阅读说明：本技术 一种光伏发电单元的灵活功率跟踪控制方法及其应用 (Flexible power tracking control method for photovoltaic power generation unit and application thereof ) 是由 薛宁 周国华 毕强 于 2021-08-04 设计创作，主要内容包括：本发明公开了一种光伏发电单元的灵活功率跟踪控制方法及其应用。所述光伏发电单元通过DC-DC变换器连接到直流母线,负载连接到直流母线。该控制方法判断光伏发电单元的参考功率与输出功率的大小,选择其工作状态为MPPT模式或恒定功率跟踪模式,实时控制光伏发电单元的输出,调节直流母线电压。本发明适用于光照强度、负载功率不断变化的场合。在光伏发电单元应用于牵引供电系统与微电网系统时,本发明可以减少制动电阻与散热装置的使用,降低了成本,并且可以减小其他稳压装置如储能装置的容量,延长了储能装置的寿命。(The invention discloses a flexible power tracking control method of a photovoltaic power generation unit and application thereof. The photovoltaic power generation unit is connected to the direct current bus through the DC-DC converter, and the load is connected to the direct current bus. The control method judges the reference power and the output power of the photovoltaic power generation unit, selects the working state of the photovoltaic power generation unit to be the MPPT mode or the constant power tracking mode, controls the output of the photovoltaic power generation unit in real time and adjusts the direct-current bus voltage. The invention is suitable for occasions with constantly changing illumination intensity and load power. When the photovoltaic power generation unit is applied to a traction power supply system and a micro-grid system, the invention can reduce the use of a brake resistor and a heat dissipation device, reduce the cost, reduce the capacity of other voltage stabilizing devices such as an energy storage device and prolong the service life of the energy storage device.)

1. A flexible power tracking control method of a photovoltaic power generation unit is disclosed, wherein the photovoltaic power generation unit is connected to a direct current bus through a DC-DC converter, and a load is connected to the direct current bus; it is characterized by comprising:

step 1: calculating a reference power P of a photovoltaic power generation unit_refAnd the output power P_PVAfter the absolute value of the error is obtained, the absolute value is multiplied by a proportionality coefficient K to obtain a voltage step length V_step；

Step 2: such as reference power P of photovoltaic power generation unit_refGreater than the output power P_PVIf not, entering a constant power tracking mode;

the MPPT mode is realized by using a disturbance observation method:

if P_PVGreater than P_{PV_old}And V is_PVLess than or equal to V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}–V_step；

If P_PVGreater than P_{PV_old}And V is_PVGreater than V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}+V_step；

If P_PVLess than or equal to P_{PV_old}And V is_PVLess than or equal to V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}+V_step；

If P_PVLess than or equal to P_{PV_old}And V is_PVGreater than V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}–V_step；

The constant power tracking mode is: updating the reference voltage V_refIs a V_{ref_old}–V_step；

Wherein, P_{PV_old}Reference power, V, obtained for the last disturbance_PVFor the present output voltage, V_{PV_old}Output voltage, V, obtained for the last disturbance_{ref_old}The reference voltage obtained for the last perturbation;

and step 3: reference voltage V after updating_refAnd the present output voltage V_PVAnd controlling the DC-DC converter through signals obtained by PID and PWM.

2. The use of a method for flexible power tracking control of a photovoltaic power generating unit according to claim 1, characterized in that it further comprises traction power supply means and braking resistance means connected to the dc bus respectively; the brake resistor device adopts a voltage closed-loop control method to control the voltage of the direct-current bus; the load is a locomotive connected to a direct current bus through a DC-AC converter.

3. The application of the flexible power tracking control method of the photovoltaic power generation unit according to claim 1, characterized by further comprising a traction power supply device and a super capacitor energy storage device which are respectively connected to the direct current bus; the super capacitor energy storage device adopts a double closed-loop control method to control the voltage of a direct current bus; the load is a locomotive connected to a direct current bus through a DC-AC converter.

4. The application of the flexible power tracking control method of the photovoltaic power generation unit according to claim 1, further comprising a super capacitor energy storage device connected to the direct current bus; the super capacitor energy storage device adopts a double closed-loop control method to control the voltage of the direct current bus.

