Non-continuous three-phase rectifier adjustable power decoupling method

Abstract

The application provides a non-continuous three-phase rectifier adjustable power decoupling method, and relates to the field of power electronics. The method is characterized in that a capacitor equivalent circuit is connected in parallel to the DC side of a three-phase PWM rectifier, the capacitor equivalent circuit is composed of a first capacitor connected in series with an active negative capacitor circuit, and a digital signal controller is used to sample the relevant voltage and current signals of the AC side and the DC side, and the active negative capacitor capacitance is adjusted by controlling the switching tube, so that the equivalent capacitor circuit can be flexibly adjusted. The application does not require an additional DC power supply, the capacitance and inductance of the passive device used are small, and the volume advantage is significant. The closed-loop control has high precision and equivalent inhibition effect as the traditional large capacitor. The equivalent capacitance is adjusted only by software, the external physical structure does not need to be changed, and the adjustment range is wide. The preset DC side voltage fluctuation amplitude can be calculated and adjusted automatically, different unbalanced working conditions can be adapted, the fluctuation suppression demand can be met, different working modes can be switched according to the AC side working condition, and the application is not continuously operated, so that the switching loss is lower.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to an adjustable power decoupling method for a non-continuous three-phase rectifier. Background Technology

[0002] With the global energy shortage, renewable energy sources such as solar, wind, and hydropower are being continuously developed and applied. Unlike traditional centralized power generation systems, renewable energy is characterized by its relatively dispersed distribution, which has led to the rapid development of distributed generation. Distributed generation systems require energy conversion based on different voltage levels and power source characteristics, necessitating the use of power electronic equipment. Among these, the three-phase voltage source pulse width modulation (PWM) rectifier is commonly used, offering core technological advantages such as adjustable power factor, adjustable AC current amplitude, and adjustable DC bus voltage.

[0003] However, three-phase PWM rectifiers only achieve high-performance output under balanced three-phase grid conditions. Unlike traditional large power grids, in weak grids such as distributed generation systems, three-phase imbalance is prevalent, easily leading to problems such as secondary power fluctuations on the DC side of the rectifier (i.e., second-harmonic voltage / power pulsations), AC current distortion and imbalance, power oscillations, and tripping of sensitive loads, significantly reducing system reliability and overall performance. To address these issues, existing technologies primarily employ power decoupling schemes, which fall into two categories:

[0004] Passive Power Decoupling (PPD) involves connecting a large-capacity conventional capacitor (such as an electrolytic capacitor) or an LC resonant circuit in parallel on the DC side to bypass secondary power fluctuation energy. However, to achieve the ideal second harmonic voltage suppression effect, ultra-large capacitance capacitors are required, resulting in a large system size and low power density. Furthermore, electrolytic capacitors have short lifespans and poor reliability, further limiting the long-term stable operation of the rectifier.

[0005] Active Power Decoupling (APD): This technology adds extra power electronic circuitry to a traditional three-phase converter, using switching transistors to buffer secondary power into long-life components such as thin-film capacitors, thus reducing size and extending lifespan. However, existing APD technology has the following problems: the suppression effect of second-harmonic voltage fluctuations is uncontrollable, it cannot be flexibly adjusted according to different unbalanced operating conditions and different voltage fluctuation requirements, and its adaptability is poor.

[0006] Meanwhile, APD (Automatic Power Decoupling) was first proposed in single-phase systems and later adapted to three-phase systems. However, the power fluctuations in single-phase and three-phase systems differ and require additional consideration. In single-phase systems, secondary power fluctuations are always present, so single-phase APD operates continuously. In contrast, in three-phase systems, the AC side voltage is usually balanced. If the AC side current is also balanced, their multiplication will not produce oscillating power. However, during a fault, the AC side voltage becomes unbalanced, and its multiplication with the balanced AC side current will generate oscillating power. Therefore, for three-phase systems, power decoupling should operate during faults to ensure power quality during fault periods, rather than continuously as in single-phase systems. Summary of the Invention

[0007] In view of this, embodiments of this application provide an adjustable power decoupling method for a non-continuous three-phase rectifier, which has the advantages of significantly reducing the size of passive components compared to PPD and adjustable voltage fluctuations compared to APD. Furthermore, considering the non-continuous operation of the three-phase power decoupling, it is designed to not operate under non-fault conditions, thereby reducing switching losses.

