CN105610323A - Wide-range input type boost-buck three-level DC converter for photovoltaic power generation - Google Patents

Abstract

The invention discloses a wide-range input type boost-buck three-level DC converter for photovoltaic power generation. The wide-range input type boost-buck three-level DC converter comprises a three-level Buck DC converter, wherein the post stage of the three-level Buck DC converter is connected in parallel with a quasi-Z-source liquid crystal display (LCD) three-end impedance network, the quasi-Z-source LCD three-end impedance network comprises a first inductor, a second inductor, a first energy storage capacitor, a second energy storage capacitor and a first diode, and the post stage of the quasi-Z-source LCD three-end impedance network is connected in parallel with a three-level Boost DC converter. In the wide-range input type boost-buck three-level DC converter, the quasi-Z-source LCD three-end impedance network is utilized, the front stage of the quasi-Z-source LCD three-end impedance network is connected in parallel with the traditional three-level Buck DC converter and the post stage of the quasi-Z-source LCD three-end impedance network is connected in parallel with the traditional three-level Boost DC converter to form a wide-gain three-level Buck-Boost DC converter topology, the Boost capability of the topology is improved, and the voltage stress borne by an original power device is reduced by half.

Description

A kind of imported buck three-level DC converter of wide region for photovoltaic generation

Technical field

The present invention relates to DC converter, particularly imported buck three electricity of wide region for a kind of photovoltaic generationStraight flow converter.

Background technology

Along with the development of economic globalization, people's living standard improves gradually, to the demand of the energy also more and moreMany, but traditional energy, as the environmental pollution day by day exhausted and that use in a large number fossil fuel to bring of oil, coal is askedTopic, makes people explore harder use new energy technology. Therefore, various new forms of energy such as solar energy,Wind energy, tide energy, nuclear energy etc. are developed, and these new forms of energy all respectively have feature, but with solar energyFor noticeable because solar energy while using cleanliness without any pollution, reserves enrich renewable. Believe along with technologyConstantly further reduction and the active support of the government of progressive, cost, solar energy will obtain more extensively, moreUtilize efficiently.

Utilize photovoltaic array that the solar energy of absorption is converted into electric energy, then it is for people to use to access electrical network, thisElectricity mode is called parallel network power generation. Photovoltaic generating system composition comprise photovoltaic array, DC-DC converter,Inverter, wave filter etc. The output voltage of photovoltaic array and weather conditions are as relevant in illumination, temperature etc. larger,And excursion is wider. In order to ensure that in whole input voltage range, DC-DC converter all has more steadyFixed Voltage-output, practical application can adopt the DC-DC converter with ascending, descending compression functions.

Although traditional Buck-Boost converter has ascending, descending compression functions and simple in structure, if willIt is applied in grid-connected occasion, can have power device voltage stress height and voltage input and output polarityDifferent problems. Although the polarity of two-tube Buck-Boost converter voltage input and output is identical, meritThe voltage stress that rate device bears is large, and, owing to requiring topological boost capability stronger in grid-connected process,Two-tube Buck-Boost converter, is subject to the impact of circuit parasitic parameter, and the gain of its reality is narrower, and power is openedGuan Yi operates in extreme dutycycle state, causes peak current and lowers efficiency, and even causes the power switch can notThe risk of effectively turn-offing. Therefore need a kind of topology of the gain of boosting that can widen ascending, descending straightening current converter,Make it be applicable to grid-connected occasion.

Summary of the invention

The object of the invention is to overcome deficiency of the prior art, provide a kind of photovoltaic generation wide region importedBuck three-level DC converter, utilizes accurate Z source LCD tri-terminal impedance networks, and by its prime and traditionThree Level Buck DC-DC Converter parallel connections, rear class is in parallel with three traditional level Boost DC converters,Form a kind of wide gain three level Buck-Boost DC converter topologys, improved topological boost capability alsoThe voltage stress that original power device is born reduces half, makes it be more applicable for grid-connected occasion.

