A half-wave alternating AC-AC converter topology and control method thereof

Abstract

The present invention discloses a half-wave alternating AC-AC converter topology and a control method thereof, which relates to the technical field of power supply system, and includes three phase unit circuits with the same structure, each phase unit circuit includes a symmetrical input side converter and an output side converter, and is respectively connected to AC systems of different frequencies; wherein a half-wave shaping switch group includes a positive terminal, a negative terminal and an AC output terminal, one end of a variable frequency half-wave generation module is connected to the positive terminal, connected to the positive terminal of the other side through a filter inductor, and the other end is connected to the negative terminal of the other side through a negative terminal, and both ends are connected to the AC system through an AC output terminal; the variable frequency half-wave generation module outputs a step sine half wave, and the half-wave shaping switch group performs translation and flipping operations on the step sine half wave to obtain a shaped half wave, and obtains an AC side phase voltage sine wave based on the shaped half wave within a cycle. Frequency isolation of the AC systems on both sides is achieved, and the output of a complete AC side phase voltage sine wave is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply systems, and in particular to a half-wave alternating AC-AC converter topology and a control method thereof. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] The modular multilevel matrix converter (M3C) uses submodules (SM) as basic power units and adopts cascaded full-bridge submodules to form three-phase nine-bridge arms. The topology is as follows: Figure 1 As shown in the figure, compared with the three-phase six-bridge-arm back-to-back system, M3C saves three bridge arms, has a more compact structure, and has the characteristics of high output voltage quality, low equivalent switching frequency and strong scalability. It is an important development direction for the research on high-voltage and large-capacity AC-AC converter topology.

[0004] As voltage levels and transmission power increase, the M3C topology using a large number of cascaded submodules has at least the following problems:

[0005] (1) M3C directly connects two AC systems of different frequencies through a three-phase nine-bridge structure. Each bridge arm realizes the transformation from the three-phase AC voltage at the input end to the three-phase AC voltage at the output end, and this transformation includes the transformation of the three-phase voltage amplitude and the three-phase voltage frequency. The bridge arm voltage and current both contain heterogeneous frequency components. Then, the maximum output voltage of each bridge arm of M3C is approximately the sum of the phase voltage peaks of the two AC systems of different frequencies, that is, each bridge arm of M3C needs to bear the sum of the phase voltage peaks of the two AC systems, which causes the number of cascaded sub-modules in the bridge arm to increase exponentially, increasing the cost of the converter, and the utilization rate is low, the loss is large, the operating efficiency and economy are low, and its engineering application is limited.

[0006] (2) Since M3C directly connects two AC systems of different frequencies through a three-phase nine-bridge-arm structure, the heterogeneous energy of the AC systems on both sides is directly coupled in the bridge arms, resulting in the M3C system having strong nonlinearity and strong coupling, and the circulation flow path is complex, with a large degree of control freedom.

[0007] (3) The fluctuation of the capacitor voltage of the submodule in each bridge arm of the M3C leads to voltage differences between the bridge arms, and the current flow path between the bridge arms causes circulating current. Due to the complex structure of the M3C system, the circulating current path exists not only between the bridge arms, but also between the phases through the input and output ends. However, in general, the operation of M3C does not require the existence of circulating current, so additional circulating current suppression strategies are usually required to suppress the circulating current to zero.

[0008] (4) The capacitor voltage balancing control of M3C includes three parts: total capacitor voltage balancing control, capacitor voltage balancing control between bridge arms, and capacitor voltage balancing control between sub-modules within the bridge arm. The control system has many levels. Moreover, since the AC systems on both sides are directly connected through the bridge arm, when the system is running stably, the spectrum of the M3C bridge arm power is complex, and there are ripple components of different frequencies in the sub-module capacitor current and ripple voltage, and the mathematical relationship is complex, which makes its voltage balancing control, especially the voltage balancing control between bridge arms, more difficult. Summary of the invention

[0009] In order to solve the above problems, the present invention proposes a half-wave alternating AC-AC converter topology and a control method thereof, wherein two AC systems with different frequencies are interconnected through a filtering inductor to achieve frequency isolation of the AC systems on both sides, and a half-wave shaping switch group is introduced. A variable frequency half-wave generation module outputs a stepped sinusoidal half-wave, and after the shaping operation of the half-wave shaping switch group, the output of a complete AC side phase voltage sinusoidal wave is achieved.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a half-wave alternating AC-AC converter topology, comprising: three phase unit circuits of the same structure and connected in parallel, each phase unit circuit comprising an input-side converter and an output-side converter of symmetrical structure, the input-side converter and the output-side converter being respectively connected to AC systems of different frequencies;

