LCL type multi-photovoltaic compatible grid-connected inverter

Abstract

The utility model discloses an LCL type multi-photovoltaic compatible grid-connected inverter which comprises a photovoltaic array, a DC / DC module, a DC bus, a DC / AC inversion module, an LCL filter and a power grid which are connected in sequence, the DC / AC inversion module is sequentially connected with a PWM generator and an adder, two paths of input of the adder are connected with a first multiplier and a second multiplier respectively, and the first multiplier and the second multiplier are connected with a power grid. Two paths of input of the first multiplier are respectively connected with a PI controller and a first analog-to-digital converter, and two paths of input of the second multiplier are respectively connected with an RC repetitive controller and a second analog-to-digital converter; the first comparison circuit generates a first output level according to the current error signal, and the second comparison circuit generates a second output level according to the harmonic signal. According to the utility model, a pure hardware circuit is constructed to realize weight switching, the fusion proportion of the PI controller and the RC repetitive controller can be switched according to the working condition of the system, the output of the inverter is adjusted according to the reference and the electric energy quality requirement, and the use effect is good.

Description

TECHNICAL FIELD

[0001] The utility model relates to circuit device technical field, and more specifically, it relates to a kind of LCL type multi photovoltaic compatible grid-connected inverter. BACKGROUND

[0002] LCL type photovoltaic inverter is the core component of photovoltaic grid-connected system, mainly used to convert the direct current generated by photovoltaic array into high-quality alternating current synchronized with power grid. Compared with traditional L-type or LC type filter, LCL filter has stronger harmonic suppression ability, can effectively reduce high-frequency noise near switching frequency, so that the total harmonic distortion rate of grid-connected current is less than 3%, meets strict grid-connected standard. In addition, LCL filter is smaller in size and lower in cost, suitable for high power density and high performance application scenarios, such as large photovoltaic power station and distributed roof photovoltaic system.

[0003] The composite optimization control based on PI control branch and repetitive control branch is to balance the dynamic response and steady-state accuracy of the system. PI control can quickly track photovoltaic power mutation, such as irradiance change caused by cloud cover, but its suppression ability to periodic harmonic is limited. RC repetitive control based on internal model principle can eliminate fixed frequency harmonic cycle by cycle, but the dynamic response is slow. By proportionally blending the two, for example, steady state 5:5, transient state 8:2, harmonic over 2:8, both fast adjustment in transient process and low harmonic output in steady state can be ensured, so as to improve the overall performance of the system.

[0004] In order to verify the effectiveness of the composite control strategy comprehensively, a detailed simulation model including photovoltaic array, DC / DC boost circuit, DC / AC inverter bridge, LCL filter and power grid needs to be constructed. The simulation model needs to support dynamic adjustment of the blending ratio of PI and repetitive control, for verifying the robustness of the weight switching logic. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the deficiencies in the prior art. The LCL type multi photovoltaic compatible grid-connected inverter has a simple structure and reasonable design. It uses pure hardware circuit to realize weight switching, can switch the blending ratio of PI controller and RC repetitive controller according to system operating conditions, adjusts the output of the inverter according to reference and power quality requirements, and has good use effect.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is: a LCL type multi-photovoltaic compatible grid-connected inverter, characterized in that: it comprises a photovoltaic array, a DC / DC module, a direct current bus, a DC / AC inversion module, an LCL filter and a power grid connected in sequence, the DC / AC inversion module is connected with a PWM generator, the PWM generator is connected with an adder, two inputs of the adder are respectively connected with a first multiplier and a second multiplier, two inputs of the first multiplier are respectively connected with a PI controller and a first analog-to-digital converter, two inputs of the second multiplier are respectively connected with an RC repetitive controller and a second analog-to-digital converter; further comprising a first comparison circuit and a second comparison circuit, the first comparison circuit generates a first output level according to a current error signal, the second comparison circuit generates a second output level according to a harmonic signal, a logic gate circuit generates an output signal according to the inputs of the first output level and the second output level; an analog switch selectively connects the voltage of a bias power supply to the first analog-to-digital converter and the second analog-to-digital converter according to the output signal of the logic gate circuit.

