A control method of a medium-voltage direct-hanging type distributed series-parallel wideband oscillation damping device

Abstract

The application provides a control method of a medium-voltage direct-hanging type distributed series-parallel broadband oscillation damping device, and belongs to the technical field of power electronics and power quality treatment equipment. The device comprises a parallel converter, three phases exist, each phase of the parallel converter adopts a cascade H-bridge conversion topology, each phase is composed of M parallel power modules in cascade, the output is filtered through an inductor filter and is connected to an AC line, and the parallel power module adopts a first H-bridge converter. The device comprises a series converter, three phases exist, each phase is composed of one three-phase multi-winding phase-shifting transformer and N series power modules, the primary winding is connected to a three-phase medium-voltage AC power grid, the secondary winding is connected to the AC side of the series power module, and the series power module is composed of a three-phase uncontrolled rectifier and a second H-bridge converter. The application can reduce the cost of the medium-voltage series-parallel broadband oscillation damping device and the complexity of capacitor voltage control, effectively solve the problem of medium-voltage system broadband oscillation, and greatly improve the safety and stability of the system.

Description

Technical Field

[0001] This invention belongs to the field of power electronics and power quality management equipment technology, specifically relating to a medium-voltage direct-connected distributed series-parallel broadband oscillation damping device and its control method. Background Technology

[0002] With the large-scale integration of high-proportion renewable energy and energy storage power electronic equipment, the resulting broadband oscillation problem is becoming increasingly prominent, seriously threatening the safety and stability of the system. Currently, broadband oscillation suppression methods are mainly divided into software and hardware approaches. Software methods typically add extra control loops to the grid-connected converter's control to reshape the impedance and avoid oscillations. However, modifying the control algorithm of commercial converters is impractical, and changing the control algorithm for each converter individually is a significant undertaking. Hardware methods can be divided into passive and active approaches. Passive approaches typically use series or parallel resistors in the converter's filter circuit to increase damping, but this results in significant losses. Therefore, using a broadband oscillation active damping device is a better solution.

[0003] Currently, broadband oscillation damping devices include three connection types: parallel, series, and series-parallel. Parallel damping devices increase system damping by simulating parallel resistance through control algorithms; a smaller simulated resistance is more conducive to stability, but a small simulated resistance can lead to stability issues. Series damping devices suppress broadband oscillations by simulating series resistance through control algorithms, but their parameter design lacks universality, resulting in low practical usage. Using a parallel broadband oscillation damping device alone cannot completely decouple the grid-connected inverter from the grid impedance, and it cannot effectively suppress the influence of grid voltage harmonics on the grid-connected current, posing a risk of low-frequency harmonic amplification. Compared to parallel damping devices, series-parallel damping devices can not only completely decouple the grid-connected inverter from the grid impedance within the control bandwidth, but also weaken the influence of grid background harmonics on the grid-connected current, making it a superior solution. Currently, broadband oscillation damping devices are mainly used in low-voltage, low-power applications, while reports on medium-voltage 10kV high-power applications are rare. In medium-voltage, high-power applications, the power conversion topology of series-parallel wideband oscillation damping devices is similar to that of the unified power quality controller (UPQC), so theoretically, the UPQC power conversion topology can be reused. Currently, series-parallel power conversion topologies mainly include two types: modular multilevel converters (MMC) and cascaded H-bridge converters (CHB). In both CHB and MMC series-parallel topologies, the parallel side is directly connected to the medium-voltage AC bus, thus requiring a large number of submodules. Because the series-parallel power conversion topology uses a back-to-back connection, even if the series side does not require a large compensation voltage, its design still requires an equal number of submodules, resulting in high costs for both solutions. For the CHB series-parallel power conversion topology, the capacitors on the parallel and series sides of the CHB are directly coupled, making capacitor voltage equalization control difficult and the system less stable. Summary of the Invention

[0004] The purpose of this invention is to provide a medium-voltage direct-connected distributed series-parallel wideband oscillation damping device and its control method, which solves the problems of multiple power sub-modules, high cost, and complex capacitor voltage control in medium-voltage series-parallel converters.

