Multi-voltage feedforward control method and system of grid-supporting inverter and storage medium

Abstract

The application discloses a multi-voltage feedforward control method and system of a grid support type inverter and a storage medium. In view of the problem that the grid support type inverter of the grid following type is prone to oscillation instability with an inductive grid, multi-voltage feedforward control is introduced, and error calculation and control of a power outer loop and a current inner loop are performed according to a feedforward value. The multi-voltage feedforward control strategy provided by the application can simultaneously solve the instability problems caused by the outer loop control link and the current inner loop control link, and can greatly improve the stability of the grid following type voltage support type inverter.

Description

TECHNICAL FIELD

[0001] The present application relates to power electronic control technology, and particularly to a multi-voltage feed-forward control method, system and storage medium of a grid-supporting inverter. BACKGROUND

[0002] The grid-connected inverter under traditional constant current or constant power control cannot effectively support the grid, and active support of frequency and voltage of the grid-connected inverter by the grid is the future development trend, such inverters are called grid-supporting inverters. Grid-supporting inverters are now mainly divided into grid-forming and grid-following inverters, and the support of grid-forming inverters to the grid has been studied more. However, the existing grid-connected inverters are mostly grid-following inverters based on phase-locked loops, and such inverters can also achieve voltage and frequency support for the grid by making slight improvements in control. However, grid-following inverters are prone to interaction with inductive grids, especially after the active support control and reactive support control of the grid are added, the interaction with the inductive grid is more likely to occur, and the stability is poorer. The grid-following grid-supporting inverter control considering active support control and reactive support control is more complex, and the existing control strategies cannot be applied to such inverters. Therefore, it is urgent to optimize the stability control of the grid-following grid-supporting inverter and improve the stability of such inverters.

[0003] Existing control schemes only optimize the inner loop or outer loop of the grid-following converter. For example, document [1] (Z. Xie, Y. Chen, W. Wu, W. Gong, and J. M. Guerrero, “Stability Enhancing Voltage Feed-Forward Inverter Control Method to Reduce the Effects of Phase-Locked Loop and Grid Impedance,” IEEE J. Emerg. Sel. Top. Power Electron. , vol. 9, no. 3, pp. 3000–3009, Jun. 2021.) only proposes a multi-voltage feed-forward control strategy for the instability problem caused by the current inner loop and phase-locked loop, and document [2] (X. Lin, H. Wen, J. Yu, J. Zhang, and J. C.-H. Peng, “Role Determination of Impedance Coupling in GCC With DC-Link Virtual Inertia Control,” IEEE Trans. Ind. Electron., vol. 71, no. 3, pp.2533–2544, Mar. 2024.)Single optimization control is proposed for active power control loop, and these controls can only solve the stability problem caused by a certain loop. However, the grid support inverter in the outer loop and the inner loop may cause instability of the system, so the existing control strategy is not applicable to this type of inverter. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a multi-voltage feedforward control method, system and storage medium for grid support type inverters, which greatly improves the stability of grid-connected voltage support type inverters.

[0005] To solve the above technical problems, the technical solution adopted by the present application is: a multi-voltage feedforward control method for grid support type inverters, comprising the following steps:

[0006] S1, sampling three-phase voltage v a , v b , v c and three-phase inductor current i La , i Lb , i Lc , performing dq coordinate transformation on three-phase voltage v a , v b , v c and three-phase inductor current i La , i Lb , i Lc , to obtain dq-axis voltage signal v d , v q and dq-axis current signal i d , i q ;

[0007] S2, obtain multi-voltage feedforward value i dref1 and i qref1 using the following formula: ; ; wherein G PI (s) is the transfer function of the PI controller in the phase-locked loop, s is a complex variable in the frequency domain, i qref is the reactive current command value, and i dref is the active current command value;

[0008] S3, calculate the output c d , c q of the current inner loop in the dq axis using the following formula: ; wherein i der and i qer are the input d-axis and q-axis errors, respectively, and i der =idref -i d +i dref1 ,i qer =i qref -i q -i qref1 ,G i (s) is a PI controller of the dq-axis current inner loop, K L is a decoupling coefficient of the current inner loop, K f is a voltage feedforward coefficient;

[0009] S4, the output c d , c q of the current inner loop in the dq-axis is subjected to dq inverse transformation, three-phase modulation signals are obtained, and the three-phase modulation signals are subjected to SPWM modulation to obtain the switching signals of the grid-supporting inverter three-phase H-bridge.

