CN110086197B - Inductive current sampling calculation method - Google Patents
Inductive current sampling calculation method Download PDFInfo
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- CN110086197B CN110086197B CN201910313722.5A CN201910313722A CN110086197B CN 110086197 B CN110086197 B CN 110086197B CN 201910313722 A CN201910313722 A CN 201910313722A CN 110086197 B CN110086197 B CN 110086197B
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- 238000005070 sampling Methods 0.000 title claims abstract description 73
- 230000001939 inductive effect Effects 0.000 title claims abstract description 58
- 238000004364 calculation method Methods 0.000 title claims abstract description 20
- 238000000034 method Methods 0.000 claims abstract description 16
- 238000006243 chemical reaction Methods 0.000 abstract description 13
- 238000010586 diagram Methods 0.000 description 3
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- H02J3/383—
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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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
Abstract
The invention relates to an inductive current sampling calculation method, which is used for acquiring an input current value of an inverter and comprises the following steps: the method comprises the steps of sampling an inductive current of a conversion circuit in an inverter to obtain a current sampling value, calculating a time difference between a sampling point of the inductive current and a midpoint of the inductive current, and calculating a current difference between the sampling point of the inductive current and the midpoint of the inductive current according to the time difference, so that a midpoint current value of the midpoint of the inductive current is obtained according to the current sampling value and the current difference, wherein the midpoint current value is an input current value of the inverter. The invention solves the problem that the PV current can not be obtained by singly sampling the inductive current, reduces the AD sampling quantity and hardware circuits, and simplifies the design, thereby reducing the complexity and the cost of the system.
Description
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a sampling calculation method for a direct-current side inductor current of an application strand photovoltaic inverter.
Background
A conventional two-stage photovoltaic inverter topology is generally divided into two stages, DC/DC and DC/AC, as shown in fig. 1. Taking a DC/DC stage as an example for explanation: the conventional DC/DC topology is a Boost converter, the circuit structure of the converter is also shown in figure 1, and the waveforms of input current Ipv and Boost inductance current Iboost are shown in figure 2. In the loop control, the inductor current Iboost needs to be sampled in real time to ensure the control stability, and as an inverter, the real-time input current Ipv needs to be detected for current limiting control, display and the like. Because the difference between Iboost and Ipv current is that Iboost current has more ripple current of inductor, it is common practice to sample the inductor current Iboost and input it to an AD (analog-to-digital converter) channel for sampling and use as control, and further, after Iboost is subjected to hardware low-pass filtering (LPF) to filter the inductor ripple current, Ipv is input to another AD channel for sampling and use as current limiting and display, as shown in fig. 3. The scheme needs to occupy two AD channels, and the AD resources are consumed relatively, and meanwhile, the system complexity and the system cost are increased by a hardware filter circuit.
Disclosure of Invention
The invention aims to provide an inductive current sampling calculation method capable of reducing the complexity and cost of a system.
In order to achieve the purpose, the invention adopts the technical scheme that:
an inductance current sampling calculation method is used for obtaining an input current value of an inverter, and the current sampling calculation method comprises the following steps: the method comprises the steps of sampling an inductive current of a conversion circuit in the inverter to obtain a current sampling value, calculating a time difference between a sampling point of the inductive current and a midpoint of the inductive current, and calculating a current difference between the sampling point of the inductive current and the midpoint of the inductive current according to the time difference, so as to obtain a midpoint current value of the midpoint of the inductive current according to the current sampling value and the current difference, wherein the midpoint current value is an input current value of the inverter.
Preferably, the time difference between the sampling point of the inductor current and the midpoint of the inductor current is calculated based on the duty ratio of the inductor current.
Preferably, the sampling point is an extreme point of the inductive current, and the time difference is obtained
Wherein t1 is the time difference between the sampling time and the starting point of the switch-on, and duty is the duty ratio of the inductive current.
Preferably, the current difference between the sampling point of the inductor current and the midpoint of the inductor current
Wherein, UdcIs the output voltage value of the converter, UpvAnd L is the input voltage value of the converter, and is the inductance in the converter.
Preferably, the inductor is electrically connectedMidpoint current value of midpoint of flow
Wherein, IsampThe current sample value is obtained.
Preferably, when the converter is in a steady state, the theoretical duty ratio value of the inductor current is used as the duty ratio of the inductor current used for calculating the time difference Δ T; when the converter is not in a steady state, the actual duty cycle value of the inductor current is taken as the duty cycle of the inductor current used in calculating the time difference Δ T.
