UPQC node impedance polymorphic flexible matching control method based on multi-task cooperation

Abstract

The invention discloses a UPQC node impedance polymorphic flexible matching control method based on multi-task cooperation, and the method comprises the steps: building a series converter control impedance model, and enabling the active power of a load to be provided by an AC power grid and a DC bus at the same time through adjusting the amplitude of the input current of the AC power grid; a parallel converter control impedance model is established, sine voltage source control is introduced, three-phase output voltage of a parallel converter system is stable, sine and balanced, and load reactive power and distortion current are compensated; according to the series converter control impedance model and the parallel converter control impedance model, a UPQC system impedance model is established, the UPQC system is equivalent to an adjustable impedance model composed of an input node, a series converter node, a parallel converter node and an output node, and the impedance of the UPQC system is adjusted by controlling the matching relation among the impedance of the four nodes. The control of multiple operation forms of the system is realized, and the requirements of UPQC multi-task multi-scene power supply guarantee are met.

Description

Technical Field

[0001] The present invention relates to the field of power quality regulation and control, and in particular to a UPQC node impedance polymorphic flexible matching control method based on multi-task collaboration. Background Art

[0002] With the rapid development of power grid technology, the power quality of power grid has received more and more attention. On the one hand, power users have higher and higher requirements for power quality; on the other hand, the large-scale access of distributed power sources and the use of nonlinear and impact loads have a serious impact on the power quality of the power grid, making the power quality of the power grid multiple and complicated; therefore, the power quality regulator that takes into account the power quality management at the end of the distribution network and guarantees the high reliability of load power consumption, and can achieve the new functions of successful uninterruptible power supply and energy flexible optimization and regulation, is an important way to solve the contemporary power supply quality problems. The series converter in the traditional UPQC uses a non-sinusoidal voltage source control method, which cannot change the active power input of the power grid, and the active power of the input load cannot be provided by the AC power grid and the DC bus at the same time. When the power supply of the power grid fails, the circuit cannot be switched in time, which affects the power supply.

[0003] For example, a "smart power quality regulation system" disclosed in Chinese patent literature, with the announcement number CN201994677U, includes the problem that the active power input from the power grid cannot be changed, and the active power of the input load cannot be provided simultaneously through the AC power grid and the DC bus. When the power supply of the power grid fails, the circuit cannot be switched in time, which affects the power supply. Summary of the invention

[0004] The present invention aims to overcome the problems in the prior art that the power quality regulation system cannot change the active power input from the power grid, and the active power of the input load cannot be provided by the AC power grid and the DC bus at the same time, and the circuit cannot be switched in time when the power grid power supply fails, which affects the power supply. A UPQC node impedance polymorphic flexible matching control method based on multi-task collaboration is provided. By adjusting the amplitude of the AC power grid input current, the load active power can be provided by both the AC power grid and the DC bus.

[0005] In order to achieve the above technical effects, the present invention adopts the following technical solutions.

[0006] The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration includes the following steps: Step S1: Establish a controlled impedance model of the series converter, and adjust the amplitude of the AC grid input current so that the load active power can be provided by the AC grid and the DC bus at the same time; Step S2: Establish a parallel converter controlled impedance model, introduce sinusoidal voltage source control, and make the three-phase output voltage of the parallel converter system stable, sinusoidal and balanced, and compensate for load reactive power and distorted current; Step S3: Establish a UPQC system impedance model based on the impedance models of steps S1 and S2.

[0007] The present invention provides a UPQC node impedance polymorphic flexible matching control method based on multi-task collaboration. By controlling the input current amplitude of the AC power grid by the series converter, the active power input to the power grid can be changed. At the same time, since the parallel converter is controlled as a sinusoidal voltage source, when the input active power changes, the parallel converter will automatically obtain energy from the DC bus to compensate for the change in active power, so as to achieve power balance of the entire system; by adjusting the amplitude of the AC power grid input current, the load active power can be provided by both the AC power grid and the DC bus.

