Direct current power generation system and control method thereof

Abstract

The invention discloses a direct-current power generation system and a control method thereof, which innovatively adopts a photovoltaic and energy storage double-cascade architecture and combines an intelligent protection and coordination control strategy. The system comprises N photovoltaic cascade subunits and M direct current energy storage modules, and each unit is provided with a bypass protection device. Each photovoltaic cascade subunit is integrated with an MPPT controller, an isolation converter and a bypass protector containing a piezoresistor and a diode; the energy storage module adopts a non-isolated DCDC conversion circuit, and a matched energy storage bypass protector is integrated with a bidirectional power electronic switch, a piezoresistor and a mechanical isolation switch. The technical problems of large voltage fluctuation, low system reliability, difficult maintenance and the like of a traditional direct current system are effectively solved, the service life of equipment is prolonged while the system stability is improved, and the system is particularly suitable for medium-high voltage direct current power supply scenes.

Description

Technical Field

[0001] The present invention belongs to the technical field of photovoltaic power generation and direct current energy storage, and in particular relates to a direct current power generation system and a control method thereof. Background Art

[0002] With the continuous growth of global energy demand and the increasing emphasis on environmental protection, photovoltaic power generation has attracted widespread attention as a clean, renewable energy source. Currently, photovoltaic power generation systems primarily use inverters to convert direct current (DC) power into alternating current (AC) before integrating it into the AC power grid. However, as installed PV capacity continues to increase, the AC power grid's ability to absorb photovoltaic energy is gradually reaching its limits, making it unable to accommodate the increasing demand for PV systems. This, to a certain extent, has limited the large-scale application of PV power generation.

[0003] Meanwhile, in the field of DC transmission, compared to traditional AC transmission, DC transmission offers numerous advantages, such as no reactive power issues and easier voltage stability control. In theory, this makes it more suitable for the direct transmission and utilization of photovoltaic power generation. However, due to the voltage ratings of power electronic components, most current mainstream DC power generation systems operate at voltage levels below 1500V. This lower voltage restricts power supply distances, making it impossible to achieve large-capacity, long-distance power supply and difficult to meet the power supply needs of certain scenarios, such as medium- and high-voltage DC power supply.

[0004] Furthermore, existing DC power generation systems face several technical challenges during actual operation. On the one hand, system voltage fluctuations are significant, impacting the stability and reliability of power supply. This is particularly true when loads fluctuate significantly or the output power of photovoltaic modules is unstable. Furthermore, system reliability needs to be improved. When photovoltaic modules or energy storage modules fail, the lack of effective protection and bypass mechanisms can cause downtime or damage to the entire system, increasing maintenance costs and difficulty. Furthermore, the coordinated control of photovoltaic modules and energy storage modules in traditional systems is not precise enough to fully leverage their respective performance advantages, further limiting improvements in overall system efficiency and stability. Summary of the Invention

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

[0006] To achieve the above objectives, the present invention provides a direct current power generation system, comprising 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 inductor, a system stability controller, a photovoltaic cascade control unit, and an energy storage cascade control unit;

[0007] The photovoltaic cascade subunits are connected in series and then connected to a first DC switch;

[0008] 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;

[0009] The second DC switch input terminal is connected to the DC energy storage system output terminal, and the second DC switch output terminal is connected in parallel to the DC bus;

[0010] The third DC switch is connected in series between the DC bus and the load;

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

[0012] The system stability controller is connected to the photovoltaic cascade control unit and the energy storage cascade control unit respectively through communication, and sends control instructions through communication.

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

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

[0015] Optionally, the photovoltaic bypass protector includes a mechanical isolation switch, a varistor, and a diode assembly;

[0016] When the diode assembly includes several 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 to the anode of the diode assembly, the negative output of the mechanical switch is connected to the cathode of the diode assembly, and the varistor is connected in parallel with the diode assembly;

[0018] The photovoltaic bypass protector will automatically turn on and suppress surge voltage when a fault occurs in the corresponding photovoltaic module. The isolation switch of the photovoltaic bypass protector is automatically or manually disconnected to maintain the corresponding photovoltaic component.

