A method for suppressing dc side voltage ripple and input current zero-crossing distortion of a unidirectional three-phase rectifier

Abstract

The application discloses a DC side voltage ripple and input current zero-crossing distortion collaborative suppression method for a unidirectional three-phase rectifier, relates to a unidirectional three-phase rectifier formed by three single-phase rectifier units connected in a Y type mode, and comprises original sinusoidal reference voltage generation, DC side voltage ripple suppression signal construction, input current zero-crossing region judgment, zero-crossing distortion suppression signal construction, composite triple-frequency harmonic signal region combination and PWM driving signal generation. The method respectively constructs a DC side voltage ripple suppression signal and an input current zero-crossing distortion suppression signal, and selects and combines according to the region of the input current to obtain a final composite triple-frequency harmonic injection signal, aiming at solving the problem that the existing harmonic injection method cannot simultaneously consider the DC side voltage ripple and the input current zero-crossing distortion. Compared with the prior art, the application can reduce the DC side voltage ripple, improve the input current zero-crossing region waveform quality, and improve the power density and operation reliability of the unidirectional three-phase rectifier without increasing additional power devices and large-capacity passive elements.

Description

Technical Field

[0001] This invention belongs to the field of power electronic converter control technology, and more specifically, relates to a composite third harmonic injection control method for a single-phase three-phase rectifier, particularly a collaborative control method capable of simultaneously suppressing DC-side voltage ripple and input current zero-crossing distortion. Background Technology

[0002] Unidirectional PWM rectifiers offer advantages such as fewer power devices, relatively simple control structures, high power density, and high operating efficiency, making them widely used in industrial frequency converters, electric vehicle charging, power systems, and new energy power generation applications where energy feedback is not required. In recent years, unidirectional three-phase rectifiers, consisting of three single-phase rectifier units connected in a Y-type configuration, have attracted significant attention. These rectifiers can be combined with subsequent multilevel inverters to form transformerless medium-voltage high-power conversion systems, reducing the need for power frequency phase-shifting transformers or high-frequency isolation converters, and demonstrating significant potential for reducing system size, weight, and cost.

[0003] However, since each phase rectifier unit has single-phase power conversion characteristics, its instantaneous AC input power contains a significant pulsating component at twice the fundamental frequency. This pulsating power, absorbed by the DC-side capacitor, generates substantial low-frequency ripple in the DC-side voltage. This DC-side voltage ripple not only increases the voltage stress on the power switching devices but also affects the output voltage and current quality of the subsequent inverter. Existing technologies typically suppress low-frequency voltage ripple by increasing the DC-side capacitor capacity; however, large capacitors increase the converter's size, weight, and cost, and reduce the system's power density and operational reliability. To reduce reliance on large capacitors, some control methods inject third harmonics into the fundamental modulation signal of each phase, altering the instantaneous power distribution of each phase rectifier unit and thus reducing DC-side voltage ripple. Compared to a single third harmonic injection, a composite harmonic injection signal composed of third, ninth, and other third harmonics offers more degrees of freedom in amplitude and phase adjustment, further improving the suppression capability of DC-side voltage ripple.

[0004] However, existing composite third harmonic injection methods typically prioritize minimizing DC-side voltage ripple, neglecting the unidirectional conduction characteristics of unidirectional rectifier power devices and diodes. When the input current is in the zero-crossing region, if the polarity relationship between the injected harmonic modulation reference voltage and the corresponding phase input current does not meet the rectifier's actual conduction conditions, erroneous pulses, pulse loss, or current stagnation may occur during pulse width modulation, leading to significant zero-crossing distortion of the input current. If the zero-crossing distortion of the input current is suppressed solely by adjusting the harmonic injection parameters, the suppression effect on DC-side voltage ripple may be weakened. Therefore, there is a coupling relationship between DC-side voltage ripple suppression and input current zero-crossing distortion suppression. Existing control methods still need further improvement in simultaneously reducing DC-side voltage ripple, improving waveform quality in the zero-crossing region of the input current, and ensuring that the modulation reference voltage remains within the linear modulation range. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, the present invention aims to provide a method for the coordinated suppression of DC-side voltage ripple and zero-crossing distortion of input current in a unidirectional three-phase rectifier. This invention constructs a first composite third harmonic injection signal targeting minimum DC-side voltage ripple and a second composite third harmonic injection signal targeting minimum zero-crossing distortion of input current. The two harmonic injection signals are then combined regionally according to the region of the input current in each phase. This achieves the coordinated suppression of DC-side voltage ripple and zero-crossing distortion of input current without increasing the amount of additional power devices or DC-side capacitors.

