Active supporting method and system for multi-port voltage frequency of power electronic transformer

Abstract

The invention discloses a multi-port voltage frequency active support method and system for a power electronic transformer, and the method comprises the following steps: achieving the voltage support of an AC port based on the reactive power-voltage active control of the residual reactive power capacity of the AC port; the reactive power-voltage droop coefficient of each port is calculated in a self-adaptive mode, and the reactive power support quantity under the voltage situation is obtained through the positive sequence voltage of the grid-connected point of the alternating current port; and realizing frequency support of an alternating current port based on active-frequency active control of a fractional order PI lambda controller: calculating a power reference value corresponding to active power of the port according to different control targets, and realizing rapid output of a PWM pulse modulation signal through power outer loop control based on the fractional order PI lambda controller. According to the invention, the AC port with power supporting capability provides voltage and frequency support, so that the voltage of the grid-connected point of the AC port is improved, and the frequency of the grid-connected point of the AC port is stabilized.

Description

Technical Field

[0001] The invention relates to the technical field of AC port control of power electronic transformers, and in particular to a method and system for actively supporting multi-port voltage and frequency of a power electronic transformer. Background Art

[0002] Due to the superiority of fractional-order controllers, more and more fractional-order controllers are applied to power electronics technology, making the control performance of power electronics better. In 1999, Igor Podlubny proposed the fractional-order PI λ D u Controller, in recent years, fractional-order controllers have achieved success in many fields. At present, some scholars have designed the optimal passive fractional-order PID (PFOPID) for grid-connected photovoltaic inverters, and compared PFOPID control with conventional PID control, FOPID control and passivity-based control (PBC), pointing out that PFOPID can achieve maximum power tracking under various working conditions and has good dynamic characteristics.

[0003] The research on power electronic control technology has promoted the rapid development of renewable energy power generation technology. Traditional converters (grid-following converters) usually operate in maximum power tracking mode or power controlled mode. This mode can flexibly adjust the output power of distributed power sources, but does not have the ability to actively support voltage / frequency. A large number of connections will lead to a decrease in the system inertia level, endangering the safe and stable operation of the system. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for active voltage and frequency support of multiple ports of a power electronic transformer, in which an AC port with power support capability provides voltage and frequency support, thereby increasing the voltage of the AC port grid connection point and stabilizing the frequency of the AC port grid connection point.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A first aspect of the present invention relates to a method for actively supporting multi-port voltage and frequency of a power electronic transformer, comprising the following steps:

[0007] Active reactive-voltage control based on the residual reactive capacity of the AC port realizes the voltage support of the AC port: the reactive-voltage active control adaptively calculates the reactive-voltage droop coefficient of each port according to the residual reactive capacity of the AC port, and obtains the reactive support amount under the voltage situation through the positive sequence voltage of the AC port grid connection point;

[0008] Based on fractional order PI λThe controller's active power-frequency active control realizes the frequency support of the AC port: the active power-frequency active control calculates the power reference value corresponding to the port active power according to different control targets, and λ The controller power outer loop control realizes the fast output of PWM pulse modulation signal.

[0009] A further improvement of the technical solution of the present invention is that: according to the real-time operation data of the AC port, the residual reactive capacity of the AC ports of different capacities is calculated to determine the ability of the AC port to participate in active voltage support. The formula for the residual reactive capacity of the AC port is as follows:

[0010]

[0011] In the formula, S i represents the total capacity of AC port i, P i, represents the output active power of AC port i, n is the number of AC ports of the power electronic transformer, Q si, is the remaining reactive capacity of AC port i.

[0012] A further improvement of the technical solution of the present invention is that each AC port calculates the port adaptive reactive power-voltage droop coefficient according to the real-time reactive power dispatch instruction:

[0013]

[0014] In the formula, is the reactive power dispatch command value of the ith AC port at time t, is the reactive power dispatch instruction per unit value based on the remaining capacity, R i,t is the reactive power-voltage droop coefficient of the ith AC port at time t, R t is the global droop coefficient of multiple AC ports, which is the same for each AC port. V i is the lower limit of the normal range of bus voltage, V low_TW It is the lowest voltage value that the AC port can withstand.

[0015] A further improvement of the technical solution of the present invention is that based on the positive sequence voltage value of each AC port grid connection point, the reactive support amount of each AC port is calculated according to the following formula:

[0016]

[0017] Where V i,t The real-time voltage of the AC port grid connection point, is the reactive support of the ith AC port at time t.