[0005] A first aspect of the present invention provides a medium-voltage direct-connected distributed series-parallel broadband oscillation damping device, the device comprising:

[0006] A parallel converter has three phases. Each phase of the parallel converter adopts a cascaded H-bridge converter topology, which consists of M parallel power modules cascaded together. The output of the three-phase cascaded H-bridge converter topology is connected to the AC line through an inductor filter. The parallel power modules are first H-bridge converters. A series converter also has three phases. Each phase of the series converter consists of one three-phase multi-winding phase-shifting transformer and N series power modules. The primary side of the three-phase multi-winding phase-shifting transformer is connected to a three-phase medium-voltage AC power grid. The N secondary windings of the three-phase multi-winding phase-shifting transformer are connected to the AC side of the N series power modules respectively. Each of the N series power modules consists of a three-phase uncontrolled rectifier and a second H-bridge converter. The DC side output of each three-phase uncontrolled rectifier is connected in parallel to the DC side of the second H-bridge converter. The outputs of the N second H-bridge converters are cascaded and connected in series in the tie line between the power grid and the load through an LC filter.

[0007] A second aspect of the present invention provides a control method for a medium-voltage direct-connected distributed series-parallel broadband oscillation damping device, used in the aforementioned medium-voltage direct-connected distributed series-parallel broadband oscillation damping device. The method includes: parallel converter control, comprising parallel converter voltage control, parallel converter current control, and parallel converter broadband oscillation suppression control; and series converter control, comprising generating a series converter broadband oscillation suppression voltage reference value, series converter voltage control, and series converter current control.

[0008] The beneficial effects of this invention are as follows:

[0009] The technical solution provided by this invention can reduce the cost of medium-voltage series-parallel broadband oscillation suppression devices and the complexity of capacitor voltage control, and effectively solve the broadband oscillation problem of medium-voltage systems, greatly improving the safety and stability of the system. Attached Figure Description

[0010] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0011] Figure 1 This is a circuit topology diagram of the medium-voltage direct-connected distributed series-parallel wideband oscillation damping device provided by the present invention;

[0012] Figure 2 This is a basic control block diagram of the parallel converter provided by the present invention, wherein, Figure 2 (a) is the overall control diagram of the parallel converter. Figure 2 (b) is the phase-to-phase voltage balance control diagram. Figure 2 (c) is the phase voltage balance control diagram;

[0013] Figure 3 This is a control block diagram of the series converter provided by the present invention;

[0014] Figure 4 This is a simulation result diagram of the grid connection point voltage provided by the present invention;

[0015] Figure 5 This is a diagram showing the simulation results of the power grid current provided by the present invention. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0017] To address the aforementioned problems, this invention proposes a medium-voltage direct-connected distributed series-parallel broadband oscillation damping device. This device includes: a parallel converter with three phases, each phase of which employs a cascaded H-bridge converter topology. Each phase of the cascaded H-bridge converter topology consists of M parallel power modules cascaded together. The output of the three-phase cascaded H-bridge converter topology is connected to the AC line via an inductor filter, wherein the parallel power modules utilize a first H-bridge converter; and a series converter with three phases, each phase of which consists of one three-phase multi-winding phase-shifting transformer and N... The system consists of series power modules, in which the primary side of a three-phase multi-winding phase-shifting transformer is connected to a three-phase medium-voltage AC power grid, and the N secondary windings of the three-phase multi-winding phase-shifting transformer are respectively connected to the AC side of N series power modules. Each of the N series power modules consists of a three-phase uncontrolled rectifier and a second H-bridge converter. The DC side output of each three-phase uncontrolled rectifier is connected in parallel with the DC side of the second H-bridge converter. The output sides of the N second H-bridge converters are cascaded and connected in series in the tie line between the power grid and the load through an LC filter.

[0018] Both parallel and series converters have three phases. Each phase of the parallel converter is a cascaded H-bridge converter topology, which consists of M parallel power modules cascaded together. Each phase of the series converter consists of one three-phase multi-winding phase-shifting transformer and N series power modules.

[0019] It should be noted that in this invention, the first H-bridge converter and the second H-bridge converter are the same H-bridge converter. In order to distinguish the H-bridge converter used in the parallel power module from the H-bridge converter used in the series power module, the H-bridge converter used in the parallel power module is called the first H-bridge converter, and the H-bridge converter used in the series power module is called the second H-bridge converter.

