A Method for Suppressing the Second-Order Power on the DC Side of a Three-Phase PWM Rectifier

Abstract

The present invention proposes a method for suppressing the second - order power on the DC side of a three - phase PWM rectifier, belonging to the field of power electronics. The method is applied to a three - phase PWM rectifier; the method includes connecting an active negative capacitance circuit composed of a DC - DC converter, an H - bridge, an LC filter circuit, and a sampling resistor in parallel on the DC side of the three - phase PWM rectifier; the active negative capacitance circuit is connected in series with a first capacitor to obtain a capacitance series equivalent circuit based on the active negative capacitance; sampling the voltage signal on the DC side of the three - phase PWM rectifier and connecting it to the input end of a digital signal controller, and the digital signal controller outputs a signal to control the H - bridge to change the capacitance of the active negative capacitance circuit, ultimately realizing the suppression of the second - order power on the DC side of the three - phase PWM rectifier. The present invention can achieve a very large capacitance value with a very small volume, and the realized capacitance equivalent circuit has the characteristic of adjustable capacitance value, and different capacitance values can be flexibly selected according to different requirements for suppressing the second - harmonic of the DC - side voltage of the three - phase PWM rectifier.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics, and particularly relates to a method for suppressing the second-order power on the DC side of a three-phase PWM rectifier. Background Art

[0002] With the rapid development of distributed generation systems, three-phase pulse width modulation (PWM) converters have been widely used in various power electronics fields due to their advantages such as adjustable power factor, adjustable AC current amplitude, and adjustable DC bus voltage.

[0003] However, a three-phase PWM converter only has high-performance output when operating under balanced conditions. Different from a stable large power grid, weak grid systems such as distributed generation systems generally face the situation of three-phase imbalance, which may cause sensitive loads to trip, thus reducing the performance of the system. When the converter is under unbalanced conditions, some problems may occur, such as DC bus voltage fluctuations, AC current distortion and imbalance, and power oscillation.

[0004] To solve these problems, a power decoupling circuit can be added to bypass high-frequency energy, thereby suppressing the second-order frequency fluctuation of the DC side output voltage of the three-phase inverter. Power decoupling can be divided into two categories: one is passive power decoupling by directly connecting a traditional capacitor or an LC resonant circuit in parallel on the DC side; the other is active power decoupling by adding an active power decoupling circuit on the basis of a conventional three-phase converter. The passive power decoupling scheme using a traditional capacitor requires a very large capacitance value to obtain an ideal second-order frequency suppression effect, which results in a very large volume of the traditional capacitor used. With the introduction of large-value capacitors, the passive power decoupling method will reduce the power density of the PWM rectifier. At the same time, the bulky electrolytic capacitor also has a negative impact on the reliability and service life of the rectifier.

[0005] The active power decoupling method of adding an active power decoupling circuit can achieve a good suppression effect on the second-order frequency fluctuation of the DC side voltage only with several switching devices and necessary support capacitors and filter circuits, and great improvements have been made in terms of volume and service life. However, most of the existing active power decoupling technologies (Active Power Decoupling, abbreviated as APD) require sampling on the AC side to calculate the second-order power, and then control the active power decoupling circuit on the DC side accordingly; and the suppression effect of APD on the second-order power on the DC side is not adjustable and cannot be flexibly adjusted according to different situations. Summary of the Invention

[0006] The object of the present invention is to provide a method for suppressing the secondary power on the DC side of a three-phase PWM rectifier, so as to solve the technical problems in the prior art that the secondary power suppression method is achieved by increasing the capacitance on the DC side of the rectifier, resulting in a large volume and an unadjustable capacitance value.

