Modular parallel photovoltaic direct current boosting device and control method

Abstract

The invention relates to the field of photovoltaic converters, in particular to a modular parallel photovoltaic direct-current boosting device and a control method. The whole boosting device is composed of a plurality of boosting modules, each boosting module comprises a low-voltage module, a transformer and a high-voltage module, the input of the low-voltage module is connected with a photovoltaic matrix in parallel, the output of the low-voltage module is connected with the primary side of the transformer in parallel, the secondary side of the transformer is connected with the input of the high-voltage module in parallel, and the output of the high-voltage module is connected with a direct-current power grid in parallel. The boost module is connected in parallel with the input and output of the boost module. The capacity of the whole machine can be adjusted, the problem of uneven current of a multi-module input parallel output parallel topology is solved, the universality is high, the stability of the system is improved through centralized control of multiple modules, current type MPPT calculation is completed to track the maximum power point at the same time, and the maximum power point tracking efficiency is improved. And energy loss caused by the fact that the photovoltaic equipment works in a non-optimal state is reduced, so that the energy utilization efficiency of the whole system is improved.

Description

Technical Field

[0001] The invention relates to the field of photovoltaic converters, and in particular to a modular parallel photovoltaic direct current boost device and a control method. Background Art

[0002] Photovoltaic DC boost devices play a vital role in photovoltaic power generation systems. They can not only boost the DC power generated by photovoltaic panels to a voltage level suitable for grid access, but also ensure the stable transmission and efficient use of electric energy. In addition, with the development of distributed power sources, photovoltaic boost stations have become important equipment to ensure the stable access of distributed power sources to the grid, which is of great significance for promoting the use of clean energy and the safety of power operation.

[0003] With the rapid development of the photovoltaic industry today, the previous photovoltaic inverter AC grid connection can no longer fully meet the existing needs. The existing AC transmission mode is gradually replaced by DC transmission due to large losses and other reasons. However, the existing distributed photovoltaic power generation scenarios are complex and changeable, and a single equipment capacity mode cannot cope with various working conditions. Therefore, a photovoltaic DC boost converter that can be flexibly adjusted is needed. Through the modularization inside the converter, the whole machine is designed to be expandable and flexible in capacity, that is, multiple modules are connected in parallel for input and output. However, when multiple modules are connected in parallel, due to inconsistent internal parameters of the modules, each module has uneven current, which leads to positive feedback of the module input current, that is, the input power of each module has a large difference and cannot work normally. Summary of the invention

[0004] In order to solve the above technical problems, the object of the present invention is to provide a modular parallel photovoltaic DC boost device and a control method.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A modular parallel photovoltaic DC boost device includes a boost module. The entire boost device is composed of multiple boost modules. Each boost module includes a low-voltage module, a transformer, and a high-voltage module. The input of the low-voltage module is connected in parallel to a photovoltaic matrix, the output of the low-voltage module is connected in parallel to the primary side of the transformer, the secondary side of the transformer is connected in parallel to the input of the high-voltage module, the output of the high-voltage module is connected in parallel to a DC grid, and the boost module is connected in parallel to the input of the boost module and the output is connected in parallel. The number of each boost module in this topology can be increased or decreased, so the overall capacity can be adjusted according to actual conditions, and it is highly flexible.

[0007] As a further solution of the present invention: the multiple boost modules are controlled by a centralized controller, and the centralized controller controls the PWM wave transmission through optical fiber. The centralized controller can realize centralized control and management of multiple modules, thereby simplifying the operation process and improving the overall operation efficiency of the system.

[0008] As a further solution of the present invention: the maximum step-up ratio of the transformer is 10 times, and the capacity of each step-up module is 50kW.

[0009] As a further solution of the present invention: SiC switching devices are used inside the boost module, and the switching frequency is 50kHz, which reduces the volume of key devices such as capacitors and inductors and reduces the cost.

[0010] A control method for modular parallel photovoltaic DC boosting, specifically comprising the following steps:

[0011] Step 1: The centralized controller sums the current values ​​of all boost modules collected to obtain the total current value I of the boost modules. PV , the voltage value is summed to get the total voltage value V of the boost module pv ;

[0012] Step 2: Set the total current value of the boost module to I pv as the total input current of the transformer, and the total voltage value of the boost module as the total input voltage of the transformer;

[0013] Step 3: The total input voltage V across the transformer pv And the total input current value I pv Complete the MPPT calculation to get the total reference current I pv-ref ; Then the total reference current I of the transformer pv-ref Divide by the number of boost modules n, and get the input current command of each boost module (1 / n)*I pv-ref ;

[0014] Step 4: Each boost module uses an input current closed loop method. After receiving the current control instruction sent by the centralized controller, the boost module completes the module duty cycle calculation through the current closed loop, so that the input current value of each module is basically the same.

