CN106787873B - Alternating current side coupled power decoupling circuit - Google Patents
Alternating current side coupled power decoupling circuit Download PDFInfo
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- CN106787873B CN106787873B CN201710115374.1A CN201710115374A CN106787873B CN 106787873 B CN106787873 B CN 106787873B CN 201710115374 A CN201710115374 A CN 201710115374A CN 106787873 B CN106787873 B CN 106787873B
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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
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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
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4835—Converters with outputs that each can have more than two voltages levels comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
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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
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Abstract
An AC side coupled power decoupling circuit includes an inductor, a main switching device, a parasitic diode, and a decoupling capacitance. The main switching device is seven switching tubes, and each switching tube is connected in anti-parallel with a parasitic diode. The power decoupling circuit is divided into four working modes, namely a PHC charging mode; PHC discharge mode; NHC charge mode and NHC discharge mode. The input end of the power decoupling circuit is connected in parallel with the output side of the inverter, the voltage amplitude of the output side of the inverter is high and varies in positive and negative periods, so that the decoupling capacitor in the decoupling circuit designed based on the step-up and step-down circuit can obtain higher average voltage and larger voltage variation range, the capacitance value of the decoupling capacitor is greatly reduced, the polarity of the decoupling capacitor is fixed, the grid-connected requirement of the inverter can be met without using a large electrolytic capacitor, the system volume and cost are greatly reduced, and the service life of the photovoltaic power generation system is greatly prolonged.
Description
Technical Field
The invention relates to a power decoupling circuit with alternating current side coupling, and belongs to the technical field of electrician.
Background
In a photovoltaic power generation system, a photovoltaic module generates constant maximum power through Maximum Power Point Tracking (MPPT) control, and instantaneous power transmitted to a power grid presents periodic pulsation, which is a problem of instantaneous power mismatch commonly existing in single-phase grid-connected inverters. In general, a large-capacity electrolytic capacitor is used as an energy storage element of a decoupling circuit, however, the introduction of the electrolytic capacitor shortens the overall service life of the photovoltaic power generation system. According to different positions of the decoupling capacitor in the photovoltaic power generation system, decoupling can be divided into decoupling at the photovoltaic array side, decoupling at the direct current bus side and decoupling at the alternating current output side. The voltage values at two ends of the decoupling capacitor of the alternating current output side decoupling circuit are larger, and larger fluctuation can be allowed, so that the magnitude of the decoupling capacitor value can be effectively reduced, the system volume is reduced, the photovoltaic power generation system can use a long-life thin film capacitor to replace an electrolytic capacitor, and the service life of the photovoltaic power generation system is prolonged.
For the power decoupling mode of the alternating current side, a plurality of students propose corresponding power decoupling circuits. Li Q and Wolfs P propose to place decoupling capacitance between inverter and electric wire netting, form the two-way AC-AC frequency conversion type inverter topology from this, but the voltage amplitude at decoupling capacitance both ends is limited by the electric wire netting voltage, does not possess the buck-boost function, and decoupling capacitance's reduction is limited. Chen Zongxiang from the university of the fertilizer industry proposes that the power grid is connected via inductive filtering in phase a and phase C and the inductor L in phase B b Connecting the network, thereby passing through two switches on phase B and the inductance L b Forms a power decoupling circuit, the energy storage element of which is an inductance L b . However, the decoupling capacity of the decoupling circuit is greatly reduced by adopting the inductor as the energy storage element of the decoupling circuit, which is determined by the inductance value and the square of the passing current, and the volume of the photovoltaic power generation system is greatly increased if the inductance value is increased.
Disclosure of Invention
The invention aims to disclose an alternating current side coupled power decoupling circuit according to various problems of an alternating current output side decoupling circuit, which has the characteristics of less energy storage elements, small capacitance value, wide input range and adjustable voltage.
The technical scheme for realizing the invention is as follows: an AC side coupled power decoupling circuit includes an inductor, a main switching device, a parasitic diode, and a decoupling capacitance. The main switching devices are seven switching tubes, namely a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube, a sixth switching tube and a seventh switching tube; each switching tube is reversely connected with a parasitic diode in parallel; the parasitic diodes are seven diodes, namely a first diode, a second diode, a third diode, a fourth diode, a fifth diode, a sixth diode and a seventh diode.
