Energy optimization control method and system for medium voltage cascade DVR with limited supercapacitor

Abstract

The present invention discloses a medium voltage cascade DVR energy optimization control method and system containing a limited super capacitor, which calculates the grid voltage u at the access point of the medium voltage cascade DVR containing a limited super capacitor through a phase-locked loop. g The grid voltage phase ωt; Taking the grid voltage phase ωt as the reference phase, the grid voltage u at the medium voltage cascade DVR access point containing limited supercapacitors g Perform dq transformation to obtain the grid voltage amplitude U g_mag ; Set the grid voltage amplitude U g_mag By comparing these values ​​with the sag thresholds, the operating status and control strategy of each converter module at different voltage sag depths are determined. By introducing supercapacitor energy storage units, additional energy supply options are provided beyond the grid. By setting different sag depth thresholds and implementing energy optimization control strategies, the voltage sag compensation depth is increased, significantly improving the DVR compensation device's performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of DVR operating state optimization control, and in particular relates to a medium-voltage cascade DVR energy optimization control method and system containing a limited supercapacitor. Background Art

[0002] With the rapid development of the economy and society, a large number of high-precision instruments and equipment have been introduced into production lines. The capacity and number of sensitive loads have continued to grow, and the demand for high-quality power supply quality from the power grid has also continued to increase. In recent years, voltage sag incidents have become the most frequently complained power supply quality issue by users.

[0003] Dynamic Voltage Restorers (DVRs) are an effective method for managing voltage sags, offering advantages such as small device capacity, low reliance on energy storage, and a wide compensation range. DVRs with energy storage, used in medium-voltage distribution networks, can centrally manage voltage sags for large, sensitive loads such as those in industrial parks. However, traditional DVR compensation devices without energy storage are unable to address deep voltage sags, and their compensation limit is generally considered to be only 50%. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide a medium-voltage cascade DVR energy optimization control method and system containing limited supercapacitors, which is used to solve the technical problem that traditional DVR compensation equipment cannot achieve deep voltage sag control.

[0005] The present invention adopts the following technical solutions:

[0006] The energy optimization control method of the medium voltage cascade DVR containing limited super capacitor is characterized in that the grid voltage u at the access point of the medium voltage cascade DVR containing limited super capacitor is calculated by a phase-locked loop g The grid voltage phase ωt; Taking the grid voltage phase ωt as the reference phase, the grid voltage u at the medium voltage cascade DVR access point containing limited supercapacitors g Perform dq transformation to obtain the grid voltage amplitude U g_mag ; Set the grid voltage amplitude U g_mag The values ​​are compared with the voltage sag thresholds respectively to determine the working status and control strategy of each converter module under different voltage sag depths.

[0007] Specifically, the voltage sag threshold includes the voltage sag threshold magThreshold0, the rectifier bridge voltage regulation working state threshold magThreshold1, the module c3_Rec and c3_Inv working state threshold magThreshold2, and the module c4_Rec, c4_Inv working state threshold and rectifier bridge locking threshold magThreshold3.

[0008] Further, if U g_mag > magThreshold0, no voltage sag occurs, the rectifier side performs voltage regulation control, the inverter bridge is in the bypass operation state, and the limited supercapacitor does not output power.

[0009] Further, if magThreshold1 < U g_mag < magThreshold0, the two H-bridge modules c1_Inv and c2_Inv on the inverter side perform cascaded output, the two H-bridge modules c3_Inv and c4_Inv are in the bypass state, the four H-bridge modules c1_Rec, c2_Rec, c3_Rec, and c4_Rec on the rectifier side perform voltage regulation control, where the two H-bridge modules c1_Rec and c2_Rec absorb active power from the power grid, the two H-bridge modules c3_Rec and c4_Rec do not exchange power with the power grid, and all the power compensated by the DVR is provided by the rectifier side, and the limited supercapacitor does not output power.

[0010] Further, if magThreshold2 < U g_mag < magThreshold1, the two H-bridge modules c1_Inv and c2_Inv perform cascaded output, the two H-bridge modules c3_Inv and c4_Inv are in the bypass state, the two H-bridge modules c1_Rec and c2_Rec on the rectifier side perform constant current control to feed energy to the load at a constant power, the two H-bridge modules c3_Inv and c4_Rec perform voltage regulation control and do not exchange power with the power grid, and the remaining energy is provided by the limited supercapacitor and output at a constant power. The power compensated by the medium-voltage cascaded DVR is provided jointly by the rectifier side and the limited supercapacitor.

[0011] Furthermore, the rectifier bridge provides active power P Rec as:

[0012]

[0013] P SC =P DVR -P Rec

[0014] where, U g_mag is the grid voltage amplitude, I Li is the fundamental input current of the i-th rectifier bridge, PSC Output active power for the super capacitor; P DVR Is the active power compensation required for the medium-voltage cascaded DVR.

