CN211046795U - Topological structure of grid-connected inverter - Google Patents

Topological structure of grid-connected inverter Download PDF

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CN211046795U
CN211046795U CN202020020286.0U CN202020020286U CN211046795U CN 211046795 U CN211046795 U CN 211046795U CN 202020020286 U CN202020020286 U CN 202020020286U CN 211046795 U CN211046795 U CN 211046795U
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power device
grid
driving signal
connected inverter
power
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郭祺
涂春鸣
高家元
龙柳
卢柏桦
姜飞
肖凡
兰征
帅智康
李庆
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Hunan University
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Abstract

The utility model discloses a grid-connected inverter topological structure, topological structure includes: DC side voltage UdcA first power device V1A second power device V2A third power device V3A fourth power device V4Inductor L1Capacitor C, output load RLSwitch SW, grid impedance ZgAC network voltage UgA first driving signal S1A second driving signal S2A third driving signal S3A fourth driving signal S4(ii) a DC side voltage UdcAnode and first power device V1A third power device V3Connected, DC side voltage UdcAnd the second power device V2A fourth power device V4Connection, inductor L1And the capacitor C forms an L C filter, and the switch SW is closed or opened to control the grid-connected inverter to run in a grid-connected mode or in an isolated island mode.

Description

Topological structure of grid-connected inverter
Technical Field
The utility model relates to a new forms of energy electricity generation technical field, in particular to grid-connected inverter topological structure.
Background
The grid-connected inverter is used as an interface between new energy and a power grid, and the better control effect and conversion efficiency of the grid-connected inverter have great and profound significance for reducing industrial production energy consumption and improving the utilization rate of the new energy. The power electronic device is a carrier for realizing the power electronic technology and is a basic composition unit of the grid-connected inverter. The single-phase full-bridge inverter topology structure has the advantages of simple structure, small number of devices, easiness in cascading expansion and the like, and is widely applied to a single-phase system.
The existing single-phase full-bridge inverter mainly adopts Si IGBT or Si MOSFET as a switching device of a bridge arm, has the problem of large loss, and is not beneficial to the high-efficiency operation of a grid-connected inverter especially in medium and high power occasions.
Disclosure of Invention
The application aims to solve the problem that a grid-connected inverter is large in operation loss.
In order to achieve the above objective, an embodiment of the present invention provides a topology structure of a grid-connected inverter. The technical scheme is as follows:
in one aspect, a grid-tied inverter topology, the topology comprising:
DC side voltage UdcA first power device V1A second power device V2A third power device V3A fourth power device V4Inductor L1Capacitor C, output load RLSwitch SW, grid impedance ZgAC network voltage UgA first driving signal S1A second driving signal S2A third driving signal S3A fourth driving signal S4；
The DC side voltage UdcAnd the first power device V1The third power device V3Connected, the DC side voltage UdcAnd the second power device V2The fourth power device V4Connection, the inductance L1And the capacitor C forms an L C filter, the switch SW is switched on or switched off to control the grid-connected inverter to run in a grid-connected mode or an isolated island mode, and the first driving signal S1For the first power device V1The second drive signal S2For the second power device V2The third drive signal S3Is the third power device V3The fourth drive signal S4Is the fourth power device V4The drive signal of (1).
Further, the first power device V1And said second power device V2Forming a power frequency branch, the third power device V3And said fourth power device V4Forming a high-frequency branch.
Further, the first power device V1And said second power device V2Is a Si IGBT device, the third power device V3And said fourth power device V4The composite device is formed by connecting a Si IGBT and a SiC MOSFET in parallel.
Further, the first driving signalS1The second driving signal S2The third driving signal S3The fourth drive signal S4Is generated by using a unipolar SPWM modulation mode.