Technical Field

The invention relates to the technical field of new energy power generation, in particular to a flexible power tracking control method of a photovoltaic power generation unit and application thereof.

Background

With the increasing urban population, subways become indispensable transportation means in people's lives. Meanwhile, along with the rapid increase of the total mileage of rail transit operation, the power consumption of the subway is huge, and the problems of energy exhaustion and environmental pollution occur. Therefore, new energy sources gradually move into the field of view of the public. Wherein, the solar energy which is clean and convenient to take and use is distinguished from a plurality of new energy sources. In recent years, research on application of new energy to urban rail transit is receiving attention. The subway traction power supply system adopts photovoltaic power generation, so that not only can a part of power supply problems be solved, but also photovoltaic electric energy can be absorbed. In the application of a photovoltaic Power generation unit, a current research focus is mainly to enable a photovoltaic array to output Maximum Power through a Maximum Power Point Tracking (MPPT) algorithm, so as to improve the energy utilization rate of a photovoltaic Power generation system. However, in areas with abundant solar energy resources, the photovoltaic power generation system may have a situation of excessive power generation, which affects the normal operation of the load.

When the photovoltaic power generation unit is applied to a subway traction power supply system, the output characteristic of a photovoltaic array is easily influenced by temperature and illumination intensity, meanwhile, the distance between adjacent stations of a subway is short, and a locomotive is frequently started and braked. Therefore, the output characteristics of the photovoltaic array and the characteristics of the traction load tend to cause the bus voltage of the overhead line system to fluctuate greatly. When the maximum output power of the photovoltaic array is lower than the traction power of the locomotive, the bus voltage drops. When the bus voltage is lower than the corresponding reference lower limit value, other power supply units of the subway traction power supply system provide electric energy which is more than that of a photovoltaic power generation part in the traction process of the locomotive, and the bus voltage is maintained to be higher than the reference lower limit value. The maximum output power of the photovoltaic array is higher than the traction power of the locomotive and the braking process of the locomotive, so that the bus voltage of the contact network can be increased, and even the direct-current bus overvoltage of the contact network is caused. It is therefore necessary to take measures to limit the busbar voltage of the catenary to a safe range. In a subway traction power supply system, a traditional energy consumption mode is that a brake resistor is adopted to consume redundant electric energy, the power difference between a photovoltaic power generation system and a locomotive is balanced, and the direct-current bus voltage is prevented from exceeding a safety range. However, the temperature of the subway traction power supply system can be increased by adopting the brake resistor to consume electric energy, and the use of the heat dissipation device causes the cost increase.

Disclosure of Invention

The invention aims to provide a flexible power tracking control method of a photovoltaic power generation unit and application thereof.

The technical scheme for realizing the purpose of the invention is as follows:

a flexible power tracking control method of a photovoltaic power generation unit is disclosed, wherein the photovoltaic power generation unit is connected to a direct current bus through a DC-DC converter, and a load is connected to the direct current bus; the method comprises the following steps:

step 1: calculating a reference power P of a photovoltaic power generation unit_refAnd the output power P_PVAfter the absolute value of the error is obtained, the absolute value is multiplied by a proportionality coefficient K to obtain a voltage step length V_step；

Step 2: such as reference power P of photovoltaic power generation unit_refGreater than the output power P_PVIf not, entering a constant power tracking mode;

the MPPT mode is realized by using a disturbance observation method:

if P_PVGreater than P_{PV_old}And V is_PVLess than or equal to V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}–V_step；

If P_PVGreater than P_{PV_old}And V is_PVGreater than V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}+V_step；

If P_PVLess than or equal to P_{PV_old}And V is_PVLess than or equal to V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}+V_step；

If P_PVLess than or equal to P_{PV_old}And V is_PVGreater than V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}–V_step；

The constant power tracking mode is: updating the reference voltage V_refIs a V_{ref_old}–V_step；

Wherein, P_{PV_old}Reference power, V, obtained for the last disturbance_PVFor the present output voltage, V_{PV_old}Output voltage, V, obtained for the last disturbance_{ref_old}The reference voltage obtained for the last perturbation;

and step 3: reference to be updatedVoltage V_refAnd the present output voltage V_PVAnd controlling the DC-DC converter through signals obtained by PID and PWM.