[0019] Optionally, the DC energy storage system includes a DC energy storage module and an energy storage bypass protector;

[0020] The DC energy storage modules are respectively connected to an energy storage bypass protector, and the bypass protectors are cascaded;

[0021] The energy storage bypass protector is used to suppress surge voltage and automatically turns on when a corresponding energy storage module fails;

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

[0023] Optionally, the DC energy storage module includes 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, i.e. a circuit consisting of two power electronic switches connected in series;

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

[0026] The energy storage battery pack is connected to the output end of the DCDC conversion circuit to store electrical energy;

[0027] 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;

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

[0029] Optionally, the energy storage bypass protector includes a mechanical isolating switch, a varistor, a bidirectional power electronic switch component, and a DC bypass switch;

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

[0031] The mechanical isolating switch and the plurality of power electronic switches have a timing action requirement. When the corresponding energy storage module needs to be bypassed, the power electronic switch is first turned on, then the mechanical isolating switch is turned off, and then the DC bypass switch is closed.

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

[0033] The varistor is connected in parallel to the positive and negative terminals of the bidirectional power electronic switch assembly;

[0034] The DC bypass switch is connected in parallel at both ends of the positive and negative poles of the bidirectional power electronic switch component.

[0035] The present invention also provides a control method for a DC power generation system, comprising: controlling a photovoltaic cascade module, controlling an energy storage cascade module, and controlling a system stability controller respectively through a photovoltaic cascade control unit, an energy storage cascade control unit, and a system stability controller;

[0036] Among them, when the energy storage module is controlled, at any time, only one power electronic switch of a DC energy storage module is in the PWM modulation state, and the upper tubes of the power electronic switch bridge arms of other DC energy storage modules are in the on state or the upper tubes are in the off state.

[0037] Optionally, the photovoltaic cascade module control via the photovoltaic cascade control unit includes:

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

[0039] When a photovoltaic cascade module fails, the corresponding photovoltaic bypass protector is activated to bypass the failed photovoltaic cascade module.

[0040] Optionally, the energy storage cascade module control includes energy storage system voltage stabilization control, energy storage module switch modulation control, energy storage SOC balancing control, and energy storage operation and protection control through the energy storage cascade control unit;

[0041] The energy storage system voltage stabilization control 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 a given current value of the energy storage system, the current given value is subtracted from the current value obtained by the energy storage current sampling unit, and then a reference voltage value is obtained through the current controller. The reference voltage value is used as the input for energy storage module control;

[0042] The energy storage module switch tube modulation control 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, and among the K started DC energy storage modules, only one DC energy storage module's power electronic switch is in the PWM modulation state, and the power electronic switch upper tubes of the other DC energy storage modules are all in the on state;

[0043] Energy storage SOC balancing control includes: adopting dynamic sorting charge and discharge control to sort the DC energy storage modules from small to large according to their SOC, and the sorting is a dynamic adjustment sorting, selecting the DC energy storage module with large SOC to discharge in the discharge state, and selecting the DC energy storage module with small SOC to charge in the charging state;

[0044] Energy storage operation and protection control include: judging whether the energy storage system has the startup conditions, and if so, executing the energy storage system startup procedure; entering the voltage stabilization control module after startup, 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 if a DC module has a fault, cutting off the faulty module and activating the bypass protector of the corresponding module.

[0045] Optionally, system stability control performed by a system stability controller includes:

[0046] Obtain the system DC bus voltage value and the SOC status of the energy storage system, and calculate the bus resonant frequency based on the bus voltage values ​​at the current time and in the past;

[0047] Active damping control algorithm is added according to the resonant frequency to output the energy storage system voltage setpoint and perform bus voltage stability control;