The embodiment of the utility model provides a beneficial effect that technical scheme brought is: the topological structure of the grid-connected inverter solves the problem of large operation loss of the grid-connected inverter. The structure of parallel combination of the Si IGBT and the SiC MOSFET is used as a device of a high-frequency bridge arm, compared with the prior art, the cost is reduced, and the operation efficiency of the grid-connected inverter is improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
Fig. 1 is a schematic diagram of a topology structure of a grid-connected inverter according to the present invention;
FIG. 2 is a waveform diagram of the single polarity SPWM modulation of the present invention;
FIG. 3 is a timing diagram illustrating gate drive control when the current level is less than or equal to the current threshold according to the present invention;
FIG. 4 is a timing diagram illustrating gate drive control when the current level is greater than the current threshold according to the present invention;
fig. 5 is a flowchart of a control method for a topology structure of a grid-connected inverter according to the present invention;
fig. 6 is a schematic diagram of a control strategy of the grid-connected inverter of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative efforts belong to the protection scope of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a grid-connected inverter topology, which includes: DC side voltage UdcA first power device V1A second power device V2A third power device V3A fourth power device V4Inductor L1Capacitor C, output load RLSwitch SW, grid impedance ZgAC network voltage UgA first driving signal S1A second driving signal S2A third driving signal S3A fourth driving signal S4。
In the present embodiment, the dc side voltage UdcAnode and first power device V1A third power device V3Connected, DC side voltage UdcAnd the second power device V2A fourth power device V4Connection, inductor L1The L C filter is formed by the capacitor C, the switch SW is closed or opened to control the grid-connected inverter to operate in a grid-connected mode or in an isolated mode, and the first driving signal S1For the first power device V1Of the second drive signal S2For the second power device V2Of the third drive signal S3For the third power device V3Of the fourth drive signal S4Is a fourth power device V4The drive signal of (1).
In the present embodiment, the first power device V1And a second power device V2Forming a power frequency branch, a third power device V3And a fourth power device V4Forming a high-frequency branch.
In the present embodiment, the first power device V1And a second power device V2Is a Si IGBT device, a third power device V3And a fourth power device V4The composite device is formed by connecting a Si IGBT and a SiC MOSFET in parallel.
In the present embodiment, it isThe topology structure of the grid-connected inverter is divided into branches with different switching frequencies, and a first driving signal S1A second driving signal S2A third driving signal S3A fourth driving signal S4Is generated by using a unipolar SPWM modulation mode.
Specifically, as shown in fig. 2, a waveform diagram of a unipolar SPWM modulation scheme is shown, in which U isdcIs a DC side voltage, UrFor modulating signals by power-frequency sine waves, UcBeing a triangular carrier signal, UcAt UrPositive half cycle of (2) is positive, in UrNegative half cycle of (1) is negative polarity, UoFor the output voltage of the bridge arm of the grid-connected inverter, UofIs UoOf the fundamental wave component.
At UrPositive half cycle of (c): first power device V1Remaining in the on state, second power device V2Remains in an off state when Ur＞UcTime-frequency fourth power device V4Conducting, third power device V3Is turned off, at this time Uo＝Udc(ii) a When U is turnedr＜UcTime-frequency fourth power device V4Off, third power device V3Is turned on at this time Uo＝0。
At UrNegative half cycle of (c): first power device V1Remaining in the off state, second power device V2Remains in the on state when Ur＜UcTime third power device V3On, the fourth power device V4Is turned off, at this time Uo＝-Udc(ii) a When U is turnedr＞UcTime third power device V3Off, fourth power device V4Is turned on at this time Uo＝0。
According to the modulation method, the first power device V1And a second power device V2For power frequency modulation, a third power device V3And a fourth power device V4For the switching frequency modulation, the power frequency branch and the high frequency branch appear when the modulation is carried out by using the unipolar SPWM modulation mode.
In the embodiment, a structure that a Si IGBT and a SiC MOSFET are combined in parallel is adopted as a bridge arm device, wherein the Si IGBT receives a large current and serves as a main device, and the SiC MOSFET receives a small current and serves as an auxiliary device, so that the characteristics of low transmission loss of the Si IGBT and low switching loss of the SiC MOSFET can be fully exerted, the problem of large operation loss of the grid-connected inverter is solved, the cost is reduced, and the operation efficiency of the grid-connected inverter is improved.
