Current sharing control method of power conversion device and power converter

Abstract

The invention relates to a current-sharing control method of a power conversion device and a power converter. The current-sharing control method comprises the following steps: acquiring current average apparent power of a plurality of power converters connected in parallel, and instantaneous current, instantaneous voltage and instantaneous angular frequency of a first power converter; determining composite virtual impedance according to the current average apparent power; generating a DQ-axis voltage regulation signal based on the composite virtual impedance, the instantaneous current DQ-axis component and the instantaneous voltage angular frequency; and generating an output driving signal according to the DQ-axis voltage regulation signal, the instantaneous voltage DQ-axis component, the instantaneous current DQ-axis component and a preset voltage reference value. The respective composite virtual impedance of the parallel power converters of the parallel operation system is adjusted through the current average apparent power of each power converter, and the corresponding reactance in the output impedance of the power converters is offset, so that the output impedance of the power converters is closer to the resistance, and each load section meets the industrial standard current-sharing degree.

Description

Technical Field

[0001] This application belongs to the field of power electronics technology, and in particular relates to a current sharing control method for a power conversion device, a power converter, and a power converter parallel system. Background Technology

[0002] The current sharing characteristics of parallel inverters have a significant impact on the system's overload capacity and overall efficiency (circulating current). Current imbalance between inverters reduces system stability and lifespan. In some scenarios, the current imbalance across the entire load range for parallel inverters must be less than 5%. Droop control, as a typical example of current sharing without communication, is widely used due to its simplicity and ease of use. Depending on the inverter's output line impedance, droop control can be divided into inductive droop control and resistive droop control. Commonly used low-voltage microgrid inverters have a much higher resistive output impedance than inductive inverters, therefore resistive droop control is often used for current sharing.

[0003] However, since the actual impedance of an inverter is not entirely resistive but contains some inductive properties, and this inductive property changes with the load size, it is difficult to guarantee that parallel inverters will meet the current sharing requirements under full load range and various load scenarios by relying solely on traditional resistive droop. Summary of the Invention

[0004] The purpose of this application is to provide a current sharing control method, a power converter, and a power converter parallel system, which aims to solve the problem that the parallel output of inverters cannot meet the current sharing requirements under traditional resistive droop control.

[0005] In a first aspect, embodiments of this application provide a current sharing control method for a power converter, applied to a first power converter among multiple power converters connected in parallel, the method comprising:

[0006] Obtain the current average apparent power of the plurality of parallel power converters, the instantaneous output current, the instantaneous output voltage, and the instantaneous voltage angular frequency of the first power converter;

[0007] The instantaneous current DQ-axis component and the instantaneous voltage DQ-axis component are obtained based on the instantaneous output current and the instantaneous output voltage;

[0008] The composite virtual impedance is determined based on the current average apparent power.

[0009] A DQ-axis voltage adjustment signal is generated based on the composite virtual impedance, the instantaneous current DQ-axis component, and the instantaneous voltage angular frequency;

[0010] An output drive signal is generated based on the DQ-axis voltage adjustment signal, the instantaneous voltage DQ-axis component, the instantaneous current DQ-axis component, and a preset voltage reference value. The drive signal is used to drive the power converter to output AC power.

[0011] In some embodiments, determining the composite virtual impedance based on the current average apparent power includes:

[0012] The composite virtual impedance is determined based on the mapping relationship between the current average apparent power, the load power of the first power converter, and the composite virtual impedance; wherein, in the mapping relationship, the composite virtual impedance is negatively correlated with the load power.

[0013] In some embodiments, the composite virtual impedance includes a virtual resistive impedance and a virtual inductive impedance, and the step of compositing the virtual impedance according to the current average apparent power includes:

[0014] The modulation range of the virtual resistive impedance and the modulation range of the virtual inductive impedance are determined based on the mapping relationship between the load power of the first power converter and the composite virtual impedance; wherein, within the modulation range of the virtual resistive impedance, the virtual resistive impedance is negatively correlated with the load power, and within the modulation range of the virtual inductive impedance, the virtual inductive impedance is negatively correlated with the load power.

[0015] In some embodiments, determining the modulation range of the virtual resistive impedance and the modulation range of the virtual inductive impedance based on the mapping relationship between the load power of the first power converter and the composite virtual impedance includes:

[0016] Based on the mapping relationship, the upper limit values ​​of the virtual resistive impedance and the virtual inductive impedance are determined when the first power converter is unloaded.

[0017] Based on the mapping relationship, the lower limit values ​​of the virtual resistive impedance and the virtual inductive impedance are determined when the first power converter is fully loaded.

[0018] The amplitude adjustment range of the virtual resistive impedance is determined based on the upper and lower limits of the virtual resistive impedance, and the amplitude adjustment range of the virtual inductive impedance is determined based on the upper and lower limits of the virtual inductive impedance.

[0019] In some embodiments, determining the composite virtual impedance based on the current average apparent power includes:

[0020] When the current average apparent power is greater than the first preset power, the virtual resistive impedance in the composite virtual impedance is determined to be the lower limit value within the amplitude adjustment range of the virtual resistive impedance, and the virtual inductive impedance in the composite virtual impedance is determined to be the lower limit value within the amplitude adjustment range of the virtual inductive impedance.

[0021] When the current average apparent power is less than the second preset power, the virtual resistive impedance in the composite virtual impedance is determined to be the upper limit value within the amplitude adjustment range of the virtual resistive impedance, and the virtual inductive impedance in the composite virtual impedance is determined to be the upper limit value within the amplitude adjustment range of the virtual inductive impedance.

[0022] When the current average apparent power is not less than the second preset power and not greater than the first preset power, the virtual resistive impedance and the virtual inductive impedance in the composite virtual impedance are negatively correlated with the current average apparent power.

