An electronic transformer system and an operating method thereof

Abstract

The present invention discloses an electronic transformer and its operation method, including a high-voltage input part, a DC isolation part, a photovoltaic substring input part, an energy storage battery input part, and the high-voltage input part, the rectified electrical signal enters the DC isolation part for secondary rectification, and outputs AC or DC power; the photovoltaic substring input part and the energy storage battery input part integrate the access of renewable energy and energy storage system. The PID control under the dq rotating coordinate system is adopted to stabilize and regulate the DC side voltage or the AC load terminal voltage by controlling the PWM signal of the H-bridge circuit; the bidirectional transmission of high and low voltage energy of the DC isolation part is achieved by adjusting the shift ratio of the square wave signal; the maximum power tracking control method or the maximum power internal power output is adopted to realize the maximum utilization of photovoltaic power generation; the coordinated control of each part completes the stable power supply of DC and AC.

Description

Technical Field

[0001] The present invention relates to the field of transformers, and in particular to an electronic transformer and an operating method thereof. Background Art

[0002] Most of the transformers used in power systems are still traditional iron-core oil-immersed power transformers. With the rapid development of power systems, the defects and shortcomings of traditional transformers have become increasingly prominent, such as heavy weight, large size, and large device losses when running without load; iron core magnetic saturation will cause the generation of harmonics in the system, resulting in large excitation inrush currents in the power grid; harmonics on one side will invade the other side, causing the fault to expand; voltage amplitude fluctuations on the primary side will affect the output voltage on the secondary side; changes in load will affect the output voltage, etc.

[0003] Like traditional power transformers, power electronic transformers can achieve voltage conversion, electrical isolation and power transmission, but they do not have the above-mentioned disadvantages of traditional iron core oil-immersed power transformers. In addition, power electronic transformers can also correct power factor, adjust output voltage, suppress harmonics, etc.

[0004] The power electronic transformer itself has both a DC link and an AC link. Conventional photovoltaic power generation equipment needs to invert DC power into AC power before it can be used by the equipment or connected to the Internet through a conventional iron core transformer. DC power equipment needs to rectify AC power into DC power before it can be used, and energy storage equipment needs to rectify DC power into AC power before it can be charged and needs to invert DC power into AC power when releasing power.

[0005] In distributed photovoltaic power generation sites, the equipment capacity is small, and the use of single-phase transformers can reduce equipment investment and have a higher cost-effectiveness. In this site, photovoltaic power generation equipment, DC power equipment and even energy storage equipment are connected to the DC link of the current electronic transformer, and the power electronic transformer controller is used to uniformly control the above equipment to form a multifunctional single-phase power electronic transformer with photovoltaic grid connection, energy storage, AC and DC power supply. Summary of the invention

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract of the specification and the title of the invention of this application to avoid blurring the purpose of this section, the abstract of the specification and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0007] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0008] Therefore, the technical problem to be solved by the present invention is to provide a photovoltaic grid-connected single-phase power electronic transformer topology structure.

[0009] To solve the above technical problems, the present invention provides the following technical solutions: an electronic transformer system, comprising: a high voltage input part, including a first H-bridge module, namely B1, B2, and B3;

[0010] The DC isolation part includes a high voltage part, a high frequency transformer and a low voltage part, and is connected to the AC output part and the DC output part at the output end;

[0011] PV substring input part, including Boost circuit;

[0012] Energy storage battery input part, including Boost Buck bidirectional conversion circuit;

[0013] The high voltage input part rectifies the electric signal through the first H-bridge module and enters the DC isolation part for secondary rectification to output AC or DC power;

[0014] The photovoltaic substring input part and the energy storage battery input part integrate the access of renewable energy and energy storage system.

[0015] As a preferred solution of the electronic transformer system described in the present invention, wherein: the B1, B2, and B3 are connected in series through a reactor 1 to the line voltage of the AC 10kV distribution network;

[0016] Furthermore, the B1, B2, B3 are respectively connected in parallel with high-voltage DC capacitors C1, C2, C3 on the DC side.

[0017] As a preferred solution of the electronic transformer system of the present invention, the high voltage part is composed of the same number of H bridges as the high voltage input part, namely B4, B5, B6;

[0018] The H-bridge DC side of the high-voltage part is connected one by one with the first H-bridge module, and the AC side is connected one by one with the high-voltage winding on the high-frequency transformer;

[0019] The low voltage part is composed of the same number of H bridges as the high voltage part, namely B7, B8, and B9. The DC side of the H bridge of the low voltage part is connected one by one with the low voltage winding on the high frequency transformer (T).

[0020] As a preferred solution of the electronic transformer system of the present invention, wherein: the AC output part includes a DC capacitor C4 and a terminal H bridge B10;

[0021] One side of the DC capacitor C4 is connected to the DC side of the H-bridge of the low voltage part, and the other side is connected to the DC side of the terminal H-bridge B10. The electrical signal is output from the AC side of the H-bridge B10 to connect to the AC load.

[0022] The DC output part is composed of a plurality of Buck step-down circuits, the input ends of all Buck step-down circuits are connected to the DC side of the H-bridge of the low-voltage part, and the output section outputs the DC voltage in stages.

