Single-stage voltage source type dc power flow controller

Abstract

The application provides a single-stage voltage source type direct current power flow controller, which comprises the voltage V1 and V2 of a first direct current network and a second direct current network, a medium-frequency transformer T r1 The equivalent inductance L is formed by the series connection of the leakage inductance and the auxiliary inductance eq The equivalent inductance L is formed by the series connection of the leakage inductance and the auxiliary inductance The application has the forward and reverse voltage output and power flow regulation capacity, and has the wide-range interconnected direct current system power flow regulation function.

Description

Technical Field

[0001] This invention relates to the field of DC power flow controller technology, and more specifically, to a single-stage voltage source type DC power flow controller. Background Technology

[0002] As the proportion of distributed renewable energy and energy storage in DC power distribution systems continues to rise, distributed DC systems, such as photovoltaic-storage DC systems, DC fast charging stations, and DC data centers, are also increasing. DC power flow controllers play a crucial role in achieving power flow regulation between interconnected DC systems of the same voltage level.

[0003] Existing DC power flow controllers can be divided into two categories: two-quadrant operating circuits and four-quadrant operating circuits. Two-quadrant power flow controllers can achieve bidirectional current regulation; however, due to the fixed polarity of the output voltage, the range of series voltage regulation in the lines is limited, resulting in weak power flow regulation capability. In contrast, four-quadrant power flow controllers can achieve both forward and reverse voltage outputs, resulting in a wider adjustable range of line voltage and stronger power flow regulation capability.

[0004] However, existing four-quadrant power flow controllers mostly adopt a two-stage DC / DC + DC / AC converter topology to achieve positive and negative voltage output, resulting in a large number of power conversion stages and low converter efficiency, cost, and reliability. To solve the above problems, this invention proposes a single-stage four-quadrant DC power flow controller.

[0005] The literature (L. Yao, H. Cui, J. Zhuang, G. Li, B. Yang and Z. Wang, "A DC power flow controller and its control strategy in the DC grid", Proc. 8th PowerElectron. Motion Control Conf., pp. 1-6, May 2016.) adopts a circuit topology based on a DAB converter, with an H-bridge converter cascaded after the DAB converter to control the polarity of the output voltage. Since there is only one power path between the input and output ports, all IGBT components and the intermediate frequency transformer need to withstand a large current stress.

[0006] Literature (S. Balasubramaniam, CEUgalde-Loo, J. Liang, T. Joseph, R. King and A. Adamczyk, "Experimental Validation of Dual H-Bridge Current Flow Controllers for Meshed HVdc Grids," in IEEE Transactions on Power The paper "Delivery" (vol. 33, no. 1, pp. 381-392, Feb. 2018) employs a 2B-CFC (Continuous Power Flow Control) scheme for DC power flow control. It uses two H-bridge converters and two pairs of anti-parallel IGBTs on either side to form a three-port converter, establishing a connection between two DC lines and an auxiliary DC voltage source. By controlling the switching of the IGBTs, the magnitude and polarity of the equivalent series voltage source of the DC lines can be controlled, thereby increasing or decreasing the current in the two DC lines. However, because this scheme requires an additional DC voltage source, while this scheme only requires a converter composed of IGBTs and an intermediate frequency transformer for DC power flow control, the equipment and construction costs of the latter scheme are relatively higher than those of the former. Furthermore, this scheme uses a hard-switching circuit, which has higher losses compared to the soft-switching circuit of this scheme. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the purpose of this invention is to provide a single-stage voltage source type DC power flow controller.

[0008] The single-stage voltage source type DC power flow controller provided by the present invention includes: voltages V1 and V2 of a first DC grid and a second DC grid, and an intermediate frequency transformer T. r1 The equivalent inductance L formed by the leakage inductance and the auxiliary inductance connected in series eq The secondary-side converter includes a voltage regulator capacitor C1, an output-side LC filter and line resistor R2, and 10 insulated-gate bipolar transistors (IGBTs), which are S... 11 S 12 S 13 S 14 S 21 S 22 S 23 S 24 S 25 S 26 The output-side LC filter consists of a filter inductor L. f With filter capacitor C f Composition: The first DC power grid is connected to one end of a converter consisting of 10 IGBTs and Tr1. The other end of the converter is connected to the voltage regulator capacitor C1. The positive terminal of the first DC power grid is connected to S. 22The emitter is connected to the phase, and the negative terminal of the first DC power grid is connected to S. 24 The emitters are connected; the output of the output-side LC filter is connected to the line resistor R2 and the second DC power grid.