[0023] In some embodiments, the instantaneous current DQ-axis component includes an instantaneous current D-axis component and an instantaneous current Q-axis component, the composite virtual impedance includes a virtual resistive impedance and a virtual inductive impedance, and the generation of a DQ-axis voltage adjustment signal based on the composite virtual impedance, the instantaneous current DQ-axis component, and the instantaneous voltage angular frequency includes:

[0024] The first D-axis voltage adjustment is generated based on the virtual resistive impedance and the instantaneous current D-axis component;

[0025] The second D-axis voltage adjustment is generated based on the virtual inductive impedance, the instantaneous current Q-axis component, and the instantaneous voltage angular frequency.

[0026] A first Q-axis voltage adjustment is generated based on the virtual resistive impedance and the instantaneous current Q-axis component;

[0027] The second Q-axis voltage adjustment is generated based on the virtual inductive impedance, the D-axis component of the instantaneous current, and the angular frequency of the instantaneous voltage.

[0028] In some embodiments, the instantaneous voltage DQ-axis component includes an instantaneous voltage D-axis component and an instantaneous voltage Q-axis component, the preset voltage reference value includes a Q-axis voltage reference value and a D-axis voltage reference value based on a droop control strategy, and the step of generating an output drive signal based on the DQ-axis voltage adjustment signal, the instantaneous voltage DQ-axis component, the instantaneous current DQ-axis component, and the preset voltage reference value includes:

[0029] A D-axis modulation voltage is generated based on the first D-axis voltage adjustment amount, the second D-axis voltage adjustment amount, the instantaneous voltage D-axis component, the instantaneous current D-axis component, and the D-axis voltage reference value;

[0030] The Q-axis modulation voltage is generated based on the first Q-axis voltage adjustment, the second Q-axis voltage adjustment, the instantaneous voltage Q-axis component, the instantaneous current Q-axis component, and the Q-axis voltage reference value;

[0031] The drive signal is generated based on the D-axis modulation voltage and the Q-axis modulation voltage.

[0032] In some embodiments, the D-axis voltage reference value determined based on the droop control strategy includes:

[0033] The reference value of the D-axis voltage is obtained based on the droop voltage and the rated output voltage determined by the droop control strategy.

[0034] Secondly, embodiments of this application also provide a power converter, the power converter including a power conversion circuit and a controller connected to the power conversion circuit; wherein, the controller is used to execute the current sharing control method of the power conversion device as described above when the power converter is connected in parallel with other power converters.

[0035] Thirdly, embodiments of this application also provide a power converter parallel system, including multiple power converters connected in parallel, each of the power converters including a power conversion circuit and a controller connected to the power conversion circuit, wherein the controller is used to execute the current sharing control method of the power conversion device as described above.

[0036] The beneficial effects of this application embodiment compared with related technologies are as follows: The current sharing control method of the power conversion device obtains the current average apparent power of multiple parallel power converters, the instantaneous output current, instantaneous output voltage, and instantaneous voltage angular frequency of the first power converter; obtains the instantaneous voltage DQ-axis component and the instantaneous current DQ-axis component based on the instantaneous output current and instantaneous output voltage; determines the composite virtual impedance based on the current average apparent power; generates a DQ-axis voltage adjustment signal based on the composite virtual impedance, the instantaneous current DQ-axis component, and the instantaneous voltage angular frequency; and generates an output drive signal based on the DQ-axis voltage adjustment signal, the instantaneous voltage DQ-axis component, the instantaneous current DQ-axis component, and a preset voltage reference value. The drive signal is used to drive the power converter to output AC power. By adjusting the composite virtual impedance of each power converter in the parallel system according to the current average apparent power of each power converter, the corresponding reactance in the output impedance of the power converter is canceled out, making the output impedance of the power converter closer to resistive, and ultimately enabling the parallel power converter to meet industry standard current sharing requirements in various load scenarios and load segments. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the equivalent circuit of a power converter parallel system.

[0038] Figure 2A flowchart of a current sharing control method for a power converter provided in an embodiment of this application.

[0039] Figure 3 A graph showing the mapping relationship between load power and virtual resistive impedance of a power converter provided in an embodiment of this application.

[0040] Figure 4 A graph showing the mapping relationship between load power and virtual inductive impedance of a power converter provided in an embodiment of this application.

[0041] Figure 5 The control loop diagram is provided for a current sharing control method of a power converter according to an embodiment of this application.

[0042] Figure 6 A flowchart of a current sharing control method for a power converter provided in an embodiment of this application.

[0043] Figure 7 This is a schematic diagram of a relay detection device provided in one embodiment of this application.

[0044] Figure 8 This is a schematic diagram of the structure of a power converter parallel system provided in an embodiment of this application.

[0045] Figure 9 This is a schematic diagram of the structure of a power converter provided in an embodiment of this application. Detailed Implementation

[0046] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0047] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0048] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0049] Please see Figure 1 , Figure 1The equivalent circuit of two inverters (or power converters) connected in parallel is shown. Here, U∠0° represents the voltage amplitude and phase at the parallel load terminals of the two inverters, and Z_load is the parallel load impedance of the two inverters. U1 and U2 represent the amplitudes of the output voltages of the two inverters, respectively. These represent the phase difference between the output voltages of the two inverters and the parallel load terminals, respectively. R1, L1 and R2, L2 represent the resistive and inductive components of the output impedances of the two inverters, respectively. ω represents the angular frequency of the voltage. θ1 and θ2 represent the output impedance angles of the two inverters, respectively.

[0050] Among them, the active power P output by the inverter i and Q i As shown in equations (1) and (2) respectively.

[0051]

[0052] For resistive droop R>>L, Approaching 0, therefore we have Equations (1) and (2) can be simplified to equations (3) and (4), that is, active power ∝ inverter output voltage amplitude, and reactive power ∝ inverter output voltage phase.

