A control method for a front-stage Vienna rectifier of a charging pile

Abstract

The present invention provides a control method for a charging pile front-stage Vienna rectifier, the control method comprising: first, detecting the input voltage uin of the Vienna rectifier, obtaining the components ud and uq of uin in the dq coordinate system through dq transformation, and then passing ud and uq through a high-pass filter to obtain respective harmonic components udh and uqh; second, multiplying udh and uqh by the control gain of the Vienna rectifier to obtain the components idh and iqh of the harmonic current in the dq coordinate system; third, injecting idh and iqh into the current inner loop setting respectively, and reshaping the closed-loop input harmonic impedance of the Vienna rectifier. The present invention is used to solve the problem of background harmonic resonance amplification that may be caused by the parasitic inductance and parasitic capacitance of the transmission cable, and can effectively improve the power quality of the grid-side current and input voltage of the Vienna rectifier while ensuring the normal and stable operation of the front-stage Vienna rectifier of the electric vehicle charging pile, and has strong engineering practicality.

Description

Technical Field

[0001] The invention belongs to the technical field of electric vehicle charging piles, and in particular relates to a control method for a front-stage Vienna rectifier of a charging pile. Background Art

[0002] With the rapid development of social economy, green and low-carbon energy has attracted more and more attention from people. At present, my country's new energy vehicles are showing a trend of rapid growth. While electric vehicles are developing rapidly, the electric vehicle charging piles that match electric vehicles have also developed rapidly. With the continuous expansion of the construction scale of electric vehicle charging piles, the interaction between the front-stage rectifier circuit of electric vehicle charging piles and the power grid has become more and more obvious.

[0003] Since a single-stage AC / DC converter cannot meet the wide range of voltage output, DC electric vehicle charging piles usually adopt the structure of AC / DC converter cascade DC / DC converter. The front-stage AC / DC converter realizes the rectification function, converting the AC power of the power grid into stable DC power while realizing the unity power factor operation of the system and minimizing the pollution of the converter to the power grid. As a three-level power factor correction circuit, the Vienna rectifier has the advantages of a small number of required switching tubes, low cost, simple structure, low input current harmonic content, high power density, and high system reliability. Therefore, it has been widely used in the field of electric vehicle charging piles.

[0004] Common control strategies for Vienna rectifiers include dual closed-loop control, single cycle control and sliding film variable structure control based on the dq coordinate system. The dual closed-loop control strategy for Vienna rectifiers based on the dq coordinate system has been widely used in engineering due to its simplicity and ease of implementation. Its advantage is that it converts the AC time-varying signal in the abc three-phase stationary coordinate system into a DC signal in the dq two-phase rotating coordinate system, and only requires a PI regulator to achieve zero-static tracking of the Vienna rectifier input current.

[0005] However, due to the decentralized spatial layout of electric vehicle charging piles, the power grid usually needs to access the charging piles via transmission cables of different lengths. When the Vienna rectifier adopts the traditional double closed-loop control strategy based on the dq coordinate system and the parasitic inductance and capacitance of the transmission cable cannot be ignored, the low-frequency background harmonics in the distribution network may produce more serious harmonic resonance amplification after passing through the transmission cable, which will not only cause the Vienna rectifier input voltage to increase and even cause system instability, but also seriously affect the power quality of the grid-side current of the Vienna rectifier, making it fail to meet the harmonic distortion standard of the grid-side current.

[0006] To solve the above problems, this paper optimizes the traditional dual closed-loop control method of Vienna rectifier based on dq coordinate system and proposes a control method of Vienna rectifier in the front stage of charging pile. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a control method for a charging pile front-stage Vienna rectifier, which can effectively suppress the harmonic resonance amplification problem caused by the parasitic inductance and parasitic capacitance of the transmission cable while ensuring the normal and stable operation of the electric vehicle charging pile front-stage Vienna rectifier, and improve the power quality of the Vienna rectifier grid-side current and input voltage, and has strong engineering practicality.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A control method for a charging pile front-stage Vienna rectifier, wherein the charging pile front-stage Vienna rectifier adopts a control method based on an output voltage outer loop and an input current inner loop in a dq coordinate system, and extracts the Vienna rectifier input voltage u according to the instantaneous reactive power. in Harmonic component u in dq coordinate system dh and u qh , and then multiply it by the Vienna rectifier control gain to obtain the component i of the Vienna rectifier harmonic current in the dq coordinate system dh and i qh , and then i dh and i qh They are injected into the current inner loop setting respectively to reshape the closed-loop input impedance of the Vienna rectifier.