The emitters of the first switching tube T1 and the fourth switching tube T4 are respectively connected with two ends of the output alternating current side of the inverter; the collectors of the first switching tube T1 and the fourth switching tube T4 are respectively connected with two ends of the inductor Lc; meanwhile, the collector of the first switching tube T1 is connected with the emitter of the second switching tube T2 and the collector of the fifth switching tube T5; the collector of the fourth switching tube T4 is connected with the emitter of the sixth switching tube T6 and the collector of the second switching tube T3; the collectors of the second switching tube T2 and the sixth switching tube T6 are connected with the collector of the seventh switching tube T7; the emitter of the seventh switching tube T7 is connected with one end of the decoupling capacitor Cc; the emitters of the third switching tube T3 and the fifth switching tube T5 are connected together and are connected to the other end of the decoupling capacitor Cc;
the power decoupling circuit can realize bidirectional flow of power, and parasitic diodes of all switching tubes can form an energy circulation path without adding additional diodes; in the power decoupling circuit, the capacitor Cc realizes the power decoupling function of the difference between the output power of the photovoltaic inverter and the instantaneous power of the power grid, and the inductor Lc realizes the transmission of the energy difference.
The power decoupling circuit can be divided into four working modes, namely a PHC charging mode, wherein the working mode is 1; the working mode 2 is PHC discharge mode; the working mode 3, namely an NHC charging mode; the mode of operation 4, NHC discharge mode.
Working mode 1: in the working mode 1, i.e. the PHC charging mode, the switches of the second switching tube T2 to the sixth switching tube T6 are all turned off, and current can flow through the second diode D2, the third diode D3 and the fourth diode D4, and when the first switching tube T1 is turned on, the seventh switching tube T7 is turned off at this time, and the inductor L c Initial current i p =0, the inverter output side gives the inductance i L Charging, inductor current i L Gradually increases, the current direction is from top to bottom, and the inductance stores energy. The boost mode can be realized by adjusting the duty ratio of the driving pulse of the first switching tube T1 to be larger than 1/2. Then the first switching tube T1 is disconnected, the seventh switching tube T7 is opened, and the inductance L c Freewheel to decoupling capacitor C c Decoupling the voltage v across the capacitor c Increase the inductance current i L Gradually decrease until i L When=0, the seventh switching tube T7 is turned off, the inductance L c The energy stored on the upper part is transferred to electricityCapacitor C c And the PHC charging mode process of the decoupling circuit is realized.
Working mode 2: in the working mode 2, that is, the PHC discharging mode, the fifth switching tube T5 and the sixth switching tube T6 are turned off, the seventh switching tube T7 is turned off, and the first switching tube T1 is turned off. The second switching tube T2 and the third switching tube T3 are simultaneously turned on, at the moment, the fourth switching tube T4 is turned off, and the capacitor C c Inductance L c Discharging, controlling the duty ratio of the second switching tube T2 and the third switching tube T3 to be larger than 1/2, which is equivalent to the decoupling circuit working in the boost mode, and the capacitor C c Voltage v of (2) c Gradually decrease, inductance current i L Gradually increasing from 0, wherein the current direction is from bottom to top, and the inductor acquires a part of energy from the capacitor; then the second switching tube T2 and the third switching tube T3 are simultaneously disconnected, the fourth switching tube T4 is turned on, and the inductor L c Discharging the output side of the inverter, and inducing current i L Gradually decrease until i L When=0, the fourth switching tube T4 is turned off, the inductance L c All the stored energy is transferred to the output side of the inverter, so that the PHC discharge mode process of the decoupling circuit is realized.
Working mode 3: in the working mode 3, i.e. the NHC charging mode, the second switching tube T2 and the third switching tube T3 are turned off, the fifth switching tube T5 and the sixth switching tube T6 are turned off, and the first switching tube T1 is turned off. The fourth switching tube T4 is turned on, and the seventh switching tube T7 is turned off, the inductor L c Initial current i p =0, the inverter output side gives inductance L c Charging, inductor current i L Gradually increasing, the current direction is from bottom to top, and the inductance stores energy. The duty ratio of the fourth switching tube T4 is controlled to be larger than 1/2, so that a boosting mode can be realized. Then the fourth switching tube T4 is disconnected, the seventh switching tube T7 is opened, and the inductance L c Freewheel to decoupling capacitor C c Decoupling the voltage v across the capacitor c Increase the inductance current i L Gradually decrease until i L When=0, the seventh switching tube T7 is turned off, the inductance L c The energy stored on is transferred to the capacitor C c And the NHC charging mode process of the decoupling circuit is realized.