[0012] The input-side converter and the output-side converter both include a half-wave shaping switch group and a variable frequency half-wave generating module, the half-wave shaping switch group includes a positive terminal, a negative terminal and an AC output terminal, one end of the variable frequency half-wave generating module is connected to the positive terminal, and is connected to the positive terminal on the other side through a filter inductor, the other end of the variable frequency half-wave generating module is connected to the negative terminal, and is connected to the negative terminal on the other side through the negative terminal, and both ends of the variable frequency half-wave generating module are connected to the AC output terminal, and are connected to the AC system through the AC output terminal;

[0013] The variable frequency half-wave generation module of the converter on each side outputs a stepped sinusoidal half-wave of corresponding frequency based on the frequency of the connected AC system. In each half-wave time period, the half-wave shaping switch group translates and flips the stepped sinusoidal half-wave to obtain a shaped half-wave, and a complete AC side phase voltage sine wave is obtained based on the shaped half-wave within one cycle.

[0014] As an optional implementation, AC systems of different frequencies are interconnected via filtering inductors to achieve power coupling and frequency isolation of the AC systems of different frequencies.

[0015] As an optional implementation, the stepped sinusoidal half-wave oscillates periodically at twice the frequency of the connected AC system.

[0016] As an optional implementation, the on-off state of the half-wave shaping switch group is controlled according to the phase voltage sinusoidal reference wave, so as to shape the stepped sinusoidal half-wave in different operation modes.

[0017] As an optional implementation, the half-wave shaping switch group includes a second switch, a first switch, a third switch and a fourth switch connected in series in sequence;

[0018] One end of the second switch is connected to one end of the first switch, the connection point between the first switch and the second switch is connected to one end of the variable frequency half-wave generating module, and the other end of the second switch is used as a positive terminal and is connected to the positive terminal on the other side through a filtering inductor;

[0019] One end of the fourth switch is connected to one end of the third switch, the connection point between the third switch and the fourth switch is connected to the other end of the variable frequency half-wave generating module, and the other end of the fourth switch is used as a negative terminal and connected to the negative terminal on the other side;

[0020] The connection point between the first switch and the third switch serves as an AC output terminal, and the variable frequency half-wave generating module is connected to the AC system through the AC output terminal.

[0021] As an optional implementation, when the phase voltage sinusoidal reference wave is positive, the first switch and the fourth switch are turned off, the second switch and the third switch are turned on, and the AC current flows to the positive terminal, which is the operation mode I;

[0022] When the phase voltage sinusoidal reference wave is negative, the first switch and the fourth switch are turned on, the second switch and the third switch are turned off, and the AC current flows to the negative terminal, which is the operation mode II.

[0023] As an optional implementation, the half-wave shaping switch group in each operating mode is divided into two groups, the on-off signals of each group of switches are consistent, the two groups of switches are alternately and complementary turned on, the on-off frequency is the frequency of the connected AC system, and the conduction angle of each group of switches in each power frequency cycle is π.

[0024] As an optional implementation, in operation mode I, the stepped sine half wave is shifted downward by U dc / 2 to the coordinate axis, and flip it upward to obtain the positive half-wave of the AC phase voltage;

[0025] In operating mode II, the stepped sine half wave is shifted downward by U dc / 2 to the coordinate axis, and the negative half-wave of the AC phase voltage is obtained; U dc is the DC bus voltage;

[0026] In one cycle, a complete AC side phase voltage sinusoidal wave is obtained based on the positive half-wave of the AC phase voltage and the negative half-wave of the AC phase voltage.

[0027] In a second aspect, the present invention provides a control method for a half-wave alternating AC-AC converter topology, which adopts the half-wave alternating AC-AC converter topology described in the first aspect, and comprises:

[0028] AC systems of different frequencies are interconnected through filtering inductors, and the variable frequency half-wave generation module of the converter on each side outputs a stepped sinusoidal half-wave of the corresponding frequency based on the frequency of the connected AC system;

[0029] In each half-wave time period, the on-off state of the half-wave shaping switch group is controlled according to the phase voltage sinusoidal reference wave, so that in different operating modes, the half-wave shaping switch group translates and flips the step sinusoidal half-wave to obtain a shaped half-wave, and a complete AC side phase voltage sinusoidal wave is obtained based on the shaped half-wave within one cycle.

