Control method for improving harmonic power grid input adaptability of Vienna rectifier

Abstract

The invention relates to the technical field of Vienna rectifiers, in particular to a control method for improving harmonic power grid input adaptability of a Vienna rectifier, which comprises the following steps of: performing coordinate transformation on acquired three-phase power grid voltage and input current to obtain voltage and current signals under a fundamental wave rotating coordinate system, extracting a fundamental wave current error signal, and calculating the harmonic power grid input adaptability of the Vienna rectifier; the method comprises the following steps: acquiring a current error component of each harmonic, converting the current error component into a rotating coordinate system corresponding to each specified harmonic to obtain the current error component of each harmonic, and in each harmonic rotating coordinate system, independently controlling the current error component of the corresponding harmonic by adopting a proportional-integral controller to generate a control voltage component of each harmonic; inversely transforming the control voltage component of each harmonic to a fundamental wave rotating coordinate system, and superposing to form a total harmonic compensation voltage; according to the invention, by adopting the control method of combining the self-adaptive loop parameters with the bus lifting strategy, the adaptability of the input current of the rectifier along with the power grid voltage under the harmonic power grid voltage is enhanced, so that the problem of overcurrent of the rectifier under different working conditions is avoided.

Description

Technical Field

[0001] This invention relates to the field of Vienna rectifier technology, specifically to a control method for improving the adaptability of Vienna rectifiers to harmonic grid input. Background Technology

[0002] Vienna rectifiers, benefiting from high power density, high efficiency, low cost, and low device stress, have become the core topology in the field of high-efficiency, high-power charging for electric vehicles. For charging applications with complex operating conditions, such as mining plants and heavy-duty truck charging stations, the input grid voltage contains a large number of harmonics. This places more stringent requirements on the input adaptability of Vienna rectifiers, specifically including good input current following the input voltage, no full-power overcurrent problems caused by abnormal spikes, and total harmonic distortion (THDi) of the input current meeting grid-connected equipment standards. The switching state of each phase arm of the Vienna rectifier is constrained by the current direction, resulting in an asymmetric modulation function, and the input current is easily affected by midpoint potential fluctuations. To improve the input characteristics of the rectifier, in addition to adjusting loop parameters to improve the system bandwidth and margin, a traditional method is to connect a resonant (PR) controller in parallel with a proportional-integral (PI) current controller. This method has high gain at specific rotating harmonics. However, traditional methods are difficult to handle the complex harmonic problems of Vienna rectifiers, have limited harmonic suppression capabilities, and have a significant impact on the phase margin of the system after grid harmonics. In addition, the resonant controller has a large computational load and high requirements for the performance of the control chip. Therefore, a control method that improves the adaptability of Vienna rectifiers to harmonic grid input is needed to address the above problems. Summary of the Invention

[0003] To address the problems of limited suppression effect, negative impact on system stability, heavy computational burden, inability of fixed loop parameters and bus input to adapt to wide-range harmonic power grids, and poor system adaptability of traditional resonant controllers, this invention provides a control method to improve the harmonic power grid input adaptability of Vienna rectifiers, thereby solving the above problems.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A control method for improving the harmonic grid input adaptability of a Vienna rectifier includes the following steps: S1: Signal Acquisition and Coordinate Transformation Real-time sampling of three-phase power grid voltage , , and three-phase input current , , Phase-locked loop (PLL) is used to extract the grid phase θ from the grid voltage. gThe three-phase current is converted to a dq coordinate system that rotates synchronously with the fundamental frequency of the power grid to obtain the feedback current i. gd and i gq， Simultaneously, the three-phase voltages are also transformed to the dq coordinate system to obtain the grid voltage component e. gd With e gq .

[0005] S2: Harmonic Extraction and Independent Coordinate System Transformation: Calculate the error e between the fundamental current setpoint and the feedback current. d1 and e q1 The fundamental error signal is transformed into the rotating coordinate system corresponding to the specified harmonics (such as the 5th and 7th harmonics) that need to be suppressed by a specific rotating coordinate transformation matrix. The transformation matrix for converting the fundamental current error signal to the 5th harmonic rotating coordinate system is: ; Wherein: the transformation matrix for converting the fundamental current error signal to the 7th harmonic rotating coordinate system is: ; Where, θ g For the grid voltage phase, e d1 and e q1 The fundamental current error signal is transformed to obtain the error signals e in each harmonic coordinate system. d5 e q5 e d7 and e q7 .

