CN111541269B

CN111541269B - A virtual synchronous machine power second-order decoupling controller and its power decoupling control method

Info

Publication number: CN111541269B
Application number: CN202010317694.7A
Authority: CN
Inventors: 戚军; 李袁超; 周丹
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Hangzhou Yunmu Technology Co ltd
Priority date: 2020-04-21
Filing date: 2020-04-21
Publication date: 2021-10-15
Anticipated expiration: 2040-04-21
Also published as: CN111541269A

Abstract

The virtual synchronous machine power second-order decoupling controller is formed by a given current calculation module (1), a reference current synthesis module (2), and a cross decoupling module (3) in series in sequence, and the controller is set in the traditional VSG control In the latter stage of the inverter, its input signal comes from the upper-level VSG controller and measurement unit, and its output signal is input to the PWM wave generating device of the VSG grid-connected inverter. The invention also includes a power decoupling control method of the virtual synchronous machine power second-order decoupling controller. The invention starts from the VSG power coupling mechanism, and on the basis of the virtual impedance method, uses the dynamic virtual current to perform dynamic power compensation, and eliminates the coupling of P-V and Q-δ; Based on the first-order decoupling strategy of virtual synchronous machine power, the second-order power angle variation is fully considered. Compared with the first-order strategy, the second-order strategy has a better decoupling effect in the face of large changes in the power angle.

Description

Virtual synchronizer power second-order decoupling controller and power decoupling control method thereof

Technical Field

The invention relates to the technical field of new energy power generation and grid connection, in particular to a virtual synchronizer power second-order decoupling controller based on dynamic virtual current feedforward and a power decoupling control method thereof.

Background

With the rapid development of economy and the gradual improvement of the permeability of renewable energy sources, the grid-connected technology of distributed energy sources is widely researched and developed. Distributed power generation systems interfaced with power electronic converters lack the inertia and damping that conventional motors have, and therefore power systems are more susceptible to power fluctuations and system faults. The Virtual Synchronous Generator (VSG) technology enables a grid-connected inverter to simulate characteristics of a body model, active frequency modulation, reactive voltage regulation and the like of a synchronous generator, so that the grid-connected inverter can be compared with a traditional synchronous generator in terms of an operation mechanism and external characteristics. By applying the VSG technology, frequency modulation on a demand side can be performed, the anti-disturbance capability of a system is improved, redundant renewable grid-connected energy in a power grid can be consumed, and the VSG technology has a good development prospect.

However, if the VSG is applied to a medium-low voltage power grid, the line impedance of the power grid is resistive, even resistive, so that an obvious power coupling problem occurs, and the problem affects the dynamic performance of the system, even causes instability. How to effectively solve the power coupling problem of the VSG is the key for the popularization and application of the VSG technology. In the prior art, most decoupling methods adopt a constraint method of increasing virtual impedance or relaxing small power angle, and these power decoupling strategies only consider the first-order small quantity of power angle change, but cannot ensure better decoupling effect in the case of large power angle change.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and designs a novel dynamic virtual current feedforward virtual synchronizer power second-order decoupling controller and a power decoupling control method thereof.

The invention can overcome the precision problem existing in the traditional VSG power decoupling, fully considers the second-order power angle variable quantity on the basis of the traditional virtual synchronous machine power first-order decoupling strategy, and realizes the coupling power compensation by utilizing a dynamic virtual current compensation mode based on the instantaneous reactive power theory.

In order to achieve the technical aim, the technical scheme provided by the invention is as follows:

the invention relates to a virtual synchronous machine (VSG) Power Second-Order Decoupling Controller (SOPDC), which is formed by sequentially connecting a given current calculation module (1), a reference current synthesis module (2) and a cross Decoupling module (3) in series, wherein the SOPDC is arranged at the rear stage of a traditional VSG Controller, input signals of the SOPDC are from a superior VSG Controller and a measuring unit, and output signals of the SOPDC are input into a PWM wave generation device of a VSG grid-connected inverter;

the given current calculation module (1) has 2 input ends and 2 output ends in total; the first and second input ends are respectively input with the induced electromotive force e output by the VSG controller and the voltage v of the grid-connected point provided by the measuring unit_gThe first output end and the second output end of the signal are respectively connected with the first input end and the second input end of the reference current synthesis module (2);

