Global stability control method and system for DC voltage synchronous control, and medium

Abstract

The invention discloses a global stability control method and system for direct current voltage synchronous control and a medium, and the method comprises the steps: building a DVSC-VSC grid-connected system model considering the frequency limitation; based on the DVSC-VSC grid-connected system model, performing synchronous stability analysis on the to-be-configured DVSC-VSC grid-connected system to obtain a damping coefficient range and a stability domain of the to-be-configured DVSC-VSC grid-connected system at the origin; configuring the to-be-configured DVSC-VSC grid-connected system based on the damping coefficient range and the stability domain to obtain the DVSC-VSC grid-connected system; the direct current voltage of the DVSC-VSC grid-connected system is detected in real time; and when the direct-current voltage exceeds the limit value, active damping is provided for the DVSC-VSC grid-connected system, so that the DVSC-VSC grid-connected system is kept stable. According to the invention, stable operation of the converter grid-connected system under the DVSC strategy can be maintained when the DC voltage exceeds the limit.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a global stable control method, system and medium for direct current voltage synchronous control. Background Art

[0002] In recent years, with the massive access of new energy sources, the proportion of power electronic converter type power sources has continued to increase, and the problem of synchronization stability has become increasingly prominent. Grid-building converters are becoming more and more popular than grid-following converters because they can spontaneously provide inertia or frequency support when the power system needs it. Compared with power synchronization control (VSG, PSL, etc.), DC voltage synchronization control (DVSC) uses DC voltage instead of active power modulation to achieve self-synchronization with the grid. Therefore, the wind turbine side can continue to use the MPPT control strategy, and the grid side is responsible for the grid-building function.

[0003] Traditional DVSC control that considers frequency limitation has poor stability under large disturbance conditions, but the control method that provides damping on the generator side also leads to large energy loss. Summary of the invention

[0004] The present invention provides a global stable control method, system and medium for DC voltage synchronous control to solve the above technical problems, which can effectively maintain the stable operation of the converter grid-connected system under the DC voltage synchronous control strategy, thereby improving the stability of the grid-connected system under DC voltage synchronous control.

[0005] In order to solve the above technical problems, the present invention provides a global stable control method for DC voltage synchronous control, comprising:

[0006] Obtain system data of the DVSC-VSC grid-connected system to be configured;

[0007] Establishing a DVSC-VSC grid-connected system model considering frequency limitation based on the system data;

[0008] Based on the DVSC-VSC grid-connected system model, a synchronous stability analysis is performed on the DVSC-VSC grid-connected system to be configured, and a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin are obtained;

[0009] Parameters of the DVSC-VSC grid-connected system to be configured are configured based on the damping coefficient range and the stability domain to obtain the DVSC-VSC grid-connected system;

[0010] Real-time detection of DC voltage of DVSC-VSC grid-connected system;

[0011] When the DC voltage exceeds the limit, active damping is provided to the DVSC-VSC grid-connected system to maintain the stability of the DVSC-VSC grid-connected system.

[0012] The beneficial effects of the present invention are:

[0013] The present invention is based on an established DVSC-VSC grid-connected system model, performs synchronous stability analysis on the DVSC-VSC grid-connected system to be configured, obtains a damping coefficient range and a stability domain, performs parameter configuration on the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain, and provides active damping to the DVSC-VSC grid-connected system when the DC voltage exceeds a limit value by real-time detection of the DC voltage of the DVSC-VSC grid-connected system, so as to maintain the stability of the DVSC-VSC grid-connected system. In this way, when the voltage exceeds the limit, the stable operation of the converter grid-connected system under the DC voltage synchronous control strategy can be effectively maintained, thereby improving the stability of the grid-connected system under the DC voltage synchronous control.

[0014] As a preferred solution, the DVSC-VSC grid-connected system model includes:

[0015]

[0016] In the above formula, θ is the phase angle of the DVSC-VSC grid-connected system to be configured; ω s is the infinite bus frequency, ω c is the inverter frequency; P ref The output power command or other given active power command obtained by the maximum power tracking algorithm on the generator side; max is the upper limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; V DC Indicates the DC voltage of the converter, V DCmax and V DCmin V DC The upper and lower limits, V DC0 is the steady-state value of DC voltage; k DC is the frequency-DC voltage droop coefficient; P in is the input power on the machine side; k D is the active damping coefficient; C is the equivalent per unit value of the DC bus capacitance; U p is the PCC voltage command value; U s is infinite bus voltage.