[0030] As an optional implementation, the half-wave shaping switch group in each operating mode is divided into two groups, the on-off signals of each group of switches are consistent, the two groups of switches are alternately and complementary turned on, the on-off frequency is the frequency of the connected AC system, and the conduction angle of each group of switches in each power frequency cycle is π;

[0031] When the phase voltage sinusoidal reference wave is positive, the stepped sinusoidal half wave is shifted downward by U dc / 2 to the coordinate axis, and flip it upward to obtain the positive half-wave of the AC phase voltage;

[0032] When the phase voltage sinusoidal reference wave is negative, the stepped sinusoidal half wave is shifted downward by U dc / 2 to the coordinate axis, and the negative half-wave of the AC phase voltage is obtained; U dc is the DC bus voltage;

[0033] In one cycle, a complete AC side phase voltage sinusoidal wave is obtained based on the positive half-wave of the AC phase voltage and the negative half-wave of the AC phase voltage.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention proposes a half-wave alternating AC-AC converter topology and a control method thereof, wherein the two ends of each phase unit circuit are respectively connected to AC systems with different operating frequencies, and the two AC systems are interconnected through a filtering inductor to achieve frequency isolation of the AC systems on both sides, thereby avoiding direct coupling of the powers of the AC systems on both sides in the bridge arm, so as to achieve weak power coupling of the AC systems with different operating frequencies; similarly, through the frequency isolation of the filtering inductor, the power frequency of each variable frequency half-wave generating module is single, which is only the frequency of the AC system on this side, and the mathematical relationship between the sub-module capacitor current and the ripple voltage component is simpler than that of the existing M3C, thereby greatly reducing the difficulty of voltage equalization control.

[0036] The present invention proposes a half-wave alternating AC-AC converter topology and a control method thereof. Each phase unit circuit is internally divided into an input side converter and an output side converter with symmetrical structures, which are used to bear the energy of the AC systems corresponding to the input side and the output side respectively. Therefore, the input side converter and the output side converter of each phase unit circuit only need to operate at the corresponding frequency of the connected AC system, and shape the AC power at the corresponding frequency into DC power containing pulsating ripples, and only need to realize the voltage output of the AC systems on their respective corresponding sides.

[0037] The present invention proposes a half-wave alternating AC-AC converter topology and a control method thereof, introduces a half-wave shaping switch group, and a frequency conversion half-wave generating module outputs a stepped sinusoidal half-wave. After the shaping operation of the half-wave shaping switch group, the output of a complete AC side phase voltage sinusoidal wave can be achieved; therefore, compared with the existing M3C in which the cascaded submodules in each bridge arm need to output the peak superposition voltage of the AC system phase voltage on both sides, the frequency conversion half-wave generating module of the present invention only needs to output the half-wave form of the AC system phase voltage on one side, which greatly reduces the number of sub-modules and realizes the lightweight design of the AC-AC converter.

[0038] The present invention proposes a half-wave alternating AC-AC converter topology and a control method thereof. By controlling the on-off state of the half-wave shaping switch group in the input side converter and the output side converter, the three-phase AC phase current of the corresponding side AC system is shaped into a DC current containing a pulsating ripple, and after filtering by the filter inductor at the common DC end, the frequency isolation of the AC systems on both sides is achieved; although the variable frequency half-wave generation module group will have capacitor voltage fluctuations with small differences, due to the alternating conduction of the half-wave shaping switch group, there is no current flow path between the variable frequency half-wave generation module groups inside the topology, so no circulating current is generated.

[0039] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0041] Figure 1 It is the topology of the existing M3C;

[0042] Figure 2 A structural diagram of a half-wave alternating AC-AC converter topology provided in Embodiment 1 of the present invention;

[0043] Figure 3(a)-Figure 3(c) A schematic diagram of single-phase frequency conversion provided in Example 1 of the present invention;

[0044] Figure 4(a)-Figure 4(c) Two operating modes of the half-wave commutation control strategy provided in Example 1 of the present invention;

[0045] Figure 5 The A-phase unit equivalent circuit provided by Embodiment 1 of the present invention;

[0046] Figure 6 A detailed flow chart of the half-wave commutation control strategy provided in Example 1 of the present invention;

[0047] Figure 7 The output voltage reference waveform of the variable frequency half-wave generation module group of phase A provided in embodiment 1 of the present invention;

[0048] Figure 8(a)-Figure 8(b) This is the voltage waveform at the terminal of the half-wave shaped switch group under the half-wave commutation control strategy provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0050] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0051] It should be noted that the terms used herein are only for describing specific embodiments, and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that the terms "include" and "have" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0052] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0053] Example 1

