Power conversion apparatus and control method therefor

Abstract

The invention provides power conversion equipment and a control method thereof, and a controller of the power conversion equipment controls a voltage phase angle output by an inverter circuit to be ahead of an alternating current end voltage phase angle when a voltage amplitude of an alternating current end is smaller than a first threshold value, so that active power output by the power conversion equipment is greater than 0; when the alternating-current end voltage amplitude is increased from being smaller than a first threshold value, the change rate of the alternating-current end voltage amplitude is larger than a second threshold value, and the voltage phase angle output by the inverter circuit is switched from being ahead of the alternating-current end voltage phase angle to being lagged behind the alternating-current end voltage phase angle. And controlling the phase angle of the voltage output by the inverter circuit to be switched from being lagged behind the phase angle of the voltage of the alternating current end to being ahead of the phase angle of the voltage of the alternating current end within the first duration, so that the active power output by the power conversion equipment is kept greater than 0. By adopting the application, the active power can be prevented from reversely flowing into the power conversion equipment when the power grid voltage rapidly recovers from deep drop, and the safe and stable operation of the power conversion equipment is ensured.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, specifically to a power conversion device and its control method. Background Technology

[0002] When a grid-connected system is connected to the power grid, the power conversion equipment in the system connects to the grid through the connection point and supplies power to the grid. When a grid fault causes a deep voltage drop, such as when the grid voltage drops to 50% or more of the rated voltage, the power conversion equipment continues to output active power to the grid by limiting output current, reducing output power, and adaptively adjusting virtual reactance to maintain the operation of the grid-connected system until the grid is restored.

[0003] However, when a grid fault is cleared and the grid voltage recovers rapidly from a deep voltage drop, the sudden increase in grid voltage and the delay in the dynamic response of the power conversion equipment cause active power at the grid connection point to flow backward into the power conversion equipment. This leads to a sharp rise in the DC bus voltage of the power conversion equipment, which may trigger the overvoltage protection of the power conversion equipment and even cause overload damage to internal electronic components. Therefore, how to prevent active power from flowing backward into the DC bus of the power conversion equipment during the rapid recovery of grid voltage from a deep voltage drop, in order to ensure the safe and stable operation of the power conversion equipment, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] This application provides a power conversion device and its control method. When the grid voltage recovers rapidly from a deep drop, the power conversion device can prevent active power from flowing back into the DC bus of the power conversion device, thus ensuring the safe and stable operation of the power conversion device, with high reliability and strong applicability.

[0005] In a first aspect, this application provides a power conversion device. The DC terminal of the power conversion device is used to connect to a DC source, and the AC terminal of the power conversion device is used to connect to the power grid. The power conversion device includes an inverter circuit and a controller. The controller is used to control the inverter circuit to convert the DC power input at the DC terminal into AC power and output it to the AC terminal. The controller is also used to: when the voltage amplitude at the AC terminal is less than a first threshold, control the voltage phase angle output by the inverter circuit to lead the voltage phase angle at the AC terminal, so that the active power output by the power conversion device to the power grid is greater than 0; when the voltage amplitude at the AC terminal increases from less than the first threshold, and the rate of change of the voltage amplitude at the AC terminal is greater than a second threshold, and the voltage phase angle output by the inverter circuit switches from leading the voltage phase angle at the AC terminal to lagging the voltage phase angle at the AC terminal, control the voltage phase angle output by the inverter circuit to switch from lagging the voltage phase angle at the AC terminal to leading the voltage phase angle at the AC terminal within a first time period, so that the active power output by the power conversion device to the power grid remains greater than 0.

[0006] In this embodiment, the AC terminal of the power conversion device is connected to the power grid, such that the voltage amplitude at the AC terminal is almost the same as the voltage amplitude of the power grid. The power conversion device can then determine whether the power grid voltage has dropped by detecting the voltage amplitude at the AC terminal through its controller. For example, the power conversion device can determine that the power grid voltage is in a deep voltage drop state when it detects that the voltage amplitude at the AC terminal is less than a first threshold. At this time, the power conversion device can adjust the voltage phase angle output by the inverter circuit to lead the voltage phase angle at the AC terminal, so that the active power output by the power conversion device to the power grid is greater than 0, meaning that the active power output by the power conversion device is flowing positively into the power grid. Furthermore, when the voltage amplitude at the AC terminal increases from below the first threshold, and the rate of change of the voltage amplitude at the AC terminal is greater than a second threshold, it means that the power grid voltage is rising rapidly, i.e., the power grid voltage is recovering rapidly from a deep voltage drop. To compensate for the impact caused by the sudden rise in power grid voltage, the voltage phase angle output by the inverter circuit will lag, causing the voltage phase angle output by the inverter circuit to switch from leading the AC terminal voltage phase angle to lagging behind the AC terminal voltage phase angle. At this time, the power conversion device, through the controller, switches the voltage phase angle output by the inverter circuit from lagging behind the AC terminal to leading the AC terminal within a first time period. This reduces the time the voltage phase angle output by the inverter circuit lags behind the AC terminal, preventing the inverter circuit's output voltage phase angle from continuously lagging behind the AC terminal. This ensures that the active power output by the power conversion device to the grid remains greater than zero, meaning active power will not flow back into the power conversion device. Therefore, in this embodiment, when the grid voltage recovers rapidly from a deep voltage drop, the power conversion device controls the inverter circuit's voltage phase angle to recover quickly (i.e., switch from lagging behind the AC terminal to leading the AC terminal), preventing the inverter circuit's output voltage phase angle from continuously lagging behind the AC terminal and causing active power to flow back into the power conversion device, thus ensuring the safe and stable operation of the power conversion device.

[0007] In one possible implementation, the controller controls the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first time period, so that the active power output by the power conversion device to the grid remains greater than 0. Specifically, this includes: controlling the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a second time period, so that the active power output by the power conversion device to the grid remains greater than or equal to the initial active power; the second time period is shorter than the first time period, and the initial active power is the magnitude of the active power output by the power conversion device when the voltage amplitude at the AC terminal is less than a first threshold.

[0008] In this embodiment, when the grid voltage recovers rapidly from a deep voltage drop, the voltage phase angle output by the inverter circuit controlled by the power conversion device switches from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a second time period, and this second time period is shorter than the first time period, allowing the voltage phase angle output by the inverter circuit to complete the switching more quickly. At this time, because the time the voltage phase angle output by the inverter circuit lags behind the AC terminal voltage phase angle is short, the active power output by the power conversion device to the grid does not have enough time to decrease. Therefore, the active power output by the power conversion device can be kept greater than or equal to the initial active power, thereby reducing fluctuations in the active power output by the power conversion device. Furthermore, reduced fluctuations in the active power output by the power conversion device can reduce the impact on grid power, thereby shortening the time required for grid fault recovery, making it highly applicable.

[0009] In one possible implementation, when the voltage phase angle of the inverter circuit output controlled by the controller switches from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first or second duration, the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal is less than or equal to 90 degrees; the second duration is less than the first duration.

[0010] In this embodiment, because the controller actively controls the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first or second time period, the voltage phase angle output by the inverter circuit completes the switching quickly. This reduces the time that the voltage phase angle output by the inverter circuit lags behind the AC terminal voltage phase angle, ensuring that the difference between the current phase angle and the voltage phase angle at the AC terminal does not change significantly. Specifically, the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal remains less than or equal to 90 degrees, making it highly applicable.

[0011] In one possible implementation, the controller is further configured to: after the voltage phase angle of the inverter circuit output switches from lagging behind the AC terminal to leading the AC terminal within a first time period or a second time period, adjust the rate of change of the voltage phase angle of the inverter circuit output continuously; the second time period is shorter than the first time period.

[0012] In this embodiment, the controller adjusts the rate of change of the voltage phase angle output by the inverter circuit to change continuously after the voltage phase angle output by the inverter circuit switches from lagging behind the AC terminal to leading the AC terminal within a first or second time period. This allows the voltage phase angle output by the inverter circuit to transition smoothly, thereby reducing output power fluctuations and making it highly applicable.

[0013] In one possible implementation, the controller is further configured to: obtain a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjust the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller adjusts the rate of change of the voltage phase angle output by the inverter circuit to continuously change, specifically including: controlling the rate of change of the amplitude of the first voltage vector and the rate of change of the amplitude of the second voltage vector to be less than a rate of change threshold, so that the rate of change of the voltage phase angle output by the inverter circuit changes continuously.

[0014] In this embodiment, when the controller adjusts the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector, the angle of the composite voltage vector of the first and second voltage vectors is equal to the angle of the inverter circuit's output voltage phase angle after being transformed into the synchronous rotating coordinate system. Therefore, by adjusting the magnitudes of the first and second voltage vectors, the controller can adjust the angle of the composite voltage vector in the synchronous rotating coordinate system, thereby adjusting the voltage phase angle of the inverter circuit's output. Furthermore, by adjusting the rate of change of the magnitudes of the first and second voltage vectors to be less than a rate of change threshold, the controller makes the angle of the composite voltage vector change smoothly. At this time, the controller controls the output voltage of the inverter circuit based on the composite voltage vector, making the rate of change of the inverter circuit's output voltage phase angle change continuously, i.e., the voltage phase angle of the inverter circuit's output transitions smoothly. This embodiment has a simple implementation principle and strong applicability.

[0015] In one possible implementation, the controller is further configured to: obtain a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjust the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein, the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller controls the voltage phase angle output by the inverter circuit to switch from a voltage phase angle lagging behind the AC terminal to a voltage phase angle leading the AC terminal within a first time period, specifically including: adjusting the amplitude of the first voltage vector to gradually increase and the amplitude of the second voltage vector to gradually decrease, until the rate of change of the voltage amplitude at the AC terminal is less than or equal to a second threshold, or until the time length for adjusting the amplitude of the first voltage vector to gradually increase and the amplitude of the second voltage vector to gradually decrease is greater than or equal to a third time period, the third time period being greater than the first time period.

