty ratio calculation unit 302 may extract the dc bus midpoint voltage fluctuation amount V by a band-pass filter mid A fluctuating component of a preset frequency in the frequency band. As described in the above embodiment, the preset frequency may include: fundamental frequency, and/or, frequency multiplication such as 3 times or 2 times; in practical applications, the setting of the preset frequency may be achieved by setting parameters of the band-pass filters, or may be achieved by setting a plurality of band-pass filters for real-time selection. When only one frequency is extracted at any time, that is, when the preset frequency includes only one frequency at any time, the controller 30 may also determine whether the ac side output current ibabc of the converter or the grid voltage occurs through the processing unitImbalance, and whether the inverter circuit 10 is operating properly, and in turn, the frequency of extraction is varied by setting or selecting parameters for the bandpass filter in different situations.
The current transformer provided by the embodiment introduces the neutral point voltage fluctuation quantity V of the direct current bus mid Extracting a fluctuation component of a preset frequency; specifically, the extraction can be performed according to the characteristic that the current transformer generates the midpoint fluctuation amount when in operation, for example, the main fluctuation amount of the current transformer is 3 times of frequency fluctuation components in normal operation, and when unbalanced power occurs, power frequency fluctuation such as 50Hz fluctuation components are generated; therefore, the 3-frequency multiplication fluctuation component and the power frequency fluctuation component can be extracted through the band-pass filter; then, the two half bus modulation voltages are compensated by the extracted fluctuation components, and PWM signals of the inverter circuit 10 are generated according to the compensation result; therefore, the harmonic compensation in steady state can be realized, the dynamic stability of the system is not influenced, and the contradiction problem of stability and midpoint disturbance can be solved.
The same and similar parts of the embodiments in this specification are all mutually referred to, and each embodiment focuses on the differences from the other embodiments. In particular, for a system or system embodiment, since it is substantially similar to a method embodiment, the description is relatively simple, with reference to the description of the method embodiment being made in part. The systems and system embodiments described above are merely illustrative, wherein the elements illustrated as separate elements may or may not be physically separate, and the elements shown as elements may or may not be physical elements, may be located in one place, or may be distributed over a plurality of network elements. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art will understand and implement the present application without undue burden.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative elements and steps are described above generally in terms of functionality in order to clearly illustrate the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
The features described in the various embodiments of the present disclosure may be interchanged or combined with one another in the description of the disclosed embodiments to enable those skilled in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (18)
1. The bus neutral point fluctuation compensation method of the converter is characterized by comprising the following steps of:
acquiring the neutral point voltage fluctuation quantity of a direct current bus of the converter in real time;
extracting fluctuation components of preset frequency in the fluctuation quantity of the neutral point voltage of the direct current bus;
compensating bus modulation voltage of an inverter circuit in the converter by using the fluctuation component;
and determining the duty ratio of the Pulse Width Modulation (PWM) signal of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit.
2. The method for compensating for bus neutral point fluctuation of a current transformer according to claim 1, wherein the preset frequency comprises: the fundamental frequency, and/or, multiple of the fundamental frequency.
3. The bus midpoint fluctuation compensation method of the current transformer according to claim 1, wherein extracting fluctuation components of a preset frequency in fluctuation amounts of the dc bus midpoint voltage comprises:
if the AC side output current of the converter or the power grid voltage is unbalanced, extracting a fluctuation component of fundamental wave frequency in the fluctuation quantity of the neutral point voltage of the DC bus;
and if the inverter circuit works normally, extracting fluctuation components which are multiple times of the frequency of the fundamental wave in the fluctuation quantity of the midpoint voltage of the direct current bus.
4. The bus midpoint fluctuation compensation method of the current transformer according to claim 1, wherein extracting fluctuation components of a preset frequency in fluctuation amounts of the dc bus midpoint voltage comprises:
and extracting the fluctuation component of the fundamental wave frequency and the fluctuation component of the frequency which is multiple times of the fundamental wave in the fluctuation quantity of the neutral voltage of the direct current bus.
5. The bus bar neutral point fluctuation compensation method of a current transformer according to any one of claims 2 to 4, wherein the frequency of the fundamental wave is multiple times that of the fundamental wave, comprising: 3 times or 2 times the frequency of the fundamental wave.