[0007] To solve the above technical problems, the specific technical solution of the present invention is as follows:

[0008] A method for suppressing the secondary power on the DC side of a three-phase PWM rectifier, the method is applied to a three-phase PWM rectifier; the method includes connecting the input terminals of a DC-DC converter in parallel at both the positive and negative ends of the DC side of the three-phase PWM rectifier. The output terminal of the DC-DC converter is connected to an H-bridge structure formed by a first switching tube , a second switching tube , a third switching tube , and a fourth switching tube . The DC-DC converter and the H-bridge structure constitute a single-phase inverter; the DC-DC converter draws power from the DC bus as the DC power supply of the single-phase inverter; the output terminal of the single-phase inverter is connected to a filter capacitor , and a filter inductor to form an LC filter circuit; the output terminal of the single-phase inverter after passing through the LC filter circuit is connected in series with a sampling resistor , and then in series with a first capacitor , and then in parallel at both the positive and negative ends of the DC side of the three-phase PWM rectifier; the single-phase inverter, the LC filter circuit composed of the filter capacitor and the filter inductor , and the sampling resistor constitute an active negative capacitance circuit; the active negative capacitance circuit is connected in series with the first capacitor to obtain an equivalent circuit of series capacitors based on the active negative capacitance; a second capacitor , and a load are connected in parallel at both the positive and negative ends of the DC side of the three-phase PWM rectifier; voltage signals are sampled at both the positive and negative ends of the DC side of the three-phase PWM rectifier and connected to the input terminal of a digital signal controller. The output terminal of the digital signal controller is connected to the first switching tube and the fourth switching tube of the single-phase inverter; the output terminal of the digital signal controller is connected to the second switching tube and the third switching tube of the single-phase inverter after passing through an inverter; the output signal of the digital signal controller is used to control the first switching tube , the second switching transistor , the third switching transistor , the fourth switching transistor 's control to change the capacitance of the active negative capacitance circuit, thereby changing the capacitance series equivalent circuit based on the active negative capacitance, and finally achieving the suppression of the secondary power on the DC side of the three-phase PWM rectifier.

[0009] Further, the collector of the first switching transistor and the third switching transistor are connected and then connected to the positive output terminal of the DC-DC converter. The emitter of the second switching transistor and the fourth switching transistor are connected and then connected to the negative output terminal of the DC-DC converter; the emitter of the first switching transistor and the collector of the second switching transistor are connected and then connected to one end of the filter inductor . The other end of the filter inductor is connected to one end of the filter capacitor ; the emitter of the third switching transistor and the collector of the fourth switching transistor are connected and then connected to the other end of the filter capacitor ; the filter capacitor and the filter inductor form an LC low-pass filter structure; one end of the resistor is connected to the point where the filter capacitor and the filter inductor are connected; the other end of the resistor is connected to one end of the first capacitor . The other end of the first capacitor is connected to the positive terminal of the DC side of the three-phase PWM rectifier; the filter capacitor is connected to the emitter of the third switching transistor and one end of the collector of the fourth switching transistor is connected to the negative terminal of the DC side of the three-phase PWM rectifier.

[0010] Further, the output terminal of the digital signal controller is connected to the gates of the first switching transistor and the fourth switching transistor , and the output terminal of the digital signal controller is connected to the inverter and then connected to the gates of the second switching transistor and the third switching transistor .

[0011] Further, the digital signal controller samples the DC side voltage of the three-phase rectifier , that is, the positive pole of the DC side of the three-phase PWM rectifier and the negative pole The voltage between the two is sent to the digital signal controller; the digital signal controller separates the DC side voltage of the three-phase rectifier through the phase-locked loop PLL to obtain a voltage signal with a specific frequency of 100 Hz, and multiply it by the voltage division coefficient to obtain the port voltage of the active negative capacitance circuit , and then multiply the port voltage of the active negative capacitance circuit by the reciprocal of the sampling coefficient to obtain the node voltage ; and multiply the node voltage by the constant term frequency-capacitance value coefficient , the differential of is multiplied by the differential term frequency-capacitance value coefficient, and the two are added to obtain the modulation signal ; finally, the modulation signal and the carrier signal are sent to the comparator, and the obtained square wave signal is the output signal of the digital signal controller, that is, the gate control signal of the first switch , the fourth switch , and pass it through an inverter to obtain the gate control signals of the second switch , the third switch , and by controlling the first switch , the second switch , the third switch , the fourth switch , the output of the H-bridge is changed, so that the circuit of the active negative capacitance exhibits the capacitance port characteristics of different capacitance values.

