Off-grid and parallel operation current sharing control method and system based on virtual impedance VSG converter
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 西安为光能源科技有限公司
- Filing Date
- 2026-05-26
- Publication Date
- 2026-08-07
AI Technical Summary
[0004]本发明的第一目的是提供基于虚拟阻抗VSG变换器离网并机均流控制方法，解决了现有技术中存在的基于固定虚拟阻抗的均流方案无法自适应线路阻抗差异，导致均流精度受限的问题
本发明基于虚拟阻抗的VSG功率变换器离网并机均流控制方法，该方法通过将各台变换器有功功率与系统平均有功功率的差值、无功功率与系统平均无功功率的差值，作为均流误差信号，实时调节虚拟阻抗值，均流误差大则增大阻抗以加强均流，均流误差小则减小阻抗；同时，该方法将虚拟内电势减去虚拟阻抗压降生成电压指令，精确补偿阻抗压降，实现了均流精度与电压质量的兼顾。
Smart Images
Figure CN122532952A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of power electronic converter control technology, specifically relating to a current sharing control method for off-grid and on-grid VSG power converters based on virtual impedance, and also relating to a current sharing control system for off-grid and on-grid VSG power converters based on virtual impedance. Background Technology
[0002] Grid-based control technologies, exemplified by Virtual Synchronous Generators (VSGs), enable power electronic converters to simulate the inertia and damping characteristics of synchronous generators, finding widespread application in microgrids, energy storage systems, and uninterruptible power supplies (UPS). To improve system capacity and power supply reliability, multiple power converters are typically operated in parallel off-grid. However, due to slight differences in the amplitude and phase of the output voltage of each converter, as well as impedance mismatch in the output lines, circulating currents are easily generated within the parallel system. This results in power not being evenly distributed according to capacity, and in severe cases, can cause overload of individual devices or even system collapse.
[0003] To suppress circulating current and improve current sharing, virtual impedance technology is commonly introduced. This technology uses control algorithms to effectively increase or reshape the output impedance of the converter, thereby achieving decoupling and equalization of active and reactive power. However, existing virtual impedance technologies are all based on current sharing schemes with fixed virtual impedance. In low-voltage distribution networks, the line impedance differences between distributed power sources are significant. Current sharing schemes based on fixed virtual impedance cannot adapt to these line impedance differences or compensate for them specifically, resulting in limited current sharing accuracy. Furthermore, during transient processes such as load changes and converter switching, fixed impedance schemes have slow response speeds and large circulating current peaks. Summary of the Invention
[0004] The primary objective of this invention is to provide a current sharing control method for off-grid and on-grid VSG converters based on virtual impedance, which solves the problem in the prior art where current sharing schemes based on fixed virtual impedance cannot adapt to line impedance differences, resulting in limited current sharing accuracy.
[0005] The second objective of this invention is to provide an off-grid and on-grid current sharing control system based on a virtual impedance VSG converter.
[0006] The first technical solution adopted in this invention is a current sharing control method for off-grid and on-grid VSG converters based on virtual impedance, which includes the following steps: Step 1: Acquire the output voltage and current of the machine. After transforming the output angle coordinates of the previous control cycle, obtain the d and q components of the voltage and current in the dq coordinate system. Calculate the active power P and reactive power Q, and obtain the system average active power. and system average reactive power ; Step 2: Based on the active power P of the machine and the active power reference value The difference, after Droop control generates output angular frequency The output angle is obtained by integration. Used for coordinate transformation in the next cycle, based on reactive power Q and reactive power reference value. Difference, after The droop control generates a virtual internal potential E; Step 3: Calculate the current sharing error signal; Step 4: Calculate the virtual impedance voltage drop , ; Step 5, virtual internal potential E decreases As a d-axis voltage reference, 0 minus As a q-axis voltage reference; Step 6: Startup and Operation.