[0006] S3: Independent harmonic PI control: In each harmonic rotating coordinate system, an independent PI controller is set up. These PI controllers are used to adjust the corresponding harmonic error signal obtained from S2, and output the control voltage component v in each harmonic coordinate system. d5 v q5 v d7 and v q7 .

[0007] S4: Inverse coordinate transformation and feedforward superposition: The control voltage components in each harmonic coordinate system are transformed back to the fundamental dq coordinate system using the corresponding inverse transformation matrix, where: 5th harmonic control quantity inverse transformation matrix : ; 7th harmonic control quantity inverse transformation matrix : ; The harmonic compensation voltages obtained after inverse transformation, , and When superimposed in the fundamental coordinate system, a total harmonic compensation voltage is formed.

[0008] S5: Composite feedforward compensation: To improve the dynamic response of the current loop and further suppress harmonics, a composite feedforward circuit is introduced, which includes: 1) Grid voltage fundamental frequency feedforward: directly add e gd With e gq。

[0009] 2) Grid voltage differential feedforward: Incorporating the first-order differential term of the grid voltage d-axis component. A feedforward circuit is formed for compensation, where k1 is the compensation coefficient used to suppress mid-frequency oscillations.

[0010] 3) The total harmonic compensation voltage obtained from S4 is added as a feedforward quantity. These feedforward quantities are added to the output of the fundamental current PI controller to form the final output modulation voltage of the current loop.

[0011] S6: Adaptive loop parameter adjustment: Based on the real-time detected bus voltage u dc And the grid voltage harmonic distortion rate, dynamically adjust the proportional coefficient k of the inner loop PI controller of the current. pi Integral coefficient k ii And the modulation ratio m of space vector modulation (SVPWM), when the harmonic content increases, k should be appropriately increased. pi k ii And m, to broaden the system loop bandwidth and ensure that the input current can still quickly and accurately follow the voltage under distorted power grid conditions.

[0012] S7: Dynamic bus voltage setting strategy: The bus voltage setpoint V is dynamically adjusted based on the actual peak value of the input grid voltage. dcref In operating conditions with severe harmonics, actively raising V dcref This ensures that the Vienna rectifier always operates within the effective boost range, avoiding intermittent input current and overcurrent problems caused by excessively low bus voltage.

[0013] As a further preferred embodiment of the present invention: based on the basic idea of ​​independent harmonic control, the control method can be further modified, that is, by adding parallel 11th and 13th harmonic controllers, or other designated harmonic controllers, to the 5th and 7th harmonic controllers. The transformation matrix used is shown in the following formula: ; ; ; .

[0014] Compared with the prior art, the present invention has the following beneficial effects: This invention enhances the adaptability of the rectifier's input current to follow the grid voltage under harmonic grid voltage by adopting a control method that combines adaptive loop parameters with a bus-raising strategy, thus preventing overcurrent problems in different operating conditions. This invention significantly reduces the harmonic content of the input current of the rectifier under harmonic grid voltage by employing an independent decoupled harmonic controller combined with a control method that compensates for the first-order differential element of the grid voltage, thereby reducing harmonic pollution to the grid. This invention uses only a traditional PI controller, eliminating the need for a complex resonant controller and its multi-frequency parallel structure. This significantly reduces the computational load of the digital controller, lowers the performance requirements of the microprocessor, and helps reduce costs and power consumption. Attached Figure Description

