A direct current power generation system and a control method thereof

Abstract

The application discloses a direct-current power generation system and a control method thereof, and is characterized in that a photovoltaic and energy storage dual cascade architecture is innovatively adopted, and an intelligent protection and coordinated control strategy is combined. The system comprises N photovoltaic cascade subunits and M direct-current energy storage modules, and each unit is provided with a bypass protection device; the photovoltaic cascade subunit is integrated with an MPPT controller, an isolation converter and a bypass protector comprising a voltage-dependent resistor and a diode; the energy storage module adopts a non-isolated DCDC conversion circuit, and is matched with an energy storage bypass protector integrated with a bidirectional power electronic switch, a voltage-dependent resistor and a mechanical isolation switch. The application effectively solves technical pain points such as large voltage fluctuation, low system reliability and difficult maintenance of a traditional direct-current system, prolongs the service life of equipment while improving the stability of the system, and is particularly suitable for a medium and high voltage direct-current power supply scene.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of photovoltaic power generation and direct current energy storage, and particularly relates to a direct current power generation system and a control method thereof. BACKGROUND

[0002] With the increasing global energy demand and the growing emphasis on environmental protection, photovoltaic power generation as a clean and renewable energy generation method has received widespread attention. Currently, photovoltaic power generation systems mainly convert direct current into alternating current through inverters and then connect to the alternating current grid. However, with the increasing installation capacity of photovoltaic power generation systems, the capacity of the alternating current grid to accommodate photovoltaic energy gradually reaches its limit, and cannot meet the access requirements of more photovoltaic power generation systems, which to some extent limits the large-scale application of photovoltaic power generation.

[0003] At the same time, in the field of direct current transmission, compared with traditional alternating current transmission, direct current transmission has many advantages such as no reactive power problem and easy voltage stability control, and is theoretically more suitable for direct transmission and utilization of photovoltaic power generation. However, due to the voltage level of power electronic devices, the current mainstream direct current power generation system is mostly concentrated in the voltage level below 1500V. The lower voltage level limits the power supply distance and cannot realize large-capacity and long-distance power supply, making it difficult to meet the power supply requirements in some specific scenarios, such as medium and high voltage direct current power supply scenarios.

[0004] In addition, the existing direct current power generation system also faces some technical challenges in actual operation. On the one hand, the system voltage fluctuates greatly, affecting the stability and reliability of power supply, especially when the load changes greatly or the output power of the photovoltaic module is unstable, the voltage fluctuation problem is more prominent. On the other hand, the reliability of the system needs to be improved, when the photovoltaic module or the energy storage module fails, there is a lack of effective protection and bypass mechanism, which may cause the shutdown or damage of the whole system, increasing the maintenance cost and difficulty. Moreover, the cooperative control of photovoltaic modules and energy storage modules in traditional systems is not precise enough, and cannot fully exert the performance advantages of each component, further limiting the improvement of the overall efficiency and stability of the system. SUMMARY

[0005] The present application proposes a direct current power generation system and a control method thereof to solve the above-mentioned problems of the prior art.

[0006] To achieve the above-mentioned purpose, the present application provides a direct current power generation system, which comprises a photovoltaic cascade subunit, a first direct current switch, a second direct current switch, a third direct current switch, a direct current energy storage system, a first voltage sampling unit, a second voltage sampling unit, an energy storage current sampling unit, an energy storage filter inductance, a system stability controller, a photovoltaic cascade control unit, and an energy storage cascade control unit.

[0007] The photovoltaic cascade subunit is connected in series and connected with the first direct-current switch;

[0008] The first voltage sampling unit is used for collecting the voltage of the direct-current bus after the photovoltaic cascade subunit is connected in series.

[0009] The second direct-current switch is connected with the output end of the direct-current energy storage system, and the output end of the second direct-current switch is connected in parallel on the direct-current bus.

[0010] The third direct-current switch is connected in series between the direct-current bus and the load.

[0011] The energy storage current sampling unit is connected in series in the energy storage module loop, one end of the energy storage current sampling unit is connected with the energy storage filter inductor, and the other end is connected with the positive electrode of the last energy storage module.

[0012] The system stability controller is connected with the photovoltaic cascade control unit and the energy storage cascade control unit through communication.