[0015] Furthermore, if magThreshold3 < U g_mag < magThreshold2, the three H-bridge modules c1_Inv, c2_Inv, and c3_Inv on the inverter side are cascaded for output, the c4_Inv H-bridge module is in the bypass state, the three H-bridge modules c1_Rec, c2_Rec, and c3_Rec on the rectifier side perform constant current control to feed energy to the load at a constant power, the c4_Rec H-bridge module performs voltage stabilization control and does not exchange power with the power grid, and the remaining energy is provided by the finite super capacitor and output at a constant power. The power compensated by the medium-voltage cascaded DVR is jointly provided by the rectifier side and the finite super capacitor.

[0016] Furthermore, the rectifier bridge provides active power P Rec Is:

[0017]

[0018] P SC = P DVR - P Rec

[0019] Where, U g_mag Is the amplitude of the grid voltage, I Li Is the fundamental input current of the i-th rectifier bridge, P SC Is the active power output by the super capacitor; P DVR Is the active power compensation required for the medium-voltage cascaded DVR.

[0020] Furthermore, if U g_mag < magThreshold3, the four H-bridge modules c1_Inv, c2_Inv, c3_Inv, and c4_Inv perform cascaded output, the four H-bridge modules c1_Rec, c2_Rec, c3_Rec, and c4_Rec on the rectifier side are blocked, and all the power compensated by the medium-voltage cascaded DVR is provided by the finite super capacitor.

[0021] In a second aspect, an embodiment of the present invention provides a medium-voltage cascaded DVR energy optimization control system including a finite super capacitor, comprising:

[0022] A calculation module that calculates the grid voltage phase ωt of the grid voltage u at the access point of the medium-voltage cascaded DVR through a phase-locked loop g Of the grid voltage;

[0023] A transformation module that uses the grid voltage phase ωt as a reference phase to transform the grid voltage u at the access point of the medium-voltage cascaded DVR gPerform dq transformation to obtain the grid voltage amplitude U g_mag ;

[0024] The control module compares the grid voltage amplitude U g_mag with the voltage sag threshold respectively to determine the operating states and control strategies of each converter module under different voltage sag depths.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects:

[0026] The energy optimization control method for medium-voltage cascaded DVR with limited supercapacitors makes full use of the characteristics of the front-stage rectifier side and the supercapacitor based on the back-to-back cascaded DVR topology. That is, the energy of the rectifier side comes from the grid and does not depend on external energy storage devices. The use of supercapacitors can increase the voltage sag compensation depth. The reasonable distribution of their powers can further reduce the dependence of DVR on the energy storage capacity. Based on the judgment of the voltage sag depth, different numbers of working modules and control methods are selected for different sag depths, and the remaining modules are bypassed. The method can achieve complete compensation of the dropped voltage under different voltage sag depths, ensure the normal power supply of the load, and achieve the treatment of deep voltage sags. The results show the feasibility and effectiveness of the proposed method.

[0027] Furthermore, according to the voltage sag characteristics and the topology of the device used, the amplitudes of the compensation voltages required to be output by the inverter-side converters under different voltage sag depths are different. By setting the voltage sag thresholds magThreshold0, magThreshold2, and magThreshold3 and then selecting the operating states of the inverter-side H-bridge modules, the utilization rate of the DC-side voltage can be increased and the switching losses can be reduced. At the same time, considering the problem that the non-energy storage DVR has a compensation limit, by setting the threshold magThreshold1 to adjust the control strategy of the rectifier-side H-bridge, the treatment of deep voltage sags can be achieved.

[0028] Furthermore, when there is no voltage sag, that is, U g_mag > magThreshold0, the grid voltage is normal and the device does not need to output. The device is bypassed through the antiparallel thyristors on the output side, and at the same time, a current conduction path is provided, and the load is directly powered by the grid.

[0029] Furthermore, when the grid voltage amplitude satisfies magThreshold1 < U g_mag < magThreshold0, a shallow voltage sag occurs. The amplitude of the compensation voltage required by the device is low, and only two H-bridge modules need to be put into operation on the inverter side. At the same time, considering the problem that the non-energy storage DVR has a compensation limit, the power absorbed by the rectifier-side converter from the grid can meet the load power deficit at this time. Therefore, voltage stabilization control is performed to stabilize the DC-side voltage, and the limited supercapacitor does not output power.

[0030] Furthermore, when the grid voltage amplitude satisfies magThreshold2 < U g_mag < magThreshold1, a relatively shallow voltage sag occurs. When two H-bridge modules are put into operation on the inverter side, the output voltage requirements can still be met. At the same time, considering the problem that the non-energy-storage DVR has a compensation limit, the power absorbed by the rectifier-side converter from the grid cannot meet the load power deficit at this time. Therefore, constant current control is performed to feed energy to the load at a constant power, and the limited supercapacitor provides the remaining power.

[0031] Furthermore, when the grid voltage amplitude satisfies magThreshold2 < U g_mag < magThreshold1, considering the problem that the non-energy-storage DVR has a compensation limit, if the rectifier side still performs voltage stabilization control, since it cannot absorb all the load deficit power from the grid, the DC voltage cannot be stabilized, resulting in the instability of the rectifier-side control loop. Therefore, the rectifier-side control mode is selected to be switched to absorb active power from the grid at a constant power P Rec which is beneficial to the stable operation of the system.

