CN111277160B - A six-switch power decoupling circuit and control method thereof - Google Patents
A six-switch power decoupling circuit and control method thereof Download PDFInfo
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
- H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
- H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
- H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—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 in a bridge configuration
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
- H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
- H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
- H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
- H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
- H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
- H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/539—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency
- H02M7/5395—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters with automatic control of output wave form or frequency by pulse-width modulation
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Abstract
The invention discloses a six-switch power decoupling circuit and a control method thereof, wherein the six switch tubes S 1-S6, six diodes D 1-D6, two capacitors C d1、Cd2 and an inductor L d;S1-S6 are respectively connected in anti-parallel with D 1-D6, an emitter of S 1 is connected with an emitter of S 2 to form a first branch, an emitter of S 3 is connected with an emitter of S 4 and connected in series with C d1 to form a second branch, an emitter of S 5 is connected with an emitter of S 6 and connected in series with C d2 to form a third branch, the three branches are simultaneously connected in parallel, and a collector of the inductor L d and a collector of S 1 are connected with an alternating current output side of a micro-inverter. According to the invention, the power decoupling circuit is connected to the AC output side of the micro-inverter, so that energy buffering is carried out, the coupling capacitance value is greatly reduced, the secondary disturbance power is reduced, and the performance and the service life of the micro-inverter are improved. The invention adopts the pulse modulation technology PEM to control the six-switch power coupling circuit, and has the characteristics of simple structure and convenient control.
Description
Technical Field
The invention relates to the technical field of micro-inversion, in particular to a six-switch power decoupling circuit and a control method thereof.
Background
Micro-inverters have many advantages, such as high power generation, ease of expansion, low cost, hot-plug and modular design, which make it increasingly the mainstay of distributed power generation systems. However, in the distributed power generation system, the input power generated by the photovoltaic module is constant under the control of maximum power point tracking (Maximum PowerPoint Tracking, abbreviated as MPPT), but the power entering the power grid is the power pulsation of twice the power frequency, and the instantaneous values of the two are inconsistent. Thus, in conventional micro-inverters, electrolytic capacitors are relied upon to balance the instantaneous input and output power, but this also results in electrolytic capacitors that have much less life than other components in the circuit. Therefore, researching the micro-inverter without the electrolytic capacitor becomes a way for improving the performance and the service life of the micro-inverter, and students at home and abroad develop researches successively.
The technology of the micro-inverter without the electrolytic capacitor is to realize energy buffering by connecting a power decoupling circuit in parallel in the micro-inverter, wherein the power decoupling circuit consists of a power switch and a passive device. There are three types of power decoupling circuits classified by access point, a direct current input side type, a DC-link (direct current supporting capacitor) intermediate side type, and an alternating current output side type.
Wherein the direct current input side power coupling circuit is generally applicable to single-stage grid-connected micro-inverters. A flyback single-stage micro-inverter proposed by Shimizu professor of university of kyoto, japan and the like, only requires a 40uF thin film capacitor after the power decoupling circuit is adopted, but the conversion efficiency is low, only 70%. The professor b.j.pierque et al, university of washington, in the united states, proposes a two-stage micro-inverter structure in which a power decoupling circuit is connected in series between the photovoltaic array and the micro-inverter, controlling energy storage and voltage fluctuations, respectively, avoiding the use of electrolytic capacitors, while maintaining reactive power transfer of the micro-inverter. However, although the circuit structure is simple, the power decoupling control of the system is complex, the MPPT and island detection operation are difficult, the system efficiency is reduced, the step-up ratio of the system is low, the photovoltaic direct current output voltage is high, and the decoupling capacitance value is still large.
In the multistage micro-inverter, the intermediate direct-current side voltage is high, so that a DC-link intermediate side power decoupling technology is adopted. G.A.J.Amaratunga et al, university of Cambridge, UK, propose a three-level structure micro-grid-connected photovoltaic micro-inverter. The micro-inverter consists of a phase-shifting full-bridge circuit, a Buck circuit and a full-bridge micro-inverter. The phase-shifting full-bridge circuit realizes the functions of boosting and MPPT, the Buck circuit generates sine half-wave current, and the final stage circuit generates sine injection current. In order to reduce the decoupling capacitance, the dc voltage fluctuations are large and still generate considerable secondary power disturbances.
