Non-isolated grid-connected inverter circuit and control method thereof

Abstract

The invention discloses a non-isolated grid-connected inverter circuit and a control method thereof, and belongs to the technical field of grid-connected power generation. The non-isolated grid-connected inverter circuit is characterized in that a first end of a photovoltaic module is connected with a first end of a first switch module and a first end of a first switch tube through a first inductor; the second end of the first switch module is connected with the first end of the bus capacitor, the first end of the second switch tube and the first end of the third switch tube, and the second end of the first switch tube is connected with the second end of the bus capacitor, the first end of the second switch module and the second end of the fourth switch tube. The second end of the second switch module is connected with the second end of the photovoltaic module, the second end of the second switch tube and the second input end of the alternating current filtering module. The second end of the third switch tube is connected with the first input end of the alternating current filtering module. According to the circuit and the control method thereof, the problems of low voltage gain and difficulty in leakage current suppression when a non-isolation topology is applied to a micro-inverse scene can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of grid-connected power generation, and in particular to a non-isolated grid-connected inverter circuit and a control method thereof. Background Art

[0002] Micro inverter is a component-level power electronic device in photovoltaic power generation system, which can realize the ( , maximum power point tracking), and converts the DC power generated by the photovoltaic module into AC power for use by the load or into the power grid. Micro inverters usually use a single-stage inverter circuit of a flyback converter cascaded with an industrial frequency flip converter as the main power topology. Figure 1 , Figure 1 FIG. 1 is a structural diagram of a single-stage inverter circuit in the prior art. Figure 1 As shown, the photovoltaic module input is connected to the switch tube The current source flyback converter composed of isolation transformer T and rectifier diode D is converted into a steamed bun wave current, and then The industrial frequency inversion circuit formed by the invention inverts the steamed bun wave current into AC current and injects it into the power grid.

[0003] because Figure 1 The circuit shown has the defects of low magnetic core utilization and poor reactive power compensation capability. Figure 1 In the prior art, a single-stage isolated inverter circuit with a resonant structure is usually used to solve the above problems of the circuit shown in FIG. Figure 2 and Figure 3 shown. Figure 2 It is a structural diagram of a single-stage isolated inverter circuit containing a resonant structure in the prior art. Figure 3 The present invention is a structural diagram of another single-stage isolated inverter circuit containing a resonant structure in the prior art.

[0004] Although the single-stage isolated inverter circuit with a resonant structure has a higher voltage gain, higher conversion efficiency and extremely strong reactive power compensation capability, the number of switch tubes in the single-stage isolated inverter circuit with a resonant structure is twice that of the flyback circuit, and the hardware cost is high. Compared with the isolated topology circuit, the non-isolated topology has advantages in cost, conversion efficiency and reactive power compensation capability. However, the existing non-isolated inverter circuit has a complex structure, high hardware cost and poor reliability. See Figure 4 , Figure 4 The figure is a structural diagram of a non-isolated inverter circuit in the prior art. Figure 4 The non-isolated inverter circuit shown uses a series The circuit structure form, this structure form of non-isolated inverter circuit will greatly weaken the reliability of the main power topology of the micro inverter during operation. At present, there is no more effective solution to this technical problem.

[0005] It can be seen from this that how to provide a non-isolated grid-connected inverter circuit with a simple structure, low design cost and reliable operation, so as to overcome the problems of low voltage gain and difficulty in suppressing leakage current when the non-isolated topology is applied to micro-inversion scenarios. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a non-isolated grid-connected inverter circuit and a control method thereof, so as to overcome the problems of low voltage gain and difficulty in suppressing leakage current when the current non-isolated topology is applied to micro-inversion scenarios. The specific scheme is as follows:

[0007] In order to solve the above technical problems, the present invention provides a non-isolated grid-connected inverter circuit, comprising: a photovoltaic component, a first inductor, a bus capacitor, a first switch module, a second switch module, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and an AC filter module for injecting AC power into a power grid;

[0008] The first end of the photovoltaic component is respectively connected to the first end of the first switch module and the first end of the first switch tube through the first inductor, the second end of the first switch module is respectively connected to the first end of the bus capacitor, the first end of the second switch tube and the first end of the third switch tube, the second end of the first switch tube is respectively connected to the second end of the bus capacitor, the first end of the second switch module and the second end of the fourth switch tube, the second end of the second switch module is respectively connected to the second end of the photovoltaic component, the second end of the second switch tube and the second input end of the AC filter module, and the second end of the third switch tube is connected to the first input end of the AC filter module.

