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Electric vehicles have become the main contributor in terms of reducing fuel consumption and CO_{2} emission. Although the government is vigorously promoting the use of electric vehicles worldwide, the range anxiety still impedes the rapid development of electric vehicles, especially when air-conditioning also adds battery power consumption and aggravates the range anxiety. To this end, this paper proposes an improved vehicle-mounted photovoltaic system energy management in intelligent transportation systems, which is a maximum power point tracking control system. Meanwhile, since the power of solar panels is usually relatively small and the power changes at any time, low power density and poor controllability are difficult to avoid. In order to solve this problem, this paper offers a tracking control method to improve the output efficiency of solar panels. For improving photovoltaic conversion efficiency and maximizing output power, traditional photovoltaic power panels are often dominated by a centralized maximum power point tracing control, which is named MPPT. Although the cost under this case is lower, the output power of all photovoltaic panels cannot be maximized under the condition of uneven illumination or local mismatch. To improve the situation, a micro-scale inverter is proposed to provide MPPT control of photovoltaic modules, which can effectively improve the output power of each photovoltaic panel. Moreover, our MPPT algorithm is applicable to cloud shadow, building shadow, and shade, and it is more suitable for the car roof. Firstly, the Diode 5-parameter model is used to deduce the

Because of the high temperature in a vehicle in summer, the vehicle owner is very uncomfortable when entering it. In particular, when children are locked in a car, they are frequently killed by heat. Based on this problem, using a photovoltaic cell to drive the air-conditioner and cool the car is very effective. The cooperative control of photovoltaic modules such as solar cells is the key to achieve it because photovoltaic panels can get extra energy and direct power to the air-conditioner without using the electricity in the dynamic battery, which can reduce mileage anxiety. However, the photovoltaic panels provide very limited power due to the limitation of the car roof area. Thus, it is significant to find the maximum power point of onboard photovoltaic panels to increase its power generation and apply this method to the solar energy controller in Figure

PV-based vehicle temperature control system.

According to the external environment, the output power of solar cell varies with the operating point of voltage and current, but the output power has a maximum value, and at this time, the photoelectric conversion efficiency reaches the peak [

The general MPPT method does not need to consider the intelligent disturbance optimization control of the model, such as the disturbance observation method increasing conductance method [

The traditional centralized inverter utilizes a master MPPT controller to control the total output power of the photovoltaic power station by disturbance observation [

Aiming at the vehicle microinverter installed in the solar cell veneer, this paper considered its mechanism mathematical model and quantified the process of finding the maximum power point. The maximum power point of three solar panels is tracked by the mathematical method by using the measured data. This avoids the traditional MPPT method to the circuit caused by multiple disturbances, which is more suitable for improving the power generation efficiency of vehicle photovoltaic panels with less power.

Figure _{ph}, _{D}, and _{sh} stand for the output current, the photogenerated current, the equivalent diode current, and the current flowing over the equivalent parallel resistor, respectively. _{sh}, _{s} are equal to parallel resistance and series resistance; _{D},

Equivalent circuit of the photovoltaic cell.

The equivalent circuit corresponds to five parameter model expressions:

In this form, ^{−19} C; ^{−23} J/K; _{s} is the equivalent diode saturated current.

Formula (_{ph}, _{sh}, _{s}, and _{s} (

The correction at different temperatures and irradiance form is

In this form, _{ph,re} is photogenerated current under standard operating conditions; _{ref} is irradiance under standard conditions ; _{T} is temperature coefficient, available from the manufacturer; _{ref} is diode saturation current in standard condition; _{ref} is temperature under standard conditions; and

The variation of these five parameters with temperature and irradiance is investigated, and the parameter values under standard conditions (ring temperature 25°C, illumination 1000 W/m^{2}) are compared and calculated:

Temperature is 0.99 times of standard temperature and irradiance

Irradiance is the standard value and the temperature is 1.01 times the standard condition (the temperature change is about 3 K, considering the temperature difference within 1 min in extreme cases)

The temperature is the standard temperature, the irradiance is the parameter value of 0.7 times under the standard condition (the irradiance variation is 300 W/m^{2}, considering the amplitude difference within 1 h under normal conditions)

The irradiance is the standard value and the temperature is 1.03 times the parameter value under the standard condition (the temperature change is about 9 K, considering the temperature difference within 1 h in extreme cases)

From Table _{s}, and _{s}, the irradiance has little effect, and it can be considered as a definite value; it means that only _{ph} and _{sh} changed within 1 h. Two calculation modes can be divided according to the time scale. If considering the whole point of timing (such as 10 : 00∼11 : 00), the time length between every two whole points can be specified as a large time scale; then, the large time scale is divided into 60 parts. That is 1 h per minute.