The problems that the existing technology of the micro-inverter without the electrolytic capacitor is complex in structure, inconvenient to control, large in decoupling capacitance value and large in secondary power disturbance are commonly found.
Disclosure of Invention
The invention aims to provide a six-switch power decoupling circuit and a control method thereof, which are used for solving the problems of complex structure, inconvenient control, larger decoupling capacitance value and larger secondary power disturbance commonly existing in the existing technology of the micro-inverter without electrolytic capacitor.
In order to achieve the above object, the present invention provides the following solutions:
a six-switch power decoupling circuit comprises a first switch tube S 1, a second switch tube S 2, a third switch tube S 3, a fourth switch tube S 4, a fifth switch tube S 5, a sixth switch tube S 6, a first diode D 1, a second diode D 2, a third diode D 3, a fourth diode D 4, a fifth diode D 5, a sixth diode D 6, a first capacitor C d1, a second capacitor C d2 and an inductor L d;
The collector of the first switching tube S 1, the collector of the third switching tube S 3 and the collector of the fifth switching tube S 5 are all connected with one end of the AC output side of the micro-inverter;
The emitter of the first switching tube S 1 is connected with the emitter of the second switching tube S 2, the first switching tube S 1 is in inverse parallel connection with the first diode D 1, and the second switching tube S 2 is in inverse parallel connection with the second diode D 2;
The emitter of the third switching tube S 3 is connected with the emitter of the fourth switching tube S 4, the collector of the fourth switching tube S 4 is connected with one end of the first capacitor C d1, the third switching tube S 3 is in anti-parallel connection with the third diode D 3, the fourth switching tube S 4 is in anti-parallel connection with the fourth diode D 4;
The emitter of the fifth switching tube S 5 is connected with the emitter of the six switching tube, the collector of the six switching tube is connected with one end of the second capacitor C d2, the fifth switching tube S 5 is in anti-parallel connection with the fifth diode D 5, and the sixth switching tube S 6 is in anti-parallel connection with the sixth diode D 6;
The collector of the second switching tube S 2, the other end of the first capacitor C d1 and the other end of the second capacitor C d2 are all connected with one end of the inductor L d, and the other end of the inductor L d is connected with the other end of the ac output side of the micro-inverter.
Optionally, the inverse parallel connection is that the emitter of the switching tube is connected with the anode of the diode, and the collector of the switching tube is connected with the cathode of the diode.
Optionally, the other end of the inductor L d is connected to a common ground terminal of the ac output side of the micro-inverter and the grid voltage.
Optionally, the first capacitor Cd1 and the second capacitor Cd2 are decoupling capacitors.
A control method of a six-switch power decoupling circuit comprises a first switch tube S 1, a second switch tube S 2, a third switch tube S 3, a fourth switch tube S 4, Fifth switch tube S 5, sixth switch tube S 6, first diode D 1, second diode D 2, Third diode D 3, fourth diode D 4, fifth diode D 5, sixth diode D 6, A first capacitor C d1, a second capacitor C d2 and an inductor L d, a collector electrode of the first switch tube S 1, the collector of the third switching tube S 3 and the collector of the fifth switching tube S 5 are connected with one end of the AC output side of the micro-inverter, the emitter of the first switching tube S 1 is connected with the emitter of the second switching tube S 2, the first switching tube S 1 is connected with the first diode D 1 in an anti-parallel manner, the second switching tube S 2 is connected with the second diode D 2 in an anti-parallel manner, the emitter of the third switching tube S 3 is connected with the emitter of the fourth switching tube S 4, the collector of the fourth switching tube S 4 is connected with one end of the first capacitor C d1, the third switching tube S 3 is connected with the third diode D 3 in an anti-parallel manner, the fourth switching tube S 4 is connected with the fourth diode D 4 in an anti-parallel manner, the emitter of the fifth switching tube S 5 is connected with the