[0013] Optionally, the photovoltaic cascade subunit comprises a photovoltaic module, a photovoltaic MPPT controller, a DC / DC isolation converter and a photovoltaic bypass protector.

[0014] The photovoltaic MPPT controller is connected with the photovoltaic module in input, and the output is connected with the input of the DC / DC isolation converter, and the output of the DC / DC isolation converter is connected with the input of the photovoltaic bypass protector.

[0015] Optionally, the photovoltaic bypass protector comprises a mechanical isolation switch, a pressure-sensitive resistor and a diode module.

[0016] When the diode module comprises a plurality of diodes, the diodes are connected in series.

[0017] The mechanical switch has positive and negative poles, the positive output of the mechanical switch is connected with the anode of the diode module, the negative output of the mechanical switch is connected with the cathode of the diode module, and the pressure-sensitive resistor is connected in parallel with the diode module.

[0018] The photovoltaic bypass protector is automatically turned on when the corresponding photovoltaic module fails, and the surge voltage is inhibited, the isolation switch of the photovoltaic bypass protector is disconnected automatically or manually, and the corresponding photovoltaic module is maintained.

[0019] Optionally, the direct-current energy storage system comprises a direct-current energy storage module and an energy storage bypass protector.

[0020] The direct-current energy storage module is connected with one energy storage bypass protector respectively, and the bypass protectors are connected in series.

[0021] The energy storage bypass protector is used for suppressing surge voltage and automatically conducting when the corresponding energy storage module fails;

[0022] The isolating switch of the energy storage bypass protector is automatically or manually disconnected for online replacement and maintenance of the corresponding energy storage module.

[0023] Optionally, the direct current energy storage module comprises a DCDC conversion circuit, an energy storage battery pack, a battery management system and a module control board.

[0024] The DCDC conversion circuit is a non-isolated topology, specifically a half-bridge circuit, that is, a circuit composed of two power electronic switches in series.

[0025] The input end of the DCDC conversion circuit is connected to the DC bus for receiving electric energy on the DC bus; and the output end is connected to the energy storage battery pack for providing electric energy conversion for charging or discharging the energy storage battery pack.

[0026] The energy storage battery pack is connected to the output end of the DCDC conversion circuit for storing electric energy.

[0027] The battery management system is used for monitoring the operating state of the energy storage battery pack and transmitting the operating state to the module control board.

[0028] The module control board controls the switching state of the switch tube in the DCDC conversion circuit through optical fiber or electrical signal.

[0029] Optionally, the energy storage bypass protector comprises a mechanical isolating switch, a pressure-sensitive resistor, a bidirectional power electronic switch assembly and a direct current bypass switch.

[0030] When the bidirectional power electronic switch assembly comprises a plurality of power electronic switches, the power electronic switches are connected in series.

[0031] The mechanical isolating switch has a time sequence action requirement with the plurality of power electronic switches, that is, when the corresponding energy storage module needs to be bypassed, the power electronic switches are first turned on, then the mechanical isolating switch is disconnected, and then the direct current bypass switch is closed.

[0032] The mechanical isolating switch has positive and negative poles, the positive pole output of the mechanical switch is connected to the positive pole of the bidirectional power electronic switch assembly, and the negative pole output of the mechanical switch is connected to the negative pole of the bidirectional power electronic switch assembly.

[0033] The pressure-sensitive resistor is connected in parallel across the positive and negative poles of the bidirectional power electronic switch assembly.

[0034] The direct current bypass switch is connected in parallel across the positive and negative poles of the bidirectional power electronic switch assembly.

[0035] The application further provides a control method of a direct-current power generation system, comprising: performing photovoltaic cascade module control, energy storage cascade module control and system stability control by a photovoltaic cascade control unit, an energy storage cascade control unit and a system stability controller respectively.

[0036] Among them, when the energy storage module is controlled, only the power electronic switch of one direct-current energy storage module is in PWM modulation state at any time, and the upper tube of the power electronic switch bridge arm of other direct-current energy storage modules is in conduction state or the upper tube is in off state.

