WO2013163780A1

WO2013163780A1 - Alternately parallel-connected grid-connected inverter and control method therefor

Info

Publication number: WO2013163780A1
Application number: PCT/CN2012/000595
Authority: WO
Inventors: 高峰
Original assignee: 上海康威特吉能源技术有限公司
Priority date: 2012-05-02
Filing date: 2012-05-02
Publication date: 2013-11-07

Abstract

An alternately parallel-connected photovoltaic grid-connected inverter and a control method therefor. The inverter comprises a power source circuit (10), a first inverter bridge leg (20), a second inverter bridge leg (30), a third inverter bridge leg (40), and a filter circuit (50). The power source circuit is constituted by a direct current power source (U_in) and a filter capacitor (C_in). The inverter bridge legs respectively are constituted by two power switch transistor series. A switch transistor in the first inverter bridge leg switches at a low frequency; switch transistors in the second and third inverter bridge legs switch at a high frequency. When the output of the inverter is greater than half of a load, the switch transistors in the second and third inverter bridge legs switch alternately at a high frequency; when the output of the inverter is less than half of the load, only one inverter bridge leg between the second and third inverter bridge legs switches at the high-frequency, while the other inverter bridge leg is not at work. The inverter allows for increased conversion efficiency during light loads, for reduced switch transistor current stress, for increased inverter reliability, and allows for reduced grid-connected current harmonics content.

Description

Interleaved parallel grid-connected inverter and control method thereof

The invention belongs to the technical field of power electronic converters, and particularly relates to the technical field of power converters in the field of new energy power generation technologies, and particularly relates to an interleaved parallel grid-connected inverter and a control method thereof. Background technique

With the energy crisis and environmental pollution problems becoming more and more serious, solar photovoltaic power generation technology has become a hot spot of concern and research in the world.

Photovoltaic grid-connected power generation is the most important way of solar power generation applications. According to statistics, the world exceeds

90% of photovoltaic power generation equipment installation capacity is grid-connected, because grid-connected applications have the advantages of low cost and maintenance-free compared to independent photovoltaic systems.

Photovoltaic grid-connected inverter is a bridge connecting solar photovoltaic power generation equipment and power grid, and is one of the most critical equipment in photovoltaic grid-connected power generation system. In the whole solar photovoltaic grid-connected power generation system, the cost of photovoltaic cells accounts for the highest proportion of the total cost of the system, and its price is relatively expensive. On the other hand, the photoelectric conversion efficiency of photovoltaic cells is low, in order to reduce the unit power generation of photovoltaic grid-connected systems. The cost of the quantity, while improving the efficiency of the entire grid-connected power generation system, requires grid-connected inverters with high efficiency, while the traditional grid-connected inverters can only guarantee the highest efficiency at full load or near full load. The efficiency at light load is very low, and photovoltaic cells generally operate at full load in only a small period of time, which results in a reduction in power generation efficiency of the entire system. With the large-scale installation and application of photovoltaic grid-connected power generation systems, users Higher requirements are placed on the reliability of grid-connected inverters and the waveform quality of grid-connected currents. Designing and implementing high-efficiency, high-reliability, low-harmonic grid-connected inverters is the constant pursuit of photovoltaic grid-connected power generation technology. The goal. Summary of the invention

The present invention is directed to the above-mentioned deficiencies of the prior art, and provides a photovoltaic grid-connected inverter having high overall efficiency and high reliability.