the given current calculation module (1) consists of a transfer function module G(s) and a Park converter; the input of the transfer function G(s) is VSG induced electromotive force e and grid-connected point voltage v_gIs output as a given current signal i^*The calculation has been madeThe equation is shown in formula (1):

in the formula, s represents a complex variable, L_eqIs the system equivalent inductance, R_eqIs the system equivalent resistance, e is the induced electromotive force of the virtual synchronous machine, v_gIs the grid-connected point voltage;

will give a current signal i^*The d-axis and q-axis outputs of the Park converter are respectively connected with a first output end and a second output end of the given current calculation module (1), and the output signals are given current signals i^*D-axis and q-axis components of

And

the reference current synthesis module (2) has 6 input ends and 2 output ends; the first input end and the second input end are respectively connected with the first output end and the second output end of the given current calculation module (1), and the third input end and the fourth input end are respectively input with a virtual current d-axis component signal delta i required by P-V, Q-delta decoupling_d(P-V)And Δ i_d(Q-δ)The fifth input end and the sixth input end respectively input a virtual current q-axis component signal delta i required by P-V, Q-delta decoupling_q(P-V)And Δ i_q(Q-δ)(ii) a The first output end and the second output end are respectively connected with the first input end and the second input end of the cross decoupling module (3);

in the reference current synthesis module (2), a first input end inputs a signal

Virtual current d-axis component Δ i required for decoupling from P-V, Q- δ_d(P-V)、Δi_d(Q-δ)D-axis component signal i of the final value of the reference current is superposed and synthesized_{d_ref}And output at a first output end of the reference current synthesis module (2) and input at a second input end

Virtual current q-axis components Δ i required for decoupling from P-V, Q- δ, respectively_q(P-V)、Δi_q(Q-δ)Superposing and synthesizing the q-axis component i of the final value of the reference current_{q_ref}And is output at a second output end of the reference current synthesis module (2);

the cross decoupling module (3) has 6 input ends and 1 output end; the first and second input ends are respectively connected with the first and second output ends of the reference current synthesis module (2), and the input signals of the third and fourth input ends are respectively d-axis and q-axis components i of the output current of the virtual synchronous machine_dAnd i_qThe input signals of the fifth and sixth input terminals are respectively d-axis and q-axis components v of the grid-connected point voltage_gdAnd v_gqThe output end of the PWM wave generator is connected with a VSG grid-connected inverter;

the cross decoupling module (3) comprises two Gain modules Gain1 and Gain2 (the Gain is respectively omega L_eqAnd- ω L_eqWhere ω is the electrical angular velocity of VSG), two proportional-integral controllers PI1, PI2, a Park inverse transform module; input signal i of the first input terminal_{d_ref}Input signal i to the third input terminal_dThe subtracted signals are input into a PI1 and an input signal i of a fourth input end_qThe output signal of PI1, the output signal of Gain2 and the input signal v of the fifth input end are sent to Gain2_gdD-axis component for generating induced electromotive force given value after superposition

Inputting a d-axis input end of a Park inverse transformation module; input signal i of the second input terminal_{q_ref}And an input signal i to a fourth input terminal_qThe subtracted signals are input into a PI2 and an input signal i of a third input end_dThe output signal of PI2, the output signal of Gain1 and the input signal v of a sixth input end are sent into Gain1_gqQ-axis component for generating induced electromotive force given value after superposition

Inputting a q-axis input end of a Park inverse transformation module; park inverse transformationThe output of the module is used as the output end of the cross decoupling module (3), and the output signal is the set value e of the induced electromotive force^*；

The invention relates to a power decoupling control method of a virtual synchronizer power second-order decoupling controller, which comprises the following steps:

step 1: calculating the equivalent inductance L of the system according to the main circuit parameters_eqEquivalent resistance R_eq：

Wherein, the equivalent inductance L_eqIs calculated as in formula (2):

L_eq＝L_s+L_v+L_g (2)

in the formula, wherein L_sFilter inductance of VSG, L_vFor decoupling the virtual inductance, L_gA network side line inductor;

equivalent resistance R_eqIs calculated as shown in equation (4):