[0010] The present application improves the stability of the current inner loop by outputting i dref1 and i qref1 , and can improve the stability of the grid-supporting inverter.

[0011] The expression of the active current instruction value i dref is: ; wherein, P ref is the final active power instruction value, P ref = P set + P add , wherein P set is the active power given value, and P add is the output value of the active support control. The present application can quickly make the active power value reach the instruction value P ref , and can change the stable output power by changing P set alone, or change the output value P add of the active support control by changing the active support control parameter alone.

[0012] ; ω n is the inherent rotation angular frequency of the grid voltage, ω g is the grid angular frequency obtained by the phase-locked loop, ω1 is the output of the multi-voltage feedforward control, , H f (s) is a high-pass filter, J is the differential coefficient of the active support control, D p is the proportional coefficient of the active support control, K fi is a first-order low-pass filter. The active support control of the present application can reduce the frequency deviation value of the power system by changing the proportional coefficient D p , and can reduce the frequency change rate of the power system by changing the differential coefficient J. D pThe range of J is often selected to be between 0.01 and 0.1.

[0013] H f The expression of (s) is: ; τ1=K P_PLL / K I_PLL , τ2=1 / ω hpf , K P_PLL and K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, ω hpf is the cut-off frequency of the high-pass filter.

[0014] The expression of the reactive current command value i qref is: ; wherein, Q ref is the final reactive power command value, Q ref = Q set + Q add – Q1, Q set is the reactive power given value, Q add is the output value of the reactive power support control, and Q1 is the output value of the multi-feedforward control. , H v (s) is a first-order high-pass filter. The present application can quickly make the reactive power value reach the command value Q ref , and can change the stable output power by changing Q set alone or change the output value Q add of the reactive power support control by changing the reactive power support control parameter alone.

[0015] ; wherein, is the given value of the point of common coupling voltage, and D v is the proportional coefficient of the reactive power support control. The reactive power support control of the present application can reduce the voltage deviation value of the power system by changing the proportional coefficient D v , and is easy to implement. The range of D v is often selected to be between 100 and 500.

[0016] H v The expression of (s) is: ; wherein, D v is the proportional coefficient of the reactive power support control, τ3=1 / ω hpv , and ω hpv is the cut-off frequency of the first-order high-pass filter.

[0017] The expressions of the three-phase modulation signals c a , c b , and c c are: ; wherein, θ PLL is the output phase angle of the phase-locked loop, , ω g is the grid angular frequency obtained by the phase-locked loop, , K P_PLL and K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, respectively, and ω n is the inherent rotation angular frequency of the grid voltage.

[0018] As an inventive concept, the application further provides a multi-voltage feedforward control system of a grid support type inverter, comprising a memory, a processor and a computer program stored in the memory; the processor executes the computer program to realize the steps of the above method.

[0019] As an inventive concept, the application further provides a computer readable storage medium having a computer program / instruction stored thereon; the computer program / instruction is executed by a processor to realize the steps of the above method.

