Method for controlling a vienna rectifier and for suppressing current zero crossing distortion thereof

Abstract

The present application relates to a kind of Vienna rectifier control and its current zero-crossing distortion inhibition method, comprising the following steps: positive and negative sequence separation is carried out to the instantaneous value of collected grid voltage, and positive and negative sequence phase angle is calculated;Based on the control target of Vienna rectifier under the unbalance of grid voltage, control method is selected, and reference current is calculated;The instantaneous value of reference voltage is sorted, and max phase, mid phase and min phase of reference voltage are obtained, and the max phase, mid phase and min phase of current follow the voltage sorting result;According to the relationship between u max 、u mid 、u min And i mid , the region where reference voltage is located is analyzed, and the modulation voltage is calculated using the synthesis method with the minimum synthesis error.The present application can make Vienna rectifier run stably under the unbalance of grid voltage, effectively reduce current zero-crossing distortion in essence, and optimize the control of Vienna rectifier.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof. Background Art

[0002] Since the development of power electronics technology in the 1970s, various topologies and control methods have been extensively studied and widely applied in various fields, including daily life and production. However, the nonlinear characteristics of power electronic devices generate a large amount of reactive power and harmonics, which inevitably pollute the power grid. Improving the power quality of power electronic devices is of great significance to the environmental purification of the power system. According to relevant reports, rectifiers account for over 70% of all power electronic devices. Failure to select the appropriate topology and control strategy will not only increase the switching stress of power devices but also cause serious grid pollution. How to ensure the normal operation of these different types of rectifiers while reducing harmonic pollution and reactive power loss is of great practical significance.

[0003] Currently, there are two main approaches to addressing the harmonic pollution and reactive power loss caused by rectifiers: one is to incorporate active power filters (APFs) into the grid to compensate for grid-side harmonics and reactive power; the other is to employ power factor correction (PFC) technology. Compared to APFs, PFC technology addresses the problem of harmonic generation and injection into the grid by rectifiers at the source, significantly reducing the need for compensation devices and offering greater economic efficiency. Among various two-level and three-level rectifiers, the Vienna rectifier has attracted considerable attention for its simple structure, control scheme, minimal drive circuitry, low device voltage stress, and high power density. It has been widely used in charging stations for plug-in hybrid vehicles and electric vehicles. Compared to traditional two-level rectifiers, the Vienna rectifier, due to its increased number of levels, is more effective at suppressing AC-side harmonics. At the same input voltage, the voltage stress on each switch is reduced, resulting in low switching losses, significantly improving energy efficiency and meeting the requirements of high-voltage and high-power applications. Compared with traditional three-level rectifiers, Vienna rectifiers require fewer power devices and do not have the bridge arm shoot-through problem, so they have good application prospects.

[0004] However, in practice, grid voltages often experience imbalance. Traditional Vienna rectifier control strategies fail, generating even harmonics on the DC side and odd harmonics on the AC side. Furthermore, Vienna rectifiers inherently suffer from current zero-crossing distortion, which causes harmonic pollution to the grid and reduces the power factor. Therefore, appropriate control and modulation strategies are needed to ensure stable operation of Vienna rectifiers even with grid voltage imbalances and to reduce or even completely eliminate current zero-crossing distortion. Summary of the Invention

[0005] The object of the present invention is to provide a method for controlling a Vienna rectifier and suppressing current zero-crossing distortion in order to solve the above problems.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] A method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof comprises the following steps:

[0008] S1: Collect the instantaneous value of the grid voltage to separate the positive and negative sequences, calculate the positive and negative sequence phase angles, and then obtain the positive and negative sequence components of the grid voltage under the d axis

[0009] S2: Based on the positive and negative sequence components of the grid voltage on the d-axis Calculate the reference current of Vienna rectifier under grid voltage imbalance;

[0010] S3: Calculating a reference voltage of the Vienna rectifier in the ABC axis system according to the reference current;

[0011] S4: sorting the instantaneous values ​​of the reference voltage to obtain the max phase, mid phase and min phase of the reference voltage, the max phase, mid phase and min phase of the reference current correspond to the reference voltage sorting result, and then obtaining the mid phase of the reference current;

[0012] S5: Analyze the region where the reference voltage is located based on the relationship between the max phase, mid phase, and min phase of the reference voltage and the mid phase of the reference current, determine whether the current zero crossing point is distorted, and calculate the modulation voltage using a synthesis method with minimal synthesis error.

