CN107154669A - A kind of outdoor light storage LED high power density transform methods of wide scope input - Google Patents

Abstract

The invention discloses a wide-range input outdoor light storage LED high power density conversion method, including a charging part with MPPT function and an LED constant current driving part; The Buck-Boost type is the main topology of the bidirectional synchronous rectification DC-DC converter. When the DC-DC converter is running in the forward direction, the charging loop adopts the Buck-type topology structure, and the battery is combined with MPPT, constant voltage and constant current. Stage charging method; when the DC-DC converter is running in reverse, the discharge loop adopts a Boost topology to realize the constant voltage output of the LED lamp and has a PWM dimming function; at the same time, it adopts an improved control method based on traditional disturbance observation, According to the I‑V characteristics of the solar cell, each increment is converted into the next actual approach to the step of the control voltage to prevent over-control and reduce frequent disturbances during the steady state of the components.

Description

A wide-range input outdoor light-storage LED high power density conversion method

technical field

The invention relates to the technical field of solar LED lighting, in particular to a wide range input outdoor light storage LED high power density conversion method.

Background technique

The perturbation and observation method is one of the most commonly used MPPT algorithms at present, and its working process is to periodically perturb the output voltage of the solar cell (V+ V), and then compared with the output power before the disturbance, if the power value is increasing, it means that the disturbance direction is consistent with the control direction and continues to move in the same direction (+ V) changes; if the power value is decreasing instead, go in the opposite direction (— V) changes so that repeated perturbations will output their maximum power value.

The perturbation and observation method is to change its voltage value at regular intervals, and the next step of the control signal is judged by the direction of output power change. The specific adjustment scheme is as follows: U and I represent the last value, and the corresponding output power is P, , represents the current value, is its power. When increasing the relative reference voltage, there are two phenomena: (1) P1>P means that the change direction is correct, and the system disturbance direction remains unchanged; (2) P1<P means that the change direction is wrong, and the next disturbance direction of the system is to change. This cycle is repeated, and the disturbance is stopped when the operating point is close to the maximum power value. The main disadvantage of the perturbation-and-observation method is that The U step size is fixed. if If U is too large, there will be particularly serious oscillations around the maximum power point, and there will be a large power loss; if △U is too small, it will take a long time to track the maximum power point, which will bring serious problems in real life. Great inconvenience.

Contents of the invention

The purpose of the present invention is to provide a wide-range input outdoor light storage LED high power density conversion method, using an improved control method based on traditional disturbance observation, according to the I-V characteristics of solar cells, each increment is converted to the next Actual approximation to the step size of the control voltage to prevent over-control and reduce frequent disturbances during the steady state of the components; at the same time, the set DC-DC converter has the advantages of simple structure, only a small number of switching devices and low loss, and the battery The output at both ends uses an LCL filter, which can better reduce the ripple current and ripple voltage on the battery side, so as to solve the problems raised in the above-mentioned background technology.

In order to achieve the above object, the present invention provides the following technical solutions: a wide-range input outdoor light storage LED high power density conversion method, including the charging part of the MPPT function and the LED constant current driving part, the charging part of the MPPT function and the LED constant current driving part The current drive part is controlled by a Buck-Boost type bidirectional main circuit designed synchronous rectification DC-DC converter and an improved PID control method based on the MPPT principle; its bidirectional main circuit design is as follows: including LED terminal, PV terminal, Battery terminal, Capacitors and their drive switches Q1, Q2, Q3, Q4, and Q5 connected in series or parallel with each other, and have three working modes:

(1) Buck works, the inductor current iL is always kept greater than zero, Q1 works and Q2 does not work, and flows from the PV terminal to the Battery terminal, and iL continues to increase until t=ton, Q1 cuts off, D2 continues to work, and Q2 has no current passing through;

(2) Boost works, the inductor current iL is always kept less than zero, and flows from the Battery terminal to the LED terminal. From ton to T, Q2 works and Q1 does not work, and iL continues to increase. When the time T is reached, Q2 stops working and D1 continues Current work, Q1 no current through;

(3) Alternate work, the positive and negative of the inductor current iL appear alternately: at the time t0-t1, Q1 is on and working, at the time t1-ton, Q1 is on and there is current passing through, D2 continues to flow, iL will continue to decrease and the value Still greater than zero; at the time ton-T, Q2 is turned on and current flows, iL keeps rising but the value is less than zero.

Its improved PID control method based on the MPPT principle is as follows:

S1: Input the given amount R, and set the R value to zero;

S2: Set the input quantity of the PID controller, that is, the negative dp/du of the system deviation;

S3: The PID controller adjusts the duty ratio of the PWM wave of the DC-DC converter to change the output equivalent load of the photovoltaic cell to achieve maximum power point tracking.

