High-power network construction type parallel DVR (Digital Video Recorder) for transformer area and control method thereof
By designing a high-power grid-connected parallel DVR for distribution areas, and adopting a main control system and a converter with a three-phase four-arm structure, the problems of voltage phase jump and high-order harmonic pollution of multi-module parallel DVRs were solved, achieving fast response and high reliability, and improving the stability and scalability of the system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-04
- Publication Date
- 2026-03-31
AI Technical Summary
Existing multi-module parallel DVRs suffer from problems such as voltage phase jumps, high-order harmonic pollution, and magnetizing inrush current. They may also have complex control algorithms, static errors, slow dynamic response, low power distribution accuracy, and a tendency to generate circulating currents. In addition, they may have single-point failure risks, complex system structures, rely on high-reliability path links, have high costs, and low scalability.
Design a high-power grid-connected parallel DVR for distribution transformer areas. It adopts a busbar, switching switches, converter parallel operation units and DC energy storage system. The switching switches and multiple three-phase converters are controlled by the main control system to achieve master-slave control, avoiding the need for transformer settings. It adopts a three-phase four-bridge structure and the main control system performs real-time signal calculation and power distribution, and has fault redundancy capability.
It achieves fast dynamic response, no circulating current, improves system reliability and stability, reduces control algorithm complexity, avoids voltage phase jumps and high-order harmonic pollution, improves power density and load adaptability, simplifies control methods, and enhances system scalability and fault handling capabilities.
Smart Images
Figure CN121770040A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a dynamic voltage restorer (DVR) and its control method, and more particularly to a high-power grid-connected parallel DVR for transformer substations and its control method. Background Technology
[0002] With the rapid development of microgrids, voltage quality issues in power grids have received increasing attention. Among the many power quality problems in power grids, such as voltage dips, harmonics, and flicker, voltage sags are one of the important reasons for reduced stability of power equipment. Voltage sag detectors (DVRs), as an important user power technology device, can protect critical loads from voltage disturbances such as voltage dips and surges at the supply end. Compared with traditional equipment used to maintain power quality, such as uninterruptible power supplies (UPS) and unified power quality controllers (UPCs), DVRs show advantages in terms of structure, cost, reliability, and speed, making them an effective means of managing voltage quality in microgrids. However, traditional DVRs introduce problems such as voltage phase jumps, high-order harmonic pollution, and inrush currents due to the introduction of transformers. Moreover, traditional control schemes, when the grid voltage is normal, charge the energy storage section as a current source, making them highly dependent on the grid.
[0003] Currently, research on DVRs mainly focuses on those with transformers, with limited research on transformerless DVRs and multi-unit parallel DVRs in network configurations. Existing multi-module parallel DVRs mainly fall into four categories: 1. Series-parallel DVRs; 2. Modular multilevel DVRs; 3. Parallel DVRs with droop control; 4. Parallel DVRs based on synchronization signals, etc. While the above solutions can improve power quality, series and parallel DVRs introduce three-phase or three single-phase transformers. The presence of these transformers can lead to problems such as voltage phase jumps, high-order harmonic pollution, and magnetizing inrush current. The bus midpoint of a modular multilevel DVR is connected to the power circuit via clamping diodes, causing current inflow and outflow at the bus midpoint, resulting in midpoint potential drift. This necessitates active control, requiring management of the equalization of submodule capacitor voltages, which makes the control algorithm very complex. A droop-controlled multi-machine parallel DVR has high requirements for the consistency of module parameters and line impedance. It suffers from static errors (voltage / frequency deviation), slow dynamic response, low power distribution accuracy, and is prone to circulating current. A multi-machine parallel DVR based on synchronization signals has the risk of single-point failure (synchronization signal source), a complex system structure, relies on high-reliability path links, has high cost, and low scalability. Summary of the Invention
[0004] The purpose of this invention is to solve the technical problems of existing multi-module parallel DVRs, such as voltage phase jump, high-order harmonic pollution and inrush current, or very complex control algorithms, or static errors, slow dynamic response, low power distribution accuracy, easy generation of circulating current, or single-point failure risk, complex system structure, reliance on high-reliability path links, high cost and low scalability. The invention provides a high-power grid-type parallel DVR for transformer substations and its control method.
[0005] To achieve the above objectives, the technical solution provided by the present invention is as follows: A high-power grid-connected parallel DVR for distribution areas is characterized by including a busbar, a switching switch, a converter parallel unit, and a DC energy storage system. The two ends of the busbar are respectively connected to the power grid and the load to be tested, and the busbar is equipped with the switching switch. The converter parallel unit includes a main control system and multiple three-phase converters connected in parallel. The main control system samples the DC bus voltage, three-phase AC voltage, and load current, and calculates the real-time active power signal and real-time reactive power signal of the converter using the three-phase AC voltage and load current. The main control system includes a DC bus voltage loop, a power loop, a phase angle calculation module, a reference voltage calculation module, and an AC voltage loop. The input of the DC bus voltage loop receives the DC bus given voltage and the DC bus sampled voltage, and adjusts to generate the converter active power given signal. The input of the power loop receives the converter active power given signal and the converter active power real-time signal, and adjusts to generate the angular frequency error signal. The input of the phase angle calculation module receives the angular frequency error signal and the angular frequency reference signal, and adjusts to generate the reference voltage phase angle. The input of the reference voltage calculation module receives the converter reactive power given signal, the converter reactive power real-time signal, and the inverter given reference voltage, and adjusts to generate the reference voltage. The input of the AC voltage loop receives the reference voltage phase angle, the reference voltage, and the three-phase AC sampled voltage, and adjusts to generate the three-phase current reference signal. One output of the main control system is connected to a switching switch, used to control the closing and opening of the switching switch based on the grid voltage detection result. The other output is connected to the input of each three-phase converter, used to send three-phase current reference signals to each three-phase converter. The main control system communicates bidirectionally with multiple three-phase converters via a CAN bus. The main control system sends command information to each three-phase converter and receives status information from each three-phase converter. The main control system is also used to receive fault information from each three-phase converter and perform fault logic processing based on the fault information. The three-phase sampling terminals of each three-phase converter are connected to the position between the corresponding switching switch and the load under test on the bus. The DC energy storage system is electrically connected to the parallel bus of each three-phase converter. When the grid voltage is normal, it is used to collect grid energy through the three-phase sampling terminals of each three-phase converter, convert the grid energy into DC energy and send it to multiple supercapacitors for storage. At the same time, when the grid voltage is abnormal, it converts the DC energy stored in the multiple supercapacitors into AC energy and outputs it to the load under test through the three-phase sampling terminals of each three-phase converter.