[0037] Optionally, the photovoltaic cascade module control performed by the photovoltaic cascade control unit comprises:

[0038] The photovoltaic cascade module performs maximum power tracking control and voltage limiting control at the same time, that is, if the voltage of the maximum power tracking control exceeds the voltage limiting value, the maximum power tracking control is no longer performed, and the voltage closed-loop control is performed according to the voltage limiting value;

[0039] When a certain photovoltaic cascade module fails, the corresponding photovoltaic bypass protector is put into operation to bypass the failed photovoltaic cascade module.

[0040] Optionally, the energy storage cascade module control performed by the energy storage cascade control unit comprises energy storage system voltage stabilization control, energy storage module switch tube modulation control, energy storage SOC balancing control and energy storage operation and protection control.

[0041] The energy storage system voltage stabilization control comprises: taking the total direct-current bus voltage of the energy storage system as a control target for negative feedback closed-loop control, the voltage closed-loop controller comprises a PI controller, the output of the voltage closed-loop controller is subjected to limiting to obtain an energy storage system current given value, the current given value is subtracted from the current value obtained by an energy storage current sampling unit, and then a reference voltage value is obtained through a current controller, and the reference voltage value is taken as an input quantity of the energy storage module control.

[0042] The energy storage module switch tube modulation control comprises: the direct-current energy storage module is controlled based on carrier superposition and carrier phase shift, that is, K direct-current energy storage modules are started according to the required voltage value, and only the power electronic switch of one direct-current energy storage module is in PWM modulation state among the K started direct-current energy storage modules, and the upper tubes of the power electronic switches of other direct-current energy storage modules are all in conduction state.

[0043] The energy storage SOC balancing control comprises: dynamic sorting charge and discharge control is adopted, the direct-current energy storage modules are sorted according to their SOC from small to large, the sorting is dynamically adjusted, the direct-current energy storage modules with large SOC are selected to discharge in the discharge state, and the direct-current energy storage modules with small SOC are selected to charge in the charge state.

[0044] The energy storage operation and protection control comprises: judging whether the energy storage system has a starting condition, and executing an energy storage system starting procedure if the starting condition is met; after the starting is completed, entering a voltage stabilization control module, and the control target of the voltage stabilization control module is the DC bus voltage of the system; judging whether each DC energy storage module has a fault, and cutting off the fault module and putting the bypass protector of the corresponding module into operation if the DC module has a fault.

[0045] Optionally, the system stability control by the system stability controller comprises:

[0046] The system DC bus voltage value and the energy storage system SOC state are acquired, and the bus resonance frequency is calculated based on the bus voltage value at the current moment and the past moment;

[0047] The active damping control algorithm is added according to the resonance frequency, the energy storage system voltage given value is output, and the bus voltage stabilization control is performed;

[0048] The photovoltaic power target value is given according to the energy storage SOC state.

[0049] Compared with the prior art, the present application has the following advantages and technical effects:

[0050] The DC power generation system and the control method thereof of the present application significantly improve the reliability and availability of the system by adopting the photovoltaic and energy storage dual cascade architecture, combining intelligent protection and coordinated control strategy. The modular cascade structure supports automatic bypass of the fault unit, can automatically suppress surge voltage, and can realize online maintenance function of the module, effectively solving the problems of shutdown and maintenance difficulty caused by faults in the traditional system. At the same time, the system adopts a dynamic energy storage management strategy, combines the SOC sorting charging and discharging algorithm and the carrier layer superposition-phase shift hybrid modulation technology, realizes precise voltage stabilization and efficient energy management, significantly reduces voltage fluctuation, and improves system stability. In addition, the system level resonance suppression algorithm further enhances the stability of the system by real-time monitoring of the bus resonance frequency and introducing active damping control. The photovoltaic-energy storage coordinated control mechanism dynamically adjusts the photovoltaic power output according to the energy storage SOC state, optimizes the overall efficiency of the system. The present application also supports medium and high voltage DC power supply, expands the application scenarios, and is particularly suitable for scenarios with high requirements for power supply quality and reliability, such as data centers, industrial production, etc. Through these technical improvements, the present application not only improves the stability and reliability of the system, but also reduces the system cost and maintenance cost, and has significant economic and social benefits. BRIEF DESCRIPTION OF DRAWINGS

[0051] The drawings constituting a part of the present application are used to provide further understanding of the present application, the illustrative embodiments of the present application and the description thereof are used to explain the present application, and do not constitute improper limitation on the present application. In the drawings:

[0052] Figure 1System electrical schematic diagram of the embodiment of the present application;

[0053] Figure 2 Photovoltaic bypass protector electrical schematic diagram of the embodiment of the present application;

[0054] Figure 3 Energy storage bypass protector electrical schematic diagram of the embodiment of the present application;

[0055] Figure 4 Energy storage system control flow chart of the embodiment of the present application;

[0056] Figure 5 Energy storage voltage stabilization control block diagram of the embodiment of the present application;

[0057] Figure 6 Energy storage SOC equalization control flow chart of the embodiment of the present application;

[0058] Figure 7 System stabilization control flow chart of the embodiment of the present application;

[0059] Wherein; 101, photovoltaic assembly; 102, photovoltaic MPPT controller; 103, DC / DC isolation converter; 104 photovoltaic bypass protector; 111, first DC switch; 113, second DC switch; 112, third DC switch; 123, first voltage sampling unit; 122, second voltage sampling unit; 120, energy storage current sampling unit; 121, energy storage filter inductor; 126, system stabilization controller; 124, photovoltaic cascade control unit; 125, energy storage cascade control unit; 201, photovoltaic bypass protector; 202, mechanical isolation switch; 204, voltage-dependent resistor; 203, diode assembly; 301, energy storage bypass protector; 302, mechanical isolation switch; 303, voltage-dependent resistor; 304, bidirectional power electronic switch assembly; 305 DC bypass switch. DETAILED DESCRIPTION

[0060] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0061] It should be noted that the steps shown in the flow chart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although the logical order is shown in the flow chart, in some cases, the steps shown or described herein can be executed in an order different from that shown herein.

[0062] Embodiment one

[0063] The direct current power generation system provided in the embodiment comprises photovoltaic cascade sub-units, a first direct current switch, a second direct current switch, a third direct current switch, a direct current energy storage system, a first voltage sampling unit, a second voltage sampling unit, an energy storage current sampling unit, an energy storage filter inductor, a system stability controller, a photovoltaic cascade control unit and an energy storage cascade control unit.

[0064] The photovoltaic cascade sub-units are connected in series and connected with the first direct current switch.

[0065] The first voltage sampling unit is used to collect the voltage of the direct current bus after the photovoltaic cascade sub-units are connected in series.

[0066] The second direct current switch input end is connected with the direct current energy storage system output end, and the second direct current switch output end is connected in parallel on the direct current bus.

[0067] The third direct current switch is connected in series between the direct current bus and the load.

[0068] The energy storage current sampling unit is connected in series in the energy storage module loop, one end of the energy storage current sampling unit is connected with the energy storage filter inductor, and the other end is connected with the positive pole of the last energy storage module.

[0069] The system stability controller is connected with the photovoltaic cascade control unit and the energy storage cascade control unit through communication, and control instructions are issued through communication.

[0070] The following will be described in detail with reference to the accompanying drawings:

[0071] As shown in the figure, the direct current power generation system provided in the embodiment comprises: Figure 1

[0072] N photovoltaic cascade sub-units (N≥2), a first direct current switch 111, a second direct current switch 113 and a third direct current switch 112, M direct current energy storage modules (M≥1), M energy storage bypass protectors, a first voltage sampling unit 123, a second voltage sampling unit 122, an energy storage current sampling unit 120, an energy storage filter inductor 121, a system stability controller 126, a photovoltaic cascade control unit 124 and an energy storage cascade control unit 125.

[0073] The photovoltaic cascade sub-unit comprises a photovoltaic module 101, a photovoltaic MPPT controller 102, a DC / DC isolation converter 103 and a photovoltaic bypass protector 104; the photovoltaic MPPT controller 102 is connected with the photovoltaic module 101 in input, and connected with the DC / DC isolation converter 103 in output; the DC / DC isolation converter 103 is connected with the photovoltaic bypass protector 104 in input, and the photovoltaic bypass protector 104 has two poles, i.e. a positive pole and a negative pole.

[0074] ​N(N≥2) photovoltaic cascade subunits are connected in series, and are connected in series through the output end of the photovoltaic bypass protector, that is, the positive electrode of the first photovoltaic bypass protector is connected with the system DC bus, the negative electrode is connected with the positive electrode of the second photovoltaic bypass protector, and so on, the positive electrode of the N photovoltaic bypass protector is connected with the negative electrode of the N-1 photovoltaic bypass protector, and the negative electrode is connected with the negative electrode of the DC bus.