In order to achieve the above object, the present invention adopts the following technical solutions:

An interleaved parallel grid-connected inverter, the staggered parallel grid-connected inverter comprising a power supply circuit (10) a first inverter bridge arm (20), a second inverter bridge arm (30), a third inverter bridge arm (40), and a filter circuit (50), wherein the power supply circuit (10) is input source and The filter capacitor (C, „) is configured, the first inverter bridge arm (20) is composed of first and second switch tubes (&, &), and the second inverter bridge arm (30) is composed of third and fourth switch tubes (&, configuration, the third inverter bridge arm (40) is composed of the fifth and sixth switch tubes (&, the filter circuit (50) is composed of the first and second inductors (, ₂ );

Wherein: the anode of the input source is connected to one end of the filter capacitor ( ), the drain of the first switch (&), the drain of the third switch (&), and the drain of the fifth switch (&), The negative poles of the source are respectively connected to the other end of the filter capacitor (C, „), the source of the second switch (&), the source of the fourth switch (03), and the source of the sixth switch, the first The source of the switching transistor is respectively connected to the drain of the second switching transistor (&) and one end of the power grid, and the source of the third switching transistor (&) is respectively connected to the drain of the fourth switching transistor (&) and the first inductor At one end of ^), the source of the fifth switch (&) is respectively connected to the drain of the sixth switch (&) and one end of the second inductor ( ₂ ), and the other end of the first inductor (^) is connected to The other end of the second inductor (Ζ) and the other end of the grid (^).

In a preferred embodiment of the present invention, the output filter circuit (50) further includes an isolation transformer (7), the isolation transformer (one end of the primary winding and the other end of the first inductor and the other end of the second inductor ( ) Connected, the other end of the primary winding of the isolation transformer (7) is connected to the source of the first bypass transistor ( ) and the drain of the second switching transistor 03⁄4, and the two ends of the secondary winding of the isolation transformer (7) are respectively connected to the grid. The ends of (^) are connected.

Further, in the interleaved parallel grid-connected inverter, the first and second switching tubes (&, &) in the first inverter bridge arm (20) are low frequency switching tubes, and the switching frequency and the power grid thereof The voltage (^;) is equal in frequency, and the third, fourth, fifth, and sixth switching tubes of the second inverter bridge arm (30) and the third inverter bridge arm (40) (&, 5 ₄ S _5, high frequency switch _ό

As a second object of the present invention, the present invention also provides a control method for the above-described interleaved parallel grid-connected inverter, the control process of which is as follows - when the second inverter bridge arm (30) is operated, the third and fourth The switching tube (&, ·3⁄4) is complementary conducting; when the third inverter arm (40) is working, the fifth and sixth switching tubes (&, S ₆ ) are complementary conducting; when the inverter output power is greater than half At the time of loading, the second inverter bridge arm (30) and the third inverter bridge arm (40) work simultaneously, and the third switch tube (&) and the fifth switch tube (&) are interleaved 180°, the fourth switch The tube G) is interleaved with the sixth switching tube 03⁄4) by 180°;

When the inverter output power is less than half load, the second inverter bridge arm (30) and the third inverter bridge arm (40) When not working at the same time, when the second inverter bridge arm (30) is working, the third inverter bridge arm (40) is not working, and when the third inverter bridge arm (40) is working, the second inverter bridge arm (30) is not working. Working, and the moment when the second inverter bridge arm (30) and the third inverter bridge arm (40) start working or stop working are at the zero crossing point of the grid voltage ( _Wc ;).

The invention obtained according to the above scheme has the following advantages:

(1) The staggered parallel grid-connected inverter of the present invention can effectively improve the efficiency of the inverter under light load conditions, thereby improving the power generation efficiency of the entire photovoltaic grid-connected power generation system;

(2) The two bridge arms which are staggered and parallel are independent of each other, and one of the bridge arms has no influence on the other bridge arm when it fails, thereby significantly improving the reliability of the grid-connected inverter and making it have a certain fault tolerance capability;

(3) When the staggered parallel bridge arms work at the same time, it is beneficial to reduce the harmonic content of the grid-connected current and improve the waveform quality of the grid-connected current;

(4) It is convenient to realize the expansion of grid-connected inverter capacity by staggered parallel connection. DRAWINGS

The invention is further described below in conjunction with the drawings and specific embodiments.

