Interrupted current mode modulation method for three-phase step-down rectifier

Abstract

The invention relates to the technical field of new energy storage systems, in particular to a three-phase step-down rectifier intermittent current mode modulation method and system, and provides an odd-even sector self-adaptive vector action sequence which is characterized in that a high-voltage vector is preferentially acted, then a low-voltage vector is acted, and finally a zero vector is applied. And it is ensured that the two active vectors can effectively participate in current synthesis in a full output voltage range. Besides, a vector action calculation model is reconstructed based on DCM mode operation characteristics, a simple implementation scheme without a phase-locked loop is further designed, inherent phase information in a three-phase input voltage sampling value is used for correspondingly replacing a complex trigonometric function calculation result containing a phase-locked angle in a traditional strategy, and the algorithm complexity is remarkably reduced. Theoretical support and an efficient engineering implementation scheme are provided for application of the three-phase step-down rectifier in light-load and variable-working-condition scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy storage systems, and in particular to a discontinuous current mode modulation method for a three-phase buck rectifier. Background Art

[0002] The operating characteristics of three-phase buck rectifiers are significantly dependent on operating conditions. For example, when the built-in rectifier in a UPS system operates under light-load conditions, the DC-side inductor current ripple may exceed the load current baseline. At this point, the system enters discontinuous current mode (DCM). In this mode, the DC-side inductor current no longer exhibits a constant current source characteristic, and the magnitude of each active current vector no longer remains constant within a switching cycle. Continuing to use the vector action time distribution scheme used in continuous conduction mode (CCM) will lead to serious problems such as AC-side current distortion and DC bus voltage imbalance. Although increasing the switching frequency and optimizing the DC inductor parameters can narrow the DCM operating range, this phenomenon cannot be completely eliminated under light-load conditions. It is worth noting that DCM is not unique to three-phase buck rectifiers; it also occurs in other current-source converters, such as current-source inverters and single-stage isolated three-phase buck rectifiers. Therefore, the research on high-performance modulation strategy of three-phase buck rectifier in DCM mode has important engineering application value.

[0003] In DCM mode, the ripple characteristics of the DC-side inductor current are non-negligible, and its dynamic variations directly impact the effectiveness of space vector synthesis. In this case, the active current vector modulus exhibits nonlinear time-varying characteristics as the instantaneous value of the DC-side inductor current changes during the switching cycle, necessitating a reconstruction of the vector action time calculation method based on the current dynamic model. Existing research strategies improve AC-side current distortion and output voltage imbalance by establishing piecewise linear equations for the inductor current under different vector actions during the switching cycle and recalculating the vector action time. However, existing research still lacks understanding of two key mechanisms: First, the impact of the coupling effect between the output voltage range and the vector action sequence on DCM operating characteristics has not been quantified; second, when the modulation index is greater than 0.577, there is a risk that the DC-side inductor current will return to zero during the power bridge arm conduction period. In this case, the corresponding active current vector loses its current synthesis capability, making it impossible to synthesize the target current vector corresponding to the sinusoidal three-phase current using only a single active vector.

[0004] Reference Drews D, Cuzner R, Venkataramanan G, et al. Operation of current source inverters in discontinuous conduction mode [J]. IEEE Transactions on Industry Applications, 2016, 52(6): 4865-4877. The proposed six-sector modulation strategy is effective when the modulation index is less than 0.577, but when the modulation index is greater than 0.577, the DC side inductor current under the strategy will maintain zero value during the action of the active vector and cannot participate in the synthesis of the target current vector. Reference Guo X, Yang Y, Wang B, et al. Generalized space vector modulation for current source converter in continuous and discontinuous current modes [J]. IEEE Transactions on Industrial Electronics, 2020, 67(11): 9348-9357. By expanding the six-sector modulation to twelve-sector modulation, that is, exchanging the order of the active current vectors in the two small sectors in the same large sector, the effective modulation index range is expanded, but its effectiveness in the full output voltage range remains to be verified. More critically, existing solutions all rely on a phase-locked loop (PLL) to achieve grid phase synchronization. Furthermore, each switching cycle requires four trigonometric operations on the phase-locked result, increasing the computational load on the digital signal processor (DSP), severely limiting real-time control and system power density in high-frequency scenarios. Notably, the three-phase input voltage samples themselves contain complete phase information. This feature provides a theoretical basis for eliminating reliance on the PLL, while also avoiding phase tracking errors caused by the PLL's dynamic response lag. It can also significantly improve the resource utilization of digital control systems. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to propose a discontinuous current mode modulation method for a three-phase buck rectifier to solve the problems of input current distortion and voltage instability and provide a high-efficiency, high-power density technical path.

