Electric energy quality comprehensive treatment device with direct current power distribution function

Abstract

The invention discloses an electric energy quality comprehensive treatment device with a direct-current power distribution function, which comprises a rear-end voltage source type converter, a front-end voltage source type converter, a front-end voltage source type converter, a rear-end voltage source type converter, a front-end voltage source type converter, a front-end voltage source type converter and a rear-end voltage source type converter, alternating current A1, B1 and C1 phase ports of the front-end voltage source type converter are connected with one ends of low-voltage side windings of the A, B and C phase coupling transformers through the LC type filter, and the ends, far away from the front-end voltage source type converter, of the low-voltage side windings of the A, B and C phase coupling transformers are connected. And two ends of the high-voltage side windings of the A, B and C phase coupling transformers are connected in parallel with quick bypass switches. According to the invention, an electric energy quality comprehensive treatment function is provided, a low-voltage direct-current power distribution interface is provided, and a stable and reliable low-voltage direct-current bus is provided, so that plug-and-play and centralized energy management of distributed renewable energy sources, energy storage systems and novel direct-current loads are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution, and in particular to a comprehensive power quality management device with a direct current power distribution function. Background Art

[0002] The continuous access of new sources and loads represented by distributed photovoltaics and electric vehicles to medium and low voltage distribution networks has become an important feature of the development and construction of urban energy Internet in my country. On the one hand, intermittent and random distributed power sources have transformed traditional distribution networks from "limited power sources" to "ubiquitous power sources", changing the power grid flow distribution and system operation characteristics. The two-way power flow control of the distribution network faces new challenges; on the other hand, large-scale, impactful and disorderly DC charging loads have put tremendous pressure on the capacity of the distribution network, leading to serious problems such as unbalanced power and poor power quality in local areas. In particular, important loads that are sensitive to power quality, such as precision instrument manufacturers and large data centers, have higher requirements for power quality. Traditional distribution areas usually use power management devices to improve the power quality on the grid side. Traditional power quality management solutions usually include static VAR compensators, thyristor-controlled series capacitors, static VAR compensators, and active filters. These solutions are respectively carried out for reactive power compensation, current harmonic management, and voltage dynamic regulation, or some of the functions are integrated, and the device integration and utilization rate are low. On the other hand, traditional power quality management devices do not have friendly access functions for distributed photovoltaics, electric vehicles and energy storage devices, which will aggravate the deterioration of power quality. Summary of the invention

[0003] The purpose of the present invention is to provide a comprehensive power quality management device with DC power distribution function, which can realize "plug and play" of distributed power sources, energy storage systems, and new DC loads, and provide comprehensive power management functions for sensitive loads, thereby solving the problem of lack of integrated equipment for managing multiple power quality events and low-voltage DC port configuration in the prior art.

[0004] In order to achieve the above-mentioned object, the present invention provides a comprehensive power quality control device with a DC power distribution function, which comprises: a rear-end voltage source converter, wherein the low-voltage DC power distribution positive port of the rear-end voltage source converter is connected to the low-voltage DC power distribution positive port of the front-end voltage source converter, the low-voltage DC power distribution negative port of the rear-end voltage source converter is connected to the low-voltage DC power distribution negative port of the front-end voltage source converter, and the AC A1 port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the A-phase coupling transformer through an LC filter. The AC B1 phase port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the B-phase coupling transformer through an LC filter, and the AC C1 phase port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the C-phase coupling transformer through an LC filter. The end of the low-voltage side winding of the A-phase coupling transformer away from the front-end voltage source converter is simultaneously connected to one end of the low-voltage side winding of the B-phase coupling transformer away from the front-end voltage source converter and one end of the low-voltage side winding of the C-phase coupling transformer away from the front-end voltage source converter to form a Y-type connection mode;

[0005] One end of the high-voltage side winding of the A-phase coupling transformer, one end of the high-voltage side winding of the B-phase coupling transformer, and one end of the high-voltage side winding of the C-phase coupling transformer are terminals connected to the corner-connected side terminals of the traditional power frequency transformer. The end of the high-voltage side winding of the A-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer is simultaneously connected to the end of the high-voltage side winding of the B-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer and the end of the high-voltage side winding of the C-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer to form a Y-type connection.