[0023] As a preferred solution of the electronic transformer system described in the present invention, wherein: the input end of the Boost circuit is connected in parallel with a photovoltaic panel, and the output end is connected to the DC side of the low-voltage part H bridge;

[0024] The input end of the Boost Buck bidirectional conversion circuit is connected to the energy storage battery, and the output end is connected to the DC side of the low voltage part H bridge.

[0025] As a preferred solution of the electronic transformer system described in the present invention, the H bridges are all power electronic switches such as IGBTs or diodes.

[0026] The beneficial effects of the present invention are as follows: a multi-dimensional power supply is realized, and an electronic transformer with small no-load loss and excitation inrush current is achieved, thereby reducing the loss cost of inversion and rectification.

[0027] Given that power electronic transformers need to operate through appropriate operating logic and rules when performing tasks such as grid connection, energy storage, and multi-dimensional power supply.

[0028] Therefore, the technical problem to be solved by the present invention is to provide a control method for a photovoltaic grid-connected single-phase power electronic transformer topology structure.

[0029] In order to solve the above technical problems, the present invention also provides the following technical solutions: an electronic transformer operation method, comprising the electronic transformer system, and, using PID control in a dq rotating coordinate system, by controlling the PWM signal of the H-bridge circuit, achieving unity power factor operation, thereby stabilizing and regulating the DC side voltage or the AC load terminal voltage;

[0030] By adjusting the shift ratio of the square wave signal, the direction and size of the power flow are controlled to achieve bidirectional transmission of high and low voltage energy in the DC isolation part;

[0031] Adopt maximum power tracking control method or maximum power internal power output to maximize the utilization of photovoltaic power generation;

[0032] Adopt square wave control to control the battery charging and discharging process and the output DC voltage level by adjusting the duty cycle;

[0033] Each part coordinates and controls to achieve stable power supply of DC and AC.

[0034] As a preferred solution of the electronic transformer operation method of the present invention, the PWM control of the power electronic switch or diode such as IGBT of the high voltage input part includes:

[0035] The single-phase input sine current signal I is equivalent to a three-phase signal, and PARK transformation is performed to obtain Id and Iq, and PID control is performed according to Id and Iq;

[0036] The rotation angle required for dq coordinate transformation is calculated using the rotating coordinate system wt;

[0037] The d-axis voltage Vd of the grid voltage is obtained through Fourier transform;

[0038] The carrier phase-shifted SPWM method is used to complete PWM control of power electronic switches such as IGBTs.

[0039] As a preferred embodiment of the operation method of an electronic transformer according to the present invention, wherein: the PWM control of power electronic switches such as IGBTs or diodes in the DC isolation part includes,

[0040] A 50% duty cycle square wave PWM input signal is adopted, and the magnitude and direction of D are controlled by adjusting the phase shift ratio within half a cycle of the square wave signals in the high-voltage part and the low-voltage part, so as to control the flow direction and magnitude of power.

[0041] When 0 < D < 1, power is transmitted from the high-voltage part to the low-voltage part; when -1 < D < 0, power is transmitted from the low-voltage part to the high-voltage part, and when D = 0, no power is transmitted.

[0042] As a preferred embodiment of the operation method of an electronic transformer according to the present invention, wherein: the PWM control of power electronic switches such as IGBTs or diodes in the AC output part includes,

[0043] The actual voltage Vx at the AC load end is equivalent to a three-phase signal, and PARK transformation is performed according to the three-phase signal to obtain the fixed values Ud and Uq in the dq rotating coordinate system;

[0044] The reference currents Id and Iq in the dq rotating coordinate system are obtained through PID regulation;

[0045] The d-axis voltage Vd and q-axis voltage Vq of the AC output side are calculated according to electrical related knowledge;

[0046] After transformation from the dq0 coordinate system to the abc coordinate system to obtain three-phase voltages, taking the A-phase voltage Ua as the reference voltage, after carrier modulation PWM, it is used as the PWM control of power electronic switches such as IGBTs in the AC output part.

[0047] As a preferred embodiment of the operation method of an electronic transformer according to the present invention, wherein: the PWM control of power electronic switches such as IGBTs or diodes in the Boost circuit and the Boost Buck bidirectional conversion circuit includes,

[0048] The boost circuit of the photovoltaic substring input part adopts the maximum power tracking MPPT control method or the maximum power internal power output;

[0049] The Boost Buck bidirectional conversion circuit of the energy storage battery input part adopts square wave control;

[0050] When the battery voltage is UB and the duty cycle is D, the battery is discharged when UB / D is greater than the H-bridge DC side voltage U of the low-voltage part of the DC isolation part, and is charged when it is less than U;

[0051] The Boost Buck bidirectional conversion circuit can adjust the output voltage level by controlling the square wave duty cycle D. When the DC side voltage of the low-voltage part of the DC isolation part of claim 2 is U, the output voltage is U*D.

