A control method of a new energy medium-voltage direct-current converter topology structure

Abstract

This invention discloses a control method for a new energy medium-voltage DC-DC converter topology, belonging to the technical field of power generation, transformation, or distribution. The topology consists of a diode-clamped three-level half-bridge, a two-level half-bridge, a transformer, and a full-bridge rectifier module. The three-level and two-level half-bridges are combined to form a low-voltage side composite inverter circuit. The two capacitors in the three-level half-bridge and the transformer leakage inductance together form a resonant cavity. This invention proposes a piecewise linear-resonant hybrid control method, employing intermediate frequency PWM modulation. In addition to achieving maximum power point tracking and a wide voltage input range, it makes the waveform of the primary-side inductor current appear sinusoidal and close to a trapezoidal wave, significantly reducing device current stress. It also achieves zero-current turn-on for all switching devices and zero-current turn-off for the two-level half-bridge switches. Combined with the intermediate frequency switching frequency, it can effectively reduce device switching losses, improve the reliability of the DC-DC converter, and increase operating efficiency while reducing converter costs.

Description

Technical Field

[0001] This invention relates to the design of DC converters for medium-voltage DC collection sections in new energy power generation, specifically disclosing a control method for the topology of a new energy medium-voltage DC converter, belonging to the technical field of power generation, transformation, or distribution. Background Technology

[0002] With the depletion of traditional fossil fuels and the increasing severity of global environmental problems, renewable energy generation, especially photovoltaic and wind power, has received growing attention worldwide. In my country, regions rich in new energy resources are often far from load centers, requiring power grids with long-distance, efficient transmission capabilities. Traditional AC systems face various difficulties and challenges when integrating large-scale new energy sources. Medium-voltage DC aggregation combined with high-voltage DC transmission is rapidly developing, reducing long-distance transmission losses, increasing transmission capacity, and improving system stability. Compared to AC aggregation technology, the DC converter in a medium-voltage DC aggregation system can interconnect photovoltaic systems with DC grids and DC transmission and distribution networks of different voltage levels. It features high power density, small size, and light weight, eliminating the need for bulky power frequency transformers, resulting in lower transportation and installation costs and a smaller footprint. The DC converter offers flexible control, functioning not only as a step-up, isolation, and power transfer mechanism but also as a port voltage regulator and power regulator. However, in practical applications, issues arise such as excessive current and voltage stress on switching devices and high switching losses due to high switching frequencies.

[0003] To address the issue of high voltage and current stress, multilevel circuits can significantly reduce the voltage stress on switching devices; in a three-level circuit, the voltage stress on the switching devices is only half that of the input voltage. Replacing the left arm of a full-bridge converter with a three-level arm while keeping the right arm as a two-level arm creates a composite full-bridge three-level converter, which can reduce the voltage stress on the three-level arm. However, the current stress on the switching devices in this composite full-bridge three-level converter is not reduced, and the overall DC transformer has high cost and losses. Using a high-frequency DC-DC converter can reduce the transformer size, and combined with appropriate control methods, can effectively solve the voltage and current stress problem; however, large-capacity high-frequency transformers are expensive, and switching losses also increase significantly.

[0004] Considering the shortcomings of existing technologies, this patent aims to provide a control method for the topology of a new energy medium-voltage DC-DC converter to overcome the above-mentioned defects. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the aforementioned background technology by providing a control method for the topology of a new energy medium-voltage DC-DC converter. This method reuses the voltage regulator capacitor in a three-level half-bridge converter as a resonant capacitor, and combines it with a piecewise linear-resonant hybrid control method. While ensuring maximum power point tracking and a wide range of input voltage variations, it reduces switching losses through intermediate frequency switching and soft switching, and achieves low current stress on the converter's switching devices through an approximately trapezoidal current waveform. This meets the current requirements of high boost ratio, high efficiency, large capacity, and low switching stress in new energy medium-voltage DC-DC aggregation systems, solving the technical challenge of reducing current stress on switching devices while maintaining high efficiency in composite full-bridge three-level converters.