[0009] Preferably, the first switch module is specifically a fifth switch tube or a first diode; the first end and the second end of the fifth switch tube are respectively the first end and the second end of the first switch module; the positive pole and the negative pole of the first diode are respectively the first end and the second end of the first switch module.

[0010] Preferably, the second switch module is specifically a second diode or a sixth switch tube; the positive pole and the negative pole of the second diode are respectively the first end and the second end of the second switch module; the first end and the second end of the sixth switch tube are respectively the first end and the second end of the second switch module.

[0011] Preferably, the AC filter module is specifically The filter circuit can be either a low-pass filter circuit or a band-pass filter circuit.

[0012] In order to solve the above technical problems, the present invention further provides a control method for a non-isolated grid-connected inverter circuit, which is applied to the above-disclosed non-isolated grid-connected inverter circuit, comprising:

[0013] During the positive half cycle of the power grid;

[0014] If the triangular carrier is at the amplitude of the sinusoidal signal and If the first switch module is between , the first switch tube and the third switch tube are turned on, and the first switch module is turned off; otherwise, the fourth switch tube is turned on;

[0015] If the triangular carrier and or and and the fourth switch tube is in the off state, then the first switch tube, the second switch tube and the third switch tube are turned on; and is the amplitude of the DC signal;

[0016] During the negative half cycle of the power grid, each switch tube in the non-isolated grid-connected inverter circuit is controlled based on symmetry.

[0017] Preferably, the absolute value of the amplitude of the DC signal is equal to the absolute value of the amplitude of the sinusoidal signal.

[0018] Preferably, it also includes:

[0019] Obtain the non-isolated grid-connected inverter circuit in various working modes in one switching cycle Time domain equations, get the target equations;

[0020] The voltage gain of the non-isolated grid-connected inverter circuit is determined according to the inductor volt-second balance characteristic and the target equation group.

[0021] Preferably, the step of obtaining the non-isolated grid-connected inverter circuit in various working modes in a switching cycle is as follows: The time domain equations give the target equations, including:

[0022] During the positive half cycle of the power grid;

[0023] If the first switch tube, the second switch module and the third switch tube are all in the on state, and the first switch module, the second switch tube and the fourth switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the first working mode, and the non-isolated grid-connected inverter circuit in the first working mode is determined. Equation, get the first time domain equation;

[0024] If the first switch module, the second switch module and the fourth switch tube are all in the on state, and the first switch tube, the second switch tube and the third switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the second working mode, and the non-isolated grid-connected inverter circuit in the second working mode is determined. Equation, and the second time domain equation is obtained;

[0025] If the first switch tube, the second switch tube and the third switch tube are all in the on state, and the first switch module, the second switch module and the fourth switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the third working mode, and the non-isolated grid-connected inverter circuit in the third working mode is determined. Equation, and we get the third time domain equation.

[0026] Preferably, the determining of the voltage gain of the non-isolated grid-connected inverter circuit according to the inductor volt-second balance characteristic and the target equation group includes:

[0027] Determining a voltage gain of the non-isolated grid-connected inverter circuit according to the inductor volt-second balance characteristic, the first time domain equation, the second time domain equation, and the third time domain equation;

[0028] The voltage gain of the non-isolated grid-connected inverter circuit is expressed as:

[0029] ;

[0030] In the formula, is the voltage of the grid, is the voltage of the photovoltaic module, is the modulation ratio, is the duty cycle of the duration of the second working mode and the third working mode in one switching cycle, The duty cycle of half the duration of the second operating mode accounts for one switching cycle, is the current of the grid, is the grid-connected power, is the series equivalent resistance of the first inductor.

[0031] Preferably, the common mode voltage to ground of the non-isolated grid-connected inverter circuit is expressed as:

[0032] ;

[0033] In the formula, is the common mode voltage to ground of the non-isolated grid-connected inverter circuit, is the voltage of the grid.

