A converter and voltage regulation control method and device thereof

Abstract

The application discloses a converter and a voltage regulation control method and device thereof. The converter comprises a novel switching valve and a switching capacitor valve, and the frequency of an alternating modulation wave voltage is determined according to the alternating modulation wave voltage. An odd harmonic wave voltage with an odd multiple of the frequency of the alternating modulation wave voltage is superimposed on the alternating modulation wave voltage, and the zero-crossing point of the alternating modulation wave voltage is overlapped with the zero-crossing point of the odd harmonic wave voltage to obtain a synthetic modulation wave. The absolute value of the synthetic modulation wave output by the switching capacitor valve in the converter is output. The number of power switching devices and the number of module capacitors can be greatly reduced, thereby greatly optimizing the cost and volume, and meanwhile, the decoupling of AC and DC voltage amplitudes is realized, the two can be controlled and regulated separately, and voltage regulation can be directly performed.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology, and in particular to a converter and its voltage regulation control method and apparatus. Background Technology

[0002] Flexible DC transmission systems are an effective means of solving the large-scale transmission and consumption of new energy sources. DC transmission requires AC / DC converters to connect to the AC grid, or the construction of DC transformers using AC / DC converters to achieve DC voltage conversion. Existing high-voltage, high-capacity AC / DC converter methods mainly utilize the Modular Multilevel Converter (MMC) scheme. The MMC converter, proposed in 2001, has seen considerable practical engineering applications. It offers advantages such as high reliability and flexibility. However, the MMC converter is based on half-bridge modules, which simultaneously output DC and AC voltages and carry DC and AC currents. Therefore, the module capacitors have very high fundamental frequency charging and discharging power, resulting in extremely large module capacitor sizes. Furthermore, the MMC converter uses a double-star connection, requiring six arms for three-phase applications. Each arm bears the DC bus voltage, leading to a large number of modules and power switching devices. These characteristics result in high costs for MMC-based DC transmission systems, severely hindering their large-scale application. Summary of the Invention

[0003] To address the aforementioned problems, the inventors have developed this invention, which, through specific embodiments, provides a converter and its voltage regulation control method and apparatus.

[0004] In a first aspect, embodiments of the present invention provide a converter, including a novel switching valve and a switched capacitor valve.

[0005] The novel switching valve includes multiple bridge arms connected in parallel, and each bridge arm includes multiple novel switching modules connected in series; the novel switching module includes a first power switching device, a diode, a voltage equalizing capacitor, and a first energy dissipation element. The first power switching device and the diode are connected in series and then in parallel across the voltage equalizing capacitor, and the first energy dissipation element is connected in parallel across the voltage equalizing capacitor.

[0006] The switched capacitor valve includes multiple switched capacitor modules connected in series; each switched capacitor module includes a second power switching device and a first capacitor, wherein the second power switching device is connected in a half-bridge and / or full-bridge configuration, and after the second power switching device is connected in a half-bridge or full-bridge configuration, it is connected in parallel across the first capacitor.

[0007] The converter port connected in parallel with the novel switching valve is port 1. The converter port with its two ends connected to the series line between the novel switching modules inside different bridge arms of the novel switching valve is port 2. The connection method of the novel switching valve and the switched capacitor valve includes:

[0008] The switched capacitor valve is connected in parallel across the two ends of the new switched valve. The two ends of the wiring at port 1 are connected in parallel with the new switched valve and the switched capacitor valve. The two ends of the wiring at port 2 are respectively connected to the series circuit between the new switched modules inside different bridge arms of the new switched valve.

[0009] Optionally, the connection method further includes: a switched capacitor valve connected in series on one of the wires of port 1; or a switched capacitor valve connected in series on each of the two wires of port 1.

[0010] Optionally, other connection methods besides the aforementioned connection method include: the switched capacitor valve is connected in parallel across the two ends of the wiring at port 2; or the switched capacitor valve is connected in series on one of the wirings at port 2.