[0006] Furthermore, it also includes the maintenance of bypasses; An input switch QF1 is installed on the busbar between the switching switch and the power grid, and an output switch QF2 is installed on the busbar between the switching switch and the load under test. One end of the maintenance bypass is connected between the power grid and the input switch QF1, and the other end is connected between the output switch QF2 and the load under test; A maintenance switch QF3 is installed on the maintenance bypass.
[0007] Furthermore, the three-phase converter includes a three-phase four-bridge structure and a control module; the three-phase four-bridge structure includes a three-phase half-bridge circuit and a single-phase half-bridge circuit; the control module is equipped with a current loop and an SPWM module; The three-phase half-bridge circuit includes switching transistors S1, S2, S3, S4, S5, and S6, capacitors C1 and C2, and inductor L. ga Inductor L fa Capacitor C a Inductor L gb Inductor L fb Capacitor C b Inductor L gc Inductor L fc and capacitor C c The single-phase half-bridge circuit includes switching transistor S7 and switching transistor S8. The switching transistors S1 and S4 are connected in series to form phase A, S2 and S5 are connected in series to form phase B, and S3 and S6 are connected in series to form phase C. The midpoint of phase A is connected in series with inductor L. fa and inductor L ga Connect phase A AC sampling voltage V a The midpoint of phase B bridge arm is successively connected to inductor L. fb and inductor L gb Connect the B-phase AC sampling voltage V b The midpoint of the C-phase bridge arm is successively connected to inductor L. fc and inductor L gc Connect the C-phase AC sampling voltage V C; The switching transistors S7 and S8 are connected in series to form a common bridge arm, with the midpoint of the common bridge arm connected to the common terminal N; the A-phase bridge arm, B-phase bridge arm, and C-phase bridge arm are connected in parallel to form a three-phase rectifier bridge, with the two ends of the parallel connection serving as the positive and negative terminals of the DC bus, respectively; the common bridge arm is connected in parallel between the positive and negative terminals of the DC bus; the capacitor C a Capacitor C b Capacitor C c One end is connected to the common terminal N, and the other end is connected to the inductor L. ga With inductor L fa Between, inductance L gb With inductor L fb Between, inductance L gc With inductor L fc between; The capacitors C1 and C2 are connected in series, with the other end of capacitor C1 connected to the positive terminal of the DC bus and the other end of capacitor C2 connected to the negative terminal of the DC bus. The current loop is used to receive the three-phase current reference signal and the three-phase inductor sampling current, and calculate the difference between the two to obtain the three-phase current error signal, which is then adjusted. The input terminal of the SPWM module is connected to the output terminal of the current loop, and is used to convert the adjusted three-phase current error signal into a sinusoidal pulse modulation wave. Its output terminal is connected to the control terminals of switches S1, S2, S3, S4, S5, S6, S7, and S8, respectively, to control the conduction and disconnection of each switch. The DC buses of multiple three-phase converters are connected in parallel as a parallel bus; the positive terminal of the DC energy storage system is connected to the positive terminal of the parallel bus, and the negative terminal is connected to the negative terminal of the parallel bus; Another output terminal of the main control system is connected to the input terminal of each control module, and is used to send three-phase current reference signals to each control module. The main control system communicates bidirectionally with each control module through the CAN bus. The main control system sends instruction information to each control module and receives status information and fault information of each three-phase converter sent by each control module.
[0008] Furthermore, the switching switch includes a bypass contactor and a bypass thyristor connected in parallel; The output terminals of the main control system are respectively connected to a bypass contactor and a bypass thyristor; The DC energy storage system includes multiple supercapacitors connected in parallel; The positive and negative terminals of the multiple supercapacitors connected in parallel are electrically connected to the positive and negative terminals of the parallel busbars of the multiple three-phase converters, respectively.
[0009] Furthermore, another output terminal of the main control system is connected to the input terminal of each three-phase converter control module through an optical fiber conversion board, which is used to send three-phase current reference signals to the control module of each three-phase converter to realize current loop control of each three-phase converter. The main control system is also used to collect load voltage signals in order to calculate the display data on the load side.
[0010] Furthermore, the DC bus voltage loop includes a first comparator and a first PI controller; The two input terminals of the first comparator are respectively used to receive the DC bus given voltage U dcset and DC bus sampling voltage U dcfd The voltage error signal is obtained by subtracting the two values. The first PI controller is used to perform proportional-integral regulation on the voltage error signal and use the regulated signal as the active power command signal for the converter. The power loop includes a second comparator and a gain regulator; The two inputs of the second comparator are used to receive the converter active power command signal and the converter active power real-time signal, respectively. The difference between the two is used to obtain the active power error signal; The gain regulator is used to proportionally adjust the active power error signal to obtain the angular frequency error signal; The phase angle calculation module includes a third comparator and an integral regulator; The two inputs of the third comparator are used to receive the angular frequency error signal and the angular frequency reference signal, respectively. Then sum the two to obtain the actual angular frequency signal; The integral regulator is used to integrally regulate the actual angular frequency signal to obtain the reference voltage phase angle θ.