[0008] This application provides the following technical solution: an adjustable power decoupling method for a non-continuous three-phase rectifier, the method being applied to a three-phase PWM rectifier; the method includes using a third capacitor... The positive and negative ports are connected to the first switching transistor. Second switching transistor The input and output terminals of the formed half-bridge structure are connected to a filter capacitor. Filter inductor The LC filter circuit forms a complete synchronous buck converter; the output terminal of the synchronous buck converter is connected to the first capacitor. It is connected in series and then in parallel to the positive terminal of the DC side of the three-phase PWM rectifier. ,negative electrode At both ends, an active negative capacitor circuit is constructed using a synchronous buck converter; the active negative capacitor circuit and the first capacitor The series connection yields a capacitor series equivalent circuit based on an active negative capacitor; the second capacitor ,load The positive terminal of the DC side of the three-phase PWM rectifier is connected in parallel. ,negative electrode Both ends; in the first capacitor Two ends, third capacitor Both ends and filter capacitor Voltage signals are sampled at both ends. Voltage and current signals sampled on the AC side of the three-phase PWM rectifier are connected to the input of a digital signal controller. The output of the digital signal controller is connected to the first switching transistor of the synchronous buck converter. The output of the digital signal controller is connected to the second switching transistor of the synchronous buck converter after passing through an inverter. The digital signal controller outputs a signal to the first switching transistor. Second switching transistor By controlling the capacitor, the capacitance of the active negative capacitor circuit is changed, which in turn changes the capacitor series equivalent circuit based on the active negative capacitor, ultimately achieving adjustable power decoupling of the three-phase PWM rectifier.

[0009] According to one embodiment of this application, the first switching transistor... collector and second switching transistor The emitters are respectively connected to the third capacitor. The positive and negative ends; the first switching transistor emitter and second switch The collector is connected to the filter inductor. One end, filter inductor The other end is connected to the filter capacitor. The positive terminal; the second switching transistor The emitter is connected to the filter capacitor. The negative terminal; filter capacitor and filter inductor Constructing an LC low-pass filter structure; filter capacitor The positive terminal is connected to the first capacitor. The negative terminal, the first capacitor The positive terminal is connected to the positive terminal of the DC side of the three-phase PWM rectifier. Second switching transistor The emitter is connected to the negative terminal of the DC side of the three-phase PWM rectifier. .

[0010] According to one embodiment of this application, the output terminal of the digital signal controller is connected to a first switching transistor. The gate of the digital signal controller is connected to the inverter, and then to the second switching transistor. The gate.

[0011] According to one embodiment of this application, the digital signal controller samples the AC side voltage. , , Calculate the zero-sequence voltage based on the AC side voltage. This is used to determine whether the current three-phase PWM rectifier is operating under unbalanced conditions; where, under balanced conditions, the first switching transistor... Second switching transistor All are turned off to reduce losses; under unbalanced conditions, the active negative capacitor circuit operates normally to adjust the DC side capacitor value of the three-phase PWM rectifier.

[0012] According to one embodiment of this application, the zero-sequence voltage The calculation is performed using the following formula:

[0013] = ( + + ) / 3; where, , , These are the AC side voltages, respectively.

[0014] According to one embodiment of this application, the zero-sequence voltage is calculated based on the AC side voltage. To determine whether the current three-phase PWM rectifier is operating under unbalanced conditions, including:

[0015] The zero-sequence voltage With minimum voltage By comparison, the zero-sequence voltage is determined. Is it less than the minimum voltage? If yes, then the current three-phase PWM rectifier is considered to be operating under balanced conditions; otherwise, it is considered to be operating under unbalanced conditions.

[0016] According to one embodiment of this application, when the active negative capacitor circuit is operating normally: the digital signal controller samples the AC side voltage on the AC side. , , With current , , The first capacitor is sampled on the DC side. Voltage at both ends Third capacitor Voltage at both ends AC voltage across the active negative capacitor The digital signal controller is based on the sampled AC side voltage. , , With current , , Further calculations yielded the secondary power. Combined with the preset DC-side voltage fluctuation amplitude Calculate the required DC-side capacitance, and then calculate the negative capacitor value in the digital signal controller based on the DC-side capacitance and the voltage divider relationship between the positive and negative capacitors. .