[0008] Preferably, the active power degree of freedom flexible control is performed through the series converter controlled impedance model of step S1, and the active power degree of freedom flexible control process includes a current amplitude reference calculation link and a degree of freedom control link.

[0009] Preferably, the parallel converter controlled impedance model in step S2 includes an output voltage amplitude control process and an AC bus voltage phase control process.

[0010] As a preference, the current amplitude reference calculation link in step S1 includes the following steps: Step S1-1: The AC grid voltage, the output AC bus voltage and the current are transformed by coordinates, and the fundamental positive sequence components are extracted by a low-pass filter. and Step S1-2: According to the fundamental positive sequence component and instantaneous power theory obtained in step S1-1, the fundamental positive sequence active power on the grid side and the AC output bus side is obtained. and The mathematical relationship between Step S1-3: The fundamental positive sequence active power on the grid side and the AC output bus side in step S1-2 is and The mathematical relationship between them can further obtain the grid input current amplitude reference

[0011] As a preference, the fundamental positive sequence active power on the grid side and the AC output bus side in step S1-2 is and The mathematical relationship is as follows:

[0012] According to the fundamental positive sequence component and instantaneous power theory, the present invention obtains the fundamental positive sequence active power on the grid side and the AC output bus side. and The mathematical relationship of .

[0013] As a preference, the grid input current amplitude reference in step S1-3 is for:

[0014] The present invention is based on the fundamental positive sequence active power of the power grid side and the AC output bus side. and The mathematical relationship between them further obtains the grid input current amplitude reference

[0015] Preferably, after obtaining the current amplitude reference through the current amplitude reference calculation link, the degree of freedom control link is added to achieve flexible control of the system active power. The specific expression is as follows: Among them, k p For degrees of freedom.

[0016] As a preference, when the degree of freedom k is adjusted p When k is used, the input current of the AC grid changes accordingly, and the active power input of the grid also changes accordingly; in order to meet the power demand of the load, the parallel converter will automatically obtain energy from the DC bus to compensate for the p The power change caused by the change of k p The active power between the AC bus and the DC bus operates flexibly in any ratio within the range of 0 to 100%.

[0017] Preferably, the output voltage amplitude control process is implemented by a voltage loop controller, and the voltage loop controller is composed of a proportional integral + quasi-resonant controller, and the amplitude control expression is as follows: Among them, k PCvp and k PCvi are the proportional and integral coefficients of the PI controller respectively; h, k r ,ω o and ω c They are the harmonic order, resonance coefficient, resonant frequency and cut-off frequency of the QR controller respectively.

[0018] Combined with the control characteristics of series-parallel converters, the UPQC system is equivalent to an adjustable impedance model consisting of input nodes, series converter nodes, parallel converter nodes and output nodes. By controlling the matching relationship between the impedances of the four nodes, the system's various operating modes can be controlled, thereby meeting the UPQC multi-task and multi-scenario power supply guarantee needs.

[0019] As a preferred method, the AC grid voltage, the output AC bus voltage, the DC grid voltage, and the output DC bus voltage are output compensated by photovoltaic cells and wind power generation, and the phase-frequency characteristics are optimized by the weight method to obtain the compensation objective function, and the gain margin in the objective function is conditionally constrained so that the gain margin is increased, and the larger the gain margin, the better, and the gain margin is increased by increasing the gain margin. The specific calculation method is as follows: △Z(s)=Lms+Rm Among them, G(s l ) is the high-pass filter transfer function of the photovoltaic generator set, G(s c ) is the high-pass filter transfer function of the wind turbine generator set, △E is the power supply compensation voltage, Tsl is the high-pass filter time constant of the photovoltaic generator set, Tsc is the high-pass filter time constant of the wind turbine generator set, s is the high-pass filter transfer function of the overall circuit, the superscripts t and t-1 are the relevant electrical quantities in the current calculation compensation cycle and the previous calculation compensation cycle, △Z(s) is the compensation impedance, Lms is the leakage inductance of the transformer, and Rm is the DC impedance value.