[0006] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0007] A control method for a new energy medium-voltage DC-DC converter topology, comprising: a diode-clamped three-level half-bridge, a two-level half-bridge, a transformer with at least one secondary winding, and at least one full-bridge rectifier module. The diode-clamped three-level half-bridge and the two-level half-bridge form a low-voltage side composite inverter circuit. The diode-clamped three-level half-bridge includes: a first capacitor, a second capacitor, a first diode, a second diode, and first to fourth switching transistors. The two-level half-bridge is composed of a fifth and a sixth switching transistor connected in series. The input port of the low-voltage side composite inverter circuit formed by the first and second capacitors connected in series is connected to a low-voltage input port. The three-level half-bridge formed by the first to fourth switching transistors connected in series is connected in parallel to the low-voltage input port. The cathode of the first diode is connected to the connection point of the first and second switching transistors. The anode of the first diode and the cathode of the second diode are connected to the connection point of the first and second capacitors. The anode of the second diode is connected to the connection point of the third and fourth switching transistors. The two-level half-bridge and the three-level half-bridge are connected in parallel. The connection point of the second and third switching transistors and the connection point of the fifth and sixth switching transistors constitute the output port of the low-voltage side composite inverter circuit. The output port of the low-voltage side composite inverter circuit is connected to the primary winding of the transformer. The input terminal of each full-bridge rectifier module is connected to a secondary winding of the transformer. The output terminal of each full-bridge rectifier module constitutes a high-voltage output port. Each high-voltage output port is connected to an output filter capacitor. The high-voltage output ports are connected in series to form a high-voltage port.

[0008] The control method uses intermediate frequency PWM modulation to make the transformer primary inductor current first increase linearly to a stable value in the positive half-cycle, then change along a sine wave trajectory, and finally decrease linearly to zero. The waveform of the transformer primary inductor current in the negative half-cycle is symmetrical to that in the positive half-cycle.

[0009] As a further optimization method for the control of the topology of a new energy medium-voltage DC-DC converter, the control method uses intermediate frequency PWM modulation to make the transformer primary-side inductor current first linearly increase to a stable value during the positive half-cycle, then change along a sine wave trajectory, and finally linearly decrease to zero. Specifically, it includes the following four operating modes:

[0010] In operating mode one, the first, second, and sixth switches, which are turned on with zero current, remain in the conducting state, and the transformer primary inductance current increases linearly from zero to a stable value;

[0011] In operating mode two, the second and sixth switches remain on while the first switch is off. The transformer leakage inductance, the first capacitor, and the second capacitor form a resonant cavity, and the transformer primary inductance current changes sinusoidally.

[0012] In operating mode three, the sixth switch remains on, the first switch remains off, the second switch is turned off, and the transformer primary inductance current decreases linearly to zero.

[0013] Operating mode four: The sixth switch, which remains on, is turned off at the end of the positive half-cycle.

[0014] As a further optimization scheme for the control method of a new energy medium-voltage DC-DC converter topology, the start time of the second operating mode is obtained by subtracting the input voltage reference value from the sampled value of the DC input voltage connected to the low-voltage input port and outputting it through a PI controller.

[0015] As a further optimization scheme for the control method of a medium-voltage DC-DC converter topology in a new energy source, the end time of the second operating mode is solved by simultaneously solving the volt-second balance equation and the expression for the power transmitted during the positive half-cycle.

[0016] As a further optimization scheme for the control method of a medium-voltage DC-DC converter topology in a new energy source, the volt-second balance equation is: The expression for the transmitted power during the positive half-cycle is: ,in, The start time of mode two The primary inductor current at time , For transformer leakage inductance, Let be the capacitance value of the first capacitor, which is equal to the capacitance value of the second capacitor. The end time of mode two. The start time of mode two The voltage of the second capacitor, This is the high-voltage port voltage. For transformer turns ratio, The end time of running mode three, This represents the power transmitted during the positive half-cycle. For the intermediate frequency period time, for The primary inductor current at time t.

[0017] The present invention, by adopting the above technical solution, has the following beneficial effects:

[0018] 1. The piecewise linear-resonant hybrid control method of the present invention reuses the two capacitors of the diode-clamped three-level half-bridge in the DC converter as resonant capacitors during the resonance stage, which can make the waveform of the primary inductor current of the converter present a sinusoidal and trapezoidal wave, significantly reducing the current stress of the switching devices.

