A direct current system and a control method thereof

Abstract

The application provides a direct current system and a control method thereof. The method comprises the following steps: detecting whether a preset output electrical parameter sudden drop phenomenon exists in the direct current system; if yes, controlling a power converter to adjust a wave generation logic, so that an input electrical parameter of the power converter is reduced to a set value under a preset condition, and energy corresponding to the output electrical parameter sudden drop phenomenon is borne by both an input side energy storage element and an output side energy storage element of the power converter, thereby avoiding the problem of excessively high input voltage caused by the fact that all the energy is stored in the input side energy storage element of the power converter. In other words, only the software wave generation logic is improved, and no additional device is added, so that the application has great advantages in cost, size, weight and the like.

Description

Technical Field

[0001] This invention belongs to the field of converter technology, and more specifically, relates to a DC system and its control method. Background Technology

[0002] In DC power distribution scenarios, the load may be suddenly disconnected. If the power supply and load are far apart, a sudden change in current in the inductance of the connection between them will induce a high voltage on the input side of the converter between the power supply and load. This high voltage may exceed the converter's tolerance, causing it to fail. Especially when the equivalent inductance is large, the energy storage capacity of the energy storage element on the converter input side is weak, and the current change is rapid, this voltage will be even greater, increasing the probability of converter damage.

[0003] In photovoltaic (PV) power generation systems, the output of the photovoltaic panels is DC power. When the downstream converter needs to shut down due to a fault, this condition is met. To address this issue, conventional PV inverters have a large-capacity capacitor connected in parallel on the input side to prevent input-side overvoltage failure during sudden shutdown. However, in some scenarios, the input capacitor does not need to be excessively large. Increasing the capacitor solely to prevent input-side overvoltage caused by sudden shutdown will lead to increased costs, size, and weight. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a DC system and its control method, which improves the software waveform generation logic and avoids the problem of excessive input voltage during instantaneous load dump.

[0005] The first aspect of this application discloses a control method for a DC system, wherein the output terminal of the DC power supply in the DC system is connected to at least one power converter, comprising:

[0006] Detect whether the DC system exhibits a sudden drop in preset output electrical parameters;

[0007] If so, the power converter is controlled to adjust the waveform generation logic so that the input electrical parameters of the power converter are reduced to a set value under preset conditions.

[0008] Optionally, in the above-described control method for a DC system, before controlling the power converter to adjust the waveform generation logic so that the input electrical parameters of the power converter decrease to a set value under preset conditions, the method further includes:

[0009] Determine whether the power converter requires emergency blocking;

[0010] If the power converter does not require emergency blocking, the control logic for adjusting the power converter's output is executed to reduce the input electrical parameters of the power converter to a set value under preset conditions.

[0011] Optionally, in the above-described control method for a DC system, after determining whether any of the power converters requires emergency blocking, if any one of the power converters requires emergency blocking, the method further includes:

[0012] Control the power converter that requires emergency blocking to perform emergency blocking.

[0013] Optionally, in the above-described control method for a DC system, when there are multiple power converters, while controlling the power converter requiring emergency blocking to perform emergency blocking, the method also includes:

[0014] Control at least one power converter that does not require emergency blocking to adjust its operating state so that the input electrical parameters of the power converter that does not require emergency blocking are reduced to a set value under preset conditions.

[0015] Optionally, in the above control method for the DC system, if there are multiple power converters that do not require emergency blocking, controlling at least one power converter that does not require emergency blocking to adjust its operating state includes:

[0016] The power converters that do not require emergency blocking are controlled to coordinate their waveform generation, thereby stabilizing the input voltage of the power converters that do not require emergency blocking.

[0017] Optionally, in the above-described control method for a DC system, if the power converter is an isolated converter, and each power converter is cascaded through its respective cascade unit, then controlling at least one power converter that does not require emergency blocking to adjust its operating state includes:

[0018] The coordinated operation of each power converter is controlled so that the energy storage element after each power converter can bear the energy.

[0019] Optionally, the control method for the above-mentioned DC system further includes:

[0020] If any of the power converters or cascade units malfunctions, the faulty power converter or cascade unit is shut down, as are all the cascade units.

[0021] The operating state of a power converter that is not faulty is adjusted so that the input electrical parameters of the power converter that is not faulty are reduced to a set value under preset conditions.

