A control method and device suitable for multi-machine parallel virtual synchronous generator

Abstract

The present application belongs to the technical field of virtual synchronous generator control, and particularly relates to a control method and device suitable for multi-machine parallel virtual synchronous generator. d_ref_调节 and the given value i q_ref_调节 of the first component of the stator current q-axis, to obtain the given value u dp_ref of the positive sequence d-axis component of the terminal voltage and the given value u qp_ref of the positive sequence q-axis component of the terminal voltage. The low-pass filter and the positive and negative sequence separation algorithm can be avoided in the loop, thereby effectively reducing the complexity of the system, facilitating engineering, and effectively solving the problems of output voltage imbalance and distortion of the existing virtual synchronous generator in multi-machine parallel off-grid with unbalanced load, and ensuring stable and reliable operation of the system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of virtual synchronous generator control, and particularly relates to a control method and device suitable for multi-machine parallel virtual synchronous generators. BACKGROUND

[0002] A paper titled "Virtual synchronous generator control strategy under unbalanced and nonlinear mixed load" by Shi Rongliang, Zhang Xing, et al. was published in the 36th issue of the 22nd volume of the Chinese Journal of Electrical Engineering in 2016, which discloses a virtual synchronous generator control strategy. The scheme conducts a detailed study on the VSG algorithm under the condition of unbalanced and nonlinear load. However, the scheme inevitably causes a "fighting" phenomenon among the multiple PR regulators of the VSGs due to the parallel connection of multiple PR regulators in the voltage loop, and the voltage is unbalanced and distorted, which leads to system instability. Therefore, the scheme must be connected in series with an inductance at the output port to ensure that the "fighting" phenomenon among the multiple PR regulators of the VSGs does not occur, but the existence of the reactance leads to an increase in the cost of additional hardware and an increase in system loss. SUMMARY

[0003] The application aims to provide a control method and device suitable for multi-machine parallel virtual synchronous generators, which can solve the problem that the virtual synchronous generator control method in the prior art easily causes system instability.

[0004] To solve the above technical problems, the application provides a control method suitable for multi-machine parallel virtual synchronous generators, which comprises a negative sequence voltage control part, a stator electrical equation part and a current loop control part.

[0005] The stator electrical equation part is used to set the positive sequence d-axis component of the terminal voltage to u dp_ref , and the positive sequence q-axis component of the terminal voltage to u dp . The difference between the two is obtained, and the difference value is adjusted and controlled by a controller to obtain the first d-axis component of the stator current given value i d_ref_调节 . The positive sequence d-axis component of the terminal voltage given value u qp_ref is subtracted from the positive sequence q-axis component of the terminal voltage given value u qp , and the difference value is adjusted and controlled by a controller to obtain the first q-axis component of the stator current given value i q_ref_调节 . The positive sequence d-axis component of the terminal voltage given value u dp_ref and the positive sequence q-axis component of the terminal voltage given value u qp_ref are calculated according to the following formula:

[0006]

[0007] In the formula, E d and E q respectively are d-axis component and q-axis component of internal potential of virtual synchronous generator; R and L respectively are stator resistance and stator inductance of virtual synchronous generator; and omega is angular velocity of virtual synchronous generator;

[0008] The negative sequence voltage control part is used to obtain a stator current d-axis second component given value and a q-axis second component given value;

[0009] The stator current d-axis component given value I d_ref of the current loop control part is the sum of a stator current d-axis first component given value i d_ref_调节 and a stator current d-axis second component given value, and a stator current q-axis component given value I q_ref is the sum of a stator current q-axis first component given value i q_ref_调节 and a stator current q-axis second component given value, and the current closed loop control is performed according to the stator current d-axis component given value I d_ref and the stator current q-axis component given value I q_ref to obtain an output voltage u abc .

[0010] The beneficial effect is that the stator electrical equation is improved in the application, the stator current d-axis first component i d_ref_调节 and the stator current d-axis second component i q_ref_调节 are used to obtain a machine terminal voltage positive sequence q-axis component given value u qp_ref and a d-axis component given value u dp_ref , the low pass filter and the positive and negative sequence separation algorithm are avoided to be introduced in the loop, so that the complexity of the system is effectively reduced, the engineering is easy, and the problems of output voltage imbalance and distortion of the virtual synchronous generator in the prior art when multiple machines are connected in parallel and off-grid with unbalanced load are effectively solved, and stable and reliable operation of the system is ensured.