Working mode 4: in the operation mode 4, i.e. NHC discharge mode, the second switching tube T2 and the third switching tubeThe switching tube T3 is turned off, the fourth switching tube T4 is turned off, and the seventh switching tube T7 is turned off. The fifth switching tube T5 and the sixth switching tube T6 are simultaneously turned on, at the moment, the first switching tube T1 is turned off, and the capacitor C c Inductance L c Discharging, controlling the duty ratio of the fifth switching tube T5 and the sixth switching tube T6 to be larger than 1/2, which is equivalent to the decoupling circuit working in the step-down mode, the capacitor C c Voltage v of (2) c Gradually decrease, inductance current i L Gradually increasing from 0, wherein the current direction is from top to bottom, and the inductor acquires a part of energy from the capacitor; then the fifth switching tube T5 and the sixth switching tube T6 are simultaneously disconnected, the first switching tube T1 is turned on, and the inductor L c Discharging the output side of the inverter, and inducing current i L Gradually decrease until i L When=0, the first switching tube T1 is turned off, the inductance L c All the stored energy is transferred to the output side of the inverter, so that the NHC discharge mode process of the decoupling circuit is realized.
The power decoupling circuit has the advantages that the input end of the power decoupling circuit is connected in parallel with the output side of the inverter, the voltage amplitude of the output side of the inverter is high, and the voltage is changed in positive and negative periods, so that the decoupling capacitor in the decoupling circuit based on the design of the buck-boost circuit can obtain higher average voltage and larger voltage change range, the capacitance value of the decoupling capacitor is greatly reduced, the polarity of the decoupling capacitor is fixed, the grid-connected requirement of the inverter can be met without using a large electrolytic capacitor, the system volume and the cost are greatly reduced, and the service life of the photovoltaic power generation system can be greatly prolonged. The power decoupling circuit is characterized in that a two-port circuit is connected in parallel with the alternating current output side of the inverter, and compared with a three-port type decoupling circuit, the power decoupling circuit can be put into a photovoltaic power generation system in a modularized mode, and is convenient to maintain.
Drawings
FIG. 1 is a schematic diagram of a power decoupling circuit with parallel coupling on the AC side of the present invention;
FIG. 2 is a schematic diagram of an equivalent circuit and current loop for PHC charging mode;
FIG. 3 is a graph of inductor current waveforms and capacitor voltage waveforms in PHC charging mode;
FIG. 4 is a schematic diagram of an equivalent circuit and a current loop of PHC discharge mode;
FIG. 5 is a graph showing the inductor current waveform and the capacitor voltage waveform in PHC discharge mode;
FIG. 6 is a schematic diagram of an equivalent circuit and current loop for NHC charging mode;
FIG. 7 is a schematic diagram of an equivalent circuit and current loop of NHC discharge mode;
FIG. 8 shows inductance L in PHC charging mode c Charging and discharging of (C) and capacitor C c A charging process;
FIG. 9 shows inductance L in PHC discharge mode c Charging and discharging of (C) and capacitor C c A discharge process;
FIG. 10 shows inductance L in NHC charging mode c Charging and discharging of (C) and capacitor C c A charging process;
FIG. 11 shows inductance L in NHC discharge mode c Charging and discharging of (C) and capacitor C c A discharge process;
FIG. 12 shows inductance L c Current and capacitance C of (2) c Is a voltage of (2);
fig. 13 is a waveform of photovoltaic output current and inverter grid-tie current and grid-tie voltage of the photovoltaic power generation system.
Detailed Description
The specific embodiments of the invention are shown in the drawings. Fig. 1 is a schematic diagram of a power decoupling circuit with parallel coupling on the ac side according to this embodiment.
The power decoupling circuit of this embodiment includes: including inductors, main switching devices, parasitic diodes, and decoupling capacitors. The inductor is Lc; the main switching devices are seven switching tubes, namely a first switching tube T1, a second switching tube T2, a third switching tube T3, a fourth switching tube T4, a fifth switching tube T5, a sixth switching tube T6 and a seventh switching tube T7; the parasitic diodes are seven diodes, namely a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6 and a seventh diode D7; the decoupling capacitor is Cc.
Due to the influence of the production process, each main switching device is reversely connected with one parasitic diode in parallel. The specific connection mode is that the anode of the diode is connected with the emitter of the switching tube, and the cathode of the diode is connected with the collector of the switching tube.
