Isolated optical storage three-port inverter integrated with multi-winding positive laser photovoltaic equalizer

Abstract

The invention discloses an isolated optical storage three-port inverter integrated with a multi-winding positive laser photovoltaic equalizer, and relates to the field of optical storage power generation. The invention aims to solve the problems that a traditional optical storage system comprises a plurality of two-port converters, so that a power generation system of the traditional optical storage system is complex in structure, large in size and low in power density, and power generation power is lost under the working condition that photovoltaic modules connected in series are mismatched. An isolated three-port inverter based on three active bridge topology and a photovoltaic equalizer are combined into a whole to form a converter topological structure. The multi-winding equalizer is integrated into the three-port inverter through the topology fusion technology, so that the problem of mismatching between boards is solved, the generating capacity under the condition of mismatching of the photovoltaic group string can be effectively improved, meanwhile, single-stage conversion of energy among three ports can be realized, the number of converter components is greatly reduced, the system loss is reduced, the system efficiency is improved, and the cost is reduced. The volume cost is reduced.

Description

Technical Field

[0001] The invention belongs to the field of photovoltaic power generation, and in particular relates to an isolated photovoltaic three-port inverter with an integrated multi-winding positive-phase volt-equalizer. Background Art

[0002] In traditional photovoltaic power generation systems, photovoltaics, batteries and loads or power grids are connected by multiple two-port converters, resulting in a complex structure, bulky volume and low power density of the power generation system. In addition, there are multiple independent control units in multiple converters, and the decentralized converter control method will affect the overall response speed of the system and increase the uncertainty and complexity of the system. Instead of multiple independent two-port converters, a three-port converter based on a three-active bridge structure is used. The photovoltaic three-port inverter topology structure consists of two DC ports and one AC port. It can not only realize the transmission and conversion of power between photovoltaics, batteries and loads or power grids, but also has a higher power density, reduces system costs and improves system efficiency.

[0003] In order to reduce the power loss caused by local shading and different degrees of aging of battery components in series-connected photovoltaic modules under mismatched working conditions, photovoltaic DC optimizers and microinverters have emerged. The DC optimizer is a separate converter connected to each photovoltaic module, which can independently adjust the working voltage and current according to the specific conditions of each panel to ensure the maximum output power of each photovoltaic panel; the microinverter is equipped with an inverter for each photovoltaic module, so that the DC power generated by each photovoltaic module is converted into AC power, and the performance of each photovoltaic module can be optimized at the same time. Although DC optimizers and microinverters can achieve maximum power tracking for each photovoltaic module and improve the power generation efficiency of the photovoltaic system. However, both require the installation of corresponding equipment for each photovoltaic panel separately, and use more converters, which will increase the system cost.

[0004] In recent years, scholars have proposed the concept of photovoltaic balancer. Photovoltaic balancer uses an energy conversion and transmission device to transfer part of the power of the unshaded component to the shaded component to change its working point and thus increase the power generation of the system. The DC-DC converter is used to replace the anti-parallel diode of the photovoltaic component, so that the current that should flow through the diode flows through the balancer, so that the voltage at both ends of the photovoltaic component can be controlled near its maximum power point instead of being clamped at a negative value by the bypass diode. At this time, the shaded photovoltaic component will no longer consume power but output power, thereby greatly improving the power generation of the photovoltaic system under shade conditions. It only handles the unmatched power between photovoltaic components, which can reduce the power level of the converter, and the power loss will also be reduced accordingly. In the case of small power mismatch or no mismatch, its processing power is very small or even zero. However, the photovoltaic balancer can only process differential power and cannot transmit the output power of the photovoltaic component to the next stage. Therefore, it needs to be used in parallel with the next-stage inverter, which increases the number of system converters and the system cost will also increase accordingly.

[0005] Therefore, integrating the photovoltaic balancer into the photovoltaic storage three-port inverter can make the multi-peak phenomenon in the photovoltaic storage system under mismatch conditions compensate for power through different forms of power flow, thereby increasing the output power. In addition, single-stage energy conversion can be achieved between the three ports, with higher power density, reducing system cost and improving system efficiency. Summary of the invention

[0006] The purpose of the present invention is to provide an isolated photovoltaic storage three-port inverter with an integrated multi-winding positive-phase volt-volt equalizer, which can not only realize the single-stage conversion of energy between photovoltaics, energy storage batteries and loads, but also integrate the photovoltaic equalizer into the photovoltaic storage system, thereby realizing power balance between photovoltaic panels under mismatch conditions, and having a higher power density, reducing system cost and improving system efficiency.