[0011] Furthermore, the reference voltage calculation module includes a fourth comparator, a second PI controller, and a fifth comparator connected in sequence according to their inputs and outputs; The two inputs of the fourth comparator are used to receive the reactive power command signal from the converter. Real-time reactive power signal of converter The reactive power error signal is obtained by subtracting the two. The second PI controller is used to perform proportional-integral regulation on the reactive power error signal; The two inputs of the fifth comparator are used to receive the reactive power error signal after proportional-integral regulation and the inverter reference voltage, respectively. And sum the two to obtain the reference voltage. ; The AC voltage loop includes a Dq / abc conversion module, three sixth comparators, and three voltage controllers (CV). The three input terminals of the Dq / abc conversion module are respectively used to receive the q-axis component, d-axis component, and reference voltage phase angle θ in the Qq coordinate system. The q-axis component of the Qq coordinate system is 0, and the reference voltage is... As the d-axis component; the Dq / abc conversion module is used to convert the q-axis component, d-axis component and reference voltage phase angle θ in the Qq coordinate system to generate a three-phase AC reference voltage; One input of each of the three sixth comparators is connected to one of the three outputs of the Dq / abc conversion module to receive the three-phase AC given voltages, respectively. The other input is used to receive the three-phase AC sampled voltage V. a V b V c And the three-phase AC given voltage and the three-phase AC sampled voltage V a V b V c By subtracting the corresponding values, the three-phase voltage error signal is obtained; The inputs of the three voltage controllers (CV) are respectively connected to the outputs of the three sixth comparators, which are used to control the three-phase voltage error signals and generate three-phase current reference signals. , , .
[0012] Furthermore, the current loop includes three seventh comparators and a current controller; One input terminal of each of the three seventh comparators is connected to the output terminal of each of the three voltage controllers (CV). The other input terminal is used to receive the sampling current of the three-phase inductor. , , To the reference signal of the three-phase current , , and three-phase inductor sampling current , , By subtracting the corresponding values, the three-phase current error signal is obtained; The current controller includes two PI regulators and one P regulator; the input terminals of the two PI regulators are respectively connected to the output terminals of the seventh comparators corresponding to phase A and phase B, and are used to perform proportional-integral regulation on the phase A current error signal and the phase B current error signal, respectively; the input terminal of the P regulator is connected to the output terminal of the seventh comparator corresponding to phase C, and is used to perform proportional regulation on the phase C current error signal. The three input terminals of the SPWM module are respectively connected to the output terminals of two PI regulators and a P regulator. It is used to convert the regulated A-phase current error signal, B-phase current error signal and C-phase current error signal into a sinusoidal pulse modulation wave and output eight PWM control signals to control the operation of switching transistors S1 to S8.
[0013] Furthermore, a DC soft-start circuit is provided between each of the three-phase converters and the DC energy storage system; The fault status of each of the three-phase converters is generated by logical AND to form slave fault information, which is then sent to the master control system. The master control system then reallocates power or sends a shutdown command based on the received slave fault information.
[0014] In addition, the present invention also provides a control method for the above-mentioned high-power grid-connected parallel DVRs used in the distribution area, which is characterized by including the following steps: Step 1: When the main control system detects that the grid voltage is normal, the control switch remains closed, and each three-phase converter is in rectification and charging mode. The DC bus voltage loop, power loop, and AC voltage loop work synchronously. When the main control system detects that the grid voltage has temporarily dropped or risen, the control switch is opened, the bus voltage loop stops working, and the power loop and AC voltage loop work. The three-phase current reference signal output by the AC voltage loop is used as the current command and sent to each three-phase converter through optical fiber. Step 2: Each three-phase converter receives the current command transmitted from the optical fiber and performs current loop control based on the three-phase current reference signal and the three-phase inductor sampled current.
[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Compared to droop-controlled multi-unit parallel DVRs, the present invention provides a high-power grid-type parallel DVR for distribution areas. A switching switch is set on the bus, and a separate master control system is set inside the converter parallel unit. The master control system controls the opening or closing of the switching switch to switch the system's operating mode. At the same time, the master control system and multiple three-phase converters form a master-slave relationship for control. Each three-phase converter, as a slave, operates in current source mode, which has fast dynamic response, no circulating current, and no static error. In addition, the multi-unit parallel connection of the present invention does not rely on synchronization signals for control, so it is not constrained by the synchronization signal source.
[0016] 2. The present invention provides a high-power grid-connected parallel DVR for distribution areas, in which each three-phase converter in parallel is a slave unit, which can be mutually redundant, greatly improving the system reliability and stability.
[0017] 3. The present invention provides a high-power grid-connected parallel DVR for distribution areas. Each parallel three-phase converter adopts a three-phase four-bridge arm structure, which avoids the setting of three-phase or single-phase transformers. It not only effectively solves the problems of voltage phase jump, high-order harmonic pollution, and inrush current caused by transformers in traditional DVRs, but also reduces the product size, increases power density, achieves better dynamic voltage compensation, and provides timely and effective inertia and support capabilities under weak power grid conditions.
[0018] 4. Compared with modular multilevel DVRs, the three-phase converter of this invention adopts a three-phase four-bridge structure with a two-level structure. Its bus midpoint (the connection point of capacitor C1 and capacitor C2) is not connected to the power circuit. Therefore, the current at the bus midpoint is basically zero. It is balanced by itself and does not require control. This not only greatly reduces the control algorithm, but also achieves a wider load adaptability and can meet 100% unbalanced load conditions.
