CN112379153B - Direct current oscillation detection circuit, direct current arc detection circuit and inverter - Google Patents
Direct current oscillation detection circuit, direct current arc detection circuit and inverter Download PDFInfo
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- CN112379153B CN112379153B CN202011195345.9A CN202011195345A CN112379153B CN 112379153 B CN112379153 B CN 112379153B CN 202011195345 A CN202011195345 A CN 202011195345A CN 112379153 B CN112379153 B CN 112379153B
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- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
- G01R19/16566—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533
- G01R19/16571—Circuits and arrangements for comparing voltage or current with one or several thresholds and for indicating the result not covered by subgroups G01R19/16504, G01R19/16528, G01R19/16533 comparing AC or DC current with one threshold, e.g. load current, over-current, surge current or fault current
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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
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
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Abstract
The invention provides a direct current oscillation detection circuit, a direct current arc detection circuit and an inverter, which are applied to the technical field of power electronics, wherein the direct current oscillation detection circuit comprises at least one path of oscillation sampling circuit, a voltage sampling circuit and an oscillation detection controller, the oscillation sampling circuit comprises a current sampling circuit and a conversion circuit which are connected in parallel, the current sampling circuit collects alternating current at the direct current side of the inverter, and the conversion circuit converts the obtained alternating current into sampling voltage; the voltage sampling circuit is respectively connected with each conversion circuit and collects sampling voltages fed back by each conversion circuit; the oscillation detection controller performs direct current oscillation detection based on the obtained sampling voltage according to a preset oscillation detection logic. By the direct current oscillation detection circuit provided by the invention, the alternating current at the direct current side of the photovoltaic system can be collected, so that the direct current oscillation detection is carried out on the photovoltaic system, and the running stability of the photovoltaic system is improved.
Description
Technical Field
The present invention relates to the field of power electronics, and in particular, to a dc oscillation detection circuit, a dc arc detection circuit, and an inverter.
Background
Along with the large-scale application of photovoltaic power generation, the current oscillation phenomenon of the direct current side of an inverter in a photovoltaic system gradually attracts attention. Because the installation positions of the photovoltaic modules in the photovoltaic system are relatively scattered, the distance between each photovoltaic module and the photovoltaic equipment such as an inverter is relatively long, the distributed inductance inevitably exists in a long-distance connecting cable, and the equivalent impedance formed by the distributed inductance and nonlinear parameters such as the capacitance of the photovoltaic module to the ground can cause the DC side of the photovoltaic system to appear larger or smaller and is an alternating current which changes periodically, namely DC oscillation occurs.
The direct current oscillation can reduce the whole generated energy of a photovoltaic system, the photovoltaic module can be damaged, the ageing of the inverter and the photovoltaic module is accelerated, and the serious direct current oscillation can even directly damage the internal circuit of the inverter.
In view of the serious influence of the direct current oscillation on the photovoltaic system, how to collect the alternating current at the direct current side of the photovoltaic system and detect the direct current oscillation of the photovoltaic system becomes one of the technical problems to be solved by the technicians in the field.
Disclosure of Invention
The invention provides a direct current oscillation detection circuit, a direct current arc detection circuit and an inverter, which can collect alternating current at the direct current side of a photovoltaic system and further perform direct current oscillation detection on the photovoltaic system.
In order to achieve the above purpose, the technical scheme provided by the application is as follows:
in a first aspect, the present invention provides a dc oscillation detection circuit, comprising: at least one path of oscillation sampling circuit, voltage sampling circuit and oscillation detection controller, wherein,
the oscillation sampling circuit comprises a current sampling circuit and a conversion circuit, wherein,
the current sampling circuit collects alternating current of the direct current side of the inverter;
the conversion circuit converts the alternating current into a sampling voltage;
the voltage sampling circuit collects the sampling voltage fed back by each conversion circuit;
and the oscillation detection controller performs direct current oscillation detection based on the sampling voltage according to preset oscillation detection logic.
Optionally, the oscillation sampling circuit further includes: a protection circuit, wherein,
the protection circuit is connected with the conversion circuit in parallel;
the protection circuit is used for clamping the sampling voltage in a preset voltage range when the sampling voltage is greater than or equal to a preset voltage threshold value;
wherein, the upper limit value of the preset voltage range is smaller than the preset voltage threshold value.
Optionally, the dc oscillation detecting circuit provided in the first aspect of the present invention further includes: at least one controllable switch circuit, wherein,
each controllable switch circuit is respectively connected in series with at least one path of oscillation sampling circuit;
the control end of each controllable switch circuit receives a first control signal, wherein the first control signal is used for controlling the controllable switch circuits to be disconnected when the duration time of the sampling voltage clamp in the preset voltage range by the protection circuit is greater than or equal to a preset duration threshold value.
