Novel direct current-alternating current-direct current three-port circuit and modulation method

Abstract

The invention discloses a novel direct current-alternating current-direct current three-port circuit and a modulation method, and belongs to the field of power electronic converters, the circuit can flexibly deal with complex multi-port, multi-energy and multi-load requirements, and performs centralized management on multi-port energy flow, so that the energy utilization efficiency is improved, and the energy loss is reduced. The design structure is simple, the use of an alternating current inductor is avoided by utilizing the coupling of the inductor and the transformer, and the transformation of the existing equipment is more convenient. Meanwhile, the circuit has high reliability and stability, mutual interference between converters in a multi-converter system can be effectively avoided, and the overall performance of the system is improved.

Description

Technical Field

[0001] The invention belongs to the field of power electronic converters, and more specifically relates to a novel DC-AC-DC three-port circuit and a modulation method. Background Art

[0002] With the popularity of renewable energy, the demand for energy conversion equipment continues to grow. These renewable energy sources are usually output in the form of DC, while the load demand may be AC ​​or DC of different voltage levels, which requires a flexible and efficient power electronic conversion technology. In addition, the widespread use of energy storage systems and electric vehicles has also put forward new requirements for multi-port power electronic conversion. Traditional power electronic converters are mainly single-function, such as DC-DC, DC-AC or AC-DC converters, but with the increase in system complexity and the improvement of energy management requirements, single-function converters have been difficult to meet the requirements.

[0003] The defects of the prior art are:

[0004] 1. Single function and lack of flexibility: Traditional power electronic converters are usually single-function, such as DC-DC, DC-AC or AC-DC converters. These converters each handle a single energy conversion task and are difficult to cope with complex multi-port, multi-energy source and multi-load requirements;

[0005] 2. Low energy management efficiency: Traditional converters lack centralized management of multi-port energy flow, resulting in inadequate energy utilization, especially in distributed energy systems and hybrid energy storage systems, which often require multiple converters to operate in series or parallel, which not only increases the complexity of the system, but also increases energy loss;

[0006] 3. Increased system volume and cost: Since traditional converters can only handle a single power conversion task, the design of a multi-converter system often takes up more space and increases the weight and cost of the overall system. For applications that require high power density and compact design, traditional technologies are difficult to meet the requirements;

[0007] 4. Insufficient reliability and stability: In a multi-converter system, the coordinated work between the converters is prone to mutual interference, which increases the instability of the system. The failure of any converter may cause the performance of the entire system to decline or be interrupted. The traditional single converter technology is difficult to ensure the overall reliability and stability of the system when dealing with multiple source inputs and multiple load outputs. Summary of the invention

[0008] The present invention aims to solve at least one problem existing in the prior art. To this end, the purpose of the present invention is to provide a novel DC-AC-DC three-port circuit and modulation method, and apply it to the field of AC-DC bidirectional power conversion technology, coupling the inductor and the transformer together, eliminating the AC inductor, making the topology have AC-DC isolation, simple structure, and convenient modification of existing equipment.

[0009] In order to achieve the above object, the present invention is implemented by adopting the following technical scheme: the three-port circuit comprises: a three-phase AC interface U A , U B , U C And two DC interfaces U DC , U DC’ ;

[0010] The DC-AC-DC three-port circuit includes a transformer, two capacitors, and a power electronic switch device; each phase winding of the transformer is T A 、T B 、T C .

[0011] In one embodiment, two of the power electronic switching devices form a bridge arm.

[0012] In one embodiment, there are 12 electronic switch devices, including: S A1 , S A2 , S B 1. S B2 , S C1 , S C2 、S1 A’ 、S2 A’ 、S1 B’ 、S2 B’ 、S1 C’ 、S2 C’ ;

[0013] Power Electronic Switching Devices A1 , S A2 Composition A Bridge arm, S B1 , S B2 Composition B Bridge arm, S C1 , S C2 Composition C Bridge arm, S1 A’ 、S2 A’ Composition A’ Bridge arm, S1 B’ 、S2 B’ Composition B’ Bridge arm, S1 C’ 、S2 C’ CompositionC’ Bridge arms, forming the midpoints A, B, C, A', B', C' of the bridge arms respectively;

[0014] DC interface U DC The positive and negative electrodes are connected to capacitor C DC The two ends are then connected to S A , S, S C The two ends of the bridge arm; similarly, the DC interface U DC’ The positive and negative electrodes are connected to capacitor C DC’ The two ends are then connected to S A’ , S B’ , S C’ Both ends of the bridge arm.