Emitters of the first switching tube T1 and the fourth switching tube T4 are respectively connected with two ends of an output alternating current side of the inverter based on hysteresis control; the collectors of the first switching tube T1 and the fourth switching tube T4 are respectively connected with two ends of the inductor Lc; meanwhile, the collector of the first switching tube T1 is connected with the emitter of the second switching tube T2 and the collector of the fifth switching tube T5; the collector of the fourth switching tube T4 is connected with the emitter of the sixth switching tube T6 and the collector of the third switching tube T3; the collectors of the second switching tube T2 and the sixth switching tube T6 are connected with the collector of the seventh switching tube T7; the emitter of the seventh switching tube T7 is connected with one end of the decoupling capacitor Cc; the emitters of the third switching tube T3 and the fifth switching tube T5 are connected together and connected to the other end of the decoupling capacitor Cc. This has the advantage that a bi-directional flow of power can be achieved, as shown in fig. 1. The parasitic diodes of each switching tube in the figure can form the energy flow path without adding extra diodes. In the circuit, the capacitor Cc realizes the power decoupling function of the difference between the output power of the photovoltaic inverter and the instantaneous power of the power grid, and the inductor Lc realizes the transmission of the energy difference.
FIG. 2 shows an equivalent circuit and a current flow path of the power decoupling circuit in the working mode 1, i.e. PHC charging mode, in the embodiment, u out The inverter is controlled by hysteresis current to output alternating square wave voltage value, i L Is an inductance current value, and when the first switching tube T1 is switched on, the on time is defined as dt r This stage satisfies the formula
When the first switching tube T1 is turned off, the seventh switching tube T7 is turned on, and the turn-on time of the seventh switching tube T7 is set to be dt f The capacitor Cc voltage at the conduction time of the seventh switching tube T7 is u c1 The capacitor Cc voltage at the turn-off time of the seventh switching tube T7 is u c2 The voltage difference between them is du c The current on the capacitor at this stage +.>
In PHC charging modeExcess energy generated by the photovoltaic power generation system will be stored in the capacitance of the decoupling circuit. FIG. 3 shows the inductor current L in PHC charging mode c And a filter capacitor voltage u C Wherein t is 1 -t 2 When the interval is the conduction of the first switching tube T1 in the working mode 1, T 2 -t 3 The interval is T when the first switching tube T1 is closed and the seventh switching tube T7 is conducted in the working mode 1 3 -t 4 For the time interval from when the seventh switching tube T7 is turned off to when the next first switching tube T1 is turned on.
Shown in the figure at t 1 -t 2 Interval i L1 From t 1 I at time 0 Rising to t 2 Time I 1 The energy storage stage is that the inductor is charged, and the energy obtained from the output side of the inverter by the inductor is that the inductor current has the relation with the voltages at two ends
Wherein the capacitance voltage u C Ideally this stage is maintained constant at u 0 。
At t 2 -t 3 The interval is the inductive discharge and the capacitor energy storage stage, and the energy acquired by the capacitor is equal to t 1 -t 2 Inductively stored energy in intervals, i.e. simultaneously with the current on the capacitor at this stage
The process of charging and storing energy for the inductor and transferring the inductive energy to the capacitor in the working mode 1 is described.
Fig. 4 shows a discharge loop and a current loop of the working mode 2 of the present embodiment, that is, the PHC discharge mode.
In the PHC discharge mode, insufficient energy of the photovoltaic power generation system is obtained from the capacitor of the decoupling circuit. FIG. 5 shows the inductor current i in PHC charging mode L And a filter capacitor voltage u c Wherein t is 1 -t 2 The interval is T before the second switching tube T2 and the third switching tube T3 are conducted after the fourth switching tube T4 is turned off in the working mode 2 2 -t 3 Interval ofIn the working mode 2, when the fourth switching tube T4 is turned off and the second switching tube T2 and the third switching tube T3 are turned on, T 3 -t 4 For the fourth switching tube T4 to be turned on, when the second switching tube T2 and the third switching tube T3 are turned off, T 4 -t 5 The fourth switching tube T4 is turned off and then the second switching tube T2 and the third switching tube T3 are turned on.