Relationship between the parameters and conditions.

Number of different environmental conditions | Temperature irradiance conditions | _{ph} (A) | _{s} (mA) | _{s} (mW) | _{sh} (W) | |
---|---|---|---|---|---|---|

Standard situation | _{ref}, | _{ph},_{ref} | _{s,ref} | _{s,ref} | _{sh,ref} | |

_{ref} | ||||||

1 | _{ref}, _{ref} | 0.99_{ph,ref} | _{s,ref} | 1.002_{s,ref} | 0.99_{sh,ref} | |

2 | _{ref}, _{ref} | _{ph,ref} + 0.01_{T} | 1.03_{s,ref} | 0.99 | 1.01_{s,ref} | _{sh,ref} |

3 | _{ref}, _{ref} | 0.7_{ph,ref} | _{s,ref} | 1.08_{s,ref} | 0.7_{sh,ref} | |

4 | _{ref}, _{ref} | _{ph,ref} + 0.03_{T} | 1.09_{s,ref} | 0.97 | 1.03_{s,ref} | _{sh,ref} |

Within the same large time scale, each small time scale corresponds to different _{ph}, _{sh}. At this time, only the _{ph}, _{sh} parameters should be identified to simplify the calculation and improve the calculation speed. The whole point needs to consider the large time scale and _{s}, and _{s} change accordingly. At this time, we need to calculate 5 parameters.

The photovoltaic module containing

Schematic diagram of PV panel and equivalent circuit of a unit in PV pane. (a) Single board diagram. (b) Schematic diagram of the equivalent circuit of a series unit of solar cell veneer and component board.

Considering the masking situation, when one or several monomers in a set are obscured, the current will go through directly through the bypass diode. The terminal voltage of each group is the forward conduction voltage of the diode, and the silicon tube is 0.3 V, so the conduction voltage _{DD} = 0.3 V.

Taking into account _{1} cells without shelter, and _{2} cells with shelter; the equivalent diode voltage of each group of cells without shelter is shown in the following formula:

Considering the

There are four different combinations for panels _{1} and _{2}:

_{1} = 0, _{2} = 60, _{1}/_{2} = 0

_{1} = 20, _{2} = 40, _{1}/_{2} = 12

_{1} = 40, _{2} = 20, _{1}/_{2} = 2

_{1} = 60, _{2} = 0, _{1}/_{2} = ∞

When the battery chip is covered, if the _{1} = 60, _{2} = 0; if the value of the _{1} = 40, _{2} = 20; if the _{1} = 20, _{2} = 40; and if the

_{MP} and _{OC} represent the voltage at the maximum power point and the open-circuit voltage, respectively. There are 3 special points on the curve in Figure

The power expression is shown in the following formula:

The derivative of the

At this point, the output power is the maximum output power:

The photoelectric conversion rate and the utilization rate of light energy are the highest. When the initial operating point is (_{1}, _{1}) and the corresponding power is _{1}, it can be seen from the _{MP}, _{MP}) through the external control device.

When the solar panel is partially shaded, the _{JMP} represents the voltage at the local maximum power point and _{JMP} represents the power at the local maximum power point. Conventional perturbation optimization _{PPT} methods have the probability of tracing to the local peak points, which are the pseudo-maximum points.

Bimodal characteristics of

Aiming at the fault of parameter identification by parameter correction method, a parameter identification method which uses real-time gaugement data is proposed in this paper. According to the analysis in Section

Adjust the external circuit of the photovoltaic module five times and then measure voltage and current values of 5 groups; thus, determine the corresponding 5-parameter model according to the voltage situation;

According to the 5-parameter model and the 5 sets of voltage and current values, the 5 equations are determined as shown in formula (

In this formation, _{i} and _{s} are the current values in the _{i} is the voltage value in group

For any moment, assuming that the irradiance is the same as the previous integral moment, we replace 3 parameters of the five which are only affected by temperature change with integral values. By measuring two sets of voltage and current values, we established two equations for the two parameters greatly affected by irradiance. The expression of the two parameters is shown in formula (

In this formula,

Simplify the I-U curve formulas (

Formulas (

Combine formulas (_{MP}, _{MP}) is solved out.

If assuming that

then

Formulas (

In these formulas,

Formula (

Taking the maximum power point of a moment as the initial iteration value and putting _{1}) and then bring it back and find out _{1}). Under the condition that _{1}) has two values, then compare the corresponding power values and take a set of values with the large corresponding power. Iterating it to the error within the allowable range, the corresponding

Assuming that the load is a combination of constant power, invariant voltage, and invariant resistance, it is connected to the photovoltaic module by Buck circuit as shown in Figure

External buck circuit and load equivalent circuit diagram.

