A method for injection pulse modulation in a multilevel injection current source converter

Abstract

This invention discloses an injection pulse modulation method for a multi-level injection current source converter, S1. Based on the main bridge switching frequency f s Determine the main bridge switching cycle T s The period T of the injection circuit switching pulse is determined based on the number of injection levels m. inj S2. Generate a carrier frequency of 6f s The triangular carrier wave; S3. The carrier amplitude A c Divide T into 2(m-1) equal parts; S4. inj Decompose into (m-1) carrier periods; S5. Traverse M1 to M in the positive and negative intervals. (m‑1) S6. Compare the modulated wave with the carrier wave to obtain the injection pulse scheme that satisfies the injection pulse condition; This invention provides an intuitive and easy-to-implement new method, which not only avoids the complexity and error-proneness of traditional counting and assignment methods, but also simplifies and accelerates the conversion process between different injection pulse schemes. In addition, the modulation wave generation technology in this invention provides a new perspective for understanding how different injection pulse schemes affect the harmonic content of the AC and DC side current of the system.

Description

Technical Field

[0001] This invention relates to a wire harness dispensing fixture, and more particularly to an injection pulse modulation method for a multi-level injection current source converter. Background Technology

[0002] High-capacity AC / DC converters, as core devices in power electronic systems, have significant application value in key areas such as smart grids, high-speed railway traction power supply, and aerospace power supplies. Among them, current source converters, with their superior control characteristics and wide-range DC voltage regulation capabilities, exhibit more significant technical advantages than VSCs (voltage source converters) in specific application scenarios. MLR-CSC, or multilevel injection current source converter, successfully achieves controllable turn-off of thyristor devices by introducing a multilevel injection circuit on the DC side of a traditional LCC (12-pulse grid commutation converter). This gives the system outstanding advantages such as four-quadrant operation capability, low switching frequency harmonic elimination, and the elimination of the need for a three-phase filter on the grid side, significantly improving the overall performance of traditional LCC converters.

[0003] In the evolution of MLR-CSC technology, the injection circuit, as a core functional module, has undergone multiple technological iterations. Early designs employed a topology of multi-tap reactors connected in parallel with self-turn-off switching devices. While this solution achieved basic level injection functionality, it had significant drawbacks: First, the injection switches needed to withstand the full DC current, imposing stringent requirements on their steady-state current capacity and dynamic di / dt tolerance, directly limiting the power rating of the converter. Second, the conduction duration of injection switches at different spatial locations varied significantly, leading to a lack of uniformity in device parameter design requirements and increasing the difficulty of system optimization. To address these technical bottlenecks, subsequent research proposed an improved injection circuit scheme, employing a combination of reverse-resistance switching devices and smoothing inductors. By using m-1 (m being the number of injection levels) parallel switches to evenly distribute the DC current, it not only effectively reduced the current stress on individual devices but also replaced the multi-tap reactors with smoothing inductors, eliminating the original excitation current loss and achieving zero-current switching of the main bridge thyristors, significantly improving system efficiency.

[0004] Despite advancements in hardware topology of existing novel injection circuits, the complexity of their control systems has increased significantly, particularly in the injection pulse generation mechanism. Literature in this field has identified the following four fundamental constraints:

[0005] 1. The injection switching frequency is 6 times the main bridge switching frequency;

[0006] 2. The injection switch combination can provide the two main converter bridges with a periodically changing, stepped current with a certain zero value range;

[0007] 3. Within a certain period, each injection switching device traverses all normal operating states;

[0008] 4. The two switching transistors in the same injection unit are interlocked.

[0009] The aforementioned basic conditions provide a reference for the specific injection method of the injection circuit; however, its digital generation method remains unclear. Currently, the main approach is to determine the specific injection pulse scheme, obtain the injection period by dividing the system clock, then generate an injection pulse for one cycle using a counting assignment method, and obtain the switching pulses of other injection units through phase shifting. However, as the number of injection levels increases, the number of injection pulse schemes that satisfy the above basic conditions increases dramatically, and the aforementioned digital generation scheme for injection pulses becomes very difficult and error-prone when switching between different pulse schemes. Currently, no simpler and more effective solution has been proposed in the field for the digital generation method of injection pulses for injection circuits. Summary of the Invention

[0010] To address the shortcomings of the aforementioned technologies, this invention provides an injection pulse modulation method for a multilevel injection current source converter.