[0009] 10 insulated gate bipolar transistors and T r1 This constitutes a dual active bridge converter (DAB) structure.

[0010] S 11 S 12 S 13 S 14 The connection relationship is: S 11 S 13 Emitter and S 12 S 14 Collector phase connection, S 11 S 13 The collector is connected to the positive terminal of the first DC power grid, S 12 S 14 The emitter is connected to the negative terminal of the first DC power grid, forming a full-bridge converter FB. The AC measurement is connected to T. r1 Connect the original edges;

[0011] S 21 S 22 S 23 S 24 S 25 S 26 The connection relationship is: S 21 S 23 Emitter and S 22 S 24 Collector phase connection, S 22 S 24 Emitter and S 25 S 26 Collector phase connection, S 25 S 26 The emitter is connected to the negative terminal of the second DC power grid, S 21 S 23 The collector is connected to the positive terminal of the second DC power grid to form a full-bridge converter FB, and the AC measurement is connected to T. r1 Secondary edges are connected, S 22 The emitter is connected to the positive terminal of voltage V1, S 24 Emitter and filter inductor L f Connected;

[0012] C f This is the output filter capacitor, with its two ends connected to the filter inductor L. f It is connected to the negative terminal of the first DC power grid.

[0013] Preferably, when V1 = V2, in the positive power regulation mode, V2 <V O ';

[0014] In boost mode, S 25 With S 24 Maintain conduction; S 11 With S 14 The driving pulse is centrally symmetrical with respect to S. 12 Drive pulse complementarity; S 21 With S 26 The driving pulse is centrally symmetrical with respect to S. 22 Drive pulse complementarity; S 13 With S 14 Drive pulse complementarity; S 23 With S 26 Drive pulse complementarity;

[0015] In positive power regulation mode, the output voltage expression of the power flow controller is as follows:

[0016] V' O =V2+i dc R2……(20)

[0017] Among them, V O ' represents the output voltage of the power flow controller, which is the sum of the voltages of R2 and V2; i dc This represents the input current of the LC filter;

[0018] According to the law of conservation of energy, i dc The average value is based on the power P transferred from the primary side to the secondary side of the DAB converter. DAB With V O The mean is calculated as shown in the formula, where, V represents O The average value over a period of time, V O S represents 24 Emitter and S 22 Voltage difference between emitters;

[0019]

[0020] Where d2 represents S 21 The duty cycle of the drive pulse; V dc This represents the voltage across the voltage regulator capacitor C1;

[0021] Output voltage V o When expressed as a function of d², it is calculated using the following formula:

[0022] V o =V1+d2V dc ……(twenty two)

[0023] When the value of resistor R2 is fixed, the output voltage V o When stable, substituting the equation into the given equation, we obtain the following equation:

[0024]

[0025] P DAB Represented as d1, d2, d ps The function is shown in the equation;

[0026]

[0027] Where n is T r1 Transformation ratio; d1 represents S 11 The duty cycle of the driving pulse; d ps S represents 11 The driving pulse leads S 21 The phase of the drive pulse; f represents the switching frequency of each IGBT;

[0028] Substituting the equation into the formula, we can calculate the voltage V of the voltage regulator capacitor C1. dc The expression is as shown in the formula:

[0029]

[0030] Based on equations 1, 2, and 3, we obtain P. 总 The expression is shown in the following formula:

[0031]

[0032] Substituting the expression into the equation, we get P. 总 The relationship between the control variables and the control variables is shown in the following formula:

[0033]

[0034] Preferably, in reverse power regulation mode when V1 = V2, V2 > V O ', S 22 With S 26 Maintain conduction; S 11 With S 14 The driving pulse is centrally symmetrical with respect to S. 12 Drive pulse complementarity; S 13 With S 14 Drive pulse complementarity; S 21 With S 24 The driving pulse is centrally symmetrical with respect to S. 25 Drive pulse complementarity; S 23 With S 25 Drive pulse complementarity;