[0012] Compared with the prior art, the present invention has the following beneficial technical effects:

[0013] 1) In the present invention, positive and negative capacitors are connected in series and added to the DC side, so that a large capacitance value can be achieved with a very small volume. The realized capacitance equivalent circuit has the characteristic of adjustable capacitance value, and different capacitance values can be flexibly selected according to the requirements of suppressing the second harmonic of the DC side voltage of different three-phase PWM rectifiers.

[0014] 2) The sampling signal of the control part of the present invention directly comes from the DC side and does not involve the sampling and calculation of the AC side, so it can be directly installed at any position on the DC side.

[0015] 3) The DC source of the single-phase inverter part of the present invention is provided by the DC-DC module connecting the DC bus for conversion output, without an additional DC voltage source, and can adapt to different power occasions. Compared with the traditional active power decoupling circuit, the breakdown voltage of the switch is also reduced, which is beneficial to extending the service life.

[0016] 4) The basic capacitance equivalent principle of the present invention is the series connection between positive and negative capacitances. Therefore, theoretically, electrolytic capacitors of a certain size can be used to equivalently obtain a capacitance value range from zero to infinity. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is the structure diagram of the DC-side secondary power suppression circuit of the three-phase rectifier of the present invention.

[0019] Figure 2 It is the control flowchart of the equivalent capacitance circuit based on the active negative capacitance of the present invention.

[0020] Figure 3 It is the waveform of the DC-side load secondary power suppression effect when the capacitance value of the active negative capacitance in the simulation of the present invention is -900 uF.

[0021] Figure 4 It is the waveform of the DC-side load secondary power suppression effect when the capacitance value of the active negative capacitance in the simulation of the present invention is -800 uF. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0023] The method for suppressing the DC-side secondary power of the three-phase PWM rectifier proposed by the present invention is based on the following principle of the port characteristics of the circuit topology with a capacitance of adjustable value. For a positive capacitance, the relationship between its voltage and current can be expressed by the following first-order differential relation:

[0024]

[0025] Among them, is the voltage across the positive capacitance, is the current flowing through the positive capacitance, is the capacitance value of the positive capacitance.

[0026] For a negative capacitor, its DC characteristics are the same as those of a traditional positive capacitor, showing the blocking of DC current, and its AC characteristics are similar to those of an inductor. Therefore, the relationship between the current and voltage of the negative capacitor can be described by first-order calculus as follows:

[0027]

[0028] where is the voltage across the negative capacitor, is the current flowing through the negative capacitor, is the capacitance value of the negative capacitor, which is negative, is to take the absolute value.

[0029] According to the equivalent capacitance calculation formula for the series connection of positive and negative capacitors:

[0030]

[0031] where is the equivalent capacitance value after the series connection of positive and negative capacitors.

[0032] It can be seen from the equivalent capacitance calculation formula for the series connection of positive and negative capacitors that when a positive capacitor is connected in series with a negative capacitor, if the capacitance value of the positive capacitor is set to a certain value, the equivalent capacitance value of the series connection of capacitors is affected by the ratio of the absolute values of the positive and negative capacitance values: the closer the absolute values of the positive and negative capacitance values are, the larger the equivalent capacitance value of the series connection of capacitors. Therefore, by changing the capacitance value of the negative capacitor, the equivalent capacitance value of the series connection of capacitors can be adjusted.

[0033] For a three-phase PWM rectifier operating under unbalanced conditions, there is a second-harmonic fluctuation of power on the DC side, that is, the DC-side power is mainly composed of a DC component and a second-harmonic AC component. Due to the characteristic of capacitors passing AC and blocking DC, the capacitor connected in parallel on the DC side can provide a path for the AC component of power at this time, so that very little AC energy flows through the load on the DC side. Obviously, the higher the capacitance value set on the DC side, the smaller the blocking effect of the capacitor branch connected in parallel on the DC side on the AC component of power, and thus the less AC energy the DC-side load has.

