CN102709940A - Design method of energy storage quasi-Z source single-phase photovoltaic power generation system - Google Patents

Abstract

The invention discloses a design method of an energy storage quasi-Z source single-phase photovoltaic power generation system. The method comprises the steps of design of the voltage and the capacity of an energy storage battery, which are required by the system, selection of a photovoltaic battery module, design of inductance and capacitor parameters of a quasi-Z source network, design of voltage and current grades of an H-bridge inverter, design of a Z-source network diode, calculation of loss of a quasi-Z source inverter and the like. The design method is based on the voltage and power requirements of a user, application of the photovoltaic power generation system and the local climatic characteristics. According to the designed energy storage quasi-Z source single-phase photovoltaic power generation system, the requirement on the 1:2 wide range variation of the voltage of a photovoltaic battery can be met; no matter how the voltage of the photovoltaic battery changes, the system can output a voltage required by a load; and the energy storage quasi-Z source single-phase photovoltaic power generation system is suitable for the requirement for completing voltage rising/reduction, inversion and energy storage by the single-stage power conversion. The invention provides a simple, convenient, effective and rapid method for designing and implementing the energy storage quasi-Z source single-phase photovoltaic power generation system.

Description

Design method of energy storage type quasi-Z source single-phase photovoltaic power generation system

Technical Field

The invention relates to the technical field of photovoltaic power generation, in particular to a design method of an energy storage type quasi-Z source single-phase photovoltaic power generation system.

Background

Photovoltaic power generation is an ideal sustainable energy source, and a power converter/inverter is indispensable in the development and utilization process of the photovoltaic power generation. However, in general, the output voltage of the photovoltaic cell can vary by a factor of 2, and the use of a conventional single-stage inverter structure will result in doubling the design capacity of the inverter. If a double-stage structure is adopted, the introduced DC/DC converter increases the cost and reduces the efficiency. To this end, researchers have begun to develop new technologies that overcome these problems with Z-source and quasi-Z-source inverters because they implement a conventional two-stage conversion function consisting of DC/DC and inverter in the form of a single-stage power conversion, do not increase inverter capacity, and are compatible with conventional systems in the photovoltaic power generation field.

On the other hand, the photovoltaic power generation has strong dependence on illumination and temperature, and because the illumination and temperature change is abnormal, the voltage and power output by the photovoltaic cell change in a wide range, and the direct grid connection or independent power supply can cause negative effects on a power grid or a load. Therefore, in addition to the scheme that the traditional independent photovoltaic power generation system applies the energy storage battery, the energy storage battery technology is also adopted in the grid-connected solar power generation system in recent years to buffer energy and stabilize grid-connected power. In a common method, an energy storage battery is connected to a direct current side through a bidirectional DC/DC converter to achieve a grid-connected power stabilizing function, but a set of DC/DC converter is additionally added to increase the cost of a system. In order to overcome the problem, an energy storage battery is connected with a direct capacitor in parallel in an invention patent [ application number 201010234868.X, a single-stage buck-boost energy storage type photovoltaic grid-connected power generation control system ], so that single-stage power conversion is realized to finish buck-boost, inversion and energy storage. In the system, the energy storage battery is directly connected in parallel to the capacitor, additional equipment is not needed, and the system is economical and practical. However, no literature has been provided so far on how to design parameters in the system, such as energy storage battery voltage, capacity, photovoltaic battery voltage level, modulation index, loss analysis of capacitors, inductors, power switching devices, and the like. For an energy storage type photovoltaic grid-connected power generation control system, the determination of the parameters is important.

Disclosure of Invention

In order to solve the above problems, the present invention discloses a design method of an energy storage type quasi-Z source single-phase photovoltaic power generation system, which includes: the power supply comprises an energy storage battery, an H-bridge inverter, a quasi-Z source network diode, a first electrolytic capacitor, a second electrolytic capacitor, a first inductor, a second inductor, an LC filter, a photovoltaic battery, a power grid and a local load; the LC filter comprises an output filter inductor and an output filter capacitor; the negative electrode of the second electrolytic capacitor is connected with the anode of the quasi-Z source network diode, and the positive electrode of the second electrolytic capacitor is connected with the positive electrode of the H-bridge inverter; the cathode of the quasi-Z source network diode is simultaneously connected with the anode of the first electrolytic capacitor and the second inductor; the other end of the second inductor is connected to the positive electrode of the H-bridge inverter; the negative electrode of the first electrolytic capacitor is connected with the negative electrode of the H-bridge inverter; one end of the first inductor is connected with the anode of the photovoltaic cell; the other end of the first inductor is connected with the cathode of the second electrolytic capacitor; the output of the H-bridge inverter is merged into a power grid or supplies power to a local load after passing through an LC filter; the energy storage battery is bridged at two ends of the first electrolytic capacitor, and the anode of the energy storage battery is connected with the anode of the first electrolytic capacitor; based on the requirements of user voltage and power, the application of a photovoltaic power generation system and the local climate characteristics, the method comprises the steps of energy storage battery voltage and capacity parameter design required by the system, photovoltaic battery module selection, quasi-Z source network inductance and capacitance parameter design, H bridge inverter voltage and current grade design, Z-source network diode design, quasi-Z source inverter loss calculation and the like.

Further, as a preferred option, the H-bridge inverter voltage and current class design includes the following steps:

step 1, calculating the voltage amplitude v output by the single-phase inverter according to the load voltage or the grid voltage at the grid-connected position_al;

Step 2, setting the working voltage variation range of the photovoltaic cell as 1: 2 and the maximum photovoltaic cell voltage is V_in=v_alMinimum is V_in＝v_alAnd/2, correspondingly, when the photovoltaic cell voltage is maximum, the inverter modulation index M =1, the through duty ratio D =0, and the peak value of the direct-current bus voltage is V_PN=v_alWhen the photovoltaic cell voltage is minimum, the direct-through duty ratio D =1/3, the inverter modulation index M =2/3 and the peak value of the direct-current bus voltage is V_PN=1.5*v_al。

Further, as a preferred option, the designing of the capacitance and inductance parameters includes:

step 3, calculating the capacitance C₁Voltage and parallel battery voltage V_C1=V_B=v_al；

Step 4, calculating the maximum voltage peak value V of the direct current bus_PN=1.5×v_al；

Step 5, calculating the capacitance C₂Maximum value of voltage V_C2=0.5×v_al；

Step 6, maximum through duty cycle D = 1/3.

Further, as a preferred option, the photovoltaic cell module includes:

step 7, depending on the load orGrid-connected power P_oConsidering that the maximum power occurs at the maximum voltage, the photovoltaic cell current is

Step 8, when the energy storage battery discharges and the photovoltaic power is insufficient, according to the design, the minimum working voltage of the photovoltaic battery is v_alSetting the supplied current to be one k times of the maximum power when the minimum power of the photovoltaic cell is the minimum power when the minimum illumination intensity of the photovoltaic cell is allowed to work; then P is to be output_oWhen power is supplied, the battery needs to supply power P_B=P_o-0.5×v_al×iL₁K, the battery current is I_B=P_B/V_B(ii) a Then inductance L₂Has a current of i_L2=i_L1+i_B。

Further, as a preferable option, the energy storage battery voltage and capacity parameter design includes:

step 9, determining the capacity of the storage battery, applying statistical data, and determining the capacity of the storage battery according to local climate characteristics and the application of a designed system; if the designed photovoltaic system is required to be under the sunshine condition at a certain place, the photovoltaic system is also supplied with power to a local load/power grid and is also supplied with the power P on average every day_xThe power of the battery is charged for x hours for use at night without sunshine, and the discharge depth of the battery is y percent each time, the required battery capacity is [ P ]_x×x/v_al]/(1-y%)(Ah)。

Further, as a preferred option, the photovoltaic cell module includes:

step 10, determining photovoltaic cell modules and the number of the photovoltaic cell modules, selecting the photovoltaic cell modules, and determining the maximum working voltage v in the maximum power point of the photovoltaic cell modules according to the local climate characteristics_pvAnd a maximum operating current i_pvThen the number of photovoltaic cells can be calculated asTaking the integer to obtain n, and obtaining the integer,

and taking an integer to obtain m, wherein the number of the photovoltaic cell modules is m x n.