[0035] Due to V dc Change the polarity, change the expression to the expression, and change the expression to the expression:

[0036]

[0037]

[0038] After the modification, V dc The expression is shown in the following formula:

[0039]

[0040] Combining the formulas, we get P. 总 The expression is as shown in the formula:

[0041]

[0042] Preferably, for L eq L f C f The design is based on the parameters of three passive components, including L. eq Calculated based on the rated power transmitted by the converter, L f C f Calculated based on the output voltage and current ripple magnitude;

[0043] In forward power regulation mode, according to the formula, the expression for the total power transmitted by the converter is obtained, as shown in the formula:

[0044]

[0045] Similarly, in buck mode, the expression for the total transmitted power is derived, as shown in the equation:

[0046]

[0047] The rated power of the power flow controller under the two operating modes is obtained from the formula. In the formula, the values ​​of each voltage and the transformer turns ratio are determined based on the DC power supply voltage and the load voltage range. Therefore, L is determined by the rated power of the converter. eq The value;

[0048] L f With C f The output port LC filter has the transfer function shown in the equation:

[0049]

[0050] Where S represents the complex frequency after the Laplace transform; ω C This represents the resonant angular frequency of the LC filter;

[0051] In the formula, Let S = jω, then the expression can be transformed into the expression:

[0052]

[0053] Where j is the complex unit; ω represents the angular frequency of the circuit;

[0054] The input voltage of the output LC filter is V f The output voltage is V O ', V f Expressed as DC quantity and ripple, when d2 = 0.5, V f The ripple amplitude is at its maximum at time t. f The expression V f (t) is shown in the equation:

[0055]

[0056] Where t is the moment in which the DC power flow controller is located;

[0057] According to the formula, V is calculated. O The expression is shown in the formula, where...

[0058]

[0059] in, This represents the phase shift angle produced by the LC filter in response to the input voltage at an angular frequency of ω.

[0060] When V1 and V dc When both are determined, a suitable LC value is calculated based on the requirements of load voltage ripple and filter current ripple.

[0061] Preferably, the soft-switching regulation capability of the power flow controller is analyzed:

[0062] For the 10 IGBT elements in the power flow controller, the conditions for achieving soft-switching ZVS are as shown in the equation:

[0063]

[0064] In the formula, i DAB (t) represents the corresponding IGBT turn-on instant. DAB The current value; v ac2 (t) represents the corresponding IGBT turn-on moment v ac2 The voltage value; Q oss (V1) indicates that the IGBT is in the off state, and the voltage across it is V1. The parasitic capacitance C... oss The value of the charge stored on the IGBT is obtained by consulting the datasheet of the selected IGBT.

[0065] Compared with the prior art, the present invention has the following beneficial effects:

[0066] (1) The present invention has the ability to output and regulate forward and reverse voltage and power flow, and has the power flow regulation function of wide-range interconnected DC system;

[0067] (2) The input and output of this invention only undergo a single-stage power conversion, which reduces the cost of the converter and the conversion loss.

[0068] (3) The power flow controller of the present invention has ZVS soft switching regulation capability, which further reduces power conversion loss. Attached Figure Description

[0069] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0070] Figure 1 For power flow controller topology;

[0071] Figure 2 The waveform for the forward power regulation mode of the power flow controller;

[0072] Figure 3 The waveform for the reverse power regulation mode of the power flow controller;

[0073] Figure 4 Simulation results of the waveform of the power flow controller in reverse regulation mode;

[0074] Figure 5 The simulation results show the waveform of the power flow controller in the forward regulation mode. Detailed Implementation

[0075] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0076] Example:

[0077] This invention provides a novel topology scheme for a single-stage voltage source power flow controller with four-quadrant power flow regulation capability, in order to Figure 1 The converter topology shown is illustrated, and its specific technical implementation scheme is explained.