[0054] This embodiment provides a half-wave alternating AC-AC converter topology, comprising: three phase unit circuits of the same structure and connected in parallel, each phase unit circuit comprising an input side converter and an output side converter of symmetrical structure, the input side converter and the output side converter being respectively connected to AC systems of different frequencies;

[0055] The input-side converter and the output-side converter both include a half-wave shaping switch group and a variable frequency half-wave generating module, the half-wave shaping switch group includes a positive terminal, a negative terminal and an AC output terminal, one end of the variable frequency half-wave generating module is connected to the positive terminal, and is connected to the positive terminal on the other side through a filter inductor, the other end of the variable frequency half-wave generating module is connected to the negative terminal, and is connected to the negative terminal on the other side through the negative terminal, and both ends of the variable frequency half-wave generating module are connected to the AC output terminal, and are connected to the AC system through the AC output terminal;

[0056] The variable frequency half-wave generation module of the converter on each side outputs a stepped sinusoidal half-wave of corresponding frequency based on the frequency of the connected AC system. In each half-wave time period, the half-wave shaping switch group translates and flips the stepped sinusoidal half-wave to obtain a shaped half-wave, and a complete AC side phase voltage sine wave is obtained based on the shaped half-wave within one cycle.

[0057] like Figure 2 The structure diagram of the half-wave alternating AC-AC converter topology is shown, including an A-phase unit circuit, a B-phase unit circuit and a C-phase unit circuit with the same structure and connected in parallel. Figure 2 Only the specific structure of the A-phase unit circuit is given;

[0058] Each phase unit circuit is a completely symmetrical structure, including a symmetrical input-side converter and an output-side converter, wherein the input-side converter and the output-side converter are respectively connected to corresponding phases of an AC system of different frequencies;

[0059] The input side converter and the output side converter both include a half-wave shaping switch group and a variable frequency half-wave generating module. The variable frequency half-wave generating modules of the input side converter and the output side converter constitute the variable frequency half-wave generating module group of each phase unit circuit, so each phase unit circuit includes a variable frequency half-wave generating module group and two half-wave shaping switch groups.

[0060] The half-wave shaping switch group includes four switches, namely the first switch D a11 , the second switch D al2 , the third switch D a21 and the fourth switch D a22 , the second switch D al2 , first switch D a11 , the third switch D a21 and the fourth switch D a22 Connect in series;

[0061] Among them, the second switch D al2 One end of the first switch D a11 One end of the first switch D a11 and the second switch D al2 The connection point is connected to one end of the variable frequency half-wave generation module, and the second switch D al2The other end is used as the positive terminal 1, through the filter inductor L f Connect to the positive terminal 4 on the other side;

[0062] Fourth switch D a22 One end of the third switch D a21 One end of the third switch D a21 and the fourth switch D a22 The connection point is connected to the other end of the variable frequency half-wave generation module, and the fourth switch D a22 The other end is used as the negative terminal 3, which is directly connected to the negative terminal 6 on the other side;

[0063] First switch D a11 and the third switch D a21 The connection point is used as the AC output terminal 2 (the other side is the AC output terminal 5), and the variable frequency half-wave generation module is connected to the AC system through the AC output terminal.

[0064] Among them, the second switch D a12 and the fourth switch D a22 It is composed of multiple integrated gate commutated thyristors (IGCT) connected in series. a11 and the third switch D a21 It is composed of multiple IGCTs connected in series and then an anti-series IGCT. The anti-series IGCT is used to bear the negative pressure. The variable frequency half-wave generation module is composed of multiple full-bridge sub-modules (full-bridge SM, FBSM) cascaded.

[0065] In this embodiment, the two ends of each phase unit circuit are respectively connected to AC systems with different operating frequencies, and a filter inductor L is connected between the two AC systems. f Interconnection to achieve power coupling of AC systems with different operating frequencies.

[0066] From the introduction of the existing M3C in the background technology, it can be seen that the existing M3C directly connects two AC systems with different frequencies through three-phase nine bridge arms. Each bridge arm realizes the transformation from the three-phase AC voltage at the input end to the three-phase AC voltage at the output end. This transformation includes the transformation of the three-phase voltage amplitude and the transformation of the three-phase voltage frequency. The bridge arm voltage and the bridge arm current both contain heterofrequency components. Therefore, the maximum output voltage of each bridge arm is approximately the sum of the phase voltage peaks of the two AC systems with different frequencies, which causes the number of cascaded sub-modules in the bridge arm to increase exponentially.