[0016] In this embodiment, when the controller adjusts the output voltage of the inverter circuit based on the synchronous phase angle, the first voltage vector, and the second voltage vector, the angle of the composite voltage vector of the first and second voltage vectors is equal to the angle of the inverter circuit output voltage phase angle after being transformed into the synchronous rotating coordinate system. Therefore, by adjusting the magnitudes of the first and second voltage vectors, the controller can adjust the angle of the composite voltage vector in the synchronous rotating coordinate system, thereby adjusting the voltage phase angle of the inverter circuit output. For example, when the grid voltage recovers rapidly from a deep drop, the controller gradually increases the magnitude of the first voltage vector and gradually decreases the magnitude of the second voltage vector, causing the composite voltage vector to rotate counterclockwise in the synchronous rotating coordinate system, thereby adjusting the voltage phase angle of the inverter circuit output to lead. Furthermore, when the controller detects that the rate of change of the AC voltage amplitude is less than or equal to a second threshold, the voltage phase angle of the inverter circuit output leads the AC voltage phase angle. The controller completes the adjustment process of switching the voltage phase angle of the inverter circuit output to lead the AC voltage phase angle within a first or second time period, which is simple to implement. Alternatively, the controller can complete the adjustment process of switching the voltage phase angle of the inverter circuit output to lead the voltage phase angle of the AC terminal when the time length during which the amplitude of the first voltage vector gradually increases and the amplitude of the second voltage vector gradually decreases is greater than or equal to the third time length, thereby improving the fault tolerance of the adjustment process and making it more applicable.

[0017] In one possible implementation, the controller is further configured to: obtain a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjust the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein, the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller controls the voltage phase angle output by the inverter circuit to switch from a voltage phase angle lagging behind the AC terminal to a voltage phase angle leading the AC terminal within a first time duration, specifically including: adjusting the synchronization phase angle to increase until the rate of change of the voltage amplitude at the AC terminal is less than or equal to a second threshold, or until the time duration for adjusting the synchronization phase angle to increase is greater than or equal to a third time duration, the third time duration being greater than the first time duration.

[0018] In this embodiment, when the controller adjusts the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector, the angle of the composite voltage vector of the first and second voltage vectors is equal to the angle of the voltage phase angle output by the inverter circuit after being transformed into the synchronous rotating coordinate system. Therefore, by adjusting the size of the synchronization phase angle, the controller can adjust the angle of the composite voltage vector in the synchronous rotating coordinate system, thereby adjusting the voltage phase angle output by the inverter circuit. For example, when the grid voltage recovers rapidly from a deep drop, the controller increases the synchronization phase angle, causing the composite voltage vector to rotate counterclockwise in the synchronous rotating coordinate system, thereby adjusting the voltage phase angle output by the inverter circuit to lead. Furthermore, when the controller detects that the rate of change of the voltage amplitude at the AC terminal is less than or equal to a second threshold, the voltage phase angle output by the inverter circuit leads the voltage phase angle at the AC terminal. The controller completes the adjustment process of switching the voltage phase angle output by the inverter circuit to lead the voltage phase angle at the AC terminal within a first or second time period, which is simple to implement. Alternatively, the controller can complete the adjustment process of switching the voltage phase angle of the inverter circuit output to lead the voltage phase angle of the AC terminal when the time length for detecting the increase of the adjustment synchronization phase angle is greater than or equal to the third time length, thereby improving the fault tolerance of the adjustment process and making it more applicable.

[0019] In one possible implementation, the third duration is equal to 10 milliseconds.

[0020] In this embodiment, when the controller adjusts the amplitude of the first voltage vector to gradually increase and the amplitude of the second voltage vector to gradually decrease for a duration of 10 milliseconds or more, it completes the adjustment process of switching the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal within the first or second duration. The implementation method is simple and highly reliable.

[0021] In one possible implementation, the first threshold is equal to the rated output voltage amplitude multiplied by 0.5.

[0022] In this embodiment, the controller can flexibly adjust the specific value of the first threshold according to the rated output voltage amplitude, which has a wide range of applications and strong applicability.

[0023] In one possible implementation, the second threshold satisfies:

[0024]

[0025] Where Vem is the rated output voltage amplitude, and t equals 1 millisecond.

[0026] In this embodiment, the controller can flexibly adjust the specific value of the second threshold according to the rated output voltage amplitude, which has a wide range of applications and strong applicability.

[0027] In one possible implementation, the first duration is positively correlated with the rated output power of the power conversion device, or the first duration ranges from 500 microseconds to 2 milliseconds.

[0028] In this embodiment, the controller can flexibly adjust the specific value of the first duration according to the rated output power of the power conversion device, which has a wide range of applications and strong applicability.

[0029] In one possible implementation, the second duration is positively correlated with the rated output power of the power conversion device, or the value of the second duration ranges from 500 microseconds to 2 milliseconds; the second duration is less than the first duration.

[0030] In this embodiment, the controller can flexibly adjust the specific value of the first duration according to the rated output power of the power conversion device, which has a wide range of applications and strong applicability.

[0031] Secondly, this application also provides a control method for a power conversion device. The method is applied to the power conversion device, where the DC terminal is connected to a DC source and the AC terminal is connected to the power grid. The power conversion device includes an inverter circuit and a controller. The controller controls the inverter circuit to convert the DC input at the DC terminal into AC power and output it to the AC terminal. The method includes:

[0032] When the voltage amplitude at the AC end is less than the first threshold, the voltage phase angle of the inverter circuit output is controlled to lead the voltage phase angle at the AC end, so that the active power output by the power conversion device to the grid is greater than 0.

[0033] When the voltage amplitude at the AC terminal increases from less than the first threshold, and the rate of change of the voltage amplitude at the AC terminal is greater than the second threshold, and the voltage phase angle output by the inverter circuit switches from leading the voltage phase angle at the AC terminal to lagging the voltage phase angle at the AC terminal, the voltage phase angle output by the inverter circuit is controlled to switch from lagging the voltage phase angle at the AC terminal to leading the voltage phase angle at the AC terminal within the first time period, so that the active power output by the power conversion device to the grid remains greater than 0.

[0034] In one possible implementation, the voltage phase angle of the inverter circuit output is controlled to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first time period, so that the active power output by the power conversion device to the grid remains greater than 0. Specifically, this includes: controlling the voltage phase angle of the inverter circuit output to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a second time period, so that the active power output by the power conversion device to the grid remains greater than or equal to the initial active power; the second time period is shorter than the first time period, and the initial active power is the magnitude of the active power output by the power conversion device when the voltage amplitude at the AC terminal is less than a first threshold.

[0035] In one possible implementation, when the voltage phase angle of the inverter circuit output switches from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first or second duration, the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal is less than or equal to 90 degrees; the second duration is less than the first duration.

[0036] In one possible implementation, the method further includes: after the voltage phase angle of the inverter circuit output changes from lagging behind the AC terminal to leading the AC terminal within a first time period or a second time period, adjusting the rate of change of the voltage phase angle of the inverter circuit output continuously; the second time period is shorter than the first time period.

[0037] In one possible implementation, the method further includes: obtaining a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjusting the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller adjusts the rate of change of the voltage phase angle output by the inverter circuit to continuously change, specifically including: controlling the rate of change of the amplitude of the first voltage vector and the rate of change of the amplitude of the second voltage vector to be less than the rate of change threshold, so that the rate of change of the voltage phase angle output by the inverter circuit changes continuously.

[0038] In one possible implementation, the method further includes: obtaining a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjusting the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller controls the voltage phase angle output by the inverter circuit to switch from a voltage phase angle lagging behind the AC terminal to a voltage phase angle leading the AC terminal within a first time period, specifically including: adjusting the amplitude of the first voltage vector to gradually increase and the amplitude of the second voltage vector to gradually decrease, until the rate of change of the voltage amplitude at the AC terminal is less than or equal to a second threshold, or until the time length for adjusting the amplitude of the first voltage vector to gradually increase and the amplitude of the second voltage vector to gradually decrease is greater than or equal to a third time period, the third time period being greater than the first time period.

[0039] In one possible implementation, the method further includes: obtaining a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjusting the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller controls the voltage phase angle output by the inverter circuit to switch from a voltage phase angle lagging behind the AC terminal to a voltage phase angle leading the AC terminal within a first time period, specifically including: adjusting the synchronization phase angle to increase until the rate of change of the voltage amplitude at the AC terminal is less than or equal to a second threshold, or until the time length for adjusting the synchronization phase angle to increase is greater than or equal to a third time period, the third time period being greater than the first time period.

[0040] In one possible implementation, the third duration is equal to 10 milliseconds.

[0041] In one possible implementation, the first threshold is equal to the rated output voltage amplitude multiplied by 0.5.

[0042] In one possible implementation, the second threshold satisfies:

[0043]

[0044] Where Vem is the rated output voltage amplitude, and t equals 1 millisecond.

[0045] In one possible implementation, the first duration is positively correlated with the rated output power of the power conversion device, or the first duration ranges from 500 microseconds to 2 milliseconds.

[0046] In one possible implementation, the second duration is positively correlated with the rated output power of the power conversion device, or the value of the second duration ranges from 500 microseconds to 2 milliseconds; the second duration is less than the first duration.

[0047] The beneficial effects of the solution provided in the second aspect above can be referred to the description in the first aspect above, and will not be repeated here. Attached Figure Description

[0048] Figure 1 A schematic diagram of an application scenario for the grid-connected system provided in this application;

[0049] Figure 2 A schematic diagram of an active power signal provided in an embodiment of this application;

[0050] Figure 3 A schematic diagram of the frame of the power conversion device provided in the embodiments of this application;

[0051] Figure 4 A schematic diagram of a voltage phase angle of a power conversion device provided in an embodiment of this application;

[0052] Figure 5 This is another schematic diagram of the voltage phase angle of the power conversion device provided in the embodiments of this application;

[0053] Figure 6 A schematic diagram of an active power signal for a power conversion device provided in an embodiment of this application;

[0054] Figure 7 Another active power signal schematic diagram of the power conversion device provided in the embodiments of this application;

[0055] Figure 8 This is a schematic diagram of an electrical signal vector at the AC terminal of a power conversion device provided in an embodiment of this application;

[0056] Figure 9 This is a schematic diagram of a phase angle difference of a power conversion device provided in an embodiment of this application;

[0057] Figure 10 This is a schematic diagram of another electrical signal vector at the AC terminal of the power conversion device provided in an embodiment of this application;

[0058] Figure 11 This is a schematic diagram of another phase angle difference of the power conversion device provided in the embodiments of this application;

[0059] Figure 12 Another schematic diagram of the power conversion device provided in the embodiments of this application;

[0060] Figure 13 This is another schematic diagram of the voltage phase angle of the power conversion device provided in the embodiments of this application;

[0061] Figure 14 Another schematic diagram of the power conversion device provided in the embodiments of this application;

[0062] Figure 15 This is another schematic diagram of the voltage phase angle of the power conversion device provided in the embodiments of this application;

[0063] Figure 16 A schematic flowchart of the control method for the power conversion device provided in this application. Detailed Implementation

[0064] The power conversion equipment provided in this application is used in grid-connected systems and can be applied to different scenarios, such as photovoltaic-storage power supply, wind-storage power supply, pure energy storage power supply, or other scenarios. The following explanation uses the photovoltaic-storage power supply scenario as an example.