[0022] Optionally, in the control method of the above DC system, the output electrical parameters are output current and / or output power; the input electrical parameters are input current and / or input power.

[0023] Optionally, in the control method of the above-mentioned DC system, the input electrical parameters of the power converter are reduced to a set value under preset conditions, including:

[0024] The input electrical parameters of the power converter decrease to zero at a preset slope.

[0025] Optionally, the control method for the DC system described above further includes: if each power converter in the DC system needs to be blocked or shut down, controlling each power converter to turn off sequentially; and / or controlling each power converter to adjust its waveform generation logic so that the input electrical parameters of each power converter are reduced to a set value under preset conditions.

[0026] The second aspect of this application discloses a DC system, including: a DC power supply, a controller, and at least one power converter;

[0027] The output terminal of the DC power supply is connected to the input terminal of each of the power converters;

[0028] Each of the power converters is equipped with a corresponding energy storage element at both its input and output terminals;

[0029] The output terminals of each power converter are connected to the corresponding loads via corresponding switches;

[0030] The power converter is controlled by the controller;

[0031] The controller, in conjunction with the power converter, implements a control method for a DC system as described in any of the first aspects of this application.

[0032] Optionally, in the above-mentioned DC system, the capacity of the energy storage element on the input side of the power converter is smaller than the capacity of the energy storage element on the output side of the power converter.

[0033] Optionally, in the above-described DC system, the DC power source is a photovoltaic array.

[0034] Optionally, in the above-described DC system, the power converter includes at least one stage of DC converter.

[0035] Optionally, the above-mentioned DC system also includes: at least one cascaded unit;

[0036] Each of the cascaded units is respectively disposed in the stage following each of the power converters;

[0037] The output terminals of each cascaded unit are connected to the corresponding loads via corresponding switches.

[0038] Optionally, in the above DC system, the cascaded unit is an H-bridge topology.

[0039] Optionally, in the above-described DC system, the power converter is an isolated converter.

[0040] As can be seen from the above technical solution, the DC system control method provided by the present invention includes: detecting whether there is a preset output electrical parameter drop phenomenon in the DC system; if so, controlling the power converter to adjust the waveform logic so that the input electrical parameter of the power converter drops to a set value under preset conditions, so that the input-side energy storage element and the output-side energy storage element of the power converter jointly bear the energy corresponding to the output electrical parameter drop phenomenon, avoiding the problem of excessively high input voltage caused by storing all the energy in the input-side energy storage element of the power converter. That is, only the software waveform logic has been improved without adding any components, so it has significant advantages in terms of cost, size, and weight. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of a DC system provided in an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of another DC system provided in an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of another DC system provided in an embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of another DC system provided in an embodiment of the present invention;

[0046] Figure 5 This is a schematic diagram of another DC system provided in an embodiment of the present invention;

[0047] Figure 6 This is a flowchart of a control method for a DC system provided in an embodiment of the present invention;

[0048] Figure 7 This is a flowchart of another control method for a DC system provided in an embodiment of the present invention;

[0049] Figure 8 This is a schematic diagram of another DC system provided in an embodiment of the present invention;

[0050] Figure 9 This is a schematic diagram of another DC system provided in an embodiment of the present invention;

[0051] Figure 10 This is a schematic diagram of another DC system provided in an embodiment of the present invention;

[0052] Figure 11 This is a schematic diagram of another cascaded unit in a DC system provided by an embodiment of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] In this application, the terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] This application provides a control method for a DC system to address the problem that conventional photovoltaic inverters in the prior art have a large-capacity capacitor energy storage element connected in parallel on the input side, which can prevent input side overvoltage failure when suddenly shutting down. However, in some scenarios, the input capacitor does not need to be set too large. If the capacitor is increased simply to prevent overvoltage problems caused by sudden shutdown, it will lead to increased costs, size, and weight.

[0056] Specifically, such as Figure 1 As shown, a DC power supply (DC) is connected to the equivalent load impedance (R1) via a long line. If K1 is suddenly disconnected (system load dump), a voltage higher than that of the DC power supply (DC) will be induced in PL+ on the left side of K1 relative to PL-. If other devices are connected between PL+ and PL-, this can cause damage to these devices due to overvoltage.

[0057] like Figure 2 As shown, it is to Figure 1 A schematic diagram showing the connection in the middle as equivalent to an inductor.