[0067] As for the present embodiment, although two AC systems of different frequencies are also connected and although there is heterofrequency energy within the topology, each phase unit circuit is divided into a symmetrical input side converter and an output side converter, which are used to bear the energy of the corresponding input side and output side AC systems respectively. Therefore, the input side converter and the output side converter of each phase unit circuit only need to operate at the corresponding frequency of the connected AC system, and shape the AC power at the corresponding frequency into DC power containing pulsating ripples, and only need to realize the voltage output of the AC system on each corresponding side.

[0068] Secondly, the AC system power on both sides of the existing M3C is directly coupled in the bridge arm, which has strong coupling. In this embodiment, the DC power output by the input side converter and the output side converter of each phase unit circuit is connected through the filter inductor of the internal common DC terminal, thereby realizing frequency isolation of the AC systems on both sides, avoiding the power of the AC systems on both sides from being directly coupled in the bridge arm, realizing weak coupling, and simple control.

[0069] Moreover, the present embodiment introduces a half-wave shaping switch group, and the frequency conversion half-wave generation module outputs a stepped sinusoidal half-wave. After the shaping operation of the half-wave shaping switch group, the output of a complete AC side phase voltage sinusoidal wave can be achieved; therefore, compared with the existing M3C in which the cascaded submodules in each bridge arm need to output the peak superposition voltage of the AC system phase voltage on both sides, the frequency conversion half-wave generation module of the present embodiment only needs to output the half-wave form of the AC system phase voltage on one side, which greatly reduces the number of sub-modules and realizes the lightweight design of the AC-converter.

[0070] like Figure 3(a)-Figure 3(c) This is a schematic diagram of single-phase frequency conversion. Based on the power transmission direction of the connected AC systems on both sides, each phase unit circuit is divided into a symmetrical input-side converter and an output-side converter, and the half-wave conversion principle implemented is also the same: first, the frequency conversion half-wave generation module generates a stepped sinusoidal half-wave of a multi-level voltage of corresponding frequency based on the frequency of the connected AC system, and periodically fluctuates at twice the frequency of the connected AC system; then, the on-off state of the half-wave shaping switch group is controlled, and the stepped sinusoidal half-wave is shaped into a complete AC side phase voltage sinusoidal wave through the half-wave shaping switch group, thereby completing power transmission and frequency conversion.

[0071] The following is a detailed description taking the input side converter of the A-phase unit circuit as an example.

[0072] Assuming that the operating frequency of the AC system is 50 Hz, this embodiment provides a half-wave commutation control strategy to minimize the number of sub-modules required for the half-wave alternating AC-AC converter. Figure 4(a)-Figure 4(c) There are two operating modes under this control strategy, specifically:

[0073] When the phase voltage sinusoidal reference wave is positive, the first switch Da11 and the fourth switch D a22 Turn off, the second switch D al2 and the third switch D a21 Conducting, AC current flows to the positive terminal, and the phase unit is in operation mode I;

[0074] When the phase voltage sinusoidal reference wave is negative, the first switch D a11 and the fourth switch D a22 The second switch D is turned on. al2 and the third switch D a21 When the phase unit is turned off, the AC current flows to the negative terminal and the phase unit is in operation mode II.

[0075] Therefore, the half-wave shaping switch group on each side of each phase unit circuit is divided into two groups, namely switch group I: the second switch D al2 and the third switch D a21 , switch group II: first switch D a11 and the fourth switch D a22 ; The on-off signals of each switch group are consistent, and the two switch groups are alternately and complementaryly turned on. The on-off frequency is the frequency of the AC system, that is, the industrial frequency is 50Hz, and the conduction angle of each switch group in each industrial frequency cycle is π.

[0076] Define the operation mode switching function S of the A phase unit circuit a for:

[0077]

[0078] By controlling the switching of the submodules, the variable frequency half-wave generation module group can be equivalent to a voltage source, and output an equivalent step waveform based on the theoretical modulation wave, such as Figure 5 The figure shows the equivalent circuit of the A phase unit. According to the equivalent circuit and the current path of the operating mode, the voltage u of the variable frequency half-wave generation module group ws and current i ws Respectively expressed as:

[0079]

[0080] i ws =(1-2S a )i a (3)

[0081] Where U dc is the DC bus voltage, u a 、i a They are the A-phase output phase voltage and the A-phase output current respectively.

[0082] The voltage and current of the four switches of the half-wave shaping switch group are expressed as:

[0083]

[0084]

[0085]

[0086] Among them, u d11 、u dl2 、u d21 and u d22 The first switch D a11 , the second switch D al2 , the third switch D a21 and the fourth switch D a22 The voltage, i d11 、i dl2 、i d21 and i d22 The first switch D a11 , the second switch D al2 , the third switch D a21 and the fourth switch D a22 of current.