[0007] The technical solution to achieve the purpose of the present invention is: the isolated photovoltaic storage three-port inverter with integrated multi-winding positive-phase volt-equalizer is composed of n photovoltaic modules PV1 to PV2 connected in series. n , where n is a positive integer greater than or equal to 2, 12 switch tubes S1~S 12 The isolated three-port full-bridge structure and multi-winding transformer T1 are constituted, wherein the turns ratio of the transformer T1 should be: N1:N2:...:N n+1 =n:1:...:1, three-winding transformer T2 and leakage inductance L of each port r1 ~L r3 , 2n diodes D1~D 2n , capacitors C1-C3, clamping capacitor C c 、Inductor L1~L n 、Inductance L i , output filter inductor Lo , AC load or power grid (V g AC source) and energy storage battery B.

[0008] Among them, port 1 is the photovoltaic port, which is composed of n photovoltaic panels PV1~PV n It is connected in series with the primary winding N1 of transformer T1 and the inductor L i , 4 switch tubes S1~S4, clamping capacitor C c The two interlaced parallel Buck-Boost circuits are formed; the second port is an AC port connected to the power grid or AC load, and the AC-AC matrix converter branch composed of two sets of reverse series switch tubes S5, S6 and S7, S8 and two non-polar capacitors C1, C2 is connected through the output filter inductor L o Realize AC output; Port 3 is the battery port, which consists of 4 switch tubes S9~S 12 The H-bridge is formed to realize the charging and discharging functions of the energy storage battery.

[0009] When the photovoltaic panel power is matched, the n secondary sides N2~N n+1 And its rectifier and freewheeling diodes D1~D 2n When the PV panel does not work, the PV port works in the ordinary staggered parallel Buck-Boost mode; when the PV panel has power mismatch due to local shadow and other problems, the topology will work in the multi-winding balancer and three-port inverter collaborative working mode. i (1≤i≤n) is partially shaded, and the voltage generated is less than winding N i+1 Voltage, at this time, PV i The corresponding balancing branch works, and part of the power flows to the solar panel PV i This changes its operating point, thereby achieving self-balancing and making its output close to maximum power.

[0010] According to the power balance between photovoltaic input power, battery charging and discharging power and load output power, there are three working modes: single input dual output mode, dual input single output mode and single input single output mode; among them, single input dual output mode: when the light is strong, the photovoltaic input power will flow into the battery port to charge the battery in addition to ensuring the constant output of the AC port; dual input single output mode: when the light is weakened, the photovoltaic module is still not enough to maintain the constant output of the AC port at the maximum input power. At this time, the battery port and the photovoltaic port jointly supply power to the AC port; single input single output mode: at night, the photovoltaic input power is 0, and the battery port alone supplies power to the AC port. The power balance relationship of the three-port converter satisfies: P in =P o +P bat ; Among them, Pin is the input power of the photovoltaic module, P o is the output power, P bat It is the battery charging and discharging power, charging is positive and discharging is negative; if you only need to control the power of two ports, the power of the remaining port will be automatically determined according to the power balance relationship.

[0011] The present invention aims at the problem that the traditional photovoltaic storage system includes multiple two-port converters, which leads to the complex structure, large volume, low power density and power loss of the power generation system under the mismatch condition of the photovoltaic components connected in series. The present invention proposes a converter topology structure that combines an isolated three-port inverter based on a three-active bridge topology and a photovoltaic equalizer. By integrating the multi-winding equalizer into the three-port inverter through the topological fusion technology, it not only solves the problem of mismatch between panels, but also can effectively improve the power generation under the mismatch condition of the photovoltaic string. At the same time, it can realize the single-stage conversion of energy between the three ports, greatly reducing the number of converter components, reducing system losses, improving system efficiency, and reducing volume costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The proposed isolated photovoltaic storage three-port inverter topology integrates a multi-winding positive-phase volt-equalizer;

[0013] Figure 2 It is a typical application of the proposed isolated photovoltaic storage three-port inverter topology with integrated multi-winding positive-phase volt-equalizer (taking four photovoltaic modules as an example);

