Converter device for multiplexing and compensating three ports of source storage network and compensation method

Abstract

The invention discloses a source storage network three-port multiplexing and compensation converter device and a compensation method, and belongs to the technical field of photovoltaic power generation and grid connection. The converter device comprises a multiplexing device and a voltage sag compensation device. The multiplex bridge circuit is commonly used in chopping and inversion processes among the photovoltaic cell, the direct current energy storage module and the power grid; the voltage sag compensation device comprises an SCR module, a dynamic voltage restorer, a rapid detection module and a control unit. The rapid detection module detects the power grid in real time and transmits the detected data to the control unit; the control unit judges whether voltage sag occurs in the power grid or not, and correspondingly generates an instruction signal to drive the SCR module to connect or disconnect the dynamic voltage restorer to or from the power grid; the dynamic voltage restorer is of a single-stage structure, adopts a super capacitor as an energy storage element, and releases energy through the energy storage element to provide electric energy compensation for a power grid, so that the voltage recovers a normal state. When the voltage sag occurs, the voltage recovery time is shortened, and the stability of the power grid voltage is ensured.

Description

Technical Field

[0001] The invention belongs to the field of photovoltaic power generation and grid connection, and more specifically, relates to a current conversion device and a compensation method for source-storage-network three-port multiplexing and compensation. Background Technique

[0002] With the rapid development of photovoltaic power generation technology, photovoltaic grid-connected systems have gradually become an important way to realize large-scale access of renewable energy to the grid. In a photovoltaic power generation system, the DC electric energy generated by photovoltaic cells needs to be converted through a current converter to adapt to the requirements of energy storage systems and grid connection. Existing photovoltaic grid-connected topologies usually include a DC-DC converter, a DC-AC inverter, and an energy storage unit, and the system mainly realizes the functions of power generation, energy storage, and grid connection. However, this traditional design generally has problems such as a large number of devices, high costs, and complex control. In particular, it is difficult to guarantee the power quality of small-scale user sides, and phenomena such as harmonic pollution, reactive power imbalance, and voltage distortion are likely to occur.

[0003] To optimize the structure of photovoltaic power generation systems and improve power quality, a new unified system for power generation, energy storage, and grid connection has been proposed in recent years. Through the multiplexing of bridge circuits, this system can realize the multiplexing of the same bridge circuit during the processes of direct current chopping (transmission from photovoltaic cells to DC energy storage modules) and energy storage to grid-connected inversion (electric energy output from DC energy storage modules to the grid), thereby reducing the number of devices and the system cost. The bridge circuit in this chopping-inversion multiplexing system can be used as a chopping circuit to realize the boost and regulation of DC voltage, or as an inversion circuit to convert the DC power of the energy storage unit into high-quality alternating current adapted to the grid, realizing the bidirectional flow and efficient conversion of electric energy.

[0004] However, during the grid connection process of photovoltaic power generation units and energy storage units, with the access of grid-side loads, power quality problems such as voltage sags may occur. Voltage sag is a common problem in power systems, and traditional treatment means mainly include reactive power compensation devices and standby power supplies. These methods have disadvantages such as slow response speed, low compensation accuracy, and high costs, and it is difficult to meet the high requirements for power quality of voltage-sensitive loads. Summary of the Invention

[0005] Aiming at the defects of related technologies, the purpose of the present invention is to provide a current conversion device and a compensation method for source-storage-network three-port multiplexing and compensation, aiming to solve the problems of slow response speed, low compensation accuracy, and high costs existing in existing methods.

[0006] To achieve the above purpose, in the first aspect, the present invention provides a current conversion device for source-storage-network three-port multiplexing, and the current conversion device includes a multiplexing device and a voltage sag compensation device;

[0007] The multiplexing device includes a photovoltaic power generation module, a DC energy storage module, a multiplexing bridge circuit, and a power grid; one side of the multiplexing bridge circuit is connected to the DC energy storage module, and the other side is connected to the photovoltaic power generation module. The photovoltaic power generation module is connected to the power grid through a transformer; the multiplexing bridge circuit is used as a chopper converter between the photovoltaic power generation module and the DC energy storage module, and as an inverter converter between the DC energy storage module and the power grid;

[0008] The voltage sag compensation device includes: an SCR module, a dynamic voltage restorer, a fast detection module, and a control unit;

[0009] The fast detection module is used to detect the power grid in real time and transmit the real-time detection data to the control unit;

[0010] The control unit determines whether a voltage sag occurs in the power grid according to the real-time detection data of the fast detection module, and correspondingly generates an instruction signal to drive the SCR module to connect or disconnect the dynamic voltage restorer from the power grid;

[0011] The dynamic voltage restorer is of a single-stage structure and uses a super capacitor as an energy storage element. The energy storage element is connected to the switching tube of the dynamic voltage restorer; the dynamic voltage restorer is used to release energy through the energy storage element when the voltage on the power grid side fluctuates, and after inversion by the switching tube, provide power compensation for the power grid to make the voltage return to the normal state.