[0015] As a further solution of the present invention: Step 4 comprises the following steps:

[0016] Step 401: multiply the current sum I(n-1) of the boost module and the transformer input voltage V(n-1) to obtain a power value P(n-1); according to the disturbance current value at this time, send a current greater than the current sampled current value to the module for current closed loop; collect the current sum I(n) of all boost modules at the next moment, and multiply it by the transformer input voltage V(n) at this time to obtain a new power value P(n) for comparison;

[0017] Step 402: If the values ​​of P(n) and P(n-1) are equal, execute step 403; if P(n) increases compared to P(n-1), execute step 404; if P(n) decreases compared to P(n-1), execute step 405;

[0018] Step 403, sending the current reference value at this moment downward;

[0019] Step 404: at the next moment, the current reference value is increased and sent downward, and step 406 is executed;

[0020] Step 405: Reduce the current reference value and send it downward at the next moment, and execute step 409;

[0021] Step 406: compare I(n) with I(n-1). If I(n) increases compared to I(n-1), execute step 407; if I(n) decreases compared to I(n-1), execute step 408;

[0022] Step 407: The duty cycle D(n+1) at the next moment is the sum of the duty cycle D(n) at the current moment and the increment ΔD;

[0023] Step 408: The duty cycle D(n+1) at the next moment is the value of the duty cycle D(n) at the current moment minus the increment △D;

[0024] Step 409: compare I(n) with I(n-1). If I(n) is smaller than I(n-1), execute step 410; if I(n) is larger than I(n-1), execute step 411.

[0025] Step 410: The duty cycle D(n+1) at the next moment is the sum of the duty cycle D(n) at the current moment and the increment ΔD;

[0026] Step 411: The duty cycle D(n+1) at the next moment is the value obtained by subtracting the increment ΔD from the duty cycle D(n) at the current moment.

[0027] By tracking the maximum power point through current-type MPPT, photovoltaic equipment can output the maximum power under various lighting conditions and temperatures, making full use of available solar energy resources and providing higher energy yields.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The present invention adopts a modular form, and the boost device adopts an input parallel output parallel topology structure. The capacity of the photovoltaic DC converter can be adjusted arbitrarily by increasing or decreasing the number of boost modules;

[0030] 2. The present invention uses a centralized controller to control the PWM wave transmission of all boost modules through the front light, and solves the problem of uneven current of multiple modules with parallel input and output by increasing or decreasing the current command. The multi-module current sharing can ensure that the load of each power module or energy conversion module is relatively balanced, reduce the problems of overheating and overload caused by uneven load, and improve the stability of the system.

[0031] 3. The present invention can complete the current-type MPPT tracking to the maximum power point while multiple modules complete the current-sharing algorithm. MPPT technology not only improves energy utilization efficiency, but also enhances the stability of the system. By continuously tracking and adjusting the working point, MPPT technology can ensure that the system can operate stably under various environmental conditions, reducing system performance fluctuations caused by environmental changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a topological schematic diagram of the present invention;

[0033] Figure 2 This is the actual waveform diagram of multi-module current sharing;

[0034] Figure 3 It is a diagram illustrating the control strategy for multiple modules;

[0035] Figure 4 This is the flow chart of current type MPPT;

[0036] Figure 5 The waveform diagram of the current-type MPPT and current-sharing algorithm completed for actual multiple modules. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] See also Figure 1In an embodiment of the present invention, a modular parallel photovoltaic DC boost device includes a boost module. The entire boost device is composed of multiple boost modules. Each boost module includes a low-voltage module, a transformer, and a high-voltage module. The input of the low-voltage module is connected in parallel to the photovoltaic matrix, the output of the low-voltage module is connected in parallel to the primary side of the transformer, the secondary side of the transformer is connected in parallel to the input of the high-voltage module, the output of the high-voltage module is connected in parallel to the DC grid, and the input of the boost module is connected in parallel to the input of the boost module and the output is connected in parallel. A current sensor is connected between the photovoltaic matrix and the boost module. The current sensor can sense the information of the measured current and can transform the sensed information into an electrical signal or other required form of information output that meets certain standard requirements according to a certain rule to meet the requirements of information transmission, processing, storage, display, recording and control.