Further, as a preferred option, the designing of the capacitance and inductance parameters includes:

step 11, capacitor C₂The design is that the system adopts a constant straight-through zero vector modulation method, and the ripple frequency of the capacitor voltage on the Quasi-Z network is 2f_s(ii) a In a steady state, the initial value and the final value of the capacitor voltage in one period are equal; taking a through case as an example, the Quasi-Z network capacitor C₂Ripple Δ V of voltage_C2Is composed of

Wherein,

-i_L1＝i_C2，f_sis a carrier frequency, and thenIf the ripple of the given capacitor voltage is DeltaV_C2≤αV_C2Then there is

To suppress the double frequency voltage ripple, a capacitor is required

In the formula, epsilon is the voltage ripple of two times frequency_PNF is the load or grid voltage frequency, then since the capacitance C is greater thanAnd a capacitor C₁In parallel with the battery, so that the capacitor C₂Is designed as <math> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>=</mo> <mfrac> <msub> <mi>P</mi> <mi>o</mi> </msub> <mrow> <mn>4</mn> <mi>&pi;f</mi> <msubsup> <mi>V</mi> <mi>PN</mi> <mn>2</mn> </msubsup> <mi>&epsiv;</mi> </mrow> </mfrac> <mo>;</mo> </mrow> </math>

Step 12, capacitor C₁The design is that the system adopts a constant straight-through zero vector modulation method, and the ripple frequency of the capacitor voltage on the Quasi-Z network is 2f_s(ii) a In steady state, the initial value and the final value of the capacitor voltage in one period are equal, taking the direct connection as an example, the Quasi-Z network capacitor C₁Ripple Δ V of voltage_C1Is composed of

Wherein,

i_C1＝i_B-i_L2，f_sis a carrier frequency, and then

If the ripple of the given capacitor voltage is DeltaV_C1≤αV_C1Then there is <math> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>&GreaterEqual;</mo> <mrow> <mo>(</mo> <msub> <mi>i</mi> <mi>B</mi> </msub> <mo>-</mo> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> <mfrac> <mi>D</mi> <mrow> <mn>2</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mi>&alpha;</mi> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </msub> </mrow> </mfrac> <mo>;</mo> </mrow> </math>

Step 13, inductor L₂In the design of (1), in a steady state, the initial value and the final value of the inductive current in a period are equal. Taking the case of a through connection as an example, the ripple Δ i of the inductor current of the Quasi-Z network_L2Is composed of

Wherein,

v_L2=V_C1is then provided with

If the ripple of the given inductive current is Δ i_L2≤bi_L2Then there is

Step 14, designing an inductor L1, wherein in a steady state, the initial value and the final value of the inductor current in one period are equal, and taking the direct connection as an example, the ripple wave delta i of the inductor current of the Quasi-Z network_L1Is composed of

Wherein,

V_in+V_C2＝v_L1is then provided with

If the ripple of the given inductive current is Δ i_L1≤bi_L1Then there is

Step 15, parameters of a diode in the Quasi-Z network, wherein the diode in the Quasi-Z network bears back voltage and is turned off in a direct-connection state, and is turned on in a non-direct-connection state, so that the diode can be designed according to voltage at two ends of the diode in the direct-connection state and current flowing through the diode in the non-direct-connection state; diode bearing in straight-through stateIs subjected to back pressure of V_PNThe current through the diode in the non-through state is i_D≤i_L1+i_C2=i_L1+i_L2-i_dIn the conventional zero vector time, i_dWhen =0, the maximum current flowing through the diode is i_D=i_L1+i_L2；

Step 16, parameters of the inverter power device are determined according to load or grid-connected power P_oCalculating the effective value of the load current according to the grid voltage at the load or grid connection

Calculating the peak value V of the DC bus voltage according to the step 4_PNAnd the calculated load current effective value is used as the selected voltage and current parameters of the inverter power device.

Further, as a preference, the quasi-Z source inverter loss calculation includes:

step 17, estimating the loss of the energy storage type quasi-Z source single-phase photovoltaic inverter, wherein the loss can be calculated according to devices by 4 IGBTs, anti-parallel diodes of the IGBTs and a Z-source network diode;

1) the loss estimation of 4 IGBTs and anti-parallel diodes thereof can be divided into loss in the traditional sense and loss caused by direct connection, the loss in the traditional sense comprises switching loss and conduction loss, and the switching loss is

<math> <mrow> <msub> <mi>P</mi> <mi>SW</mi> </msub> <mo>=</mo> <mfrac> <mn>4</mn> <mi>&pi;</mi> </mfrac> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>E</mi> <mrow> <mi>ON</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>V</mi> <mi>PN</mi> </msub> <msub> <mi>V</mi> <mi>ref</mi> </msub> </mfrac> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>i</mi> <mi>L</mi> </msub> <msub> <mi>i</mi> <mi>ref</mi> </msub> </mfrac> <mo>,</mo> </mrow> </math> In the formula, E_ON，I、E_off，I、E_OFF，DRespectively at voltage V for power devices_refAnd current i_refThe turn-on loss, turn-off loss and diode reverse recovery loss energy of the time can be obtained from a device manual; i.e. i_LIs the peak value of the load current i_L=1.414*i_a,f_sIs the switching frequency; for the conduction loss of each IGBT in the conventional sense, the conduction loss is calculated according to the following formula

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>V</mi> <mrow> <mi>CE</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <msub> <mi>i</mi> <mi>L</mi> </msub> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>&pi;M</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mi>CE</mi> </msub> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mfrac> <mi>&pi;</mi> <mn>4</mn> </mfrac> <mo>+</mo> <mfrac> <mrow> <mn>2</mn> <mi>M</mi> </mrow> <mn>3</mn> </mfrac> <mo>-</mo> <mfrac> <mi>&pi;D</mi> <mn>4</mn> </mfrac> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>V</mi> <mrow> <mi>F</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <mo>&CenterDot;</mo> <msub> <mi>i</mi> <mi>L</mi> </msub> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mfrac> <mi>&pi;M</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mi>F</mi> </msub> <mo>&CenterDot;</mo> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mfrac> <mi>&pi;</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mfrac> <mrow> <mn>2</mn> <mi>M</mi> </mrow> <mn>3</mn> </mfrac> <mo>-</mo> <mfrac> <mi>&pi;D</mi> <mn>4</mn> </mfrac> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math> In the formula, V_CE0、V_F，0The saturation voltage drop and the conduction voltage drop of the IGBT and the diode are obtained; r is_CE、r_FThe on-resistance of the IGBT and the diode; m and D are respectively a modulation index and a through duty ratio, and the conduction loss of the 4 IGBTs and the diodes thereof is P_CV=4*(P_CV，I+P_CV，D) For the losses caused by shoot-through, only the switching losses and conduction losses from the IGBT need to be calculated, i.e. the switching losses are <math> <mrow> <msub> <mi>P</mi> <mrow> <mi>SW</mi> <mo>,</mo> <mi>SH</mi> </mrow> </msub> <mo>=</mo> <mn>4</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>E</mi> <mrow> <mi>ON</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>V</mi> <mi>PN</mi> </msub> <msub> <mi>V</mi> <mi>ref</mi> </msub> </mfrac> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <msub> <mi>i</mi> <mi>ref</mi> </msub> </mfrac> <mo>,</mo> </mrow> </math> Conduction loss of $P_{\mathrm{CV},\mathrm{SH}}=4*(V_{\mathrm{CE},0}{i}_{L1}D+r_{\mathrm{CE}}{i}_{L1}^{2}D+\frac{r_{\mathrm{CE}}{i}_L^{2}D}{8})$