[0006] Based on the above objectives, the present invention provides a discontinuous current mode modulation method for a three-phase buck rectifier, comprising the following steps:

[0007] S1. Determine the system modulation sequence and use "I k -I n-0" sequence, odd-numbered small sectors use "I n -I k -0" sequence, to ensure that the pulse width modulation of the space vector is performed in each switching cycle to synthesize the target vector in each small sector. pn The timing characteristics are always "v h -v l -0", where I k , I n Represents two adjacent active vectors appearing in sequence at the boundary of each sector, v pn is the output voltage of the power conversion circuit. In each small sector, v pn The higher value is denoted as v h , v pn The lower value is denoted as v l ;

[0008] S2. By allocating the vector action time, the duty cycle of the switch tube in the three-phase buck rectifier is modulated to achieve discontinuous current mode modulation of the three-phase buck rectifier.

[0009] Preferably, allocating the vector action time includes a vector action time calculation model, calculating the vector action time:

[0010] Vector action time T in even-numbered small sectors k for,

[0011]

[0012] in,

[0013]

[0014] Where, T k Represents the action time of the voltage vector with a smaller angle in the current small sector, T s is the switching period, I m is the target three-phase input current amplitude, V o is the DC side output voltage, θ is the phase angle of the three-phase input voltage, L dc is the DC side inductance, V m_l-l is the input line voltage amplitude;

[0015] Vector action time T in even-numbered small sectors n for,

[0016]

[0017] in,

[0018]

[0019] Where, T nRepresents the action time of the larger angle voltage vector in the current small sector, S k Represents vector I k The rate of change of the inductor current during the action period, S n Represents vector I n The rate of change of the inductor current during the action period;

[0020] The zero vector action time T0 is,

[0021] T0=T s -T k -T n (1-17)

[0022] The vector action time in the odd small sector is,

[0023]

[0024] Preferably, the vector action time calculation model is replaced by a simple implementation scheme based on the inherent phase information of the three-phase input voltage to establish a phase-locked loop-free system. The scheme includes:

[0025] In even-numbered sectors,

[0026]

[0027] In odd-numbered sectors,

[0028]

[0029] Each sector The corresponding value is: by sector number, Corresponding values Corresponding values

[0030]

[0031] Where, v a , v b , v c is the three-phase input voltage, V m is the three-phase input phase voltage amplitude;

[0032] S k 、S n The two trigonometric function calculations in the above example are done by dividing the v in each sector by k , v n Substitute the mapping relationship into formula (1-2) and formula (1-4) to achieve simplification;

[0033] v in each sector k , v nThe mapping relationship is obtained based on the relationship between the DC side output voltage and the bridge arm output voltage, the basic current vector, the target current vector phase angle and the sector within the grid cycle.

[0034] Preferably, the construction process of the simple implementation solution includes:

[0035] Based on the trigonometric identities, the substitution rules of the trigonometric function values ​​of the phase-locked loop results in each sector are obtained, and based on the relationship between the DC side output voltage and the bridge arm output voltage, the basic current vector, the target current vector phase angle and the sector within the grid cycle, the v in each sector is obtained. k , v n The mapping relationship;

[0036] Substitute the obtained trigonometric function values ​​into the rules and v in each sector k , v n Substituting the mapping relationship into equations (1-1) to (1-7), we can obtain a simple implementation solution for the vector action time in each sector.

[0037] Beneficial effects of the present invention:

[0038] 1. This invention proposes an odd-even sector adaptive vector action sequence. By prioritizing the high-voltage vector, followed by the low-voltage vector, and finally applying the zero vector, this ensures that both active vectors can effectively participate in current synthesis across the entire output voltage range when the three-phase buck rectifier operates in DCM mode. Furthermore, the vector action calculation model is reconstructed based on the dynamic characteristics of the DC-side inductor current in DCM mode, ensuring the correctness of the modulation strategy in DCM mode and avoiding input current distortion and output voltage imbalance.