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

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

[0050] The DC power generation system and control method of the present invention significantly improve system reliability and availability by utilizing a dual-cascade architecture of photovoltaic and energy storage, combined with intelligent protection and coordinated control strategies. The modular cascade structure supports automatic bypass of faulty units and automatically suppresses surge voltage, enabling online module maintenance and effectively addressing the downtime and maintenance difficulties associated with faults in traditional systems. Furthermore, the system utilizes a dynamic energy storage management strategy, combined with a SOC-sequencing charge-discharge algorithm and carrier stacking-phase-shifting hybrid modulation technology, to achieve precise voltage stabilization and efficient energy management, significantly reducing voltage fluctuations and improving system stability. Furthermore, a system-level resonance suppression algorithm further enhances system stability by real-time monitoring of the busbar resonant frequency and introducing active damping control. The photovoltaic-energy storage coordinated control mechanism dynamically adjusts photovoltaic power output based on the energy storage SOC status, optimizing overall system efficiency. The present invention also supports medium- and high-voltage DC power supply, expanding its application scenarios and making it particularly suitable for scenarios requiring high power quality and reliability, such as data centers and industrial production. Through these technical improvements, the present invention not only improves system stability and reliability but also reduces system and maintenance costs, resulting in significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0052] Figure 1This is a system electrical schematic diagram of an embodiment of the present invention;

[0053] Figure 2 This is an electrical schematic diagram of a photovoltaic bypass protector according to an embodiment of the present invention;

[0054] Figure 3 This is an electrical schematic diagram of an energy storage bypass protector according to an embodiment of the present invention;

[0055] Figure 4 This is a control flow chart of an energy storage system according to an embodiment of the present invention;

[0056] Figure 5 This is a block diagram of energy storage voltage stabilization control according to an embodiment of the present invention;

[0057] Figure 6 This is a flow chart of energy storage SOC balancing control according to an embodiment of the present invention;

[0058] Figure 7 This is a flow chart of system stability control according to an embodiment of the present invention;

[0059] Among them: 101, photovoltaic module; 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 stability controller; 124, photovoltaic cascade control unit; 125, energy storage cascade control unit; 201, photovoltaic bypass protector; 202, mechanical isolation switch; 204, varistor; 203, diode assembly; 301, energy storage bypass protector; 302, mechanical isolation switch; 303, varistor; 304, bidirectional power electronic switch assembly; 305 DC bypass switch. DETAILED DESCRIPTION

[0060] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. 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 flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0062] Example 1

[0063] In this embodiment, a DC power generation system is provided, which includes a photovoltaic cascade sub-unit, 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;

[0064] The photovoltaic cascade subunits are connected in series and then connected to the first DC switch;

[0065] 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;

[0066] The second DC switch input terminal is connected to the DC energy storage system output terminal, and the second DC switch output terminal is connected in parallel to the DC bus;

[0067] The third DC switch is connected in series between the DC bus and the load;

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

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

[0070] The following is a detailed description with reference to the accompanying drawings:

[0071] like Figure 1 As shown, the DC power generation system proposed in this embodiment includes:

[0072] N (N≥2) photovoltaic cascade sub-units, a first DC switch 111, a second DC switch 113, a third DC switch 112, M (M≥1) DC energy storage modules, 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 subunit includes: 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 input is connected to the photovoltaic module 101, and the output is connected to the input of the DC / DC isolation converter 103, and the output of the DC / DC isolation converter 103 is connected to the input of the photovoltaic bypass protector 104. The output of the photovoltaic bypass protector 104 has two poles, namely, a positive pole and a negative pole.

[0074] N (N≥2) photovoltaic cascade sub-units are connected in series and connected in series through the output end of the photovoltaic bypass protector. That is, the positive pole of the first photovoltaic bypass protector is connected to the system DC bus, and the negative pole is connected to the positive pole of the second photovoltaic bypass protector. Similarly, the positive pole of the Nth photovoltaic bypass protector is connected to the negative pole of the N-1th photovoltaic bypass protector, and the negative pole is connected to the negative pole of the DC bus.

[0075] N (N≥2) photovoltaic cascade subunits are connected in series and then connected to the first DC switch 111; the first voltage sampling unit 123 is connected to the DC bus of the N (N≥2) photovoltaic cascade subunits connected in series.

[0076] The input end of the second DC switch 113 is connected to 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 serves as a load power supply switch and is connected in series between the DC bus and the load.

[0078] The DC energy storage modules are respectively 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; the M-th energy storage module 118 is connected to the M-th energy storage bypass protector 119; M bypass protectors are cascaded, that is, the negative pole of the first energy storage bypass protector 115 is connected to the positive pole of the second energy storage bypass protector 117, the negative pole of the second energy storage bypass protector 117 is connected to the positive pole of the third bypass protector, and so on. The positive pole of the M-th energy storage bypass protector 119 is connected to the negative pole of the M-1-th energy storage bypass protector, and the negative pole is connected to the negative pole of the DC bus.