[0012] Optionally, the dynamic voltage restorer includes a compensation mode and a standby mode;

[0013] The dynamic voltage restorer further includes a full-bridge inverter circuit; the full-bridge inverter circuit is connected in parallel with both ends of the super capacitor. In the compensation mode, it is used to convert the energy of the super capacitor into a compensation voltage matching the voltage sag of the power grid. The compensation voltage is superimposed on the power grid voltage and injected into the load side to make the voltage return to the normal state; in the standby mode, it is also used to transfer the energy of the power grid to the super capacitor for charging and energy storage.

[0014] Optionally, the control unit includes a PWM control algorithm module and a driving module;

[0015] The PWM control algorithm module is used to receive the real-time detection data transmitted by the fast detection module, calculate the power required for compensation according to the real-time detection data, and correspondingly generate a PWM instruction signal;

[0016] The driving module converts the PWM instruction signal into a high-power output to control the charging / discharging of the super capacitor.

[0017] Optionally, the multiplexing bridge circuit adopts a three-phase full-bridge circuit composed of IGBT switching tubes.

[0018] Optionally, the multiplexed bridge circuit includes an inverter mode and a chopper mode;

[0019] In the inverter mode, the multiplexed bridge circuit is used to invert the direct current of the DC energy storage module into alternating current and transmit it to the power grid, or rectify the alternating current of the power grid into direct current and transmit it to the DC energy storage module; in the chopper mode, each phase arm of the multiplexed bridge circuit independently serves as a chopper circuit, and is used to transmit the direct current generated by the photovoltaic power generation module to the DC energy storage module through chopper control.

[0020] Optionally, the photovoltaic power generation module includes a photovoltaic cell and a Z-type grounding transformer;

[0021] The output end of the photovoltaic cell is connected to one end of the Z-type grounding transformer, the other end of the Z-type grounding transformer is respectively connected to the three-phase center point of the multiplexed bridge circuit, and the negative electrode of the photovoltaic cell is connected to the negative electrode of the DC energy storage module through the three-phase center point of the multiplexed bridge circuit.

[0022] Optionally, a voltage stabilizing capacitor is connected in parallel at both ends of the photovoltaic cell; a voltage stabilizing capacitor is connected in parallel at both ends of the DC energy storage module.

[0023] In a second aspect, the present invention also provides a voltage sag compensation method for a current conversion device, which is applied to the current conversion device with three-port multiplexing of source, energy storage and grid as described in any item of the first aspect, and includes:

[0024] S1. After collecting the grid voltage signal and performing low-pass filtering processing, obtain the real-time detection data of the voltage;

[0025] S2. Separate the three-phase voltages in the real-time detection data, and respectively extract the positive-sequence voltage component U L+ (s) and the negative-sequence voltage component U L- (s);

[0026] S3. According to the expected positive-sequence load voltage and the positive-sequence component U L+ (s) of the actual load voltage, calculate the positive-sequence error signal At the same time, compensate the negative-sequence voltage component U L- (s) to 0 to obtain the negative-sequence error signal;

[0027] S4. The control unit generates a PWM command signal according to the positive-sequence error signal and the negative-sequence error signal, and controls the switching tube according to the PWM command signal to make the dynamic voltage restorer generate a compensation voltage.

[0028] Through the above technical solutions conceived by the present invention, compared with the prior art, the following beneficial effects can be achieved:

[0029] 1. The present invention provides a three-port multiplexing converter device for source storage network. The fast detection module detects the power grid in real time. The control unit determines whether a voltage sag occurs, and controls the SCR module to access the dynamic voltage restorer during the power grid voltage sag, so as to adjust and restore the load side voltage in real time, compensate for the sag amplitude and phase deviation of the power grid voltage, ensure the stability of the load side power quality, and thus ensure the normal operation of sensitive loads. The dynamic voltage restorer is a single-stage structure using supercapacitors. When a voltage sag occurs in the power grid, the supercapacitor energy storage unit serves as a DC energy source to provide fast and stable energy support for the dynamic voltage restorer (DVR) during the voltage sag. Based on the control principle of DVR, it has a fast response speed and high compensation accuracy. The single-stage DVR used in this solution can reduce the use of inverter equipment, and at the same time, compared with the bipolar voltage compensation device, it reduces the parameter requirements of the energy storage link, making the voltage sag control device more economical and reliable. It can provide fast and high-power energy support for the power grid voltage sag, significantly shorten the voltage recovery time, and ensure the stability of the sensitive load voltage.