[0019] 2. The piecewise linear-resonant hybrid control method of the present invention adopts intermediate frequency PWM modulation and realizes zero-current turn-on of all switching devices and zero-current turn-off of two-level half-bridge switching transistors, thereby reducing the switching losses of the converter and improving operating efficiency.

[0020] 3. By designing the switching frequency and resonant frequency at the intermediate frequency, this invention reduces switching losses and transformer costs compared to high-frequency converters, and reduces transformer size compared to low-frequency converters. This allows for more flexible transformer design, improves the reliability of DC-DC converters, and reduces costs and losses. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0022] Figure 1 This is a topology diagram of a new energy medium-voltage DC-DC converter provided in an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the basic working waveforms of the new energy medium-voltage DC converter in an embodiment of the present invention.

[0024] Figure 3 This is the equivalent circuit diagram of the resonant cavity of the converter in mode 2 during the positive half-cycle in an embodiment of the present invention.

[0025] Figure 4 This is a control block diagram of a new energy medium-voltage DC converter in an embodiment of the present invention.

[0026] Figure 5 This is the polynomial fitting result of t2=f(t1) during the converter control process in the embodiment of the present invention.

[0027] Figures 6(a) to 6(c)The following are simulated waveforms of the input voltage at the low-voltage input port, the output voltage of the low-voltage side composite inverter, and the leakage inductance current when the DC input voltage reference value of the converter is equal to 1000V, 1250V, and 1500V under rated load in the embodiments of the present invention.

[0028] Figures 7(a) to 7(c) The following are simulated waveforms of the input voltage at the low-voltage input port, the output voltage of the low-voltage side composite inverter, and the leakage inductance current when the DC input voltage reference value of the converter is equal to 1000V, 1250V, and 1500V under half-load conditions in the embodiments of the present invention.

[0029] Figures 8(a) to 8(b) This is a dynamic simulation waveform diagram of the converter under rated load and half load conditions when the DC input voltage jumps in an embodiment of the present invention.

[0030] Explanation of the labels in the diagram: V in For DC input voltage, C r1 ~C r2 The first and second capacitors are represented by Q1 to Q6, the first to sixth switching transistors are represented by D1 to D2, the first and second diodes are represented by D, and the transformer is represented by L. r For transformer leakage inductance, N p For the primary winding, N s1 ~N s2 For the first secondary winding and the second secondary winding, D R1 ~D R8 For the first to eighth secondary-side diodes, C o1 ~C o2 These are the first output filter capacitor and the second output filter capacitor. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0032] Please see Figure 1 The illustrated new energy medium-voltage DC-DC converter topology consists of a diode-clamped three-level half-bridge, a two-level half-bridge, a transformer T, at least one full-bridge rectifier module, and at least one output filter capacitor. The diode-clamped three-level half-bridge and the two-level half-bridge together form a low-voltage side composite inverter circuit. The DC input voltage V inThe AC power output from the low-voltage side composite inverter circuit is stepped up by transformer T and transmitted to each full-bridge rectifier module. After being rectified by each full-bridge rectifier module, the AC power is output to the high-voltage output port. The high-voltage output ports are connected in series to form a high-voltage port, which is used to collect high-voltage DC power.

[0033] In the low-voltage side composite inverter circuit, the first capacitor C r1 Second capacitor C r2 After being connected in series to form the input port of the low-voltage side composite inverter circuit, the first switch Q1 to the fourth switch Q4 are connected in series to form a three-level half-bridge and then connected in parallel to the low-voltage input port. The fifth switch Q5 and the sixth switch Q6 are connected in series and then connected in parallel to the three-level half-bridge. The connection point of the second switch Q2 and the third switch Q3 forms the midpoint A of the bridge arm of the three-level half-bridge. The connection point of the fifth switch Q5 and the sixth switch Q6 forms the midpoint B of the bridge arm of the two-level half-bridge. The midpoint A of the three-level half-bridge and the midpoint B of the two-level half-bridge form the output port of the low-voltage side composite inverter circuit. The cathode of the first diode D1 is connected to the connection point of the first switch Q1 and the second switch Q2. The anode of the first diode D1 and the cathode of the second diode D2 are connected to the first capacitor C. r1 Second capacitor C r2 The connection point of the first diode is connected, and the anode of the second diode D2 is connected to the connection point of the third switch Q3 and the fourth switch Q4.