[0017] Compared with the prior art, the beneficial effects that at least one technical solution adopted in the embodiments of this specification can achieve include at least:

[0018] 1) This invention uses power electronic circuits to perform port equivalence on traditional capacitors. The passive components used have very small capacitance and inductance values, yet they can be equivalent to larger capacitors, thus achieving a significant advantage in terms of size.

[0019] 2) This invention adopts closed-loop control with high precision, which is equivalent to the suppression effect of traditional large capacitors. When using it, you only need to set the required fluctuation amplitude. The system can automatically calculate the DC side capacitor value and implement control based on this and the real-time operating conditions. There is no need to manually adjust the capacitance value. It can adapt to different unbalanced operating conditions and flexibly meet the fluctuation suppression requirements.

[0020] 3) This invention includes the ability to determine the imbalance of the three-phase voltage on the AC side, enabling it to operate in both offline and online states. Compared with the power decoupling method that operates continuously, it can reduce switching losses under balanced conditions. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a flowchart illustrating the operation of the non-continuous adjustable power decoupling circuit on the DC side of the three-phase rectifier according to the present invention.

[0023] Figure 2 The waveforms show a comparison of the suppression effects of the proposed method (top) and the traditional capacitor (bottom) on DC-side voltage fluctuations under the simulation conditions of this invention.

[0024] Figure 3 The waveforms show a comparison of the suppression effects of the proposed method (top) and the traditional capacitor (bottom) on DC-side voltage fluctuations under simulation condition two of this invention.

[0025] Figure 4 The DC-side voltage spectrum analysis is performed under the simulation conditions of this invention when the proposed method and the traditional capacitor are used respectively.

[0026] Figure 5 Spectral analysis of DC-side voltage under simulation condition 2 of this invention when the proposed method and the traditional capacitor are respectively applied;

[0027] Figure 6 These are the AC / DC side waveforms of the steady-state and transition processes before and after switching from the three-phase balanced operating condition to the simulated operating condition in this invention.

[0028] Figure 7 The AC / DC side waveforms are shown before and after the steady-state and transition processes of the present invention when switching from three-phase balanced operating condition to simulated operating condition two. Detailed Implementation

[0029] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0030] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0031] The adjustable power decoupling method for non-continuous three-phase rectifiers proposed in this invention is based on the following principle: positive and negative capacitors connected in series, and the principle of achieving equivalent capacitor port characteristics using power electronic circuits.

[0032] For a positive capacitor, the relationship between its voltage and current can be described by the following first-order differential equation:

[0033] (1)

[0034] in, The voltage across a traditional capacitor. The current flowing through a traditional capacitor, This is the capacitance value of a traditional capacitor.

[0035] For a negative capacitor, it exhibits the same DC blocking characteristic as a traditional capacitor, and AC characteristics similar to a traditional inductor. Its voltage-current relationship can be expressed as:

[0036] (2)

[0037] in, This is the voltage across the negative capacitor. The current flowing through the negative capacitor. The capacitance value is negative.

[0038] Based on the formula for calculating the equivalent capacitance of capacitors connected in series, the equivalent capacitance of positive and negative capacitors connected in series can be obtained as follows:

[0039] (3)

[0040] in, This is the equivalent capacitance of the positive and negative capacitors connected in series.

[0041] As can be seen from equation (3), since the capacitance of the negative capacitor is negative, the closer the absolute values ​​of the capacitance of the positive capacitor and the negative capacitor are to each other, the larger the equivalent capacitance will be. Moreover, this is a non-linear process. Therefore, by slightly changing the capacitance of the negative capacitor connected in series with the positive capacitor, the equivalent capacitance can be changed over a large range.

[0042] Based on the concept of passive power decoupling, the larger the DC-side capacitor value, the lower the DC-side voltage fluctuation. The following is the relationship between DC-side voltage fluctuation and current-side capacitor value:

[0043] The DC link voltage, including the second-order fluctuation, can be expressed as:

[0044] (4)

[0045] in, It is the DC-side voltage of a three-phase PWM rectifier. It is the DC component of the DC-side voltage. It is the second harmonic component of the DC side voltage.