[0015] In one embodiment, the transformer winding T A 、T B 、T C There are two sets of coils on the AC system side and the converter side, of which T A 、T B 、T C The coil on the AC system side is connected to the three-phase AC system, and the two ends of the coil on the converter side are connected to the corresponding bridge arm midpoints, namely T A The two ends of the transformer coil are connected to A and A'; T B The two ends of the transformer coil are connected to B and B'; T C Both ends of the converter side coil are connected to C and C'.

[0016] In another aspect, a novel DC-AC-DC three-port circuit modulation method is provided. The modulation method is applicable to the DC-AC-DC three-port circuit. The circuit includes two working modes, namely:

[0017] Working mode 1: bidirectional energy flow between a single DC system and an AC system;

[0018] Working mode 2: Two-way energy flow between two DC systems and the AC system.

[0019] In one embodiment, the working mode is as follows:

[0020] Modulation method 1: Power electronic switching device S2 A’ 、S2 B’ 、S2 C’ Normally on, S1 A’ 、S1 B’ 、S1 C’ Normally off, the controller controls the power electronic switching device S A1 , S A2 , S B1 , S B2 , S C1, S C2 Modulation is performed to enable bidirectional energy control between the DC system and the AC system;

[0021] Since the power electronic switch device does not allow two switch devices in the same bridge arm to be turned on or off at the same time, the following working mode is obtained: 3 =8 switching states. By writing the KVL equation based on the volt-second balance, the 8 voltage vectors corresponding to each switching state can be obtained.

[0022] Modulation method 2: Power electronic switching device S1 A’ 、S1 B’ 、S1 C’ Normally on, S A’2 、S2 B’ 、S2 C’ Normally off, the controller controls the power electronic switching device S A1 , S A2 , S B1 , S B2 , S C1 , S C2 Modulation is performed so that the DC system and the AC system can perform bidirectional energy control, and the modulation method is exactly the same as that described in modulation method 1.

[0023] Modulation method three: power electronic switching device S A2 , S B2 , S C2 Normally on, S A1 , S B1 , S C1 Normally off, the controller controls the power electronic switching device S1 A’ 、S1 B’ 、S1 C’ 、S2 A’ 、S2 B’ 、S2 C’ Modulation is performed to enable bidirectional energy control between the DC system and the AC system; the eight voltage vectors corresponding to each switching state can be obtained by writing the KVL equation based on the volt-second balance.

[0024] Modulation method 4: Power electronic switching device S A1 , S B1 , S C1 Normally on, S A2 , S B2 , S C2 Normally off, the controller controls the power electronic switching device S1 A’ 、S1 B’ 、S1 C’ 、S2 A’ 、S2 B’ 、S2 C’Modulation is performed so that the DC system and the AC system can perform bidirectional energy control, and the modulation method is exactly the same as that described in modulation method three.

[0025] In one embodiment, the second working mode is as follows:

[0026] Based on working mode one, the voltage vectors of the AC system and the DC system are synthesized with the voltage vectors of the AC system and the DC system two, and it is obtained that the novel DC-AC-DC three-port circuit has 64 switching states. The voltage vector corresponding to each switching state can be obtained by writing the KVL equation according to the volt-second balance.

[0027] In one embodiment, in the second working mode,

[0028] Modulation method 5: Modulation is performed using the middle hexagon 26′-31′-42′-53′-64′-15′, i.e., 120° space vector decoupling. At this time, the hexagon has a rotation angle θ0 with respect to the alpha-beta coordinate system.

[0029] Create a rotation matrix, rotate the alpha-beta coordinate system, make the 15' point on the alpha axis, and divide it into six sectors according to the voltage vector;

[0030] Project the desired synthesized voltage vector onto the rotated alpha'-beta' coordinate system through the rotation matrix;

[0031] Referring to modulation method 1, sector judgment is performed, and the corresponding vector can be selected to synthesize the target vector through sector judgment.

[0032] In one scheme, modulation method six: using the middle hexagon 46′-51′-62′-13′-24′-35′, that is, 120° space vector decoupling for modulation, at which the hexagon has a rotation angle θ0 with respect to the alpha-beta coordinate system;

[0033] A rotation matrix is ​​established to rotate the alpha-beta coordinate system so that the 24' point is on the alpha axis and the voltage vector is divided into six sectors. The subsequent calculation method is exactly the same as that described in modulation method five, and the calculation result is obtained by substituting modulation method five.