[0053]

[0054] However, since the actual output impedance of an inverter is not entirely resistive but contains some inductive impedance, and this inductance varies with the load size, it is difficult to guarantee that parallel inverters will meet the industry's current sharing requirements across the entire load range and various load scenarios by relying solely on traditional resistive droop control.

[0055] Please see Figure 2 To address the aforementioned problems, one embodiment of this application provides a current sharing control method for a power converter, applied to a first power converter in a plurality of parallel-connected power converters, wherein the first power converter is any one of the plurality of parallel-connected power converters. In this embodiment, the current sharing control method includes:

[0056] Step S110: Obtain the current average apparent power of multiple parallel power converters, the instantaneous output current, instantaneous output voltage, and instantaneous voltage angular frequency of the first power converter.

[0057] In a parallel power converter configuration, one can be configured as the master and the others as slaves. The master can then acquire the current apparent power of each power converter, calculate the current average apparent power, and subsequently distribute the average apparent power to each slave. Alternatively, a single current sharing controller can be configured for the parallel power converters. This controller can acquire the current apparent power of each power converter, calculate the current average apparent power, and then distribute the average apparent power to each power converter.

[0058] The instantaneous output current, instantaneous output voltage, and instantaneous voltage angular frequency of the first power converter (or power converter) can be obtained by the first power converter itself, or they can be obtained by the host or current sharing controller mentioned above and sent to the first power converter.

[0059] Step S120: Obtain the instantaneous current DQ-axis component and the instantaneous voltage DQ-axis component based on the instantaneous output current and instantaneous output voltage.

[0060] The instantaneous output current is obtained by Clarke-Park transformation to obtain the instantaneous current DQ-axis component, and the instantaneous output voltage is obtained by Clarke-Park transformation to obtain the instantaneous voltage DQ-axis component.

[0061] Step S130: Determine the composite virtual impedance based on the current average apparent power.

[0062] Among them, impedance includes one or more of resistive impedance (R), inductive impedance (L) and capacitive impedance (C); composite virtual impedance includes one or more of virtual resistive impedance, virtual inductive impedance and virtual capacitive impedance.

[0063] Based on the effect of DC bias (i.e., the DC component of the inductive reactance current) on inductance: the fixed magnetic field generated by the DC bias current will cause the magnetic material to approach or enter a saturation state, resulting in a decrease in permeability and thus a decrease in inductance. Although the attenuation characteristics of different inductors (core material, inductor type, manufacturing process) vary, the inductance and the effective value of the current still have an approximately linear attenuation relationship, that is, as the effective value of the current increases, the inductance decreases approximately linearly. Therefore, an increase in the effective value of the current means an increase in the current average apparent power of the parallel power converter. This characteristic can be used to configure a composite virtual impedance to improve the reliability of the droop algorithm.

[0064] In various load scenarios and load segments of power converters, under light load scenarios (i.e., when the average apparent power of the parallel power converters is low), the output current of the power converters is small, the proportion of circulating current in the load current increases, and the influence of circulating current becomes greater. Externally, this manifests as a worse current sharing effect for the parallel power converters under lighter loads. Under heavy load scenarios (i.e., when the average apparent power of the parallel power converters is high), the output current of the power converters is large, the proportion of circulating current in the load current decreases, and the influence of circulating current becomes smaller. Externally, this manifests as a better current sharing effect for the parallel power converters under heavier loads. Therefore, based on this principle, a composite virtual impedance can be adaptively configured according to the average apparent power of the parallel power converters to improve the current sharing effect under various load scenarios and load segments. For example, as the average apparent power of the parallel power converters increases, the composite virtual impedance gradually decreases; conversely, the composite virtual impedance increases.

[0065] Step S140: Generate a DQ-axis voltage adjustment signal based on the composite virtual impedance, the instantaneous current DQ-axis component, and the instantaneous voltage angular frequency.

[0066] In some cases, the output impedance of the power converter is not completely resistive, requiring optimization of the current sharing characteristics. Therefore, a composite virtual impedance is introduced into the control loop to cancel out the corresponding reactance (including inductive and / or capacitive impedance) in the output impedance of the power converter, making the output impedance of the power converter closer to resistive, and the current sharing characteristics closer to active frequency regulation and reactive amplitude regulation, thereby improving the dynamic and steady-state current sharing capabilities of the system.

[0067] Step S150: Generate an output drive signal based on the DQ axis voltage adjustment signal, the instantaneous voltage DQ axis component, the instantaneous current DQ axis component, and the preset voltage reference value. The drive signal is used to drive the power converter to output AC power.

[0068] In the droop control loop of the power converter, based on the preset voltage reference value, the instantaneous voltage DQ axis component, and the instantaneous current DQ axis component, the output voltage of the power converter is adjusted by the DQ axis voltage adjustment signal based on the composite virtual impedance. By controlling the output voltage through the composite virtual impedance, the current sharing characteristics of the parallel power converter are made closer to active frequency regulation and reactive amplitude regulation.

[0069] The purpose of adding a composite virtual impedance is to adaptively adjust the resistive and / or inductive components of the power converter's output impedance. This prevents deviations in output impedance calculations caused by sampling errors, sampling interference, or other factors. Adjusting the composite virtual impedance further emphasizes the resistive impedance component, making the output impedance closer to resistive characteristics. This effectively improves the reliability of the resistive droop algorithm based on line impedance, ensuring that the parallel power converter meets industry-standard current sharing requirements across various load scenarios and load segments. Furthermore, appropriately adding a virtual resistive impedance to the adaptively adjusted output impedance of the power converter can effectively improve the reliability of the droop algorithm, thereby enhancing the system's dynamic and steady-state current sharing capabilities.

[0070] In some embodiments, step S130 includes: determining the composite virtual impedance based on the current average apparent power and the mapping relationship between the load power of the first power converter and the composite virtual impedance; wherein, in the mapping relationship, the composite virtual impedance is negatively correlated with the load power.