[0087] like Figure 6 The following is a detailed flow chart of the half-wave commutation control strategy. Taking phase A as an example, based on the sinusoidal reference wave of the phase voltage Determine the operation mode, specifically:

[0088] when The phase unit operates in operation mode I, that is, the operation mode switching function S a =1, and switch group I(D al2 , D a21 ) is turned on, switch group II (D a11 , D a22 ) is turned off; when S a =0, switch group I(D al2 , D a21 ) is turned off, switch group II (D a11 , D a22 ) is turned on;

[0089] Based on the phase voltage sinusoidal reference wave And the operation mode switch function S a , combined with formula (2), we can get the reference voltage waveform Based on the reference voltage waveform The switching submodule performs the nearest level approximation and outputs a stepped sine half-wave u ws ;

[0090] The step sine half-wave u wsPerform translation and flip operations, namely:

[0091] In the operating mode I state, switch group I is turned on and switch group II is turned off, and the step sine half wave u ws Shift downU dc / 2 to the coordinate axis, and flip it upward to obtain the positive half-wave of the AC phase voltage;

[0092] In the operating mode II, switch group I is turned off and switch group II is turned on, and the step sine half wave u ws Shift downU dc / 2 to the coordinate axis, and the negative half-wave of the AC phase voltage is obtained;

[0093] In a complete power frequency cycle, a complete AC side phase voltage sinusoidal wave is obtained based on the positive half-wave of the AC phase voltage and the negative half-wave of the AC phase voltage obtained by shaping.

[0094] In this embodiment, when the phase voltage passes through zero, the 50 Hz power frequency switching of the two half-wave shaping switch groups in each phase is performed, and the output voltage extreme value required by the variable frequency half-wave generation module group is the lowest, which is only U dc / 2, thus minimizing the number of submodules required for the variable frequency half-wave generation module group.

[0095] Since the sub-module capacitor is the carrier for heterogeneous energy exchange based on the multi-level converter of sub-module cascade, if the system is to be operated safely and stably, a corresponding capacitor voltage balancing control strategy is required to stabilize the capacitor voltage of each sub-module at the rated value; and based on the analysis in the background technology, the control system of the existing M3C has many levels, and since the AC systems on both sides are directly connected through the bridge arm, the existing M3C needs to adopt additional voltage balancing control to ensure the stable operation of the system, and the existing M3C has circulating current, and an additional circulating current suppression strategy is also required to suppress the circulating current to zero.

[0096] In this embodiment, by controlling the on-off state of the half-wave shaping switch group in the input side converter and the output side converter, the three-phase AC current of the corresponding side AC system is shaped into a DC current containing a pulsating ripple, and after filtering by the filter inductor at the common DC end, the frequency isolation of the AC systems on both sides is achieved; although the variable frequency half-wave generation module group will have capacitor voltage fluctuations with small differences, due to the alternating conduction of the half-wave shaping switch group, there is no current flow path between the variable frequency half-wave generation module groups within the topology, so no circulating current will be generated;

[0097] Furthermore, in the present application, the input side converter and the output side converter are connected through a filter inductor, and there is only a weak coupling relationship between the two. Each side only includes a variable frequency half-wave generation module composed of cascaded sub-modules, so the capacitor voltage balancing control only includes the total capacitor voltage of each converter and the capacitor voltage balancing control between sub-modules. The control system is simplified compared to the existing M3C.

[0098] Finally, the frequency isolation of the AC systems on both sides is achieved through filtering inductors, so the power frequency of each variable frequency half-wave generation module is single, which is only the frequency of the AC system on that side. The mathematical relationship between the sub-module capacitor current and ripple voltage components is simpler than that of the existing M3C, making its voltage equalization control less difficult.

[0099] In order to verify the stable operation conditions of the half-wave alternating AC-AC converter topology under the half-wave commutation control strategy, the expressions of the phase voltage and current on the AC side of phase A are defined as:

[0100]

[0101] Where U m ,I m They represent the phase voltage amplitude and current amplitude respectively, w is the power frequency angular frequency, and j is the power factor angle.

[0102] Substituting equation (7) into equation (2) and equation (3), we can obtain u within one power frequency cycle: ws 、i ws for:

[0103]

[0104] Where m = U m / (U dc / 2) is the voltage modulation ratio.

[0105] In order to ensure the energy conservation of the submodule capacitor, the variable frequency half-wave generation module group should have no energy accumulation within one power frequency cycle T, that is:

[0106]

[0107] According to formula (9), the half-wave alternating AC-AC converter topology of this embodiment operates stably at m=4 / π under the half-wave commutation control strategy.

