CN114583951A

CN114583951A - High-gain converter for photovoltaic direct current module and control method thereof

Info

Publication number: CN114583951A
Application number: CN202210237775.5A
Authority: CN
Inventors: 秦岭; 许兴; 饶家齐; 刘宇涵; 周磊; 段冰莹; 钱天泓; 田民; 钱娇
Original assignee: Nantong University
Current assignee: Nantong University
Priority date: 2022-03-11
Filing date: 2022-03-11
Publication date: 2022-06-03

Abstract

The invention belongs to the technical field of DC-DC boost converters, and discloses a high-gain converter for a photovoltaic direct current module and a control method thereof, wherein the converter can change the number of boost units in the boost module according to the actual voltage range of a photovoltaic cell panel and a direct current bus, thereby flexibly changing the boost capability and having strong expandability; only two switching tubes form a half-bridge structure, a low-cost bootstrap driver can be adopted, and the structure is simple and easy to realize; the inductance values of the rear-stage inductor and the boosting inductors in all the boosting units are small, so that the size is small, and the power density is high; the voltage stress of all power tubes is the same and is far smaller than the output voltage, and low-voltage-resistant devices can be adopted, so that the system cost and the power loss are reduced; all power tubes realize soft switching, so that the system efficiency is higher; the input and the output are connected to the same ground, so that the sampling circuit is simple in structure, and the photovoltaic direct current module can pass the EMI related test requirements more easily.

Description

High-gain converter for photovoltaic direct current module and control method thereof

Technical Field

The invention belongs to the technical field of DC-DC boost converters, and particularly relates to a high-gain converter for a photovoltaic direct-current module and a control method thereof.

Background

The photovoltaic direct current module can effectively solve the problem that the solar energy utilization rate of the string type photovoltaic power generation system is low under the condition of partial shadow shielding. The output voltage of the photovoltaic cell panel is low, the variation range is wide, and the power generation efficiency or the service life is closely related to the output current ripple rate, so that the photovoltaic direct current module needs to adopt a high-gain converter with continuous input current as a main circuit and then can be integrated into a public power grid through a traditional voltage source type grid-connected inverter. High gain converters can be classified into two types, including a transformer (including coupled inductors) type and a transformer-less type. Compared with the former, the transformerless high-gain converter has the advantages of small volume, low cost, high efficiency and the like without a high-frequency transformer. Moreover, the current leakage current suppression strategy of the non-isolated grid-connected inverter is mature day by day, and the electrical safety problem is well solved. Therefore, it is more advantageous to use the transformerless high-gain converter as the main circuit of the photovoltaic dc module.

Various scholars introduce Boost networks such as a switch inductor, a switch capacitor, a quasi-Z source or a Boost and the like into a traditional Boost converter respectively to obtain various transformer-free high-gain Boost schemes. Most of the schemes can realize single-stage conversion of energy, the conversion efficiency is high, but the voltage gain is usually not more than twice of that of the traditional Boost converter. To this end, the scholars further propose high gain schemes based on boost network expansion. Although the scheme of adopting the extended boost network can obviously improve the boost capability, the volume and the weight of the converter are obviously increased due to the increase of the number of the energy storage elements. The switching frequency of the converter is improved, the volume and the weight of the energy storage element can be effectively reduced, the power density is improved, the switching loss of the power tube is also increased rapidly, and the conversion efficiency is reduced seriously. The introduction of soft switching technology can effectively solve these problems. To this end, researchers have further proposed many ZVS high-gain converters based on boost network extensions. However, these topologies have the following problems in common: (1) the number of diodes is large, and the structure is complex; (2) part of power tubes still work in a hard switching state, so that the efficiency is difficult to further improve; (3) the power tube has higher voltage stress, and a high-voltage-resistant semiconductor device is required, so that the on-state loss is larger, and the cost is higher; (4) there is a loss of duty cycle.

Disclosure of Invention

In view of this, the present invention provides a high-gain converter for a photovoltaic dc module and a control method thereof, which have the advantages of low Voltage stress, small number of power tubes, Zero Voltage Switching (ZVS) of Switching tubes, Zero current turn-off of diodes, high conversion efficiency, no duty cycle loss, simple control, low cost, and the like, and can flexibly adjust the number of boost units in a boost module according to the boost capability requirements under different application environments to change the Voltage gain of the converter.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

a high-gain converter for a photovoltaic direct current module comprises a basic module and a boosting module;

the boost module includes n boost units, and each boost unit includes: boost diode D_aFilter capacitor C_aAnd an auxiliary capacitor C_bBoost inductor L_a；