2) The loss of the Z-Source network diode and the conduction loss of the Z-Source network diode of each module are <math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>V</mi> <mrow> <mi>DF</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <mo>[</mo> <msub> <mrow> <mn>2</mn> <mi>i</mi> </mrow> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>-</mo> <mfrac> <msub> <mi>Mi</mi> <mi>L</mi> </msub> <mn>2</mn> </mfrac> <mo>)</mo> <mo>+</mo> <msub> <mi>r</mi> <mi>DF</mi> </msub> <mfrac> <mrow> <mn>1</mn> <mo>-</mo> <mi>D</mi> </mrow> <mn>2</mn> </mfrac> <mo>[</mo> <msubsup> <mrow> <mn>8</mn> <mi>i</mi> </mrow> <mrow> <mi>L</mi> <mn>1</mn> </mrow> <mn>2</mn> </msubsup> <mo>+</mo> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> <mo>]</mo> <mo>-</mo> <msub> <mi>r</mi> <mi>DF</mi> </msub> <mfrac> <mrow> <mn>8</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> <mi>&pi;</mi> </mfrac> <msub> <mi>i</mi> <mi>L</mi> </msub> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mo>,</mo> </mrow> </math> In the formula, V_DF，0Is the conduction voltage drop of the Z-source network diode, r_DFIs the on-resistance of a Z-source network diode with reverse recovery losses of

In the formula, E_recFor Z-source network diodes in I_FMAnd V_RReverse recovery of time losses energy; total loss of P_SW+P_CV+P_SW，SH+P_CV，SH+P_CV，D+P_CV，DRBy estimating the losses, alternative devices can be compared as conditions for optimizing device selection.

By the method, the energy storage type quasi-Z source single-phase photovoltaic power generation system can be designed simply, conveniently, effectively and quickly.

Drawings

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein the accompanying drawings are included to provide a further understanding of the invention and form a part of this specification, and wherein the illustrated embodiments and descriptions thereof are intended to illustrate and not limit the invention, wherein:

FIG. 1 is a schematic structural diagram of an energy storage quasi-Z source single-phase photovoltaic power generation inverter;

fig. 2 is a design method of the energy storage type quasi-Z source single-phase photovoltaic power generation system.

Detailed Description

Embodiments of the present invention are described below with reference to fig. 1-2.

In order to make the aforementioned objects, features and advantages more comprehensible, the present invention is described in detail below with reference to the accompanying drawings and the detailed description.

The embodiment of the design method of the energy storage type quasi-Z source single-phase photovoltaic power generation control system.

As shown in fig. 1, the energy storage quasi-Z source single-phase photovoltaic power generation inverter according to the present invention includes: the system comprises an energy storage battery, an H-bridge inverter, a quasi-Z source network diode, a first electrolytic capacitor C1, a second electrolytic capacitor C2, a first inductor L1, a second inductor L2, an LC filter, a photovoltaic battery, a power grid and a local load; the LC filter comprises an output filter inductor L_fAnd an output filter capacitor C_fComposition is carried out; the cathode of the second electrolytic capacitor C2 is connected with the anode of the quasi-Z source network diode, and the anode of the second electrolytic capacitor C2 is connected with the anode of the H-bridge inverter; the cathode of the quasi-Z source network diode is simultaneously connected with the anode of the first electrolytic capacitor C1 and the second inductor L2; the other end of the second inductor L2 is connected to the positive electrode of the H-bridge inverter; the negative electrode of the first electrolytic capacitor C1 is connected with the negative electrode of the H-bridge inverter; one end of the first inductor L1 is connected with the anode of the photovoltaic cell; the other end of the first inductor L1 is connected with the negative electrode of the second electrolytic capacitor C2; the output of the H-bridge inverter is merged into a power grid or supplies power to a local load after passing through an LC filter; the energy storage battery is connected across two ends of the first electrolytic capacitor C1, and the anode of the energy storage battery is connected to the anode of the first electrolytic capacitor C1.

As shown in fig. 2, a method for designing an energy storage type quasi-Z source single-phase photovoltaic power generation system includes:

s1, acquiring the voltage and power requirements of users, the application of the photovoltaic power generation system and the local climate characteristics;

s2, designing voltage and capacity parameters of the energy storage battery;

s3, selecting a photovoltaic cell module;

s4, designing inductance and capacitance parameters of the quasi-Z source network;

s5, designing voltage and current grades of the H-bridge inverter;

s6, designing a Z-source network diode;

and S7, calculating loss of the quasi-Z source inverter.

Examples

The aim is to design an energy storage type quasi-Z source single-phase photovoltaic power generation control system, wherein the phase voltage of a load/power grid is 120V, and the power is 1700W. Then it can be determined in the following steps:

step 1, calculating single-phase voltage amplitude v_al=120×1.414=170V;

Step 2, setting the photovoltaic cell working voltage variation range 1: 2, and the maximum photovoltaic cell voltage is 170V and the minimum is 85V. Correspondingly, when the photovoltaic cell voltage is maximum, the inverter modulation index M =1, the through duty ratio D =0, and the peak value of the direct current bus voltage is

V_PN=170

V when the photovoltaic cell voltage is minimum_in=85V, through duty ratio D =1/3, inverter modulation index M =2/3, and dc bus voltage peak value is

V_PN=85*3=255V

Step 3, designing a capacitor C₁Voltage ofAnd parallel battery voltage

V_C1=V_B=v_al＝170 V

Step 4, calculating the maximum voltage peak value of the direct current bus

V_PN=170+85=255 V

Step 5, calculating the capacitance C₂A maximum value of voltage of

V_C2=85 V

Step 6, maximum through duty cycle D = 1/3;

step 7, according to the load or the grid-connected power P_OThe photovoltaic cell assembly current is, considering that the maximum power occurs at the maximum voltage

$i_{L1}=\frac{P_o}{V_{\mathrm{in}}}=\frac{P_o}{v_{\mathrm{al}}}=\frac{1700}{170}=10A$

Step 8, when the energy storage battery discharges and the photovoltaic power is insufficient, according to the design, the lowest working voltage of the photovoltaic battery is 85V, and the current provided when the lowest photovoltaic power is set is one third of the current provided when the maximum power is provided (for example, the maximum illumination is 1000W/m)²Minimum 200W/m²). Then the battery needs to provide power of 1700W to be output

P_B=1700-85×10/3=1416.7W

The battery current is

i_B=P_B/V_B=8.3A

Then inductance L₂Current of

i_L2=i_L1+i_B=8.3+3.3=11.6 A

Step 9, determining the capacity of the storage battery

And (4) determining the capacity of the storage battery by applying statistical data and combining the use of the designed system according to the local climate characteristics. For example, the photovoltaic system is required to be designed to charge the battery with 1000W of power for 4 hours per day under the sunshine condition of a certain place, besides supplying power to a local load/power grid, so as to be used when the sunshine is absent at night, and the discharging depth of the battery is y% each time. The battery capacity is required to be

[1000*4/170]/(1-y%)=23.5/(1-y%)Ah

Step 10, determining photovoltaic cell modules and the number thereof

Suppose a photovoltaic panel is at S =1000W/m²T =25 °, maximum power point voltage v_pv42.4V, maximum power point current i_pvAnd = 5A. As the temperature of the panel rises, its maximum power point voltage drops, considering 1: 2, the minimum is v_pv＝21.2V。

Then, the number of photovoltaic cells can be calculated as

$n=\frac{v_{\mathrm{al}}}{v_{\mathrm{pv}}}=\frac{170}{42.4}=4,$ $m=\frac{10}{5}=2$

The number of photovoltaic cell modules is m × n = 8.

