Method for suppressing power oscillation of parallel system of network construction type energy storage converter

Abstract

The invention discloses a power oscillation suppression method for a grid-forming type energy storage converter parallel system, and belongs to the field of micro-grid power utilization. Acquiring a three-phase output voltage and a three-phase current; calculating instantaneous active power and reactive power by using the three-phase voltage and the three-phase current, and constructing an active power control loop and a reactive power control loop; calculating an active damping compensation amount; angular frequency required by the system and a system phase damping an oscillation component in the active power are calculated; calculating a reactive power damping compensation amount; calculating a reference voltage amplitude required by the system and damping an oscillation component in reactive power; a three-phase voltage, a three-phase current, a system phase damping an oscillation component in active power and a reference voltage amplitude damping an oscillation component in reactive power are sent to a voltage control loop and a current control loop to generate a modulation signal and convert the modulation signal into a control signal, and the control signal acts on a converter so as to suppress oscillation. Damping compensation branches are designed from an active control loop and a reactive control loop, system damping is greatly increased, and the interactive oscillation phenomenon of the grid-forming type energy storage converter parallel system can be effectively restrained.

Description

Technical Field

[0001] This invention belongs to the field of microgrid power consumption, and specifically relates to a method for suppressing power oscillations in a grid-connected energy storage converter parallel system. Background Technology

[0002] Energy storage converters play a crucial role in microgrids by mitigating power fluctuations and supporting stable system operation. Traditional energy storage converter control strategies often employ a grid-following model, whose stability depends on grid support. However, in islanded or weak grid conditions, the system lacks stable voltage and frequency references, placing higher demands on the grid-building capabilities of the energy storage converters themselves. To address this, Virtual Synchronous Generator (VSG) technology, which simulates the operating characteristics of synchronous generators, has emerged. This technology endows energy storage converters with virtual inertia, damping characteristics, and primary frequency regulation capabilities, enabling them to actively build and stabilize the grid like traditional synchronous generators. Therefore, energy storage converters controlled by VSGs are also called grid-based energy storage converters. However, due to differences in circuit parameters and limitations in practical applications, it is impossible to control multiple parallel energy storage converters to have identical external characteristics when using VSG control. Therefore, when multiple energy storage converters operate in parallel, power oscillations may occur between the converters, causing overload and equipment damage, threatening the safe, stable, and efficient operation of the entire system.

[0003] To address the power oscillation problem in parallel grid-connected converter systems, current suppression methods mainly fall into three categories: optimizing control parameters, modifying control loops, and virtual impedance. Among these, the first category, optimizing control parameters, while simple, inevitably affects the dynamic and static characteristics of the system and requires parameter readjustment under different load power conditions, thus having limited applicability.

[0004] For the second type of method, centralized control, agent-based distributed control, or the addition of auxiliary control loops and damping elements can all effectively suppress interactive oscillations based on the basic control strategy of the energy storage converter. However, these methods either increase the cost and system complexity due to dependence on communication links, or rely on complex control algorithms for parameter tuning, placing a significant computational burden on the controller.

[0005] Besides the methods mentioned above, a third type of virtual impedance strategy is widely used to suppress power oscillations. However, the effectiveness of this type of virtual impedance method is highly dependent on the degree to which specific relationships of VSG parameters are satisfied. In practical applications, the precise value of the line impedance is difficult to obtain, leading to significant challenges in the rational design of virtual impedance. It is particularly noteworthy that, due to the inherent characteristics of the system topology and the complexity of parallel interconnected systems, current methods can only attenuate the oscillation amplitude to a certain allowable range, making it difficult to completely eliminate power oscillations.

[0006] Against this backdrop, the above three strategies focus only on suppressing active power oscillations, while ignoring reactive power oscillations with coupling characteristics. This means that the suppression effect of existing methods often has significant room for improvement in practical applications.

[0007] Among existing oscillation suppression methods, Chinese invention patent CN117239797A, entitled "A Control Method for a Grid-type Energy Storage Converter," discloses the following: Analysis of the synchronous generator frequency and voltage regulation characteristics of a single energy storage converter (PCS) to establish a mathematical model of the single PCS; generation of a mathematical model for a grid-type energy storage converter PCS using a multi-unit parallel configuration based on the mathematical model of the single PCS; and achieving uniform power distribution to the grid-type energy storage converter PCS based on the droop characteristics of the virtual synchronous generator control VSG; and establishment of a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS to achieve power decoupling and power oscillation suppression control.

