High-power-density non-isolated photovoltaic grid-connected inverter
Technical Field
The utility model relates to a power electronics field especially relates to a non-isolated form photovoltaic grid-connected inverter of high power density.
Background
With the continuous progress of human civilization, the energy demand is increasing, and the non-renewable energy mainly based on fossil fuel is rapidly reduced. Moreover, the global warming is aggravated by using a large amount of fossil fuels, and the natural environment is worsened. The search for green and environmentally friendly renewable energy sources is a great challenge facing mankind. Solar energy is used as an inexhaustible green renewable energy source, photovoltaic power generation is highly concerned by governments of various countries, and the photovoltaic power generation industry is being vigorously popularized all over the world.
The photovoltaic inverter is used as a core device of photovoltaic power generation, so that the size and the cost of the photovoltaic grid-connected inverter directly restrict the popularization of the photovoltaic power generation industry. At present, a three-phase isolation type split winding transformer is adopted as a grid-connected transformer in a traditional photovoltaic grid-connected inverter, so that the photovoltaic grid-connected inverter is large in size, low in power density and high in price.
SUMMERY OF THE UTILITY MODEL
The embodiment of the utility model provides a technical problem that will solve lies in, provides a high power density non-isolated form photovoltaic grid-connected inverter to make and improve the electric energy quality.
In order to solve the technical problem, the embodiment of the utility model provides a high power density non-isolated photovoltaic grid-connected inverter, including first photovoltaic array, the second photovoltaic array, first three-phase inverter, the second three-phase inverter, first wave filter, second wave filter and grid-connected transformer, first photovoltaic array, first three-phase inverter, first wave filter links to each other in proper order, the second photovoltaic array, the second three-phase inverter, the second wave filter links to each other in proper order, grid-connected transformer is connected with the output of first wave filter and second wave filter, grid-connected transformer is by first single-phase three-winding auto-transformer, the single-phase three-winding auto-transformer of second, the single-phase three-winding auto-transformer of third is constituteed, auto-transformer's three single-phase three-winding transformer winding structure adopts the multiple connection mode of shifting phase.
Further, the first photovoltaic array and the second photovoltaic array have the same structure and specification, the first three-phase inverter and the second three-phase inverter have the same structure and specification, and the first filter and the second filter have the same structure and specification; the positive electrodes of the output ends of the first photovoltaic array and the second photovoltaic array are respectively connected with the positive electrodes of the input ends of the first three-phase inverter and the second three-phase inverter, the negative electrodes of the output ends of the first photovoltaic array and the second photovoltaic array are respectively connected with the negative electrodes of the input ends of the first three-phase inverter and the second three-phase inverter, and the three-phase output ends of the first three-phase inverter and the second three-phase inverter are respectively connected with the three-phase input ends of the first filter and the second filter; the phase-a output end of the first filter is connected with the input end of the phase-a 1 winding of the second single-phase three-winding autotransformer, the phase-b output end of the first filter is connected with the input end of the phase-b 1 winding of the third single-phase three-winding autotransformer, and the phase-c output end of the first filter is connected with the input end of the phase-c 1 winding of the first single-phase three-winding autotransformer; the a-phase output end of the second filter is connected with the input end of the a2 winding of the second single-phase three-winding autotransformer, the b-phase output end of the second filter is connected with the input end of the b2 winding of the third single-phase three-winding autotransformer, and the c-phase output end of the second filter is connected with the input end of the c2 winding of the first single-phase three-winding autotransformer.