[0014] FIG3 is a working mode diagram of a typical application of the proposed isolated photovoltaic storage three-port inverter topology with integrated multi-winding positive-phase volt-equalizer, taking four photovoltaic modules as an example;

[0015] Figure 3 (a) Mode 1; Figure 3 (b) Mode 2; Figure 3 (c) Mode 3; Figure 3 (d) Mode 4; Figure 3 (e) Mode 5; Figure 3 (f) Mode 6; Figure 3 (g) Mode 7; Figure 3 (h) Mode 8; Figure 3 (i) Mode 9; Figure 3 (j) Mode 10; Figure 3 (k) Mode 11; Figure 3 (l) Mode 12; DETAILED DESCRIPTION

[0016] The present invention proposes an isolated photovoltaic storage three-port inverter with integrated multi-winding positive photovoltaic equalizer. To facilitate the description of the operating principle of the present invention, only the case where photovoltaic and storage batteries simultaneously supply power to AC loads or power grids is considered. The present invention is described in detail below with four photovoltaic modules as an example in combination with the accompanying drawings and specific embodiments.

[0017] like Figure 2As shown in the figure, the isolated photovoltaic storage three-port inverter with integrated multi-winding positive-phase volt-equalizer consists of four photovoltaic modules PV1 to PV4 connected in series, 12 switch tubes S1 to S 12 The isolated three-port full-bridge structure and multi-winding transformer T1 are composed of the following: N1:N2:N3:N4:N5=4:1:1:1:1, three-winding transformer T2 and leakage inductance L of each port. r1 ~L r3 , 8 diodes D1~D8, capacitors C1-C3, clamping capacitor C c , inductors L1~L4, inductors L i , output filter inductor L o , AC load or power grid (V g AC source) and energy storage battery B.

[0018] The three-port inverter adopts single-phase shift SPS control. With port 1 as the reference end, the switch phase shift angles between port 2 and port 3 relative to port 1 are expressed as Control the AC output voltage to be constant, Used for photovoltaic maximum power point tracking, the duty cycle of the bridge circuit switch tube of each port is 50%. Photovoltaic port: S1, S2 and S3, S4 are complementary, and S1, S4 and S2, S3 are simultaneously turned on; AC port: When the AC voltage is greater than 0, S6 and S8 are continuously turned on, and S5 and S7 act complementary; when the AC voltage is less than 0, S5 and S7 are continuously turned on, and S6 and S8 act complementary. Battery port: S9, S 10 and S 11 , S 12 Complementary conduction, while S9, S 12 and S 10 , S 11 Then they are turned on at the same time.

[0019] When the power of the photovoltaic panel is matched, the four secondary sides N2~N5 of the multi-winding transformer T1 and its rectifier and freewheeling diodes D1~D8 do not work, and the photovoltaic port works in the ordinary staggered parallel Buck-Boost boost mode. When the photovoltaic panel has power mismatch due to problems such as local shadows, the topology will work in the coordinated working mode of the balancer and inverter. At this time, assuming that PV1 is partially shaded, the voltage generated is less than the voltage of winding N2, the diode D1 is turned on, the diode D2 is turned off, the current of the inductor L1 gradually increases, and part of the power flows to the solar panel PV1, thereby changing its operating point and making its output close to the maximum power. Therefore, mode 7 to mode 12 adds the working state of diode D1 turning on to charge the photovoltaic panel PV1 to achieve self-balancing, and in the process of mode 1 to mode 6, the inductor L1 is freewheeling through the diode D2.

[0020] Assuming that PV1 is partially shaded, the gray ellipse on PV1 in Figure 3 represents partial shading. When the converter is in dual-output mode, it can be subdivided into 12 different working intervals according to the switching state of its switch tube, and both the voltage and current will show a specific change pattern. The working mode within a cycle is analyzed as follows:

[0021] Mode 1: As shown in Figure 3(a), at the PV port, switches S1 and S4 are turned on, while switches S2 and S3 are turned off, and the inductor current flows out of the transformer i L1 <0. At the same time, PV1 is partially shaded, and the multi-winding balancer works in the state of freewheeling of inductor L1 through diode D2. AC port: switches S7 and S8 are turned on, while switches S5 and S6 are turned off, and the inductor current flows into transformer i L2 > 0. Battery port: switch S 10 and S 11 is turned on, while switches S9 and S 12 disconnected, the inductor current flows out of the transformer i L3 <0.