[0020] Compared with the prior art, the application has the beneficial effects that: the application simultaneously solves the instability caused by the power support outer ring and the current inner ring through the multi-voltage feedforward method. Specifically, the stability of the power outer ring is improved through the output of ω1 and Q1, and the stability of the current inner ring is improved through the output of i dref1 and i qref1 , which can simultaneously solve the instability problem caused by the outer ring control link and the current inner ring control link, and greatly improve the stability of the grid-connected voltage support type inverter. BRIEF DESCRIPTION OF DRAWINGS

[0021] Fig. 1 is the control block diagram of the grid support type inverter and the structure diagram of the grid-connected system;

[0022] Fig. 2 is the three-phase voltage waveform and current waveform diagram of the grid support type inverter when the grid impedance changes without using the multi-feedforward control in the embodiment of the application;

[0023] Fig. 3 is the three-phase voltage waveform and current waveform diagram of the grid support type inverter when the grid impedance changes after using the multi-feedforward control in the embodiment of the application. DETAILED DESCRIPTION

[0024] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0025] Embodiment 1

[0026] The embodiment is directed to the problem that grid-supporting inverters of the grid-connected type are prone to oscillation instability with inductive grids, and proposes a control method of multi-voltage feedforward, which can greatly improve the stability of grid-supporting inverters. Embodiment 1 of the present application comprises the following steps:

[0027] S1, sampling three-phase voltage v at the point of common coupling (PCC) abc and three-phase inductor current i Labc . abc Labc Perform dq coordinate transformation on the three-phase voltage v d and the three-phase inductor current i q to obtain dq-axis voltage signal v d and dq-axis current signal i q .

[0028] The dq coordinate transformation formula is:

[0029] ;

[0030] wherein θ PLL is the output phase angle of the phase-locked loop. The vector symbols in the above formula , , may refer to three-phase voltage v a , v b , v c and three-phase inductor current i La , i Lb , i Lc .

[0031] S2, obtaining grid phase θ q after controlling v PLL . The expression of the phase-locked loop is:

[0032] ;

[0033] ω g is the grid angular frequency obtained by the phase-locked loop, and the expression of ω g is:

[0034] ​ ;

[0035] wherein: v q is the q-axis voltage signal, K P_PLL and K I_PLL are the proportional and integral coefficients of the PI controller in the phase-locked loop, and s is a complex variable in the frequency domain. ω n is the inherent rotational angular frequency of the grid voltage, and in the embodiment of the present application ω n = 2πf, f is the voltage frequency of the grid, and in the embodiment of the present application f = 50.

[0036] S3, a multi-voltage feedforward control is adopted to obtain feedforward values ω1, Q1, i dref1 and i qref1 , wherein ω1 is fed forward to the active power support control, Q1 is fed forward to the reactive power control, and i dref1 and i qref1 are fed forward to the error calculation of the current inner loop.

[0037] wherein the expression formula of ω1 is:

[0038] ;

[0039] wherein v q is the q-axis voltage signal, G PI (s) is the transfer function of the PI controller in the phase-locked loop, H f (s) is a high-pass filter, and the expression of H f (s) is: wherein τ1=K P_PLL / K I_PLL , τ2=1 / ω hpf , K P_PLL and K I_PLL are the proportional and integral coefficients of the PI controller in the phase-locked loop. ω hpf is the cut-off frequency of the high-pass filter of this feedforward branch. s is a complex variable in the frequency domain. The advantage of this feedforward control loop is that the value of τ1 is determined by the PI parameters of the phase-locked loop, and thus no design is needed, only the related parameters of τ2 need to be designed.

[0040] wherein the expression formula of Q1 is: ; wherein v d is the d-axis voltage signal, H v (s) is a first-order high-pass filter, and the expression of H v (s) is: wherein D v is the proportional coefficient in the reactive power support control, τ3=1 / ω hpv , and ω hpvIt is the cutoff frequency of the first-order high-pass filter. s is a complex variable in the frequency domain. The advantage of this feedforward control loop is its simplicity; only the relevant parameters of τ3 need to be designed.

[0041] Among them, i dref1 The formula for expressing it is: ; where v q It is the q-axis voltage signal, G PI (s) is the transfer function of the PI controller in the phase-locked loop, i qref This is the reactive current command value output by the reactive power control loop. 's' is a complex variable in the frequency domain. The advantage of this feedforward control loop is that the G involved in the loop... PI (s) is a PI controller for a phase-locked loop, so no additional parameter design is required.