Further, the first single-phase three-winding autotransformer, the second single-phase three-winding autotransformer and the third single-phase three-winding autotransformer have the same structure and are composed of two core columns of a first core column and a second core column, the first core column is a first primary winding and a second primary winding, the second core column is a common winding, the number of corresponding turns of the first primary winding and the number of corresponding turns of the second primary winding are respectively N1 and N2, the number of corresponding turns of the common winding is N3, and the turn ratio among the three windings is N1: n2: n3= 0.1547: 0.1547: 1.
furthermore, the output ends of two primary windings of the first single-phase three-winding autotransformer are connected, the output ends of two primary windings of the second single-phase three-winding autotransformer are connected, the output ends of two primary windings of the third single-phase three-winding autotransformer are connected, the secondary sides of the first single-phase three-winding autotransformer and the second single-phase three-winding autotransformer are connected in a triangular mode, the first end of the secondary winding of the first single-phase three-winding autotransformer is connected with the output ends of the two primary windings of the second single-phase three-winding autotransformer and a phase of a power grid, and the second end of the secondary winding of the first single-phase three-winding autotransformer is connected with the first end; the first end of the secondary winding of the second single-phase three-winding autotransformer is connected with the output ends of the two primary windings of the third single-phase three-winding autotransformer and the grid b, and the second end of the secondary winding of the second single-phase three-winding autotransformer is connected with the first end of the secondary winding of the third single-phase three-winding autotransformer; and the second end of the secondary winding of the third single-phase three-winding autotransformer is connected with the first end of the secondary winding of the first single-phase three-winding autotransformer.
Further, the phase voltages of the non-inverting outputs of the first three-phase inverter and the second three-phase inverter have a phase difference of 30 °.
Further, the first photovoltaic array and the second photovoltaic array are both formed by connecting a plurality of photovoltaic cell plates with the same specification in series and parallel; the first three-phase converter and the second three-phase converter respectively comprise a three-phase four-leg inverter circuit with a neutral point, and the three-phase four-leg inverter circuit is formed by 8 insulated gate bipolar transistors with the same specification; the first filter and the second filter are composed of three inductors with the same inductance value and three capacitors with the same capacitance value.
The utility model has the advantages that: the utility model adopts a single-phase three-winding autotransformer as the grid-connected transformer of the photovoltaic grid-connected inverter, so that the capacity of the grid-connected transformer in the photovoltaic grid-connected inverter is reduced by 82 percent compared with the capacity of the grid-connected transformer using the traditional power frequency transformer, the power density of the photovoltaic grid-connected inverter is greatly improved, the number of turns of the winding is reduced, and the cost is saved; three single-phase three-winding autotransformer winding structures adopt a phase-shifting multiple connection mode, when two groups of photovoltaic arrays run in parallel, SPWM is adopted to control two groups of three-phase inverters, so that a phase difference of 30 degrees exists between voltages of two primary windings of the same phase at the output end of a filter, characteristic subharmonic grid-connected current can be inhibited, and the electric energy quality is improved.
Drawings
Fig. 1 is a schematic structural diagram of a high power density non-isolated photovoltaic grid-connected inverter according to an embodiment of the present invention when two sets of photovoltaic arrays are both in operation.
Fig. 2 is a schematic diagram of a high power density non-isolated pv grid-connected inverter according to an embodiment of the present invention when only the first pv array is in operation.
Fig. 3 is a schematic structural diagram of a high power density non-isolated pv grid-connected inverter according to an embodiment of the present invention when only the second pv array is in operation.
Fig. 4 is a first three-phase inverter and first filter circuit configuration diagram according to an embodiment of the present invention.
Fig. 5 is a second three-phase inverter and second filter circuit configuration diagram according to an embodiment of the present invention.
Fig. 6 is a phasor diagram of three single phase three winding autotransformer winding couplings according to an embodiment of the invention.
Detailed Description
It should be noted that, in the present application, the embodiments and features of the embodiments may be combined with each other without conflict, and the present invention is further described in detail with reference to the accompanying drawings and specific embodiments.
In the embodiment of the present invention, if there is directional indication (such as upper, lower, left, right, front, and rear … …) only for explaining the relative position relationship between the components and the motion situation under a certain posture (as shown in the drawing), if the certain posture is changed, the directional indication is changed accordingly.