[0010] A charging pile front-stage Vienna rectifier control method comprises the following steps:

[0011] (1) Detect the input voltage u of the Vienna rectifier in , after dq transformation, we get u in The component u in the dq coordinate system d and u q , then u d and u q After high-pass filtering, the respective harmonic components u are obtained dh and u qh ;

[0012] (2) will u dh and u qh Multiply them by the Vienna rectifier control gain to get the harmonic current component i in the dq coordinate system dh and i qh ;

[0013] (3) Change i dh and i qh They are injected into the current inner loop setting respectively to reshape the closed-loop input harmonic impedance of the Vienna rectifier.

[0014] A further improvement of the technical method of the present invention is that in step (1)

[0015] A. Input voltage u to Vienna rectifier in Sampling and phase locking are performed to obtain the phase ωt, using a single synchronous reference frame for software phase locked loop (SSRF_SPLL) suitable for grid voltage balance;

[0016] B. Perform sine and cosine function calculations on the obtained phase ωt to obtain sin(ωt) and cos(ωt), and provide phase signals for dq transformation and dq inverse transformation, where the expressions of dq transformation and dq inverse transformation are as follows:

[0017]

[0018] C. The three-phase current u containing fundamental and harmonic components a 、u b 、u c After dq transformation, we get u d 、u q , and then extract the respective harmonic components u through a high-pass filter (HPF) dh 、u qh .

[0019] A further improvement of the technical method of the present invention is that in step (2), u dh and u qh Multiply them by the Vienna rectifier control gain to get the harmonic component i of the Vienna rectifier current in the dq coordinate system dh and i qh , and obtain the harmonic compensation current i dh and i qh The calculation formula is:

[0020]

[0021] Among them, u dh and u qh is the harmonic component of the Vienna rectifier input voltage; Z v_ch k is the closed-loop input harmonic impedance of the Vienna rectifier; v is the control gain of the Vienna rectifier, and its corresponding value is the inverse of the characteristic impedance of the transmission cable, k v =1 / Z c .

[0022] A further improvement of the technical method of the present invention is that in step (3), i dh and i qh Injected into the given current inner loop of the Vienna rectifier control strategy, the purpose of reshaping the closed-loop input harmonic impedance of the Vienna rectifier is achieved, so that the new given current inner loop is obtained as follows:

[0023]

[0024] Among them, i d * is the command current of the current inner loop obtained after the DC voltage outer loop passes through the PI regulator; i d1 * is the d-axis component of the inner current loop after adding the harmonic component; i q1 * It is given by the q-axis component of the inner current loop after adding the harmonic component.

[0025] Due to the adoption of the above control method, the technical effects achieved by the present invention are as follows:

[0026] The control method of the present invention not only ensures the normal and stable operation of the front-stage Vienna rectifier of the electric vehicle charging pile, but also can effectively suppress the background harmonic resonance amplification of the distribution network caused by the parasitic inductance and parasitic capacitance of the transmission cable, thereby improving the power quality of the input voltage.

[0027] The control method of the present invention can improve the power quality of the grid-side current of the front-stage Vienna rectifier of the electric vehicle charging pile, reduce the distortion degree of the grid-side current, and meet the grid-side current harmonic distortion standard.

[0028] The Vienna rectifier of the electric vehicle charging pile using the control method of the present invention only needs to be fine-tuned on the basis of the double closed-loop control method based on the dq coordinate system, without introducing more complex calculations and without increasing the burden of the controller too much. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A charging pile front-stage Vienna rectifier control method of the present invention;

[0030] Figure 2 It is a schematic diagram of the interaction between electric vehicle charging piles and the power grid;

[0031] Figure 3 It is the main circuit topology and control circuit diagram of the present invention;

[0032] Figure 4 This is the fifth harmonic voltage magnification diagram when the end of a 3km transmission cable is connected to resistors of different sizes;

[0033] Figure 5This is the seventh harmonic voltage magnification diagram when the end of a 3km transmission cable is connected to resistors of different sizes;

[0034] Figure 6 : is the Bode diagram of the closed-loop input impedance of the Vienna rectifier under the traditional control method and the control method proposed by the present invention;

[0035] Figure 7 This is a theoretical diagram of the 5th harmonic voltage magnification of the Vienna rectifier on a 3km transmission cable under the traditional control method and the control method of the present invention;

