A topology device and method of direct current power supply quality active promotion equipment

Abstract

The application discloses a kind of topology circuit, device and method of active promotion equipment of direct current power supply quality, circuit includes: double active converter DAB and direct current active filter DC-APF;Device includes direct current distribution system power quality management circuit and control module;Method includes: real-time detection whether there is voltage deviation and direct current ripple condition;When detecting voltage deviation, control the conduction of diagonal switch tube in first DC-APF and second DC-APF;When detecting direct current ripple, control first DC-APF and second DC-APF output reverse compensation current to suppress ripple;The application can realize voltage, harmonic self-regulating coordination, with direct current ripple management, voltage deviation suppression capability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power distribution network, and particularly relates to a topology device and method of active promotion equipment for DC power supply quality. BACKGROUND

[0002] The progress of new energy generation technology and power electronics technology has changed the ecology of the development of DC distribution network. Compared with AC distribution network, the adaptability of DC distribution network to DC type load and DC type distributed power source has obvious advantages. Although the power quality of DC distribution network is better than that of AC distribution network and is easy to control, the disturbance characteristics have unique characteristics, and the steady-state events such as voltage deviation, voltage fluctuation and ripple still deeply affect the planning, operation, protection and control of DC distribution network. The steady-state events in the DC microgrid affect the power supply quality and safe operation of electrical equipment.

[0003] For the above power quality event control of DC distribution network, the voltage and harmonic can be self-regulated through the access of power quality management equipment, so as to have the ability of DC ripple management and voltage fluctuation suppression.

[0004] Since the equivalent model of the DC distribution network is not an infinite power source, the power exchange of the distributed power source power fluctuation, local load change, converter and flexible switch and other power electronic equipment ports will cause the DC distribution network voltage deviation. At present, most of the DC power quality management devices realize the active power-voltage balance through the charging and discharging of the battery. If the dependence on the battery is to be reduced and the configuration and investment of the energy storage equipment are to be reduced, some existing technologies configure the energy storage at the sensitive load and design a current inner loop feedforward control strategy to suppress the DC voltage fluctuation caused by the load change. Some existing technologies propose a local droop and distributed control coordination control to adjust the charging and discharging of the battery storage to suppress the voltage fluctuation for the high photovoltaic penetration power grid. Some existing technologies also use controllable loads to suppress the voltage change of the DC power grid by referring to the research experience of the electrical spring in the AC power grid. Since the capacity of the controllable load is limited, the control of the voltage fluctuation has a maximum boundary. When the capacity is outside the boundary, the voltage cannot be controlled to the rated value, and the control ability of the DC voltage is limited. In view of this problem, some researchers have proposed a comprehensive control strategy based on controllable load and battery storage. Although the controllable load can reduce the capacity requirement of the battery storage and improve the economy, the investment of the energy storage equipment is still needed. The DC voltage deviation requires a larger capacity of the management device. At present, most of the researches on the voltage deviation management need the investment of the energy storage equipment. However, from the aspects of the early investment and land occupation requirements, the research on the voltage deviation management equipment without relying on the energy storage equipment is very promising and necessary.

[0005] The current ripple suppression treatment method is divided into active treatment and passive treatment. The active treatment is to improve the device generating ripple, but it will make the system structure and control strategy more complex, increase the cost and reduce the efficiency. The passive treatment is to eliminate the ripple by installing active filter device or passive filter. In order to solve the above problems, different ripple extraction methods and current tracking control strategies can be used to realize the fast response tracking of the compensation current by DC-APF. The Bode plot of the impedance equivalent to DC-APF is analyzed, and it is found that DC-APF has good filtering effect on the second-order frequency ripple, but the filtering effect on high-frequency ripple is poor. Therefore, DC-APF and LC filter are combined to achieve the effect of suppressing various ripples. Other invention patents propose an active filter for suppressing second-order ripple, which is composed of a single-phase voltage source converter (VSC) AC side series inductor. When used, the DC side is connected to the DC bus that needs to suppress the second-order ripple.

[0006] From the above prior art, it can be seen that most of the power quality equipment proposed at present can only treat a single power quality problem, such as voltage deviation and ripple. However, due to the zero frequency characteristics of DC voltage and the structure of DC power distribution network, there is a coupling characteristic between ripple and fluctuation, voltage deviation and steady-state voltage imbalance. How to provide a device that can simultaneously treat voltage deviation and ripple is an urgent problem for those skilled in the art. SUMMARY

[0007] Therefore, the present application provides a topology device and method of active improvement equipment for DC power supply quality, which at least solves the problem of lack of integrated equipment for treating multiple power quality events in the prior art.