[0034] Transformer T includes at least one secondary winding and primary winding N. p The upper end is connected to the midpoint A of the bridge arm of the three-level half-bridge, and the primary winding N p The lower end is connected to the midpoint B of the two-level half-bridge arm. The first capacitor C... r1 Second capacitor C r2 In this embodiment of the invention, the transformer leakage inductance L is used as a resonant capacitor. r With two resonant capacitors C r1 and C r2 Together they form a resonant cavity.

[0035] In the secondary rectifier circuit, the first secondary winding N s1 Connect the input port of the full-bridge rectifier module 1, and the second secondary winding N s2 Connect the input port of the full-bridge rectifier module 2; in the full-bridge rectifier module 1, the first secondary diode D R1 Secondary diode D R2 The first bridge arm of the full-bridge rectifier module 1 is formed by connecting diodes in series, and the third secondary diode is D. R3 and the fourth secondary diode D R4The two bridge arms are connected in series to form the second bridge arm of the full-bridge rectifier module 1. The midpoint of the two bridge arms constitutes the input port of the full-bridge rectifier module 1. The second bridge arm is connected in parallel with the first bridge arm to form the high-voltage output port 1. The first output filter capacitor C is connected in parallel to the high-voltage output port 1. o1 The full-bridge rectifier module 2 has the same circuit structure as the full-bridge rectifier module 1, consisting of the fifth secondary diode D. R5 Up to the eighth secondary diode D R8 and the second output filter capacitor C o2 Composition: Full-bridge rectifier module 1 and full-bridge rectifier module 2 can output reverse polarity medium-voltage DC voltage.

[0036] Please see Figure 2 As shown Figure 1 The basic operating waveforms and timing sequence of the example DC-DC converter under the control method proposed in this invention are as follows:

[0037] At time t0, which marks the start of a positive half-cycle, the first switch Q1, the second switch Q2, and the sixth switch Q6 are simultaneously turned on, driven by the primary inductor current i. Lr The waveform shows that before time t0, no current flows through the first switch Q1, the second switch Q2, and the sixth switch Q6. The first switch Q1, the second switch Q2, and the sixth switch Q6 are ZCS turned on.

[0038] The time period t0-t1 is operating mode 1. During this period, the first switch Q1, the second switch Q2, and the sixth switch Q6 in the three-level half-bridge remain on, and the output voltage v of the low-voltage side composite inverter is... AB =V in Leakage L r The voltage on is the DC input voltage V. in Subtract the primary voltage of the transformer, and the primary inductor current i Lr Starting from zero, it increases linearly; during this period, the first secondary diode D... R1 Fourth secondary diode D R4 and the fifth secondary diode D R5 The eighth secondary diode D R8 Activation;

[0039] (1)

[0040] During the time period t1-t2, in operating mode 2, the sixth switch Q6 and the second switch Q2 remain on, while the first switch Q1 in the three-level half-bridge is turned off, and the low-voltage side composite inverter output voltage v AB =v Cr2 Leakage L r and the first capacitor C r1 Second capacitor C r2Resonance occurs; please refer to the equivalent circuit diagram of this modal resonator. Figure 3 Primary inductor current i Lr Sinusoidal variation can effectively reduce device current stress compared to the intermediate frequency triangular wave operation mode;

[0041] (2)

[0042] (3)

[0043] (4)

[0044] During the time period t2-t3, operating mode 3 is in which the sixth switch Q6 remains on, the first switch Q1 remains off, and the second switch Q2 in the three-level half-bridge is off. The inverter output voltage v AB =0, leakage inductance L r The voltage across the transformer is the negative primary voltage, and the primary inductor current is i. Lr The linear decrease is rapid, and it drops to zero at time t3. At time t3, the first secondary diode D... R1 Fourth secondary diode D R4 and the fifth secondary diode D R5 The eighth secondary diode D R8 Achieve ZCS shutdown;

[0045] (5)

[0046] During the time period t3-t4, which is operating mode 4, although the sixth switch Q6 is on, the output current i Lr The voltage is always zero. At time t4, the lower bridge arm switch Q6 in the two-level half-bridge is turned off, which obviously achieves ZCS turn-off. Time t4 is the end of the first half-switching cycle and the beginning of the second half-switching cycle. After the dead time, the upper bridge arm switch Q5 is turned on, the output voltage of the low-voltage side composite inverter bridge is reversed, and the negative half-cycle begins. The working state is similar to that of the positive half-cycle.