[0020] Therefore, the beneficial effects of the present invention are as follows: (1) By controlling the input current amplitude of the AC grid through the series converter, the active power input to the grid can be changed. At the same time, since the parallel converter is controlled as a sinusoidal voltage source, when the input active power changes, the parallel converter will automatically obtain energy from the DC bus to compensate for the change in active power, thereby achieving power balance for the entire system. (2) Combining the control characteristics of the series-parallel converter, the UPQC system is equivalent to an adjustable impedance model consisting of an input node, a series converter node, a parallel converter node, and an output node. By controlling the matching relationship between the impedances of the four nodes, the system can be controlled in various operating modes, thereby meeting the needs of UPQC multi-task and multi-scenario power supply guarantee. (3) By adjusting the amplitude of the AC grid input current, the load active power can be provided by both the AC grid and the DC bus; (4) The grid switches the output active power and can automatically switch the circuit to achieve uninterrupted power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural diagram of the impedance model of the UPQC system of the present invention.

[0022] Figure 2 It is a structural diagram of the controlled impedance model of the series converter of the present invention.

[0023] Figure 3 It is a structural diagram of the Norton equivalent impedance model of the series converter of the present invention.

[0024] Figure 4 It is a structural diagram of the parallel converter controlled impedance model of the present invention.

[0025] Figure 5 It is a structural diagram of the Thevenin equivalent impedance model of the parallel converter of the present invention.

[0026] Figure 6 It is a diagram of the power conservation performance of MTCO-UPQC when the grid voltage fluctuates according to the present invention.

[0027] Figure 7 This is the MTCO-UPQC power conservation performance diagram of the present invention when the nonlinear number is negative.

[0028] Figure 8 This is a diagram of the simulation results of the energy flexible operation of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0030] Embodiment 1.

[0031] The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration includes the following steps: Step S1: Establish a series converter controlled impedance model, and adjust the amplitude of the AC grid input current so that the load active power can be provided by the AC grid and the DC bus at the same time; perform active power degree of freedom flexible control through the series converter controlled impedance model, and the active power degree of freedom flexible control process includes a current amplitude reference calculation link and a degree of freedom control link; Step S2: Establish a parallel converter controlled impedance model, introduce sinusoidal voltage source control, the three-phase output voltage of the parallel converter system is stable, sinusoidal and balanced, and the load reactive power and distorted current are compensated; the parallel converter controlled impedance model includes the output voltage amplitude control process and the AC bus voltage phase control process; Step S3: Based on the impedance models of step S1 and step S2, establish the UPQC system impedance model; Figure 1 As shown in the figure, combined with the control characteristics of the series-parallel converter, the UPQC system is equivalent to an adjustable impedance model consisting of an input node, a series converter node, a parallel converter node and an output node. By controlling the matching relationship between the impedances of the four nodes, the system's various operating modes can be controlled, thereby meeting the needs of UPQC multi-task and multi-scenario power supply assurance.

[0032] This embodiment provides a UPQC node impedance multi-form flexible matching control method based on multi-task collaboration. By controlling the amplitude of the AC power grid input current through the series converter, the active power of the power grid input can be changed. At the same time, since the parallel converter is controlled as a sinusoidal voltage source, when the input active power changes, the parallel converter will automatically obtain energy from the DC bus to compensate for the change in active power, so as to achieve power balance of the entire system; by adjusting the amplitude of the AC power grid input current, the load active power can be provided by both the AC power grid and the DC bus.

[0033] Active power degree of freedom flexible control is performed through the series converter controlled impedance model of step S1, and the active power degree of freedom flexible control process includes a current amplitude reference calculation link and a degree of freedom control link.

[0034] The parallel converter controlled impedance model in step S2 includes an output voltage amplitude control process and an AC bus voltage phase control process.