emitter of the sixth switching tube, the second capacitor C5393 is connected with the emitter of the fourth switching tube S 4 in an anti-parallel manner, the collector of the fourth switching tube S43943 is connected with the fourth switching tube S43962 in an anti-parallel manner, the fourth switching tube S3563 is connected with the collector of the fifth switching tube S4356 in an anti-parallel manner, the fifth switching tube S5326 is connected with the fourth switching tube S, The other end of the first capacitor C d1 and the other end of the second capacitor C d2 are connected with one end of the inductor L d, and the other end of the inductor L d is connected with the other end of the AC output side of the micro-inverter;
The control method comprises the following steps:
obtaining output voltage of the AC output side of the micro-inverter and decoupling current of the six-switch power decoupling circuit;
judging whether the output voltage of the AC output side of the micro-inverter is greater than 0 or not to obtain a first judgment result;
if the first judgment result is that the output voltage of the AC output side of the micro-inverter is greater than 0, judging whether the decoupling current is in the same direction as the output voltage, and obtaining a second judgment result;
if the second judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to work in a first working mode to absorb energy;
If the second judgment result is that the decoupling current is opposite to the output voltage, controlling the six-switch power decoupling circuit to work in a second working mode to release energy;
if the first judgment result is that the output voltage of the AC output side of the micro-inverter is smaller than 0, judging whether the decoupling current is in the same direction as the output voltage or not, and obtaining a third judgment result;
If the third judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to work in a third working mode to absorb energy;
And if the third judgment result is that the decoupling current is opposite to the output voltage, controlling the six-switch power decoupling circuit to work in a fourth working mode to release energy.
Optionally, the controlling the six-switch power decoupling circuit to operate in the first working mode absorbs energy specifically includes:
The second switching tube S 2, the fourth switching tube S 4, the fifth switching tube S 5 and the sixth switching tube S 6 are controlled to be turned off, the third switching tube S 3 is turned on, the first switching tube S 1 is used as a master control switch and controlled by pulse energy modulation PEM signals, and at this time, the first capacitor C d1 absorbs energy.
Optionally, the controlling the six-switch power decoupling circuit to operate in the second working mode absorbs energy specifically includes:
the first switching tube S 1, the third switching tube S 3, the fifth switching tube S 5 and the sixth switching tube S 6 are controlled to be disconnected, the second switching tube S 2 is connected, the fourth switching tube S 4 is controlled by a PEM signal as a master control switch, and at the moment, the first capacitor C d1 releases energy.
Optionally, the controlling the six-switch power decoupling circuit to operate in the third working mode absorbs energy specifically includes that the first switch tube S 1, the third switch tube S 3, the fourth switch tube S 4 and the fifth switch tube S 5 are all disconnected, the sixth switch tube S 6 is connected, the second switch tube S 2 is controlled by PEM signals as a master control switch, and at this time, the second capacitor C d2 absorbs energy.
Optionally, the controlling the six-switch power decoupling circuit to operate in the fourth operation mode absorbs energy specifically includes that the second switch tube S 2, the third switch tube S 3, the fourth switch tube S 4 and the sixth switch tube S 6 are all disconnected, the first switch tube S 1 is connected, the fifth switch tube S 5 is controlled by PEM signals as a master control switch, and at this time, the second capacitor C d2 releases energy.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