[0020] The circuit topology of the medium-voltage direct-connected distributed series-parallel wideband oscillation damping device provided by this invention is as follows: Figure 1 As shown, Figure 1 This is the circuit topology diagram of the medium-voltage direct-connected distributed series-parallel broadband oscillation damping device provided by the present invention.

[0021] Figure 1 The circuit topology shown consists of parallel converters and series converters. The parallel converters are cascaded first H-bridge converters (specifically, H-bridge multilevel converters) directly connected to the AC bus. The series converters are cascaded second H-bridge converters (specifically, H-bridge multilevel converters) directly connected in series to the medium-voltage line. Since the capacitor energy of the series second H-bridge converter cannot be obtained from the AC side, an additional three-phase multi-winding phase-shifting transformer is required for energy extraction. Simultaneously, a thyristor bypass switch is configured on the series side for protection.

[0022] Compared with conventional CHB and MMC series-parallel power conversion topologies, Figure 1 The circuit topology shown does not require a shared DC bus, and the number of submodules on the parallel and series sides can be selected according to actual needs, thus reducing the number of submodules and lowering costs. Furthermore, since the capacitors of the series and parallel converters are not directly connected, voltage equalization control is easier to implement, reducing control complexity.

[0023] According to a first aspect of the present invention, a medium-voltage direct-connected distributed series-parallel broadband oscillation damping device is proposed, the device comprising a series converter and a parallel converter, such as... Figure 1 As shown.

[0024] The parallel converter of the wideband oscillation damping device adopts a three-phase cascaded H-bridge converter topology. Each phase consists of M parallel power modules cascaded together. The parallel power modules adopt the first H-bridge converter. The output of the three-phase parallel power modules is connected to the AC line through an inductor filter.

[0025] The series converter of the broadband oscillation damping device has three phases, each phase consisting of one three-phase multi-winding phase-shifting transformer and N series power modules. The primary winding of the three-phase multi-winding phase-shifting transformer is connected to the three-phase medium-voltage AC power grid of the series converter, and the N secondary windings of the three-phase multi-winding phase-shifting transformer are respectively connected to the AC side of the N power modules. Each of the N series power modules consists of a three-phase uncontrolled rectifier and a second H-bridge converter. The DC output of the three-phase uncontrolled rectifier is connected in parallel with the DC side of the second H-bridge converter. The outputs of the N second H-bridge converters are cascaded and connected in series through an LC filter in the tie line between the power grid and the load. Figure 1 In the middle, M parallel power modules are respectively used by A 11 A 12 A 13 A 1M This indicates that N series-connected power modules are respectively equipped with A 21 A 22 A 2N It should be noted that, for the sake of simplifying the illustrations, Figure 1 The diagram only shows the M parallel power modules of phase A in the parallel converter and the N series power modules of phase A in the series converter. It does not show the M parallel power modules of phases B and C in the parallel converter, nor the N parallel power modules of phases B and C in the series converter.

[0026] This invention also proposes a control method for a medium-voltage direct-connected distributed series-parallel broadband oscillation damping device. The control method includes: parallel converter control, comprising parallel converter voltage control, parallel converter current control, and parallel converter broadband oscillation suppression control; and series converter control, comprising generating a series converter broadband oscillation suppression voltage reference value, series converter voltage control, and series converter current control.

[0027] Figure 2 This is a basic control block diagram of the parallel converter provided by the present invention, wherein, Figure 2 (a) is the overall control diagram of the parallel converter. Figure 2 (b) is the phase-to-phase voltage balance control diagram. Figure 2 (c) is the phase voltage balance control diagram.

[0028] The voltage control of the parallel converter adopts a three-level voltage control, including global voltage control, inter-phase voltage balance control, and intra-phase voltage balance control.

[0029] Figure 2 (a) shows the overall control diagram of the parallel converter, as follows: Figure 2As shown in (a), the parallel converter control method includes voltage control, current control, and wideband oscillation suppression control. The voltage control adopts a three-level voltage control, including global voltage control, inter-phase voltage balance control, and intra-phase voltage balance control.