[0006] To achieve the above objectives, this invention provides a method for the coordinated suppression of DC-side voltage ripple and zero-crossing distortion of input current in a unidirectional three-phase rectifier. The unidirectional three-phase rectifier is composed of three single-phase rectifier units connected in a Y-shape. By injecting a composite third harmonic signal into the fundamental modulation signal of each phase rectifier unit, the coordinated suppression of DC-side voltage ripple and zero-crossing distortion of input current is achieved, specifically including the following steps.

[0007] Step 1: Obtain DC voltage feedback and grid synchronization information. Acquire the DC-side voltage of the single-phase three-phase rectifier to obtain the DC-side voltage feedback signal U of the three-phase rectifier unit. dcx The DC-side voltage feedback signal U dcx With DC side voltage setpoint U * dc The difference is calculated, and the resulting DC voltage deviation signal is input to the outer loop PI regulator to obtain the d-axis reference component i of the three-phase input current in the synchronous rotating coordinate system. * d Under unity power factor operating conditions, the q-axis reference component i * qSet to zero; collect the voltages of phases A, B, and C of the power grid to obtain the three-phase power grid voltage signals e. a e b and e c The grid voltage phase angle θ=ωt and grid angular frequency ω are obtained through a three-phase phase-locked loop (PLL).

[0008] Step 2: Simultaneously acquire the input currents of phases A, B, and C to obtain the three-phase input current signals i. a i b and i c The coordinate transformation of the three-phase input current is performed to obtain the d-axis current component i in the synchronous rotating coordinate system. d and q-axis current component i q ; Calculate the d-axis reference component i respectively * d With d-axis current component i d The deviation between and the q-axis reference component i * q With q-axis current component i q Deviation between:

[0009]

[0010]

[0011] The obtained current deviation signal is input into the inner current loop regulator to obtain the d-axis reference voltage and q-axis reference voltage in the synchronous rotating coordinate system; the DC side voltage U dcx The d-axis and q-axis reference voltages are further normalized based on the reference voltage, and the original sinusoidal reference voltage signals u before harmonic injection of phases A, B, and C are obtained through inverse coordinate transformation. sa u sb and u sc .

[0012] Step 3: Define U m I represents the phase voltage amplitude on the grid side. m Let L be the amplitude of the three-phase input current, M be the AC side filter inductance, M be the modulation index of the original sinusoidal reference voltage, and φ be the phase difference between the input current and the original sinusoidal reference voltage under unity power factor operation conditions. The phase difference is calculated using the following formula:

[0013]

[0014] According to U m and U dcx The normalization relationship between them determines the modulation scheme M, which can be expressed as:

[0015]

[0016] Step 4: Based on the grid voltage phase angle θ, modulation index M, and phase difference φ, represent the original sinusoidal reference voltage signals for phases A, B, and C respectively:

[0017]

[0018]

[0019]

[0020] The three-phase original sinusoidal reference voltages are sequentially 120° apart, and the original sinusoidal reference voltages are used as the fundamental component of the composite third harmonic injection.

[0021] Step 5: Construct a composite third harmonic injection signal m for suppressing DC-side voltage ripple. a (θ); the composite third harmonic injection signal includes at least a third harmonic component and a ninth harmonic component, defined as K. 1a and K 2a Let φ be the amplitude coefficients of the third and ninth harmonic components, respectively. 1a and φ 2a These are the initial phases of the third and ninth harmonic components, respectively; utilizing the characteristic that the third harmonic is in phase in a three-phase system, m... a (θ) are superimposed on the original sinusoidal reference voltage signals of phases A, B, and C.