[0015] Figure 1 This is a diagram of the Vienna rectifier topology. Figure 2 This is a traditional control structure block diagram; Figure 3 The simulation waveforms are for traditional control methods. Figure 4 This is a structural block diagram of the novel control method; Figure 5 The simulation waveforms for the novel control method are shown below. Figure 6 A comparison chart of measured input voltage and current under harmonic power grid conditions; Figure 7 A comparison chart of measured input voltage and current under weak power grid conditions; Figure 8 Comparison of measured input current spectrum under harmonic power grid conditions; Figure 9 This is a topology diagram of a three-phase half-bridge rectifier. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] Example 1: Please refer to Figure 1-8The control method shown here for improving the harmonic grid input adaptability of a Vienna rectifier includes the following steps: S1: Signal Acquisition and Coordinate Transformation Real-time sampling of three-phase power grid voltage , , and three-phase input current , , Phase-locked loop (PLL) is used to extract the grid phase θ from the grid voltage. g The three-phase current is converted to a dq coordinate system that rotates synchronously with the fundamental frequency of the power grid to obtain the feedback current i. gd and i gq， Simultaneously, the three-phase voltages are also transformed to the dq coordinate system to obtain the grid voltage component e. gd With e gq .

[0018] In the above embodiments, such as Figure 1 As shown, from left to right, the topology consists of three-phase AC grid voltages Va to Vc; input filter inductors L1 to L3, with a filter inductance value of L. f Input filter capacitors C3~C5; D1~D6 are a three-phase half-bridge composed of six rectifier diodes; six IGBT modules IGBT1~IGBT6 constitute a three-phase bidirectional controllable switch; output filter capacitors C1 and C2 are connected to a common midpoint O; finally, there is the load RL, and gA~gC are the three-phase drive signals of the IGBTs.

[0019] like Figure 2 As shown, the three-phase sampling voltage V is in the order from left to right. a ~V c The output grid phase θ is obtained through a phase-locked loop (PLL). g The control angle used in coordinate transformation is achieved using a voltage PI controller. To achieve V of the rectifier bus dc The control transforms the three-phase sampled input current into a right-angle (dq) transformation, which serves as the feedback quantity i in the inner loop of the dq current. gd and i gq This constitutes a high-performance voltage and current dual-loop control, in which... and These are the dq-axis current controllers, i gqref The q-axis current is given; when reactive power compensation is not considered, i gqref Zero can be given. The fundamental frequency dq-axis component e of the grid voltage. gd With e gq This is used to improve the response speed of the current loop and suppress low-order harmonics. The output of the current loop is modulated by space vector modulation (SVPWM) to obtain a modulated wave, which is then coupled with a triangular carrier wave v.saw By comparison, the drive signal g for controlling the bidirectional switch is obtained. ABC Furthermore, the midpoint potential of the Vienna rectifier is controlled by zero-sequence voltage injection, where G... PI_mid It is a midpoint potential PI controller.

[0020] To suppress input current harmonics, conventional control systems connect a quasi-resonant (QPR) controller in parallel with the current PI controller. Its transfer function is shown in the following equation, where k... r It is the resonant gain that determines the peak gain at the resonant frequency ω0; ω c The cutoff frequency determines the bandwidth of the resonant peak. Since the 5th and 7th harmonics account for a large portion of the input current harmonics, they are used as examples here. The rotation frequencies of the 5th and 7th harmonics in the fundamental dq coordinate system are both the 6th grid frequency, but their rotation directions are opposite. Therefore, a 6th PR controller can be used to suppress the 5th and 7th harmonics. However, the current path and voltage output of the Vienna rectifier strongly depend on the current direction. The state of each phase arm is determined by the sign of the current in that phase and the on / off state of the switching transistor. This strong nonlinearity limits the effectiveness of the PR controller in controlling harmonics in the dq coordinate system of the Vienna rectifier. In addition, considering issues such as digital control delay, PR control is prone to insufficient phase margin. ; Traditional control methods use fixed loop parameters. However, when harmonics are present in the power grid, the loop needs to provide sufficient bandwidth. Simply adjusting the loop parameters can easily lead to system divergence, causing current spikes and triggering overcurrent. Furthermore, when the harmonic content of the Vienna rectifier's input voltage increases, the uncontrolled rectifier bus may be significantly higher than the uncontrolled rectifier bus value under sinusoidal power grid input. Traditional bus control methods do not consider this issue, making it highly susceptible to intermittent input current under low bus control conditions, which can also cause overcurrent problems.