The invention discloses a six-switch power decoupling circuit and a control method thereof, wherein the six switch tubes S 1-S6, six diodes D 1-D6, two capacitors C d1、Cd2 and an inductor L d;S1-S6 are respectively connected in anti-parallel with D 1-D6, an emitter of S 1 is connected with an emitter of S 2 to form a first branch, an emitter of S 3 is connected with an emitter of S 4 and connected in series with C d1 to form a second branch, an emitter of S 5 is connected with an emitter of S 6 and connected in series with C d2 to form a third branch, the three branches are simultaneously connected in parallel, and a collector of the inductor L d and a collector of S 1 are connected with an alternating current output side of a micro-inverter. According to the invention, the power decoupling circuit is connected to the AC output side of the micro-inverter, so that energy buffering is carried out, the coupling capacitance value is greatly reduced, the secondary disturbance power is reduced, and the performance and the service life of the micro-inverter are improved. The invention adopts the pulse modulation technology PEM to control the six-switch power coupling circuit, and has the characteristics of simple structure and convenient control.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of a topology structure of a six-switch power decoupling circuit provided by the present invention;
Fig. 2 is a schematic diagram of a structure and a power relationship of a micro-inverter without electrolytic capacitor of a six-switch power decoupling circuit provided by the invention;
Fig. 3 is a schematic diagram of a relationship between input power (P I), output power (P o) and decoupling power (P c) in the micro-inverter according to the present invention;
FIG. 4 is a schematic diagram of a sequence of operation modes of the coupling circuit in one power grid cycle according to the present invention;
fig. 5 is a schematic diagram of four operation modes of the power decoupling circuit provided by the invention, fig. 5 (a) is a schematic diagram of a first operation mode of the power decoupling circuit, fig. 5 (B) is a schematic diagram of a second operation mode of the power decoupling circuit, fig. 5 (C) is a schematic diagram of a third operation mode of the power decoupling circuit, and fig. 5 (D) is a schematic diagram of a fourth operation mode of the power decoupling circuit;
fig. 6 is a schematic diagram of a six-switch power decoupling circuit provided by the invention operating in a first operating mode, fig. 6 (a) is a schematic diagram of a main control switch on-off control and current flow path, and fig. 6 (b) is an equivalent circuit schematic diagram of the six-switch power decoupling circuit operating in the first operating mode;
Fig. 7 is a schematic diagram of the six-switch power decoupling circuit provided by the invention operating in the second operating mode, fig. 7 (a) is a schematic diagram of the on-off control and current flow path of the main control switch, and fig. 7 (b) is an equivalent circuit schematic diagram of the six-switch power decoupling circuit operating in the second operating mode;
Fig. 8 is a schematic diagram of the six-switch power decoupling circuit provided by the invention operating in a third operating mode, fig. 8 (a) is a schematic diagram of the on-off control and current flow path of the main control switch, and fig. 8 (b) is an equivalent circuit schematic diagram of the six-switch power decoupling circuit operating in the third operating mode;
Fig. 9 is a schematic diagram of a six-switch power decoupling circuit according to the present invention operating in a fourth operating mode, fig. 9 (a) is a schematic diagram of a main control switch on-off control and a current flow path, and fig. 9 (b) is an equivalent circuit schematic diagram of the six-switch power decoupling circuit operating in the fourth operating mode;
FIG. 10 is a schematic diagram of MATLAB simulation models of a control circuit of six switching tubes, wherein NOT is an NOT, AND is an AND gate, OR is an OR gate, bootan is a Matlab function for converting values into Boolean values, AND T1-T6 are driving signals of six corresponding switching tubes;
FIG. 11 is a schematic diagram of MATLAB simulation of a PEM signal generation circuit according to the present invention;
Fig. 12 is a MATLAB simulation diagram of a power decoupling circuit composed of six switch tubes provided by the invention;
Fig. 13 is a schematic diagram of a driving signal of a switching tube of a six-switch decoupling circuit according to the present invention, where fig. 13 (a) is a driving signal of the decoupling circuit S 1S2, (b) is a driving signal of the decoupling circuit S 3S4, and (c) is a driving signal of the decoupling circuit S 5S6.