[0007] The first technical solution of the present invention is further characterized in that: The specific process of step 1 is as follows: Step 1.1: Acquire the three-phase voltage and three-phase current output from the machine, and perform Clark transformation on the three-phase voltage and three-phase current to obtain the voltage components in the two-phase stationary Clark coordinate system. , and current components , ; Step 1.2: Call the real-time angle θ output by the phase-locked loop from the previous control cycle and adjust the voltage component. , and current components , Perform the Park transformation to obtain the voltage components in the synchronously rotating dq coordinate system. , and current components , ; Step 1.3: Based on the instantaneous reactive power theory, utilize the voltage component... , and current components , The formula for calculating the active power P and reactive power Q output by this machine is as follows: (1) (2) Step 1.4: Exchange the output active current of each converter via the communication bus. and reactive current And based on this, calculate the system's average active power. and system average reactive power .
[0008] Step 2 Droop control generates output angular frequency The specific calculation process is as follows: (3) in, This is the rated angular frequency; This is the droop coefficient; This is a reference value for active power.
[0009] Step 2 The droop control generates a virtual internal potential E, and the specific calculation process is as follows: (4) in, This is the no-load electromotive force; This is the droop coefficient; This is a reference value for reactive power.
[0010] Step 3 calculates the current sharing error signal, the specific process is as follows: Calculate the active power P of the local machine and the average active power of the system. The difference The reactive power Q of the machine and the average reactive power of the system The difference As the current sharing error signal, the specific calculation formula is as follows: (5).
[0011] Step 4 calculates the virtual impedance voltage drop. , The specific process is as follows: Step 4.1: Based on the current sharing error signal, generate a virtual resistance that increases with the increase of error using a dynamic virtual impedance adjustment function. ,inductance The specific calculation formula is as follows: (6) in, As a reference virtual resistor; As a reference virtual inductance; and This is the proportionality coefficient; This is the error threshold.
[0012] Step 4.2, based on the virtual resistance ,inductance Combining the d and q components of the current , and angular frequency Calculate virtual impedance voltage drop , The specific calculation formula is as follows: (7) Step 5: Subtract the virtual internal potential E d-axis voltage reference value 0 minus q-axis voltage reference value The specific calculation formula is as follows; (8) Step 6 involves starting and running the program, and the specific process is as follows: Referring to the d-axis voltage reference values and q-axis voltage reference values given in step 5, the internal voltage-current dual closed-loop and PWM modulation drive converter controls the output to achieve multi-machine off-grid parallel current sharing operation. Specifically, during the converter's grid-connection startup phase, the virtual resistor is first... and virtual inductance The value is preset to more than 5 times the rated operating value. After grid connection is detected and current is balanced, it is gradually reduced to the value of the dynamic virtual impedance adjustment function described in step 4.
[0013] The second technical solution adopted in this invention is a virtual impedance VSG converter off-grid parallel current sharing control system, which includes multiple VSG power converters connected in parallel. Each VSG power converter includes a DC energy storage unit, a three-phase inverter bridge, a filter, a sampling circuit, and a controller. The controller includes: The power calculation and communication module is used to obtain the local active power P, reactive power Q, and the system's average active power and average reactive power based on the sampled voltage, current, and communication. The VSG control module is used to generate the output angle from the active power deviation and to generate the virtual internal potential E from the reactive power deviation. The current sharing error calculation module is used to calculate... and ; The dynamic virtual impedance adjustment module is used to dynamically generate a virtual resistance that increases as the current sharing error increases. Virtual inductance And calculate the virtual impedance voltage drop. , ; Voltage and current dual closed-loop module, with E reduced 0 minus Dual-loop control is performed as a reference to generate a modulated signal.
[0014] The beneficial effects of this invention are: This invention relates to a virtual impedance-based off-grid and on-grid current sharing control method for VSG power converters. This method uses the difference between the active power of each converter and the average active power of the system, and the difference between the reactive power of each converter and the average reactive power of the system, as current sharing error signals. The virtual impedance value is adjusted in real time. If the current sharing error is large, the impedance is increased to strengthen current sharing; if the current sharing error is small, the impedance is decreased. At the same time, this method generates a voltage command by subtracting the virtual impedance voltage drop from the virtual internal potential, which accurately compensates for the impedance voltage drop, thus achieving a balance between current sharing accuracy and voltage quality.