[0011] Optionally, other connection methods besides the aforementioned connection method include: the converter includes three conversion units, each conversion unit being connected in series; each conversion unit includes a novel switching valve and a switched capacitor valve, the switched capacitor valve being connected in parallel across the two ends of the novel switching valve; a port 1 is provided on the wiring at both ends of the series circuit of the three conversion units, and a port 2 is provided on the series line between the novel switching modules inside different bridge arms of the novel switching valve in each conversion unit, each port 2 being connected in series with an AC transformer, and the three ports 2 respectively outputting one phase of AC power.

[0012] Optionally, a first switch is connected in parallel across the two ends of the first power switching device.

[0013] Specifically, when the connection method of the second power switching device includes a half-bridge connection, the switching capacitor module where the second power switching device in the half-bridge connection is located also includes a second energy-consuming element and / or a second switch. The second energy-consuming element is connected in parallel across the two ends of the first capacitor, and the second switch is connected in parallel across the two ends of one of the second power switching devices in the half-bridge connection. When the connection method of the second power switching device includes a full-bridge connection, the switching capacitor module where the second power switching device in the full-bridge connection is located also includes a second energy-consuming element and / or a second switch. The second energy-consuming element is connected in parallel across the two ends of the first capacitor. One end of the second switch is connected to the line in series of two second power switching devices in one of the full-bridge connection arms, and the connection point is located between the two second power switching devices. The other end of the second switch is connected to the line in series of two second power switching devices in another of the full-bridge connection arms, and the connection point is located between the two second power switching devices.

[0014] Secondly, embodiments of the present invention provide a converter voltage regulation control method, comprising the following steps:

[0015] The frequency of the AC modulation wave voltage is determined based on the AC modulation wave voltage.

[0016] An odd harmonic voltage, which is an odd multiple of the frequency of the AC modulation wave voltage, is superimposed on the AC modulation wave voltage, and the zero-crossing point of the AC modulation wave voltage coincides with the zero-crossing point of the odd harmonic voltage to obtain a synthesized modulation wave.

[0017] The absolute value of the synthesized modulated wave is output by the switched capacitor valve in the converter.

[0018] Specifically, when the odd harmonic voltage is the third harmonic, the converter transformer blocks the path of the third harmonic flowing into the AC system, and the voltage regulation range of the converter voltage regulation control method is 0.82 pu to 1 p.u.

[0019] Thirdly, embodiments of the present invention provide a converter voltage regulation control device, comprising:

[0020] A voltage frequency determination module is used to determine the frequency of the AC modulation wave voltage based on the AC modulation wave voltage.

[0021] A modulation wave synthesis module is used to superimpose odd harmonic voltages that are odd multiples of the frequency of the AC modulation wave voltage onto the AC modulation wave voltage, and to make the zero-crossing point of the AC modulation wave voltage coincide with the zero-crossing point of the odd harmonic voltage to obtain a synthesized modulation wave.

[0022] The modulation wave output module is used to output the absolute value of the synthesized modulation wave from the switched capacitor valve in the converter.

[0023] Specifically, when the odd harmonic voltage is the third harmonic, the converter transformer blocks the path of the third harmonic flowing into the AC system, and the voltage regulation range of the converter voltage regulation control method is 0.82 pu to 1 p.u.

[0024] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0025] This invention significantly reduces the number of power switching devices and module capacitors, resulting in substantial cost and size optimization. In single-phase applications, the switched capacitor module in this embodiment only needs to withstand the peak DC bus voltage, while the bridge arm of the novel switching valve withstands only one times the peak DC bus voltage. Furthermore, the novel switching module contains only one fully controlled power switching device. Therefore, the number of power switching devices in the converter provided by this invention is reduced by more than 25% compared to MMC. Because the novel switching valve bridge arm of the converter in this invention has no bridge arm reactance, there is no freewheeling current after the bridge arm is turned off. Therefore, the novel switching module does not have large charging and discharging power, and the module capacitor is smaller.

[0026] The voltage regulation control method proposed in this invention decouples the AC and DC voltage amplitudes, allowing them to be controlled and regulated independently, and enabling direct voltage adjustment.

[0027] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings.