R_eq＝R_s+R_v+R_g (3)

in the formula, wherein R_sFilter resistance, R, for VSG_vTo decouple the virtual resistance, R_gA network side line resistor;

step 2: determining k of proportional-integral element in cross-decoupling module (3) according to conventional method_p，k_iA parameter;

and step 3: based on the system equivalent inductance and resistance calculated in step 1, a given current i is calculated according to formula (1)^*；

And 4, step 4: the dynamic virtual current required for power decoupling is calculated by using an instantaneous power theory in the following specific mode:

step 41: calculating the decoupling components delta i of the virtual current d axis and the q axis P-V needed by P-V decoupling_d(P-V)And Δ i_q(P-V)As shown in formula (4), wherein i_dAnd i_qD-axis and q-axis components of the VSG steady-state stator current, respectively, and Δ V is the voltage variation caused by the disturbance, V₀Is the VSG steady state operating point voltage;

step 42: calculating the required virtual current d-axis and Q-axis Q-delta decoupling components delta i for Q-delta decoupling_d(Q-δ)And Δ i_q(Q-δ)The method comprises the following steps:

step 421: calculating the decoupling components delta i of the d-axis and the Q-axis of the virtual current for compensating the Q-delta first-order coupling quantity_d(Q-δ(1))And Δ i_q(Q-δ(1))The calculation method is shown as formula (5), wherein i_dAnd i_qD-axis and q-axis components of the VSG steady-state stator current, respectively, Δ δ is the power angle variation caused by the disturbance:

step 422: calculating decoupling components delta i of a d axis and a Q axis of virtual current for compensating Q-delta second-order coupling quantity_d(Q-δ(2))And Δ i_q(Q-δ(2))The calculation method is shown as formula (6), wherein i_dAnd i_qD-and q-axis components, V, respectively, of VSG steady-state stator current_gTo the grid-connected point voltage amplitude, X_eqIs a virtual inductor L_eqThe corresponding reactance, Δ δ, is the power angle variation caused by the disturbance:

step 423: synthesizing the virtual current decoupling components obtained in the step 421 and the step 422 into a Q-delta virtual current decoupling component Δ i_d(Q-δ)And Δ i_q(Q-δ)As shown in formula (7):

and 5: as shown in equation (8), a current i is given^*D-axis component i of_d ^*And q-axis component i_q ^*And the one obtained in step 4The P-V decoupling component and the Q-delta virtual current decoupling component are synthesized into a reference current final value i_{d_ref}And i_{q_ref}：

Step 6: the dq axis component i of the final value of the reference current_{d_ref}And i_{q_ref}An input cross decoupling module for outputting a given value e of an induced electromotive force^*After the voltage is sent to a PWM generating device, a control signal is generated, and then the output of VSG is controlled;

the invention has the advantages that: the VSG power second-order decoupling controller based on dynamic virtual current feedforward is designed, the precision problem existing in the traditional VSG power decoupling is solved, the second-order power angle variable quantity is fully considered on the basis of the traditional first-order power decoupling strategy, and the coupling power compensation is realized by utilizing a dynamic virtual current compensation mode based on the instantaneous reactive power theory.

Drawings

Fig. 1 is a typical VSG grid-connected system.

Figure 2 is a control block diagram of a typical VSG system and a system for a new type of SOPDC.

Fig. 3 a-3 b are active and reactive dynamic curve comparisons of VSG outputs using a constant power mode, resistive line parameter conditions, and different decoupling strategies. Wherein FIG. 3a is a graph comparing the dynamic variation curves of active power; fig. 3b is a graph comparing the dynamic change curves of reactive power.

Fig. 4 a-4 b are active and reactive dynamic curve comparisons of VSG outputs using a Q-V droop control mode, resistive line parameter conditions, and different decoupling strategies for the VSG. Wherein FIG. 4a is a graph comparing the dynamic variation curves of active power; fig. 4b is a graph comparing the dynamic variation curves of reactive power.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited to these examples. The embodiment adopts a typical VSG grid-connected system as shown in FIG. 1, the topology is widely applied to research of VSG, and the effect of the invention can be tested by performing simulation analysis on the topology. The specific parameters of the main circuit are shown in table 1.