[0078] DC power flow controller topology design

[0079] for Figure 1 The power flow controller topology shown is illustrated, where V1 and V2 represent the voltages of the two DC power grids, respectively, and L...eq Indicates intermediate frequency transformer T r1 The equivalent inductance formed by the leakage inductance and the auxiliary inductance connected in series, C1 represents the voltage regulator capacitor of the secondary converter, L f With C f This forms the output-side LC filter, with R2 representing the resistance of the second DC grid. The power flow controller contains a total of 10 Insulated Gate Bipolar Transistors (IGBTs), of which S... 11 S 12 S 13 S 14 This forms a full-bridge converter (FB), and is connected to T. r1 The original edges are connected; S 21 S 22 S 23 S 24 S 25 S 26 Construct a full-bridge converter, and with T r1 Secondary side connection; 10 IGBTs and T r1 This constitutes a Double Active Bridge (DAB) converter structure. 22 The emitter is connected to the positive terminal of port V1, S 24 Emitter and filter inductor L f Connected, i DAB T represents r1 Primary input current, v ac1 v ac2 T respectively r1 Primary and secondary voltages, n is T r1 Transformation ratio, V dc This represents the voltage across the voltage regulator capacitor C1, v O S represents 24 Emitter and S 22 The voltage difference between the emitters, v f i represents the input current of the LC filter. dc V represents the input current of the LC filter. O ' represents the output voltage of the power flow controller, which is the sum of the voltages of R2 and V2.

[0080] DC power flow controller operation control and power characteristics

[0081] Positive power regulation mode:

[0082] Figure 1 The converter shown can operate in forward power regulation (V2) by changing the modulation mode of each IGBT. <V O ') or reverse power regulation (V2>VO In the following section, we will discuss the forward and reverse power regulation modes of the DC power flow controller when V1 = V2.

[0083] In positive power regulation mode, the AC and DC voltage and current waveforms of the power flow controller are as follows: Figure 2 As shown in the figure. In the figure, T represents the time of one switching cycle, and d1 and d2 represent S respectively. 11 S 21 The duty cycle of the driving pulse, d ps S represents 11 The driving pulse leads S 21 Phase of the drive pulse. In boost mode, S 25 With S 24 Maintain conduction. S 11 With S 14 The driving pulse is centrally symmetrical with respect to S. 12 Drive pulse complementarity, S 21 With S 26 The driving pulse is centrally symmetrical with respect to S. 22 Complementary driving pulses. S 13 With S 14 Drive pulse complementarity, S 23 With S 26 Complementary driving pulses.

[0084] The following section will calculate the total power P transferred from V1 to V2 in boost mode. 总 The relationship between d1 and d2 and various control variables. In boost mode, the values ​​of d1 and d2 range from [0.5, 1]. ps The value range is [-0.25, 0.75].

[0085] In positive power regulation mode, the output voltage expression of the power flow controller is as follows:

[0086] V' O =V2+i dc R2……(39)

[0087] According to the law of conservation of energy, i dc The average value can be determined based on the power P transferred from the primary side to the secondary side of the DAB converter. DAB With V O The mean is calculated as shown in the formula, where, V represents O The average value over a period of time.

[0088]

[0089] Output voltage V o It can also be expressed as a function of d², and calculated using the following formula:

[0090] V o =V1+d2V dc ……(41)

[0091] When the value of resistor R2 is fixed, the output voltage V o When stable. Substituting the equation into the expression, we get the following expression:

[0092]

[0093] P DAB It can be represented as d1, d2, d ps The function is shown in the equation, where f(d1,d2,d) ps The expressions for ) are shown in Table 1;

[0094]

[0095] Substituting the equation into the formula, the voltage V of the voltage regulator capacitor C1 can be calculated. dc The expression is as shown in the formula:

[0096]

[0097] Based on equations , , and , we can derive P. 总 The expression is shown in the following formula:

[0098]

[0099] Substituting the equation into the expression, we get P. 总 The relationship between the control variables and the control variables is shown in the following formula:

[0100]

[0101] According to d1, d2, d ps The DAB converter can be divided into 12 operating modes, and the values ​​of f(d1,d2,d) vary in different operating modes. ps The expression is shown in Table 1. The expression f(d1,d2,d...) in Table 1... ps Substituting the expression into the formula, we can obtain P. 总 With control quantities d1, d2, d ps The relationship between them.

[0102] Table 1. Operating modes of DAB converters and corresponding power relationships

[0103]

[0104] Reverse power regulation mode:

[0105] In reverse power regulation mode, S 22 With S 26 Maintain conduction. S 11-S 14 The drive pulse remains consistent with that in boost mode, S 21 With S 24 The driving pulse is centrally symmetrical with respect to S. 25 Complementary driving pulses. S 23 With S 25 Complementary driving pulses. d ps S represents 11 The driving pulse leads S 21 The phase of the drive pulse. In buck mode, d1 and d2 range from [0.5, 1]. ps The value range is [-0.75, 0.25]. The following section will calculate P under reverse power regulation mode. 总 The relationship between the control variables and the control variables.