[0035] The current amplitude reference calculation link in step S1 includes the following steps: Step S1-1: The AC grid voltage, output AC bus voltage and current are transformed by coordinates, and the fundamental positive sequence components are extracted by low-pass filters. and Step S1-2: According to the fundamental positive sequence component and instantaneous power theory obtained in step S1-1, the fundamental positive sequence active power on the grid side and the AC output bus side is obtained. and The mathematical relationship between Step S1-3: The fundamental positive sequence active power on the grid side and the AC output bus side in step S1-2 is and The mathematical relationship between them can further obtain the grid input current amplitude reference

[0036] The fundamental positive sequence active power on the grid side and the AC output bus side in step S1-2 and The mathematical relationship is as follows:

[0037] In this embodiment, based on the fundamental positive sequence component and instantaneous power theory, the fundamental positive sequence active power on the grid side and the AC output bus side is obtained: and The mathematical relationship of .

[0038] The grid input current amplitude reference in step S1-3 for:

[0039] In this embodiment, the fundamental positive sequence active power of the grid side and the AC output bus side is calculated based on and The mathematical relationship between them further obtains the grid input current amplitude reference

[0040] After obtaining the current amplitude reference through the current amplitude reference calculation link, the degree of freedom control link is added to achieve flexible control of the system active power. The specific expression is as follows: Among them, k p For degrees of freedom.

[0041] When the degree of freedom k p When k is used, the input current of the AC grid changes accordingly, and the active power input of the grid also changes accordingly; in order to meet the power demand of the load, the parallel converter will automatically obtain energy from the DC bus to compensate for the p The power change caused by the change of k p The active power between the AC bus and the DC bus operates flexibly in any ratio within the range of 0 to 100%.

[0042] The output voltage amplitude control process is realized by the voltage loop controller, which is composed of proportional integral + quasi-resonant controller. The amplitude control expression is as follows: Among them, k PCvp and k PCvi are the proportional and integral coefficients of the PI controller respectively; h, k r ,ω o and ω c They are the harmonic order, resonance coefficient, resonant frequency and cut-off frequency of the QR controller respectively.

[0043] Combined with the control characteristics of series-parallel converters, the UPQC system is equivalent to an adjustable impedance model consisting of input nodes, series converter nodes, parallel converter nodes and output nodes. By controlling the matching relationship between the impedances of the four nodes, the system's various operating modes can be controlled, thereby meeting the UPQC multi-task and multi-scenario power supply guarantee needs.

[0044] The AC grid voltage, output AC bus voltage, DC grid voltage, and output DC bus voltage are compensated by photovoltaic cells and wind power generation. The phase-frequency characteristics are optimized by weight method to obtain the compensation objective function. The gain margin in the objective function is conditionally constrained to increase the gain margin. The larger the gain margin, the better. The specific calculation method is as follows: △Z(s)=Lms+Rm Among them, G(s l ) is the high-pass filter transfer function of the photovoltaic generator set, G(s c ) is the high-pass filter transfer function of the wind turbine generator set, △E is the power supply compensation voltage, Tsl is the high-pass filter time constant of the photovoltaic generator set, Tsc is the high-pass filter time constant of the wind turbine generator set, s is the high-pass filter transfer function of the overall circuit, the superscripts t and t-1 are the relevant electrical quantities in the current calculation compensation cycle and the previous calculation compensation cycle, △Z(s) is the compensation impedance, Lms is the leakage inductance of the transformer, and Rm is the DC impedance value.

[0045] Embodiment 2.

[0046] Different from the non-sinusoidal voltage source control mode of the series converter in the traditional UPQC, the series converter in the MTCO-UPQC is controlled as a sinusoidal current source, which is mainly used to control the input current of the three-phase AC grid and stabilize the DC bus voltage. Therefore, by controlling the amplitude of the AC grid input current through the series converter, the active power input to the grid can be changed. At the same time, since the parallel converter is controlled as a sinusoidal voltage source, when the input active power changes, the parallel converter will automatically obtain energy from the DC bus to compensate for the change in active power, so as to achieve power balance of the entire system. It can be seen that by adjusting the amplitude of the AC grid input current, the load active power can be provided by both the AC grid and the DC bus.