[0034] In one scheme, modulation method seven: modulation is performed using the maximum hexagon 36′-41′-52′-63′-14′-25′, that is, 60° space vector decoupling. At this time, the hexagon is the same as modulation method one for the alpha-beta coordinate system, and the same analysis method is used to calculate the results.

[0035] Beneficial effects of the present invention:

[0036] Powerful functions and high flexibility: The new DC-AC-DC three-port circuit and modulation method can realize flexible conversion between DC and AC or different voltage test tube levels, and can cope with complex multi-port, multi-energy and multi-load requirements, improving its scope of use and convenience.

[0037] High energy management efficiency: This technical solution can centrally manage multi-port energy flows, making energy utilization more adequate and efficient, reducing energy loss, and improving the efficiency of energy conversion and use.

[0038] Simple structure, easy to modify existing equipment: This circuit couples the inductor and the transformer together, avoiding AC inductance, making the circuit structure simpler, reducing the size and cost of the equipment, and facilitating modification and application on existing equipment.

[0039] High system stability and reliability: The new power electronic conversion technology solution can effectively avoid mutual interference between converters in a multi-converter system, increase system stability, improve the reliability of the entire system, and reduce the risk of failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a novel DC-AC-DC three-port circuit diagram of the present invention;

[0041] Figure 2 It is the energy flow diagram of the new DC-AC-DC three-port circuit;

[0042] Figure 3 The voltage vector is the three-phase voltage synthesis;

[0043] Figure 4 is the projected composite vector in the alpha-beta coordinate system;

[0044] Figure 5 It is working mode 1: DC system 1 and AC system;

[0045] Figure 6 8 voltage vectors, vector diagrams in alpha-beta coordinate system;

[0046] Figure 7 This is the circuit diagram of modulation method 2;

[0047] Figure 8 The circuit diagram for modulation method three is shown;

[0048] Fig. 9 There are 8 voltage vectors, vector diagrams in the alpha-beta coordinate system;

[0049] Fig.10 The circuit diagram for modulation method 4 is shown below;

[0050] Fig.11 It is a form of 120° space vector decoupling;

[0051] Fig.12 To rotate the alpha-beta coordinate system, six sectors are divided according to the voltage vector;

[0052] Fig.13 To rotate the alpha-beta coordinate system so that the 24' point is on the alpha axis, and divide it into six sectors according to the voltage vector;

[0053] Fig.14 A three-port network in which two energy storage systems are coupled to an AC bus through a novel DC-AC-DC circuit of the present invention;

[0054] Fig.15 A duty cycle diagram generated in real time;

[0055] Fig.16 is the current waveform;

[0056] Fig.17 is the voltage waveform. DETAILED DESCRIPTION

[0057] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0058] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the present invention in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described in the present invention. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0059] A new type of DC-AC-DC three-port circuit, such as Figure 1 As shown. It includes a three-phase AC interface U A , U B , U C And two DC interfaces U DC , U DC’ The novel DC-AC-DC three-port circuit includes a transformer (each phase winding is T A 、TB , T), two capacitors (C DC , C DC’ ), 12 power electronic switching devices (S A1 , S A2 , S B1 , S B2 , S C1 , S C2 、S1 A’ 、S2 A’ 、S1 B’ 、S2 B’ 、S1 C’ 、S2 C’ ).

[0060] Power Electronic Switching Devices A1 , S A2 Composition A Bridge arm, S B1 , S B2 Composition B Bridge arm, S C1 , S C2 Composition C Bridge arm, S1 A’ 、S2 A’ Composition A’ Bridge arm, S1 B’ 、S2 B’ Composition B’ Bridge arm, S C’1 、S2 C’ Composition C’ The bridge arms respectively form the midpoints A, B, C, A', B', and C' of the bridge arms. DC interface U DC The positive and negative electrodes are connected to capacitor C DC The two ends are then connected to S A , S B , S C The two ends of the bridge arm; similarly, the DC interface U DC’ The positive and negative electrodes are connected to capacitor C DC’ The two ends are then connected to S A’ , S B’ , S C’ Both ends of the bridge arm.

[0061] Transformer winding T A 、T B 、T C There are two sets of coils on the AC system side and the converter side, of which T A 、T B 、T C The coil on the AC system side is connected to the three-phase AC system, and the two ends of the coil on the converter side are connected to the corresponding bridge arm midpoints, namely T AThe two ends of the transformer coil are connected to A and A'; T B The two ends of the transformer coil are connected to B and B'; T C Both ends of the converter side coil are connected to C and C'.