1 is a schematic diagram of an interleaved parallel grid-connected inverter without an isolation transformer according to the present invention; FIG. 2 is a schematic diagram of an interleaved parallel grid-connected inverter including an isolation transformer according to the present invention; Inverter specific embodiment control block diagram;

4 is an equivalent circuit schematic diagram of the interleaved parallel grid-connected inverter of the present invention when the first and second inverter bridge arms are simultaneously operated;

FIG. 5 is an equivalent circuit schematic diagram of the staggered parallel grid-connected inverter of the present invention when the first and third inverter bridge arms are simultaneously operated.

The symbols in the figure illustrate: 1—power circuit; 20~—first inverter bridge arm; 30·—second inverter bridge arm; 40—third inverter bridge arm; 50~ filter circuit; one input source; „A filter capacitor; S„ S ₂ , &, S ₄ , S ₅ , < ^ a first, second, third, fourth, fifth and sixth switch; L!, L "first, Second inductance; Γ一 transformer; "c ~ grid; iu, first and second inductor currents; "GS1, UGS!, UGS3, WC54 U _G S5, «G56 ~ first, second, third, fourth Driving signals of the fifth and sixth switching tubes.

In order to make the technical means, creation features, achievement goals and effects achieved by the present invention easy to understand It is to be understood that the invention is further described below in conjunction with the specific drawings.

The specific embodiment of the present invention includes two parts: an interleaved parallel grid-connected inverter and a control method thereof.

The interleaved parallel grid-connected inverter includes a power supply circuit (10), a first inverter bridge arm (20), a second inverter bridge arm (30), a third inverter bridge arm (40), and a filter circuit (50).

The power supply circuit (10) is composed of an input source and a filter capacitor ((:,··), and the first inverter bridge arm (20) is composed of first and second switch tubes (&, &), and the second inverter bridge The arm (30) is composed of a third and fourth switch tube (&, and the third inverter bridge arm (40) is composed of a fifth and sixth switch tube (&,).

The first and second switching tubes (, &) in the first inverter bridge arm (20) are low frequency switching tubes whose switching frequency is equal to the grid voltage frequency.

The third, fourth, fifth, and sixth switching tubes (&, 5 ₄ & of the second inverter bridge arm (30) and the third inverter bridge arm (40) are high frequency switching tubes.

The staggered parallel grid-connected inverter provided by the invention has two forms according to whether or not the isolation transformer includes an interleaved grid-connected inverter with an isolation transformer and a grid-connected inverter without an isolation transformer.

The interleaved parallel grid-connected inverter without isolation transformer is shown in Fig. 1. The filter circuit (50) is composed of first and second inductors (where: the input source (the positive pole of t/ is connected to the filter capacitor respectively) One end of (C, „), the drain of the first 幵 (&), the drain of the third switch (&), and the drain of the fifth switch (&), the negative of the input source is connected to the filter The other end of the capacitor (C _IN ), the source of the second switch (&), the source of the fourth switch (·3⁄4), and the source of the sixth switch (&); the first switch ( ) The source is respectively connected to the drain of the second switch (&) and one end of the grid, and the source of the third switch (&) is connected to the drain of the fourth switch (3) and the first inductor (^) At one end, the source of the fifth switch (&) is respectively connected to the drain of the sixth switch (&) and the end of the second inductor (£ ₂ ), and the other end of the first inductor is connected to the second inductor, respectively. The other end and the other end of the grid ( _Wc ).

An interleaved parallel grid-connected inverter with an isolating transformer is shown in Fig. 2. The output filter circuit (50) includes an isolation transformer in addition to the first and second inductors (^, £ ₂ ). 7), wherein one end of the primary winding of the isolation transformer (7) is connected to the other end of the first inductor (Z) and the other end of the second inductor, and the other end of the primary winding of the isolation transformer (Γ) is connected to the first switching transistor The source is connected to the drain of the second switch (&), and the two ends of the secondary winding of the isolation transformer (7) are respectively connected to both ends of the power grid.