[0034] Based on the above principle, the present invention provides a method for suppressing the secondary power on the DC side of a three-phase PWM rectifier, which is applied to a three-phase PWM rectifier. As Figure 1 shown, the method includes connecting the input end of a DC-DC converter in parallel to the positive and negative ends of the DC side of the three-phase PWM rectifier, and connecting the output end of the DC-DC converter to a circuit composed of a first switching tube a second switching tube a third switching tube and a fourth switching tube The formed H-bridge structure. The DC-DC converter and the H-bridge structure constitute a single-phase inverter. The DC-DC converter draws power from the DC bus and serves as the DC power supply for the single-phase inverter. The output terminal of the single-phase inverter is connected to a filter capacitor , a filter inductor to form an LC filter circuit. The output terminal of the single-phase inverter after passing through the LC filter circuit is connected in series with a sampling resistor and then connected in series with a first capacitor , and then connected in parallel to the positive electrode , negative electrode of the DC side of the three-phase PWM rectifier. The single-phase inverter, the LC filter circuit composed of the filter capacitor and the filter inductor and the sampling resistor form an active negative capacitance circuit. The active negative capacitance circuit is connected in series with the first capacitor to obtain an equivalent circuit of series-connected capacitors based on the active negative capacitance. A second capacitor , a load are connected in parallel to the positive electrode , negative electrode of the DC side of the three-phase PWM rectifier. Voltage signals are sampled at the positive electrode , negative electrode of the DC side of the three-phase PWM rectifier and connected to the input terminal of the digital signal controller. The output terminal of the digital signal controller is connected to the first switching tube , the fourth switching tube of the single-phase inverter; the output terminal of the digital signal controller is connected to the second switching tube , the third switching tube of the single-phase inverter after passing through an inverter. By controlling the first switching tube , the second switching tube , the third switching tube , the fourth switching tube with the output signal of the digital signal controller, the capacitance of the active negative capacitance circuit is changed, and then the equivalent circuit of series-connected capacitors based on the active negative capacitance is changed, and finally the secondary power suppression of the DC side of the three-phase PWM rectifier is realized.

[0035] The collector of the first switching tube is connected to the third switching tube and then connected to the positive output terminal of the DC-DC converter. The emitter of the second switching tube is connected to the fourth switching tube and then connected to the negative output terminal of the DC-DC converter. The emitter of the first switching tube is connected to the collector of the second switching tube and then connected to one end of the filter inductor , the filter inductor The other end is connected to a filter capacitor at one end; The third switching transistor has its emitter connected to the fourth switching transistor and the collector is connected to the filter capacitor at the other end. The filter capacitor and the filter inductor form an LC low-pass filter structure. The resistor has one end connected to the filter capacitor , the filter inductor at the connection point. The resistor has its other end connected to one end of the first capacitor , and the other end of the first capacitor is connected to the positive pole of the DC side of the three-phase PWM rectifier . The filter capacitor is connected to the emitter of the third switching transistor and the collector of the fourth switching transistor , and one end of the connection is connected to the negative pole of the DC side of the three-phase PWM rectifier .

[0036] The output terminal of the digital signal controller is connected to the gate of the first switching transistor and the fourth switching transistor , and the output terminal of the digital signal controller is connected to the inverter and then connected to the gates of the second switching transistor and the third switching transistor .

[0037] Based on the principle of the port characteristics of the capacitor with adjustable capacitance value in the circuit topology and combining with the method described in the present invention, a method for suppressing the secondary power on the DC side of a three-phase PWM rectifier is briefly described based on the active negative capacitance series equivalent circuit of the capacitor.

[0038] For the active negative capacitance, the voltage-current relationship at its port can be expressed in the S domain as:

[0039]

[0040] Wherein, is the current flowing through the active negative capacitance circuit, is the port voltage of the active negative capacitance circuit, is the absolute value of the capacitance value of the active negative capacitance, is the Laplace operator.

[0041] For the structure of series connection of positive and negative capacitances, the voltage division relationship between the two can be deduced:

[0042]

[0043] Among them, is the voltage on the DC side of the three-phase rectifier, represents the capacitance value of the positive capacitor, that is, the capacitance value of the first capacitor . is the voltage division coefficient of the active negative capacitor for the entire series structure of positive and negative capacitors.