[0036] Figure 8 This is a theoretical diagram of the seventh harmonic voltage magnification of the Vienna rectifier on a 3km transmission cable under the traditional control method and the control method of the present invention;

[0037] Fig. 9 It is a simulation result diagram of the 5th harmonic voltage magnification on a 3km transmission cable using the traditional control method and the control method of the present invention for the Vienna rectifier;

[0038] Fig.10 It is a simulation result diagram of the seventh harmonic voltage magnification on a 3km transmission cable using the traditional control method and the control method of the present invention for the Vienna rectifier;

[0039] Fig.11 It is a simulation waveform diagram of the output voltage and the positive and negative bus capacitor voltages of the Vienna rectifier using the traditional control method and the control method of the present invention;

[0040] Fig.12 It is a simulation waveform diagram of input voltage and grid-side current of Vienna rectifier when the Vienna rectifier adopts the traditional control method and the control method of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below with reference to examples:

[0042] A control method for a charging pile front-stage Vienna rectifier, wherein the charging pile front-stage Vienna rectifier adopts a control method based on an output voltage outer loop and an input current inner loop in a dq coordinate system, and extracts the Vienna rectifier input voltage u according to the instantaneous reactive power. in Harmonic component u in dq coordinate system dh and u qh , and then multiply it by the Vienna rectifier control gain to obtain the component i of the Vienna rectifier harmonic current in the dq coordinate system dh and i qh , and then i dh and i qh They are injected into the current inner loop setting respectively to reshape the closed-loop input impedance of the Vienna rectifier.

[0043] like Figure 1 As shown, a charging pile front-stage Vienna rectifier control method, the control method mainly includes:

[0044] (1) Detect the input voltage u of the Vienna rectifier in , and then through dq transformation to get u in The component u in the dq coordinate system d and u q , then u d and u q After high-pass filtering, the respective harmonic components u are obtained dh and u qh ;

[0045] (2) will u dh and u qh Multiply them by the Vienna rectifier control gain to get the harmonic current component i in the dq coordinate system dh and i qh ;

[0046] (3) Change i dh and i qh They are injected into the current inner loop setting respectively to reshape the closed-loop input harmonic impedance of the Vienna rectifier.

[0047] Figure 2 is the equivalent lumped parameter model of the transmission cable and the connection position of the electric vehicle charging pile; in the figure, R0 and L0 are the parasitic resistance and parasitic inductance per unit length of the transmission cable, R0 = 0.05Ω / km, L0 = 1.98mH / km; C0 is the parasitic capacitance per unit length of the transmission cable, C0 = 25uF / km; according to the uniform transmission line theorem, the characteristic impedance Z of the transmission cable under the current parameters can be obtained c It is 8.9Ω.

[0048] Figure 3 The main circuit diagram and control circuit diagram of the scheme of the present invention are shown. The scheme is mainly based on optimizing the Vienna rectifier double closed-loop control method based on the dq coordinate system. The specific control loop is: first, let the DC side output voltage given value U o * The actual value of the DC output voltage U o After the PI regulator, the inner loop d-axis component i is obtained. d * And the extracted harmonic voltage u dh Multiply by the control gain k of the Vienna rectifier v The d-axis component i of the obtained harmonic component dh The sum is used to obtain the current inner loop given value i d1 * ,i d1* The output value obtained by subtracting the d-axis component of the input current and passing through the PI regulator is the same as the d-axis component of the input voltage U d After adding, add the q-axis component i of the inner current loop q With ωL f The output value after multiplication realizes the d Feedforward decoupling; harmonic voltage u qh Multiply by the control gain k of the Vienna rectifier v The q-axis component i of the obtained harmonic component qh As the q-axis component given value i of the current inner loop q1 * ,i q1 * The q-axis component of the input current i q The output value obtained by subtracting and passing through the PI regulator is added to the q-axis component of the input voltage, and then the q-axis component of the input current i is subtracted. q With ωL f The output value after multiplication realizes the q The decoupling values ​​of the above two steps are transformed by dq inverse transformation to obtain the three-phase modulation component e a 、e b 、e c , the three-phase modulation component e a 、e b 、e c With the positive bus capacitor voltage U c1 and negative bus capacitor voltage U c2 The output Δu obtained after the difference is passed through the PI regulator m After the difference is made, the driving signal S of the three-phase switch tube is obtained by the carrier stacking modulation method. a , S b , S c .