[0106] In reverse power regulation mode, V O The calculation method is basically the same as in boost mode, because V dc To change the polarity, the expression needs to be changed to the expression, and the expression needs to be changed to the expression:

[0107]

[0108]

[0109] After the modification, V dc The expression is shown in the following formula:

[0110]

[0111] Combining the formulas, we can obtain P. 总 The expression is as shown in the formula:

[0112]

[0113] Power flow controller parameter design:

[0114] like Figure 1 In the power flow controller circuit topology shown, it is necessary to consider L eq L f C f The design is based on the parameters of three passive components. Among them, L... eq L can be calculated based on the rated power transmitted by the converter. f C f It can be calculated based on the output voltage and current ripple magnitude.

[0115] In forward power regulation mode, according to the formula, the expression for the total power transmitted by the converter can be obtained, as shown in the formula:

[0116]

[0117] Similarly, in buck mode, the expression for the total transmitted power can be derived, as shown in the equation:

[0118]

[0119] The rated power of the power flow controller under both operating modes can be obtained from the formula. In the formula, the values ​​of each voltage and the transformer turns ratio can be determined based on the DC power supply voltage and the load voltage range. Therefore, L can be determined from the rated power of the converter. eq The value.

[0120] L f With C f The output port LC filter has the transfer function shown in the equation:

[0121]

[0122] In the formula, Let S = jω, then the expression can be transformed into the expression:

[0123]

[0124] like Figure 1 As shown, the input voltage of the LC filter at the output terminal is V. f The output voltage is V O '。 V f It can be expressed as DC quantity and ripple. When d2 = 0.5, V f The ripple amplitude is at its maximum, as shown in the following expression:

[0125]

[0126] According to the formula, V can be calculated. O The expression is shown in the formula, where...

[0127]

[0128] As shown in the equation, V O It can be expressed as the sum of the DC component and the AC component, when V1 and V dc When both are determined, a suitable LC value can be calculated based on the requirements of load voltage ripple and filter current ripple.

[0129] Analysis of the soft-switching regulation capability of the power flow controller:

[0130] For the 10 IGBT elements in the power flow controller, the conditions for achieving zero voltage switching (ZVS) are as follows:

[0131]

[0132] In the formula, i DAB (t) represents the corresponding IGBT turn-on instant. DAB The current value, v ac2 (t) represents the corresponding IGBT turn-on moment v ac2 The voltage value. Q oss (V1) indicates that the IGBT is in the off state, and the voltage across it is V1. The parasitic capacitance C... oss The value of the charge stored on the IGBT can be obtained by consulting the datasheet of the selected IGBT.

[0133] Of the 12 operating modes in Table 1, 7 modes can potentially achieve ZVS for all 8 IGBTs in switching states. The ZVS conditions for the power flow controller are shown in Table 2. The table lists the i values ​​for each mode. DAB (t0)—i DAB (t3) should meet the requirements of equation ③.

[0134] Table 2 ZVS Conditions for Power Flow Controller

[0135]

[0136] To verify the technical solution proposed in this invention, a simulation environment based on Plesc was established as follows: Figure 1 The system model shown is shown.

[0137] Application scenario: DC power flow control

[0138] Based on the proposed DC power flow controller topology and actual engineering requirements, the application scenario is set as follows: DC system voltages on both sides V1 = V2 = 48V; in reverse power regulation mode, DC grid 2 outputs 169.59W; in forward power regulation mode, DC grid 2 receives 169.43W; transformer T... r1 The turns ratio n = 50, and the line resistance R2 = 0.2Ω.

[0139] Buck mode simulation verification

[0140] Based on the determined application scenario, and further using the formula, the AC equivalent inductance L is determined. eq The inductance is 100uH, and the output LC filter parameters are: L f =500uH, C f =1mF.