[0019] 5. The present invention provides a high-power grid-connected parallel DVR for distribution areas. The fault status of each three-phase converter is generated by logical AND to form slave fault information and then sent to the master control system. The master control system reallocates power or sends a shutdown command based on the received slave fault information, which effectively improves the reliability of system operation. In the fault state, the control mode can be switched at the switching cycle level, making the dynamic characteristics of the system better.
[0020] 6. The present invention provides a control method for a high-power grid-connected parallel DVR for distribution areas. It adopts a grid-connected mode of main control system and each three-phase converter, unifies the control mode of charging mode and off-grid mode, making the control simpler and more flexible, and the switching between grid connection and off-grid is smoother and the stability of grid-connected operation is higher. Attached Figure Description
[0021] Figure 1 This is a schematic diagram of a high-power grid-type parallel DVR embodiment for a distribution area according to the present invention; Figure 2 This is a schematic diagram of master-slave control in an embodiment of the present invention; Figure 3 This is a circuit topology diagram of a three-phase four-bridge arm structure of a three-phase converter in an embodiment of the present invention; Figure 4 This is a schematic diagram of the DC bus voltage loop, power loop, and phase angle calculation module of the main control system in an embodiment of the present invention; Figure 5 This is a schematic diagram of the reference voltage calculation module of the main control system in an embodiment of the present invention; Figure 6 This is a schematic diagram of the AC voltage loop of the main control system in an embodiment of the present invention; Figure 7This is a schematic diagram of the control module of a three-phase converter in an embodiment of the present invention.
[0022] The attached figures are labeled as follows: 1-Changeover switch; 2-Converter parallel unit; 21-Main control system; 22-Three-phase converter; 3-DC energy storage system; 31-Supercapacitor; 4-Fiber optic conversion board; 5-DC soft start circuit. Detailed Implementation
[0023] To make the advantages and features of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0024] like Figure 1 As shown, a high-power grid-connected parallel DVR for distribution areas includes a busbar, a switching switch 1, an input switch QF1, an output switch QF2, a maintenance bypass, a converter parallel unit 2, and a DC energy storage system 3.
[0025] One end of the busbar is connected to the power grid to receive the input voltage from the grid, and the other end is connected to the load under test to transmit the transmitted busbar voltage as the output voltage to the load under test. Input switch QF1, switching switch 1, and output switch QF2 are sequentially arranged on the busbar from the power grid to the load under test. Input switch QF1 connects or disconnects the busbar from the power grid, output switch QF2 connects or disconnects the busbar from the load under test, and switching switch 1 transmits or disconnects the busbar voltage. Preferably, switching switch 1 includes a bypass contactor and a bypass thyristor connected in parallel. The bypass thyristor enables dynamic and rapid switching, such as contactless conduction during startup and switching. The bypass contactor closes after the bypass thyristor has stabilized, thus enabling long-term current carrying.
[0026] like Figure 2As shown, the converter parallel unit 2 includes a main control system 21 and multiple three-phase converters 22 connected in parallel. The main control system 21 acts as the master unit, and the multiple three-phase converters 22 act as slave units, achieving master-slave control. The main control system 21 includes a DC bus voltage loop, a power loop, a phase angle calculation module, a reference voltage calculation module, and an AC voltage loop. Simultaneously, the main control system 21 samples the DC bus voltage, three-phase AC voltage, and load current, and calculates the real-time active power signal and reactive power signal of the converter using the three-phase AC voltage and load current, thereby controlling the operation of the DC bus voltage loop, power loop, phase angle calculation module, reference voltage calculation module, and AC voltage loop. Specifically, the input of the DC bus voltage loop is used to receive the DC bus given voltage and the DC bus sampled voltage, and adjust to generate the converter active power given signal; the input of the power loop is used to receive the converter active power given signal and the converter active power real-time signal, and adjust to generate the angular frequency error signal; the input of the phase angle calculation module is used to receive the angular frequency error signal and the angular frequency reference signal, and adjust to generate the reference voltage phase angle; the input of the reference voltage calculation module is used to receive the converter reactive power given signal, the converter reactive power real-time signal, and the inverter given reference voltage, and adjust to generate the reference voltage; the input of the AC voltage loop is used to receive the reference voltage phase angle, the reference voltage, and the three-phase AC sampled voltage, and adjust to generate the three-phase current reference signal. In this embodiment, the main control system 21 also samples the load voltage, which is only used to calculate the display data on the load side. One output of the main control system 21 is connected to the bypass contactor and bypass thyristor in the switching switch 1, respectively. This allows the main control system to control the switching on and off of the bypass contactor based on the grid voltage detection results, and to control the closing and opening of the bypass thyristor based on the status of the bypass contactor. The other output of the main control system 21 is connected to the input of each three-phase converter 22 via an optical fiber conversion board 4. This allows the main control system to transmit the three-phase current reference signal output from the AC voltage loop to each three-phase converter 22 via optical fiber, thereby controlling each three-phase converter 22. The main control system 21 also communicates bidirectionally with multiple three-phase converters 22 via a CAN bus. Through the CAN bus, the main control system 21 not only sends start-up, stop-up, and rectifier-inverter switching logic commands to each three-phase converter 22, but also receives status information from each three-phase converter 22.
[0027] The fault status of each three-phase converter 22 is used to form slave fault information through a logical AND relationship. The formed slave fault information is sent to the master control system 21. The master control system 21 reallocates power or sends a shutdown command based on the received slave fault information. In addition, the master control system 21 is also used to communicate with the host computer to realize reference signal input.