[0065] Please see Figure 1 , Figure 1 This is a schematic diagram illustrating an application scenario of the grid-connected system provided in this application. Figure 1 In the photovoltaic-storage power supply scenario shown, the grid-connected system includes an energy storage converter and a photovoltaic inverter. The DC terminal of the energy storage converter is connected to the energy storage battery, and the AC terminal is connected to the grid at the grid connection point. The energy storage converter converts the DC power from the energy storage battery into AC power and supplies it to the grid. The DC terminal of the photovoltaic inverter is connected to the photovoltaic modules, and the AC terminal is connected to the grid at the grid connection point. The photovoltaic inverter converts the DC power from the photovoltaic modules into AC power and supplies it to the grid. Both the energy storage converter and the photovoltaic inverter provide power conversion functions in the grid-connected system and can be collectively referred to as power conversion devices. Both the photovoltaic modules and the energy storage battery provide DC power in the grid-connected system and can be collectively referred to as DC sources.

[0066] exist Figure 1 In the application scenario shown, the power conversion device can operate in grid-connected mode. In grid-connected mode, the power conversion device can autonomously adjust the voltage parameters output to the grid, such as voltage frequency and voltage amplitude, based on the grid's voltage parameters to help maintain grid stability and improve its anti-interference capability. For example, when the grid voltage drops, the power conversion device in grid-connected mode can continuously supply power to the grid while actively adjusting its output voltage, thereby helping the grid voltage recover to stability. Alternatively, when grid power fluctuates, the power conversion device in grid-connected mode can adjust its output power according to changes in grid power, thus ensuring stable and controllable power. Therefore, in Figure 1In the application scenarios shown, the photovoltaic inverter can specifically be a grid-type photovoltaic inverter, and the energy storage converter can specifically be a grid-type energy storage converter. In other application scenarios, when the DC source connected to the power conversion device includes photovoltaic modules and energy storage batteries, the power conversion device can specifically be a grid-type photovoltaic-energy storage converter. Alternatively, when the DC source connected to the power conversion device is a supercapacitor, depending on the control method, the power conversion device can specifically be a static synchronous condenser, a grid-type static var generator (SVG), or a grid-type voltage source converter-high voltage direct current (VSC-HVDC). Alternatively, when the DC source connected to the power conversion device is wind power generation equipment, the power conversion device can specifically be a grid-type wind power inverter. Depending on the application scenario, the specific type of power conversion device can be flexibly selected; this application's embodiments do not provide detailed examples.

[0067] In practical applications, grid-connected systems also include box-type transformers. These transformers adjust and distribute the input AC power before outputting it to meet the voltage requirements of different power transmission nodes. For example, the AC voltage amplitude transmitted via the AC bus is typically high. Therefore, power conversion equipment can transmit the AC power to the box-type transformer for step-up before supplying it to the AC bus. Alternatively, the AC power transmitted via the AC bus can be stepped down by the box-type transformer before being supplied to the load. Or, if the rated voltage amplitude of the load matches the AC voltage amplitude transmitted via the AC bus, the AC bus can directly supply power to the load. When the grid-connected switch is closed and the grid-connected system is running, the AC power transmitted via the AC bus can be stepped up by one or more box-type transformers before being output to the grid. The specific location and number of box-type transformers can be flexibly adjusted according to the actual application scenario, and this application embodiment does not impose any limitations on this.

[0068] It should be noted that, in Figure 1In the application scenario shown, when a short-circuit fault occurs in the power grid, the grid is equivalent to being connected to ground through a resistor with a small resistance value, causing a voltage drop. Typically, when the grid voltage drops to 50% or more of its rated voltage, the grid enters a deep low-voltage ride-through phase. At this time, the power conversion equipment operating in grid-connected mode acts as a voltage source, actively adjusting the output voltage amplitude, frequency, and phase to help maintain grid voltage stability and prevent large-scale grid disconnection. However, when the grid fault is cleared and the grid voltage recovers rapidly from the deep voltage drop, the sudden increase in grid voltage and the delay in the dynamic response process of the power conversion equipment in grid-connected mode cause active power at the grid connection point to flow backwards into the DC side of the power conversion equipment. For an example, please refer to [link to example]. Figure 2 , Figure 2 This is a schematic diagram of an active power signal provided in an embodiment of this application. Figure 2 Before time T, the grid voltage is in a deep dip. At time T, the grid voltage recovers rapidly from the deep dip, and simultaneously, the active power output of the power conversion equipment fluctuates significantly until it equals the reference active power. Specifically, when the active power output of the power conversion equipment rapidly changes to less than zero, the active power flows back into the DC side of the power conversion equipment. In some application scenarios, when active power flows back into the DC side of the power conversion equipment, it may cause a sharp rise in the DC bus voltage of the power conversion equipment, potentially triggering overvoltage protection and even causing overload damage to internal electronic components. Therefore, how to prevent active power from flowing back into the DC bus of the power conversion equipment when the grid voltage recovers rapidly from a deep dip, in order to ensure the safe and stable operation of the power conversion equipment, is a technical problem that urgently needs to be solved by those skilled in the art.

[0069] Therefore, this application provides a power conversion device that can prevent active power from flowing back into the DC bus of the power conversion device when the grid voltage recovers rapidly from a deep drop, thus ensuring the safe and stable operation of the power conversion device, with high reliability and strong applicability.

[0070] The above are merely examples of application scenarios for the power conversion device provided in this application, and are not exhaustive. This application does not limit the application scenarios.

[0071] The following content combines Figures 3 to 15 The specific implementation principle of the power conversion device provided in the embodiments of this application will be introduced.

[0072] In this embodiment, the DC terminal of the power conversion device is connected to a DC source, and the AC terminal is connected to the power grid. The power conversion device includes an inverter circuit and a controller. The inverter circuit is positioned between the DC and AC terminals of the power conversion device. The power conversion device, through the controller, controls the inverter circuit to convert the DC input at the DC terminal into AC power and output it to the AC terminal, thereby supplying power to the power grid.

[0073] For example, please refer to Figure 3 , Figure 3 This is a schematic diagram of a frame of a power conversion device provided in an embodiment of this application. Figure 3 As shown, the DC terminal dc1 of the power conversion device can be connected to the positive terminal of the DC source, and the DC terminal dc2 of the power conversion device can be connected to the negative terminal of the DC source. Simultaneously, the DC terminal dc1 of the power conversion device is connected to the inverter circuit via the positive terminal BUS+ of the DC bus, and the DC terminal dc2 of the power conversion device is connected to the inverter circuit via the negative terminal BUS- of the DC bus. The DC power output from the DC source can be transmitted to the inverter circuit through the DC terminals (DC terminals dc1 and dc2) of the power conversion device and the DC bus. The output terminal out of the inverter circuit is connected to the AC terminal ac of the power conversion device, which is used to connect to the power grid. The controller controls the inverter circuit to convert the DC power input at the DC terminal into AC power and output it to the AC terminal ac of the power conversion device to supply power to the power grid. The power conversion device can be configured with corresponding functional modules between the output terminal out and the AC terminal ac of the inverter circuit according to the needs of the actual application scenario. For example, since the voltage signal output by the inverter circuit contains a large number of high-frequency harmonics (stepped AC), in order to filter out the high-frequency harmonics of the voltage signal output by the inverter circuit, the power conversion device can set a filter capacitor module and a filter inductor module between the output terminal (out) and the AC terminal (ac) of the inverter circuit, thereby converting the stepped AC output by the inverter circuit into fundamental AC and outputting it to the AC terminal (ac). Alternatively, the power conversion device can set a grid-connected switch between the output terminal (out) and the AC terminal (ac) of the inverter circuit, which can realize the power conversion device to be off-grid or connected to the grid. It is understood that the power conversion device can also set more other functional modules between the output terminal (out) and the AC terminal (ac) of the inverter circuit, which will not be described in detail in this embodiment.

[0074] Understandably, during the power conversion equipment's supply of power to the grid, since the AC terminal of the power conversion equipment is connected to the grid through the grid connection point, when a grid fault causes a deep voltage drop, the voltage at the AC terminal of the power conversion equipment will also drop significantly. Therefore, the power conversion equipment can determine whether the grid voltage has experienced a deep voltage drop based on the voltage amplitude at its AC terminal (hereinafter referred to as the AC terminal). To promptly help maintain grid voltage stability during a deep voltage drop, the power conversion equipment uses a controller to monitor the voltage amplitude at the AC terminal in real time during operation to determine whether the grid voltage has experienced a deep voltage drop.

[0075] In some feasible implementations, such as Figure 3 As shown, the controller can be electrically connected to the AC terminal and obtain the voltage amplitude of the AC terminal by sampling the electrical signal of the AC terminal. Alternatively, the controller can obtain the voltage amplitude of the AC terminal through an external sampling module. This sampling module is electrically connected to the AC terminal and can sample the voltage amplitude of the AC terminal. Simultaneously, this sampling module is communicatively connected to the controller and can send the sampled voltage amplitude of the AC terminal to the controller. It is understood that the above are merely examples, and the embodiments of this application do not limit the implementation method of the controller obtaining the voltage amplitude of the AC terminal.

[0076] Specifically, when the controller detects that the voltage amplitude at the AC terminal has dropped below a first threshold, it indicates a deep voltage descent in the mains grid. The first threshold can be understood as the maximum voltage amplitude at the AC terminal when a deep voltage descent occurs. This first threshold can be obtained from the rated output voltage amplitude. For example, assuming the rated output voltage amplitude is 800 volts, when the voltage amplitude at the AC terminal drops to less than 50% of this rated output voltage amplitude, it means a deep voltage descent has occurred in the mains grid. Therefore, the controller can set the first threshold to 400 volts (800 volts × 50%), and determine a deep voltage descent in the mains grid when the detected AC terminal voltage amplitude is less than 400 volts. It should be noted that the specific value of the first threshold can be flexibly adjusted according to the needs of the actual application scenario, and this embodiment does not impose any limitations on this.