[0013] As a further optimization solution of the present invention, step S1 specifically includes the following steps:

[0014] S101: collecting instantaneous voltage value of the power grid;

[0015] S102: Separating the positive and negative sequence of the instantaneous voltage value to obtain the positive and negative sequence components of the instantaneous voltage value under the αβ axis

[0016] S103: According to the positive and negative sequence components of the instantaneous voltage value under the αβ axis Calculate the instantaneous phase angle δ of the positive and negative sequence components of the grid voltage + , δ - ;

[0017] S104: According to the instantaneous phase angle δ of the positive and negative sequence components of the grid voltage + , δ - Calculate the positive and negative sequence components of the grid voltage under the d-axis

[0018] As a further optimization solution of the present invention, step S2 specifically includes the following: adopting a balanced current control method based on the Vienna rectifier under the condition of unbalanced grid voltage, and calculating a reference current:

[0019] Keep the average input power on the AC side equal to the required power on the DC side, and the three-phase currents sinusoidal and symmetrical. The reference current calculation formula is as follows:

[0020]

[0021] Where, They represent the positive and negative sequence components of the reference current under the dq axis, respectively, 0,ref Indicates the required power on the DC side.

[0022] As a further optimization solution of the present invention, step S2 specifically includes the following: adopting an instantaneous power control method based on the Vienna rectifier under the condition of unbalanced grid voltage, and calculating a reference current:

[0023] Ensure that the instantaneous value of the AC side input power is equal to the required power on the DC side. The three-phase current is sinusoidal but asymmetrical. The reference current calculation formula is as follows:

[0024]

[0025] As a further optimization solution of the present invention, step S3 specifically includes the following steps:

[0026] S301: Convert the reference current under the dq axis to the αβ axis to obtain the reference current under the αβ axis. The formula is as follows:

[0027]

[0028] S302: Calculate the reference voltage of the Vienna rectifier under the αβ axis according to the reference current under the αβ axis. The calculation formula is as follows:

[0029]

[0030] Where, e α 、e β are the components of the grid voltage under the α and β axes, L is the inductance, T s is the sampling period, Δu α and Δu β are the components of the inductor voltage drop under the α and β axes respectively;

[0031] S303: Convert the reference voltage under the αβ axis to the ABC axis system. The calculation formula is as follows:

[0032]

[0033] As a further optimization solution of the present invention, the formula for sorting the instantaneous values ​​of the reference voltages in step S4 is as follows:

[0034]

[0035] Where u max 、u mid 、u min They are the max phase, mid phase and min phase of the reference voltage respectively.

[0036] As a further optimization solution of the present invention, the step S5 specifically includes the following contents: according to the relationship between the max phase, mid phase, min phase of the reference voltage and the mid phase of the reference current:

[0037] ①If u mid i mid ≥0, where i mid is the mid phase of the reference current, which is in the non-current zero-crossing region. The modulation voltage is:

[0038]

[0039] ②If u mid >0,i mid <0 and u mid -u min <0.5u dc or u mid <0,i mid >0 and u max -u mid >0.5u dc , at this time it is in the current zero-crossing distortion area, but the DPWM modulation method can be used to completely eliminate the current zero-crossing distortion, and its modulation voltage should be:

[0040]

[0041] ③If u mid >0,i mid <0 and u mid -u min >0.5u dc or u mid <0,i mid >0 and u max -u mid >0.5u dc At this time, the vertical foot approximate synthesis method is used in the current zero-crossing distortion area to alleviate the current zero-crossing distortion problem, where:

[0042] If u mid >0,i mid <0 and u mid -u min >0.5u dc , the modulation voltage should be:

[0043]

[0044] If u mid <0,i mid >0 and u max -u mid >0.5u dc , the modulation voltage should be:

[0045]

[0046] The beneficial effects of the present invention are:

[0047] 1. The present invention adopts corresponding control methods based on different control objectives, so that the Vienna rectifier can also operate stably when the grid voltage is unbalanced;

[0048] 2. The present invention addresses the fundamental cause of zero-crossing distortion in Vienna rectifier current and effectively reduces current distortion in essence.

[0049] 3. The present invention does not require any additional peripherals, has strong applicability, is simple to control, and is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a flowchart of the present invention;

[0051] Figure 2 This is the topology diagram of the Vienna rectifier;

[0052] Figure 3 This is the experimental result of using balanced current control when the grid voltage phase A suddenly drops by 30%;

[0053] Figure 4 This is the experimental result of using instantaneous power control when the grid voltage phase A suddenly drops by 30%;

[0054] Figure 5 This is the experimental result of the traditional modulation method when the grid voltage drops by 10% and instantaneous power control is performed;

[0055] Figure 6 This is a graph showing the experimental results of the modulation method of the present invention when the grid voltage drops by 10% and instantaneous power control is performed;

[0056] Figure 7 This is the experimental result of the traditional modulation method when the grid voltage drops by 30% and instantaneous power control is performed;

[0057] Figure 8 This is a diagram showing the experimental results of the modulation method of the present invention when the grid voltage drops by 30% and instantaneous power control is performed. DETAILED DESCRIPTION

