Energy storage converter damping enhancement control method based on feedforward control

Abstract

The invention discloses an energy storage converter damping enhancement control method based on feedforward control. The method comprises the following steps: establishing an active power flow model of an energy storage converter system; adding an additional degree of freedom to the model to generate an improved active power flow model; ignoring a voltage loop and a current loop, and simplifying the improved active power flow model to obtain a small signal model; designing a feedforward controller Gc (s); and substituting the Gc (s) into the small signal model to obtain a damping-enhanced active power flow model of the energy storage converter. According to the method, a feed-forward path is introduced to improve the damping level, and by applying the method, power oscillation can be effectively attenuated under the condition that original inertial response is not affected; the damping effect and the power dynamic state can be flexibly adjusted to any specific level; and under the condition that system parameters are available, automatic setting and real-time self-adaption of the feedforward controller are realized. Meanwhile, under the condition that the power grid frequency suddenly changes, the rapid change of the active power generated by the original inertia response is beneficial to maintaining the stability of the power grid frequency.

Description

Technical field:

[0001] The invention relates to the technical field of power electronics, and in particular to a damping enhancement control method for an energy storage converter based on feedforward control. Background technology:

[0002] The rate of change of frequency (ROCOF) is an important indicator to measure the dynamic performance of the energy storage inverter system. Droop control and virtual synchronous generator (VSG) control are widely used control strategies for DC-AC conversion. The poles of the VSG control transfer function are closer to the imaginary axis than the poles of the droop control transfer function. Therefore, the dynamic performance of VSG control is slower than that of droop control. Therefore, when the load power changes or disturbs in off-grid mode, the inverter based on VSG control has greater inertia than the inverter based on droop control and has better frequency stability.

[0003] The transfer function of VSG control is a second-order system with two negative complex poles close to the imaginary axis. Therefore, it is an underdamped system. When the inverter output active power changes stepwise, there is obvious overshoot and oscillation, which will lead to instability of the energy storage converter system. Therefore, it is urgent to design a control method to improve the stability of VSG control. Summary of the invention:

[0004] In view of the above problems, the present invention provides a damping enhancement control method for an energy storage converter based on feedforward control to improve the damping level of a VSG control model.

[0005] A damping enhancement control method for an energy storage converter based on feedforward control, the method comprising: establishing an active power flow model of an energy storage converter system; adding an extra degree of freedom to the model to generate an improved active power flow model; ignoring the voltage loop and the current loop, simplifying the improved active power flow model to obtain a small signal model, ignoring the high-order system generated when the voltage and current loops are ignored, and only focusing on the power loop to simplify the system model is conducive to focusing on the core functions of VSG: simulating the frequency and voltage regulation services provided by traditional synchronous machines; by simplifying the model, factors that have little impact on the dynamic performance of the energy storage converter system can be ignored, and the focus can be placed on the key control strategy and system response; this simplification can not only reduce the complexity of the model, but also effectively reduce the calculation cost; designing a feedforward controller G c (s); G c (s) is introduced into the small signal model to obtain the active power flow model of the energy storage converter with enhanced damping.

[0006] Preferably, the active power flow model of the energy storage converter system is specifically:

[0007]

[0008] Among them, P * is the output power of the energy storage converter system; J is the inertia coefficient of active power regulation; D is the droop coefficient of active power regulation; ω n and ω g are the angular frequencies of the energy storage converter system and the power grid respectively;

[0009] The improved active power flow model is specifically:

[0010]

[0011] Where s is the domain; D v and T ω are the virtual damping coefficient and bandwidth coefficient of the additional degrees of freedom, respectively; is an additional degree of freedom;

[0012] The small signal model is:

[0013]

[0014] Among them, V n is the rated voltage; V is the voltage amplitude on the grid side; X is the total impedance on the grid side;

[0015] The feedforward controller G c (s) is: Among them, k1 and k2 are two adjustable parameters;

[0016] The feedforward controller G c (s) is brought into the small signal model to obtain the damping-enhanced active power flow model of the energy storage converter, and the damping-enhanced active power flow model of the energy storage converter is specifically:

[0017]

[0018] Preferably, the specific method for establishing the small signal model is: obtaining the relationship expression between the phase angle and angular velocity of the energy storage inverter system; deriving the expressions of active power and reactive power of the energy storage inverter system; linearizing the relationship expression between the phase angle and angular velocity, the active power and the reactive power expression to obtain the small signal model.

[0019] Preferably, the relationship between the phase angle and angular velocity of the energy storage converter system is expressed as: δ = ∫ (ω n -ω g )dt, where δ is the phase angle of the energy storage converter system; the active power expression is: The expression of reactive power is: Where V0 is the converter output voltage; V g is the grid voltage.

[0020] Preferably, the damping strategy and parameter design method of the feedforward controller are specifically as follows:

[0021] Assume that the active power signal model is a second-order model:

[0022]

[0023] Wherein, ζ is the damping coefficient, ω0 is the standard natural angular frequency of the second-order model; the phase angle of the energy storage converter and the phasor representation of the active power are substituted into the active power signal model to obtain:

[0024]

[0025] in, b2=D+2Jζω n .