[0008] The aforementioned existing technology has the following problems: 1. Using existing technologies to suppress interactive oscillations can only attenuate the oscillation amplitude to a certain allowable range, and it is difficult to completely eliminate power oscillations.

[0009] 2. The effectiveness of the virtual impedance method is highly dependent on the degree to which the specific relationship of VSG parameters is satisfied. However, in practical applications, it is difficult to obtain the accurate value of the line impedance, which makes the rational design of virtual impedance a significant challenge. Summary of the Invention

[0010] The purpose of this invention is to overcome the aforementioned problems and propose a power oscillation suppression method for a grid-type energy storage converter parallel system, which solves the problem that existing technologies can only attenuate the oscillation amplitude to a certain allowable range and are difficult to completely eliminate power oscillations.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for suppressing power oscillations in a grid-connected energy storage converter parallel system, characterized by the following specific steps: Step s1: Connect the energy storage converter to the three-phase load and collect the three-phase output voltage and three-phase current of the energy storage converter on the grid side; Step s2: Calculate the instantaneous active power and reactive power based on the collected three-phase voltage and three-phase current; construct an active power control loop using the instantaneous active power; construct a reactive power control loop using the instantaneous reactive power. Step s3: Calculate the active power damping compensation using the instantaneous active power; calculate the system angular frequency and system phase of the active power damping oscillation component required by the energy storage converter using the active power control loop and the active power damping compensation. Step s4: Calculate the reactive power damping compensation using instantaneous reactive power; calculate the reference voltage amplitude of the damped reactive power oscillation component required by the energy storage converter using the reactive power control loop and the reactive power damping compensation. Step s5: The collected three-phase voltage, three-phase current, calculated system phase and system frequency with damped active power oscillation components, and reference voltage amplitude with damped reactive power oscillation components are sent to the voltage control loop and current control loop to generate modulation signals. The modulation signals are converted into control pulse signals and applied to the energy storage converter to suppress oscillations.

[0012] In step s1, the three-phase output voltage is u abc and three-phase current is i abc .

[0013] In step s2, instantaneous active power P e and reactive power Q e The formula is as follows:

[0014] u a 、u b and u c It is the grid-side phase voltage; i a , i b and i c It is the grid-side phase current.

[0015] In step s2, the mathematical equation for the active power control loop is as follows:

[0016] J It is the moment of inertia, D It is the damping coefficient, ω m It is the angular frequency of the VSG control output. ω 0 is the rated angular frequency. P ref Active power reference value θIt is the phase of the VSG control output, Δ ω It is the difference between the output angular frequency and the rated angular frequency.

[0017] In step s2, the mathematical equation for the reactive power control loop is as follows:

[0018] Q ref This is a reference value for reactive power. Q e The actual value of reactive power. k q It is the reactive power droop coefficient, E and E 0 represents the actual output voltage and the rated voltage under steady-state conditions of the energy storage system.

[0019] In step s3, the actual output instantaneous active power is... P e A branch path is drawn from the feedback point, which passes through a first-order high-pass filter and is then multiplied by the active power suppression loop damping compensation coefficient. m p Calculate the active damping compensation amount P e_com .

[0020] The active power damping compensation amount is calculated using the following formula:

[0021] m p For the active power suppression ring damping compensation coefficient, τ p The time constant of the high-pass filter for the active power suppression loop, s It is a differential operator.

[0022] In step s3, the active damping compensation amount is... P e_com At the torque error point acting on the active frequency loop, the required angular frequency of the system and the system phase after damping the oscillating component in the active power are calculated using the following formulas: .

[0023] In step s4, the actual output reactive power is... Q e A branch path is drawn from the feedback point, and after passing through a high-pass filter, it is multiplied by the reactive power suppression loop damping compensation coefficient. m q Calculate the reactive power damping compensation amount Q e_com .

[0024] The reactive power damping compensation amount is calculated using the following formula:

[0025] m q For reactive power suppression ring damping compensation coefficient, τ q This is the time constant of the high-pass filter in the reactive power suppression loop.