[0017] As a preferred solution, after establishing the DVSC-VSC grid-connected system model considering frequency limitation based on the system data, the method further includes:

[0018] Based on x=θ-θ s ,y=ω c -ω s , The DVSC-VSC grid-connected system model is standardized to update the DVSC-VSC grid-connected system model and obtain:

[0019]

[0020] In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower limit of the frequency limiter; U p is the PCC voltage command value; U s is the infinite bus voltage; C is the equivalent per unit value of the DC bus capacitance; k DC is the frequency-DC voltage droop coefficient; P ref is the output power command or other given active power command obtained by the machine-side maximum power tracking algorithm; D is the damping coefficient; k D is the active damping coefficient.

[0021] As a preferred solution, based on the DVSC-VSC grid-connected system model, a synchronous stability analysis is performed on the DVSC-VSC grid-connected system to be configured, and a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin are obtained, including:

[0022] Based on the DVSC-VSC grid-connected system model, the minimum damping loss energy in a single cycle and the potential energy change of the DVSC-VSC grid-connected system to be configured on two adjacent UEPs are obtained;

[0023] Based on the minimum damping loss energy and potential energy change, the damping coefficient range is solved;

[0024] Establishing an energy function based on the DVSC-VSC grid-connected system model;

[0025] The energy function is solved to obtain the stability domain of the DVSC-VSC grid-connected system to be configured at the origin.

[0026] As a preferred solution, the parameter configuration of the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain includes:

[0027] The active damping coefficient of the DVSC-VSC grid-connected system to be configured is configured based on the damping coefficient range, so that the change in potential energy of the DVSC-VSC grid-connected system in any period is always less than the damping loss energy;

[0028] The switching fixed point of the DVSC-VSC grid-connected system to be configured is configured within the stable domain, so that the DVSC-VSC grid-connected system is in a synchronous stable state when the DC voltage is within the limit.

[0029] As a preferred solution, the energy of the switching fixed point satisfies the following formula:

[0030]

[0031] In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; E(x b ,0) is the energy of the stability boundary of the infinite DVSC-VSC grid-connected system to be configured.

[0032] As a preferred solution, the step of configuring the switching fixed point of the DVSC-VSC grid-connected system to be configured within the stable domain includes:

[0033] Based on the energy of the switching fixed point, a frequency limit requirement is obtained; the frequency limit requirement is specifically:

[0034]

[0035] In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; E(x b ,0) is the energy of the stability boundary of the infinite-amplitude DVSC-VSC grid-connected system to be configured;

[0036] Based on the frequency limit requirement, the frequency limit of the frequency limiter of the DVSC-VSC grid-connected system to be configured is configured to configure the switching fixed point of the DVSC-VSC grid-connected system to be configured within the stable domain.

[0037] Accordingly, in order to solve the above technical problems, the present invention also provides a global stability control system for DC voltage synchronous control, comprising: a model building module, a stability analysis module, a system configuration module, a voltage detection module and a stability control module;

[0038] The model building module is used to obtain system data of the DVSC-VSC grid-connected system to be configured; and to establish a DVSC-VSC grid-connected system model taking frequency restrictions into consideration based on the system data;

[0039] The stability analysis module is used to perform synchronous stability analysis on the DVSC-VSC grid-connected system to be configured based on the DVSC-VSC grid-connected system model, and obtain a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin;

[0040] The system configuration module is used to perform parameter configuration on the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain to obtain the DVSC-VSC grid-connected system;

[0041] The voltage detection module is used to detect the DC voltage of the DVSC-VSC grid-connected system in real time;

[0042] The stability control module is used to provide active damping to the DVSC-VSC grid-connected system when the DC voltage exceeds the limit value, so as to maintain the stability of the DVSC-VSC grid-connected system.

[0043] As a preferred solution, the DVSC-VSC grid-connected system model includes:

[0044]

[0045] In the above formula, θ is the phase angle of the DVSC-VSC grid-connected system to be configured; ω s is the infinite bus frequency, ω c is the inverter frequency; P ref The output power command or other given active power command obtained by the maximum power tracking algorithm on the generator side; max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; V DC Indicates the DC voltage of the converter, V DC0 is the steady-state value of DC voltage; k DC is the frequency-DC voltage droop coefficient; P in is the input power on the machine side; k D is the active damping coefficient; C is the equivalent per unit value of the DC bus capacitance; U p is the PCC voltage command value; U s is infinite bus voltage.