[0028] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0029] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0030] Figure 1a This is a converter topology diagram according to an embodiment of the present invention;

[0031] Figure 1b This is a converter-derived topology diagram in an embodiment of the present invention;

[0032] Figure 1c This is a converter-derived topology diagram in an embodiment of the present invention;

[0033] Figure 1d This is a converter-derived topology diagram in an embodiment of the present invention;

[0034] Figure 1e This is a converter-derived topology diagram in an embodiment of the present invention;

[0035] Figure 1f This is a converter-derived topology diagram in an embodiment of the present invention;

[0036] Figure 2 This is a topology diagram of the novel switch module in an embodiment of the present invention;

[0037] Figure 3 This is a topology diagram of the switched capacitor module of the half-bridge in an embodiment of the present invention;

[0038] Figure 4 This is a topology diagram of the full-bridge switched capacitor module in an embodiment of the present invention;

[0039] Figure 5 This is a topology diagram of a hybrid half-bridge and full-bridge switched capacitor valve in an embodiment of the present invention;

[0040] Figure 6 The AC and DC voltage waveforms of the converter in this embodiment of the invention are shown.

[0041] Figure 7 This is the AC side voltage waveform after odd harmonic injection in an embodiment of the present invention;

[0042] Figure 8 This is the DC-side voltage waveform after odd harmonic injection in an embodiment of the present invention;

[0043] Figure 9 This is a converter topology diagram in the voltage regulation control method of this invention embodiment;

[0044] Figure 10 This is the DC-side voltage waveform after third harmonic injection in an embodiment of the present invention;

[0045] Figure 11a This is a schematic diagram of the voltage regulation range when Um = 1p.u. in an embodiment of the present invention;

[0046] Figure 11b This is a schematic diagram of the voltage regulation range when Um = 0.82pu in an embodiment of the present invention. Detailed Implementation

[0047] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0048] Example 1

[0049] To address the high cost of DC transmission systems based on MMC converters, embodiments of this invention provide a converter, the structure of which is as follows: Figure 1a As shown, it includes a new type of switching valve and a switched capacitor valve.

[0050] The novel switching valve includes multiple bridge arms connected in parallel, and each bridge arm includes multiple novel switching modules connected in series; the novel switching module includes a first power switching device, a diode, a voltage equalizing capacitor, and a first energy dissipation element. The first power switching device and the diode are connected in series and then in parallel across the voltage equalizing capacitor, and the first energy dissipation element is connected in parallel across the voltage equalizing capacitor.

[0051] The switched capacitor valve includes multiple switched capacitor modules connected in series; each switched capacitor module includes a second power switching device and a first capacitor, wherein the second power switching device is connected in a half-bridge and / or full-bridge configuration, and after the second power switching device is connected in a half-bridge or full-bridge configuration, it is connected in parallel across the first capacitor.

[0052] The converter port connected in parallel with the novel switching valve is port 1. The converter port with its two ends connected to the series line between the novel switching modules inside different bridge arms of the novel switching valve is port 2. The connection method of the novel switching valve and the switched capacitor valve includes:

[0053] The switched capacitor valve is connected in parallel across the two ends of the new switched valve. The two ends of the wiring at port 1 are connected in parallel with the new switched valve and the switched capacitor valve. The two ends of the wiring at port 2 are respectively connected to the series circuit between the new switched modules inside different bridge arms of the new switched valve.

[0054] Optionally, the connection method further includes: a switched capacitor valve connected in series on one of the wires of port 1; or a switched capacitor valve connected in series on each of the two wires of port 1.

[0055] Optionally, other connection methods besides the aforementioned connection method include: the switched capacitor valve is connected in parallel across the two ends of the terminal block of port 2; or the switched capacitor valve is connected in series on one terminal block of port 2.

[0056] Optionally, other connection methods besides the aforementioned connection method include: the converter includes three conversion units, each conversion unit being connected in series; each conversion unit includes a novel switching valve and a switched capacitor valve, the switched capacitor valve being connected in parallel across the two ends of the novel switching valve; a port 1 is provided on the wiring at both ends of the series circuit of the three conversion units, and a port 2 is provided on the series line between the novel switching modules inside different bridge arms of the novel switching valve in each conversion unit, each port 2 being connected in series with an AC transformer, and the three ports 2 respectively outputting one phase of AC power.