[0047] The present invention uses photovoltaic cells and wind power generation to output compensation for AC grid voltage, output AC bus voltage, DC grid voltage, and output DC bus voltage, and uses a weighting method to optimize the phase-frequency characteristics to obtain a compensation objective function, and conditionally constrains the gain margin in the objective function so that the gain margin is increased, and the larger the gain margin, the better. The specific calculation method is as follows: △Z(s)=Lms+Rm.

[0048] Among them, G(s l ) is the high-pass filter transfer function of the photovoltaic generator set, G(s c ) is the high-pass filter transfer function of the wind turbine generator set, △E is the power supply compensation voltage, Tsl is the high-pass filter time constant of the photovoltaic generator set, Tsc is the high-pass filter time constant of the wind turbine generator set, s is the high-pass filter transfer function of the overall circuit, the superscripts t and t-1 are the relevant electrical quantities in the current calculation compensation cycle and the previous calculation compensation cycle, △Z(s) is the compensation impedance, Lms is the leakage inductance of the transformer, and Rm is the DC impedance value.

[0049] like Figure 2 As shown, the AC grid voltage u Sabc , output AC bus voltage u Labc and current i Labc After dq coordinate transformation, the fundamental positive sequence components are extracted using a low pass filter (LPF) and Ignoring the loss, according to the instantaneous power theory, the fundamental positive sequence active power on the grid side and the AC output bus side is and Equal, that is: Further, the grid input current amplitude reference can be obtained for: It can be seen from this formula that under the action of CRC, It changes with the load active power and can adjust the grid-side input current i according to the actual load conditions. S size.

[0050] After obtaining the current amplitude reference through CARC, adding DFC can realize flexible control of the system active power, that is: From this formula, we can see that when the degree of freedom k is adjusted p When the AC grid input current changes, the active power input from the grid also changes. To meet the power demand of the load, the parallel converter will automatically obtain energy from the DC bus to compensate for the k p Therefore, the active power between the AC grid and the DC bus can be flexibly operated in any ratio within the range of 0 to 100%.

[0051] The total AC grid input current reference i Srefd i generated by the APDFFC link ap And the DC bus voltage loop control result Δi dc Together they form: i S refd=(iap+Δidc) / n In the formula, Δi dc =G dcV (s)[u dcref (s)-u dc+ (s)-u dc- (s)], n is the transformer ratio; i ap It is used to control the active power input from the grid, and Δi dc The power required to stabilize the DC bus voltage and compensate for the internal operating losses of the system.

[0052] according to Figure 2 , current reference i Srefd It can be expressed as: In the formula, H SC (s) = G SCI (s) / [sL SC +R SC +G SCI (s)] is the closed-loop transfer function of the grid current control loop; Z SCs (s) = [sL SC +R SC +G SCI (s)] and Z SCp (s) = n 2 Z SCs (s) are the equivalent impedances of the series converter on the primary and secondary sides of the transformer respectively; G SCI (s) is the PI controller; R SC is the inductance L SC The equivalent resistance of C (s) and u Cd (s) are the primary and secondary voltages of the transformer respectively.

[0053] like Figure 3As shown, according to the above formula, the Norton equivalent impedance model of the series converter can be established, as follows: Figure 3 (a); further, the equivalent impedance of the series converter and transformer is considered as a whole. Figure 3 (b) as shown.

[0054] Based on u Cd (s) and i Sd (s) Circuit relationship, the series converter can be equivalent to an output impedance Z SCout (s), expressed as: From this formula, we can see that the output impedance Z SCout (s) with current reference The degree of freedom k can be adjusted p To change the series converter output impedance Z SCout form, thus meeting the multi-task operation requirements of UPQC.

[0055] Embodiment three.