[0039] 2. The present invention further designs a simple implementation scheme that does not require a phase-locked loop to execute the proposed modulation strategy, using the inherent phase information in the three-phase input voltage sampling values ​​to replace the complex trigonometric function calculation results containing the phase-locked angle in the traditional strategy, significantly reducing the algorithm complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 This is a schematic diagram of the circuit operating mode when the DC side inductor current of the three-phase buck rectifier analyzed in the present invention is discontinuous.

[0042] Figure 2This is a schematic diagram of the relationship between the DC side output voltage and the bridge arm output voltage, basic current vector, target current vector phase angle and sector within the grid cycle analyzed by the present invention.

[0043] Figure 3 This is a schematic diagram of the relative relationship between the DC side output voltage and the bridge arm output voltage in sector I used in the present invention.

[0044] Figure 4 Schematic diagram of the modulation strategy effective in the full output voltage range in the DCM mode adopted by the present invention.

[0045] Figure 5 This is a schematic diagram of the SVPWM vector synthesis analyzed in the present invention.

[0046] Figure 6 This is a schematic diagram of SVPWM vector synthesis based on equal three-phase current components analyzed by the present invention.

[0047] Figure 7 m under the DCM mode analyzed by the present invention v =0.49, where (a) shows the vector action time in each sector under the CCM modulation strategy; (b) shows the vector action time in each sector after the proposed strategy is updated.

[0048] Figure 8 m under the DCM mode analyzed by the present invention v =0.49, where (a) shows the DC-side inductor current under the CCM modulation strategy; (b) shows the DC-side inductor current under the proposed strategy.

[0049] Figure 9 m under the DCM mode analyzed by the present invention v =0.49, where (a) shows the three-phase input current on the AC side under the CCM modulation strategy; (b) shows the three-phase input current on the AC side under the proposed strategy.

[0050] Figure 10 m under the DCM mode analyzed by the present invention v =0.49, where (a) shows the DC side output voltage under the CCM mode modulation strategy; (b) shows the DC side output voltage under the proposed strategy.

[0051] Figure 11 The present invention analyzes m under DCM mode v= 0.7, where (a) shows the vector action time under the CCM modulation strategy; (b) shows the vector action time under the proposed strategy.

[0052] Figure 12 m under the DCM mode analyzed by the present invention v =0.7, where (a) shows the DC-side inductor current under the CCM modulation strategy; (b) shows the DC-side inductor current under the proposed strategy.

[0053] Figure 13 m under the DCM mode analyzed by the present invention v =0.7, where (a) shows the three-phase input current on the AC side under the CCM modulation strategy; (b) shows the three-phase input current on the AC side under the proposed strategy.

[0054] Figure 14 m under the DCM mode analyzed by the present invention v =0.7, where (a) shows the DC side output voltage under the CCM mode modulation strategy; (b) shows the DC side output voltage under the proposed strategy. DETAILED DESCRIPTION

[0055] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0056] It should be noted that, unless otherwise defined, the technical or scientific terms used in the present invention should have the usual meanings understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0057] The embodiments of this specification provide a three-phase buck rectifier system operating in DCM mode, which is used to implement the above-mentioned modulation strategy that is effective in the full output voltage range, as follows:

[0058] 1. Effective vector action sequence within the full output voltage range

[0059] The effective modulation sequence in the full output voltage range under the DCM mode proposed by the present invention is as follows: Figure 4 As shown. In even-numbered small sectors, “I k -I n -0" sequence, odd-numbered small sectors use "I n -I k -0" sequence, to ensure that v in each small sector when SVPWM synthesizes the target vector in each switching cycle pn The timing characteristics are always "v h -v l -0". Among them, I k , I n Respectively Figure 2 Two adjacent active vectors appearing in sequence at the boundaries of each sector; v pn for Figure 1 The output voltage of the medium power conversion circuit is given by Figure 3 It can be seen that the relative magnitudes of the two active vectors in the two small sectors within the large sector are opposite, so in each small sector, v pn The higher value is denoted as v h , v pn The lower value is denoted as v l Therefore, in the even sector, v k v h , v n v l , and the opposite is true for odd sectors.

[0060] like Figure 3 As shown, in m v In the full range, v h >V o and 0 <V o Always holds true, so when the two corresponding vectors act, i Ldc The change is fixed, and is always rising and falling. Let the circuit modulation index be m v , its mathematical expression is as follows, where V m_l-l is the input line voltage amplitude.

[0061]

[0062] In m v Below 0.577 and m v In the P1 and P3 intervals above 0.577, v l >V o , so when the corresponding active vector acts i Ldc Rising; and in m v In the P2 interval above 0.577, v l <Vo , so when the corresponding active vector acts i Ldc Will decrease, and its corresponding active vector may not be able to participate in the SVPWM synthesis process in DCM mode. l Place v h Afterwards, ensure that v l The corresponding active vector participates in the SVPWM synthesis process normally, meeting the basic premise of correct synthesis of the target current vector. The DC side inductor terminal voltage v in each small sector under the proposed vector action sequence is Ldc 、i Ldc and v pn The changes in Figure 4 Given in.

[0063] 2. Vector action time model

[0064] 2.1 DC side inductor current dynamic model

[0065] The vector action time in traditional CCM mode is derived based on the assumption that the DC side inductor current is constant. However, the inductor current ripple in DCM mode cannot be ignored. Directly using the traditional calculation results will lead to the failure of the target current vector synthesis. Therefore, it is necessary to reconstruct the vector action time calculation model based on the dynamic change of the inductor current in DCM mode. When the three-phase buck rectifier enters DCM mode, the circuit mode is as follows: Figure 1 As shown, at this time i Ldc When the zero vector action ends, it returns to zero, such as Figure 4 As shown, therefore,

[0066] i Ldc0 =i Ldc3 =0 (1-26)

[0067] Then, in v h During the active vector action period, i Ldc rise,

[0068]

[0069] In even-numbered small sectors, v h The corresponding active vector is I k , therefore,

[0070]

[0071] In odd-numbered small sectors, v h The corresponding active vector is I n , therefore,

[0072]

[0073] v h After the effect, in vl During the active vector action period, i Ldc The changes are as follows,

[0074]

[0075] In even-numbered small sectors, v l The corresponding active vector is I n , therefore,

[0076]

[0077] In odd-numbered small sectors, v l The corresponding active vector is I k , therefore,

[0078]

[0079] 2.2SVPWM Vector Synthesis

[0080] Figure 5 The schematic diagram of SVPWM vector synthesis in CCM mode. In DCM mode, the essence of SVPWM vector synthesis process is that the active vector action time i Ldc The integration of time is equivalent to synthesizing the target current vector, so the vector synthesis process is:

[0081]

[0082] Combine Figure 4 , Equation (1-33) can be decomposed into Equations (1-34) and (1-35) in even-numbered small sectors.

[0083]

[0084] In odd-numbered small sectors, the equations are (1-36) and (1-37).

[0085]

[0086] Substituting equation (1-28) into equation (1-34), we can obtain the vector action time T in the even-numbered small sector. k for,

[0087]

[0088] in,

[0089]

[0090] At this time T k So, we substitute formula (1-31) into formula (1-35) and solve for the vector action time T in the even-numbered small sector. n for,

[0091]

[0092] in,

[0093]

[0094] S k Represents vector I k The rate of change of the inductor current during the action period, S n Represents vector I n The rate of change of the inductor current during the action period, at this time T k 、T n It is known that, so the zero vector action time T0 is,

[0095] T0=T s -T k -T n (1-42)

[0096] Similarly, the vector action time in the odd-numbered small sector is solved as follows:

[0097]

[0098]

[0099] T0 is still calculated according to formula (1-42).

[0100] 3. Simple implementation without phase-locked loop

[0101] Vector time calculations based on equations (1-38) to (1-44) rely on the PLL to acquire phase information in real time and involve four trigonometric operations. These algorithms have significant limitations in engineering applications: trigonometric calculations must be performed through real-time iteration or table lookup. The former increases the controller's timing complexity, while the latter consumes significant storage resources, placing stringent demands on the computing power and storage capacity of the control chip. Furthermore, algorithmic complexity directly constrains increases in control frequency, limiting the system's dynamic response speed, increasing hardware costs, and hindering the design of high-power-density topologies. These issues are common in existing solutions.

[0102] A simple scheme for vector time calculation without a phase-locked loop can be realized by utilizing the inherent phase information in the three-phase input voltage sampling values. Figure 6 The following is a schematic diagram of SVPWM vector synthesis based on equal three-phase current components. In DCM mode, the synthesis of the target current vector is essentially equivalent to the integral of the DC side inductor current during the active vector action time, so the vector synthesis process is:

[0103]

[0104] In the I large sector, formula (1-45) can be decomposed into:

[0105]

[0106] Simplifying,

[0107]

[0108] Comparing formula (1-50) with formula (1-34) and formula (1-37), it can be used in large sector I. Replace the trigonometric function value sin(π / 6-θ) containing the phase-locked loop phase-locked result; compare formula (1-51) with formula (1-35) and formula (1-36), and you can use Substitute the trigonometric function value sin(π / 6+θ) containing the phase-locked loop phase-locked result. Similarly, further analysis of the mapping relationships within other large sectors yields Table 3.

[0109] Table 3 Mapping relationship of trigonometric function values ​​of each sector including phase-locked loop results

[0110]

[0111] At the same time, based on Figure 2 Get v in each sector k , v n The mapping relationship is shown in Table 4.

[0112] Table 4 Sector v k , v n Mapping relationship

[0113]

[0114] Substituting the conclusions in Table 3 and Table 4 into equations (1-38) to (1-44), we can obtain a simple implementation scheme for the vector action time in each sector:

[0115] In even-numbered sectors,

[0116]

[0117] In odd-numbered sectors,

[0118]

[0119] Among them, each sector j k 、j n The corresponding values ​​are shown in Table 5.

[0120] Table 5 Sectors Corresponding value

[0121]

[0122] S k 、S n The two trigonometric function calculations in are simplified by substituting the mapping relationships in Table 4 into Equations (1-39) and (1-41). Thus, the four complex trigonometric function calculations involving the phase-locking angle in the vector action time model of the three-phase buck rectifier in DCM mode are transformed into a mapping relationship between each sector and the three-phase input voltage, making full use of the inherent phase information in the three-phase input voltage and significantly reducing the algorithm complexity.

[0123] 4. Implementation and Verification

[0124] In order to verify the effectiveness of the proposed strategy, a three-phase buck rectifier simulation system was built based on the PSIM simulation platform. When it works in DCM mode, the main circuit parameters are shown in Table 6.

[0125] Table 6 Three-phase buck rectifier simulation parameters (DCM working condition)

[0126]

[0127] Figure 7 Shows the DCM mode m v =0.49 when the vector action time simulation results comparison. Figure 7 (a) is the vector action time calculated in the CCM mode analysis, where the zero vector action time accounts for less than 40%; Figure 7 (b) shows the vector action time calculated using equations (1-21) to (1-24) after the proposed strategy is updated. The zero vector time accounts for more than 70%, which is consistent with the theoretical characteristic that the average DC-side inductor current is low under DCM light-load conditions, requiring an extended zero vector action.

[0128] Further analysis Figure 8 The DC side inductor current waveform: Under the traditional solution, the DC side inductor current ripple amplitude reaches 3.4A. Figure 8 As shown in (a); the proposed strategy suppresses the DC side inductor current ripple amplitude to 2.7A by optimizing the vector timing, as shown in Figure 8 (b) shown.

[0129] Figure 9 Shows the DCM mode m v =0.49, the simulation results of the three-phase input current on the AC side are compared. Figure 9 (a) is the three-phase input current on the AC side under the traditional vector action time. The current waveform is severely distorted due to vector failure. THD i Up to 27% Figure 9 (b) is the three-phase input current of the AC side under the vector action time of the proposed strategy. The current waveform quality is significantly improved, and the THD iReduced to 4%.

[0130] Figure 10 The comparison of DC side output voltage simulation results further verifies the effectiveness of the strategy. v =0.49, its theoretical output voltage value should be 119.54V. Figure 10 (a) The DC side output voltage under the traditional vector action time is seriously unregulated, reaching 207V, and the output voltage accuracy is only 73%; Figure 10 The DC side voltage under the strategy vector action time proposed in (b) is stable at 120V, and the output voltage accuracy is optimized to 0.38%. Figures 7 to 10 The simulation results show that the proposed modulation strategy effectively improves the m in DCM mode by reconstructing the vector timing and time calculation model. v =0.49, the AC side three-phase input current waveform quality and DC side output voltage accuracy.

[0131] further, Figures 11 to 14 Shows m v = 0.7, the vector action time, DC side inductor current, AC side three-phase input current and DC output voltage simulation results are compared. v =0.49. Similarly, the proposed modulation strategy suppresses the DC-side inductor current ripple amplitude from 3.5A to 3.0A after updating the vector action time. It also effectively improves the waveform quality of the three-phase input current on the AC side, lowering its THD from 26.8% to 4%. Furthermore, it significantly optimizes the output voltage control, bringing it consistent with the theoretical value of 170.8V, and reduces the output voltage accuracy from 21.2% to 2.3%.

[0132] So far, for m v The working condition below 0.577 is v For working conditions higher than 0.577, Figures 7 to 10 and Figures 11 to 14 The effectiveness of the proposed modulation strategy is demonstrated. The proposed modulation strategy significantly improves input current distortion and output voltage imbalance caused by the vector action time values ​​analyzed in CCM mode, improving input current THD to within 4% and optimizing output voltage accuracy to within 2.5%. These conclusions demonstrate that the proposed modulation sequence is effective across the full output voltage range of a three-phase buck rectifier operating in DCM mode.

[0133] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples. Within the scope of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0134] The present invention is intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A discontinuous current mode modulation method for a three-phase buck rectifier, characterized in that: The following steps are involved: S1. Determine the system modulation sequence and use "I" in even-numbered small sectors. k -I n -0" sequence, odd-numbered small sectors use "I n -I k -0" sequence, to ensure that the pulse width modulation of the space vector is performed in each switching cycle to synthesize the target vector in each small sector. pn The timing characteristics are always "v h -v l -0", where I k , I n Represents two adjacent active vectors appearing in sequence at the boundary of each sector, v pn is the output voltage of the power conversion circuit. In each small sector, v pn The higher value is denoted as v h , v pn The lower value is denoted as v l ; S2. By allocating the vector action time, the duty cycle of the switch tube in the three-phase buck rectifier is modulated to achieve discontinuous current mode modulation of the three-phase buck rectifier.

2. The discontinuous current mode modulation method for a three-phase buck rectifier according to claim 1, characterized in that: The allocating vector action time includes a vector action time calculation model, which calculates the vector action time: Vector action time T in even-numbered small sectors k for, in, Where, T k Represents the action time of the voltage vector with a smaller angle in the current small sector, T s is the switching period, I m is the target three-phase input current amplitude, V o is the DC side output voltage, θ is the phase angle of the three-phase input voltage, L dc is the DC side inductance, V m_l-l is the input line voltage amplitude; Vector action time T in even-numbered small sectors n for, in, Where, T n Represents the action time of the larger angle voltage vector in the current small sector, S k Represents vector I k The rate of change of the inductor current during the action period, S n Represents vector I n The rate of change of the inductor current during the action period; The zero vector action time T0 is, T0=T s -T k -T n (0-5) The vector action time in the odd small sector is, T0=T s -T k -T n 。 3. The discontinuous current mode modulation method for a three-phase buck rectifier according to claim 2, characterized in that: The vector action time calculation model is replaced by a simple implementation scheme based on the inherent phase information of the three-phase input voltage to establish a phase-locked loop-free system. The scheme includes: In even-numbered sectors, In odd-numbered sectors, Each sector The corresponding value is: by sector number, Corresponding values Corresponding values Where, v a , v b , v c is the three-phase input voltage, V m is the three-phase input phase voltage amplitude; S k 、S n The two trigonometric function calculations in the above example are done by dividing the v in each sector by k , v n Substitute the mapping relationship into formula (0-2) and formula (0-4) to achieve simplification; v in each sector k , v n The mapping relationship is obtained based on the relationship between the DC side output voltage and the bridge arm output voltage, the basic current vector, the target current vector phase angle and the sector within the grid cycle.

4. The discontinuous current mode modulation method for a three-phase buck rectifier according to claim 3, characterized in that: The process of building a simple implementation includes: Based on the trigonometric identities, the substitution rules of the trigonometric function values ​​of the phase-locked loop results in each sector are obtained, and based on the relationship between the DC side output voltage and the bridge arm output voltage, the basic current vector, the target current vector phase angle and the sector within the grid cycle, the v in each sector is obtained. k , v n The mapping relationship; Substitute the obtained trigonometric function values ​​into the rules and v in each sector k , v n Substituting the mapping relationship into equations (0-1) to (0-7), we can obtain a simple implementation solution for the vector action time in each sector.

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