[0026] In step s4, the reactive power damping compensation amount is... Q e_com The torque error applied to the reactive power control loop serves as compensation for the reactive power error value. This is used to calculate the reference voltage amplitude required by the system to dampen the oscillating component in the reactive power. E 1. The calculation formula is as follows: .

[0027] In step s5, the modulation signal is converted into a control signal by a modulation signal generator.

[0028] The advantages of using this invention are: I. Compared with the prior art, the present invention designs damping compensation branches in both active and reactive power control loops, which greatly increases the system damping and can effectively suppress the interactive oscillation phenomenon of the grid-type energy storage converter parallel system.

[0029] Second, compared with the prior art, the damping compensation strategy designed in this invention does not affect the steady-state operating point of the system, nor does it depend on the system model. The specific structure is simple and the implementation is easy.

[0030] Third, this invention does not require changes to the original control structure of the system, thus avoiding negative impacts on the dynamic and static characteristics of the system.

[0031] Fourth, this invention does not require obtaining the precise value of the line impedance, nor does it require an additional communication link, thus avoiding the increased system complexity caused by centralized or distributed control. It also eliminates the need for complex parameter adjustment algorithms, reducing the computational burden on the controller. Attached Figure Description

[0032] Figure 1 This is a block diagram of the power interaction oscillation suppression strategy of the present invention with active and reactive power dual damping compensation; Figure 2 The diagram shows the active and reactive power of the energy storage parallel system under operating condition 1. Figure 3 The waveform diagram of grid-side voltage and current of the energy storage converter under operating condition 1; Figure 4 The diagram shows the active and reactive power of the energy storage parallel system under operating condition 2. Figure 5The waveform diagram of grid-side voltage and current of the energy storage converter under operating condition 2; Figure 6 This is a diagram showing the active and reactive power of the energy storage parallel system under operating condition 3 of this invention. Figure 7 This is a waveform diagram of the grid-side voltage and current of the energy storage converter under operating condition 3 of the present invention. Detailed Implementation

[0033] Example 1 A method for suppressing power oscillations in a grid-connected energy storage converter parallel system, characterized by the following specific steps: Step s1: Connect the energy storage converter to the three-phase load and collect the three-phase output voltage and three-phase current of the energy storage converter on the grid side; Step s2: Calculate the instantaneous active power and reactive power based on the collected three-phase voltage and three-phase current; construct an active power control loop using the instantaneous active power; construct a reactive power control loop using the instantaneous reactive power. Step s3: Calculate the active power damping compensation using the instantaneous active power; calculate the system angular frequency and system phase of the active power damping oscillation component required by the energy storage converter using the active power control loop and the active power damping compensation. Step s4: Calculate the reactive power damping compensation using instantaneous reactive power; calculate the reference voltage amplitude of the damped reactive power oscillation component required by the energy storage converter using the reactive power control loop and the reactive power damping compensation. Step s5: The collected three-phase voltage, three-phase current, calculated system phase and system frequency of the damped active power oscillation component, and reference voltage amplitude of the damped reactive power oscillation component are sent to the voltage control loop and current control loop to generate modulation signals. The modulation signals are converted into control pulse signals and applied to the energy storage converter to suppress oscillations.

[0034] In step s1, the three-phase output voltage is u abc and three-phase current is i abc .

[0035] In step s2, instantaneous active power P e and reactive power Q e The formula is as follows:

[0036] u a 、u b and uc It is the grid-side phase voltage; i a , i b and i c It is the grid-side phase current.

[0037] In step s2, the mathematical equation for the active power control loop is as follows:

[0038] J It is the moment of inertia, D It is the damping coefficient, ω m It is the angular frequency of the VSG control output. ω 0 is the rated angular frequency. P ref Active power reference value θ It is the phase of the VSG control output, Δ ω It is the difference between the output angular frequency and the rated angular frequency.

[0039] In step s2, the mathematical equation for the reactive power control loop is as follows:

[0040] Q ref This is a reference value for reactive power. Q e The actual value of reactive power. k q It is the reactive power droop coefficient, E and E 0 represents the actual output voltage and the rated voltage under steady-state conditions of the energy storage system.