[0008] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0009] A topology circuit of active improvement equipment for DC power supply quality, comprising: a dual active converter DAB and a DC active filter DC-APF; wherein,

[0010] The dual active converter DAB is connected to two DC buses through the DC active filter DC-APF on both sides, wherein the two DC buses are BUS1 and BUS2, the DC active filter DC-APF connected to both ends of BUS1 is the first DC-APF, the DC active filter DC-APF connected to both ends of BUS2 is the second DC-APF, the first DC-APF is connected to the primary side full-bridge of the dual active converter DAB through the voltage stabilizing capacitor C1, and the second DC-APF is connected to the secondary side full-bridge of the dual active converter DAB through the voltage stabilizing capacitor C2.

[0011] The application discloses a topology device of active equipment for improving DC power supply quality, and relates to the technical field of power supply quality improvement.

[0012] The control module comprises a detection unit and a switch control unit.

[0013] The detection unit is used for detecting voltage deviation and DC ripple.

[0014] When the detection unit detects voltage deviation, the switch control unit controls the diagonal switch tubes in the first DC-APF and the second DC-APF to be turned on, controls the double active converter DAB to adopt a voltage control mode to realize voltage balance through power mutual assistance, filters high-frequency ripple components generated in a high-frequency switching state by the double active converter DAB, and controls the DC / AC converter to take power from the BUS1 to supply power to the sensitive load.

[0015] When the detection unit detects DC ripple, the switch control unit controls the double active converter DAB to adopt a voltage control mode to suppress the DC-side capacitor voltage fluctuation of the first DC-APF and the second DC-APF and maintain the stability of the DC-side voltage, controls the first DC-APF and the second DC-APF to output reverse compensation current to suppress ripple through tracking of the ripple current on the DC bus side, and controls the DC / AC converter to take power from the BUS1 to supply power to the sensitive load.

[0016] The application further discloses a topology method of active equipment for improving DC power supply quality.

[0017] The application further discloses a topology method of active equipment for improving DC power supply quality.

[0018] When the detection unit detects voltage deviation, the switch control unit controls the diagonal switch tubes in the first DC-APF and the second DC-APF to be turned on, controls the double active converter DAB to adopt a voltage control mode to realize voltage balance through power mutual assistance, filters high-frequency ripple components generated in a high-frequency switching state by the double active converter DAB, and controls the DC / AC converter to take power from the BUS1 to supply power to the sensitive load.

[0019] When the detection unit detects DC ripple, the switch control unit controls the double active converter DAB to adopt a voltage control mode to suppress the DC-side capacitor voltage fluctuation of the first DC-APF and the second DC-APF and maintain the stability of the DC-side voltage, controls the first DC-APF and the second DC-APF to output reverse compensation current to suppress ripple through tracking of the ripple current on the DC bus side, and controls the DC / AC converter to take power from the BUS1 to supply power to the sensitive load.

[0020] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a topology device and method for actively improving the quality of DC power supply, which has the following beneficial effects:

[0021] The present invention first utilizes a segmented DC bus for power supply, connecting two bus segments via a management device capable of bidirectional power flow. When voltage deviation occurs on one bus segment, the other bus segment compensates for the power generated by the device to achieve active power balance, thereby maintaining its DC bus voltage reference value. This solution achieves active power balance and voltage balance by leveraging power between the segmented buses, eliminating the need for energy storage equipment and significantly reducing initial capital investment. The first consideration is the well-researched dual-active bridge converter (DAB), capable of bidirectional power flow, connected in parallel to the segmented buses on both sides.

[0022] Secondly, in the current research on DC microgrid ripple control, a DC-APF can be used to compensate for the AC component of the DC bus output to achieve the goal of suppressing current ripple. If the DC-APF is combined with the above-mentioned control equipment, the expected integrated voltage fluctuation and ripple control can be achieved. When controlling voltage fluctuations, the DC-APF does not need to participate in the control, that is, it can be directly turned on diagonally. When controlling ripple, the DC-APF on the bus side outputs a compensation current to suppress the ripple, and the DAB part is used to achieve reactive compensation to control the capacitor voltage stability in the DC-APF. Since both bus sections may need to suppress ripple, the DC-APF can be connected in parallel to the bus and then connected in parallel with the above-mentioned DAB part.