Another application of the control method is that the control method further comprises a traction power supply device and a brake resistance device which are respectively connected to the direct current bus; the brake resistor device adopts a voltage closed-loop control method to control the voltage of the direct-current bus; the load is a locomotive connected to a direct current bus through a DC-AC converter.

One application of the control method is that the control method further comprises a traction power supply device and a super capacitor energy storage device which are respectively connected to the direct current bus; the super capacitor energy storage device adopts a double closed-loop control method to control the voltage of a direct current bus; the load is a locomotive connected to a direct current bus through a DC-AC converter.

The control method further comprises a super capacitor energy storage device connected to the direct current bus; the super capacitor energy storage device adopts a double closed-loop control method to control the voltage of the direct current bus.

Compared with the prior art, the invention has the beneficial effects that:

firstly, the disturbance step length of the invention is determined by the error between the reference power and the output power of the photovoltaic array, so that the output power of the photovoltaic array can quickly follow the change of the reference power, and the invention is suitable for occasions with constantly changing illumination intensity and load power. The invention limits the working point of the constant power tracking mode to the left side of the maximum power point, and ensures that the photovoltaic array can normally work under the condition of illumination intensity fluctuation.

Compared with the control method of the existing photovoltaic access subway traction power supply system, the method provided by the invention not only reduces the waste of traditional energy and the use of a heat dissipation device of the system, reduces the cost, but also can reduce the capacity of other voltage stabilizing devices of the system and prolong the service life of other voltage stabilizing devices.

Compared with the control method of the existing photovoltaic access subway traction power supply system, the method can control the output of the photovoltaic array in real time to realize the stability of the bus voltage of the overhead line system, and omits the division of working condition modes and the complex process of mutual conversion in the existing control method.

Drawings

Fig. 1 is a schematic diagram of a circuit topology and a control method according to a first embodiment.

Fig. 2 is a schematic diagram of a power increment calculation principle in the first embodiment.

Fig. 3 is a schematic diagram illustrating a principle of calculating traction power according to a first embodiment.

Fig. 4 is a schematic diagram of a reference power calculation principle in the first embodiment.

Fig. 5 is a flow chart of the flexible power tracking control method of the present invention.

FIG. 6 is a power curve diagram of a locomotive running in the first embodiment. When the power is positive, the power is the traction power of the locomotive; when the power is negative, the power is the braking power of the locomotive.

Fig. 7a, 7b, 7c and 7d are simulation waveform diagrams of bus voltage, photovoltaic array output power, grid output power and brake resistance consumption power of a contact network in the locomotive operation process achieved by the control method of the existing photovoltaic access subway traction power supply system.

Fig. 8a, 8b, 8c and 8d are simulation waveform diagrams of bus voltage, photovoltaic array output power, grid output power and brake resistance consumed power of a contact network in the locomotive operation process achieved by the flexible power tracking control method of the photovoltaic access subway traction power supply system.

The simulation conditions of fig. 7 and 8 are as follows: the high-voltage power grid is 110kV three-phase alternating current with the frequency of 50Hz, and the direct-current bus capacitor C_dc9600. mu.F. The photovoltaic array is composed of 13 x 30 photovoltaic cells connected in series and parallel, and the maximum output power is 105241.5W. The maximum power of the photovoltaic cell is 269.85W, and the corresponding output voltage at the maximum power point is 44.5V. Inductor L of 200 μ H, input capacitor C_i1000 muF, switching frequency 100 kHz. The sampling period of the maximum power tracking control of fig. 7 and the sampling period of the flexible power tracking control of fig. 8 are both 0.05 ms.

Fig. 9 is a schematic diagram of a circuit topology and a control method according to a second embodiment.

Fig. 10 is a schematic diagram of a circuit topology and a control method according to a third embodiment.