[0041] In step s3, the actual output instantaneous active power is... P e A branch path is drawn from the feedback point, which passes through a first-order high-pass filter and is then multiplied by the active power suppression loop damping compensation coefficient. m p Calculate the active damping compensation amount P e_com .

[0042] The active power damping compensation amount is calculated using the following formula:

[0043] m p For the active power suppression ring damping compensation coefficient, τ p The time constant of the high-pass filter for the active power suppression loop,s It is a differential operator.

[0044] In step s3, the active damping compensation amount is... P e_com At the torque error point acting on the active frequency loop, the required angular frequency of the system and the system phase after damping the oscillating component in the active power are calculated using the following formulas: .

[0045] In step s4, the actual output reactive power is... Q e A branch path is drawn from the feedback point, and after passing through a high-pass filter, it is multiplied by the reactive power suppression loop damping compensation coefficient. m q Calculate the reactive power damping compensation amount Q e_com .

[0046] The reactive power damping compensation amount is calculated using the following formula:

[0047] m q For reactive power suppression ring damping compensation coefficient, τ q This is the time constant of the high-pass filter in the reactive power suppression loop.

[0048] In step s4, the reactive power damping compensation amount is... Q e_com The torque error applied to the reactive power control loop is used as the compensation for the reactive power error value. The reference voltage amplitude required by the system to dampen the oscillating component in the reactive power is calculated. E 1. The calculation formula is as follows: .

[0049] In step s5, the modulation signal is converted into a control signal by a modulation signal generator.

[0050] To achieve the above objectives, the present invention includes the following steps: Step 1: Connect the energy storage converter to the three-phase load and collect the three-phase output voltage of the energy storage converter on the grid side. u abc and three-phase current i abc ; Step 2: Control the energy storage converter using the VSG method. Based on the acquired three-phase voltage... u abc and three-phase current i ab Calculate instantaneous active power Pe and reactive power Q e Instantaneous active power P e and reactive power Q e The formula is as follows:

[0051] Utilizing instantaneous active power P e The mathematical equation for the active power control loop can be calculated as follows:

[0052] In the formula: J It is the moment of inertia, D It is the damping coefficient, ω m It is the angular frequency of the VSG control output. ω 0 is the rated angular frequency. P ref Active power reference value θ It is the phase of the VSG control output, Δ ω It is the difference between the output angular frequency and the rated angular frequency.

[0053] At the same time, utilize reactive power Q e The mathematical equations for the reactive power control loop can be written as follows:

[0054] Q ref and Q e These are the reference value and the actual value of reactive power, respectively. k q It is the reactive power droop coefficient, E and E 0 represents the actual output voltage and the rated voltage under steady-state conditions of the energy storage system.

[0055] Step 3: Calculate the active power damping compensation component and the system phase after damping the oscillating component in the active power. Based on normal VSG active power control, draw a branch from the feedback of the actual output active power control loop, pass it through a first-order high-pass filter, and multiply it by the compensation coefficient to obtain the active power damping compensation amount:

[0056] In the formula, m p For the active power suppression ring damping compensation coefficient, τ pThe time constant of the high-pass filter for the active power suppression loop is... s It is a differential operator.

[0057] Active damping compensation P e_com At the torque error point acting on the active frequency loop, the required angular frequency of the system and the system phase after damping the oscillating component in the active power are calculated using the following formulas: .

[0058] Step 4: Calculate the reactive power damping compensation component and the reference voltage amplitude of the oscillating component in the damped reactive power required by the system. Draw a branch from the feedback of the actual output reactive power control loop, pass it through a first-order high-pass filter, and multiply it by the reactive power compensation coefficient to obtain the compensation amount for the reactive power error value. That is, the calculated reactive power damping compensation amount is:

[0059] m q For reactive power suppression ring damping compensation coefficient, τ q This is the time constant of the high-pass filter in the reactive power suppression loop.

[0060] Based on normal VSG reactive power control, the reactive power damping compensation amount will be increased. Q e_com Applying this to the torque error in the reactive power control loop, we can then write the reference voltage amplitude required by the system after adopting the proposed suppression strategy to dampen the oscillating component of the reactive power. E The mathematical equation for 1 is: .