[0046] The present invention also provides a storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of the global stabilization control method for direct current voltage synchronous control as described in any one of the above items are implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 : A flow chart of an embodiment of a global stabilization control method for direct current voltage synchronous control provided by the present invention;

[0048] Figure 2 : A control block diagram of a DVSC-VSC grid-connected system to be configured provided by an embodiment of the present invention;

[0049] Figure 3 : A schematic diagram of calculating the damping loss energy of a DVSC-VSC grid-connected system to be configured according to an embodiment of the present invention;

[0050] Figure 4 : A schematic diagram of a critical curve of minimum damping loss energy provided by an embodiment of the present invention;

[0051] Figure 5: Schematic diagram of two switching processes provided by an embodiment of the present invention;

[0052] Figure 6 : A schematic diagram of the dynamic behavior of the DVSC-VSC grid-connected system when the active damping coefficient is 10 provided in an embodiment of the present invention;

[0053] Figure 7 : A schematic diagram of a dynamic response of a DVSC-VSC grid-connected system considering frequency restriction and a dynamic response of a DVSC-VSC grid-connected system not considering frequency restriction provided by an embodiment of the present invention;

[0054] Figure 8 : A structural schematic diagram of an embodiment of a global stable control system for DC voltage synchronous control provided by the present invention. DETAILED DESCRIPTION

[0055] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Embodiment 1

[0057] The present invention provides a global stable control method, system and medium for DC voltage synchronous control to solve the above technical problems, which can effectively maintain the stable operation of the converter grid-connected system under the DC voltage synchronous control strategy, thereby improving the stability of the grid-connected system under DC voltage synchronous control.

[0058] Please refer to Figure 1 , which is a flow chart of an embodiment of a global stability control method for DC voltage synchronous control provided in an embodiment of the present invention.

[0059] like Figure 1 As shown, the global stability control method of DC voltage synchronous control includes steps 101 to 106, specifically:

[0060] Step 101: Acquire system data of the DVSC-VSC grid-connected system to be configured;

[0061] Step 102: establishing a DVSC-VSC grid-connected system model considering frequency limitation based on the system data;

[0062] Step 103: Based on the DVSC-VSC grid-connected system model, a synchronous stability analysis is performed on the DVSC-VSC grid-connected system to be configured, and a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin are obtained;

[0063] Step 104: Parameter configuration is performed on the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain to obtain the DVSC-VSC grid-connected system;

[0064] Step 105: Real-time detection of the DC voltage of the DVSC-VSC grid-connected system;

[0065] Step 106: When the DC voltage exceeds the limit, active damping is provided to the DVSC-VSC grid-connected system to maintain the stability of the DVSC-VSC grid-connected system.

[0066] In this embodiment, the DVSC-VSC grid-connected system is a voltage source converter grid-connected system under the DVSC control strategy.

[0067] In this embodiment, the limit value is artificially set according to actual engineering, and is generally 10% of the rated voltage.

[0068] In this embodiment, active damping is provided specifically by the machine side.

[0069] The present invention is based on an established DVSC-VSC grid-connected system model, performs synchronous stability analysis on the DVSC-VSC grid-connected system to be configured, obtains a damping coefficient range and a stability domain, performs parameter configuration on the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain, and provides active damping to the DVSC-VSC grid-connected system when the DC voltage exceeds a limit value by real-time detection of the DC voltage of the DVSC-VSC grid-connected system, so as to maintain the stability of the DVSC-VSC grid-connected system. In this way, when the voltage exceeds the limit, the stable operation of the converter grid-connected system under the DC voltage synchronous control strategy can be effectively maintained, thereby improving the stability of the grid-connected system under the DC voltage synchronous control.

[0070] Further, when the DC voltage does not exceed the limit value, the DVSC-VSC grid-connected system is maintained stable by the frequency limit value. In this embodiment, when the DC voltage does not exceed the limit value, no active damping is provided for the DVSC-VSC grid-connected system.

[0071] Furthermore, in step 102, the DVSC-VSC grid-connected system model includes:

[0072]

[0073] In the above formula, θ is the phase angle of the DVSC-VSC grid-connected system to be configured; ω sis the infinite bus frequency, ω c is the inverter frequency; P ref The output power command or other given active power command obtained by the maximum power tracking algorithm on the generator side; max is the upper limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; V DC Indicates the DC voltage of the converter, V DCmax and V DCmin V DC The upper and lower limits, V DC0 is the steady-state value of DC voltage; k DC is the frequency-DC voltage droop coefficient; P in is the input power on the machine side; k D is the active damping coefficient; C is the equivalent per unit value of the DC bus capacitance; U p is the PCC voltage command value; U s is infinite bus voltage.

[0074] Please refer to the following Figure 2 , Figure 2 A control block diagram of a DVSC-VSC grid-connected system to be configured provided in an embodiment of the present invention.

[0075] In this embodiment, based on Figure 2 A dynamic model based on generation switching of the DVSC-VSC grid-connected system to be configured can be established; the dynamic model is specifically:

[0076]

[0077] In the above formula, θ is the phase angle of the DVSC-VSC grid-connected system to be configured; ω s is the infinite bus frequency, ω c is the inverter frequency; P ref The output power command or other given active power command obtained by the maximum power tracking algorithm on the generator side; max is the upper limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; V DC Indicates the DC voltage of the converter, V DCmax and V DCmin V DC The upper and lower limits, V DC0 is the steady-state value of DC voltage; k DC is the frequency-DC voltage droop coefficient; P c is the actual output power of the converter; P in is the input power on the machine side; k D is the active damping coefficient; C is the equivalent per unit value of the DC bus capacitance; U p is the PCC voltage command value; Us is infinite bus voltage.