Shown in FIG. 5 at t 2 -t 3 Interval i L1 From t 2 I at time 0 Increase in reverse to t 3 Time I 1 To decouple the capacitor discharge into the inductive phase, the capacitor voltage u C From u 0 Reduced to u 1 At the moment, the inductor obtains energy from the decoupling capacitor, and meanwhile, the relationship between the discharging current of the decoupling capacitor exists
At t 3 -t 4 The interval is the phase of discharging the inductance to the output side of the inverter, and the energy output by the inductance to the inverter is equal to t 2 -t 3 Energy stored by the inductor in the interval, and the voltage on the inductor at the stage meets the relation
The process of discharging the capacitor to the inductor and transferring the inductive energy to the output side of the inverter in mode 2 is illustrated.
Fig. 6 shows an equivalent circuit and a current loop of the operation mode 3 of the present embodiment, i.e. the NHC charging mode.
Fig. 7 shows an equivalent circuit and a current loop of the operation mode 4 of the present embodiment, i.e. the NHC charge-discharge mode.
In operating modes 3 and 4, the inverter output is during the negative half cycle of the mains voltage, but the waveform analysis of the inductor current and capacitor voltage is similar to operating modes 1, 2.
FIG. 8 shows the output side of the inverter at the positive half cycle of the grid voltage, u, in mode 1 of operation of the present embodiment out Under the condition of=400V, inductance L c Waveform and capacitor C during charge and discharge c Charging of (2)And (5) an energy storage process. Fig. 8 shows, from top to bottom, curve 1 as the decoupling circuit inductance L c Current (unit: A), curve 2 is capacitance C c Curve 3 is the drive signal of the first switching tube T1 and curve 4 is the drive signal of the seventh switching tube T7. When the first switching tube T1 is closed, the inductance of the decoupling circuit is in a charging process and u is used for simultaneously out The linear rate of/L1 increases while the capacitor voltage remains unchanged. When the first switching tube T1 is opened and the seventh switching tube T7 is closed, the decoupling circuit inductively discharges while the capacitor C c During the charging process, the capacitor voltage increases.
FIG. 9 shows the output side of the inverter at the positive half cycle of the grid voltage, u, in mode 2 of operation out Under the condition of=400V, inductance L c Waveform and capacitor C during charge and discharge c Is provided. Fig. 9 shows, from top to bottom, curve 1 as the decoupling circuit inductance L c Current (unit: A), curve 2 is capacitance C c Curve 3 is the drive signal of the second switching tube T2, the third switching tube T3, and curve 4 is the drive signal of the fourth switching tube T4. When the second switching tube T2 and the third switching tube T3 are closed, the capacitor of the decoupling circuit is in a discharging process, the capacitor voltage is reduced, and the inductor current is reversely increased. When the second switching tube T2 and the third switching tube T3 are disconnected and the fourth switching tube T4 is closed, the decoupling circuit is in inductive discharge, energy is released to the output side of the inverter, the inductive current is reduced, and the capacitor voltage is kept unchanged at the moment.
Fig. 10 shows the negative half cycle of the grid voltage, u, at the output side of the inverter in mode 3 of operation of the present embodiment out Under the condition of=400V, inductance L c Waveform and capacitor C during charge and discharge c Is provided. Fig. 10 shows, from top to bottom, curve 1 as the decoupling circuit inductance L c Current (unit: A), curve 2 is capacitance C c Curve 3 is the drive signal of the fourth switching tube T4 and curve 4 is the drive signal of the seventh switching tube T7. When the fourth switching tube T4 is closed, the inductance of the decoupling circuit is in the charging process, the inductance current is reversely increased, and u is the same time out L1The linear rate increases, while the capacitor voltage remains unchanged. When the fourth switching tube T4 is disconnected and the seventh switching tube T7 is closed, the decoupling circuit inductively discharges, the inductance current is reduced and the capacitance C is reduced c During the charging process, the capacitor voltage increases.
Fig. 11 shows the negative half cycle of the grid voltage, u, at the output side of the inverter in mode 4 of operation of the present embodiment out Under the condition of=400V, inductance L c Waveform and capacitor C during charge and discharge c Is provided. Fig. 11 shows, from top to bottom, curve 1 as the decoupling circuit inductance L c Current (unit: A), curve 2 is capacitance C c Curve 3 is the drive signal of the fifth switching tube T5, the sixth switching tube T6, and curve 4 is the drive signal of the first switching tube T1. When the fifth switching tube T5 and the sixth switching tube T6 are closed, the capacitor of the decoupling circuit is in a discharging process, the capacitor voltage is reduced, and the inductor current is increased. When the fifth switching tube T5 and the sixth switching tube T6 are opened and the first switching tube T1 is closed, the decoupling circuit discharges the inductance to release energy to the output side of the inverter, the inductance current is reduced, and the capacitance voltage is kept unchanged at the moment.