[0071] Based on the above analysis, and considering the negative correlation between the composite virtual impedance and load power, the magnitude of the composite virtual impedance can be configured for various load scenarios and load segments of the first power converter, thus forming this mapping relationship. Therefore, when performing current sharing control using the droop control loop, the current composite virtual impedance can be configured according to the current average apparent power within this mapping relationship. It can be understood that the current average apparent power corresponds to the load power in the mapping relationship; in this relationship, the load power can be directly taken as the current average apparent power to determine the current composite virtual impedance. The goal is to cancel out the corresponding reactance in the output impedance of the first power converter, making the output impedance of the first power converter closer to resistive characteristics, and the current sharing characteristics closer to active power frequency regulation and reactive power amplitude regulation. Simultaneously, by adding the corresponding virtual impedance, the dynamic and steady-state current sharing capabilities of the system are improved.

[0072] In some embodiments, the composite virtual impedance includes virtual resistive impedance and virtual inductive impedance. Before step S130, the following steps are included:

[0073] The modulation range of the virtual resistive impedance and the modulation range of the virtual inductive impedance are determined based on the mapping relationship between the load power and the composite virtual impedance of the first power converter. Among them, in the modulation range of the virtual resistive impedance, the virtual resistive impedance is negatively correlated with the load power, and in the modulation range of the virtual inductive impedance, the virtual inductive impedance is negatively correlated with the load power.

[0074] Please see Figure 3 and Figure 4 S ratedThis represents the rated apparent power of the first power converter. In some embodiments, the upper limit value R0 of the virtual resistive impedance, the upper limit value L0 of the virtual inductive impedance, the lower limit value R1 of the virtual resistive impedance, and the lower limit value L1 of the virtual inductive impedance can typically be determined through simulation calculations. These values ​​are then fine-tuned based on actual testing to form the modulation ranges for the virtual resistive and inductive impedances. When the parallel power converters are initially in operation (no load), i.e., the load power is very small, the composite virtual impedances are the upper limit values ​​R0 and L0 of the virtual resistive impedance, respectively. As the load power gradually increases, the virtual resistive and inductive impedances gradually decrease, eventually decreasing to the lower limit values ​​R1 and L1 of the virtual resistive and inductive impedances under full load.

[0075] In some embodiments, determining the modulation range of the virtual impedance and the modulation range of the virtual inductive impedance based on the mapping relationship between the load power of the first power converter and the virtual impedance includes:

[0076] Based on the mapping relationship, the upper limits of the virtual resistive impedance and the virtual inductive impedance are determined when the first power converter is unloaded. For example, when the output of the first power converter is at 10% of its rated power, the corresponding values ​​of the virtual resistive impedance and the virtual inductive impedance are the upper limit value R0 of the virtual resistive impedance and the upper limit value L0 of the virtual inductive impedance, respectively.

[0077] Based on the mapping relationship, the lower limits of the virtual resistive impedance and the virtual inductive impedance are determined when the first power converter is fully loaded. For example, when the output of the first power converter is at its rated power, the corresponding values ​​of the virtual resistive impedance and the virtual inductive impedance are the lower limit value R1 of the virtual resistive impedance and the lower limit value L1 of the virtual inductive impedance, respectively.

[0078] The amplitude adjustment range of the virtual resistive impedance is determined based on the upper limit R0 and lower limit R1 of the virtual resistive impedance, and the amplitude adjustment range of the virtual inductive impedance is determined based on the upper limit L0 and lower limit L1 of the virtual inductive impedance.

[0079] in, Figure 3 and Figure 4 The virtual impedance curve shown is merely an example of one scenario. Due to differences in the output characteristics and control parameters of power converters, the rate of change of the virtual impedance curve is not perfectly linear. In practical applications, under the condition that the uneven current distribution across the full load range of the parallel power converters meets industry requirements, the rate of change of the virtual impedance curve can exhibit different characteristics, requiring adaptive adjustment of the values ​​of virtual resistive impedance and virtual inductive impedance.

[0080] In some embodiments, determining the composite virtual impedance based on the current average apparent power includes:

[0081] When the current average apparent power is greater than the first preset power, the virtual resistive impedance in the composite virtual impedance is determined to be the lower limit value R1 within the amplitude adjustment range of the virtual resistive impedance, and the virtual inductive impedance in the composite virtual impedance is determined to be the lower limit value L1 within the amplitude adjustment range of the virtual inductive impedance. (Refer to...) Figure 3 and Figure 4 For example, the first preset power can be the rated power of the first power converter.

[0082] When the current average apparent power is less than the second preset power, the virtual resistive impedance in the composite virtual impedance is determined to be the upper limit value R0 within the amplitude adjustment range of the virtual resistive impedance, and the virtual inductive impedance in the composite virtual impedance is determined to be the upper limit value L0 within the amplitude adjustment range of the virtual inductive impedance. (Refer to...) Figure 3 and Figure 4 For example, the value of the second preset power can be 5% to 20% of the rated power of the first power converter, with a typical value of 10% of the rated power.

[0083] When the current average apparent power is not less than the second preset power and not greater than the first preset power, the virtual resistive impedance and virtual inductive impedance in the composite virtual impedance are negatively correlated with the current average apparent power. During droop control, the virtual resistive impedance and virtual inductive impedance can be set according to the preset mapping relationship in various load scenarios and load segments of the power converter, thereby canceling the corresponding reactance in the output impedance of the first power converter, making the output impedance of the first power converter closer to resistive, and the current sharing characteristics closer to active frequency regulation and reactive amplitude regulation, improving the dynamic and steady-state current sharing capabilities of the system.