Preferably, the method for determining whether the converter is in a stable state includes: continuously sampling the input voltage U of the conversion circuit a plurality of timespvAnd an output voltage UdcAnd after each sampling, according to the sampled input voltage U of the conversion circuitpvAnd an output voltage UdcCalculating a theoretical duty ratio value of the inductive current, calculating an actual duty ratio value of the inductive current according to a loop control method of an inverter, and correspondingly comparing the theoretical duty ratio value with the actual duty ratio value to obtain a deviation value of the theoretical duty ratio value and the actual duty ratio value, wherein if the deviation values obtained by continuous multiple comparisons are within an allowable range, the converter is considered to be in a stable state, otherwise, the converter is not in the stable state.
Preferably, the theoretical duty cycle value of the inductor current
Preferably, if the deviation values obtained by 10 consecutive comparisons are within an allowable range, the converter is considered to be in a steady state.
Preferably, the allowable range is 5%.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages: the invention solves the problem that the PV current can not be obtained by singly sampling the inductive current, reduces the AD sampling quantity and hardware circuits, and simplifies the design, thereby reducing the complexity and the cost of the system.
Drawings
Fig. 1 is a two-stage photovoltaic inverter topology.
Fig. 2 is a waveform diagram of input current and inductor current of a conversion circuit in a photovoltaic inverter.
Fig. 3 is a schematic diagram of a generic inductor current sampling.
Fig. 4 is a schematic diagram of inductor current versus duty cycle.
Fig. 5 is a flow chart of an inductor current sampling calculation method of the present invention.
Detailed Description
The invention will be further described with reference to examples of embodiments shown in the drawings to which the invention is attached.
The first embodiment is as follows: an inductance current sampling calculation method for obtaining an input current value of an inverter is characterized by comprising the following core ideas: sampling the inductive current of the conversion circuit in the inverter to obtain a current sampling value IsampCalculating the time difference between the sampling point of the inductive current and the midpoint of the inductive current, and then calculating the current difference between the sampling point of the inductive current and the midpoint of the inductive current according to the time difference, so as to obtain the midpoint current value of the midpoint of the inductive current according to the current sampling value and the current difference, wherein the midpoint current value is the input current value of the inverter.
As shown in fig. 5, the inductor current sampling calculation method is implemented by the following steps:
1. sampling input voltage U of a conversion circuit (e.g. Boost conversion circuit)pvAnd an output voltage Udc。
2. According to the input-output voltage formula of the conversion circuit
Calculation formula for calculating theoretical duty ratio value duty1 of inductor current
3. The theoretical duty ratio value duty1 of the inductor current at this time is calculated according to the formula 2, the actual duty ratio value duty2 of the inductor current is calculated by using a loop control method according to the inverter, and then the theoretical duty ratio value duty1 and the actual duty ratio value duty2 of the inductor current are compared, so that whether the conversion circuit is in a stable state or not is judged according to the comparison.
The method for judging whether the converter is in a stable state comprises the following steps: input voltage U of continuous multi-sampling conversion circuitpvAnd an output voltage UdcAnd after each sampling, according to the sampled input voltage U of the conversion circuitpvAnd an output voltage UdcThe method comprises the steps of calculating a theoretical duty ratio value duty1 of the inductive current, calculating an actual duty ratio value duty2 of the inductive current according to a loop control method of the inverter, correspondingly comparing the theoretical duty ratio value duty1 with the actual duty ratio value duty2 to obtain a deviation value of the theoretical duty ratio value duty1 and the actual duty ratio value duty2, and if the deviation values obtained through continuous multiple comparisons are within an allowable range, considering that the converter is in a stable state, otherwise, considering that the converter is in an unstable state.
The comparison condition may be determined according to a specific debugging situation, for example, if the deviation values obtained by comparing for 10 times are all within an allowable range, the converter is considered to be in a stable state, otherwise, the converter is considered to be in an unstable state. The allowable range of the deviation value between the theoretical duty1 and the actual duty2 is 5%.