[0108] Combining formula (8), the output voltage reference waveform of the variable frequency half-wave generation module group of phase A is as follows: Figure 7 As shown, a full-bridge submodule should be used to output negative voltage to support the AC side voltage output of the converter. Figure 7 It can be seen that the maximum output voltage of the variable frequency half-wave generation module group is U dc / 2.

[0109] Assume the submodule capacitor voltage is U c , based on this control strategy, the number of submodules required for each phase unit variable frequency half-wave generation module group is only N / 2, where:

[0110]

[0111] At this time, the output voltage level of the AC side is:

[0112]

[0113] In the formula, round() is the integer function, so N' is greater than N+1, and the output voltage quality on the AC side is good.

[0114] In addition, based on equations (4) and (5), the voltage waveform of the half-wave shaped switch group under the proposed control strategy can be obtained as follows: Figure 8(a)-Figure 8(b) As shown, switch D 11 , D 21 The output voltage of the variable frequency half-wave generation module group needs to be borne, and the maximum positive voltage and maximum negative voltage that can be borne are:

[0115]

[0116] Switch D 12 , D 22 The maximum voltage it can withstand is:

[0117]

[0118] So when m=4 / π, switch D 11 , D 21 All with 0.64N withstand voltage U c The IGCTs are connected in series, of which 0.5N are connected in the forward direction and 0.14N are connected in the reverse direction; switch D 12 , D 22 The withstand voltage is 1.14N U c The IGCT cascade is composed of

[0119] Example 2

[0120] This embodiment provides a control method for a half-wave alternating AC-AC converter topology, which adopts the half-wave alternating AC-AC converter topology described in Embodiment 1, including:

[0121] AC systems of different frequencies are interconnected through filtering inductors, and the variable frequency half-wave generation module of the converter on each side outputs a stepped sinusoidal half-wave of the corresponding frequency based on the frequency of the connected AC system;

[0122] In each half-wave time period, the on-off state of the half-wave shaping switch group is controlled according to the phase voltage sinusoidal reference wave, so that in different operating modes, the half-wave shaping switch group translates and flips the step sinusoidal half-wave to obtain a shaped half-wave, and a complete AC side phase voltage sinusoidal wave is obtained based on the shaped half-wave within one cycle.

[0123] In this embodiment, the half-wave shaping switch group in each operation mode is divided into two groups, the on-off signals of each group of switches are consistent, the two groups of switches are alternately and complementary turned on, the on-off frequency is the frequency of the connected AC system, and the conduction angle of each group of switches in each power frequency cycle is π;

[0124] When the phase voltage sinusoidal reference wave is positive, the stepped sinusoidal half wave is shifted downward by U dc / 2 to the coordinate axis, and flip it upward to obtain the positive half-wave of the AC phase voltage;

[0125] When the phase voltage sinusoidal reference wave is negative, the stepped sinusoidal half wave is shifted downward by U dc / 2 to the coordinate axis, and the negative half-wave of the AC phase voltage is obtained; U dc is the DC bus voltage;

[0126] In one cycle, a complete AC side phase voltage sinusoidal wave is obtained based on the positive half-wave of the AC phase voltage and the negative half-wave of the AC phase voltage.

[0127] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A half-wave alternating AC-AC converter topology, characterized in that: include: Three phase unit circuits with the same structure and connected in parallel, each phase unit circuit includes an input side converter and an output side converter with symmetrical structures, and the input side converter and the output side converter are respectively connected to AC systems with different frequencies; The input-side converter and the output-side converter both include a half-wave shaping switch group and a variable frequency half-wave generating module, the half-wave shaping switch group includes a positive terminal, a negative terminal and an AC output terminal, one end of the variable frequency half-wave generating module is connected to the positive terminal, and is connected to the positive terminal on the other side through a filter inductor, the other end of the variable frequency half-wave generating module is connected to the negative terminal, and is connected to the negative terminal on the other side through the negative terminal, and both ends of the variable frequency half-wave generating module are connected to the AC output terminal, and are connected to the AC system through the AC output terminal; The variable frequency half-wave generation module of the converter on each side outputs a stepped sinusoidal half-wave of corresponding frequency based on the frequency of the connected AC system. In each half-wave time period, the half-wave shaping switch group translates and flips the stepped sinusoidal half-wave to obtain a shaped half-wave, and a complete AC side phase voltage sine wave is obtained based on the shaped half-wave within one cycle.