[0084] In some embodiments, the instantaneous current DQ-axis component includes the instantaneous current D-axis component and the instantaneous current Q-axis component, and the composite virtual impedance includes virtual resistive impedance and virtual inductive impedance. Step S140 includes:

[0085] Please see Figure 5 The first D-axis voltage regulation is generated based on the virtual resistive impedance and the D-axis component of the instantaneous current. For example, the first D-axis voltage regulation is defined as Id_reaf·R, where Id_reaf is the D-axis component of the instantaneous current and R is the virtual resistive impedance. Adding a virtual resistive impedance to the D-axis voltage control loop effectively improves the reliability of the droop algorithm, reduces or even eliminates the voltage amplitude difference between parallel power converters, thereby achieving high-precision power allocation among parallel power converters and suppressing circulating current. This enhances the system's dynamic and steady-state current sharing capabilities, reduces the impact of multiple power converters in parallel on system stability, and provides a reference for the operation demonstration of large-scale renewable energy systems.

[0086] The second D-axis voltage regulation is generated based on the virtual inductive impedance, the Q-axis component of the instantaneous current, and the instantaneous voltage angular frequency. For example, the second D-axis voltage regulation is calculated as -Iq_reaf·ωL, where Iq_reaf is the Q-axis component of the instantaneous current, ω is the instantaneous voltage angular frequency, and L is the virtual inductive impedance. By influencing the D-axis voltage control through the Q-axis current and incorporating the virtual inductive impedance, the corresponding reactance in the output impedance of the first power converter is offset, making the active power control in the droop control closer to resistive characteristics. This effectively improves the reliability of the droop algorithm, ensuring that the parallel power converter meets industry-standard current sharing requirements in various load scenarios and load segments.

[0087] The first Q-axis voltage regulation is generated based on the virtual resistive impedance and the instantaneous current Q-axis component. For example, the first Q-axis voltage regulation is given by Iq_reaf·R, where Iq_reaf is the instantaneous current Q-axis component. By adding a virtual resistive impedance to the Q-axis voltage control loop, the reliability of the resistive droop algorithm based on line impedance can be effectively improved, reducing or even eliminating the phase difference between the voltages of parallel power converters. This achieves high-precision power allocation among parallel power converters and suppresses circulating current, reducing the impact on system stability when multiple power converters are connected in parallel. This provides a reference for the operation demonstration of large-scale renewable energy systems.

[0088] The second Q-axis voltage regulation is generated based on the virtual inductive impedance, the D-axis component of the instantaneous current, and the instantaneous voltage angular frequency. For example, the second Q-axis voltage regulation is equal to Id_reaf·ωL. By influencing the Q-axis voltage control through the D-axis current and adding the virtual inductive impedance, the corresponding reactance in the output impedance of the first power converter is offset, making the reactive power control in the droop control closer to resistive characteristics. This effectively improves the reliability of the droop algorithm, ensuring that the parallel power converter meets industry-standard current sharing requirements in various load scenarios and load segments.

[0089] The instantaneous voltage DQ-axis components include the instantaneous voltage D-axis component Vd_real and the instantaneous voltage Q-axis component Vd_real. Preset voltage reference values ​​include the Q-axis voltage reference value Vq_ref and the D-axis voltage reference value Vd_ref determined based on a droop control strategy. In some embodiments, the Q-axis voltage reference value Vq_ref is generally set to 0, with the goal of controlling the reactive power output of the power converter to be 0. The D-axis voltage reference value Vd_ref is the target D-axis voltage value assigned to each power converter based on the droop control strategy, corresponding to the target output voltage value of the power converter, achieving high-precision power allocation.

[0090] Please see Figure 6 In some embodiments, step S150 includes:

[0091] Step S151: Generate D-axis modulation voltage based on the first D-axis voltage adjustment amount, the second D-axis voltage adjustment amount, the instantaneous voltage D-axis component Vd_real, the instantaneous current D-axis component Id_real, and the D-axis voltage reference value Vd_ref.

[0092] Specifically, the first D-axis voltage adjustment amount and the second D-axis voltage adjustment amount are summed to obtain the D-axis voltage adjustment amount. Then, the difference between the sum of the D-axis voltage adjustment amounts and the D-axis voltage reference value Vd_ref is obtained to obtain the D-axis target voltage reference value. Then, the difference between the D-axis target voltage reference value and the instantaneous voltage D-axis component Vd_real is obtained to obtain the D-axis voltage deviation value. The first PI controller performs deviation calculation on the D-axis voltage deviation value to obtain the D-axis current reference value. The second PI controller performs deviation calculation on the difference between the D-axis current reference value and the instantaneous current D-axis component Id_real to obtain the D-axis modulation voltage.

[0093] Step S152: Generate the Q-axis modulation voltage based on the first Q-axis voltage adjustment amount, the second Q-axis voltage adjustment amount, the instantaneous voltage Q-axis component Vq_real, the instantaneous current Q-axis component Iq_real, and the Q-axis voltage reference value Vq_ref.

[0094] Specifically, the first and second Q-axis voltage regulation values ​​are summed to obtain the Q-axis voltage regulation value. The difference between the Q-axis voltage regulation value and the Q-axis voltage reference value Vq_ref is then calculated to obtain the Q-axis target voltage reference value. The difference between the Q-axis target voltage reference value and the instantaneous voltage Q-axis component Vq_real is then calculated to obtain the Q-axis voltage deviation value. The deviation value of the Q-axis voltage is then calculated by the third PI controller to obtain the Q-axis current reference value. Finally, the difference between the Q-axis current reference value and the instantaneous current Q-axis component Iq_real is calculated by the fourth PI controller to obtain the Q-axis modulation voltage.

[0095] Step S153: Generate a drive signal based on the D-axis modulation voltage and the Q-axis modulation voltage.

[0096] Specifically, the α-axis voltage and β-axis voltage are obtained by performing Park inverse transformation on the D-axis and Q-axis modulation voltages. The PWM controller can calculate the given active power and droop coefficient of each phase live wire based on the α-axis and β-axis voltages of the power converter, as well as the output of the power converter. Then, it modulates (e.g., sinusoidal pulse width modulation, SPWM) to obtain a three-phase modulation wave as the driving signal, thereby driving the current sharing output of each power converter.