[0075] N(N≥2) photovoltaic cascade subunits are connected in series, and are connected in series through the output end of the photovoltaic bypass protector, that is, the positive electrode of the first photovoltaic bypass protector is connected with the system DC bus, the negative electrode is connected with the positive electrode of the second photovoltaic bypass protector, and so on, the positive electrode of the N photovoltaic bypass protector is connected with the negative electrode of the N-1 photovoltaic bypass protector, and the negative electrode is connected with the negative electrode of the DC bus.

[0076] The input end of the second DC switch 113 is connected with the output end of the DC energy storage system, and the output end of the second DC switch 113 is connected in parallel to the DC bus.

[0077] The third DC switch 112 is used as a load power supply switch and is connected in series between the DC bus and the load.

[0078] The DC energy storage module is connected to an energy storage bypass protector, the first energy storage module 114 is connected to the first energy storage bypass protector 115, the second energy storage module 116 is connected to the second energy storage bypass protector 117, and the Mth energy storage module 118 is connected to the Mth energy storage bypass protector 119; the M bypass protectors are connected in cascade, that is, the negative electrode of the first energy storage bypass protector 115 is connected with the positive electrode of the second energy storage bypass protector 117, the negative electrode of the second energy storage bypass protector 117 is connected with the positive electrode of the third bypass protector, and so on, the positive electrode of the Mth energy storage bypass protector 119 is connected with the negative electrode of the M-1 energy storage bypass protector, and the negative electrode is connected with the negative electrode of the DC bus.

[0079] The energy storage current sampling unit 120 is connected in series in the energy storage module loop, and preferably, one end of the energy storage current sampling unit is connected with the energy storage filter inductor 121, and the other end is connected with the positive electrode of the Mth energy storage module.

[0080] The system stability controller 126 is connected with the photovoltaic cascade control unit 124 through communication, and control instructions are issued through communication; the system stability controller 126 is connected with the energy storage cascade control unit 125 through communication.

[0081] Figure 2 The electrical schematic diagram of the photovoltaic bypass protector provided by the embodiment is schematically shown as follows: Figure 2 As shown in the figure, the photovoltaic bypass protector 201 comprises a mechanical isolation switch 202, a pressure-sensitive resistor 204, and a diode assembly 203.

[0082] The diode assembly 203 comprises one or more diodes, and if a plurality of diodes are included, the diodes are connected in series.

[0083] Wherein, the mechanical switch 202 has positive and negative poles, the positive pole output of the mechanical switch 202 is connected with the anode of the diode assembly 203, the negative pole output of the mechanical switch 202 is connected with the cathode of the diode assembly 203, and the pressure-sensitive resistor 204 is connected in parallel with the diode assembly 203;

[0084] The photovoltaic bypass protector can automatically conduct when the corresponding photovoltaic module fails, does not need additional control, and can inhibit the function of surge voltage. The isolating switch 202 of the photovoltaic bypass protector can be automatically or manually disconnected, realizing the maintenance of the corresponding photovoltaic module.

[0085] Figure 3 The electrical schematic diagram of the energy storage bypass protector provided by the embodiment is schematically shown as follows: Figure 3 As shown in the figure, the energy storage bypass protector 301 comprises a mechanical isolating switch 302, a pressure-sensitive resistor 303, a bidirectional power electronic switch assembly 304, and a direct current bypass switch 305. The bidirectional power electronic switch assembly 304 comprises one or more power electronic switches, the current of the power electronic switch can flow in two directions, if a plurality of power electronic switches are included, the power electronic switches are connected in series, and the power electronic switch in the bidirectional power electronic switch assembly 304 can be selected from power devices such as GTO (gate turn-off thyristor), IGBT, bidirectional thyristor, and IGCT. The mechanical isolating switch 302 has positive and negative poles, the positive pole output of the mechanical switch is connected with the positive pole of the bidirectional power electronic switch assembly, the negative pole output of the mechanical switch 302 is connected with the negative pole of the bidirectional power electronic switch assembly 304, the pressure-sensitive resistor 303 is connected in parallel across the positive and negative poles of the bidirectional power electronic switch assembly 304, and the direct current bypass switch 305 is connected in parallel across the positive and negative poles of the bidirectional power electronic switch assembly 304.