Optionally, the oscillation detection controller is respectively connected with a control end of each controllable switch circuit, and the oscillation detection controller is further configured to generate the first control signal according to the sampling voltage.
Optionally, the protection circuit includes: a first protection resistor and a first bidirectional transient diode connected in series.
Optionally, the protection circuit includes: a forward protection circuit and a reverse protection circuit, wherein,
the forward protection circuit and the reverse protection circuit are connected in parallel, and the conduction directions of the forward protection circuit and the reverse protection circuit are opposite;
the forward protection circuit comprises a first voltage dividing resistor, a second protection resistor, a first unidirectional transient diode and a first switching tube, wherein,
the first voltage dividing resistor and the second voltage dividing resistor are connected in series to form a first series branch;
the second protection resistor, the first unidirectional transient diode and the first switching tube are connected in series to form a second series branch;
the first serial branch and the second serial branch are connected in parallel;
the control end of the first switching tube is connected with a series connection point of the first voltage dividing resistor and the second voltage dividing resistor;
the reverse protection circuit comprises a third voltage dividing resistor, a fourth voltage dividing resistor, a third protection resistor, a second unidirectional transient diode and a second switching tube, wherein,
the third voltage dividing resistor and the fourth voltage dividing resistor are connected in series to form a third series branch;
the third protection resistor, the second unidirectional transient diode and the second switching tube are connected in series to form a fourth series branch;
the third series branch and the fourth series branch are connected in parallel;
and the control end of the second switching tube is connected with the series connection point of the third voltage dividing resistor and the fourth voltage dividing resistor.
Optionally, the protection circuit includes: a fourth protection resistor, a second bidirectional transient diode and a third switching tube, wherein,
the fourth protection resistor is connected with the third switching tube in series through the second bidirectional transient diode;
and the control end of the third switching tube receives a second control signal, wherein the second control signal is used for controlling the third switching tube to be conducted when the sampling voltage is greater than or equal to the preset voltage threshold value.
Optionally, the oscillation detection controller is connected with a control end of the third switching tube;
the oscillation detection controller is further configured to generate the second control signal according to the sampling voltage.
Optionally, the controllable switching circuit includes one of a relay, a contactor, and a semiconductor switch without an anti-parallel diode.
Optionally, the oscillation sampling circuit comprises one of a current transformer and a hall current sensor;
the switching circuit includes a switching resistor.
Optionally, the oscillation detection controller includes an inverter controller inside the inverter.
Optionally, the oscillation detection controller is further configured to perform a preset oscillation protection function according to a dc oscillation detection result;
the preset oscillation protection function comprises the steps of sending an early warning signal and controlling the inverter to stop.
In a second aspect, the invention provides a direct current arc detection circuit comprising an arc detection main circuit and the direct current oscillation detection circuit according to any one of the first aspects of the invention, wherein,
the arc detection main circuit is respectively connected with the conversion circuits of the oscillation sampling circuits in the direct current oscillation detection circuit in parallel;
the arc detection main circuit is used for executing a preset arc detection function according to the sampling voltage fed back by each conversion circuit.
In a third aspect, the present invention provides an inverter comprising: an inverter main circuit, an inverter controller, and a direct current oscillation detection circuit according to any one of the first aspect of the present invention, wherein,
the direct current oscillation detection circuit collects alternating current of the direct current side of the inversion main circuit and carries out direct current oscillation detection based on the alternating current;
the inversion controller is used for controlling the inversion main circuit to execute a preset inversion function.
In a fourth aspect, the present invention provides an inverter, including an inverter main circuit, an inverter controller, and the dc arc detection circuit according to the second aspect of the present invention, wherein,
the direct current arc detection circuit collects alternating current of the direct current side of the inversion main circuit and carries out direct current arc detection based on the alternating current;
the inversion controller is used for controlling the inversion main circuit to execute a preset inversion function.
Based on the above, the direct current oscillation detection circuit provided by the invention comprises at least one path of oscillation sampling circuit, a voltage sampling circuit and an oscillation detection controller, wherein the oscillation sampling circuit comprises a current sampling circuit and a conversion circuit which are connected in parallel, the current sampling circuit collects alternating current of the direct current side of the inverter, and the conversion circuit converts the obtained alternating current into sampling voltage; the voltage sampling circuit is respectively connected with each conversion circuit and collects sampling voltages fed back by each conversion circuit; the oscillation detection controller performs direct current oscillation detection based on the obtained sampling voltage according to a preset oscillation detection logic. By the direct current oscillation detection circuit provided by the invention, the alternating current at the direct current side of the photovoltaic system can be collected, so that the direct current oscillation detection is carried out on the photovoltaic system, and the running stability of the photovoltaic system is improved.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are necessary for the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention and that other drawings may be obtained from them without inventive effort for a person skilled in the art.