[0030] 2. The present invention provides a three-port multiplexing converter for source-storage network, in which the control unit drives the SCR module, DVR voltage restorer and supercapacitor energy storage unit to work together to achieve efficient and rapid compensation for voltage sag. Orthogonal components are constructed by the short delay method for coordinate transformation to reduce voltage detection delay, ensure the stability of the voltage of sensitive loads on the grid side and rapid recovery during voltage sag; the control unit quickly separates the positive-sequence component and negative-sequence component of the voltage sag based on the real-time data of the detection module to detect the depth and imbalance of the voltage sag, generate command signals for accurately controlling the phase and waveform of the compensation voltage, and improve the compensation effect.

[0031] 3. The present invention provides a three-port multiplexing converter device for source, storage and network. The device uses a three-port multiplexing design to realize both boost chopping conversion from photovoltaic cells to DC energy storage modules and inverter conversion from DC energy storage modules to the power grid on the same bridge circuit. This allows the same bridge circuit to be reused in the flow of electric energy at the three ports of the source, storage and network during the chopping and inversion processes. The capacity requirement of the energy storage system can be significantly reduced in three-phase inverter and direct chopping, while improving voltage stability during the grid-connected process.

[0032] 4. A voltage sag compensation method for a converter device provided by the present invention detects the voltage signal of the power grid in real time, constructs orthogonal components through the short-delay method and then performs coordinate transformation, which can reduce the detection delay and achieve rapid detection of voltage sags. The control unit uses the positive and negative sequence separation method of voltage to accurately detect the depth and unbalance degree of voltage sags, thereby accurately judging whether a voltage sag occurs, and dynamically controlling the connected dynamic voltage restorer in real time to provide a compensation voltage matching the sag voltage for the power grid, so as to provide accurate power compensation for the power grid and restore the voltage to the normal state. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The overall topology of a converter device with three-port multiplexing of source, storage and grid provided by the present invention;

[0034] Figure 2 The positive and negative sequence separation algorithm used for rapid detection of voltage sags according to the present invention;

[0035] Figure 3 The algorithm of positive and negative sequence components for rapid detection of voltage sags according to the present invention;

[0036] Figure 4 The control block diagram of the dynamic voltage restorer with a super capacitor according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present 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 only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] The following describes the content involved in the above embodiments in conjunction with a preferred embodiment.

[0039] Embodiment 1

[0040] As Figure 1 shown, the present invention provides a converter device with three-port multiplexing of source, storage and grid, and the converter device includes a multiplexing device and a voltage sag compensation device;

[0041] The multiplexing device includes a photovoltaic power generation module, a DC energy storage module, a multiplexing bridge circuit and a power grid; one side of the multiplexing bridge circuit is connected to the DC energy storage module, and the other side is connected to the photovoltaic power generation module. The photovoltaic power generation module is connected to the power grid through a transformer; the multiplexing bridge circuit is used as a chopper converter between the photovoltaic power generation module and the DC energy storage module, and as an inverter converter between the DC energy storage module and the power grid;

[0042] The voltage sag compensation device includes: an SCR module, a dynamic voltage restorer, a fast detection module, and a control unit;

[0043] The fast detection module is used to detect the power grid in real time and transmit the real-time detection data to the control unit;

[0044] The control unit determines whether a voltage sag occurs in the power grid according to the real-time detection data of the fast detection module, and correspondingly generates a command signal to drive the SCR module to connect or disconnect the dynamic voltage restorer from the power grid;

[0045] The dynamic voltage restorer has a single-stage structure and uses a super capacitor as an energy storage element. The energy storage element is connected to the switch tube of the dynamic voltage restorer; the dynamic voltage restorer is used to release energy through the energy storage element when the voltage on the power grid side fluctuates, and after inversion by the switch tube, provide power compensation for the power grid to make the voltage return to the normal state.

[0046] The entire converter device can realize three-port conversion from power generation to energy storage and then to grid connection. The photovoltaic cells of the photovoltaic power generation module generate DC power, which is chopped and boosted to the DC energy storage module through a multiplexed bridge circuit, and then the electric energy of the DC energy storage module is inverted into AC power through the multiplexed bridge circuit and connected to the grid. During the grid connection process, when a voltage sag occurs on the load side, the voltage fast detection module quickly detects and calculates the voltage sag value, and at the same time issues a command signal to drive the SCR to actuate and input DVR compensation, and the control unit generates a PWM signal command to make the switch tube of the DVR actuate to generate the required voltage compensation amount, so that the voltage sag can be quickly restored.