[0006] In a preferred manner, an A-phase fast bypass switch is connected in parallel at both ends of the high-voltage side winding of the A-phase coupling transformer, a B-phase fast bypass switch is connected in parallel at both ends of the high-voltage side winding of the B-phase coupling transformer, and a C-phase fast bypass switch is connected in parallel at both ends of the high-voltage side winding of the C-phase coupling transformer.

[0007] In a preferred manner, the AC A2 port of the rear-end voltage source converter is a port connected to the A-phase port on the user side, the AC B2 port of the rear-end voltage source converter is a port connected to the B-phase port on the user side, the AC C2 port of the rear-end voltage source converter is a port connected to the C-phase port on the user side, and the AC O neutral port of the rear-end voltage source converter is a port connected to the neutral point on the user side.

[0008] The beneficial effects of the present invention are as follows: the present invention adopts a centralized energy management system to achieve friendly interaction between source, grid, load and storage within the substation, improve the penetration rate of distributed power sources and the utilization rate of electric energy, and avoid further deterioration of the power quality of user-side loads caused by new intermittent and impactful sources and loads; in addition, the low-voltage DC bus distribution port also provides the possibility for energy mutual assistance and interconnection across regional distribution substations, thereby reducing the configuration and investment of energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The circuit diagram of the comprehensive power quality control device with DC power distribution function of the present invention;

[0010] Figure 2 This is a waveform diagram of the voltage compensation operation mode of the present invention;

[0011] Figure 3 This is a waveform diagram of the current harmonic suppression operation mode of the present invention;

[0012] Figure 4 It is a waveform diagram of the peak-to-valley arbitrage operation mode of the present invention. DETAILED DESCRIPTION

[0013] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0014] Embodiment 1:

[0015] A comprehensive power quality control device with a DC power distribution function, comprising: a rear-end voltage source converter, wherein the low-voltage DC power distribution positive port of the rear-end voltage source converter is connected to the low-voltage DC power distribution positive port of the front-end voltage source converter, the low-voltage DC power distribution negative port of the rear-end voltage source converter is connected to the low-voltage DC power distribution negative port of the front-end voltage source converter, the AC A1 phase port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the A-phase coupling transformer through an LC filter, the AC B1 phase port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the B-phase coupling transformer through an LC filter, the AC C1 phase port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the C-phase coupling transformer through an LC filter, and the end of the low-voltage side winding of the A-phase coupling transformer away from the front-end voltage source converter is simultaneously connected to one end of the low-voltage side winding of the B-phase coupling transformer away from the front-end voltage source converter and one end of the low-voltage side winding of the C-phase coupling transformer away from the front-end voltage source converter to form a Y-type connection mode;

[0016] One end of the high-voltage side winding of the A-phase coupling transformer, one end of the high-voltage side winding of the B-phase coupling transformer, and one end of the high-voltage side winding of the C-phase coupling transformer are terminals connected to the corner-connected side terminals of the traditional power frequency transformer. The end of the high-voltage side winding of the A-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer is simultaneously connected to the end of the high-voltage side winding of the B-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer and the end of the high-voltage side winding of the C-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer to form a Y-type connection.

[0017] The two ends of the high-voltage side winding of the A-phase coupling transformer are connected in parallel with an A-phase fast bypass switch, the two ends of the high-voltage side winding of the B-phase coupling transformer are connected in parallel with a B-phase fast bypass switch, and the two ends of the high-voltage side winding of the C-phase coupling transformer are connected in parallel with a C-phase fast bypass switch.