Fig. 1 is a block diagram of a dc oscillation detecting circuit according to an embodiment of the present invention;
fig. 2 is a schematic diagram of an application scenario of a dc oscillation detection circuit according to an embodiment of the present invention;
fig. 3 is a circuit topology diagram of a dc oscillation detecting circuit according to an embodiment of the present invention;
fig. 4 is a circuit topology diagram of another dc oscillation detecting circuit according to an embodiment of the present invention;
fig. 5 is a circuit topology diagram of a protection circuit according to an embodiment of the present invention;
FIG. 6 is a circuit topology of another protection circuit provided by an embodiment of the present invention;
FIG. 7 is a circuit topology of yet another protection circuit provided by an embodiment of the present invention;
fig. 8 is a schematic diagram of an application scenario of a dc arc detection circuit according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.
Optionally, referring to fig. 1, fig. 1 is a block diagram of a dc oscillation detection circuit according to an embodiment of the present invention, where the dc oscillation detection circuit according to the embodiment of the present invention includes: at least one oscillating sampling circuit 10, a voltage sampling circuit 20 and an oscillating detection controller 30, wherein,
the oscillation sampling circuit 10 specifically includes a current sampling circuit 110 and a conversion circuit 120. The current sampling circuit 110 and the conversion circuit 120 are connected in parallel to form a closed sampling loop. In practical applications, the current sampling circuit 110 is used to collect ac current on the dc side of the inverter, and of course, the ac current mentioned herein refers to oscillating current existing on the dc side of the inverter. The current sampling circuit 110 collects the ac current and transmits the ac current to the conversion circuit 120, and the conversion circuit 120 converts the ac current into a sampling voltage.
Optionally, in practical application, the electric energy transmission manner from the output end of the photovoltaic module to the dc side of the inverter is implemented in a dc manner, so that a specific position where the current sampling circuit 110 collects ac current on the dc side of the inverter may have multiple positions, for example, a connection line between the photovoltaic module and the MPPT, a connection line between the MPPT and the bus, and a connection line between the bus and the dc side of the inverter may be used as a position where the current sampling circuit 110 collects ac current, and the specific position where the current sampling circuit 110 collects ac current on the dc side of the inverter is not limited.
The voltage sampling circuit 20 collects the sampling voltages fed back from the respective conversion circuits. Specifically, in practical application, the oscillating current is often periodically changed, that is, the oscillating current is similar to the power frequency current, and there is a possibility that an interference current exists on the dc side of the inverter, and the interference current does not belong to the dc current, but does not have the characteristic of the ac current, so the voltage sampling circuit 20 should obtain the characteristic of the ac current as accurately and comprehensively as possible in the process of collecting the sampled voltage, and effectively distinguish the oscillating current from the interference current, thereby providing powerful support for the subsequent oscillation detection controller 30 to analyze the ac current.
Optionally, to achieve the above objective, the voltage sampling circuit 20 may collect the sampled voltage fed back by the conversion circuit 120 in each path of oscillation sampling circuit 10 according to a preset period, so as to obtain the amplitude-frequency characteristic of the oscillation current, and on the basis of accurately analyzing the oscillation current, can also distinguish the oscillation current from the interference current according to the amplitude-frequency characteristic obtained by sampling.
It should be noted that, for the specific implementation of the voltage sampling circuit 20, the implementation may refer to the prior art, any voltage sampling circuit capable of implementing periodic sampling of the sampling voltage fed back by each oscillation sampling circuit 10 is optional, and the specific configuration of the voltage sampling circuit 20 is not limited in the present invention.
Further, the oscillation detection controller 30 receives the sampling voltage collected by the voltage sampling circuit 20, and performs dc oscillation detection according to a preset oscillation detection logic. For example, the dc oscillation can be determined if the corresponding deviation requirement is satisfied by comparing the preset typical oscillation current curve with the ac current curve obtained based on the sampling and spotting. For another example, it may be determined whether the corresponding ac current has periodicity according to the obtained sampling voltage, and whether the amplitude of the ac current exceeds a preset amplitude threshold value, and if it is determined that the ac current that alternates according to a certain period and that the amplitude exceeds the preset threshold value does exist in the dc side of the inverter according to the obtained sampling voltage, it may be determined that the dc oscillation does occur in the dc side of the inverter.
It should be noted that, how to determine whether dc oscillation occurs in the dc loop based on the obtained voltage sampling value may be implemented by referring to a dc oscillation determination theory in the prior art, which is not particularly limited in the present invention.