[0058] The present application is described in further detail below in conjunction with the accompanying drawings. It is necessary to point out that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technicians in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0059] Example 1

[0060] like Figure 1-8 As shown, a method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof includes the following steps:

[0061] Table 1 Parameters of the rectifier system in the embodiment of the present invention

[0062]

[0063] Step S1: Separate the positive and negative sequence of the collected instantaneous value of the grid voltage to obtain And calculate the positive and negative sequence phase angle δ + , δ - , and then get

[0064] Step S2: selecting a control method based on the control target of the Vienna rectifier under grid voltage imbalance, and calculating a reference current;

[0065] The Vienna rectifier has two control objectives under grid voltage imbalance, and their reference current calculation methods are as follows:

[0066] ①Balanced current control

[0067] Keep the average input power on the AC side equal to the required power on the DC side, and the three-phase currents sinusoidal and symmetrical.

[0068]

[0069] Where, They represent the positive and negative sequence components of the reference current under the dq axis, respectively, 0,ref Indicates the required power on the DC side, Represents the positive sequence component of the grid voltage under the d-axis.

[0070] ②Instantaneous power control

[0071] Ensure that the instantaneous value of the AC side input power is equal to the required power on the DC side, and the three-phase current is sinusoidal but asymmetrical.

[0072]

[0073] Where, Represents the negative sequence component of the grid voltage under the d-axis.

[0074] Figure 3 The current, voltage and DC side waveform results of balanced current control are given when the grid voltage phase A suddenly drops by 30%. Figure 4 The current, voltage, and DC-side waveforms for instantaneous power control are presented when the grid voltage suddenly drops by 30% on phase A. When balanced current control is used, the three-phase currents are sinusoidal and symmetrical, but the DC-side bus voltage fluctuates. When instantaneous power control is used, the DC-side bus voltage remains almost constant, but the three-phase currents are asymmetrical.

[0075] Step S3: transform the current in the dq axis in S2 to the αβ axis, calculate the reference voltage of the Vienna rectifier in the αβ axis, and transform it to the ABC axis system;

[0076] Convert the current under the dq axis in step S2 to the αβ axis:

[0077]

[0078] Where, δ + , δ - Represent the instantaneous phase angles of the positive and negative sequence components of the grid voltage respectively.

[0079] According to the following formula, the reference voltage of the rectifier under the αβ axis is calculated:

[0080]

[0081] Where, e α 、e β are the components of the grid voltage under the α and β axes, L is the inductance, which is 5mH in this example, and Ts is the sampling period, take 0.1ms, Δu α and Δu β They are the components of the inductor voltage drop under the α and β axes respectively.

[0082] Transform it to the ABC axis system:

[0083]

[0084] Step S4: Sort the instantaneous values ​​of the reference voltage to obtain the max phase, mid phase, and min phase of the reference voltage, and the max phase, mid phase, and min phase of the current follow the voltage sorting result;

[0085] The ranking formula for reference voltage is:

[0086]

[0087] Step S5: According to u max 、u mid 、u min and i mid The relationship between them is analyzed, the area where the reference voltage is located is analyzed, and the modulation voltage is calculated using the synthesis method with the minimum synthesis error.

[0088] ①If u mid i mid ≥0, it is in the non-current zero-crossing region, then the modulation voltage is:

[0089]

[0090] ②If u mid >0,i mid <0 and u mid -u min <0.5u dc or u mid <0,i mid >0 and u max -u mid >0.5u dc , at this time it is in the current zero-crossing distortion region, but the DPWM method can be used to completely eliminate the current zero-crossing distortion, and its modulation voltage should be:

[0091]

[0092] ③If u mid >0,i mid <0 and u mid -u min >0.5u dc or u mid <0,i mid >0 and u max -umid >0.5u dc At this time, the vertical foot approximate synthesis method is used in the current zero-crossing distortion area to alleviate the current zero-crossing distortion problem, where:

[0093] If u mid >0,i mid <0 and u mid -u min >0.5u dc , the modulation voltage should be:

[0094]

[0095] If u mid <0,i mid >0 and u max -u mid >0.5u dc , the modulation voltage should be:

[0096]

[0097] picture Figure 5 and Figure 6 The results of the traditional modulation method and the modulation method of the present invention are respectively given when the A-phase grid voltage drops by 10% and instantaneous power control is adopted. Figure 7 and Figure 8 The results of the traditional modulation method and the modulation method of the present invention are given respectively when the A phase grid voltage drops by 30% and instantaneous power control is adopted. Figure 5 and Figure 6 、 Figure 7 and Figure 8 It can be seen that when the grid voltage is unbalanced, the modulation method of the present invention can reduce the degree of current zero-crossing distortion and significantly improve the THD of the current. The deeper the grid voltage drops, the more obvious the improvement effect is.