[0044] Based on Kirchhoff's voltage and current laws, as well as the port characteristics of inductors and capacitors, the following expressions can be written:

[0045]

[0046]

[0047] Among them, is the capacitance value of the filter capacitor, is the current flowing through the filter capacitor, is the inductance value of the filter inductor, is the output voltage of the single-phase inverter before being processed by the filter circuit, is the resistance value of the sampling resistor in the active negative capacitor circuit.

[0048] Through the above formulas, the following relational expressions can be obtained:

[0049]

[0050] Transforming formula (8) into the time domain, the following expression can be obtained:

[0051]

[0052] Among them, is the time-domain expression of the voltage on the DC side of the three-phase rectifier, is the time-domain expression of the output voltage of the single-phase inverter.

[0053] Since the output voltage of the single-phase inverter is in the same phase as the modulation signal inside the digital signal controller and is proportional in amplitude, the output signal of the digital signal controller can be obtained as:

[0054]

[0055] Among them, is the output voltage of the digital signal controller, is the reciprocal of the sampling coefficient of the digital signal controller.

[0056] The port voltage of the active negative capacitor circuit is expressed as follows:

[0057]

[0058] Among them, represents the time-domain expression of the port voltage of the active negative capacitance circuit, represents the inverse Laplace transform, represents the amplitude of the port voltage signal of the active negative capacitance circuit, represents the angular frequency of the port voltage signal of the active negative capacitance circuit.

[0059] There is the following relationship for the voltage division coefficient of the entire positive and negative capacitance series structure by the active negative capacitance:

[0060]

[0061] Substituting formulas (11) and (12) into formula (10), the relationship formula between the sampling signal and the modulation signal can be obtained:

[0062]

[0063] Among them, represents the constant term frequency-capacitance value coefficient. Let ; represents the differential term frequency-capacitance value coefficient. Let , then formula (12) can be simplified to:

[0064]

[0065] It can be seen from formula (14) that by changing the voltage division coefficient , the constant term frequency-capacitance value coefficient and the differential term frequency-capacitance value coefficient , the modulation signal of the digital signal controller can be changed, and then the output voltage of the digital signal controller can be changed to control the first switching transistor , the second switching transistor , the third switching transistor , the fourth switching transistor , change the output of the H-bridge to change the capacitance value of the active negative capacitance circuit. The setting of the voltage division coefficient is adjusted by the capacitance value of the target active negative capacitance; the change of the constant term frequency-capacitance value coefficient and the differential term frequency-capacitance value coefficient is adjusted by the angular frequency of the port voltage signal of the active negative capacitance circuit and the capacitance value of the active negative capacitance.

[0066] According to the calculation of the equivalent capacitance value of capacitors in series, by changing the capacitance value of the active negative capacitor, the adjustment of the equivalent capacitance value of capacitors in series can be achieved. The closer the absolute values of the positive and negative capacitance values are, the larger the equivalent capacitance value of capacitors in series, making the equivalent circuit of capacitors in series equivalent to a large capacitor with adjustable capacitance value, thereby realizing the suppression of the second-order power on the DC side of the three-phase PWM rectifier. Based on the above conversion relationship of the output signals of the digital signal controller, now combined with Figure 2 , the process of suppressing the second-order power on the DC side of the three-phase PWM rectifier will be described.

[0067] During operation, the digital signal controller samples the DC-side voltage of the three-phase rectifier , that is, the voltage between the positive electrode and the negative electrode of the DC side of the three-phase PWM rectifier, and sends it into the digital signal controller. The digital signal controller separates the DC-side voltage of the three-phase rectifier through the phase-locked loop PLL to obtain a voltage signal with a specific frequency of 100 Hz, multiplies it by the voltage division coefficient to obtain the port voltage of the active negative capacitor circuit, and then multiplies the port voltage of the active negative capacitor circuit by the reciprocal of the sampling coefficient to obtain the node voltage . And multiply the node voltage by the constant term frequency-capacitance coefficient , the differential of multiplied by the differential term frequency-capacitance coefficient, and add the two to obtain the modulation signal . Finally, send the modulation signal and the carrier signal into the comparator, and the obtained square-wave signal is the output signal of the digital signal controller, which is the gate control signal of the first switching tube , the fourth switching tube . Pass it through an inverter to obtain the gate control signal of the second switching tube , the third switching tube . By controlling the first switching tube , the second switching tube , the third switching tube , the fourth switching tube , the output of the H-bridge is changed, so that the circuit of the active negative capacitor exhibits the capacitance port characteristics with different capacitance values.