[0056] Since MTCO-UPQC has the ability to use the DC bus to power the load, the control mode of the parallel converter is changed from the traditional non-sinusoidal current source control to the sinusoidal voltage source control, which can avoid the energy impact problem caused by the switching between the current source and the voltage source control mode. The parallel converter is used to control the three-phase output voltage of the system to be stable, sinusoidal and balanced, and to compensate for the reactive power and distorted current of the load. Its control strategy is as follows Figure 4 shown.

[0057] Considering unbalanced and nonlinear loads, the voltage loop controller G PCVd,q,0 (s) is composed of a proportional integral + quasi-resonant (PI+QR) controller and can be expressed as: In the formula, k PCvp and k PCvi are the proportional and integral coefficients of the PI controller respectively; h, k r ,ω o and ω c They are the harmonic order, resonance coefficient, resonant frequency and cut-off frequency of the QR controller respectively.

[0058] According to the above current reference i Srefd The calculation formula can be used to calculate the system output voltage u L (s) is expressed as: In the formula, In the formula, H PC(s) and Z PC (s) are the output voltage control closed-loop transfer function and the equivalent impedance of the parallel converter respectively.

[0059] According to the above formula, the Thevenin equivalent impedance model of the parallel converter can be obtained, as follows: Figure 5 As shown, it is embodied in the form of a controllable sinusoidal voltage source connected in series with an equivalent impedance.

[0060] Based on u L (s) and i PC (s) circuit relationship, the parallel converter can be equivalent to an output impedance Z PCout (s), expressed as: From this formula, we can see that Z PCout (s) and i PC (s). When the load is constant, the change of grid input current will cause i PC (s) changes, thereby changing the output impedance Z of the parallel converter PCout form.

[0061] Embodiment 4.

[0062] Based on the above analysis of the first and second embodiments, a UPQC system impedance model can be established, such as Figure 1 shown. Among them, Z S (s) and Z out (s) are the input and output equivalent impedances respectively, which can be expressed as: Combined with the control characteristics of series-parallel converters, this project equates the UPQC system to an adjustable impedance model consisting of input nodes, series converter nodes, parallel converter nodes, and output nodes. By controlling the matching relationship between the impedances of the four nodes, the system's various operating modes can be controlled, thereby meeting the UPQC's multi-task and multi-scenario power supply guarantee needs.

[0063] Embodiment five.

[0064] The multi-task collaborative power supply guarantee capability of MTCO-UPQC is simulated, verified and analyzed through the Matlab / Simulink environment. The simulation parameters are shown in Table 1: Table 1 System circuit parameters AC input side filter inductor Ls 6μH Positive and negative DC bus capacitance Cdc± 8800μF Series converter filter inductor LSC 7mH Positive and negative DC bus voltage udc± ±375V Parallel converter filter inductor LPC 0.3mH Output voltage uLabc effective value 220V Parallel converter filter capacitor CPC 40μF Switching frequency fs 10kHz Transformer ratio n 1:5 Grid voltage frequencyω 100rad / s According to the above table, the multi-task collaborative power supply guarantee capability of the power grid is simulated and verified by the UPQC node impedance polymorphic flexible matching control method based on multi-task collaboration of the present invention, which specifically includes the following three parts.

