CN108599560A - More bootstrapping cascade connection type DC-DC converters of two capacitor-clampeds of photovoltaic system - Google Patents

Abstract

The invention discloses a multi-bootstrap cascaded DC-DC converter clamped by two capacitors for a photovoltaic system, which incorporates a leakage inductance clamp circuit structure of two capacitors, and uses a coupled inductor to improve the boosting capability of the converter. , so that the energy of the leakage inductance of the coupled inductor has a release loop, avoiding the circuit resonance problem caused by the leakage inductance energy, and also improving the efficiency of the circuit; the cascaded boost circuit structure is integrated, the voltage gain is further improved, and there is no Increase the number of switch tubes S, the control difficulty of the system does not increase, and the electrical stress of the switch tube S and the output rectifier diode D _o will not be affected; Compared with the converter, the boost performance is improved; compared with the boost unit of the traditional single bootstrap unit structure, as the duty cycle increases, the converter has superior boost voltage performance.

Description

Multi-bootstrap cascaded DC-DC converter with two capacitor clamps for photovoltaic system

technical field

The invention relates to a DC-DC converter, in particular to a multi-bootstrap cascaded DC-DC converter clamped by two capacitors for a photovoltaic system.

Background technique

With the depletion of traditional fossil energy and the deteriorating environment of human beings, the development of clean renewable energy is imminent. All countries in the world are committed to the research and development of new energy applications, of which solar energy and wind energy have been obtained a wider range of applications. However, for these systems, how to operate grid-connected and meet the high voltage requirements in the grid is still the most important issue. At present, a large number of boost converters have been developed to meet these applications. Among different converters, the traditional BOOST converter can theoretically increase the voltage gain by increasing the duty cycle. However, in practical applications, due to the limitation of parasitic parameters, very high voltage gain cannot be achieved. If a cascaded topology is adopted, the problem of low efficiency caused by the increase in the number of devices will be highlighted again.

Contents of the invention

Purpose of the invention: The purpose of the invention is to provide a cascaded multi-bootstrap DC-DC converter for photovoltaic systems that can improve efficiency and gain ratio.

Technical scheme: in order to achieve this goal, the present invention adopts following technical scheme:

The multi-bootstrap cascaded DC-DC converter clamped by two capacitors for a photovoltaic system according to the present invention includes an input power supply V _in , and the positive pole of the input power supply V _in is respectively connected to one end of the inductor L ₁ and the freewheeling diode D _{4 The} anode of the inductor L1, the other end of the inductor L1 is respectively connected to _one end _of the capacitor C3 and the anode _of the freewheeling diode D2, and the other end of the capacitor C3 is respectively connected to the anode _of the freewheeling diode _D1 and the cathode of the freewheeling diode D4, continued _The cathode of the current diode D1 is respectively connected to _one end of the coupling inductor primary winding L2, one end of the clamping capacitor _Cb and one end of the capacitor _C1 , and the other end of the coupling inductor primary winding _L2 is respectively connected to the clamping diode _{Db The} anode, the cathode of the freewheeling diode D2 and the drain of the switching tube S, the cathode of the clamping diode _Db are respectively connected to one end of the capacitor _C4 and the anode of the freewheeling diode _D5 , and the other end of the capacitor _C4 is respectively connected to the clamp The other end of the capacitor C _b and one end of the secondary winding L3 _of the coupled inductor, the other end of the secondary winding L3 _of the coupled inductor are respectively connected to the cathode of the freewheeling diode _D5 and the anode of the output diode D _o , and the output rectifier diode D _o The cathode is respectively connected to one end of the output capacitor C _o and one end of the load resistor R, and the other end of the output capacitor C _o , the other end of the load resistor R, the source of the switch tube S, and the other end of the capacitor _C1 are respectively connected to the input power supply V _in the negative pole.

Further, it also includes a freewheeling diode _D3 , the anode of the freewheeling diode _D3 is connected to one end of the secondary winding L3 _of the coupling inductor, and the cathode of the freewheeling diode _D3 is connected to the anode of the output diode D _o . Provide a way for the energy of the secondary winding L3 _of the coupled inductor to flow through, realize simultaneous charging of two circuits, and increase the boosting capability of the converter.