Table 1 main circuit parameters using VSG

Parameter(s)	Numerical value	Parameter(s)	Numerical value
				Voltage V at DC side_dc	42V	Network side inductor L_g	4.5mH
Filter inductance L_s	0.15mH	Network side resistor R_g	0.045Ω
				Filter capacitor C_s	22uf	Effective value v of grid voltage_g	12V
Filter resistor R_s	0.27Ω

Fig. 2 shows a control block diagram of the SOPDC proposed in the present patent in cooperation with a conventional VSG control method, wherein the VSG control shown in the first part of fig. 2 adopts a classical VSG structure, and its control parameters are listed in table 2:

TABLE 2 control parameters of VSG

Parameter(s)	Numerical value	Parameter(s)	Numerical value
				Active droop coefficient D_P	0.2026	Reactive sag factor D_Q	117.88
Reactive sag factor D_Q	117.88	Coefficient of inertia without power K	74.0286
				Virtual moment of inertia J	0.004	Reference angular velocity omega_r	314rad/s
Virtual resistance R_v	0.005Ω	Virtual inductor L_v	0.15mH

In addition, according to the socdc connection structure, as shown in the second part of fig. 2, building the socdc controller, and according to the built VSG and the structure frame of the socdc, the steps of applying the socdc are as follows:

step 1: calculating the equivalent inductance L of the system by using the formula (2) and the formula (3) according to the main circuit parameters_eqEquivalent resistance R_eq:

L_eq＝L_s+L_v+L_g＝0.15mH+0.15mH+4.5mH＝4.8mH

R_eq＝R_s+R_v+R_g＝0.27Ω+0.005Ω+0.045Ω＝0.32Ω

Step 2: the parameters in the cross-decoupling module (3) are determined according to conventional methods, in this embodiment K_p＝2，K_i＝5；

And step 3: based on the system equivalent inductance and resistance calculated in step 1, given current i is calculated by using formula (1)^*

And 4, step 4: the dynamic virtual current required by power decoupling is calculated by utilizing an instantaneous reactive power theory in the following specific mode:

step 41: calculating the d-axis and q-axis components Delta i of the virtual current required for P-V decoupling by using the formula (4)_d(P-V)And Δ i_q(P-V)

Step 42: calculating the required d-axis and Q-axis components Δ i of virtual current for Q-delta decoupling_d(Q-δ)And Δ i_q(Q-δ)The method comprises the following steps;

step 421: according to the equation (5), the d-axis and Q-axis components Δ i of the virtual current for compensating the Q- δ first-order coupling amount are calculated_d(Q-δ(1))And Δ i_q(Q-δ(1))；

Step 422:according to the equation (6), the d-axis and Q-axis components Δ i of the virtual current for compensating the Q- δ second-order coupling amount are calculated_d(Q-δ(2))And Δ i_q(Q-δ(2))；

Step 423: synthesizing the virtual currents obtained in the steps 321 and 322 into Δ i according to equation (7)_d(Q-δ)And Δ i_q(Q-δ)

And 5: according to equation (8), a given current i^*Synthesized with the dummy current to a reference current final value i_{d_ref}And i_{q_ref}；

Step 6: the final value i of the reference current_{d_ref}And i_{q_ref}An input cross decoupling module for outputting a given value e of an induced electromotive force^*And sending the control signal to a PWM generating device to generate a control signal so as to control the output of VSG;

in order to verify the superiority of the SOPDC provided by the present invention, this section sets the power decoupling effect of the VSG under two modes of common constant power control and Q-V droop control, comparing the following three control strategies under common inductive working condition: no decoupling strategy, a first-order decoupling strategy and a second-order decoupling strategy.

When VSG adopts constant power control, the simulation sets the initial state P of the system_set＝0W，Q_setAt 0.8s, the breaker is closed and the VSG is tied to the grid, 0 Var. Adjusting Q at 1.5s_setAdjusting P to 60Var, 6s_setTo 80W. Under the inductance resistance line parameters, active and reactive dynamic curves of VSG are respectively shown in fig. 3a and fig. 3b, both decoupling strategies have decoupling effects, the second-order decoupling strategy is higher in adjusting speed and smaller in reactive power impact compared with the first-order decoupling strategy, and the control effect of the SOPDC is obvious at the moment;

when VSG adopts Q-V control, setting initial time P in simulation_set＝0W，Q_setWhen the value is 0Var, VSG grid connection is set at 0.8s, and P is set at 3s_setWhen the voltage is changed from 0 to 80W, Q is kept to be 0Var, and the active and reactive dynamic curves of VSG are respectively shown in fig. 4a and 4b under the resistance-inductance line parameter, after the SOPDC is adopted, the steady state deviation of the reactive power is obviously reduced compared with the other two control strategies, and the best decoupling effect among the three is achieved.