[0018] A further improvement of the technical solution of the present invention is that each AC port is based on the capacity of the internal converter, and then further allocates reactive support as the reactive power output instruction of each converter according to the proportion of the converter's remaining reactive capacity, so that the reactive power output of each converter during reactive-voltage support is proportional to its own remaining reactive capacity.

[0019] A further improvement of the technical solution of the present invention is that the process of calculating the power reference value corresponding to the active power of the port according to different control targets is as follows:

[0020] According to Newton's laws of motion, the virtual synchronous generator simulates the synchronous generator rotor motion equation, and the AC port active power-frequency control is as follows:

[0021]

[0022] Where J is the virtual moment of inertia, D is the virtual damping coefficient, ω0 is the rated voltage angular frequency, ω is the port output voltage angular frequency, P m is the port virtual mechanical power, P out is the AC port output active power, K m It is the adjustment coefficient of the port virtual speed regulator.

[0023] A further improvement of the technical solution of the present invention is: based on the fractional order PI λ The AC port output active power under the controller power outer loop control is as follows:

[0024]

[0025] Where K P =3U d U g / X,U g is the grid voltage amplitude; U d is the port output voltage; ω g is the frequency of the port grid-connected point; P0 is the active reference value set for the port; X is the sum of the port equivalent output impedance, transformer leakage inductance and line impedance.

[0026] A further improvement of the technical solution of the present invention is that: the fractional-order PI λ The controller obtains the target angular frequency ω by the virtual synchronous generator control strategy * and virtual electromotive force E * On this basis, the synchronous reactance of the traditional synchronous generator is simulated by virtual reactance, and E * Transformed into the synchronous rotating coordinate system, the reference value U of the d-axis component of the port voltage is obtained d * and the q-axis component reference value U q *Finally, the PWM pulse width modulation control wave required by the inverter is obtained through voltage and current dual-loop control.

[0027] The further improvement of the technical solution of the present invention is that: the voltage and current dual-loop control process is: firstly, the voltage and current at the LC filter port are collected to calculate the active power and reactive power output by the virtual synchronous generator; the outer loop generates the voltage loop reference voltage amplitude and phase through the control algorithm according to the output power; then, the voltage loop generates the voltage reference voltage amplitude and phase according to the deviation between the voltage reference value and the actual value through the PI λ The controller generates a current reference value for the inner current loop. λ The controller generates a PWM modulation signal, and finally realizes power conversion after PWM control.

[0028] The second aspect of the present invention relates to a multi-port voltage-frequency active support system for a power electronic transformer, comprising a distributed reactive-voltage secondary coordinated controller and a fractional-order PI λ The distributed reactive-voltage two-level coordinated controller realizes the voltage support of the AC port based on the reactive-voltage active control of the residual reactive capacity of the AC port: the reactive-voltage active control adaptively calculates the reactive-voltage droop coefficient of each port according to the residual reactive capacity of the AC port, and obtains the reactive support amount under the voltage situation through the positive sequence voltage of the AC port grid connection point;

[0029] Based on the fractional-order PI λ The controller's active power-frequency active control realizes the frequency support of the AC port: the active power-frequency active control calculates the power reference value corresponding to the port active power according to different control targets, and λ The controller power outer loop control realizes the fast output of PWM pulse modulation signal.

[0030] Due to the adoption of the above technical solution, the technical progress achieved by the present invention is:

[0031] The present invention considers the reactive voltage active control of the remaining reactive capacity of the AC port to realize the voltage support of the AC port, and based on the fractional order PI λ The controller actively controls the active frequency to achieve frequency support of the AC port; the reactive voltage active control adaptively calculates the reactive-voltage droop coefficient of each port according to the remaining reactive capacity of the AC port, and obtains the reactive support amount under the voltage situation through the positive sequence voltage of the AC port grid connection point; the active-frequency active control calculates the power reference value corresponding to the active power of the port according to different control targets, and calculates the power reference value based on the fractional-order PI λThe controller power outer loop control realizes the rapid output of PWM pulse modulation signal. The present invention can provide voltage and frequency support by the AC port with power support capability, thereby improving the voltage of the AC port grid connection point and stabilizing the frequency of the AC port grid connection point. The voltage and frequency active support method ensures that the AC port of the power electronic transformer provides reactive power support according to the proportion of its own residual capacity, gives full play to the power support capability of the AC port, and improves the economy of operation. The introduction of the fractional-order active frequency control strategy and the introduction of the adjustable parameter λ not only reduce the order of the system and weaken the oscillation of active power, but also change the pole position and increase the freedom of dynamic performance control, so that the parameter D obtains the minimum value and maintains the best steady-state performance. By adjusting λ to improve the dynamic performance, the problem of contradiction between parameters D and J in the adjustment of dynamic performance and steady-state performance can be solved, thereby providing effective help to the active-frequency support capability of the AC port grid connection point. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is an overall flow chart of the multi-port voltage-frequency active support method for power electronic transformer of the present invention;