[0007] The LCL type multi-photovoltaic compatible grid-connected inverter described above is characterized in that: the first comparison circuit comprises a first comparator, two inputs of the first comparator are respectively connected with a subtractor and a second input module; the second comparison circuit comprises a second comparator, and a filter group and a third input module connected with two inputs of the second comparator respectively; further comprising a subtractor, two inputs of the subtractor are respectively connected with a first input module and a current sensor for collecting a current signal of the power grid, the output of the current sensor is also connected with the filter group; the output end of the subtractor is divided into two paths, one path is connected with the input of the PI controller, and the second path is connected with the input of the RC repetitive controller.

[0008] The LCL type multi-photovoltaic compatible grid-connected inverter described above is characterized in that: the logic gate circuit comprises a NOT gate and an exclusive-OR gate, the input end of the NOT gate is connected with the output end of the first comparator; two input ends of the exclusive-OR gate are respectively connected with the output ends of the first comparator and the second comparator.

[0009] The LCL type multi-photovoltaic compatible grid-connected inverter described above is characterized in that: the NOT gate and the exclusive-OR gate are connected in parallel and output, the output of the NOT gate is high, and the output of the exclusive-OR gate is low.

[0010] The LCL type multi-photovoltaic compatible grid-connected inverter described above is characterized in that: four groups of two-way output voltages of a bias power supply are connected with the inputs of an analog switch, and the analog switch switches four groups of two-way input signals to two-way outputs.

[0011] The LCL type multi-photovoltaic compatible grid-connected inverter described above is characterized in that: the analog switch is a chip CD4052.

[0012] The LCL type multi-photovoltaic compatible grid-connected inverter has the characteristics that the filter set comprises a band-stop filter, a high-pass filter and a band-pass filter connected in sequence.

[0013] The LCL type multi-photovoltaic compatible grid-connected inverter has the characteristics that the output of the current sensor is connected to the filter set through a rectifier circuit.

[0014] The LCL type multi-photovoltaic compatible grid-connected inverter has the characteristics that the rectifier circuit is a full-wave rectifier bridge.

[0015] Compared with the prior art, the application has the following advantages:

[0016] 1. The application has simple structure, reasonable design, and convenient implementation and operation.

[0017] 2. The application can monitor the current error and harmonic signal in real time through the first comparison circuit and the second comparison circuit, and can switch the fusion ratio of the PI controller and the RC repetitive controller according to the system working condition, and can adjust the output of the inverter according to the reference and the power quality demand, by the synergistic control of the logic gate circuit and the analog switch.

[0018] 3. The application uses a pure hardware circuit composed of the first analog-to-digital converter and the second analog-to-digital converter, the analog switch and the bias power supply to realize weight switching, without relying on software algorithm, avoiding software processing delay, and providing a basis for simulation.

[0019] 4. The application uses a composite control strategy to ensure stable operation when the grid voltage fluctuates or the photovoltaic power suddenly changes, and has good use effect.

[0020] In summary, the application constructs a pure hardware circuit to realize weight switching, can switch the fusion ratio of the PI controller and the RC repetitive controller according to the system working condition, and can adjust the output of the inverter according to the reference and the power quality demand, and has good use effect.

[0021] The technical solutions of the application will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a circuit principle diagram of the application.

[0023] Figure 2 It is a circuit principle diagram of the photovoltaic grid-connected power generation system of the application.

[0024] Figure 3 It is a schematic diagram of the logic gate circuit of the application.

[0025] Figure 4 It is a circuit principle diagram of the analog switch of the application.