[0023] By using segmented busbar power mutual assistance to manage voltage deviation, it not only solves the problem of relying on energy storage equipment to achieve active power-voltage balance, but also improves economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 A topological circuit of a device for actively improving the quality of DC power supply provided by the present invention;

[0026] Figure 2 A schematic diagram of the voltage deviation management operation mode provided by an embodiment of the present invention;

[0027] Figure 3 A schematic diagram of the DC ripple suppression operating mode provided by an embodiment of the present invention;

[0028] Figure 4 The experimental principle diagram provided by the embodiment of the application is shown in the following figure;

[0029] Wherein, 1-first DC-APF, 2-dual active bridge DAB, 3-second DC-APF, 4-DC / AC converter. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the application will be clearly and completely described in connection with the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0031] The application provides a topology circuit of a direct current power supply quality active promotion equipment, as shown in the following figure, comprising a dual active bridge DAB 2 and a direct current active filter DC-APF; wherein, Figure 1

[0032] The dual active bridge DAB 2 is connected to two direct current buses through the direct current active filters DC-APF on both sides, wherein the two direct current buses are BUS1 and BUS2, the direct current active filter DC-APF connected to both ends of BUS1 is the first DC-APF 1, the direct current active filter DC-APF connected to both ends of BUS2 is the second DC-APF 3, the first DC-APF 1 is connected to the primary side full bridge of the dual active bridge DAB 2 through a voltage stabilizing capacitor C1, and the second DC-APF 3 is connected to the secondary side full bridge of the dual active bridge DAB 2 through a voltage stabilizing capacitor C2.

[0033] A topology device of a direct current power supply quality active promotion equipment, based on a topology circuit of a direct current power supply quality active promotion equipment, connected to a DC / AC converter on the direct current side, comprising a direct current power distribution system power quality management circuit and a control module;

[0034] The control module comprises a detection unit and a switch control unit; wherein,

[0035] The detection unit is used for detecting voltage deviation and direct current ripple;

[0036] When the detection unit detects the voltage deviation, the switch control unit controls the diagonal switch tubes in the first DC-APF 1 and the second DC-APF 3 to be turned on, controls the dual active bridge DAB 2 to adopt a voltage control mode to realize voltage balance through power mutual aid, and filters out high-frequency ripple components generated in the high-frequency switching state by the dual active bridge DAB 2, and the DC / AC converter 4 takes power from BUS1 to supply power to the sensitive load;

[0037] ​When the detection unit detects the direct current ripple, the switch control unit controls the dual active converter DAB2 to adopt the voltage control mode to suppress the first DC-APF1 and the second DC-APF3 direct current side capacitor voltage fluctuation and maintain the direct current side voltage stability, the first DC-APF1 and the second DC-APF3 suppress the ripple by tracking the direct current bus side ripple current control output reverse compensation current, and the DC / AC converter 4 takes power from the BUS1 to supply power to the sensitive load.

[0038] It should be noted that:

[0039] Since the traditional direct current power quality treatment device realizes bidirectional power flow through the H bridge to control the grid voltage balance, and the energy storage device adjusts the active balance-voltage balance through the H bridge, the loss and cost of the system are increased, which is not conducive to its promotion. The present application is based on the design of the topology by replacing the energy storage device with the segmented bus power interconnection. The dual active converter DAB2 can realize bidirectional power flow, and the dual active converter DAB2 is connected in parallel across two buses, which is used for maintaining voltage balance in the treatment of voltage deviation.

[0040] The direct current microgrid is because the non-ideal characteristics of the alternating current side contain a large amount of second harmonic components, and the notch characteristics in the amplitude-frequency characteristic diagram of the active filter DC-APF are used to filter out the second harmonic. In order to suppress the ripple current of the two buses, a DC-APF is connected in parallel on each bus side, and the compensation current with opposite phase to the ripple current is output to achieve it. When treating voltage deviation, the diagonal switches of the first DC-APF1 and the second DC-APF3 are turned on, and are directly connected to the dual active converter DAB2 relative to the bus, and the voltage balance is realized by the power interconnection of the voltage control mode of the dual active converter DAB2, and the high-frequency ripple components generated in the high-frequency switching state are filtered out by the L and C filters at the output port of the dual active converter DAB2; when treating direct current ripple, the dual active converter DAB2 adopts the voltage control mode to suppress the DC-APF direct current side capacitor voltage fluctuation and maintain the direct current side voltage stability, and the first DC-APF1 and the second DC-APF3 suppress the ripple by tracking the direct current bus side ripple current control output reverse compensation current.