[0022]

[0023] Step 6:

[0024] Based on the three-phase grid voltage, three-phase input current, DC-side voltage, and DC-side capacitor parameters, establish the instantaneous power balance relationship between the AC-side input power, DC-side output power, and DC-side capacitor charging / discharging power of each phase rectifier unit, satisfying the following relationship:

[0025]

[0026] K is changed sequentially within the preset range. 1a K 2a φ 1a and φ 2a First composite third harmonic injection signals corresponding to different parameter combinations are generated, and the DC-side voltage ripple evaluation value corresponding to each parameter group is calculated. The peak-to-peak value, amplitude, or root mean square value of the DC-side voltage ripple corresponding to different parameter combinations are compared, and the parameter group that minimizes the DC-side voltage ripple evaluation value is selected as the first composite third harmonic injection signal. The parameters.

[0027] Step 7: During the search for composite third harmonic parameters, the superimposed m... a Applying a linear modulation constraint to the three-phase reference voltage after (θ), for a modulation scheme using a normalized bipolar carrier, the linear modulation constraint is:

[0028]

[0029] Determine whether all three-phase reference voltages are within the carrier amplitude range; if none of the three-phase reference voltages exceed the carrier amplitude range, retain the current parameter combination and calculate the corresponding DC-side voltage ripple evaluation; if any phase reference voltage exceeds the carrier amplitude range, determine that the current parameter combination does not meet the linear modulation requirements, discard the current parameter combination, and continue searching for other parameter combinations.

[0030] Step 8: Based on the three-phase input current signal i a i b and i c The amplitude or phase of the input current is used to determine the zero-crossing region of each phase input current. The region where the absolute value of the input current is less than the preset current threshold, or the region where the phase of the input current is within the preset zero-crossing angle range, is determined as the zero-crossing region of the corresponding phase input current, and the remaining regions are determined as non-zero-crossing regions.

[0031] Step 9: Construct a composite third harmonic injection signal m to suppress zero-crossing distortion of the input current. b (θ); Determine m based on the polarity relationship between the reference voltage and the corresponding phase input current within the zero-crossing region of the input current. b The third harmonic amplitude coefficient K in (θ) 1b The initial phase φ of the third harmonic 1b Ninth harmonic amplitude coefficient K 2b and the initial phase φ of the ninth harmonic 2b This ensures that the corrected reference voltage meets the preset polarity constraint within the input current region.

[0032]

[0033] At the same time, m b (θ) The injected composite third harmonic signal must satisfy the linear modulation constraint:

[0034]

[0035] Step 10: Based on whether the input current of each phase is in the zero-crossing region, adjust the DC-side voltage ripple suppression signal m. a (θ) and input current zero-crossing distortion suppression signal m b (θ) is combined in regions to obtain a composite third harmonic injection signal m that balances DC-side voltage ripple suppression and input current zero-crossing distortion suppression. ab(θ); when the corresponding phase input current is in the zero-crossing region, m is used. b (θ), when the corresponding phase input current is in the non-zero crossing region, m is used. a (θ).

[0036]

[0037] Step 11: Inject the composite third harmonic into signal m ab (θ) is superimposed onto the original sinusoidal reference voltage signals u of phases A, B, and C, respectively. sa u sb and u sc The final reference voltage signals u for phases A, B, and C are obtained. * sa u * sb and u * sc The three-phase final reference voltage signals are limited or parameter-constrained to ensure that they are all within the linear modulation range.

[0038]

[0039] Step 12: Convert the final reference voltage signals u of phases A, B, and C. * sa u * sb and u * sc Each phase is compared with its corresponding triangular carrier wave. When the final reference voltage of a phase is greater than the corresponding triangular carrier wave, a high-level drive signal is output; when the final reference voltage of a phase is less than or equal to the corresponding triangular carrier wave, a low-level drive signal is output. Based on the comparison results, PWM drive signals are generated for the power switching devices in the three single-phase rectifier units to control the operation of the unidirectional three-phase rectifier.