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

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

[0081] Figure 2 The electrical schematic diagram of the photovoltaic bypass protector provided in this embodiment is shown schematically. Figure 2 As shown, the photovoltaic bypass protector 201 includes a mechanical isolation switch 202, a varistor 204, and a diode assembly 203;

[0082] The diode assembly 203 includes one or more diodes. If multiple diodes are included, these diodes are connected in series.

[0083] The mechanical switch 202 has positive and negative poles. The positive output of the mechanical switch 202 is connected to the anode of the diode component 203, and the negative output of the mechanical switch 202 is connected to the cathode of the diode component 203. The varistor 204 is connected in parallel with the diode component 203.

[0084] The photovoltaic bypass protector can automatically turn on when a fault occurs in the corresponding photovoltaic module without the need for additional control, and can suppress the surge voltage. The isolation switch 202 of the photovoltaic bypass protector can be automatically or manually disconnected to achieve maintenance of the corresponding photovoltaic component.

[0085] Figure 3 The electrical schematic diagram of the energy storage bypass protector provided in this embodiment is shown schematically. Figure 3 As shown, the energy storage bypass protector 301 includes a mechanical isolation switch 302, a varistor 303, a bidirectional power electronic switch assembly 304, and a DC bypass switch 305. The bidirectional power electronic switch assembly 304 includes one or more power electronic switches, and the current of the power electronic switches can flow in both directions. If multiple power electronic switches are included, these power electronic switches are connected in series. The power electronic switches in 304 can be selected from power devices such as GTO (gate turn-off thyristor), IGBT, bidirectional thyristor, or IGCT. The mechanical isolation switch 302 has positive and negative poles. 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 302 is connected to the negative pole of the bidirectional power electronic switch assembly 304. The varistor 303 is connected in parallel to the positive and negative poles of the bidirectional power electronic switch assembly 304. The DC bypass switch 305 is connected in parallel to the positive and negative poles of the bidirectional power electronic switch assembly 304.

[0086] The energy storage bypass protector can automatically turn on when a corresponding energy storage module fails, without the need for additional control, and can suppress surge voltage. The isolation switch 302 of the energy storage bypass protector can be automatically or manually disconnected to achieve online replacement and maintenance of the corresponding energy storage module;

[0087] Figure 4 The energy storage system control flow chart provided by this embodiment is schematically shown. The energy storage cascade module control includes energy storage module control, energy storage SOC balancing control, energy storage system voltage stabilization control, and energy storage operation and protection control. The specific control steps are:

[0088] First, the system fault determination module 401 is executed. If a fault is detected, the next step is not performed. If the system is fault-free, the energy storage system startup module 402 is executed. After startup is complete, the module 403 is executed to determine whether the startup is complete. After startup is complete, the module 404 is entered into the energy storage voltage stabilization control module. After that, the module 405 enters the energy storage SOC balance control module to perform energy storage SOC balance control. Next, the module 406 is entered into the fault determination module. The energy storage module fault detection module 407 determines which energy storage module is faulty. The faulty module is then removed and the bypass protector 408 is activated. If there is no fault, the above process is repeated.

[0089] Figure 5 The energy storage voltage stabilization control block diagram provided by this embodiment is schematically shown. The energy storage system voltage stabilization control is specifically as follows: the overall DC bus voltage of the energy storage system is used as the control target for negative feedback closed-loop control. The voltage closed-loop controller is preferably a PI controller. The output of the voltage closed-loop controller is limited to obtain a given current value of the energy storage system. This current given value is subtracted from the current value obtained by the energy storage current sampling unit, and then a reference voltage value is obtained through the current controller. The reference voltage value is used as the input for energy storage module control. The M DC energy storage modules in the energy storage system are based on carrier stacking and carrier phase shift control, that is, K (K≤M) DC energy storage modules are started according to the required voltage value. Among these K started DC energy storage modules, only one DC energy storage module has its power electronic switch in the PWM modulation state, and the upper tubes of the power electronic switches of the other DC energy storage modules are all in the on state.