[0086] The energy storage bypass protector can automatically conduct when the corresponding energy storage module fails, does not need additional control, and can inhibit the function of surge voltage. The isolating switch 302 of the energy storage bypass protector can be automatically or manually disconnected, realizing the online replacement and maintenance of the corresponding energy storage module.

[0087] Figure 4 The control flow chart of the energy storage system provided by the embodiment is schematically shown as follows. The energy storage cascade module control comprises energy storage module control, energy storage SOC equalization control, energy storage system voltage stabilization control, and energy storage operation and protection control. The specific control steps are as follows:

[0088] First, the system fault judgment module 401 is executed, if there is a fault, it does not enter the next step procedure, if the system has no fault, the energy storage system starting module 402 is executed, after starting, it enters 403 to judge whether the starting is completed, after the starting is completed, it enters the energy storage voltage stabilization control module 404, then it enters the energy storage SOC equalization control module 405, and the energy storage SOC equalization control is executed. Then, it enters the fault judgment module 406, and judges which energy storage module is faulty through the energy storage module fault module 407, then the fault removal module is executed, the bypass protector 408 is operated, if there is no fault, the above process is repeatedly executed.

[0089] Figure 5 The energy storage voltage stabilization control block diagram provided by the embodiment is schematically shown. The energy storage system voltage stabilization control is specifically: the overall direct current bus voltage of the energy storage system is taken as a control target to perform negative feedback closed loop control, the voltage closed loop controller is preferably a PI controller, the voltage closed loop controller output is subjected to amplitude limiting to obtain an energy storage system current given value, the current given value is subtracted from the current value obtained by the energy storage current sampling unit, then the reference voltage value is obtained through the current controller, and the reference voltage value is taken as an input quantity of the energy storage module control. The M direct current energy storage modules in the energy storage system are based on carrier layering and carrier phase shift control, that is, K (K≤M) direct current energy storage modules are started according to the required voltage value, the K started direct current energy storage modules have only one direct current energy storage module power electronic switch in the PWM modulation state, and the power electronic switches of the other direct current energy storage modules are all in the conduction state.

[0090] Figure 6 The energy storage SOC equalization control flowchart provided by the embodiment is schematically shown. The energy storage SOC control adopts dynamic sequencing charge and discharge control, which is specifically: first, the power judgment module 4051 is entered, it is judged whether the system is in a charging state or a discharging state, if the power is greater than or equal to 0, the sequencing and chopping module 4052 is entered, in this procedure, the battery module SOC is sequenced from large to small to determine the charging module; the sequencing is discharged first, and it is ensured that the total voltage of the charging module is greater than or equal to the actual direct current bus voltage, and the number of modules participating in charging is less than or equal to the total voltage of one module. Then, the battery module adjustment control procedure 4053 is entered, the battery module SOC sequenced last is subjected to PWM modulation, and the switch tubes of the other modules are completely turned on in the discharging direction, and the battery discharge power is controlled through the voltage closed loop control.

[0091] If the system is in the discharging state, the power < 0, enter the sorting module 4054, sort the battery module SOC from small to large, determine the charging module; the sorting is discharged in advance, and ensure that the total voltage of the charging module is ≤ the actual DC bus voltage, and the number of modules participating in charging + 1 module voltage sum ≥ the actual DC bus voltage, then enter module 4055, the last module of the battery module SOC is sorted for PWM modulation, and the switch tube of the other module is fully on in the charging direction, and the battery charging power is controlled through voltage closed loop control.

[0092] Figure 7 The system stability control flowchart provided by the embodiment is schematically shown. The system stability control method: first, acquire the system DC bus voltage value 601, acquire the energy storage system SOC state 602, calculate the bus resonance frequency based on the current time and the past time bus voltage value, then enter the resonance suppression algorithm module 603, in the resonance suppression algorithm module, according to the resonance frequency, add the active damping control algorithm, output the energy storage system voltage given value through the energy storage system voltage given instruction module 604, realize the bus voltage stability control; then enter the photovoltaic power instruction given module 605, in the photovoltaic power instruction given module, according to the energy storage SOC state, give the photovoltaic power value, and the system stability control is realized in the system stability controller.