[0062] A new type of DC-AC-DC three-port circuit energy flow diagram is shown in Figure 2 As shown, it includes the following three types of modulation methods and seven working modes. It should be understood that the present invention only describes the necessary and universal modulation methods and working modes.

[0063] Here, the modulation scheme is explained using a three-phase symmetrical AC system. It should be understood that the circuit and control method proposed in the present invention can be applied to various AC systems. The three-phase symmetrical AC system is only a simplified analysis, and the corresponding modulation scheme can be obtained by substituting different AC system parameters into the formula.

[0064] Let's assume the three-phase voltage is:

[0065]

[0066] When added to the three-phase coordinate system, the corresponding voltage vector will be synthesized. As time changes, the vector rotates counterclockwise and the amplitude remains unchanged, as shown below Figure 3 :

[0067] Here A , U B , U C is a fixed three-phase coordinate system, and sinusoidal quantities are distributed in the coordinate system. As the sinusoidal quantities change, the resultant vector V also changes. According to the principle of equal amplitude transformation, U A , U B , U C The synthetic vector expression of the three-phase coordinate system is as follows:

[0068]

[0069] In this way, the quantities in the original three directions can be expressed using quantities in two directions. Let:

[0070] V=V α +jV β

[0071] Then we have:

[0072]

[0073] V α ,V β That is, the components in the two-phase stationary coordinate system, and the corresponding coordinates are as follows Figure 4 As shown:

[0074] Special note if u a,u b ,u c , is an asymmetric three-phase sinusoidal quantity, then their amplitudes are different, but the angles are still 120° apart. Here we deduce the case where the amplitudes are unequal. When the amplitudes are unequal, that is, u a ,u b ,u c When asymmetric, there is always a three-phase symmetrical voltage u a ′,u b ′,u c ′:

[0075]

[0076] According to the properties of symmetrical three-phase electricity:

[0077] ″′

[0078] u a +u b +u c =0

[0079] The zero-sequence component can be obtained:

[0080]

[0081] Working mode 1: Bidirectional energy flow between a single DC system and an AC system.

[0082] Modulation method 1: Figure 5 As shown, under this method, the power electronic switching device S2 A’ 、S2 B’ 、S2 C’ Normally on, S1 A’ 、S1 B’ 、S1 C’ Normally off, the controller is based on the above theoretical analysis to control the power electronic switch device S A1 , S A2 , S B1 , S B2 , S C1 , S C2 Modulation is performed to enable bidirectional energy control of the DC system 1 and the AC system. Since the power electronic switch device does not allow two switch devices in the same bridge arm to be turned on or off at the same time, that is, a bridge arm has only two switch states (in terms of S A Bridge arm example: S A1 On, S A2 The shutdown is marked as 1 and S A1 Shutdown, S A2 The conduction is recorded as 0), so we can get the working mode of 2 3=8 switching states. By writing the KVL equation based on the volt-second balance, the 8 voltage vectors corresponding to each switching state can be obtained, which can be shown in the figure in the alpha-beta coordinate system.

[0083] Depend on Figure 6 It can be seen that the voltage vectors V0 (000) and V7 (111) are both at the origin of the coordinate system, and V1, V2, V3, V4, V5, and V6 together form a regular hexagon, which is divided into six equal sectors according to the voltage vectors.

[0084]

[0085] The corresponding vector can be selected by sector judgment to synthesize the target vector. Here, the voltage vector working time is calculated by taking sector 1 as an example. It should be understood that the described sector 1 is only a part of the modulation method of the present invention, and other sectors can be re-derived and solved by this method.

[0086] Assume the switching period is T s , the working time of voltage vector 1 is T1, the working time of voltage vector 2 is T2, and voltage vectors 0 and 7 are both 0 vectors, so the working time of the same function is uniformly recorded as T 0,7 , we can get the following system of equations:

[0087]

[0088] The synthesized voltage vector forms a triangle with voltage vectors 1 and 2, so let the voltage vector V * The angle with the alpha axis is θ, and the following formula can be obtained:

[0089]

[0090] The solution is:

[0091]

[0092] The duty cycle is synthesized by the time of the voltage vector in the sector. Since the two switching tubes in each bridge arm are complementary, only the duty cycle D of the tube on each bridge arm is listed here.