Detailed Description

With the increase of the installed photovoltaic capacity, the photovoltaic power generation unit plays a crucial role in maintaining the stability of the subway traction system. The single MPPT algorithm of the existing photovoltaic power generation system cannot maintain the bus voltage balance of the overhead contact system, and the output of the photovoltaic array needs to be controlled in real time according to the working condition of a locomotive so as to adjust the bus voltage of the overhead contact system. When the electric energy generated by the photovoltaic array is lower than the load demand, adjusting the output power of the photovoltaic array to increase; when the electric energy generated by the photovoltaic array is higher than the demand of the load, the output power of the photovoltaic array is adjusted to be reduced to the demand power of the load, the braking resistor is only used in the braking process of the locomotive, and the generation of heat and the use of a heat dissipation device are reduced. Based on the method, the invention provides a flexible power tracking control method of a photovoltaic power generation unit and application thereof, and stable control of direct current bus voltage of a contact network is realized.

The present invention is further illustrated by the following specific examples.

Example one

As shown in fig. 1, the specific method is as follows:

step 1: and initializing parameters. The method specifically comprises the following steps: the method comprises the following steps of measuring parameters such as the upper limit and the lower limit of the voltage of the direct current bus, the reference voltage of the direct current bus, the sampling period of flexible power tracking, the initial reference voltage of the photovoltaic array and the like.

Step 2: and calculating a power reference value of the photovoltaic power generation. Firstly, collecting direct current bus voltage, calculating the difference value between the bus voltage and a corresponding reference value, and calculating power increment by combining the voltage difference value and the input current of the locomotive. The traction power of the locomotive is then calculated from the bus voltage and the input current of the locomotive. And finally, calculating the power required to be provided by the traction power supply system by combining the power increment and the locomotive traction power, and using the power as a power reference value of the photovoltaic power generation.

And step 3: the flexible power tracking control regulates the output of the photovoltaic array. Firstly, the system collects the output voltage and the output current of the photovoltaic array and calculates the output power of the photovoltaic array. And then, multiplying the absolute value of the error between the reference power and the output power of the photovoltaic array by a proportionality coefficient to obtain a voltage step. And judging the output power of the photovoltaic array and the reference power and selecting different working modes. If the reference Power is larger than the output Power of the photovoltaic array, the Maximum Power Point Tracking (MPPT) mode is entered, otherwise, the constant Power Tracking mode is entered. The MPPT mode is realized by using a disturbance observation method, and the reference voltage is updated according to the power difference value before and after disturbance, the positive and negative of the voltage difference value and the voltage step length. The constant power tracking mode decreases the reference voltage according to the voltage step. And finally, the system outputs periodic pulses according to the output voltage of the photovoltaic array and the reference voltage, and controls the output power of the photovoltaic array to be stable at the reference power so as to adjust the bus voltage stability of the contact network.

And 4, step 4: and (6) judging and stabilizing the voltage. And (5) collecting the voltage of the direct current bus, judging whether the voltage is greater than the upper limit value of the direct current bus, if so, entering a step 5, and otherwise, entering a step 6.

And 5: and the voltage closed loop controls the brake resistor to stabilize the bus voltage. And (3) obtaining periodic pulses by the direct current bus voltage and the corresponding reference voltage through PID (Proportion Integration Differentiation) and PWM (Pulse Width Modulation), controlling a brake resistor to participate in working so as to regulate the bus voltage of the overhead contact system to be stabilized to the upper limit value of the bus voltage, and returning to the step 2.

Step 6: and (6) judging and stabilizing the voltage. And (4) judging whether the voltage of the direct current bus is smaller than the lower limit value of the direct current bus, if so, entering the step (7), and otherwise, returning to the step (2).

And 7: the power grid outputs energy to stabilize the bus voltage. And (3) actively participating in work by an AC-DC device of the power grid part to adjust the bus voltage of the overhead contact system to be stabilized to the lower limit value of the DC bus voltage, and returning to the step (2).