[0042] Among them, i qref1 The formula for expressing it is: ; where v q It is the q-axis voltage signal, G PI (s) is the transfer function of the PI controller in the phase-locked loop, i dref This is the active current command value output by the active power control loop. 's' is a complex variable in the frequency domain. The advantage of this feedforward control loop is that the G involved in the loop... PI (s) are the PI parameters of the phase-locked loop, so no additional parameter design is required.

[0043] Although the entire multi-feedforward control involves four feedforward loops, only the relevant parameters ω of τ2 and τ3 need to be designed. hpf With ω hpv It is simple to use and easy to implement in actual controllers.

[0044] S4. P is obtained through active power support control and reactive power support control respectively. add With Q add .

[0045] Among them, P add The formula for expressing it is: ; where ω n ω is the natural rotational angular frequency of the grid voltage. g ω1 is the grid angular frequency obtained by the phase-locked loop, J is the differential coefficient of the active power support control, and D is the output of the multi-voltage feedforward control. p The proportional coefficient for active power support control, K fi It is a first-order low-pass filter when performing differentiation, K fi The expression form is , τ fi =1 / ω fi ω fiis the cut-off frequency of the first-order low-pass filter; Q add The expression formula of the active power control is: ; wherein, is a given value of the point of common coupling voltage, v d is a d-axis voltage signal of the three-phase voltage at the PCC, D v is a proportional coefficient of the reactive power support control;

[0046] S5, obtaining active current command values i dref and reactive current command values i qref respectively through power control, wherein the power control comprises active power control and reactive power control.

[0047] The expression formula of the active power control is:

[0048] ;

[0049] wherein v d is a d-axis voltage signal of the three-phase voltage at the PCC; P ref is a final active power command value, P ref =P set + P add , wherein P set is an active power given value, and P add is an output value of the active power support control.

[0050] The expression formula of the reactive power control is:

[0051] ;

[0052] wherein v d is a d-axis voltage signal of the three-phase voltage at the PCC; Q ref is a final reactive power command value, Q ref =Q set + Q add – Q1, wherein Q set is a reactive power given value, Q add is an output value of the reactive power support control, and Q1 is an output of the multi-feedforward control.

[0053] S6, performing error calculation and control of the current inner loop according to the feedforward value.

[0054] The expression formula of the current inner loop control is:

[0055] ;

[0056] wherein c d , c q are outputs of the current inner loop in the dq axis, i der and iqer are the input d-axis and q-axis errors, respectively. der The expression of is der = i dref - i d + i dref1 , i dref is the output of the active power control loop, i d is the d-axis signal of the three-phase inductor current, i dref1 is the output of the multi-feedforward control. qer The expression of is qer = i qref - i q - i qref1 , i qref is the output of the reactive power control loop, i q is the q-axis signal of the three-phase inductor current, i qref1 is the output of the multi-feedforward control.

[0057] G i (s) = K pi +K ii / s is the PI controller of the dq-axis current inner loop, K pi and K ii are the proportional coefficient and integral coefficient of the current inner loop PI controller. K L = ω n L f / (V dc / 2) is the decoupling coefficient of the current inner loop, ω n is the inherent rotation angular frequency of the grid voltage, L f is the filter inductance, K f = 2 / V dc is the voltage feedforward coefficient, V dc is the DC side voltage.

[0058] S7, performing dq inverse transformation according to the output values c d , c q of the current inner loop, and then performing SPWM modulation to obtain the switching signals S1-S6 of the three-phase H-bridge.

[0059] The dq coordinate inverse transformation has a formula as follows:

[0060] ;

[0061] Wherein, θ PLL is the output phase angle of the phase-locked loop, c d , c q are the output values of the dq-axis current inner loop, c a , c b , c cis the three-phase modulation signal obtained after dq inverse transformation. a is the three-phase modulation signal obtained after dq inverse transformation. b is the three-phase modulation signal obtained after dq inverse transformation. c After SPWM modulation, the switching signals S1-S6 of the three-phase H-bridge are obtained.