Step 11, capacitor C₂Design of

The system adopts a constant direct-through zero vector modulation method, so that the ripple frequency of the capacitor voltage on the Quasi-Z network is 2f_s。

In steady state, the initial and final values of the capacitor voltage are equal during a cycle. Taking a through case as an example, the Quasi-Z network capacitor C₂Ripple Δ V of voltage_C2Is composed of

<math> <mrow> <msub> <mi>&Delta;V</mi> <mrow> <mi>C</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <msub> <mi>i</mi> <mrow> <mi>C</mi> <mn>2</mn> </mrow> </msub> <mfrac> <mi>&Delta;t</mi> <msub> <mi>C</mi> <mn>2</mn> </msub> </mfrac> </mrow> </math>

Wherein,-i_L1=i_C2，f_sis a carrier frequency, and then

<math> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>=</mo> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mfrac> <mi>D</mi> <mrow> <mn>2</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mi>&Delta;</mi> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>2</mn> </mrow> </msub> </mrow> </mfrac> </mrow> </math>

If the ripple of the given capacitor voltage is

ΔV_C2≤αV_C2

Then there is

<math> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>&GreaterEqual;</mo> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mfrac> <mi>D</mi> <mrow> <msub> <mrow> <mn>2</mn> <mi>f</mi> </mrow> <mi>s</mi> </msub> <mi>&alpha;</mi> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>2</mn> </mrow> </msub> </mrow> </mfrac> </mrow> </math>

If α =1% is set, carrier frequency f_s=10kHz, then

<math> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>&GreaterEqual;</mo> <mn>10</mn> <mo>&times;</mo> <mfrac> <mrow> <mn>1</mn> <mo>/</mo> <mn>3</mn> </mrow> <mrow> <mn>2</mn> <mo>&times;</mo> <mn>10000</mn> <mo>&times;</mo> <mn>0.01</mn> <mo>&times;</mo> <mn>85</mn> </mrow> </mfrac> <mo>=</mo> <mn>196</mn> <mi>&mu;F</mi> </mrow> </math>

For a single phase system, there is a double frequency ripple. To pairIn the system of FIG. 1, capacitor C₁Connected in parallel with the energy storage battery and then connected with the capacitor C₂Are connected in series. To suppress double frequency ripple, the total capacitance required is

<math> <mrow> <mi>C</mi> <mo>=</mo> <mfrac> <msub> <mi>P</mi> <mi>o</mi> </msub> <mrow> <mn>4</mn> <mi>&pi;f</mi> <msub> <mi>V</mi> <mi>PN</mi> </msub> <mi>&Delta;</mi> <msub> <mi>V</mi> <mi>PN</mi> </msub> </mrow> </mfrac> <mo>=</mo> <mfrac> <msub> <mi>P</mi> <mn>0</mn> </msub> <mrow> <mn>4</mn> <mi>&pi;f</mi> <msubsup> <mi>V</mi> <mi>PN</mi> <mn>2</mn> </msubsup> <mi>&epsiv;</mi> </mrow> </mfrac> </mrow> </math>

In the formula, epsilon is the voltage ripple of two times frequency_PNRatio of (1), Δ V_PN=εV_PNAnd f is the load or grid voltage frequency. Setting the pulse ratio of double frequency voltage to be epsilon =1%, f is 50Hz, V_PN=255V，P_PV=1700W, then

<math> <mrow> <mi>C</mi> <mo>=</mo> <mfrac> <mn>1700</mn> <mrow> <mn>4</mn> <mi>&pi;</mi> <mo>&times;</mo> <mn>50</mn> <mo>&times;</mo> <msup> <mn>255</mn> <mn>2</mn> </msup> <mo>&times;</mo> <mn>1</mn> <mo>%</mo> </mrow> </mfrac> <mo>=</mo> <mn>4.16</mn> <mi>mF</mi> </mrow> </math>

Due to the capacitance C₁The energy storage battery is connected in parallel and can be regarded as infinite capacitance during design. Therefore, the capacitanceC₂It was 4.16 mF.

Step 12, capacitor C₁Design of

The system adopts a constant direct-through zero vector modulation method, so that the ripple frequency of the capacitor voltage on the Quasi-Z network is 2f_s。

In steady state, the initial and final values of the capacitor voltage are equal during a cycle. Taking a through case as an example, the Quasi-Z network capacitor C₁Ripple Δ V of voltage_C1Is composed of

<math> <mrow> <mi>&Delta;</mi> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </msub> <mo>=</mo> <msub> <mi>i</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </msub> <mfrac> <mi>&Delta;t</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </mfrac> </mrow> </math>

Wherein,

i_C1＝i_B-i_L2，f_sis a carrier frequency, and then

<math> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>=</mo> <mrow> <mo>(</mo> <msub> <mi>i</mi> <mi>B</mi> </msub> <mo>-</mo> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> <mfrac> <mi>D</mi> <mrow> <mn>2</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mi>&Delta;</mi> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </msub> </mrow> </mfrac> </mrow> </math>

If the ripple of the given capacitor voltage is

ΔV_C1≤αV_C1，

Then there is

<math> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>&GreaterEqual;</mo> <mrow> <mo>(</mo> <msub> <mi>i</mi> <mi>B</mi> </msub> <mo>-</mo> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> <mfrac> <mi>D</mi> <mrow> <msub> <mrow> <mn>2</mn> <mi>f</mi> </mrow> <mi>s</mi> </msub> <mi>&alpha;</mi> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </msub> </mrow> </mfrac> </mrow> </math>

Setting other parameters as above, and I_B-I_L2=-I_L1=10A, then

<math> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>&times;</mo> <mn>10</mn> <mo>&times;</mo> <mfrac> <mrow> <mn>1</mn> <mo>/</mo> <mn>3</mn> </mrow> <mrow> <mn>2</mn> <mo>&times;</mo> <mn>10000</mn> <mo>&times;</mo> <mn>0.01</mn> <mo>&times;</mo> <mn>170</mn> </mrow> </mfrac> <mo>=</mo> <mn>98</mn> <mi>&mu;F</mi> </mrow> </math>

Step 13, inductor L₂Design (2) of

In a steady state, the initial value and the final value of the inductive current in one period are equal. Taking the case of a through connection as an example, the ripple Δ i of the inductor current of the Quasi-Z network_L2Is composed of

<math> <mrow> <mi>&Delta;</mi> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <msub> <mi>v</mi> <mrow> <mi>L</mi> <mn>2</mn> </mrow> </msub> <mfrac> <mi>&Delta;t</mi> <msub> <mi>L</mi> <mn>2</mn> </msub> </mfrac> </mrow> </math>