[0065] Grid voltage fluctuations In order to verify the power protection performance of MTCO-UPQC under the condition of grid voltage fluctuation, the simulation process is divided into three intervals, namely: interval I [0.1s~0.2s]: grid voltage balance; interval II [0.2s~0.3s]: grid voltage increases by 15%; interval III [0.3s~0.4s]: grid voltage decreases by 15%. The simulation results are shown in Figure 2. Figure 6 As shown; Interval I [0.1s~0.2s]: Grid voltage u Sabc and current i Sabc Equal to the output voltage u Labc and current i Labc , the power on the grid side and the load side is naturally balanced. Cabc Withstand input inductance L s and the voltage drop of its own impedance, the output current i of the series converter SCabc Controls the grid current i Sabc , and is i Sabc 1 / 5 of the system loss current i Pcabc ; Interval II [0.2s~0.3s]: u Sabc Increase by 15% (effective value 253V), i Sabc The corresponding decrease is 13%. Labc with i Labc It remains unchanged, indicating that through the control of the two converters, u Sabc The increase in u has no effect on the load. Due to the voltage regulation effect of the parallel converter, u Cabc Withstand 15% reverse voltage to compensate u Sabc The elevated portion. SCabc with u Cabc Reverse phase, indicating that the series converter is working in the rectification state and absorbing energy. PCabc Increase and with u Labc In phase, it means that the parallel converter works in the inverter state and emits energy; Interval III [0.3s~0.4s]: The analysis process for interval III [0.3s~0.4s] is the same as that for interval II.

[0066] Non-linear load Figure 7 is the three-phase nonlinear load MTCO-UPQC simulation waveform under the grid voltage balance state. Under the nonlinear load condition, the grid current i Sabc And the output voltage u Labc The grid provides active power to the load, and the parallel converter provides all the required harmonic currents to the load; in addition, since the grid current i SabcWith the load current i Labc The asynchronism of the DC bus and the unbalanced current caused by the nonlinear load will cause the DC bus voltage u dc± and u dc The fluctuations of 3 times and 6 times of frequency appeared respectively, and the grid-side neutral line current i SN Much smaller than the load side neutral current i LN .

[0067] Energy flexible operation Figure 8 is the simulation result of active power flow flexible operation, where the load active power P L The range changes from 1pu to 2pu, which is divided into four stages: 1) GOM[0.1s,0.2s]:P L =1pu,k p =1 Because k p =1, so that the grid transmits all active power to the load, so U Labc ,I Labc and I Sabc are 1 pu, and the current I output by PC PCabc is zero, such as Figure 8 As shown in (a), the corresponding power relationship is P S =P L =1pu,P SC =P PC =0, such as Figure 8 (b) 2)IOM[0.2s,0.3s]:P L =1pu,k p =0 Different from GOM, due to k p = 0, so that I Sabc =0, indicating that the power input from the power grid is P S =0; therefore, the DC bus transmits active power to the load through PC, that is, I PCabc =1pu,P PC =1pu; 3)FOM[0.3s,0.4s]:P L =1pu,k p =0.5 k p = 0.5, the AC grid and DC busbar each bear 50% of the active power transmission task, which is expressed as I Sabc =I PCabc =0.5pu and P S =P PC =0.5pu; It can be seen that MTCO-UPQC achieves flexible operation of active power. When adjusting kp When the active power ratio between the grid side and the DC bus side changes, the flexibility of power transmission is increased, which can play a role in timely absorbing distributed energy. 4)FOM[0.4s,0.5s]:P L =2pu,k p =0.5 Load active power P L When it increases to 2pu, k needs to be controlled p = 0.5, so that the grid side and the DC bus side transmit active power in the range of 100% respectively, expressed as I Sabc =I PCabc =1pu and P S =P PC =1pu. Considering the limitations of input power distribution and system capacity, MTCO-UPQC can transmit a maximum of 200% active power, breaking through the 100% active power transmission limit of traditional routers.

[0068] The above describes in detail the structure, features and effects of the present invention based on the embodiments shown in the drawings, but the above is only a preferred embodiment of the present invention. It should be noted that the technical features involved in the above embodiments and their preferred methods can be reasonably combined and matched into a variety of equivalent schemes by those skilled in the art without departing from or changing the design ideas and technical effects of the present invention; therefore, the present invention is not limited to the scope of implementation shown in the drawings, and all changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which still do not exceed the spirit covered by the specification and drawings, should be within the protection scope of the present invention.