The control method can be conveniently and quickly realized by adopting the following devices: the device for realizing the control method of the photovoltaic access subway traction power supply system comprises a DC-DC converter, a chopper, a brake resistor and a controller. The input end of the DC-DC converter is connected with the photovoltaic array, and the output end of the DC-DC converter is connected with a direct current bus of a contact net. The chopper and the brake resistor form a brake resistor device which is connected with a direct current bus of the contact network. The controller comprises three sampling modules, a traction power calculation module, a power increment calculation module, a reference power calculation module, a flexible power tracking control module, a PID module and a PWM module.

The working process and principle of the device are as follows: the sampling module 2 and the sampling module 3 respectively collect the DC bus voltage V_dcInput current I of locomotive_trainAnd the data are input into a power increment calculation module and a traction power calculation module. The power increment calculation module firstly calculates the bus voltage V_dcAnd a bus voltage reference value V_refThe difference between the two and then comparing the calculated difference with the input current I of the locomotive_trainMultiplying to obtain power increment d_p. The traction power calculation module calculates the traction power P of the locomotive by utilizing the relation between the power and the voltage and the current_train. Output d of reference power calculation module combined with power increment module_pWorking condition P of locomotive_trainObtaining a reference power P of the photovoltaic array_ref. Reference power P of photovoltaic array_refAnd the output current I of the photovoltaic array collected by the sampling module 1_PVAnd an output voltage V_PVThe common input is the flexible power tracking control module. Reference voltage V of photovoltaic array output by flexible power tracking control module_refAnd the output voltage V of the photovoltaic array_PVAre commonly input to a PID1 module. The PID1 module obtains the duty ratio through links such as proportion, integration and the like and inputs the duty ratio into the PWM1 module. The PWM1 module outputs a periodic pulse waveform to control the DC-DC converter. Simultaneously, the sampled DC bus voltage V_dcAnd its reference voltage V_{dc_ref}The signals are jointly input into a PID2 module, and the PID2 module obtains the duty ratio through links such as proportion, integration and the like and inputs the duty ratio into a PWM2 module. The PWM2 module outputs a periodic pulse waveform to control the chopper.

FIG. 2 shows the reference voltage V of the photovoltaic array during the power increment calculation operation of the present example_refWith the busbar voltage V of the contact network_dcMaking a difference between the difference and the input current I of the locomotive_trainMultiplying to obtain power increment d_p。

FIG. 3 shows the bus voltage V during the calculation of the traction power according to this example_dcInput current I to locomotive_trainTo obtain the traction power P of the locomotive_train。

FIG. 4 shows the calculation of the reference power according to the power increment d during the operation of the present example_pAnd the traction power P of the locomotive_trainObtaining the output power reference value P of the photovoltaic array_ref。

Fig. 5 shows a flow chart of the flexible power tracking control. Firstly, initializing a proportionality coefficient K and an initial reference voltage V of a photovoltaic array_{ref_old}Using the output current I of the photovoltaic array_PVAnd the output voltage V of the photovoltaic array_PVCalculating the output power P of a photovoltaic array_PV. Wherein the proportionality coefficient K is equal to the initial reference voltage V_{ref_old}All are selected by empirical values. Reference power P through photovoltaic array_refAnd P_PVThe absolute value of the error is multiplied by a proportionality coefficient K to calculate the voltage step V_step. Then, by comparing the reference power P of the photovoltaic array_refAnd P_PVThe working mode of the photovoltaic array is judged according to the size of the photovoltaic array. If P_refGreater than P_PVAnd entering an MPPT mode. The MPPT mode is realized by using a disturbance observation method, namely, the output parameters P of the current photovoltaic arrays are respectively compared_PV、V_PVOutput parameter P obtained from last disturbance_{PV_old}、V_{PV_old}The size of (2). In MPPT mode, if P_PVGreater than P_{PV_old}And V is_PVLess than or equal to V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}–V_step(ii) a If P_PV、V_PVAre respectively greater than P_{PV_old}、V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}+V_step(ii) a If P_PV、V_PVAre respectively less than or equal to P_{PV_old}、V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}+V_step(ii) a If P_PVLess than or equal to P_{PV_old}And V is_PVGreater than V_{PV_old}Then the reference voltage V is updated_refIs a V_{ref_old}–V_step. If P_refLess than or equal to P_PVAnd entering a constant power tracking mode. Updating the reference voltage V in constant power tracking mode_refIs a V_{ref_old}–V_step. Finally, the updated V_refIs assigned to V_{ref_old}And output. In flexible power tracking control, the voltage step size V_stepDependent on P_refAnd P_PVAbsolute value of error of (1). When P is present_PVDeviation P_refWhen the voltage step is larger, the voltage step length is larger, the variable quantity of the reference voltage is larger, and the photovoltaic array is quickly adjusted to operate to a target power point; when P is present_PVDeviation P_refWhen the voltage step is smaller, the voltage step becomes smaller, the variation of the reference voltage becomes smaller, and the condition that the fixed voltage step is larger and the fixed voltage step oscillates near the target power point is avoided. In addition, the reduction of the output power of the photovoltaic array can be realized by increasing or decreasing the reference voltage, and the photovoltaic array is correspondingly adjusted to work on two sides of the maximum power point. Increasing the reference voltage causes the photovoltaic array to operate to the right of the maximum power point, while decreasing the reference voltage causes the photovoltaic array to operate to the left of the maximum power point. The working point on the right side of the maximum power point is easily affected by illumination intensity and is unstable, but the photovoltaic array is limited to work on the left side of the maximum power point by the constant power tracking mode, and the photovoltaic array can work normally under the condition of illumination intensity fluctuation.