[0049] like Figure 4 and Figure 5 As shown in the figure, the 5th and 7th harmonic voltage oscillation amplification law on a 3km transmission cable is used as an example to illustrate. In order to better observe the amplification law of the 5th and 7th harmonics in the 3km transmission cable, the transmission cable length is taken as 3km, and the drawing range of the virtual extended transmission cable is 8km, that is, nodes 3 to 8 (dashed line part). When the impedance Z at the end of the transmission cable is L When it is a pure resistor, as Z L As the impedance Z increases, the harmonic voltages at some nodes will be effectively attenuated, while the harmonic voltages at some nodes will be amplified, which is the so-called "whack-a-mole" phenomenon. L Meet the characteristic impedance Z of the transmission cable cWhen the transmission cable is connected to a power supply, the harmonics at each node can be effectively suppressed.

[0050] Figure 6 The figure is a Bode diagram of the closed-loop input impedance of the Vienna rectifier under the traditional control method and the control method proposed by the present invention. When the traditional control method is adopted, the amplitude-frequency characteristic of the closed-loop input impedance of the Vienna rectifier is relatively large. In the range of 200 to 10kHz, the amplitude of the input impedance is about 45dB, and the corresponding actual impedance value is about 177.8Ω; when the control method proposed by the present invention is adopted, the amplitude-frequency characteristic of the closed-loop input impedance of the Vienna rectifier in the range of 200 to 10kHz is 19dB, and the corresponding amplitude is 8.9Ω, which is the amplitude of the characteristic impedance of the transmission cable, and the phase-frequency characteristic is basically 0 degrees, which is approximately a resistance characteristic, satisfying the impedance matching at the end of the transmission cable.

[0051] Figure 7 and Figure 8 The figures are respectively the theoretical diagrams of the 5th and 7th harmonic voltage magnification factors on a 3km transmission cable when the Vienna rectifier uses the traditional control method and the control method of the present invention. When the Vienna rectifier uses the traditional control method, both the 5th and 7th harmonic voltages are amplified, and the 7th harmonic voltage is amplified seriously; when the Vienna rectifier uses the control method of the present invention, the 5th and 7th harmonic voltage magnification factors are suppressed to about 1, and there is no harmonic resonance amplification phenomenon on the entire transmission cable.

[0052] Fig. 9 and Fig.10 The following are simulation results of the 5th and 7th harmonic voltage magnifications on a 3km transmission cable using the traditional control method and the control method of the present invention for the Vienna rectifier. The simulation results show that when the end of the transmission cable is connected to the Vienna rectifier, the 5th and 7th harmonics are amplified to varying degrees, and the 7th harmonic is amplified severely; when the control method of the present invention is used, the 5th and 7th harmonic voltages are effectively suppressed.

[0053] Fig.11 This is a simulation waveform diagram of the output voltage of the Vienna rectifier and the positive and negative bus capacitor voltages. There are 1.5% of the 5th and 7th harmonics at the beginning of the transmission cable, and the length of the transmission cable is 3km. The traditional control method was used before 0.2s, and the control method of the present invention was used after 0.2s. The simulation results show that compared with the traditional control method of the Vienna rectifier, the control method of the present invention effectively improves the output DC bus voltage ripple of the Vienna rectifier, and the deviation range of the positive and negative bus capacitor voltages remains basically unchanged, thereby verifying that the control method of the present invention can effectively ensure the stable output of the Vienna rectifier.

[0054] Fig.12This is a simulation waveform diagram of the Vienna rectifier input voltage and grid-side current. There are 1.5% 5th and 7th harmonics at the beginning of the transmission cable, and the length of the transmission cable is 3km. The traditional control method is used before 0.2s, and the control method of the present invention is used after 0.2s. The simulation results show that: under the control method of the present invention, the input voltage is effectively suppressed and the suppression effect is good, and the power quality of the grid-side current is also greatly improved, meeting the distortion standard of the grid-side current. It is further verified that the control method of the present invention can suppress the background harmonic voltage amplification while improving the power quality of the grid-side current and enhancing the stability of the system.

[0055] The implementation described above is only a description of the preferred implementation mode of the present invention, and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solution of the present invention by ordinary technicians in this field should fall within the protection scope determined by the claims of the present invention.