[0057] Optionally, a first switch is connected in parallel across the two ends of the first power switching device.

[0058] Specifically, when the connection method of the second power switching device includes a half-bridge connection, the switching capacitor module where the second power switching device in the half-bridge connection is located also includes a second energy-consuming element and / or a second switch. The second energy-consuming element is connected in parallel across the two ends of the first capacitor, and the second switch is connected in parallel across the two ends of one of the second power switching devices in the half-bridge connection. When the connection method of the second power switching device includes a full-bridge connection, the switching capacitor module where the second power switching device in the full-bridge connection is located also includes a second energy-consuming element and / or a second switch. The second energy-consuming element is connected in parallel across the two ends of the first capacitor. One end of the second switch is connected to the line in series of two second power switching devices in one of the full-bridge connection arms, and the connection point is located between the two second power switching devices. The other end of the second switch is connected to the line in series of two second power switching devices in another of the full-bridge connection arms, and the connection point is located between the two second power switching devices.

[0059] In some embodiments, such as Figure 1a , 1bAs shown in Figure 1c, a switched capacitor valve is connected in parallel across the two ends of a novel switching valve. The port connected in parallel with the novel switching valve is port 1, and the port whose terminals are respectively connected to the series circuit between the novel switching modules inside different bridge arms of the novel switching valve is port 2. The input or output current of ports 1 and 2 can be either DC or AC. In some embodiments, such as... Figure 1a As shown, the two ends of port 1 are connected in parallel with the novel switching valve and the switched capacitor valve, and the two ends of port 2 are respectively connected to the series circuit between the novel switching modules inside different bridge arms of the novel switching valve. In some embodiments, such as Figure 1b As shown, a switched capacitor valve is also connected in series on one of the port connections that are in parallel with the novel switching valve and the switched capacitor valve. In some embodiments, such as Figure 1c As shown, a switched capacitor valve is also connected in series on each of the two terminals connected in parallel with the novel switching valve and the switched capacitor valve. In some embodiments, as Figure 1d As shown, the switched capacitor valve is connected in parallel across the two ends of the terminal block at port 2, or as... Figure 1e As shown, the switched capacitor valve is connected in series on one of the wires at port 2. In some embodiments, such as Figure 1f As shown, the converter includes three conversion units, each connected in series. Each conversion unit includes a novel switching valve and a switched capacitor valve, with the switched capacitor valve connected in parallel across the novel switching valve. Port 1 is provided on the wiring at both ends of the series circuit of the three conversion units, and port 2 is provided on the series circuit between the novel switching modules inside different bridge arms of the novel switching valve in each conversion unit. Each port 2 is connected in series with an AC transformer, and each of the three ports 2 outputs one phase of AC power.

[0060] The novel switching valve comprises multiple parallel bridge arms, each of which includes multiple novel switching modules connected in series. The structure of the novel switching module is as follows: Figure 2 As shown, the device includes a power switch T1, a diode D1, a voltage equalizing capacitor C1, and a power dissipating element H1. The power switch T1 and diode D1 are connected in series and then in parallel across the voltage equalizing capacitor C1. The power dissipating element H1 is also connected in parallel across the voltage equalizing capacitor C1. Optionally, in some embodiments, a switch K1 is connected in parallel across the power switch T1.

[0061] The switched capacitor valve comprises multiple switched capacitor modules connected in series. Each switched capacitor module consists of a power switching device T2 and a capacitor C2. The power switching device T2 can be configured in either a half-bridge or full-bridge configuration. The structure of a half-bridge switched capacitor module is as follows... Figure 3As shown, in each half-bridge switched capacitor module, two power switching devices T2 are connected in series and then in parallel across the capacitor C2. Optionally, in some embodiments, each half-bridge switched capacitor module further includes a power dissipation element H2 and / or a switch K2. The power dissipation element H2 is connected in parallel across the capacitor C2, and the switch K2 is connected in parallel across one of the power switching devices T2. The power dissipation element H1 or H2 can be any one or a combination of a power source, a power dissipation resistor, and a switchable power dissipation resistor.