[0061] Step 5: Collect the three-phase output voltage u abc and three-phase current i abc The calculated system phase (damped by the oscillating component in active power) and reference voltage amplitude (damped by the oscillating component in reactive power) are fed into the voltage control loop and current control loop to generate modulation signals. m α and m β and modulate the signal m α and m β The signal is fed into a modulation signal generator (PWM generator) to generate a control signal that acts on the converter switching transistors, thereby controlling the converter.

[0062] To further verify the effectiveness of this invention, a simulation model was built for testing. The simulation conditions were set as follows: In islanded mode, two energy storage converters were connected in parallel and then supplied power to a hydrogen production load. At t=0.3s, approximately 1.5MW of active load was switched on, and after 0.2s (t=0.5s), another 1MW of active load was switched on. Under these basic simulation conditions, the following three sets of operating conditions were tested: Operating condition 1: No suppression strategy is applied; Operating Condition 2: Only active power suppression control is applied; Operating Condition 3: Simultaneous application of active and reactive power suppression control (i.e., the proposed suppression strategy).

[0063] When the system is in operating condition 1, i.e., without any suppression strategy applied, the active / reactive power curves, output angular frequency, and grid-side voltage and current waveforms of the two energy storage converters are as follows: Figure 2 and Figure 3 As shown. (From the appendix) Figure 2 It can be seen that when the load power changes from 0 to 1.5MW, each of the two energy storage converters outputs approximately 0.725MW of active power with slight oscillations. At t=0.5s, when the load power increases from 1.5MW to 2.5MW, the active power output of both energy storage converters increases accordingly, but there is a significant interactive oscillation phenomenon between active and reactive power. Specifically, as the power output of the first energy storage converter decreases / increases, the power output of the other energy storage converter increases / decreases, and the amplitude of the interactive oscillation between active and reactive power increases with time. Meanwhile, Figure 3 The results show that before and after load changes (between 0.2s and 0.5s), the voltage at the parallel connection point of the energy storage converters is relatively stable, and the current amplitude of the two energy storage converters changes from 0 to about 800A with only a short-term imbalance. However, when the load increases to the rated value, although the grid-side voltage of the energy storage converter system remains unchanged, its current gradually becomes distorted, and the amplitude exhibits increasingly larger oscillations. The test results under this condition indicate that, without the application of suppression strategies, the frequency response difference between the two parallel energy storage VSG systems causes power interaction oscillations in the parallel system during load switching, which greatly affects the stability of the parallel system.

[0064] When only the active power suppression loop is applied, i.e., the system is in operating condition 2, the active / reactive power curves, output angular frequency, and grid-side voltage and current waveforms of the two energy storage converters are as follows: Figure 4 and Figure 5 As shown. Under the same load variation, after using active power suppression control, Figure 4 The active / reactive power curves shown no longer exhibit the alternating oscillations with gradually increasing amplitude, and... Figure 2Compared to the previous system, stability has been significantly improved. However, under rated load conditions, the active and reactive power of the two energy storage converters still exhibit slight interactive oscillations. Further analysis reveals... Figure 5 It can be observed that the amplitude of the grid-side output current of the energy storage converter no longer exhibits significant oscillations, but its amplitude is not completely balanced. The test results under this operating condition indicate that the active power suppression loop alone can suppress the power interaction oscillation phenomenon of parallel energy storage converters to a certain extent, but the oscillation suppression effect needs to be improved.

[0065] When the proposed dual-damping suppression strategy is adopted, i.e., active power suppression control and reactive power suppression control are applied simultaneously, the test results are as follows: Figure 6 and Figure 7 As shown. Figure 6 and Figure 2 and attached Figure 4 The comparison reveals that throughout the entire load change process, the active and reactive power curves of the proposed energy storage parallel system remain stable, exhibiting no interactive oscillations other than normal fluctuations. Similarly, Figure 7 The voltage and grid-side current at the parallel connection point of the two energy storage converters are shown. Figure 7 Before and after the load change, it was observed that the amplitudes of each phase of the grid-side current were balanced and stable, and no longer exhibited oscillation. This test condition verified the effectiveness of the proposed suppression strategy.

[0066] comprehensive Figures 2-7 The test results show that, compared with no suppression strategy, the proposed oscillation suppression strategy can effectively avoid the interactive oscillation phenomenon exhibited by the parallel energy storage system under load changes. Furthermore, compared with applying only active power suppression control, the scheme of applying both active and reactive power suppression control has a better suppression effect.

