CN107612349A - The common ground type isolation quasi- Z source converters of high-gain of fuel cell and photovoltaic generation - Google Patents

Abstract

The invention provides a common-ground isolated high-gain quasi-Z source converter for fuel cells and photovoltaic power generation, which mainly includes an input DC voltage source, composed of a first inductor, a first capacitor, a first diode, a second inductor and a second inductor. The quasi-Z source network composed of two capacitors, the quasi-switching boost unit composed of the second diode, the third diode, the third capacitor, the third MOS tube and the fourth MOS tube, the first MOS tube, the second MOS tube, a high-frequency transformer with a transformation ratio of 1: n , a voltage doubler rectifier and a load resistor composed of the fourth capacitor, the fifth capacitor, the fourth diode and the fifth diode. The whole circuit structure is simple, the input current of the power supply is continuous, combined with the single-stage buck-boost characteristics of the quasi-Z source impedance network and the quasi-switching boost network, it has a higher output voltage gain, and realizes the transformation through a high-frequency transformer Electrical isolation between the output and input of the device, and there is no inrush current in the circuit and the inrush current at the moment the switch tube is turned on.

Description

Common Ground Isolated High Gain Quasi-Z Source Converter for Fuel Cell and Photovoltaic Power Generation

technical field

The invention relates to the technical field of power electronic converters, in particular to a ground-common isolated high-gain quasi-Z source DC converter suitable for fuel cells and photovoltaic power generation.

Background technique

In recent years, with the development of the economy, the increasing demand for energy and the environmental pollution caused by traditional fossil energy have become increasingly serious. In order to achieve sustainable development, people began to pay attention to the development and application of renewable clean new energy. New energy power generation is one of the applications. Renewable energy power generation mainly includes water conservancy, solar energy, wind energy, and fuel cells. However, because the output voltage level of fuel cells and solar photovoltaic panels is low and the fluctuation range is large, it cannot meet the requirements of some existing electrical equipment and grid connection, so it is usually necessary to convert low-voltage power through a step-up DC/DC converter It is a stable high-voltage direct current, and then connected to the grid through the inverter. In recent years, relevant scholars have proposed Z-source DC-DC converters and switch boost DC-DC converters. Although they respectively use the Z-source impedance network and switch boost network to increase the output voltage, due to parasitic parameters and Due to the limitation of loss, their corresponding voltage gains still have a lot of room for improvement, and in many applications, there is often a need for electrical isolation between the output and input of the converter, so the isolated high-gain DC-DC converter Research and development are becoming increasingly important.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a common-ground type isolated quasi-Z source DC-DC converter with higher output voltage gain suitable for fuel cells and photovoltaic power generation. The specific technical scheme is as follows.

The common-ground isolation high-gain quasi-Z source DC converter suitable for fuel cells and photovoltaic power generation of the present invention specifically includes an input DC voltage source, which consists of a first inductor, a first capacitor, a first diode, a second inductor and The quasi-Z source network composed of the second capacitor, the quasi-switch boost unit composed of the second diode, the third diode, the third capacitor, the third MOS transistor and the fourth MOS transistor, the first MOS transistor, the second MOS transistor Two MOS tubes, a high-frequency transformer T with a transformation ratio of 1:n, a voltage doubler rectifier composed of the fourth capacitor C _o1 , the fifth capacitor C _o2 , the fourth diode D _o1 and the fifth diode D _o2 and load resistance R _L .

Further, one end of the DC input voltage source is connected to one end of the first inductance; the other end of the first inductance is respectively connected to the anode of the first diode and the cathode of the first capacitor; the first diode The cathode of the tube is respectively connected to one end of the second inductance and the positive pole of the second capacitor; the other end of the second inductor is respectively connected to the anode of the second diode, the drain of the MOS transistor and the positive pole of the first capacitor; The cathode of the second diode is respectively connected to the anode of the third capacitor and the drain of the first MOS transistor; the cathode of the third capacitor is respectively connected to the source of the fourth MOS transistor and the anode of the third diode ; The source of the first MOS transistor is respectively connected to the primary side positive input terminal of the high frequency transformer and the drain of the second MOS transistor; the cathode of the third diode is respectively connected to the source of the second MOS transistor , the negative pole of the second capacitor and the negative pole of the input DC power supply; the source of the third MOS tube is connected to the drain of the fourth MOS tube and the negative input terminal of the primary side of the high-frequency transformer; the fourth capacitor The positive pole of the fourth diode is connected to the cathode of the fourth diode and one end of the load; the negative pole of the fourth capacitor is respectively connected to the positive terminal of the secondary side of the transformer and the positive pole of the fifth capacitor; the negative pole of the fifth capacitor is respectively It is connected with the anode of the fifth diode and the other end of the load; the cathode of the fifth diode is respectively connected with the anode of the fourth diode and the negative terminal of the secondary side of the transformer.