[0011] Further, the machine terminal voltage negative sequence d-axis component given value u dn_ref and the q-axis component given value u qn_ref in the negative sequence voltage control part are respectively calculated according to the following formulas:

[0012]

[0013] In the formula, i dn and i qn respectively are negative sequence d-axis component and q-axis component of output current.

[0014] The beneficial effect is that the negative sequence virtual impedance is added on the negative sequence voltage loop, the unbalanced degree of alternating current bus voltage is reduced when multiple machines are connected in parallel with unbalanced load, and accurate power distribution is achieved.

[0015] Further, the electromagnetic torque T of the virtual synchronous generator m is:

[0016] T m = P ref / ω-k f (ω-ω0)

[0017] In the formula, ω0 is the rated angular frequency of the terminal voltage; k f is the frequency modulation coefficient, P ref is the active power given value.

[0018] Further, the d-axis component E of the internal voltage of the virtual synchronous generator d is:

[0019] E d =E0+G(s)[(Q ref -Q)-k u (u N -u m )]

[0020] In the formula, E0 is the no-load internal voltage; G(s) is the transfer function of the used controller; Q ref is the reactive power given value; Q is the reactive power of the virtual synchronous generator; k u is the voltage modulation coefficient; u N is the rated value of the terminal voltage; u m is the terminal voltage.

[0021] Further, the calculation formula of the active power P and the reactive power Q of the virtual synchronous generator is respectively:

[0022]

[0023] Its beneficial effects are: using i d_ref_调节 and i q_ref_调节 to extract the active power P and the reactive power Q, which can ensure that the active loop output frequency of the virtual synchronous generator has no double-frequency fluctuation, and the excitation voltage of the reactive loop has no double-frequency fluctuation.

[0024] Further, the used controller is a PI controller.

[0025] Its beneficial effects are: using the PI controller, the control is simple but the control precision is high.

[0026] To solve the above technical problems, the application further provides a control device suitable for a multi-machine parallel virtual synchronous generator, comprising a memory and a processor, the processor is used for executing the computer program instructions stored in the memory to realize the control method suitable for the multi-machine parallel virtual synchronous generator and achieve the same beneficial effects as the method. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is the overall block diagram of the virtual synchronous generator control of the present application;

[0028] Figure 2 is the control block diagram of obtaining the power angle θ of the virtual synchronous generator of the present application;

[0029] Figure 3 is the control block diagram of obtaining the three-phase internal electromotive force E of the virtual synchronous generator of the present application; d

[0030] Fig. 4(a) is the waveform diagram of the current I of the first inverter when the conventional VSG is connected in parallel; abc1

[0031] Fig. 4(b) is the waveform diagram of the current I of the second inverter when the conventional VSG is connected in parallel; abc2

[0032] Fig. 4(c) is the waveform diagram of the circulating current I of the two inverters when the conventional VSG is connected in parallel; h

[0033] Fig. 4(d) is the overall waveform diagram of the AC bus voltage V when the conventional VSG is connected in parallel; abc

[0034] Fig. 4(e) is the partial enlarged view of the AC bus voltage V when the conventional VSG is connected in parallel; abc

[0035] Fig. 5(a) is the waveform diagram of the current I of the first inverter when the VSG control based on the present application is connected in parallel; abc1

[0036] Fig. 5(b) is the waveform diagram of the current I of the second inverter when the VSG control based on the present application is connected in parallel; abc2

[0037] Fig. 5(c) is the waveform diagram of the circulating current I of the two inverters when the VSG control based on the present application is connected in parallel; h

[0038] Fig. 5(d) is the overall waveform diagram of the AC bus voltage V when the VSG control based on the present application is connected in parallel; abc

[0039] Fig. 5(e) is the partial enlarged view of the AC bus voltage V when the VSG control based on the present application is connected in parallel. abc DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present application more clear and explicit, the present application is further described in detail below in combination with the drawings and examples.​​​​​​​​​​​

[0041] Method Example:

[0042] The present invention is a method for controlling a virtual synchronous generator with multiple machines in parallel. The method is a method for controlling a virtual synchronous generator with multiple machines in parallel and with an unbalanced load function. Figure 1 As shown, the overall control includes the output voltage positive and negative sequence separation part ( Figure 1 Not drawn in the figure), stator electrical equation part and current loop control part.

[0043] The output voltage positive and negative sequence separation part is used to separate the positive and negative sequences of the output voltage, and adopts the voltage closed-loop control technology of positive and negative sequence separation to realize positive and negative sequence voltage decoupling control.