[0093] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A DC power generation system, characterized in that, The system includes a photovoltaic cascade subunit, a first DC switch, a second DC switch, a third DC switch, a DC energy storage system, a first voltage sampling unit, a second voltage sampling unit, an energy storage current sampling unit, an energy storage filter inductor, a system stability controller, a photovoltaic cascade control unit, and an energy storage cascade control unit. The photovoltaic cascade sub-units are connected in series and then connected to the input terminal of the first DC switch, and the output terminal of the first DC switch is connected to the bus. The photovoltaic cascade subunit includes a photovoltaic module, a photovoltaic MPPT controller, a DC / DC isolation converter, and a photovoltaic bypass protector; The photovoltaic MPPT controller's input is connected to the photovoltaic module, and its output is connected to the input of the DC / DC isolation converter. The output of the DC / DC isolation converter is connected to the input of the photovoltaic bypass protector. The first voltage sampling unit is used to collect the voltage of the DC bus after the photovoltaic cascade sub-units are connected in series; the second voltage sampling unit is used to collect the voltage of the DC energy storage system. The input terminal of the second DC switch is connected to the output terminal of the DC energy storage system, and the output terminal of the second DC switch is connected in parallel to the DC bus. The third DC switch is connected in series between the DC bus and the load; The DC energy storage system includes M cascaded DC energy storage modules and M energy storage bypass protectors. The M DC energy storage modules and the M energy storage bypass protectors are connected in a one-to-one correspondence, and the M energy storage bypass protectors are connected in series with each other. The energy storage current sampling unit is connected in series with the DC energy storage system. One end of the energy storage current sampling unit is connected to one end of the energy storage filter inductor, and the other end is connected to the positive terminal of the last energy storage bypass protector. One end of the energy storage filter inductor and the other end of the first energy storage bypass protector are both connected to the input terminal of the second DC switch. The output terminal of the second DC switch is connected to the bus. The photovoltaic cascade control unit is communicatively connected to the photovoltaic cascade subunit and is used to control the photovoltaic cascade module to perform maximum power point tracking control and voltage limiting control. The energy storage cascade control unit communicates with the DC energy storage module in the DC energy storage system and is used to control the energy storage cascade module, including energy storage system voltage regulation control, energy storage module switching transistor modulation control, energy storage SOC equalization control, and energy storage operation and protection control. The system stability controller is connected to the photovoltaic cascade control unit and the energy storage cascade control unit via communication, and issues control commands through communication.

2. The system according to claim 1, characterized in that, Photovoltaic bypass protectors include mechanical disconnect switches, varistors, and diode components; When a diode assembly comprises several diodes, the diodes are connected in series; The mechanical switch has positive and negative terminals. The positive output of the mechanical switch is connected to the anode of the diode assembly, and the negative output of the mechanical switch is connected to the cathode of the diode assembly. The varistor is connected in parallel with the diode assembly. The photovoltaic bypass protector will automatically turn on when the corresponding photovoltaic module fails and suppress surge voltage. The isolating switch of the photovoltaic bypass protector will automatically or manually disconnect to perform maintenance on the corresponding photovoltaic module.

3. The system according to claim 1, characterized in that, The positive and negative terminals of the kth DC energy storage module are connected to the positive and negative input terminals of the kth bypass protector, respectively, k=1,2…M, and the output terminals of the M bypass protectors are connected in series. The energy storage bypass protector is used to suppress surge voltage and automatically turns on when the corresponding energy storage module fails. The isolating switch of the energy storage bypass protector can be automatically or manually disconnected to allow for online replacement and maintenance of the corresponding energy storage module.

4. The system according to claim 3, characterized in that, The DC energy storage module includes a DC-DC converter circuit, an energy storage battery pack, a battery management system, and a module control board; The DC-DC converter circuit is a non-isolated topology, specifically a half-bridge circuit, which is a circuit consisting of two power electronic switches connected in series. The input terminal of the DC-DC converter circuit is connected to the energy storage bypass protector corresponding to the DC energy storage module it belongs to, for receiving electrical energy from the DC bus; the output terminal is connected to the energy storage battery pack, for providing electrical energy conversion for charging or discharging the energy storage battery pack. The energy storage battery pack is connected to the output of the DC-DC converter circuit to store electrical energy; The battery management system is used to monitor the operating status of the energy storage battery pack and transmit the operating status to the module control board; The module control board controls the operating status of the DC-DC conversion circuit.