Claims

1. A charging pile front-stage Vienna rectifier control method, characterized in that: The charging pile front-stage Vienna rectifier adopts a control method based on the output voltage outer loop and input current inner loop in the dq coordinate system, and extracts the Vienna rectifier input voltage u according to the instantaneous reactive power. in Harmonic component u in dq coordinate system dh and u qh , and then multiply it by the Vienna rectifier control gain to obtain the component i of the Vienna rectifier harmonic current in the dq coordinate system dh and i qh , and then i dh and i qh Injected into the current inner loop respectively to reshape the closed-loop input impedance of the Vienna rectifier; The control method comprises the following steps: (1) Detect the input voltage u of the Vienna rectifier in , after dq transformation, we get u in The component u in the dq coordinate system d and u q , then u d and u q After high-pass filtering, the respective harmonic components u are obtained dh and u qh ; (2) will u dh and u qh Multiply them by the Vienna rectifier control gain to get the harmonic current component i in the dq coordinate system dh and i qh ; (3) Change i dh and i qh Injected into the current inner loop setting respectively to reshape the closed-loop input harmonic impedance of the Vienna rectifier; In the step (1), it specifically includes: A. Sample the input voltage of the Vienna rectifier and phase-lock it to obtain its phase ωt, using a single synchronous coordinate system software phase-locked loop suitable for grid voltage balance; B. Perform sine and cosine function calculations on the obtained phase ωt to obtain sin(ωt) and cos(ωt), and provide phase signals for dq transformation and dq inverse transformation, where the expressions of dq transformation and dq inverse transformation are as follows: C. The three-phase current u containing fundamental and harmonic components a 、u b 、u c After dq transformation, we get u d 、u q , and then extract the respective harmonic components u through high-pass filters dh 、u qh ; Step (3) specifically includes: i dh and i qh Injected into the given current inner loop of the Vienna rectifier control strategy, the purpose of reshaping the closed-loop input harmonic impedance of the Vienna rectifier is achieved, so that the new given current inner loop is obtained as follows: Among them, i d * is the command current of the current inner loop obtained after the DC voltage outer loop passes through the PI regulator; i d1 * is the d-axis component of the inner current loop after adding the harmonic component; i q1 * It is given by the q-axis component of the inner current loop after adding the harmonic component.

2. A charging pile front-stage Vienna rectifier control method according to claim 1, characterized in that: In the step (2), the steps specifically include: dh and u qh Multiply them by the Vienna rectifier control gain to get the harmonic component i of the Vienna rectifier current in the dq coordinate system dh and i qh , and obtain the harmonic compensation current i dh and i qh The calculation formula is: Among them, u dh and u qh is the harmonic component of the Vienna rectifier input voltage; Z v_ch k is the closed-loop input harmonic impedance of the Vienna rectifier; v is the control gain of the Vienna rectifier, and its corresponding value is the inverse of the characteristic impedance of the transmission cable, k v =1 / Z c .

3. A charging pile front-stage Vienna rectifier control method according to claim 1, characterized in that: The specific control loop is: First, let the DC side output voltage set value U o * The actual value of the DC output voltage U o After the PI regulator, the inner loop d-axis component i is obtained. d * And the extracted harmonic voltage u dh Multiply by the control gain k of the Vienna rectifier v The d-axis component i of the obtained harmonic component dh The sum is used to obtain the current inner loop given value i d1 * ,i d1 * The output value obtained by subtracting the d-axis component of the input current and passing through the PI regulator is the same as the d-axis component of the input voltage U d After adding, add the q-axis component i of the inner current loop q With ωL f The output value after multiplication realizes the d Feedforward decoupling; harmonic voltage u qh Multiply by the control gain k of the Vienna rectifier v The q-axis component i of the obtained harmonic component qh As the q-axis component given value i of the current inner loop q1 * ,i q1 * The q-axis component of the input current i q The output value obtained by subtracting and passing through the PI regulator is added to the q-axis component of the input voltage, and then the q-axis component of the input current i is subtracted. q With ωL f The output value after multiplication realizes the q The decoupling values ​​of the above two steps are transformed by dq inverse transformation to obtain the three-phase modulation component e a 、e b 、e c , the three-phase modulation component e a 、e b 、e c With the positive bus capacitor voltage U c1 and negative bus capacitor voltage U c2 The output Δu obtained after the difference is passed through the PI regulator m After the difference is made, the driving signal S of the three-phase switch tube is obtained by the carrier stacking modulation method. a , S b , S c .

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