[0022] Mode 2: As shown in Figure 3(b), the photovoltaic port: the switch state remains unchanged, and the inductor current i L1 From negative to positive, it flows into the transformer. L1 >0, and since the switch state of the photovoltaic side remains unchanged, the balancer still works in the state of inductor L1 flowing through diode D2. L2 、i L3 The direction does not change, therefore, the working state of mode 1 is maintained.

[0023] Mode 3: As shown in Figure 3(c), the PV port and AC port, the switch conduction state and the inductor current i L1 、i L2 The direction of has not changed, therefore, the working state of mode 2 is maintained; Battery port: switches S9 and S 12 is turned on, and the switch S 10 and S 11 disconnected, due to the inductor current i L3 Cannot be mutated, can only be switched by switching S9 and S 12 The body diode is naturally turned on to continue current.

[0024] Mode 4: As shown in Figure 3(d), the photovoltaic port and battery port, the switch conduction state and the inductor current i L1 、i L3 The direction of has not changed, therefore, the working state of mode 3 is maintained; AC port: the inductor current i L2 The current flows out of the transformer from positive to negative. L2<0.

[0025] Mode 5: As shown in Figure 3(e), the PV port and AC port, the switch conduction state and the inductor current i L1 、i L2 The direction of has not changed, therefore, the working state of mode 4 is maintained; battery port: inductor current i L3 From negative to positive, it flows into the transformer. L3 >0, switch S9 and S 12 The body diode freewheeling phase ends, and the inductor current i L3 Flow switches S9 and S 12 .

[0026] Mode 6: As shown in Figure 3(f), the photovoltaic port and battery port, the switch tube conduction state and the inductor current i L1 、i L3 The direction of has not changed, therefore, the working state of mode 5 is maintained; AC port: switches S5 and S6 are turned on, while switches S7 and S8 are turned off, and the inductor current i L2 The direction remains unchanged and still flows out of the transformer. L2 <0.

[0027] Since the inductor current in the converter has reverse symmetry within a switching cycle, the principles of the second half of the cycle from mode 7 to mode 12 are similar to the previous ones and will not be repeated here. The only thing worth noting is that in the state from mode 7 to mode 12, the diode D1 is turned on, the diode D2 is turned off, and the current of the inductor L1 gradually increases. At this time, the multi-winding forward balancer works in the process of transferring energy from the primary side to the secondary side.

[0028] At the same time, when other photovoltaic modules are partially shaded, the working conditions are similar and will not be repeated here.

Claims

1. An isolated photovoltaic storage three-port inverter with integrated multi-winding positive-phase volt-equalizer, characterized in that: It includes n photovoltaic modules PV1~PV n , where n is a positive integer greater than or equal to 2, 12 switch tubes S1~S 12 The isolated three-port full-bridge structure and multi-winding transformer T1 are constituted, wherein the turns ratio of the transformer T1 should be: N1:N2:...:N n+1 =n:1:...:1, three-winding transformer T2 and leakage inductance L of each port r1 ~L r3 , 2n diodes D1~D 2n , capacitors C1-C3, clamping capacitor C c 、Inductor L1~L n 、Inductance L i , output filter inductor L o , AC load or grid V g And energy storage battery B.

2. An isolated photovoltaic storage three-port inverter with integrated multi-winding positive-phase volt-equalizer, characterized in that: Port 1 is a photovoltaic port, which consists of n photovoltaic panels PV1~PV n It is connected in series with the primary winding N1 of transformer T1 and the inductor L i , 4 switch tubes S1~S4, clamping capacitor C c The two interlaced parallel Buck-Boost circuits are formed; the second port is an AC port connected to the power grid or AC load, and the AC-AC matrix converter branch composed of two sets of reverse series switch tubes S5, S6 and S7, S8 and two non-polar capacitors C1, C2 is connected through the output filter inductor L o Realize AC output; Port 3 is the battery port, which consists of 4 switch tubes S9~S 12 The H-bridge is formed to realize the charging and discharging functions of the energy storage battery.