Optionally, in the case that it is determined that the dc side of the inverter does generate dc oscillation, the oscillation detection controller 30 provided in the embodiment of the present invention is further configured to perform a preset oscillation protection function according to a dc oscillation detection result, for example, may send an early warning signal when the dc oscillation is not very serious; in the case of very severe dc oscillations, the inverter can be controlled directly to stop.
Optionally, referring to fig. 2, fig. 2 is a schematic diagram of an application scenario of a dc oscillation detection circuit provided in an embodiment of the present invention. As shown in the figure, every two photovoltaic modules PV are connected with the same MPPT, the output end of each MPPT is connected with the direct current side of the inverter through a direct current bus, and after the conversion of direct current-alternating current is completed by the inverter, alternating current is transmitted to a power grid. In this application scenario, the current sampling circuit 110 collects the ac current in the connection line between the photovoltaic module and the MPPT, and after passing through the conversion circuit 120, the voltage sampling circuit 20, and the oscillation detection controller 30, the dc oscillation detection process is implemented.
Further, in practical application, in order to reduce the number of controllers, improve the overall integration level of the system, reduce the hardware cost, the oscillation detection controller 30 in this embodiment and other embodiments may be further implemented based on an inverter controller inside the inverter, that is, the function implemented by the oscillation detection controller 30 is integrated into the inverter controller, the voltage sampling circuit 20 directly feeds back the obtained sampling voltage to the inverter controller, and the inverter controller directly completes the dc oscillation detection and the aforementioned preset oscillation protection function.
In summary, the dc oscillation detection circuit provided by the present invention includes at least one path of oscillation sampling circuit, a voltage sampling circuit, and an oscillation detection controller, where the oscillation sampling circuit includes a current sampling circuit and a conversion circuit connected in parallel, the current sampling circuit collects an ac current on a dc side of the inverter, and the conversion circuit converts the obtained ac current into a sampling voltage; the voltage sampling circuit is respectively connected with each conversion circuit and collects sampling voltages fed back by each conversion circuit; the oscillation detection controller performs direct current oscillation detection based on the obtained sampling voltage according to a preset oscillation detection logic. By the direct current oscillation detection circuit provided by the invention, the alternating current at the direct current side of the photovoltaic system can be collected, so that the direct current oscillation detection is carried out on the photovoltaic system, and the running stability of the photovoltaic system is improved.
Optionally, fig. 3 is a circuit topology diagram of a dc oscillation detecting circuit provided in the embodiment of the present invention, and in the embodiment shown in fig. 3, an optional configuration manner of the oscillation sampling circuit is specifically shown.
Specifically, the current sampling circuit 110 in the oscillation sampling circuit is realized by a current transformer (shown as T1 to Tn in the figure), and the switching circuit 120 is realized by a switching resistor (shown as R1 to Rn in the figure). Based on the basic principle of the current transformer, the primary winding of the current transformer can be a connecting line used for transmitting a direct current circuit in a photovoltaic system, when an oscillating alternating current exists in the connecting line, a corresponding alternating current is induced in the secondary winding of the current transformer 110 based on the electromagnetic induction principle and flows through the switching resistor 120, and the switching resistor 120 is used for realizing the conversion from current to voltage. The specific connection mode of the current sampling circuit and the dc-to-dc connection line of the inverter, which is realized by using the current transformer, can be realized by referring to the prior art, and will not be described herein.
Optionally, the current sampling circuit may be further implemented by a hall current sensor, and the hall current sensor is used to collect an ac current in the dc current. Similarly, the connection between the hall current sensor and the dc link of the dc side of the inverter can be realized by referring to the prior art.
It should be noted that any implementation manner capable of implementing ac current collection and converting current into sampling voltage is optional, and belongs to the protection scope of the present invention without exceeding the core idea of the present invention.
In practical application, the ac current existing on the dc side of the inverter is larger or smaller, and the ac current tolerance of the inverter and the dc oscillation detection circuit provided by the invention to oscillation is different. When weak oscillation occurs, the inverter and the direct current oscillation detection circuit are not affected, and can normally operate. However, as the oscillation process is further increased, the ac current is larger and larger, and in the case of using the dc oscillation detection circuit provided in the embodiment shown in fig. 3, the power consumption on the switching resistor is also rapidly increased, and if the ac current is continuously increased, the switching resistor may be burned out.
To solve this problem, another dc oscillation detecting circuit is provided in the embodiments of the present invention. Optionally, referring to fig. 4, fig. 4 is a circuit topology diagram of another dc oscillation detecting circuit according to an embodiment of the present invention, where the oscillation sampling circuit of the dc oscillation detecting circuit according to the embodiment further includes a protection circuit 40 based on any of the above embodiments.