[0077] It should be noted that the direction of the active power output by the power conversion equipment is related to the voltage phase angle of the inverter circuit output and the voltage phase angle of the AC terminal (equivalent to the voltage phase angle of the power grid). Specifically, when the voltage phase angle of the inverter circuit output leads the voltage phase angle of the AC terminal, the peak voltage of the inverter circuit output arrives earlier than the peak voltage of the AC terminal. At the same moment, the output voltage of the inverter circuit is higher than the AC terminal voltage, allowing the inverter circuit to actively drive current into the power grid, thus injecting the electrical energy provided by the DC source into the power grid as active power. Conversely, when the voltage phase angle of the inverter circuit output lags the voltage phase angle of the AC terminal, the peak voltage of the inverter circuit output arrives later than the peak voltage of the AC terminal. At the same moment, the output voltage of the inverter circuit is lower than the AC terminal voltage, allowing the inverter circuit to actively absorb grid current, thus injecting the electrical energy transmitted from the grid into the power conversion equipment as active power. Therefore, when the voltage phase angle of the inverter circuit leads the voltage phase angle of the AC terminal, the active power output by the power conversion device flows into the grid in the positive direction, meaning the active power output by the power conversion device to the grid is greater than 0. When the voltage phase angle of the inverter circuit lags behind the voltage phase angle of the AC terminal, the active power flows into the power conversion device in the reverse direction from the grid, meaning the active power output by the power conversion device to the grid is less than 0.

[0078] In order to prevent active power from flowing back into the power conversion device, in this embodiment of the application, after the controller detects a deep voltage drop in the grid, it controls the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal, thereby controlling the active power output by the power conversion device to be greater than 0, thus ensuring that active power will not flow back into the power conversion device.

[0079] Furthermore, after a grid fault is cleared, the grid voltage begins to recover from a deep voltage dip. In some application scenarios, when the grid voltage recovers rapidly from a deep voltage dip, it may suddenly surge. To compensate for this sudden voltage surge, the controller uses a phase-locked loop (PLL) to adjust the inverter's output voltage phase angle, causing it to lag behind the AC input voltage phase angle. Simultaneously, the controller's response to the inverter's output voltage phase angle in grid-connected mode exhibits a dynamic delay, resulting in the inverter's output voltage phase angle consistently lagging behind the AC input voltage phase angle. Conversely, in other application scenarios, when the grid voltage recovers slowly from a deep voltage dip, the controller can dynamically adjust its response in a timely manner, allowing the inverter's output voltage phase angle to lead the AC input voltage phase angle. This prevents active power from flowing backwards into the power conversion equipment.

[0080] For example, please refer to Figure 4 , Figure 4 A schematic diagram of a voltage phase angle of a power conversion device provided in an embodiment of this application. Figure 4 The figures show Vo as the output voltage vector of the inverter circuit after conversion to the synchronous rotating coordinate system during a deep grid voltage dip; Vg as the AC voltage vector after conversion to the synchronous rotating coordinate system during a deep grid voltage dip; Vo' as the output voltage vector of the inverter circuit after conversion to the synchronous rotating coordinate system during a rapid recovery of the grid voltage from the deep dip; and Vg' as the AC voltage vector after conversion to the synchronous rotating coordinate system during a rapid recovery of the grid voltage from the deep dip. From the above, it can be seen that during a deep grid voltage dip, the phase angle of the inverter circuit output voltage leads the phase angle of the AC voltage, i.e. Figure 4 The voltage phase angle of Vo leads the voltage phase angle of Vg. Furthermore, during the rapid recovery of the grid voltage from a deep dip, the voltage phase angle of the inverter output switches from leading the AC terminal voltage phase angle to lagging behind the AC terminal voltage phase angle, i.e. Figure 4 The voltage phase angle of Vo' lags behind the voltage phase angle of Vg'.

[0081] In summary, as the grid voltage rapidly recovers from a deep voltage dip, the voltage phase angle output by the inverter circuit switches from leading the AC voltage phase angle to lagging behind the grid voltage phase angle. Simultaneously, due to the dynamic delay in the controller's adjustment response, the voltage phase angle output by the inverter circuit continues to lag behind the AC voltage phase angle, leading to active power flowing back into the power conversion device. In this embodiment, to promptly control the direction of active power output from the power conversion device and prevent active power from flowing back into the device, the controller can detect in real time whether the AC voltage is rapidly recovering from a deep voltage dip, thereby determining whether the grid voltage has begun its rapid recovery from a deep voltage dip.

[0082] Specifically, when the controller detects that the voltage amplitude at the AC terminal is increasing from below the first threshold, it means that the voltage amplitude of the power grid is also increasing from below the first threshold, i.e., the power grid voltage is recovering from a deep drop. Simultaneously, if the controller detects that the rate of change of the voltage amplitude at the AC terminal is greater than the second threshold, it indicates that the voltage amplitude of the power grid is recovering rapidly. The second threshold is the minimum rate of change of the voltage amplitude at the AC terminal when the power grid voltage is rapidly recovering from a deep drop. The second threshold can be obtained from the rated output voltage amplitude. For example, the specific value of the second threshold can be calculated using the following formula (1), which is as follows:

[0083]

[0084] Where Vem is the rated output voltage amplitude, and t equals 1 millisecond. The specific value of the second threshold can be flexibly adjusted according to the needs of the actual application scenario, and this application embodiment does not impose any restrictions on it.

[0085] Understandably, when the controller detects that the rate of change of the AC voltage amplitude is greater than the second threshold, it means that the grid voltage is recovering rapidly. Therefore, the controller can determine that the grid voltage is rapidly recovering from a deep drop when it detects that the AC voltage amplitude has started to increase from below the first threshold and that the rate of change of the AC voltage amplitude is greater than the second threshold.

[0086] As described above, during the rapid recovery of the grid voltage from a deep drop, the voltage phase angle output by the inverter circuit switches from leading the AC terminal to lagging behind it. At this time, the controller controls the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal to leading it within a first time period. This prevents the voltage phase angle output by the inverter circuit from continuously lagging behind the AC terminal, thus ensuring that the active power output by the power conversion device to the grid remains greater than zero, preventing active power from flowing back into the power conversion device. The first time period is positively correlated with the rated output power of the power conversion device; for example, the value of the first time period ranges from 500 microseconds to 2 milliseconds. Furthermore, in different application scenarios, the controller can flexibly adjust the size of the first time period according to actual needs; this embodiment does not impose any limitations on this.

[0087] For example, please refer to Figure 5 , Figure 5 This is another voltage phase angle diagram of the power conversion device provided in this application embodiment. When the grid voltage experiences a deep voltage drop, the voltage vector obtained by converting the output voltage of the inverter circuit to the synchronous rotating coordinate system is shown as Vo, and the voltage vector obtained by converting the AC terminal voltage to the synchronous rotating coordinate system is shown as Vg. When the grid voltage rapidly recovers from the deep voltage drop, the voltage vector obtained by converting the output voltage of the inverter circuit to the synchronous rotating coordinate system is shown as Vo', and the voltage vector obtained by converting the AC terminal voltage to the synchronous rotating coordinate system is shown as Vg'. From the above, it can be seen that when the grid fault is cleared and the grid voltage rapidly recovers from the deep voltage drop, the voltage phase angle of the inverter circuit output changes from leading the AC terminal voltage phase angle to lagging behind the AC terminal voltage phase angle, i.e. Figure 5The voltage phase angle of Vo' lags behind the voltage phase angle of Vg'. In order to prevent active power from flowing back into the power conversion device, the controller can adjust the voltage phase angle of the inverter circuit output to lead within the first time period. This makes the voltage vector of the inverter circuit output voltage after conversion to the synchronous rotating coordinate system equal to Vo', and the voltage phase angle of Vo' leads the voltage phase angle of Vg'. Thus, within the first time period, the controller controls the voltage phase angle of the inverter circuit output to switch from lagging behind the AC terminal to leading the AC terminal.

[0088] In some feasible implementations, during the process where the voltage phase angle of the inverter circuit controlled by the controller switches from lagging behind the AC terminal to leading the AC terminal within a first time period, the specific changes in the active power output of the power conversion device can be found in [reference needed]. Figure 6 , Figure 6 This is a schematic diagram of an active power signal for a power conversion device provided in an embodiment of this application. Figure 6 As shown, before time T, the grid voltage is in a deep dip, and the active power output by the power conversion device to the grid is greater than 0. At time T, the controller detects that the grid voltage is rapidly recovering from the deep dip. The controller controls the voltage phase angle of the inverter circuit to switch from lagging behind the AC terminal to leading the AC terminal within the first time period, ensuring that the active power output by the power conversion device remains greater than 0 and gradually changes to equal the reference active power. This prevents active power from flowing back into the power conversion device, improving its stability and safety. In contrast, Figure 2 The active power output of the power conversion device shown will rapidly decrease to less than 0, thereby causing the active power to flow back into the power conversion device.

[0089] In some feasible implementations, fluctuations in the active power output of the power conversion device (e.g., when the grid voltage recovers rapidly from a deep dip) are addressed. Figure 2 As shown, this can impact grid power and affect grid fault recovery. Therefore, in this embodiment, the controller can, when detecting a rapid recovery of the grid voltage from a deep voltage drop, control the active power output of the power conversion device to remain greater than or equal to the initial active power, thereby reducing the impact on grid power and shortening the time required for grid fault recovery. The initial active power refers to the active power output of the power conversion device when the AC voltage amplitude is less than a first threshold, i.e., before the grid voltage has begun to recover from a deep voltage drop. For an example, please refer to [link to example]. Figure 7 , Figure 7 Another active power signal schematic diagram of the power conversion device provided in this application embodiment. For example... Figure 7As shown, before time T, the grid voltage is in a deep voltage dip, and the active power output by the power conversion device is equal to the initial active power P1. After time T, the grid voltage recovers rapidly from the deep voltage dip. At this time, the controller can reduce the fluctuations in the active power output by the power conversion device by keeping it greater than or equal to the initial active power P1, thereby reducing the impact on the grid power and shortening the time required for grid fault recovery. Furthermore, as mentioned above, during the deep voltage dip, the controller controls the active power output by the power conversion device to the grid to remain greater than 0, i.e., the initial active power P1 is greater than 0. Therefore, when the controller controls the active power output by the power conversion device to remain greater than or equal to the initial active power P1, the active power output by the power conversion device will also remain greater than 0 and gradually change to equal the reference active power, thus preventing active power from flowing back into the power conversion device. In contrast, Figure 6 The active power output of the power conversion device shown will decrease to less than the initial active power P1, and then increase to greater than or equal to the initial active power P1. The fluctuation of active power is significantly larger.