The internal connection mode of the boosting unit is as follows: the boost diode D_aAnd the boost inductor L_aFirst terminal of, said filter capacitor C_aThe positive electrodes of the two electrodes are connected; the boost inductor L_aAnd the second terminal of the auxiliary capacitor C_bThe positive electrodes of the two electrodes are connected;

the boost pressureThe connection mode between the units is as follows: boost diode D in the latter boost unit_aAnode and auxiliary capacitor C in the previous booster unit_bPositive pole of (1), boost inductor L in the previous boost unit_aAre connected with each other; auxiliary capacitor C of n boosting units_bThe negative electrode of (a) is uniformly crossed with the point b; the filter capacitors C of the n boosting units_aThe negative electrode of (a) is crossed with the point a;

the base module includes: photovoltaic cell panel U_inAn input filter capacitor C_inAn input inductor L_inA rear stage inductor L_mA first switch tube S₁A second switch tube S₂A first capacitor C₁A second capacitor C₂And an output diode D_oAn output filter capacitor C_oA load R;

the connection mode of the basic module and the boosting module is as follows: the photovoltaic cell panel U_inAnd the input inductance L_inFirst terminal of, said input filter capacitance C_inThe positive electrodes of the two electrodes are connected; the input inductance L_inAnd the second end of the first switch tube S₁Drain electrode of (1), the second switching tube S₂Source electrode of, the second capacitor C₂The negative pole of the voltage boosting module is connected with the point b of the voltage boosting module; the second switch tube S₂And the post-stage inductor L_mFirst terminal of, said first capacitor C₁The positive electrodes of the two electrodes are connected; the back stage inductor L_mAnd the second terminal of the second capacitor C₂Positive pole of (2), boost diode D of the first boost unit in the boost module_aThe anodes of the anode groups are connected; the output diode D_oAnd the boost inductance L of the last boost unit in the boost module_aAnd an auxiliary capacitor C_bThe positive electrodes of the two electrodes are connected; the output diode D_oAnd the output filter capacitor C_oThe positive electrode of (a) is connected with the first end of the load R; a second terminal of the load R and the output filter capacitor C_oThe negative pole of (1), the point a of the boosting module, the first switch tube S₁Source electrode of, said input filter capacitor C_inThe negative electrode of,The first capacitor C₁And the photovoltaic cell panel U_inThe negative electrodes are connected;

the input inductance L_inThe inductance value of (a) satisfies:

in the above formula, D_eff＝D+T_d/T_s，D_effFor an effective duty cycle, D is a first switching tube S₁Duty cycle of the drive signal of (1), T_dIs a first switch tube S₁And a second switch tube S₂With a dead time of the drive signal, T_sIs a first switch tube S₁And a second switch tube S₂Period of the drive signal of (1), L_inFor input of an inductor L_inInductance value of, Δ I_LinIs an input inductance L_inCurrent peak-to-peak value of, U_inFor the photovoltaic cell panel voltage, f_sDelta% is the input inductance L for the switching frequency_inMaximum permissible current ripple and input inductance L_inA percentage of maximum average current; p is_o,maxIs the maximum output power;

the back stage inductor L_mAnd a boost inductor L in the boost unit_aThe inductance value of (a) satisfies:

in the above formula, L_mIs a post-stage inductor L_mInductance value of, L_aIs a boost inductor L_aInductance value of, U_oIs the output voltage; n is the number of booster cells.

The invention also provides a control method of the high-gain converter for the photovoltaic direct-current module, which specifically comprises the following steps:

sampling the voltage and current of the photovoltaic cell panel to obtain a voltage sampling value u of the photovoltaic cell panel_in,fCurrent sample value i_in,fGenerating photovoltaic cell panel electricity through MPPT calculationPressure reference value u_in,refSampling the voltage u of the photovoltaic cell panel_in,fWith the voltage reference value u of the photovoltaic cell panel_in,refComparing to obtain an error signal u_in,f-u_in,ref；

The error signal is sent to a voltage controller to obtain an adjusting signal u_r；

The regulating signal u_rWith a unipolar triangular carrier u_cCrossing to generate a first switch tube S₁PWM drive signal u_gs1；

The first switch tube S₁PWM drive signal u_gs1Negation is carried out to obtain a second switch tube S₂PWM drive signal u_gs2。

Further, the ideal voltage gain of the high-gain converter for the photovoltaic DC module is [1+ (1+ n) D_eff]/(1-D_eff) By adjusting the number n of the boosting units, the voltage gain can be flexibly adjusted to enable the boosting units to work under a proper duty ratio D so as to meet boosting requirements on different occasions.

Further, in the high-gain converter for the photovoltaic dc module, the first switch tube S₁A second switch tube S₂And an output diode D_oAnd a boost diode D in the boost unit_aAll bear the same voltage stress and are [ (n +1) U_in+U_o]V (n +2), much smaller than the output voltage U_o。

The invention also provides a photovoltaic direct current module which comprises the high-gain converter for the photovoltaic direct current module.