In order to solve the problems of the technologies described above, the invention provides the imported buck three of a kind of photovoltaic generation wide regionLevel DC converter, comprises three Level Buck DC-DC Converters, described three Level Buck DC-DC ConvertersRear class is parallel with accurate Z source LCD tri-terminal impedance networks, and described accurate Z source LCD tri-terminal impedance networks are by firstInductance, the second inductance, the first storage capacitor, the second storage capacitor, the first diode form; Described accurate ZLCD tri-terminal impedance network rear classes in source are parallel with three level Boost DC converters.

Operate under Boost pattern in topology, described the first inductance carries out energy storage by the first diode and releases can;Described the first storage capacitor carries out energy storage by the first diode.

Described three Level Buck DC-DC Converter primes connect solar cell; The left end of described the first inductance andThree Level Buck DC-DC Converters described in the negative polarity termination of the second storage capacitor; The right-hand member of described the first inductanceConnect respectively the negative polarity end of the first storage capacitor and the anode of the first diode, the negative electrode of described the first diodeConnect respectively the positive ends of the second storage capacitor and the left end of the second inductance, the right-hand member of described the second inductance andThe positive ends of one storage capacitor is connected; The negative polarity end of the right-hand member of described the second inductance and the second storage capacitorConnect described three level Boost DC converters.

Described photovoltaic generation is defeated under boost mode with the imported buck three-level DC converter of wide regionGo out voltage gain M₁For:

$M_1=\frac{U_0}{U_{PV}}=\frac{2m}{3-4m},0.5<m<0.75$

Described photovoltaic generation is defeated under decompression mode with the imported buck three-level DC converter of wide regionGo out voltage gain M₂For:

$M_2=\frac{U_0}{U_{PV}}=m,0<m<1$

Wherein, U_PVFor input voltage, U₀For output voltage, m is modulation degree.

The invention has the beneficial effects as follows: the new molded breadth of the present invention three level Buck-Boost DC converters that gainTopology, has not only retained the low advantage of traditional three-level DC converter power switch voltage stress, and has widenedVoltage gain while boosting. Modulation degree is trending towards at 0.75 o'clock, has in theory greatly gain, has avoidedCause the problem of the extreme dutycycle operation of power switch because increasing gain. In addition, this topology has also retained traditionThe dropping voltage characteristic of three level Buck circuit, therefore, is highly suitable for grid-connected occasion.

Brief description of the drawings

Fig. 1: the circuit diagram of the accurate Z of the present invention source LCD tri-terminal impedance networks;

Fig. 2: the circuit diagram of traditional three Level Buck DC-DC Converters;

Fig. 3: the circuit diagram of traditional three level Boost DC converters;

Fig. 4: the circuit signal of the imported buck three-level DC converter of wide region for photovoltaic generation of the present inventionFigure;

Fig. 5: the modulation strategy of topology when Boost operational mode of the present invention;

Fig. 6: the modulation strategy of topology when Buck operational mode of the present invention;

Fig. 7: the equivalence of topology operation circuit diagram when Buck operational mode of the present invention.

In accompanying drawing, the list of parts of each label representative is as follows:

U_PVFor solar cell output voltage, be the input voltage of converter;

U₀For the output voltage of converter;

L₁, L2 is respectively first, second energy storage inductor;

D₁、D₂、D₃、D₄、D₅Be respectively fly-wheel diode;

C₁、C₂For the input capacitance of converter; C₃、C₄For outlet side storage capacitor;

C₅、C₆For the output capacitance of converter;

Q₁、Q₂、Q₃、Q₄For the power switch of converter;

C_r1、C_r2Be respectively carrier phase shift;

M is modulation degree; T is carrier cycle;

d₁、d₂While being respectively boost mode, power switch Q₁Q₃、Q₂Q₄Dutycycle;

S₁S₂S₃S₄For power switch Q₁、Q₂、Q₃、Q₄On off state;

(1) be three Level Buck DC-DC Converters;

(2) accurate Z source LCD tri-terminal impedance networks;

(3) three level Boost DC converters.

Detailed description of the invention

Below in conjunction with accompanying drawing, the invention will be further described.

