阅读说明：本技术 一种静止坐标系下的复矢量电流环解耦控制装置及方法 (Complex vector current loop decoupling control device and method under static coordinate system ) 是由 吕建国 刘蕊 解艳宇 于 2021-01-18 设计创作，主要内容包括：本发明公开了一种静止坐标系下复矢量的电流环解耦控制的装置及方法。该装置包括VIENNA整流器、数字处理控制模块和驱动电路,其中数字处理控制模块包括采样单元、电压控制单元、参考电流计算单元、复矢量电流控制单元、正弦脉宽调制单元。方法为：采样单元分别采集VIENNA整流器直流侧上下电容电压、交流侧三相电流及电压；采集到的直流侧上下电容电压经过电压控制单元及参考电流生成单元得到静止坐标系下的参考电流信号；参考电流信号经过电流环解耦控制单元得到三相基波调制信号；三相基波调制信号经过正弦脉宽调制单元处理,得到脉宽调制信号,该信号通过驱动电路控制VIENNA整流器每个开关管的工作状态。本发明能够有效减小功率间的耦合,提高系统的动态性能。(The invention discloses a device and a method for decoupling control of a current loop of a complex vector under a static coordinate system. The device comprises a VIENNA rectifier, a digital processing control module and a driving circuit, wherein the digital processing control module comprises a sampling unit, a voltage control unit, a reference current calculation unit, a complex vector current control unit and a sine pulse width modulation unit. The method comprises the following steps: the sampling unit respectively collects the upper and lower capacitor voltage at the DC side of the VIENNA rectifier and the three-phase current and voltage at the AC side; the collected direct current side upper and lower capacitor voltages pass through a voltage control unit and a reference current generation unit to obtain a reference current signal under a static coordinate system; the reference current signal passes through a current loop decoupling control unit to obtain a three-phase fundamental wave modulation signal; the three-phase fundamental wave modulation signal is processed by the sine pulse width modulation unit to obtain a pulse width modulation signal, and the pulse width modulation signal controls the working state of each switching tube of the VIENNA rectifier through a driving circuit. The invention can effectively reduce the coupling between powers and improve the dynamic performance of the system.)

1. A complex vector current loop decoupling control device under a static coordinate system is characterized by comprising a VIENNA rectifier, a digital processing control module and a driving circuit, wherein the digital processing control module comprises a sampling unit, a voltage control unit, a reference current calculation unit, a complex vector current control unit and a sine pulse width modulation unit;

the sampling unit respectively collects voltage signals of an upper capacitor and a lower capacitor on the direct current side of the VIENNA rectifier, three-phase voltage signals on the alternating current side of the VIENNA rectifier and three-phase current signals on the alternating current side of the VIENNA rectifier;

the voltage control unit processes the voltage signals of the upper capacitor and the lower capacitor on the direct current side into active power reference signals;

the reference current calculation unit processes the active power reference signal and the voltage and current signals obtained after coordinate transformation into a current reference signal under a static coordinate system;

the complex vector current control unit processes the current reference signal to obtain a modulated wave signal, and the modulated wave signal is sent to the sine pulse width modulation unit;

the output end of the sine pulse width modulation unit is connected to each switching tube of each phase bridge arm in the three-level VIENNA rectifier through the driving circuit.

2. The device according to claim 1, wherein the digital processing control module is a TMS320F28377D chip and an EPM1270T chip.

3. A complex vector current loop decoupling control method under a static coordinate system is characterized by comprising the following steps:

step 1, in each switching period, a sampling unit of a digital control module respectively collects three-phase voltage e at an alternating current side_a、e_b、e_cAlternating side three-phase current i_a、i_b、i_cCapacitor voltage U on the DC side_C1And the capacitor voltage U under the DC side_C2；

Step 2, according to the signals collected in the step 1, converting alternating-current side voltage and alternating-current side current in a static abc coordinate system into a static alpha beta coordinate system through Clarke transformation, comparing direct-current side capacitor voltage with a voltage reference signal, obtaining an error signal through proportional-integral adjustment, and multiplying the error signal with the voltage reference signal to obtain an active power reference signal;

step 3, extracting a grid voltage characteristic value according to the obtained active power reference signal, and calculating a reference current to obtain a reference current i under an alpha beta coordinate system^* _α、i^* _β；

Step 4, according to the switching frequency f of the three-level VIENNA rectifier_sDetermining the delay time tau of a system_dComprises the following steps:

step 5, determining a complex vector decoupling loop according to the calculated delay time, and verifying the effectiveness of the complex vector current controller through the coupling coefficient analysis of the system;

step 6, converting the obtained current i_α、i_βComparing with reference current, and obtaining a three-phase modulation signal u through a complex vector decoupling loop and Clark inverse transformation_a、u_b、u_c；

And 7, generating a pulse width modulation signal by the three-phase modulation signal through a sine pulse width modulation unit, and controlling the work of a VIENNA rectifier switching tube through a driving circuit.