[0078] In this embodiment, the DVSC-VSC grid-connected system model can be obtained by arranging the dynamic model.

[0079] Further, after the DVSC-VSC grid-connected system model considering frequency limitation is established based on the system data, the method further includes:

[0080] Based on x=θ-θ s ,y=ω c -ω s , The DVSC-VSC grid-connected system model is standardized to update the DVSC-VSC grid-connected system model and obtain:

[0081]

[0082] in,

[0083]

[0084] In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; U p is the PCC voltage command value; U s is the infinite bus voltage; C is the equivalent per unit value of the DC bus capacitance; k DC is the frequency-DC voltage droop coefficient; P ref is the output power command or other given active power command obtained by the machine-side maximum power tracking algorithm; D is the damping coefficient; k D is the active damping coefficient; X1 is the equivalent reactance of the transmission line; θ s is the steady-state value of the state variable θ.

[0085] Further, in step 103, based on the DVSC-VSC grid-connected system model, a synchronous stability analysis is performed on the DVSC-VSC grid-connected system to be configured, and a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin are obtained, including:

[0086] Based on the DVSC-VSC grid-connected system model, the minimum damping loss energy in a single cycle and the potential energy change of the DVSC-VSC grid-connected system to be configured on two adjacent UEPs are obtained;

[0087] Based on the minimum damping loss energy and potential energy change, the damping coefficient range is solved;

[0088] Establishing an energy function based on the DVSC-VSC grid-connected system model;

[0089] The energy function is solved to obtain the stability domain of the DVSC-VSC grid-connected system to be configured at the origin.

[0090] In this embodiment, based on the DVSC-VSC grid-connected system model, the DVSC-VSC grid-connected system to be configured is subjected to synchronous stability analysis to obtain the damping coefficient range and the stability domain of the DVSC-VSC grid-connected system to be configured at the origin, specifically: according to the DVSC-VSC grid-connected system model, a Lyapunov function is established for the DVSC-VSC grid-connected system to be configured whose voltage (frequency) exceeds the limit, and synchronous stability analysis is performed. Among them, the Lyapunov function is established for the DVSC-VSC grid-connected system to be configured whose voltage (frequency) exceeds the limit, and the analysis process of synchronous stability analysis is as follows:

[0091] The following energy function is constructed to solve the stability domain of the DVSC-VSC grid-connected system to be configured at the origin:

[0092]

[0093] In the above formula, γ is the integral variable;

[0094] The time derivative of E(x,y) is not positive.

[0095]

[0096] Let E(x,y)>0, then the stability region of the DVSC-VSC grid-connected system to be configured is (x a ,x b ),

[0097]

[0098] By performing inverse coordinate transformation, the stability domain of the original system within any period k is obtained as:

[0099]

[0100] Among them, θ uep,k is the phase angle of UEP in the kth cycle of the DVSC-VSC grid-connected system to be configured.

[0101] If the phase angle of any system trajectory is within the interval shown, the DVSC-VSC grid-connected system to be configured can be stabilized at the SEP of the kth cycle. In other words, only when the system phase angle θ of the DVSC-VSC grid-connected system to be configured does not exceed the phase angle θ of the unstable equilibrium point of the system in the k+1th cycle uep,k+1 When , the system trajectory of the DVSC-VSC grid-connected system to be configured can converge on the SEP of the kth cycle.

[0102] The state equation when the voltage exceeds the limit, that is, equation (4), is rearranged to obtain:

[0103]

[0104] For any system trajectory (PQ), P(x p ,y p ), Q(x q ,y q ), integrate and sort out:

[0105]

[0106] When the damping of the DVSC-VSC grid-connected system to be configured is not considered, that is, the damping coefficient D = 0, the energy of the DVSC-VSC grid-connected system to be configured is conserved, that is, V q =V p , that is, the energy change of the DVSC-VSC grid-connected system to be configured is equal to the energy of the system damping loss.

[0107] Please refer to the following Figure 3 and Figure 4 , Figure 3 A schematic diagram of the calculation of damping loss energy of a DVSC-VSC grid-connected system to be configured provided in an embodiment of the present invention. Figure 4 A schematic diagram of a critical curve of minimum damping loss energy provided by an embodiment of the present invention.