[0011] To solve the above technical problems, the technical solution adopted by the present invention is: an injection pulse modulation method for a multi-level injection current source converter, comprising the following steps:

[0012] S1. Based on the main bridge switching frequency f s Determine the main bridge switching cycle T s ,and T s =1 / f s According to the number of injection levels m Determine the period of the injection circuit switching pulse T inj Then the following relationship is satisfied:

[0013] ;

[0014] S2. The generated carrier frequency is 6. f s The triangular carrier wave, the carrier period of which T c for:

[0015] ;

[0016] Furthermore, the triangular carrier wave, in the first half of a cycle, starts from carrier amplitude A. c The amplitude drops to 0, and in the second half of the cycle, it rises from 0 to the carrier amplitude A. c ;

[0017] S3. The carrier amplitude A c Divide the wave into 2(m-1) equal parts and obtain the possible values ​​of the modulated wave:

[0018] ,

[0019] make ;

[0020] S4. T inj It is decomposed into (m-1) carrier periods, each carrier period is divided into positive intervals and negative intervals, and the two are alternately arranged on the time axis;

[0021] S5. Within the positive interval, the modulated wave takes values ​​from M1 to M... (m-1) Each value appears only once; within the negative interval, the modulated wave also takes values ​​from M1 to M... (m-1) Each value appears only once;

[0022] S6. Compare the modulated wave with the carrier wave to obtain an injection pulse scheme that satisfies the injection pulse condition.

[0023] Furthermore, with the injection level number m Increase, T inj Increased and by one-sixth T s Integer multiples of the period of the injection circuit switching pulse T inj This is the period value of the modulation wave.

[0024] Further, in step S1, when the injected level number m =3, then T inj = T s / 3.

[0025] Further, in step S1, when the injected level number m =5, then T inj =2 T s / 3.

[0026] Furthermore, in step S2, if the externally synthesized injected current is 6 times the main bridge switching frequency and the carrier waveform is a triangular wave, then the carrier frequency... f c Fixed at 6 f s .

[0027] Furthermore, in step S2, the first half of the cycle, i.e. (0~T c / 2), the second half of the cycle is ( T c / 2~ T c ).

[0028] Furthermore, in step S4, the positive interval is the first half of the cycle (0~ T c / 2), the negative interval is the second half of the cycle ( T c / 2~ T c ),but T inj It contains (m-1) positive intervals and (m-1) negative intervals.

[0029] This invention discloses an injection pulse modulation method for a multilevel injection current source converter. Addressing the injection pulse generation method for multilevel injection current source converters, this invention proposes a novel and intuitive method that avoids the cumbersome and error-prone nature of traditional counting and assignment methods. It also simplifies and speeds up the switching between different injection pulse schemes. Furthermore, the modulation wave generation method in this invention may provide a new perspective on revealing the essence of the differences in harmonic content between the AC and DC currents caused by different injection pulse schemes. Attached Figure Description

[0030] Figure 1 This is a multi-level injection current source converter topology.

[0031] Figure 2 The structure of the three-level injection circuit and the injection current waveform are shown.

[0032] Figure 3 A three-level pulse digital generation method.

[0033] Figure 4 The structure of the five-level injection circuit and the injection current waveform are shown.

[0034] Figure 5 A five-level pulse digital generation method. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0036] like Figure 1 The diagram shows the system topology of a multilevel injection current source converter. The shaded area represents the injection circuit, where a pair of switches are connected to points p and q, respectively. S Yri and S Dri (i (e.g., 1, 2, 3, ..., m-1) are all connected to a smoothing inductor. L i At one end, the three components form an injection unit; m-1 injection units connected in parallel form an m-level injection circuit.

[0037] It should be noted that the common injection level numbers are three-level, five-level, and seven-level. The higher the level number, the more injection units are required, and the number of additional switching transistors and smoothing inductors needed for the injection circuit increases linearly, but the suppression effect on AC side harmonics gradually slows down. In actual implementation, considering factors such as system cost and size, the injection level number generally does not exceed seven levels.