6. The bus neutral point fluctuation compensation method of the current transformer according to any one of claims 1 to 4, wherein obtaining the dc bus neutral point voltage fluctuation amount of the current transformer in real time comprises:
acquiring at least two of three voltages of direct-current bus voltage and two half bus voltages of the converter in real time to determine the two half bus voltages;
and calculating the difference between the voltages of the two half buses as the fluctuation amount of the neutral point voltage of the direct current bus.
7. The method for compensating for the fluctuation of the midpoint of a bus of a current transformer according to claim 6, wherein the fluctuation of the midpoint voltage of the dc bus is: the difference between the positive half bus voltage minus the negative half bus voltage.
8. The bus neutral point fluctuation compensation method of a current transformer according to any one of claims 1 to 4, wherein compensating a bus modulation voltage of an inverter circuit in the current transformer with the fluctuation component comprises:
and respectively overlapping half of the fluctuation component to corresponding half bus modulation voltage in the bus modulation voltage in two directions to obtain the compensation result.
9. The bus midpoint fluctuation compensation method of the current transformer according to claim 8, wherein the step of superimposing half of the fluctuation components to corresponding half bus modulation voltages of the bus modulation voltages in two directions, respectively, comprises:
adding half of the ripple component to the positive half bus modulation voltage; the method comprises the steps of,
and inverting half of the fluctuation component and then adding the inverted half of the fluctuation component to the negative half bus modulation voltage.
10. The method for compensating for bus midpoint fluctuation of a current transformer according to claim 8, wherein the two half bus modulation voltages are: half of the dc bus voltage.
11. The bus bar midpoint fluctuation compensation method of any one of claims 1 to 4, wherein determining the duty ratio of the PWM signal of the inverter circuit based on the compensation result and the inverter modulation voltage of the inverter circuit comprises:
for the phase modulation voltage which is larger than zero in the inversion modulation voltage, taking the ratio of the phase modulation voltage to the positive half bus modulation voltage in the compensation result as the duty ratio of the corresponding phase bridge arm in the inversion circuit;
for the phase modulation voltage smaller than zero in the inversion modulation voltage, taking the ratio of the phase modulation voltage to the negative half bus modulation voltage in the compensation result as the duty ratio of the corresponding phase bridge arm in the inversion circuit;
and regarding zero phase modulation voltage in the inversion modulation voltage as the duty ratio of a corresponding phase bridge arm in the inversion circuit.
12. The bus bar midpoint fluctuation compensation method of any one of claims 1 to 4, further comprising, before determining a duty ratio of a PWM signal of the inverter circuit based on a compensation result and an inverter modulation voltage of the inverter circuit:
acquiring an alternating-current side output current of the inverter circuit and an alternating-current side output voltage of the converter in real time;
performing current loop control on the inverter circuit according to the two to obtain an inverter modulation voltage of the inverter circuit;
after determining the duty ratio of the PWM signal of the inverter circuit according to the compensation result and the inverter modulation voltage of the inverter circuit, the method further comprises:
and generating the corresponding PWM signal according to the duty ratio.
13. A current transformer, comprising: an inverter circuit, a filter and a controller; wherein,,
the alternating current side of the inverter circuit is connected with the alternating current side of the converter through the filter;
the direct-current side positive and negative poles of the inverter circuit are respectively connected with corresponding poles of a direct-current bus, a bus capacitor branch is arranged between the positive and negative poles of the direct-current bus, and the midpoint of the bus capacitor branch is used as the midpoint of the direct-current bus to be connected with the midpoint of the direct-current side of the inverter circuit;
the inverter circuit is controlled by the controller;
the controller is configured to perform the bus bar midpoint fluctuation compensation method of the converter according to any one of claims 1 to 12.
14. The current transformer of claim 13, wherein the controller comprises: the device comprises a duty ratio calculation unit, a current loop control unit and a PWM control unit; wherein,,
the current loop control unit is used for determining the inversion modulation voltage of the inverter circuit according to the alternating-current side output current of the inverter circuit and the alternating-current side output voltage of the converter;
the duty ratio calculation unit is used for generating a duty ratio according to the DC bus midpoint voltage fluctuation quantity of the converter obtained in real time and outputting the duty ratio to the PWM control unit;
the PWM control unit is used for generating PWM signals according to the duty ratio and controlling the inverter circuit.