[0026] In the figure: 11, photovoltaic array; 12, DC / DC module; 13, DC bus; 14, DC / AC inverter module; 15, LCL filter; 16, power grid; 17, PWM generator; 21 first input module; 22, current sensor; 23, subtractor; 24, PI controller; 25, RC repetitive controller; 26, first analog-to-digital converter; 27, second analog-to-digital converter; 28, first multiplier; 29, second multiplier; 30, adder; 31, rectifier circuit; 33, second input module; 34, first comparator; 35, filter bank; 36, third input module; 37, second comparator; 38, logic gate circuit; 39, analog switch; 40, DETAILED DESCRIPTION

[0027] The application will be further described below in conjunction with the drawings and embodiments of the present application.

[0028] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and embodiments.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should be understood that the use of the term "comprise" and / or "include" in the specification indicates the presence of features, steps, operations, devices, components and / or their combinations.

[0030] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but can include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0031] For purposes of the description hereinafter, spatially relative terms, such as "above", "below", "up", "down", "between", "within", "left", "right", "rear", "front", "upper", "lower", "horizontal", "vertical", "above", "below", "up", "down", "top", "bottom", "under" and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the figures. For example, if a device in the figures is inverted, elements described as "above" or "up" other elements or features would then be oriented "below" or "down" the other elements or features. Thus, the exemplary term "above" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. The terms "first", "second", "third", etc. can be used herein to describe various elements, regions, layers and / or sections but are not intended to be used herein to designate importance or a specific order of employment.

[0032] As shown in Figure 1 and Figure 2 A LCL type multi-photovoltaic compatible grid-connected inverter of the present application includes a photovoltaic array 11, a DC / DC module 12, a DC bus 13, a DC / AC inversion module 14, an LCL filter 15 and a power grid 16 connected in sequence, the DC / AC inversion module 14 is connected with a PWM generator 17, the PWM generator 17 is connected with an adder 30, two inputs of the adder 30 are respectively connected with a first multiplier 28 and a second multiplier 29, two inputs of the first multiplier 28 are respectively connected with a PI controller 24 and a first analog-to-digital converter 26, two inputs of the second multiplier 29 are respectively connected with an RC repetitive controller 25 and a second analog-to-digital converter 27.

[0033] In actual use, the photovoltaic array 11, the DC / DC module 12, the DC bus 13, the DC / AC inversion module 14, the LCL filter 15 and the power grid 16 constitute a photovoltaic grid-connected power generation system. The DC / DC module 12 can adopt a Boost circuit.

[0034] The photovoltaic array 11 converts solar energy into direct current, the output characteristic is affected by light intensity and temperature, showing nonlinearity, the DC / DC module 12 boosts the photovoltaic output voltage to the required level of the DC bus 13, the DC bus 13 stabilizes the direct current voltage, providing energy buffer for the inverter, the DC / AC inversion module 14 converts the direct current into sinusoidal alternating current synchronized with the power grid 16, the sinusoidal alternating current passes through the LCL filter 15, the LCL filter 15 filters out high-frequency noise, and the current is merged into the power grid 16 in a pure waveform.

[0035] The PWM generator 17 is used to generate a pulse width modulation signal U PI according to a time-domain continuous signal U RCThe weighted results generate PWM modulation signals, which adjust the on-off time ratio of the upper and lower tubes of each bridge arm of the inverter bridge of the DC / AC inverter module 14, so as to control the amplitude and phase of the output voltage.

[0036] The first comparison circuit generates a first output level according to the current error signal, and the second comparison circuit generates a second output level according to the harmonic signal. The logic gate circuit 38 generates an output signal according to the input of the first output level and the second output level. The analog switch 39 selectively connects the voltage of the bias power supply 40 to the first analog-to-digital converter 26 and the second analog-to-digital converter 27 according to the output signal of the logic gate circuit 38.

[0037] It should be noted that the first comparison circuit generates a first output level according to the current error signal, and the second comparison circuit generates a second output level according to the harmonic signal. The first output level and the second output level are input to the logic gate circuit 38, and the output signal of the logic gate circuit 38 is obtained.