2. A half-wave alternating AC-AC converter topology as claimed in claim 1, characterized in that: AC systems of different frequencies are interconnected through filtering inductors to achieve power coupling and frequency isolation of AC systems of different frequencies.

3. A half-wave alternating AC-AC converter topology as claimed in claim 1, characterized in that: The stepped sinusoidal half-wave oscillates periodically at twice the frequency of the connected AC system.

4. A half-wave alternating AC-AC converter topology as claimed in claim 1, characterized in that: According to the phase voltage sinusoidal reference wave, the on-off state of the half-wave shaping switch group is controlled to shape the stepped sinusoidal half-wave in different operation modes.

5. A half-wave alternating AC-AC converter topology as claimed in claim 1, characterized in that: The half-wave shaping switch group comprises a second switch, a first switch, a third switch and a fourth switch connected in series in sequence; One end of the second switch is connected to one end of the first switch, the connection point between the first switch and the second switch is connected to one end of the variable frequency half-wave generating module, and the other end of the second switch is used as a positive terminal and is connected to the positive terminal on the other side through a filtering inductor; One end of the fourth switch is connected to one end of the third switch, the connection point between the third switch and the fourth switch is connected to the other end of the variable frequency half-wave generating module, and the other end of the fourth switch is used as a negative terminal and connected to the negative terminal on the other side; The connection point between the first switch and the third switch serves as an AC output terminal, and the variable frequency half-wave generating module is connected to the AC system through the AC output terminal.

6. A half-wave alternating AC-AC converter topology as claimed in claim 4 or 5, characterized in that: When the phase voltage sinusoidal reference wave is positive, the first switch and the fourth switch are turned off, the second switch and the third switch are turned on, and the AC current flows to the positive terminal. This is the operation mode I. When the phase voltage sinusoidal reference wave is negative, the first switch and the fourth switch are turned on, the second switch and the third switch are turned off, and the AC current flows to the negative terminal. This is the operation mode II.

7. A half-wave alternating AC-AC converter topology as claimed in claim 6, characterized in that: The half-wave shaping switch group in each operating mode is divided into two groups. The on-off signals of each group of switches are consistent. The two groups of switches are alternately and complementary turned on. The on-off frequency is the frequency of the connected AC system. The conduction angle of each group of switches in each power frequency cycle is π.

8. A half-wave alternating AC-AC converter topology as claimed in claim 6, characterized in that: In operating mode I, the stepped sine half wave is shifted downward by U dc / 2 to the coordinate axis, and flip it upward to obtain the positive half-wave of the AC phase voltage; In operating mode II, the stepped sine half wave is shifted downward by U dc / 2 to the coordinate axis, and the negative half-wave of the AC phase voltage is obtained; U dc is the DC bus voltage; In one cycle, a complete AC side phase voltage sinusoidal wave is obtained based on the positive half-wave of the AC phase voltage and the negative half-wave of the AC phase voltage.

9. A control method for a half-wave alternating AC-AC converter topology, characterized in that: The half-wave alternating AC-AC converter topology according to any one of claims 1 to 8 comprises: AC systems of different frequencies are interconnected through filtering inductors, and the variable frequency half-wave generation module of the converter on each side outputs a stepped sinusoidal half-wave of the corresponding frequency based on the frequency of the connected AC system; In each half-wave time period, the on-off state of the half-wave shaping switch group is controlled according to the phase voltage sinusoidal reference wave, so that in different operating modes, the half-wave shaping switch group translates and flips the step sinusoidal half-wave to obtain a shaped half-wave, and a complete AC side phase voltage sinusoidal wave is obtained based on the shaped half-wave within one cycle.

10. A control method for a half-wave alternating AC-AC converter topology as claimed in claim 9, characterized in that: The half-wave shaping switch group in each operation mode is divided into two groups. The on-off signals of each group of switches are consistent. The two groups of switches are turned on alternately and complementary. The on-off frequency is the frequency of the connected AC system. The conduction angle of each group of switches in each power frequency cycle is π. When the phase voltage sinusoidal reference wave is positive, the stepped sinusoidal half wave is shifted downward by U dc / 2 to the coordinate axis, and flip it upward to obtain the positive half-wave of the AC phase voltage; When the phase voltage sinusoidal reference wave is negative, the stepped sinusoidal half wave is shifted downward by U dc / 2 to the coordinate axis, and the negative half-wave of the AC phase voltage is obtained; U dc is the DC bus voltage; In one cycle, a complete AC side phase voltage sinusoidal wave is obtained based on the positive half-wave of the AC phase voltage and the negative half-wave of the AC phase voltage.

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