[0030] Global voltage control includes: obtaining the average value of the three-phase capacitor voltages of the parallel converter based on the capacitor voltage of the first H-bridge converter of the parallel power module; obtaining the global average voltage based on the average value of the three-phase capacitor voltages of the parallel converter; and obtaining the output current for global voltage control using a proportional-integral regulator based on the pre-known capacitor voltage reference value and the global average voltage. The details are as follows:

[0031] First, the capacitor voltage u of the first H-bridge converter in the parallel converter is collected. cxj (The subscript x represents a phase, x=a represents phase A, x=b represents phase B, x=c represents phase C; the subscript j represents the serial number of the parallel power module in the parallel converter, j=1,2,……,M), the average value of the three-phase capacitor voltage of the parallel converter is calculated as follows:

[0032] (1)

[0033] (2)

[0034] (3)

[0035] Among them, u caav u cbav and u ccav These are the average capacitor voltages for phases A, B, and C, respectively. Let J be the capacitor voltage of the j-th parallel power module in phase A of the parallel converter. The capacitor voltage of the j-th parallel power module in phase B of the parallel converter is... Let be the capacitor voltage of the j-th parallel power module in phase C of the parallel converter, and M be the total number of parallel power modules.

[0036] The global average voltage is calculated using formulas (1) to (3) as follows:

[0037] (4)

[0038] Among them, u dcav This represents the global average voltage.

[0039] The output current for global voltage control is obtained by subtracting the known capacitor voltage reference value from the global voltage average value and then passing it through a proportional-integral (PI) regulator:

[0040] (5)

[0041] in, For the output current of global voltage control, u dcref k is the reference value for capacitor voltage. vp and k vi are the proportional and integral coefficients of the global voltage controller, respectively, and s is the complex frequency.

[0042] Figure 2 (b) shows the phase-to-phase voltage balance control diagram. To achieve voltage balance among the three phases of the parallel converter, the following method is used: Figure 2 The phase-to-phase voltage balance control shown in (b) includes: using a proportional-integral regulator and combining the phase of the grid connection point voltage of the parallel converter with the known reference value of the capacitor voltage and the average value of the three-phase capacitor voltage of the parallel converter, the three-phase phase-to-phase compensation current of the parallel converter is obtained; the three-phase phase-to-phase compensation current of the parallel converter is transformed by Park to obtain the compensation components of the three-phase phase-to-phase compensation current on the d-axis and q-axis.

[0043] Specifically, after subtracting the reference value of the capacitor voltage from the average value of the three-phase capacitor voltages of the parallel converter, the result is passed through a proportional-integral (PI) regulator and then multiplied by sinθ, sin(θ-120°), and sin(θ+120°) respectively to obtain the three-phase interphase compensation current components:

[0044] (6)

[0045] (7)

[0046] (8)

[0047] Among them, i app i bpp and i cpp These are the three-phase interphase compensation currents of the parallel converter, k p,pp and k i,pp These are the proportional and integral coefficients of the three-phase phase-to-phase voltage balance controller of the parallel converter, respectively, and θ is the phase of the grid-connected voltage of the parallel converter.

[0048] The three-phase interphase compensation current of the parallel converter is transformed using Park transformation to obtain the d-axis and q-axis compensation components, respectively:

[0049] (9)

[0050] Among them, i dpp and i qpp These are the d-axis and q-axis compensation components of the three-phase interphase compensation current of the parallel converter, respectively.

[0051] Figure 2(c) shows a diagram of intra-phase voltage balance control. To achieve capacitor voltage balance among parallel power modules in each phase, the following method is used: Figure 2 The phase voltage balance control shown in (c) includes: based on the known capacitor voltage reference value and the three-phase capacitor voltage of the parallel converter, using a proportional-integral regulator and combining the phase of the output current of the parallel converter, to obtain the three-phase modulation signal compensation component of the parallel converter.

[0052] The known capacitor voltage reference value is subtracted from the three-phase capacitor voltage of the parallel converter, and then passed through a proportional-integral (PI) regulator before being compared with... , and Multiplying them together yields the three-phase modulation signal compensation component:

[0053] (10)

[0054] (11)

[0055] (12)

[0056] Where, m apj m bpj and m cpj These are the three-phase intra-phase modulation signal compensation components of the parallel converter, where the subscript j indicates the power module number of each phase in the parallel converter, j=1,2,……,M; k p,ip and k i,ip These are the proportional and integral coefficients of the phase voltage controller in the parallel converter, respectively; θ i This represents the phase of the output current of the parallel converter.