[0090] Figure 6 The energy storage SOC balancing control flow chart provided by this embodiment is schematically shown. The energy storage SOC control adopts dynamic sorting charge and discharge control, specifically: first enter the power judgment module 4051 to determine whether the system is in the charging state or the discharging state. If the power ≥ 0, then enter the sorting and chopping module 4052. In this program, the battery module SOC is sorted from large to small to determine the charging module; the top-ranked modules are discharged first, and it is ensured that the sum of the voltages of the modules involved in charging ≥ the actual DC bus voltage, and the sum of the voltages of the modules involved in charging - 1 ≤ the actual DC bus voltage. Then enter the battery module adjustment control program 4053, PWM modulate the module with the last battery module SOC sorting, and fully turn on the discharge direction of the switch tubes of other modules, and control the battery discharge power through the voltage closed loop.

[0091] If the system is in the discharge state and the power is less than 0, the system enters the sorting module 4054, sorts the battery module SOC from small to large, and determines the charging module; the modules with the highest SOC are discharged first, and the sum of the voltages of the modules involved in charging is ensured to be ≤ the actual DC bus voltage, and the sum of the voltages of the number of modules involved in charging + 1 module is ≥ the actual DC bus voltage. Then the system enters the module 4055, performs PWM modulation on the module with the lowest SOC in the sorting, and fully turns on the charging direction of the switches of other modules, and controls the battery charging power through the voltage closed loop.

[0092] Figure 7 The system stability control flow chart provided by this embodiment is schematically shown. The system stability control method includes the following steps: first, obtaining the system DC bus voltage value 601 and the energy storage system SOC state 602; calculating the bus resonant frequency based on the current and past bus voltage values; then entering the resonance suppression algorithm module 603; in this module, an active damping control algorithm is added based on the resonant frequency; and outputting the energy storage system voltage setpoint via the energy storage system voltage setting instruction module 604 to achieve bus voltage stability control; then entering the photovoltaic power command setting module 605; in this module, a photovoltaic power value is set based on the energy storage SOC state. System stability control is implemented in the system stability controller.

[0093] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection 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 subunits are connected in series and then connected to a first DC switch; 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 second DC switch input terminal is connected to the DC energy storage system output terminal, and the second DC switch output terminal is connected in parallel to the DC bus; The third DC switch is connected in series between the DC bus and the load; The energy storage current sampling unit is connected in series to the energy storage module loop, one end of the energy storage current sampling unit is connected to the energy storage filter inductor, and the other end is connected to the positive electrode of the last energy storage module; The system stability controller is connected to the photovoltaic cascade control unit and the energy storage cascade control unit respectively through communication, and sends control instructions through communication.

2. The system according to claim 1, wherein: The photovoltaic cascade subunit includes a photovoltaic module, a photovoltaic MPPT controller, a DC / DC isolation converter, and a photovoltaic bypass protector; The input of the photovoltaic MPPT controller is connected to the photovoltaic module, the output is connected to the input of the DC / DC isolation converter, and the output of the DC / DC isolation converter is connected to the input of the photovoltaic bypass protector.

3. The system according to claim 2, characterized in that The photovoltaic bypass protector includes a mechanical isolation switch, a varistor, and a diode assembly; When the diode assembly includes several diodes, the diodes are connected in series; The mechanical switch has positive and negative poles, the positive output of the mechanical switch is connected to the anode of the diode assembly, the negative output of the mechanical switch is connected to the cathode of the diode assembly, and the varistor is connected in parallel with the diode assembly; The photovoltaic bypass protector will automatically turn on and suppress surge voltage when a fault occurs in the corresponding photovoltaic module. The isolation switch of the photovoltaic bypass protector is automatically or manually disconnected to maintain the corresponding photovoltaic component.

4. The system according to claim 1, wherein: The DC energy storage system includes a DC energy storage module and an energy storage bypass protector; The DC energy storage modules are respectively connected to an energy storage bypass protector, and the bypass protectors are cascaded; The energy storage bypass protector is used to suppress surge voltage and automatically turns on when a corresponding energy storage module fails; The isolating switch of the energy storage bypass protector is automatically or manually disconnected to perform online replacement and maintenance of the corresponding energy storage module.