In the present embodiment, since the high-frequency branch circuit is configured by combining the Si IGBT and the SiC MOSFET in parallel, the gate drive timing of the Si IGBT and the SiC MOSFET varies. Therefore, a current value corresponding to an intersection point of the volt-ampere characteristic curves of the Si IGBT and the SiCMOS is set as a current threshold, when the running current of the grid-connected inverter is smaller than or equal to the current threshold, the grid-connected inverter runs under light load, and the SiC MOSFET has better transmission and switching characteristics than the Si IGBT at the moment, so that the SiC MOSFET is selected to work by the high-frequency branch, the Si IGBT is driven to be blocked and does not participate in the running of the circuit, and a corresponding gate driving control timing diagram is shown in FIG. 3; when the operation current of the grid-connected inverter is larger than the current threshold value, the SiC MOSFET and the Si IGBT are in parallel coordinated operation, and the corresponding gate drive control timing diagram is shown in FIG. 4. In FIG. 3 or FIG. 4, VGS_MOS、VGE_IGBTGate drive control signals, T, for SiC MOSFET and Si IGBT, respectivelyoff_delayDelay time, T, for the SiC MOSFET to delay the SiIGBT turn-offoff_IGBTIs the off tail time of the Si IGBT, wherein Toff_delayGreater than Toff_IGBTSo as to ensure the reliable turn-off of the Si IGBT.
As shown in fig. 1 and 5, an embodiment of the present invention provides a control method for a grid-connected inverter topology, where the method includes:
501: and generating a driving signal by using a unipolar SPWM modulation mode.
In the present embodiment, the generated driving signal is the first driving signal S1A second driving signal S2A third driving signal S3A fourth driving signal S4. Wherein the first drive signal S1For the first power device V1Of the second drive signal S2Is a secondPower device V2Of the third drive signal S3For the third power device V3Of the fourth drive signal S4Is a fourth power device V4The drive signal of (1).
502: and distinguishing a power frequency branch circuit and a high-frequency branch circuit according to the driving signal.
In the present embodiment, the power frequency branch comprises a first power device V1And a second power device V2The high-frequency branch comprises a third power device V3And a fourth power device V4。
503: and executing a control strategy aiming at the power frequency branch and the high-frequency branch.
In the present embodiment, as shown in fig. 6, the first power device V1And a second power device V2Is modulated at power frequency, and the first power device V1And a second power device V2Complementary conduction, wherein fgA third power device V with the frequency of the fundamental wave of the power grid set to 50HZ3And a fourth power device V4For a switching frequency fSWIs set to 10 kHZ. By a sine-wave modulation signal and a triangular-wave carrier signal ucAnd performing comparison, wherein m is a modulation degree (the value is between 0 and 1), and NOT represents the inversion of the signal. When the first power device V1At turn-on, the second power device V2Remaining in the off state, third power device V3And a fourth power device V4Carrying out high-frequency modulation complementary conduction by using SPWM; when the second power device V2When it is on, the first power device V1Remaining in the off state, third power device V3And a fourth power device V4And carrying out high-frequency modulation complementary conduction by using SPWM. Meanwhile, since the combination devices of the SiIGBT and the SiC MOSFET are adopted for V3 and V4, the turn-on and turn-off processes follow the gate drive control sequence shown in fig. 3 and 4. According to the device combination and mixed use mode and the modulation control strategy, the operation loss of the grid-connected inverter can be effectively reduced, and the operation efficiency of the inverter is improved.
In the present embodiment, the on/off of the switch SW is used to control the grid-connected operation or the isolated island operation of the grid-connected inverter.
With reference to fig. 1 to 6, the embodiment of the present invention further provides a grid-connected inverter testing platform, wherein the power P is 8kw, the device is selected from Si IGBT of 1200V/75A and SiC MOSFET of 1200V/19A, and the rest parameters are as shown in table 1 below.
TABLE 1
Parameter(s) Numerical value Parameter(s) Numerical value
Udc 400V RL 5Ω
L1 3mH m 0.5
C 50μF fSW 10kHZ
Wherein, UdcIndicating the DC bus voltage, L1C constituting an L C filter, RLIs the output load, m is the modulation degree, fSWIs the switching frequency. According to single/doubleThe output alternating voltage U of the bridge arm of the grid-connected inverter can be obtained by the basic working principle of polarity SPWM modulationolThe effective value of the fundamental component of (a) is:
Uol＝m·Udc＝0.5×400＝200V (1)
because the L C filter plays a role in filtering high and low frequency harmonic components and almost does not attenuate the fundamental component, the effective value of the end voltage output to the load by the inverter can also be considered as 200V, and the output current I can be obtainedoHas effective values of:
Io＝P÷Uol＝8000÷200＝40A (2)
the transmission loss of the single-tube transmission Si IGBT is calculated as follows:
when bipolar modulation is employed, the transmission loss of the Si IGBT is as shown in equation (3).