[0047] At the beginning of each intermediate frequency negative half-cycle, the fifth switch Q5 in the two-level half-bridge turns on and remains on throughout the entire negative half-cycle. The third switch Q3 and the fourth switch Q4 in the three-level half-bridge turn on. The output voltage of the low-voltage side composite inverter is equal to the negative DC input voltage, i.e., v. AB =-V in Leakage L r The voltage across the transformer is the DC input voltage minus the negative value of the transformer primary voltage, and the primary inductor current i Lr The voltage drops rapidly and linearly; subsequently, the fourth switch Q4 of the three-level half-bridge turns off, but the third switch Q3 remains on, and the output voltage of the low-voltage side composite inverter equals the first capacitor C.r1 The negative value of the voltage, i.e., v AB =-v Cr1 At this time, leakage L r First capacitor C r1 Second capacitor C r2 Resonance occurs, and the resonant frequency is designed to be lower than the switching frequency. The primary inductor current i Lr It exhibits a slow sinusoidal change; after the resonance phase ends, the third switch Q3 of the three-level half-bridge is turned off, and the output voltage of the low-voltage side composite inverter is equal to zero, i.e., v AB =0, leakage inductance L r The voltage on the transformer is positive, and its absolute value is equal to the voltage on the primary winding of the transformer. The output current rises rapidly and linearly, and drops to zero before the end of the negative half-cycle. At the end of the negative half-cycle, the fifth switch Q5 in the two-level half-bridge is turned off, realizing zero-current turn-off of the fifth switch Q5.

[0048] Since the negative half-cycle and the positive half-cycle operate symmetrically, design C r1 =C r2 =C r Combining equations (2) and (4), the expression for the primary inductor current in mode 2 during the positive half-cycle is:

[0049] (6)

[0050] Equations (1), (6), and (5) together constitute the inductance L within a half-cycle. r From the expression for the current, we obtain the volt-second balance equation:

[0051] (7)

[0052] In equations (6) and (7), for The primary inductor current at time , The start time of mode two The primary inductor current at time , For transformer leakage inductance, Let be the capacitance value of the first capacitor, which is equal to the capacitance value of the second capacitor. The end time of mode two. The start time of mode two The voltage of the second capacitor, This is the high-voltage port voltage. For transformer turns ratio, This is the end time of running mode three.

[0053] From equations (1), (6), and (5), we can also obtain the expression for the transmitted power within half a cycle:

[0054] (8)

[0055] In equation (8), This represents the power transmitted during the positive half-cycle. This is the intermediate frequency cycle time.

[0056] Please see Figure 2 The basic operating waveform of the DC-DC converter shown in the embodiment of the present invention is presented. The present invention proposes a novel piecewise linear-resonant hybrid control strategy. The linear components in mode 1 and mode 3 cause the primary inductor current i to... Lr Rapid rise and fall are employed to minimize the current amplitude under the same power conditions; the resonant operation section in mode 2 mitigates the primary inductor current i by rationally designing the resonant cavity parameters. Lr The rate of change makes the waveform of the primary inductor current exhibit a sinusoidal and trapezoidal effect, which significantly reduces the current stress of the device; Mode 4 realizes soft switching of the switching transistors on the two-level half-bridge, reducing switching losses.