Compared with the prior art, the high-gain converter for the photovoltaic direct-current module can change the number of the boosting units in the boosting module according to the actual voltage ranges of the photovoltaic cell panel and the direct-current bus, so that the boosting capacity is flexibly changed, and the high-gain converter has strong expandability; only two switching tubes are arranged, and the two switching tubes form a half-bridge structure, so that various bootstrap drivers with low price and mature technology can be adopted, and the structure is simple and easy to realize; and a back-stage inductor L_mAnd all boost unitsVoltage boosting inductor L in element_aThe inductance value of the photovoltaic direct current module is small, so that the photovoltaic direct current module is small in size and high in power density; the voltage stress of all the switching tubes and the voltage stress of all the diodes are the same and are far smaller than the output voltage, and low-voltage-resistant devices can be adopted, so that the system cost and the power loss are reduced; ZVS switching-on is realized for all the switching tubes, all the diodes can be approximately naturally turned off under the heavy load condition, and can be completely naturally turned off under the light load condition, so that the system efficiency of the photovoltaic direct current module is higher; the input and the output are connected to the same ground, so that the sampling circuit is simple in structure, and the photovoltaic direct current module can pass the EMI related test requirements more easily.

Drawings

Fig. 1 is a schematic circuit diagram of a high-gain converter for a photovoltaic dc module according to the present invention;

FIG. 2 is a control block diagram of a high gain converter for a photovoltaic DC module provided by the present invention;

fig. 3 is a schematic circuit structure diagram of an embodiment of a high-gain converter for a photovoltaic dc module according to the present invention;

FIG. 4 is an equivalent circuit diagram of 4 operating modes of the converter shown in FIG. 3 during a switching cycle;

FIG. 5 shows the converter of FIG. 3 during a switching period T_sThe main working waveform diagram in the inner part;

FIG. 6 is an average current equivalent circuit diagram of the converter of FIG. 3;

FIG. 7 is a schematic diagram of a circuit configuration of the converter shown in FIG. 3 including 1 boost unit;

FIG. 8 is an experimental waveform of steady state characteristics of the converter shown in FIG. 3 with 1 boost unit;

fig. 9 is a simulated waveform diagram of load switching when the converter shown in fig. 3 includes 1 boost unit.

Detailed Description

The technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, the present invention provides a high gain converter for a photovoltaic dc module, comprising a base module and a boost module; the boost module includes n boost units, and each boost unit includes: boost diode D_aFilter capacitor C_aAnd an auxiliary capacitor C_bBoost inductor L_a(ii) a The internal connection mode of the boosting unit is as follows: boost diode D_aCathode and boost inductor L_aFirst terminal of (1), filter capacitor C_aThe positive electrodes of the two electrodes are connected; boost inductor L_aSecond terminal and auxiliary capacitor C_bThe positive electrodes of the two electrodes are connected;

the connection mode between the boosting units is as follows: boost diode D in the latter boost unit_aAnode and auxiliary capacitor C in the previous booster unit_bPositive pole of (1), boost inductor L in the previous boost unit_aAre connected with each other; auxiliary capacitor C of n boosting units_bAll the negative electrodes are intersected at a point b; the filter capacitors C of the n boosting units_aThe negative electrode of (a) is crossed with the point a;

the connection mode of the basic module and the boosting module is as follows: photovoltaic cell panel U_inPositive pole and input inductance L_inFirst terminal, input filter capacitor C_inThe positive electrodes of the two electrodes are connected; input inductance L_inSecond terminal and first switch tube S₁Drain electrode of the first switching tube S₂Source electrode of the first capacitor C₂The negative pole of the voltage boosting module is connected with the point b of the voltage boosting module; a second switch tube S₂Drain electrode of and post-stage inductor L_mFirst terminal of (1), first capacitor C₁The positive electrodes of the two electrodes are connected; rear stageInductor L_mSecond terminal and second capacitor C₂Anode of the boosting module, and the boosting diode D of the first boosting unit in the boosting module_aThe anodes of the anode groups are connected; output diode D_oAnd the boost inductor L of the last boost unit in the boost module_aSecond terminal and auxiliary capacitance C_bThe positive electrodes of the two electrodes are connected; output diode D_oCathode and output filter capacitor C_oThe anode of the load R is connected with the first end of the load R; the second end of the load R and the output filter capacitor C_oNegative pole, a point of the boost module, the first switch tube S₁Source electrode, input filter capacitor C_inNegative electrode of (1), first capacitor C₁Negative pole and photovoltaic cell board U_inAre connected with each other.

As shown in fig. 2, the control method of the high-gain converter for the photovoltaic dc module includes: to photovoltaic cell panel U_inThe voltage and the current are sampled to obtain a voltage sampling value u of the photovoltaic cell panel_in,fCurrent sample value i_in,fAnd generating a photovoltaic cell panel voltage reference value u through MPPT calculation_in,refSampling the voltage of the photovoltaic cell panel u_in,fWith reference value u of the voltage of the photovoltaic cell panel_in,refComparing to obtain an error signal u_in,f-u_in,ref(ii) a Error signal u_in,f-u_in,refSending to a voltage controller to obtain a regulation signal u_r(ii) a Regulating signal u_rWith a unipolar triangular carrier u_cCrossing to generate a first switch tube S₁PWM drive signal u_gs1(ii) a A first switch tube S₁PWM drive signal u_gs1Negation is carried out to obtain a second switch tube S₂PWM drive signal u_gs2。