[0062] The structure of the full-bridge switched capacitor module is as follows: Figure 4 As shown, each full-bridge switched capacitor module includes two bridge arms, with two power switching devices T2 connected in series in each bridge arm, and each bridge arm connected in parallel across the capacitor C2. Optionally, in some embodiments, each full-bridge switched capacitor module further includes a power dissipation element H2 and / or a switch K2. The power dissipation element H2 is connected in parallel across the capacitor C2, one end of the switch K2 is connected to the line connecting the two power switching devices in series in one bridge arm, and the connection point is located between the two power switching devices. The other end of the switch K2 is connected to the line connecting the two power switching devices in series in the other bridge arm, and the connection point is also located between the two power switching devices.

[0063] Optionally, the AC / DC converter provided in this embodiment of the invention may include a switched capacitor valve comprising a half-bridge switched capacitor module, a full-bridge switched capacitor module, or both. A switched capacitor valve comprising a hybrid of a half-bridge and a full-bridge switched capacitor module has the following structure: Figure 5 As shown, it consists of a half-bridge switched capacitor module and a full-bridge switched capacitor module connected in series.

[0064] The basic control method of the above converter is as follows:

[0065] Let the AC modulation wave voltage be Um. Um can be a sine wave, a rectangular wave, a trapezoidal wave, a triangular wave, etc., and be a periodic waveform with odd-symmetric or even-symmetric functions.

[0066] (1) New type of switching valve control: The zero-crossing point detection of Um is performed, and the new switching valve switches the output state only when Um crosses zero.

[0067] (2) Switched capacitor valve control: Take the absolute value of Um to obtain |Um|. The switched capacitor valve outputs |Um| through conventional modulation strategies, such as carrier phase shift modulation, nearest level modulation, etc.

[0068] Through the above operations, the AC side can output voltage Um, and the DC side can output pulsating DC voltage |Um|. After filtering, the pulsating DC voltage can be converted into a stable DC voltage. Thus, AC / DC conversion is achieved.

[0069] The converter provided in this embodiment of the invention can significantly reduce the number of power switching devices and module capacitors, thereby resulting in substantial cost and size optimization. In single-phase applications, the switched capacitor module of this embodiment only needs to withstand the peak DC bus voltage, and the bridge arm of the novel switching valve withstands a total of 1 times the peak DC bus voltage. Furthermore, the novel switching module contains only one fully controlled power switching device. Therefore, the number of power switching devices in the converter provided by this invention is reduced by more than 25% compared to MMC. Since the novel switching valve bridge arm of the converter of this invention has no bridge arm reactance and no freewheeling current after the bridge arm is turned off, the novel switching module does not have a large charging and discharging power, and the module capacitor is small.

[0070] Example 2

[0071] In terms of control methods, the converter provided in Embodiment 1 has voltage coupling between its AC and DC ports, such as... Figure 6 As shown, the AC voltage waveform after its zero-crossing reversal is the DC-side pulsating DC voltage waveform. Therefore, adjusting the AC voltage peak value will change the DC voltage, making direct voltage adjustment impossible. In view of this, to achieve decoupling between the AC and DC side voltages, Embodiment 2 of this invention provides a converter voltage regulation control method, including the following steps:

[0072] Step S1: Determine the frequency of the AC modulation wave voltage based on the AC modulation wave voltage.

[0073] Let the AC modulation voltage be Um. Um can be a sine wave, rectangular wave, trapezoidal wave, triangular wave, etc., and be a periodic waveform with either odd or even symmetric functions. The period of Um is defined as the time length from one positive zero-crossing to one negative zero-crossing. The frequency of Um is the reciprocal of its period.

[0074] Step S2: Superimpose an odd harmonic voltage, which is an odd multiple of the frequency of the AC modulation wave voltage, onto the AC modulation wave voltage, and make the zero-crossing point of the AC modulation wave voltage coincide with the zero-crossing point of the odd harmonic voltage to obtain a synthesized modulation wave.

[0075] Based on the modulated wave Um, an odd-order harmonic voltage Um2, which is an odd multiple of the frequency of Um, is superimposed (again, the frequency here is calculated based on the zero-crossing point mentioned above, not the frequency of the fundamental sinusoidal wave in the spectrum obtained from the Fourier transform), ensuring that the zero-crossing point of Um coincides with the zero-crossing point of the odd-order harmonic voltage. For example... Figure 7 The diagram shows the case where Um is a sine wave and Um2 is the third harmonic. The resulting modulated wave after superposition is Um + Um2.