FIG. 6 illustrates a traction or braking power curve during locomotive operation. Starting the locomotive in an accelerated manner within 0-0.4 s; the locomotive runs at a constant speed within 0.4-0.8 s; in 0.8-1.2 s, decelerating and braking the locomotive; and stopping the locomotive from running within 1.2-1.4 s. In the period of 0-0.8 s, the locomotive presents a traction load and absorbs electric energy provided by power supply units such as a high-voltage power grid and a photovoltaic array; during the period of 0.8-1.2 s, the locomotive is represented as a power generation unit and transmits electric energy to a contact net; and during the period of 1.2-1.4 s, the locomotive stops running and does not absorb energy.

The subway traction power supply system comprises a high-voltage power grid, a transformer, a traction substation, a photovoltaic array, a DC-DC converter, a locomotive, a brake resistor and a chopper. The traction substation comprises a rectifier transformer and a rectifier unit, wherein the rectifier unit adopts a 24-pulse rectifier device. In two cases of adopting the existing control method and the control method of the invention in the subway traction system, Matlab/simulink is used for simulating the control of the invention, and the result is as follows.

Fig. 7a, 7b, 7c and 7d are simulation waveform diagrams of bus voltage, photovoltaic array output power, grid output power and brake resistance consumption power of a contact network in the locomotive operation process achieved by the control method of the existing photovoltaic access subway traction power supply system. According to a simulation oscillogram, the bus voltage of the overhead line system is always kept in a safe range (1000-1800V), but fluctuates above and below a threshold 1800V for a long time. During the operation of the locomotive, the photovoltaic array continuously and stably outputs the maximum power. In the initial stage of locomotive operation, the bus voltage rises from 0V, and the power grid provides energy due to the fact that the bus voltage is lower than 1000V; within 0.08-0.2 s, the output power of the photovoltaic array is greater than the traction power required by the locomotive, so that the voltage of a bus is increased, and the brake resistor participates in the work; the bus voltage is kept within a safe range within 0.2-0.3 s, and the power grid and the brake resistor do not participate in work; in 0.3-0.48 s, the maximum power of the photovoltaic array is lower than the traction power of the locomotive, the voltage of a bus is reduced, and the power grid provides the residual energy required by the locomotive; within 0.48-0.8 s, the output power of the photovoltaic array is greater than the traction power of the locomotive, the voltage of the bus rises, and the brake resistor participates in the work; and (3) braking the locomotive within 0.8-1.2 s, outputting energy to a contact network, outputting power to the contact network by the photovoltaic array, increasing the bus voltage, enabling the brake resistor to participate in working, and consuming the brake power generated by the locomotive and the output power of the photovoltaic array. And (3) stopping the locomotive within 1.2-1.4 s, but because the photovoltaic array still keeps the maximum power output, the voltage of a contact network rises, and the braking resistor consumes the energy generated by the photovoltaic array.