[0058] like Figure 3 As shown, it is Figure 1The schematic diagram of the actual circuit shows that the DC power supply is connected to the power converter via a long line, and the power converter is then connected to the equivalent load (load consumption or grid-connected power generation, etc.). At a certain moment, if the equivalent load is disconnected or the power converter is protected by wave blocking, the capacitor C1 will be subjected to an induced voltage superimposed on the DC power supply output voltage, which may cause C1 and the power converter to fail.

[0059] like Figure 4 The diagram illustrates a photovoltaic power generation system where a photovoltaic array is connected to an inverter via a long line, and the inverter generates electricity in a grid-connected manner. Existing conventional inverters have a large-capacity capacitor connected to their input to suppress voltage rise caused by inverter blocking.

[0060] like Figure 5 As shown, this is a schematic diagram of another photovoltaic power generation system. The input-side capacitor C1 is relatively small, but when the system is blocked, capacitor C2 is effectively short-circuited with C1. The presence of C2 can also suppress the rise of induced voltage.

[0061] The output terminals of the DC power supply in this DC system are connected to at least one power converter, such as... Figure 3 As shown.

[0062] See Figure 6 The control method for this DC system includes:

[0063] S101. Detect whether there is a sudden drop in the preset output electrical parameters of the DC system.

[0064] It should be noted that the DC system has a preset output electrical parameter sudden drop phenomenon, such as instantaneous load dump. In this case, the DC power energy in the DC system will accumulate in the corresponding energy storage element, which will lead to high voltage damage to the devices on both sides of the energy storage element. Therefore, if the DC system detects a preset output electrical parameter sudden drop phenomenon, the following step S102 is executed to avoid overvoltage phenomenon when the DC system output electrical parameter sudden drop phenomenon occurs.

[0065] Specifically, the pre-defined sudden drop in output electrical parameters can include: the current loop between at least one power converter and its downstream devices being disconnected. Of course, this is not limited to the examples above, and will not be elaborated further here; it depends on the actual situation, and all are within the scope of protection of this application.

[0066] If a preset drop in output electrical parameters is detected in the DC system, then step S102 is executed.

[0067] S102, Control the power converter to adjust the waveform generation logic so that the input electrical parameters of the power converter are reduced to the set value under preset conditions.

[0068] It should be noted that the duty cycle of each switch in the power converter can be controlled to adjust the waveform generation logic.

[0069] The input electrical parameters can be input power and / or input current, which will not be elaborated here, but can be determined according to the actual situation, and are all within the protection scope of this application.

[0070] The output electrical parameters can be output power and / or output current, which will not be elaborated here. They can be determined according to the actual situation and are all within the scope of protection of this application.

[0071] The preset condition can be a preset slope, or other methods, which will not be elaborated here. It depends on the actual situation and is all within the scope of protection of this application.

[0072] The preset value can be zero, or other values, which will not be elaborated here. It depends on the actual situation and is within the scope of protection of this application.

[0073] In other words, the input electrical parameters of the power converter can be reduced to a set value under preset conditions, or the input electrical parameters of the power converter can be reduced to zero at a preset slope. Of course, this is not the only possibility, but it will not be elaborated here, and all of them are within the scope of protection of this application.

[0074] In practical applications, the specific process of controlling the power converter to adjust the waveform generation logic so that the input electrical parameters of the power converter are reduced to a set value under preset conditions can be as follows:

[0075] The power converter with the current loop disconnected adjusts the waveform logic so that the input electrical parameters of the power converter with the current loop disconnected drop to a set value under preset conditions.

[0076] In other words, as long as the power converter that controls the current loop to disconnect adjusts the wave generation logic, other power converters can operate normally. Of course, it is not excluded that other power converters may perform other operational adjustments, such as absorbing energy from the DC power supply. These will not be elaborated here, but will be determined according to the actual situation, and are all within the scope of protection of this application.

[0077] Specifically, explain the energy contribution, such as Figure 3 In the DC system shown, if the energy storage elements C1 and C2 cannot be connected in equivalent parallel under the ripple blocking condition, and the equivalent load R1 is suddenly disconnected at a certain moment, that is, the switch K1 is opened, so that the power converter and the downstream device cannot form a current loop, the power converter is controlled to adjust the ripple generation logic so that the input power / current of the power converter decreases at a set low slope.