[0034] Beneficial effect: In this circuit, the voltage output by the photovoltaic component can be filtered through the first inductor, the first switch tube, the first switch module and the bus capacitor to obtain filtered direct current; then, the filtered direct current can be converted into alternating current using the second switch tube, the third switch tube, the fourth switch tube and the second switch module to obtain three-phase alternating current; finally, the three-phase alternating current can be filtered using the alternating current filter module, and the filtered three-phase alternating current can be injected into the power grid.

[0035] Compared with the prior art, the high-gain non-isolated inverter circuit disclosed in the present invention overcomes the problems of low voltage gain and difficulty in suppressing leakage current in the traditional non-isolated topology when applied to micro-inversion scenarios. Compared with the isolated topology, it can not only reduce the hardware cost, but also has a stronger reactive power compensation capability, with the advantages of low cost and high return.

[0036] Correspondingly, a control method for a non-isolated grid-connected inverter circuit provided by the present invention also has the above-mentioned beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0038] Figure 1 It is a structural diagram of a single-stage inverter circuit in the prior art;

[0039] Figure 2 It is a structural diagram of a single-stage isolated inverter circuit containing a resonant structure in the prior art;

[0040] Figure 3 It is a structural diagram of another single-stage isolated inverter circuit containing a resonant structure in the prior art;

[0041] Figure 4 It is a structural diagram of a non-isolated grid-connected inverter circuit in the prior art;

[0042] Figure 5 A structural diagram of a non-isolated grid-connected inverter circuit provided by an embodiment of the present invention;

[0043] Figure 6 A structural diagram of another non-isolated grid-connected inverter circuit provided by an embodiment of the present invention;

[0044] Figure 7 A flow chart of a control method for a non-isolated grid-connected inverter circuit provided by an embodiment of the present invention;

[0045] Figure 8 for Figure 6 The working timing diagram of the non-isolated grid-connected inverter circuit shown;

[0046] Fig. 9 for Figure 6 The circuit diagram of the non-isolated grid-connected inverter circuit shown in the first working mode;

[0047] Fig.10 for Figure 6 A circuit diagram of a non-isolated grid-connected inverter circuit in a second working mode;

[0048] Fig.11 for Figure 6 A circuit diagram of a non-isolated grid-connected inverter circuit in a third working mode;

[0049] Fig.12 This is a curve diagram of the voltage gain change of the non-isolated grid-connected inverter circuit. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] See also Figure 5 , Figure 5 A structural diagram of a non-isolated grid-connected inverter circuit provided by an embodiment of the present invention, the circuit includes: a photovoltaic module , First Inductor , busbar capacitance , the first switch module , the second switch module , the first switch tube , the second switch tube , the third switch tube , the fourth switch tube and AC filter modules for injecting AC power into the grid ;

[0052] Photovoltaic panels The first end of the first inductor The first switch module The first end and the first switch tube The first end of the first switch module is connected to The second end of the bus capacitor The first end of the second switch tube The first end and the third switch tube The first end of the first switch tube is connected to The second end of the bus capacitor The second end of the second switch module The first end and the fourth switch tube The second end of the second switch module is connected to The second end of each The second end of the second switch tube The second end and AC filter module The second input terminal of the third switch is connected to The second end of the AC filter module is connected to the first input terminal of .

[0053] In this embodiment, a non-isolated grid-connected inverter circuit is provided. Figure 5 The non-isolated grid-connected inverter circuit shown is composed of photovoltaic modules , First Inductor , busbar capacitance , the first switch module , the second switch module , the first switch tube , the second switch tube , the third switch tube , the fourth switch tube and AC filter modules In Figure 5 middle, is the voltage of the grid.

[0054] exist Figure 5 In the non-isolated grid-connected inverter circuit shown in the figure, when the photovoltaic module After storing solar energy, the first inductor , the first switch tube , the first switch module and bus capacitance Photovoltaic panels The output voltage is filtered to obtain filtered direct current; then, the second switch tube is used to , the third switch tube , the fourth switch tube and the second switch module The filtered DC power can be converted into AC power to obtain three-phase AC power; finally, the AC filter module The three-phase alternating current can be filtered and the filtered three-phase alternating current can be injected into the power grid.