[0052] As a preferred solution of the electronic transformer operation method of the present invention, the method of coordinated control of the various parts includes:

[0053] The AC output part and the DC output part maintain their respective rated voltage outputs, and the remaining parts adjust the active power according to the DC side voltage U of the H-bridge of the low-voltage part of the DC isolation part;

[0054] Assume k1 and k2 are margin coefficients and k1<1, k2>1, Un is the rated value of U;

[0055] When U<Un*k1, determine whether the photovoltaic power generation is at full power. If not, increase the power generation;

[0056] When the power is full, determine whether the energy storage battery can be discharged. If it can be discharged and the discharge has reached the limit, control the DC isolation part of the transformer to increase the input active power;

[0057] When Un*k1≤U≤Un*k2, the energy storage battery does not charge or discharge, and it is determined whether the photovoltaic power generation is at full power. If not, the photovoltaic power generation power is increased to increase the input active power of the transformer high voltage part and DC isolation part;

[0058] If the photovoltaic power generation is at full power, the input active power of the photovoltaic power generation and the DC isolation part of the transformer remains unchanged.

[0059] When U>Un*k2, determine whether the energy storage battery can increase the charging power. If it can, increase it. If it cannot be increased or it is already full, increase the output of the transformer DC isolation part to the transformer input end.

[0060] As a preferred solution of the electronic transformer operation method of the present invention, wherein:

[0061] The beneficial effects of the present invention are as follows: according to the size of the DC side voltage, the photovoltaic power generation, the charging and discharging of the energy storage battery and the power transmission of the DC isolation part are coordinated and controlled, the photovoltaic power generation is consumed first, the impact on the power grid is reduced, and the stable power supply of the DC and AC loads is guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. 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 creative labor. Among them:

[0063] Figure 1 A main circuit diagram of a power electronic transformer of an electronic transformer system according to an embodiment of the present invention;

[0064] Figure 2 An H-bridge main circuit diagram of an electronic transformer system according to an embodiment of the present invention;

[0065] Figure 3 A Boost Buck bidirectional conversion circuit diagram of an electronic transformer system according to an embodiment of the present invention;

[0066] Figure 4 A schematic diagram of the single-phase current signal PARK conversion principle of an electronic transformer control method according to an embodiment of the present invention;

[0067] Figure 5 A schematic diagram of an input part control method of an electronic transformer control method according to an embodiment of the present invention;

[0068] Figure 6 A schematic diagram of an equivalent circuit of a DC isolation part of an electronic transformer control method according to an embodiment of the present invention;

[0069] Figure 7 A schematic diagram of a DC isolation part control method of an electronic transformer control method according to an embodiment of the present invention;

[0070] Figure 8 A schematic diagram of the single-phase voltage signal PARK conversion principle of an electronic transformer control method according to an embodiment of the present invention;

[0071] Fig. 9 A schematic diagram of a control method for an AC output part of an electronic transformer control method according to an embodiment of the present invention;

[0072] Fig.10A logic diagram of a coordinated control method of various parts of an electronic transformer control method described in an embodiment of the present invention. DETAILED DESCRIPTION

[0073] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0074] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0075] Secondly, the present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0076] Furthermore, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0077] Example 1

[0078] Reference Figures 1 to 3 , this embodiment provides an electronic transformer system, including a high voltage input part, including a first H-bridge module, namely B1, B2, and B3;

[0079] The DC isolation part includes a high voltage part, a high frequency transformer (T) and a low voltage part, and is connected to the AC output part and the DC output part at the output end;

[0080] PV substring input part, including Boost circuit;

[0081] Energy storage battery input part, including Boost Buck bidirectional conversion circuit;

[0082] The high voltage input part rectifies the electric signal through the first H-bridge module and enters the DC isolation part for secondary rectification to output AC or DC power;

[0083] The photovoltaic substring input part and the energy storage battery input part integrate the access of renewable energy and energy storage system.

[0084] At present, the rated voltage of high-voltage power electronic switch devices is 3300V, 4500V, 6500V, etc. This transformer is usually used in 10kV distribution network. The input part usually contains 3 to 4 H bridges connected in series on the AC side. Figure 1 In this example, there are three H-bridges, namely B1, B2, and B3. The H-bridges connected in series are connected to the line voltage AC1 of the 10kV AC distribution network through the reactor 1, namely L1. A high-voltage DC capacitor is connected in parallel on the DC side of each H-bridge, such as Figure 1 Among C1, C2, and C3.

[0085] The input end uses H-bridge series connection, which can not only reduce the voltage level of a single H-bridge, but also facilitate multiple inversion to reduce harmonics. Figure 2 As shown, BD1~BD4 are composed of diodes connected in reverse parallel to high-voltage power electronic switch tubes such as IGBT, IGCT, MOSFET, etc. In this example, it is IGBT, and as shown in Figure 2 The wiring shown forms a rectifier and inverter bidirectional bridge.

[0086] Example 2

[0087] Reference Figures 1 to 3 , which is the second embodiment of the present invention, and is based on the previous embodiment, and is different from the previous embodiment in that: the B1, B2, and B3 are connected in series through the reactor 1 to the line voltage of the AC 10kV distribution network;

[0088] Furthermore, the B1, B2, B3 are respectively connected in parallel with high-voltage DC capacitors C1, C2, C3 on the DC side.