Further, a capacitor C ₂ is also included, one end of the capacitor C ₂ is connected to the cathode of the freewheeling diode D ₅ , and the other end of the capacitor C ₂ is connected to the anode of the output diode D _o . Capacitor C ₂ and freewheeling diode D ₃ form a bootstrap boost unit, which stores the energy of the secondary winding L ₃ of the coupling inductor and releases it to the load to improve the boost capability of the converter.

Beneficial effects: the present invention discloses a multi-bootstrap cascaded DC-DC converter clamped by two capacitors for a photovoltaic system. Compared with the prior art, it has the following beneficial effects:

1) The present invention combines the structure of the two-capacitor leakage inductance clamping circuit, and on the basis of using the coupled inductance to improve the boosting capability of the converter, the energy of the leakage inductance of the coupling inductance can be released, avoiding the circuit resonance caused by the energy of the leakage inductance problem, but also improve the efficiency of the circuit;

2) The present invention combines the cascaded boost circuit structure, the voltage gain is further improved, and the number of switch tubes S is not increased at the same time, the control difficulty of the system is not increased, and the electrical stress of the switch tube S and the output rectifier diode D _o will not affected;

3) The present invention combines the boost unit structure of multiple bootstrap units, and compared with the traditional boost converter, the boost performance is improved; compared with the boost unit of the traditional single bootstrap unit structure, with the With increased duty cycle, this converter has superior boost voltage performance.

Description of drawings

Fig. 1 is a circuit diagram of a boost converter in a first embodiment of the present invention;

Fig. 2 is a circuit diagram of a boost converter in a second specific embodiment of the present invention;

3 is an equivalent circuit diagram of a boost converter in a second specific embodiment of the present invention;

FIG. 4 is a modal diagram of a boost converter in a second specific embodiment of the present invention;

5 is an equivalent diagram of the first switching mode of the boost converter in the second specific embodiment of the present invention;

6 is an equivalent diagram of the second switching mode of the boost converter in the second specific embodiment of the present invention;

7 is an equivalent diagram of the third switching mode of the boost converter in the second specific embodiment of the present invention;

Fig. 8 is an equivalent diagram of the fourth switching mode of the boost converter in the second specific embodiment of the present invention;

Fig. 9 is an equivalent diagram of the fifth switching mode of the boost converter in the second specific embodiment of the present invention;

10 is a waveform diagram of the voltage at both ends of the drain source of the switch tube S of the boost converter, the output voltage V _o and the current of the output rectifier diode D _o in the second embodiment of the present invention;

11 is a waveform diagram of the voltage at _both ends of the drain source of the switching tube S of the boost converter in the _second embodiment of the present invention, the current of the primary winding L2 of the coupling inductor, and the voltage at both ends of the primary winding L2 of the coupling inductor;

12 is a waveform diagram of the voltage at both ends of the drain source of the switch tube _S of the boost converter, the current of the capacitor C2 and the current of the capacitor C3 in the _second specific embodiment of the present invention;

13 is a waveform diagram of the voltage across the drain-source of the switching tube S of the boost converter, the current of the freewheeling diode D2 and the current of the freewheeling diode _D3 in the _second embodiment of the present invention.

Detailed ways

The technical solution of the present invention will be further introduced below in combination with specific embodiments.