In addition, the descriptions of the first, second, etc. in the present invention are for descriptive purposes only and are not to be construed as indicating or implying any relative importance or implicit indication of the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature.
Referring to fig. 1 to 6, the high power density non-isolated pv grid-connected inverter according to an embodiment of the present invention includes a first pv array 1, a second pv array 2, a first three-phase inverter 3, a second three-phase inverter 4, a first filter 5, a second filter 6, and a grid-connected transformer.
The grid-connected transformer is composed of a first single-phase three-winding autotransformer 7, a second single-phase three-winding autotransformer 8 and a third single-phase three-winding autotransformer 9, and three single-phase three-winding autotransformers of the grid-connected transformer adopt a phase-shift multiple connection mode.
As an embodiment, the first photovoltaic array 1 and the second photovoltaic array 2 have the same structure and specification, the first three-phase inverter 3 and the second three-phase inverter 4 have the same structure and specification, and the first filter 5 and the second filter 6 have the same structure and specification; the positive electrodes of the output ends of the first photovoltaic array 1 and the second photovoltaic array 2 are respectively connected with the positive electrodes of the input ends of the first three-phase inverter 3 and the second three-phase inverter 4, the negative electrodes of the output ends of the first photovoltaic array 1 and the second photovoltaic array 2 are respectively connected with the negative electrodes of the input ends of the first three-phase inverter 3 and the second three-phase inverter 4, and the three-phase output ends of the first three-phase inverter 3 and the second three-phase inverter 4 are respectively connected with the three-phase input ends of the first filter 5 and the second filter 6; the a-phase output end a1 of the first filter 5 is connected with the input end of the a1 winding of the second single-phase three-winding autotransformer 8, the b-phase output end b1 of the first filter 5 is connected with the input end of the b1 winding of the third single-phase three-winding autotransformer 9, and the c-phase output end c1 of the first filter 5 is connected with the input end of the c1 winding of the first single-phase three-winding autotransformer 7; the a-phase output a2 of the second filter 6 is connected to the input of the a2 winding of the second single phase three winding autotransformer 8, the b-phase output b2 of the second filter 6 is connected to the input of the b2 winding of the third single phase three winding autotransformer 9, and the c-phase output c2 of the second filter 6 is connected to the input of the c2 winding of the first single phase three winding autotransformer 7.
As an embodiment, the first single-phase three-winding autotransformer 7, the second single-phase three-winding autotransformer 8, and the third single-phase three-winding autotransformer 9 have the same structure, and are each composed of two core columns of a first core column and a second core column, the first core column is a first primary winding and a second primary winding, the second core column is a common winding, the number of corresponding turns of the first primary winding and the number of corresponding turns of the second primary winding are N1 and N2, the number of corresponding turns of the common winding is N3, and the turn ratio between the three windings is N1: n2: n3= 0.1547: 0.1547: 1.
as an embodiment, the output ends of the two primary windings of the first single-phase three-winding autotransformer 7 are connected, the output ends of the two primary windings of the second single-phase three-winding autotransformer 8 are connected, the output ends of the two primary windings of the third single-phase three-winding autotransformer 9 are connected, the secondary sides of the first, second and third single-phase three-winding autotransformers are connected in a triangular mode, the first end of the secondary side winding of the first single-phase three-winding autotransformer 7 is connected with the output ends of the two primary windings of the second single-phase three-winding autotransformer 8 and the grid a, and the second end of the secondary side winding of the first single-phase three-winding autotransformer 7 is connected with the first end of the secondary side winding of the second single-phase three; the first end of the secondary winding of the second single-phase three-winding autotransformer 8 is connected with the output ends of the two primary windings of the third single-phase three-winding autotransformer 9 and the grid b, and the second end of the secondary winding of the second single-phase three-winding autotransformer 8 is connected with the first end of the secondary winding of the third single-phase three-winding autotransformer 9; the first end of the secondary winding of the third single-phase three-winding autotransformer 9 is connected with the output ends of the two primary windings of the first single-phase three-winding autotransformer 7 and the power grid c, and the second end of the secondary winding of the third single-phase three-winding autotransformer 9 is connected with the first end of the secondary winding of the first single-phase three-winding autotransformer 7.