[0041] Dual active converter DAB2→treat long-time-scale voltage deviation, such as Figure 2 As shown, the diagonal switches of the first DC-APF1 and the second DC-APF3 are opened, which is equivalent to that the dual active converter DAB2 is directly connected in parallel to the bus end. Since the dual active converter DAB2 can realize bidirectional energy flow through part of the topology, the power interconnection between the buses is realized, and the configuration and investment of the energy storage are reduced; the sensitive load takes power from the BUS1 through the DC / AC converter 4;

[0042] First DC-APF1+second DC-APF3→treat long-time-scale direct current ripple, such as Figure 3As shown, the first DC-APF1 governs the ripple voltage on BUS1, the second DC-APF3 governs the ripple voltage on BUS2, and the double active bridge DAB2 adopts a voltage control mode to stabilize the capacitor voltage by charging and discharging the capacitor; the sensitive load takes power from BUS1 through the DC / AC converter 4;

[0043] A topology method of a direct current power supply quality active promotion equipment, based on a topology device of a direct current power supply quality active promotion equipment, comprising the following steps:

[0044] Real-time detection of voltage deviation and direct current ripple;

[0045] When the voltage deviation is detected, the diagonal switch tubes in the first DC-APF1 and the second DC-APF3 are turned on, the double active bridge DAB2 adopts a voltage control mode to realize voltage balance through power mutual aid, and the double active bridge DAB2 filters out the high-frequency ripple component generated in the high-frequency switching state, and the DC / AC converter 4 takes power from BUS1 to supply power to the sensitive load;

[0046] When the direct current ripple is detected, the double active bridge DAB2 adopts a voltage control mode to suppress the direct current side capacitor voltage fluctuation of the first DC-APF1 and the second DC-APF3 and maintain the stability of the direct current side voltage, the first DC-APF1 and the second DC-APF3 suppress the ripple by outputting reverse compensation current through tracking the ripple current on the direct current bus side, and the DC / AC converter 4 takes power from BUS1 to supply power to the sensitive load.

[0047] The application will be further described below through specific experiments:

[0048] As Figure 4 shown, the voltage levels of the direct current buses BUS1 and BUS2 are selected as 750V, the power of the double active bridge DAB2 is 120kW, the single bus power is 990kW, and the support capacity that can be provided when governing the steady-state power quality problem is 240kW / 660kW>10%. Since the voltage levels of BUS1 and BUS2 are the same, the transformer level can be selected as 1:1.

[0049] Governance of direct current ripple: the first DC-APF1 / second DC-APF3 switch tube bears 750V, and the double active bridge DAB2 switch tube bears Uc;

[0050] Governance of voltage deviation: the double active bridge DAB2 switch tube bears 750V, and the first DC-APF1 / second DC-APF3 non-conducting bridge arm bears 750V;

[0051] Considering the overload capacity of the switch tube and voltage spikes, a switch tube with 1200V voltage resistance (medium voltage level) is selected.

[0052] The transformer primary and secondary side square wave signals in the interconnection unit DAB2 are equivalent to sine waves, and the voltage is calculated to the primary side,

[0053]

[0054] In the formula, φ is the outward phase angle; δ1 is the inner phase angle of the transformer primary side H bridge; δ2 is the inner phase angle of the transformer secondary side H bridge; U1 is the BUS1 voltage; U2 is the BUS2 voltage; w is the switching frequency of the interconnection part.

[0055] The power transmitted by the DAB2 part,

[0056]

[0057] The large number of distributed energy access, combined with the frequent switching of the load causes the BUS1 voltage deviation, and the active power gap caused by the compensation of BUS2 to the BUS1 voltage stabilizes to 750V. The input φ, δ1, δ2 of the interconnection part DAB2, the control output P and U1 exist coupling, if the output U 1ref is controlled to 750V, the output of the DAB2 active power compensates the BUS1 energy gap to realize the bus voltage stabilization.

[0058] When the first DC-APF1 / second DC-APF3 outputs the compensation current, since it is in a high-frequency switching state, there may be some high-frequency ripple current in the compensation current, so a filter inductor needs to be set on the AC side, so that the output compensation current passes through the filter inductor and then realizes ripple suppression. When the filter inductor is selected to be too large, the ripple component in the compensation current will be eliminated, but the dynamic response speed of the system and the compensation current tracking performance will be reduced; the smaller the inductance value is selected, the ripple content in the output compensation current will not be completely eliminated, which is easy to cause system oscillation and affect the current tracking performance.