[0068] Based on the above circuit topology, briefly describe its control method and working principle: Through the circuit structure and control strategy described above, an active negative capacitor with adjustable capacitance value can be obtained. Connect it in series with an ideal positive capacitor, so that the entire branch is equivalent to a large capacitor with adjustable capacitance value.

[0069] When this branch is operating, the DC - side voltage of the three - phase rectifier is sampled. As the input signal, the signal obtained after being processed by the digital signal controller and the signal obtained after its inversion through an inverter are used to drive the H - bridge of the single - phase inverter. By adjusting the parameters of the transfer function to change the output of the H - bridge, the entire additional circuit with an active negative capacitor can exhibit capacitive port characteristics with different capacitance values, thus achieving the purpose of using this additional circuit to replace the traditional capacitor with the same capacitance value. This also provides a path for the double - frequency energy, realizes power decoupling, and suppresses the double - frequency fluctuation of the DC - side voltage of the three - phase PWM rectifier.

[0070] Taking the case of the voltage dip in phase C as an example, the effect of the present invention in suppressing the secondary power fluctuation on the DC side is as Figures 3 - 4 shown. The parameters of the power grid, negative - capacitor circuit, etc. are shown in Table 1.

[0071] Table 1 is the partial parameter table of the power grid, negative - capacitor circuit, etc.

[0072]

[0073] According to Figure 1 and Figure 2 Build a simulation module in MATLAB, set the predetermined control parameters according to Table 1, and start running the simulation. First, without connecting the circuit with an active negative capacitor to the DC side, observe the double - frequency voltage fluctuation as Figures 3 - 4 shown. It can be seen that the load power waveform on the DC side shows a power - frequency double - frequency fluctuation. At t = 0.25 s, connect the circuit with an active negative capacitor in parallel to the DC side.

[0074] According to the two sets of positive - capacitor capacitance values and the equivalent capacitance values of the negative - capacitor circuit given in Table 2, perform simulations respectively, and obtain the corresponding DC - side power waveforms as Figures 3 - 4 shown.

[0075] Table 2 Simulation table of positive - capacitor capacitance value and equivalent capacitance value of negative - capacitor circuit

[0076]

[0077] The operation implementation process of the system is as follows:

[0078] The system samples the DC - side voltage of the three - phase rectifier, obtains the 100 - Hz component through PLL, calculates the signal wave through an operation, and compares it with a carrier wave with a certain frequency to control the switching tubes. In order to make the circuit with an active negative capacitor equivalent to capacitors with different capacitance values, and thus obtain different suppression effects, the parameter can be adjusted, that is, the absolute value of the capacitance of the active negative capacitor.

[0079] FromFigure 3 The overall simulation waveform shows that the equivalent capacitance circuit with a source negative capacitance can provide a high-frequency path for the energy of the power frequency double frequency, consume the double-frequency energy in the branch with the source negative capacitance, and effectively suppress the double-frequency fluctuation phenomenon of the DC-side voltage. Through comparative analysis Figures 3 - 4 , it can be seen that as the equivalent capacitance value of the whole branch increases, the suppression effect of the second-order power becomes better, which also proves the correctness of the adjustable suppression effect of the method proposed by the present invention.