[0055] exist Figure 5 In the circuit shown, in order to reduce the AC filter module The structural complexity of is to set it to Filter circuit. Among them, the second inductor and the second capacitor composition Filter circuit. In the filter circuit, the second inductor The first end is the AC filter module The first input terminal of the third switch tube The second end of the second inductor is connected to The second end of the second capacitor The first end of the capacitor is connected to the live wire of the power grid, and the second capacitor The second end of the switch is connected to the neutral line of the grid and the second switch tube The second end of the second capacitor is connected to The second end is the AC filter module Of course, in practical applications, the AC filter circuit can also be It can be set as a low-pass filter circuit or a band-pass filter circuit as long as it can filter the alternating current injected into the power grid.

[0056] In practical applications, the first switch module can be Set as the fifth switch Or the first diode ; Among them, the fifth switch tube The first end and the second end are respectively a first switch module A first end and a second end of a first diode The positive and negative electrodes of the first switch module are Furthermore, the second switch module can also be Set as the second diode Or the sixth switch ; Wherein, the second diode The positive and negative electrodes of the second switch module are The first end and the second end of the sixth switch tube The first end and the second end are respectively a second switch module Obviously, by such a setting, the structure of the non-isolated grid-connected inverter circuit can be made more flexible and diverse.

[0057] It should be noted that, in this embodiment, the first switch tube , the second switch tube , the third switch tube , the fourth switch tube , the fifth switch tube And the sixth switch They are all NMOS tubes, wherein the gate of the NMOS tube is the control end of the switch tube, and the drain and source of the NMOS tube are the first end and the second end of the switch tube respectively.

[0058] See also Figure 6 , Figure 6 This is a structural diagram of another non-isolated grid-connected inverter circuit provided by an embodiment of the present invention. Figure 6 In the inverter circuit shown, Figure 5 The first switch module in Set as the fifth switch , and Figure 5 The second switch module in Set as the second diode .

[0059] because Figure 6 The circuit shown is a non-isolated grid-connected inverter circuit, so it has excellent electrical performance and low design cost. Figure 6 When all the switch tubes in the non-isolated inverter circuit shown adopt the sinusoidal pulse width modulation method, the grid freewheeling stage can also be increased, thereby significantly improving the voltage gain of the non-isolated grid-connected inverter circuit.

[0060] See also Figure 7 , Figure 7 A flow chart of a control method for a non-isolated grid-connected inverter circuit provided by an embodiment of the present invention, the method is applied to Figure 5 The non-isolated grid-connected inverter circuit shown in the figure comprises:

[0061] Step S11: During the positive half cycle of the power grid;

[0062] Step S12: If the triangle carrier is at the amplitude of the sinusoidal signal and The first switch is turned on. And the third switch , turn off the first switch module Otherwise, turn on the fourth switch ;

[0063] Step S13: If the triangle carrier is and or and and the fourth switch tube In the off state, the first switch tube is turned on , the second switch tube And the third switch ; and is the amplitude of the DC signal;

[0064] Step S14: During the negative half cycle of the power grid, each switch tube in the non-isolated grid-connected inverter circuit is controlled based on symmetry.

[0065] In this non-isolated grid-connected inverter circuit, all switch tubes use sinusoidal pulse width modulation, which includes: sinusoidal signal, triangular carrier and DC signal. Among them, the amplitude of the sinusoidal signal is and , the amplitude of the DC signal is and , the amplitude of the triangular carrier is and .

[0066] In order to enable those skilled in the art to more clearly understand the implementation principle of the present invention, Figure 6 The non-isolated grid-connected inverter circuit shown in the figure is used as an example for specific explanation. Figure 8 , Figure 8 for Figure 6 The working timing diagram of the non-isolated grid-connected inverter circuit shown.

[0067] In the positive half cycle of the power grid, if the amplitude of the triangular carrier is within the amplitude of the sinusoidal signal and The first switch is turned on. And the third switch , turn off the fifth switch Otherwise, turn on the fourth switch ; If the amplitude of the triangular carrier is and or and and the fourth switch tube In the off state, the first switch tube is turned on , the second switch tube And the third switch .