[0021] like Figure 3 As shown, 40% fifth harmonic and 40% seventh harmonic were injected into the three-phase grid voltage, with phase offsets of -25° and 35° respectively. The input grid voltage was 220V, the bus voltage was 750V, and the input power was 28kW. It was observed that when the grid voltage contained a high content of harmonics, the input current contained a large number of harmonics, and the current exhibited abnormal spikes and severe waveform distortion. The input current THDi = 19.85%. Furthermore, through... Figure 3 It was also observed that the bus capacitor voltage fluctuated violently, which led to the bus capacitor overheating. This is because the loop parameters of the traditional control method are fixed, the bandwidth provided by the loop is limited, and the resonant controller has limited suppression of input harmonics in the strongly coupled Vienna topology.

[0022] S2: Harmonic Extraction and Independent Coordinate System Transformation: Calculate the error e between the fundamental current setpoint and the feedback current. d1 and e q1 The fundamental error signal is transformed into the rotating coordinate system corresponding to the specified harmonics (such as the 5th and 7th harmonics) that need to be suppressed by a specific rotating coordinate transformation matrix. The transformation matrix for converting the fundamental current error signal to the 5th harmonic rotating coordinate system is: ; Wherein: the transformation matrix for converting the fundamental current error signal to the 7th harmonic rotating coordinate system is: ; Where, θ g For the grid voltage phase, e d1 and e q1 The fundamental current error signal is transformed to obtain the error signals e in each harmonic coordinate system. d5 e q5 e d7 and e q7 .

[0023] S3: Independent harmonic PI control: In each harmonic rotating coordinate system, an independent PI controller is set up. These PI controllers are used to adjust the corresponding harmonic error signal obtained from S2, and output the control voltage component v in each harmonic coordinate system. d5 v q5 v d7 and v q7 .

[0024] S4: Inverse coordinate transformation and feedforward superposition: The control voltage components in each harmonic coordinate system are transformed back to the fundamental dq coordinate system using the corresponding inverse transformation matrix, where: 5th harmonic control quantity inverse transformation matrix : ; 7th harmonic control quantity inverse transformation matrix : ; The harmonic compensation voltages obtained after inverse transformation , , and When superimposed in the fundamental coordinate system, a total harmonic compensation voltage is formed.

[0025] S5: Composite feedforward compensation: To improve the dynamic response of the current loop and further suppress harmonics, a composite feedforward circuit is introduced, which includes: 4) Grid voltage fundamental frequency feedforward: directly add e gd With e gq 5) Grid voltage differential feedforward: Incorporating the first-order differential term of the grid voltage d-axis component. A feedforward circuit is formed for compensation, where k1 is the compensation coefficient used to suppress mid-frequency oscillations.

[0026] 6) The total harmonic compensation voltage obtained from S4 is added as a feedforward quantity. These feedforward quantities are added to the output of the fundamental current PI controller to form the final output modulation voltage of the current loop.

[0027] S6: Adaptive loop parameter adjustment: Based on the real-time detected bus voltage u dc And the grid voltage harmonic distortion rate, dynamically adjust the proportional coefficient k of the inner loop PI controller of the current. pi Integral coefficient k ii And the modulation ratio m of space vector modulation (SVPWM), when the harmonic content increases, k should be appropriately increased. pi k ii And m, to broaden the system loop bandwidth and ensure that the input current can still quickly and accurately follow the voltage under distorted power grid conditions.

[0028] S7: Dynamic bus voltage setting strategy: The bus voltage setpoint V is dynamically adjusted based on the actual peak value of the input grid voltage. dcref In operating conditions with severe harmonics, actively raising V dcref This ensures that the Vienna rectifier always operates within the effective boost range, avoiding intermittent input current and overcurrent problems caused by excessively low bus voltage.