As shown in fig. 3, an embodiment of the present invention provides a circuit structure diagram of an embodied high-gain converter, where the converter includes: 1 basic module and 1 boosting module; wherein: the boosting module comprises n boosting units; the components and the internal connection forms of the n boosting units are the same, and the ith boosting unit is taken as an example for explanation and comprises the following components: ith boost diode D_aiIth filter capacitor C_aiThe ith auxiliary capacitor C_biIth boost inductorL_aiWherein the ith boost diode D_aiCathode and ith boost inductor L_aiFirst terminal of (1), ith filter capacitor C_aiIs connected with the positive pole of the ith boost inductor L_aiSecond terminal and ith auxiliary capacitor C_biThe positive electrodes of the two electrodes are connected;

the connection form between the individual booster cells is as follows, 1<i is not more than n: boost diode D in ith boost unit_aiAnd the auxiliary capacitor C in the (i-1) th booster unit_b(i-1)Positive electrode of (1) th boosting unit, and boosting inductor L in (i-1) th boosting unit_a(i-1)Are connected with each other; the cathodes of the auxiliary capacitors of the n boosting units in the boosting module are intersected with a point b; the cathodes of the filter capacitors of n boosting units in the boosting module are intersected with a point a;

the connection mode of the basic module and the boosting module is as follows: photovoltaic cell panel U_inPositive pole and input inductance L_inFirst terminal, input filter capacitor C_inThe positive electrodes of the two electrodes are connected; input inductance L_inSecond terminal and first switch tube S₁Drain electrode of the first switching tube S₂Source electrode of the first capacitor C₂The negative pole of the voltage boosting module is connected with the point b of the voltage boosting module; a second switch tube S₂Drain electrode of (2) and back-stage inductor L_mFirst terminal, first capacitor C₁The positive electrodes of the two electrodes are connected; rear stage inductance L_mSecond terminal and second capacitor C₂Anode of the boosting module, and the boosting diode D of the 1 st boosting unit in the boosting module_a1The anodes of the anode groups are connected; output diode D_oAnd the boosting inductance L of the nth boosting unit in the boosting module_anSecond terminal and filter capacitor C_anThe positive electrodes of the two electrodes are connected; output diode D_oCathode and output filter capacitor C_oThe anode of the load R is connected with the first end of the load R; second terminal and output of load ROutput filter capacitor C_oNegative pole, a point of the boost module, the first switch tube S₁Source electrode, input filter capacitor C_inNegative electrode of (1), first capacitor C₁Negative pole and photovoltaic cell board U_inAre connected with each other.

The operation of the high gain converter shown in fig. 3 is explained below. To simplify the analysis, the following assumptions were made: first switch tube S₁A second switch tube S₂And an output diode D_oA first capacitor C₁A second capacitor C₂Output filter capacitor C_oAn input inductor L_inA rear stage inductor L_mBoosting inductors, boosting diodes, filter capacitors and auxiliary capacitors in all the boosting units are ideal devices; a first capacitor C₁A second capacitor C₂An output filter capacitor C_oThe filter capacitors and the auxiliary capacitors in all the boosting units are large enough, and voltage ripples can be ignored; photovoltaic cell panel U_inThe negative end is a zero potential reference point; first switch tube S₁And a second switch tube S₂With a dead time of T of the drive signal_d(ii) a Input inductance L_inCurrent i of_LinUnidirectional, continuous flow, back-stage inductor L_mAnd the current of the boosting inductor in all the boosting units flows in two directions, and the current i is synthesized_LTrough i of_L,valSatisfies the following conditions: i_L,val|>|i_Lin,val|，i_Lin,valFor inputting an inductive current i_LinValley value of, resulting current i_LIs a post-stage inductor L_mThe sum of the currents of the boost inductors in all the booster cells, i_L＝i_Lm+i_La1……i_L(n-1)+i_Lan。

Based on the above assumptions, after entering a steady state, the working process of the high-gain converter for the photovoltaic dc module according to the present invention in one switching cycle can be divided into 4 modes. The equivalent circuits of the modes are shown in fig. 4(a) to 4 (d). The main waveforms during one switching cycle are shown in fig. 5.

The following are distinguished:

t₀before the moment, the first switch tube S₁Body diode ofThe tube has already conducted freewheeling.