[0093]

[0094]

[0095] ΙΙ <![CDATA[V0]]> <![CDATA[V3]]> <![CDATA[V2]]> <![CDATA[V7]]> <![CDATA[V2]]> <![CDATA[V3]]> <![CDATA[V0]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[S B1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S C1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 4]]>

[0096] ΙΙΙ <![CDATA[V0]]> <![CDATA[V3]]> <![CDATA[V4]]> <![CDATA[V7]]> <![CDATA[V4]]> <![CDATA[V3]]> <![CDATA[V0]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S B1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S C1 ]]> 0 0 1 1 1 0 0 <![CDATA[T1+T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 4]]>

[0097] ΙV <![CDATA[V0]]> <![CDATA[V5]]> <![CDATA[V4]]> <![CDATA[V7]]> <![CDATA[V4]]> <![CDATA[V5]]> <![CDATA[V0]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S B1 ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[S C1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 4]]>

[0098]

[0099]

[0100] VΙ <![CDATA[V0]]> <![CDATA[V1]]> <![CDATA[V6]]> <![CDATA[V7]]> <![CDATA[V6]]> <![CDATA[V1]]> <![CDATA[V0]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S B1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S C1 ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 4]]>

[0101] Modulation method 2: Figure 7 As shown, under this method, the power electronic switching device S1 A’ 、S1 B’ 、S1 C’ Normally on, S2 A’ 、S2 B’ 、S2 C’ Normally off, the controller is based on the above theoretical analysis to control the power electronic switch device S A1 , S A2 , S B1 , S B2 , S C1 , S C2 Modulation is performed so that the DC system 1 and the AC system can perform bidirectional energy control, and the modulation method is exactly the same as that described in modulation method 1.

[0102] Modulation method three: Figure 8 As shown, under this method, the power electronic switching device S A2 , S B2 , S C2 Normally on, S A1 , S B1 , S C1 Normally off, the controller is based on the above theoretical analysis, the power electronic switch device S1 A’ 、S1 B’ 、S1 C’ 、S2 A’ 、S2 B’ 、S2 C’ Modulation is performed to achieve bidirectional energy control between the DC system 2 and the AC system. The 8 voltage vectors corresponding to each switching state can be obtained by writing the KVL equation based on the volt-second balance. In the alpha-beta coordinate system, it can be obtained as follows Fig. 9 shown.

[0103] Depend on Fig. 9 It can be seen that S A’ S with modulation method 1 A Bridge arm, S B’ S with modulation method 1 B Bridge arm, S C’ S with modulation method 1 C The bridge arm modulation method is exactly the same.

[0104] Modulation method 4: Fig.10As shown, under this method, the power electronic switching device S A1 , S B1 , S C1 Normally on, S A2 , S B2 , S C2 Normally off, the controller is based on the above theoretical analysis, the power electronic switch device S1 A’ 、S1 B’ 、S1 C’ 、S2 A’ 、S2 B’ 、S2 C’ Modulation is performed so that the DC system 2 and the AC system can perform bidirectional energy control, and the modulation method is exactly the same as that described in the modulation method three.

[0105] Working mode 2: Two DC systems and two AC systems with bidirectional energy flow

[0106] Based on the analysis of working mode 1, the voltage vectors of AC system and DC system 1 and AC system and DC system 2 are synthesized, and it can be obtained that the novel DC-AC-DC three-port circuit has 64 switching states. The voltage vector corresponding to each switching state can be obtained by writing the KVL equation according to the volt-second balance. Here, U DC Higher than U DC’ For example, it should be understood that the circuit and control method proposed in the present invention can be applied to various types of DC systems. The above is just an example of an application scenario. Different DC system parameters can be substituted into the formula to obtain the corresponding modulation scheme. As shown in the figure, all 64 voltage vectors after synthesis are shown. The voltage vector is abbreviated in the figure. For example, V1+V4′ is represented as 14′. A total of one 0 vector and 10 hexagons are synthesized. Four hexagons have been used in one working mode, of which 16′-21′-32′-43′-54′-65′ and 56′-61′-12′-23′-34′-45′ both require the use of two DC systems to work at the same time, and the voltage utilization rate is not high. They are not described in detail as modulation methods here. It should be understood that 64 switching vectors can be combined into a variety of vector synthesis methods. The present invention only describes the necessary and universal vector synthesis and modulation methods. The modulation methods of the above two hexagons can be calculated by referring to the modulation schemes of modulation methods five and six.

[0107] Modulation method 5: Fig.11 As shown, the middle hexagon 26′-31′-42′-53′-64′-15′, that is, 120° space vector decoupling is used for modulation. At this time, the hexagon has a rotation angle θ0 with respect to the alpha-beta coordinate system.