Fig. 14 is a schematic diagram of waveforms associated with a micro-inverter according to the present invention without a six-switch power decoupling circuit;
fig. 15 is a schematic diagram of waveforms associated with a micro-inverter according to the present invention when connected to a six-switch power decoupling circuit;
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a six-switch power decoupling circuit and a control method thereof, which are used for solving the problems of complex structure, inconvenient control, larger decoupling capacitance value and larger secondary power disturbance commonly existing in the existing technology of the micro-inverter without electrolytic capacitor.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Fig. 1 is a schematic diagram of a topology structure of a six-switch power decoupling circuit provided by the present invention. As shown in FIG. 1, the six-switch power decoupling circuit comprises a first switch tube S 1, a second switch tube S 2, a third switch tube S 3, a fourth switch tube S 4, Fifth switch tube S 5, sixth switch tube S 6, first diode D 1, second diode D 2, Third diode D 3, fourth diode D 4, fifth diode D 5, sixth diode D 6, First capacitor C d1, second capacitor C d2, and inductor L d. Wherein S 1-S6 is respectively connected in anti-parallel with D 1-D6, the emitter of the switch tube S 1 is connected with the emitter of the switch tube S 2 to form a first branch, the emitter of the switch tube S 3 is connected with the emitter of the switch tube S 4 and is connected in series with C d1 to form a second branch, the emitter of the switch tube S 5 is connected with the emitter of the switch tube S 6 and is connected in series with C d2 to form a third branch, and the three branches are simultaneously connected in parallel. One end of an inductor L d is connected with the common ground end of the AC output side of the micro-inverter and the power grid voltage, the other end of the inductor L d is connected with the collector of a switching tube S 2, and the collector of the switching tube S 1 is connected with one end of the AC output side of the micro-inverter. The anti-parallel connection is that the emitter of the switching tube is connected with the positive electrode of the corresponding diode, and the collector of the switching tube is connected with the negative electrode of the corresponding diode.
Specifically, as shown in fig. 1, the collector of the first switching tube S 1, the collector of the third switching tube S 3 and the collector of the fifth switching tube S 5 are connected with one end of the AC output side of the micro-inverter, the emitter of the first switching tube S 1 is connected with the emitter of the second switching tube S 2, the first switching tube S 1 is connected with the first diode D 1 in an anti-parallel manner, the second switching tube S 2 is connected with the second diode D 2 in an anti-parallel manner, the emitter of the third switching tube S 3 is connected with the emitter of the fourth switching tube S 4, the collector of the fourth switching tube S 4 is connected with one end of the first capacitor C d1, the third switching tube S 3 is connected with the third diode D 3 in an anti-parallel manner, the fourth switching tube S 4 is connected with the fourth diode D 4 in an anti-parallel manner, the emitter of the fifth switching tube S 5 is connected with the emitter of the sixth switching tube, the second capacitor C5393 is connected with the emitter of the fourth switching tube S 4 in an anti-parallel manner, the collector of the fourth switching tube S43943 is connected with the fourth switching tube S43962 in an anti-parallel manner, the fourth switching tube S3563 is connected with the collector of the fifth switching tube S4356 in an anti-parallel manner, the fifth switching tube S5326 is connected with the fourth switching tube S, The other end of the first capacitor C d1 and the other end of the second capacitor C d2 are connected with one end of the inductor L d, and the other end of the inductor L d is connected with the other end of the AC output side of the micro-inverter.
The other end of the inductor L d is connected with the common ground end of the AC output side of the micro-inverter and the power grid voltage.
The first capacitor Cd1 and the second capacitor Cd2 are decoupling capacitors.
Only when two switching tubes of the same branch are simultaneously opened, the branch is completely opened. The working mode of the circuit is changed by controlling the on-off of the switching tube, so that energy buffering is realized.
Fig. 2 is a schematic diagram of the structure and power relationship of a six-switch power decoupling circuit (abbreviated as power decoupling circuit) micro-inverter according to the present invention. As shown in fig. 2, the micro-inverter and the power decoupling circuit form a micro-inverter, the micro-inverter adopts a common structure, the power decoupling circuit part adopts the six-switch power decoupling circuit provided by the invention, the alternating current output side of the micro-inverter is connected in parallel to the power decoupling circuit, and the inductor L and the capacitor C form a filter device. Wherein V dc is dc side voltage, I dc is dc side current, U inv is ac output side voltage of the micro-inverter, V grid is grid voltage, I grid is injection current of the micro-inverter to the grid, P I is dc side input power, P o is output power of the micro-inverter, and P c is decoupling power of the power decoupling circuit.
Because the input power at the direct current side is inconsistent with the instantaneous output power of the micro-inverter, the traditional method adopts an electrolytic capacitor to balance the input power and the instantaneous output power of the micro-inverter, but the service life of the micro-inverter is greatly shortened. The three-phase six-switch power decoupling circuit provided by the invention can be used for replacing an electrolytic capacitor, so that the stability and the service life of the micro-inverter can be greatly improved.