Claims

1. A UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration is characterized by: The following steps are involved: Step S1: Establish a controlled impedance model of the series converter, and adjust the amplitude of the AC grid input current so that the load active power can be provided by the AC grid and the DC bus at the same time; Step S2: Establish a parallel converter controlled impedance model, introduce sinusoidal voltage source control, and make the three-phase output voltage of the parallel converter system stable, sinusoidal and balanced, and compensate for load reactive power and distorted current; Step S3: Establish a UPQC system impedance model based on the impedance models of steps S1 and S2.

2. The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration according to claim 1 is characterized in that: The active power degree of freedom flexible control is performed through the series converter control impedance model of step S1, and the active power degree of freedom flexible control process includes a current amplitude reference calculation link and a degree of freedom control link.

3. The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration according to claim 1 is characterized in that: The parallel converter controlled impedance model in step S2 includes an output voltage amplitude control process and an AC bus voltage phase control process.

4. The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration according to claim 2 is characterized in that: The current amplitude reference calculation link in step S1 includes the following steps: Step S1-1: The AC grid voltage, output AC bus voltage and current are transformed by coordinates, and the fundamental positive sequence components are extracted by low-pass filters. and Step S1-2: According to the fundamental positive sequence component and instantaneous power theory obtained in step S1-1, the fundamental positive sequence active power on the grid side and the AC output bus side is obtained. and The mathematical relationship between Step S1-3: The fundamental positive sequence active power on the grid side and the AC output bus side in step S1-2 is and The mathematical relationship between them can further obtain the grid input current amplitude reference 5. The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration according to claim 4 is characterized in that: The fundamental positive sequence active power on the grid side and the AC output bus side in step S1-2 and The mathematical relationship is as follows:

6. The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration according to claim 4 is characterized in that: The grid input current amplitude reference in step S1-3 for:

7. The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration according to claim 4, 5 or 6, characterized in that: After obtaining the current amplitude reference through the current amplitude reference calculation link, the degree of freedom control link is added to realize flexible control of the system active power. The specific expression is as follows: Among them, k p For degrees of freedom.

8. The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration according to claim 7 is characterized in that: When the degree of freedom k p When k is used, the input current of the AC grid changes accordingly, and the active power input of the grid also changes accordingly; in order to meet the power demand of the load, the parallel converter will automatically obtain energy from the DC bus to compensate for the p The power change caused by the change of k p The active power between the AC and DC buses operates flexibly in any ratio within the range of 0 to 100%.

9. The UPQC node impedance polymorphic flexible matching control method based on multi-task collaboration according to claim 3 is characterized in that: The output voltage amplitude control process is implemented by a voltage loop controller, which is composed of a proportional integral + quasi-resonant controller. The amplitude control expression is as follows: Among them, k PCvp and k PCvi are the proportional and integral coefficients of the PI controller respectively; h, k r ,ω o and ω c They are the harmonic order, resonance coefficient, resonant frequency and cut-off frequency of the QR controller respectively.

10. The UPQC node impedance multi-modal flexible matching control method based on multi-task collaboration according to claim 1 is characterized in that: The AC grid voltage and the output AC bus voltage, as well as the DC grid voltage and the output DC bus voltage are compensated by photovoltaic cells and wind power generation. The phase-frequency characteristics are optimized by the weight method to obtain the compensation objective function, and the gain margin in the objective function is conditionally constrained to increase the gain margin. The specific calculation method is as follows: △Z(s)=Lms+Rm Among them, G(s l ) is the high-pass filter transfer function of the photovoltaic generator set, G(s c ) is the high-pass filter transfer function of the wind turbine generator set, △E is the power supply compensation voltage, Tsl is the high-pass filter time constant of the photovoltaic generator set, Tsc is the high-pass filter time constant of the wind turbine generator set, s is the high-pass filter transfer function of the overall circuit, the superscripts t and t-1 are the relevant electrical quantities in the current calculation compensation cycle and the previous calculation compensation cycle, △Z(s) is the compensation impedance, Lms is the leakage inductance of the transformer, and Rm is the DC impedance value.

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