[0080] It can be understood that the present invention is described by some embodiments. Those skilled in the art know that various changes or equivalent replacements can be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teaching of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A method for suppressing secondary power on the DC side of a three-phase PWM rectifier, characterized in that: The method is applied to a three-phase PWM rectifier; the method comprises: ,negative electrode The two ends are connected in parallel to the input end of the DC-DC converter, and the output end of the DC-DC converter is connected to the first switch tube. , the second switch tube , the third switch tube , the fourth switch tube The H-bridge structure formed; The DC-DC converter and H-bridge structure form a single-phase inverter; The DC-DC converter takes power from the DC bus as the DC power supply for the single-phase inverter; the output end of the single-phase inverter is connected to a filter capacitor , filter inductor The LC filter circuit is composed of a sampling resistor connected in series with the output end of the single-phase inverter after the LC filter circuit. After the first capacitor Connect in series and then in parallel to the positive pole of the DC side of the three-phase PWM rectifier ,negative electrode Two ends; single-phase inverter, filter capacitor And filter inductor LC filter circuit and sampling resistor An active negative capacitance circuit is formed; the active negative capacitance circuit and the first capacitor The capacitor series equivalent circuit based on active negative capacitance is obtained by connecting in series; the second capacitor ,load Connect in parallel to the positive pole of the DC side of the three-phase PWM rectifier ,negative electrode Both ends; on the positive pole of the DC side of the three-phase PWM rectifier ,negative electrode The voltage signal is sampled at both ends and connected to the input end of the digital signal controller, and the output end of the digital signal controller is connected to the first switch tube of the single-phase inverter. , the fourth switch tube The output end of the digital signal controller is connected to the second switch tube of the single-phase inverter after passing through the inverter. , the third switch tube ; The digital signal controller outputs a signal to the first switch tube , the second switch tube , the third switch tube , the fourth switch tube By controlling the active negative capacitor circuit, the capacitance of the active negative capacitor circuit is changed, and then the capacitor series equivalent circuit based on the active negative capacitor is changed, and finally the secondary power suppression on the DC side of the three-phase PWM rectifier is achieved.

2. The method for suppressing secondary power on the DC side of a three-phase PWM rectifier according to claim 1, characterized in that: The first switch With the third switch The collector of the second switch is connected to the positive output terminal of the DC-DC converter. With the fourth switch The emitter of the first switch is connected to the negative output terminal of the DC-DC converter; The emitter of the second switch tube The collector of the filter inductor is connected to One end of the filter inductor The other end is connected to the filter capacitor One end of the third switch tube The emitter of the fourth switch tube The collector of the The other end of the filter capacitor and filter inductor Constitute an LC low-pass filter structure; resistor One end of the filter capacitor , filter inductor The points that are connected are connected; resistance The other end is connected to the first capacitor One end of the first capacitor The other end is connected to the positive electrode of the DC side of the three-phase PWM rectifier ; Filter capacitor Connect to the third switch The emitter of the fourth switch tube One end of the collector is connected to the negative electrode of the DC side of the three-phase PWM rectifier .

3. The method for suppressing secondary power on the DC side of a three-phase PWM rectifier according to claim 2, characterized in that: The output terminal of the digital signal controller is connected to the first switch tube And the fourth switch The gate of the digital signal controller is connected to the inverter. Then connected to the second switch With the third switch of the gate.

4. The method for suppressing secondary power on the DC side of a three-phase PWM rectifier according to claim 3, characterized in that: The digital signal controller samples the DC side voltage of the three-phase rectifier , that is, the positive electrode on the DC side of the three-phase PWM rectifier With negative electrode The voltage between the two is sent to the digital signal controller; the digital signal controller converts the DC side voltage of the three-phase rectifier The voltage signal with a specific frequency of 100Hz is obtained by separation through the phase-locked loop PLL and multiplied by the voltage division coefficient Get the terminal voltage of the active negative capacitance circuit , and then the terminal voltage of the active negative capacitor circuit Multiply by the inverse of the sampling factor Get the node voltage ; and the node voltage Multiply by the constant term frequency-capacitance coefficient , The differential multiplied by the differential term frequency-capacitance coefficient , the two are added to get the modulated signal ; Finally, the modulated signal and carrier signal The square wave signal is sent to the comparator and is the output signal of the digital signal controller, that is, the first switch tube , the fourth switch tube The gate control signal is passed through the inverter to obtain the second switch tube , the third switch tube The gate control signal is applied to the first switch tube , the second switch tube , the third switch tube , the fourth switch tube The control changes the output of the H-bridge, making the active negative capacitor circuit exhibit capacitor port characteristics with different capacitance values.

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