[0047] The multiplexed bridge circuit distributes the photovoltaic cells, the DC energy storage module, and the power grid on both sides of the multiplexed bridge circuit. The power grid and the DC energy storage module are located on both sides of the multiplexed bridge circuit respectively, so that the chopping conversion from the photovoltaic cells to the DC energy storage module and the inversion conversion from the DC energy storage module to the power grid can be realized. At the same time, the rectification conversion from the power grid to the DC energy storage module can be taken into account. The same bridge circuit is multiplexed during the chopping and inversion processes, optimizing the structure and reducing the volume of the device.

[0048] The voltage sag phenomenon has a serious impact on the normal operation of sensitive equipment. The voltage sag compensation device realizes the fast detection and compensation of the voltage sag generated after the power grid accesses the load by introducing feedback control technology, significantly improving the stability of the load voltage and the overall power quality.

[0049] The rapid detection module is connected in series between the power supply and the load, and can monitor the changes in the grid voltage in real time. Once a voltage sag is detected, the rapid detection module sends the real-time detection data to the control unit for judgment. The control unit determines whether a voltage sag occurs in the grid based on the real-time detection data, and generates a command signal accordingly to control the SCR module to connect the dynamic voltage restorer to the grid. The dynamic voltage restorer switches to the compensation mode, using the energy in the energy storage device (such as a supercapacitor) to provide a stable voltage to the load through the inverter to restore the voltage to normal. Since the rapid detection module performs real-time detection, the control unit can monitor the voltage changes on the load side in real time through feedback control, and adjust the size and phase of the compensation voltage according to the set target value.

[0050] like Figure 1 As shown, the dynamic voltage restorer is connected to the SCR module through an LC filter and then connected to the power grid. In this scheme, a single-stage structure is adopted. Through the cooperation of the SCR module and the supercapacitor, the voltage sag compensation device is quickly connected when the voltage sags, so as to achieve full-phase compensation when the voltage is deeply sagged. Effectively suppress voltage fluctuations, ensure the normal operation of sensitive loads, and improve the overall power quality. Since the voltage sag compensation device of this scheme adopts supercapacitors as energy storage elements, the supercapacitor energy storage unit is used to directly provide high-power fast power support to the connected power grid through a single-stage structure, which significantly shortens the voltage recovery time; at the same time, the SCR module is used to quickly switch the power grid path when a voltage sag is detected, and complete the rapid cut-in of the voltage sag compensation device. Compared with traditional methods, the voltage sag control of this scheme has a faster response speed and higher compensation accuracy (supercapacitor), which can not only deal with voltage sag problems, but also cope with other types of voltage fluctuations, such as short-term voltage over-rise, and can maintain voltage stability through rapid response in different voltage disturbance scenarios. The invention has the advantages of simple structure and fast regulation speed, and provides an efficient and reliable solution for the rapid detection and compensation of voltage sag in the power system.

[0051] Optionally, the dynamic voltage restorer includes a compensation mode and a standby mode;

[0052] The dynamic voltage restorer also includes a full-bridge inverter circuit; the full-bridge inverter circuit is connected in parallel with both ends of the supercapacitor, and in compensation mode, is used to convert the energy of the supercapacitor into a compensation voltage that matches the grid voltage sag, and the compensation voltage is superimposed on the grid voltage and injected into the load side to restore the voltage to a normal state; in standby mode, it is also used to transfer the energy of the grid to the supercapacitor for charging and energy storage.

[0053] Optionally, the control unit includes a PI controller, a PWM control algorithm module and a drive module;

[0054] The PWM control algorithm module is used to receive the real-time detection data transmitted by the fast detection module, calculate the voltage required for compensation according to the real-time detection data, generate a PWM command signal, and after stabilization by a PI controller, send it to the drive module;

[0055] The drive module converts the PWM command signal into a high-power output to control the charging / discharging of the super capacitor.

[0056] The control unit realizes energy conversion between the super capacitor energy storage unit on the DC side and the AC side power grid through controlling a full-bridge inverter. The super capacitor energy storage unit serves as the DC energy source to provide fast and stable energy support for the Dynamic Voltage Restorer (DVR) during voltage sags. The control unit adopts the phase sequence separation short delay method to achieve fast voltage detection, accurately extracts the characteristic components of the voltage sag through the control unit, calculates the power required for compensation according to the real-time detection data, generates a PWM command signal, drives the full-bridge inverter of the DVR to generate a compensation voltage, compensates for the voltage sag amplitude and phase deviation of the power grid voltage, and after the compensation voltage is superimposed with the power grid voltage, injects it into the load side to achieve dynamic compensation of the voltage sag.