[0108] Defining a variable To characterize the energy of the system's damping loss on any trajectory PQ. Any second-order nonlinear system trajectory can be drawn in the phase plane diagram. The damping loss energy is equal to the damping coefficient D multiplied by the area enclosed by the system trajectory and the x-axis in the phase plane diagram, such as Figure 3 shown.

[0109] Assume that there is a system trajectory whose UEP in the kth cycle and the k+1th cycle are (θ uep,k ,ω c,k ) and (θ uep,k+1 ,ω c,k+1 ), then the stability region of the SEP in the kth period is [θ uep,k ,θ uep,k+1 ]. The system trajectory of the kth period, that is, from point (θ uep,k ,ω c,k ) moves to point (θ uep,k+1 ,ω c,k+1 ), and is transformed into the coordinate system from point (x a ,y k ) to point (x b ,y k+1), denoted as l k,k+1 .in:

[0110] y k =ω c,k -ω s ,y k+1 =ω c,k+1 -ω s ;

[0111] Then we have:

[0112]

[0113] in, is a constant, indicating that from point (x a ,y k ) to point (x b ,y k+1 )The change in potential energy of the system. System trajectory l k,k+1 The damping loss energy on the curve is equal to the damping coefficient D multiplied by the curve l k,k+1 The area enclosed by the x-axis is:

[0114]

[0115] If there exists a system trajectory that satisfies y(x b )=0, the damping loss energy can be minimized, which is called the minimum damping loss energy in a single cycle and is recorded as The corresponding curve is called the critical curve, denoted by l min ,like Figure 4 As shown, then:

[0116]

[0117] If the minimum damping loss energy in a single cycle is greater than the potential energy change of the DVSC-VSC grid-connected system to be configured on two adjacent UEPs, the global stability of the DVSC-VSC grid-connected system can be ensured, that is:

[0118]

[0119] By choosing a suitable active damping coefficient k D So that the above formula is established, the active damping coefficient k is calculated to be D The requirements are met when the following damping coefficient range is met:

[0120]

[0121] In the above formula, S eq is the area enclosed by the critical curve and the x-axis.

[0122] The larger the active damping coefficient is, the easier it is for the DVSC-VSC grid-connected system to be stable. D When the requirements are met, the change in potential energy of the DVSC-VSC grid-connected system in any period is always less than the damping loss energy, resulting in a continuous decrease in the kinetic energy of the DVSC-VSC grid-connected system, and eventually decreasing to 0, thereby ensuring the global stability of the DVSC-VSC grid-connected system. Therefore, the present invention obtains a damping coefficient range by analyzing the critical energy of the DVSC-VSC grid-connected system, and selects a suitable active damping coefficient to configure the DVSC-VSC grid-connected system based on the damping coefficient range, so that when the DC voltage of the DVSC-VSC grid-connected system exceeds the limit, the DC voltage of the DVSC-VSC grid-connected system can be guaranteed to return to the limit.

[0123] In this embodiment, based on the switching theory, the DVSC-VSC grid-connected system to be configured can be divided into three subsystems h1 to h3, specifically:

[0124]

[0125] in,

[0126]

[0127] In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; U p is the PCC voltage command value; U s is the infinite bus voltage; P ref is the output power command or other given active power command obtained by the machine-side maximum power tracking algorithm; D is the damping coefficient; k D is the active damping coefficient; θ0 is the initial steady-state angle; L l is the transmission line inductance; ω s is the infinite bus frequency; and is the switching line of the subsystem; T c I is the inertia of the DVSC-VSC grid-connected system to be configured; cmax is the saturation current amplitude.

[0128] In this embodiment, θ s is the steady-state value of the state variable θ in subsystem h2.

[0129] In this embodiment, the transmission line inductance L l The value may be, but is not limited to, 15mH.

[0130] There are two switching processes between these three subsystems.

[0131] Please refer to the following Figure 5 , Figure 5 A schematic diagram of two switching processes provided by an embodiment of the present invention.

[0132] like Figure 5 As shown in the figure, the first switching process is that the system trajectory is from the first subsystem h1 to the upper bound, then leaves the upper bound and returns to the first subsystem h1, which is recorded as h1→h2→h1; the second switching process is that the system trajectory is from the first subsystem h1 to the lower bound, then leaves the lower bound and returns to the first subsystem h1, which is recorded as h1→h3→h1.

[0133] For the first switching process of h1 h1→h2→h1, it is assumed that the DVSC-VSC grid-connected system to be configured reaches the upper limit at point A. And there are Then we have:

[0134]

[0135] Then, the system trajectory follows Move and leave the upper limit at point B, which is recorded as and Then we have:

[0136]

[0137] For the second switching process of h1 h1→h3→h1, the system reaches the lower limit at point C. And there are Then we have:

[0138]

[0139] Then, the system trajectory follows Move and leave the upper limit at point D, which is recorded as and Then we have:

[0140]

[0141] When the frequency limit value (y max ,y min ) is determined, then the solutions of the following two equations are also fixed, denoted as and

[0142]

[0143] Further we can get:

[0144]

[0145] It can be seen that the system trajectory located within the left and right switching lines is and The two switching fixed points leave the upper and lower limits, regardless of the number of switching times.