[0108]

[0109] Create a rotation matrix, rotate the alpha-beta coordinate system, make the 15' point on the alpha axis, and divide it into six sectors according to the voltage vector, such as Fig.12 shown.

[0110]

[0111] Assume the currently required synthetic vector is:

[0112]

[0113] The desired synthesized voltage vector is projected onto the rotated alpha'-beta' coordinate system through the rotation matrix. for:

[0114]

[0115] Refer to modulation method 1. Perform sector judgment.

[0116]

[0117] The corresponding vector can be selected by sector judgment to synthesize the target vector. Here, the voltage vector working time is calculated by taking sector 1 as an example. It should be understood that the described sector 1 is only a part of the modulation method of the present invention, and other sectors can be re-derived and solved by this method.

[0118] Assume the switching period is T s , the working time of voltage vector 15' is T1, the working time of voltage vector 26' is T2, and voltage vectors 00' and 77' are both 0 vectors, so the working time of the same function is uniformly recorded as T 0,7 , we can get the following system of equations:

[0119]

[0120] The synthesized voltage vector forms a triangle with the voltage vectors 15' and 26', so let the voltage vector The angle with the alpha axis is θ, and the following formula can be obtained:

[0121]

[0122] The solution is:

[0123]

[0124] The duty cycle is synthesized by the time of the voltage vector in the sector. Since the two switching tubes in each bridge arm are complementary, only the duty cycle D of the tube on each bridge arm is listed here.

[0125] Ι <![CDATA[V 00′ ]]> <![CDATA[V 15′ ]]> <![CDATA[V 26′ ]]> <![CDATA[V 77′ ]]> <![CDATA[V 26′ ]]> <![CDATA[V 15′ ]]> <![CDATA[V 00′ ]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S B1 ]]> 0 0 1 1 1 0 0 <![CDATA[T1+T0 / 2]]> <![CDATA[S C1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S1 A’ ]]> 0 0 1 1 1 0 0 <![CDATA[T1+T0 / 2]]> <![CDATA[S1 B’ ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S1 C’ ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 4]]>

[0126] ΙΙ <![CDATA[V 00′ ]]> <![CDATA[V 31′ ]]> <![CDATA[V 26′ ]]> <![CDATA[V 77′ ]]> <![CDATA[V 26′ ]]> <![CDATA[V 31′ ]]> <![CDATA[V 00′ ]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[S B1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S C1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S1 A’ ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S1 B’ ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S1 C’ ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 4]]>

[0127] ΙΙΙ <![CDATA[V 00′ ]]> <![CDATA[V 31′ ]]> <![CDATA[V 42′ ]]> <![CDATA[V 77′ ]]> <![CDATA[V 42′ ]]> <![CDATA[V 31′ ]]> <![CDATA[V 00′ ]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S B1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S C1 ]]> 0 0 1 1 1 0 0 <![CDATA[T1+T0 / 2 <!-- 10 -->]]> <![CDATA[S1 A’ ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S1 B’ ]]> 0 0 1 1 1 0 0 <![CDATA[T1+T0 / 2]]> <![CDATA[S1 C’ ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 4]]>

[0128] ΙV <![CDATA[V 00′ ]]> <![CDATA[V 53′ ]]> <![CDATA[V 42′ ]]> <![CDATA[V 77′ ]]> <![CDATA[V 42′ ]]> <![CDATA[V 53′ ]]> <![CDATA[V 00′ ]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S B1 ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[S C1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S1 A’ ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[S1 B’ ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S1 C’ ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 4]]>

[0129]

[0130]

[0131] VΙ <![CDATA[V 00′ ]]> <![CDATA[V 15′ ]]> <![CDATA[V 64′ ]]> <![CDATA[V 77′ ]]> <![CDATA[V 64′ ]]> <![CDATA[V 15′ ]]> <![CDATA[V 00′ ]]> <![CDATA[D*T s ]]> <![CDATA[S A1 ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[S B1 ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S C1 ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[S1 A’ ]]> 0 0 0 1 0 0 0 <![CDATA[T1+T2+T0 / 2]]> <![CDATA[S1 B’ ]]> 0 0 1 1 1 0 0 <![CDATA[T2+T0 / 2]]> <![CDATA[S1 C’ ]]> 0 1 1 1 1 1 0 <![CDATA[T0 / 2]]> <![CDATA[T0 / 4]]> <![CDATA[T2 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T0 / 2]]> <![CDATA[T1 / 2]]> <![CDATA[T2 / 2]]> <![CDATA[T0 / 4]]>

[0132] Modulation method six: Fig.13 As shown, the middle hexagon 46′-51′-62′-13′-24′-35′, that is, 120° space vector decoupling is used for modulation. At this time, the hexagon has a rotation angle θ0 with respect to the alpha-beta coordinate system.