[0076] Specifically, the amplitude of Um2 must ensure that Um+Um2 does not generate a new zero-crossing point different from Um. A zero-crossing point refers to the point on the 0 axis where the waveform changes from positive to negative or from negative to positive. That is, the waveform must cross the 0 axis.

[0077] Step S3: Output the absolute value of the synthesized modulated wave from the switched capacitor valve in the converter.

[0078] Take the absolute value of the synthesized modulated wave, |Um+Um2|, and output |Um+Um2| from the switched capacitor valve. For example... Figure 8 As shown, after the superposition of odd harmonics, the DC-side voltage after rectification by the novel switched-capacitor valve exhibits a DC bias. Therefore, without changing the AC-side modulation voltage Um, the magnitude of the DC-side voltage is adjusted, thereby achieving decoupling of the AC and DC-side voltages. Due to the injection of odd harmonics, an odd harmonic voltage Um2 appears on the AC-side voltage, which can be filtered out by a filter. Alternatively, for a three-phase system without a neutral wire, there is no zero-sequence path. If the injected odd harmonic voltage is the 3rd harmonic voltage, this voltage is a zero-sequence voltage. Without a zero-sequence path, no zero-sequence current will be generated, therefore, there is no need to set up a filter to filter out this voltage.

[0079] For example, with Figure 9 The analysis will take the AC / DC conversion application with a sinusoidal wave Um as an example, as shown in the diagram. Figure 6 As shown:

[0080] Without employing special control methods Figure 9 In the topology, this relationship always holds: Udc*1.57 = N*Usm. Here, Udc is the DC-side voltage, N is the number of switched capacitor modules, and Usm is the capacitor voltage of the switched capacitor module. Let the modulation ratio be M, then Udc*1.57 = N*M*Usm = N*Upeak. Here, Upeak is the peak value of the modulated wave Um. It is evident that when Usm remains constant, without special measures, adjusting the peak value Upeak of the AC phase voltage will inevitably lead to a change in the DC bus voltage Udc.

[0081] This implementation proposes a method for injecting odd-order harmonics, specifically the third harmonic: (e.g.) Figure 7 As shown, a third harmonic voltage is generated on the AC side. This voltage is rectified by a novel switching valve to form a pulsating positive DC voltage, as shown below. Figure 8 As shown, DC-side voltage regulation is achieved without changing the peak value of the AC fundamental voltage.

[0082] The third harmonic is zero sequence, and its path into the AC system can be blocked by the converter transformer. Therefore, the injection of third harmonic voltage has no effect on the AC system and will not generate harmonic current, thus having no adverse effect on the converter valve.

[0083] The three harmonic voltages are in phase, so when they are superimposed on the DC side, a harmonic voltage will be generated at the DC port. Since it is obtained by rectification, the frequency is mainly the sixth harmonic, so the harmonic impedance is relatively large and can be filtered out by a DC filter.

[0084] The following is an analysis of the ratio of the third harmonic to the AC modulated wave Um: (e.g.) Figure 8 The diagram shows the DC-side waveforms Um and the third harmonic waveform (Um2) after rectification (waveform inversion) by the new switching valve. Within one fundamental cycle, the average value of the rectified third harmonic is 1 / 3 of Um. Therefore, for every change of dU in the amplitude of Um, the third harmonic changes by 3*dU. Because the rate of change of the third harmonic is higher than that of Um, the converter cannot achieve full-range voltage regulation with a modulation ratio M = 0 to 1.

[0085] The following is an analysis of the third harmonic phase: Figure 8 In this process, the third harmonic, after rectification, generates a positive DC voltage. Similarly, if the third harmonic voltage is reversed, a negative DC voltage can be generated. However, if... Figure 10 As shown, the inverted third harmonic voltage occurs at the same time as the peak value of Um. In this case, for every change of dU in the Um voltage, the third harmonic voltage changes by 3*dU, and the modulation amplitude changes by 4*dU. This results in a very low utilization rate of the voltage regulation range. Therefore, the injection of a third harmonic voltage with DC negative bias after rectification should be avoided.