[0057] The current conversion device provided by the present invention can work in the voltage sag compensation mode and the standby mode to meet the power quality regulation requirements under different working conditions. In the voltage sag compensation mode, when a voltage sag occurs in the power grid, the control unit quickly detects the voltage sag amplitude and phase information through the phase sequence separation short delay method, and controls the full-bridge inverter to convert the DC energy in the super capacitor energy storage unit into an AC compensation voltage and inject it into the power grid in a timely manner. The photovoltaic power generation module provides a grounding reference for the compensation voltage in this mode and eliminates the third harmonic of the AC voltage generated by inversion, ensuring the stability of the power quality. In the standby mode, the DVR is in a low-power operation state, only monitors the power grid voltage and maintains the charging state of the super capacitor energy storage unit to ensure that the system can quickly respond when a power grid fault occurs.

[0058] Regarding the control of the above-mentioned dynamic voltage restorer, the control unit controls the full-bridge inverter based on a PI controller to ensure that the amplitude and phase of its output compensation voltage match the power grid sag voltage, so as to achieve dynamic restoration of the load-side voltage. Through the phase sequence separation short delay method, the control unit can quickly separate the positive sequence component and the negative sequence component of the voltage sag, accurately control the phase and waveform of the compensation voltage, and further improve the compensation effect. This device accesses the DVR during the power grid voltage sag, adjusts and restores the load-side voltage in real time, compensates for the voltage sag amplitude and phase deviation of the power grid voltage, ensures the stability of the load-side power quality, and thus guarantees the normal operation of sensitive loads.

[0059] Optionally, the multiplexed bridge circuit is a three-phase full-bridge circuit composed of IGBT switching tubes.

[0060] Optionally, the multiplexed bridge circuit includes an inverter mode and a chopper mode;

[0061] In the inverter mode, the multiplexed bridge circuit is used to invert the direct current of the DC energy storage module into alternating current and transmit it to the power grid; in the chopper mode, each phase arm of the multiplexed bridge circuit independently serves as a chopper circuit, which is used to transmit the direct current generated by the photovoltaic power generation module to the DC energy storage module through chopper control.

[0062] It can flexibly switch between the inverter and chopper modes, realizing efficient energy flow among the photovoltaic, power grid, and energy storage. The system reliability is enhanced: the optimized topology and control method effectively reduce device losses and improve operation stability.

[0063] Optionally, the photovoltaic power generation module includes a photovoltaic cell and a Z-type grounding transformer;

[0064] The output end of the photovoltaic cell is connected to one end of the Z-type grounding transformer, the other end of the Z-type grounding transformer is respectively connected to the three-phase center point of the multiplexed bridge circuit, and the negative pole of the photovoltaic cell is connected to the negative pole of the DC energy storage module through the three-phase center point of the multiplexed bridge circuit.

[0065] The Z-type grounding transformer realizes the functions of voltage transformation and grid connection on the one hand, provides a grounding reference for the power grid on the other hand, and eliminates the third harmonic of the alternating voltage generated by inversion.

[0066] Specifically, in the compensation mode, the Z-type grounding transformer in the high-power-quality compensation device serves as an AC path for the compensation voltage, controls the dynamic voltage restorer in the high-power-quality compensation device to access the power grid, and realizes the dynamic regulation of the power quality. In the standby mode, the Z-type grounding transformer in the high-power-quality compensation device maintains the grounding reference, and the dynamic voltage restorer is in the monitoring state, ensuring that the energy storage unit maintains the charging state and can quickly respond to voltage sag events.

[0067] Optionally, a voltage stabilizing capacitor is connected in parallel at both ends of the photovoltaic cell; a voltage stabilizing capacitor is connected in parallel at both ends of the DC energy storage module. The voltage stabilizing capacitor is set to reduce the voltage fluctuation of the power grid and improve the overall stability of the system.

[0068] The present invention performs real-time detection on the power grid through a fast detection module. The control unit determines whether a voltage sag occurs and controls the SCR module to connect a dynamic voltage restorer during the voltage sag of the power grid, so as to perform real-time regulation and restoration on the load-side voltage, compensate for the voltage sag amplitude and phase deviation of the power grid, ensure the stability of the load-side power quality, and solve the technical problems of slow response speed, low compensation accuracy, and high cost existing in the existing methods. The beneficial effects of providing fast and stable energy support during the voltage sag, significantly shortening the voltage recovery time, and ensuring the stability of the sensitive load voltage are achieved.