Fig. 3 is a relationship between input power (P I), output power (P o), and decoupling power (P c) in a micro-inverter. As shown in fig. 3, in the micro-inverter, the power decoupling circuit balances the input power and the instantaneous output power. In particular, P c >0 when P I<Po, the power decoupling circuit supplements the input power, and P c <0 when P I>Po, the power decoupling circuit absorbs the excess input power. Dc side input power P I, instantaneous output power P o.
As shown in fig. 2, the micro-inverter output voltage U inv has positive and negative values, so that the input voltage of the power decoupling circuit has positive and negative values, and the decoupling current has positive and negative values, so that the power decoupling circuit has four operation modes:
Mode 1 (i.e., the first mode of operation) when U inv >0, decoupling current in the same direction as voltage, the power decoupling circuit absorbing energy;
Mode 2 (i.e., the second mode of operation) when U inv >0, decoupling current in the opposite direction from voltage, the power decoupling circuit releasing energy;
Mode 3 (i.e., the third mode of operation) when U inv <0, the decoupling current is in the same direction as the voltage, the power decoupling circuit absorbs energy;
Mode 4 (i.e., the fourth mode of operation) when U inv <0, the decoupling current and voltage are reversed and the power decoupling circuit releases energy.
Fig. 4 is a schematic diagram of the sequence of operation modes of the coupling circuit during a grid cycle. As shown in fig. 4, mode 1 and mode 2 operate on positive half-cycles of the grid voltage and mode 3 and mode 4 operate on negative half-cycles. One period can be divided into 6 parts, and the sequence of the power decoupling circuit is respectively mode 1, mode 2, mode 1, mode 3, mode 4 and mode 3, and the power decoupling circuit is respectively used for absorbing, releasing, absorbing, releasing and absorbing input power.
Fig. 5 is a schematic diagram of four modes of operation of the power decoupling circuit. As shown in fig. 5, the power decoupling circuit realizes the power decoupling function through an inductor and a capacitor, the inductor is connected with the voltage and the current of the micro-inverter and the power decoupling circuit, and the capacitor absorbs and releases energy. The two ends of the decoupling capacitor are fixed in polarity, if the power decoupling circuit absorbs energy, the voltage and the current are in the same direction, and the capacitance direction is the same as the current direction, and if the power decoupling circuit releases energy, the voltage and the current are in reverse direction, and the capacitance direction is also opposite to the current direction. The positive direction of the voltage is assumed to be positive up and negative down, the positive direction of the current is from left to right.
When U inv >0, the power decoupling circuit absorbs energy, the capacitance voltage rises to judge the voltage current direction, the power decoupling circuit can be equivalent to a Boost circuit as shown in fig. 5 (A), when U inv >0, the power decoupling circuit releases energy, the capacitance voltage decreases to judge the voltage current direction, the power decoupling circuit can be equivalent to a Buck circuit as shown in fig. 5 (B), when U inv <0, the power decoupling circuit absorbs energy, the capacitance voltage rises to judge the voltage current direction, the power decoupling circuit can be equivalent to a Boost circuit as shown in fig. 5 (C), when U inv <0, the power decoupling circuit releases energy, the capacitance voltage decreases to judge the voltage current direction, the power decoupling circuit can be equivalent to a Buck circuit as shown in fig. 5 (D).
Based on the six-switch power decoupling circuit provided by the invention, the invention also provides a control method of the six-switch power decoupling circuit, which comprises the following steps:
obtaining output voltage of the AC output side of the micro-inverter and decoupling current of the six-switch power decoupling circuit;
judging whether the output voltage of the AC output side of the micro-inverter is greater than 0 or not to obtain a first judgment result;
if the first judgment result is that the output voltage of the AC output side of the micro-inverter is greater than 0, judging whether the decoupling current is in the same direction as the output voltage, and obtaining a second judgment result;
if the second judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to work in a first working mode to absorb energy;
If the second judgment result is that the decoupling current is opposite to the output voltage, controlling the six-switch power decoupling circuit to work in a second working mode to release energy;
if the first judgment result is that the output voltage of the AC output side of the micro-inverter is smaller than 0, judging whether the decoupling current is in the same direction as the output voltage or not, and obtaining a third judgment result;
If the third judgment result is that the decoupling current and the output voltage are in the same direction, controlling the six-switch power decoupling circuit to work in a third working mode to absorb energy;
And if the third judgment result is that the decoupling current is opposite to the output voltage, controlling the six-switch power decoupling circuit to work in a fourth working mode to release energy.