[0032] Furthermore, when the grid voltage amplitude satisfies magThreshold3 < U g_mag < magThreshold2, a relatively deep voltage sag occurs. The output voltage amplitude on the inverter side further increases, and three H-bridge modules need to be put into operation to meet the output voltage requirements. At the same time, considering the problem that the non-energy-storage DVR has a compensation limit, the power absorbed by the rectifier-side converter from the grid cannot meet the load power deficit at this time. Therefore, constant current control is performed to feed energy to the load at a constant power, and the limited supercapacitor provides the remaining power.

[0033] Furthermore, when the grid voltage amplitude satisfies magThreshold3 < U g_mag < magThreshold2, considering the problem that the non-energy-storage DVR has a compensation limit, if the rectifier side still performs voltage stabilization control, since it cannot absorb all the load deficit power from the grid, the DC voltage cannot be stabilized, resulting in the instability of the rectifier-side control loop. Therefore, the rectifier-side control mode is selected to be switched to absorb active power from the grid at a constant power P Rec which is beneficial to the stable operation of the system.

[0034] Furthermore, when the grid voltage amplitude satisfies U g_magWhen \(\text{magThreshold}< 3\), a deep voltage sag occurs, and the amplitude of the output voltage on the inverter side further increases. Four H-bridge modules need to be put into operation to meet the output voltage requirements. At the same time, considering the problem that the non-energy storage type DVR has a compensation limit, the power absorbed by the rectifier side converter from the power grid cannot meet the load power deficit at this time, and the amplitude of the grid voltage is very low. If active power is still absorbed from the power grid, it may cause the grid situation to deteriorate further. Therefore, the rectifier side is blocked, and the limited supercapacitor provides all the power.

[0035] It can be understood that the beneficial effects of the second aspect can be referred to the relevant descriptions in the first aspect above, and will not be elaborated here.

[0036] To sum up, the present invention combines two energy sources, namely the pre-stage rectifier side and the supercapacitor, and flexibly adjusts through a control strategy to achieve an optimized cooperation of the power outputs of both the rectifier side and the supercapacitor. Based on the judgment of the depth of voltage sag, by setting different voltage sag thresholds, the switching of the number of working modules on the rectifier side and the inverter side of the compensation device and the adjustment of the control mode of the rectifier side converter are realized, thereby improving the depth of voltage sag compensation and greatly enhancing the governance performance of the DVR compensation device.

[0037] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Brief Description of the Drawings

[0038] Figure 1 is the circuit topology diagram of the traditional non-energy storage cascaded DVR;

[0039] Figure 2 is the circuit topology diagram of the cascaded DVR adopted by the present invention;

[0040] Figure 3 is the control block diagram of the phase-locked loop;

[0041] Figure 4 is the block diagram of the voltage amplitude detection method based on dq transformation;

[0042] Figure 5 is the control block diagram for the rectifier side to perform voltage stabilization control;

[0043] Figure 6 is the control block diagram for the rectifier side to perform constant current control;

[0044] Figure 7 is the control strategy block diagram of the inverter side;

[0045] Figure 8 is the control mode block diagram of the inverter bridge bypass mode; <00所提到的“

[0046] Figure 9 is the simulation waveform diagram of the rectifier bridge voltage and current at a voltage sag depth of 0.85;

[0047] Figure 10 This is the simulated waveform of the supercapacitor voltage at a sag depth of 0.85;

[0048] Figure 11 This is the simulated waveform of DVR compensation effect under 0.85 sag depth;

[0049] Figure 12 This is the simulated waveform of the voltage and current of the rectifier bridge under a 0.7 sag depth;

[0050] Figure 13 This is the simulated waveform of the supercapacitor voltage at a 0.7 sag depth;

[0051] Figure 14 This is the simulated waveform of DVR compensation effect under 0.7 sag depth;

[0052] Figure 15 This is the simulated waveform of the voltage and current of the rectifier bridge under a 0.5 sag depth;

[0053] Figure 16 This is the simulated waveform of the supercapacitor voltage at a 0.5 sag depth;

[0054] Figure 17 This is the simulated waveform of DVR compensation effect under 0.5 sag depth;

[0055] Figure 18 This is the simulated waveform of the voltage and current of the rectifier bridge under a 0.35 sag depth;

[0056] Figure 19 This is the simulated waveform of the supercapacitor voltage at a 0.35 sag depth;

[0057] Figure 20 The simulation waveform of DVR compensation effect under 0.35 sag depth. DETAILED DESCRIPTION

[0058] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0059] In the description of the present invention, it is to be understood that the terms “include” and “comprise” indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0060] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0061] It should be further understood that the term "and / or" as used in the present specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items. For example, A and / or B may represent: A alone, A and B simultaneously, or B alone. In addition, the character " / " herein generally indicates that the associated items are in an "or" relationship.

[0062] It should be understood that although the terms "first," "second," and "third" may be used to describe preset ranges in embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are merely used to distinguish one preset range from another. For example, without departing from the scope of embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0063] The word "if," as used herein, may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to the determination" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)," depending on the context.