[0028] In this embodiment, each three-phase converter includes a three-phase four-arm structure and a control module. For example... Figure 3 As shown, the three-phase four-bridge structure includes a three-phase half-bridge circuit and a single-phase half-bridge circuit. The three-phase half-bridge circuit includes switching transistors S1, S2, S3, S4, S5, and S6, capacitors C1 and C2, and inductor L. ga Inductor L fa Capacitor C a Inductor L gb Inductor L fb Capacitor C b Inductor L gc Inductor L fc Capacitor C c The circuit includes capacitor C1, and a single-phase half-bridge circuit comprising switching transistors S7 and S8. Switches S1 and S4 are connected in series to form phase A, with the connection point between them being the midpoint of phase A. Switches S2 and S5 are connected in series to form phase B, with the connection point between them being the midpoint of phase B. Switches S3 and S6 are connected in series to form phase C, with the connection point between them being the midpoint of phase C. The midpoint of phase A is connected sequentially by inductor L. fa and inductor L ga Connect phase A AC sampling voltage V a The midpoint of phase B bridge arm is successively connected to inductor L. fb and inductor L gb Connect the B-phase AC sampling voltage V b The midpoint of the C-phase bridge arm is successively connected to inductor L. fc and inductor L gc Connect the C-phase AC sampling voltage V C Used for sampling the AC voltage V of phase A. a Phase B AC sampling voltage V b AC sampling voltage V of phase C C Filtering and energy storage are performed separately.
[0029] Switches S7 and S8 are connected in series to form a common bridge arm. The connection point between S7 and S8 is the midpoint of the common bridge arm, which is connected to the common terminal N. Phase A, phase B, and phase C bridge arms are connected in parallel to form a three-phase rectifier bridge. The two ends of the parallel connection serve as the positive and negative terminals of the DC bus, respectively. The common bridge arm is connected in parallel between the positive and negative terminals of the DC bus. The common bridge arm forms the neutral point. That is, phase A bridge arms connected in parallel with the common bridge arm form a phase A full-bridge circuit, phase B bridge arms connected in parallel with the common bridge arm form a phase B full-bridge circuit, and phase C bridge arms connected in parallel with the common bridge arm form a phase C full-bridge circuit. Capacitor C a Capacitor C b Capacitor C c One end is connected to the common terminal N, and the other end is connected to the inductor L.ga With inductor L fa Between, inductance L gb With inductor L fb Between, inductance L gc With inductor L fc Between them. Capacitor C1 and capacitor C2 are connected in series, with the other end of capacitor C1 connected to the positive terminal of the DC bus and the other end of capacitor C2 connected to the negative terminal of the DC bus.
[0030] Another output terminal of the main control system 21 is connected to the input terminal of each control module, and is used to send three-phase current reference signals to each control module. The main control system 21 communicates bidirectionally with each control module through the CAN bus. The main control system 21 sends instruction information to each control module and receives status information and fault information of each three-phase converter 22 sent by each control module.
[0031] like Figure 4 As shown, the DC bus voltage loop is an outer loop control, including a first comparator and a first PI controller; the two inputs of the first comparator are used to receive the DC bus given voltage U. dcset and DC bus sampling voltage U dcfd The voltage error signal is obtained by subtracting the two signals. The first PI controller is used to perform proportional-integral regulation on the voltage error signal and uses the regulated signal as the converter active power setpoint signal. The power loop includes a second comparator and a gain regulator; the two inputs of the second comparator are used to receive the converter active power setpoint signal and the converter active power real-time signal, respectively. The active power error signal is obtained by subtracting the two signals. A gain regulator is used to proportionally adjust the active power error signal to obtain the angular frequency error signal. The phase angle calculation module includes a third comparator and an integral regulator; the two inputs of the third comparator are used to receive the angular frequency error signal and the angular frequency reference signal, respectively. The two signals are summed to obtain the actual angular frequency signal; the integral regulator is used to integrally regulate the actual angular frequency signal to obtain the reference voltage phase angle θ.
[0032] like Figure 5 As shown, the reference voltage calculation module is an outer loop control, including a fourth comparator, a second PI controller, and a fifth comparator connected in sequence according to their inputs and outputs; the two inputs of the fourth comparator are used to receive the reactive power command signal from the converter. Real-time reactive power signal of converter The difference between the two is used to obtain the reactive power error signal; the second PI controller is used to perform proportional-integral regulation on the reactive power error signal; the two inputs of the fifth comparator are used to receive the proportional-integral regulated reactive power error signal and the inverter reference voltage, respectively. It is used to compare the proportional-integral regulated reactive power error signal and the inverter reference voltage through the fifth comparator. Summing, we obtain the reference voltage. and the reference voltage As the given voltage of the AC voltage loop.
[0033] Due to the obtained reference voltage Since it is a DC quantity, it needs to be converted to AC quantity before AC voltage loop control can be implemented. For example... Figure 6 As shown, the AC voltage loop is an inner loop control, which includes a Dq / abc conversion module, three sixth comparators, and three voltage controllers (CVs). The three input terminals of the Dq / abc conversion module are used to receive the q-axis component, the d-axis component in the Qq coordinate system, and the reference voltage phase angle θ output by the DC bus voltage loop, respectively. In this invention, the q-axis component in the Qq coordinate system is set to 0, and the reference voltage is set to... As the d-axis component in the Qq coordinate system, it is input together with the reference voltage phase angle θ into the Dq / abc conversion module for conversion to generate the three-phase AC reference voltage. One input of each of the three sixth comparators is connected to one of the three outputs of the Dq / abc conversion module to receive the three-phase AC reference voltage, and the other input is used to receive the three-phase AC sample voltage V. a V b V c And the three-phase AC given voltage and the three-phase AC sampled voltage V a V b V c The corresponding subtraction is used to obtain the three-phase voltage error signal; the input terminals of the three voltage controllers CV are respectively connected to the output terminals of the three sixth comparators, which are used to control the three-phase voltage error signals and generate three-phase current reference signals. , , .