Wherein,v_L2=V_C1is then provided with

<math> <mrow> <msub> <mi>L</mi> <mn>2</mn> </msub> <mo>=</mo> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </msub> <mfrac> <mi>D</mi> <mrow> <msub> <mrow> <mn>2</mn> <mi>f</mi> </mrow> <mi>s</mi> </msub> <mi>&Delta;</mi> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>2</mn> </mrow> </msub> </mrow> </mfrac> </mrow> </math>

If the ripple of the given inductor current is

Δi_L2≤bi_L2

Then there is

<math> <mrow> <msub> <mi>L</mi> <mn>2</mn> </msub> <mo>&GreaterEqual;</mo> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </msub> <mfrac> <mi>D</mi> <mrow> <mn>2</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mi>b</mi> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>2</mn> </mrow> </msub> </mrow> </mfrac> </mrow> </math>

Set b =20%, i_L2Then =11.6A

<math> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&GreaterEqual;</mo> <mn>170</mn> <mo>&times;</mo> <mfrac> <mrow> <mn>1</mn> <mo>/</mo> <mn>3</mn> </mrow> <mrow> <mn>2</mn> <mo>&times;</mo> <mn>10000</mn> <mo>&times;</mo> <mn>0.2</mn> <mo>&times;</mo> <mn>11.6</mn> </mrow> </mfrac> <mo>=</mo> <mn>1.22</mn> <mi>mH</mi> </mrow> </math>

Step 14, inductor L₁Design (2) of

In a steady state, the initial value and the final value of the inductive current in one period are equal. Taking the case of a through connection as an example, the ripple Δ i of the inductor current of the Quasi-Z network_L1Is composed of

<math> <mrow> <msub> <mi>&Delta;i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mo>=</mo> <msub> <mi>v</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mfrac> <mi>&Delta;t</mi> <msub> <mi>L</mi> <mn>1</mn> </msub> </mfrac> </mrow> </math>

Wherein,

V_in+V_C2＝v_L1is then provided with

<math> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>=</mo> <mrow> <mo>(</mo> <msub> <mi>V</mi> <mi>in</mi> </msub> <mo>+</mo> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> <mfrac> <mi>D</mi> <mrow> <mn>2</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mi>&Delta;</mi> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> </mrow> </mfrac> </mrow> </math>

If the ripple of the given inductor current is

Δi_L1≤bi_L1

Then there is

<math> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&GreaterEqual;</mo> <mrow> <mo>(</mo> <msub> <mi>V</mi> <mi>in</mi> </msub> <mo>+</mo> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> <mfrac> <mi>D</mi> <mrow> <mn>2</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mi>b</mi> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> </mrow> </mfrac> </mrow> </math>

V_in=85V, current i_L1=10A, then

<math> <mrow> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>&GreaterEqual;</mo> <mrow> <mo>(</mo> <mn>85</mn> <mo>+</mo> <mn>85</mn> <mo>)</mo> </mrow> <mo>&times;</mo> <mfrac> <mrow> <mn>1</mn> <mo>/</mo> <mn>3</mn> </mrow> <mrow> <mn>2</mn> <mo>&times;</mo> <mn>10000</mn> <mo>&times;</mo> <mn>0.2</mn> <mo>&times;</mo> <mn>10</mn> </mrow> </mfrac> <mo>=</mo> <mn>1.42</mn> <mi>mH</mi> </mrow> </math>

Step 15, parameters of diodes in the Quasi-Z network

The diodes in the Quasi-Z network are turned off under reverse voltage in a through state and turned on in a non-through state. The diode can therefore be designed according to the voltage across it in the through state and the current it flows in the non-through state.

Maximum V of reverse voltage borne by the diode in the direct-through state_PN=255V。

The current through the diode in the non-shoot-through state is

i_D≤i_L1+i_C2=i_L1+i_L2-i_d

In the conventional zero vector time, i_dWhen the current is not less than 0, the maximum current flowing through the diode is

i_D=i_L1+i_L2=20 A

Step 16, parameters of inverter power device

According to load or grid-connected power P_oCalculating the effective value of the load current according to the grid voltage at the load or grid connection

<math> <mrow> <msub> <mi>i</mi> <mi>a</mi> </msub> <mo>=</mo> <mfrac> <mrow> <msqrt> <mn>2</mn> </msqrt> <msub> <mi>P</mi> <mi>o</mi> </msub> </mrow> <msub> <mi>v</mi> <mi>al</mi> </msub> </mfrac> <mo>=</mo> <mfrac> <mrow> <msqrt> <mn>2</mn> </msqrt> <mo>&times;</mo> <mn>1700</mn> </mrow> <mn>170</mn> </mfrac> <mo>=</mo> <mn>14.1</mn> <mi>A</mi> </mrow> </math>

Calculating the peak value V of the DC bus voltage according to the step 4_PNAnd the calculated load current effective value is used as the selected voltage and current parameters of the inverter power device.

Step 17, estimating loss of the energy storage type quasi-Z source photovoltaic inverter

For the circuit shown in fig. 1, there are 4 IGBTs (and their anti-parallel diodes), one Z-source network diode, whose losses can be calculated separately from device to device.

1) Loss estimation of 4 IGBTs (and their anti-parallel diodes)

This loss can be classified into loss in the conventional sense and loss due to shoot-through. Losses in the conventional sense include switching losses and conduction losses, and switching losses are

<math> <mrow> <msub> <mi>P</mi> <mi>SW</mi> </msub> <mo>=</mo> <mfrac> <mn>4</mn> <mi>&pi;</mi> </mfrac> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>E</mi> <mrow> <mi>ON</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>V</mi> <mi>PN</mi> </msub> <msub> <mi>V</mi> <mi>ref</mi> </msub> </mfrac> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>i</mi> <mi>L</mi> </msub> <msub> <mi>i</mi> <mi>ref</mi> </msub> </mfrac> </mrow> </math>

In the formula, E_ON，I、E_off，I、E_OFF，DRespectively at voltage V for power devices_refAnd current i_refTurn-on loss, turn-off loss and diode reverse recovery loss energy in time; i.e. i_LIs the peak value of the load current i_L=i_a*1.414A,f_sIs the switching frequency. And (4) selecting the IGBT module SGH30N60RUFD as an inverter power switch according to the voltage and current parameters calculated in the steps 4 and 16, and calculating the loss of the inverter power switch. Providing data according to the device, at V_ref＝300V，i_refWhen the voltage is 30A, the switching loss energy at the time of conduction is E_ON，IWhen the voltage is 0.919mJ/P, the switching loss energy is E_off，I0.814mJ/P, reverse recovery switching loss energy E_OFF，D=0.067mJ/P。i_L=14.1*1.414=19.94A,V_PN=255V，f_sIf =10kHz, P is calculated_SW＝12.9W。

For the conduction loss of each IGBT in the conventional sense, the conduction loss is calculated according to the following formula

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>V</mi> <mrow> <mi>CE</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <msub> <mi>i</mi> <mi>L</mi> </msub> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mo>&CenterDot;</mo> <msubsup> <mo>&Integral;</mo> <mn>0</mn> <mi>&pi;</mi> </msubsup> <mi>sin</mi> <mi>&omega;t</mi> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mfrac> <mrow> <mn>1</mn> <mo>+</mo> <mi>M</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> <mn>2</mn> </mfrac> <mo>-</mo> <mfrac> <mi>D</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mi>d&omega;t</mi> <mo>+</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mi>CE</mi> </msub> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mo>&CenterDot;</mo> <msubsup> <mo>&Integral;</mo> <mn>0</mn> <mi>&pi;</mi> </msubsup> <msup> <mi>sin</mi> <mn>2</mn> </msup> <mi>&omega;t</mi> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mfrac> <mrow> <mn>1</mn> <mo>+</mo> <mi>M</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> <mn>2</mn> </mfrac> <mo>-</mo> <mfrac> <mi>D</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mi>d&omega;t</mi> </mrow> </math>