Compared with the prior art, the present invention has the following advantages: a MOS tube hidden in the quasi-switching boost unit is developed and utilized, and a full-bridge structure can be realized without adding an additional power switch tube, the structure is simple, and the control is convenient; Compared with the traditional isolated cascaded quasi-Z source DC-DC converter (its output voltage gain is G=2n/(1-3D)), under the same input voltage and duty cycle, the circuit of the present invention can In the case of using one less inductor and capacitor, the higher output voltage gain is G=2n/(1-4D). Moreover, the input power supply current is continuous, and there is no circuit start-up inrush current, etc., so the circuit of the present invention has very wide application prospects.

Description of drawings

Fig. 1 is the circuit diagram of the embodiment of a kind of common ground type isolation high-gain quasi-Z source DC-DC converter of the present invention;

Fig. 2a, Fig. 2b, Fig. 2c and Fig. 2d are diagrams of main working modes of the circuit diagram shown in Fig. 1 in one switching cycle.

Fig. 3a is a comparative graph of output voltage gain between the converter of the present invention and a traditional isolated cascaded quasi-Z source DC-DC converter.

Fig. 3b has provided the _emulation result figure of relevant variable in the circuit of the present invention and the waveform of inductive current i _L1 and i _L2 and The waveform of the input voltage V _pr on the primary side of the high frequency transformer.

detailed description

The present invention will be described in further detail below in conjunction with the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. It should be noted that, if there are any processes or parameters that are not specifically described in detail below, those skilled in the art can understand or implement them with reference to the prior art.

The basic topology structure of this embodiment is shown in FIG. 1 . For the convenience of verification, the devices in the circuit structure are regarded as ideal devices. Let the current of the first inductor L ₁ be i _L1 , the current of the second inductor L ₂ be i _L2 , the voltage of the first capacitor C ₁ is V _C1 , the voltage of the second capacitor C ₂ is V _C2 , and the voltage of the third capacitor C ₃ is V _C3 .

Fig. 2a, Fig. 2b, Fig. 2c and Fig. 2d are diagrams of main working modes of the circuit diagram shown in Fig. 1 in one switching cycle. Figure 2a is the equivalent circuit diagram of working mode 1 (MOS tubes S ₁ , S ₂ , S ₃ , and S ₄ are all on), and Figure 2b is working mode 2 (MOS tubes S ₁ , S ₄ are off, S ₂ , S ₃ conduction), Fig. 2c is the circuit diagram of working mode 3 (MOS transistors S ₁ and S ₃ are turned off, S ₂ and S ₄ are turned on), Fig. 2d is the circuit diagram of working mode 4 (MOS transistor S ₁ , S ₄ open, S ₂ , S ₃ off) circuit diagram. The solid line in the figure indicates the part where current flows in the converter.

As shown in Fig. 2a, Fig. 2b, Fig. 2c and Fig. 2d, the common-ground isolated high-gain quasi-Z source DC-DC converter mainly has four working modes in one switching cycle, which are described as follows:

Working mode 1: As shown in Figure 2a, the MOS transistors (S ₁ , S ₂ , S ₃ , S ₄ ) are all turned on, and the first diode D ₁ , the second diode D ₂ and the third diode Tube _D3 is turned off by reverse cutoff. At this time, the input voltage source V _dc is connected in series with the first capacitor C ₁ and the third capacitor C ₃ to charge the first inductor L ₁ together; the second capacitor C ₂ and the third capacitor C ₃ are connected in series to charge the second inductor L ₂ Charge. At this time, since the primary side of the high-frequency transformer is connected in parallel with the third capacitor C3, its primary-side input voltage is V _pr =V _C3 , and the secondary-side voltage V _sc after passing through the high-frequency transformer is a positive value n*V _C3 , Then the fourth diode D _o1 is turned off in reverse cutoff, and the fifth diode D _o2 is forward biased and turned on.