[0089] The high voltage part is composed of the same number of H bridges as the high voltage input part, namely B4, B5, and B6;

[0090] The H-bridge DC side of the high-voltage part is connected one by one with the first H-bridge module, and the AC side is connected one by one with the high-voltage winding on the high-frequency transformer (T);

[0091] The low voltage part is composed of the same number of H bridges as the high voltage part, namely B7, B8, and B9. The DC side of the H bridge of the low voltage part is connected one by one with the low voltage winding on the high frequency transformer (T).

[0092] The AC output part includes a DC capacitor C4 and an end H bridge B10;

[0093] One side of the DC capacitor C4 is connected to the DC side of the H-bridge of the low voltage part, and the other side is connected to the DC side of the terminal H-bridge B10. The electrical signal is output from the AC side of the H-bridge B10 to connect to the AC load.

[0094] The DC output part is composed of a plurality of Buck step-down circuits, the input ends of all Buck step-down circuits are connected to the DC side of the H-bridge of the low-voltage part, and the output section outputs the DC voltage in stages.

[0095] The DC isolation part includes a high voltage part, a multi-winding high frequency transformer and a low voltage part. The high voltage part is composed of the same number of H bridges as the high voltage input part. In this example, there are also three H bridges, namely B4, B5, and B6. Figure 1 The DC side of the H-bridge shown is connected to the high voltage input part H-bridge, and the AC part is connected to one of the high voltage windings of the multi-winding high-frequency transformer T; the frequency of the high-frequency transformer is usually selected to be above 5kHz, which is greatly increased compared with the 50Hz frequency of the conventional electromagnetic transformer. From the transformer knowledge, it can be known that the transformer turn voltage is proportional to the frequency and the core flux. Therefore, at the same rated voltage, the flux of the high-frequency transformer can be greatly reduced, so that the core cross-section and volume of the high-frequency transformer are smaller.

[0096] The low voltage part includes the same number of H bridges as the high voltage part and connected in parallel on the AC side. The parallel connection of H bridges is beneficial to increase the output current on the low voltage side of the transformer. In this example, there are also three H bridges, namely B7, B8, and B9, and each H bridge is connected to the low voltage winding of a multi-winding high frequency transformer on the AC side.

[0097] The transformation ratio of the high-frequency transformer is related to the voltage level of the DC side of the high-voltage part and the low-voltage part. For example, when the DC voltage of the H-bridge at the input end is 6000V and the DC bus voltage at the output end is 750V, the transformer transformation ratio is 6000 / 750. The AC output part includes a DC capacitor C4 and an H-bridge B10. One side of the DC capacitor C4 is connected to the DC side of the H-bridge of the DC isolation part, and the other side is connected to the DC side of the H-bridge of the output part. The AC part of the H-bridge is connected to the AC load through the reactor 2, namely L2.

[0098] Example 3

[0099] Reference Figures 1 to 3 , which is the third embodiment of the present invention, and is based on the previous embodiment, and is different from the previous embodiment in that: the input end of the Boost circuit is connected in parallel with the photovoltaic panel, and the output end is connected to the DC side of the low-voltage part H bridge;

[0100] The input end of the Boost Buck bidirectional conversion circuit is connected to the energy storage battery, and the output end is connected to the DC side of the low voltage part H bridge. The H bridge is a power electronic switch such as IGBT or a diode.

[0101] The PV string input part is as follows Figure 1The Boost in the middle is composed of a Boost circuit. The Boost circuit is a mature technology and will not be described in detail. The input end of the Boost circuit is connected to the photovoltaic panels PV connected in series and parallel, and the output of the Boost circuit is connected to the DC side of the low-voltage part H bridge of the above-mentioned DC isolation part.

[0102] Energy storage battery input part Figure 1 Boost & Buck, which is composed of Boost and Buck bidirectional conversion circuits. Figure 3 The input part is connected between BD1 and BD2 through the connecting inductor L. BD1 and BD2 are composed of diodes connected in reverse parallel to power electronic switching tubes such as IGBT, IGCT, MOSFET, etc. In this case, it is IGBT. The output part OUT and the common terminal COM are indirectly connected by capacitor C.

[0103] like Figure 1 The input end of the Boost&Buck conversion circuit is connected to the energy storage battery BAT, and the output end is connected to the DC side of the low-voltage part H bridge of the above-mentioned DC isolation part.

[0104] The DC output part is composed of several Buck step-down circuits, such as Figure 1 The Buck circuit is also a mature technology and will not be described in detail. The input end of all circuits is connected to the low voltage part of the H bridge DC side of the DC isolation part of claim 2, and the output part is divided into several DC voltage levels such as DC400V, DC220V, DC48V, DC24V, DC12V, DC5V, etc. according to the purpose.

[0105] Example 4

[0106] Reference Figures 1 to 10 , which is the fourth embodiment of the present invention, and this embodiment provides an electronic transformer operation method. This embodiment is based on the previous embodiment, and the difference from the previous embodiment is that:

[0107] Adopt PID control under dq rotating coordinate system, and realize unity power factor operation by controlling the PWM signal of H-bridge circuit, so as to stabilize and regulate the DC side voltage or AC load terminal voltage;

[0108] By adjusting the shift ratio of the square wave signal, the direction and size of the power flow are controlled to achieve bidirectional transmission of high and low voltage energy in the DC isolation part;

[0109] Adopt maximum power tracking control method or maximum power internal power output to maximize the utilization of photovoltaic power generation;

[0110] Adopt square wave control to control the battery charging and discharging process and the output DC voltage level by adjusting the duty cycle;

[0111] Each part coordinates and controls to achieve stable power supply of DC and AC.