[0068] In the negative half cycle of the power grid, the switches in the non-isolated grid-connected inverter circuit are controlled based on symmetry. That is, if the amplitude of the triangular carrier is within the amplitude of the sinusoidal signal and The fourth switch is turned on. Otherwise, turn on the first switch And the third switch , turn off the fifth switch ; If the amplitude of the triangular carrier is and or and and the fourth switch tube In the off state, the first switch tube is turned off. , the second switch tube And the third switch .

[0069] In practical applications, in order to reduce the complexity of controlling a non-isolated grid-connected inverter circuit, the absolute value of the amplitude of the DC signal may be made equal to the absolute value of the amplitude of the sinusoidal signal.

[0070] Compared with the prior art, when controlling the non-isolated grid-connected inverter circuit, because all the switch tubes in the non-isolated grid-connected inverter circuit adopt the sinusoidal pulse width modulation method, the freewheeling stage of the power grid can be increased under this control mode. Therefore, this method can significantly improve the voltage gain of the non-isolated grid-connected inverter circuit.

[0071] Based on the above embodiment, this embodiment further illustrates and optimizes the technical solution. As a preferred implementation, the above control method further includes:

[0072] Obtain the non-isolated grid-connected inverter circuit in various working modes in one switching cycle Time domain equations, get the target equations;

[0073] The voltage gain of the non-isolated grid-connected inverter circuit is determined according to the inductor volt-second balance characteristics and the target equation group.

[0074] In this embodiment, when the absolute value of the amplitude of the DC signal is equal to the absolute value of the amplitude of the sinusoidal signal, based on Figure 8 From the timing diagram shown, the voltage gain of the non-isolated grid-connected inverter circuit can be derived.

[0075] Specifically, when each switch tube in the non-isolated grid-connected inverter circuit is turned on and off in different time periods, the non-isolated grid-connected inverter circuit will work in different working modes. ( , Kirchhoff's voltage law) determines the non-isolated grid-connected inverter circuit in various working modes within a switching cycle. The time domain equations are obtained to obtain the target set of equations.

[0076] The inductor volt-second balance characteristic ( ) is a key indicator for the non-isolated grid-connected inverter circuit to achieve a stable operating state. Therefore, in practical applications, the voltage gain of the non-isolated grid-connected inverter circuit can be determined based on the inductor volt-second balance characteristics and the target equation group.

[0077] As a preferred implementation, the above steps: obtaining the non-isolated grid-connected inverter circuit in various working modes in one switching cycle The time domain equations give the target equations, including:

[0078] During the positive half cycle of the power grid;

[0079] If the first switch tube, the second switch module and the third switch tube are all in the on state, and the first switch module, the second switch tube and the fourth switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the first working mode, and the non-isolated grid-connected inverter circuit in the first working mode is determined. Equation, get the first time domain equation;

[0080] If the first switch module, the second switch module and the fourth switch tube are all in the on state, and the first switch tube, the second switch tube and the third switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the second working mode, and the non-isolated grid-connected inverter circuit in the second working mode is determined. Equation, and the second time domain equation is obtained;

[0081] If the first switch tube, the second switch tube and the third switch tube are all in the on state, and the first switch module, the second switch module and the fourth switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the third working mode, and the non-isolated grid-connected inverter circuit in the third working mode is determined. Equation, and we get the third time domain equation.

[0082] In one switching cycle, Figure 6 The non-isolated grid-connected inverter circuit shown has three working modes, which are described in detail by taking the positive half cycle of the grid as an example.

[0083] See also Fig. 9 , Fig. 9 for Figure 6 The circuit diagram of the non-isolated grid-connected inverter circuit shown in FIG. And the third switch are both in the on state, and the fifth switch tube , the second switch tube And the fourth switch When both are in the off state, the non-isolated grid-connected inverter circuit is in the first working mode At this time, the non-isolated grid-connected inverter circuit is in the energy transmission stage. The second diode The fifth switch tube is turned on by the forward voltage. The body diode of the photovoltaic module is reverse biased and cut off. and inductance The energy on the grid is transferred to the grid through the capacitor, and the extra energy is transferred to the grid through the second diode. Flow Back .