In any oscillation sampling circuit, the protection circuit 40 is connected in parallel with the conversion circuit 120, and when the sampling voltage corresponding to the two ends of the conversion circuit 120 is greater than or equal to a preset voltage threshold, the sampling voltage, that is, the voltage clamp at the two ends of the conversion circuit 120 is located in a preset voltage range.
In practical application, the specific setting of the preset voltage threshold needs to be selected in combination with the actual protection requirement and the bearing capacity of the conversion circuit, and the specific value of the preset voltage threshold is not limited.
It is conceivable that the upper limit value of the preset voltage range should be smaller than the aforementioned preset voltage threshold value in order to ensure that the loss of the switching resistor can be reduced rapidly and effectively. Further, since the resistance of the conversion resistor is determined, in this embodiment, the sampling voltage of the conversion resistor is clamped within the preset voltage range, which is equivalent to positioning the ac current clamp flowing through the conversion resistor within the preset current range, so that the loss generated by the conversion resistor can be effectively reduced, and the burnout of the conversion resistor is avoided.
Optionally, referring to fig. 5, fig. 5 is a circuit topology diagram of a protection circuit according to an embodiment of the present invention. In this embodiment, the protection circuit includes: a first protection resistor R1' and a first bidirectional transient diode D1. The first protection resistor R1' and the first bidirectional transient diode D1 are connected in series, forming a series branch. The resulting series branch is connected in parallel with the switching resistor.
Based on the circuit shown in fig. 5, under the condition that the alternating current flowing through the converting resistor continuously increases, the voltages at two ends of the converting resistor, namely, the sampling voltage, are greater than or equal to the voltages at two ends of the first bidirectional transient diode D1 and the first protection resistor R1', so that the first bidirectional transient diode D1 works, and based on the basic working principle of the bidirectional transient diode, the voltage clamp at two ends A, B shown in fig. 5, namely, the voltage clamp at two ends of the converting circuit, can be located in a preset voltage range.
Optionally, referring to fig. 6, fig. 6 is a circuit topology diagram of another protection circuit according to an embodiment of the present invention. In this embodiment, the protection circuit includes: the device comprises a forward protection circuit and a reverse protection circuit, wherein the forward protection circuit and the reverse protection circuit are connected in parallel, and the conduction directions of the forward protection circuit and the reverse protection circuit are opposite.
Specifically, the forward protection circuit includes a first voltage dividing resistor R2', a second voltage dividing resistor R3', a second protection resistor R4', a first unidirectional transient diode D2, and a first switching tube Q1, wherein,
the first voltage dividing resistor R2 'and the second voltage dividing resistor R3' are connected in series to form a first series branch. One end of the second protection resistor R4' is connected with one end of the first unidirectional transient diode D2, the other end of the first unidirectional transient diode D2 is connected with the first switching tube Q1 in series, and the first unidirectional transient diode D2, the first switching tube Q1 and the second unidirectional transient diode D2 form a second series branch.
The first and second series branches are connected in parallel, and the control end of the first switching tube Q1 is connected to the series connection point of the first voltage dividing resistor R2 'and the second voltage dividing resistor R3'.
In practical application, along with the gradual rise of the voltage at the A, B end, i.e. the two ends of the conversion circuit, the voltage at the series connection point of the first voltage dividing resistor R2 'and the second voltage dividing resistor R3' in the first series branch is also gradually raised, so that the first switching tube Q1 is turned on, and meanwhile, the first unidirectional transient diode D2 is also turned on, so as to absorb most of the alternating current, and the voltage clamp at the two ends of A, B is located in the preset voltage range.
The reverse protection circuit includes a third voltage dividing resistor R6', a fourth voltage dividing resistor R7', a third protection resistor R5', a second unidirectional transient diode D3, and a second switching tube Q2, similar to the circuit structure of the forward protection circuit, wherein,
the third voltage dividing resistor R6 'and the fourth voltage dividing resistor R7' are connected in series to form a third series branch; the third protection resistor R5', the second unidirectional transient diode D3 and the second switching tube Q2 are sequentially connected in series to form a fourth series branch.
The third serial branch and the fourth serial branch are connected in parallel, and the control end of the second switching tube Q2 is connected with the serial connection point of the third voltage dividing resistor R6 'and the fourth voltage dividing resistor R7'.
In practical application, the action process and protection principle of each component in the reverse protection circuit are similar to those of the forward protection circuit, and are not repeated here. The only difference is that the forward protection circuit is responsible for protecting forward alternating current, and the reverse protection circuit is responsible for protecting reverse alternating current, and the protection effect of the protection circuit shown in fig. 5 can be achieved only if the forward protection circuit and the reverse protection circuit are mutually matched. It is conceivable that, in order to achieve the above technical effect, the first unidirectional transient diode and the second unidirectional transient diode should be connected in an antiparallel manner.