[0112] Example 5

[0113] Reference Figures 1 to 10 , which is the fifth embodiment of the present invention, is based on the previous embodiment, and is different from the previous embodiment in that: the PWM control method of the power electronic switch such as IGBT in the high-voltage input part is: first, the single-phase input sinusoidal current signal I is equivalent to a three-phase signal, and the PARK transformation is performed according to the three-phase signal to the fixed values ​​Id and Iq in the dq rotating coordinate system. I is a sinusoidal change, and Id and Iq are constant when the peak value of I and the initial phase value remain unchanged, and Id and Iq are convenient for PID control.

[0114] Electrical knowledge shows that after Clark transformation of three-phase voltage signals UA, UB, UC or current signals IA, IB, IC, Uα and Uβ or Iα and Iβ in αβ coordinate system can be obtained when the three phases are balanced. Uα or Iα has the same waveform as UA or IA, and Uβ or Iβ lags UA or IA by 90 degrees. In this way, the corresponding three-phase current signals IA, IB, IC can be represented by signals I and I processed by the delay link Delay, and the three-phase signals can be obtained by PARK transformation. It is equivalent to directly transforming Iα and Iβ into Id and Iq and transforming the three-phase signals corresponding to Iα and Iβ into Id and Iq.

[0115] Therefore, Figure 4 This method firstly converts the single-phase input sinusoidal current signal I and the signal lagging 90 degrees to Iα and Iβ in the αβ coordinate system. When the three phases are balanced, I0=0, and then it is converted to Id and Iq through the αβ-dq coordinate transformation. The rotation angle wt used in the αβ-dq coordinate transformation is given by Figure 1 The voltage signal V1 is collected at both ends of the power grid voltage AC1 and calculated by the phase-locked loop PLL. wt also provides the rotation angle wt for other transformations of the dq rotation coordinate system. At the same time, V1 is transformed by Fourier transform to obtain its amplitude, which is equal to the d-axis voltage Vd of the power grid voltage AC1 in the dq coordinate system.

[0116] Then, according to the electrical knowledge, the relationship between the grid voltage, current, filter reactor and inverter output voltage in the dq coordinate system is calculated. Figure 5 The method is used to carry out PID regulation control in rotating coordinate system.

[0117] use Figure 1 The total reference voltage of the DC side parallel capacitors of the medium and high voltage input part is 18000V in this example minus the terminal voltages CV1, CV2, CV3 of the DC side parallel capacitors C1, C2, C3, and is adjusted by PID to obtain the d-axis reference current Id* in the rotating coordinate system of the input part.

[0118] The voltage drop after PID regulation of Vd minus (Id* - Id) is added to Iq multiplied by the angular velocity w of the rotating coordinate system. In this example, w = 2π * 50 and Figure 1 the reactance value L of the reactor L1 in it to obtain the d-axis voltage ud.

[0119] When the three-phase voltages are symmetrical, the q-axis voltage Vq of AC1 = 0, and it is required that the input power factor is 1. Therefore, let the reference current Iq* = 0. After Vq minus (Iq* - Iq) is PI-regulated and then minus Id*w*L, the q-axis voltage uq of the series H-bridge AC side is obtained.

[0120] Finally, let the 0-axis voltage u0 = 0 when the three phases are balanced in the rotating coordinate system. The voltages ud, uq, and u0 use wt as the rotation angle of the rotating coordinate system. Through the transformation from the dq0 coordinate system to the abc coordinate system, the three-phase voltages can be obtained. Taking the A-phase voltage as the reference voltage, it is multiplied by the coefficient K through the amplitude limiting link S1 to convert it into a value between -1 and 1, and then modulated by the carrier phase-shifted SPWM method CPS-SPWM as the PWM control of the power electronic switches such as IGBT in the high-voltage input part. The carrier phase-shifting method is a prior art and will not be elaborated here.

[0121] Embodiment 6

[0122] Referring to Figures 1 to 8 , this is the sixth embodiment of the present invention. This embodiment is based on the previous embodiment, and the difference from the previous embodiment is that the PWM control method of the power electronic switches such as IGBT in the DC isolation part is as follows: as Figure 7 , when BD1 to BD8 are conducting, they are 1 corresponding to the PWM1 to PWM inputs being 1, and when they are off, they are 0. When BD1 and BD4 are 1 and conducting, and BD2 and BD3 are 0 and off, the high-voltage winding of the transformer T bears a positive voltage;

[0123] When BD1 and BD4 are 0 and off, and BD2 and BD3 are 1 and closed, the high-voltage winding of the transformer T bears a reverse voltage. Repeating this way and with equal time, it is the 50% duty cycle square wave control method. The low-voltage sides BD5, BD4 and BD6, BD4 also adopt this 50% duty cycle square wave control method.