[0018] The AC A2 phase port of the rear-end voltage source converter is a port connected to the A phase port on the user side, the AC B2 phase port of the rear-end voltage source converter is a port connected to the B phase port on the user side, the AC C2 phase port of the rear-end voltage source converter is a port connected to the C phase port on the user side, and the AC O neutral port of the rear-end voltage source converter is a port connected to the neutral point on the user side.

[0019] Embodiment 2:

[0020] like Figure 1 As shown, the present invention is a comprehensive power quality control device with DC power distribution function, wherein the output ports A1, B1, and C1 of the front-end voltage source converter F-VSC are respectively connected to the coupling transformer T through LC filters. SE One of the ports of the independent winding on the low voltage side and the other port are connected to each other in a Y-type manner. Vga, Vgb, and Vgc are the A, B, and C phase voltages on the grid side, respectively.

[0021] In addition, the coupling transformer T SE The high-voltage side winding terminals of the conventional power frequency transformer are connected to the delta-connected side terminals and the grid-side ports, respectively, to form a series circuit. The bypass switches of each phase are connected to the coupling transformer T SE The two ports of the high-voltage side winding are connected in parallel. When a sudden rise or drop in the grid voltage is detected, the fast bypass responds quickly and closes the switch, making the coupling transformer and the main line a series circuit. The grid-side voltage regulation is achieved by controlling the output port voltage of the front-end voltage source converter F-VSC. The DC ports of the front-end voltage source converter F-VSC and the rear-end voltage source converter E-VSC are directly connected in parallel to form a low-voltage DC bus V bus The positive and negative terminals V dc+ and V dc-, which can realize the friendly access of distributed power sources, electric vehicles and energy storage devices. The back-end voltage source converter E-VSC adopts a three-phase four-bridge arm topology structure, and its output ports A1, B1, C1 and O1 are respectively connected in parallel to the three-phase ports and neutral point on the user side. In the figure, 1 is the fast bypass switch S, 2 is the coupling transformer Tse, 3 is the front-end voltage source converter F-VSC, 4 is the front-end voltage source converter E-VSC, and 5 is the low-voltage DC distribution port V bus .

[0022] The present invention includes a circuit and a control module for comprehensive power quality management based on DC power distribution function. The control module includes a detection unit and a switch control unit; wherein the detection unit is used to detect grid-side voltage deviation, user-side harmonic current and DC port voltage.

[0023] When the grid voltage is in the rated operating state, the fast bypass switch S is closed, thereby reducing the switching loss generated by the front-end voltage source converter F-VSC. When the grid voltage rises or falls suddenly, the fast bypass switch S is disconnected, so that the front-end voltage source converter F-VSC can form a series loop with the grid side. In this embodiment, the voltage compensation range is rated voltage +15 to -10%, and the series coupling transformer T se The turns ratio k is designed to be 3. Series coupling transformer T se The high-voltage side winding is connected in series in the distribution line to realize the voltage compensation function, and the low-voltage side winding is connected to the output port of the front-end voltage source converter F-VSC filter device. Figure 2 As shown in the figure, it is assumed that the grid-side phase voltage amplitude is 8164V. In a certain period of time, the grid-side three-phase voltage suddenly fluctuates, such as rising or falling, and the fluctuation amplitude is within 10%. At this time, the detection module can calculate the amplitude of each phase voltage based on the conversion relationship between the abc three-phase stationary coordinate system and the dq two-phase rotating coordinate system. n In the wiring mode, the grid-side voltage and the user-side voltage have a phase difference of 30°. When performing voltage compensation control, the 30° phase difference needs to be compensated to the modulation duty cycle of the front-end voltage source converter F-VSC, as shown in formula (1).

[0024]

[0025] Where: V dref is the d-axis voltage reference value of the F-VSC front-end converter, V refd is the reference value of the rated voltage of the d-axis on the user side, θ is the phase difference between the primary and secondary sides of the transformer, and k is the voltage of each phase a, b, and c.