Fig. 8a, 8b, 8c, and 8d are simulation waveform diagrams of bus voltage, photovoltaic array output power, grid output power, and brake resistance consumption power of a catenary in the locomotive operation process, which are realized by the flexible power tracking control method of the photovoltaic access subway traction power supply system. The simulation oscillogram shows that the bus voltage of the overhead line system is always kept in a safe range, and the bus voltage only exceeds 1800V in the locomotive braking process. And in the running process of the locomotive, the photovoltaic array controls the output power in real time according to the requirement of the locomotive. Within 0-0.2 s, the maximum output power of the photovoltaic array is greater than the traction power of the locomotive, the photovoltaic array works in a constant power tracking mode, and the output power of the photovoltaic array changes along with the traction power of the locomotive; within 0.2-0.4 s, the maximum output power of the photovoltaic array is less than the traction power of the locomotive, the photovoltaic array works in an MPPT mode, the maximum power output is kept, but the generated energy of the photovoltaic array cannot meet the requirement of the locomotive, so that the voltage of a bus is reduced, and the power grid provides the residual traction power required by the locomotive for the voltage of the bus not to be lower than 1000V; within 0.4-0.8 s, the maximum output power of the photovoltaic array is greater than the traction power of the locomotive, the photovoltaic array works in a constant power tracking mode, and the power grid does not provide electric energy; within 0.8-1.2 s, the locomotive brakes and outputs energy to the direction of the direct current bus to cause the voltage of the bus to rise, in order to enable the voltage of the bus not to exceed 1800V, the output power of the photovoltaic array is limited to 0, and the braking power of the locomotive is consumed through a braking resistor. And in 1.2-1.4 s, the locomotive stops, and the photovoltaic array and the power grid do not provide energy.

Compared with the prior art, the flexible power tracking control method can control the output of the photovoltaic array in real time and adjust the bus voltage of the contact network to be stabilized in a safe range. Meanwhile, the flexible power tracking control method reduces the work of a brake resistor, reduces the generation of heat and the use of a heat dissipation device, and reduces the cost. If the voltage stabilizing device for balancing the power difference between the locomotive and the photovoltaic power generation is replaced by the energy storage device through the braking resistor, the energy storage device only needs to absorb the braking energy of the locomotive and does not need to absorb redundant solar energy due to the constant power control of the photovoltaic array, and the capacity of the energy storage device can be effectively reduced; and when the locomotive power is less than the output power of the photovoltaic array, the recycling frequency of the energy storage device is reduced, and the service life of the energy storage device is prolonged.

Example two

As shown in fig. 9, the difference from the first embodiment is: the system controlled by the embodiment is a direct current micro-grid system. Compared with the first embodiment, the system of the embodiment can be applied to remote power grid-free areas with inconvenient power supply. The invention can be used for the direct current system in the above embodiment, and can also be used for other systems containing photovoltaic power generation units, such as other rail traction power supply systems, alternating current micro-grid systems and the like.

EXAMPLE III

As shown in fig. 10, the difference from the first embodiment is: the subway traction power supply system of the embodiment comprises a high-voltage power grid, a transformer, a traction substation, a photovoltaic array, a DC-DC converter, a locomotive, a super capacitor and a bidirectional DC-DC converter. The energy of the super capacitor flows in two directions through a voltage inner ring and a current outer ring to control the two-way DC-DC converter. Compared with the first embodiment, the system of the embodiment can balance the power difference between the photovoltaic array and the locomotive by using the super capacitor, and when the bus voltage of a contact network is reduced, the super capacitor is used for releasing energy; when the bus voltage of the contact network rises, the super capacitor is utilized to absorb redundant energy, and energy waste is reduced. The invention can be used for the subway traction power supply system in the above embodiment, and can also be used for the subway traction power supply system comprising a battery or a hybrid energy storage device of a super capacitor and the battery.