A kind of imported buck three-level DC converter of wide region for photovoltaic generation, comprises three level BuckDC converter, three level Boost DC converters and accurate Z source LCD tri-terminal impedance networks.

As shown in Figure 1, these accurate Z source LCD tri-terminal impedance networks are by the first inductance L₁, the second inductance L₂,One storage capacitor C₃, the second storage capacitor C₄, the first diode D₃Form; Operate in Boost mould in topologyUnder formula, described the first inductance carries out energy storage by the first diode and releases can; Described the first storage capacitor is by theOne diode carries out energy storage.

As shown in Figure 2, three traditional Level Buck DC-DC Converters, by the first input capacitance C₁, second is defeatedEnter capacitor C₂, 2 power switch (Q₁And Q₂), the second diode D₁With the 3rd diode D₂Composition. ShouldThe concrete structure of circuit is conventionally known to one of skill in the art, and the embodiment of the present invention is to concrete circuit connecting relationRepeat no more.

As shown in Figure 3, three traditional level Boost DC converters, by the first power switch Q₃, secondPower switch Q₄, 2 diode (D₄And D₅) and 2 output capacitance (C₅And C₆) composition. This circuitConcrete structure be conventionally known to one of skill in the art, the embodiment of the present invention is to concrete circuit connecting relation no longerRepeat.

As shown in Figure 4, this photovoltaic generation comprises with the imported buck three-level DC converter of wide region: tooSun can battery U_PV, three Level Buck DC-DC Converters, accurate Z source LCD tri-terminal impedance networks and three levelBoost DC converter. Solar cell U_PVTwo ends be connected in parallel three Level Buck DC-DC Converters (Solar cell U_PVPositive ends connect the first input capacitance C₁Positive ends, solar cell U_PVNegative polarity end connect the second input capacitance C₂Negative polarity end, follow-up circuit is connected to three level BuckThe inside of DC converter connects, and for conventionally known to one of skill in the art, the embodiment of the present invention does not repeat this);The two ends of the three Level Buck DC-DC Converters accurate Z source LCD tri-terminal impedance networks that are connected in parallel, accurate Z source LCDThe two ends of three terminal impedance networks three level Boost DC converters (i.e. the second diode D that is connected in parallel₁The moonThe utmost point connects the first inductance L₁Left end, the first inductance L₁Right-hand member connect respectively the first storage capacitor C₃Negative poleProperty end and the first diode D₃Anode, the first diode D₃Negative electrode connect respectively the second storage capacitor C₄Positive ends and the second inductance L₂Left end, the second inductance L₂Right-hand member and the first storage capacitor C₃Positive poleProperty end is connected, and is jointly connected to the first power switch Q₃Colelctor electrode, the second storage capacitor C₄Negative poleProperty end connects respectively the 3rd diode D₂Anode and the second power switch Q₄Emitter stage, follow-up circuit connectsConnecing is the inside connection of three level Boost DC converters, and for conventionally known to one of skill in the art, the present invention is realExecuting example does not repeat this).

, the output 1,2 of three Level Buck DC-DC Converters respectively with accurate Z source LCD tri-ends of Fig. 11,2 ends of impedance network are in parallel, and 2,3 ends of accurate Z source LCD tri-terminal impedance networks are respectively with Fig. 3'sThe input 2,3 of three level Boost DC converters is in parallel, solar cell U_PVWith three level BuckDC converter is in parallel, thereby forms wide gain three level Buck-Boost DC convertings as shown in Figure 4Device topology. And L₁＝L₂，C₁＝C₂、U_C1＝U_C2＝U_PV/2，C₅＝C₆、U_C5＝U_C6＝U_o/2(U_C1、U_C2Be the first input capacitance C₁, the second input capacitance C₂Voltage; U_C5、U_C6For output capacitance C₅、C₆'sVoltage).