[0040] Compared with existing technologies, the significant advantages of the technical solutions conceived in this invention are as follows: This invention separately constructs DC-side voltage ripple suppression signals and input current zero-crossing distortion suppression signals, and combines them in zones according to the region where the input current is located. This achieves synergistic suppression of DC-side voltage ripple and input current zero-crossing distortion without adding additional power devices or large-capacity passive components. Simultaneously, by increasing the modulation freedom through third and ninth harmonic composites, the DC-side capacitor requirements and power device voltage stress can be reduced, improving input current quality and enhancing system power density, operating efficiency, and reliability.

[0041] The following will provide a detailed explanation with reference to examples and accompanying diagrams. Attached Figure Description

[0042] The accompanying drawings, which form part of this specification, illustrate embodiments of the invention and, together with the specification, explain the technical principles of the invention.

[0043] Figure 1 This is a schematic diagram of the topology of a unidirectional three-phase rectifier, which consists of three single-phase rectifier units connected in a Y-shape, as involved in this invention.

[0044] Figure 2 This is a block diagram of the dual closed-loop control of DC voltage and input current provided by the present invention;

[0045] Figure 3 This is a flowchart of the DC-side voltage ripple suppression composite third harmonic parameter search provided by the present invention;

[0046] Figure 4 This is a flowchart of the parameter determination for input current zero-crossing distortion suppression composite third harmonic provided by the present invention;

[0047] Figure 5 This is the overall control block diagram of the method for coordinated suppression of DC-side voltage ripple and zero-crossing distortion of input current provided by the present invention;

[0048] Figure 6 These are the DC-side voltage and input current waveforms of a single-phase three-phase rectifier when using traditional modulation methods.

[0049] Figure 7 These are the DC-side voltage and input current waveforms of a single-phase three-phase rectifier when the DC-side voltage ripple suppression signal is used.

[0050] Figure 8 These are the DC-side voltage and input current waveforms of a unidirectional three-phase rectifier when the synergistic suppression method provided by this invention is used. Detailed Implementation

[0051] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention.

[0052] like Figure 1As shown, the unidirectional three-phase rectifier involved in this embodiment consists of a phase A single-phase rectifier unit, a phase B single-phase rectifier unit, and a phase C single-phase rectifier unit. The AC sides of the three single-phase rectifier units are connected in a Y-type configuration. The AC input terminals of each phase rectifier unit are connected to the A-phase, B-phase, and C-phase power grids respectively through AC-side filter inductors. Each phase rectifier unit adopts a unidirectional power flow structure. The controller collects the DC-side voltage, the three-phase power grid voltage, and the three-phase input current, and generates PWM drive signals for the power switching devices in each phase rectifier unit based on the collected voltage, current, and power grid phase information. The method for coordinated suppression of DC-side voltage ripple and zero-crossing distortion of input current provided by this invention mainly includes the generation of three-phase original sinusoidal reference voltage, determination of DC-side voltage ripple suppression composite third harmonic parameters, determination of input current zero-crossing region, determination of input current zero-crossing distortion suppression composite third harmonic parameters, regional combination of two types of composite third harmonic injection signals, and generation of PWM drive signals.

[0053] like Figure 2 As shown, the controller acquires the DC-side voltage of the single-phase three-phase rectifier and obtains the DC-side voltage feedback signal U. dcx The DC-side voltage feedback signal U dcx With DC side voltage setpoint U * dc The difference is calculated, and the resulting DC voltage deviation signal is input to the outer loop PI regulator to obtain the d-axis reference component i of the three-phase input current in the synchronous rotating coordinate system. * d Under unity power factor operating conditions, the q-axis reference component i * q Set to zero. The controller samples the voltages of phases A, B, and C of the power grid to obtain the three-phase power grid voltage signal e. a e b and e c The three-phase grid voltage signal is input into a three-phase phase-locked loop (PLL) to obtain the grid voltage phase angle θ = ωt and the grid angular frequency ω. Simultaneously, the input currents of phases A, B, and C are sampled to obtain the three-phase input current signal i. a i b and i c Based on the phase angle of the grid voltage output from the three-phase phase-locked loop, a coordinate transformation is performed on the three-phase input current to obtain the d-axis current component i in the synchronous rotating coordinate system. d and q-axis current component i q .