[0086] The following is an analysis of the voltage regulation range: Based on the above approach, when the modulation ratio M = 1, the amplitude of Um is 1 p.u. As the modulation ratio decreases, the amplitude of the third harmonic voltage gradually increases, generating a positive DC bias after rectification to compensate for the drop in DC bus voltage caused by the decrease in the amplitude of Um voltage. (See details below.) Figure 11a and 11b As shown, when Um is 1 p.u. and 0.82 pu, M = 1. Therefore, the voltage regulation range is 0.82 pu to 1 p.u., which is 18%.

[0087] In the method described in this embodiment, the AC and DC voltage amplitudes are decoupled, allowing for independent control and voltage regulation, and enabling direct voltage adjustment.

[0088] The converter and its voltage regulation control of this invention can significantly reduce the number of power switching devices and module capacitors, thereby resulting in substantial cost and size optimization. In single-phase applications, the switched capacitor module of this embodiment only needs to withstand the peak DC bus voltage, while the bridge arm of the novel switching valve withstands a total of 1 times the peak DC bus voltage. Furthermore, the novel switching module contains only one fully controlled power switching device. Therefore, the number of power switching devices in the converter provided by this invention is reduced by more than 25% compared to MMC. The novel switching valve bridge arm of this converter, because it has no bridge arm reactance, has no freewheeling current after the bridge arm is turned off. Therefore, the novel switching module does not have large charging and discharging power, and the module capacitor is small. However, the switched capacitor valve, because its current is twice the frequency of the rectified current obtained by the novel switching valve, has a capacitor voltage fluctuation frequency twice that of MMC. After offsetting the DC port current, the fluctuation power of the switched capacitor module is 1 / 8 of that of MMC, and the module capacitor is 1 / 8 of that of MMC.

[0089] Those skilled in the art can change the above order without departing from the scope of protection of this disclosure.

[0090] Example 3

[0091] This invention provides a converter voltage regulation control device, comprising:

[0092] A voltage frequency determination module is used to determine the frequency of the AC modulation wave voltage based on the AC modulation wave voltage.

[0093] A modulation wave synthesis module is used to superimpose odd harmonic voltages that are odd multiples of the frequency of the AC modulation wave voltage onto the AC modulation wave voltage, and to make the zero-crossing point of the AC modulation wave voltage coincide with the zero-crossing point of the odd harmonic voltage to obtain a synthesized modulation wave.

[0094] The modulation wave output module is used to output the absolute value of the synthesized modulation wave from the switched capacitor valve in the converter.

[0095] Specifically, when the odd harmonic voltage is the third harmonic, the converter transformer blocks the path of the third harmonic flowing into the AC system, and the voltage regulation range of the converter voltage regulation control method is 0.82 pu to 1 p.u.

[0096] The specific implementation methods of each module of the above-mentioned device have been described in detail in a converter voltage regulation control method, and will not be repeated here.

[0097] In the device described in this embodiment, the AC and DC voltage amplitudes are decoupled, and the two can be controlled and regulated independently, enabling direct voltage adjustment.

[0098] Any modifications, additions, and equivalent substitutions made within the scope of the principles of this invention shall still fall within the patent coverage of this invention.

[0099] Unless otherwise stated, the term "connection" as used above refers to a logical relationship of current transmission and does not necessarily indicate a direct electrical connection. Furthermore, terms such as "first" and "second" do not indicate a sequential order but are merely used to identify related units or devices.