[0069] Embodiment 2

[0070] The present invention also provides a voltage sag compensation method for a current conversion device, which is applied to the current conversion device with source-storage-network three-port multiplexing described in any one of the embodiments, and includes:

[0071] S1. After collecting the power grid voltage signal and performing low-pass filtering processing, obtain the real-time detection data of the voltage;

[0072] S2. Separate the three-phase voltages in the real-time detection data, and respectively extract the positive-sequence voltage component U L+ (s) and the negative-sequence voltage component U L- (s);

[0073] S3. According to the expected positive-sequence load voltage and the positive-sequence component U L+ (s) of the actual load voltage, calculate the positive-sequence error signal At the same time, compensate the negative-sequence voltage component U L- (s) to 0 to obtain the negative-sequence error signal;

[0074] S4. The control unit generates a PWM command signal according to the positive-sequence error signal and the negative-sequence error signal, and controls the switching tube according to the PWM command signal to make the dynamic voltage restorer generate a compensation voltage.

[0075] The voltage sag compensation method of this solution includes the short-time delay construction orthogonal component method and the extraction part of the positive and negative sequence voltage components.

[0076] Traditional delay construction methods include the quarter-cycle delay method and the derivative method, but it is difficult to overcome the disadvantages such as the high delay of the quarter-cycle delay method and the noise amplification of the derivative method. The present invention adopts an orthogonal signal construction method - the short-time delay method, which can not only quickly and accurately obtain orthogonal signals but also has good anti-noise performance.

[0077] As Figure 2 shown, orthogonal signals are constructed by the short-delay method. First, assume that the time to be delayed is one sampling period T s , then the voltage vector U mThe projection expression in the αβ coordinate system can be rewritten as:

[0078]

[0079] After expansion, we can get

[0080]

[0081] Therefore, we can obtain:

[0082]

[0083] Simplify the above formula to get u α (t) and u β (t) at each sampling time T s The relationship after:

[0084]

[0085] Taking the detected single-phase grid voltage signal u(t) as u β (t), then the obtained virtual orthogonal signal u α (t) can be expressed as:

[0086]

[0087] In actual situations, each voltage quantity appears in a discrete form. Therefore, in the virtual orthogonal signal constructed by the short-time delay method, the (k + 1)-th sampling and the k-th sampling are used to replace the (t + T s ) moment and the t moment, and it can be expressed as:

[0088]

[0089] For the orthogonal signal constructed by the difference method, the sampling period determines the accuracy of the constructed orthogonal component effect. The longer the sampling period, the greater the deviation of the constructed effect from the ideal value; the shorter the sampling period, the closer the constructed orthogonal component is to the ideal value, but there will always be a certain error from the ideal orthogonal signal. The accuracy of the orthogonal signal constructed by the short-time delay method proposed in this paper does not change with the sampling period Ts. Regardless of the length of the sampling period, it can follow the ideal orthogonal signal well in time.

[0090] As Figure 3 shown, the method for quickly extracting positive and negative sequence components adopted in this scheme is proposed based on the classical symmetrical component method. For the extraction process of the positive sequence component, the phasor form of the positive sequence component based on the symmetrical component method can be expressed as:

[0091]

[0092] In the formula, is the voltage phasor expression of a three-phase unbalanced power grid; is the positive-sequence voltage component expression; is the positive-sequence coordinate transformation matrix, and its expression is:

[0093]

[0094] where,

[0095] The positive-sequence component of the power grid voltage can be expressed in the two-phase stationary coordinate system as:

[0096] The three-phase unbalanced power grid voltage can be described in the two-phase stationary coordinate system as:

[0097] where, The orthogonal component U α and U β Using the orthogonal coordinate construction method, only one orthogonal component of the power grid voltage needs to be obtained by sampling, and then the other orthogonal component of the power grid voltage can be constructed by the short-time delay method. In this method, the voltage signal directly collected during the detection process is used as the original voltage signal, i.e., the α component, and the orthogonal component constructed by the short-time delay method is used as the β component.