[0133]

[0134] Create a rotation matrix, rotate the alpha-beta coordinate system, make the 24' point on the alpha axis, and divide it into six sectors according to the voltage vector, as shown in the figure. The subsequent calculation method is exactly the same as that described in modulation method 5, and the calculation result can be obtained by substituting modulation method 5.

[0135] Modulation method seven: use the largest hexagon 36′-41′-52′-63′-14′-25′, that is, 60° space vector decoupling for modulation. At this time, the hexagon is basically the same as modulation method one for the alpha-beta coordinate system, and the same analysis method can be used to calculate the result.

[0136] Embodiment 1:

[0137] like Fig.14 , shows a three-port network in which two energy storage systems are coupled to an AC bus through a novel DC-AC-DC circuit of the present invention, and modulation method five is used to perform open-loop control on it.

[0138] like Fig.15 As shown, modulation method 5 is used to design T s = 20kHz triangular carrier wave, can generate duty cycle as shown in the figure in real time. The green part in the upper half of the figure is the power electronic switch device S A1 Duty cycle, blue is the power electronic switching device S B1 Duty cycle, red is the power electronic switch device S C1The green part in the lower part of the figure is the power electronic switch device S1 A’ Duty cycle, blue is the power electronic switch device S1 B’ Duty cycle, red is the power electronic switch device S1 C’ duty cycle.

[0139] The turn-on or turn-off sequence of the power electronic switch devices in each sector is obtained by comparing each duty cycle with the triangular carrier, as shown in the figure. By controlling the power electronic switch devices, the voltage and current required by the transformer can be achieved, such as Fig.16 and Fig.17 shown.

[0140] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium, and when the program is executed, it can include the processes of the embodiments of the above-mentioned methods. The storage medium can be a disk, an optical disk, a read-only memory (ROM) or a random access memory (RAM).

[0141] It should be understood that the detailed description of the technical solutions of the present invention by means of the preferred embodiments is illustrative rather than restrictive. A person skilled in the art may modify the technical solutions described in the embodiments, or replace some of the technical features by equivalents, based on reading the specification of the present invention; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A novel DC-AC-DC three-port circuit, characterized in that: The three-port circuit includes: a three-phase AC interface U A , U B , U C And two DC interfaces U DC , U DC’ ; The DC-AC-DC three-port circuit includes a transformer, two capacitors, and a power electronic switch device; each phase winding of the transformer is T A , T B , T C .

2. A novel DC-AC-DC three-port circuit according to claim 1, characterized in that: The two power electronic switch devices form bridge arms.

3. A novel DC-AC-DC three-port circuit according to claim 1, characterized in that: There are 12 electronic switch devices, including: S A1 , S A2 , S B1 , S B2 , S C1 , S C2 、S1 A’ 、S2 A’ 、S1 B’ 、S2 B’ 、S1 C’ 、S2 C’ ; Power Electronic Switching Devices A1 , S A2 Composition A Bridge arm, S B1 , S B2 Composition B Bridge arm, S C1 , S C2 Composition C Bridge arm, S1 A’ 、S2 A’ Composition A’ Bridge arm, S1 B’ 、S2 B’ Composition B’ Bridge arm, S1 C’ 、S2 C’ Composition C’ Bridge arms, forming the midpoints A, B, C, A', B', C' of the bridge arms respectively; DC interface U DC The positive and negative electrodes are connected to capacitor C DC The two ends are then connected to S A , S, S C The two ends of the bridge arm; similarly, the DC interface U DC’ The positive and negative electrodes are connected to capacitor C DC’ The two ends are then connected to S A’ , S B’ , S C’ Both ends of the bridge arm.

4. A novel DC-AC-DC three-port circuit according to claim 1, characterized in that: The transformer winding T A , T B , T C There are two sets of coils on the AC system side and the converter side, of which T A , T B , T C The coil on the AC system side is connected to the three-phase AC system, and the two ends of the coil on the converter side are connected to the corresponding bridge arm midpoints, namely T A The two ends of the transformer coil are connected to A and A'; T B The two ends of the transformer coil are connected to B and B'; T C Both ends of the converter side coil are connected to C and C'.