As a second part of the present invention: an interleaved parallel grid-connected inverter control method, the control method is implemented based on the staggered parallel grid-connected inverter formed by the above scheme, and the specific control is as follows: When the second inverter bridge arm (30) is working, the third and fourth switch tubes (&, complementary conduction; when the third inverter bridge arm (40) is working, the fifth and sixth switch tubes (&, Complementary conduction; when the inverter output power is greater than half load, the second inverter bridge arm (30) and the third inverter bridge arm (40) work simultaneously, and the third bypass tube (&) and the fifth switch The tube (&) is staggered by 180°, and the fourth switch tube 03⁄4) and the sixth switch tube 03⁄4) are interleaved by 180°;

When the inverter output power is less than half load, the second inverter bridge arm (30) and the third inverter bridge arm (40) do not work at the same time, and the second inverter bridge arm (30) operates, the third inverter The bridge arm (40) does not work. When the third inverter bridge arm (40) is in operation, the second inverter bridge arm (30) does not work, and the second inverter bridge arm (30) and the third inverter bridge arm ( 40) The moment when starting work or stopping work is at the zero crossing point of the grid voltage (^).

In the specific implementation, when the output power efficiency of the grid-connected inverter is half load, the second inverter bridge arm (30) and the third inverter bridge arm (40) can be alternated by using one grid voltage cycle. The work can also be alternated by using half of the grid voltage ( _Wc ) cycle for each work. It is also possible to use only one of the inverter bridge arms working all the time and the other inverter bridge arm not working.

Based on the above scheme, the control principle and working process of the specific implementation of the present invention are as shown in FIG. 3 to FIG. 5 - in the specific embodiment of the present invention, the first and second switching tubes (&, the insulated gate type bipolar type is selected The transistor (IGBT), the third, fourth, fifth, and sixth switching transistors are selected from metal oxide semiconductor field effect transistors (MOSFETs) with a switching frequency of 50 kHz, and the control of the grid-connected inverter is completed by a digital signal processor (DSP). .

The system control block diagram is shown in Figure 3. The entire control system includes the grid voltage sampling circuit, the input voltage sampling circuit, the inductor current sampling circuit, the digital signal processor (DSP), and the drive circuit.

The digital signal processor (DSP) includes a phase locked loop, an inductor current regulation, an input voltage adjustment, and the like, and is composed of a phase locked loop, a first error amplifier, a current reference generation module, a voltage reference generation module, a second error amplifier, and an operation. The processing module, the current sharing adjustment module and the PWM modulation module are composed.

The phase locked loop is connected to the current reference generating module and is connected to the grid voltage sampling circuit. The first error amplifier is connected to the current reference generating module and the voltage reference generating module, and is connected to the input voltage sampling circuit. The current reference generation module is coupled to the second error amplifier. The arithmetic processing module and the current sharing adjustment module are connected to the inductor current sampling circuit, and the operation processing module and the second error The amplifier is connected, and the current sharing adjustment module is connected to the PWM modulation module. The second error amplifier is connected to the PWM modulation module, and the PWM modulation module is connected to the drive circuit.

When the control system is running, the grid voltage sampling circuit collects the voltage of the grid (w _c ), the input voltage sampling circuit collects the voltage of the input source, and the inductor current sampling circuit collects the first and second of the first and second inductors (^, 2). Inductor current U _Ll , i _L2 ) o

The digital signal processor (DSP) forms a corresponding control signal according to the signal collected by the sampling circuit, and controls the driving circuit to form driving signals for driving the first, second, third, fourth, fifth and sixth switching tubes ( _Wrai , UGS2, UG i, MGS4, UGS5, U _GS6 ) o According to the drive signal, the following control is implemented:

When the output power of the grid-connected inverter is greater than the half-load power, all the inverter bridge arms work, wherein the first inverter bridge arm low-frequency switch works, and the second and third inverter bridge arm high-frequency switches work.