[0033] Figure 2 It is a block diagram of the fractional-order power synchronization loop of the present invention;

[0034] Figure 3 The present invention is based on fractional order PI λ The controller's AC port voltage-frequency active support control control structure diagram. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below in conjunction with embodiments:

[0036] like Figure 1 As shown, a method for active voltage-frequency support of a power electronic transformer with multiple ports includes the following steps:

[0037] Step S1, active reactive-voltage control based on the residual reactive capacity of the AC port to achieve voltage support of the AC port: the active reactive-voltage control adaptively calculates the reactive-voltage droop coefficient of each port according to the residual reactive capacity of the AC port, and obtains the reactive support amount under the voltage situation through the positive sequence voltage of the AC port grid connection point.

[0038] Step S11: According to the real-time operation data of the AC port, the residual reactive capacity of the AC ports of different capacities is calculated to determine the ability of the AC port to participate in active voltage support. The formula for the residual reactive capacity of the AC port is as follows:

[0039]

[0040] In the formula, S irepresents the total capacity of AC port i, P i, represents the output active power of AC port i, n is the number of AC ports of the power electronic transformer, Q si, is the remaining reactive capacity of AC port i.

[0041] Step S12: Each AC port calculates the port adaptive reactive power-voltage droop coefficient according to the real-time reactive power dispatch instruction:

[0042]

[0043] In the formula, is the reactive power dispatch command value of the ith AC port at time t, is the reactive power dispatch instruction per unit value based on the remaining capacity, R i,t is the reactive power-voltage droop coefficient of the ith AC port at time t, R t is the global droop coefficient of multiple AC ports, which is the same for each AC port. V i is the lower limit of the normal range of bus voltage, V low_TW It is the lowest voltage value that the AC port can withstand.

[0044] Step S13: adopting the reactive power-voltage droop control method, based on the positive sequence voltage value of each AC port grid connection point, calculate the reactive power support amount of each AC port according to the following formula:

[0045]

[0046] Where V i,t The real-time voltage of the AC port grid connection point, is the reactive support of the ith AC port at time t.

[0047] Step S2: Each AC port is further allocated reactive power based on the capacity of the internal converter and the proportion of the converter's remaining reactive power capacity. As the reactive power output instruction of each converter, the reactive power output of each converter is proportional to its own residual reactive capacity during reactive-voltage support.

[0048] Step S3: Based on fractional order PI λ The controller's active power-frequency active control realizes the frequency support of the AC port: the active power-frequency active control calculates the power reference value corresponding to the port active power according to different control targets, and λ The controller power outer loop control realizes the fast output of PWM pulse modulation signal.

[0049] Step S31, the process of calculating the power reference value corresponding to the port active power according to different control targets is as follows:

[0050] According to Newton's laws of motion, the virtual synchronous generator simulates the synchronous generator rotor motion equation, and the AC port active power-frequency control is as follows:

[0051]

[0052] Where J is the virtual moment of inertia, D is the virtual damping coefficient, ω0 is the rated voltage angular frequency, ω is the port output voltage angular frequency, P m is the port virtual mechanical power, P out is the AC port output active power, K m It is the adjustment coefficient of the port virtual speed regulator.

[0053] Step S32: To solve the coupling problem of parameter setting in the power synchronization link, a method based on fractional-order PI is proposed. λ The controller's port active power-frequency control link improves the contradiction between the dynamic performance, steady-state performance and parameter adjustment of the AC port output active power, thereby providing more reliable frequency support. Figure 2 As shown:

[0054] As can be seen from the figure, the active power output of the AC port under this control link is as follows:

[0055]

[0056] Where K P =3U d U g / X,U g is the grid voltage amplitude; U d is the port output voltage; ω g is the frequency of the port grid connection point; P0 is the active reference value set for the port; X is the sum of the equivalent output impedance of the port, the leakage inductance of the transformer and the line impedance. It can be seen that K m and D are related to the steady-state error of the output power. Generally, Δω is specified in the steady state. max =S rate / (K m +D)≤1%ω0,S rate K is the rated capacity of the port. m Same effect as D, K m It is a known parameter, so the steady-state performance of active power is only related to the damping coefficient D, and the larger the damping coefficient D is, the larger the steady-state error of active power is.