Figure BDA0002357369750000061
When unipolar modulation is employed, the transmission loss of the Si IGBT is as shown in equation (4).
Figure BDA0002357369750000062
Where m is a modulation ratio of 0.5, cos θ is 1, and VCEOIs a threshold voltage rCEIs an on-state resistance, IcpIs the peak value of the current flowing.
The switching loss of a single-tube Si IGBT can be calculated with the following formula:
Figure BDA0002357369750000063
wherein f isSWTo the switching frequency, EswonTo turn-on losses (including diode reverse recovery losses), EswoffFor turn-off losses (including diode reverse recovery losses), IcnRated current peak value, V, of Si IGBTCENIs the rated voltage of the Si IGBT.
As can be seen from the above formula for calculating the loss, the formulaMost parameters are determined by the selected device model and working frequency, and the parameters related to the operation state of the grid-connected inverter are only the current peak value I flowing through the devicecp. Similarly, the calculation method is also suitable for the transmission and switching loss calculation of the SiC MOSFET.
When the grid-connected inverter topological structure and the modulation strategy are adopted, the transmission loss of the high-frequency branch power device is calculated by adopting the formula (4). With the parameters in table 1, the loss of each device can be obtained as follows: pss-IGBT1＝9.2356W，Psw-IGBT1＝0W，Pss-MOSFET＝4.110W，Psw-MOSFET0.11818W, the loss of the single-phase full-bridge inverter with the structure provided by the invention is (9.2356+0) × 4+ (4.110+0.11818) × 2 is 45.399W.
The analysis of combining to current grid-connected inverter can know, the utility model discloses grid-connected inverter loss obviously reduces, and efficiency has improved 0.83%, and the cost is 129.25% of traditional structure only. The relevant index pairs are shown in table 2 below.
TABLE 2
Figure BDA0002357369750000064
Figure BDA0002357369750000071
According to the analysis results in table 2, the structure of parallel combination of the Si IGBT and the SiC MOSFET is used as a bridge arm device, so that the cost is reduced, and the operating efficiency of the grid-connected inverter is improved.
Therefore, the problem of large operation loss of the grid-connected inverter is solved through the topological structure of the grid-connected inverter and the control method of the topological structure. The structure of parallel combination of the Si IGBT and the SiC MOSFET is used as a device of a high-frequency bridge arm, compared with the prior art, the cost is reduced, and the operation efficiency of the grid-connected inverter is improved.
The above-described embodiments of the apparatus are merely illustrative, and the units illustrated by the separate components may or may not be physically separate, and the components displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. Can be understood and carried out by those skilled in the art without inventive effort.
Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented by software plus a necessary general hardware platform, and certainly can also be implemented by hardware. With this understanding in mind, the above-described technical solutions may be embodied in the form of a software product, which can be stored in a computer-readable storage medium such as ROM/RAM, magnetic disk, optical disk, etc., and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the methods described in the embodiments or some parts of the embodiments.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims (4)

1. A grid-tied inverter topology, comprising:
DC side voltage UdcA first power device V1A second power device V2A third power device V3A fourth power device V4Inductor L1Capacitor C, output load RLSwitch SW, grid impedance ZgAC network voltage UgA first driving signal S1A second driving signal S2A third driving signal S3A fourth driving signal S4；
The DC side voltage UdcAnd the first power device V1The third power device V3Connected, the DC side voltage UdcAnd the second power device V2The fourth power device V4Connection, the inductance L1And the capacitor C forms an L C filter, the switch SW is switched on or switched off to control the grid-connected inverter to run in a grid-connected mode or an isolated island mode, and the first driving signal S1For the first power device V1The second drive signal S2For the second power device V2The third drive signal S3Is the third power device V3The fourth drive signal S4Is the fourth power device V4The drive signal of (1).
2. The topology of claim 1, wherein the first power device V1And said second power device V2Forming a power frequency branch, the third power device V3And said fourth power device V4Forming a high-frequency branch.
3. The topology of claim 2, wherein the first power device V1And said second power device V2Is a Si IGBT device, the third power device V3And said fourth power device V4The composite device is formed by connecting SiIGBT and SiC MOSFET in parallel.
4. The topology of claim 1, wherein the first drive signal S1The second driving signal S2The third driving signal S3The fourth drive signal S4Is generated by using a unipolar SPWM modulation mode.
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