<math> <mrow> <mo>=</mo> <mfrac> <mrow> <msub> <mi>V</mi> <mrow> <mi>CE</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <msub> <mi>i</mi> <mi>L</mi> </msub> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>&pi;M</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mi>CE</mi> </msub> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mfrac> <mi>&pi;</mi> <mn>4</mn> </mfrac> <mo>+</mo> <mfrac> <mrow> <mn>2</mn> <mi>M</mi> </mrow> <mn>3</mn> </mfrac> <mo>-</mo> <mfrac> <mi>&pi;D</mi> <mn>4</mn> </mfrac> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>V</mi> <mrow> <mi>F</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <msub> <mrow> <mo>&CenterDot;</mo> <mi>i</mi> </mrow> <mi>L</mi> </msub> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mo>&CenterDot;</mo> <msubsup> <mo>&Integral;</mo> <mn>0</mn> <mi>&pi;</mi> </msubsup> <mi>sin</mi> <mi>&omega;t</mi> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mfrac> <mrow> <mn>1</mn> <mo>-</mo> <mi>M</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> <mn>2</mn> </mfrac> <mo>-</mo> <mfrac> <mi>D</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mi>d&omega;t</mi> <mo>+</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mi>F</mi> </msub> <msubsup> <mrow> <mo>&CenterDot;</mo> <mi>i</mi> </mrow> <mi>L</mi> <mn>2</mn> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mo>&CenterDot;</mo> <msubsup> <mo>&Integral;</mo> <mn>0</mn> <mi>&pi;</mi> </msubsup> <msup> <mi>sin</mi> <mn>2</mn> </msup> <mi>&omega;t</mi> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <mfrac> <mrow> <mn>1</mn> <mo>-</mo> <mi>M</mi> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> <mn>2</mn> </mfrac> <mo>-</mo> <mfrac> <mi>D</mi> <mn>2</mn> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mi>d&omega;t</mi> </mrow> </math>

<math> <mrow> <mo>=</mo> <mfrac> <mrow> <msub> <mi>V</mi> <mrow> <mi>F</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <mo>&CenterDot;</mo> <msub> <mi>i</mi> <mi>L</mi> </msub> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mfrac> <mi>&pi;M</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mi>F</mi> </msub> <mo>&CenterDot;</mo> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mfrac> <mi>&pi;</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mfrac> <mrow> <mn>2</mn> <mi>M</mi> </mrow> <mn>3</mn> </mfrac> <mo>-</mo> <mfrac> <mi>&pi;D</mi> <mn>4</mn> </mfrac> <mo>)</mo> </mrow> </mrow> </math>

In the formula, V_CE0、V_F，0The saturation voltage drop and the conduction voltage drop of the IGBT and the diode are obtained; r is_CE、r_FThe on-resistances of the IGBT and the diode respectively; m and D are modulation index and through duty, respectivelyAnd (4) the ratio. Due to V_CE0=2.2V，V_F，0＝1.3V，r_CE=0.02Ω,r_F=0.01 Ω, M =2/3, D =1/3, the conduction loss of 4 IGBTs and diodes thereof is

P_CV=4*(P_CV，I+P_CV，D)=45.8W

For the losses caused by shoot-through, only the switching losses and conduction losses from the IGBT need to be calculated, i.e. the switching losses are

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>SW</mi> <mo>,</mo> <mi>SH</mi> </mrow> </msub> <mo>=</mo> <mn>4</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>E</mi> <mrow> <mi>ON</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>V</mi> <mi>PN</mi> </msub> <msub> <mi>V</mi> <mi>ref</mi> </msub> </mfrac> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <msub> <mi>i</mi> <mi>ref</mi> </msub> </mfrac> <mo>=</mo> <mn>19.6</mn> <mi>W</mi> </mrow> </math>

Conduction loss of

$P_{\mathrm{CV},\mathrm{SH}}=4*(V_{\mathrm{CE},0}{i}_{L1}D+r_{\mathrm{CE}}{i}_{L1}^{2}D+\frac{r_{\mathrm{CE}}{i}_L^{2}D}{8})=6.2W$

2) Losses in Z-source network diodes

The conduction loss of the Z-Source network diode of each module is

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>V</mi> <mrow> <mi>DF</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <mo>[</mo> <msub> <mrow> <mn>2</mn> <mi>i</mi> </mrow> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>-</mo> <mfrac> <msub> <mi>Mi</mi> <mi>L</mi> </msub> <mn>2</mn> </mfrac> <mo>)</mo> <mo>+</mo> <msub> <mi>r</mi> <mi>DF</mi> </msub> <mfrac> <mrow> <mn>1</mn> <mo>-</mo> <mi>D</mi> </mrow> <mn>2</mn> </mfrac> <mo>[</mo> <msubsup> <mrow> <mn>8</mn> <mi>i</mi> </mrow> <mrow> <mi>L</mi> <mn>1</mn> </mrow> <mn>2</mn> </msubsup> <mo>+</mo> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> <mo>]</mo> <mo>-</mo> <msub> <mi>r</mi> <mi>DF</mi> </msub> <mfrac> <mrow> <mn>8</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> <mi>&pi;</mi> </mfrac> <msub> <mi>i</mi> <mi>L</mi> </msub> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> </mrow> </math>

Having a reverse recovery loss of

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>DR</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <mn>2</mn> <msub> <mi>E</mi> <mi>rec</mi> </msub> <msub> <mi>V</mi> <mi>PN</mi> </msub> <mrow> <mo>(</mo> <msub> <mi>&pi;i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mo>-</mo> <msub> <mi>i</mi> <mi>L</mi> </msub> <mo>)</mo> </mrow> </mrow> <mrow> <mi>&pi;</mi> <msub> <mi>I</mi> <mi>FM</mi> </msub> <msub> <mi>V</mi> <mi>R</mi> </msub> </mrow> </mfrac> <mn>2</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> </mrow> </math>

Selecting APT40DQ60B as a Z-source network diode according to the diode parameters calculated in the step 15, and calculating the current value of the diode in the I_FM=30A,V_RReverse recovery loss energy E in case of =600V_rec=0.06mJ/P，V_PN＝255V，V_DF0= 1.7V. Then P is_CV，D=14.7W，P_CV，DR=0.124W。

Total loss of P_SW+P_CV+P_SW，SH+P_CV，SH+P_CV，D+P_CV，DR=118.2W。

By estimating the losses, alternative devices can be compared as one of the conditions for optimizing device selection.

From the above embodiments, it can be seen that the main parameters of the energy storage type quasi-Z source photovoltaic power generation system can be effectively designed according to the invention. When the voltage of the photovoltaic cell is low, the designed system boosts the voltage of the circuit to meet the load requirement; when the voltage of the photovoltaic cell is higher, the requirement can be met without boosting; at night, the energy storage battery may provide energy directly to the load. The whole system is realized by a single-stage power circuit, has the simplest structure and is low in cost. And the system is suitable for independent photovoltaic power generation and is also suitable for grid-connected photovoltaic power generation.

As described above, although the embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that many modifications are possible without substantially departing from the spirit and scope of the present invention. Therefore, such modifications are also all included in the scope of protection of the present invention.