[0057] Combining the above reactive support calculation method and power control link, a fractional-order PI λ The controller's AC port voltage and frequency actively supports the control strategy, and its control structure is as follows: Figure 3As shown in the figure, J is the virtual moment of inertia of the AC port, θ is the virtual rotor angle of the port, ω is the virtual rotor angular frequency of the port, ω n is the rated angular frequency, D is the damping coefficient, P m , P out are the virtual mechanical power and output active power of the port respectively. m , Q out is the output reactive power reference value and the actual output reactive power value, k q is the reactive power-voltage regulation coefficient. E is the virtual internal potential of the port, U ref is the port reference voltage. d 、u q 、i Ld 、i Lq are the dq axis components of the port voltage and current, respectively, U d * , U q * 、i Ld_ref 、i Lq_ref It is the reference value of the dq-axis component of the port voltage and current.

[0058] Depend on Figure 3 It can be seen that fractional-order PI λ The controller obtains the target angular frequency ω by the virtual synchronous generator control strategy * and virtual electromotive force E * On this basis, the synchronous reactance of the traditional synchronous generator is simulated by virtual reactance, and E * Transformed into the synchronous rotating coordinate system, the reference value U of the d-axis component of the port voltage is obtained d * and the q-axis component reference value U q * Finally, the PWM pulse width modulation control wave required by the inverter is obtained through voltage and current dual-loop control.

[0059] The voltage and current dual-loop control process is as follows: first, the voltage and current at the LC filter port are collected to calculate the active power and reactive power output by the virtual synchronous generator. The outer loop generates the voltage loop reference voltage amplitude and phase through the control algorithm according to the output power; then, the voltage loop is based on the deviation between the voltage reference value and the actual value through PI λ The controller generates a current reference value for the inner current loop. λ The controller generates a PWM modulation signal, and finally realizes power conversion after PWM control.

[0060] In addition, the embodiment of the present invention also provides a multi-port voltage-frequency active support system for a power electronic transformer, including a distributed reactive-voltage secondary coordinated controller and a fractional-order PI λThe distributed reactive-voltage two-level coordinated controller realizes the voltage support of the AC port based on the reactive-voltage active control of the residual reactive capacity of the AC port: the reactive-voltage active control adaptively calculates the reactive-voltage droop coefficient of each port according to the residual reactive capacity of the AC port, and obtains the reactive support amount under the voltage situation through the positive sequence voltage of the AC port grid connection point;

[0061] Based on the fractional-order PI λ The controller's active power-frequency active control realizes the frequency support of the AC port: the active power-frequency active control calculates the power reference value corresponding to the port active power according to different control targets, and λ The controller power outer loop control realizes the fast output of PWM pulse modulation signal.

[0062] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0063] Those of ordinary skill in the art will appreciate that the templates, units, and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0064] If the module / unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned embodiments of the inertia evaluation method of each grid-type converter. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. Computer-readable media may include: any entity or device capable of carrying computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium.

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the protection scope of the present invention.

Claims

1. A method for active multi-port voltage-frequency support of a power electronic transformer, characterized in that: The steps include: Active reactive-voltage control based on the residual reactive capacity of the AC port realizes the voltage support of the AC port: the reactive-voltage active control adaptively calculates the reactive-voltage droop coefficient of each port according to the residual reactive capacity of the AC port, and obtains the reactive support amount under the voltage situation through the positive sequence voltage of the AC port grid connection point; Based on fractional order PI λ The controller's active power-frequency active control realizes the frequency support of the AC port: the active power-frequency active control calculates the power reference value corresponding to the port active power according to different control targets, and λ The controller power outer loop control realizes the fast output of PWM pulse modulation signal.

2. The method for active multi-port voltage-frequency support of a power electronic transformer according to claim 1, characterized in that: According to the real-time operation data of the AC port, the residual reactive capacity of the AC ports of different capacities is calculated to determine the ability of the AC port to participate in active voltage support. The formula for the residual reactive capacity of the AC port is as follows: In the formula, S i represents the total capacity of AC port i, P i, represents the output active power of AC port i, n is the number of AC ports of the power electronic transformer, Q si, is the remaining reactive capacity of AC port i.