(1) Mode 1, t₀～t₁Stage (2): (the equivalent circuit is shown in FIG. 4 (a))

t₀At the moment, the first switch tube S is switched on by zero voltage₁Its body diode is naturally turned off. In this mode, the second switch tube S₂Boost diode and output diode D in all boost units_oAre all reverse biased; input inductance L_inAnd a rear stage inductor L_mThe boosting inductors in all the boosting units bear forward voltage; input of inductor current i_LinLinearly increasing, post-stage inductance L_mAnd the current of the boosting inductor in all the boosting units is linearly decreased in the reverse direction and then linearly increased in the forward direction. At this time, there are:

wherein L is_inFor input of an inductor L_inInductance value of, L_mAnd L_aiAre respectively a rear stage inductor L_mAnd boost inductor L in the ith boost unit_aiThe inductance value of (a); i.e. i_LinFor input of an inductor L_inCurrent value of i_LmAnd i_LaiRespectively, a rear stage inductor L_mAnd boost inductor L in the ith boost unit_aiThe current value of (a); u shape_C1And U_C2Are respectively a first capacitor C₁And a second capacitor C₂The terminal voltage of (a); u shape_Cai、U_CbiAre respectively an ith filter capacitor C_aiThe ith auxiliary capacitor C_bi1,2, … …, n.

(2) Mode 2, t₁～t₂Stage (2): (the equivalent circuit is shown in FIG. 4 (b))

t₁At any moment, the first switch tube S is turned off₁Modality 2 begins. In the first switch tube S₁At the moment of turn-off, the input inductance L_inA rear stage inductor L_mAnd the current of the boost inductor in all the boost units flows into the node m to force the second switch tube S₂The body diode of (1) conducts freewheeling; at the same time, step up two in all the step-up unitsPolar tube and output diode D_oAre all forward biased; input inductance L_inA rear stage inductor L_mAnd all the boosting inductors in the boosting units bear reverse voltage, and the current of the boosting inductors is linearly decreased in the forward direction. At this time, there are:

(3) mode 3, t₂～t₃Stage (2): (the equivalent circuit is shown in FIG. 4 (c))

t₂At the moment, the second switch tube S is switched on by zero voltage₂With its body diode naturally turned off, mode 3 begins. In this mode, the inductor current i is input_LinContinuously decreases in a forward linear way, and then the inductor L at the later stage_mAnd the current of the boosting inductor in all the boosting units is linearly increased in the reverse direction after being reduced to zero in the forward direction. The current expression is the same as that of the formula (2).

(4) Mode 4, t₃～t₄: (the equivalent circuit is shown in FIG. 4 (d))

t₃At the moment, the second switch tube S is turned off₂Modality 4 begins. Input of inductor current i_LinAn inflow node m; rear stage inductance L_mAnd the current of the boost inductor in all the boost units flows out of the node m and synthesizes a current i_LSatisfies the following conditions: i_L|>|i_LinI, so the first switch tube S₁The body diode of (1) conducts a freewheeling current. Input inductance L_inAnd a rear stage inductor L_mAnd the current expression of the boost inductor in all the booster cells is similar to that in mode 1. t is t₄At the moment, the first switch tube S is switched on by zero voltage₁And entering the next switching period.

Based on the above operating principle, the steady-state characteristics of the converter of the present invention are analyzed below.

According to the input inductance L_inA rear stage inductor L_mAnd the ith boost inductor L_aiThe voltage-second balance of (a) can be obtained:

D_eff＝D+T_d/T_s (4)

wherein D is_effFor an effective duty cycle, D is a first switching tube S₁Duty cycle of the drive signal of (1), T_dIs a first switch tube S₁And a second switch tube S₂The dead time of the drive signal, T_sIs a first switch tube S₁And a second switch tube S₂The period of the drive signal.

Further, from fig. 4(c), it can be obtained:

from equations (3) - (5), the voltage gain of the high gain converter for photovoltaic dc modules presented herein can be derived when it contains n boost units:

disregarding losses, there are:

U_inI_in＝U_oI_o (7)

in the formula of U_inFor photovoltaic cell panel voltage, U_oIs the average value of the output voltage, I_inAnd I_oThe average values of the input current and the output current are respectively, and n is the number of the boosting units.

From formulae (6) and (7), it is possible:

as can be seen from the modal analysis, the first switch tube S of the high-gain converter for the photovoltaic DC module provided by the invention₁A second switch tube S₂Ith boost diode D_aiAnd an output diode D_oThe voltage stress of (a) is:

in the above formula, U_S1Is a first switch tube S₁Withstand voltage stress, U_S2Is a second switch tube S₂Withstand voltage stress, U_DaiFor the ith boost diode D_aiWithstand voltage stress, U_DoTo output a diode D_oThe applied voltage stress, i ═ 1,2, … …, n.

A first capacitor C₁A second capacitor C₂A second module capacitor C_biFirst module capacitor C_aiAn output filter capacitor C_oThe voltage stress of (a) is:

U_Co＝U_o (14)

in the formula of U_CoFor outputting filter capacitors C_oThe terminal voltage of (c).

It can be seen that the first switch tube S of the high-gain converter for the photovoltaic dc module according to the present invention₁A second switch tube S₂And an output diode D_oAnd ith boost diode D_aiHas the same voltage stress and is far smaller than the output voltage. In addition, the voltage stress is continuously reduced along with the increase of the expansion number of the boosting unitsIs small. Therefore, a low voltage rated MOS transistor with a lower on-resistance can be selected.