[0038] Under ideal assumptions, the DC-side smoothing inductor Li is infinite and the inductor current is approximately constant for different injection pulse schemes. However, in reality, the smoothing inductor cannot be infinite, and due to the limitations of the actual system size, the inductance value needs to be as small as possible. Therefore, when the number of injection levels m is greater than 3, i.e., three-level injection, the harmonics of the two injection pulses are the same. The key is to analyze the specific impact of each injection pulse scheme on the system harmonics and to select the optimal injection pulse scheme. However, due to the large number of injection pulse schemes and the difficulty in switching between different injection pulse schemes due to the digital implementation method, traditional methods are quite challenging in solving the above problems.

[0039] Existing methods also involve using counting assignment to optimize all injection pulse schemes in simulation through program optimization in an attempt to obtain the injection pulse scheme that minimizes system current harmonics. However, this method cannot reveal the common characteristics under different injection level numbers. When it is necessary to obtain the optimal injection pulse scheme for seven-level injection, existing methods still require complicated simulation and program writing.

[0040] Example 1

[0041] This embodiment relates to an injection pulse modulation method for a multilevel injection current source converter, including the following steps:

[0042] S1. Based on the main bridge switching frequency f s Determine the main bridge switching cycle T s In other words, assuming the main bridge switching frequency of the MLR-CSC is equal to the power supply frequency (AC power supply frequency), then the main bridge switching cycle... T s =1 / f s According to the number of injection levels m Determine the period of the injection circuit switching pulse T inj It satisfies the following relationship:

[0043] .

[0044] In step S1, as the number of injection levels increases... m The increase in the period of the injection circuit switching pulse T inj The period is increased and is an integer multiple of one-sixth of the main bridge switching cycle. It should be noted that the period of the injected circuit switching pulse... T inj That is, the period value of the modulation wave.

[0045] Based on the above findings, when the number of injected levels m =3, then T inj = T s / 3; When the injection level number m =5, then T inj =2 T s / 3.

[0046] S2. The generated carrier frequency is 6. f s The triangular carrier wave; since the synthesized injected current is 6 times the main bridge switching frequency and the carrier waveform is a stepped triangular wave, the carrier frequency... f c It should be equal to the frequency of the injected current, which is 6. f s This achieves one of the four fundamental limitations of existing injection pulse generation mechanisms; based on this, the carrier period... T c satisfy:

[0047] ;

[0048] It should be noted that the carrier frequency f c Only related to power frequency f s It is related to the frequency of the injected switching pulses, therefore the power supply frequency is equal to the main bridge switching frequency. f s carrier frequency f c Not affected by injection level number m The impact of change.

[0049] In this step, when the injected current is zero as the starting point of a carrier cycle, since the high-level interval of the injected pulse is always in the middle position, the carrier waveform must adopt a triangular wave shape, and the first half of a carrier cycle (0~ Tc / 2) From carrier amplitude A c Drops to 0, the second half of the cycle ( T c / 2~ T c From 0 to carrier amplitude A c .

[0050] S3. Based on the time width occupied by each triangular carrier step in the injected current, the carrier amplitude A is... c Divide the wave into 2(m-1) equal parts and obtain the possible values ​​of the modulated wave:

[0051] ,

[0052] Next, order .

[0053] S4. T inj That is, the period of the injection circuit switching pulse, or the period of the modulation wave, is decomposed into (m-1) carrier periods. Each carrier period is divided into positive intervals and negative intervals, and the two are arranged alternately on the time axis.

[0054] Preferably, the first half of each carrier cycle (0~ T c / 2) is defined as the positive interval, and the second half of the cycle ( T c / 2~ T c If ) is defined as a negative interval, then T inj It contains (m-1) positive intervals and (m-1) negative intervals.

[0055] S5. Within the positive interval, the modulated wave values ​​traverse M1~M (m-1) Each value appears only once; within the negative interval, the modulated wave also takes values ​​traversing M1 to M... (m-1) Each value appears only once;

[0056] It should be noted that the purpose of this step is to ensure that each injection switching device traverses all normal operating states, which is one of the four basic constraints of the existing injection pulse generation mechanism; specifically, to ensure that the values ​​within all positive intervals traverse M1~M (m-1) The value is M, because the number of positive intervals equals M. i The number of (i=1,2,…,m-1), therefore M1~M (m-1) Each value appears exactly once in all positive intervals; similarly, M1~M (m-1) Each value will appear exactly once in all negative intervals.

[0057] The modulated wave is compared with the carrier wave to obtain an injection pulse scheme that meets the injection pulse conditions. In addition, when the amplitude of the modulated wave is greater than that of the carrier wave, the corresponding switch is turned on. The two switches in the same injection unit need to be interlocked to avoid shoot-through short circuit.

[0058] Example 2

[0059] Based on Example 1, this example discloses a case where the number of injection levels is three levels.

[0060] like Figure 2 As shown in (a), the injection circuit consists of two injection units, with a total of four switching transistors and two smoothing inductors; by controlling the four injection circuit switching transistors... S Yr1 , S Yr2 , S Dr1 , S Dr2 To achieve such Figure 2 (b) shows the injected current waveform I Y , I D Furthermore, it must be ensured that each injected switching device traverses all normal operating states within the specified period. S Yr1 , S Dr1 Interlocking S Yr2 , S Dr2 Interlocking.

[0061] Based on this, the steps for digitally generating the switching pulses of the injection circuit are as follows:

[0062] Step 1: Using the power supply frequency of the three-level injection current source converter as a reference, determine the period of the injection circuit switching pulse as 2p / 3 according to the number of injection levels.

[0063] Step 2: Carrier Frequency f c Only related to power frequency f s It is related to the injection switch pulse frequency, so the carrier period is always p / 3. It should be noted that each injection pulse period contains two carrier periods.

[0064] If we take zero injection current as the starting point of a carrier cycle, since the high-level interval of the injection pulse is always in the middle position, the carrier must adopt a triangular wave shape. In the first half of a carrier cycle (0~ T c / 2) The carrier amplitude drops from 1 (per unit) to 0, and then rises from 0 to ( ) in the second half of the cycle. T c / 2~ T c Carrier amplitude 1 (per unit).

[0065] Step 3: Based on the time width of each step in the synthesized stepped injection current, the carrier amplitude is divided into 4 equal parts, and the possible values ​​of the modulated wave are only 1 / 4 and 3 / 4.

[0066] Step 4: Decompose the two carrier cycles contained in one cycle of the injected pulse. Each carrier cycle is divided into two intervals, where the first half of each carrier cycle (0~) T c / 2) is defined as the positive (+) interval, the second half of the cycle ( T c / 2~ T c If is defined as a negative (-) interval, then a modulation wave period contains two positive intervals and two negative intervals, and the positive and negative intervals alternate on the time axis;

[0067] Step 5: Within one cycle, in order to ensure that each injected switching device traverses all normal operating states, the modulated wave should take values ​​of 1 / 4 and 3 / 4 in its two positive intervals, meaning that each value will appear exactly once; similarly, the 1 / 4 and 3 / 4 values ​​will each appear exactly once in the two negative intervals.

[0068] Step Six: This allows for the creation of different modulation waves. In this embodiment, for example... Figure 3 (a) Figure 3 (b) As shown in the diagram, there are two cases of modulation wave, and two different injection pulse schemes can be obtained by comparing them with the carrier wave.

[0069] Example 3

[0070] Based on Example 1, this example discloses a case where the number of injection levels is five.

[0071] like Figure 4 The diagram shows the topology of the five-level injection circuit and the injection current. The steps of the digital generation method for the injection pulse in this embodiment are the same as those in Embodiments 1 and 2, and will not be repeated here. The difference between this embodiment and Embodiments 1 and 2 is as follows:

[0072] The injection circuit switching pulse period changes to 4p / 3, thus containing four carrier cycles, namely four positive intervals and four negative intervals.