The first operation mode (ModeI) to the fourth operation mode (ModeIV) are shown in fig. 6 to 9, respectively, the diagrams (a) in fig. 6 to 9 are schematic diagrams of the on-off control and current flow path of the main control switch, and the diagrams (b) are schematic diagrams of equivalent circuits. The output of the micro-inverter is used as an equivalent voltage source, denoted by U inv, U inv+ is the positive electrode of the equivalent voltage source, U inv- is the negative electrode of the equivalent voltage source, wherein P pv is the power of the micro-inverter at the direct current input side, P ac is the output power of the micro-inverter at the alternating current side, C d1+ represents the positive electrode of the coupling capacitor C d1, and C d1- represents the negative electrode of the coupling capacitor C d1.
Specifically, fig. 6 is a schematic diagram of the six-switch power decoupling circuit provided by the present invention operating in the first operation mode. In the first operation mode, U inv >0, and P pv>Pac,S2,S4,S5 and S 6 are off, S 3 is on, and S 1 is controlled by PEM signals as a master switch, as shown in fig. 6. At this time, the decoupling capacitor C d1 absorbs energy and the voltage rises. When S 1 is on, the i d flow path is U inv+→S1→D2→Ld→Uinv-,S1, and when it is off, the i d flow path is U inv+→S3→D4→Cd1→Ld→Uinv-.
Fig. 7 is a schematic diagram of a six-switch power decoupling circuit according to the present invention operating in a second mode of operation. In this mode of operation, U inv >0, as shown in FIG. 7, and P pv<Pac,S1,S3,S5 and S 6 are off, S 2 is on, and S 4 is controlled by the PEM signal as a master switch. At this time, the decoupling capacitor C d1 releases energy and the voltage drops. When S 4 is on, the i d flow path is C d1+→S4→D3→Uinv→Ld→Cd1-,S4, and when it is off, the i d flow path is U inv-→Ld→S2→D1→Uinv+. Where C d1+ represents the positive electrode of coupling capacitor C d1 and C d1- represents the negative electrode of coupling capacitor C d1.
Fig. 8 is a schematic diagram of a six-switch power decoupling circuit operating in a third mode of operation. As shown in fig. 8, the circuit is a step-up and step-down circuit, and operates as Boost. In this mode of operation, U inv <0, and P pv>Pac,S1,S3,S4 and S 5 are off, S 6 is on, and S 2 is controlled by PEM signals as a master switch. At this time, the decoupling capacitor C d2 absorbs energy and the voltage rises. When S 2 is on, the i d flow path is U inv+→Ld→S2→D1→Uinv-,S2, and when it is off, the i d flow path is C d2-→S6→D5→Uinv→Ld→Cd2+. Where C d2+ represents the positive electrode of coupling capacitor C d2 and C d2- represents the negative electrode of coupling capacitor C d2.
Fig. 9 is a schematic diagram of a six-switch power decoupling circuit according to the present invention operating in a fourth mode of operation. As shown in fig. 9, the circuit is a step-up/step-down circuit, and operates as a Buck. In this mode of operation, U inv <0, and P pv<Pac,S2,S3,S4 and S 6 are off, S 1 is on, and S 5 is controlled by PEM signals as a master switch. At this time, the decoupling capacitor C d2 releases energy and the voltage rises. When S 5 is on, the i d flow path is C d2+→Ld→U inv→S5→D6→Cd2-,S5, and when it is off, the i d flow path is U inv-→S1→D2→Ld→Uinv+.