In this working mode, the relevant electrical parameter relational formula is:

V _L1 =V _dc +V _C1 +V _C3 (1)

V _L2 =V _C2 +V _C3 (2)

V _pr ＝V _C3 , V _sc ＝nV _C3 (3)

Working mode 2: As shown in Figure 2b, the first MOS transistor S ₁ and the fourth MOS transistor S ₄ are turned off, the second MOS transistor S ₂ and the third MOS transistor S ₃ are turned on, and the first diode D ₁ , The _second diode D2 and the third diode _D3 are turned on. At this time, the input voltage source V _dc is connected in series with the _first inductor L1 to charge the second capacitor C ₂ ; the second inductor L _{2 charges} the first capacitor C ₁ ; L ₂ charges the third capacitor C ₃ in series. At this time, the primary side of the high-frequency transformer is connected in antiparallel with the third capacitor C ₃ , so its primary-side input voltage is V _pr =-V _C3 , and the secondary-side voltage V _sc after passing through the high-frequency transformer is also a negative value V _sc =-n*V _C3 , then the fourth diode D _o1 is forward-biased and turned on, and the fifth diode D _o2 is reverse-biased and turned off. In this working mode, the relevant electrical parameter relational formula is:

V _L1 =V _dc -V _C2 (4)

V _L2 = - V _C1 (5)

V _C3 =V _C1 +V _C2 (6)

V _pr ＝-V _C3 , V _sc ＝-nV _C3 (7)

Working mode 3: as shown in FIG. 2 c , the first MOS transistor S ₁ and the third MOS transistor S ₃ are turned off, and the second MOS transistor S ₂ and the fourth MOS transistor S ₄ are turned on. At this time, since the primary side of the high-frequency transformer is short-circuited together through the third diode D ₃ , the voltages of its primary side and secondary side are equal to zero: V _pr =V _sc =0, then the fourth diode D Both _o1 and the fifth diode D _o2 are reverse-biased and turned off. In this working mode, the relevant electrical parameter relational formula is:

V _L1 =V _dc -V _C2 (8)

V _L2 = - V _C1 (9)

V _C3 =V _C1 +V _C2 (10)

V _pr =V _sc =0 (11)

Working mode 4: as shown in FIG. 2d , the first MOS transistor S ₁ and the fourth MOS transistor S ₄ are turned on, and the second MOS transistor S ₂ and the third MOS transistor S ₃ are turned off. At this time, the primary side of the high-frequency transformer is connected in parallel with the third capacitor C ₃ , so the input voltage on the primary side is V _pr =V _C3 , and the secondary-side voltage V _sc after passing through the high-frequency transformer is a positive value V _sc =nV _C3 , the fourth diode D _o1 is reverse-biased and turned off, and the fifth diode D _o2 is forward-biased and turned on. In this working mode, the relevant electrical parameter relational formula is:

V _L1 =V _dc -V _C2 (12)

V _L2 = -V _C1 (13)

V _C3 =V _C1 +V _C2 (14)

V _pr ＝V _C3 , V _sc ＝nV _C3 (15)

According to the above analysis, the principle of volt-second balance is applied to the first inductance L ₁ and the second inductance L ₂ respectively, that is, the average value of the inductance voltage in one switching cycle is zero, and the time when all MOS transistors are turned on (that is, The duration of working mode 1) is DT _s , where D represents the corresponding through-duty cycle, and T _s represents the corresponding switching period, then the other three working modes are all non-through-state, and the duration is (1- D) T _s . Simultaneous formulas (1), (2), (4), (5) and (6) can obtain the expression of capacitor voltage in steady state as follows:

After passing through the high-frequency transformer and voltage doubler rectifier, the output voltage at both ends of the load resistor is:

Then the voltage gain G when the steady-state output of a kind of common ground type isolation high-gain quasi-Z source DC-DC converter of the present invention is:

As shown in Figure 3 a, it is the output voltage gain curve of the circuit of the present invention and the voltage gain curve comparison figure of the traditional isolation type cascaded quasi-Z source DC-DC converter; Among the figure, the red solid line represents the output voltage gain curve of the circuit of the present invention, The blue solid line represents the voltage gain curve of a traditional isolated cascaded quasi-Z source DC-DC converter. It can be seen from the figure that the circuit of the present invention can achieve a large output voltage gain G when the duty cycle D is not more than 0.25, which is obviously higher than the voltage gain of its traditional isolated cascaded quasi-Z source DC-DC converter. And the duty ratio D of the circuit of the present invention will not exceed 0.25.