[0124] Let the total period of the square wave be T, and the high-voltage square wave leads the low-voltage square wave by Dt. Use D = 2 * Dt / T as the phase shift ratio within half a cycle. Through research and experiments, it shows that by controlling the magnitude and direction of D, the flow direction and magnitude of the power can be controlled. When 0 < D < 1, the power is transmitted from the high-voltage part to the low-voltage part;

[0125] When -1 < D < 0, the low-voltage part of the power is transmitted to the high-voltage part; when D = 0, no power is transmitted; when |D| = 0.5, the transmitted power is the largest. Using the above rules, it is convenient to control the power transmission direction and magnitude, facilitating the reverse power supply from new energy sources such as photovoltaics to the power grid.

[0126] Embodiment 7

[0127] Refer to Figures 1 to 8 , which is the seventh embodiment of the present invention. This embodiment is based on the previous embodiment, and the difference from the previous embodiment is that the PWM control method of power electronic switches such as IGBT in the AC output part is as follows: First, the sinusoidal current signal Vx of the actual voltage at the AC load end is equivalent to a three-phase signal, and PARK transformation is performed according to the three-phase signal to obtain the fixed values Ud and Uq in the dq rotating coordinate system.

[0128] This method has been introduced in detail in the PWM control method of power electronic switches such as IGBT in the high-voltage input part. Since there is no reference rotation angle wt in the AC output part of this patent, therefore, as Figure 8 In Figure 1 , the actual voltage Vx at the end of the AC load AC_load and the voltage after delaying it by 90 degrees are used as the voltages Uα and Uβ in the αβ coordinate system, and U0 = 0 is set. The angular velocity w of the rotating coordinate system is set as 50Hz multiplied by 2π, and the rotation angle wt of the rotating coordinate system is set as w multiplied by the system time t.

[0129] Through the transformation from the αβ coordinate system to the dq coordinate system, the voltages Ud and Uq in the dq coordinate system can be obtained. Since the best case for control is that the voltage at the AC load end is always the rated voltage of 220V, and its amplitude is 311V, therefore, the reference voltage Ud* = 311 is subtracted from Ud and after PID adjustment, the reference current Id* in the dq rotating coordinate system is obtained. It is required that the phase angle of the voltage at the AC load AC_load end is consistent with wt, so Uq* = 0. The actual voltage Uq is subtracted from 0 and after PID adjustment, the reference current Iq* is obtained.

[0130] Then, according to the mutual relationship between the inverter output voltage, current, filter reactor, and load voltage in the dq coordinate system in electrical related knowledge, PID adjustment control in the rotating coordinate system is performed according to the Fig. 9 method. Using the same method as above for inverting the single-phase voltage to Ud and Uq, the actual current I of the AC output part and the current after delaying it by 90 degrees are used as the currents Iα and Iβ in the αβ coordinate system, and I0 = 0 is set. Using wt as the rotation angle of the rotating coordinate system, through the transformation from the αβ coordinate system to the dq coordinate system, the d-axis current Id and q-axis current Iq of I in the dq rotating coordinate system can be obtained.

[0131] (Id*-Id) is adjusted by PID and then added with Ud and Iq multiplied by the angular velocity w of the rotating coordinate system and the reactance value L of the reactor 2 described in claim 2 is subtracted to obtain the d-axis voltage Vd on the AC output side in claim 2. (Iq*-Iq) is adjusted by PID and then added with Uq and Id multiplied by w and L to obtain the q-axis voltage Vq on the AC output side in claim 2.

[0132] Finally, wt is used as the rotation angle of the rotating coordinate system, and the AC output 0-axis voltage V0=0. The AC output dq0-axis voltage is transformed from the dq0 coordinate system to the abc coordinate system to obtain the three-phase voltage. The A-phase voltage Ua is used as the reference voltage and is modulated by the carrier PWM as the PWM control of the power electronic switches such as IGBT in the AC output part. The carrier modulation PWM technology has various forms such as unipolar and bipolar, which are mature and will not be repeated.

[0133] When the PID regulation control output voltage signal Ua exceeds the value between -1 and 1, you can also add the following before PWM modulation: Figure 5 The medium amplitude limiting link S1 is multiplied by the coefficient K and converted into a value between -1 and 1 to facilitate modulation.

[0134] Example 8

[0135] Reference Figures 1 to 10 , which is the eighth embodiment of the present invention, is based on the previous embodiment, and is different from the previous embodiment in that the photovoltaic power generation control method is an existing mature technology and is not described in detail.

[0136] The energy storage battery input part is controlled by a Boost and Buck bidirectional conversion circuit using square wave control. When the battery voltage is UB and the duty cycle is D, D is controlled so that UB / D is greater than the DC side voltage U of the low-voltage part of the DC isolation part, the battery discharges, and when it is less than U, the battery charges.

[0137] The Buck step-down circuit of the DC output part adopts square wave control. The output voltage level can be adjusted by controlling the square wave duty cycle D. When the DC side voltage of the low-voltage part of the DC isolation part is U, the output voltage is U*D.

[0138] Example 9

[0139] Reference Figures 1 to 10 , which is the ninth embodiment of the present invention, is based on the previous embodiment, and is different from the previous embodiment in that: the AC output part and the DC output part of the transformer maintain their respective rated voltage outputs and are not affected by the DC side voltage U of the H-bridge of the low-voltage part of the DC isolation part, while other parts adjust the active power according to the size of U.