Claims

1. A converter, characterized in that, Including new types of switching valves and switched capacitor valves, The novel switching valve includes multiple bridge arms connected in parallel, and each bridge arm includes multiple novel switching modules connected in series; the novel switching module includes a first power switching device, a diode, a voltage equalizing capacitor, and a first energy dissipation element. The first power switching device and the diode are connected in series and then in parallel across the voltage equalizing capacitor, and the first energy dissipation element is connected in parallel across the voltage equalizing capacitor. The switched capacitor valve includes multiple switched capacitor modules connected in series; each switched capacitor module includes a second power switching device and a first capacitor, wherein the second power switching device is connected in a half-bridge and / or full-bridge configuration, and after the second power switching device is connected in a half-bridge or full-bridge configuration, it is connected in parallel across the first capacitor. The converter port connected in parallel with the novel switching valve is port 1. The converter port with its two ends connected to the series line between the novel switching modules inside different bridge arms of the novel switching valve is port 2. The connection method of the novel switching valve and the switched capacitor valve includes: The switched capacitor valve is connected in parallel across the two ends of the new switched valve. The two ends of the wiring at port 1 are connected in parallel with the new switched valve and the switched capacitor valve. The two ends of the wiring at port 2 are respectively connected to the series circuit between the new switched modules inside different bridge arms of the new switched valve. Wherein, when the connection method of the second power switching device includes a half-bridge connection, the switching capacitor module where the second power switching device in the half-bridge connection is located also includes a second energy-consuming element and / or a second switch, the second energy-consuming element is connected in parallel across the two ends of the first capacitor, and the second switch is connected in parallel across the two ends of one of the second power switching devices in the half-bridge connection; When the connection method of the second power switching device includes a full-bridge connection, the switching capacitor module where the second power switching device in the full-bridge connection is located also includes a second energy-consuming element and / or a second switch. The second energy-consuming element is connected in parallel across the two ends of the first capacitor. One end of the second switch is connected to the line in series of two second power switching devices in one of the full-bridge connection arms, and the connection point is located between the two second power switching devices. The other end of the second switch is connected to the line in series of two second power switching devices in another of the full-bridge connection arms, and the connection point is located between the two second power switching devices. The converter determines the frequency of the AC modulation wave voltage based on the AC modulation wave voltage; it superimposes an odd harmonic voltage, which is an odd multiple of the AC modulation wave voltage frequency, onto the AC modulation wave voltage, and the zero-crossing point of the AC modulation wave voltage coincides with the zero-crossing point of the odd harmonic voltage to obtain a composite modulation wave; the absolute value of the composite modulation wave is output by the switched capacitor valve in the converter.

2. The converter as described in claim 1, characterized in that, The connection method also includes: A switched capacitor valve is connected in series on one of the wires of port 1; Alternatively, a switched capacitor valve can be connected in series on each of the two wires of port 1.

3. The converter as described in claim 1, characterized in that, Other connection methods besides the aforementioned connection method include: The switched capacitor valve is connected in parallel across the two ends of the wiring at port 2; Alternatively, a switched capacitor valve can be connected in series on one of the wires at port 2.

4. The converter as claimed in claim 1, characterized in that, Other connection methods besides the aforementioned connection method include: The converter includes three conversion units, each connected in series. Each conversion unit includes a novel switching valve and a switched capacitor valve, with the switched capacitor valve connected in parallel across the two ends of the novel switching valve. Port 1 is provided on the wiring at both ends of the series circuit of the three conversion units. Port 2 is provided on the series circuit between the novel switching modules inside different bridge arms of the novel switching valve in each conversion unit. Each port 2 is connected in series with an AC transformer, and the three ports 2 output one phase of AC power respectively.

5. The converter as described in any one of claims 1 to 4, characterized in that, A first switch is connected in parallel across the two ends of the first power switching device.

6. The converter as claimed in claim 1, characterized in that, When the odd harmonic voltage is the third harmonic, the converter transformer blocks the path of the third harmonic flowing into the AC system. The voltage regulation range of the converter voltage regulation control is 0.82pu~1p.u.

7. A converter voltage regulation control device, applied to a converter as described in any one of claims 1 to 6, characterized in that, include: A voltage frequency determination module is used to determine the frequency of the AC modulation wave voltage based on the AC modulation wave voltage. A modulation wave synthesis module is used to superimpose odd harmonic voltages that are odd multiples of the frequency of the AC modulation wave voltage onto the AC modulation wave voltage, and to make the zero-crossing point of the AC modulation wave voltage coincide with the zero-crossing point of the odd harmonic voltage to obtain a synthesized modulation wave. The modulation wave output module is used to output the absolute value of the synthesized modulation wave from the switched capacitor valve in the converter.

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