[0038] The output voltage of the bias power supply 40 includes 4 groups, each group having 2 output voltages. The 4 groups of 2-way voltage of the bias power supply 40 are connected to the 4 groups of 2-way input pins of the analog switch 39. The two-way output of the analog switch 39 is connected to the first analog-to-digital converter 26 and the second analog-to-digital converter 27, respectively. When the output signal of the logic gate circuit 38 is different, the analog switch 39 selectively outputs a certain group of voltage of the bias power supply 40 to the first analog-to-digital converter 26 and the second analog-to-digital converter 27 according to the output signal of the logic gate circuit 38.

[0039] The output of the first analog-to-digital converter 26 is input to the first multiplier 28 and is the weight of the time-domain continuous signal U PI output by the PI controller 24, which is used by the adder 30 to calculate the synthesis signal u(t).

[0040] The output of the second analog-to-digital converter 27 is input to the second multiplier 29 and is the weight of the modified signal U RC output by the RC repetitive controller 25, which is used by the adder 30 to calculate the synthesis signal u(t).

[0041] In the embodiment, in actual use, the two inputs of the subtracter 23 are connected with the first input module 21 and the current sensor 22 for collecting the current signal of the power grid 16 respectively. The grid-connected current reference value is inputted by the staff through the first input module 21, the current sensor 22 is used for collecting the actual grid-connected current feedback, the subtracter 23 is used for calculating the current difference e(t) between the grid-connected current reference value and the actual grid-connected current feedback, and the current difference e(t) is taken as the input of the first comparator 34. The staff inputs the current difference threshold value through the second input module 33, if the current difference is greater than the current difference threshold value, the first comparator 34 outputs high level 1; otherwise, if the current difference is less than the current difference threshold value, the first comparator 34 outputs low level 0.

[0042] The second comparison circuit includes the second comparator 37, and the filter set 35 and the third input module 36 connected with the two inputs of the second comparator 37 respectively. In actual use, the filter set 35 is connected with the current sensor 22 through the rectifier circuit 31, the actual grid-connected current feedback collected by the current sensor 22 is extracted to input the second comparator 37, the staff inputs the harmonic threshold value through the third input module 36, if the current single harmonic is greater than the harmonic threshold value, the second comparator 37 outputs high level 1; otherwise, if the current single harmonic is less than the harmonic threshold value, the second comparator 37 outputs low level 0.

[0043] In actual use, the first path of the output end of the subtracter 23 is connected with the input of the PI controller 24, and the second path is connected with the input of the RC repetitive controller 25. The PI controller 24 outputs the time-domain continuous signal U PI according to the current difference e(t). RC The RC repetitive controller 25 outputs the correction signal U

[0044] As shown in Figure 3 , in the embodiment, the logic gate circuit 38 includes the NOT gate and the XNOR gate, the input end of the NOT gate is connected with the output end of the first comparator 34; the two inputs of the XNOR gate are connected with the output ends of the first comparator 34 and the second comparator 37 respectively.

[0045] In actual use, as shown in Table 1, there are four cases:

[0046] ①The first comparator 34 outputs high level 1, the high level 1 is outputted as low level 0 through the NOT gate; the second comparator 37 outputs low level 0; the high level 1 and the low level 0 are inputted into the XNOR gate, the XNOR gate outputs 0, so the output of the logic gate circuit 38 is 00;

[0047] ② The first comparator 34 outputs high level 1, which is outputted as low level 0 by the NOT gate; the second comparator 37 outputs high level 1; high level 1 and high level 1 are inputted into the XNOR gate, and the output of the XNOR gate is 1; the output of the NOT gate is high bit, and the output of the XNOR gate is low bit, so the output of the logic gate circuit 38 is 01;

[0048] ③ The first comparator 34 outputs low level 0, which is outputted as high level 1 by the NOT gate; the second comparator 37 outputs high level 1; low level 0 and high level 1 are inputted into the XNOR gate, and the output of the XNOR gate is 0, so the output of the logic gate circuit 38 is 10;

[0049] ④ The first comparator 34 outputs low level 0, which is outputted as high level 1 by the NOT gate; the second comparator 37 outputs low level 0; low level 0 and low level 0 are inputted into the XNOR gate, and the output of the XNOR gate is 1, so the output of the logic gate circuit 38 is 11.