In one embodiment, the first three-phase inverter 3 and the second three-phase inverter 4 adopt an SPWM control method, so that phase voltages at the in-phase output ends of the first three-phase inverter 3 and the second three-phase inverter 4 have a phase difference of 30 °, and after the phase voltages are fed into three single-phase three-winding autotransformers, characteristic subharmonic grid-connected current can be suppressed, and the power quality can be improved. The utility model discloses a but first photovoltaic array 1 and second photovoltaic array 2 parallel operation also can only first photovoltaic array 1 or the operation of second photovoltaic array 2. When two groups of the first photovoltaic array 1 and the second photovoltaic array 2 are operated in parallel, the utility model discloses a there is a phase difference of 30 degrees in the voltage between two primary windings of the same phase of two filter output ends, will be able to restrain the characteristic subharmonic and be incorporated into the power networks the current after sending into three single-phase three-winding autotransformers, improve the electric energy quality; when only first photovoltaic array 1 or the operation of second photovoltaic array 2, the utility model discloses a single-phase three-winding autotransformer is equivalent to single-phase two-winding autotransformer.
As an embodiment, the first photovoltaic array 1 and the second photovoltaic array 2 are composed of a plurality of photovoltaic cell plates with the same specification connected in series and parallel. The first three-phase converter 3 and the second three-phase inverter 4 both have a three-phase four-leg structure, and the first three-phase converter 3 and the second three-phase converter 4 both include a three-phase four-leg inverter circuit with a neutral point formed by 8 Insulated Gate Bipolar Transistors (IGBTs) having the same specification (the first three-phase converter 3 includes insulated gate bipolar transistors S1, S2, S3, S4, S5, S6, S7, and S8, and the second three-phase converter 4 includes insulated gate bipolar transistors S9, S10, S11, S12, S13, S14, S15, and S16). The first filter 5 and the second filter 6 are each composed of three inductors having the same inductance value and three capacitors having the same capacitance value.
In one embodiment, the first filter 5 includes a first filter inductor L1, a second filter inductor L2, a third filter inductor L3, a first filter capacitor C1, a second filter capacitor C2 and a third filter capacitor C3, the a-phase output terminal of the first three-phase converter 3 is connected to the left end of the first filter inductor L1, the b-phase output terminal of the first three-phase converter 3 is connected to the left end of the second filter inductor L2, the C-phase output terminal of the first three-phase converter 3 is connected to the left end of the third filter inductor L3, the right end of the first filter inductor L1 is connected to the first end of the first filter capacitor C1, the second end of the first filter capacitor C1 is connected to the center point n of the first three-phase converter 3, the right end of the second filter inductor L2 is connected to the first end of the second filter capacitor C2, the second end of the second filter capacitor C2 is connected to the center point n of the first three-phase converter 3, the right end of the third filter inductor L3 is connected to the first end of the third filter capacitor C3, and the second end of the third filter capacitor C3 is connected to the center point n of the first three-phase converter 3; the a-phase output end of the second three-phase converter 4 is connected with the left end of a fourth filter inductor L4, the b-phase output end of the second three-phase converter 4 is connected with the left end of a fifth filter inductor L5, the C-phase output end of the second three-phase converter 4 is connected with the left end of a sixth filter inductor L6, the right end of the fourth filter inductor L4 is connected with the first end of a fourth filter capacitor C4, the second end of a fourth filter capacitor C4 is connected with the central point n of the second three-phase converter 4, the right end of a fifth filter inductor L5 is connected with the first end of a fifth filter capacitor C5, the second end of a fifth filter capacitor C5 is connected with the central point n of the second three-phase converter 4, the right end of a sixth filter inductor L6 is connected with the first end of a sixth filter capacitor C6, and the second end of a sixth filter capacitor C6 is connected with the central point n of the second three-phase converter 4.