[0057] Please see Figure 4 The converter control block diagram shown illustrates a control method for a new energy medium-voltage DC converter as follows:

[0058] This converter uses intermediate frequency PWM modulation, with the input voltage reference value V in_ref DC input voltage sample value V connected to the low-voltage input port in The difference is the controlled variable R, and the output after the controlled variable passes through the PI control loop is the primary inductor current i. Lr At time t1, when the linear rise phase transitions to the resonance phase, PWM modulation is applied to obtain the modulation waves of the first switch Q1 and the fourth switch Q4. Using the relationship t2=f(t1) between the turn-on time t1 of the first switch Q1 and the turn-on time t2 of the second switch Q2, the modulation waves of the second switch Q2 and the third switch Q3 can be obtained from the modulation waves of the first switch Q1 and the fourth switch Q4. The modulation waves are compared with an intermediate frequency unipolar sawtooth carrier wave, and the output pulse sequence controls the four switches on the three-level half-bridge arm, realizing the on / off state of the three-level half-bridge. The two-level half-bridge arms undergo complementary on / off control with a fixed 50% duty cycle at the intermediate frequency.

[0059] The expression for t2=f(t1) is obtained from equations (7) and (8). By combining the two transcendental equations, the DC input voltage V under different transmission powers can be obtained iteratively. in The numerical solution corresponding to the change can be obtained by plotting all the numerical solutions within the range of DC input voltage variation. Figure 5 The trend depicted by the blue data points is obtained by polynomial fitting, as shown below. Figure 5The red curve represents the polynomial function, i.e., the expression for t2=f(t1), which enables closed-loop control.

[0060] Please see Figures 6(a) to 6(c) The input voltage v at the low-voltage input port of the converter in the embodiment of the present invention is shown when the DC input voltage reference value is equal to 1000V, 1250V, and 1500V under rated load conditions. in Low-voltage side composite inverter output voltage v AB Leakage inductance L r Current i Lr The simulated waveform shows that the rate of rise of the primary inductor current increases with the input voltage v. in The rise time of the primary inductor current increases with the increase of the input voltage v. in The current decreases as the input voltage increases. Throughout the entire input voltage range, the primary-side inductor current rises rapidly at the beginning of each half-cycle, then undergoes a slow sinusoidal change through inductor-capacitor resonance, and finally drops rapidly to zero before the end of the half-cycle. The primary-side inductor current i... Lr The waveform exhibits a sinusoidal shape and is close to a trapezoidal wave, which matches the theoretical waveform.

[0061] Please see Figures 7(a) to 7(c) The input voltage v at the low-voltage input port of the converter in the embodiment of the present invention is shown when the DC input voltage reference value is equal to 1000V, 1250V, and 1500V under half-load conditions. in Low-voltage side composite inverter output voltage v AB Leakage inductance L r Current i Lr The simulation waveforms show that the overall trend of the primary inductor current waveform under half load is the same as that under rated load, but the peak current is reduced, and the zero current time of mode 4 is significantly increased in order to meet the power demand.

[0062] Please refer to Figures 8(a) and 8(b) for the dynamic response waveforms of the converter under rated load and half load conditions when the DC input voltage changes. The DC input voltage jumps from 1500V to 1250V in 0.5s and then abruptly changes to 1000V in 1s. The converter can track the given value within 0.1s and continue to operate stably, indicating that the converter has good dynamic performance when the DC input voltage jumps.

[0063] The control method proposed in this invention first meets the requirements for maximum power point tracking and wide-range input voltage variation under the condition of medium-voltage DC collection of new energy sources. Analysis of the above working process shows that the piecewise linear-resonant hybrid control method adopted in this invention allows the inductor current i... LrThe waveform rapidly rises to near its steady-state value, then forms a slowly changing plateau through resonance. This sinusoidal and trapezoidal waveform significantly reduces the current stress on the devices. Furthermore, the use of a medium-frequency switching frequency facilitates low-cost and flexible transformer design, while also greatly reducing switching losses compared to common high-frequency DC-DC converters. In addition, it enables ZCS turn-on of all switches and ZCS turn-off of the two-level bridge arm switches, further reducing switching losses and improving converter efficiency. This invention's topology, by employing a composite inverter circuit on the low-voltage side, achieves reduced voltage stress on switching devices and increased control flexibility with fewer components, thereby reducing costs. Therefore, the DC-DC converter in this embodiment, combined with the proposed control strategy, can achieve high-efficiency, low-cost, and low-device-stress operation in a new energy medium-voltage DC-DC aggregation system.

[0064] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0065] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention.