When the output power of the grid-connected inverter is less than the half-load power, the first inverter bridge arm still operates at a low frequency, and only one of the second and third inverter bridge arms operates at a high frequency switch, and the other bridge arm does not work. When the first and second inverter bridge arms are working at the same time, the equivalent circuit of the grid-connected inverter is as shown in FIG. 4, when the first and third inverter bridge arms are working at the same time, the grid-connected inverter, etc. The effect circuit is shown in Figure 5.

The basic principles, main features and advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited by the foregoing embodiments, and that the present invention is only described in the foregoing embodiments and the description of the present invention, without departing from the spirit and scope of the invention. Various changes and modifications are intended to fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and their equivalents.

Claims

Rights request

An interleaved parallel grid-connected inverter, characterized in that the staggered parallel grid-connected inverter comprises a power supply circuit (10), a first inverter bridge arm (20), and a second inverter bridge arm (30). a third inverter bridge arm (40) and a filter circuit (50), wherein the power supply circuit (10) is composed of an input source and a filter capacitor (C, „), and the first inverter bridge arm (20) is first, The second switch tube (&, &) is configured, the second inverter bridge arm (30) is composed of the third and fourth switch tubes (&, S ₄ ), and the third inverter bridge arm (40) is composed of the fifth and the third a six-switch (&, configuration, filter circuit (50) is composed of first and second inductors (, ₂ );

Wherein: the anode of the input source is respectively connected to one end of the filter capacitor, the drain of the first switch ( ), the drain of the third switch (&), and the drain of the fifth switch (&), and the negative of the input source Connected to the other end of the filter capacitor (C, „), the source of the second switch (&), the source of the fourth switch (·3⁄4), and the source of the sixth switch 03⁄4) The source of a switching transistor ( ) is respectively connected to the drain of the second switching transistor (&) and one end of the power grid ( _Wc ), and the source of the third switching transistor (&) is respectively connected to the fourth switching transistor

The drain of the G) and the first inductor (the end of the Z^, the source of the fifth switch (&) is connected to the drain of the sixth switch transistor and the end of the second inductor, respectively, and the other end of the first inductor Connected to the other end of the second inductor ( ₂ ) and the other end of the grid.

2. An interleaved parallel grid-connected inverter according to claim 1, wherein said output filter circuit (50) further comprises an isolation transformer (7), said isolation transformer (7) having a primary winding One end is connected to the other end of the first inductor (^) and the other end of the second inductor (^), and the other end of the primary winding of the isolation transformer (7) and the source of the first bypass tube and the second switching tube 03⁄4) The drains are connected, and the two ends of the secondary winding of the isolation transformer (7) are respectively connected to the two ends of the power grid (^).

The interleaved parallel grid-connected inverter according to claim 1 or 2, wherein in the interleaved parallel grid-connected inverter, the first inverter bridge arm (20) The first and second switch tubes (&, &) are low frequency switch tubes whose switching frequency is equal to the grid voltage (^) frequency, and the second inverter bridge arm (30) and the third inverter bridge arm (40) The third, fourth, fifth, and sixth switch tubes (&, &, &, are high frequency switch tubes).

4. A control method for an interleaved parallel grid-connected inverter, characterized in that the control method is as follows:

When the second inverter bridge arm (30) is working, the third and fourth switch tubes (&, complementary conduction; when the third inverter bridge arm (40) is working, the fifth and sixth switch tubes (&, Complementary conduction When the inverter output power is greater than half load, the second inverter bridge arm (30) and the third inverter bridge arm (40) work simultaneously, and the third switch tube (&) and the fifth switch tube 03⁄4) are interleaved 180 ° Conduction, the fourth switch tube (&) and the sixth switch tube are interleaved 180°;

When the inverter output power is less than half load, the second inverter bridge arm (30) and the third inverter bridge arm (40) do not work at the same time, and the second inverter bridge arm (30) operates, the third inverter The bridge arm (40) does not work. When the third inverter bridge arm (40) is in operation, the second inverter bridge arm (30) does not work, and the second inverter bridge arm (30) and the third inverter bridge arm ( 40) The moment when starting work or stopping work is at the zero crossing point of the grid voltage.