[0050] As shown in Figure 4 , the analog switch 39 adopts the chip CD4052B, and the four different outputs of the logic gate circuit 38 are inputted into the A pin and the B pin of the analog switch 39, and the XCOM channel and the YCOM channel of the analog switch 39 correspond to select different gating channels.

[0051] Table 1 truth table of logic gate

[0052] First comparator Second comparator Logic gate circuit Analog switch output channel 1 0 00 X0 and Y0 1 1 01 X1 and Y1 0 1 10 X2 and Y2 0 0 11 X3 and Y3

[0053] The 4 groups of 2-way output voltages of the bias power supply 40 are connected with the inputs of the analog switch 39, and the analog switch 39 switches the 4 groups of 2-way input signals to two-way outputs. The output voltages of the bias power supply 40 include 4 groups, and each group has 2-way output voltages. For example, the first group of voltages U 01 , U 02 are connected with the X0 channel and the Y0 channel respectively; the second group of voltages U 11 , U 12 are connected with the X1 channel and the Y1 channel respectively; the third group of voltages U 21 , U 22 are connected with the X2 channel and the Y2 channel respectively; and the fourth group of voltages U 31 , U 32 are connected with the X3 channel and the Y3 channel respectively.

[0054] When the output of the logic gate circuit 38 is 00, the XCOM channel and the YCOM channel of the analog switch 39 select the X0 channel and the Y0 channel, and the output voltage U 01 is inputted into the first analog-digital converter 26, and the output value proportional to the voltage U 01 ; the output voltage U 02 is inputted into the second analog-digital converter 27, and the output value proportional to the voltage U02 proportional value. Thus by adjusting the output voltage of the bias power supply 40, the weight of the time-domain continuous signal U PI output by the PI controller 24, and the weight of the correction signal U RC output by the RC repetitive controller 25 can be adjusted.

[0055] The first and second analog-to-digital converters 26 and 27 are used to convert the input voltage into a value proportional to the input voltage. In one possible embodiment, the first and second analog-to-digital converters 26 and 27 both employ the analog-to-digital converter LTC1298, which operates at a 5V working voltage and outputs a full-scale code value of 2 12 = 4096, with the first and second voltage U 01 and U 02 being 9.77mV and 2.44mV respectively. Then the first and second analog-to-digital converters 26 and 27 output digital 8 and 2 respectively as the weight of the time-domain continuous signal U PI and the weight of the correction signal U RC . Similarly, by setting corresponding other three voltage values, the output of the inverter can be adjusted according to the reference and the power quality requirement.

[0056] In the present embodiment, the output of the current sensor 22 is connected to the filter bank 35 via the rectifier circuit 31. The filter bank 35 comprises a band-stop filter, a high-pass filter and a band-pass filter connected in sequence. The rectifier circuit 31 is a full-wave rectifier bridge. Both the positive and negative half cycles of the full-wave rectifier bridge are utilized, so that all harmonic components can be retained.

[0057] In actual use, the grid current collected by the current sensor 22 is rectified by the rectifier circuit 31 to output a direct current component carrying fundamental and harmonic waves. The fundamental wave is suppressed by the band-stop filter, the direct current is filtered out by the high-pass filter, the remaining high-order harmonic waves are extracted by the band-pass filter. In one possible embodiment, the power quality monitoring usually focuses on odd harmonics, and the band-pass filter selects 150Hz to extract the third harmonic.