[0064] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0065] See also Figure 1Traditional medium-voltage cascade DVRs lack energy storage. When a voltage sag occurs, the parallel-side rectifier absorbs active power from the grid and transfers it to the load, compensating for the power shortfall and ensuring normal power supply to sensitive loads. However, in traditional circuit topologies, the compensation device only serves as an energy transfer device. Since there is no external energy storage, the entire load power is still provided by the grid. Theoretically, the compensation depth limit of a DVR without energy storage is 50%, making it impossible to guarantee normal power supply to sensitive loads during deep voltage sags.

[0066] The present invention provides a medium voltage cascade DVR energy optimization control method containing a limited supercapacitor. In order to solve the problem that the medium voltage DVR compensation equipment has a high power level and requires a lot of energy, a converter topology and control strategy are studied. A cascade DVR circuit is adopted. Based on the back-to-back H-bridge structure, the left rectifier bridge is connected to the power grid in parallel through a step-up multi-winding transformer, and the right inverter bridge is connected between the power grid and the sensitive load in a cascade form through a series transformer to achieve voltage sag compensation. In order to achieve deeper compensation, a supercapacitor energy storage is connected on the DC side. Therefore, when a voltage sag occurs, there are two energy sources, namely the active power absorbed by the rectifier bridge from the power grid and the energy stored by the supercapacitor; a medium voltage DVR energy optimization control strategy is designed to improve the compensation depth of the DVR, thereby improving the performance of the compensation device, thereby ensuring the normal power supply of sensitive loads in the case of deep voltage sag.

[0067] See also Figure 2 , the cascade DVR circuit topology is as follows:

[0068] The rectifier-side converters c1_Rec, c2_Rec, c3_Rec, and c4_Rec are connected in parallel to the grid via a multi-winding transformer T1, absorbing active power from the grid to stabilize the DC bus voltage. The inverter-side H-bridge inverters c1_Inv, c2_Inv, c3_Inv, and c4_Inv are cascaded to reduce the withstand voltage of each unit. They are connected between the load and the grid via a series transformer T2 to compensate for voltage sags. Anti-parallel thyristors VT1 and VT2 are connected in parallel on the primary side of the series transformer T2 to enable rapid switching of the DVRs. A supercapacitor energy storage device is connected to the DC side to compensate for deep voltage sags and improve device performance.

[0069] Among them, U N is the rated voltage of the load; P N is the rated power of the load; U dci is the DC side voltage of the i-th module, i=1, 2, 3, 4; U dcref is the DC side voltage reference value; I Li I is the fundamental current input to the i-th rectifier bridge; dref The fundamental current reference value of the rectifier bridge input; PRec Provide active power for the rectifier bridge; P SC The active power output of the supercapacitor; P DVR The active power u required for DVR compensation g is the instantaneous value of the grid voltage; ωt is the grid voltage phase; U g_mag is the grid voltage amplitude; magThreshold0 is the voltage sag threshold; magThreshold1 is the rectifier bridge voltage regulation working state threshold; magThreshold2 is the module c3_Rec and c3_Inv working state threshold; magThreshold3 is the module c4_Rec, c4_Inv working state threshold and the rectifier bridge lockout threshold.

[0070] The present invention provides a medium voltage cascade DVR energy optimization control method containing a limited supercapacitor, comprising the following steps:

[0071] S1, collect the grid voltage u at the medium voltage cascade DVR access point containing limited super capacitors g ;

[0072] S2, calculating the grid voltage phase ωt by using the grid voltage sampling value in step S1 through a phase-locked loop;

[0073] See also Figure 3 and Figure 4 , transform the collected grid voltage to the dq coordinate system through abc-dq. The coordinate transformation formula is as follows:

[0074]

[0075] Where ω′ is the grid frequency estimated by the phase-locked loop.

[0076] Taking phase A as a reference, the three-phase grid voltage expression is as follows:

[0077]

[0078] Among them, U g_mag is the grid voltage amplitude; ω is the actual grid angular frequency.

[0079] Substituting the grid voltage expression into the abc-dq transformation expression, we can obtain:

[0080]

[0081] It is found that after the grid voltage is transformed by abc-dq, u q The component contains frequency (phase) error information, so u qThe component is controlled to 0 by the PI regulator. At this time, it can be seen from the expression that ω′t=ωt, that is, the output frequency (phase) of the phase-locked loop is consistent with the power grid, achieving phase locking.

[0082] S3, using the ωt calculated in step S2 as the reference phase, perform dq transformation on the grid voltage sampling value in step S1 to obtain the grid voltage amplitude U g_mag ;

[0083] See also Figure 4 , the abc-dq transformation formula is the same as formula (1). At this time, the phase output of the phase-locked loop in step S2 is the actual phase of the grid voltage ωt. Therefore, after simplification, u in formula (3) is d The component becomes u d =U g_mag , and thus the grid voltage amplitude is obtained.

[0084] S4. Set voltage sag thresholds magThreshold0, magThreshold1, magThreshold2, and magThreshold3 respectively to select the working state and control strategy of each converter module under different voltage sag depths;

[0085] See also Figure 5 and Figure 6 , which are the voltage stabilization control and constant current control adopted by the rectifier bridge respectively. The voltage stabilization control absorbs active power from the grid with a unity power factor. The inverter bridge adopts the dual-loop control strategy of outer loop proportional resonance and inner loop proportional control as shown in the block diagram. Figure 7 shown.