[0078] The induced voltage on the inductor can be obtained by the following formula (1).

[0079]

[0080] Where V is the induced voltage across the inductor; L is the inductance value; The current change rate is denoted as .

[0081] As can be seen from formula (1), the decrease in the rate of change of current can cause the induced voltage on the long line equivalent inductance to decrease significantly.

[0082] From an energy perspective, the energy on the equivalent inductance L can be calculated using the following formula (2):

[0083]

[0084] Where W represents energy and I represents current.

[0085] If all the energy is absorbed by the input capacitor, the voltage across the energy storage element C1 in steady state will be higher than the initial voltage as shown in formula (3):

[0086]

[0087] In this context, it is assumed that the rising voltage is relatively small compared to the DC power supply output voltage; C1 is the capacitance of the energy storage element C1; ΔU is the rising voltage; and U0 is the initial voltage.

[0088] If the energy is shared by energy storage elements C1 and C2, assuming that the voltages of energy storage elements C1 and C2 are equivalent (energy conversion), then the voltage rise will become formula (4):

[0089]

[0090] In some specific applications, the energy storage element C2 is designed to be much larger than the energy storage element C1, thus the voltage rise rate will be well suppressed.

[0091] In this embodiment, the system detects whether a preset output electrical parameter drop occurs in the DC system. If so, the power converter is controlled to adjust its waveform generation logic so that the input electrical parameters of the power converter drop to a set value under preset conditions. This allows the input-side and output-side energy storage elements of the power converter to jointly bear the energy corresponding to the output electrical parameter drop, avoiding the problem of excessively high input voltage caused by storing all the energy in the input-side energy storage elements of the power converter. The input voltage is suppressed, and the system reliability is improved. In other words, only the software waveform generation logic is improved without adding any components, thus offering significant advantages in terms of cost, size, and weight.

[0092] In practical applications, see Figure 7 Before step S102, which controls the power converter to adjust the waveform generation logic so that the input electrical parameters of the power converter drop to a set value under preset conditions, the method further includes:

[0093] S201. Determine whether the power converter requires emergency blocking.

[0094] In other words, there are situations in this DC system where emergency wave blocking is necessary. In these cases, the harm caused by not implementing emergency wave blocking is less than the harm caused by implementing it. Specific situations requiring emergency wave blocking will not be detailed here; they will be determined based on the actual circumstances and are all within the scope of the applied protection.

[0095] If the power converter does not require emergency blocking, then step S102 is executed to control the power converter to adjust the transmission logic so that the input electrical parameters of the power converter are reduced to the set value under preset conditions.

[0096] In other words, to the extent that the environment permits, damage and danger to the DC system should be minimized.

[0097] In practical applications, after determining whether a power converter requires emergency blocking, if any power converter requires emergency blocking, the following steps are also included:

[0098] S202, Control the power converter that requires emergency blocking to perform emergency blocking.

[0099] The power converter that requires emergency blocking should be controlled to perform emergency blocking in order to avoid the harm and damage caused by failure to perform emergency blocking.

[0100] In practical applications, when there are multiple power converters, in addition to executing step S202 and controlling the power converter requiring emergency blocking to perform emergency blocking, the following is also included:

[0101] S203. Control at least one power converter that does not require emergency blocking to adjust its operating state so that the input electrical parameters of the power converter that does not require emergency blocking are reduced to a set value under preset conditions.

[0102] In other words, power converters that require emergency blocking should perform emergency blocking to avoid damage caused by failure to perform emergency blocking. At the same time, power converters that do not require emergency blocking should adjust their operating status so that the input electrical parameters of the power converters that do not require emergency blocking are reduced to the set value under preset conditions to avoid damage caused by emergency blocking.

[0103] It should be noted that the preset conditions may be the same or different under different circumstances. That is, the preset conditions may be the same or different depending on whether there is an emergency wave blocking situation or not. These will not be elaborated here, but are all within the scope of protection of this application.

[0104] Specifically, such as Figure 8As shown, a DC system of a multi-stage power converter is illustrated, where L1 is the equivalent inductance of the connecting line. In power converter 1, energy storage elements C21 and C11 cannot be directly connected in equivalent parallel under ripple blocking conditions. Similarly, in power converter 2, energy storage elements C22 and C12 cannot be connected in equivalent parallel under ripple blocking conditions. If switch K1 is turned off at a certain moment, power converter 1 can execute the aforementioned regulation and transmission logic. When power converter 1 needs emergency ripple blocking, power converter 2 can act as a regulator to mitigate sudden changes in input electrical parameters, suppressing the rate of current decrease on L1 and thus reducing the rate of voltage rise at the input terminals of energy storage elements C11 and C12.

[0105] In practical applications, if there are multiple power converters that do not require emergency blocking, step S203, which controls at least one power converter that does not require emergency blocking to adjust its operating state, can be: controlling the power converters that do not require emergency blocking to coordinate the generation of waves so that the input voltage that does not require emergency blocking tends to be stable.

[0106] Specifically, such as Figure 9 As shown, if there are three or more power converters connected in parallel, a single power converter may suddenly be blocked by a waveform protection mechanism. Other power converters can achieve stable control of the input voltage through a suitable coordinated waveform generation mechanism.

[0107] It should be noted that if the power converter is an isolated converter and each power converter is cascaded through its own cascade unit, then the specific process of step S203, controlling at least one power converter that does not require emergency blocking to adjust its working state, can also be: controlling the coordinated operation of each power converter so that the energy storage element after each power converter can bear the energy.

[0108] Specifically, Figure 10 As shown, the pre-amplifier is an isolated converter. Its input capacitor only needs to handle the energy of the high-frequency isolation frequency, and therefore can be designed to be extremely small. If one pre-amplifier needs to block the voltage, and other power converters simultaneously perform blocking, the voltage on the left side will rise extremely rapidly, potentially causing system failure. The cascaded unit output may be power frequency energy, therefore the capacitor on the right side needs to handle power frequency energy, and its equivalent capacitance is much larger than that of the capacitor on the left side. Through the coordinated processing of the pre-amplifier power converters, the voltage rise on the left side can be effectively suppressed, thus protecting the devices on the left side of the converter.

[0109] In practical applications, before and after any step, the following steps are also included: if any power converter or cascade unit is faulty, the faulty power converter or cascade unit is shut down, and each of the cascade units is shut down.

[0110] The operating state of a power converter that is not faulty is adjusted so that the input electrical parameters of the power converter that is not faulty are reduced to a set value under preset conditions.

[0111] Specifically, taking cascade unit 1 and power converter 1 as examples, if cascade unit 1 or power converter 1 fails, all cascade units will be shut down first, and power converter 1 will also be shut down. Subsequently, power converters 2 to n will adjust their operating states so that their input electrical parameters are reduced to a set value under preset conditions. Here, N is the total number of power converters.

[0112] In practical applications, before and after any step, the following steps are also included: if each power converter in the DC system needs to be blocked or shut down, control each power converter to be turned off sequentially; and / or control the adjustment and output logic of each power converter so that the input electrical parameters of each power converter are reduced to the set value under preset conditions.

[0113] In other words, when the output electrical parameters of a power converter suddenly drop, the current loop corresponding to that power converter is essentially broken. At this time, the current flow path of other converters in the system needs to be provided, or the power converter itself needs to adjust its waveform logic to achieve a slow reduction in current. If all power converters are turned off at the same time, there is no current flow path, which is equivalent to a sudden drop from a certain value to 0, thus inducing a large voltage. Therefore, when it is necessary to turn off all power converters, the way to achieve a slow reduction in current can be: turning off multiple power converters in sequence, or slowly decreasing the current command value of multiple power converters, etc. The specific process will not be elaborated here, and all are within the protection scope of this application.

[0114] Another embodiment of this application provides a DC system.

[0115] See Figure 3 The DC system includes: a DC power supply (DC), a controller, and at least one power converter. Figure 3 (This will be demonstrated using a single power converter as an example.)

[0116] The output terminal of the DC power supply is connected to the input terminal of each power converter.

[0117] Each power converter has corresponding energy storage elements (such as...) at its input and output terminals. Figure 3 (as shown in C1 and C2).

[0118] In practical applications, the capacity of the energy storage element on the input side of the power converter is smaller than the capacity of the energy storage element on the output side of the power converter.

[0119] The output terminals of each power converter are connected to the corresponding load R1 through the corresponding switch K1.

[0120] Specifically, the positive terminal (+) of the DC power supply is connected to the positive terminal of the energy storage element C1 and the positive input terminal of the power converter; the negative terminal (-) of the DC power supply is connected to the negative terminal of the energy storage element C1 and the negative input terminal of the power converter. The positive output terminal of the power converter is connected to the positive terminal of the energy storage element C2 and one end of the switch K1; the negative output terminal of the power converter is connected to the negative terminal of the energy storage element C2 and one end of the load R1; the other end of the switch K1 is connected to the other end of the load R1.

[0121] The number of power converters is 1 (e.g., Figure 3 (as shown); or, the number of power converters is 2 (as shown). Figure 8 (as shown); or, the number of power converters is multiple (such as...). Figure 9 (as shown); the number of power converters is not specifically limited here, but can be determined according to the actual situation, and all are within the protection scope of this application.

[0122] It should be noted that, Figures 8-10 In this context, C11, C12...C1n, and C21, C22, and C2n are all energy storage elements; K1, K2...Kn are all switches; and R1, R2...Rn are all loads.

[0123] Each power converter is controlled by a controller.

[0124] This controller, in conjunction with the power converter, implements the control method for the DC system provided in any of the above embodiments.

[0125] For details on the specific processes and principles of the controller and power converter, please refer to the control method of the DC system provided in the above embodiments. They will not be repeated here, and are all within the protection scope of this application.

[0126] In this embodiment, the power converter is controlled to adjust the waveform generation logic so that the input electrical parameters of the power converter drop to a set value under preset conditions. This allows the input-side energy storage element and the output-side energy storage element of the power converter to jointly bear the energy corresponding to the sudden drop in output electrical parameters, avoiding the problem of excessively high input voltage caused by storing all the energy in the input-side energy storage element of the power converter. In other words, only the software waveform generation logic has been improved without adding any components, thus having significant advantages in terms of cost, size, and weight.

[0127] In practical applications, this power converter includes at least one stage of DC-DC converter.

[0128] Specifically, such as Figure 4 As shown, the DC power source is a photovoltaic array; that is, the DC system is a photovoltaic system.

[0129] Correspondingly, the power converter is a photovoltaic inverter (such as...) Figure 4 (The inverter shown). Where C0 is a capacitor.

[0130] like Figure 5 As shown, DC / DC conversion circuits can also be installed between the photovoltaic inverter and the photovoltaic array.

[0131] Specifically, the DC / DC converter circuit includes: capacitor C1, capacitor C2, inductor L2, diode D1, and switching transistor Q1.

[0132] One end of the first capacitor C1 is connected to one end of the inductor L2; the other end of the inductor L2 is connected to the anode of the diode D1 and one end of the switch Q1 respectively; the cathode of the diode D1 is connected to one end of the capacitor C2 and the positive terminal of the inverter (which includes the switch Q2); the other end of the capacitor C1, the other end of the switch Q1, the other end of the capacitor C2, and the negative terminal of the inverter are connected.

[0133] In practical applications, such as Figure 10 As shown, it also includes at least one cascaded unit.

[0134] Each cascaded unit is located after the power converter; the outputs of each cascaded unit are connected to the corresponding loads via corresponding switches.

[0135] Specifically, the output terminals of each power converter are connected to the input terminals of their respective cascaded units; the two ends of each cascaded unit serve as the output terminals of the DC system and are connected to the corresponding loads.

[0136] The power converter is an isolated converter.

[0137] The cascaded unit is an H-bridge topology.

[0138] Specifically, such as Figure 11 As shown, the cascaded unit includes: a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4.

[0139] The first terminal of the first switch Q1 is connected to the first terminal of the third switch Q3, and the connection point serves as the positive input terminal of the cascade unit; the second terminal of the first switch Q1 is connected to the first terminal of the second switch Q2, and the connection point serves as one output terminal of the cascade unit; the second terminal of the third switch Q3 is connected to the first terminal of the fourth switch Q4, and the connection point serves as the other output terminal of the cascade unit; the second terminal of the second switch Q2 is connected to the second terminal of the fourth switch Q4, and the connection point serves as the negative input terminal of the cascade unit.

[0140] The features described in the various embodiments of this specification can be substituted for or combined with each other. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0141] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0142] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method of a direct current system, characterized by, The output terminals of the direct current power supply in the direct current system are connected with at least one power converter respectively, the input terminal and the output terminal of each power converter are provided with a corresponding energy storage element, and the method comprises the following steps: Detecting whether a preset output electrical parameter sudden drop phenomenon exists in the direct current system; If yes, controlling the power converter to adjust the wave emission logic, so that the input electrical parameter of the power converter is decreased to a set value under a preset condition, and the preset condition is a preset slope.