[0146] Therefore, it is only necessary to change the fixed point position by configuring the frequency limit of the frequency limiter in the DVSC-VSC grid-connected system to be configured so that the fixed point is located within the stability domain of the system, thereby ensuring the synchronous stability of the system under study within the DC voltage limit.

[0147] Further, in step 104, the parameter configuration of the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain includes:

[0148] The active damping coefficient of the DVSC-VSC grid-connected system to be configured is configured based on the damping coefficient range, so that the change in potential energy of the DVSC-VSC grid-connected system in any period is always less than the damping loss energy;

[0149] The switching fixed point of the DVSC-VSC grid-connected system to be configured is configured within the stable domain, so that the DVSC-VSC grid-connected system is in a synchronous stable state when the DC voltage is within the limit.

[0150] Furthermore, the energy of the switching fixed point satisfies the following formula:

[0151]

[0152] In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; E(x b ,0) is the energy of the stability boundary of the infinite DVSC-VSC grid-connected system to be configured.

[0153] Further, configuring the switching fixed point of the DVSC-VSC grid-connected system to be configured within the stable domain includes:

[0154] Based on the energy of the switching fixed point, a frequency limit requirement is obtained; the frequency limit requirement is specifically:

[0155]

[0156] In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; E(x b ,0) is the energy of the stability boundary of the infinite-amplitude DVSC-VSC grid-connected system to be configured;

[0157] Based on the frequency limit requirement, the frequency limit of the frequency limiter of the DVSC-VSC grid-connected system to be configured is configured to configure the switching fixed point of the DVSC-VSC grid-connected system to be configured within the stable domain.

[0158] The present invention configures the frequency limit of the frequency limiter of the DVSC-VSC grid-connected system to be configured based on the frequency limit requirement, so as to configure the switching fixed point of the DVSC-VSC grid-connected system to be configured within the stable domain, and configures the parameters of the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stable domain, so that when the DC voltage of the DVSC-VSC grid-connected system exceeds the limit, the stability of the DVSC-VSC grid-connected system is maintained by providing active damping on the machine side, and when the DC voltage is within the limit range, the stability of the DVSC-VSC grid-connected system is maintained by frequency limitation, thereby effectively maintaining the stable operation of the converter grid-connected system under the DC voltage synchronous control strategy, improving the stability of the grid-connected system under the DC voltage synchronous control, and achieving economic operation under small interference and synchronous stability under large interference.

[0159] The present invention reasonably configures the frequency limit of the frequency limiter of the DVSC-VSC grid-connected system to be configured, so that when the DC voltage of the DVSC-VSC grid-connected system does not exceed the limit, the frequency limit can be used to ensure the synchronization stability of the system.

[0160] Please refer to the following Figure 6 and Figure 7 .in, Figure 6 A schematic diagram of the dynamic behavior of a DVSC-VSC grid-connected system when the active damping coefficient is 10 provided in an embodiment of the present invention; Figure 7 A schematic diagram of a dynamic response of a DVSC-VSC grid-connected system considering frequency limitation and a dynamic response of a DVSC-VSC grid-connected system not considering frequency limitation provided in an embodiment of the present invention.

[0161] like Figure 6 As shown, when the active damping coefficient meets the requirements, the DVSC-VSC grid-connected system can maintain synchronous stability no matter how long the fault lasts, which verifies the effectiveness of the active damping coefficient theory proposed in the present invention.

[0162] exist Figure 7 In the figure, the dotted line represents the dynamic response of the DVSC-VSC grid-connected system without considering the frequency limit, and the solid line represents the dynamic response of the DVSC-VSC grid-connected system with considering the frequency limit. Figure 7As shown in the figure, when the frequency limit is not considered, the DVSC-VSC grid-connected system will experience non-periodic instability, while the DVSC-VSC grid-connected system considering the frequency limit can still return to the steady-state point. This shows that the frequency limit can increase the stability domain of the DVSC-VSC grid-connected system and greatly improve the system stability.

[0163] In this embodiment, the PCC voltage command value U p The value can be, but is not limited to, 10 kV; infinite bus voltage U s The value may be, but is not limited to, 10.5 kV.

[0164] Accordingly, in order to solve the above technical problems, the embodiment of the present invention also provides a global stable control system for DC voltage synchronous control. Figure 8 , which is a structural schematic diagram of an embodiment of a global stable control system for DC voltage synchronous control provided by the present invention.