[0098] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof, characterized in that: The following steps are involved: S1: Collect the instantaneous value of the grid voltage to separate the positive and negative sequences, calculate the positive and negative sequence phase angles, and then obtain the positive and negative sequence components e of the grid voltage under the d axis. + d 、e - d ; S2: Based on the positive and negative sequence components e of the grid voltage on the d axis + d 、e - d Calculate the reference current of Vienna rectifier under grid voltage imbalance; S3: Calculating a reference voltage of the Vienna rectifier in the ABC axis system according to the reference current; S4: sorting the instantaneous values ​​of the reference voltage to obtain the max phase, mid phase and min phase of the reference voltage, the max phase, mid phase and min phase of the reference current correspond to the reference voltage sorting result, and then obtaining the mid phase of the reference current; S5: Analyze the region where the reference voltage is located based on the relationship between the max phase, mid phase, and min phase of the reference voltage and the mid phase of the reference current, determine whether the current zero crossing point is distorted, and calculate the modulation voltage using a synthesis method with minimal synthesis error.

2. The method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof according to claim 1, characterized in that: The step S1 specifically includes the following steps: S101: collecting instantaneous voltage value of the power grid; S102: Separating the positive and negative sequence of the instantaneous voltage value to obtain the positive and negative sequence components of the instantaneous voltage value under the αβ axis S103: According to the positive and negative sequence components of the instantaneous voltage value under the αβ axis Calculate the instantaneous phase angle δ of the positive and negative sequence components of the grid voltage + , δ - ; S104: According to the instantaneous phase angle δ of the positive and negative sequence components of the grid voltage + , δ - Calculate the positive and negative sequence components of the grid voltage under the d-axis 3. The method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof according to claim 2, characterized in that: The step S2 specifically includes the following contents: Based on the Vienna rectifier, a balanced current control method is used under unbalanced grid voltage, and the reference current is calculated: Keep the average input power on the AC side equal to the required power on the DC side, and the three-phase currents sinusoidal and symmetrical. The reference current calculation formula is as follows: Where, They represent the positive and negative sequence components of the reference current under the dq axis, respectively, 0,ref Indicates the required power on the DC side.

4. The method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof according to claim 3, characterized in that: The step S2 specifically includes the following contents: Based on the Vienna rectifier, the instantaneous power control method is used under the condition of unbalanced grid voltage, and the reference current is calculated: Ensure that the instantaneous value of the AC side input power is equal to the required power on the DC side. The three-phase current is sinusoidal but asymmetrical. The reference current calculation formula is as follows:

5. A method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof according to any one of claims 3 or 4, characterized in that: The step S3 specifically includes the following steps: S301: Convert the reference current under the dq axis to the αβ axis to obtain the reference current under the αβ axis. The formula is as follows: i α,ref 、i β,ref They represent the positive and negative sequence components of the reference current under the α and β axes respectively; S302: Calculate the reference voltage of the Vienna rectifier under the αβ axis according to the reference current under the αβ axis. The calculation formula is as follows: Where, e α 、e β are the components of the grid voltage under the αβ axis, i α 、i β are the current components in the α and β axes, L is the inductance, T s is the sampling period, Δu α and Δu β are the components of the inductor voltage drop under the α and β axes respectively; S303: Convert the reference voltage under the αβ axis to the ABC axis system. The calculation formula is as follows:

6. The method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof according to claim 5, characterized in that: The formula for sorting the instantaneous values ​​of the reference voltages in step S4 is as follows: Where u max 、u mid 、u min They are the max phase, mid phase and min phase of the reference voltage respectively.

7. The method for controlling a Vienna rectifier and suppressing current zero-crossing distortion thereof according to claim 6, characterized in that: The step S5 specifically includes the following: according to the relationship between the max phase, mid phase, min phase of the reference voltage and the mid phase of the reference current: ①If u mid i mid ≥0, where i mid is the mid phase of the reference current, which is in the non-current zero-crossing region. The modulation voltage is: ②If u mid >0,i mid <0 and u mid -u min <0.5u dc or u mid <0,i mid >0 and u max -u mid >0.5u dc , at this time it is in the current zero-crossing distortion area, but the DPWM modulation method can be used to completely eliminate the current zero-crossing distortion, and its modulation voltage should be: ③If u mid >0,i mid <0 and u mid -u min >0.5u dc or u mid <0,i mid >0 and u max -u mid >0.5u dc At this time, the vertical foot approximate synthesis method is used in the current zero-crossing distortion area to alleviate the current zero-crossing distortion problem, where: If u mid >0,i mid <0 and u mid -u min >0.5u dc , the modulation voltage should be: If u mid <0,i mid >0 and u max -u mid >0.5u dc , the modulation voltage should be: u dc is the DC bus voltage.

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