[0029] In the above embodiments: like Figure 5 As shown, the three-phase grid voltage waveform and operating conditions remain consistent with those described above. It was observed that even with high grid voltage harmonic content, the input current harmonics were significantly suppressed, and no current spikes were observed. The input current THDi = 3.85%, indicating that the new control method effectively improves loop margin and bandwidth, and is more effective at suppressing specific harmonics of the grid current, significantly enhancing the input current adaptability of the Vienna rectifier under harmonic grid conditions. Furthermore, the new control method uses only a PI controller, reducing the computational load on the control chip. Additionally, if the grid harmonic composition is complex, controllers for corresponding harmonic orders can be connected in parallel to further improve the system's harmonic grid adaptability.

[0030] like Figure 6As shown in the figure, the yellow curve represents the grid voltage, the green curve represents the input current, (a) represents the traditional control method, and (b) represents the new control method. Figure 6 In the experiment, the Vienna rectifier had an input voltage of 220V, a bus setpoint of 600V, and an input power of 40kW. The input voltage waveform simulated an actual mining charging station under a harmonic grid. It was observed that under a lower bus setpoint, the measured waveform under the traditional control method exhibited discontinuous input current and abnormal spikes, eventually triggering overcurrent. This was partly due to the lower uncontrolled rectifier bus in the harmonic grid compared to the sinusoidal input, and partly due to the fixed loop parameters of the traditional control method, which could not provide sufficient bandwidth under these conditions, leading to system divergence. Comparing the measured results of the new control method under the same conditions, it was observed that the input current followed the input voltage better, and the system could stably output maximum power. This indicates that the adaptive loop parameters and bus-raising strategy of the new control method significantly improve the harmonic grid voltage adaptability of the Vienna rectifier.

[0031] exist Figure 7 and Figure 8 In the diagram (the pink curve represents the grid voltage and the yellow curve represents the input current), (a) represents the traditional control method, and (b) indicates the new control method: Figure 7 and Figure 8 The measured spectrum comparisons of input voltage and current under weak grid conditions are given, as well as the corresponding measured spectrum comparison of input current. The input voltage of the Vienna rectifier is 220V, the bus setpoint is 600V, the input power is 40kW, and the input grid simulates the actual weak grid operating conditions.

[0032] It was observed that the input current under the traditional control method exhibits a large number of low-order harmonics and mid-frequency oscillations, with the input voltage also oscillating accordingly. This is due to the strong coupling characteristics of the Vienna rectifier and the complexity of the input current harmonic composition. The low-order harmonic suppression effect of the resonant controller in the traditional control method is limited. Furthermore, since the first-order differential of the grid voltage is not considered, the mid-frequency current oscillations also significantly affect the input current quality. In contrast, the new control method significantly suppresses the low-order harmonics of the input current, and the mid-frequency current oscillation problem is also well suppressed. Comparing the current spectrum, it can be seen that the new control method can significantly reduce the content of odd-order harmonics in the low-order harmonics, but the even-order harmonics increase slightly. This can be solved by subsequently connecting a PI controller of a specified order in parallel. In summary, the new control method can effectively suppress the low-order and mid-frequency current harmonics of the Vienna rectifier, and has low computational complexity, making it widely applicable.

[0033] Example 2: Further optimization of the control method for improving the adaptability of Vienna rectifier to harmonic grid input proposed in Embodiment 1 above includes extension to suppress 11th and 13th harmonics: For the 11th and 13th harmonics that may exist in the grid, the architecture of Embodiment 1 can be extended completely, only requiring the addition of corresponding transformation and inverse transformation matrices, as well as independent PI controllers.

[0034] 11th harmonic transformation matrix: ; Inverse transformation matrix: ; 13th harmonic (represented as +12th rotation in the fundamental dq system) transformation matrix: ; Inverse transformation matrix: ; After inversely transforming the control values ​​of these two channels, they can be added together to the composite feedforward compensation in S4 of Example 1.

[0035] Further supplementary explanations based on the above two embodiments, such as Figure 9 The three-phase half-bridge rectifier shown also includes an inner current loop and an outer voltage loop in its control structure. Applying the control method described in the above embodiments to this topology can also significantly improve its input current quality and system stability under harmonic power grids.