[0015] This invention relates to a VSG converter off-grid and on-grid current sharing control system based on virtual impedance. This system adjusts the impedance value in real time through a dynamic virtual impedance module, adapts to line impedance differences, effectively suppresses circulating current, and improves current sharing accuracy and system stability. Attached Figure Description
[0016] Figure 1 This is a flowchart of the off-grid and on-grid current sharing control method based on virtual impedance VSG converters. Detailed Implementation
[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.
[0018] Example 1 The first technical solution provided by this invention is a current sharing control method for off-grid and on-grid VSG converters based on virtual impedance, such as... Figure 1 As shown, it includes the following steps: Step 1: Acquire the output voltage and current of the machine. After transforming the output angle coordinates of the previous control cycle, obtain the d and q components of the voltage and current in the dq coordinate system. Calculate the active power P and reactive power Q, and obtain the system average active power. and system average reactive power ; Step 2: Based on the active power P of the machine and the active power reference value The difference, after Droop control generates output angular frequency The output angle is obtained by integration. Used for coordinate transformation in the next cycle, based on reactive power Q and reactive power reference value. Difference, after The droop control generates a virtual internal potential E; Step 3: Calculate the current sharing error signal; Step 4: Calculate the virtual impedance voltage drop , ; Step 5, virtual internal potential E decreases As a d-axis voltage reference, 0 minus As a q-axis voltage reference; Step 6: Startup and Operation.
[0019] Example 2 Based on Example 1, this example further discloses the detailed process of step 1, as follows: Step 1.1: Acquire the three-phase voltage and three-phase current output by the machine, and perform Clark transformation on the three-phase voltage and three-phase current to obtain the voltage components in the two-phase stationary Clark coordinate system. , and current components , ; Step 1.2: Call the real-time angle θ output by the phase-locked loop from the previous control cycle and adjust the voltage component. , and current components , Perform the Park transformation to obtain the voltage components in the synchronously rotating dq coordinate system. , and current components , ; Step 1.3: Based on the instantaneous reactive power theory, utilize the voltage component... , and current components , The formula for calculating the active power P and reactive power Q output by this machine is as follows: (1) (2) Step 1.4: Exchange the output active current of each converter via the communication bus. and reactive current And based on this, calculate the system's average active power. and system average reactive power .
[0020] Example 3 Based on Example 2, this example further discloses the process in step 2... Droop control generates output angular frequency ,through The detailed process of droop control generating the virtual internal potential E is as follows: Step 2 Droop control generates output angular frequency The specific calculation process is as follows: (3) in, This is the rated angular frequency; This is the droop coefficient; This is a reference value for active power.
[0021] Step 2 The droop control generates a virtual internal potential E, and the specific calculation process is as follows: (4) in, This is the no-load electromotive force; This is the droop coefficient; This is a reference value for reactive power. In off-grid conditions, it is usually set to 0 depending on the load characteristics.
[0022] Example 4 Based on Example 3, this example discloses the detailed processes of steps 3, 4, and 5, as follows: Step 3 calculates the current sharing error signal, the specific process is as follows: Calculate the active power P of the local machine and the average active power of the system. The difference The reactive power Q of the machine and the average reactive power of the system The difference As the current sharing error signal, the specific calculation formula is as follows: (5).
[0023] By comparing the active power P of each converter with the system average active power The difference between reactive power Q and system average reactive power The difference is used as the current sharing error signal, and the virtual impedance is dynamically adjusted according to the current sharing error signal. If the current sharing error is large, the impedance is increased to strengthen current sharing, and if the current sharing error is small, the impedance is decreased to reduce voltage drop.