[0026] Preferably, the damping coefficient ζ is greater than 0.707.

[0027] In order to solve the problem of poorly damped active power oscillation in energy storage converter VSG control, the present invention discloses a damping enhancement control method for energy storage converter based on feedforward control, which introduces a feedforward path to improve the damping level. By applying this method, power oscillation can be effectively attenuated without affecting the original inertial response; the damping effect and power dynamics can be flexibly adjusted to any specific level; when system parameters are available, the feedforward controller is automatically adjusted and self-adapted in real time. At the same time, in the case of sudden changes in grid frequency, the rapid change of active power generated by the original inertial response is conducive to maintaining the stability of grid frequency. Description of the drawings:

[0028] Attached Figure 1 The present invention provides a block diagram of a three-level NPC type VSG damping enhancement control circuit for use in an energy storage converter.

[0029] Attached Figure 2 Attached is a structural block diagram of the three-level NPC type VSG active loop feedforward controller provided by the present invention. Figure 3 The present invention provides G c (s) Zero-pole change diagram of the parameter k1 tuning process in the controller.

[0030] Attached Figure 4 The G provided by the present invention c (s) Zero-pole change diagram of the parameter k2 tuning process in the controller.

[0031] Attached Figure 5 The invention provides an active power response simulation waveform of the energy storage converter damping enhancement control system based on active power feedforward during the active power jump period. Specific implementation method:

[0032] In order to make the technical solution of the present invention easier to understand, a damping enhancement control method of an energy storage converter based on feedforward control designed by the present invention is now clearly and completely described in conjunction with the accompanying drawings.

[0033] A damping enhancement control method for an energy storage converter based on feedforward control specifically comprises the following steps:

[0034] Step 100: Establish an active power flow model for the energy storage converter system: Assume that the total impedance on the grid side is an inductive impedance X, as shown in the attached figure. Figure 1 As shown, the active power flow model of the energy storage converter system is specifically:

[0035]

[0036] Among them, P * is the output power of the energy storage converter system; J is the inertia coefficient of active power regulation; D is the droop coefficient of active power regulation; ω n and ω g are the angular frequencies of the energy storage converter system and the power grid respectively;

[0037] Step 110: Adding additional degrees of freedom to the model generates an improved active power flow model:

[0038]

[0039] Where s is the domain; D v and T ω are the virtual damping coefficient and bandwidth coefficient of the additional degrees of freedom, respectively; For additional degrees of freedom, generally, only when the additional degrees of freedom (ADOF) introduced by the additional damping term is greater than or equal to ΔP / ΔP * When the closed-loop poles are in the order of magnitude of , they can be freely adjusted without changing the coefficients J and D.

[0040] Step 120: Simplify the improved active power flow model to obtain a small signal model: In general, the control strategy of the VSG system usually includes three control loops: voltage, current and power; these control loops are differentiated according to the time scale of action and the different control objects. The voltage and current control loops have a faster response speed and are mainly responsible for maintaining the voltage and current stability on the transmission line, while the power control loop has a relatively slow response speed and is mainly responsible for regulating the active and reactive output of electricity. In most VSG application scenarios, the goal of power control is to simulate the frequency and voltage regulation behavior of the synchronous machine, which is a relatively slow process. Therefore, the model can be simplified by distinguishing fast dynamics (such as instantaneous regulation of voltage and current) from the slow dynamics of power control.

[0041] By simplifying the model, we can ignore factors that have little impact on the system's dynamic performance and focus on key control strategies and system responses. In addition, by ignoring the high-order systems generated by the voltage and current loops and focusing only on the power loop to simplify the system model, we can focus on studying and optimizing the core functions of VSG: simulating the frequency and voltage regulation services provided by traditional synchronous machines. This simplification not only reduces the complexity of the model, but also effectively reduces the computational cost.

[0042] The specific method for establishing the small signal model is:

[0043] Get the relationship between the phase angle and angular velocity of the energy storage converter system: δ=∫(ω n -ω g )dt, where δ is the phase angle of the energy storage converter system;

[0044] The expressions of active power and reactive power of the energy storage converter system are derived: The expression of active power is: The expression of reactive power is: Where V0 is the converter output voltage; V g is the grid voltage; generally, the phase angle δ is very small, so it can be approximately expressed as cos(δ)≈1 and sin(δ)≈δ, and V0≈V g ≈V n , where V n is the rated voltage.