[0034] like Figure 7 As shown, the control module of the three-phase converter includes a current loop and an SPWM module. Each three-phase converter also samples the three-phase inductor current. The current loop is an inner-loop control, consisting of three seventh comparators and a current controller. One input of each of the three seventh comparators is connected to the output of one of the three voltage controllers (CV), respectively, to receive the three-phase current reference signals. , , The other input terminal is used to receive the sampling current of the three-phase inductor. , , and the three-phase current reference signal , , and three-phase inductor sampling current , , The three-phase current error signals are obtained by subtracting the corresponding values. The current controller includes two PI regulators and one P regulator. The inputs of the two PI regulators are connected to the outputs of the seventh comparators corresponding to phases A and B, respectively, for proportional-integral regulation of the phase A and phase B current error signals. The input of the P regulator is connected to the output of the seventh comparator corresponding to phase C, for proportional regulation of the phase C current error signal. The three inputs of the SPWM module are connected to the outputs of the two PI regulators and the P regulator, respectively, for converting the regulated phase A, phase B, and phase C current error signals into sinusoidal pulse modulation waves to output eight PWM control signals. The outputs of the SPWM module are connected to the control terminals of switches S1, S2, S3, S4, S5, S6, S7, and S8, respectively, for controlling the operation of switches S1-S8 through the eight PWM control signals.
[0035] The DC energy storage system 3 includes multiple supercapacitors 31 connected in parallel, and multiple three-phase converters 22 with their DC buses connected in parallel as parallel buses. The positive and negative terminals of the multiple supercapacitors 31 connected in parallel are electrically connected to the positive and negative terminals of the parallel buses of the multiple three-phase converters 22, respectively. Simultaneously, the three-phase sampling terminals of each three-phase converter 22 are connected to the bus between the corresponding switching switch 1 and output switch QF2. When the grid voltage is normal, the system collects grid energy through the three-phase sampling terminals of each three-phase converter 22, converts the grid energy into DC energy, and sends it to the multiple supercapacitors 31 for storage. When the grid voltage is abnormal, the DC energy stored in the multiple supercapacitors 31 is converted into AC energy and output to the load under test through the three-phase sampling terminals of each three-phase converter 22.
[0036] In this embodiment, a DC soft-start circuit 5 is provided between each three-phase converter 22 and the DC energy storage system 3 to achieve soft start of each supercapacitor 31. Specifically, the input terminal of the DC soft-start circuit 5 is connected to the positive terminal of the parallel bus of each three-phase converter 22, the output terminal of the DC soft-start circuit 5 is connected to the positive terminal of each supercapacitor 31 connected in parallel, and the negative terminal of each supercapacitor 31 connected in parallel is connected to the negative terminal of the parallel bus of each three-phase converter 22.
[0037] In addition, to ensure that the power grid can continue to supply power to the load under test stably in the event of a failure of switch 1, a maintenance bypass is also provided in this invention. Specifically, one end of the maintenance bypass is connected between the power grid and the input switch QF1, and the other end is connected between the output switch QF2 and the load under test. A maintenance switch is provided on the maintenance bypass, which is used to allow the power grid to supply power to the load under test through the maintenance bypass by closing the maintenance switch.
[0038] The control method for the above-mentioned high-power grid-type parallel DVRs in the distribution area specifically includes the following steps: Step 1: When the main control system 21 detects that the grid voltage is normal, the main control system 21 controls the switching switch 1 to remain closed, and each three-phase converter 22 is in rectification and charging mode. At this time, the DC bus voltage loop, power loop and AC voltage loop in the main control system 21 work synchronously. When the main control system 21 detects a voltage dip or rise in the mains voltage, it will control the switching switch 1 to open, stopping the bus voltage loop and activating the power loop and AC voltage loop. The three-phase current reference signal output by the AC voltage loop will be... , , As the current loop reference, it is transmitted to each three-phase converter 22 via optical fiber. It is worth noting that when the DC bus voltage loop stops working, the power loop reference (converter active power reference signal) is the average power value of each three-phase converter 22.
[0039] Step 2: Each three-phase converter 22 receives the current command transmitted via optical fiber and, based on the three-phase current reference signal... , , With the sampling current of the three-phase inductor , , Perform current loop control.
[0040] The above description is only used to illustrate the technical solutions of the present invention, and is not intended to limit them. For those skilled in the art, modifications can be made to the specific technical solutions described in the above embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions protected by the present invention.