[0097] In some embodiments, the D-axis voltage reference value determined based on the droop control strategy includes:

[0098] The D-axis voltage reference value Vd_ref is obtained based on the droop voltage Vd_droop determined by the droop control strategy and the rated output voltage V0_ref. The rated output voltage V0_ref is, for example, 220V. The droop coefficient includes the phase angle droop coefficient and the voltage droop coefficient.

[0099] Specifically, in some embodiments, the D-axis voltage reference value Vd_ref can be obtained based on the phase droop coefficient, voltage droop coefficient, instantaneous output current, instantaneous output voltage, instantaneous voltage angular frequency, and rated output voltage V0_ref of the first power converter.

[0100] In other embodiments, the droop voltage Vd_droop can be obtained directly from the voltage droop coefficient and the instantaneous active power, and the D-axis voltage reference value Vd_ref can be obtained by summing it with the rated output voltage V0_ref.

[0101] In some embodiments, the D-axis voltage reference value Vd_ref is obtained based on the phase droop coefficient, voltage droop coefficient, instantaneous output current, instantaneous output voltage, instantaneous voltage angular frequency, and rated output voltage V0_ref of the power converter, including:

[0102] Step S11: Determine the given active power and given reactive power of the first power converter based on the phase angle droop coefficient and voltage droop coefficient of the first power converter.

[0103] Step S12: Obtain the actual active power and actual reactive power of the first power converter based on the instantaneous output current, instantaneous output voltage and instantaneous voltage angular frequency of the power converter.

[0104] Step S13: Obtain the voltage amplitude setpoint based on the actual active power, the given active power, and the rated output voltage V0_ref of the power converter. Use a PI controller to perform deviation calculation on the difference between the actual active power and the given active power to obtain the total voltage amplitude regulation, i.e., the droop voltage Vd_droop. Then, sum the total voltage amplitude regulation with the three-phase rated total voltage to obtain the voltage amplitude setpoint. The given active power can be determined by averaging the active power of multiple parallel power converters.

[0105] Step S14: Obtain the voltage phase angle setpoint based on the actual reactive power, the given reactive power, and the rated output frequency of the power converter. Specifically, a PI controller is used to calculate the deviation between the actual reactive power and the given reactive power to obtain the frequency adjustment. Then, the frequency adjustment is summed with the three-phase rated frequency to obtain the voltage phase angle setpoint. The given reactive power can be determined by averaging the reactive power of multiple parallel power converters.

[0106] Step S15: Obtain the D-axis voltage reference value Vd_ref and the Q-axis voltage reference value based on the given voltage amplitude and voltage phase angle. Specifically, the D-axis voltage reference value Vd_ref and the Q-axis voltage reference value are obtained through coordinate transformation from a three-phase stationary coordinate system to a two-phase stationary coordinate system.

[0107] In some embodiments, the D-axis voltage reference value determined based on the droop control strategy includes:

[0108] The D-axis voltage reference value Vd_ref is calculated based on the droop voltage Vd_droop, voltage amplitude compensation value Vd_comp, and rated output voltage V0_ref determined by the droop control strategy. The voltage amplitude compensation value Vd_comp compensates for the value subtracted from the power converter's output due to droop control and virtual impedance, preventing the output voltage from deviating too much from the original setpoint after current sharing control. In some cases, the droop voltage Vd_droop and voltage amplitude compensation value Vd_comp are between 20V and 30V.

[0109] The embodiments of this application adapt to virtual impedance by using the current average apparent power, which can cover various load types (R, RCD, L, C, half-wave, etc.) and ensure that the uneven current distribution of the power converter parallel system meets industry requirements across the entire load range of various loads.

[0110] Please see Figure 7 This application embodiment also provides a current sharing control device for a power converter, used to control a first power converter among multiple parallel power converters. The current sharing control device includes:

[0111] The acquisition module 601 is used to acquire the current average apparent power of the plurality of parallel power converters, the instantaneous output current, the instantaneous output voltage and the instantaneous voltage angular frequency of the first power converter;

[0112] The control module 602 is configured to obtain the instantaneous current DQ-axis component and the instantaneous voltage DQ-axis component based on the instantaneous output current and the instantaneous output voltage; determine the composite virtual impedance based on the current average apparent power; generate a DQ-axis voltage adjustment signal based on the composite virtual impedance, the instantaneous current DQ-axis component, and the instantaneous voltage angular frequency; and generate an output drive signal based on the DQ-axis voltage adjustment signal, the instantaneous voltage DQ-axis component, the instantaneous current DQ-axis component, and a preset voltage reference value. The drive signal is used to drive the power converter to output AC power.

[0113] In some embodiments, the control module 602 is further configured to:

[0114] The composite virtual impedance is determined based on the mapping relationship between the current average apparent power, the load power of the first power converter, and the composite virtual impedance; wherein, in the mapping relationship, the composite virtual impedance is negatively correlated with the load power.

[0115] In some embodiments, the control module 602 is further configured to determine the amplitude adjustment range of the virtual resistive impedance and the amplitude adjustment range of the virtual inductive impedance based on the mapping relationship between the load power of the first power converter and the composite virtual impedance; wherein, in the amplitude adjustment range of the virtual resistive impedance, the virtual resistive impedance is negatively correlated with the load power, and in the amplitude adjustment range of the virtual inductive impedance, the virtual inductive impedance is negatively correlated with the load power.

[0116] In some embodiments, the flow sharing control device further includes:

[0117] A first limiter is used to determine the upper limit values ​​of the virtual resistive impedance and the virtual inductive impedance based on the mapping relationship when the first power converter is unloaded.

[0118] A second limiter is used to determine the lower limit of the virtual resistive impedance and the lower limit of the virtual inductive impedance based on the mapping relationship when the first power converter is fully loaded.