[0044] To address the problem of output voltage command fluctuations in the traditional stator electrical equation under unbalanced load conditions, an improved stator electrical equation is designed to achieve this. This avoids the introduction of low-pass filters and positive-negative sequence separation algorithms in the loop, effectively reducing the complexity of the system and facilitating engineering. Specifically, the stator electrical equation is used to set the positive-sequence d-axis component of the terminal voltage to a given value u dp_ref The positive sequence d-axis component u of the terminal voltage dp The difference is adjusted and controlled by the PI controller to obtain the given value i of the first component of the stator current d axis d_ref_PI ; Set the positive sequence q-axis component of the terminal voltage to a given value u qp_ref The positive sequence q-axis component u of the terminal voltage qp The difference is adjusted by the controller to obtain the given value i of the first component of the stator current q axis. q_ref_PI Among them, the given value u of the positive sequence d-axis component of the terminal voltage is calculated according to the following formula: dp_ref and q-axis component given value u qp_ref :

[0045]

[0046] Where, E d and E q are the d-axis component and q-axis component of the potential inside the virtual synchronous generator, respectively; R and L are the stator resistance and stator inductance of the virtual synchronous generator, respectively; and ω is the angular velocity of the virtual synchronous generator. Therefore, the specific implementation formula of the stator electrical equation is:

[0047]

[0048] Where G PI (s) is the PI controller transfer function.

[0049] The negative sequence voltage control part is used to obtain the given value of the second component of the stator current d axis and the second component of the q axis. In this control link, by adding a negative sequence virtual impedance to the negative sequence voltage loop, the AC bus voltage imbalance is reduced when multiple machines are connected in parallel with unbalanced loads, achieving accurate power distribution. Specifically, the given value of the negative sequence d axis component of the machine terminal voltage in the negative sequence voltage control part is u dn_ref and q-axis component given value u qn_ref They are calculated according to the following formulas:

[0050]

[0051] Where i dn and i qn They are the negative sequence d-axis component and q-axis component of the output current respectively.

[0052] The stator current d-axis component of the current loop control part is given by I d_ref is the given value of the first component of the stator current d axis i d_ref_调节 The sum of the given value of the second component of the stator current d axis and the given value of the stator current q axis component I q_ref is the given value of the first component of the stator current q axis i q_ref_调节 The sum of the given value of the second component of the stator current q axis and the given value of the stator current d axis component I d_ref and the stator current q-axis component given value I q_ref Perform current closed-loop control to obtain the output voltage u abc .

[0053] Among them, Figure 2 As shown, the virtual synchronous generator model includes:

[0054]

[0055] Where J is the moment of inertia of the virtual synchronous generator; ω is the angular velocity of the virtual synchronous generator; T m 、T e are the mechanical torque and electromagnetic torque of the virtual synchronous generator respectively; D is the damping coefficient; P m P is the input power of the VSG prime mover; e is the electromagnetic power output by VSG; δ is the power angle of the virtual synchronous generator; ω0 is the rated angular velocity of the virtual synchronous generator; u dp_ref and u qp_ref are the given values ​​of the d-axis component and q-axis component of the positive sequence voltage at the machine end respectively; E d and E q are the d-axis and q-axis components of the potential inside the virtual synchronous generator ( Figure 1 China E q =0); R and L are the stator resistance and stator inductance of the virtual synchronous generator respectively.

[0056] The electromagnetic torque in the virtual synchronous generator model is:

[0057] T m = P ref / ω-k f (ω-ω0)

[0058] In the formula, T m is the electromagnetic torque of the virtual synchronous generator; ω is the terminal voltage frequency; ω0 is the rated angular frequency of the terminal voltage; k f is the frequency modulation coefficient; P ref is the active power given value.

[0059] As shown in the formula, the excitation control in the virtual synchronous generator model is: Figure 3

[0060]

[0061] In the formula, E d is the d-axis component of the internal potential of the virtual synchronous generator; E0 is the no-load internal potential; k p and k I are respectively the proportional coefficient and the integral coefficient of the reactive power PI closed loop; Q ref is the reactive power given value; Q is the reactive power of the virtual synchronous generator; k u is the voltage regulation coefficient; u N is the rated value of the terminal voltage; u m is the terminal voltage.