[0059] i L The change rate of the compensation current satisfies

[0060]

[0061] In the formula, f max is the maximum frequency of the ripple current (Hz); I P is the peak value of the ripple current; w x is the angular frequency.

[0062] According to the operation structure characteristics of the H bridge type DC-APF, we can get,

[0063]

[0064] In the formula, U dc DC bus voltage effective value; U c DC-APF DC side capacitor voltage effective value.

[0065] U dc = 750V, U c = 1000V

[0066]

[0067] When the current rate of change is minimum, the ripple can still be effectively compensated, and the output current of the filter can be reduced from the maximum to 0, then the following formula is obtained

[0068]

[0069] I P The field investigation is needed to determine the ripple current to be treated on the DC side, in this embodiment, the bus current is 1320A, which can be obtained from the 750V, 990KW treatment scene, and the ripple current content is about 5%, that is, I P = 90A, f max = 100HZ, then L is 4mH.

[0070] The first DC-APF1 / second DC-APF3 DC side capacitor can suppress voltage fluctuation and maintain DC side voltage stability, and the capacity of the capacitor is related to the voltage stability effect, the larger the capacity, the better the voltage stabilization effect, but as the capacity increases, the size of the device also increases, so when selecting the DC-APF DC side capacitor, it should be considered comprehensively, and under the premise of ensuring the stable compensation current of the DC-APF output, the capacitor with smaller capacity is selected as much as possible.

[0071] The DC side capacitor is designed according to the energy flow:

[0072]

[0073] Where Δu c is the capacitor voltage deviation; i 2m is the DC-APF side compensation current value.

[0074] After further simplification, we get

[0075]

[0076] Take I 2m = 50A, w = 628 rad / s, U dc = 750V, Uc = 1000V, Δu c= 10V, C=0.005971F can be obtained, and 5mF is taken.

[0077] The above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A topological device for actively improving the quality of DC power supply, based on a topological circuit for actively improving the quality of DC power supply, connected to a DC / AC converter on the DC side, comprising: A dual active converter (DAB) and a DC active filter (DC-APF); wherein both sides of the dual active converter (DAB) are connected to two DC bus sections through DC active filters (DC-APFs), wherein the two DC bus sections are BUS1 and BUS2, respectively; the DC active filter (DC-APF) connected to both ends of BUS1 is a first DC-APF; the DC active filter (DC-APF) connected to both ends of BUS2 is a second DC-APF; the first DC-APF is connected to the primary full bridge of the dual active converter (DAB) through a stabilizing capacitor (C1); the second DC-APF is connected to the secondary full bridge of the dual active converter (DAB) through a stabilizing capacitor (C2); and the device comprises a DC power distribution system power quality management circuit and a control module; The control module includes a detection unit and a switch control unit; wherein, The detection unit is used to detect voltage deviation and DC ripple; When the detection unit detects a voltage deviation, the switch control unit turns on the diagonal switches in the first and second DC-APFs, controls the dual active converters (DABs) to adopt a voltage control mode to achieve voltage balance through power mutual assistance, and filters out the high-frequency ripple components generated by the high-frequency switching state. The DC / AC converter draws power from BUS1 to supply power to sensitive loads. When the detection unit detects DC ripple, the switch control unit controls the dual active converter DAB to adopt the voltage control mode to suppress the voltage fluctuation of the DC side capacitors of the first DC-APF and the second DC-APF and maintain the DC side voltage stability. The first DC-APF and the second DC-APF control the output reverse compensation current to suppress the ripple by tracking the DC bus side ripple current. The DC / AC converter draws power from BUS1 to supply power to sensitive loads.

2. A topology method for a DC power supply quality active improvement device, based on the topology device for a DC power supply quality active improvement device according to claim 1, characterized in that: The following steps are involved: Real-time detection of voltage deviation and DC ripple; When a voltage deviation is detected, the diagonal switches in the first and second DC-APFs are turned on, and the dual active converter (DAB) is controlled to adopt a voltage control mode to achieve voltage balance through power mutual assistance. The dual active converter (DAB) filters out the high-frequency ripple components generated by the high-frequency switching state, and the DC / AC converter draws power from BUS1 to supply power to sensitive loads. When DC ripple is detected, the dual active converter (DAB) is controlled to adopt voltage control mode to suppress the voltage fluctuation of the DC-side capacitors of the first and second DC-APFs and maintain DC-side voltage stability. The first and second DC-APFs control the output reverse compensation current to suppress ripple by tracking the DC bus side ripple current. The DC / AC converter draws power from BUS1 to supply power to sensitive loads.

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