[0046] Based on the characteristics of a capacitor, the expression for the current flowing through the DC side capacitor is:

[0047] (5)

[0048] in, It is the current flowing through the capacitor. This is the DC-side capacitance value.

[0049] Let the secondary power be:

[0050] (6)

[0051] Based on the power relationship, another expression for the current flowing through the DC-side capacitor can be determined:

[0052] (7)

[0053] Secondary voltage fluctuations can be expressed as:

[0054] (8)

[0055] in, It is the amplitude of the second harmonic component of the voltage.

[0056] From equations (5), (7), and (8), we can obtain the voltage fluctuation on the DC side as follows: Required DC-side capacitor value:

[0057] (9)

[0058] When positive and negative capacitors are connected in series, their voltage division relationship can be expressed as:

[0059] (10)

[0060] (11)

[0061] Based on the above principles, this invention provides an adjustable power decoupling method for a non-continuous three-phase rectifier. For example... Figure 1 As shown, the method includes using a third capacitor. The positive and negative ports are connected to the first switching transistor. Second switching transistor The input and output terminals of the formed half-bridge structure are connected to a filter capacitor. Filter inductor The LC filter circuit forms a complete synchronous buck converter; the output terminal of the synchronous buck converter is connected to the first capacitor. It is connected in series and then in parallel to the positive terminal of the DC side of the three-phase PWM rectifier. ,negative electrode Two ends; an active negative capacitor circuit is constructed using a synchronous buck converter; the active negative capacitor circuit and the first capacitor The series connection yields a capacitor series equivalent circuit based on an active negative capacitor; the second capacitor ,load The positive terminal of the DC side of the three-phase PWM rectifier is connected in parallel. ,negative electrode Both ends; in the first capacitor Two ends, third capacitor Both ends and filter capacitor Voltage signals are sampled at both ends. Voltage and current signals sampled on the AC side of the three-phase PWM rectifier are connected to the input of a digital signal controller. The output of the digital signal controller is connected to the first switching transistor of the synchronous buck converter. The output of the digital signal controller is connected to the second switching transistor of the synchronous buck converter after passing through an inverter. The digital signal controller outputs a signal to the first switching transistor. Second switching transistor By controlling the capacitor, the capacitance of the active negative capacitor circuit is changed, which in turn changes the capacitor series equivalent circuit based on the active negative capacitor, ultimately achieving adjustable power decoupling of the three-phase PWM rectifier.

[0062] Furthermore, the first switching transistor collector and second switching transistor The emitters are respectively connected to the third capacitor. The positive and negative ends; the first switching transistor emitter and second switch The collector is connected to the filter inductor. One end, filter inductor The other end is connected to the filter capacitor. The positive terminal; the second switching transistor The emitter is connected to the filter capacitor. The negative terminal; filter capacitor and filter inductor Constructing an LC low-pass filter structure; filter capacitor The positive terminal is connected to the first capacitor. The negative terminal, the first capacitor The positive terminal is connected to the positive terminal of the DC side of the three-phase PWM rectifier. Second switching transistor The emitter is connected to the negative terminal of the DC side of the three-phase PWM rectifier. .

[0063] Furthermore, the output of the digital signal controller is connected to the first switching transistor. The gate of the digital signal controller is connected to the inverter, and then to the second switching transistor. The gate.

[0064] Based on the above principle of adjusting the equivalent capacitance of the series-connected positive and negative capacitors and the relationship between DC-side voltage fluctuations and capacitance value, the following is combined with... Figure 1 The decoupling process for non-continuous adjustable power of a three-phase rectifier is explained.

[0065] During operation, the digital signal controller samples the AC side voltage. , , Calculate the zero-sequence voltage ,according to The magnitude of this value determines the operating condition of the AC side of the three-phase rectifier: when the zero-sequence voltage... Less than minimum voltage At this time, it is assumed that the three phases on the AC side are balanced, and the first switching transistor... Second switching transistor All are off, with only the first capacitor on the DC side. With filter capacitor Series and second capacitor They are connected in parallel; otherwise, it is assumed that there is a three-phase imbalance on the AC side, and the active negative capacitor works normally to adjust the DC side capacitance value and suppress DC voltage fluctuations to be near the preset value.