[0141] When the converter operates in buck mode, with d1 = 0.6 and d2 = 0.7, d ps When = 0.016, the circuit's operating waveform is as follows: Figure 4 As shown, the total power P transmitted by the converter at this time总 =2.432W, DAB transmission power P DAB = -169.59W. LC filter input current i dc The volatility is 1.207%, and the load voltage V O The volatility is 0.000846%.

[0142] Boost mode simulation verification

[0143] When the converter operates in boost mode, with d1 = 0.6 and d2 = 0.7, d ps When = 0.016, the circuit's operating waveform is as follows: Figure 5 As shown, the total power P transmitted by the converter at this time 总 =169.43W, DAB transmission power P DAB =2.435W. LC filter input i dc The current fluctuation rate is 1.206%, and the load voltage V O The volatility is 0.000821%.

[0144] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0145] Those skilled in the art will understand that, in addition to implementing the system, apparatus, and their modules provided by this invention in purely computer-readable program code, the same program can be implemented in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system, apparatus, and their modules provided by this invention can be considered a hardware component, and the modules included therein for implementing various programs can also be considered structures within the hardware component; alternatively, modules for implementing various functions can be considered both software programs implementing the method and structures within the hardware component.

[0146] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A single-stage voltage source type DC power flow controller, characterized in that, include: The voltages V1 and V2 of the first and second DC power grids, and the intermediate frequency transformer T r1 The equivalent inductance L formed by the leakage inductance and the auxiliary inductance connected in series eq The secondary-side converter includes a voltage regulator capacitor C1, an output-side LC filter and line resistor R2, and 10 insulated-gate bipolar transistors (IGBTs), which are S... 11 S 12 S 13 S 14 S 21 S 22 S 23 S 24 S 25 S 26 The output-side LC filter consists of a filter inductor L. f With filter capacitor C f Composition: The first DC power grid is connected to one end of a converter consisting of 10 IGBTs and Tr1. The other end of the converter is connected to the voltage regulator capacitor C1. The positive terminal of the first DC power grid is connected to S. 22 The emitter is connected to the phase, and the negative terminal of the first DC power grid is connected to S. 24 The emitters are connected; the output of the output-side LC filter is connected to the line resistor R2 and the second DC power grid. 10 insulated gate bipolar transistors and T r1 This constitutes a dual active bridge converter (DAB) structure. S 11 S 12 S 13 S 14 The connection relationship is: S 11 S 13 Emitter and S 12 S 14 Collector phase connection, S 11 S 13 The collector is connected to the positive terminal of the first DC power grid, S 12 S 14 The emitter is connected to the negative terminal of the first DC power grid, forming a full-bridge converter FB. The AC measurement is connected to T. r1 Connect the original edges; S 21 S 22 S 23 S 24 S 25 S 26 The connection relationship is: S 21 S 23 Emitter and S 22 S 24 Collector phase connection, S 22 S 24 Emitter and S 25 S 26 Collector phase connection, S 25 S 26 The emitter is connected to the voltage regulator capacitor C1, S 21 S 23 The collector and the voltage regulator capacitor C1 are connected to form a full-bridge converter FB, and the AC measurement is connected to T. r1 Secondary edges are connected, S 22 The emitter is connected to the positive terminal of voltage V1, S 24 Emitter and filter inductor L f Connected; C f This is the output filter capacitor, with its two ends connected to the filter inductor L. f Connected to the negative terminal of the first DC power grid; When V1 = V2, in positive power regulation mode, V2 <V O '; When V1 = V2, in reverse power regulation mode, V2 > V O '; Among them, V O ' represents the output voltage of the power flow controller, which is the sum of the voltages of R2 and V2; n is the voltage of T. r1 Transformation ratio; d1 represents S 11 The duty cycle of the driving pulse; d ps S represents 11 The driving pulse leads S 21 The phase of the drive pulse; f represents the switching frequency of each IGBT; d2 represents S 21 The duty cycle of the driving pulse; P 总 Transmits total power to the converter.