[0039] Among them, multiple boost modules are controlled by a centralized controller, and the centralized controller controls the PWM wave transmission through optical fiber. The centralized controller is a central control device, which collects real-time data of multiple devices or systems through various sensors or monitoring devices, and determines whether the current device or system status needs to be adjusted or controlled according to the set control strategy and algorithm, and determines the corresponding control action.

[0040] Among them, the maximum step-up ratio of the transformer is 10 times, and the capacity of each step-up module is 50kW.

[0041] The boost module uses SiC switching devices with a switching frequency of 50kHz. SiC materials have high breakdown field robustness and high thermal conductivity, so SiC switching devices can withstand greater power while maintaining a small size.

[0042] See also Figure 1-5 , a control method for modular parallel photovoltaic DC boost, specifically comprising the following steps:

[0043] Step 1: The centralized controller sums the current values ​​of all boost modules collected to obtain the total current value I of the boost module. PV , the voltage value is summed to get the total voltage value V of the boost module pv ;

[0044] Step 2: Set the total current value of the boost module to I pv As the total input current of the transformer, the total voltage value of the boost module is used as the total input voltage of the transformer;

[0045] Step 3: The total input voltage V across the transformer pv And the total input current value I pv Complete the MPPT calculation to get the total reference current I pv-ref ; Then the total reference current I of the transformer pv-refDivide by the number of boost modules n, and get the input current command of each boost module (1 / n)*I pv-ref ;

[0046] Step 4: Each boost module uses an input current closed loop method. After receiving the current control instruction sent by the centralized controller, the boost module completes the module duty cycle calculation through the current closed loop, so that the input current value of each module is basically the same.

[0047] Wherein, step 4 comprises the following steps:

[0048] Step 401: multiply the current sum I(n-1) of the boost module and the transformer input voltage V(n-1) to obtain a power value P(n-1); according to the disturbance current value at this time, send a current greater than the current sampled current value to the module for current closed loop; collect the current sum I(n) of all boost modules at the next moment, and multiply it by the transformer input voltage V(n) at this time to obtain a new power value P(n) for comparison;

[0049] Step 402: If the values ​​of P(n) and P(n-1) are equal, execute step 403; if P(n) increases compared to P(n-1), execute step 404; if P(n) decreases compared to P(n-1), execute step 405;

[0050] Step 403, sending the current reference value at this moment downward;

[0051] Step 404: at the next moment, the current reference value is increased and sent downward, and step 406 is executed;

[0052] Step 405: Reduce the current reference value and send it downward at the next moment, and execute step 409;

[0053] Step 406: compare I(n) with I(n-1). If I(n) increases compared to I(n-1), execute step 407; if I(n) decreases compared to I(n-1), execute step 408;

[0054] Step 407: The duty cycle D(n+1) at the next moment is the sum of the duty cycle D(n) at the current moment and the increment ΔD;

[0055] Step 408: The duty cycle D(n+1) at the next moment is the value of the duty cycle D(n) at the current moment minus the increment △D;

[0056] Step 409: compare I(n) with I(n-1). If I(n) is smaller than I(n-1), execute step 410; if I(n) is larger than I(n-1), execute step 411.

[0057] Step 410: The duty cycle D(n+1) at the next moment is the sum of the duty cycle D(n) at the current moment and the increment ΔD;

[0058] Step 411: The duty cycle D(n+1) at the next moment is the value obtained by subtracting the increment ΔD from the duty cycle D(n) at the current moment.

[0059] like Figure 5 As shown, in actual experiments of the present invention, multiple boost modules complete current-type MPPT, as well as the actual waveform of the multi-module current sharing algorithm. Multiple modules can track the maximum power point very well, and the input currents of multiple modules are basically consistent.

[0060] The working principle of the present invention is:

[0061] The inputs and outputs of n boost modules are connected in parallel. An input current closed-loop method is adopted in each boost module. After receiving a current control instruction from a centralized controller, the boost module completes the duty cycle calculation of the module through a current closed-loop, so that the input current value of each boost module is basically the same.

[0062] The current-type MPPT control strategy is adopted to change the traditional voltage-type MPPT control, and the operating point is disturbed by increasing or decreasing the current command.