[0066] When the active negative capacitor is working normally, the digital signal controller samples the AC side voltage. , , With current , , And further calculate the secondary power Combined with the preset DC-side voltage fluctuation amplitude Calculate the required DC-side capacitance, and based on this, calculate the required negative capacitance value according to the voltage divider relationship between the positive and negative capacitors. .

[0067] During operation, the digital signal controller extracts... The AC component in the signal is obtained Multiply it by the first capacitor Capacitance value and negative capacitance value The negative capacitor port voltage reference signal is then obtained. and connect it to the AC voltage across the active negative capacitor. The first voltage error signal is obtained by subtraction. The sampled signal Multiply by a magnification factor (Pick Then with the third capacitor Voltage at both ends The second voltage error signal is obtained by subtraction. First voltage error signal With the second voltage error signal The modulation signal is obtained by subtracting the two signals after passing them through a PI controller. Finally, the modulated signal and The square wave signal obtained by the comparator is the output signal of the digital signal controller, which is the first switching transistor. The gate control signal is passed through an inverter to obtain the second switch. The gate control signal causes the port of the active negative capacitor circuit to exhibit the negative capacitor port characteristics of the corresponding capacitance value.

[0068] When this capacitor equivalent circuit is working, it samples and calculates the voltage and current signals on the AC side, and can automatically determine the current AC side operating condition of the three-phase rectifier, enabling power decoupling to operate in online and offline states. In online state, it can adjust the equivalent capacitance value according to the calculated real-time secondary power value and the preset DC side voltage fluctuation amplitude, suppressing DC side voltage fluctuations to achieve the same preset value under different unbalanced operating conditions of the three-phase PWM rectifier, while the preset value is also flexible and variable.

[0069] Based on the above circuit structure and workflow, the proposed power decoupling method for non-continuous operation of a three-phase rectifier is simulated and verified.

[0070] Table 1 shows two different unbalanced operating conditions and the same DC voltage fluctuation preset value set for the same three-phase PWM rectifier.

[0071] Table 1 Unbalanced operating condition parameters and preset values ​​for DC side voltage fluctuation

[0072]

[0073] according to Figure 1 A simulation model was built in PSIM, and the parameters of each passive device are shown in Table 2. Experiments were conducted under two different operating conditions as set in Table 1.

[0074] Table 2 Parameters of passive components in the circuit

[0075]

[0076] In the simulation experiment, the DC-side voltage fluctuation was first suppressed using the method proposed in this invention, and then suppressed using a traditional capacitor of the same capacitance value. The two methods were compared, and this process was repeated to conduct simulation experiments for the two operating conditions. Figure 2 and Figure 3 The DC-side voltage waveform is shown.

[0077] To facilitate observation of the comparison between the proposed method and traditional capacitors of the same capacitance in suppressing DC-side voltage fluctuations, Figure 4 and Figure 5 The results of the spectral analysis of the DC-side voltage under two operating conditions are presented.

[0078] Depend on Figure 2 and Figure 4 It can be seen that, under operating condition 1, the proposed method has a similar suppression effect on the voltage components of the three frequencies, with a maximum relative error of only 3.7%; similarly, Figure 3 and Figure 5 The results show that when switching to operating condition two, the maximum relative error of the proposed method compared to the traditional capacitor is 2.0%. This proves that the proposed method does have a certain accuracy in the equivalent of the traditional capacitor, and can suppress DC-side voltage fluctuations to a certain extent according to the preset standard.

[0079] Figure 6 and Figure 7The AC / DC voltage waveforms demonstrated in the operating condition switching experiment show that when the AC side operating condition abruptly changes from balanced to unbalanced at a time interval of 3 seconds, the DC side voltage reacts almost instantaneously and reaches a steady state after a certain transition time, maintaining a certain voltage fluctuation. Specifically, the DC side voltage changes almost simultaneously with the change in AC side operating condition, indicating that the invention has a rapid response capability to sudden changes in operating conditions. Within 0.05 seconds of the change in operating condition, the DC voltage fluctuation can reach a new steady state under different unbalanced operating conditions, demonstrating that the invention can successfully switch between offline and online states.