[0119] The control module 602 is also used to determine the amplitude adjustment range of the virtual resistive impedance based on the upper limit and lower limit of the virtual resistive impedance, and to determine the amplitude adjustment range of the virtual inductive impedance based on the upper limit and lower limit of the virtual inductive impedance.

[0120] In some embodiments, the control module 602 is further configured to:

[0121] When the current average apparent power is greater than the first preset power, the virtual resistive impedance in the composite virtual impedance is determined to be the lower limit value within the amplitude adjustment range of the virtual resistive impedance, and the virtual inductive impedance in the composite virtual impedance is determined to be the lower limit value within the amplitude adjustment range of the virtual inductive impedance.

[0122] When the current average apparent power is less than the second preset power, the virtual resistive impedance in the composite virtual impedance is determined to be the upper limit value within the amplitude adjustment range of the virtual resistive impedance, and the virtual inductive impedance in the composite virtual impedance is determined to be the upper limit value within the amplitude adjustment range of the virtual inductive impedance.

[0123] When the current average apparent power is not less than the second preset power and not greater than the first preset power, the virtual resistive impedance and the virtual inductive impedance in the composite virtual impedance are negatively correlated with the current average apparent power.

[0124] In some embodiments, the instantaneous current DQ-axis component includes the instantaneous current D-axis component Id_real and the instantaneous current Q-axis component Iq_real, the composite virtual impedance includes virtual resistive impedance and virtual inductive impedance, and the control module 602 is further configured to:

[0125] The first D-axis voltage adjustment is generated based on the virtual resistive impedance and the instantaneous current D-axis component Id_real;

[0126] The second D-axis voltage adjustment is generated based on the virtual inductive impedance, the instantaneous current Q-axis component Iq_real, and the instantaneous voltage angular frequency;

[0127] The first Q-axis voltage adjustment is generated based on the virtual resistive impedance and the instantaneous current Q-axis component Iq_real;

[0128] The second Q-axis voltage adjustment is generated based on the virtual inductive impedance, the instantaneous current D-axis component Id_real, and the instantaneous voltage angular frequency.

[0129] In some embodiments, the instantaneous voltage DQ-axis component includes the instantaneous voltage D-axis component Vd_real and the instantaneous voltage Q-axis component Vq_real, and the preset voltage reference value includes the Q-axis voltage reference value Vq_ref and the D-axis voltage reference value Vd_ref based on the droop control strategy. The control module 602 is further configured to:

[0130] The D-axis modulation voltage is generated based on the first D-axis voltage adjustment amount, the second D-axis voltage adjustment amount, the instantaneous voltage D-axis component Vd_real, the instantaneous current D-axis component Id_real, and the D-axis voltage reference value Vd_ref;

[0131] The Q-axis modulation voltage is generated based on the first Q-axis voltage adjustment, the second Q-axis voltage adjustment, the instantaneous voltage Q-axis component Vq_real, the instantaneous current Q-axis component Iq_real, and the Q-axis voltage reference value Vq_ref;

[0132] The drive signal is generated based on the D-axis modulation voltage and the Q-axis modulation voltage.

[0133] In some embodiments, the control module 602 is further configured to: obtain the D-axis voltage reference value Vd_ref based on the droop voltage Vd_droop determined by the droop control strategy and the rated output voltage V0_ref.

[0134] For details on the specific implementation method and related beneficial effects of the current sharing control device for the power converter, please refer to the description of the specific embodiment of the current sharing control method for the power converter described above, which will not be repeated here.

[0135] Please see Figure 8 This application also provides a power converter 100, which includes a power conversion circuit 101 and a controller 102 connected to the power conversion circuit 101; wherein, the controller 102 is used to execute the current sharing control method of the power conversion device as described in any of the above embodiments when the power converter 100 is connected in parallel with other power converters 100.

[0136] Please see Figure 8 This application also provides a power converter parallel system, including multiple power converters 100 connected in parallel. Each power converter 100 includes a power conversion circuit 101 and a controller 102 connected to the power conversion circuit 101. The controller 102 is used to execute the current sharing control method of the power conversion device as described in any of the above embodiments.

[0137] Please see Figure 9 It is understood that the power converter 100 also includes a memory 103, a controller 102, and a computer program 104 stored in the memory 103 and executable on the controller 102. When the controller 102 executes the computer program 104, it implements the steps of the current sharing control method of the power conversion device described above.

[0138] Those skilled in the art will understand that Figure 9 This is merely an example of power converter 100 and does not constitute a limitation on power converter 100. It may include more or fewer components than shown, or combine certain components, or different components, such as input / output devices, network access devices, etc.

[0139] The controller 102 can be a central processing unit (CPU), or it can be other general-purpose controllers, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose controller can be a microcontroller or any conventional controller.

[0140] In some embodiments, memory 103 may be an internal storage unit of the power converter 100, such as a hard disk or RAM of the power converter 100. In other embodiments, memory 103 may be an external storage device of the power converter 100, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., equipped on the power converter 100. Furthermore, memory 103 may include both internal storage units and external storage devices of the power converter 100. Memory 103 is used to store the operating system, applications, boot loader, data, and other programs. Memory 103 may also be used to temporarily store data that has been output or will be output.

[0141] One embodiment of this application also provides a power device, including a battery module and a power converter 100 as described in any of the above embodiments. The battery module is used to supply power to the power converter 100 or receive power from the power converter 100. The battery module and the power converter 100 can be integrated into one unit or can be separate units.

[0142] This application provides a computer program product that, when run on a computer, causes the computer to perform the steps described in the various method embodiments above.