[0140] Assume k1 and k2 are margin coefficients and k1<1, k2>1, Un is the rated value of U, when U<Un*k1, first determine whether the photovoltaic is generating power at full power, if not, increase the generating power, if it is at full power, determine whether the energy storage battery can be discharged, if it can be discharged, discharge it, when the discharge has reached the limit, control the DC isolation part of the transformer to increase the input active power, that is, reduce the output when it is outputting, if U always meets this condition, until it becomes the input to the maximum input power.

[0141] When Un*k1≤U≤Un*k2, the energy storage battery does not charge or discharge, and it is determined whether the photovoltaic power generation is at full power. If not, the photovoltaic power generation power is increased, and at the same time, the input active power of the high-voltage part and the DC isolation part of the transformer is reduced by the same value. That is, when the power is being input, the output power is reduced to increase the power of the photovoltaic power. When the power is not being output or is being output, the output power is increased to increase the power of the photovoltaic power.

[0142] If the photovoltaic power is at full power, the active power input of the photovoltaic power generation and the DC isolation part of the transformer remains unchanged. When U>Un*k2, it is determined whether the charging power of the energy storage battery can be increased. If it can be increased, it is increased. If it is at the maximum power and cannot be increased or it is full, the DC isolation part of the transformer is increased to the output of the transformer input end to transfer energy to the high-voltage side grid.

[0143] According to the size of the DC side voltage, the photovoltaic power generation, energy storage battery charging and discharging, and power transmission of the DC isolation part are coordinated and controlled to give priority to photovoltaic power generation, reduce the impact on the power grid, and ensure stable power supply for DC and AC loads.

[0144] Importantly, it should be noted that the construction and arrangement of the present application shown in a plurality of different exemplary embodiments are only exemplary. Although only a few embodiments are described in detail in this disclosure, it should be readily understood by those who refer to this disclosure that many modifications are possible (e.g., the size, scale, structure, shape and proportion of various elements, and parameter values ​​(e.g., temperature, pressure, etc.), installation arrangement, use of materials, color, directional changes, etc.) without substantially departing from the novel teachings and advantages of the subject matter described in the application. For example, the element shown as integrally formed can be composed of multiple parts or elements, the position of the element can be inverted or otherwise changed, and the nature or number or position of the discrete element can be changed or changed. Therefore, all such modifications are intended to be included in the scope of the present invention. The order or sequence of any process or method steps can be changed or reordered according to alternative embodiments. In the claims, any "device plus function" clause is intended to cover the structure of performing the function described herein, and is not only structurally equivalent but also equivalent structure. Without departing from the scope of the present invention, other replacements, modifications, changes and omissions can be made in the design, operating conditions and arrangement of the exemplary embodiments. Therefore, the invention is not limited to a specific embodiment, but extends to numerous modifications still falling within the scope of the appended claims.

[0145] Additionally, in order to provide a concise description of exemplary embodiments, all features of an actual embodiment (ie, those features that are not relevant to the best mode presently contemplated for carrying out the invention or those that are not relevant to implementing the invention) may not be described.

[0146] It will be appreciated that in the development of any actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but will be a routine task of design, fabrication, and production for those of ordinary skill having the benefit of this disclosure without undue experimentation.

[0147] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. An electronic transformer system, characterized in that: include, The high voltage input part includes the first H-bridge module, namely B1, B2, and B3; The DC isolation part includes a high voltage part, a high frequency transformer (T) and a low voltage part, and is connected to the AC output part and the DC output part at the output end; PV substring input part, including Boost circuit; Energy storage battery input part, including Boost Buck bidirectional conversion circuit; The high voltage input part rectifies the electric signal through the first H-bridge module and enters the DC isolation part for secondary rectification to output AC or DC power; The photovoltaic substring input part and the energy storage battery input part integrate the access of renewable energy and energy storage system.

2. An electronic transformer system according to claim 1, characterized in that: The B1, B2, and B3 are connected in series through a reactor L to the line voltage of the AC 10kV distribution network; Furthermore, the B1, B2, B3 are respectively connected in parallel with high-voltage DC capacitors C1, C2, C3 on the DC side.

3. An electronic transformer system according to claim 2, characterized in that: The high voltage part is composed of the same number of H bridges as the high voltage input part, namely B4, B5, and B6; The H-bridge DC side of the high-voltage part is connected one by one with the first H-bridge module, and the AC side is connected one by one with the high-voltage winding on the high-frequency transformer (T); The low voltage part is composed of the same number of H bridges as the high voltage part, namely B7, B8, and B9. The DC side of the H bridge of the low voltage part is connected one by one with the low voltage winding on the high frequency transformer (T).

4. An electronic transformer system according to claim 3, characterized in that: The AC output part includes a DC capacitor C4 and an end H bridge B10; One side of the DC capacitor C4 is connected to the DC side of the H-bridge of the low voltage part, and the other side is connected to the DC side of the terminal H-bridge B10. The electrical signal is output from the AC side of the H-bridge B10 to connect to the AC load. The DC output part is composed of a plurality of Buck step-down circuits, the input ends of all Buck step-down circuits are connected to the DC side of the H-bridge of the low-voltage part, and the output section outputs the DC voltage in stages.