[0084] When the non-isolated grid-connected inverter circuit is in the first working mode, it can be determined that the non-isolated grid-connected inverter circuit is in the first working mode. Equation, get the first time domain equation. The expression of the first time domain equation is:

[0085] Formula 1: ;

[0086] In the formula, For inductance The voltage, For photovoltaic modules The voltage, For inductance The current on For inductance The series equivalent resistance, Capacitor The current on Capacitor The voltage on is the grid-connected current, is the grid voltage.

[0087] See also Fig.10 , Fig.10 for Figure 6 The circuit diagram of the non-isolated grid-connected inverter circuit shown in FIG. And the fourth switch is in the on state, and the first switch tube , the second switch tube And the third switch When both are in the off state, the non-isolated grid-connected inverter circuit is in the second working mode At this time, the non-isolated grid-connected inverter circuit is in the freewheeling stage. The second diode The second switch tube is turned on by the forward voltage. And the third switch The body diode of the inductor is reverse biased and cut off. The voltage across the two ends is Voltage minus capacitance Voltage on the inductor The current on the capacitor decreases rapidly. The voltage on the second diode gradually increases. And the fourth switch Provides a freewheeling circuit for the power grid.

[0088] When the non-isolated grid-connected inverter circuit is in the second working mode, the non-isolated grid-connected inverter circuit in the second working mode can be determined. Equation, the second time domain equation is obtained; wherein the expression of the second time domain equation is:

[0089] Formula 2: ;

[0090] In the formula, For inductance The voltage, For photovoltaic modules The voltage, For inductance The current on For inductance The series equivalent resistance, Capacitor The current on Capacitor The voltage on is the grid-connected current, is the grid voltage.

[0091] See also Fig.11 , Fig.11 for Figure 6 The circuit diagram of the non-isolated grid-connected inverter circuit shown in FIG. The second switch And the third switch are both in the on state, and the fifth switch tube , the second diode And the fourth switch All are in the off state, and the non-isolated grid-connected inverter circuit is in the third working mode At this time, the non-isolated grid-connected inverter circuit is in the boost stage. and capacitor At the same time, give the inductor Charging, Inductor The voltage across the two ends is Voltage plus capacitance Voltage, inductance The current on the second switch increases rapidly. And the third switch A freewheeling loop is provided for a non-isolated grid-connected inverter circuit.

[0092] When the non-isolated grid-connected inverter circuit is in the third working mode, it can be determined that the non-isolated grid-connected inverter circuit is in the third working mode. Equation, the third time domain equation is obtained. The expression of the third time domain equation is:

[0093] Formula 3: ;

[0094] In the formula, For inductance The voltage, For photovoltaic modules The voltage, For inductance The current on For inductance The series equivalent resistance, Capacitor The current on Capacitor The voltage on is the grid-connected current, is the grid voltage.

[0095] As a preferred implementation, the above step of determining the voltage gain of the non-isolated grid-connected inverter circuit according to the inductor volt-second balance characteristic and the target equation group includes:

[0096] Determine the voltage gain of the non-isolated grid-connected inverter circuit according to the inductor volt-second balance characteristic, the first time domain equation, the second time domain equation and the third time domain equation;

[0097] Among them, the expression of the voltage gain of the non-isolated grid-connected inverter circuit is:

[0098] ;

[0099] In the formula, is the voltage of the grid, For photovoltaic modules The voltage, is the modulation ratio, is the duty cycle of the duration of the second working mode and the third working mode in one switching cycle, The duty cycle of one switching cycle is half of the duration of the second working mode, is the grid current, is the grid-connected power, is the series equivalent resistance of the first inductor.