After entering a steady state, the first capacitor C₁A second capacitor C₂The ith auxiliary capacitor C_biIth filter capacitor C_aiOutput filter capacitor C_oIs zero, thereby obtaining an average current equivalent circuit for a high gain converter of a photovoltaic dc module, as can be taken from fig. 6, the input inductance L_inA rear stage inductor L_mAnd the ith boost inductor L_aiThe average current of (d) is:

ith boost diode D_aiAnd an output diode D_oThe average current of (d) is:

I_Dai＝I_Do＝I_o (16)

it can be seen that: rear stage inductance L_mIth boost inductor L_aiIth boost diode D_aiAnd an output diode D_oAre all equal to the average value I of the output current_oRegardless of the number of booster cells, i ═ 1,2, … …, n.

Furthermore, the input inductance L_inA rear stage inductor L_mAnd the ith boost inductor L_aiThe effective values of the currents are respectively:

wherein, I_Lin,rms、I_Lm,rmsAre respectively an input inductance L_inA rear stage inductor L_mThe current effective value of (a); i is_Lin、I_LmAre respectively an input inductance L_inA rear stage inductor L_mAverage value of current of (a); delta I_Lin、ΔI_LmAre respectively an input inductance L_inA rear stage inductor L_mCurrent peak to peak value.

First switch tube S₁And a second switching tube S₂The effective values of the currents are respectively:

in the formula (I), the compound is shown in the specification,

I_S1,rms、I_S2,rmsare respectively a first switch tube S₁A second switch tube S₂Effective value of current of, Δ I_LmIs a post-stage inductor L_mCurrent peak-to-peak value of,. DELTA.I_LaiBoost the inductance L for the ith_aiCurrent peak-to-peak value of (I)_LFor synthesizing a current i_LMean value,. DELTA.I_LFor synthesizing a current i_LPeak to peak value of (a).

The ZVS turn-on conditions of the present invention are discussed below.

From the modal analysis, it can be known that: a second switch tube S₂ZVS switching-on can be naturally realized, and the first switching tube S is required to be realized₁ZVS on, then requires the inductor L of the later stage in the mode 4_mAnd the ith boost inductor L_aiAll the currents flow out of the node m and satisfy the following conditions:

due to dead time T_dVery short, so it can be approximated as the input inductance L in mode 4_inA rear stage inductor L_mAnd the ith boost inductor L_aiAll the currents of (a) remain unchanged, i.e.:

in the formula i_Lin,valFor input of an inductor L_inCurrent valley of (i)_Lm,peakIs a post-stage inductor L_mPeak of current ofValue i_Lai,peakBoost the inductance L for the ith_aiWherein i is 1,2, … …, n.

From formulas (20) and (21), it is possible to obtain:

in the formula i_L,peakFor synthesizing a current i_LThe peak value of (c).

Namely:

from the formulas (10) to (13), the latter-stage inductance L can be obtained_mAnd the ith boost inductor L_aiSustained forward voltage:

further, a post-stage inductance L can be obtained_mAnd the ith boost inductor L_aiCurrent peak-to-peak value of (c):

if the input inductance L is required_inCurrent pulsation amount Δ I of_LinNot exceeding its maximum average current I_Lin,maxδ% of (d) then:

if the latter stage inductance L_mAnd the ith boost inductor L_aiWith the same inductance, the peak-to-peak current values are also equal, and thus the value can be obtained from equation (23):

thus, the ZVS turn-on conditions of the present invention are:

wherein i is 1,2, … …, n.

The converter of the present invention is designed with the following parameters.

Under the condition of different numbers of boosting units, the working principle of the converter provided by the invention for realizing ZVS (zero voltage switching) opening and high gain is similar. Therefore, the present invention takes the case of containing 1 boosting unit (as shown in fig. 7) as an example to design an experimental prototype, and the design indexes are as follows: photovoltaic cell panel voltage U _in40V, output voltage U _o400V, switching frequency f_s110kHz, maximum output power P_o,max250W, dead time T_d＝400ns。

From the above index, the duty ratio at this time can be obtained from equation (8):

if the input inductance L is required_inCurrent pulsation amount Δ I of_LinNot exceeding its maximum average current I_Lin,max30% of (I), i.e.. DELTA.I_Lin≤0.3I_Lin,maxThen, there are:

input inductor L_in＝0.2mH。

Thus, from equation (28):

get the 1 st boost inductance L_a125 muH, post-stage inductance L_m＝25μH。

Based on the modal analysis, the working condition analysis and the parameter design of the converter, an experiment prototype is manufactured to carry out an open loop experiment to verify the boosting capacity of the converter. The specific technical indexes and circuit parameters are as follows: photovoltaic cell panel voltage U _in40V, output voltage U _o400V, switching frequency f_s110kHz, maximum output power P_o,max250W, dead time T _d400 ns; input inductance L_in0.2mH, 1 st boost inductor L_a125 muH, post-stage inductance L_m25 muh; input filter capacitor C_in47 muF, first capacitance C₁10 muF, second capacitance C₂10 muF, 1 st filter capacitance C_a110 muF, 1 st auxiliary capacitance C_b110 muF, output filter capacitance C_o10 μ F; theoretical voltage gain G-10.