3. An isolated photovoltaic storage three-port inverter with integrated multi-winding positive-phase volt-equalizer, characterized in that: The port 1 is powered by n photovoltaic modules connected in series (n≥2); when 1≤i≤n, the inductor L i The left end of PV i The positive pole is connected to the inductor L i The right end of the diode D 2i The cathode of diode D 2i-1 The cathode of diode D is connected; 2i-1 The anode of transformer T1 is connected to the N i+1 The same-name ends of the windings are connected; diode D 2i Anode and PV i The negative pole of transformer T1 and the N i+1 The non-same-name ends of the windings are connected; the positive pole of PV1, the left end of the inductor L1, the same-name end of the N1 winding of the transformer T1, and the inductor L i The non-same-name end of the N1 winding of the transformer T1 is connected to the source of the switch tube S1, the drain of the switch tube S2, and the series leakage inductance L of the transformer T2. r1 The same-name end of the N1 winding is connected; the inductor L i The lower end of is connected to the source of the switch tube S3, the drain of the switch tube S4 and the non-same-name end of the N1 winding of the transformer T2; the clamping capacitor C c The positive electrode of PV is connected to the drain of switch tube S1 and the drain of switch tube S3; n The cathode of the diode D 2n Anode of transformer T1 n+1 The non-same-name end of the winding, the source of the switch tube S2, and the clamping capacitor C c The negative electrode of the switch tube S2 is connected to the source electrode of the switch tube S2; in port 2, the AC-AC matrix converter branch includes two bidirectional switch tubes and two non-polar capacitors, the two bidirectional switch tubes are connected in series and then connected in parallel with the two series-connected non-polar capacitors, and finally output through the output filter inductor L o Connect to the grid or AC load; Among them, transformer T2 contains series leakage inductance L r2 The same-name end of the N2 winding of the transformer T2 is connected to the drain of the switch tube S6 and the drain of the switch tube S7; the non-same-name end of the N2 winding of the transformer T2 is connected to the lower end of the capacitor C1 and the upper end of the capacitor C2; the source of the switch tube S5 is connected to the source of the switch tube S6; the source of the switch tube S7 is connected to the source of the switch tube S8; the drain of the switch tube S5 is connected to the upper end of the capacitor C1 and the output filter inductor L o The left end is connected to the output filter inductor L o The other end of the power grid is connected to one end of the power grid; the other end of the power grid is connected to the drain of the switch tube S8 and the lower end of the capacitor C2; in port three, the battery energy storage port is composed of four switch tubes S9~S 12 The H-bridge structure realizes the charging and discharging function of the energy storage battery; wherein the transformer T2 contains a series leakage inductor L r3 The same-name end of the N3 winding is connected to the source of the switch tube S9 and the switch tube S 10 The non-same-name end of the N3 winding of transformer T2 is connected to the switch tube S 11 The source of the switch tube S 12 The drain of the switch tube S9 and the switch tube S 11 The drain of the filter capacitor C3 is connected to the positive electrode of the battery; the switch tube S 10 The source of the switch tube S 12 The source electrode and the negative electrode of the filter capacitor C3 are connected to the negative electrode of the battery.

4. An isolated photovoltaic storage three-port inverter with integrated multi-winding positive-phase volt-equalizer, characterized in that: When the photovoltaic panel power is matched, the n secondary sides N2~N n+1 And its rectifier and freewheeling diodes D1~D 2n When the PV panel does not work, the PV port works in the ordinary staggered parallel Buck-Boost mode; when the PV panel has power mismatch due to local shadow and other problems, the topology will work in the multi-winding balancer and three-port inverter collaborative working mode. i (1≤i≤n) is partially shaded, and the voltage generated is less than winding N i+1 Voltage, at this time, PV i The corresponding balancing branch works, and part of the power flows to the solar panel PV i This changes its operating point, thereby achieving self-balancing and making its output close to maximum power.

5. An isolated photovoltaic storage three-port inverter with integrated multi-winding positive-phase volt-equalizer, characterized in that: According to the power balance between photovoltaic input power, battery charging and discharging power and load output power, there are three working modes: single-input dual-output mode, dual-input single-output mode and single-input single-output mode; among them, single-input dual-output mode: when the light is strong, the photovoltaic input power will not only ensure the constant output of the AC port, but the excess power will flow into the battery port to charge the battery; dual-input single-output mode: when the light is weakened, the photovoltaic module is still not enough to maintain the constant output of the AC port at the maximum input power. At this time, the battery port and the photovoltaic port jointly supply power to the AC port; single-input single-output mode: at night, the photovoltaic input power is 0, and the battery port alone supplies power to the AC port.

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