Injection pulse modulation method of multi-level injection type current source converter

Abstract

The invention discloses an injection pulse modulation method for a multi-level injection type current source converter, and the method comprises the steps: S1, determining a main bridge switching period Ts based on a main bridge switching frequency fs, and determining a period Tinj of an injection circuit switching pulse according to the number m of injection levels; s2, generating a triangular carrier with the carrier frequency of 6fs; s3, equally dividing the carrier amplitude Ac into 2 (m-1) parts; s4, decomposing the Tinj into (m-1) carrier wave periods; s5, traversing M1-M (m-1) values in the positive interval and the negative interval; s6, comparing the modulated wave with the carrier wave to obtain an injection pulse scheme meeting an injection pulse condition; the invention provides a novel method which is intuitive and easy to implement, which not only avoids the complexity and error-prone property of the traditional counting assignment method, but also simplifies and accelerates the conversion process among different injection pulse schemes, and in addition, the method has the advantages of high accuracy and high reliability. The modulation wave generation technology provides a new perspective for understanding how different injection pulse schemes affect the harmonic content of the alternating current and direct current side current of the system.

Description

Technical Field

[0001] The invention relates to a wire harness dispensing jig, and in particular to an injection pulse modulation method of a multi-level injection current source converter. Background Art

[0002] As the core device of power electronics systems, large-capacity AC / DC converters have important application value in key areas such as smart grids, high-speed railway traction power supply, and aerospace power supply. Among them, current source converters, with their superior control characteristics and wide-range DC voltage regulation capabilities, demonstrate significant technical advantages over VSCs (voltage source converters) in specific application scenarios. The MLR-CSC, or multi-level injection current source converter, successfully achieves controlled shutdown of thyristor devices by introducing a multi-level injection circuit on the DC side of a traditional LCC (twelve-pulse grid-commutated converter). This enables the system to combine outstanding advantages such as four-quadrant operation capability, low switching frequency harmonic elimination, and the elimination of grid-side three-phase filters, significantly improving the overall performance of traditional LCC converters.

[0003] During the evolution of MLR-CSC technology, the injection circuit, as a core functional module, has undergone multiple technical iterations. Early designs employed a topology consisting of multi-tap reactors connected in parallel with self-shutoff switching devices. While this approach achieved basic level injection functionality, it had significant drawbacks: First, the injection switches needed to withstand the full DC current, placing stringent requirements on their steady-state current capacity and dynamic di / dt withstand capability, directly restricting the converter's power level. Second, the injection switches' on-times varied significantly at different spatial locations, resulting in 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. This scheme utilizes a combination of reverse-resistance switching devices and smoothing inductors. The DC current is evenly distributed across m-1 (m is the number of injection levels) parallel switches. This not only effectively reduces the current stress on individual devices, but also replaces the multi-tap reactors with smoothing inductors, eliminating the original excitation current losses and achieving zero-current switching of the main bridge thyristors, significantly improving system efficiency.

[0004] Although new injection circuits have made progress in hardware topology, the complexity of their control systems has increased significantly, especially in the injection pulse generation mechanism. Public literature in the field has identified the following four basic 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 sets of main conversion bridges with a certain zero-value interval and periodically changing equal-increment step wave current;

[0007] 3. Each injection switch device traverses all normal working states within a certain period;

[0008] 4. The two switch tubes of the same injection unit are interlocked.

[0009] The above basic conditions provide a reference for the specific injection method of the injection circuit, but its digital generation method is still unclear. At present, the main method is to obtain the injection period by dividing the system clock after determining the specific injection pulse scheme, and then use the counting assignment method to generate a period of injection pulses, and obtain the switching pulses of other injection units by phase shifting. However, as the number of injection levels increases, the number of injection pulse schemes that meet the above basic conditions increases sharply, and the above injection pulse digital generation scheme becomes very difficult and error-prone when switching between different pulse schemes. For the digital generation method of injection pulses for injection circuits, a simpler and more effective solution has not yet been proposed in the field. Summary of the Invention

[0010] In order to solve the deficiencies of the above technologies, the present invention provides an injection pulse modulation method for a multi-level injection current source converter.

[0011] In order to solve the above technical problems, the technical solution adopted by the present invention is: an injection pulse modulation method of 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 period T s , and T s =1 / f s , determine the period T of the injection circuit switching pulse according to the injection level number m inj , then the following relationship is satisfied:

[0013] T inj =(m-1)T s 6;

[0014] S2. Generate a carrier frequency of 6f s The triangular carrier wave has a carrier period of T c for:

[0015] T c =T s 6=T inj (m-1);

[0016] And the first half of the triangular carrier in one cycle is from the carrier amplitude A c Drops to 0, and rises from 0 to the carrier amplitude A in the second half of the cycle c ;

[0017] S3. Set the carrier amplitude to Ac Divide it into 2(m-1) equal parts, and get the possible values of the modulated wave:

[0018]

[0019] make

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

[0021] S5. In the positive interval, the modulation wave takes values ​​from M1 to M (m-1) value and each value appears only once; in the negative interval, the modulation wave value also traverses M1~M (m-1) value and each value appears only once;

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

[0023] Furthermore, as the number of injection levels m increases, T inj Increased and one-sixth of T s The cycle T of the switching pulse injected into the circuit is an integer multiple of inj This is the period value of the modulation wave.

[0024] Furthermore, in step S1, when the number of injection levels m=3, then T inj =T s / 3.

[0025] Furthermore, in step S1, when the number of injection levels m=5, then T inj =2T s / 3.

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

[0027] Furthermore, in step S2, the first half cycle (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 ), then T injContains (m-1) positive intervals and (m-1) negative intervals.

[0029] Furthermore, when the amplitude of the modulation wave is greater than the carrier wave, the corresponding switch tube S Yr1 conduction, S Dr1 Shutdown;

[0030] When the amplitude of the modulation wave is smaller than the carrier wave, the corresponding switch tube S Yr1 Shutdown, S Dr1 conduction;

[0031] Switch tube S Yr2 ~S Yr(m-1) The switching pulse is S Yr1 The switching pulses are phase-shifted by T inj / (m-1);

[0032] The two switches of the same injection unit need to be interlocked to avoid direct short circuit, that is, S Yri With S Dri The trigger pulses are complementary (i=1, 2,…, m-1).

[0033] A method for modulating injection pulses of a multi-level injection current source converter. Regarding the injection pulse generation method of a multi-level injection current source converter, the present invention proposes a new method that is intuitive and easy to implement, which avoids the tedious and error-prone problems of traditional counting and assignment methods, while making switching between different injection pulse schemes simpler and faster. In addition, the modulation wave generation method in the present invention may provide a new perspective for revealing the essence of the differences in the harmonic content of the system's AC and DC side currents caused by different injection pulse schemes. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a multi-level injection current source converter topology.

[0035] Figure 2 This is the three-level injection circuit structure and injection current waveform.

[0036] Figure 3 This is the five-level injection circuit structure and injection current waveform.

[0037] Figure 4 It is a three-level injection pulse digital generation method.

[0038] Figure 5 It is a five-level injection pulse digital generation method. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] like Figure 1The figure shows the system topology of the multi-level injection current source converter. The shaded area is the injection circuit, where a pair of switch tubes S connected to points p and q respectively Yri and S Dri (i=1,2,3,…,m-1) are connected to a smoothing inductor L i The three constitute an injection unit; m-1 injection units are connected in parallel to form an m-level injection circuit.

[0041] It should be noted that the common injection levels are three, five, and seven. The higher the number of levels, the more injection units are required. The number of additional switches and smoothing inductors required in the injection circuit increases linearly, but the suppression effect on AC-side harmonics gradually slows down. In actual implementation, considering system factors including cost and volume, the number of injection levels generally does not exceed seven. For MLR-CSC systems with a fixed number of injection levels, there is no unique injection pulse scheme that can achieve the injection current waveform, and as the number of injection levels m increases, the number of feasible injection pulse schemes increases sharply.

[0042] For different injection pulse schemes, under ideal assumptions (DC side smoothing inductor L i In practice, however, the smoothing inductance cannot be infinite, and due to system size limitations, the inductance value needs to be kept as small as possible. This causes different injection pulses to affect the current ripple shape and harmonic content on the AC and DC sides of the MLR-CSC system. Therefore, the key to studying injection pulse schemes lies in analyzing the specific impact of each injection pulse scheme on system harmonics and selecting the optimal injection pulse scheme. However, due to the numerous injection pulse schemes and the cumbersome digital implementation methods, switching between different injection pulse schemes is difficult, making traditional experimental methods more difficult to solve this problem.

[0043] To select the injection pulse scheme that minimizes the harmonic content of the system's AC current, existing methods implement all injection pulse schemes through counting assignment and then attempt to obtain the optimal five-level injection pulse scheme through program optimization in simulation. However, this method cannot reveal the common characteristics of different injection level numbers. When it comes to obtaining the optimal injection pulse scheme for seven-level injection, the conclusions obtained by the above method cannot be directly extended and still require complex simulation and programming.

[0044] Example 1

[0045] This embodiment provides an injection pulse modulation method for a multi-level injection current source converter, including the following steps:

[0046] S1. Based on the main bridge switching frequency f s Determine the main bridge switching period T s, that is to say, the premise is that the main bridge switching frequency of MLR-CSC is the power supply frequency, which is equal to the AC power supply frequency, then the main bridge switching period T s =1 / f s , determine the period T of the injection circuit switching pulse according to the injection level number m inj , satisfying the following relationship:

[0047] T inj =(m-1)T s 6.

[0048] In step S1, as the number of injection levels m increases, the period T of the injection circuit switch pulse increases. inj Increase and be an integer multiple of one-sixth of the main bridge switching period. It should be noted that the period of the injection circuit switching pulse T inj That is, the period value of the modulation wave.

[0049] Based on the above identification, when the number of injection levels m = 3, then T inj =T s / 3; when the number of injection levels m = 5, then T inj =2T s / 3.

[0050] S2. Generate a carrier frequency of 6f s triangular carrier; since the synthetic injection current is 6 times the main bridge switching frequency and the carrier waveform is a triangular step waveform, the carrier frequency f c Should be equal to the frequency of the injected current, which is 6f s , in order to achieve one of the four basic limiting conditions of the existing injection pulse generation mechanism; on this basis, the carrier period T c satisfy:

[0051] T c =T s 6=T inj / (m-1);

[0052] It should be noted that the carrier frequency f c Only with power frequency f s It is related to the injected switching pulse frequency, so the power supply frequency is equal to the main bridge switching frequency f s , carrier frequency f c It is not affected by changes in the number of injection levels m.

[0053] In this step, when the injection current is zero as the starting point of a carrier cycle, since the interval of the injection pulse being high level is always in the middle, the carrier waveform must adopt a triangular wave shape, and the first half of a carrier cycle (0~T c / 2) from the carrier amplitude A cFalls to 0, the second half cycle (T c / 2~T c ) rises from 0 to the carrier amplitude A c .

[0054] S3. According to the time width of each triangle carrier step in the injected current, the carrier amplitude A c Divide it into 2(m-1) equal parts, and get the possible values of the modulated wave:

[0055]

[0056] Next, let

[0057] S4.T inj That is, the cycle of the switching pulse injected into the circuit or the modulation wave cycle is decomposed into (m-1) carrier cycles, each carrier cycle is divided into a positive interval and a negative interval, and the two are arranged alternately on the time axis;

[0058] Preferably, the first half of each carrier cycle (0~T c / 2) is defined as the positive interval, and the second half period (T c / 2~T c ) is defined as a negative interval, then T inj Contains (m-1) positive intervals and (m-1) negative intervals.

[0059] S5. In the positive interval, the modulated wave value traverses M1~M (m-1) value and each value appears only once; in the negative interval, the modulation wave value also traverses M1~M (m-1) value and each value appears only once;

[0060] It should be noted that the purpose of this step is to satisfy the requirements of all injection switch devices to traverse all normal working states, that is, to achieve one of the four basic limiting conditions of the existing injection pulse generation mechanism; specifically, to make all values in the positive interval traverse M1~M (m-1) value, because the number of positive intervals is equal to M i (i=1,2,…,m-1), so M1~M (m-1) Each value will appear once and only once in all positive intervals; similarly, M1~M (m-1) Each value appears exactly once in all negative intervals.

[0061] Compare the modulation wave with the carrier wave to obtain the injection pulse scheme that meets the injection pulse conditions. In addition, when the modulation wave amplitude is greater than the carrier wave, the corresponding switch tube S Yr1 conduction, S Dr1 Turn off; when the modulation wave amplitude is less than the carrier, the corresponding switch tube SYr1 Shutdown, S Dr1 On; switch tube S Yr2 ~S Yr(m-1) The switching pulse is S Yr1 The switching pulses are phase-shifted by T inj / (m-1); the two switches of the same injection unit need to be interlocked to avoid direct short circuit, that is, S Yri With S Dri The trigger pulses are complementary (i=1, 2,…, m-1).

[0062] Example 2

[0063] Based on the first embodiment, this embodiment discloses a case where the number of injection levels is three.

[0064] like Figure 2 As shown in (a), the injection circuit consists of two injection units, a total of 4 switching tubes and 2 smoothing inductors; by controlling the four injection circuit switching tubes S Yr1 、S Yr2 、S Dr1 、S Dr2 , to achieve Figure 2 (b) The injected current waveform I Y , I D , and ensure that each injection switch device traverses all normal working states within the specified period, S Yr1 、S Dr1 Interlock, S Yr2 、S Dr2 Interlock.

[0065] On this basis, the digital generation method of the injection circuit switching pulse is as follows:

[0066] Step 1: Taking the power supply frequency of the three-level injection current source converter as a reference, determine the period of the injection circuit switch pulse as 2π / 3 according to the number of injection levels.

[0067] Step 2: Carrier frequency f c Only with power frequency f s It is related to the injection switching pulse frequency, so the carrier period is always π / 3. It should be noted that each injection pulse period contains two carrier periods;

[0068] If the injection current is zero as the starting point of a carrier cycle, since the interval where the injection pulse is high level is always in the middle, the carrier must adopt a triangular wave shape. In the first half of a carrier cycle (0~T c / 2) drops from the carrier amplitude 1 (per unit value) to 0, and rises from 0 to (T c / 2~T c)Carrier amplitude 1 (per unit value).

[0069] Step 3: Based on the time width of each step in the synthesized step-shaped 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.

[0070] Step 4: Decompose the two carrier cycles contained in one cycle of the injected pulse. Each carrier cycle is divided into two intervals. 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 ) is defined as the negative (-) interval, then one modulation wave cycle contains two positive intervals and two negative intervals, and the positive and negative intervals appear alternately on the time axis;

[0071] Step 5: In one cycle of the modulation wave, in order to satisfy that each injection switch device traverses all normal working states, the values in its two positive intervals should traverse the 1 / 4 and 3 / 4 values, that is, each value will appear and only appear once; similarly, the 1 / 4 and 3 / 4 values will appear and only appear once in the two negative intervals.

[0072] Step 6: In this way, different modulation waves can be formed. In this embodiment, Figure 4 (a) Figure 4 As shown in (b), there are two situations in which the modulated wave appears. After comparing with the carrier, two different injection pulse schemes can be obtained.

[0073] Example 3

[0074] Based on the first embodiment, this embodiment discloses a case where the number of injection levels is five.

[0075] like Figure 3 The topology of the five-level injection circuit and the injection current are shown. The steps of the digital injection pulse generation method of this embodiment are the same as those of Example 1 and Example 2 and are not repeated here. The difference between this embodiment and Example 1 and Example 2 is that:

[0076] The switching pulse period of the injection circuit varies as 4p / 3, so it contains four carrier periods, namely four positive intervals and four negative intervals.

[0077] The carrier amplitude should be divided into 8 equal parts, and the possible values of the modulated wave are 1 / 8, 3 / 8, 5 / 8, and 7 / 8. The four positive intervals and the four negative intervals should all traverse the above four values. According to the permutations and combinations, the number of schemes for the modulated wave increases significantly compared to the three-level injection disclosed in Example 2, totaling It should be noted that it is very cumbersome to remove the scheme with phase shift but consistent waveform from the data. It can be understood that using traditional methods will be very cumbersome.

[0078] like Figure 5 (a) Figure 5 (b) Figure 5 (c) The modulation waves corresponding to the three five-level injection pulses are given respectively. It can be seen that Figure 5 In (a), the amplitude of the modulated wave is equal in each carrier cycle and is arranged from large to small in different carrier cycles. The corresponding injected pulse is symmetrical within a carrier cycle, and the pulse width is arranged from wide to narrow within an injection cycle. Figure 5 In (b), the sum of the two values of the modulated wave in each carrier cycle is 1. The modulated wave is bilaterally symmetrical throughout the injection cycle. The corresponding injected pulses have the same pulse width in each carrier cycle, and the arrangement is also bilaterally symmetrical within one injection cycle. Figure 5 In (c), the modulation wave decreases from the maximum value and then increases from the minimum value within one injection cycle. The modulation wave is symmetrical left and right within the entire injection cycle. The corresponding injection pulses are also arranged symmetrically left and right within one injection cycle, but the width is not consistent within one carrier cycle, and there is no obvious trend of sequential change. Based on the above discussion, the other 141 schemes among the 144 injection pulse schemes are obtained by the same logic.

[0079] The situation of this embodiment is very convenient when using the digital generation method of embodiment 1. At the same time, as mentioned above, since the above steps are the same, they will not be repeated in this embodiment.

[0080] The present application discloses an injection pulse modulation method for a multi-level injection current source converter. For the injection pulse generation method of the multi-level injection current source converter, the present invention proposes a new method that is intuitive and easy to implement, which not only avoids the tedious and error-prone problems of the traditional counting and assignment method, but also makes the switching between different injection pulse schemes simpler and faster. In addition, the modulation wave generation method in the present invention may provide a new perspective for revealing the essence of the difference in harmonic content of the system AC and DC side currents caused by different injection pulse schemes.

[0081] The above embodiments are not limitations of the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by technicians in this technical field within the scope of the technical solution of the present invention also fall within the scope of protection of the present invention.

Claims

1. A method for modulating an injection pulse of a multi-level injection current source converter, characterized in that: The following steps are involved: S1. Based on the main bridge switching frequency f s Determine the main bridge switching period T s , and T s =1 / f s , determine the period T of the injection circuit switching pulse according to the injection level number m inj , then the following relationship is satisfied: T inj =(m-1)T s / 6; S2. Generate a carrier frequency of 6f s The triangular carrier wave has a carrier period of T c for: T c =T s / 6=T inj / (m-1); And the first half of the triangular carrier in one cycle is from the carrier amplitude A c Drops to 0, and rises from 0 to the carrier amplitude A in the second half of the cycle c ; S3. Set the carrier amplitude to A c Divide it into 2(m-1) equal parts, and get the possible values of the modulated wave: make S4. The T inj Decomposed into (m-1) carrier cycles, each carrier cycle is divided into positive intervals and negative intervals, and the two are arranged alternately on the time axis; S5. In the positive interval, the modulated wave value traverses M1~M (m-1) value and each value appears only once; In the negative interval, the modulation wave value also traverses M1~M (m-1) value and each value appears only once; S6. Compare the modulated wave with the carrier wave to obtain an injection pulse scheme that meets the injection pulse conditions.

2. The injection pulse modulation method of a multi-level injection current source converter according to claim 1, wherein: As the number of injection levels m increases, T inj Increased and one-sixth of T s The cycle T of the switching pulse of the injection circuit is an integer multiple of inj This is the period value of the modulation wave.

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

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

5. The injection pulse modulation method of a multi-level injection current source converter according to claim 1, wherein: In step S2, the externally synthesized injection current is 6 times the main bridge switching frequency and the carrier waveform is a triangular wave, then the carrier frequency f c Fixed to 6f s .

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

7. The injection pulse modulation method of a multi-level injection current source converter according to claim 1, wherein: 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 Contains (m-1) positive intervals and (m-1) negative intervals.

8. The injection pulse modulation method of a multi-level injection current source converter according to claim 1, wherein: In step S6, When the amplitude of the modulation wave is greater than the carrier, the corresponding switch tube S Yr1 conduction, S Dr1 Shutdown; When the amplitude of the modulation wave is smaller than the carrier wave, the corresponding switch tube S Yr1 Shutdown, S Dr1 conduction; Switch tube S Yr2 ~S Yr(m-1) The switching pulse is S Yr1 The switching pulses are phase-shifted by T inj / (m-1); The two switches of the same injection unit need to be interlocked to avoid direct short circuit, that is, S Yri With S Dri The trigger pulses are complementary (i=1, 2,…, m-1).

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