Fig. 5 is that New Topological operates in the PWM modulation strategy under Boost pattern, and its wide voltage gain is as followsLiterary composition is described:

Be operated in continuous current mode at photovoltaic generation with the imported buck three-level DC converter of wide regionWhen stable state, all capacitance voltages suppose that its capacity is enough large, capacitance voltage all constant, capacitance current be zero.As topological on off state S₁S₂S₃S₄=1010 or 0101 o'clock, the first inductance L₁, the second inductance L₂All dischargeEnergy, the first storage capacitor C₃, the second storage capacitor C₄All stored energys. Mode (S₁S₂S₃S₄＝1010)By three voltage closed-loop path: U_PV-Q₁-L₁-D₃-L₂-Q₃-C₆-D₅-D₂-C₂-U_PV、L₂-C₃-D₃-L₂WithU_PV-Q₁-L₁-D₃-C₄-D₂-C₂-U_PV. Obtained by Kirchhoff's first law

$\left\{\begin{array}{c}\frac{U_{PV}}{2}+u_{L1\_dis}+u_{L2\_dis}=\frac{U_o}{2}\\ u_{L2\_dis}=U_{C3}\\ \frac{U_{PV}}{2}+u_{L1\_dis}=U_{C4}\end{array}\right.---\left(1\right)$

U in formula_{L1_dis}、u_{L2_dis}Be respectively the first inductance L₁, the second inductance L₂Voltage while all releasing energy,U_PV、U_oBe respectively input, output voltage, U_C3、U_C4Be respectively the first storage capacitor C₃, the second energy storageCapacitor C₄Voltage.

As topological on off state S₁S₂S₃S₄=1111 o'clock, the first inductance L₁, the second inductance L₂All storage power,The first storage capacitor C₃, the second storage capacitor C₄All release energy. There are two voltage closed-loop paths:U_PV-Q₁-L₁-C₃-Q₃-Q₄-Q₂-U_PVAnd C₄-L₂-Q₃-Q₄-C₄. Obtained by Kirchhoff's first law

$\left\{\begin{array}{c}{U}_{PV}+U_{C3}=u_{L1\_ch}\\ U_{C4}=u_{L2\_ch}\end{array}\right.---\left(2\right)$

U in formula_{L1_ch}、u_{L2_ch}Be respectively the first inductance L₁, the second inductance L₂Voltage when equal storage power.

The time cycle of having supposed a charge and discharge process is T, by the modulation strategy of Fig. 5, when modulation degree isWhen m, in one-period, the first inductance L₁, the second inductance L₂The time that discharges and recharges be respectively

$\left\{\begin{array}{c}{T}_{ch}=(2m-1)*T\\ T_{dis}=(2-2m)*T\end{array}\right.---\left(3\right)$

According to weber balance, inductance stores and discharges power consumption and equates in a switch periods, right respectivelyThe first inductance L₁, the second inductance L₂Row are write equation

$\left\{\begin{array}{c}{u}_{L1\_dis}*T_{dis}=u_{L1\_ch}*T_{ch}\\ u_{L2\_dis}*T_{dis}=u_{L2\_ch}*T_{ch}\end{array}\right.---\left(4\right)$

Formula (1), (2), (3) are brought in formula (4) and obtained

$\left\{\begin{array}{c}(U_{C4}-\frac{U_{PV}}{2})*(2-2m)=(U_{PV}+U_{C3})*(2m-1)\\ U_{C3}*(2-2m)=U_{C4}*(2m-1)\end{array}\right.---\left(5\right)$

Formula (5) is arranged

$\left\{\begin{array}{c}{U}_{C3}=\frac{m(2m-1)}{3-4m}{U}_{PV}\\ U_{C4}=\frac{m(2-2m)}{3-4m}{U}_{PV}\end{array}\right.---\left(6\right)$

When in mode S₁S₂S₃S₄=1010 or 0101, now exist loop by U_C3、U_C4、U_C6OrU_C3、U_C4、U_C5The loop forming. If ignore the loss on loop, by Kirchhoff's first law, three electricityThe relation of flat circuit output voltage and storage capacitor voltage obtains

$U_{C3}+U_{C4}=U_{C5}=U_{C6}=\frac{Uo}{2}---\left(7\right)$

When in mode S₁S₂S₃S₄=1111, diode D now₄、D₅In the state of reverse cut-off, defeatedGoing out voltage is hold mode, in the permanent establishment of whole charge and discharge process Chinese style (7).