Fig. 3b shows the simulation results of relevant variables in the circuit of the present invention by taking V _dc = 10V, duty cycle D = 0.2, and high frequency transformer transformation ratio n = 1 as an example. D=0.2, n=1, the corresponding output voltage gain G=10, capacitor voltage V _C1 =20V, V _C2 =30V, V _C3 =50V, after passing through the high-frequency transformer and voltage doubler rectifier, the output voltage V _o = 100V. In addition, the waveforms of the inductor current i _L1 and i _L2 and the waveform of the primary side input voltage V _pr of the high-frequency transformer are also shown in Fig. 3b.

In summary, the present invention proposes a common-ground isolated high-gain quasi-Z source DC-DC converter, compared with the traditional isolated cascaded quasi-Z source DC-DC converter, it reduces the cost of passive components. Quantity used, without additional power switch tube, simple structure, convenient control; continuous input power supply current; and under the same input voltage and duty cycle, it has higher output voltage gain, and there is no startup at the moment of circuit startup Inrush current, so the circuit of the present invention has a very wide application prospect.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (3)

1. The common-ground type isolated high-gain quasi-Z source converter for fuel cell and photovoltaic power generation is characterized in that it comprises a DC voltage source (V _dc ), composed of a first inductance (L ₁ ), a first capacitor (C ₁ ), The quasi-Z source impedance network composed of the first diode (D ₁ ), the second inductor (L ₂ ), and the second capacitor (C ₂ ), consists of the second diode (D ₂ ), the third diode ( D ₃ ), the third capacitor (C ₃ ), the third MOS transistor (S ₃ ) and the fourth MOS transistor (S ₄ ) constitute the quasi-switch boost unit, the first MOS transistor (S ₁ ), the second MOS transistor (S ₂ ), a high-frequency transformer T with a transformation ratio of 1:n, composed of the fourth capacitor (C _o1 ), the fifth capacitor (C _o2 ), the fourth diode (D _o1 ) and the fifth diode ( D _o2 ) composed of voltage doubler rectifier and load resistance R _L . 2. The common-ground type isolation high-gain quasi-Z source converter for fuel cells and photovoltaic power generation according to claim 1 is characterized in that: one end of the DC voltage source (V _dc ) is connected to the first inductance (L ₁ ) is connected to one end; the other end of the first inductance (L ₁ ) is respectively connected to the anode of the first diode (D ₁ ) and the cathode of the first capacitor (C ₁ ); the first diode ( The cathode of D ₁ ) is respectively connected to one end of the second inductance (L ₂ ) and the anode of the second capacitor (C ₂ ); the other end of the second inductance (L ₂ ) is respectively connected to the second diode (D ₂ ), the drain of the MOS transistor (S ₃ ) and the positive pole of the first capacitor (C ₁ ); the cathode of the second diode (D ₂ ) is connected to the positive pole of the third capacitor (C ₃ ) and The drain of the first MOS transistor (S ₁ ) is connected; the cathode of the third capacitor (C ₃ ) is respectively connected to the source of the fourth MOS transistor (S ₄ ) and the anode of the third diode (D ₃ ). ; The source of the first MOS transistor (S ₁ ) is respectively connected to the primary side positive input terminal of the high frequency transformer (T) and the drain of the second MOS transistor (S ₂ ); the third diode The cathode of (D3) is respectively connected to the source of the second MOS transistor (S2), the negative pole of the second capacitor (C2) and the negative pole of the input DC power supply (Vdc); the source of the third MOS transistor (S ₃ ) respectively connected to the drain of the fourth MOS transistor (S ₄ ) and the negative input end of the primary side of the high frequency transformer (T); the anode of the fourth capacitor (C _o1 ) is respectively connected to the fourth diode (D _o1 ) is connected to one end of the load (R _L ); the negative pole of the fourth capacitor (C _o1 ) is respectively connected to the positive terminal of the secondary side of the transformer (T) and the positive pole of the fifth capacitor (C _o2 ); The cathode of the fifth capacitor (C _o2 ) is respectively connected to the anode of the fifth diode (D _o2 ) and the other end of the load ( _RL ); the cathode of the fifth diode (D _o2 ) is respectively connected to the first The anodes of the four diodes (D _o1 ) are connected to the negative terminal of the secondary side of the transformer (T). 3. The common-ground type isolation high-gain quasi-Z source converter for fuel cell and photovoltaic power generation according to claim 1 is characterized in that: the voltage gain G during steady-state output is: V _o is the output voltage across the load resistor, V _{dc is the} DC voltage source voltage, and D is the duty cycle.