5. The system according to claim 3, characterized in that, The energy storage bypass protector includes a mechanical disconnect switch, a varistor, a bidirectional power electronic switch assembly, and a DC bypass switch; When a bidirectional power electronic switch assembly includes several power electronic switches, the power electronic switches are connected in series; The mechanical disconnect switch and several power electronic switches have timing operation requirements. When it is necessary to bypass the corresponding energy storage module, the power electronic switch is turned on first, then the mechanical disconnect switch is turned off, and then the DC bypass switch is closed. The mechanical disconnect switch has two poles, positive and negative. The positive output of the mechanical switch is connected to the positive pole of the bidirectional power electronic switch assembly, and the negative output of the mechanical switch is connected to the negative pole of the bidirectional power electronic switch assembly. The varistor is connected in parallel across the positive and negative terminals of the bidirectional power electronic switch assembly; The DC bypass switch is connected in parallel across the positive and negative terminals of the bidirectional power electronic switch assembly.

6. A control method for a DC power generation system according to any one of claims 1-5, characterized in that, include: The photovoltaic cascaded module control, energy storage cascaded module control, and system stability control are respectively achieved through the photovoltaic cascaded control unit, energy storage cascaded control unit, and system stability controller. During energy storage module control, at any given time, only one DC energy storage module's power electronic switch is in PWM modulation state, while the upper transistors of the power electronic switch bridge arms of other DC energy storage modules are either in an on state or in an off state.

7. The method according to claim 6, characterized in that, Controlling photovoltaic cascaded modules through a photovoltaic cascade control unit includes: The photovoltaic cascaded module performs maximum power point tracking (MPPT) control and voltage limiting control simultaneously. That is, if the MPPT control voltage exceeds the voltage limit value, MPPT control will no longer be performed, and voltage closed-loop control will be performed according to the voltage limit. When a photovoltaic cascade module fails, the corresponding photovoltaic bypass protector is activated to bypass the failed photovoltaic cascade module.

8. The method according to claim 6, characterized in that, The voltage regulation control of the energy storage system includes: using the overall DC bus voltage of the energy storage system as the control target for negative feedback closed-loop control. The voltage closed-loop controller includes a PI controller. The output of the voltage closed-loop controller is limited to obtain the current setpoint of the energy storage system. The difference between the current setpoint and the current value obtained by the energy storage current sampling unit is calculated and then passed through the current controller to obtain the reference voltage value. The reference voltage value is used as the input quantity for the control of the energy storage module. The modulation control of the switching transistors of the energy storage module includes: the DC energy storage module is based on carrier stacking and carrier phase shift control, that is, K DC energy storage modules are started according to the required voltage value. Among the K started DC energy storage modules, only one DC energy storage module's power electronic switch is in PWM modulation state, and all the upper transistors of the power electronic switches of the other DC energy storage modules are in the on state. The energy storage SOC equalization control includes: adopting dynamic sorting charge and discharge control, sorting the DC energy storage modules according to their SOC from small to large, the sorting is dynamically adjusted, in the discharge state the DC energy storage module with large SOC is selected for discharge, in the charging state the DC energy storage module with small SOC is selected for charging. Energy storage operation and protection control includes: determining whether the energy storage system meets the start-up conditions; if the start-up conditions are met, executing the energy storage system start-up procedure; after start-up, entering the voltage regulation control module, the control target of the voltage regulation control module is the DC bus voltage of the system; determining whether each DC energy storage module is faulty; if a DC module is faulty, disconnecting the faulty module and engaging the bypass protector of the corresponding module.

9. The method according to claim 6, characterized in that, System stability control through a system stability controller includes: Obtain the DC bus voltage value and the SOC state of the energy storage system, and calculate the bus resonant frequency based on the bus voltage values ​​at the current and past times. Based on the resonant frequency, an active damping control algorithm is added to output the voltage setpoint of the energy storage system for bus voltage stabilization control. The photovoltaic power target value is given based on the energy storage SOC state.

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