In each mode of operation, only one switch is in the On/Off state, the switch being the master switch, the drive signal being generated by the PEM and the remaining switch states being fixed. Master switches S 1、S2、S4、S5 and S 6 are controlled by R 1、R2 and PEM, and their logical relationship is shown in formula (1):
Wherein R 1 represents a power grid voltage sign, R 1 =0 in the positive half cycle and R 1 =1 in the negative half cycle, R 1＝sgn(-uo can be used for the sign, R 2 represents a micro-inverter decoupling power sign, the decoupling power is positive R 2 =1, the decoupling power is negative R 2 =0, R 2＝sgn[-Ppv cos (2 ωt) can be used for the sign, sgn is a sign function, and ω is an angular frequency.
The embodiment of the invention establishes a control circuit for controlling six switching tubes as shown in fig. 10, wherein an MATLAB simulation diagram of a PEM signal generating circuit is shown in fig. 11, and an MATLAB simulation diagram of a power decoupling circuit consisting of six switching tubes is shown in fig. 12. The driving signal shown in fig. 13 is a driving signal of a six-switch power decoupling circuit according to an embodiment of the present invention. Experiments are carried out on the basis of simulation, the experiment main circuit is a two-stage micro-inverter, and the power supply is a 1500W stabilized DC power supply. The voltage stabilizing large electrolytic capacitor of the front stage Boost circuit in the two-stage micro-inverter replaces a film capacitor of 10 mu F, an experimental waveform is shown in figure 14 when the decoupling capacitor is not connected, the input voltage of the experimental Boost is 30V, the output of the Boost circuit can be seen to measure the secondary ripple with obvious jitter at two ends of the film capacitor when the decoupling circuit is not connected, the ripple amplitude of the secondary ripple is about 20V, and the waveform can be seen to generate obvious distortion at the output side of the H bridge. The experimental effect achieved by connecting the decoupling circuit is shown in fig. 15, the secondary ripple with obvious jitter at the two ends of the output test film capacitor of the Boost circuit can be seen, the ripple amplitude of the secondary ripple is about 15V, and the waveform can be seen at the output side of the H bridge to be obviously improved. The decoupling circuit obviously plays a role in reducing the capacitance value of the Boost side capacitor.
The invention discloses a novel technology of a micro-inverter without an electrolytic capacitor, which is innovatively embodied on a topological structure of a power coupling circuit. The inversion part adopts the traditional voltage source topology, the power coupling circuit is connected in parallel to the alternating current output end of the micro-inverter, replaces an electrolytic capacitor to realize the power coupling function, and improves the efficiency of the micro-inverter. Since the input power of the direct current side is constant and the alternating current output power is sinusoidal, the instantaneous values of the input power and the alternating current output power are inconsistent, and the power coupling circuit plays a role in energy buffering, the micro-inverter circuit has the following advantages and innovations:
1. the power decoupling circuit is connected to the AC output side of the micro-inverter, so that energy buffering is carried out, the coupling capacitance value is greatly reduced, the performance and the service life of the micro-inverter are improved, and the micro-inverter without electrolytic capacitor is realized.
2. The closed loop control is carried out on the whole system, the switching tube duty ratio of the front-stage Boost circuit is controlled by measuring the bus voltage U dc and the bus current I dc, and the duty ratio of the four-switch H bridge is controlled by measuring the power grid voltage U ac, the micro-inverter alternating-current side output voltage U inv and the decoupling capacitor voltage U d, so that the effects of controlling the power grid voltage waveform and reducing the secondary disturbance power are achieved.
3. The micro-inverter AC output side is connected with a six-switch power decoupling circuit in parallel, which is equivalent to the balance pulse energy of an active power filter, so that the secondary disturbance power in the micro-inverter is restrained, and the coupling capacitance value is greatly reduced by utilizing the high voltage of the AC side.
4. The pulse modulation technology PEM is adopted, and the six-switch power coupling circuit is controlled in a DCM mode, so that the structure is simple and the control is convenient.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, which are intended to facilitate an understanding of the principles and embodiments of the invention and are to be varied in scope and detail by persons skilled in the art in light of the teachings of the invention. In view of the foregoing, this description should not be construed as limiting the invention.
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