The first specific embodiment of the present invention discloses a multi-bootstrap cascaded DC-DC converter clamped by two capacitors for photovoltaic systems, as shown in Figure 1, including input power V _in and the positive pole of input power V _in Connect _one end of the inductor L1, the other end _of the inductor L1 is respectively connected to the anode _of the freewheeling diode D1 and the anode of the _freewheeling diode D2, and the cathode of the freewheeling diode D1 is respectively connected to _one end of the primary winding _L2 of the coupled inductor, _One end of the capacitor C1 and the anode of the freewheeling diode _D5 , the other end of the primary winding _L2 of the coupling inductor are respectively connected to one end of the capacitor _C4 , the cathode of the _freewheeling diode D2 and the drain of the switching tube S, and the capacitor _{C4 The} other end of the capacitor C3 is respectively connected to the cathode of the freewheeling diode D5, one end _of the capacitor C3 and the anode _of the _freewheeling diode D4, and the other end of the capacitor C3 is respectively connected to the anode of the freewheeling diode _D3 and the secondary winding L3 _of the coupled inductor One end of the coupling inductor secondary winding L3, the other end _of the secondary winding L3 is respectively connected to the cathode of the _freewheeling diode D4 and one end of the capacitor _C2 , and the other end of the capacitor _C2 is respectively connected to the cathode of the freewheeling diode _D3 and the output diode D _o The anode and the cathode of the output rectifier diode D _o are respectively connected to one end of the output capacitor C _o and one end of the load resistor R, the other end of the output capacitor C _o , the other end of the load resistor R, the source of the switch tube S and the capacitor _C1 The other end is respectively connected to the negative pole of the input power supply V _in .

The second specific embodiment of the present invention adds a freewheeling diode D ₃ and a capacitor C ₂ on the basis of the first specific embodiment, as shown in Figure 2, the anode of the freewheeling diode _D3 is connected to the secondary winding L of the coupling inductor ₃ , the cathode of the freewheeling diode _D3 is connected to the anode of the output diode D _{o ;} one end of the capacitor C2 is connected to the cathode of the freewheeling diode D5, and the other end of the capacitor _C2 is connected _to the anode of the output diode _Do.

Wherein, the switch tube S is a MOSFET or an IGBT.

The equivalent circuit diagram of the boost converter in the second specific embodiment of the present invention is shown in Figure ₃ , the equivalent circuit of the primary side winding L1 of the coupling inductor is the leakage inductance L _K and the excitation inductance L _M , the ideal transformer turn on the primary side The number N ₁ and the number of turns of the ideal transformer on the secondary side N ₂ . The current of the input power supply is i _in , the voltage of the input power supply is V _in , and the current of the inductor L ₁ is _The voltage across the inductor L1 is The current of the excitation inductance L _M of the primary winding of the coupled inductor is The voltage on both sides of the excitation inductance L _M of the primary winding of the coupled inductor is The current of the leakage inductance L _K of the primary winding of the coupled inductor is The voltage on both sides of the leakage inductance L _K of the primary winding of the coupled inductor is The current of the secondary winding L ₃ of the coupled inductor is The voltage on both sides of the secondary winding L3 _of the coupled inductor is The current of the output rectifier diode D _o is The voltage across the output rectifier diode D _o is The current flowing through the switch tube S is i _S , the voltage across the switch tube S is V _S , and the current of the diode D _b is The voltage across the diode D _b is Diode _D1 current is _The voltage across diode D1 is Diode _D2 current is _The voltage across diode D2 is Diode _D3 current is The voltage across diode _D3 is Diode _D4 current is _The voltage across diode D4 is Diode _D5 current is _The voltage across diode D5 is The current of capacitor C _b is The voltage across the capacitor _Cb is The current in capacitor _C1 is The voltage across capacitor _C1 is _The current in capacitor C2 is _The voltage across capacitor C2 is _The current in capacitor C3 is _The voltage across capacitor C3 is The current in capacitor _C4 is The voltage across capacitor _C4 is The current of the output capacitor C _o is The voltage across the output capacitor C _o is The current of the load resistor R is i _o .

Figure 4 is a modal diagram of a boost converter. The working process of the boost converter is divided into 5 switching modes, namely the first switching mode to the fifth switching mode, and the resistance _R is the load. The specific description is as follows:

The first switching mode corresponds to [t ₀ , t ₁ ] in Figure ₄ : the equivalent circuit is shown in Figure ₅ , the switch tube S, the freewheeling diode D2, the freewheeling diode D4 and the output diode D _o are turned on, The flow path of the current is shown in Figure 5. The power supply charges the inductor L ₁ and the capacitor C ₃ at the same time, the inductor L ₁ stores energy, the capacitor C ₁ charges the primary winding L ₂ of the coupled inductor, and the secondary winding L ₃ of the coupled inductor passes through the output The loop formed by the diode D _o , the capacitor C ₂ , the clamping capacitor C _b and the capacitor C ₁ freewheels to the output capacitor C _o and the load R.