[0057] The cosine values ​​of formulas (10) to (12) can be calculated from the instantaneous and peak values ​​of the three-phase currents of the parallel converter:

[0058] (13)

[0059] (14)

[0060] (15)

[0061] Among them, i ap i bp and i cp These are the instantaneous values ​​of the three-phase currents of the parallel converter; I apm I bpm and I cpm These are the peak values ​​of the three-phase currents of the parallel converter.

[0062] The wideband oscillation suppression control of the parallel converter includes: acquiring the grid connection point voltage through a voltage Hall sensor, sending the grid connection point voltage to a notch filter to extract the wideband oscillation voltage component, dividing the wideband oscillation voltage component by the virtual resistance of the parallel converter to obtain the three-phase current compensation component of the parallel converter, performing Park transformation on the three-phase current compensation component of the parallel converter to obtain the d-axis and q-axis current compensation components of the parallel converter, and then generating the inner current loop reference value of the parallel converter based on the d-axis and q-axis current compensation components of the parallel converter, the output current of the global voltage control, and the d-axis and q-axis compensation components of the phase-to-phase compensation current of the phase-to-phase voltage balance control.

[0063] The following section elaborates on the wideband oscillation suppression strategy for parallel converters.

[0064] First, the grid connection point voltage u is acquired using a voltage Hall sensor. pcc The grid connection point voltage u pcc The signal is fed into a notch filter to extract the wideband oscillation voltage component, i.e., the wideband oscillation component u. pcch The extraction algorithm is as follows:

[0065] (16)

[0066] Among them, u pcc The grid connection point voltage, u pcch F(s) represents the wideband oscillating voltage component of the grid connection point voltage, and F(s) is the notch filter transfer function.

[0067] The transfer function of the notch filter is:

[0068] (17)

[0069] Where ω1 is the fundamental angular frequency; ξ is the damping ratio; and s is the complex frequency.

[0070] wideband oscillation voltage component u pcch Divide by the virtual resistance R of the parallel converter p The three-phase current compensation components (i.e., three-phase harmonic current compensation components) of the parallel converter are obtained as follows:

[0071] (18)

[0072] Among them, R p For virtual resistance; i phref This refers to the three-phase current compensation component of the parallel converter.

[0073] The three-phase current compensation component i of the parallel converter phrefThe d-axis and q-axis current compensation components of the parallel converter are obtained through Park transformation. Then, the d-axis and q-axis current compensation components of the parallel converter are added to the d-axis and q-axis compensation components of the output current of the global voltage control and the phase-to-phase voltage balance control to obtain the following inner-loop current reference value of the parallel converter:

[0074] (19)

[0075] (20)

[0076] Among them, i dpref and i qpref These are the d-axis and q-axis components of the current inner loop reference value of the parallel converter, respectively; i dphref and i qphref These are the d-axis and q-axis compensation components of the phase-to-phase compensation current, respectively.

[0077] The current control of the parallel converter includes: performing Park transformation on the three-phase output current of the parallel converter to obtain the d-axis and q-axis components of the three-phase output current of the parallel converter; using a proportional-integral regulator to obtain the modulation signal of the parallel converter based on the current inner loop reference value of the parallel converter and the d-axis and q-axis components of the three-phase output current of the parallel converter; and using a carrier phase-shift modulation strategy based on the modulation signal of the parallel converter to obtain the drive signal of the switching device of the parallel power module of the parallel converter, which is a pulse signal.

[0078] Specifically, the current control of the parallel converter is performed in the dq coordinate system. The inner loop reference values ​​of the current on the d-axis and q-axis are subtracted from the d-axis and q-axis components of the three-phase output current of the parallel converter, respectively, and then passed through a proportional-integral (PI) regulator to obtain the following:

[0079] (twenty one)

[0080] (twenty two)

[0081] Where, m dp and m qp These are the d-axis and q-axis components of the modulated signal from the parallel converter, respectively. and These are the d-axis and q-axis components of the three-phase output current of the parallel converter, respectively, k ip and k ii These are the proportional and integral coefficients for current control, respectively.