[0067] The voltage control loop and current control loop use TMS320F2806.

Claims

1. A method for suppressing power oscillation of a grid-forming energy storage converter interconnection system, characterized in that: The specific steps are as follows: Step s1: connecting the energy storage converter to a three-phase load, collecting three-phase output voltage and three-phase current of the energy storage converter; Step s2: calculating instantaneous active power and reactive power according to the collected three-phase voltage and three-phase current, using the instantaneous active power to build an active power control loop; using the instantaneous reactive power to build a reactive power control loop; Step s3: using the instantaneous active power to calculate an active damping compensation amount; using the active power control loop and the active damping compensation amount to calculate the system angular frequency and system phase of the oscillation component in the active power required by the energy storage converter after damping; Step s4: using the instantaneous reactive power to calculate a reactive power damping compensation amount; using the reactive power control loop and the reactive power damping compensation amount to calculate the reference voltage amplitude of the oscillation component in the reactive power required by the energy storage converter after damping; Step s5: sending the collected three-phase voltage, three-phase current, calculated system phase and system frequency of the oscillation component in the active power after damping, and calculated reference voltage amplitude of the oscillation component in the reactive power after damping into a voltage control loop and a current control loop to generate a modulation signal, converting the modulation signal into a control pulse signal, and applying the control pulse signal to the energy storage converter, thereby suppressing the oscillation.

2. The method of claim 1, wherein the method comprises: The step s1, three-phase output voltage is u abc And three-phase current is i abc .

3. The method of claim 1 or 2, wherein the method comprises: In the step s2, the instantaneous active power P e and the reactive power Q e The formula is as follows: u a 、u b and u c is the net-side phase voltage; i a , i b and i c is the net-side phase current.

4. The method of claim 3, wherein the method comprises: In the step s2, the mathematical equation of the active power control loop is as follows: J is the moment of inertia, D is the damping coefficient, ω m is the angular frequency of the VSG control output, ω 0 is the rated angular frequency, P ref is the active power reference value, θ is the phase of the VSG control output, Δ ω is the difference between the output angular frequency and the rated angular frequency.

5. The method of claim 4, wherein the method comprises: In the step s2, the mathematical equation of the reactive power control loop is as follows: Q ref is a reference value for the reactive power, Q e is an actual value for the reactive power, k q is a reactive droop coefficient, E and E 0 is the actual output voltage of the energy storage system and the rated voltage in steady state.

6. The method of claim 5, wherein the method comprises: The step s3, from the actual output of the instantaneous active power P e A branch is introduced at the feedback, and after a first-order high-pass filter, it is multiplied by the active suppression loop damping compensation coefficient m p The active damping compensation amount is calculated P e_com .

7. The method of claim 6, wherein the method comprises: The active damping compensation amount is as follows: m p for the active damping loop compensation coefficient, τ p for the high-pass filter time constant of the active damping loop, s is a differential operator.

8. The method of claim 6, wherein the method comprises: The step s3, the active damping compensation quantity P e_com The torque error acting on the active frequency ring, the angular frequency and the system phase required by the system to damp the oscillation component in the active power are calculated, and the calculation formula is as follows: 。 9. The method of claim 8, wherein the method comprises: In the step s4, the actual output reactive power Q e A branch is introduced at the feedback, and after high-pass filtering, it is multiplied by the reactive power suppression loop damping compensation coefficient m q The reactive power damping compensation amount is calculated Q e_com .

10. The method of claim 9, wherein the method comprises: The reactive damping compensation amount is as follows: m q Kd is the damping compensation factor for the reactive suppression loop, τ q Kf is the high pass filter time constant for the reactive suppression loop.

11. The method of claim 10, wherein the method comprises: The reactive power damping compensation amount Q e_com The torque error acting on the reactive power control loop is used as a compensation amount of the reactive power error value, and a reference voltage amplitude of the system required to damp the oscillation component in the reactive power is calculated E 1, The calculation formula is as follows: 。 12. The method of claim 11, wherein the method comprises: In the step s5, the modulation signal is converted into a control signal by a modulation signal generator.

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