The second switching mode corresponds to [t ₁ , t ₂ ] in Figure 4: the equivalent circuit is shown in Figure 6, the switch tube S and the freewheeling diode D ₂ , the freewheeling diode D ₃ , the freewheeling diode D ₅ and the continuous The current flow diode D ₄ is turned on, and the current flow path is shown in Figure 6. The power supply continues to charge the inductor L ₁ and the capacitor C ₃ at the same time, the inductor L ₁ and the capacitor C ₃ continue to store energy, and the capacitor C ₁ continues to charge the coupling inductor. The side winding L ₂ is charged, the voltage of the primary winding L ₂ of the coupled inductor rises, and at the same time, the voltage of the secondary winding L ₃ of the coupled inductor also rises accordingly, so the secondary winding L ₃ of the coupled inductor passes through the freewheeling diode D ₃ and the freewheeling Diode D5 _charges capacitor _C2 and capacitor _C4 , and output capacitor C _o discharges to load R.

The third switching mode corresponds to [t ₂ , t ₃ ] in Figure 4: the equivalent circuit is shown in Figure 7, the switch tube S is turned off at t ₂ , and at the same time, the freewheeling diode D ₁ , output diode D _o and The clamping diode _Db is turned _on , the freewheeling diode D2 and the freewheeling diode D4 are turned off, the current flow path is shown in Figure ₇ , the power supply, the inductor L1 and the capacitor _C3 charge the capacitor _C1 , and the primary side _of the coupling inductor Winding leakage inductance L _K energy is released through the loop formed by clamping diode _Db , capacitor _C4 and clamping capacitor _Cb , and the secondary winding L3 _of the coupling inductor discharges to the output capacitor through freewheeling diode _D5 and freewheeling diode _D3 C _o and give load R.

The fourth switching mode corresponds to [t ₃ , t ₄ ] in Figure 4: the equivalent circuit is shown in Figure 8, the switch tube S continues to be turned off, the freewheeling diode D ₁ , the output diode D _o and the clamping diode D _b Continue to turn _on , the freewheeling diode D ₃ and the freewheeling diode D5 are turned off, and the current flow path is shown in Figure 8, power supply, inductor L ₁ , capacitor C ₃ , coupling inductor primary winding L ₂ , coupling inductor secondary The winding L ₃ , the capacitor C ₂ and the capacitor C ₄ discharge to the load R together, and charge the capacitor C ₁ and the output capacitor C _o at the same time. The energy of the leakage inductance L _K of the primary winding of the coupled inductor is released through the loop formed by the clamping diode D _b , the capacitor C ₄ and the clamping capacitor C _b .

The fifth switching mode corresponds to [t ₄ , t ₅ ] in Figure 4: the equivalent circuit is shown in Figure 9, the switching tube continues to be turned off, and at the same time, the freewheeling diode D ₁ and the output rectifier diode D _o continue to be turned on, and the clamp _The bit diode D _b is turned off, the freewheeling diode D2, the freewheeling diode D5 and the freewheeling diode _D3 continue to be turned off, and the current flow path is shown in Figure ₉ , the power supply, the inductor _L1 , the capacitor _C3 , and the coupling inductor The secondary winding L ₃ , the clamping capacitor C _b and the capacitor C ₂ release energy to the load at the same time, and charge the capacitor C ₁ and the output capacitor C _o , and at the same time, the energy release of the leakage inductance L _K of the coupling inductor ends.

From the above analysis, the gain expression can be obtained as:

Among them, D is the duty ratio of the switch tube S, N is the turns ratio of the primary side and the secondary side of the coupled inductor, and K is the coupling coefficient of the coupled inductor.