[0062] Under the system parameters and control parameters shown in Table 1, the grid impedance variation of the grid support inverter with and without the multi-voltage feedforward control is simulated, and the simulation waveforms are shown in Fig. 2. Figs. 2-3

[0063]

[0064] 1. When the grid support inverter does not use the multi-voltage feedforward control method of the present application, Fig. 2 the PCC point three-phase voltage waveform and three-phase inductor current waveform when the grid inductance L g changes from 2.3mH to 15.3mH are shown in Fig. 2. From the figure, it can be seen that when L g = 2.3mH, the grid support inverter has lost stability, and there are a large number of harmonics in the voltage and current waveforms; when L g increases to 15.3mH, the stability of the grid support inverter deteriorates further, and the waveform quality is worse. This shows that the grid support inverter has poor adaptability to grid impedance and is very easy to lose stability.

[0065] 2. When the grid support inverter uses the multi-voltage feedforward control method proposed in the present application, Fig. 3 the PCC point three-phase voltage waveform and three-phase inductor current waveform when the grid inductance L g changes from 2.3mH to 15.3mH are shown in Fig. 3. From the figure, it can be seen that when the grid impedance L g = 2.3mH, the grid support inverter system remains stable, and the waveform is a standard sine wave; when the grid impedance L g increases to 15.3mH, the grid support inverter continues to maintain system stability after about 0.2s of adjustment, and the quality of the voltage and current waveforms is still good. This shows that the multi-voltage feedforward control proposed in the embodiment of the present application can greatly improve the adaptability of the grid support inverter to the grid impedance and the stability of the overall system.

[0066] Embodiment 2

[0067] The embodiment 2 of the present application provides a control system corresponding to the above-mentioned embodiment 1, which comprises a memory, a processor and a computer program stored in the memory; the processor executes the computer program in the memory to realize the steps of the method of the above-mentioned embodiment 1.

[0068] ​In some implementations, the memory can be a high-speed random access memory (RAM), and can also include a non-volatile memory, such as at least one disk memory.

[0069] In some implementations, the processor can be a central processing unit (CPU), a digital signal processor (DSP), or other types of general purpose processors, without limitation.

[0070] Embodiment 3

[0071] Embodiment 3 of the present application provides a computer readable storage medium corresponding to the above-mentioned embodiment 1, which stores computer programs / instructions. The computer programs / instructions are executed by the processor to implement the steps of the method of embodiment 1.

[0072] The computer readable storage medium can be a tangible device that maintains and stores instructions for use by an instruction execution device. The computer readable storage medium can be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0073] Those skilled in the art will understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) containing computer usable program code. The solutions in the embodiments of the present application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript, etc.

[0074] The present application is described with reference to flowcharts and / or block diagrams according to the methods, devices (systems), and computer program products of the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to produce a machine, so that the instructions executed by the computer or other programmable data processing devices produce a device that implements the functions specified in the flowcharts and / or block diagrams. Fig. 1 The function of the device specified in one flow or multiple flows and / or blocks Fig. 1 The function of the device specified in one flow or multiple flows and / or blocks

[0075] These computer program instructions can also be loaded into a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Fig. 1 These computer program instructions can also be loaded into a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Fig. 1 These computer program instructions can also be loaded into a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.

[0076] While the preferred embodiments of the application have been described, it should be apparent that further modifications and improvements can be made by those skilled in the art without departing from the scope of the application. Therefore, the scope of the application should be determined by the following claims, including any equivalents thereto.