[0080] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for decoupling adjustable power in a non-continuous three-phase rectifier, characterized in that, The method is applied to a three-phase PWM rectifier; the method includes using a third capacitor. The positive and negative ports are connected to the first switching transistor. Second switching transistor The input and output terminals of the formed half-bridge structure are connected to a filter capacitor. Filter inductor The LC filter circuit is thus formed, thereby constituting a complete synchronous buck converter; The output of the synchronous buck converter and the first capacitor It is connected in series and then in parallel to the positive terminal of the DC side of the three-phase PWM rectifier. ,negative electrode At both ends, an active negative capacitor circuit is constructed using a synchronous buck converter; the active negative capacitor circuit and the first capacitor The series connection yields a capacitor series equivalent circuit based on an active negative capacitor; the second capacitor ,load The positive terminal of the DC side of the three-phase PWM rectifier is connected in parallel. ,negative electrode Both ends; in the first capacitor Two ends, third capacitor Both ends and filter capacitor Voltage signals are sampled at both ends. Voltage and current signals sampled on the AC side of the three-phase PWM rectifier are connected to the input of a digital signal controller. The output of the digital signal controller is connected to the first switching transistor of the synchronous buck converter. The output of the digital signal controller is connected to the second switching transistor of the synchronous buck converter after passing through an inverter. The digital signal controller outputs a signal to the first switching transistor. Second switching transistor By controlling the capacitor, the capacitance of the active negative capacitor circuit is changed, thereby changing the capacitor series equivalent circuit based on the active negative capacitor, and finally achieving adjustable power decoupling of the three-phase PWM rectifier. Among them, the first switching transistor collector and second switching transistor The emitters are respectively connected to the third capacitor. The positive and negative ends; the first switching transistor emitter and second switch The collector is connected to the filter inductor. One end, filter inductor The other end is connected to the filter capacitor. The positive terminal; the second switching transistor The emitter is connected to the filter capacitor. The negative terminal; filter capacitor and filter inductor Constructing an LC low-pass filter structure; filter capacitor The positive terminal is connected to the first capacitor. The negative terminal, the first capacitor The positive terminal is connected to the positive terminal of the DC side of the three-phase PWM rectifier. Second switching transistor The emitter is connected to the negative terminal of the DC side of the three-phase PWM rectifier. ; The digital signal controller samples the AC side voltage. , , Calculate the zero-sequence voltage based on the AC side voltage. This is used to determine whether the current three-phase PWM rectifier is operating under unbalanced conditions; where, under balanced conditions, the first switching transistor... Second switching transistor All are turned off to reduce losses; under unbalanced conditions, the active negative capacitor circuit operates normally to adjust the DC side capacitor value of the three-phase PWM rectifier.

2. The adjustable power decoupling method for a non-continuous three-phase rectifier according to claim 1, characterized in that, The output of the digital signal controller is connected to the first switching transistor. The gate of the digital signal controller is connected to the inverter, and then to the second switching transistor. The gate.

3. The adjustable power decoupling method for a non-continuous three-phase rectifier according to claim 1, characterized in that, The zero-sequence voltage The calculation is performed using the following formula: = ( + + ) / 3; where, , , These are the AC side voltages, respectively.

4. The adjustable power decoupling method for a non-continuous three-phase rectifier according to claim 1, characterized in that, Calculate the zero-sequence voltage based on the AC side voltage. To determine whether the current three-phase PWM rectifier is operating under unbalanced conditions, including: The zero-sequence voltage With minimum voltage By comparison, the zero-sequence voltage is determined. Is it less than the minimum voltage? If yes, then the current three-phase PWM rectifier is considered to be operating under balanced conditions; otherwise, it is considered to be operating under unbalanced conditions.

5. The adjustable power decoupling method for a non-continuous three-phase rectifier according to claim 1, characterized in that, When the active negative capacitor circuit is working normally: the digital signal controller samples the AC side voltage on the AC side. , , With current , , The first capacitor is sampled on the DC side. Voltage at both ends Third capacitor Voltage at both ends AC voltage across the active negative capacitor The digital signal controller is based on the sampled AC side voltage. , , With current , , Further calculations yielded the secondary power. Combined with the preset DC-side voltage fluctuation amplitude Calculate the required DC-side capacitance, and then calculate the negative capacitor value in the digital signal controller based on the DC-side capacitance and the voltage divider relationship between the positive and negative capacitors. .

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