FIG. 8(a) shows a driving signal u of the first switch tube_gs1Input inductor current i_LinVoltage u of photovoltaic cell panel_inAnd an output voltage u_oThe experimental waveform of (2); FIG. 8(b) shows the driving signal u of the second switch tube_gs21 st boost inductor current-i_La1And the inductor current-i of the later stage_LmThe experimental waveform of (2); FIG. 8(C) shows the first capacitor C₁A second capacitor C₂1 st filter capacitor C_a1And 1 st auxiliary capacitor C_b1Experimental waveforms of the voltages at both ends; FIG. 8(d) shows the driving signal u of the first switch tube_gs1Voltage u between drain and source of the first switching tube_S1A driving signal u of the second switch tube_gs2And the voltage u between the drain and the source of the second switch tube_S2The experimental waveform of (2); FIG. 8(e) shows the terminal voltage u of the 1 st boost diode at full load (output power 250W)_Da11 st boost diode current i_Da1And the terminal voltage u of the output diode_DoCurrent i of the output diode_DoThe experimental waveform of (2); FIG. 8(f) shows the terminal voltage u of the 1 st boost diode at light load (output power 50W)_Da11 st boost diode current i_Da1And the terminal voltage u of the output diode_DoCurrent i of the output diode_DoExperimental waveforms of (4).

As can be seen from fig. 8(a) and 8 (b): input inductance L_inAnd a post-stage inductor L_m1 st boost inductor L_a1All work in a current continuous mode; input of inductor current i_LmAnd 1 st boost inductor current i_La1Are equal to, and-i_Lm,peak-i_La1,peak>i_Lin,val(ii) a The actual value of the effective duty ratio is D_effAbout 0.76, and the theoretical value D_eff0.75 is very close. As can be seen from fig. 8 (c): each capacitor having a first capacitor C₁A second capacitor C₂1 st filter capacitor C_a1And 1 st auxiliary capacitor C_b1Respectively of voltage stress of U_C1＝160V、U_C2＝120V、U_Ca1＝280V、U _Cb1240V, all of which are substantially in agreement with the theoretical values. As can be seen from fig. 8 (d): first switch tube S₁A first switch tube S₂Performing complementary work; first switch tube S₁A first switch tube S₂Has a voltage stress of U_S1＝U _S2160V, which is basically consistent with a theoretical value; drive signal u_gs1、u_gs2Before the positive pressure comes, the first switch tube S₁、S₂Terminal voltage u of_S1、u_S2Both have decreased to zero, indicating that both achieve ZVS switching on. As can be seen from fig. 8(e) and 8 (f): under full load condition, D₁、D₂Is small (1A), approximately a natural turn-off (ZCS); under the condition of light load, the two are completely naturally turned off; low voltage stress of U_D1＝U _Do160V, which basically coincides with the theoretical value.

And then carrying out closed-loop simulation on the voltage of the photovoltaic cell panel to verify the feasibility of the control scheme provided by the invention, wherein the specific technical indexes and circuit parameters are as follows: photovoltaic cell plate voltage reference value u _in,ref40V, output voltage U _o400V, switching frequency f_s110kHz, dead time T _d400 ns; input inductance L_in0.2mH, 1 st boost inductor L_a125 muH, post-stage inductance L_m25 muh; input filter capacitorC_in47 muF, first capacitance C₁10 muF, second capacitance C₂10 muF, 1 st filter capacitance C_a110 muF, 1 st auxiliary capacitance C_b110 muF, output filter capacitance C_o10 μ F; theoretical voltage gain G ═ 10; the output end of the photovoltaic cell panel is connected with a storage battery in parallel to simulate a direct current bus and clamp the output voltage at 400V, and the photovoltaic cell panel is simulated by connecting a 47.5V constant-voltage direct current power supply and a variable resistor in series. When the simulation proceeded to 50ms, the variable resistance was momentarily switched from 1 Ω to 1.5 Ω.

FIG. 9 shows the converter of FIG. 3 with input power P_inSwitching to input power P of 300W_inAs for the dynamic adjustment process at 200W, it can be seen that at the time of 50ms, the current of the photovoltaic panel changes from 7.5A to 5A, the output power of the converter changes, and the input power changes from 300W to 200W; before and after the input power changes, the voltage of the converter photovoltaic cell panel is stabilized at 40V, and the output voltage U is_o400V, consistent with theory.