[0077] Obviously, numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A multi-voltage feedforward control method of a grid-supporting inverter, characterized by, comprising the steps of: S1, the three-phase voltage v at the sampling common coupling point a v b v c With the three-phase inductor current i La i Lb i Lc For three-phase voltage v a v b v c With the three-phase inductor current i La i Lb i Lc Perform a dq coordinate transformation to obtain the dq-axis voltage signal v. d v q With dq axis current signal i d i q ; S2, the multi-voltage feedforward value i is obtained using the following equation dref1 with i qref1 : ； ； wherein G PI (s) is a transfer function of a PI controller in a phase-locked loop, s is a complex variable in a frequency domain, i qref is a reactive current command value, i dref is an active current command value; S3, calculate the output c of the current inner loop in dq axis by the following formula d 、 q : ； wherein, i der and i qer are the input d-axis and q-axis errors, respectively, i der = i dref - i d + i dref1 , i qer = i qref - i q - i qref1 , G i (s) is a PI controller of the dq-axis current inner loop, K L is a decoupling coefficient of the current inner loop, and K f is a voltage feedforward coefficient. S4, the output c of the current inner loop on the dq axis d , c q dq inverse transformation is performed to obtain a three-phase modulation signal, and SPWM modulation is performed on the three-phase modulation signal to obtain a switching signal of a grid support type inverter three-phase H bridge.

2. The multi-voltage feedforward control method of a grid-supporting inverter according to claim 1, characterized by, Active current command value i dref The expression is: ; wherein P ref is the final active power command value, P ref = P set + P add , wherein P set is the active power given value and P add is the output value of the active support control.

3. The multi-voltage feedforward control method of a grid-supporting inverter according to claim 2, characterized by, ; ω n is the inherent rotational angular frequency of the grid voltage, ω g is the grid angular frequency obtained by the phase-locked loop, ω1is the output of the multi-voltage feedforward control, , H f (s) is a high-pass filter, J is the differential coefficient of the active power support control, D p is the proportional coefficient of the active power support control, K fi is a first-order low-pass filter.

4. The multi-voltage feedforward control method of a grid-supporting inverter according to claim 3, characterized by, H f The expression of (s) is: ; τ1=K P_PLL / K I_PLL , τ2=1 / ω hpf , K P_PLL and K I_PLL are the proportional coefficient and the integral coefficient of the PI controller in the phase-locked loop, respectively, and ω hpf is the cut-off frequency of the high-pass filter.

5. The multi-voltage feedforward control method of a grid-supporting inverter according to claim 1, characterized by, Reactive current command value i qref The expression of Q ; wherein Q ref is the final reactive power command value, Q ref = Q set + Q add - Q1, Q set is the reactive power given value, Q add is the output value of the reactive power support control, Q1 is the output of the multi-feedforward control, , H v (s) is a first-order high-pass filter.

6. The multi-voltage feedforward control method of a grid-supporting inverter according to claim 5, wherein, ; wherein, is a given value of the point of common coupling voltage, D v is a proportional coefficient of the reactive support control.

7. The multi-voltage feedforward control method of a grid-supporting inverter according to claim 5, wherein, H v The expression of (s) is: ; wherein, D v is the proportional coefficient of the reactive power support control, τ3=1 / ω hpv , ω hpv is the cut-off frequency of the first-order high-pass filter.

8. The multi-voltage feedforward control method of a grid-supporting inverter according to claim 1, characterized by, Three-phase modulation signal c a , c b , c c is expressed as: ; wherein θ PLL is the output phase angle of the phase-locked loop, , ω g is the grid angular frequency obtained by the phase-locked loop, , K P_PLL and K I_PLL are the proportional coefficient and the integral coefficient of the PI controller in the phase-locked loop, respectively, and ω n is the inherent rotational angular frequency of the grid voltage.

9. A multi-voltage feedforward control system for a grid-supporting inverter, comprising a memory, a processor, and a computer program stored on the memory; characterized in that, The processor executes the computer program to implement the steps of the method of any one of claims 1-8.

10. A computer readable storage medium having stored thereon computer programs / instructions; characterized in that, The computer program / instructions, when executed by the processor, implement the steps of the method of any one of claims 1-8.

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