In whole charge and discharge process, the first storage capacitor C₃, the second storage capacitor C₄The voltage bearingStress sum is 0.5 times of output voltage, the first storage capacitor C₃, the second storage capacitor C₄Voltage stressAll be in lower state.

Formula (6) is brought into must the imported buck three level DC conversion of photovoltaic generation wide region in formula (7)Device is output voltage gain M under boost mode₁For

$M_1=\frac{2m}{3-4m}---\left(8\right)$

In above formula, m is that modulation degree is also power switch Q₁、Q₂、Q₃、Q₄Dutycycle, 0.5 < m < 0.75.

Fig. 6 is that New Topological operates in the PWM modulation strategy under Buck pattern, and its wide voltage gain is as followsLiterary composition is described:

Be operated in continuous current mode at photovoltaic generation with the imported buck three-level DC converter of wide regionWhen stable state, due to the first power switch Q₃, the second power switch Q₄All in off state, the first diodeD₃In conducting state always, New Topological is equivalent to traditional three Level Buck DC-DC Converters, its equivalent electricRoad figure is shown in Fig. 7, and the running status under this state is conventionally known to one of skill in the art, the embodiment of the present inventionThis is not repeated.

Photovoltaic generation is operated in defeated under decompression mode with the imported buck three-level DC converter of wide regionGo out voltage gain M₂For

M₂＝m(9)

In above formula, m is that modulation degree is also power switch Q₁、Q₂Dutycycle, now Q₃、Q₄In turn-offing shapeState, 0 < m < 1.

At a carrier cycle, photovoltaic generation boosts with the imported buck three-level DC converter of wide region(Boost) three on off states of pattern experience, step-down (Buck) pattern also experiences three on off states, byBe traditional three level Buck circuit in step-down (Buck) equivalent topologies, below only to (Boost) pattern of boostingDescribe:

(1) on off state S₁S₂S₃S₄=1111 o'clock, the first inductance L₁, the second inductance L₂All stored energys,The first storage capacitor C₃, the second storage capacitor C₄All release energy, the imported lifting of wide region for photovoltaic generationPress three-level DC converter to have two voltage closed-loop paths:

Closed-loop path 1-a:U_PV-Q₁-L₁-C₃-Q₃-Q₄-Q₂-U_PV, now, solar cell U_PVWith firstStorage capacitor C₃To the first inductance L₁Storage power;

Closed-loop path 1-b:L₂-Q₃-Q₄-C₄-L₂, now, the second storage capacitor C₄To the second inductance L₂StoreEnergy.

In one-period, the total time t of this on off state experience₁₁₁₁＝[d₁-(1-d₂)]T。

(2) on off state S₁S₂S₃S₄=1010 o'clock, the first inductance L₁, the second inductance L₂All release energy,The first storage capacitor C₃, the second storage capacitor C₄All stored energys, the imported lifting of wide region for photovoltaic generationPress three-level DC converter to have three voltage closed-loop paths:

Closed-loop path 2-a:U_PV-Q₁-L₁-D₃-L₂-Q₃-C₆-D₅-D₂-C₂-U_PV, now, solar cell U_PVWith the first inductance L₁, the second inductance L₂To the second input capacitance C₂, output capacitance C₆Charging, and to load(inverter dc bus side) energy supply, now the first input capacitance C₁, output capacitance C₅Electric discharge;

Closed-loop path 2-b:L₂-C₃-D₃-L₂, now, the second inductance L₂By the first diode D₃To firstStorage capacitor C₃Charge;

Closed-loop path 2-c:U_PV-Q₁-L₁-D₃-C₄-D₂-C₂-U_PV, now, solar cell U_PVWith the first electricitySense L₁By the first diode D₃To the second input capacitance C₂, the second storage capacitor C₄Charge, nowThe first input capacitance C₁Electric discharge.