[0026] By adjusting the reference value of the AC output voltage of the front-end voltage source converter F-VSC, the voltage on the user side is ensured to be stable at the rated voltage value. The dynamic voltage compensation control strategy can adopt a dual closed-loop control strategy of voltage outer loop and current inner loop. The outer loop uses a PR controller to control the voltage error. The PR controller is a proportional resonant controller, which is expressed in English as Proportional Resonance Controller; the inner loop uses a P controller to control the current error. The P controller is a proportional controller, which is expressed in English as Proportional Controller. Feedforward compensation is added to improve the dynamic response characteristics of the closed-loop system. The error signal is input into the controller to adjust the output port voltage of the front-end voltage source converter F-VSC to achieve the stability of the voltage on the user side at the reference voltage value.

[0027] The back-end voltage source converter E-VSC can usually adopt a three-phase four-bridge-arm converter, thus avoiding the complex capacitor voltage balancing control strategy. The fourth bridge arm of the back-end voltage source converter E-VSC is connected to the neutral point of the three-phase four-wire distribution system, and the three-phase current of the user-side load is collected. After Clark transformation, the stationary coordinate system αβ two-phase current i can be obtained. ɑ and i β The instantaneous active current i can be calculated by instantaneous reactive power theory. p and instantaneous reactive current i q Value. Instantaneous active current i p and instantaneous reactive current i q The DC component and the instantaneous active current and the instantaneous reactive current are obtained by the LPF low-pass filter, and the fundamental component of the load three-phase current is obtained by the Clark inverse transformation. The harmonic current can be obtained by subtracting the instantaneous value of the user-side current from the fundamental component of the three-phase current. The DC bus voltage is related to the active current. dc After the collected value is subtracted from the expected voltage of the DC bus, it is output to the harmonic current d-axis reference value i after passing through the PI proportional integral controller. dref The current is added to achieve harmonic current compensation and DC side voltage stability control. The effect after realization is as follows Figure 3 shown.

[0028] The low voltage DC power distribution energy management method of the present invention can be flexibly regulated in combination with the operating status of distributed resources and different desired goals. Taking the peak-valley arbitrage model as an example, the operating results are as follows: Figure 4 Assume that there is a 75kW distributed photovoltaic array in the distribution area, and the light intensity is 1000W / m 2, the electric vehicle load is 50kW, the energy storage system SOC is 25%, and the user-side load is at peak hours. At this time, the surplus power generated by the photovoltaic array is transferred to the user-side load through the back-end voltage source converter E-VSC, and the energy storage system provides the difference power to the distribution station area according to the maximum power of the droop curve.

[0029] At t = 0.3s, the light intensity drops to 700W / m 2 , the output power of the photovoltaic array is reduced to 52.5kW, the charging power of electric vehicles suddenly increases to 70kW, the SOC of the energy storage system is 23%, the user-side load is at peak time, the energy storage system supplements power according to the droop curve, and the shortfall power of the DC distribution system is drawn from the grid side by the back-end voltage source converter F-VSC.

[0030] At t = 0.5s, the light intensity rises to 1000W / m 2 , the output power of the distributed photovoltaic array is 75kW, the charging power of electric vehicles drops sharply to 60kW, and the user-side load is in the off-peak period. The energy storage system absorbs the surplus power generated by photovoltaics in the DC distribution network, and the back-end voltage source converter F-VSC is in standby mode.

[0031] The present invention first adopts a high-voltage side series coupling transformer T SE , the voltage on the grid side is regulated by outputting the voltage of the front-end voltage source converter F-VSC. When the voltage on the grid side rises or falls suddenly, the shortfall voltage is borne by the series coupling transformer, while the power frequency transformer can still maintain the rated voltage, thus ensuring the service life and good operation of the power frequency transformer. The voltage fluctuation range of the distribution network is between 15% and -10% of the rated voltage. This solution is achieved by designing a series coupling transformer T SE The turns ratio k achieves the voltage regulation range.