[0143] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A current sharing control method for a power converter, applied to the first power converter in a series of multiple parallel power converters, characterized in that, The method includes: Obtain the current average apparent power of the plurality of parallel power converters, the instantaneous output current, the instantaneous output voltage, and the instantaneous voltage angular frequency of the first power converter; The instantaneous current DQ-axis component and the instantaneous voltage DQ-axis component are obtained based on the instantaneous output current and the instantaneous output voltage; The composite virtual impedance is determined based on the current average apparent power. A DQ-axis voltage adjustment signal is generated based on the composite virtual impedance, the instantaneous current DQ-axis component, and the instantaneous voltage angular frequency; An output drive signal is generated based on the DQ-axis voltage adjustment signal, the instantaneous voltage DQ-axis component, the instantaneous current DQ-axis component, and a preset voltage reference value. The drive signal is used to drive the power converter to output AC power.

2. The method according to claim 1, characterized in that, The step of determining the composite virtual impedance based on the current average apparent power includes: The composite virtual impedance is determined based on the mapping relationship between the current average apparent power, the load power of the first power converter, and the composite virtual impedance; wherein, in the mapping relationship, the composite virtual impedance is negatively correlated with the load power.

3. The method according to claim 1, characterized in that, The composite virtual impedance includes virtual resistive impedance and virtual inductive impedance. Before determining the composite virtual impedance based on the current average apparent power, the process includes: The modulation range of the virtual resistive impedance and the modulation range of the virtual inductive impedance are determined based on the mapping relationship between the load power of the first power converter and the composite virtual impedance; wherein, within the modulation range of the virtual resistive impedance, the virtual resistive impedance is negatively correlated with the load power, and within the modulation range of the virtual inductive impedance, the virtual inductive impedance is negatively correlated with the load power.

4. The method according to claim 3, characterized in that, The step of determining the modulation range of the virtual resistive impedance and the modulation range of the virtual inductive impedance based on the mapping relationship between the load power of the first power converter and the composite virtual impedance includes: Based on the mapping relationship, the upper limit values ​​of the virtual resistive impedance and the virtual inductive impedance are determined when the first power converter is unloaded. Based on the mapping relationship, the lower limit values ​​of the virtual resistive impedance and the virtual inductive impedance are determined when the first power converter is fully loaded. The amplitude adjustment range of the virtual resistive impedance is determined based on the upper and lower limits of the virtual resistive impedance, and the amplitude adjustment range of the virtual inductive impedance is determined based on the upper and lower limits of the virtual inductive impedance.

5. The method according to claim 4, characterized in that, The step of determining the composite virtual impedance based on the current average apparent power includes: When the current average apparent power is greater than the first preset power, the virtual resistive impedance in the composite virtual impedance is determined to be the lower limit value within the amplitude adjustment range of the virtual resistive impedance, and the virtual inductive impedance in the composite virtual impedance is determined to be the lower limit value within the amplitude adjustment range of the virtual inductive impedance. When the current average apparent power is less than the second preset power, the virtual resistive impedance in the composite virtual impedance is determined to be the upper limit value within the amplitude adjustment range of the virtual resistive impedance, and the virtual inductive impedance in the composite virtual impedance is determined to be the upper limit value within the amplitude adjustment range of the virtual inductive impedance. When the current average apparent power is not less than the second preset power and not greater than the first preset power, the virtual resistive impedance and the virtual inductive impedance in the composite virtual impedance are negatively correlated with the current average apparent power.

6. The method according to any one of claims 1-5, characterized in that, The instantaneous current DQ-axis component includes an instantaneous current D-axis component and an instantaneous current Q-axis component; the composite virtual impedance includes a virtual resistive impedance and a virtual inductive impedance; the generation of a DQ-axis voltage adjustment signal based on the composite virtual impedance, the instantaneous current DQ-axis component, and the instantaneous voltage angular frequency includes: The first D-axis voltage adjustment is generated based on the virtual resistive impedance and the instantaneous current D-axis component; The second D-axis voltage adjustment is generated based on the virtual inductive impedance, the instantaneous current Q-axis component, and the instantaneous voltage angular frequency. A first Q-axis voltage adjustment is generated based on the virtual resistive impedance and the instantaneous current Q-axis component; The second Q-axis voltage adjustment is generated based on the virtual inductive impedance, the D-axis component of the instantaneous current, and the angular frequency of the instantaneous voltage.

7. The method according to claim 6, characterized in that, The instantaneous voltage DQ-axis component includes an instantaneous voltage D-axis component and an instantaneous voltage Q-axis component. The preset voltage reference value includes a Q-axis voltage reference value and a D-axis voltage reference value based on a droop control strategy. Generating an output drive signal based on the DQ-axis voltage adjustment signal, the instantaneous voltage DQ-axis component, the instantaneous current DQ-axis component, and the preset voltage reference value includes: A D-axis modulation voltage is generated based on the first D-axis voltage adjustment amount, the second D-axis voltage adjustment amount, the instantaneous voltage D-axis component, the instantaneous current D-axis component, and the D-axis voltage reference value; The Q-axis modulation voltage is generated based on the first Q-axis voltage adjustment, the second Q-axis voltage adjustment, the instantaneous voltage Q-axis component, the instantaneous current Q-axis component, and the Q-axis voltage reference value; The drive signal is generated based on the D-axis modulation voltage and the Q-axis modulation voltage.

8. The method according to claim 1, characterized in that, The D-axis voltage reference value determined based on the droop control strategy includes: The reference value of the D-axis voltage is obtained based on the droop voltage and the rated output voltage determined by the droop control strategy.

9. A power converter, characterized in that, The power converter includes a power conversion circuit and a controller connected to the power conversion circuit; wherein the controller is used to execute the current sharing control method of the power conversion device as described in any one of claims 1 to 8 when the power converter is connected in parallel with other power converters.

10. A power converter parallel system, comprising a plurality of power converters connected in parallel, each of the power converters comprising a power conversion circuit and a controller connected to the power conversion circuit, characterized in that, The controller is used to execute the current sharing control method of the power conversion device as described in any one of claims 1 to 8.

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