[0058] The above description is only an embodiment of the present application, and does not limit the present application in any way. Any simple modification, change and equivalent structural change made according to the technical essence of the present application to the above embodiment are still within the protection scope of the technical solution of the present application.

Claims

1. A LCL type multi-photovoltaic compatible grid-connected inverter, characterized by: The LCL type multi-photovoltaic compatible grid-connected inverter comprises a photovoltaic array (11), a DC / DC module (12), a direct current bus (13), a DC / AC inversion module (14), an LCL filter (15) and a power grid (16) connected in sequence, the DC / AC inversion module (14) is connected with a PWM generator (17), the PWM generator (17) is connected with an adder (30), two inputs of the adder (30) are connected with a first multiplier (28) and a second multiplier (29) respectively, two inputs of the first multiplier (28) are connected with a PI controller (24) and a first analog-to-digital converter (26) respectively, two inputs of the second multiplier (29) are connected with an RC repetitive controller (25) and a second analog-to-digital converter (27) respectively; The LCL type multi-photovoltaic compatible grid-connected inverter further comprises a first comparison circuit and a second comparison circuit, the first comparison circuit generates a first output level according to a current error signal, the second comparison circuit generates a second output level according to a harmonic signal, and a logic gate circuit (38) generates an output signal according to inputs of the first output level and the second output level; an analog switch (39) selectively connects a voltage of a bias power supply (40) to the first analog-to-digital converter (26) and the second analog-to-digital converter (27) according to the output signal of the logic gate circuit (38).

2. The LCL type multi-photovoltaic compatible grid-connected inverter according to claim 1, characterized in that: The first comparison circuit comprises a first comparator (34), and two inputs of the first comparator (34) are connected with a subtractor (23) and a second input module (33) respectively; The second comparison circuit comprises a second comparator (37), and a filter set (35) and a third input module (36) are connected with two inputs of the second comparator (37) respectively; The LCL type multi-photovoltaic compatible grid-connected inverter further comprises the subtractor (23), two inputs of the subtractor (23) are connected with a first input module (21) and a current sensor (22) for collecting a current signal of the power grid (16) respectively, an output of the current sensor (22) is further connected with the filter set (35), and an output end of the subtractor (23) is divided into two paths, one path is connected with an input of the PI controller (24), and the second path is connected with an input of the RC repetitive controller (25).

3. The LCL type multi-photovoltaic compatible grid-connected inverter according to claim 2, characterized in that: The logic gate circuit (38) comprises a NOT gate and an XNOR gate, an input end of the NOT gate is connected with an output end of the first comparator (34), and two input ends of the XNOR gate are connected with output ends of the first comparator (34) and the second comparator (37) respectively.

4. The LCL type multi-photovoltaic compatible grid-connected inverter according to claim 3, characterized in that: The NOT gate and the XNOR gate are connected in parallel and output, the output of the NOT gate is high, and the output of the XNOR gate is low.

5. The LCL type multi-photovoltaic compatible grid-connected inverter according to claim 1, characterized in that: Four groups of two-way output voltages of the bias power supply (40) are connected with inputs of the analog switch (39), and the analog switch (39) switches the four groups of two-way input signals to two-way outputs.

6. The LCL type multi-photovoltaic compatible grid-connected inverter according to claim 1 or 5, characterized in that: The analog switch (39) is a chip CD4052.

7. The LCL type multi-photovoltaic compatible grid-connected inverter according to claim 1, characterized in that: The filter set (35) comprises a band-stop filter, a high-pass filter and a band-pass filter connected in sequence.

8. The LCL type multi-photovoltaic compatible grid-connected inverter according to claim 1, characterized in that: The output of the current sensor (22) is connected with the filter set (35) through a rectifier circuit (31).

9. The LCL type multi-photovoltaic compatible grid-connected inverter according to claim 8, characterized in that: The rectifier circuit (31) is a full-wave rectifier bridge.

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