[0086] Figure 5 The figure shows the voltage regulation control block diagram used by the rectifier bridge, the DC reference voltage U dcref Its sampling value U dc The comparison is done and the PI regulator outputs the inductor current active power instruction I dref , the inductor current reactive power command is set to 0 to achieve unity power factor to absorb active power from the grid. The two are added to the phase cosine value and sine value of the phase-locked loop output phase to generate the instantaneous value of the inductor current i Lref , and then with its sampling value i L The PR controller makes a comparison and outputs the modulation signal of the H-bridge converter on the rectifier side.

[0087] Figure 6 The figure shows the constant current control block diagram used by the rectifier bridge. The inductor current active power instruction is the set value I dref , the inductor current reactive power command is set to 0 to achieve unity power factor to absorb active power from the grid. The two are added to the phase cosine value and sine value of the phase-locked loop output phase to generate the instantaneous value of the inductor current i Lref , and then with its sampling value i LThe output of the PR controller is used as the modulation signal for the rectifier-side H-bridge converter after comparison.

[0088] Figure 6 The figure shows the block diagram of the double-loop control strategy of the outer-loop proportional-resonant and inner-loop proportional control adopted by the inverter bridge. The rated value of the grid voltage is U N is subtracted from the sampled value U g to generate the DVR output voltage command U dvrref , and then it is compared with its output voltage sampled value U dvr to generate the inductor current reference value i Lref through the PR controller. This reference value is compared with the inductor current sampled value i L to generate the modulation signal for the inverter-side H-bridge converter through the proportional link.

[0089] S5. Compare U g_mag with the set voltage sag threshold to obtain the working states and control strategies of each module.

[0090] The working states and control strategies of each module are as follows:

[0091] 1. If U g_mag > magThreshold0, no voltage sag occurs and each module is in the standby state;

[0092] Please refer to Figure 8 , the inverter bridge is in the bypass operation state through the control strategy. At this time, since there is no power deficit in the load, the rectifier bridge does not absorb power from the grid, and the limited supercapacitor does not output power.

[0093] 2. If magThreshold1 < U g_mag < magThreshold0, a shallow voltage sag occurs, and the two modules are put into operation. The four H-bridge modules c1_Rec, c2_Rec, c3_Rec, and c4_Rec on the rectifier side perform voltage stabilization control. All the power compensated by the medium-voltage cascaded DVR is provided by the rectifier side, and the limited supercapacitor does not output power;

[0094] On the inverter side, the two H-bridge modules c1_Inv and c2_Inv perform cascaded output, and the two H-bridge modules c3_Inv and c4_Inv are in the bypass state. Since only the two H-bridge modules c1_Inv and c2_Inv on the inverter side are working, only the corresponding two H-bridge modules c1_Rec and c2_Rec on the rectifier side absorb active power from the grid, and the two H-bridge modules c3_Rec and c4_Rec do not exchange power with the grid. All the power compensated by the medium-voltage cascaded DVR is provided by the rectifier side, and the limited supercapacitor does not output power.

[0095] 3. If magThreshold2 < U g_mag<When magThreshold1, a relatively shallow voltage sag occurs. At this time, the power deficit of the load cannot be fully provided by the rectifier bridge. The two H-bridge modules c1_Inv and c2_Inv on the inverter side are cascaded for output, and the two H-bridge modules c3_Inv and c4_Inv are in the bypass state. The two H-bridge modules c1_Rec and c2_Re on the rectifier side perform constant current control to feed energy to the load at a constant power. The two modules c3_Rec and c4_Rec perform voltage stabilization control and do not exchange power with the power grid. The remaining energy is provided by the limited supercapacitor and output at a constant power. The power compensated by the medium-voltage cascaded DVR is jointly provided by the rectifier side and the limited supercapacitor;

[0096] 4. If magThreshold3 < U g_mag <When magThreshold2, a relatively deep voltage sag occurs, and the required output voltage on the inverter side increases. Therefore, the three H-bridge modules c1_Inv, c2_Inv, and c3_Inv are cascaded for output, and the H-bridge module c4_Inv is in the bypass state. The three H-bridge modules c1_Rec, c2_Rec, and c3_Rec on the rectifier side perform constant current control to feed energy to the load at a constant power. The H-bridge module c4_Rec performs voltage stabilization control and does not exchange power with the power grid. The remaining energy is provided by the limited supercapacitor and output at a constant power. The power compensated by the medium-voltage cascaded DVR is jointly provided by the rectifier side and the limited supercapacitor;

[0097] 5. If U g_mag <When magThreshold3, a deep voltage sag occurs, and the required output voltage on the inverter side further increases. Therefore, all four H-bridge modules c1_Inv, c2_Inv, c3_Inv, and c4_Inv of the inverter bridge are cascaded for output. At this time, since the residual voltage of the power grid is very low, if the rectifier bridge absorbs active power to further deteriorate the power grid voltage, all four H-bridge modules c1_Rec, c2_Rec, c3_Rec, and c4_Rec on the rectifier side are blocked, and the power compensated by the medium-voltage cascaded DVR is all provided by the limited supercapacitor.