[0090] In some feasible implementations, the active power output by the power conversion device is related to the voltage phase angle of the inverter circuit output and the voltage phase angle of the AC terminal. Specifically, when the grid voltage recovers rapidly from a deep drop, the voltage phase angle of the inverter circuit output switches from leading the AC terminal voltage phase angle to lagging behind it. If the controller does not quickly switch the inverter circuit output voltage phase angle back to leading the AC terminal voltage phase angle, the active power output by the power conversion device to the grid will gradually decrease. Conversely, if the controller quickly switches the inverter circuit output voltage phase angle from lagging behind the AC terminal voltage phase angle to leading it, the active power output by the power conversion device to the grid does not have enough time to decrease because the lag time is short. This allows the active power output by the power conversion device to remain greater than or equal to the initial active power, thereby reducing the impact on grid power and shortening the time required for grid fault recovery.

[0091] Specifically, when the controller detects a rapid recovery of the grid voltage from a deep drop and the voltage phase angle output by the inverter circuit switches from leading the AC terminal voltage phase angle to lagging behind it, it controls the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a second time period. This ensures that the active power output by the power conversion device remains greater than or equal to the initial active power. The second time period is shorter than the first time period, and its magnitude is positively correlated with the rated output power of the power conversion device. For example, the value of the second time period ranges from 500 microseconds to 2 milliseconds. Furthermore, in different application scenarios, the controller can flexibly adjust the magnitude of the second time period according to actual needs; this embodiment does not impose any limitations on this.

[0092] Understandably, since the second duration is shorter than the first duration, compared to the controller controlling the inverter circuit output voltage phase angle to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within the first duration, the controller controlling the inverter circuit output voltage phase angle to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within the second duration allows for a faster switching of the inverter circuit output voltage phase angle. Furthermore, this reduces the time the inverter circuit output voltage phase angle lags behind the AC terminal voltage phase angle, preventing the active power output from the power conversion equipment from decreasing in time, thus ensuring that the active power output from the power conversion equipment remains greater than or equal to the initial active power.

[0093] In some feasible implementations, in the embodiments of this application, during the process where the voltage phase angle output by the inverter circuit is switched from lagging behind the AC terminal to leading the AC terminal during a first or second time period, the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal is less than or equal to 90 degrees. Conversely, if the controller does not actively control the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal to leading the AC terminal, the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal will be greater than 90 degrees during this process.

[0094] For example, when the voltage phase angle output by the controller to the inverter circuit switches from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first or second time period, the change in the current phase angle at the AC terminal can be referred to... Figure 8 As shown, Figure 8This is a schematic diagram of an electrical signal vector at the AC terminal of a power conversion device provided in an embodiment of this application. During a deep voltage dip in the grid, the voltage vector obtained by converting the AC terminal voltage to a synchronous rotating coordinate system is shown as Vg, and the voltage vector obtained by converting the AC terminal current to a synchronous rotating coordinate system is shown as Ig. After the grid voltage rapidly recovers from the deep voltage dip, the voltage vector obtained by converting the AC terminal voltage to a synchronous rotating coordinate system is shown as Vg', and the voltage vector obtained by converting the AC terminal current to a synchronous rotating coordinate system is shown as Ig'. During the rapid recovery of the grid voltage, Ig rotates counterclockwise to Ig', ensuring that the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal remains less than or equal to 90 degrees.

[0095] Specifically, during the process where the voltage phase angle of the inverter circuit controlled by the controller switches from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within the first or second time duration, the specific change in the difference between the current phase angle and the voltage phase angle at the AC terminal can be found in [reference needed]. Figure 9 , Figure 9 This is a schematic diagram of a phase angle difference in a power conversion device provided in an embodiment of this application. Figure 9 As shown, before time T, the grid voltage is in a deep dip, and the difference between the current phase angle and the voltage phase angle at the AC end is equal to -65 degrees, meaning the current phase angle at the AC end lags behind the voltage phase angle by 65 degrees. At time T, the grid voltage recovers rapidly from the deep dip. The controller controls the voltage phase angle of the inverter circuit to switch from lagging behind the AC end voltage phase angle to leading the AC end voltage phase angle within a first or second time period, ensuring that the absolute value of the difference between the current phase angle and the voltage phase angle at the AC end is always less than or equal to 90 degrees.

[0096] In contrast, in some application scenarios, if the controller does not actively control the voltage phase angle of the inverter circuit output to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle, the change in the current phase angle at the AC terminal can be found in [reference needed]. Figure 10 As shown, Figure 10This is another schematic diagram of the electrical signal vector at the AC terminal of the power conversion device provided in this application embodiment. During a deep voltage dip in the grid, the voltage vector obtained after converting the AC terminal voltage to a synchronous rotating coordinate system is shown as Vg, and the voltage vector obtained after converting the AC terminal current to a synchronous rotating coordinate system is shown as Ig. After the grid voltage rapidly recovers from the deep voltage dip, the voltage vector obtained after converting the AC terminal voltage to a synchronous rotating coordinate system is shown as Vg', and the voltage vector obtained after converting the AC terminal current to a synchronous rotating coordinate system is shown as Ig'. During the rapid recovery of the grid voltage, Ig rotates clockwise to Ig', causing the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal to exceed 90 degrees.

[0097] Specifically, during the process where the controller does not actively control the voltage phase angle of the inverter circuit output to switch to a position leading the voltage phase angle of the AC terminal, the specific changes in the difference between the current phase angle and the voltage phase angle at the AC terminal can be found in [reference needed]. Figure 11 , Figure 11 This is a schematic diagram illustrating another phase angle difference of the power conversion device provided in an embodiment of this application. For example... Figure 11 As shown, before time T, the grid voltage is in a deep dip, and the difference between the current phase angle and the voltage phase angle at the AC end is -65 degrees, meaning the current phase angle at the AC end lags behind the voltage phase angle by 65 degrees. At time T, the grid voltage recovers rapidly from the deep dip. The controller does not actively adjust the voltage phase angle of the inverter circuit to lead the voltage phase angle at the AC end, causing the absolute value of the difference between the current phase angle and the voltage phase angle at the AC end to be greater than 90 degrees, and the fluctuation of the difference between the current phase angle and the voltage phase angle is large.

[0098] In some feasible implementations, the power conversion device provided in this application embodiment can be based on... Figure 12 The logical framework shown implements the above adjustments. Figure 12 Another schematic diagram of the power conversion device provided in an embodiment of this application. (See attached diagram.) Figure 12 As shown, in the power conversion equipment, the output of the inverter circuit is connected to the AC terminal (ac) via a filter module. This filter module includes a filter inductor and a filter capacitor, which can filter out impurity signals in the AC output of the inverter circuit.

[0099] During the operation of the power conversion equipment, the controller detects the voltage Vg and current Ig at the AC terminal ac. Based on Vg and Ig, it calculates the actual output active power P and reactive power Q of the power conversion equipment. Furthermore, it calculates the reference power Pref for the output active power and the reference power Qref for the reactive power based on Vg. Further, the controller performs active power synchronization control based on the calculated Pref and P to generate a synchronization phase angle θ, where θ is the angle between the synchronous rotating coordinate system and the stationary coordinate system. Simultaneously, the controller transforms Vg and Ig into the synchronous rotating coordinate system based on θ to obtain Vd, Vq, Id, and Iq. Here, Vd and Id are the voltage and current vectors on the d-axis of the synchronous rotating coordinate system, and Vq and Iq are the voltage and current vectors on the q-axis of the synchronous rotating coordinate system. The angle of the combined voltage vector of Vd and Vq is the same as the angle of the current output voltage phase angle of the inverter circuit after being transformed into the synchronous rotating coordinate system. Similarly, the angle of the combined current vector of Id and Iq is the same as the angle of the current output current phase angle of the inverter circuit after being transformed into the synchronous rotating coordinate system. Furthermore, the controller performs reactive power control based on Qref and Q to generate Vdref and Vqref. The controller then performs vector voltage control based on these Vdref, Vqref, Vd, Vq, and Ig to obtain Idref and Iqref. From these Idref, Iqref, Id, and Iq, the first voltage vector Vod and the second voltage vector Voq can be calculated. Vod is the voltage vector on the d-axis of the synchronous rotating coordinate system, and Voq is the voltage vector on the q-axis of the synchronous rotating coordinate system. The angle of the combined voltage vector of Vod and Voq is the same as the target angle (i.e., the adjusted angle) of the voltage phase angle of the inverter circuit output after being transformed into the synchronous rotating coordinate system. After the controller performs coordinate transformation on Vod and Voq based on θ, it can obtain the pulse width modulation signal of the inverter circuit, which drives the inverter circuit to adjust the output voltage amplitude, voltage phase angle, or voltage frequency to the target value.

[0100] Furthermore, the controller can determine whether the grid voltage is rapidly recovering from a deep voltage drop based on the voltage amplitude of Vg, the voltage amplitude Vo output by the inverter circuit, and the rate of change of the voltage amplitude of Vg, so as to control the active power from flowing back into the power conversion equipment. Specifically, when the controller detects that the grid voltage is rapidly recovering from a deep voltage drop, the controller adaptively adjusts the weighting coefficients K1 and K2 of Vd and Vq to update the aforementioned Vod and Voq. K1 gradually increases from 1, and K2 gradually decreases from 1, so that the voltage amplitude of Voa gradually increases and the voltage amplitude of Voq gradually decreases. It can be understood that the angle of the combined voltage vector of Vod and Voq is the same as the target angle after the voltage phase angle of the inverter circuit output is converted to the synchronous rotating coordinate system. Therefore, by adjusting the voltage amplitude of Voa to gradually increase and the voltage amplitude of Voq to gradually decrease, the controller can make the combined voltage vector rotate counterclockwise, thereby allowing the voltage phase angle of the inverter circuit output to lead the voltage phase angle of the AC terminal.