Preferably, there are two working modes of the bidirectional main circuit based on the Buck-Boost type, that is, step-down mode and boost mode; in the step-down mode, when energy flows from PV to Battery, the power supply terminal is the PV terminal, and Q1 drives , Q3 and Q4 are turned on, Q5 is turned off, forming a Buck step-down circuit; the boost mode is when the battery flows to the LED, the power supply terminal is the Battery, at this time Q2 is driven, Q3 and Q5 are turned on, and Q4 is turned off, forming a Boost step-up circuit.

Preferably, the charging part of the MPPT function includes MPPT charging mode, constant voltage equalizing charging mode, constant voltage floating charging mode, waiting mode, ready-to-discharge mode and ready-to-charge mode.

Preferably, the LED constant current driving part includes a first time period constant current driving mode, a second time period constant current driving mode and a third time period constant current driving mode.

Preferably, when the DC-DC converter is running in the forward direction, the charging loop adopts a Buck topology to charge the battery in a three-stage charging method combining MPPT, constant voltage and constant current; when the DC-DC converter is running in the reverse direction , The discharge loop adopts a Boost topology to realize the constant voltage output of the LED lamp and has a PWM dimming function.

Compared with prior art, the beneficial effect of the present invention is:

The design method of outdoor solar storage LED high power density conversion device with wide range input adopts the improved control method based on traditional disturbance observation, and according to the I-V characteristics of solar cells, each increment is converted into the next actual approximation control voltage step size to prevent over-control, and reduce frequent disturbances during the steady state of components; at the same time, the set DC-DC converter has the advantages of simple structure, only a small number of switching devices and low loss, and the output at both ends of the battery uses The LCL filter is used, which can better reduce the ripple current and ripple voltage on the battery side, realize the constant voltage output of the LED lamp, and have PWM dimming function.

Description of drawings

Fig. 1 is the program design flowchart of the present invention;

Fig. 2 is the improved PID control schematic diagram based on the MPPT principle of the present invention;

Fig. 3 is the structural block diagram of PID control of the present invention;

Fig. 4 is the output P-U curve of photovoltaic cell of the present invention;

Fig. 5 is the basic schematic diagram of the bidirectional Buck-Boost converter of the present invention;

Fig. 6 is the inductance current waveform diagram under three working modes of the Buck-Boost converter of the present invention;

Fig. 7 is the equivalent circuit diagram of photovoltaic array of the present invention;

Fig. 8 is a simulation model diagram of a photovoltaic array of the present invention;

Fig. 9 is the output U-I characteristic curve diagram of photovoltaic array of the present invention;

Fig. 10 is the output U-P characteristic curve of the photovoltaic array of the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to Figure 1-10, the present invention provides a technical solution: a wide-range input outdoor light storage LED high power density conversion method, including the charging part of the MPPT function and the LED constant current drive part, the charging part of the MPPT function includes MPPT charging mode, constant voltage equalizing charging mode, constant voltage floating charging mode, waiting mode, ready discharge mode and ready charging mode; MPPT charging mode is when there is a certain irradiance, the voltage output of the solar panel is greater than a certain value (12V system 14V , 24V system 28V), if the battery voltage is lower than the constant voltage equalizing charging voltage, the controller will perform MPPT tracking on the solar panel and charge the battery with the maximum power; the constant voltage equalizing charging mode is when there is a certain irradiance, the solar battery When the board is normal, the battery voltage reaches the constant voltage equalization charging voltage, the controller will give up MPPT tracking, and carry out constant voltage equalization charging on the battery to protect the battery; the constant voltage floating charge mode is when there is a certain irradiance, the solar panel is normal When the battery voltage reaches the constant voltage equalizing charging voltage and the charging current decreases to 0.5A, the controller will give up the constant voltage equalizing charging and perform constant voltage floating charging on the battery to protect the battery; when the waiting mode is dusk, the light radiation The illuminance is getting weaker and weaker, the output voltage of the solar panel is less than a certain value (12V system corresponds to 14V, 24V system corresponds to 28V), the energy provided cannot charge the battery, the controller gives up charging, and enters the waiting mode; the ready discharge mode is when the solar energy When the voltage of the battery board is lower than a certain value (12V system corresponds to 6V, 24V system corresponds to 12V, the user can set this parameter), enter the ready discharge mode, confirm for 30s, enter the constant current drive mode; the ready charge mode is at dawn, the light is getting more and more Strong, when the output voltage of the solar panel is greater than a certain value (12V system corresponds to 12V, 24V system corresponds to 24V), after a delay of 30s, stop the constant current drive LED and enter the charging preparation mode; the LED constant current drive part includes the first time period Constant current driving mode, that is, entering the first time period of constant current driving LED, the LED driving current changes slowly, and finally reaches the percentage of the driving current in the first time period, and the second time period constant current driving mode, that is, when the first time period constant After the current driving, it will automatically enter the second time period, and the LED brightness will change slowly, and finally reach the percentage of the driving current in the second time period. In the three time periods, the brightness of the LED changes slowly, and finally reaches the percentage drive current of the third time period; the charging part of the MPPT function and the LED constant current driving part are controlled by the synchronous rectification DC-DC of the Buck-Boost type bidirectional main circuit design The converter and the improved PID control method based on the MPPT principle; when the DC-DC converter is running forward, the charging loop adopts a Buck topology, and the battery is charged with a three-stage charging method combining MPPT, constant voltage and constant current; When the DC-DC converter operates in reverse, the discharge loop adopts Boost topology to realize constant voltage output of LED lamps. output, and has PWM dimming function, its two-way main circuit design is as follows: including LED terminal, PV terminal, Battery terminal, capacitor and its driving switches Q1, Q2, Q3, Q4, Q5 connected in series or parallel with each other, its working mode setting There are two types, namely buck mode and boost mode; in the buck mode, when energy flows from PV to Battery, the power supply terminal is PV terminal, Q1 is driven, Q3 and Q4 are turned on, and Q5 is turned off, forming a Buck step-down circuit; The voltage mode is when the battery flows to the LED, the power supply terminal is the battery, at this time Q2 is driven, Q3 and Q5 are turned on, and Q4 is turned off to form a Boost boost circuit, and there are 3 working modes:

(1) Buck works, the inductor current iL is always kept greater than zero, Q1 works and Q2 does not work, and flows from the PV terminal to the Battery terminal, and iL continues to increase until t=ton, Q1 cuts off, D2 continues to work, and Q2 has no current passing through;

(2) Boost works, the inductor current iL is always kept less than zero, and flows from the Battery terminal to the LED terminal. From ton to T, Q2 works and Q1 does not work, and iL continues to increase. When the time T is reached, Q2 stops working and D1 continues Current work, Q1 no current through;

(3) Alternate work, the positive and negative of the inductor current iL appear alternately: at the time t0-t1, Q1 is on and working, at the time t1-ton, Q1 is on and there is current passing through, D2 continues to flow, iL will continue to decrease and the value Still greater than zero; at the time ton-T, Q2 is turned on and current flows, iL keeps rising but the value is less than zero.

Its improved PID control method based on the MPPT principle is as follows:

It can be seen from the attached figure that the maximum power point (MPP) of a photovoltaic cell is the point on the curve where the corresponding slope is zero, and such a point is unique; on both sides of the maximum power point, the absolute value of the slope corresponding to the operating point is , is positively correlated with the distance from the current operating point to the maximum power point; thus, the output of the solar photovoltaic cell array can be Feedback to the input terminal, and the input given amount R is set to zero, and its system deviation, that is, the negative one, is used as the input of the PID controller; therefore, the PID control can continuously Adjust the duty cycle of the PWM wave of the DC-DC converter to change the output equivalent load of the photovoltaic cell, thereby adjusting the output voltage of the photovoltaic cell until the output voltage of the photovoltaic cell works at the voltage corresponding to the maximum power point to achieve the maximum Power point tracking.

Embodiment one:

Mathematical physical model of solar cell: In reality, when the solar cell connected to the load is illuminated, the photo-generated current passes through the load, and a terminal voltage will be formed at both ends of the load. At this time, the circuit working process of the solar cell can be shown in the figure, etc. In the figure, the solar cell is regarded as a current source that can generate stable photocurrent (the light source is stable); in the figure, it is the series resistance of the solar cell, which is mainly composed of the bulk resistance of the solar cell, the surface resistance of the solar cell, The solar cell electrode conductor resistance and the contact resistance between the electrode and the Gui surface are the leakage resistance of the photovoltaic cell, also known as the crossover resistance, which is caused by the unclean edge of the silicon wafer or the defect in the body; the positive current flowing through the diode The total diffusion current and bypass current to the current passing through the junction are provided, and the remaining photogenerated current passes through, flows out of the solar cell and enters the load; according to the characteristics of the photovoltaic array, its working mode can be determined by the circuit shown in Figure 7 Equivalent;

In Figure 8, ISC represents the excitation current of the photovoltaic array, which is determined by factors such as light intensity and temperature, and the stronger the light intensity, the greater the ISC. IVD represents the diffusion current of the photovoltaic array, and its magnitude can be obtained by formula (7)

(7)

In the formula, q——electron charge;

A - constant factor;

K - Boltzmann's constant.