5. A novel DC-AC-DC three-port circuit modulation method, the modulation method is applicable to the DC-AC-DC three-port circuit according to any one of claims 1 to 4, characterized in that: The circuit includes two working modes, namely: Working mode 1: bidirectional energy flow between a single DC system and an AC system; Working mode 2: Two-way energy flow between two DC systems and the AC system.

6. A novel DC-AC-DC three-port circuit modulation method according to claim 5, characterized in that: The working mode is as follows: Modulation method 1: Power electronic switching device S2 A’ 、S2 B’ 、S2 C’ Normally on, S1 A’ 、S1 B’ 、S1 C’ Normally off, the controller controls the power electronic switching device S A1 , S A2 , S B1 , S B2 , S C1 , S C2 Modulation is performed to enable bidirectional energy control between the DC system and the AC system; Since the power electronic switch device does not allow two switch devices in the same bridge arm to be turned on or off at the same time, the following working mode is obtained: 3 =8 switching states. By writing the KVL equation based on the volt-second balance, the 8 voltage vectors corresponding to each switching state can be obtained. Modulation method 2: Power electronic switching device S1 A’ 、S1 B’ 、S1 C’ Normally on, S A’2 、S2 B’ 、S2 C’ Normally off, the controller controls the power electronic switching device S A1 , S A2 , S B1 , S B2 , S C1 , S C2 Modulation is performed so that the DC system and the AC system can perform bidirectional energy control, and the modulation method is exactly the same as that described in modulation method 1. Modulation method three: power electronic switching device S A2 , S B2 , S C2 Normally on, S A1 , S B1 , S C1 Normally off, the controller controls the power electronic switching device S1 A’ 、S1 B’ 、S1 C’ 、S2 A’ 、S2 B’ 、S2 C’ Modulation is performed to enable bidirectional energy control between the DC system and the AC system; the eight voltage vectors corresponding to each switching state can be obtained by writing the KVL equation based on the volt-second balance. Modulation method 4: Power electronic switching device S A1 , S B1 , S C1 Normally on, S A2 , S B2 , S C2 Normally off, the controller controls the power electronic switching device S1 A’ 、S1 B’ 、S1 C’ 、S2 A’ 、S2 B’ 、S2 C’ Modulation is performed so that the DC system and the AC system can perform bidirectional energy control, and the modulation method is exactly the same as that described in modulation method three.

7. A novel DC-AC-DC three-port circuit modulation method according to claim 5, characterized in that: The working mode 2 is as follows: Based on working mode one, the voltage vectors of the AC system and the DC system are synthesized with the voltage vectors of the AC system and the DC system two, and it is obtained that the novel DC-AC-DC three-port circuit has 64 switching states. The voltage vector corresponding to each switching state can be obtained by writing the KVL equation according to the volt-second balance.

8. A novel DC-AC-DC three-port circuit modulation method according to claim 7, characterized in that: In the second working mode, Modulation method 5: Modulation is performed using the middle hexagon 26′-31′-42′-53′-64′-15′, i.e., 120° space vector decoupling. At this time, the hexagon has a rotation angle θ0 with respect to the alpha-beta coordinate system. Create a rotation matrix, rotate the alpha-beta coordinate system, make the 15' point on the alpha axis, and divide it into six sectors according to the voltage vector; Project the desired synthesized voltage vector onto the rotated alpha'-beta' coordinate system through the rotation matrix; Referring to modulation method 1, sector judgment is performed, and the corresponding vector can be selected to synthesize the target vector through sector judgment.

9. A novel DC-AC-DC three-port circuit modulation method according to claim 7, characterized in that: Modulation method six: using the middle hexagon 46′-51′-62′-13′-24′-35′, that is, 120° space vector decoupling for modulation, at which the hexagon has a rotation angle θ0 with respect to the alpha-beta coordinate system; A rotation matrix is ​​established to rotate the alpha-beta coordinate system so that the 24' point is on the alpha axis and the voltage vector is divided into six sectors. The subsequent calculation method is exactly the same as that described in modulation method five, and the calculation result is obtained by substituting modulation method five.

10. A novel DC-AC-DC three-port circuit modulation method according to claim 7, characterized in that: Modulation method seven: Modulation is performed using the largest hexagon 36′-41′-52′-63′-14′-25′, i.e., 60° space vector decoupling. The hexagon at this time is the same as modulation method one for the alpha-beta coordinate system, and the same analysis method is used to calculate the results.

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