[0045] The small signal model is obtained by linearizing the relationship expression between the phase angle and the angular velocity, the active power and the active power expression:

[0046] Step 130: Design the feedforward controller G c (s)(If attached Figure 2 shown): k1 and k2 are two adjustable parameters; wherein, the damping strategy and parameter design method of the feedforward controller are specifically as follows: the limitation of ADOF cannot be solved by adjusting the zero point, therefore, it is assumed that the active power signal model is a second-order model:

[0047]

[0048] Wherein, ζ is the damping coefficient, ω0 is the standard natural angular frequency of the second-order model; the phase angle of the energy storage converter and the phasor representation of the active power are substituted into the active power signal model to obtain:

[0049]

[0050] in, b2=D+2Jζω n Generally, the controller coefficients are calculated from the system parameters, the second-order damping coefficient and the natural frequency, which simplifies the parameter tuning. The selection of J and D can be set according to the criteria of the classic second-order system. For example, the damping coefficient can be considered to be set to above 0.707, and the natural frequency can be set according to the adjustment time.

[0051] Step 140: G c (s) is brought into the small signal model to obtain the damping enhanced active power flow model of the energy storage converter:

[0052] Attached Figure 3 The G provided by the present invention is c (s) Zero-pole change diagram of the controller parameter k1 tuning process. Since the feedforward control introduces new parameters, additional poles and zeros are generated. In order to minimize the impact of the poor damping pole, the additional zero can be set at the position closest to the poor damping pole through zero-pole parameter tuning. It can be seen that the optimal value of k1 is around 0.015, and k2 defaults to 1000.

[0053] Attached Figure 4 The G provided by the present invention is c (s) Zero-pole change diagram of the controller parameter k2 tuning process. Since the feedforward control introduces new parameters, additional poles and zeros are generated. In order to minimize the impact of the poor damping pole, the additional zero can be set at the position closest to the poor damping pole through zero-pole parameter tuning. It can be seen that the optimal value of k2 is around 1200, where k1 defaults to 0.010.

[0054] Attached Figure 5 The active power response simulation waveform of the energy storage converter damping enhancement control system based on active power feedforward provided by the present invention during the active power jump period. In order to verify that this method improves the traditional method to a certain extent, simulation tests and experimental tests of power, frequency and other responses are designed, and the parameter design is shown in Table 1.

[0055] Table 1 Parameter design table

[0056]

[0057] It should be pointed out that for ordinary technicians in this technical field, several improvements, substitutions, modifications and embellishments can be made without departing from the principles and purpose of the present invention. These improvements, substitutions, modifications and embellishments should also be regarded as the scope of protection of the present invention.

Claims

1. A damping enhancement control method for an energy storage converter based on feedforward control, characterized in that: The method comprises: Establish an active power flow model of the energy storage converter system; add additional degrees of freedom to the model to generate an improved active power flow model; ignore the voltage loop and the current loop, simplify the improved active power flow model to obtain a small signal model; design a feedforward controller G c (s); G c (s) is introduced into the small signal model to obtain the active power flow model of the energy storage converter with enhanced damping.

2. A damping enhancement control method for an energy storage converter based on feedforward control as claimed in claim 1, characterized in that: The active power flow model of the energy storage converter system is specifically: Among them, P * is the output power of the energy storage converter system; J is the inertia coefficient of active power regulation; D is the droop coefficient of active power regulation; ω n and ω g are the angular frequencies of the energy storage converter system and the power grid respectively; The improved active power flow model is specifically: Where s is the domain; D V and T ω are the virtual damping coefficient and bandwidth coefficient of the additional degrees of freedom, respectively; is an additional degree of freedom; The small signal model is: Among them, V n is the rated voltage; V is the voltage amplitude on the grid side; X is the total impedance on the grid side; The feedforward controller G c (s) is: Among them, k1 and k2 are two adjustable parameters; The feedforward controller G c (s) is brought into the small signal model to obtain the damping-enhanced active power flow model of the energy storage converter, and the damping-enhanced active power flow model of the energy storage converter is specifically:

3. A damping enhancement control method for an energy storage converter based on feedforward control as claimed in claim 2, characterized in that: The specific method for establishing the small signal model is: obtaining the relationship expression between the phase angle and angular velocity of the energy storage inverter system; deriving the expressions of active power and reactive power of the energy storage inverter system; linearizing the relationship expression between the phase angle and angular velocity, the active power and the reactive power expression to obtain the small signal model.

4. A damping enhancement control method for an energy storage converter based on feedforward control as claimed in claim 3, characterized in that: The relationship between the phase angle and angular velocity of the energy storage converter system is expressed as: δ=∫(ω n -ω g )dt, where δ is the phase angle of the energy storage converter system; the active power expression is: The expression of reactive power is: Where V0 is the converter output voltage; V g is the grid voltage.

5. The damping enhancement control method of an energy storage converter based on feedforward control as claimed in claim 2, characterized in that: The damping strategy and parameter design method of the feedforward controller are specifically as follows: Assume that the active power signal model is a second-order model: Wherein, ζ is the damping coefficient, ω0 is the standard natural angular frequency of the second-order model; the phase angle of the energy storage converter and the phasor representation of the active power are substituted into the active power signal model to obtain: in, b2=D+2Jζω n .

6. A damping enhancement control method for an energy storage converter based on feedforward control as claimed in claim 5, characterized in that: The damping coefficient ζ is greater than 0.707.

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