[0063] The n boost modules send the input current values ​​to the centralized controller, which sums up the current values ​​of all the boost modules to get the total input current of the converter, completes the MPPT calculation through the input voltage and the total input current value, and then divides the total input current value by the number of boost modules to get the input current instruction of each boost module.

[0064] Then add the currents collected from n boost modules, collect the converter input voltage at the same time, multiply the total current and voltage to get a power value, and then disturb the current value, and send a value greater than the current sampled current to the boost module for current closed loop. At the next moment, collect the currents of N boost modules, add them, and multiply them by the input voltage at this time to get a power value for comparison. If the power increases, the current reference value will continue to increase and be sent downward at the next moment. If the power decreases, the current reference value will be reduced and sent downward.

[0065] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A modular parallel photovoltaic DC boost device, comprising a boost module, characterized in that: The entire boost device is composed of multiple boost modules, each of which includes a low-voltage module, a transformer, and a high-voltage module. The low-voltage module input is connected in parallel to the photovoltaic matrix, the low-voltage module output is connected in parallel to the primary side of the transformer, the secondary side of the transformer is connected in parallel to the high-voltage module input, and the high-voltage module output is connected in parallel to the DC power grid. The inputs of the multiple boost modules are connected in parallel and the outputs are connected in parallel.

2. A modular parallel photovoltaic DC boost device according to claim 1, characterized in that: The multiple boost modules are controlled by a centralized controller, and the centralized controller controls the transmission of PWM waves via optical fibers.

3. A modular parallel photovoltaic DC boost device according to claim 1, characterized in that: The maximum step-up ratio of the transformer is 10 times, and the capacity of each step-up module is 50kW.

4. A modular parallel photovoltaic DC boost device according to claim 1, characterized in that: The boost module uses SiC switching devices inside, and the switching frequency is 50kHz.

5. A control method for modular parallel photovoltaic DC boost, comprising a modular parallel photovoltaic DC boost device according to any one of claims 1 to 4, characterized in that: The specific steps include: Step 1: The centralized controller sums the current values ​​of all boost modules collected to obtain the total current value I of the boost module. PV , the voltage value is summed to get the total voltage value V of the boost module pv ; Step 2: Set the total current value of the boost module to I pv as the total input current of the transformer, and the total voltage value of the boost module as the total input voltage of the transformer; Step 3: The total input voltage V across the transformer pv And the total input current value I pv Complete the MPPT calculation to get the total reference current I pv-ref ; Then the total reference current I of the transformer pv-ref Divide by the number of boost modules n, and get the input current command of each boost module (1 / n)*I pv-ref ; Step 4: Each boost module uses an input current closed loop method. After receiving the current control instruction sent by the centralized controller, the boost module completes the module duty cycle calculation through the current closed loop, so that the input current value of each module is basically the same.

6. A control method for modular parallel photovoltaic DC boost according to claim 5, characterized in that: In step 4, the current closed loop method specifically includes the following steps: Step 401: multiply the current sum I(n-1) of the boost module and the transformer input voltage V(n-1) to obtain a power value P(n-1); according to the disturbance current value at this time, send a current greater than the current sampled current value to the module for current closed loop; collect the current sum I(n) of all boost modules at the next moment, and multiply it by the transformer input voltage V(n) at this time to obtain a new power value P(n) for comparison; Step 402: If the values ​​of P(n) and P(n-1) are equal, execute step 403; if P(n) increases compared to P(n-1), execute step 404; if P(n) decreases compared to P(n-1), execute step 405; Step 403, sending the current reference value at this moment downward; Step 404: at the next moment, the current reference value is increased and sent downward, and step 406 is executed; Step 405: Reduce the current reference value and send it downward at the next moment, and execute step 409; Step 406: compare I(n) with I(n-1). If I(n) increases compared to I(n-1), execute step 407; if I(n) decreases compared to I(n-1), execute step 408; Step 407: The duty cycle D(n+1) at the next moment is the sum of the duty cycle D(n) at the current moment and the increment ΔD; Step 408: The duty cycle D(n+1) at the next moment is the value of the duty cycle D(n) at the current moment minus the increment △D; Step 409: compare I(n) with I(n-1). If I(n) is smaller than I(n-1), execute step 410; if I(n) is larger than I(n-1), execute step 411. Step 410: The duty cycle D(n+1) at the next moment is the sum of the duty cycle D(n) at the current moment and the increment ΔD; Step 411: The duty cycle D(n+1) at the next moment is the value obtained by subtracting the increment ΔD from the duty cycle D(n) at the current moment.

Images