[0098] By extracting the real part component in the operation formula, the positive-sequence component of the three-phase unbalanced power grid voltage can be obtained i.e.,

[0099] U + = T 1α U α + T 1β U β

[0100] where, T 1α and T 1β are the coordinate transformation matrices of the positive-sequence α component and the positive-sequence β component respectively,

[0101]

[0102] Similarly, the extraction of the negative-sequence component is similar to that of the positive-sequence component. The phasor form of the positive-sequence component based on the symmetrical component method can be expressed as:

[0103]

[0104] where

[0105] By extracting the real part component in the operation formula, the negative-sequence component of the three-phase unbalanced power grid voltage can be obtained i.e., U- = T 2α U α + T 2β U β ;

[0106] Among them, T 2α and T 2β are the coordinate transformation matrices of the positive-sequence α component and the positive-sequence β component respectively.

[0107]

[0108] Finally, the zero-sequence component in the three-phase unbalanced voltage must be detected. According to the symmetrical component principle, the zero-sequence instantaneous component in the unbalanced grid voltage can be expressed as:

[0109]

[0110] Through the above process, the positive, negative, and zero sequences can be successfully separated. The decrease of the positive sequence reflects the depth (amplitude) of the voltage sag, and the change of the negative sequence reflects the asymmetry of the voltage sag, so as to realize the rapid detection of the voltage sag, and further bring a faster response speed for the DVR sag compensation.

[0111] In the control link of the DVR, if an open-loop control is introduced, problems such as overshoot and voltage deviation are likely to occur. Therefore, in order to improve the adaptability of the system, this method adopts a closed-loop control with a feedback link. The feedback control strategy feeds the compensated load voltage back to the reference voltage, uses the error quantity as the adjustment quantity, generates a voltage modulation wave signal through the PI control link and converts it into a PWM modulation signal through the pulse generation circuit, and then precisely adjusts the voltage sag.

[0112] The transfer function of the PI controller is:

[0113] This scheme adopts a double closed-loop control link with load voltage feedback, and the control block diagram is as Figure 4 shown. Among them, the compensated load voltage U L (s) is fed back to the reference voltage U dc (s), the difference between the two is used as the adjustment quantity, and then a voltage modulation signal is generated through the PI control link and passed through the pulse trigger circuit to convert the signal into a PWM modulation signal, so that the control link can have a faster response speed.

[0114] In Figure 4 , the input signal represents the required desired load voltage. By comparing it with the actual load voltage U L (s), an error signal is generated. Combining Figure 1 and Figure 4, the error signal is adjusted by a proportional-integral controller, and a control signal is output to adjust the compensation voltage. The control signal passes through a gain k PWM and a current regulator, and then adjusts the compensation current I f (s) to compensate for the voltage deviation. After being superimposed with the power supply voltage U(s), the stable load voltage U L (s) is finally output. Among them, the gains of the current and voltage are k α and k β .

[0115] The closed-loop transfer function of the load voltage U L (s) with respect to the reference voltage is:

[0116]

[0117] In addition, the closed-loop transfer function of the load voltage U L (s) with respect to the system voltage U S (s) is:

[0118]

[0119] The open-loop transfer function of the load voltage U L (s) with respect to the reference voltage is:

[0120]

[0121] The closed-loop transfer function of the load voltage U L (s) with respect to the load current I L (s) is:

[0122]

[0123] Specifically, the desired load voltage and the actual load voltage U L (s) are obtained, and the error signal is calculated. The error signal is input into the proportional controller, the parameters of the PI controller are set, and the adjusted signal is amplified by the gain k PWM to generate the control signal k PWM U dc U C (s). The control signal is input into the electric regulator to calculate the compensation current and then a stable signal is obtained through the filter. The error signal is feedback-adjusted by k α and k β to obtain dynamic feedback control.

[0124] The control of the DVR realizes the rapid detection and compensation of voltage sags by introducing feedback control, ensuring the stability of the load voltage and the improvement of power quality, while guaranteeing the fast response of the compensation control.

[0125] To further improve the compensation effect, the DVR usually adopts a double-loop control strategy with a voltage outer loop and a current inner loop. The voltage outer loop is responsible for monitoring the voltage deviation on the load side and outputting the command for the compensation voltage; the current inner loop then accurately controls the magnitude and phase of the compensation current according to the command of the voltage outer loop, ensuring the rapidity and stability of the compensation process. This double-loop control structure not only improves the compensation accuracy but also reduces the dynamic deviation during the compensation process, enhancing the overall performance of the system. For voltage-sensitive occasions, by using the voltage sag compensation method provided in this solution to control the DVR voltage restorer, a fast and high-power energy support is provided through the supercapacitor energy storage unit, significantly shortening the voltage recovery time and ensuring the stability of the voltage of sensitive loads.