FIG. 12 shows the inductance L of the photovoltaic system under the condition that the output voltage of the photovoltaic side of the photovoltaic system is 240V c Waveform and capacitor C during charge and discharge c Is a waveform of the charge-discharge process of (a). Fig. 11 shows, from top to bottom, curve 1 as the decoupling circuit inductance L c Current (unit: A), curve 2 is capacitance C c Is set in units of V.
Fig. 13 shows waveforms of the grid-connected voltage and the grid-connected current of the inverter output side of the photovoltaic power generation system according to the present embodiment under the condition that the output voltage of the photovoltaic power generation system is 240V and the load of the photovoltaic power generation system is 550W resistive load. Fig. 13 shows, from top to bottom, a graph 1 showing the photovoltaic side output current (unit: a) of the photovoltaic power generation system when the decoupling circuit of the present embodiment is operated, a graph 2 showing the photovoltaic side output current (unit: a) of the photovoltaic power generation system when the power decoupling circuit of the present embodiment is not operated, a graph 3 showing the grid-connected current (unit: a) of the photovoltaic power generation system inverter output side, and a graph 4 showing the grid-connected voltage (unit: V) of the photovoltaic power generation system inverter output side. As can be seen from comparing curve 1 and curve 2, when the power decoupling circuit of the embodiment works, the output current of the photovoltaic side of the photovoltaic power generation system is kept to be fluctuating in a narrow range up and down to 2.8A, and when the power decoupling circuit of the embodiment does not work, the output current of the photovoltaic side of the photovoltaic power generation system is greatly fluctuating between 0 and 10A, and the working efficiency of the photovoltaic power generation system is seriously affected by such great fluctuation.
In order to verify the correctness of the mathematical model and analysis of the power decoupling circuit in this embodiment, the simulation is performed by using the professional simulation software Matlab R2014a, the control strategy adopts the PWM technology based on pulse energy control (PEM), the simulation parameters are shown in the following table, and the simulation results are shown in fig. 8 to 13.
Table simulation parameters
| Parameters (parameters) | Size and dimensions of |
| Peak grid voltage, u grid.pk (V) | 311 |
| Inverter output voltage u out (V) | 400 |
| Capacitor C c (μF) | 20 |
| Inductance, L c (μH) | 200 |
Simulation results show that the total capacitance of the photovoltaic power generation system applying the power decoupling circuit of the embodiment is greatly reduced, and the micro-inversion technology without electrolytic capacitors can be realized, so that the feasibility of the power decoupling circuit is demonstrated.
Claims (6)
1. An ac side coupled power decoupling circuit, the circuit comprising an inductor, a main switching device, a parasitic diode, and a decoupling capacitance; the main switching devices are seven switching tubes, namely a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, a fifth switching tube, a sixth switching tube and a seventh switching tube; each switching tube is reversely connected with a parasitic diode in parallel; the parasitic diodes are seven diodes, namely a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a sixth diode D6 and a seventh diode D7;
the emitters of the first switching tube and the fourth switching tube are respectively connected with two ends of the output alternating current side of the inverter; the collectors of the first switching tube and the fourth switching tube are respectively connected with two ends of the inductor; meanwhile, the collector electrode of the first switching tube is connected with the emitter electrode of the second switching tube and the collector electrode of the fifth switching tube; the collector of the fourth switching tube is connected with the emitter of the sixth switching tube and the collector of the second switching tube; the collectors of the second switching tube and the sixth switching tube are connected with the collector of the seventh switching tube; the emitter of the seventh switching tube is connected with one end of the decoupling capacitor; the emitters of the third switching tube and the fifth switching tube are connected together and are connected to the other end of the decoupling capacitor;
the power decoupling circuit is divided into four working modes, namely a PHC charging mode, and the working mode is 1; the working mode 2 is PHC discharge mode; the working mode 3, namely an NHC charging mode; the mode of operation 4, NHC discharge mode.