[0165] like Figure 8 As shown, the global stability control system 20 of DC voltage synchronous control includes: a model building module 201, a stability analysis module 202, a system configuration module 203, a voltage detection module 204 and a stability control module 205;

[0166] The model building module 201 is used to obtain system data of the DVSC-VSC grid-connected system to be configured; and to establish a DVSC-VSC grid-connected system model taking frequency restrictions into consideration based on the system data;

[0167] The stability analysis module 202 is used to perform synchronous stability analysis on the DVSC-VSC grid-connected system to be configured based on the DVSC-VSC grid-connected system model, and obtain a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin;

[0168] The system configuration module 203 is used to perform parameter configuration on the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain to obtain the DVSC-VSC grid-connected system;

[0169] The voltage detection module 204 is used to detect the DC voltage of the DVSC-VSC grid-connected system in real time;

[0170] The stability control module 205 is used to provide active damping to the DVSC-VSC grid-connected system when the DC voltage exceeds the limit value, so as to maintain the stability of the DVSC-VSC grid-connected system.

[0171] Furthermore, the DVSC-VSC grid-connected system model includes:

[0172]

[0173] In the above formula, θ is the phase angle of the DVSC-VSC grid-connected system to be configured; ω s is the infinite bus frequency, ω c is the inverter frequency; P ref The output power command or other given active power command obtained by the maximum power tracking algorithm on the generator side; max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; V DC Indicates the DC voltage of the converter, V DC0 is the steady-state value of DC voltage; k DC is the frequency-DC voltage droop coefficient; P in is the input power on the machine side; k D is the active damping coefficient; C is the equivalent per unit value of the DC bus capacitance; U p is the PCC voltage command value; U s is infinite bus voltage.

[0174] The present invention also provides a storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of the global stabilization control method for direct current voltage synchronous control as described in any one of the above items are implemented.

[0175] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0176] Compared with the traditional DVSC control considering frequency limitation, the stability is poor under large disturbance conditions, but the control method of providing damping on the machine side will also lead to technical problems such as large energy loss. The present invention first establishes a DVSC-VSC grid-connected system model, and based on the model, analyzes the system stability conditions of the voltage (frequency) exceeding the limit, establishes a switching subsystem function within the frequency limit, obtains the damping coefficient range, frequency limit requirements and stability domain, and configures the frequency limit of the frequency limiter of the DVSC-VSC grid-connected system to be configured based on the frequency limit requirements, so as to configure the switching fixed point of the DVSC-VSC grid-connected system to be configured within the stability domain, and configures the parameters of the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain. , so that when the DC voltage of the DVSC-VSC grid-connected system exceeds the limit, the stability of the DVSC-VSC grid-connected system is maintained by providing active damping on the machine side, and when the DC voltage is within the limit, the stability of the DVSC-VSC grid-connected system is maintained by frequency limitation. This can effectively maintain the stable operation of the converter grid-connected system under the DC voltage synchronization control strategy, achieve global stable control of the DVSC-VSC grid-connected system, improve the stability of the grid-connected system under DC voltage synchronization control, and achieve economic operation under small interference and synchronous stability under large interference.

[0177] The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A global stable control method for DC voltage synchronous control, characterized in that: include: Obtain system data of the DVSC-VSC grid-connected system to be configured; Establishing a DVSC-VSC grid-connected system model considering frequency limitation based on the system data; Based on the DVSC-VSC grid-connected system model, a synchronous stability analysis is performed on the DVSC-VSC grid-connected system to be configured, and a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin are obtained; Parameters of the DVSC-VSC grid-connected system to be configured are configured based on the damping coefficient range and the stability domain to obtain the DVSC-VSC grid-connected system; Real-time detection of DC voltage of DVSC-VSC grid-connected system; When the DC voltage exceeds the limit, active damping is provided to the DVSC-VSC grid-connected system to maintain the stability of the DVSC-VSC grid-connected system.

2. A global stable control method for DC voltage synchronous control according to claim 1, characterized in that: The DVSC-VSC grid-connected system model includes: In the above formula, θ is the phase angle of the DVSC-VSC grid-connected system to be configured; ω s is the infinite bus frequency, ω c is the inverter frequency; P ref The output power command or other given active power command obtained by the maximum power tracking algorithm on the generator side; max is the upper limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; V DC Indicates the DC voltage of the converter, V DCmax and V DCmin V DC The upper and lower limits, V DC0 is the steady-state value of DC voltage; k DC is the frequency-DC voltage droop coefficient; P in is the input power on the machine side; k D is the active damping coefficient; C is the equivalent per unit value of the DC bus capacitance; U p is the PCC voltage command value; U s is infinite bus voltage.