3. A method for active multi-port voltage and frequency support of a power electronic transformer according to claim 2, characterized in that: Each AC port calculates the port adaptive reactive power-voltage droop coefficient according to the real-time reactive power dispatch instruction: In the formula, is the reactive power dispatch command value of the ith AC port at time t, is the reactive power dispatch instruction per unit value based on the remaining capacity, R i,t is the reactive power-voltage droop coefficient of the ith AC port at time t, R t is the global droop coefficient of multiple AC ports, which is the same for each AC port. V i is the lower limit of the normal range of bus voltage, V low_TW It is the lowest voltage value that the AC port can withstand.

4. The method for active multi-port voltage-frequency support of a power electronic transformer according to claim 3, characterized in that: Based on the positive sequence voltage value of each AC port grid connection point, the reactive power support of each AC port is calculated according to the following formula: Where V i,t The real-time voltage of the AC port grid connection point, is the reactive support of the ith AC port at time t.

5. The method for active multi-port voltage-frequency support of a power electronic transformer according to claim 1, characterized in that: Each AC port is based on the capacity of the internal converter, and then further allocates reactive support as the reactive power output instruction of each converter according to the proportion of the converter's remaining reactive capacity, so that the reactive power output of each converter during reactive-voltage support is proportional to its own remaining reactive capacity.

6. The method for active multi-port voltage-frequency support of a power electronic transformer according to claim 1, characterized in that: The process of calculating the power reference value corresponding to the port active power according to different control targets is as follows: According to Newton's laws of motion, the virtual synchronous generator control strategy simulates the synchronous generator rotor motion equation, and the AC port active power-frequency control is as follows: Where J is the virtual moment of inertia, D is the virtual damping coefficient, ω0 is the rated voltage angular frequency, ω is the port output voltage angular frequency, P m is the port virtual mechanical power, P out is the AC port output active power, K m It is the adjustment coefficient of the port virtual speed regulator.

7. A method for active multi-port voltage and frequency support of a power electronic transformer according to claim 6, characterized in that: Based on fractional order PI λ The AC port output active power under the controller power outer loop control is as follows: Where K P =3U d U g / X,U g is the grid voltage amplitude; U d is the port output voltage; ω g is the frequency of the port grid-connected point; P0 is the active reference value set for the port; X is the sum of the port equivalent output impedance, transformer leakage inductance and line impedance.

8. The method for active multi-port voltage and frequency support of a power electronic transformer according to claim 7, characterized in that: The fractional PI λ The controller obtains the target angular frequency ω by the virtual synchronous generator control strategy * and virtual electromotive force E * On this basis, the synchronous reactance of the traditional synchronous generator is simulated by virtual reactance, and E * Transformed into the synchronous rotating coordinate system, the reference value U of the d-axis component of the port voltage is obtained d * and the q-axis component reference value U q * Finally, the PWM pulse width modulation control wave required by the inverter is obtained through voltage and current dual-loop control.

9. The method for active multi-port voltage and frequency support of a power electronic transformer according to claim 8, characterized in that: The voltage and current dual-loop control process is as follows: first, the voltage and current at the LC filter port are collected to calculate the active power and reactive power output by the virtual synchronous generator; the outer loop generates the voltage loop reference voltage amplitude and phase through the control algorithm according to the output power; Then, the voltage loop is based on the deviation between the voltage reference value and the actual value through PI λ The controller generates a current reference value for the inner current loop. λ The controller generates a PWM modulation signal, and finally realizes power conversion after PWM control.

10. A multi-port voltage-frequency active support system for a power electronic transformer, characterized in that: Including distributed reactive power-voltage two-level coordinated controller and fractional order PI λ The distributed reactive-voltage two-level coordinated controller realizes the voltage support of the AC port based on the reactive-voltage active control of the residual reactive capacity of the AC port: the reactive-voltage active control adaptively calculates the reactive-voltage droop coefficient of each port according to the residual reactive capacity of the AC port, and obtains the reactive support amount under the voltage situation through the positive sequence voltage of the AC port grid connection point; Based on the fractional-order PI λ The controller's active power-frequency active control realizes the frequency support of the AC port: the active power-frequency active control calculates the power reference value corresponding to the port active power according to different control targets, and λ The controller power outer loop control realizes the fast output of PWM pulse modulation signal.

Images