[0054] d-axis reference component With d-axis current component i d Subtract the reference component i along the q-axis. * q With q-axis current component iq The difference is calculated, and the resulting d-axis current deviation signal and q-axis current deviation signal are input into the inner current loop regulator to obtain the d-axis reference voltage and q-axis reference voltage in the synchronous rotating coordinate system.

[0055]

[0056]

[0057] DC side voltage U dcx The d-axis and q-axis reference voltages are normalized based on the reference voltage, and then subjected to inverse coordinate transformation to obtain the original sinusoidal reference voltage signals u before harmonic injection in phases A, B, and C. sa u sb and u sc .

[0058] Define U m I represents the phase voltage amplitude on the grid side. m Let U be the amplitude of the three-phase input current, L be the AC-side filter inductance, M be the modulation index of the original sinusoidal reference voltage, and φ be the phase difference between the input current and the original sinusoidal reference voltage under unity power factor operating conditions. Based on the grid-side phase voltage amplitude U... m With DC side voltage U dcx The normalization relationship between them determines the modulation scheme M.

[0059]

[0060] Based on the grid voltage phase angle θ, modulation index M, and phase difference φ, represent the original sinusoidal reference voltage signals u for phases A, B, and C, respectively. sa u sb and u sc .

[0061]

[0062]

[0063]

[0064] The original three-phase sinusoidal reference voltage is used as the fundamental component for subsequent composite third harmonic injection.

[0065] like Figure 3 As shown, to reduce DC-side voltage ripple, a composite third harmonic injection signal m is constructed to suppress DC-side voltage ripple. a (θ); the composite third harmonic injection signal includes at least a third harmonic component and a ninth harmonic component, defined as K. 1a and K 2aLet φ be the amplitude coefficients of the third and ninth harmonic components, respectively. 1a and φ 2a These are the initial phases of the third and ninth harmonic components, respectively. The controller sequentially changes these phases within a preset parameter range. K 2a φ 1a and φ 2a Based on different parameter combinations, the corresponding first composite third harmonic injection signal is generated and superimposed onto the original sinusoidal reference voltage signals of phases A, B and C respectively.

[0066]

[0067] For each parameter combination, the controller determines whether the three-phase reference voltages after superimposing the first composite third harmonic injection signal are within the carrier amplitude range. If any phase reference voltage exceeds the carrier amplitude range, the current parameter combination is deemed not to meet the linear modulation requirements and is discarded. If all three phase reference voltages are within the carrier amplitude range, the current parameter combination is retained, and the DC-side voltage ripple evaluation value corresponding to that parameter combination is calculated. The DC-side voltage ripple evaluation value uses at least one of the following: peak-to-peak value, ripple amplitude, or root mean square value of the DC-side voltage ripple. The controller compares the DC-side voltage ripple evaluation values ​​corresponding to each feasible parameter combination and selects the parameter combination that minimizes the DC-side voltage ripple evaluation value as the first composite third harmonic injection signal. The parameters are as follows. The first composite third harmonic injection signal utilizes the characteristic that the third harmonic is in phase in a three-phase system, and is superimposed on the original sinusoidal reference voltage of the three phases, thereby changing the modulation voltage and instantaneous power distribution of the three single-phase rectifier units, reducing the fluctuation of the DC side capacitor charging and discharging power, and thus suppressing the low-frequency voltage ripple on the DC side.

[0068] However, when the unidirectional three-phase rectifier operates in the zero-crossing region of the input current, using a first composite third harmonic injection signal determined solely by minimizing DC-side voltage ripple may cause the polarity relationship between the reference voltage and the corresponding phase input current to fail to meet the actual conduction requirements of the unidirectional rectifier unit. Therefore, it is necessary to further construct a composite third harmonic injection signal to suppress zero-crossing distortion of the input current. The controller determines the input current based on the input current signals i of phases A, B, and C. a i b and i c The amplitude or phase of the input current is used to determine whether the input current of each phase has entered the zero-crossing region.