5. The system according to claim 4, characterized in that The DC energy storage module includes a DCDC conversion circuit, an energy storage battery pack, a battery management system, and a module control board; The DCDC conversion circuit is a non-isolated topology, specifically a half-bridge circuit, i.e. a circuit consisting of two power electronic switches connected in series; The input end of the DCDC conversion circuit is connected to the DC bus for receiving electric energy from the DC bus; the output end is connected to the energy storage battery pack to provide charging or discharging electric energy conversion for the energy storage battery pack; The energy storage battery pack is connected to the output end of the DCDC conversion 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 working status of the DCDC conversion circuit.

6. The system according to claim 4, characterized in that The energy storage bypass protector includes a mechanical isolating switch, a varistor, a bidirectional power electronic switch component, and a DC bypass switch; When the bidirectional power electronic switch assembly includes a plurality of power electronic switches, the power electronic switches are connected in series; The mechanical isolating switch and the plurality of power electronic switches have a timing action requirement. When the corresponding energy storage module needs to be bypassed, the power electronic switch is first turned on, then the mechanical isolating switch is turned off, and then the DC bypass switch is closed. The mechanical isolating switch has positive and negative poles. The positive output of the mechanical switch is connected to the positive pole of the bidirectional power electronic switch component, and the negative output of the mechanical switch is connected to the negative pole of the bidirectional power electronic switch component. The varistor is connected in parallel to the positive and negative terminals of the bidirectional power electronic switch assembly; The DC bypass switch is connected in parallel at both ends of the positive and negative poles of the bidirectional power electronic switch component.

7. A control method for the DC power generation system according to any one of claims 1 to 6, characterized in that: include: The photovoltaic cascade module control, energy storage cascade module control and system stability control are respectively performed through the photovoltaic cascade control unit, the energy storage cascade control unit and the system stability controller; Among them, when the energy storage module is controlled, at any time, only one power electronic switch of a DC energy storage module is in the PWM modulation state, and the upper tubes of the power electronic switch bridge arms of other DC energy storage modules are in the on state or the upper tubes are in the off state.

8. The method according to claim 7, characterized in that The photovoltaic cascade module control through the photovoltaic cascade control unit includes: The photovoltaic cascade module performs maximum power tracking control and voltage limit control at the same time. That is, if the maximum power tracking control voltage exceeds the voltage limit value, the maximum power tracking control is no longer performed and the voltage closed-loop control is 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.

9. The method according to claim 7, characterized in that The energy storage cascade module control is performed through the energy storage cascade control unit, including energy storage system voltage stabilization control, energy storage module switch modulation control, energy storage SOC balancing control, and energy storage operation and protection control; The energy storage system voltage stabilization control 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 a given current value of the energy storage system, the current given value is subtracted from the current value obtained by the energy storage current sampling unit, and then a reference voltage value is obtained through the current controller. The reference voltage value is used as the input for energy storage module control; The energy storage module switch tube modulation control 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, and among the K started DC energy storage modules, only one DC energy storage module's power electronic switch is in the PWM modulation state, and the power electronic switch upper tubes of the other DC energy storage modules are all in the on state; Energy storage SOC balancing control includes: adopting dynamic sorting charge and discharge control to sort the DC energy storage modules from small to large according to their SOC, and the sorting is a dynamic adjustment sorting, selecting the DC energy storage module with large SOC to discharge in the discharge state, and selecting the DC energy storage module with small SOC to charge in the charging state; Energy storage operation and protection control include: judging whether the energy storage system has the startup conditions, and if so, executing the energy storage system startup procedure; entering the voltage stabilization control module after startup, 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 if a DC module has a fault, cutting off the faulty module and activating the bypass protector of the corresponding module.

10. The method according to claim 7, characterized in that System stability control by the system stability controller includes: Obtain the system DC bus voltage value and the SOC status of the energy storage system, and calculate the bus resonant frequency based on the bus voltage values ​​at the current time and in the past; Active damping control algorithm is added according to the resonant frequency to output the energy storage system voltage setpoint and perform bus voltage stability control; The photovoltaic power target value is given according to the energy storage SOC state.

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