[0100] According to the three working modes of the non-isolated grid-connected inverter circuit in one switching cycle, Formula 1, Formula 2 and Formula 3, combined with the inductor volt-second balance characteristics, Formula 4 can be obtained:

[0101] ;

[0102] In the formula, For photovoltaic modules The voltage, For inductance The current on For inductance The series equivalent resistance, is the duty cycle of the duration of the second working mode and the third working mode in one switching cycle, Capacitor The voltage on The duty cycle in a switching cycle when the non-isolated grid-connected inverter circuit is in the second working mode, When the non-isolated grid-connected inverter circuit is in the third working mode, the duty cycle in a switching cycle is: is the current of the grid.

[0103] That is, Formula 5:

[0104] ;

[0105] In the formula, for one switching cycle.

[0106] According to formula 4 and formula 5, it can be concluded that the non-isolated grid-connected inverter circuit is Input voltage to capacitor The voltage gain is obtained, thus formula 6:

[0107] ;

[0108] Defining the modulation ratio According to Formula 6, the non-isolated grid-connected inverter circuit can be obtained from the photovoltaic module The gain from input voltage to AC voltage gives Equation 7:

[0109] .

[0110] According to formula 1, the voltage gain of the non-isolated grid-connected inverter circuit is affected by and In the control of Figure 8 Under the sinusoidal pulse width modulation strategy shown, there is a linear relationship ,therefore, The impact on the voltage gain of the non-isolated grid-connected inverter circuit can be attributed to By changing and The change curve of the voltage gain of the non-isolated grid-connected inverter circuit can be obtained.

[0111] See also Fig.12 , Fig.12 This is a curve diagram of the voltage gain change of the non-isolated grid-connected inverter circuit. It should be noted that Fig.12 The voltage gain curve shown does not take into account the parasitic parameters of the line, such as the equivalent series resistance of the inductor, etc. On the basis of considering the parasitic parameters of the line, the voltage gain of the non-isolated grid-connected inverter circuit is , When the power consumption is less than 15 times, the power consumption is at least 15 times. Therefore, the non-isolated grid-connected inverter circuit can be used as the main power topology of the micro inverter.

[0112] Depend on Figure 6 It can be seen that the common-mode voltage to ground of the non-isolated grid-connected inverter circuit can be expressed as:

[0113] Formula 8: ;

[0114] In the formula, is the common mode voltage to ground of the non-isolated grid-connected inverter circuit. is the voltage of the grid.

[0115] It can be seen from Formula 8 that the common-mode voltage to ground of the non-isolated grid-connected inverter circuit does not contain high-frequency components. Therefore, the ground leakage current of the non-isolated grid-connected inverter circuit is almost zero, and it has the technical characteristics of low leakage current. In addition, through the analysis of the non-isolated grid-connected inverter circuit in different working modes, it can be seen that the grid current of the isolated inverter circuit can be opposite to the grid voltage. Therefore, the non-isolated grid-connected inverter circuit has four-quadrant operation capability and has extremely strong reactive power compensation capability.

[0116] Obviously, the non-isolated grid-connected inverter circuit provided in this application example not only overcomes the problems of low voltage gain and difficulty in leakage current suppression of the non-isolated grid-connected inverter circuit in the micro-inverter, but also reduces the hardware cost and improves the reactive power compensation capability of the non-isolated grid-connected inverter circuit compared to the traditional isolated inverter circuit, and has the advantages of low cost and high return.

[0117] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0118] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0119] The above is a detailed introduction to a non-isolated grid-connected inverter circuit and a control method thereof provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for a person skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A non-isolated grid-connected inverter circuit, characterized in that: include: Photovoltaic components, a first inductor, a bus capacitor, a first switch module, a second switch module, a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and an AC filter module for injecting AC power into a power grid; The first end of the photovoltaic component is respectively connected to the first end of the first switch module and the first end of the first switch tube through the first inductor, the second end of the first switch module is respectively connected to the first end of the bus capacitor, the first end of the second switch tube and the first end of the third switch tube, the second end of the first switch tube is respectively connected to the second end of the bus capacitor, the first end of the second switch module and the second end of the fourth switch tube, the second end of the second switch module is respectively connected to the second end of the photovoltaic component, the second end of the second switch tube and the second input end of the AC filter module, and the second end of the third switch tube is connected to the first input end of the AC filter module.