The embodiments described in this specification are merely illustrative of implementations of the inventive concept and the scope of the present invention should not be considered limited to the specific forms set forth in the embodiments but rather by the equivalents thereof as may occur to those skilled in the art upon consideration of the present inventive concept.

Claims

1. Virtual synchronous machine VSG power second order decoupling control ware SOPDC, its characterized in that: the SOPDC is arranged at the rear stage of a traditional VSG controller, input signals of the SOPDC are from a superior VSG controller and a measuring unit, and output signals of the SOPDC are input into a PWM wave generating device of a VSG grid-connected inverter;

the given current calculation module (1) has 2 input ends and 2 output ends in total; the first and second input ends are respectively input with the induced electromotive force e output by the VSG controller and the voltage v of the grid-connected point provided by the measuring unit_gThe first output end and the second output end are respectively connected with the first input end and the second input end of the reference current synthesis module (2);

the given current calculation module (1) consists of a transfer function G(s) and a Park converter; the input of the transfer function G(s) is VSG induced electromotive force e and grid-connected point voltage v_gIs output as a given current signal i^*The calculation process is shown as formula (1):

will give a current signal i^*The d-axis and q-axis outputs of the Park converter are respectively connected with a first output end and a second output end of the given current calculation module (1), and the output signals are given current signals i^*D-axis and q-axis ofMeasurement of

And

Virtual current d-axis component Δ i required for decoupling from P-V, Q- δ_d(P-V)、Δi_d(Q-δ)D-axis component signal i of the final value of the reference current is superposed and synthesized_{d_ref}And is output at a first output end of the reference current synthesis module (2); input signal of second input terminal

the cross decoupling module (3) has 6 input ends and 1 output end; the first and second input ends are respectively connected with the first and second output ends of the reference current synthesis module (2), and the input signals of the third and fourth input ends are respectively d-axis and q-axis components i of the output current of the virtual synchronous machine_dAnd i_qFifth, fifth,The input signals of the sixth input end are respectively d-axis and q-axis components v of the grid-connected point voltage_gdAnd v_gqThe output end of the PWM wave generator is connected with a VSG grid-connected inverter;

the cross decoupling module (3) comprises two Gain modules Gain1 and Gain2, and the Gain is omega L_eqAnd- ω L_eqThe device comprises two proportional-integral controllers PI1 and PI2 and a Park inverse transformation module, wherein omega is the electrical angular velocity of VSG; input signal i of the first input terminal_{d_ref}Input signal i to the third input terminal_dThe subtracted signals are input into a PI1 and an input signal i of a fourth input end_qThe output signal of PI1, the output signal of Gain2 and the input signal v of the fifth input end are sent to Gain2_gdD-axis component for generating induced electromotive force given value after superposition

Inputting a q-axis input end of a Park inverse transformation module; the output of the Park inverse transformation module is used as the output end of the cross decoupling module (3), and the output signal is the induced electromotive force given value e^*。

2. The virtual synchronous machine VSG power second-order decoupling controller, SOPDC, of claim 1, wherein: the power decoupling control method comprises the following steps:

Wherein, the equivalent inductance L_eqIs calculated as in formula (2):

L_eq＝L_s+L_v+L_g (2)

equivalent resistance R_eqIs calculated as shown in equation (4):

R_eq＝R_s+R_v+R_g (3)

and 5: as shown in equation (8), a current i is given^*D-axis component i of_d ^*And q-axis component i_q ^*Synthesizing the P-V decoupling component and the Q-delta virtual current decoupling component obtained in the step 4 into a reference current final value i_{d_ref}And i_{q_ref}：

Step 6: the dq axis component i of the final value of the reference current_{d_ref}And i_{q_ref}Input cross decoupling module and output induced electromotive forceGiven value e^*And after being sent to a PWM generating device, the PWM generating device generates a control signal so as to control the output of the VSG.