[0024] Step 4: Calculate the virtual impedance voltage drop , The specific process is as follows: Step 4.1: Based on the current sharing error signal, generate a virtual resistance that increases with the increase of error using a dynamic virtual impedance adjustment function. ,inductance The specific calculation formula is as follows: (6) in, As a reference virtual resistor; As a reference virtual inductance; and This is the proportionality coefficient; This is the error threshold.
[0025] Step 4.2, based on the virtual resistance ,inductance Combining the d and q components of the current , and angular frequency Calculate virtual impedance voltage drop , The specific calculation formula is as follows: (7) Step 5: Subtract the virtual internal potential E d-axis voltage reference value 0 minus q-axis voltage reference value The specific calculation formula is as follows; (8).
[0026] Example 5 Based on the above embodiment 4, this embodiment discloses the detailed process of step 6, as follows: Referring to the d-axis voltage reference values and q-axis voltage reference values given in step 5, the internal voltage-current dual closed-loop and PWM modulation drive converter controls the output to achieve multi-machine off-grid parallel current sharing operation. Specifically, during the converter's grid-connection startup phase, the virtual resistor is first... and virtual inductance The preset value is more than 5 times the rated operating value. After the grid connection is completed and the current is balanced, the value is gradually reduced to the value of the dynamic virtual impedance adjustment function described in step 4. Before the equipment is started and connected to the AC bus, the impedance is increased to suppress the AC inrush current. After the parallel system is running, the impedance is reduced to reduce voltage drop.
[0027] Example 6 Based on Embodiment 5 above, this embodiment provides an off-grid parallel current sharing control system for virtual impedance VSG converters adapted to the above control method, including multiple VSG power converters connected in parallel. Each VSG power converter includes a DC energy storage unit, a three-phase inverter bridge, a filter, a sampling circuit, and a controller. The controller includes: The power calculation and communication module is used to obtain the local active power P, reactive power Q, and the system's average active power and average reactive power based on the sampled voltage, current, and communication. The VSG control module is used to generate the output angle from the active power deviation and to generate the virtual internal potential E from the reactive power deviation. The current sharing error calculation module is used to calculate... and ; The dynamic virtual impedance adjustment module is used to dynamically generate a virtual resistance that increases as the current sharing error increases. Virtual inductance And calculate the virtual impedance voltage drop. , By adjusting the impedance value in real time through the dynamic virtual impedance module, it adapts to the line impedance difference, effectively suppresses circulating current, and improves current sharing accuracy and system stability.
[0028] Voltage and current dual closed-loop module, with E reduced 0 minus Dual-loop control is performed as a reference to generate a modulated signal.
Claims
1. A current sharing control method for off-grid and on-grid VSG converters based on virtual impedance, characterized in that, Includes the following steps: Step 1: Acquire the output voltage and current of the machine. After transforming the output angle coordinates of the previous control cycle, obtain the d and q components of the voltage and current in the dq coordinate system. Calculate the active power P and reactive power Q, and obtain the system average active power. and system average reactive power ; Step 2: Based on the active power P of the machine and the active power reference value The difference, after Droop control generates output angular frequency The output angle is obtained by integration. Used for coordinate transformation in the next cycle, based on reactive power Q and reactive power reference value. Difference, after The droop control generates a virtual internal potential E; Step 3: Calculate the current sharing error signal; Step 4: Calculate the virtual impedance voltage drop , ; Step 5, virtual internal potential E decreases As a reference value for the d-axis voltage, 0 minus Used as a reference value for the q-axis voltage; Step 6: Startup and Operation.
2. The off-grid and on-grid current sharing control method based on virtual impedance VSG converter according to claim 1, characterized in that, The specific process of step 1 is as follows: Step 1.1: Acquire the three-phase voltage and three-phase current output by the machine, and perform Clark transformation on the three-phase voltage and three-phase current to obtain the voltage components in the two-phase stationary Clark coordinate system. , and current components , ; Step 1.2: Call the real-time angle θ output by the phase-locked loop from the previous control cycle and adjust the voltage component. , and current components , Perform the Park transformation to obtain the voltage components in the synchronously rotating dq coordinate system. , and current components , ; Step 1.3: Based on the instantaneous reactive power theory, utilize the voltage component... , and current components , The formula for calculating the active power P and reactive power Q output by this machine is as follows: （1） （2） Step 1.4: Exchange the output active current of each converter via the communication bus. and reactive current And based on this, calculate the system's average active power. and system average reactive power .