[0069] When using input current amplitude for judgment, the absolute value of each phase's input current is compared with a preset current threshold. If the absolute value of a phase's input current is less than or equal to the preset current threshold, the phase's input current is determined to be in the zero-crossing region; if the absolute value is greater than the preset current threshold, the phase's input current is determined to be in the non-zero-crossing region. When using input current phase for judgment, the theoretical zero-crossing point of each phase's input current is determined based on the grid voltage phase angle and the input current phase. If the phase of a phase's input current is within a preset zero-crossing angle range, the phase's input current is determined to be in the zero-crossing region; other regions are determined to be non-zero-crossing regions.

[0070] like Figure 4 As shown, to suppress zero-crossing distortion of the input current, a second composite third harmonic injection signal m is constructed. b (θ). The second composite third harmonic injection signal includes at least a third harmonic component and a ninth harmonic component, wherein K 1b and K 2b φ represents the amplitude coefficients of the third and ninth harmonic components, respectively. 1b and φ 2b These are the initial phases of the third and ninth harmonic components, respectively. The controller adjusts K sequentially within a preset range. 1b K 2b , and φ 2b The system generates second composite third harmonic injection signals corresponding to different parameter combinations and superimposes them onto the original three-phase sinusoidal reference voltages. Within the zero-crossing region of the input current, the polarity relationship between the corrected reference voltage and the corresponding phase input current is determined. If the polarity relationship satisfies the conduction requirements of the unidirectional rectifier unit, the current parameter combination is retained; otherwise, it is discarded, and the amplitude coefficient and initial phase of the second composite third harmonic injection signal are adjusted. Simultaneously with polarity determination, the controller also checks whether the three-phase reference voltages after superimposing the second composite third harmonic injection signal are all within the carrier amplitude range. Only when the corrected reference voltage satisfies the polarity constraint of the zero-crossing region of the input current, and all three phase reference voltages meet the linear modulation requirements, is the current parameter combination selected as the second composite third harmonic injection signal m. b The parameters of (θ).

[0071] like Figure 5 As shown, the cooperative suppression method provided by this invention, based on the region where the input current is located, injects a signal into the first composite third harmonic. Second composite third harmonic injection signal m b(θ) Regional selection is performed. When the input currents of phases A, B, and C are all in the non-zero-crossing region, the controller selects the first composite third harmonic injection signal. The main control objective is to suppress DC-side voltage ripple. When the input current of any phase enters the zero-crossing region, the controller selects the second composite third harmonic injection signal m. b (θ), with the primary control objective being the suppression of zero-crossing distortion of the input current. The first and second composite third harmonic injection signals, selected based on the input current operating region, are combined to obtain the coordinated suppression signal m for DC-side voltage ripple and zero-crossing distortion of the input current. ab (θ). The cooperative suppression signal m ab (θ) is superimposed onto the original sinusoidal reference voltage signals u of phases A, B, and C, respectively. sa u sb and u sc The final reference voltage signals u for phases A, B, and C are obtained. * sa u * sb and u * sc .

[0072] The controller determines whether the final reference voltages of the three phases are within the carrier amplitude range. If the final reference voltage of any phase exceeds the carrier amplitude range, the injection parameters of the composite third harmonic are limited or the final reference voltage is limited to ensure that the final reference voltages of all three phases meet the linear modulation requirements. The final reference voltage signals of phases A, B, and C are compared with their corresponding triangular carriers. When the final reference voltage of a phase is greater than the corresponding triangular carrier, a high-level drive signal is output; when the final reference voltage of a phase is less than or equal to the corresponding triangular carrier, a low-level drive signal is output. Based on the comparison results, PWM drive signals for the power switching devices in the three single-phase rectifier units are generated.

[0073] Figure 6 These are the DC-side voltage and input current waveforms of a unidirectional three-phase rectifier using traditional modulation methods. Because the pulsating power at twice the fundamental frequency of each phase rectifier unit is not actively adjusted, there is a noticeable low-frequency ripple in the DC-side voltage. Simultaneously, due to the conduction characteristics of the unidirectional power devices, the input current exhibits a certain degree of waveform distortion near the zero-crossing point.