15. The converter according to claim 14, wherein the duty ratio calculation unit includes: and the band-pass filter is used for extracting fluctuation components of preset frequency in the fluctuation quantity of the midpoint voltage of the direct current bus.
16. The current transformer of claim 14, wherein the controller further comprises: and the processing unit is used for judging whether unbalance occurs in the alternating-current side output current or the power grid voltage of the converter and whether the inverter circuit works normally.
17. A converter according to any of claims 13 to 16, wherein the inverter circuit is a neutral point clamped converter topology.
18. A converter according to any of claims 13-16, wherein the dc bus is connected to a dc side of the converter, the dc side of the converter being adapted to be connected to a dc power source;
alternatively, the current transformer further includes: and one side of the front-stage conversion circuit is connected with the direct current bus, the other side of the front-stage conversion circuit is connected with an external power supply through the other side of the converter, and the front-stage conversion circuit is controlled by the controller.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310903891.0A CN116915035A (en) | 2023-07-21 | 2023-07-21 | Current transformer and bus midpoint fluctuation compensation method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202310903891.0A CN116915035A (en) | 2023-07-21 | 2023-07-21 | Current transformer and bus midpoint fluctuation compensation method thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN116915035A true CN116915035A (en) | 2023-10-20 |
Family
ID=88366437
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202310903891.0A Pending CN116915035A (en) | 2023-07-21 | 2023-07-21 | Current transformer and bus midpoint fluctuation compensation method thereof |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN116915035A (en) |
-
2023
- 2023-07-21 CN CN202310903891.0A patent/CN116915035A/en active Pending
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN104218590B (en) | Unbalance voltage compensating control method based on virtual synchronous machine | |
| US9490724B2 (en) | Methods for controlling electrical inverters and electrical inverters and systems using the same | |
| CN104377727B (en) | A kind of combining inverter multiple target works in coordination with the unbalance control method of optimization | |
| CN109638863B (en) | Multifunctional energy storage converter design method based on double deviation compensation control algorithm | |
| CN103683319A (en) | Grid connected inverter control method based on hysteresis modulation under unbalanced grid voltage condition | |
| US7778053B2 (en) | Power system having a voltage regulator with a notch filter | |
| Zhang et al. | Study on grid connected inverter used in high power wind generation system | |
| Azab | A finite control set model predictive control scheme for single-phase grid-connected inverters | |
| CN112653342B (en) | Complex vector current loop decoupling control device and method under static coordinate system | |
| US11309786B2 (en) | Controller for power inverter | |
| CN112636348B (en) | Control method of modular three-phase current type grid-connected inverter | |
| Marei et al. | PV interface system with LVRT capability based on a current controlled HFAC link converter | |
| Guerrero-Rodríguez et al. | Modelling, simulation and experimental verification for renewable agents connected to a distorted utility grid using a Real-Time Digital Simulation Platform | |
| CN110266044B (en) | Microgrid grid-connected control system and method based on energy storage converter | |
| Karafil et al. | Power control of single phase active rectifier | |
| JP5944670B2 (en) | Control circuit for power conversion circuit, grid-connected inverter system using this control circuit, and single-phase PWM converter system | |
| Yang et al. | Stability assessment of a three-phase grid-tied PV inverter with eigenvalue-based method | |
| Jeong et al. | High-performance control of three-phase four-wire DVR systems using feedback linearization | |
| CN116915035A (en) | Current transformer and bus midpoint fluctuation compensation method thereof | |
| Li et al. | Control stratories for grid-connected and island dualmode operated inverter under unbalanced grid voltage conditions | |
| Chelli et al. | A terminal Voltage Source Converter Control Connected to an Unbalanced grid | |
| Yepes et al. | Ineffectiveness of orthogonal axes cross-coupling decoupling technique in dual sequence current control | |
| Lin et al. | Design of fuzzy probabilistic wavelet neural network controller and its application in power control of grid-connected PV system during grid faults | |
| Ciuşdel et al. | Internal Model Repetitive Control for an Active Power Filter | |
| Sun et al. | VSG Sequence Impedance Modeling and Stability Analysis of Dead-Beat Control |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination |