Power conversion device, control method thereof and power supply system

Abstract

The invention discloses a power conversion device, a control method thereof and a power supply system. The power conversion device comprises a power conversion module, a pre-charging module and a switch module. The pre-charging module comprises a pre-charging switch unit; the first side of the power conversion module is connected with a DC bus. The pre-charging module and the switch module are connected in parallel between the second side of the power conversion module and a power grid. The control method of the power conversion device comprises the following steps: controlling the pre-charging switch unit to be closed; and after the pre-charging condition is met, when the power grid voltage is zero, the switch module is controlled to reach a closed state. According to the technical scheme, it is guaranteed that when the power grid is connected to the power conversion device, the power grid current is small, and the effect of protecting the power conversion device is achieved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a power conversion device and its control method, and a power supply system. Background Technology

[0002] With the rapid development of new energy technologies, batteries are being used more and more widely. Power conversion devices can convert the electrical energy discharged from batteries into another form of electrical energy to supply loads, and can also use an external power source to charge batteries. This external power source can be the power grid.

[0003] When an external power source charges a battery through a power conversion device, capacitors or inductors are typically used to filter and smooth the input current to improve the power factor and efficiency of the power supply. However, these components have low resistance during the initial startup phase, which can lead to large transient current spikes, especially in high-capacity or high-power applications. To avoid this, bus pre-charge logic must be introduced to gradually increase the voltage of the capacitors or inductors during the pre-charge process, thereby reducing the current surge during initial startup.

[0004] During the pre-charging process, the pre-charging relay needs to be closed to perform pre-charging. After the pre-charging bus is completed, the pre-charging relay needs to be opened and the inverter relay closed.

[0005] After the pre-charge bus is completed, improper operation logic of the pre-charge relay and inverter relay can still cause undesirable grid current overcurrent problems, resulting in instantaneous high current surges. These peak current surges can not only affect the normal operation of other components in the power system, but may also damage the contacts of the relays inside the power conversion device, shortening their service life and thus reducing the reliability and durability of the power conversion device. Summary of the Invention

[0006] This application provides a power conversion device and its control method, as well as a power supply system, to solve the problem that a large current is easily generated after the power conversion device has completed pre-charging.

[0007] According to one aspect of this application, a control method for a power conversion device is provided. The power conversion device includes a power conversion module, a pre-charge module, and a switching module. The pre-charge module includes a pre-charge switching unit. A first side of the power conversion module is connected to a DC bus, and the pre-charge module and the switching module are connected in parallel between a second side of the power conversion module and the power grid.

[0008] The control method for the power conversion device includes:

[0009] Control the precharge switch unit to close;

[0010] After the pre-charging conditions are met, when the grid voltage is zero, the switch module is controlled to reach the closed state.

[0011] Optionally, after controlling the switch module to reach the closed state, the method further includes:

[0012] At any time after the switch module reaches the closed state, a disconnection control signal is sent to the precharge switch unit.

[0013] Optionally, after the pre-charging condition is met, when the mains voltage is zero, controlling the switch module to reach the closed state includes:

[0014] After the pre-charge conditions are met, when the mains voltage is zero, the pre-charge switch unit is controlled to reach the open state;

[0015] After the precharge switch unit reaches the open state, when the mains voltage is zero, the switch module is controlled to reach the closed state.

[0016] Optionally, after the pre-charging condition is met, when the mains voltage is zero, controlling the switch module to reach the closed state includes:

[0017] After the pre-charging condition is met, a closing control signal is sent to the switch module at a first preset time before the grid voltage becomes zero; wherein, the first preset time is spaced apart from the time when the grid voltage becomes zero by a first preset duration.

[0018] Optionally, the step of sending a closing control signal to the switch module at a first preset moment before the grid voltage reaches zero after the pre-charging condition is met includes:

[0019] After the pre-charging conditions are met, the actual phase of the grid voltage is sampled and obtained. When the actual phase reaches the first preset phase, a closing control signal is sent to the switching module.

[0020] Wherein, the first preset phase is the phase of the grid voltage corresponding to the first preset time.

[0021] Optionally, the step of controlling the pre-charge switch unit to reach the open state when the mains voltage is zero after the pre-charge condition is met includes:

[0022] After the pre-charging condition is met, at a second preset time before the grid voltage becomes zero, a disconnection control signal is sent to the pre-charging switch unit; wherein, the second preset time and the time when the grid voltage becomes zero are separated by a second preset time.

[0023] Optionally, the step of sending a disconnection control signal to the precharge switch unit at a second preset time before the grid voltage reaches zero after the precharge condition is met includes:

[0024] After the pre-charging conditions are met, the actual phase of the grid voltage is sampled and obtained. When the actual phase reaches the second preset phase, a disconnection control signal is sent to the pre-charging switch unit.

[0025] Wherein, the second preset phase is the phase of the grid voltage corresponding to the second preset time.

[0026] Optionally, the pre-charge condition being met includes:

[0027] When the bus voltage of the power conversion module reaches the preset voltage, the power conversion device reaches the pre-charge condition after the pre-charge switch unit is kept on for a third preset time.

[0028] According to another aspect of this application, a power conversion device is provided, the power conversion device comprising:

[0029] A power conversion module, wherein the first side of the power conversion module is connected to the DC bus;

[0030] The precharge module includes a precharge switch unit;

[0031] A switching module, wherein the switching module and the precharge module are connected in parallel between the second side of the power conversion module and the power grid;

[0032] A control module is connected to the precharge switch unit and the switch module respectively. The control module is configured to control the precharge switch unit to close and, after the precharge condition is met, control the switch module to close when the grid voltage is zero.

[0033] According to another aspect of this application, a power supply system is provided, which includes the power conversion device described in any embodiment of this application;

[0034] The first side of the power conversion device is connected to the DC bus;

[0035] The second side of the power conversion device is connected to the power grid and is used to charge the DC bus with AC input power from the power grid.

[0036] The technical solution of this application embodiment, after reaching the pre-charge condition, controls the switch module to reach the closed state when the grid voltage is zero, so that the voltage of the DC bus increases, and the switch module reaches the closed state exactly at the moment when the grid voltage is zero. Therefore, when the switch module is closed, the grid voltage and the inverter capacitor voltage will not differ significantly, which can avoid generating a large grid current, achieve the effect of protecting the power conversion device, and improve the reliability and durability of the power conversion device.

[0037] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of this application, nor is it intended to limit the scope of this application. Other features of this application will become readily apparent from the following description. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of signal waveforms in a power conversion device in related technologies;

[0040] Figure 2 yes Figure 1 A magnified view of a portion of the image;

[0041] Figure 3 This is a flowchart of a control method for a power conversion device provided in an embodiment of this application;

[0042] Figure 4 This is a flowchart of another control method for a power conversion device provided in an embodiment of this application;

[0043] Figure 5 This is a flowchart of another control method for a power conversion device provided in the embodiments of this application;

[0044] Figure 6 This is a schematic diagram comparing signal waveforms in the power conversion device provided in the embodiments of this application;

[0045] Figure 7 yes Figure 6 A magnified view of a portion of the image;

[0046] Figure 8 This is a schematic diagram of the structure of a power conversion device provided in an embodiment of this application. Detailed Implementation

[0047] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0048] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover 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. Unless otherwise specified, 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 that element. It should be further understood that, as used herein, the singular forms "a," "an," and "the" are intended to also include the plural forms, unless the context indicates otherwise. Furthermore, the terms "or," "and / or," "including at least one of the following," etc., as used herein, can be interpreted as inclusive, or mean any one or any combination thereof. Exceptions to this definition only arise when combinations of elements, functions, steps, or operations are inherently mutually exclusive in some manner.

[0049] It should be understood that although the terms first, second, third, etc., may be used herein to describe various parameters or modules, these parameters or modules should not be limited to these terms. These terms are only used to distinguish parameters or modules of the same type from each other. For example, without departing from the scope of this document, a first parameter may also be referred to as a second parameter, and similarly, a second parameter may also be referred to as a first parameter. Depending on the context, the words “if” or “when” as used herein may be interpreted as “when…” or “when…” or “in response to determination” or “in response to detection.” Similarly, depending on the context, the phrases “if determination” or “if detection (of the stated condition or event)” may be interpreted as “when determination” or “in response to determination” or “when detection (of the stated condition or event)” or “in response to detection (of the stated condition or event).” Furthermore, components, features, and elements with the same names in different embodiments of this application may have the same meaning or may have different meanings, the specific meaning of which needs to be determined by its interpretation in that specific embodiment or further in conjunction with the context of that specific embodiment.

[0050] It should be understood that although the steps in the flowcharts of this application's embodiments are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some of the steps in the figures may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0051] It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application.

[0052] The DC bus is connected to the inverter circuit in the power conversion device. The inverter circuit is connected to the power grid through the pre-charge relay and inverter relay in the power conversion device, and is also connected to the inverter capacitor. In related technologies, when the power conversion device starts working, the pre-charge relay is closed first. The power grid charges the DC bus through the pre-charge relay to avoid a large voltage difference between the DC bus and the grid during normal startup, which would generate a current spike. After the pre-charge bus is fully charged, the pre-charge relay needs to be opened and the inverter relay closed. If the activation or deactivation logic of the pre-charge relay and inverter relay is not designed properly after the pre-charge bus is fully charged, an overcurrent problem may occur in the grid. Figure 1 This is a schematic diagram of signal waveforms in a power conversion device in related technologies. Figure 2 yes Figure 1 A magnified view of a portion, such as Figure 1 and Figure 2 As shown, the horizontal axis represents time, and the vertical axis represents waveform amplitude. Curve ① represents the grid voltage waveform, curve ② represents the inverter capacitor voltage waveform, and curve ③ represents the grid current waveform. Figure 1 and Figure 2 As shown, when the inverter relay is activated at time t1, the grid current is large at the instant the relay activates, with a peak current reaching 98A, significantly exceeding the safe range for grid current. The inventors discovered that this problem arises because a significant voltage difference exists between the grid voltage and the inverter capacitor voltage at the moment the inverter relay activates, resulting in a large grid current. In other words, the control of the inverter relay in related technologies is unreasonable, leading to a high current problem after the power conversion device has completed its pre-charge.

[0053] To address the aforementioned technical problems, this application provides a control method for a power conversion device. This control method can be executed by a control module, which may include at least one of a digital signal processor (DSP), a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), a central processing unit (CPU), or a microcontroller unit (MCU). The power conversion device includes a power conversion module, a pre-charge module, and a switching module. The pre-charge module includes a pre-charge switching unit. A first side of the power conversion module is connected to a DC bus, and the pre-charge module and the switching module are connected in parallel between the second side of the power conversion module and the power grid.

[0054] The power conversion module converts input electrical energy into another form of output to meet specific power demands. This module can be DC to AC, DC to DC, or AC to DC. It can also be a bidirectional module, where one side is the input and the other the output; or vice versa. The first side of the power conversion module is connected to the DC bus, and the second side is connected to the power grid. It can convert high-voltage AC power from the grid into low-voltage DC power, which is then output to the DC bus and subsequently to the battery to charge it.

[0055] The power conversion module may include an inverter circuit, which can be a half-bridge inverter circuit or a full-bridge inverter circuit, etc., and this embodiment is not limited to this. The pre-charge switching unit may include a pre-charge relay and a pre-charge current limiting element (such as a pre-charge resistor). The switching module may include an inverter relay. The DC bus may be connected to the battery, for example, through a DC-DC converter circuit. When the pre-charge switching unit is closed, the power grid can charge the DC bus through the pre-charge module and the power conversion module, that is, charge the bus capacitor connected to the DC bus. This can avoid a large current peak caused by a large voltage difference between the bus capacitor and the grid voltage when the power conversion device is started. After the pre-charge condition is met, the switching module is closed, so that the grid charges the battery through the switching module and the power conversion module. The power conversion module is also connected to the inverter capacitor, and the pre-charge module and the switching module are connected between the inverter capacitor and the power grid.

[0056] Figure 3 This is a flowchart of a control method for a power conversion device provided in an embodiment of this application, see reference. Figure 3 The control methods for the power conversion device include:

[0057] S101, Control the precharge switch unit to close.

[0058] Specifically, the pre-charge switch unit is first closed, so that the power grid is connected to the power conversion module through the pre-charge module. The power conversion module pre-charges the DC bus, which increases the voltage of the DC bus. This avoids the problem that the DC bus voltage is low when the power conversion device is initially started, which would result in a large difference between the DC bus voltage and the grid voltage and easily generate peak current.

[0059] S102. After the pre-charge condition is met, when the grid voltage is zero, the control switch module reaches the closed state.

[0060] The conditions for pre-charging can be either reaching a preset charging time or the DC bus voltage reaching a preset voltage; there are no specific limitations on this.

[0061] Specifically, after the pre-charge conditions are met, the DC bus voltage approaches the grid voltage, at which point the switch module can be closed to officially start the power conversion device. By controlling the switch module to reach the closed state when the grid voltage is zero, that is, the switch module reaches the closed state precisely at the moment when the grid voltage is zero, the grid voltage and the inverter capacitor voltage will not differ significantly when the switch module is closed, thus avoiding the generation of large grid currents.

[0062] Specifically, when the grid voltage is zero, meaning its amplitude is zero; when the grid voltage is sinusoidal, its phase is zero or π; and when the grid voltage is cosine, its phase is... or This ensures that the voltage amplitude of the inverter capacitor is close to or the same as the voltage amplitude of the grid, and that the voltage phase of the inverter capacitor is close to or the same as the phase of the grid voltage. In other words, when the grid is connected, the grid voltage and the inverter capacitor voltage will not differ significantly.

[0063] Furthermore, when the grid voltage is zero, the control switch module reaches the closed state. If the closing process of the switch module is short, it can begin closing at zero grid voltage by sending a closing control signal. If the closing process is longer, the closing control signal can be sent before the grid voltage reaches zero. This ensures that the switch module reaches the closed state precisely at the moment the grid voltage is zero, guaranteeing connection at zero grid voltage. It also ensures that the grid voltage is close to or the same as the inverter capacitor voltage, further minimizing the grid current when the power conversion device is connected, thus protecting the power conversion device and improving its reliability and durability.

[0064] The technical solution of this embodiment, after reaching the pre-charge condition, controls the switch module to reach the closed state when the grid voltage is zero, so that the voltage of the DC bus increases, and the switch module reaches the closed state exactly at the moment when the grid voltage is zero. Therefore, when the switch module is closed, the grid voltage and the inverter capacitor voltage will not differ significantly, which can avoid generating a large grid current, achieve the effect of protecting the power conversion device, and improve the reliability and durability of the power conversion device.

[0065] Based on the above technical solution, the control method of the power conversion device will be further explained below in conjunction with the disconnection control of the precharge switch unit, but this is not intended to limit this application.

[0066] In one implementation, Figure 4 This is a flowchart of another control method for a power conversion device provided in an embodiment of this application. Optionally, refer to... Figure 4 The control methods for the power conversion device include:

[0067] S201, Control the precharge switch unit to close.

[0068] S202. After the pre-charge condition is met, when the grid voltage is zero, the control switch module reaches the closed state.

[0069] S203. At any time after the switch module reaches the closed state, send a disconnection control signal to the precharge switch unit.

[0070] Specifically, since the pre-charge module is connected in parallel with the switching module, the pre-charge module is short-circuited after the switching module is closed. Therefore, the pre-charge module will no longer affect the voltage of the inverter capacitor, and can be disconnected at any time after the switching module reaches the closed state. This ensures connection when the grid voltage is zero, guarantees that the grid voltage is close to or the same as the inverter capacitor voltage, reduces the requirements on the control unit, and lowers control costs. Furthermore, disconnecting the pre-charge switching unit saves the additional energy consumed when the pre-charge switching unit is closed.

[0071] Furthermore, since the voltage of the inverter capacitor changes with the grid voltage during the pre-charging phase, meaning the voltage of the inverter capacitor is the same as or basically consistent with the grid voltage, after the pre-charging conditions are met, closing the switch module first and then opening the pre-charging switch unit can further ensure that the voltage of the inverter capacitor is the same as or basically consistent with the grid voltage when the switch module is closed. That is, the voltage amplitude of the inverter capacitor is the same as or basically consistent with the amplitude of the grid voltage, and the voltage phase of the inverter capacitor is the same as or basically consistent with the phase of the grid voltage. This ensures that no large grid current is generated when the switch module is closed, thus avoiding the occurrence of peak current.

[0072] In another implementation, Figure 5This is a flowchart of another control method for a power conversion device provided in the embodiments of this application. Optionally, refer to... Figure 5 The control methods for the power conversion device include:

[0073] S301, Control the precharge switch unit to close.

[0074] S302. After the pre-charge conditions are met, when the grid voltage is zero, control the pre-charge switch unit to reach the open state.

[0075] Specifically, after the pre-charge conditions are met, the DC bus voltage approaches the grid voltage, at which point the pre-charge switch unit can be disconnected. By setting the pre-charge switch unit to be in the off state when the grid voltage is zero, the inverter capacitor voltage remains zero, meaning the inverter capacitor voltage amplitude is zero. For example, if the inverter capacitor voltage is a sine wave, its phase is zero or π; if it is a cosine wave, its phase is π. or

[0076] Furthermore, when the mains voltage is zero, the pre-charge switch unit is controlled to reach the open state. If the opening process of the pre-charge switch unit is short, it can begin to open precisely when the mains voltage is zero, i.e., a disconnection control signal is sent to the pre-charge switch unit. If the opening process is longer, the disconnection control signal can be sent to the pre-charge switch unit before the mains voltage reaches zero. This ensures that the pre-charge switch unit reaches the open state exactly when the mains voltage is zero.

[0077] S303. After the precharge switch unit reaches the open state, when the mains voltage is zero, the control switch module reaches the closed state.

[0078] Specifically, after the precharge switch unit reaches the open state, the switch module can be controlled to close. After the precharge switch unit reaches the open state, when the grid voltage is zero, the switch module is controlled to close. That is, the time when the grid voltage crosses zero when the precharge switch unit is in the open state and the time when the grid voltage crosses zero when the switch module is in the closed state can be the same time or not.

[0079] By controlling the switch module to be closed when the grid voltage is zero, the grid voltage and inverter capacitor voltage are both zero upon connection. This ensures that the grid voltage and inverter capacitor voltage are the same upon connection; that is, the phase of the grid voltage and the inverter capacitor voltage are the same or nearly the same, and their amplitudes are close to or the same. This guarantees that the grid voltage and inverter capacitor voltage are the same or nearly the same upon connection, avoiding large grid currents and protecting the power conversion device, thus improving its reliability and durability.

[0080] Based on the above technical solutions, optionally, in step S102, after the pre-charging conditions are met, when the grid voltage is zero, the control switch module reaches a closed state, including:

[0081] After the pre-charging conditions are met, a closing control signal is sent to the switch module at a first preset time before the grid voltage becomes zero; wherein, the first preset time and the time when the grid voltage becomes zero are separated by a first preset time.

[0082] The first preset duration is the duration required during the closing process of the switch module, which is the duration required from the time the switch module receives the closing control signal to the time the switch module reaches the closed state.

[0083] In other words, after the pre-charging conditions are met, a closing control signal is sent to the switching module at a time before the grid voltage reaches zero, which is the first preset time.

[0084] Specifically, by sending a closing control signal to the switching module at a first preset moment before the grid voltage reaches zero, that is, by adding a first preset time before the grid voltage crosses zero, the time required for the switching module to close is taken into account, ensuring that the switching module reaches the closed state when the grid voltage is zero. This ensures that the grid voltage is zero when the grid is connected, and that the grid voltage is close to or the same as the inverter capacitor voltage, thereby avoiding excessive grid current.

[0085] Optionally, after the pre-charge condition is met, at a first preset moment before the grid voltage reaches zero, a closing control signal is sent to the switching module, including:

[0086] After the pre-charging conditions are met, the actual phase of the grid voltage is sampled and obtained. When the actual phase reaches the first preset phase, a closing control signal is sent to the switching module.

[0087] The first preset phase is the phase of the grid voltage at the first preset time. The first preset phase can be calculated in advance based on the first preset duration. That is, at the first preset time before the grid voltage is zero, the grid voltage is at the first preset phase. Then, after the pre-charging condition is met, when the actual phase reaches the first preset phase, a closing control signal is sent to the switch module, so that the switch module reaches the closed state when the grid voltage is zero.

[0088] Specifically, when the power conversion device is working, a phase-locked loop can be used to sample and obtain the actual phase of the grid voltage in real time or periodically. After the pre-charge condition is met, if the actual phase of the grid voltage reaches the first preset phase, that is, the first preset moment before the grid voltage crosses zero, a closing control signal is sent to the switching module to ensure that the switching module reaches the closed state when the grid voltage is zero.

[0089] Optionally, after the pre-charge condition is met, step S302, when the mains voltage is zero, controls the pre-charge switch unit to reach the open state, including:

[0090] After the pre-charging conditions are met, a disconnection control signal is sent to the pre-charging switch unit at a second preset time before the grid voltage becomes zero; wherein, the second preset time is separated from the time when the grid voltage becomes zero by a second preset duration.

[0091] The second preset duration is the duration required for the precharge switch unit to disconnect, which is the duration required from the time the precharge switch unit receives the disconnection control signal to the time the precharge switch unit becomes disconnected.

[0092] Specifically, by sending a disconnection control signal to the pre-charge switch unit at a second preset time before the grid voltage reaches zero, that is, by adding a second preset time before the grid voltage crosses zero, the time required for the disconnection process of the pre-charge switch unit is taken into account. This ensures that the pre-charge switch unit reaches the disconnected state when the grid voltage is zero. In this way, when the pre-charge switch unit is disconnected, the voltage of the inverter capacitor is zero, thus maintaining the inverter capacitor voltage at zero. Therefore, when the switch module reaches the closed state when the grid voltage is zero, the connected grid voltage and the inverter capacitor voltage have the same amplitude and are close to or identical in phase. This avoids generating large grid currents, achieving the effect of protecting the power conversion device and improving its reliability and durability.

[0093] Optionally, after the pre-charge condition is met, at a second preset time before the grid voltage reaches zero, a disconnection control signal is sent to the pre-charge switching unit, including:

[0094] After the pre-charge conditions are met, the actual phase of the grid voltage is sampled and obtained. When the actual phase reaches the second preset phase, a disconnection control signal is sent to the pre-charge switch unit.

[0095] The second preset phase is the phase of the grid voltage corresponding to the second preset time. The second preset phase can be calculated in advance based on the second preset duration.

[0096] Specifically, when the power conversion device is working, a phase-locked loop can be used to sample and obtain the actual phase of the grid voltage in real time or periodically. After the pre-charge condition is met, if the actual phase of the grid voltage reaches the second preset phase, that is, the second preset time before the grid voltage crosses zero, a disconnection control signal is sent to the pre-charge switch unit, which can ensure that the pre-charge switch unit is in the disconnected state when the grid voltage crosses zero.

[0097] Optionally, the pre-charge conditions are met, including:

[0098] When the bus voltage of the power conversion module reaches the preset voltage, the power conversion device reaches the pre-charge condition after the pre-charge switch unit is kept on for a third preset time.

[0099] Specifically, when the DC bus voltage reaches the preset voltage, that is, when the bus capacitor connected to the power conversion module reaches the preset voltage, the voltage of the bus capacitor is made larger, close to the amplitude of the grid voltage, which can avoid current spikes when the power conversion device starts up. By setting a third preset duration, misjudgments can be avoided, ensuring that the bus voltage reaches the preset voltage.

[0100] For example, Figure 6 This is a schematic diagram comparing signal waveforms in the power conversion device provided in the embodiments of this application. Figure 7 yes Figure 6 A magnified view of a portion, such as Figure 6 and Figure 7 As shown, the horizontal axis represents time, and the vertical axis represents waveform amplitude. Curve ④ is the waveform of grid voltage in related technologies, curve ⑤ is the waveform of inverter capacitor voltage in related technologies, curve ⑥ is the waveform of grid current in related technologies, curve ⑦ is the waveform of grid voltage in the embodiment of this application, curve ⑧ is the waveform of inverter capacitor voltage in the embodiment of this application, and curve ⑨ is the waveform of grid current in the embodiment of this application. Figure 6 and Figure 7 As shown, in related technologies, the pre-charge relay is disconnected at time t01 and the inverter relay is closed at time t02, resulting in a large grid current after the inverter relay is closed. In this embodiment, the pre-charge switch unit is disconnected at time t03 and the switch module is closed at time t04. That is, the pre-charge switch unit is disconnected when the grid voltage is zero, and the switch module is closed when the grid voltage is zero after the pre-charge switch unit is in the open state. When the switch module is closed at time t04, the grid current is very small, close to zero. Therefore, the technical solution of this embodiment, by disconnecting the pre-charge switch unit when the grid voltage is zero after the pre-charge condition is met, and closing the switch module when the grid voltage is zero after the pre-charge switch unit is in the open state, can effectively reduce the grid current and achieve the effect of protecting the power conversion device.

[0101] This application also provides a power conversion device. Figure 8 This is a schematic diagram of a power conversion device provided in an embodiment of this application, with reference to... Figure 8 The power conversion device includes:

[0102] Power conversion module 110, the first side of power conversion module 110 is connected to DC bus L;

[0103] Precharge module 120, which includes precharge switch unit 121;

[0104] Switching module 130 and precharge module 120 are connected in parallel between the second side of power conversion module 110 and the power grid Vac;

[0105] The control module 140 is connected to the precharge switch unit 121 and the switch module 130 respectively. The control module 140 is configured to control the precharge switch unit 121 to close, and after the precharge condition is met, when the grid voltage is zero, control the switch module 130 to reach the closed state.

[0106] The DC bus L includes a positive bus L1 and a negative bus L2, and the voltage of the DC bus is the voltage between the positive bus L1 and the negative bus L2. The power conversion module 110 can convert the input electrical energy into another form of electrical energy output to meet specific power demands. The power conversion module 110 can be a DC-to-AC converter, a DC-to-DC converter, or an AC-to-DC converter. The power conversion module can also be a bidirectional power conversion module, i.e., the first side of the power conversion module 110 is the input side and the second side is the output side; or the second side of the power conversion module 110 is the input side and the first side is the output side. The first side of the power conversion module is connected to the DC bus, and the second side of the power conversion module 110 is connected to the power grid. It can convert high-voltage AC power from the power grid into low-voltage DC power output to the battery to charge it. The power conversion module 110 may include an inverter circuit, and the DC bus L can be connected to the battery, for example, through a DC-DC converter circuit. For example, control module 140 includes at least one of digital signal processing (DSP), complex programmable logic device (CPLD), field programmable gate array (FPGA), central processing unit (CPU), or microcontroller unit (MCU).

[0107] Specifically, the control module 140 first controls the pre-charge switch unit 121 to close, allowing the power grid to connect to the power conversion module 110 via the pre-charge module 120. The power conversion module 110 then pre-charges the DC bus L, increasing its voltage. This prevents the DC bus L from having a low voltage during initial startup, which could lead to a large voltage difference with the grid and generate spike current. Once the pre-charge conditions are met, the DC bus L voltage approaches the grid voltage, at which point the switch module 130 can be closed to officially start the power conversion device. By controlling the switch module 130 to close when the grid voltage is zero—meaning the switch module 130 closes precisely at the moment the grid voltage is zero—the grid voltage and the inverter capacitor voltage are not significantly different when the switch module 130 is closed, thus avoiding large grid currents. Furthermore, when the grid voltage is zero, the control switch module 130 reaches the closed state. If the closing process of the switch module 130 is short, it can begin closing at zero grid voltage, i.e., a closing control signal can be sent to the switch module 130. If the closing process is longer, the closing control signal can be sent to the switch module 130 before the grid voltage reaches zero. This ensures that the switch module 130 reaches the closed state precisely at the moment the grid voltage is zero, guaranteeing connection at zero grid voltage. It also ensures that the grid voltage is close to or the same as the inverter capacitor voltage, further preventing excessive grid current and protecting the power conversion device, thus improving its reliability and durability.

[0108] The power conversion module 110 may include at least two transistors. The control module 140 is connected to the control electrode of the transistors to control the conduction state of the transistors, thereby controlling the electrical parameters (such as power or voltage) of the output power of the power conversion module 110.

[0109] Optionally, such as Figure 8 As shown, the pre-charge module 120 also includes a pre-charge resistor R. The first end of the pre-charge resistor R is connected to the power grid Vac, and the second end of the pre-charge resistor R is connected to the first end of the pre-charge switch unit 121. The second end of the pre-charge switch unit 121 is connected to the second side of the power conversion module 110. Thus, when the pre-charge switch unit 121 is closed, the power grid Vac can charge the DC bus L through the pre-charge resistor R, the pre-charge switch unit 121, and the power conversion module 110.

[0110] Optionally, such as Figure 8As shown, the precharge switch unit 121 includes a precharge relay. The control module 140 can control the state of the precharge relay. For example, during the precharge phase, the control module 140 controls the precharge relay to close, allowing the grid Vac to charge the DC bus L through the precharge resistor R, the precharge relay, and the power conversion module 110. At any time after the switch module 130 reaches the closed state, the control module 140 sends a disconnect control signal to the precharge relay. Alternatively, after the precharge condition is met, when the grid voltage is zero, the control module 140 controls the precharge relay to reach the open state.

[0111] Optionally, such as Figure 8 As shown, the switching module 130 includes an inverter relay. The control module 140 can control the state of the inverter relay. After the pre-charge condition is met, when the grid voltage is zero, the control module 140 controls the inverter relay to reach the closed state, ensuring that the grid voltage is zero and that the grid voltage is close to or the same as the voltage of the inverter capacitor, which can further ensure that the grid current is not too large.

[0112] Optionally, such as Figure 8 As shown, the power conversion device also includes an inverter capacitor C1, which is connected to the second side of the power conversion module 110. The grid Vac can charge the inverter capacitor C1 through the pre-charge module 120 or the switching module 130.

[0113] Optionally, such as Figure 8 As shown, the power conversion device also includes a bus capacitor C2, and a bus capacitor C1 is connected between the positive bus L1 and the negative bus L2. When the pre-charge switch unit 121 or the switch module 130 is closed, the power conversion module 110 can convert the grid voltage to charge the bus capacitor C1.

[0114] Optionally, the power conversion device may further include a phase-locked loop (PLL) circuit connected to the control module 140. The PLL circuit is also connected to the pre-charge module 120 and the switching module 130. The PLL circuit samples the actual phase of the grid voltage from the pre-charge module 120 or the switching module 130 and sends the actual phase to the control module 140. This allows the control module 140 to determine whether to close the switching module 130 and whether to open the pre-charge switching unit 121 based on the actual phase of the grid voltage.

[0115] This application also provides a power supply system, which includes the power conversion device provided in any embodiment of this application;

[0116] The first side of the power conversion device is connected to the DC bus;

[0117] The second side of the power conversion device is connected to the power grid to charge the DC bus with AC input power from the power grid.

[0118] The power system of this embodiment includes the power conversion device provided in any embodiment of this application. Therefore, the power system of this embodiment has the same beneficial effects as the power conversion device provided in any embodiment of this application, and will not be described again here.

[0119] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0120] In this application, the same or similar terms, concepts, technical solutions and / or application scenario descriptions are generally described in detail only when they appear for the first time. When they appear again, they are generally not repeated for the sake of brevity. When understanding the technical solutions and other contents of this application, the same or similar terms, concepts, technical solutions and / or application scenario descriptions that are not described in detail later can be referred to their previous relevant detailed descriptions.

[0121] In this application, the descriptions of the various embodiments have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0122] The technical features of the present application can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present application.

[0123] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes several instructions to cause a terminal device (which may be an electrical device or a network device, etc.) to execute the methods of each embodiment of this application.

[0124] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A control method for a power conversion device, characterized in that, The power conversion device includes a power conversion module, a pre-charge module, and a switching module; the pre-charge module includes a pre-charge switching unit; the first side of the power conversion module is connected to the DC bus, and the pre-charge module and the switching module are connected in parallel between the second side of the power conversion module and the power grid. The method includes: Control the precharge switch unit to close; After the pre-charging conditions are met, when the grid voltage is zero, the switch module is controlled to reach the closed state.

2. The method according to claim 1, characterized in that, After the switch module is controlled to reach the closed state, the method further includes: At any time after the switch module reaches the closed state, a disconnection control signal is sent to the precharge switch unit.

3. The method according to claim 1, characterized in that, The step of controlling the switch module to reach a closed state after the pre-charging condition is met and the mains voltage is zero includes: After the pre-charge conditions are met, when the mains voltage is zero, the pre-charge switch unit is controlled to reach the open state; After the precharge switch unit reaches the open state, when the mains voltage is zero, the switch module is controlled to reach the closed state.

4. The method according to claim 1, characterized in that, The step of controlling the switch module to reach a closed state after the pre-charging condition is met and the mains voltage is zero includes: After the pre-charging condition is met, a closing control signal is sent to the switch module at a first preset time before the grid voltage becomes zero; wherein, the first preset time is spaced apart from the time when the grid voltage becomes zero by a first preset duration.

5. The method according to claim 4, characterized in that, The step of sending a closing control signal to the switch module at a first preset moment before the grid voltage reaches zero after the pre-charging condition is met includes: After the pre-charging conditions are met, the actual phase of the grid voltage is sampled and obtained. When the actual phase reaches the first preset phase, a closing control signal is sent to the switching module. Wherein, the first preset phase is the phase of the grid voltage corresponding to the first preset time.

6. The method according to claim 3, characterized in that, The step of controlling the pre-charge switch unit to reach the open state when the mains voltage is zero after the pre-charge condition is met includes: After the pre-charging condition is met, at a second preset time before the grid voltage becomes zero, a disconnection control signal is sent to the pre-charging switch unit; wherein, the second preset time and the time when the grid voltage becomes zero are separated by a second preset time.

7. The method according to claim 6, characterized in that, The step of sending a disconnection control signal to the precharge switch unit at a second preset time before the grid voltage reaches zero after the precharge condition is met includes: After the pre-charging conditions are met, the actual phase of the grid voltage is sampled and obtained. When the actual phase reaches the second preset phase, a disconnection control signal is sent to the pre-charging switch unit. Wherein, the second preset phase is the phase of the grid voltage corresponding to the second preset time.

8. The method according to any one of claims 1-7, characterized in that, The conditions for achieving pre-charge include: When the bus voltage of the power conversion module reaches the preset voltage, the power conversion device reaches the pre-charge condition after the pre-charge switch unit is kept on for a third preset time.

9. A power conversion device, characterized in that, The power conversion device includes: A power conversion module, wherein the first side of the power conversion module is connected to the DC bus; The precharge module includes a precharge switch unit; A switching module, wherein the switching module and the precharge module are connected in parallel between the second side of the power conversion module and the power grid; A control module is connected to the precharge switch unit and the switch module respectively. The control module is configured to control the precharge switch unit to close and, after the precharge condition is met, control the switch module to close when the grid voltage is zero.

10. A power supply system, characterized in that, Includes the power conversion device as described in claim 9; The first side of the power conversion device is connected to the DC bus; The second side of the power conversion device is connected to the power grid and is used to charge the DC bus with AC input power from the power grid.

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