[0074] Figure 7 It uses the first composite third harmonic injection signal. The waveforms of the DC-side voltage and input current of the unidirectional three-phase rectifier are shown. After injecting the first composite third harmonic signal, the DC-side voltage ripple is significantly suppressed. However, in the zero-crossing region of the input current, zero-crossing distortion may still occur because the polarity relationship between the reference voltage and the input current does not meet the conduction requirements of the unidirectional rectifier unit.

[0075] Figure 8 The waveforms of the DC-side voltage and input current of a unidirectional three-phase rectifier when using the synergistic suppression method provided by this invention are shown. By employing a first composite third harmonic injection signal in the non-zero-crossing region and a second composite third harmonic injection signal in the zero-crossing region, the waveform quality in the zero-crossing region of the input current can be improved while maintaining the DC-side voltage ripple suppression effect, thus achieving synergistic suppression of DC-side voltage ripple and zero-crossing distortion of the input current.

[0076] The composite third harmonic used in this invention is not limited to the third and ninth harmonics; other integer multiples of the third harmonic can also be added as needed for control. The method for determining the parameters of the first and second composite third harmonic injection signals is not limited to traversal search; genetic algorithms, particle swarm optimization, differential evolution algorithms, or other parameter optimization methods can also be used. The method for determining the zero-crossing region of the input current is not limited to a fixed current threshold or a fixed angle threshold; the zero-crossing region can also be adaptively adjusted based on the input current amplitude, modulation index, AC side filter inductor parameters, or load status.