Optionally, referring to fig. 7, fig. 7 is a circuit topology diagram of a further protection circuit according to an embodiment of the present invention, where the protection circuit provided in the embodiment includes: a fourth protection resistor R8', a second bidirectional transient diode D4, and a third switching tube Q3, wherein,
the fourth protection resistor R8' is connected in series with the third switching tube Q3 via a second bidirectional transient diode D4. The control end of the third switching tube Q3 receives a second control signal, where the second control signal is used to control the third switching tube to be turned on when the voltages at two ends of A, B, that is, the sampling voltage of the conversion circuit is greater than or equal to a preset voltage threshold. After the third switching tube Q3 is turned on, the second bidirectional transient diode D4 is also turned on, and based on the basic principle of the transient diode, the voltage clamp at two ends of A, B is located within the preset voltage range.
Optionally, the oscillation detection controller 30 in the dc oscillation detection circuit provided in any of the foregoing embodiments may be further connected to a control end of the third switching tube in the protection circuit provided in this embodiment, and generate the second control signal according to the sampling voltage fed back by the conversion circuit, that is, the protection circuit provided in this embodiment is controlled by the oscillation detection controller to protect the conversion circuit.
Further, if the sampling voltage clamp at both ends of the conversion circuit is located within the preset voltage range after the protection circuit is operated, the ac current in the system is still continuously increased, which may damage the protection circuit, and in order to solve this problem, in the embodiment shown in fig. 4, a controllable switch circuit 50 is further provided, and each protection circuit 40 is protected by the controllable switch circuit 50.
In the example shown in fig. 4, only one controllable switching circuit 50 is provided in the detection circuit. The controllable switch circuits are connected in series in the loops of the oscillation sampling circuits, and the communication state of the loops of the oscillation sampling circuits can be controlled through the controllable switch circuits 50, namely, when the controllable switch circuits 50 are conducted, the loops corresponding to the oscillation sampling circuits are in a closed state, and the oscillation sampling circuits can work normally; when the controllable switch circuit 50 is turned off, the loop of each oscillation sampling circuit is also turned off, and the oscillating ac current cannot flow through each oscillation sampling circuit.
The first control signal is used for controlling the controllable switch circuit to be turned off when the duration time of the sampling voltage clamp in the preset voltage range is longer than or equal to a preset duration time threshold value by the protection circuit.
Based on the foregoing, it is known that when the protection circuit is operated, the sampling voltage of the conversion circuit is clamped within the preset voltage range, and the ac current flowing through the conversion circuit is also within a certain corresponding current range. When the timing time is longer than or equal to a preset time threshold, the controllable switch is controlled to be turned off, and alternating current does not circulate through the protection circuit, so that the protection of the protection circuit is realized.
It is conceivable that there may be various determination manners for the starting time of the protection circuit to clamp the sampling voltage of the conversion circuit within the preset voltage range, for example, by determining the change of the sampling voltage of the conversion circuit, by determining the connection state of the protection circuit, or by determining the voltage change at both ends of the protection circuit, etc., and the specific statistical method of the duration of the sampling voltage clamp for the protection circuit within the preset voltage range is not limited.
It is further conceivable that in practical application of the oscillation detection circuit, it is completely possible that each oscillation sampling circuit collects ac currents with different oscillation degrees, that is, in the case that the dc oscillation detection circuit is provided with multiple oscillation sampling circuits, there is a case that a certain or part of the protection circuits act first, and if the controllable switch circuit is provided with one path, the whole dc oscillation detection circuit will control the controllable switch circuit to act according to the duration of the protection circuit that acts first, that is, the whole dc oscillation detection circuit is protected according to the oscillation detection circuit with the worst oscillation.
Based on the above, two or more controllable switch circuits may be further provided, where the cost and the equipment space allow, where each controllable switch circuit is connected in series with at least one of the oscillation sampling circuits. Under the most ideal condition, a controllable switch circuit can be arranged for each path of oscillation sampling circuit to realize independent protection control, and the cost and the space occupation of the arrangement are higher.
Alternatively, as an alternative implementation, the first control signal for controlling the controllable switching circuit may also be generated by the oscillation detection controller 30 described above. The oscillation detection controller 30 is connected to the control terminals of the controllable switch circuits, respectively, and controls the controllable switch circuits according to the control logic.
Alternatively, the controllable switching circuit described in any of the above embodiments may be implemented using any of a relay, a contactor, and a semiconductor switch without an anti-parallel diode.
Optionally, referring to fig. 8, fig. 8 is a schematic diagram of an application scenario of a dc arc detection circuit provided in an embodiment of the present invention, and meanwhile, fig. 8 also provides a basic structural block diagram of the dc arc detection circuit. The direct current arc detection circuit provided in this embodiment includes: the arc detection main circuit and the direct current oscillation detection circuit provided by any one of the embodiments above, wherein,
the arc detection main circuit is respectively connected with the conversion circuits of the oscillation sampling circuits in the direct current oscillation detection circuit in parallel, and the conversion circuits of the direct current oscillation detection circuit provide sampling voltages.