[0082] The d-axis and q-axis components of the obtained parallel converter modulation signal are subjected to an inverse Park transform to obtain the three-phase modulation signal m of the parallel converter. ap mbp and m cp Then, the three-phase modulation signal of the parallel converter is subtracted from the compensation component of the three-phase modulation signal of the parallel converter output by the phase voltage balance control to obtain the modulation signal of each parallel power module in each phase. Finally, the drive signal of the switching device of the parallel converter is obtained by using a carrier phase-shift modulation strategy.

[0083] Figure 3 This is a control block diagram of the series converter provided by the present invention, which is described below in conjunction with... Figure 3 The control of the series converter of the present invention will be described.

[0084] Series converter control includes generating a wideband oscillation suppression voltage reference value for the series converter, series converter voltage control, and series converter current control.

[0085] The generation of the wideband oscillation suppression voltage reference value for the series converter includes: acquiring the current of the series converter through a current Hall sensor, sending the series converter current into a notch filter to extract the wideband oscillation current component, multiplying the wideband oscillation current component by the virtual resistance of the series converter to obtain the voltage reference value of the series converter, and performing Park transformation on the voltage reference value of the series converter to obtain the d-axis component and q-axis component of the voltage reference value of the series converter.

[0086] Specifically, in the wideband oscillation suppression control of the series converter, the current i of the series converter is first acquired by a current Hall sensor. g The series converter current i g The broadband oscillating current component i is obtained by inputting it into a notch filter. gh The extraction method is as follows:

[0087] (twenty three)

[0088] In the formula: i gh This represents the broadband oscillating current component of the series converter current.

[0089] Multiply the broadband oscillating current component of the series converter current by the virtual resistance R of the series converter. s Obtain the voltage reference value for the series converter:

[0090] (twenty four)

[0091] Among them, R s u is the virtual resistance of the series converter. shref This is the voltage reference value for the series converter.

[0092] The voltage reference value u of the series converter shref The d-axis and q-axis components of the voltage reference value of the series converter are obtained through Park transformation.

[0093] The voltage control of the series converter includes: performing Park transformation on the three-phase output voltage of the series converter to obtain the d-axis and q-axis components of the three-phase output voltage of the series converter; and using a proportional-integral regulator to obtain the inner loop reference value of the current of the series converter based on the d-axis and q-axis components of the three-phase output voltage of the series converter and the d-axis and q-axis components of the voltage reference value of the series converter.

[0094] Specifically, the three-phase output voltage u of the series converter is first collected. as u bs and u cs The grid connection point voltage u of the series converter g The phase θ of the grid-connected voltage of the series converter is obtained through a phase-locked loop (PLL). s The three-phase output voltage of the series converter is transformed using Parker transformation to obtain the d-axis and q-axis components of the three-phase output voltage:

[0095] (25)

[0096] Among them, u ds and u qs These are the d-axis and q-axis components of the three-phase output voltage of the series converter, respectively; θ s This represents the phase of the grid connection point voltage of the series converter.

[0097] The voltage control (i.e., voltage outer loop control) of the series converter is executed in the dq coordinate system. The d-axis and q-axis components of the voltage reference value of the series converter are subtracted from the d-axis and q-axis components of the three-phase output voltage of the series converter, respectively, and then passed through a proportional-integral (PI) regulator to obtain the current inner loop reference value of the series converter.

[0098] (26)

[0099] (27)

[0100] Among them, i dsref and i qsref These are the d-axis and q-axis components of the inner current loop reference value of the series converter, respectively. dsref and u qsref These represent the d-axis and q-axis components of the voltage reference value of the series converter, respectively, k vp,s and k vi,s These are the proportional and integral coefficients of the voltage PI controller, respectively.

[0101] The current control of the series converter includes: performing Park transformation on the three-phase output current of the series converter to obtain the d-axis and q-axis components of the three-phase output current of the series converter; using a proportional-integral regulator to obtain the modulation signal of the series converter based on the current inner loop reference value of the series converter and the d-axis and q-axis components of the three-phase output current of the series converter; and using a carrier phase-shift modulation strategy based on the modulation signal of the series converter to obtain the drive signal of the switching device of the series power module of the series converter, which is a pulse signal.