In one-period, the total time t of this on off state experience₁₀₁₀＝(1-d₂)T。

(3) on off state S₁S₂S₃S₄=0101 o'clock, the first inductance L₁, the second inductance L₂All release energy,The first input capacitance C₁, the second input capacitance C₂All stored energys, the imported lifting of wide region for photovoltaic generationPress three-level DC converter to have three voltage closed-loop paths:

Closed-loop path 3-a:U_PV-C₁-D₁-L₁-D₃-L₂-D₄-C₅-Q₄-Q₂-U_PV, now, solar cell U_PVWith the first inductance L₁, the second inductance L₂To the first input capacitance C₁, output capacitance C₅Charging, and to load(inverter dc bus side) energy supply, now the second input capacitance C₂, output capacitance C₆Electric discharge;

Closed-loop path 3-b:L₂-C₃-D₃-L₂, now, the second inductance L₂By the first diode D₃To firstStorage capacitor C₃Charge;

Closed-loop path 3-c:U_PV-C₁-D₁-L₁-D₃-C₄-Q₂-U_PV, now, solar cell U_PVWith firstInductance L₁By the first diode D₃To the first input capacitance C₁, the second storage capacitor C₄Charge, thisTime the second input capacitance C₂Electric discharge.

In one-period, the total time t of this on off state experience₀₁₀₁＝(1-d₁)T。

To sum up state three kinds of on off states, S₁S₂S₃S₄=1111 o'clock, solar cell U_PVWith the first storage capacitorC₃It is the first inductance L₁Storage power, the second storage capacitor C₄It is the second inductance L₂Storage power;S₁S₂S₃S₄=1010 or 0101 o'clock, the second inductance L₂Be the first storage capacitor C₃Stored energy, solar-electricityPond U_PVWith the first inductance L₁Be the second storage capacitor C₄Stored energy, simultaneously solar cell U_PVWith firstInductance L₁, the second inductance L₂Remaining energy provides for outlet side.

Therefore, transmit in a manner described by the energy of photovoltaic array, inductance, electric capacity, reached and reduced deviceSwitch stress, widen the effect of Buck-Boost converter boost ability, be highly suitable for grid-connectedBuck occasion.

Claims (5)

1. the imported buck three-level DC converter of wide region for photovoltaic generation, comprise three Level Buck DC-DC Converters, it is characterized in that, described three Level Buck DC-DC Converter rear classes are parallel with accurate Z source LCD tri-terminal impedance networks, and described accurate Z source LCD tri-terminal impedance networks are made up of the first inductance, the second inductance, the first storage capacitor, the second storage capacitor, the first diode; Described accurate Z source LCD tri-terminal impedance network rear classes are parallel with three level Boost DC converters.

2. the imported buck three-level DC converter of wide region for photovoltaic generation according to claim 1, is characterized in that, operates under Boost pattern in topology, and described the first inductance carries out energy storage by the first diode and releases can; Described the first storage capacitor carries out energy storage by the first diode.

3. the imported buck three-level DC converter of wide region for photovoltaic generation according to claim 1, is characterized in that, described three Level Buck DC-DC Converter primes connect solar cell; Three Level Buck DC-DC Converters described in the negative polarity termination of the left end of described the first inductance and the second storage capacitor; The right-hand member of described the first inductance connects respectively the negative polarity end of the first storage capacitor and the anode of the first diode, the negative electrode of described the first diode connects respectively the positive ends of the second storage capacitor and the left end of the second inductance, and the right-hand member of described the second inductance is connected with the positive ends of the first storage capacitor; Three level Boost DC converters described in the negative polarity termination of the right-hand member of described the second inductance and the second storage capacitor.

4. the imported buck three-level DC converter of wide region for photovoltaic generation according to claim 1, is characterized in that, described photovoltaic generation is the output voltage gain M under boost mode with the imported buck three-level DC converter of wide region₁For:

Wherein, U_PVFor input voltage, U₀For output voltage, m is modulation degree.

5. the imported buck three-level DC converter of wide region for photovoltaic generation according to claim 1, is characterized in that, described photovoltaic generation is the output voltage gain M under decompression mode with the imported buck three-level DC converter of wide region₂For:

。