[0101] In some feasible implementations, the controller can also obtain the adjustment result after adaptive parameter adjustment of the weighting coefficient K1 of Vd and the weighting coefficient K2 of Vq during the process of vector voltage control or vector current control, so as to directly calculate the new Vod and Voq.

[0102] Please see Figure 13 , Figure 13 This is another voltage phase angle diagram of the power conversion device provided in this application embodiment. When the grid voltage recovers rapidly from a deep drop, the voltage vector obtained after converting the output voltage of the inverter circuit to the synchronous rotating coordinate system is shown as Vo', and the voltage vector obtained after converting the AC terminal voltage to the synchronous rotating coordinate system is shown as Vg'. Simultaneously, the first voltage vector inside the controller is Vd1, and the second voltage vector is Vq1. Further, the controller adaptively adjusts the weighting coefficients K1 and K2 of the first and second voltage vectors within a first or second time period, causing the amplitude of the first voltage vector to gradually increase from Vd1 to Vd2, and the amplitude of the second voltage vector to gradually decrease from Vq1 to Vq2. This causes the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within the first or second time period. During this process, Vo' rotates counterclockwise to Vo'.

[0103] In some feasible implementations, the controller, according to the above... Figure 12 and Figure 13In the specific embodiment shown, during the adjustment of the voltage phase angle of the inverter circuit output, the voltage amplitude at the AC terminal is detected. When the rate of change of the AC terminal voltage amplitude is less than or equal to a second threshold, the adjustment process of switching the voltage phase angle of the inverter circuit output to lead the AC terminal voltage phase angle is completed. That is, when the rate of change of the AC terminal voltage amplitude is less than or equal to the second threshold, the controller switches the voltage phase angle of the inverter circuit output from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first time period or a second time period.

[0104] Alternatively, in some feasible implementations, the controller can also complete the adjustment process of switching the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal when the time length during which the amplitude of the first voltage vector gradually increases and the second voltage vector gradually decreases is greater than or equal to a third duration. The third duration is greater than the first duration; for example, the third duration is equal to 10 milliseconds. The specific value of the third duration can be flexibly adjusted according to actual needs, and will not be illustrated in detail in this application. It is understood that by completing the adjustment process of switching the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal when the time length during which the amplitude of the first voltage vector gradually increases and the second voltage vector gradually decreases is greater than or equal to a third duration, the controller can improve the adjustment fault tolerance and ensure the stable operation of the power conversion equipment.

[0105] In some feasible implementations, after the controller controls the voltage phase angle of the inverter circuit output to switch from lagging behind the AC terminal to leading the AC terminal within a first or second time period, in order to reduce power fluctuations, the controller can adjust the rate of change of the voltage phase angle of the inverter circuit output to change continuously, so that the voltage phase angle of the inverter circuit output transitions smoothly.

[0106] Specifically, the controller can ensure that the rate of change of the amplitude of the first voltage vector and the rate of change of the amplitude of the second voltage vector are less than a rate of change threshold, so that the rate of change of the voltage phase angle output by the inverter circuit changes continuously. This rate of change threshold is when the rate of change of the amplitudes of the first and second voltage vectors changes smoothly, thereby avoiding power fluctuations caused by sudden changes in the voltage phase angle output by the inverter circuit. For example, please refer again... Figure 12 As shown, the controller can smoothly restore the weighting coefficient K1 of the first voltage vector and the weighting coefficient K2 of the second voltage vector to 1 in a ramp manner, thereby controlling the amplitude change rate of the first voltage vector and the amplitude change rate of the second voltage vector to change smoothly (less than the change rate threshold), so that the change rate of the voltage phase angle output by the inverter circuit changes continuously.

[0107] In some feasible implementations, the power conversion device provided in this application embodiment can also be based on... Figure 14 The logical framework shown implements the above adjustments. Figure 14 This is another schematic diagram of the framework of the power conversion device provided in the embodiments of this application. Figure 14 As shown, in the power conversion equipment, the output terminal of the inverter circuit is connected to the AC terminal ac through a filter module.

[0108] During the operation of the power conversion equipment, the controller detects the voltage Vg and current Ig at the AC terminal ac. Based on Vg and Ig, it calculates the actual output active power P and reactive power Q of the power conversion equipment. It also calculates the reference power Pref for the output active power and the reference power Qref for the reactive power based on Vg. Furthermore, the controller performs active power synchronization control based on the calculated Pref and P to generate a synchronization phase angle θ. Simultaneously, the controller performs reactive power control based on Qref and Q to calculate the first voltage vector Vod and the second voltage vector Voq based on Ig. After the controller performs coordinate transformation on Vod and Voq using θ, it obtains the pulse width modulation signal for the inverter circuit, which drives the inverter circuit to adjust the output voltage amplitude, voltage phase angle, or voltage frequency to the target value.

[0109] Furthermore, the controller can determine whether the grid voltage is rapidly recovering from a deep voltage drop based on the voltage amplitude of Vg, the voltage amplitude Vo output by the inverter circuit, and the rate of change of the voltage amplitude of Vg, so as to control the active power from flowing back into the power conversion equipment. Specifically, when the controller detects that the grid voltage is rapidly recovering from a deep voltage drop, the controller performs phase compensation on the aforementioned θ to increase θ. Then, the controller performs coordinate transformation on Vod and Voq based on the phase-compensated θ to update the pulse width modulation signal of the inverter circuit. It can be understood that after the controller increases θ, the angle of the combined voltage vector of Vod and Voq in the synchronous rotating coordinate system is compensated, which allows the combined voltage vector to rotate counterclockwise, thereby allowing the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal.

[0110] For example, please refer to Figure 15 , Figure 15This is another schematic diagram of the voltage phase angle of the power conversion device provided in this application embodiment. When the grid voltage recovers rapidly from a deep drop, the voltage vector obtained after converting the output voltage of the inverter circuit to the synchronous rotating coordinate system is shown as Vo', and the voltage vector obtained after converting the AC terminal voltage to the synchronous rotating coordinate system is shown as Vg'. Furthermore, the controller compensates for the voltage phase angle of Vo' by a corresponding angle Δθ within a first or second time period, causing Vo' to rotate counterclockwise to Vo'', thereby switching the voltage phase angle output by the inverter circuit from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within the first or second time period.

[0111] In some feasible implementations, the controller, according to the above... Figure 14 and Figure 15 In the specific embodiment shown, during the adjustment of the voltage phase angle of the inverter circuit output, the voltage amplitude at the AC terminal is detected. When the rate of change of the AC terminal voltage amplitude is less than or equal to a second threshold, the adjustment process of switching the voltage phase angle of the inverter circuit output to lead the AC terminal voltage phase angle is completed. In other words, when the rate of change of the AC terminal voltage amplitude is less than or equal to the second threshold, the controller switches the voltage phase angle of the inverter circuit output from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first or second time period.

[0112] Alternatively, in some feasible implementations, the controller can also complete the adjustment process of switching the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal when the time duration for detecting the increase in the synchronization phase angle is greater than or equal to a third duration. Here, the third duration is longer than the first duration. It is understood that by completing the adjustment process of switching the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal when the time duration for detecting the increase in the synchronization phase angle is greater than or equal to a third duration, the controller can improve fault tolerance and ensure the stable operation of the power conversion equipment.

[0113] It should be noted that the controller can flexibly adjust the logic framework and implementation principle according to the actual needs of the scenario. Any technical solution that can realize the voltage phase angle adjustment of the inverter circuit output is applicable to this application. The embodiments of this application will not be described one by one here.

[0114] In summary, in this embodiment, the power conversion device can determine that the grid voltage is in a deep slump when it detects that the voltage amplitude at the AC terminal is less than a first threshold. At this time, the power conversion device adjusts the voltage phase angle output by the inverter circuit to lead the voltage phase angle at the AC terminal, ensuring that the active power output by the power conversion device to the grid is greater than zero, meaning the active power output by the power conversion device flows positively into the grid. Furthermore, when the voltage amplitude at the AC terminal increases from below the first threshold, and the rate of change of the voltage amplitude at the AC terminal is greater than a second threshold, it means that the grid voltage is rapidly increasing, i.e., the grid voltage is rapidly recovering from the deep slump. To compensate for the impact caused by the sudden rise in grid voltage, the voltage phase angle output by the inverter circuit will lag, causing the voltage phase angle output by the inverter circuit to switch from leading the AC terminal voltage phase angle to lagging behind the AC terminal voltage phase angle. At this time, the power conversion device, through its controller, switches the voltage phase angle output by the inverter circuit from lagging behind the AC terminal to leading the AC terminal within a first time period. This reduces the time the inverter circuit's output voltage phase angle lags behind the AC terminal, preventing it from continuously lagging behind. This ensures that the active power output by the power conversion device to the grid remains greater than zero, meaning active power will not flow back into the power conversion device. Alternatively, the power conversion device can control the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal to leading the AC terminal within a second time period shorter than the first time period, allowing for a faster switching of the inverter circuit's output voltage phase angle. At this point, because the voltage phase angle output by the inverter circuit lags behind the AC terminal voltage phase angle by a short period, the active power output by the power conversion equipment to the grid does not have enough time to decrease. This allows the active power output by the power conversion equipment to remain greater than or equal to the initial active power, thereby reducing fluctuations in the active power output of the power conversion equipment, thus reducing the impact on grid power and shortening the time required for grid fault recovery. This design offers broad applicability. Furthermore, after the power conversion equipment switches the voltage phase angle output by the inverter circuit to lead the AC terminal voltage phase angle, it can continuously control the rate of change of the inverter circuit's output voltage phase angle to reduce output power fluctuations.

[0115] Please see Figure 16 , Figure 16 This is a flowchart illustrating a control method for a power conversion device provided in this application. The control method for a power conversion device provided in this application is applicable to... Figures 3 to 15 The controller in the corresponding specific implementation. Specifically, the control method for the power conversion device may include the following steps:

[0116] S101. When the voltage amplitude at the AC terminal is less than the first threshold, the voltage phase angle of the inverter circuit output is controlled to lead the voltage phase angle at the AC terminal, so that the active power output by the power conversion device to the grid is greater than 0.