[0102] Furthermore, by subtracting the inner current loop reference value of the series converter from the d-axis and q-axis components of the three-phase output current of the series converter, and then passing the result through a proportional-integral (PI) regulator, the d-axis and q-axis components of the modulated signal of the series converter are obtained as follows:

[0103] (28)

[0104] (29)

[0105] Among them, i ds and i qs These are the d-axis and q-axis components of the three-phase output current of the series converter, respectively. ds and m qs These are the d-axis and q-axis components of the modulated signal from the series converter, respectively. and These are the proportional and integral coefficients of the current PI regulator, respectively.

[0106] The d-axis and q-axis components of the obtained series converter modulation signal are subjected to an inverse Park transform to obtain the three-phase modulation signal m of the series converter modulation signal. as m bs and m cs Finally, based on the three-phase modulation signal of the series converter modulation signal, and using a carrier phase-shift modulation strategy, the drive signals of the switching devices of the series power module of the series converter are obtained.

[0107] The technical solution of the present invention will be described in more detail below through specific implementation examples.

[0108] To verify the effectiveness of the medium-voltage direct-connected distributed series-parallel broadband oscillation damping device and its control method provided by this invention, a simulation model was built in Matlab / Simulink. In the parallel converter, each phase is set to consist of 5 parallel power modules, the AC filter inductor is 5mH, the DC capacitor of the first H-bridge converter is 2mF, and the reference value of the capacitor voltage is 2000V. In the series converter, each phase is set to consist of 3 series power modules, the AC filter inductor of the series converter is 3mH, and the AC filter capacitor is 50μF.

[0109] In the simulation model, the parallel converter adopts Figure 2 The control algorithm adopted by the series converter is as follows: Figure 3 The control algorithm and simulation results are as follows: Figure 4 and Figure 5 As shown, Figure 4 This is a simulation result diagram of the grid connection point voltage provided by the present invention. Figure 5 This is a diagram showing the simulation results of the power grid current provided by the present invention.

[0110] pass Figure 4 and Figure 5 The simulation results show that before 0.2s, the grid connection point voltage and grid current exhibit large broadband oscillation components, resulting in severe voltage and current distortion. After 0.2s, the broadband oscillation suppression control function of the parallel and series converters is enabled, the grid connection point voltage and grid current become sinusoidal, and the broadband oscillation components are effectively suppressed, improving the system's safety and stability.

[0111] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0112] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

[0113] Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A control method of a medium voltage directly grounded type distributed series and shunt parallel wideband oscillation damping device, for a medium voltage directly grounded type distributed series and shunt parallel wideband oscillation damping device, characterized by, The device includes: The parallel converter has three phases. Each phase of the parallel converter adopts a cascaded H-bridge converter topology. Each phase cascaded H-bridge converter topology is composed of M parallel power modules cascaded together. The output of the three-phase cascaded H-bridge converter topology is connected to the AC line through an inductor filter. The parallel power module adopts the first H-bridge converter. The series converter has three phases. Each phase of the series converter consists of one three-phase multi-winding phase-shifting transformer and N series power modules. The primary side of the three-phase multi-winding phase-shifting transformer is connected to a three-phase medium-voltage AC power grid. The N secondary windings of the three-phase multi-winding phase-shifting transformer are respectively connected to the AC side of the N series power modules. Each of the N series power modules consists of a three-phase uncontrolled rectifier and a second H-bridge converter. The DC output of each three-phase uncontrolled rectifier is connected in parallel with the DC side of the second H-bridge converter. The output sides of the N second H-bridge converters are cascaded and connected in series in the tie line between the power grid and the load through an LC filter. There is no common DC bus between the parallel converter and the series converter; The control method includes: The parallel converter control includes parallel converter voltage control, parallel converter current control, and parallel converter wideband oscillation suppression control. The parallel converter voltage control adopts a three-level voltage control, including global voltage control, inter-phase voltage balance control, and intra-phase voltage balance control. Series converter control includes generation of wideband oscillation suppression voltage reference value for series converter, voltage control of series converter, and current control of series converter; The wideband oscillation suppression control of the parallel converter includes: acquiring the grid connection point voltage through a voltage Hall sensor, sending the grid connection point voltage into a notch filter to extract the wideband oscillation voltage component, dividing the wideband oscillation voltage component by the virtual resistance of the parallel converter to obtain the three-phase current compensation component of the parallel converter, performing Park transformation on the three-phase current compensation component of the parallel converter to obtain the d-axis and q-axis current compensation components of the parallel converter, and then generating the inner current loop reference value of the parallel converter based on the d-axis and q-axis current compensation components of the parallel converter, the output current of the global voltage control, and the d-axis and q-axis compensation components of the phase-to-phase compensation current of the phase-to-phase voltage balance control output. The generation of the wideband oscillation suppression voltage reference value for the series converter includes: acquiring the current of the series converter through a current Hall sensor, sending the series converter current into a notch filter to extract the wideband oscillation current component, multiplying the wideband oscillation current component by the virtual resistance of the series converter to obtain the voltage reference value of the series converter; and performing Park transformation on the voltage reference value of the series converter to obtain the d-axis component and q-axis component of the voltage reference value of the series converter.