[0098] In another embodiment of the present invention, a medium-voltage cascaded DVR energy optimization control system containing a limited supercapacitor is provided. This system can be used to implement the above-mentioned medium-voltage cascaded DVR energy optimization control method with a limited supercapacitor. Specifically, the medium-voltage cascaded DVR energy optimization control system containing a limited supercapacitor includes a calculation module, a transformation module, and a control module.

[0099] Among them, the calculation module calculates the grid voltage phase ωt of the grid voltage u at the access point of the medium-voltage cascaded DVR through a phase-locked loop g of the grid voltage;

[0100] A transformation module that uses the grid voltage phase ωt as the reference phase to perform a dq transformation on the grid voltage u at the access point of the medium-voltage cascaded DVR to obtain the grid voltage amplitude U g ; g_mag ;

[0101] A control module that compares the grid voltage amplitude U g_mag with the voltage sag threshold respectively to determine the operating states and control strategies of each converter module under different voltage sag depths.

[0102] Please refer to Figure 2 , and by judging the voltage sag depth, select the control methods for the rectifier side and the inverter side, and then realize the optimized control of the energy distribution between the rectifier bridge and the supercapacitor, so that the medium-voltage cascaded DVR further reduces its dependence on the energy storage device.

[0103] Assume that a voltage sag event occurs, that is, at this time the grid voltage U g_mag < magThreshold0. According to the basic principle of the medium-voltage cascaded DVR compensation, P DVR =(1 - U g_mag ) * P N , P SC =P DVR -P Rec . The following discusses the energy distribution relationship between the rectifier bridge and the supercapacitor in several cases:

[0104] When magThreshold1 < U g_mag < magThreshold0, all the power compensated by the medium-voltage cascaded DVR is provided by the rectifier bridge. Therefore, P Rec =P DVR , P SC =0;

[0105] When magThreshold2 < U g_mag [[ID=,47]]< magThreshold1, the power compensated by the medium-voltage cascaded DVR is provided by the rectifier bridge and the supercapacitor together. Among them, P SC =P DVR -P Rec ;

[0106] When magThreshold3 < U g_mag < magThreshold2, the power compensated by the medium-voltage cascaded DVR is provided by the rectifier bridge and the supercapacitor together. Among them, P SC =P DVR -R Rec ;

[0107] When U g_magWhen magThreshold < 3, the power compensated by the medium-voltage cascaded DVR is only provided by the supercapacitors together, so P SC = P DVR .

[0108] Please refer to Figures 9 to 20 , which is the simulation results under different voltage sag depths. The system used for verification is a single-phase 10 kV distribution network, and the rated power of the load is P N = 0.67 MW. The set thresholds are magThreshold0 = 0.9U N , magThreshold1 = 0.8U N , magThreshold2 = 0.6U N , magThreshold3 = 0.4U N . When 2 modules are working, set I dref = 60 A. When 3 modules are working, set I dref = 50 A. The theoretical values of the power distribution under each voltage sag depth are shown in the following table:

[0109]

[0110] Please refer to Figure 9 , Figure 10 and Figure 11 , which are the simulation results when the voltage sag depth is 0.85. According to Figure 9 , it can be obtained that the rectifier bridge in the voltage stabilization control absorbs active power from the power grid with a unity power factor, and then combined with Figure 10 , it can be obtained that in the initial stage of the voltage sag, due to the fast response speed of the supercapacitors, they discharge first for a period of time. After entering the steady state, the voltage of the supercapacitors remains unchanged, and the power is all provided by the rectifier side. Since only 2 modules are working, the remaining supercapacitors do not discharge, Figure 11 showing that the DVR can achieve fast and accurate voltage sag compensation.

[0111] Please refer to 12 Figure 13 and Figure 14 , which are the simulation results when the voltage sag depth is 0.7. According to Figure 12 , it can be seen that the rectifier bridge in the constant current control absorbs active power from the power grid with a unity power factor, and P Rec = 410.9 × 56.8 × 2 = 46.7 kW. Then combined with Figure 13 , it can be found that the two working supercapacitors discharge after the voltage sag occurs and have the same discharge characteristics. The output power of a single supercapacitor Figure 14 showing that the DVR can achieve fast and accurate voltage sag compensation.

[0112] See also Figure 15 、 Figure 15 and Figure 17 , is the simulation result when the voltage sag depth is 0.5, according to Figure 15 It can be seen that the rectifier bridge in constant current control absorbs active power from the grid with unity power factor, and P Rec =291.3×51.3×3=44.8kW, then combined Figure 16 It can be found that the three supercapacitors in working state discharge after the voltage sag occurs and the discharge characteristics are consistent. The output power of a single supercapacitor is Figure 17 Display DVR can achieve fast and accurate voltage sag compensation.

[0113] See also Figure 18 、 Figure 19 and Figure 20 , is the simulation result when the voltage sag depth is 0.35, according to Figure 18 It can be seen that the rectifier bridge is in shutdown state and the input current is zero, so the rectifier bridge does not absorb energy from the grid, P Rec = 0, then combine Figure 19 It can be found that the four supercapacitors in working state discharge after the voltage sag occurs and the discharge characteristics are consistent. The output power of a single supercapacitor is All the power required by the DVR is provided by supercapacitors Figure 17 Display DVR can achieve fast and accurate voltage sag compensation.