[0126] It is easy for those skilled in the art to understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A three-port multiplexing and compensation converter for source, storage and network, characterized in that: The current conversion device includes a multiplexing device and a voltage sag compensation device; The multiplexing device includes a photovoltaic power generation module, a DC energy storage module, a multiplexing bridge circuit and a power grid; one side of the multiplexing bridge circuit is connected to the DC energy storage module, and the other side is connected to the photovoltaic power generation module, and the photovoltaic power generation module is connected to the power grid through a transformer; the multiplexing bridge circuit is used as a chopper converter between the photovoltaic power generation module and the DC energy storage module, and as an inverter converter between the DC energy storage module and the power grid; The voltage sag compensation device comprises: an SCR module, a dynamic voltage restorer, a fast detection module and a control unit; The rapid detection module is used to perform real-time detection on the power grid and transmit the real-time detection data to the control unit; The control unit determines whether a voltage sag occurs in the power grid according to the real-time detection data of the fast detection module, and generates a command signal to drive the SCR module to connect or disconnect the dynamic voltage restorer from the power grid accordingly; The dynamic voltage restorer is a single-stage structure, using a supercapacitor as an energy storage element, and the energy storage element is connected to the switch tube of the dynamic voltage restorer; the dynamic voltage restorer is used to release energy through the energy storage element and then invert it through the switch tube to provide electric energy compensation for the grid when the voltage on the grid side fluctuates, so as to restore the voltage to a normal state.

2. The current conversion device according to claim 1, characterized in that: The dynamic voltage restorer includes a compensation mode and a standby mode; The dynamic voltage restorer also includes a full-bridge inverter circuit; the full-bridge inverter circuit is connected in parallel with both ends of the supercapacitor, and in compensation mode, is used to convert the energy of the supercapacitor into a compensation voltage that matches the grid voltage sag, and the compensation voltage is superimposed on the grid voltage and injected into the load side to restore the voltage to a normal state; in standby mode, it is also used to transfer the energy of the grid to the supercapacitor for charging and energy storage.

3. The current conversion device according to claim 2, characterized in that: The control unit includes a PI controller, a PWM control algorithm module and a drive module; The PWM control algorithm module is used to receive the real-time detection data transmitted by the fast detection module, calculate the voltage required for compensation according to the real-time detection data, generate a PWM command signal, and transmit it to the drive module after being stabilized by the PI controller; The driving module generates a PWM control signal to control the switch action of the dynamic voltage restorer to generate the required voltage compensation amount.

4. The current conversion device according to claim 1, characterized in that: The multiplexing bridge circuit adopts a three-phase full-bridge circuit composed of IGBT switching tubes.

5. The current conversion device according to claim 4, characterized in that: The multiplexed bridge circuit includes an inverter mode and a chopper mode; In inverter mode, the multiplexed bridge circuit is used to invert the DC power of the DC energy storage module into AC power and transmit it to the power grid, or to rectify the AC power of the power grid into DC power and transmit it to the DC energy storage module; in chopping mode, each phase arm of the multiplexed bridge circuit independently serves as a chopping circuit, which is used to transmit the DC power generated by the photovoltaic power generation module to the DC energy storage module through chopping control.

6. The current conversion device according to claim 1, characterized in that: The photovoltaic power generation module includes a photovoltaic cell and a Z-type grounding transformer; The output end of the photovoltaic cell is connected to one end of the Z-type grounding transformer, the other end of the Z-type grounding transformer is respectively connected to the three-phase center points of the multiplexed bridge circuit, and the negative electrode of the photovoltaic cell is connected to the negative electrode of the DC energy storage module through the three-phase center point of the multiplexed bridge circuit.

7. The current conversion device according to claim 1, characterized in that: Two ends of the photovoltaic cell are connected in parallel with a voltage-stabilizing capacitor; two ends of the DC energy storage module are connected in parallel with a voltage-stabilizing capacitor.

8. A method for compensating voltage sag of a converter, applied to a converter with three-port multiplexing of a source, storage and network as claimed in any one of claims 1 to 7, characterized in that: include: S1, collect the grid voltage signal and perform low-pass filtering to obtain real-time voltage detection data; S2, separate the three-phase voltage in the real-time detection data, and extract the positive sequence voltage component U L+ (s) and negative sequence voltage component U L- (s); S3, according to the expected positive sequence load voltage and the positive sequence component U of the actual load voltage L+ (s) Calculate the positive sequence error signal At the same time, the negative sequence voltage component U L- (s) to 0, and a negative sequence error signal is obtained; S4. The control unit generates a PWM command signal according to the positive-sequence error signal and the negative-sequence error signal, and controls the switch tube according to the PWM command signal to enable the dynamic voltage restorer to generate a compensation voltage.

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