[0077] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. All modifications, equivalent substitutions, and improvements 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 method for co-suppressing DC-side voltage ripple and zero-crossing distortion of input current in a unidirectional three-phase rectifier, wherein the unidirectional three-phase rectifier is composed of three single-phase rectifier units connected in a Y-type configuration, characterized in that... By injecting a composite third harmonic signal into the fundamental modulation signal of each phase rectifier unit, the coordinated suppression of DC-side voltage ripple and zero-crossing distortion of input current is achieved. Specifically, this includes the following steps: Step 1: Acquire the DC-side voltage of the single-phase three-phase rectifier to obtain the DC-side voltage feedback signal U of the three-phase rectifier unit. dcx The DC-side voltage feedback signal U dcx With DC side voltage setpoint U * dc The difference is calculated, and the resulting DC voltage deviation signal is input to the outer loop PI regulator to obtain the d-axis reference component i of the three-phase input current in the synchronous rotating coordinate system. * d Under unity power factor operating conditions, the q-axis reference component i * q Set to zero; collect the voltages of phases A, B, and C of the power grid to obtain the three-phase power grid voltage signals e. a e b and e c The grid voltage phase angle θ=ωt and grid angular frequency ω are obtained through a three-phase phase-locked loop (PLL). Step 2: Simultaneously acquire the input currents of phases A, B, and C to obtain the three-phase input current signals i. a i b and i c The coordinate transformation of the three-phase input current is performed to obtain the d-axis current component i in the synchronous rotating coordinate system. d and q-axis current component i q ; Calculate the d-axis reference component i respectively * d With d-axis current component i d The deviation between and the q-axis reference component i * q With q-axis current component i q The deviation between them is used to input the obtained current deviation signal into the current inner loop regulator to obtain the d-axis reference voltage and q-axis reference voltage in the synchronous rotating coordinate system; with the DC side voltage U dcx The d-axis and q-axis reference voltages are normalized based on the reference voltage, and the original sinusoidal reference voltage signals u before harmonic injection of phases A, B, and C are obtained by inverse coordinate transformation. sa u sb and u sc . Step 3: Define U m I represents the phase voltage amplitude on the grid side. m Let L be the amplitude of the three-phase input current, M be the AC side filter inductance, φ be the modulation index of the original sinusoidal reference voltage, and φ be the phase difference between the input current and the original sinusoidal reference voltage under unity power factor operation conditions. The phase difference can be expressed as: According to U m and U dcx The normalization relationship between them determines the modulation scheme M, which can be expressed as: Step 4: Based on the grid voltage phase angle θ, modulation index M, and phase difference φ, represent the original sinusoidal reference voltage signals of phase A, phase B, and phase C respectively; the three-phase original sinusoidal reference voltages are sequentially 120° out of phase, and the original sinusoidal reference voltages are used as the fundamental component of the composite third harmonic injection. Step 5: Construct a composite third harmonic injection signal m for suppressing DC-side voltage ripple. a (θ); the composite third harmonic injection signal includes at least a third harmonic component and a ninth harmonic component, defined as K. 1a and K 2a Let φ be the amplitude coefficients of the third and ninth harmonic components, respectively. 1a and φ 2a These are the initial phases of the third and ninth harmonic components, respectively; utilizing the characteristic that the third harmonic is in phase in a three-phase system, m... a (θ) are superimposed on the original sinusoidal reference voltage signals of phases A, B, and C. Step 6: Based on the instantaneous power balance relationship of the three-phase grid voltage, three-phase input current, and DC-side capacitor, establish a DC-side voltage ripple model under the condition of composite third harmonic injection; [The last part, "K," appears to be an incomplete sentence or fragment and doesn't translate directly. It's left as is.] 1a K 2a φ 1a and φ 2a As the variable to be optimized, with the minimum DC-side voltage ripple evaluation value as the optimization objective, the variable to be optimized is searched to obtain the composite third harmonic parameter for suppressing DC-side voltage ripple; the DC-side voltage ripple evaluation value is at least one of the DC-side voltage ripple peak-to-peak value, ripple amplitude, or ripple root mean square value. Step 7: During the search for composite third harmonic parameters, the superimposed m... a Linear modulation constraints are applied to the three-phase reference voltages after (θ) so that the reference voltages of phases A, B and C are all within the carrier amplitude range; when any phase reference voltage exceeds the carrier amplitude range, the current parameter combination is discarded and the search continues for parameter combinations that satisfy the linear modulation constraints. Step 8: Based on the three-phase input current signal i a i b and i c The amplitude or phase of the input current is used to determine the zero-crossing region of each phase input current. The region where the absolute value of the input current is less than the preset current threshold, or the region where the phase of the input current is within the preset zero-crossing angle range, is determined as the zero-crossing region of the corresponding phase input current, and the remaining regions are determined as non-zero-crossing regions. Step 9: Construct a composite third harmonic injection signal m to suppress zero-crossing distortion of the input current. b (θ); Determine m based on the polarity relationship between the reference voltage and the corresponding phase input current within the zero-crossing region of the input current. b The third harmonic amplitude coefficient K in (θ) 1b The initial phase φ of the third harmonic 1b Ninth harmonic amplitude coefficient K 2b and the initial phase φ of the ninth harmonic 2b This ensures that the corrected reference voltage meets the preset polarity constraint within the zero-crossing region of the input current and remains within the linear modulation range. Step 10: Based on whether the input current of each phase is in the zero-crossing region, adjust the DC-side voltage ripple suppression signal m. a (θ) and input current zero-crossing distortion suppression signal m b (θ) is combined in regions to obtain a composite third harmonic injection signal m that balances DC-side voltage ripple suppression and input current zero-crossing distortion suppression. ab (θ); when the corresponding phase input current is in the zero-crossing region, m is used. b (θ), when the corresponding phase input current is in the non-zero crossing region, m is used. a (θ). At the same time, m b (θ) The injected composite third harmonic signal must satisfy the linear modulation constraint: Step 11: Inject the composite third harmonic into signal m ab (θ) is superimposed onto the original sinusoidal reference voltage signals u of phases A, B, and C, respectively. sa u sb and u sc The final reference voltage signals u for phases A, B, and C are obtained. * sa u * sb and u * sc The three-phase final reference voltage signals are limited or parameter-constrained to ensure that they are all within the linear modulation range. Step 12: Convert the final reference voltage signals u of phases A, B, and C. * sa u * sb and u * sc Each phase is compared with its corresponding triangular carrier wave. When the final reference voltage of a phase is greater than the corresponding triangular carrier wave, a high-level drive signal is output; when the final reference voltage of a phase is less than or equal to the corresponding triangular carrier wave, a low-level drive signal is output. Based on the comparison results, PWM drive signals are generated for the power switching devices in the three single-phase rectifier units to control the operation of the unidirectional three-phase rectifier.

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