Claims
1. A high-power grid-type parallel DVR for distribution areas, characterized in that: It includes a busbar, a switching switch (1), a converter parallel unit (2), and a DC energy storage system (3); The two ends of the busbar are connected to the power grid and the load to be tested, respectively, and the busbar is equipped with the switching switch (1). The converter parallel unit (2) includes a main control system (21) and multiple three-phase converters (22) connected in parallel. The main control system (21) samples the DC bus voltage, three-phase AC voltage, and load current respectively, and calculates the real-time active power signal and the real-time reactive power signal of the converter through the three-phase AC voltage and load current. The main control system (21) is equipped with a DC bus voltage loop, a power loop, a phase angle calculation module, a reference voltage calculation module, and an AC voltage loop. The input terminal of the DC bus voltage loop is used to receive the DC bus given voltage and the DC bus sampled voltage, and adjusts to generate the converter active power given signal. The input terminal of the power loop is used to receive the converter active power given signal. The system receives the active power setpoint signal and the real-time active power signal of the converter, and adjusts to generate an angular frequency error signal; the input of the phase angle calculation module is used to receive the angular frequency error signal and the angular frequency reference signal, and adjusts to generate a reference voltage phase angle; the input of the reference voltage calculation module is used to receive the reactive power setpoint signal of the converter, the real-time reactive power signal of the converter, and the inverter setpoint reference voltage, and adjusts to generate a reference voltage; the input of the AC voltage loop is used to receive the reference voltage phase angle, the reference voltage, and the three-phase AC sampling voltage, and adjusts to generate a three-phase current reference signal. One output terminal of the main control system (21) is connected to the switching switch (1) to control the closing and opening of the switching switch (1) according to the grid voltage detection result. The other output terminal is connected to the input terminal of each three-phase converter (22) to send three-phase current reference signals to each three-phase converter (22). The main control system (21) communicates bidirectionally with multiple three-phase converters (22) through the CAN bus. The main control system (21) sends instruction information to each three-phase converter (22) and receives the status information of each three-phase converter (22). The main control system (21) is also used to receive the fault information of each three-phase converter (22) and perform fault logic processing according to the fault information. The three-phase sampling terminals of each three-phase converter (22) are connected to the position between the corresponding switching switch (1) and the load under test on the bus. The DC energy storage system (3) is electrically connected to the parallel bus of each three-phase converter (22). It is used to collect grid energy through the three-phase sampling terminals of each three-phase converter (22) when the grid voltage is normal, and convert the grid energy into DC energy and send it into multiple supercapacitors (31) for storage. At the same time, when the grid voltage is abnormal, the DC energy stored in multiple supercapacitors (31) is converted into AC energy and output to the load under test through the three-phase sampling terminals of each three-phase converter (22).
2. The high-power grid-type parallel DVR for distribution areas according to claim 1, characterized in that: This also includes maintenance bypass; An input switch QF1 is installed on the busbar between the switching switch (1) and the power grid, and an output switch QF2 is installed on the busbar between the switching switch (1) and the load to be tested. One end of the maintenance bypass is connected between the power grid and the input switch QF1, and the other end is connected between the output switch QF2 and the load under test; A maintenance switch QF3 is installed on the maintenance bypass.
3. A high-power grid-type parallel DVR for distribution areas according to claim 1 or 2, characterized in that: The three-phase converter (22) includes a three-phase four-bridge structure and a control module; the three-phase four-bridge structure includes a three-phase half-bridge circuit and a single-phase half-bridge circuit; the control module is equipped with a current loop and an SPWM module; The three-phase half-bridge circuit includes switching transistors S1, S2, S3, S4, S5, and S6, capacitors C1 and C2, and inductor L. ga Inductor L fa Capacitor C a Inductor L gb Inductor L fb Capacitor C b Inductor L gc Inductor L fc and capacitor C c The single-phase half-bridge circuit includes switching transistor S7 and switching transistor S8. The switching transistors S1 and S4 are connected in series to form phase A, S2 and S5 are connected in series to form phase B, and S3 and S6 are connected in series to form phase C. The midpoint of phase A is connected in series with inductor L. fa and inductor L ga Connect phase A AC sampling voltage V a The midpoint of phase B bridge arm is successively connected to inductor L. fb and inductor L gb Connect the B-phase AC sampling voltage V b The midpoint of the C-phase bridge arm is successively connected to inductor L. fc and inductor L gc Connect the C-phase AC sampling voltage V C ; The switching transistors S7 and S8 are connected in series to form a common bridge arm, with the midpoint of the common bridge arm connected to the common terminal N; the A-phase bridge arm, B-phase bridge arm, and C-phase bridge arm are connected in parallel to form a three-phase rectifier bridge, with the two ends of the parallel connection serving as the positive and negative terminals of the DC bus, respectively; the common bridge arm is connected in parallel between the positive and negative terminals of the DC bus; the capacitor C a Capacitor C b Capacitor C c One end is connected to the common terminal N, and the other end is connected to the inductor L. ga With inductor L fa Between, inductance L gb With inductor L fb Between, inductance L gc With inductor L fc between; The capacitors C1 and C2 are connected in series, with the other end of capacitor C1 connected to the positive terminal of the DC bus and the other end of capacitor C2 connected to the negative terminal of the DC bus. The current loop is used to receive the three-phase current reference signal and the three-phase inductor sampling current, and calculate the difference between the two to obtain the three-phase current error signal, which is then adjusted. The input terminal of the SPWM module is connected to the output terminal of the current loop, and is used to convert the adjusted three-phase current error signal into a sinusoidal pulse modulation wave. Its output terminal is connected to the control terminals of switches S1, S2, S3, S4, S5, S6, S7, and S8, respectively, to control the conduction and disconnection of each switch. The DC buses of multiple three-phase converters (22) are connected in parallel as parallel buses; the positive terminal of the DC energy storage system (3) is connected to the positive terminal of the parallel bus, and the negative terminal is connected to the negative terminal of the parallel bus; The other output terminal of the main control system (21) is connected to the input terminal of each control module and is used to send three-phase current reference signals to each control module. The main control system (21) communicates bidirectionally with each control module through the CAN bus. The main control system (21) sends instruction information to each control module and receives status information and fault information of each three-phase converter (22) sent by each control module.
4. The high-power grid-type parallel DVR for distribution areas according to claim 3, characterized in that: The switching switch (1) includes a bypass contactor and a bypass thyristor connected in parallel; The output terminals of the main control system (21) are respectively connected to the bypass contactor and the bypass thyristor; The DC energy storage system (3) includes multiple supercapacitors (31) connected in parallel. The positive and negative terminals of the multiple supercapacitors (31) connected in parallel are electrically connected to the positive and negative terminals of the parallel busbars of the multiple three-phase converters (22), respectively.