2. A non-isolated grid-connected inverter circuit according to claim 1, characterized in that: The first switch module is specifically a fifth switch tube or a first diode; the first end and the second end of the fifth switch tube are respectively the first end and the second end of the first switch module; the positive electrode and the negative electrode of the first diode are respectively the first end and the second end of the first switch module.

3. A non-isolated grid-connected inverter circuit according to claim 1, characterized in that: The second switch module is specifically a second diode or a sixth switch tube; the positive pole and the negative pole of the second diode are respectively the first end and the second end of the second switch module; the first end and the second end of the sixth switch tube are respectively the first end and the second end of the second switch module.

4. A non-isolated grid-connected inverter circuit according to claim 1, characterized in that: The AC filter module is specifically The filter circuit can be either a low-pass filter circuit or a band-pass filter circuit.

5. A control method for a non-isolated grid-connected inverter circuit, characterized in that: A non-isolated grid-connected inverter circuit as claimed in any one of claims 1 to 4, comprising: During the positive half cycle of the power grid; If the triangular carrier is at the amplitude of the sinusoidal signal and If the first switch module is between , the first switch tube and the third switch tube are turned on, and the first switch module is turned off; otherwise, the fourth switch tube is turned on; If the triangular carrier and or and and the fourth switch tube is in the off state, then the first switch tube, the second switch tube and the third switch tube are turned on; and is the amplitude of the DC signal; During the negative half cycle of the power grid, each switch tube in the non-isolated grid-connected inverter circuit is controlled based on symmetry.

6. The control method of a non-isolated grid-connected inverter circuit according to claim 5, characterized in that: The absolute value of the amplitude of the DC signal is equal to the absolute value of the amplitude of the sinusoidal signal.

7. A control method for a non-isolated grid-connected inverter circuit according to claim 6, characterized in that: Also includes: Obtain the non-isolated grid-connected inverter circuit in various working modes in one switching cycle Time domain equations, get the target equations; The voltage gain of the non-isolated grid-connected inverter circuit is determined according to the inductor volt-second balance characteristic and the target equation group.

8. The control method of a non-isolated grid-connected inverter circuit according to claim 7, characterized in that: The method of obtaining the non-isolated grid-connected inverter circuit in various working modes in a switching cycle The time domain equations give the target set of equations, including: During the positive half cycle of the power grid; If the first switch tube, the second switch module and the third switch tube are all in the on state, and the first switch module, the second switch tube and the fourth switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the first working mode, and the non-isolated grid-connected inverter circuit in the first working mode is determined. Equation, get the first time domain equation; If the first switch module, the second switch module and the fourth switch tube are all in the on state, and the first switch tube, the second switch tube and the third switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the second working mode, and the non-isolated grid-connected inverter circuit in the second working mode is determined. Equation, and the second time domain equation is obtained; If the first switch tube, the second switch tube and the third switch tube are all in the on state, and the first switch module, the second switch module and the fourth switch tube are all in the off state, it is determined that the non-isolated grid-connected inverter circuit is in the third working mode, and the non-isolated grid-connected inverter circuit in the third working mode is determined. Equation, and we get the third time domain equation.

9. The control method of a non-isolated grid-connected inverter circuit according to claim 8, characterized in that: The step of determining the voltage gain of the non-isolated grid-connected inverter circuit according to the inductor volt-second balance characteristic and the target equation group includes: Determining a voltage gain of the non-isolated grid-connected inverter circuit according to the inductor volt-second balance characteristic, the first time domain equation, the second time domain equation, and the third time domain equation; The voltage gain of the non-isolated grid-connected inverter circuit is expressed as: ； In the formula, is the voltage of the grid, is the voltage of the photovoltaic module, is the modulation ratio, is the duty cycle of the duration of the second working mode and the third working mode in one switching cycle, The duty cycle of half the duration of the second operating mode accounts for one switching cycle, is the current of the grid, is the grid-connected power, is the series equivalent resistance of the first inductor.

10. The control method of a non-isolated grid-connected inverter circuit according to claim 6, characterized in that: The expression of the common mode voltage to ground of the non-isolated grid-connected inverter circuit is: ； In the formula, is the common mode voltage to ground of the non-isolated grid-connected inverter circuit, is the voltage of the grid.

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