The high-gain converter for the photovoltaic direct-current module has the following advantages: (1) voltage gain of [1+ (1+ n) D_eff]/(1-D_eff). By adjusting the number of the boosting units, the voltage gain can be flexibly adjusted to enable the boosting units to work under a proper duty ratio D so as to meet the boosting requirements on different occasions; (2) has 2 switching tubes and (n +1) diodes, and the first switching tube S₁A second switch tube S₂Ith boost diode D_aiAnd an output diode D_oAll bear the same voltage stress and are [ (n +1) U_in+U_o](n +2), much smaller than the output voltage; (3) first switch tube S₁And a second switching tube S₂ZVS opening can be realized in the whole load range; ith boost diode D_aiAnd an output diode D_oThe approximate natural shutoff can be realized under the heavy load condition, and the complete natural shutoff can be realized under the light load condition; wherein i is 1,2, … …, n.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea, and not to limit it. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall into the protection scope of the present invention.

Claims

1. A high-gain converter for a photovoltaic direct current module is characterized by comprising a boosting module and a basic module;

the connection mode between the boosting units is as follows: boost diode D in the latter boost unit_aAnode and auxiliary capacitor C in the previous booster unit_bPositive pole of (1), boost inductor L in the previous boost unit_aIs connected with the second end of the first end; n auxiliary capacitors C of the boosting units_bAll of which are negative electrodesIntersecting with point b; n filter capacitors C of the boosting units_aThe negative electrode of (a) is crossed with the point a;

the basic module comprises a photovoltaic cell panel U_inAn input filter capacitor C_inAn input inductor L_inA rear stage inductor L_mA first switch tube S₁A second switch tube S₂A first capacitor C₁A second capacitor C₂And an output diode D_oAn output filter capacitor C_oAnd a load R;

the connection mode of the basic module and the boosting module is as follows: the photovoltaic cell panel U_inAnd the input inductance L_inFirst terminal of, said input filter capacitance C_inThe positive electrodes of the two electrodes are connected; the input inductance L_inAnd the second end of the first switch tube S₁Drain electrode of (1), the second switching tube S₂Source electrode of, the second capacitor C₂The negative pole of the voltage boosting module is connected with the point b of the voltage boosting module; the second switch tube S₂And the post-stage inductor L_mFirst terminal of, said first capacitor C₁The positive electrodes of the two electrodes are connected; the back stage inductor L_mAnd the second terminal of the second capacitor C₂Positive pole of (2), boost diode D of the first boost unit in the boost module_aThe anodes of the anode groups are connected; the output diode D_oAnd the boost inductance L of the last boost unit in the boost module_aSecond terminal and auxiliary capacitance C_bThe positive electrodes of the two electrodes are connected; the output diode D_oAnd the output filter capacitor C_oThe positive electrode of (a) is connected with the first end of the load R; a second terminal of the load R and the output filter capacitor C_oThe negative pole of (1), the point a of the boosting module, the first switch tube S₁Source electrode of, the input filter capacitor C_inNegative pole of (1), the first capacitor C₁And the photovoltaic cell panel U_inThe negative electrodes are connected;

the input inductance L_inThe inductance value of (a) satisfies:

in the above formula, D_eff＝D+T_d/T_s，D_effFor an effective duty cycle, D is a first switching tube S₁Duty cycle of the drive signal of (1), T_dIs a first switch tube S₁And a second switch tube S₂The dead time of the drive signal, T_sIs a first switch tube S₁And a second switch tube S₂Period of the drive signal of (1), L_inFor input of an inductor L_inPeak to peak value of,. DELTA.I_LinIs an input inductance L_inCurrent pulsation amount of U_inFor the photovoltaic cell panel voltage, f_sIs the switching frequency, delta% is the input inductance L_inMaximum permissible current ripple and input inductance L_inPercentage of maximum average current; p_o,maxIs the maximum output power;

in the above formula, L_mIs a post-stage inductor L_mInductance value of, L_aFor the step-up inductor L_aInductance value of, U_oIs the output voltage; n is the number of booster cells.

2. A method of controlling a high gain converter according to claim 1, comprising the steps of:

to photovoltaic cell panel U_inIs sampled to obtain a voltage sampling value u_in,fFor the photovoltaic cell panel U_inIs sampled to obtain a current sampling value i_in,fSampling the voltage value u_in,fCurrent sample value i_in,fSending the voltage into MPPT, and calculating to generate a voltage reference value u of the photovoltaic cell panel through the MPPT_in,refSampling the voltage of the photovoltaic cell panel u_in,fWith the voltage reference value u of the photovoltaic cell panel_in,refComparing to obtain an error signal u_in,f-u_in,ref；

The error signal u_in,f-u_in,refSending to a voltage controller to obtain a regulation signal u_r；

The first switch tube S₁The PWM driving signal is inverted to obtain a second switching tube S₂PWM drive signal u_gs2。

3. The control method of claim 2, wherein the ideal voltage gain of the high-gain converter is [1+ (1+ n) D_eff]/(1-D_eff)。

4. Control method according to claim 2, characterized in that the first switching tube S₁A second switch tube S₂And an output diode D_oAnd a boost diode D_aAll bear the same voltage stress and are [ (n +1) U_in+U_o]/(n+2)。