The arc detection main circuit is used for executing a preset arc detection function according to the sampling voltage fed back by each conversion circuit.
As can be seen from fig. 8, the dc arc detection circuit provided in this embodiment multiplexes the oscillation sampling circuit with the dc oscillation detection circuit, and the oscillation sampling circuit provides sampling voltages for the dc arc detection main circuit and the dc oscillation detection circuit, respectively. Through multiplexing oscillation sampling circuit, not only can reduce the use of a portion components and parts, more importantly, can also realize the protection to direct current arc detection circuit through controllable switch circuit: when each controllable switch circuit is disconnected, the direct current arc detection main circuit can not continuously obtain sampling voltage, so that the safety of the direct current arc detection main circuit is protected.
It should be emphasized that in the example shown in fig. 8, the oscillation detection controller is specifically implemented by an inverter controller, and the inverter controller also integrates the dc arc detection function. The arc detection main circuit sends an arc detection result obtained based on the sampling voltage provided by the conversion circuit to the inverter controller, and the inverter controller determines further protection operation related to the direct current arc according to preset protection logic (the implementation can be referred to in the prior art, and details are not repeated here). Of course, a controller may also be provided separately, if the cost of the system permits.
Optionally, an embodiment of the present invention further provides an inverter, including: an inverter main circuit, an inverter controller, and a direct current oscillation detection circuit provided by any of the above embodiments, wherein,
the direct current oscillation detection circuit collects alternating current of the direct current side of the inversion main circuit and carries out direct current oscillation detection based on the alternating current;
the inversion controller is used for controlling the inversion main circuit to execute a preset inversion function.
Optionally, an embodiment of the present invention further provides an inverter, including an inverter main circuit, an inverter controller, and a dc arc detection circuit provided in any one of the foregoing embodiments of the present invention, where,
the direct current arc detection circuit collects alternating current of the direct current side of the inversion main circuit and carries out direct current arc detection based on the alternating current;
the inversion controller is used for controlling the inversion main circuit to execute a preset inversion function.
In the invention, each embodiment is described in a progressive manner, and each embodiment is mainly used for illustrating the difference from other embodiments, and the same similar parts among the embodiments are mutually referred. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
The above description is only of the preferred embodiment of the present invention, and is not intended to limit the present invention in any way. While the invention has been described with reference to preferred embodiments, it is not intended to be limiting. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present invention or modifications to equivalent embodiments using the methods and technical contents disclosed above, without departing from the scope of the technical solution of the present invention. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.
Claims (14)
1. A dc oscillation detection circuit for performing dc oscillation detection on a photovoltaic system, comprising: at least one path of oscillation sampling circuit, voltage sampling circuit and oscillation detection controller, wherein,
the oscillation sampling circuit comprises a current sampling circuit and a conversion circuit, wherein,
the current sampling circuit collects alternating current of the direct current side of the inverter;
the conversion circuit converts the alternating current into a sampling voltage;
the voltage sampling circuit collects the sampling voltage fed back by each conversion circuit;
the oscillation detection controller performs direct current oscillation detection based on the sampling voltage according to preset oscillation detection logic;
wherein, the oscillation sampling circuit further includes: a protection circuit, wherein,
the protection circuit is connected with the conversion circuit in parallel;
the protection circuit is used for clamping the sampling voltage in a preset voltage range when the sampling voltage is greater than or equal to a preset voltage threshold value;
wherein, the upper limit value of the preset voltage range is smaller than the preset voltage threshold value.
2. The direct current oscillation detection circuit according to claim 1, further comprising: at least one controllable switch circuit, wherein,
each controllable switch circuit is respectively connected in series with at least one path of oscillation sampling circuit;
the control end of each controllable switch circuit receives a first control signal, wherein the first control signal is used for controlling the controllable switch circuits to be disconnected when the duration time of the sampling voltage clamp in the preset voltage range by the protection circuit is greater than or equal to a preset duration threshold value.
3. The direct current oscillation detection circuit of claim 2, wherein the oscillation detection controller is respectively connected to the control terminals of the controllable switch circuits, and the oscillation detection controller is further configured to generate the first control signal according to the sampling voltage.
4. The direct current oscillation detection circuit according to claim 1, wherein the protection circuit includes: a first protection resistor and a first bidirectional transient diode connected in series.