I _DO represents the saturation current of the photovoltaic array when there is no light, and its magnitude can be obtained by formula (8)

(8)

In the formula, A——pn junction area of photovoltaic module;

E _g - the band gap of the material;

N _V , N _C —the effective density of states of the valence band and the conduction band;

N _D , N _A ——the density of donor impurity and acceptor impurity;

D _p , D _n ——diffusion coefficients of holes and electrons;

, - Minority carrier lifetimes of holes and electrons.

According to the equivalent circuit in Figure 8, the load current I _L can be obtained as

(2-3)

Where R _S - bypass resistance;

R _sh ——side leakage group.

According to the mathematical model and equivalent circuit of the photovoltaic array, the model is established in MATLAB/Simulink as shown in Figure 8.

Among them, T _C is the temperature of the outside world, and S is the intensity of sunlight, which is taken in MATLAB/Simulink in this paper , S=500W/m ² . Change the load values at both ends of the photovoltaic array PV to obtain the values of the output voltage U and current I corresponding to the PV, and fit the above multiple sets of data to obtain the UI characteristic curve as shown in Figure 9, and the UP characteristic curve as shown in Figure 10; Write the above data into the photovoltaic simulator through the host computer to simulate the output characteristics of the photovoltaic array.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (5)

1. the outdoor light storage LED high power density transform methods of a kind of wide scope input, it is characterised in that including MPPT functions Live part and LED constant current drive part, the live part and LED constant current drive part of its MPPT function are controlled by Buck- The synchronous rectified DC-DC converter of the two-way main circuit design of Boost type and based on the improved PID control method of MPPT principles； Its two-way main circuit design is as follows：Opened including LED ends, PV ends, Battery ends, electric capacity and its driving in series or in parallel with each other Q1, Q2, Q3, Q4, Q5 are closed, and is provided with 3 kinds of working methods：

（1）Buck is worked, and inductive current iL is always maintained at not working more than zero, Q1 work Q2, and Battery ends are flow to by PV ends, IL is continuously increased when t=ton, and Q1 cut-offs, D2 afterflows work, Q2 no currents pass through；

（2）Boost is worked, and inductive current iL is always maintained at being less than zero, and LED ends, in ton to T, Q2 are flowed to by Battery ends Work Q1 is not worked, and iL is continuously increased, when reaching T moment, and Q2 cut-offs are stopped, and D1 afterflows work, Q1 no currents pass through；

（3）Alternation, inductive current iL is positive and negative to be alternately present:At t0-t1 moment, Q1 ON operations, at t1-ton moment, Q1 Conducting has electric current to pass through simultaneously, D2 afterflows, and iL can constantly diminish and value is still more than zero；At the ton-T moment, Q2 is turned on and is had electricity Stream flows through, and iL constantly rises but value is less than zero；

It is as follows that it is based on the improved PID control method of MPPT principles：

S1：Specified rate R is inputted, and R values are set as zero；

S2：Set the negative dp/du of the input quantity of PID controller, i.e. system deviation amount；

S3：The dutycycle of PID controller regulation DC-DC converter PWM ripples loads to change the output equivalent of photovoltaic cell, realizes MPPT maximum power point tracking.

2. a kind of outdoor light storage LED high power density transform methods of wide scope input according to claim 1, its feature It is, the mode of operation of the two-way main circuit based on Buck-Boost types is provided with two kinds, i.e. decompression mode and boost mode；Its When decompression mode is that energy flow to Battery by PV, power end is PV ends, and Q1 drivings, Q3, Q4 are opened, and Q5 is closed, composition Buck reduction voltage circuits；Boost mode is when flowing to LED by Battery, power end is Battery, and now Q2 drives, Q3, Q5 Open, Q4 is closed, constitute Boost circuit.

3. a kind of outdoor light storage LED high power density transform methods of wide scope input according to claim 1, its feature It is, the live part of MPPT functions includes MPPT charge modes, constant pressure charge mode, constant voltage floating charge pattern, standby mode, standard Standby discharge mode and preparation charge mode.

4. a kind of outdoor light storage LED high power density transform methods of wide scope input according to claim 1, its feature It is, when LED constant current drive part is including first time period constant current drive pattern, second time period constant current drive pattern and the 3rd Between section constant current drive pattern.

5. a kind of outdoor light storage LED high power density transform methods of wide scope input according to claim 1, its feature Be, DC-DC converter forward direction operation when, charge loop use Buck type topological structures, to battery carry out MPPT, constant pressure, The three stage charging methods that constant current is combined；When DC-DC converter inverted running, electric discharge loop is using Boost type topology knot Structure, realizes the constant pressure output of LED, and with PWM dimming functions.