[0062] In view of the problem that the output power of the VSG contains a double-frequency fluctuation component when the VSG is connected with an unbalanced load, an active and reactive power DC component extraction method using a voltage outer loop PI output current instruction is proposed, so that the active loop output frequency of the VSG is ensured to have no double-frequency fluctuation, and the reactive loop output excitation voltage has no double-frequency fluctuation. Specifically, the active power P and the reactive power Q extraction formulas are respectively:

[0063]

[0064] Figures 4(a) to 4(e) Fig. 2 is an output voltage and current waveform diagram of the traditional VSG in parallel. As can be seen, after being connected in parallel, the two VSGs can realize current sharing, but the unbalanced line voltage of the AC bus voltage is relatively serious, the maximum phase is 620V, and the minimum phase is 500V. Figures 5(a) to 5(e) Fig. 1 is an output voltage and current waveform diagram of the virtual synchronous generator control method designed by the application and suitable for multi-machine parallel connection with an unbalanced load. As can be seen, after being connected in parallel, the two VSGs can realize current sharing, and the unbalanced line voltage of the AC bus voltage is smaller than that of the traditional one, the maximum phase is 570V, and the minimum phase is 530V. ​

[0065] Device embodiments:

[0066] One of the device embodiments suitable for the multi-machine parallel virtual synchronous generator control method introduced in the method embodiments of the application, comprising a memory, a processor and an internal bus, the processor, the memory and the internal bus complete the communication and data interaction between each other. The memory is used to execute the computer program instructions stored in the memory to realize the method embodiments of the application. Among them, the processor can be a microprocessor MCU, programmable logic device FPGA and other processing devices. The memory can be various memories for storing information by using electrical energy, such as RAM, ROM and other memories.

Claims

1. A control method for a plurality of parallel-connected virtual synchronous generators, characterized in that, The control method comprises a negative sequence voltage control part, a stator electric equation part and a current loop control part. The stator electric equation part is used to give the machine terminal voltage positive sequence d-axis component a given value u dp_ref The machine terminal voltage positive sequence d-axis component u dp The difference is obtained, and the difference value is adjusted and controlled by the controller to obtain a stator current d-axis first component given value i d_ref_调节 The machine terminal voltage positive sequence q-axis component given value u qp_ref The machine terminal voltage positive sequence q-axis component u qp The difference is obtained, and the difference value is adjusted and controlled by the controller to obtain a stator current q-axis first component given value i q_ref_调节 u is obtained according to the following formula dp_ref And u qp_ref : wherein E d and E q are the d-axis and q-axis components of the internal voltage of the virtual synchronous generator, respectively; R and L are the stator resistance and stator inductance of the virtual synchronous generator, respectively; and ω is the angular speed of the virtual synchronous generator. The negative sequence voltage control part is used to obtain the stator current d-axis second component given value and q-axis second component given value, and the machine terminal voltage negative sequence d-axis component given value u dn_ref and q-axis component given value u qn_ref is obtained according to the following formula: In the formula, i dn and i qn are output current negative sequence d-axis and q-axis components, respectively; The stator current d-axis component given value I of the current loop control part d_ref is i d_ref_调节 The sum of the stator current q-axis component given value I and the stator current d-axis second component given value q_ref is i q_ref_调节 The sum of the stator current q-axis second component given value and the stator current d-axis component given value I, and according to I d_ref and I q_ref The output voltage u is obtained by performing current closed loop control abc .

2. The control method for a multi-machine parallel virtual synchronous generator according to claim 1, characterized in that, The electromagnetic torque T of the virtual synchronous generator m is: T m = P ref / ω-k f (ω-ω0) where ω0is the rated angular frequency of the machine terminal voltage; k f is the frequency modulation coefficient, and P ref is the active power reference.

3. The control method for a multi-machine parallel virtual synchronous generator according to claim 1, characterized in that, The d-axis component of the internal voltage of a virtual synchronous generator E d is: E d = E0+ G(s)[(Q ref -Q)-k u (u N -u m )] where E0 is the no-load internal potential; G(s) is the transfer function of the controller used; Q ref is the given value of the reactive power; Q is the virtual synchronous generator reactive power; k u is the voltage regulation coefficient; u N is the rated value of the terminal voltage; u m is the terminal voltage.

4. The control method for a multi-machine parallel virtual synchronous generator according to claim 3, characterized in that, The calculation formulae of the active power P and the reactive power Q of the virtual synchronous generator are respectively:

5. The control method for a multi-parallel virtual synchronous generator according to any one of claims 1 to 4, characterized in that, The controllers used are all PI controllers.

6. A control device for a plurality of parallel connected virtual synchronous generators, characterized in that The control method comprises a memory and a processor, the processor being used to execute computer program instructions stored in the memory to realize the control method for the multi-parallel virtual synchronous generator according to any one of claims 1-5.

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