The embodiment of the utility model provides a scheme is applicable to two sets of photovoltaic array parallel operation or singly organize photovoltaic array operation or multiunit photovoltaic array parallel operation, introduces the condition when two sets of photovoltaic array parallel operation and singly organize photovoltaic array operation below.
The first embodiment is as follows:
as shown in fig. 1, the two groups of photovoltaic arrays of the high power density non-isolated photovoltaic grid-connected inverter of the embodiment of the present invention operate in parallel, when the first photovoltaic array 1 and the second photovoltaic array 2 both work normally, the electric energy emitted from the first photovoltaic array 1 is converted into three-phase power with phase voltage difference of 120 ° in sequence by the first three-phase inverter 3 through the SPWM control method, and then is filtered by the LC first filter 5 to be power frequency three-phase sine voltage and then is sent into the autotransformer; electric energy emitted by the second photovoltaic array 2 is converted into three-phase electricity with phase voltages sequentially different by 120 degrees by a second three-phase inverter 4 through an SPWM control method, then the three-phase electricity is filtered into power frequency three-phase sinusoidal voltage by an LC second filter 6 and then is sent into an autotransformer, and finally the electric energy is sent into a power grid.
The embodiment of the utility model adopts SPWM to control two groups of three-phase inverters, so that the voltage between two primary windings of the same phase at the output end of the filter has a phase difference of 30 degrees, and the electric energy sent by the photovoltaic array is finally sent into a power grid through a single-phase three-winding autotransformer, so that the characteristic subharmonic grid-connected current can be inhibited, and the electric energy quality is improved; by adopting the autotransformer, the three windings share one common winding, so that the capacity of the grid-connected transformer in the photovoltaic grid-connected inverter is reduced by 82% compared with the capacity of the grid-connected transformer using the traditional power frequency transformer, the power density of the photovoltaic grid-connected inverter is greatly improved, the number of turns of the windings is reduced, and the cost is saved.
Example two:
as shown in fig. 2, the utility model discloses high power density non-isolated photovoltaic grid-connected inverter introduces in detail only the operating condition when first photovoltaic array 1 moves, and when first photovoltaic array 1 normally operated second photovoltaic array 2 trouble, the electric energy that first photovoltaic array 1 sent changed into the three-phase electricity that the looks phase voltage differs 120 in proper order through first three-phase inverter 3, sent into autotransformer after being power frequency three-phase sinusoidal voltage through the filtering of LC first filter 5 again; because the second photovoltaic array 2 has a fault, no current flows through the windings a2, b2 and c2 in the autotransformer, so that the single-phase three-winding autotransformer is equivalent to a single-phase two-winding autotransformer, at the moment, the primary windings a1, b1 and c1 and the secondary windings a, b and c of the autotransformer are mutually coupled, and therefore the electric energy generated by the first photovoltaic array 1 is sent to a power grid.
Example three:
as shown in fig. 3, the utility model discloses high power density non-isolated photovoltaic grid-connected inverter introduces in detail only the operating condition when second photovoltaic array 2 moves, when second photovoltaic array 2 normally operates first photovoltaic array 1 trouble, the electric energy that second photovoltaic array 2 sent changes into the three-phase electricity that the looks phase voltage differs 120 in proper order through first three-phase inverter 3, sends into autotransformer after being power frequency three-phase sinusoidal voltage through the filtering of LC second wave filter 6 again; because the first photovoltaic array 1 has a fault, no current flows through the windings a1, b1 and c1 in the autotransformer, so that the single-phase three-winding autotransformer is equivalent to a single-phase two-winding autotransformer, at the moment, the primary windings a2, b2 and c2 and the secondary windings a, b and c of the autotransformer are mutually coupled, and therefore the electric energy generated by the second photovoltaic array 2 is sent to a power grid.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.