[0117] Understandably, if the AC terminal of a power conversion device is connected to the power grid, ensuring that the voltage amplitude at the AC terminal matches the voltage amplitude of the power grid, the power conversion device can determine whether the grid voltage has dropped by detecting the voltage amplitude at the AC terminal. For example, the power conversion device can determine that the grid voltage is in a deep voltage drop state when it detects that the voltage amplitude at the AC terminal is less than a first threshold. This first threshold refers to the maximum voltage amplitude at the AC terminal during a deep voltage drop. In this case, by adjusting the phase angle of the voltage output from the inverter circuit to lead the phase angle of the voltage at the AC terminal, the power conversion device can ensure that the active power output to the grid is greater than zero, meaning that the active power output by the power conversion device flows positively into the grid.

[0118] For a detailed implementation of S101, please refer to the above. Figures 3 to 15 The implementation method executed by the controller is not described in detail in this application embodiment.

[0119] S102. When the voltage amplitude at the AC terminal increases from less than the first threshold, and the rate of change of the voltage amplitude at the AC terminal is greater than the second threshold, and the voltage phase angle output by the inverter circuit switches from leading the voltage phase angle at the AC terminal to lagging the voltage phase angle at the AC terminal, the voltage phase angle output by the inverter circuit is controlled to switch from lagging the voltage phase angle at the AC terminal to leading the voltage phase angle at the AC terminal within the first time period, so that the active power output by the power conversion device to the grid remains greater than 0.

[0120] Understandably, when the AC voltage amplitude increases from below the first threshold and the rate of change of the AC voltage amplitude exceeds the second threshold, it means that the grid voltage is rising rapidly, i.e., the grid voltage is recovering quickly from a deep drop. To compensate for the impact caused by the sudden rise in grid voltage, the voltage phase angle output by the inverter circuit will lag, causing the voltage phase angle output by the inverter circuit to switch from leading the AC voltage phase angle to lagging behind the AC voltage phase angle. At this time, the power conversion equipment controls the voltage phase angle output by the inverter circuit to switch from lagging behind the AC voltage phase angle to leading the AC voltage phase angle within the first time period. This reduces the time that the voltage phase angle output by the inverter circuit lags behind the AC voltage phase angle, preventing the voltage phase angle output by the inverter circuit from continuously lagging behind the AC voltage phase angle. As a result, the active power output by the power conversion equipment to the grid remains greater than 0, i.e., active power will not flow back into the power conversion equipment. Therefore, in this embodiment, when the grid voltage recovers rapidly from a deep drop, the power conversion device can control the voltage phase angle of the inverter circuit to recover rapidly (i.e., switch from a voltage phase angle lagging behind the AC terminal to a voltage phase angle leading the AC terminal). This can prevent the voltage phase angle output by the inverter circuit from continuously lagging behind the AC terminal voltage phase angle, thus avoiding the reverse flow of active power into the power conversion device and ensuring the safe and stable operation of the power conversion device.

[0121] For a detailed implementation of S102, please refer to the above. Figures 3 to 15 The implementation method executed by the controller is not described in detail in this application embodiment.

[0122] In an optional implementation, the voltage phase angle of the inverter circuit output is controlled to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first time period, so that the active power output by the power conversion device to the grid remains greater than 0. Specifically, this includes: controlling the voltage phase angle of the inverter circuit output to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a second time period, so that the active power output by the power conversion device to the grid remains greater than or equal to the initial active power; the second time period is shorter than the first time period, and the initial active power is the magnitude of the active power output by the power conversion device when the voltage amplitude at the AC terminal is less than a first threshold.

[0123] Understandably, when the grid voltage recovers rapidly from a deep voltage drop, the voltage phase angle controlled by the power conversion device to control the inverter circuit switches from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a second time period, and this second time period is shorter than the first time period. This allows the voltage phase angle of the inverter circuit output to switch more quickly. At this time, because the time the voltage phase angle of the inverter circuit output lags behind the AC terminal voltage phase angle is short, the active power output by the power conversion device to the grid does not have enough time to decrease. Therefore, the active power output by the power conversion device can remain greater than or equal to the initial active power, thereby reducing fluctuations in the active power output of the power conversion device. Furthermore, reduced fluctuations in the active power output of the power conversion device can reduce the impact on grid power, thus shortening the time required for grid fault recovery, demonstrating strong applicability.

[0124] In an optional implementation, when the voltage phase angle of the inverter circuit output switches from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first or second duration, the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal is less than or equal to 90 degrees; the second duration is less than the first duration.

[0125] Understandably, because the power conversion device actively controls the voltage phase angle of the inverter circuit output to switch from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first or second time period, the voltage phase angle of the inverter circuit output can be switched quickly. This reduces the time that the inverter circuit output voltage phase angle lags behind the AC terminal voltage phase angle, ensuring that the difference between the current phase angle and the voltage phase angle at the AC terminal does not change significantly. Specifically, the absolute value of the difference between the current phase angle and the voltage phase angle at the AC terminal remains less than or equal to 90 degrees, making it highly applicable.

[0126] In an optional embodiment, the method further includes: after the voltage phase angle of the inverter circuit output changes from lagging behind the AC terminal to leading the AC terminal within a first time period or a second time period, adjusting the rate of change of the voltage phase angle of the inverter circuit output continuously; the second time period is shorter than the first time period.

[0127] It is understandable that after the voltage phase angle output by the inverter circuit switches from lagging behind the AC terminal to leading the AC terminal within the first or second time period, the power conversion device can continuously adjust the rate of change of the voltage phase angle output by the inverter circuit to make the voltage phase angle output by the inverter circuit transition smoothly, thereby reducing output power fluctuations and making it highly applicable.

[0128] In an optional embodiment, the method further includes: obtaining a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjusting the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller adjusts the rate of change of the voltage phase angle output by the inverter circuit to continuously change, specifically including: controlling the rate of change of the amplitude of the first voltage vector and the rate of change of the amplitude of the second voltage vector to be less than the rate of change threshold, so that the rate of change of the voltage phase angle output by the inverter circuit changes continuously.

[0129] It is understandable that when the power conversion device adjusts the output voltage of the inverter circuit based on the synchronous phase angle, the first voltage vector, and the second voltage vector, the angle of the composite voltage vector of the first and second voltage vectors is equal to the angle of the inverter circuit's output voltage phase angle after being transformed into the synchronous rotating coordinate system. Therefore, by adjusting the amplitudes of the first and second voltage vectors, the power conversion device can adjust the angle of the composite voltage vector in the synchronous rotating coordinate system, thereby adjusting the voltage phase angle of the inverter circuit's output. Furthermore, by adjusting the rate of change of the amplitudes of the first and second voltage vectors to be less than a rate of change threshold, the power conversion device makes the angle of the composite voltage vector change smoothly. At this time, the power conversion device controls the output voltage of the inverter circuit based on the composite voltage vector, and can adjust the rate of change of the inverter circuit's output voltage phase angle to change continuously, that is, the voltage phase angle of the inverter circuit's output smoothly transitions. The implementation principle of this embodiment is simple and its applicability is strong.

[0130] In an optional embodiment, the method further includes: obtaining a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjusting the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein, the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller controls the voltage phase angle output by the inverter circuit to switch from a voltage phase angle lagging behind the AC terminal to a voltage phase angle leading the AC terminal within a first time period, specifically including: adjusting the amplitude of the first voltage vector to gradually increase and the amplitude of the second voltage vector to gradually decrease, until the rate of change of the voltage amplitude at the AC terminal is less than or equal to a second threshold, or until the time length for adjusting the amplitude of the first voltage vector to gradually increase and the amplitude of the second voltage vector to gradually decrease is greater than or equal to a third time period, the third time period being greater than the first time period.

[0131] It is understandable that when a power conversion device adjusts the output voltage of an inverter circuit based on the synchronous phase angle, a first voltage vector, and a second voltage vector, the angle of the composite voltage vector formed by the first and second voltage vectors is equal to the angle of the inverter circuit's output voltage phase angle after being transformed into a synchronous rotating coordinate system. Therefore, by adjusting the magnitudes of the first and second voltage vectors, the power conversion device can adjust the angle of the composite voltage vector in the synchronous rotating coordinate system, thereby adjusting the voltage phase angle of the inverter circuit's output. For example, when the grid voltage recovers rapidly from a deep drop, the power conversion device gradually increases the magnitude of the first voltage vector and gradually decreases the magnitude of the second voltage vector, causing the composite voltage vector to rotate counterclockwise in the synchronous rotating coordinate system, thereby adjusting the inverter circuit's output voltage phase angle to lead. Furthermore, when the power conversion device detects that the rate of change of the AC voltage amplitude is less than or equal to the second threshold, the voltage phase angle output by the inverter circuit leads the voltage phase angle of the AC terminal. The power conversion device completes the adjustment process of switching the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal within a first or second time period, which is simple to implement. Alternatively, the power conversion device can complete the adjustment process of switching the voltage phase angle output by the inverter circuit to lead the voltage phase angle of the AC terminal when it detects that the amplitude of the first voltage vector gradually increases and the amplitude of the second voltage vector gradually decreases for a period of time greater than or equal to a third time period, thereby improving the fault tolerance of the adjustment process and making it more applicable.

[0132] In an optional embodiment, the method further includes: obtaining a synchronization phase angle, a first voltage vector, and a second voltage vector based on the output power and reference power of the power conversion device, and adjusting the output voltage of the inverter circuit based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein the first voltage vector is a voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is a voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; the controller controls the voltage phase angle output by the inverter circuit to switch from a voltage phase angle lagging behind the AC terminal to a voltage phase angle leading the AC terminal within a first time period, specifically including: adjusting the synchronization phase angle to increase until the rate of change of the voltage amplitude at the AC terminal is less than or equal to a second threshold, or until the time length for adjusting the synchronization phase angle to increase is greater than or equal to a third time period, the third time period being greater than the first time period.

[0133] It is understandable that when the power conversion device adjusts the output voltage of the inverter circuit based on the synchronous phase angle, the first voltage vector, and the second voltage vector, the angle of the composite voltage vector of the first and second voltage vectors is equal to the angle of the inverter circuit's output voltage phase angle after being transformed into the synchronous rotating coordinate system. Therefore, by adjusting the size of the synchronous phase angle, the power conversion device can adjust the angle of the composite voltage vector in the synchronous rotating coordinate system, thereby adjusting the output voltage phase angle of the inverter circuit. For example, when the grid voltage recovers rapidly from a deep drop, the power conversion device increases the synchronous phase angle, causing the composite voltage vector to rotate counterclockwise in the synchronous rotating coordinate system, thereby adjusting the output voltage phase angle of the inverter circuit to lead. Furthermore, when the power conversion device detects that the rate of change of the AC voltage amplitude is less than or equal to a second threshold, the output voltage phase angle of the inverter circuit leads the AC voltage phase angle. The power conversion device completes the adjustment process of switching the output voltage phase angle of the inverter circuit to lead the AC voltage phase angle within a first or second time period, which is simple to implement. Alternatively, the power conversion device can complete the adjustment process of switching the voltage phase angle of the inverter circuit output to lead the voltage phase angle of the AC terminal when the time length of the detected increase in the adjustment synchronization phase angle is greater than or equal to the third time length, so as to improve the fault tolerance of the adjustment process and have strong applicability.