[0114] Combining the simulation results with the theoretical analysis, it can be seen that by introducing supercapacitors through the adopted circuit topology and combining the medium-voltage cascade DVR energy optimization control strategy based on limited supercapacitors proposed in the present invention, the energy supply path other than the power grid is increased, and by setting different voltage sag thresholds, the energy optimization distribution of the rectifier bridge and the supercapacitor is achieved without affecting the voltage sag compensation effect, thereby increasing the voltage sag compensation depth and greatly improving the governance performance of the DVR compensation device.

[0115] In summary, the present invention provides a medium-voltage cascade DVR energy optimization control method and system containing a limited supercapacitor. By introducing supercapacitors, an energy supply path other than the power grid is added, and an energy optimization control strategy is implemented by setting different sag depth thresholds. The voltage sag compensation depth is increased, and the management performance of the DVR compensation device is greatly improved.

[0116] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A medium voltage cascade DVR energy optimization control method with limited supercapacitors, characterized in that: Calculation of grid voltage at the access point of a medium voltage cascaded DVR with limited supercapacitors using a phase-locked loop u g The grid voltage phase ωt ; Based on the grid voltage phase ωt As the reference phase, the grid voltage at the access point of the medium voltage cascaded DVR with limited supercapacitors is u g conduct dq Transformation to obtain the grid voltage amplitude U g_mag ; Set the grid voltage amplitude U g_mag Compare with the sag threshold respectively to determine the working status and control strategy of each converter module under different voltage sag depths; The sag thresholds include the voltage sag threshold magThreshold0, the rectifier bridge voltage regulation working state threshold magThreshold1, the module c3_Rec and c3_Inv working state threshold magThreshold2, the module c4_Rec, c4_Inv working state threshold and the rectifier bridge locking threshold magThreshold3; If magThreshold1 < U g_mag <magThreshold0, the H-bridge inverters c1_Inv and c2_Inv on the inverter side perform cascaded output, and the H-bridge inverters c3_Inv and c4_Inv on the inverter side are in the bypass state. The rectifier-side converters c1_Rec, c2_Rec, c3_Rec, and c4_Rec perform voltage stabilization control. The rectifier-side converters c1_Rec and c2_Rec absorb active power from the power grid. The rectifier-side converters c3_Rec and c4_Rec do not exchange power with the power grid. All the power compensated by the DVR is provided by the rectifier side, and the limited supercapacitor does not output power; If magThreshold2 < U g_mag <magThreshold1, the H-bridge inverters c1_Inv and c2_Inv on the inverter side are cascaded for output, the H-bridge inverters c3_Inv and c4_Inv on the inverter side are in the bypass state, the rectifier-side converters c1_Rec and c2_Rec perform constant-current control to feed energy to the load at a constant power, the rectifier-side converters c3_Inv and c4_Rec perform voltage stabilization control and do not exchange power with the power grid, the remaining energy is provided by a limited supercapacitor and output at a constant power, and the power compensated by the medium-voltage cascaded DVR is jointly provided by the rectifier side and the limited supercapacitor; If magThreshold3 < U g_mag < magThreshold2, the H-bridge inverters c1_Inv, c2_Inv, and c3_Inv on the inverter side are cascaded for output, the H-bridge inverter c4_Inv on the inverter side is in the bypass state, the converters c1_Rec, c2_Rec, and c3_Rec on the rectifier side perform constant current control to feed energy to the load at a constant power, the converter c4_Rec on the rectifier side performs voltage stabilization control and does not exchange power with the power grid, the remaining energy is provided by a finite supercapacitor and output at a constant power, and the power compensated by the medium-voltage cascaded DVR is jointly provided by the rectifier side and the finite supercapacitor; If U g_mag <When the magnetic threshold 3 is reached, the H-bridge inverters c1_Inv, c2_Inv, c3_Inv, and c4_Inv on the inverter side perform cascaded output, and the converters c1_Rec, c2_Rec, c3_Rec, and c4_Rec4 on the rectifier side are blocked. All the power compensated by the medium-voltage cascaded DVR is provided by the finite supercapacitor; The rectifier-side converters c1_Rec, c2_Rec, c3_Rec, and c4_Rec are connected to the grid in parallel through a multi-winding transformer T1, absorbing active power from the grid to stabilize the DC bus voltage. The inverter-side H-bridge inverters c1_Inv, c2_Inv, c3_Inv, and c4_Inv are cascaded to reduce the withstand voltage level of each unit and are connected between the load and the grid through the series transformer T2 to achieve voltage sag compensation.

2. The energy optimization control method of a medium voltage cascade DVR containing a limited supercapacitor according to claim 1 is characterized in that: If the grid voltage amplitude U g_mag > Voltage sag threshold magThreshold0, no voltage sag occurs, the rectifier side performs voltage regulation control, the inverter bridge is in bypass operation, and the limited supercapacitor does not contribute.

3. The energy optimization control method of a medium voltage cascade DVR with a limited supercapacitor according to claim 1 is characterized in that: The rectifier bridge provides active power for: in, is the grid voltage amplitude, Input fundamental current for the i-th rectifier bridge, P SC Output active power to the supercapacitor; P DVR This is the active power compensation required for the medium voltage cascade DVR.