2. An ac side coupled power decoupling circuit as claimed in claim 1, wherein the power decoupling circuit is configured to enable bi-directional flow of power, and the parasitic diodes of each switching tube are configured to form a path for energy flow; in the power decoupling circuit, the capacitor realizes the power decoupling function of the difference between the output power of the photovoltaic inverter and the instantaneous power of the power grid, and the inductor realizes the transmission of the difference between the output power of the photovoltaic inverter and the instantaneous power of the power grid.
3. The ac side-coupled power decoupling circuit of claim 1, wherein in said operational mode 1, in the PHC charging mode, the second through sixth switching tube switches are all turned off, current flows through the second, third and fourth diodes, and when the first switching tube is turned on, the seventh switching tube is turned off, the inductor
Initial current
The output side of the inverter gives the inductance +.>
Charging, inductor current->
Gradually increasing the current direction from top to bottom, and storing energy by the inductor; the driving pulse duty ratio of the first switching tube is regulated to be larger than 1/2, so that a boosting mode is realized; then the first switching tube is disconnected, the seventh switching tube is opened, the inductance freewheels to the decoupling capacitor, and the voltage on the decoupling capacitor is +.>
Increase, inductor current->
Gradually decrease until
And when the seventh switch tube is turned off, the energy stored in the inductor is transferred to the capacitor, so that the PHC charging mode process of the decoupling circuit is realized.
4. The ac side coupled power decoupling circuit of claim 1, wherein in said operational mode 2, in a PHC discharge mode, the fifth and sixth switching tubes are turned off, the seventh switching tube is turned off, and the first switching tube is turned off; the second switching tube and the third switching tube are simultaneously turned on, at the moment, the fourth switching tube is turned off, the capacitor discharges the inductor, the duty ratio of the second switching tube and the third switching tube is controlled to be more than 1/2, the decoupling circuit works in a boosting mode, and the voltage of the capacitor is equivalent to that of the decoupling circuit
Gradually decrease, inductor current +>
Gradually increasing from 0, wherein the current direction is from bottom to top, and the inductor acquires a part of energy from the capacitor; then the second switching tube and the third switching tube are simultaneously disconnected, the fourth switching tube is turned on, the inductor discharges to the output side of the inverter, and the inductor current is +.>
Gradually decrease until +>
And when the fourth switching tube is turned off, all the energy stored in the inductor is transferred to the output side of the inverter, so that the PHC discharge mode process of the decoupling circuit is realized.
5. The ac side coupled power decoupling circuit of claim 1, wherein the operating mode 3, in NHC charging mode, the second and third switching tubes are open, the fifth and sixth switching tubes are open, and the first switching tube is open; the fourth switching tube is turned on, and when the seventh switching tube is turned off, the inductor
Initial current->
The output side of the inverter charges the inductor, inductor current +.>
Gradually increasing, wherein the current direction is from bottom to top, and the inductance stores energy; the duty ratio of the fourth switching tube is controlled to be larger than 1/2, so that a boosting mode is realized; then the fourth switching tube is disconnected, the seventh switching tube is turned on, the inductance freewheels to the decoupling capacitor, and the voltage on the decoupling capacitor is +.>
Increase, inductor current->
Gradually decrease until +>
And when the seventh switching tube is turned off, the energy stored in the inductor is transferred to the capacitor, so that the NHC charging mode process of the decoupling circuit is realized.
6. The ac side coupled power decoupling circuit of claim 1, wherein in the NHC discharge mode, the second and third switching tubes are open, the fourth switching tube is open, and the seventh switching tube is open in the operation mode 4; the fifth switching tube and the sixth switching tube are simultaneously turned on, at the moment, the first switching tube is turned off, the capacitor discharges the inductor, the duty ratio of the fifth switching tube and the sixth switching tube is controlled to be larger than 1/2, the decoupling circuit works in a voltage-reducing mode, and the voltage of the capacitor is equivalent to that of the decoupling circuit
Gradually decrease, inductor current +>
Gradually increasing from 0, wherein the current direction is from top to bottom, and the inductor acquires a part of energy from the capacitor; then the fifth switching tube and the sixth switching tube are simultaneously disconnected, and the first switching tube is turned onThe inductor discharges the output side of the inverter, the inductor current +.>
Gradually decrease until +>
When the first switching tube is turned off, all the energy stored in the inductor is transferred to the output side of the inverter, and the NHC discharging mode process of the decoupling circuit is realized.
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| CN108322072B (en) * | 2018-01-19 | 2022-11-25 | 中电普瑞电力工程有限公司 | Capacity reduction operation method and device of modular multilevel converter |
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