2. The control method of a direct current system according to claim 1, characterized by, Before the step of controlling the power converter to adjust the wave emission logic, so that the input electrical parameter of the power converter is decreased to a set value under a preset condition, the method further comprises the following steps: Judging whether the power converter needs emergency wave blocking; If the power converter does not need emergency wave blocking, the step of controlling the power converter to adjust the wave emission logic, so that the input electrical parameter of the power converter is decreased to a set value under a preset condition is performed.

3. The control method of a direct current system according to claim 2, characterized by, After the step of judging whether the power converter needs emergency wave blocking, if any power converter needs emergency wave blocking, the method further comprises the following step: Controlling the power converter needing emergency wave blocking to perform emergency wave blocking.

4. The control method of a direct current system according to claim 3, characterized by, When the number of the power converters is multiple, after the step of controlling the power converter needing emergency wave blocking to perform emergency wave blocking, the method further comprises the following step: Controlling at least one power converter not needing emergency wave blocking to adjust the working state, so that the input electrical parameter of the power converter not needing emergency wave blocking is decreased to a set value under a preset condition.

5. The control method of a direct current system according to claim 4, characterized by, When the number of the power converters not needing emergency wave blocking is multiple, the step of controlling at least one power converter not needing emergency wave blocking to adjust the working state comprises the following step: Controlling the power converters not needing emergency wave blocking to coordinate wave emission, so that the input voltage of the power converters not needing emergency wave blocking tends to be stable.

6. The control method of a DC system according to claim 4, characterized by, When the power converter is an isolated converter, and each power converter is cascaded through a corresponding cascade unit, the step of controlling at least one power converter not needing emergency wave blocking to adjust the working state comprises the following step: Controlling the power converters to coordinate operation, so that the energy storage elements of the power converters are charged.

7. The control method of a direct current system according to claim 6, characterized by, The method further comprises the following steps: If any power converter or the cascade unit has a fault, controlling the power converter or the cascade unit having the fault to be shut down, and each cascade unit to be shut down; Controlling the power converter not having the fault to adjust the working state, so that the input electrical parameter of the power converter not having the fault is decreased to a set value under a preset condition.

8. The control method of a DC system according to claim 1, characterized by, The output electrical parameter is output current and / or output power; and the input electrical parameter is input current and / or input power.

9. The control method of a direct current system according to claim 1, characterized by, The step of controlling the power converter to adjust the wave emission logic, so that the input electrical parameter of the power converter is decreased to a set value under a preset condition comprises the following step: The input electrical parameter of the power converter is decreased to zero under a preset slope.

10. The control method of a direct current system according to any one of claims 1 to 9, characterized by, The method further comprises the following steps: If each power converter in the direct current system needs to be blocked or shut down, controlling each power converter to be turned off in sequence; and / or, controlling each power converter to adjust the wave emission logic, so that the input electrical parameter of each power converter is decreased to a set value under a preset condition.

11. A direct current system, characterized by The method comprises the following steps: A direct current power supply, a controller and at least one power converter. The output terminals of the direct current power supply are connected to the input terminals of the power converters respectively; The input terminals and the output terminals of the power converters are provided with corresponding energy storage elements respectively; The output terminals of the power converters are connected to corresponding loads through corresponding switches respectively; The power converters are controlled by the controller; The controller and the power converters realize the control method of the direct current system according to any one of claims 1-10.

12. The direct current system of claim 11, wherein, The capacity of the energy storage elements on the input side of the power converters is less than the capacity of the energy storage elements on the output side of the power converters.

13. The direct current system of claim 12, wherein, The direct current power supply is a photovoltaic array.

14. The direct current system of claim 13, wherein, The power converters comprise at least one stage of direct current converters.

15. A direct current system according to any of claims 11-14, characterized in that Further comprising: at least one cascade unit; Each of the cascade units is arranged at the rear stage of each of the power converters; The output terminals of the cascade units are connected to corresponding loads through corresponding switches after cascading.

16. The direct current system of claim 15, wherein, The cascade units are H-bridge topologies.

17. The direct current system of claim 15, wherein, The power converters are isolated converters.

Images