5. The direct current oscillation detection circuit according to claim 1, wherein the protection circuit includes: a forward protection circuit and a reverse protection circuit, wherein,
the forward protection circuit and the reverse protection circuit are connected in parallel, and the conduction directions of the forward protection circuit and the reverse protection circuit are opposite;
the forward protection circuit comprises a first voltage dividing resistor, a second protection resistor, a first unidirectional transient diode and a first switching tube, wherein,
the first voltage dividing resistor and the second voltage dividing resistor are connected in series to form a first series branch;
the second protection resistor, the first unidirectional transient diode and the first switching tube are connected in series to form a second series branch;
the first serial branch and the second serial branch are connected in parallel;
the control end of the first switching tube is connected with a series connection point of the first voltage dividing resistor and the second voltage dividing resistor;
the reverse protection circuit comprises a third voltage dividing resistor, a fourth voltage dividing resistor, a third protection resistor, a second unidirectional transient diode and a second switching tube, wherein,
the third voltage dividing resistor and the fourth voltage dividing resistor are connected in series to form a third series branch;
the third protection resistor, the second unidirectional transient diode and the second switching tube are connected in series to form a fourth series branch;
the third series branch and the fourth series branch are connected in parallel;
and the control end of the second switching tube is connected with the series connection point of the third voltage dividing resistor and the fourth voltage dividing resistor.
6. The direct current oscillation detection circuit according to claim 1, wherein the protection circuit includes: a fourth protection resistor, a second bidirectional transient diode and a third switching tube, wherein,
the fourth protection resistor is connected with the third switching tube in series through the second bidirectional transient diode;
and the control end of the third switching tube receives a second control signal, wherein the second control signal is used for controlling the third switching tube to be conducted when the sampling voltage is greater than or equal to the preset voltage threshold value.
7. The direct current oscillation detection circuit according to claim 6, wherein the oscillation detection controller is connected to a control terminal of the third switching tube;
the oscillation detection controller is further configured to generate the second control signal according to the sampling voltage.
8. The direct current oscillation detection circuit of claim 2, wherein the controllable switching circuit comprises one of a relay, a contactor, and a semiconductor switch without an anti-parallel diode.
9. The direct current oscillation detection circuit according to any one of claims 1 to 8, wherein the oscillation sampling circuit includes one of a current transformer and a hall current sensor;
the switching circuit includes a switching resistor.
10. The direct current oscillation detection circuit according to any one of claims 1 to 8, wherein the oscillation detection controller includes an inverter controller inside the inverter.
11. The direct current oscillation detection circuit according to any one of claims 1 to 8, wherein the oscillation detection controller is further configured to perform a preset oscillation protection function according to a direct current oscillation detection result;
the preset oscillation protection function comprises the steps of sending an early warning signal and controlling the inverter to stop.
12. The direct current arc detection circuit is characterized by comprising an arc detection main circuit and a direct current oscillation detection circuit, wherein the direct current oscillation detection circuit comprises: at least one path of oscillation sampling circuit, voltage sampling circuit and oscillation detection controller, wherein,
the oscillation sampling circuit comprises a current sampling circuit and a conversion circuit, wherein,
the current sampling circuit collects alternating current of the direct current side of the inverter;
the conversion circuit converts the alternating current into a sampling voltage;
the voltage sampling circuit collects the sampling voltage fed back by each conversion circuit;
the oscillation detection controller performs direct current oscillation detection based on the sampling voltage according to preset oscillation detection logic;
the arc detection main circuit is respectively connected with the conversion circuits of the oscillation sampling circuits in the direct current oscillation detection circuit in parallel;
the arc detection main circuit is used for executing a preset arc detection function according to the sampling voltage fed back by each conversion circuit.
13. An inverter, comprising: an inversion main circuit, an inversion controller, and a direct current oscillation detection circuit, wherein the inversion main circuit comprises: at least one path of oscillation sampling circuit, voltage sampling circuit and oscillation detection controller, wherein,
the oscillation sampling circuit comprises a current sampling circuit and a conversion circuit, wherein,
the current sampling circuit collects alternating current of the direct current side of the inverter;
the conversion circuit converts the alternating current into a sampling voltage;
the voltage sampling circuit collects the sampling voltage fed back by each conversion circuit;
the oscillation detection controller performs direct current oscillation detection based on the sampling voltage according to preset oscillation detection logic;
the direct current oscillation detection circuit collects alternating current of the direct current side of the inversion main circuit and carries out direct current oscillation detection based on the alternating current;
the inversion controller is used for controlling the inversion main circuit to execute a preset inversion function.
14. An inverter comprising an inverter main circuit, an inverter controller, and the direct current arc detection circuit of claim 12, wherein,
the direct current arc detection circuit collects alternating current of the direct current side of the inversion main circuit and carries out direct current arc detection based on the alternating current;
the inversion controller is used for controlling the inversion main circuit to execute a preset inversion function.
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