[0032] Secondly, the technical solution of configuring a voltage regulating module on the traditional low-voltage side often requires the selection of low-voltage, high-current power semiconductor devices, which creates unfavorable factors for the power circuit design and cost of the power quality device. Compared with the technical solution on the low-voltage side, the selection of power semiconductor devices for the front-end voltage source converter F-VSC of the present invention is more flexible, and power semiconductor devices with more mature technology and lower cost can be used. At the same time, the back-end voltage source converter E-VSC can meet the DC functions of electric energy such as reactive power compensation, three-phase imbalance, and current harmonic suppression. Therefore, the present invention realizes the integration and integrated design of multiple power quality management functions, avoiding repeated investment in power quality management devices.

[0033] Finally, the public low-voltage DC bus port constructed by the front-end voltage source converter F-VSC and the rear-end voltage source converter E-VSC can flexibly access new sources and loads such as distributed power sources, energy storage devices and electric vehicles. The use of a centralized energy management system can achieve friendly interaction between source-grid-load-storage within the substation area, improve the penetration rate of distributed power sources and power utilization, and avoid further deterioration of the power quality of user-side loads caused by new sources and loads with intermittent and impact characteristics. In addition, the low-voltage DC bus distribution port also provides the possibility for energy mutual assistance and interconnection across regional distribution substations, thereby reducing the configuration and investment of energy storage.

[0034] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A comprehensive power quality control device with DC power distribution function, characterized in that: It comprises: a rear-end voltage source converter, wherein the low-voltage DC power distribution positive electrode port of the rear-end voltage source converter is connected to the low-voltage DC power distribution positive electrode port of the front-end voltage source converter, the low-voltage DC power distribution negative electrode port of the rear-end voltage source converter is connected to the low-voltage DC power distribution negative electrode port of the front-end voltage source converter, the AC A1 port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the A-phase coupling transformer through an LC filter, the AC B1 phase port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the B-phase coupling transformer through an LC filter, the AC C1 phase port of the front-end voltage source converter is connected to one end of the low-voltage side winding of the C-phase coupling transformer through an LC filter, and the end of the low-voltage side winding of the A-phase coupling transformer away from the front-end voltage source converter is simultaneously connected to one end of the low-voltage side winding of the B-phase coupling transformer away from the front-end voltage source converter and one end of the low-voltage side winding of the C-phase coupling transformer away from the front-end voltage source converter, forming a Y-type connection mode; One end of the high-voltage side winding of the A-phase coupling transformer, one end of the high-voltage side winding of the B-phase coupling transformer, and one end of the high-voltage side winding of the C-phase coupling transformer are terminals connected to the corner-connected side terminals of the traditional power frequency transformer. The end of the high-voltage side winding of the A-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer is simultaneously connected to the end of the high-voltage side winding of the B-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer and the end of the high-voltage side winding of the C-phase coupling transformer away from the corner-connected side terminals of the traditional power frequency transformer to form a Y-type connection.

2. The comprehensive power quality control device with DC power distribution function according to claim 1 is characterized in that: The two ends of the high-voltage side winding of the A-phase coupling transformer are connected in parallel with an A-phase fast bypass switch, the two ends of the high-voltage side winding of the B-phase coupling transformer are connected in parallel with a B-phase fast bypass switch, and the two ends of the high-voltage side winding of the C-phase coupling transformer are connected in parallel with a C-phase fast bypass switch.

3. The comprehensive power quality control device with DC power distribution function according to claim 1 is characterized in that: The AC A2 port of the rear-end voltage source converter is a port connected to the A-phase port on the user side, the AC B2 port of the rear-end voltage source converter is a port connected to the B-phase port on the user side, the AC C2 port of the rear-end voltage source converter is a port connected to the C-phase port on the user side, and the AC O neutral port of the rear-end voltage source converter is a port connected to the neutral point on the user side.

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