[0073] The carrier amplitude should be divided into 8 equal parts, resulting in four possible values ​​for the modulation wave: 1 / 8, 3 / 8, 5 / 8, and 7 / 8. All four positive and four negative intervals should traverse these four values. Based on the permutations and combinations, the number of modulation wave schemes significantly increases compared to the three-level injection disclosed in Example 2, totaling... It should be noted that removing schemes with phase shifts but consistent waveforms from this data would be very cumbersome using traditional methods.

[0074] like Figure 5 (a)~5(c) respectively give the modulation waves corresponding to the three five-level injection pulses. It can be seen that Figure 5 In (a), the amplitude of the modulated wave is equal in each carrier period and is arranged from large to small in different carrier periods. The corresponding injection pulses are symmetrical in one carrier period and the pulse width is arranged from wide to narrow in one injection period. Figure 5 In (b), the sum of the two values ​​of the modulated wave in each carrier period is 1. The modulated wave is symmetrical from left to right in the entire injection period. The pulse width of the corresponding injection pulse is equal in each carrier period. It also presents a symmetrical arrangement in one injection period. Based on the above discussion, the other 141 modulated wave schemes in the 144 injection pulse schemes are obtained in the same way.

[0075] In this embodiment, the method of generating numbers in Embodiment 1 is very convenient. As mentioned above, since the above steps are the same, this embodiment will not be described again.

[0076] This application discloses an injection pulse modulation method for a multilevel injection current source converter. Regarding the injection pulse generation method for multilevel injection current source converters, this invention proposes a novel and intuitive method that is easy to implement. This avoids the cumbersome and error-prone nature of traditional counting and assignment methods, while making the switching between different injection pulse schemes simpler and faster. Furthermore, the modulation wave generation method in this invention may provide a new perspective on revealing the essence of the differences in harmonic content between the AC and DC currents caused by different injection pulse schemes.

[0077] The above embodiments are not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the technical solution of the present invention are also within the protection scope of the present invention.

Claims

1. A method for modulating injection pulses in a multi-level injection current source converter, characterized in that, Includes the following steps: S1. Based on the main bridge switching frequency f s Determine the main bridge switching cycle T s ,and T s =1 / f s According to the number of injection levels m Determine the period of the injection circuit switching pulse T inj Then the following relationship is satisfied: ； S2. The generated carrier frequency is 6. f s The triangular carrier wave, the carrier period of which T c for: ； Furthermore, the triangular carrier wave, in the first half of a cycle, starts from carrier amplitude A. c The amplitude drops to 0, and in the second half of the cycle, it rises from 0 to the carrier amplitude A. c ; S3. The carrier amplitude A c Divide the wave into 2(m-1) equal parts and obtain the possible values ​​of the modulated wave: ， make ; S4. The above T inj It is decomposed into (m-1) carrier periods, each carrier period is divided into positive intervals and negative intervals, and the two are alternately arranged on the time axis; S5. Within the positive interval, the modulated wave values ​​traverse M1~M (m-1) Each value appears only once; Within the negative interval, the modulated wave values ​​also traverse M1~M (m-1) Each value appears only once; S6. Compare the modulated wave with the carrier wave to obtain an injection pulse scheme that satisfies the injection pulse condition.

2. The injection pulse modulation method for a multi-level injection current source converter according to claim 1, characterized in that: With the number of injection levels m Increase, T inj Increased and by one-sixth T s The period of the injection circuit switching pulse is an integer multiple of the period ... T inj This is the period value of the modulation wave.

3. The injection pulse modulation method for a multi-level injection current source converter according to claim 2, characterized in that: In step S1, when the injection level number m =3, then T inj = T s / 3.

4. The injection pulse modulation method for a multi-level injection current source converter according to claim 2, characterized in that: In step S1, when the injection level number m =5, then T inj =2 T s / 3.

5. The injection pulse modulation method for a multi-level injection current source converter according to claim 1, characterized in that: In step S2, the first half of the cycle, i.e. (0~ T c / 2), the second half of the cycle is ( T c / 2~ T c ).

6. The injection pulse modulation method for a multi-level injection current source converter according to claim 5, characterized in that: In step S4, the positive interval is the first half of the cycle (0~ T c / 2), the negative interval is the second half of the cycle ( T c / 2~ T c ), then the T inj It contains (m-1) positive intervals and (m-1) negative intervals.

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