2. The control method for the medium-voltage direct-connected distributed series-parallel broadband oscillation damping device according to claim 1, characterized in that, The global voltage control includes: The average value of the three-phase capacitor voltages of the parallel converter is obtained from the capacitor voltage of the first H-bridge converter of the parallel power module; The global voltage average is obtained from the average value of the three-phase capacitor voltages of the parallel converter; Based on the pre-known capacitor voltage reference value and the global voltage average value, a proportional-integral regulator is used to obtain the output current for global voltage control.

3. The control method for the medium-voltage direct-connected distributed series-parallel broadband oscillation damping device according to claim 2, characterized in that, The interphase voltage balance control includes: Based on the known reference values ​​of capacitor voltage and the average value of the three-phase capacitor voltage of the parallel converter, a proportional-integral regulator is used, and combined with the phase of the grid connection point voltage of the parallel converter, the three-phase interphase compensation current of the parallel converter is obtained. The d-axis and q-axis compensation components of the three-phase interphase compensation current of the parallel converter are obtained by Park transformation.

4. The control method for the medium-voltage direct-connected distributed series-parallel broadband oscillation damping device according to claim 3, characterized in that, The intra-phase voltage balance control includes: Based on the known reference values ​​of the capacitor voltage and the three-phase capacitor voltage of the parallel converter, a proportional-integral regulator is used, and combined with the phase of the output current of the parallel converter, the compensation component of the three-phase modulation signal of the parallel converter is obtained.

5. The control method for the medium-voltage direct-connected distributed series-parallel broadband oscillation damping device according to claim 4, characterized in that, The current control of the parallel converter includes: The three-phase output current of the parallel converter is transformed by Park to obtain the d-axis and q-axis components of the three-phase output current of the parallel converter. Based on the current inner loop reference value of the parallel converter and the d-axis and q-axis components of the three-phase output current of the parallel converter, a proportional-integral regulator is used to obtain the modulation signal of the parallel converter. Based on the modulation signal of the parallel converter, and using a carrier phase-shift modulation strategy, the drive signal of the switching device of the parallel power module of the parallel converter is obtained.

6. The control method for the medium-voltage direct-connected distributed series-parallel broadband oscillation damping device according to claim 5, characterized in that, Series converter voltage control includes: The three-phase output voltage of the series converter is transformed by Park transformation to obtain the d-axis and q-axis components of the three-phase output voltage of the series converter. Based on the d-axis and q-axis components of the three-phase output voltage of the series converter and the d-axis and q-axis components of the voltage reference value of the series converter, a proportional-integral regulator is used to obtain the current inner loop reference value of the series converter.

7. The control method for the medium-voltage direct-connected distributed series-parallel broadband oscillation damping device according to claim 6, characterized in that, Series converter current control includes: The three-phase output current of the series converter is transformed by Park transformation to obtain the d-axis and q-axis components of the three-phase output current of the series converter. Based on the current inner loop reference value of the series converter and the d-axis and q-axis components of the three-phase output current of the series converter, a proportional-integral regulator is used to obtain the modulation signal of the series converter. Based on the modulation signal of the series converter, and using a carrier phase-shift modulation strategy, the drive signals of the switching devices of the series power module of the series converter are obtained.

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