4. The energy optimization control method of a medium voltage cascade DVR with a limited supercapacitor according to claim 1 is characterized in that: The rectifier bridge provides active power for: in, is the grid voltage amplitude, Input fundamental current for the i-th rectifier bridge, P SC Output active power to the supercapacitor; P DVR This is the active power compensation required for the medium voltage cascade DVR.

5. A medium voltage cascade DVR energy optimization control system containing limited supercapacitors, characterized in that: include: Calculation module, calculates the grid voltage of the medium voltage cascade DVR access point through the phase-locked loop u g The grid voltage phase ωt ; Conversion module, based on grid voltage phase ωt The grid voltage of the medium voltage cascade DVR access point is the reference phase. u g conduct dq Transformation to obtain the grid voltage amplitude U g_mag ; Control module, the grid voltage amplitude U g_mag Compare with the voltage sag threshold respectively to determine the working status and control strategy of each converter module under different voltage sag depths; The sag thresholds include the voltage sag threshold magThreshold0, the rectifier bridge voltage regulation working state threshold magThreshold1, the module c3_Rec and c3_Inv working state threshold magThreshold2, the module c4_Rec, c4_Inv working state threshold and the rectifier bridge locking threshold magThreshold3; If magThreshold1 < U g_mag < magThreshold0, the H-bridge inverters c1_Inv and c2_Inv on the inverter side are cascaded for output, and the H-bridge inverters c3_Inv and c4_Inv on the inverter side are in the bypass state. The rectifier-side converters c1_Rec, c2_Rec, c3_Rec, and c4_Rec perform voltage stabilization control. The rectifier-side converters c1_Rec and c2_Rec absorb active power from the power grid. The rectifier-side converters c3_Rec and c4_Rec do not exchange power with the power grid. All the power compensated by the DVR is provided by the rectifier side, and the limited supercapacitor does not output power; If magThreshold2 < U g_mag < magThreshold1, the H-bridge inverters c1_Inv and c2_Inv on the inverter side are cascaded for output, and the H-bridge inverters c3_Inv and c4_Inv on the inverter side are in the bypass state. The converters c1_Rec and c2_Rec on the rectifier side perform constant current control to feed energy to the load at a constant power. The converters c3_Inv and c4_Rec on the rectifier side perform voltage stabilization control and do not exchange power with the power grid. The remaining energy is provided by a limited supercapacitor and output at a constant power. The power compensated by the medium-voltage cascaded DVR is jointly provided by the rectifier side and the limited supercapacitor; If magThreshold3 < U g_mag < magThreshold2, the H-bridge inverters c1_Inv, c2_Inv, and c3_Inv on the inverter side are cascaded for output, the H-bridge inverter c4_Inv on the inverter side is in a bypass state, the converters c1_Rec, c2_Rec, and c3_Rec on the rectifier side perform constant current control to feed energy to the load at a constant power, the converter c4_Rec on the rectifier side performs voltage stabilization control and does not exchange power with the power grid, the remaining energy is provided by a finite supercapacitor and output at a constant power, and the power compensated by the medium-voltage cascaded DVR is jointly provided by the rectifier side and the finite supercapacitor; If U g_mag <When the magnitude of the fault current is greater than magThreshold3, the H-bridge inverters c1_Inv, c2_Inv, c3_Inv, and c4_Inv on the inverter side perform cascaded output, and the converters c1_Rec, c2_Rec, c3_Rec, and c4_Rec4 on the rectifier side are blocked. All the power compensated by the medium-voltage cascaded DVR is provided by the finite supercapacitor; The rectifier-side converters c1_Rec, c2_Rec, c3_Rec, and c4_Rec are connected to the grid in parallel through a multi-winding transformer T1, absorbing active power from the grid to stabilize the DC bus voltage. The inverter-side H-bridge inverters c1_Inv, c2_Inv, c3_Inv, and c4_Inv are cascaded to reduce the withstand voltage level of each unit and are connected between the load and the grid through the series transformer T2 to achieve voltage sag compensation.

6. The medium voltage cascade DVR energy optimization control system containing limited supercapacitors according to claim 5 is characterized in that: If the grid voltage amplitude U g_mag > Voltage sag threshold magThreshold0, no voltage sag occurs, the rectifier side performs voltage regulation control, the inverter bridge is in bypass operation, and the limited supercapacitor does not contribute.

7. The medium voltage cascade DVR energy optimization control system containing limited supercapacitors according to claim 5 is characterized in that: The rectifier bridge provides active power for: in, is the grid voltage amplitude, Input fundamental current for the i-th rectifier bridge, P SC Output active power to the supercapacitor; P DVR This is the active power compensation required for the medium voltage cascade DVR.

8. The medium voltage cascade DVR energy optimization control system containing limited supercapacitors according to claim 5 is characterized in that: The rectifier bridge provides active power for: in, is the grid voltage amplitude, Input fundamental current for the i-th rectifier bridge, P SC Output active power to the supercapacitor; P DVR This is the active power compensation required for the medium voltage cascade DVR.

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