Claims

1. A control method for a new energy medium-voltage DC-DC converter topology, wherein the new energy medium-voltage DC-DC converter topology includes: The circuit includes a diode-clamped three-level half-bridge, a two-level half-bridge, a transformer with at least one secondary winding, and at least one full-bridge rectifier module. The diode-clamped three-level half-bridge and the two-level half-bridge form a low-voltage side composite inverter circuit. The diode-clamped three-level half-bridge includes a first capacitor (C...). r1 ), second capacitor (C) r2 The first diode (D1), the second diode (D2), and the first to fourth switching transistors (Q1~Q4) are used. The two-level half-bridge is composed of the fifth switching transistor (Q5) and the sixth switching transistor (Q6) connected in series. The first capacitor (C) r1 ) and second capacitor (C r2 The input port of the low-voltage side composite inverter circuit, which is composed of series connections, is connected to the low-voltage input port. A three-level half-bridge, formed by the first to fourth switches (Q1~Q4) connected in series, is connected in parallel to the low-voltage input port. The cathode of the first diode (D1) is connected to the connection point of the first switch (Q1) and the second switch (Q2). The anode of the first diode (D1), the cathode of the second diode (D2), and the first capacitor (C) are connected to each other. r1 ) and second capacitor (C r1 The connection points of the second diode (D2) and the third and fourth switches (Q3 and Q4) are connected. The two-level half-bridge and the three-level half-bridge are connected in parallel. The connection points of the second and third switches (Q2 and Q3) and the fifth and sixth switches (Q5 and Q6) constitute the output port of the low-voltage side composite inverter circuit. The output port of the low-voltage side composite inverter circuit is connected to the primary winding of the transformer. The input terminal of each full-bridge rectifier module is connected to a secondary winding of the transformer. The output terminals of each full-bridge rectifier module constitute a high-voltage output port. Each high-voltage output port is connected to an output filter capacitor. The high-voltage output ports are connected in series to form a high-voltage port. The characteristic feature is that the control method uses intermediate frequency PWM modulation to make the transformer primary inductor current first linearly increase to a stable value in the positive half-cycle, then change along a sine wave trajectory, and finally linearly decrease to zero. The waveform of the transformer primary inductor current in the negative half-cycle is symmetrical to that in the positive half-cycle.

2. The control method for a new energy medium-voltage DC-DC converter topology according to claim 1, characterized in that, The control method uses intermediate frequency PWM modulation to make the transformer primary inductor current first linearly increase to a stable value during the positive half-cycle, then change along a sinusoidal trajectory, and finally linearly decrease to zero. Specifically, it includes the following four operating modes: In operating mode one, the first, second, and sixth switches, which are turned on with zero current, remain in the conducting state, and the transformer primary inductance current increases linearly from zero to a stable value; In operating mode two, the second and sixth switches remain on while the first switch is off. The transformer leakage inductance, the first capacitor, and the second capacitor form a resonant cavity, and the transformer primary inductance current changes sinusoidally. In operating mode three, the sixth switch remains on, the first switch remains off, the second switch is turned off, and the transformer primary inductance current decreases linearly to zero. Operating mode four: The sixth switch, which remains on, is turned off at the end of the positive half-cycle.

3. The control method for a new energy medium-voltage DC-DC converter topology according to claim 2, characterized in that, The start time of the second operating mode is obtained by subtracting the input voltage reference value from the sampled DC input voltage value connected to the low-voltage input port and outputting the result through a PI controller.

4. The control method for a new energy medium-voltage DC-DC converter topology according to claim 3, characterized in that, The end time of the second operating mode is solved by combining the volt-second balance equation and the expression for the transmitted power during the positive half-cycle.

5. The control method for a new energy medium-voltage DC-DC converter topology according to claim 4, characterized in that, The volt-second balance equation is: The expression for the transmitted power during the positive half-cycle is: ,in, For the start time of mode two The primary inductor current at time , For transformer leakage inductance, Let be the capacitance value of the first capacitor, which is equal to the capacitance value of the second capacitor. The end time of mode two. For the start time of mode two The voltage of the second capacitor, This is the high-voltage port voltage. For transformer turns ratio, The end time of running mode three, This represents the power transmitted during the positive half-cycle. For the intermediate frequency period time, for The primary inductor current at time t.

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