Claims (8)

1. A design method of an energy storage type quasi-Z source single-phase photovoltaic power generation system comprises the following steps: the power supply comprises an energy storage battery, an H-bridge inverter, a quasi-Z source network diode, a first electrolytic capacitor, a second electrolytic capacitor, a first inductor, a second inductor, an LC filter, a photovoltaic battery, a power grid and a local load; the LC filter comprises an output filter inductor and an output filter capacitor; the negative electrode of the second electrolytic capacitor is connected with the anode of the quasi-Z source network diode, and the positive electrode of the second electrolytic capacitor is connected with the positive electrode of the H-bridge inverter; the cathode of the quasi-Z source network diode is simultaneously connected with the anode of the first electrolytic capacitor and the second inductor; the other end of the second inductor is connected to the positive electrode of the H-bridge inverter; the negative electrode of the first electrolytic capacitor is connected with the negative electrode of the H-bridge inverter; one end of the first inductor is connected with the anode of the photovoltaic cell; the other end of the first inductor is connected with the cathode of the second electrolytic capacitor; the output of the H-bridge inverter is merged into a power grid or supplies power to a local load after passing through an LC filter; the energy storage battery is bridged at two ends of the first electrolytic capacitor, and the anode of the energy storage battery is connected with the anode of the first electrolytic capacitor;

the method is characterized by comprising the steps of designing energy storage battery voltage and capacity parameters required by the system, selecting a photovoltaic battery module, designing quasi-Z source network inductance and capacitance parameters, designing the voltage and current grade of an H bridge inverter, designing a Z-source network diode and calculating the loss of the quasi-Z source inverter based on user voltage and power requirements, the application of a photovoltaic power generation system and local climate characteristics.

2. The design method of the energy storage type quasi-Z source single-phase photovoltaic power generation system according to claim 1, wherein the design of the voltage and current levels of the H-bridge inverter comprises the following steps:

step 1, calculating the voltage amplitude v output by the single-phase inverter according to the load voltage or the grid voltage at the grid-connected position_al;

Step 2, setting the working voltage variation range of the photovoltaic cell to be 1: 2, and setting the maximum photovoltaic cell voltage to be V_in=v_alMinimum is V_in=v_alAnd/2, correspondingly, when the photovoltaic cell voltage is maximum, the inverter modulation index M =1, the through duty ratio D =0, and the peak value of the direct-current bus voltage is V_PN=v_alWhen the photovoltaic cell voltage is minimum, the direct-through duty ratio D =1/3, the inverter modulation index M =2/3 and the peak value of the direct-current bus voltage is V_PN=1.5*val。

3. The design method of the energy storage type quasi-Z source single-phase photovoltaic power generation system according to claim 1, wherein the capacitance and inductance parameter design comprises the following steps:

step 3, calculating the capacitance C₁Voltage and parallel battery voltage V_C1=V_B=v_al；

Step 4, calculating the maximum voltage peak value V of the direct current bus_PN=1.5×v_al；

Step 5, calculating the capacitance C₂Maximum value of voltage V_C2=0.5×v_al；

Step 6, maximum through duty cycle D = 1/3.

4. The design method of an energy storage type quasi-Z source single-phase photovoltaic power generation system according to claim 1, wherein the photovoltaic cell module selection comprises:

step 7, according to the load or the grid-connected power P_oConsidering that the maximum power occurs at the maximum voltage, the photovoltaic cell current is

Step 8, when the energy storage battery discharges and the photovoltaic power is insufficient, according to the design, the minimum working voltage of the photovoltaic battery is v_alSetting the supplied current to be one k times of the maximum power when the minimum power of the photovoltaic cell is the minimum power when the minimum illumination intensity of the photovoltaic cell is allowed to work; then P is to be output_oWhen power is supplied, the battery needs to supply power P_B=P_o-0.5×v_al×i_L1K, the battery current is I_B=P_B/V_B(ii) a Then inductance L₂Has a current of i_L2=i_L1+i_B。

5. The method for designing an energy storage type quasi-Z source single-phase photovoltaic power generation system according to claim 1, wherein the energy storage battery voltage and capacity parameter design comprises:

step 9, determining the capacity of the storage battery, applying statistical data, and determining the use of the designed system according to the local climate characteristicsThe capacity of the battery; if the designed photovoltaic system is required to be under the sunshine condition at a certain place, the photovoltaic system is also supplied with power to a local load/power grid and is also supplied with the power P on average every day_xThe power of the battery is charged for x hours for use at night without sunshine, and the discharge depth of the battery is y percent each time, the required battery capacity is [ P ]_x×x/v_al]/(1-y%)(Ah)。

6. The design method of an energy storage type quasi-Z source single-phase photovoltaic power generation system according to claim 1, wherein the photovoltaic cell module selection comprises:

step 10, determining photovoltaic cell modules and the number of the photovoltaic cell modules, selecting the photovoltaic cell modules, and determining the maximum working voltage v in the maximum power point of the photovoltaic cell modules according to the local climate characteristics_pvAnd a maximum operating current i_pvThen the number of photovoltaic cells can be calculated as

Taking the integer to obtain n, and obtaining the integer,

get the whole

And counting to obtain m, wherein the number of the photovoltaic cell modules is m x n.

7. The design method of the energy storage type quasi-Z source single-phase photovoltaic power generation system according to claim 1, wherein the capacitance and inductance parameter design comprises the following steps:

step 11, capacitor C₂The design is that the system adopts a constant straight-through zero vector modulation method, and the ripple frequency of the capacitor voltage on the Quasi-Z network is 2f_s(ii) a In a steady state, the initial value and the final value of the capacitor voltage in one period are equal; taking a through case as an example, the Quasi-Z network capacitor C₂Ripple Δ V of voltage_C2Is composed of

Wherein,-i_L1＝i_C2，f_sis a carrier frequency, and thenIf the ripple of the given capacitor voltage is DeltaV_C2≤αV_C2Then there is

To suppress the double frequency voltage ripple, a capacitor is requiredIn the formula, epsilon is the voltage ripple of two times frequency_PNF is the load or grid voltage frequency, then since the capacitance C is greater than

And a capacitor C₁In parallel with the battery, so that the capacitor C₂Is designed as

Step 12, capacitor C₁The design is that the system adopts a constant straight-through zero vector modulation method, and the ripple frequency of the capacitor voltage on the Quasi-Z network is 2f_s(ii) a In steady state, the initial value and the final value of the capacitor voltage in one period are equal, taking the direct connection as an example, the Quasi-Z network capacitor C₁Ripple Δ V of voltage_C1Is composed of

Wherein,

i_C1＝i_B-i_L2f_sis a carrier frequency, and then

If the ripple of the given capacitor voltage is DeltaV_C1≤αV_C1Then there is <math> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>&GreaterEqual;</mo> <mrow> <mo>(</mo> <msub> <mi>i</mi> <mi>B</mi> </msub> <mo>-</mo> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>2</mn> </mrow> </msub> <mo>)</mo> </mrow> <mfrac> <mi>D</mi> <mrow> <mn>2</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mi>&alpha;</mi> <msub> <mi>V</mi> <mrow> <mi>C</mi> <mn>1</mn> </mrow> </msub> </mrow> </mfrac> <mo>;</mo> </mrow> </math>

Step 13, inductor L₂In the design of (1), in a steady state, the initial value and the final value of the inductive current in a period are equal. Taking the case of a through connection as an example, the ripple Δ i of the inductor current of the Quasi-Z network_L2Is composed of

Wherein,

v_L2=V_C1is then provided with

If the ripple of the given inductive current is Δ i_L2≤bi_L2Then there is

Step 14, inductor L₁In steady state, the initial value and the final value of the inductive current in one period are equal, taking the straight-through time as an example, the ripple wave delta i of the inductive current of the Quasi-Z network_L1Is composed of

Wherein,

V_in+V_C2＝v_L1is then provided with

If the ripple of the given inductive current is Δ i_L1≤bi_L1Then there is

Step 15, parameters of a diode in the Quasi-Z network, wherein the diode in the Quasi-Z network bears back voltage and is turned off in a direct-connection state, and is turned on in a non-direct-connection state, so that the diode can be designed according to voltage at two ends of the diode in the direct-connection state and current flowing through the diode in the non-direct-connection state; the diode bears reverse voltage V in the direct-through state_PNThe current through the diode in the non-through state is i_D≤i_L1+i_C2=i_L1+i_L2-i_dIn the conventional zero vector time, i_dWhen =0, the maximum current flowing through the diode is i_D=i_L1+i_L2；

Step 16, parameters of the inverter power device are determined according to load or grid-connected power P_oCalculating the effective value of the load current according to the grid voltage at the load or grid connectionCalculating the peak value V of the DC bus voltage according to the step 4_PNAnd the calculated load current effective value is used as the selected voltage and current parameters of the inverter power device.