4. After the state of the conversion circuit is judged, the actual midpoint current value I of the midpoint of the inductive current is calculated according to the formula 3mid
In the calculation process, firstly, the time difference Δ T between the sampling point (time T0) of the inductor current and the middle point (time T1) of the inductor current is calculated based on the duty ratio duty of the inductor current, and Δ T is calculated. The sampling point is the extreme point of the inductive current, the time difference
Where t1 is the time difference between the sampling time and the on starting point, and since the sampling time is the on starting point here, t1 is 0. duty is the duty ratio of the inductive current, and when the converter is in a stable state, the theoretical duty ratio duty1 of the inductive current is used as the duty ratio duty of the inductive current used when the time difference delta T is calculated; when the converter is not in a steady state, the actual duty value duty2 of the inductor current is taken as the duty of the inductor current used in calculating the time difference Δ T.
Then, the current difference between the sampling point of the inductive current and the midpoint of the inductive current is calculated according to the time difference delta T
Wherein, UdcIs the output voltage value of the converter, UpvL is the inductance in the converter, which is determined and measured well in the software during the product development phase, for the value of the input voltage of the converter.
Finally according to the current sampling value IsampCalculating the sum current difference delta I to obtain the midpoint current value of the midpoint of the inductive current
The midpoint current value Δ ImidI.e. the value of the input current to the inverter.
5. And (6) ending.
A program based on the above inductor current sampling calculation method is written in the inverter controller, thereby forming an inverter controller having an inductor current sampling calculation function.
The scheme can be used for calculating the current midpoint of the inductor in various circuit topologies, and is not limited to the Boost circuit exemplified in the invention.
After the scheme is adopted, the inductive current Iboost and the input current Ipv of the inverter can be obtained without two AD channels, so that the problem that the inductive current can not be obtained by independently sampling the inductive current is solved, the AD sampling quantity and hardware circuits are reduced, and the design is simplified.
The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (10)
1. An inductance current sampling calculation method is used for obtaining an input current value of an inverter, and is characterized in that: the current sampling calculation method comprises the following steps: sampling an inductive current of a converter in the inverter to obtain a current sampling value, calculating a time difference between a sampling point of the inductive current and a midpoint of the inductive current, and calculating a current difference between the sampling point of the inductive current and the midpoint of the inductive current according to the time difference, so as to obtain a midpoint current value of the midpoint of the inductive current according to the current sampling value and the current difference, wherein the midpoint current value is an input current value of the inverter.
2. The inductor current sampling computation method of claim 1, wherein: and calculating the time difference between the sampling point of the inductive current and the middle point of the inductive current based on the duty ratio of the inductive current.
3. The inductor current sampling computation method of claim 2, wherein: the sampling point is the extreme point of the inductive current, and the time difference is obtained
T1 is the time difference between the sampling time and the starting point of the switch-on, duty is the duty ratio of the inductive current, and T is the switching period of the switching tube in the converter.
4. The inductor current sampling computation method of claim 3, wherein: current difference between the sampling point of the inductive current and the midpoint of the inductive current
Wherein, UdcIs the output voltage value of the converter, UpvAnd L is the input voltage value of the converter, and is the inductance in the converter.
5. The inductor current sampling computation method of claim 4, wherein: midpoint current value of the inductor current midpoint
Wherein, IsampThe current sample value is obtained.
6. The inductor current sampling calculation method according to claim 3, wherein: when the converter is in a steady state, taking a theoretical duty ratio value of the inductive current as a duty ratio of the inductive current used when calculating the time difference Δ T; when the converter is not in a steady state, the actual duty cycle value of the inductor current is taken as the duty cycle of the inductor current used in calculating the time difference Δ T.
7. The inductor current sampling calculation method according to claim 6, wherein: the method for judging whether the converter is in a stable state comprises the following steps: continuously sampling the input voltage U of the converter a plurality of timespvAnd an output voltage UdcAnd according to the sampled input voltage U of the converter after each samplingpvAnd an output voltage UdcCalculating a theoretical duty ratio value of the inductive current, calculating an actual duty ratio value of the inductive current according to a loop control method of an inverter, and correspondingly comparing the theoretical duty ratio value with the actual duty ratio value to obtain a deviation value of the theoretical duty ratio value and the actual duty ratio value, wherein if the deviation values obtained by continuous multiple comparisons are within an allowable range, the converter is considered to be in a stable state, otherwise, the converter is not in the stable state.
8. The inductor current sampling calculation method according to claim 7, wherein: the theoretical duty ratio of the inductor current
9. The inductor current sampling computation method of claim 7, wherein: and if the deviation values obtained by continuous 10 times of comparison are within an allowable range, the converter is considered to be in a stable state.
10. The inductor current sampling calculation method according to claim 7, wherein: the allowable range is 5%.
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