2. The single-stage voltage source type DC power flow controller according to claim 1, characterized in that, In boost mode, S 25 With S 24 Maintain conduction; S 11 With S 14 The driving pulse is centrally symmetrical with respect to S. 12 Drive pulse complementarity; S 21 With S 26 The driving pulse is centrally symmetrical with respect to S. 22 Drive pulse complementarity; S 13 With S 14 Drive pulse complementarity; S 23 With S 26 Drive pulse complementarity; In the forward power regulation mode, the output voltage expression of the power flow controller is shown in equation (1): V' O =V2+i dc R2……(1) Among them, i dc This represents the input current of the LC filter; according to the law of conservation of energy, i dc The average value is based on the power P transferred from the primary side to the secondary side of the DAB converter. DAB With V O The mean is calculated as shown in equation (2), where, V represents O The average value over a period of time, V O S represents 24 Emitter and S 22 Voltage difference between emitters; Among them, V dc This represents the voltage across the voltage regulator capacitor C1; Output voltage V o When expressed as a function of d2, it is calculated using equation (3): In o '=V1+d2V dc ……(3) When the value of resistor R2 is fixed, the output voltage V o When stable, substituting equations (2) and (3) into equation (1) yields equation (4): P DAB Represented as d1, d2, d ps The function is shown in equation (5); Substituting equation (5) into equation (4), the voltage V of the stabilizing capacitor C1 is calculated. dc The expression is shown in equation (6): Based on equations (2), (3), and (5), we obtain P. 总 The expression for is shown in equation (7): Substituting equation (6) into equation (7), we get P 总 The relationship between the control variables and the control variables is shown in Equation (8).

3. The single-stage voltage source type DC power flow controller according to claim 2, characterized in that, In reverse power regulation mode, S 22 With S 26 Maintain conduction, S 11 With S 14 The driving pulse is centrally symmetrical with respect to S. 12 Drive pulse complementarity; S 13 With S 14 Drive pulse complementarity; S 21 With S 24 The driving pulse is centrally symmetrical with respect to S. 25 Drive pulse complementarity; S 23 With S 24 Drive pulse complementarity; Due to V dc By changing the polarity, equation (3) is changed to equation (9), and equation (2) is changed to equation (10): After the modification, V dc The expression is shown in equation (11): Combining equations (5), (6), (7), and (10), we obtain P. 总 The expression is shown in equation (12).

4. The single-stage voltage source type DC power flow controller according to claim 3, characterized in that, For L eq L f C f The design is based on the parameters of three passive components, including L. eq Calculated based on the rated power transmitted by the converter, L f C f Calculated based on the output voltage and current ripple magnitude; In the forward power regulation mode, according to equation (7), the expression for the total power transmitted by the converter is obtained, as shown in equation (13): Similarly, in buck mode, the expression for the total transmitted power is derived, as shown in equation (14): From equations (13) and (14), the rated power of the power flow controller under the two operating modes is obtained. In the equations, the values ​​of each voltage and the transformer turns ratio are determined according to the DC power supply voltage and the load voltage range. Therefore, L is determined by the rated power of the converter. eq The value; L f With C f The output port LC filter is constructed, and its transfer function is shown in equation (15): Where S represents the complex frequency after the Laplace transform; ω C This represents the resonant angular frequency of the LC filter; In equation (15), Let S = jω, then equation (15) can be transformed into equation (16): Where j is the complex unit; ω represents the angular frequency of the circuit; The input voltage of the output LC filter is V f The output voltage is V O ', V f Expressed as DC quantity and ripple, when d2 = 0.5, V f The ripple amplitude is at its maximum at time t. f The expression V f (t) is shown in equation (17): Where t is the moment in which the DC power flow controller is located; According to equations (16) and (17), V is calculated. O The expression is shown in equation (18), where... in, This represents the phase shift angle produced by the LC filter in response to the input voltage at an angular frequency of ω. When V1 and V dc When both are determined, a suitable LC value is calculated based on the requirements of load voltage ripple and filter current ripple.

5. The single-stage voltage source type DC power flow controller according to claim 4, characterized in that, Analysis of the soft-switching regulation capability of the power flow controller: For the 10 IGBT elements in the power flow controller, the condition for achieving soft-switching ZVS is shown in equation (19): In equation (19), i DAB (t) represents the corresponding IGBT turn-on instant. DAB The current value; v ac2 (t) represents the corresponding IGBT turn-on moment v ac2 The voltage value; Q oss (V1) indicates that the IGBT is in the off state, and the voltage across it is V1. The parasitic capacitance C... oss The value of the charge stored on the IGBT is obtained by consulting the datasheet of the selected IGBT.

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