8. The method for designing an energy storage type quasi-Z source single-phase photovoltaic power generation system according to claim 1, wherein the quasi-Z source inverter loss calculation comprises:

step 17, estimating the loss of the energy storage type quasi-Z source single-phase photovoltaic inverter, wherein the loss can be calculated according to devices by 4 IGBTs, anti-parallel diodes of the IGBTs and a Z-source network diode;

1) the loss estimation of 4 IGBTs and anti-parallel diodes thereof can be divided into loss in the traditional sense and loss caused by direct connection, the loss in the traditional sense comprises switching loss and conduction loss, and the switching loss is <math> <mrow> <msub> <mi>P</mi> <mi>SW</mi> </msub> <mo>=</mo> <mfrac> <mn>4</mn> <mi>&pi;</mi> </mfrac> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>E</mi> <mrow> <mi>ON</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>V</mi> <mi>PN</mi> </msub> <msub> <mi>V</mi> <mi>ref</mi> </msub> </mfrac> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>i</mi> <mi>L</mi> </msub> <msub> <mi>i</mi> <mi>ref</mi> </msub> </mfrac> <mo>,</mo> </mrow> </math> In the formula, E_ON，I、E_off，I、E_OFF，DRespectively at voltage V for power devices_refAnd current i_refThe turn-on loss, turn-off loss and diode reverse recovery loss energy of the time can be obtained from a device manual; i.e. i_LIs the peak value of the load current i_L=1.414*i_a,f_sIs the switching frequency; for the conduction loss of each IGBT in the traditional sense, the conduction loss is calculated according to the following formulaCalculating out

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>V</mi> <mrow> <mi>CE</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <msub> <mi>i</mi> <mi>L</mi> </msub> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <mi>&pi;M</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mi>CE</mi> </msub> <msup> <mi>i</mi> <mn>2</mn> </msup> <mi>L</mi> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mfrac> <mi>&pi;</mi> <mn>4</mn> </mfrac> <mo>+</mo> <mfrac> <mrow> <mn>2</mn> <mi>M</mi> </mrow> <mn>3</mn> </mfrac> <mo>-</mo> <mfrac> <mi>&pi;D</mi> <mn>4</mn> </mfrac> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>V</mi> <mrow> <mi>F</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <mo>&CenterDot;</mo> <msub> <mi>i</mi> <mi>L</mi> </msub> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mfrac> <mi>&pi;M</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mrow> <msub> <mi>r</mi> <mi>F</mi> </msub> <mo>&CenterDot;</mo> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> </mrow> <mrow> <mn>2</mn> <mi>&pi;</mi> </mrow> </mfrac> <mrow> <mo>(</mo> <mfrac> <mi>&pi;</mi> <mn>4</mn> </mfrac> <mo>-</mo> <mfrac> <mrow> <mn>2</mn> <mi>M</mi> </mrow> <mn>3</mn> </mfrac> <mo>-</mo> <mfrac> <mi>&pi;D</mi> <mn>4</mn> </mfrac> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math> In the formula, V_CE0、V_F，0The saturation voltage drop and the conduction voltage drop of the IGBT and the diode are obtained; r is_CE、r_FThe on-resistance of the IGBT and the diode; m and D are respectively a modulation index and a through duty ratio, and the conduction loss of the 4 IGBTs and the diodes thereof is P_CV=4*(P_CV，I+P_CV，D) For the losses caused by shoot-through, only the switching losses and conduction losses from the IGBT need to be calculated, i.e. the switching losses are <math> <mrow> <msub> <mi>P</mi> <mrow> <mi>SW</mi> <mo>,</mo> <mi>SH</mi> </mrow> </msub> <mo>=</mo> <mn>4</mn> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>E</mi> <mrow> <mi>ON</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>E</mi> <mrow> <mi>OFF</mi> <mo>,</mo> <mi>I</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>V</mi> <mi>PN</mi> </msub> <msub> <mi>V</mi> <mi>ref</mi> </msub> </mfrac> <mo>&CenterDot;</mo> <mfrac> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <msub> <mi>i</mi> <mi>ref</mi> </msub> </mfrac> <mo>,</mo> </mrow> </math> Conduction loss of $P_{\mathrm{CV},\mathrm{SH}}=4*(V_{\mathrm{CE},0}{i}_{L1}D+r_{\mathrm{CE}}{i}_{L1}^{2}D+\frac{r_{\mathrm{CE}}{i}_L^{2}D}{8})$

2) The loss of the Z-Source network diode and the conduction loss of the Z-Source network diode of each module are <math> <mrow> <msub> <mi>P</mi> <mrow> <mi>CV</mi> <mo>,</mo> <mi>D</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>V</mi> <mrow> <mi>DF</mi> <mo>,</mo> <mn>0</mn> </mrow> </msub> <mo>[</mo> <msub> <mrow> <mn>2</mn> <mi>i</mi> </mrow> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> <mo>-</mo> <mfrac> <msub> <mi>Mi</mi> <mi>L</mi> </msub> <mn>2</mn> </mfrac> <mo>)</mo> <mo>+</mo> <msub> <mi>r</mi> <mi>DF</mi> </msub> <mfrac> <mrow> <mn>1</mn> <mo>-</mo> <mi>D</mi> </mrow> <mn>2</mn> </mfrac> <mo>[</mo> <msubsup> <mrow> <mn>8</mn> <mi>i</mi> </mrow> <mrow> <mi>L</mi> <mn>1</mn> </mrow> <mn>2</mn> </msubsup> <mo>+</mo> <msubsup> <mi>i</mi> <mi>L</mi> <mn>2</mn> </msubsup> <mo>]</mo> <mo>-</mo> <msub> <mi>r</mi> <mi>DF</mi> </msub> <mfrac> <mrow> <mn>8</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>D</mi> <mo>)</mo> </mrow> </mrow> <mi>&pi;</mi> </mfrac> <msub> <mi>i</mi> <mi>L</mi> </msub> <msub> <mi>i</mi> <mrow> <mi>L</mi> <mn>1</mn> </mrow> </msub> <mo>,</mo> </mrow> </math> In the formula, V_DF，0Is the conduction voltage drop of the Z-source network diode, r_DFIs the on-resistance of a Z-source network diode with reverse recovery losses of

In the formula, E_recFor Z-source network diodes in I_FMAnd V_RReverse recovery of time losses energy; total loss of P_SW+P_CV+P_SW，SH+P_CV，SH+P_CV，D+P_CV，DRBy estimating the losses, alternative devices can be compared as conditions for optimizing device selection.

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