[0134] In an optional implementation, the third duration is equal to 10 milliseconds.

[0135] It is understandable that when the duration of the adjustment of the amplitude of the first voltage vector gradually increasing and the amplitude of the second voltage vector gradually decreasing is greater than or equal to 10 milliseconds, the power conversion device completes the adjustment process of switching the voltage phase angle of the inverter circuit output to lead the voltage phase angle of the AC terminal within the first or second duration. The implementation method is simple and highly reliable.

[0136] In an alternative implementation, the first threshold is equal to the rated output voltage amplitude multiplied by 0.5.

[0137] Understandably, power conversion equipment can flexibly adjust the specific value of the first threshold according to the rated output voltage amplitude, making it suitable for a wide range of applications and with strong applicability.

[0138] In one alternative implementation, the second threshold satisfies:

[0139]

[0140] Where Vem is the rated output voltage amplitude, and t equals 1 millisecond.

[0141] Understandably, power conversion equipment can flexibly adjust the specific value of the second threshold according to the rated output voltage amplitude, making it suitable for a wide range of applications and with strong applicability.

[0142] In one alternative implementation, the first duration is positively correlated with the rated output power of the power conversion device, or the first duration ranges from 500 microseconds to 2 milliseconds.

[0143] Understandably, power conversion equipment can flexibly adjust the specific value of the first duration according to the rated output power of the power conversion equipment, making it suitable for a wide range of applications and with strong applicability.

[0144] In one optional implementation, the second duration is positively correlated with the rated output power of the power conversion device, or the value of the second duration ranges from 500 microseconds to 2 milliseconds; the second duration is less than the first duration.

[0145] Understandably, power conversion equipment can flexibly adjust the specific value of the first duration according to the rated output power of the power conversion equipment, making it suitable for a wide range of applications and with strong applicability.

Claims

1. A power conversion device, characterized in that, The DC terminal of the power conversion device is used to connect to a DC source, and the AC terminal of the power conversion device is used to connect to the power grid. The power conversion device includes an inverter circuit and a controller. The controller is used to control the inverter circuit to convert the DC power input at the DC terminal into AC power and output it to the AC terminal. The controller is also used to: When the voltage amplitude at the AC terminal is less than a first threshold, the voltage phase angle output by the inverter circuit is controlled to lead the voltage phase angle at the AC terminal, so that the active power output by the power conversion device to the power grid is greater than 0. When the voltage amplitude at the AC terminal increases from less than the first threshold, and the rate of change of the voltage amplitude at the AC terminal is greater than the second threshold, and the voltage phase angle output by the inverter circuit switches from leading the voltage phase angle at the AC terminal to lagging behind the voltage phase angle at the AC terminal, the voltage phase angle output by the inverter circuit is controlled to switch from lagging behind the voltage phase angle at the AC terminal to leading the voltage phase angle at the AC terminal within a first time period, so that the active power output by the power conversion device to the power grid remains greater than 0.

2. The power conversion device according to claim 1, characterized in that, The controller controls the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal to leading the AC terminal within a first time period, so that the active power output by the power conversion device to the grid remains greater than 0, specifically including: The voltage phase angle output by the inverter circuit is controlled to switch from lagging behind the voltage phase angle of the AC terminal to leading the voltage phase angle of the AC terminal within a second time period, so that the active power output by the power conversion device to the power grid remains greater than or equal to the initial active power; the second time period is shorter than the first time period, and the initial active power is the amount of active power output by the power conversion device when the voltage amplitude of the AC terminal is less than the first threshold.

3. The power conversion device according to claim 1 or 2, characterized in that, When the voltage phase angle output by the inverter circuit is controlled by the controller to switch from lagging behind the voltage phase angle of the AC terminal to leading the voltage phase angle of the AC terminal within the first duration or the second duration, the absolute value of the difference between the current phase angle and the voltage phase angle of the AC terminal is less than or equal to 90 degrees; the second duration is less than the first duration.

4. The power conversion device according to any one of claims 1 to 3, characterized in that, The controller is also used for: After the voltage phase angle output by the inverter circuit switches from lagging behind the AC terminal to leading the AC terminal within the first time period or the second time period, the rate of change of the voltage phase angle output by the inverter circuit is continuously adjusted; the second time period is shorter than the first time period.

5. The power conversion device according to claim 4, characterized in that, The controller is also used for: The synchronization phase angle, the first voltage vector, and the second voltage vector are obtained based on the output power and reference power of the power conversion device, and the output voltage of the inverter circuit is adjusted based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein, the first voltage vector is the voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is the voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; The controller continuously adjusts the rate of change of the voltage phase angle output by the inverter circuit, specifically including: The rate of change of the amplitude of the first voltage vector and the rate of change of the amplitude of the second voltage vector are controlled to be less than the rate of change threshold, so that the rate of change of the voltage phase angle output by the inverter circuit changes continuously.

6. The power conversion device according to any one of claims 1 to 5, characterized in that, The controller is also used for: The synchronization phase angle, the first voltage vector, and the second voltage vector are obtained based on the output power and reference power of the power conversion device, and the output voltage of the inverter circuit is adjusted based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein, the first voltage vector is the voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is the voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; The controller controls the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal to leading the AC terminal within the first time period, specifically including: The amplitude of the first voltage vector is gradually increased and the amplitude of the second voltage vector is gradually decreased until the rate of change of the voltage amplitude at the AC terminal is less than or equal to the second threshold, or until the duration of the time for which the amplitude of the first voltage vector is gradually increased and the amplitude of the second voltage vector is gradually decreased is greater than or equal to a third duration, wherein the third duration is greater than the first duration.

7. The power conversion device according to any one of claims 1 to 5, characterized in that, The controller is also used for: The synchronization phase angle, the first voltage vector, and the second voltage vector are obtained based on the output power and reference power of the power conversion device, and the output voltage of the inverter circuit is adjusted based on the synchronization phase angle, the first voltage vector, and the second voltage vector; wherein, the first voltage vector is the voltage vector on the d-axis of the synchronous rotating coordinate system, the second voltage vector is the voltage vector on the q-axis of the synchronous rotating coordinate system, and the synchronization phase angle is the angle between the synchronous rotating coordinate system and the stationary coordinate system; the angle of the combined voltage vector of the first voltage vector and the second voltage vector is the same as the angle of the voltage phase angle output by the inverter circuit after being converted to the synchronous rotating coordinate system; The controller controls the voltage phase angle output by the inverter circuit to switch from lagging behind the AC terminal to leading the AC terminal within the first time period, specifically including: The synchronization phase angle is increased until the rate of change of voltage amplitude at the AC terminal is less than or equal to the second threshold, or until the duration of the adjustment of the synchronization phase angle is greater than or equal to the third duration, wherein the third duration is greater than the first duration.

8. The power conversion device according to claim 6 or 7, characterized in that, The third duration is equal to 10 milliseconds.

9. The power conversion device according to any one of claims 1 to 8, characterized in that, The first threshold is equal to the rated output voltage amplitude multiplied by 0.

5.

10. The power conversion device according to any one of claims 1 to 9, characterized in that, The second threshold satisfies: Where Vem is the rated output voltage amplitude, and t equals 1 millisecond.

11. The power conversion device according to any one of claims 1 to 10, characterized in that, The first duration is positively correlated with the rated output power of the power conversion device, or the value of the first duration ranges from 500 microseconds to 2 milliseconds.

12. The power conversion device according to any one of claims 2 to 11, characterized in that, The second duration is positively correlated with the rated output power of the power conversion device, or the value of the second duration is in the range of 500 microseconds to 2 milliseconds; the second duration is less than the first duration.

13. A control method for a power conversion device, the method being applied to the power conversion device, wherein the DC terminal of the power conversion device is used to connect to a DC source, the AC terminal of the power conversion device is used to connect to a power grid, the power conversion device includes an inverter circuit and a controller, the controller being used to control the inverter circuit to convert the DC power input at the DC terminal into AC power and output it to the AC terminal, characterized in that, The method includes: When the voltage amplitude at the AC terminal is less than a first threshold, the voltage phase angle output by the inverter circuit is controlled to lead the voltage phase angle at the AC terminal, so that the active power output by the power conversion device to the power grid is greater than 0. When the voltage amplitude at the AC terminal increases from less than the first threshold, and the rate of change of the voltage amplitude at the AC terminal is greater than the second threshold, and the voltage phase angle output by the inverter circuit switches from leading the voltage phase angle at the AC terminal to lagging behind the voltage phase angle at the AC terminal, the voltage phase angle output by the inverter circuit is controlled to switch from lagging behind the voltage phase angle at the AC terminal to leading the voltage phase angle at the AC terminal within a first time period, so that the active power output by the power conversion device to the power grid remains greater than 0.

14. The method according to claim 13, characterized in that, The control of the voltage phase angle output by the inverter circuit switches from lagging behind the AC terminal voltage phase angle to leading the AC terminal voltage phase angle within a first time period, so that the active power output by the power conversion device to the grid remains greater than 0, specifically including: The voltage phase angle output by the inverter circuit is controlled to switch from lagging behind the voltage phase angle of the AC terminal to leading the voltage phase angle of the AC terminal within a second time period, so that the active power output by the power conversion device to the power grid remains greater than or equal to the initial active power; the second time period is shorter than the first time period, and the initial active power is the amount of active power output by the power conversion device when the voltage amplitude of the AC terminal is less than the first threshold.

15. The method according to claim 13 or 14, characterized in that, When the voltage phase angle output by the inverter circuit switches from lagging behind the voltage phase angle of the AC terminal to leading the voltage phase angle of the AC terminal within the first duration or the second duration, the absolute value of the difference between the current phase angle and the voltage phase angle of the AC terminal is less than or equal to 90 degrees; the second duration is less than the first duration.

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