When the converter operates according to the first switching mode to the fifth switching mode, the drain-source voltage of the switching tube S in the circuit, the voltage and current at _both ends of the primary winding L2 of the coupled inductor, the current of the output rectifier diode D _o , and the output _The waveforms of the voltage, the current of the freewheeling diode D2, the current of the freewheeling diode _D3 , the current of the capacitor _C2 and the current _of the capacitor C3 are specifically described as follows:

In Fig. 10, the input voltage V _in = 24V, the output voltage V _o = 380V, the ordinate of the voltage difference V _DS between the drain and source of the switch tube S is 50 V/cell, and the current of the output diode D _o The ordinate is 2.5 A/cell, and the ordinate of the output voltage V _o is 100 V/cell.

In Fig. 11, the input voltage V _in = 24V, the output voltage V _o = 380V, the ordinate of the voltage difference V _DS between the drain and source of the switch tube S is 50 V/cell, and the voltage of the primary winding L ₂ of the coupled inductor The ordinate is 50 V/cell, the current of the primary winding L ₂ of the coupled inductor The vertical axis is 5 amps/cell.

In Fig. 12, the input voltage V _in = 24V, the output voltage V _o = 380V, the ordinate of the voltage difference V _DS between the drain and source of the switch tube S is 50 V/cell, and the current of the capacitor C ₂ The ordinate is 2.5A/cell, the current _of capacitor C3 The vertical axis is 10 amps/cell.

In Fig. 13, the input voltage V _in =24V, the output voltage V _o =380V, the ordinate of the voltage difference V _DS between the drain and source of the switch tube S is 50 V/cell, and the current of the diode _D2 The ordinate is 10A/cell, the current of diode _D3 The vertical axis is 2.5 amps/cell.

Claims (3)

1. A multi-bootstrap cascaded DC-DC converter clamped by two capacitors for a photovoltaic system, characterized in that it includes an input power supply V _in , and the positive pole of the input power supply V _in is connected to _one end of the inductor L1 and the freewheeling diode D ₄ , the other end of the inductor L1 is respectively connected to _one end _of the capacitor C3 and the anode _of the _freewheeling diode D2, and the other end of the capacitor C3 is respectively connected to the anode _of the freewheeling diode _D1 and the cathode of the freewheeling diode D4, _The cathode of the freewheeling diode D1 is respectively connected to _one end of the primary winding L2 of the coupling inductor, one end of the clamping capacitor _Cb and one end of the capacitor _C1 , and the other end of the primary winding _L2 of the coupling inductor is respectively connected to the clamping diode _{Db The} anode of the freewheeling diode D2, the cathode of the freewheeling diode D2 and the drain of the switching tube S, the cathode of the clamping diode _Db are respectively connected to one end of the capacitor _C4 and the anode of the freewheeling diode _D5 , and the other end of the capacitor _C4 is respectively connected to the clamp The other end of the bit capacitor C _b and one end of the secondary winding L3 _of the coupled inductor, the other end of the secondary winding L3 _of the coupled inductor are respectively connected to the cathode of the freewheeling diode _D5 and the anode of the output diode D _o , and the output rectifier diode D _o The cathode of the output capacitor C _o is connected to one end of the load resistor R, and the other end of the output capacitor C _o , the other end of the load resistor R, the source of the switch tube S, and the other end of the capacitor _C1 are respectively connected to the input power supply V _in the negative pole. 2. The multi-bootstrap cascaded DC-DC converter of two capacitor clamps for photovoltaic system according to claim 1 is characterized in that: it also includes freewheeling diode D ₃ , and the anode connection coupling of freewheeling diode D ₃ One end of the inductance secondary winding L3, the cathode _of the freewheeling diode _D3 is connected to the anode of the output diode D _o . 3. The multi-bootstrap cascaded DC-DC converter clamped by two capacitors for a photovoltaic system according to claim 2, characterized in that: it also includes a capacitor C ₂ , and one end of the capacitor C ₂ is connected to the freewheeling diode D ₅ The cathode of the capacitor _C2 is connected to the anode of the output diode D _o at the other end.