3. A global stable control method for DC voltage synchronous control as claimed in claim 2, characterized in that: After the DVSC-VSC grid-connected system model considering frequency limitation is established based on the system data, the method further includes: Based on x=θ-θ s ,y=ω c -ω s , The DVSC-VSC grid-connected system model is standardized to update the DVSC-VSC grid-connected system model and obtain: In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; U p is the PCC voltage command value; U s is the infinite bus voltage; C is the equivalent per unit value of the DC bus capacitance; k DC is the frequency-DC voltage droop coefficient; P ref is the output power command or other given active power command obtained by the machine-side maximum power tracking algorithm; D is the damping coefficient; k D is the active damping coefficient.

4. A global stable control method for DC voltage synchronous control as claimed in claim 3, characterized in that: Based on the DVSC-VSC grid-connected system model, performing synchronous stability analysis on the DVSC-VSC grid-connected system to be configured, obtaining a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin, including: Based on the DVSC-VSC grid-connected system model, the minimum damping loss energy in a single cycle and the potential energy change of the DVSC-VSC grid-connected system to be configured on two adjacent UEPs are obtained; Based on the minimum damping loss energy and potential energy change, the damping coefficient range is solved; Establishing an energy function based on the DVSC-VSC grid-connected system model; The energy function is solved to obtain the stability domain of the DVSC-VSC grid-connected system to be configured at the origin.

5. A global stable control method for DC voltage synchronous control according to claim 1, characterized in that: The parameter configuration of the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain includes: The active damping coefficient of the DVSC-VSC grid-connected system to be configured is configured based on the damping coefficient range, so that the change in potential energy of the DVSC-VSC grid-connected system in any period is always less than the damping loss energy; The switching fixed point of the DVSC-VSC grid-connected system to be configured is configured within the stable domain, so that the DVSC-VSC grid-connected system is in a synchronous stable state when the DC voltage is within the limit.

6. A global stable control method for direct current voltage synchronous control as claimed in claim 5, characterized in that: The energy of the switching fixed point satisfies the following formula: In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; E(x b ,0) is the energy of the stability boundary of the infinite DVSC-VSC grid-connected system to be configured.

7. A global stable control method for direct current voltage synchronous control as claimed in claim 6, characterized in that: The step of configuring the switching fixed point of the DVSC-VSC grid-connected system to be configured within the stable domain includes: Based on the energy of the switching fixed point, a frequency limit requirement is obtained; the frequency limit requirement is specifically: In the above formula, y max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; E(x b ,0) is the energy of the stability boundary of the infinite amplitude DVSC-VSC grid-connected system to be configured; Based on the frequency limit requirement, the frequency limit of the frequency limiter of the DVSC-VSC grid-connected system to be configured is configured to configure the switching fixed point of the DVSC-VSC grid-connected system to be configured within the stable domain.

8. A global stable control system for DC voltage synchronous control, characterized in that: include: Model building module, stability analysis module, system configuration module, voltage detection module and stability control module; The model building module is used to obtain system data of the DVSC-VSC grid-connected system to be configured; and to establish a DVSC-VSC grid-connected system model taking frequency restrictions into consideration based on the system data; The stability analysis module is used to perform synchronous stability analysis on the DVSC-VSC grid-connected system to be configured based on the DVSC-VSC grid-connected system model, and obtain a damping coefficient range and a stability domain of the DVSC-VSC grid-connected system to be configured at the origin; The system configuration module is used to perform parameter configuration on the DVSC-VSC grid-connected system to be configured based on the damping coefficient range and the stability domain to obtain the DVSC-VSC grid-connected system; The voltage detection module is used to detect the DC voltage of the DVSC-VSC grid-connected system in real time; The stability control module is used to provide active damping to the DVSC-VSC grid-connected system when the DC voltage exceeds the limit value, so as to maintain the stability of the DVSC-VSC grid-connected system.

9. A global stable control system for DC voltage synchronous control as claimed in claim 8, characterized in that: The DVSC-VSC grid-connected system model includes: In the above formula, θ is the phase angle of the DVSC-VSC grid-connected system to be configured; ω s is the infinite bus frequency, ω c is the inverter frequency; P ref The output power command or other given active power command obtained by the maximum power tracking algorithm on the generator side; max is the upper frequency limit of the frequency limiter, y min is the lower frequency limit of the frequency limiter; V DC Indicates the DC voltage of the converter, V DC0 is the steady-state value of DC voltage; k DC is the frequency-DC voltage droop coefficient; P in is the input power on the machine side; k D is the active damping coefficient; C is the equivalent per unit value of the DC bus capacitance; U p is the PCC voltage command value; U s is infinite bus voltage.

10. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the global stabilization control method for DC voltage synchronous control as claimed in any one of claims 1 to 7 are implemented.

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