The voltage and current at the end of the system in relation to the duty cycle

After calculating the corresponding

Data in this article is simulated by PVsyst6.61. We establish a system that adopts a microinverter structure in PVsyst6.61 and each photovoltaic panel is equipped with a microinverter. Each PV module consists of 60 batteries.

We simulated a module board in PVsyst6.61 which has 6 series battery cells, and every two parallels have bypass diodes.

Select a panel in PVsyst to verify the feasibility of this method under the condition of no shading, 2 shadings, and 4 shadings, respectively. The simulation of cloud shadow masking and the internal mismatch is carried out through artificial masking, which causes some interference to the circuit. The data of panel current and voltage (3 groups in total) is collected as shown in Table

Data of current and voltage of PV panel.

_{2}/_{1} | (_{1}, _{1}) | (_{2}, _{2}) | (_{3}, _{3}) | (_{4}, _{4}) | (_{5}, _{5}) |
---|---|---|---|---|---|

0 | 17.6, 5.3 | 23.0, 5.2 | 27.5, 5.0 | 29.1, 4.3 | 30.85, 3.6 |

0.5 | 11.4, 5.3 | 14.5, 5.2 | 17.9, 4.9 | 19.7, 4.2 | 21.0, 3.3 |

2 | 5.9, 5.2 | 7.11, 5.2 | 8.33, 5.0 | 9.22, 4.3 | 9.86, 4.0 |

By using the data in Table _{ph}, _{s}, _{s}, _{sh}] = [6, 0.000001, 25, 0.0002, 6000]. The initial values are gained from the factory parameters of photovoltaic modules, which is the corresponding 5 parameter values under the standard working condition. When the quasi-Newton method is used for iterative calculation, the selection of the initial values is related to the iterative speed and the convergence of the results. In the actual operation, the result of the last parameter identification can be taken as the initial value of the next iteration to ensure the reliability of the iteration and obtain the parameters. The identification results are shown in Table

Result of parameter identification.

Experimental group | _{ph} (A) | _{s} (mA) | _{s} (mW) | _{sh} (W) | |
---|---|---|---|---|---|

No shelter | 5.4 | 2.2 | 25.5 | 3.3 | 12354 |

2-line shelter | 5.3 | 2.1 | 25.5 | 4.2 | 8891 |

4-line shelter | 5.2 | 2.5 | 25.7 | 3.8 | 9192 |

The photovoltaic characteristic curve equation can be written by using the 5 parameters. According to the steps described in Section

Maximum power point computation.

Experimental group | _{ph} (A) | Relative power error (%) | |||
---|---|---|---|---|---|

No shelter | MPP1 | 28.2 | 4.8 | 135.36 | −2.04 |

MPP2 | 29.4 | 4.7 | 138.18 | ||

2-line shelter | MPP1 | 18.2 | 4.9 | 89.18 | 7.39 |

MPP2 | 17.3 | 4.8 | 83.04 | ||

4-line shelter | MPP1 | 9.1 | 4.8 | 43.68 | −2.1 |

MPP2 | 9.5 | 4.7 | 44.65 |

Maximum power point computation under three different real-weather environments.

Experimental group | |||
---|---|---|---|

Sunny days | 27.92 | 4.65 | 129.83 |

Cloudy days | 9.12 | 4.70 | 42.86 |

Cloud shading days | 16.56 | 4.77 | 78.99 |

The value of the maximum power point calculated by the method described in this paper is consistent with the value of the maximum power point tracked by the MPPT control strategy basically. However, because there are errors during measure and model, the results will not be completely consistent.

Using the five-parameter model of the solar cell to model the mechanism of photovoltaic module and the mathematical model to solve the maximum power point directly, the conclusion is as follows:

Different combinations of temperature and irradiance correspond to different values of 5 parameters; the disturbance circuit can gain equations for solving 5 parameters by measuring the values of voltage and current. In order to get the real-time value of 5 parameters, the maximum power point is solved directly by a mathematical equation. Compared with the traditional disturbance observation method, this direct mathematical method has fewer interference times with the circuit and it can provide faster MPPT speed.

The selection of initial values is related to the iteration speed and convergence of the results. The identification results of the parameters at the last moment offer the best iterative initial value for the next moment, and the iterative results have preferable convergence.

By dividing the unused time scale and utilizing the relationship between 5 parameters and temperature and irradiance, the parameters with less influence can be regarded as invariant for a period of time, so only two parameters need to be identified. Different time scales correspond to different parameter identification numbers; thus, this method simplifies the calculation process.

The data used to support the findings of this study are included within the article.

The authors declare that there are no conflicts of interest regarding the publication of this paper.

The project was supported by the Key Program of National Natural Science Foundation of China (61433004).