5. A high-power grid-type parallel DVR for distribution areas according to claim 4, characterized in that: The other output of the main control system (21) is connected to the input of the control module of each three-phase converter (22) through the fiber optic conversion board (4), which is used to send three-phase current reference signals to the control module of each three-phase converter (22) to realize the current loop control of each three-phase converter (22); The main control system (21) is also used to collect load voltage signals to calculate the display data on the load side.
6. A high-power grid-type parallel DVR for distribution areas according to claim 5, characterized in that: The DC bus voltage loop includes a first comparator and a first PI controller; The two input terminals of the first comparator are respectively used to receive the DC bus given voltage U dcset and DC bus sampling voltage U dcfd The voltage error signal is obtained by subtracting the two values. The first PI controller is used to perform proportional-integral regulation on the voltage error signal and use the regulated signal as the active power command signal for the converter. The power loop includes a second comparator and a gain regulator; The two inputs of the second comparator are used to receive the converter active power command signal and the converter active power real-time signal, respectively. The difference between the two is used to obtain the active power error signal; The gain regulator is used to proportionally adjust the active power error signal to obtain the angular frequency error signal; The phase angle calculation module includes a third comparator and an integral regulator; The two inputs of the third comparator are used to receive the angular frequency error signal and the angular frequency reference signal, respectively. Then sum the two to obtain the actual angular frequency signal; The integral regulator is used to integrally regulate the actual angular frequency signal to obtain the reference voltage phase angle θ.
7. A high-power grid-type parallel DVR for distribution areas according to claim 6, characterized in that: The reference voltage calculation module includes a fourth comparator, a second PI controller, and a fifth comparator connected in sequence according to their input and output. The two inputs of the fourth comparator are used to receive the reactive power command signal from the converter. Real-time reactive power signal of converter The reactive power error signal is obtained by subtracting the two. The second PI controller is used to perform proportional-integral regulation on the reactive power error signal; The two inputs of the fifth comparator are used to receive the reactive power error signal after proportional-integral regulation and the inverter reference voltage, respectively. And sum the two to obtain the reference voltage. ; The AC voltage loop includes a Dq / abc conversion module, three sixth comparators, and three voltage controllers (CV). The three input terminals of the Dq / abc conversion module are respectively used to receive the q-axis component, d-axis component, and reference voltage phase angle θ in the Qq coordinate system. The q-axis component of the Qq coordinate system is 0, and the reference voltage is... As the d-axis component; the Dq / abc conversion module is used to convert the q-axis component, d-axis component and reference voltage phase angle θ in the Qq coordinate system to generate a three-phase AC reference voltage; One input of each of the three sixth comparators is connected to one of the three outputs of the Dq / abc conversion module to receive the three-phase AC given voltages, respectively. The other input is used to receive the three-phase AC sampled voltage V. a V b V c And the three-phase AC given voltage and the three-phase AC sampled voltage V a V b V c By subtracting the corresponding values, the three-phase voltage error signal is obtained; The inputs of the three voltage controllers (CV) are respectively connected to the outputs of the three sixth comparators, which are used to control the three-phase voltage error signals and generate three-phase current reference signals. , , .
8. A high-power grid-type parallel DVR for distribution areas according to claim 7, characterized in that: The current loop includes three seventh comparators and a current controller; One input terminal of each of the three seventh comparators is connected to the output terminal of each of the three voltage controllers (CV). The other input terminal is used to receive the sampling current of the three-phase inductor. , , To the reference signal of the three-phase current , , and three-phase inductor sampling current , , By subtracting the corresponding values, the three-phase current error signal is obtained; The current controller includes two PI regulators and one P regulator; the input terminals of the two PI regulators are respectively connected to the output terminals of the seventh comparators corresponding to phase A and phase B, and are used to perform proportional-integral regulation on the phase A current error signal and the phase B current error signal, respectively; the input terminal of the P regulator is connected to the output terminal of the seventh comparator corresponding to phase C, and is used to perform proportional regulation on the phase C current error signal. The three input terminals of the SPWM module are respectively connected to the output terminals of two PI regulators and a P regulator. It is used to convert the regulated A-phase current error signal, B-phase current error signal and C-phase current error signal into a sinusoidal pulse modulation wave and output eight PWM control signals to control the operation of switching transistors S1 to S8.
9. A high-power grid-type parallel DVR for distribution areas according to claim 1, characterized in that: A DC soft-start circuit (5) is provided between each of the three-phase converters (22) and the DC energy storage system (3); The fault status of each of the three-phase converters (22) is generated by logical AND to form slave fault information and then sent to the master control system (21). The master control system (21) re-allocates power or sends a shutdown command based on the received slave fault information.
10. A control method for a high-power grid-type parallel DVR used in any one of claims 1-9, characterized in that, Includes the following steps: Step 1: When the main control system (21) detects that the grid voltage is normal, it controls the switching switch (1) to remain closed, and each three-phase converter (22) is in rectification and charging mode. The DC bus voltage loop, power loop and AC voltage loop work synchronously. When the main control system (21) detects that the grid voltage is temporarily reduced or increased, it controls the switching switch (1) to open, the bus voltage loop stops working, and the power loop and AC voltage loop work. The three-phase current reference signal output by the AC voltage loop is used as the current command and sent to each three-phase converter (22) through optical fiber. Step 2: Each three-phase converter (22) receives the current command transmitted from the optical fiber and performs current loop control based on the three-phase current reference signal and the three-phase inductor sampling current.