5. An electronic transformer system according to claim 4, characterized in that: The input end of the Boost circuit is connected in parallel with the photovoltaic panel, and the output end is connected to the DC side of the H bridge of the low voltage part; The input end of the Boost Buck bidirectional conversion circuit is connected to the energy storage battery, and the output end is connected to the DC side of the low voltage part H bridge.

6. An electronic transformer system according to claim 5, characterized in that: The H bridges are all power electronic switches such as IGBTs or diodes.

7. An electronic transformer operating method, acting on an electronic transformer system, characterized in that: Adopt PID control under dq rotating coordinate system, and realize unity power factor operation by controlling the PWM signal of H-bridge circuit, so as to stabilize and regulate the DC side voltage or AC load terminal voltage; By adjusting the shift ratio of the square wave signal, the direction and size of the power flow are controlled to achieve bidirectional transmission of high and low voltage energy in the DC isolation part; Adopt maximum power tracking control method or maximum power internal power output to maximize the utilization of photovoltaic power generation; Adopt square wave control to control the battery charging and discharging process and the output DC voltage level by adjusting the duty cycle; Each part coordinates and controls to achieve stable power supply of DC and AC.

8. An electronic transformer operating method according to claim 7, characterized in that: The PWM control of the power electronic switch or diode such as IGBT of the high voltage input part includes: The single-phase input sinusoidal current signal I is equivalent to a three-phase signal, and PARK transformation is performed to obtain Id and Iq, and PID control is carried out according to Id and Iq; The rotation angle required for dq coordinate transformation is calculated using the rotating coordinate system wt; The d-axis voltage Vd of the grid voltage is obtained through Fourier transform; The carrier phase-shifted SPWM method is used to complete PWM control of power electronic switches such as IGBTs.

9. An electronic transformer operation method according to claim 7, characterized in that: The PWM control of power electronic switches such as IGBTs or diodes in the DC isolation part includes, A 50% duty cycle square wave PWM input signal is used, and the magnitude and direction of D are controlled by adjusting the phase shift ratio within half a cycle of the square wave signals of the high-voltage part and the low-voltage part, so as to control the flow direction and magnitude of power. When 0 < D < 1, power is transmitted from the high-voltage part to the low-voltage part; when -1 < D < 0, power is transmitted from the low-voltage part to the high-voltage part, and when D = 0, no power is transmitted.

10. An electronic transformer operation method according to claim 7, characterized in that: The PWM control of power electronic switches such as IGBTs or diodes in the AC output part includes, The actual voltage Vx at the AC load end is equivalent to a three-phase signal, and PARK transformation is performed according to the three-phase signal to obtain the fixed values Ud and Uq in the dq rotating coordinate system; The reference currents Id and Iq in the dq rotating coordinate system are obtained through PID regulation; The d-axis voltage Vd and q-axis voltage Vq of the AC output side are calculated according to electrical relevant knowledge; After transformation from the dq0 coordinate system to the abc coordinate system, three-phase voltages are obtained, and the PWM control of power electronic switches such as IGBTs in the AC output part is carried out after carrier modulation PWM with the phase A voltage Ua as the reference voltage.

11. An electronic transformer operation method according to claim 7, characterized in that: The PWM control of power electronic switches such as IGBTs or diodes in the Boost circuit and the Boost Buck bidirectional conversion circuit includes, The Boost circuit in the photovoltaic sub-string input part adopts the maximum power point tracking MPPT control method or maximum power internal fixed power output; The Boost Buck bidirectional conversion circuit in the energy storage battery input part adopts square wave control; When the battery voltage is UB and the duty cycle is D, control D so that when UB / D is greater than the DC side voltage U of the low-voltage part H bridge of the DC isolation part, the battery discharges, and when it is less than U, the battery charges; The Boost Buck bidirectional conversion circuit can adjust the output voltage level by controlling the square wave duty cycle D. When the DC side voltage of the low-voltage part of the DC isolation part described in claim 2 is U, the output voltage is U*D.

12. An electronic transformer operation method according to claim 7, characterized in that: The method for coordinated control of each part includes, The AC output part and the DC output part maintain their respective rated voltage outputs, and the remaining parts adjust the active power according to the magnitude U of the DC side voltage of the low-voltage part H bridge of the DC isolation part. Assume k1 and k2 are margin coefficients and k1<1, k2>1, Un is the rated value of U; When U<Un*k1, determine whether the photovoltaic power generation is at full power. If not, increase the power generation; When the power is full, determine whether the energy storage battery can be discharged. If it can be discharged and the discharge has reached the limit, control the DC isolation part of the transformer to increase the input active power; When Un*k1≤U≤Un*k2, the energy storage battery does not charge or discharge, and it is determined whether the photovoltaic power generation is at full power. If not, the photovoltaic power generation power is increased to increase the input active power of the transformer high voltage part and DC isolation part; If the photovoltaic power generation is at full power, the input active power of the photovoltaic power generation and the DC isolation part of the transformer remains unchanged. When U>Un*k2, determine whether the charging power of the energy storage battery can be increased. If so, increase it. If not or it is already fully charged, increase the output of the DC isolation part of the transformer to the transformer input end.

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