3. The off-grid and on-grid current sharing control method based on virtual impedance VSG converter according to claim 1, characterized in that, Step 2 described Droop control generates output angular frequency The specific calculation process is as follows: （3） in, This is the rated angular frequency; This is the droop coefficient; This is a reference value for active power.
4. The off-grid and on-grid current sharing control method for VSG converters based on virtual impedance as described in claim 3, characterized in that, Step 2 described The droop control generates a virtual internal potential E, and the specific calculation process is as follows: （4） in, This is the no-load electromotive force; This is the droop coefficient; This is a reference value for reactive power.
5. The off-grid and on-grid current sharing control method based on virtual impedance VSG converter according to claim 1, characterized in that, Step 3 involves calculating the current sharing error signal, and the specific process is as follows: Calculate the active power P of the local machine and the average active power of the system. The difference The reactive power Q of the machine and the average reactive power of the system The difference As the current sharing error signal, the specific calculation formula is as follows: （5）。 6. The off-grid and on-grid current sharing control method based on virtual impedance VSG converter according to claim 1, characterized in that, Step 4 describes the calculation of the virtual impedance voltage drop. , The specific process is as follows: Step 4.1: Based on the current sharing error signal, generate a virtual resistance that increases with the increase of error using a dynamic virtual impedance adjustment function. ,inductance The specific calculation formula is as follows: （6） in, As a reference virtual resistor; As a reference virtual inductance; and This is the proportionality coefficient; This is the error threshold; Step 4.2, based on the virtual resistance ,inductance Combining the d and q components of the current , and angular frequency Calculate virtual impedance voltage drop , The specific calculation formula is as follows: （7）。 7. The off-grid and on-grid current sharing control method based on virtual impedance VSG converter according to claim 1, characterized in that, The virtual internal potential E reduction mentioned in step 5 As a reference value for d-axis voltage 0 minus As a reference value for q-axis voltage The specific calculation formula is as follows; （8）。 8. The off-grid and on-grid current sharing control method for VSG converters based on virtual impedance as described in claim 1, characterized in that, The startup and operation process described in step 6 is as follows: Referring to the d-axis and q-axis voltage reference values given in step 5, the internal voltage-current dual closed-loop and PWM modulation drive converter controls the output to achieve multi-unit off-grid parallel current sharing operation. Specifically, during the converter's grid-connection startup phase, the virtual resistor is first... and virtual inductance The value is preset to more than 5 times the rated operating value. After the grid connection is completed and the current is balanced, it is gradually reduced to the value of the dynamic virtual impedance adjustment function in step 4.
9. The off-grid parallel current sharing control system based on a virtual impedance VSG converter according to any one of claims 1-8, characterized in that, include: Multiple VSG power converters connected in parallel, each VSG power converter including a DC energy storage unit, a three-phase inverter bridge, a filter, a sampling circuit, and a controller, wherein the controller includes: The power calculation and communication module is used to obtain the local active power P, reactive power Q, and the system's average active power and average reactive power based on the sampled voltage, current, and communication. The VSG control module is used to generate the output angle from the active power deviation and to generate the virtual internal potential amplitude E from the reactive power deviation. The current sharing error calculation module is used to calculate... and ; The dynamic virtual impedance adjustment module is used to dynamically generate a virtual resistance that increases as the current sharing error increases. Virtual inductance And calculate the virtual impedance voltage drop. , ; Voltage and current dual closed-loop module, with E reduced 0 minus Dual-loop control is performed as a reference to generate a modulated signal.