[0036] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A control method for improving the harmonic grid input adaptability of a Vienna rectifier, characterized in that, Includes the following steps: S1: Perform coordinate transformation on the collected three-phase grid voltage and three-phase input current to obtain the voltage and current in the fundamental rotating coordinate system. Current signal; S2: Extract the fundamental current error signal and convert it to the rotating coordinate system corresponding to each specified harmonic to obtain the current error components of each harmonic; S3: In each harmonic rotating coordinate system, a proportional-integral controller is used to independently control the corresponding harmonic current error components, generating the control voltage components of each harmonic. S4: Transform the control voltage components of each harmonic back to the fundamental rotating coordinate system and superimpose them to form the total harmonic compensation voltage. S5: Feed the total harmonic compensation voltage to the current loop output, and combine it with the fundamental component of the grid voltage and its first-order differential term to perform composite feedforward compensation, generating the final modulation signal. S6: Based on the real-time detected harmonic content of the grid voltage, adaptively adjust the proportional coefficient, integral coefficient, and modulation ratio parameters of the current loop controller; S7: Dynamically adjust the bus voltage setpoint according to the peak voltage or harmonic content of the power grid to ensure that the rectifier operates in boost mode.

2. The control method for improving the harmonic grid input adaptability of a Vienna rectifier according to claim 1, characterized in that, The specified subharmonics include at least the 5th and 7th harmonics; The transformation matrix for converting the fundamental current error signal to the 5th harmonic rotating coordinate system is: ； Wherein: the transformation matrix for converting the fundamental current error signal to the 7th harmonic rotating coordinate system is: ； Where, θ g For the grid voltage phase, e d1 and e q1 For the fundamental current error signal; e d5 e q5 e d7 and e q7 These are the 5th and 7th harmonic current error signals, respectively.

3. The control method for improving the harmonic grid input adaptability of a Vienna rectifier according to claim 2, characterized in that, The transformation matrix for inversely transforming the 5th harmonic control voltage component back to the fundamental coordinate system is: ； The transformation matrix for inversely transforming the 7th harmonic control voltage component back to the fundamental coordinate system is: ； v d5 v q5 v d7 and v q7 The outputs of the PI controller are shown in the 5th and 7th harmonic coordinate systems, respectively.

4. The control method for improving the harmonic grid input adaptability of a Vienna rectifier according to claim 1, characterized in that, The composite feedforward compensation includes: the dq-axis component of the grid voltage fundamental wave e gd With e gq The feedforward and the first-order differential element of the d-axis component of the grid voltage fundamental. A feedforward loop is formed for compensation, where k1 is the compensation coefficient.

5. The control method for improving the harmonic grid input adaptability of a Vienna rectifier according to claim 1, characterized in that, The specific method for adaptively adjusting the current loop controller parameters is as follows: based on the real-time bus voltage u... dc Adaptively adjust the current loop ratio k to the grid voltage harmonic distortion rate. pi and integral coefficient k ii And adjust the modulation ratio parameter m of space vector modulation accordingly to broaden the system loop bandwidth.

6. The control method for improving the harmonic grid input adaptability of a Vienna rectifier according to claim 1, characterized in that, The dynamic adjustment of the bus voltage setpoint V dcref The specific method is as follows: using the peak value of the current input grid voltage as the minimum reference value of the uncontrolled rectifier bus voltage, and raising V when the harmonic content is high. dcref This ensures that the Vienna rectifier is always in an effective boosting state, avoiding intermittent input current.

7. A control method for improving the harmonic grid input adaptability of a Vienna rectifier according to any one of claims 1-6, characterized in that, The method further includes: on the basis of the 5th and 7th harmonic controllers, an independent decoupling controller for higher harmonics is connected in parallel, the higher harmonics including the 11th and 13th harmonics, and the corresponding transformation and inverse transformation matrices are constructed according to the relationship between the harmonic order and the frequency of the fundamental wave.

8. The control method for improving the adaptability of a Vienna rectifier to harmonic grid input according to claim 7, characterized in that, For the 11th and 13th harmonics, their transformation matrices are as follows: ； ； The corresponding inverse transformation matrices are as follows: ； 。

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