4. The complex vector current loop decoupling control method based on the static coordinate system as claimed in claim 3, wherein in step 3, according to the active power reference signal, the grid voltage characteristic value is extracted and the reference current is calculated to obtain the reference current i in the α β coordinate system^* _α、i^* _βThe method comprises the following steps:

(4.1) non-ideal grid Voltage e_a(t)、e_b(t)、e_c(t) can be decomposed into positive and negative sequence components, and the expression under the abc coordinate system is:

wherein subscripts a, b, c represent a phase a, b phase, c phase; superscript +, -respectively represents positive sequence component and negative sequence component;representing the magnitude of the positive sequence component,representing the magnitude of the negative sequence component; omega is the fundamental angular frequency of the grid voltage;

(4.2) obtaining the network side voltage e under the alpha beta coordinate system through Clark transformation_α(t)、e_β(t) is:

wherein the content of the first and second substances,represents the magnitude of the positive sequence component in the alpha beta coordinate system,representing the magnitude of the negative sequence component in the α β coordinate system.

(4.3) according to the characteristics of Clark transformation,rotates counterclockwise with an angular velocity omega relative to the alpha axis in the alpha beta coordinate system,clockwise at an angular velocity ω relative to the α axis in the α β coordinate system;is stationary relative to the fundamental positive-sequence rotational coordinate system,relative rest with the fundamental frequency negative sequence rotating coordinate system;

(4, 4) rotating the coordinate system in the positive sequence of the fundamental frequency counterclockwise with respect to the angular velocity ω of the α axis in the α β coordinate system; the fundamental frequency negative sequence rotating coordinate system rotates clockwise with an angular velocity omega relative to the alpha axis in the alpha beta coordinate system;

(4.5) definition: characteristic value of network voltageAre respectively asProjections on a d axis and a q axis in a fundamental frequency positive sequence rotating coordinate system; characteristic value of network voltageAre respectively asFor projection on d-axis and q-axis in fundamental frequency negative sequence rotating coordinate systemShadow;

similarly to the steps (4.1) to (4.5), the current characteristic value can be obtained

(4.6) according to the instantaneous reactive power theory, the complex power s (t) can be expressed as:

wherein j is a complex number unit, p (t) is instantaneous active power, q (t) is instantaneous reactive power, e_α、e_βRespectively three-phase network voltage e_a、e_b、e_cAlpha-axis component, beta-axis component, i after Clark transformation_a、i_βAre respectively three-phase currents i_a、i_b、i_cAlpha-axis component and beta-axis component after Clark transformation;

three-phase voltage and current are represented as direct current quantities under a two-phase dq rotating coordinate system, the derivation process of reference current can be effectively simplified, and the network-access instantaneous active power p (t) and the network-access instantaneous reactive power q (t) can be obtained according to the formula:

in the formula, p_c2(t)、p_s2(t) is a coefficient corresponding to a second harmonic contained in the instantaneous active power; p is a radical of₀(t) is the dc component in the net-entry instantaneous active power; q. q.s_c2(t)、q_s2(t) is a coefficient corresponding to a second harmonic contained in the instantaneous reactive power; q. q.s₀(t) is the dc component in the network-entry instantaneous reactive power;

the specific expressions are respectively as follows:

when the coordinate system is changed back to the α β coordinate system, the expression is:

wherein

After integration, it can be represented in matrix form as:

(4.7) inverse solving the matrix equation, and obtaining the reference current under different control targetsAnd introducing a coefficient k into the reference current expression, the reference current expression can be simplified as follows:

wherein

Different controls are realized mainly by changing the k value in the control process: when k is-1, constant active power control is mainly used for eliminating secondary fluctuation of active power; when k is 0, the negative sequence current is restrained, and the output three-phase current is balanced; when k is 1, the constant reactive power control mainly eliminates the secondary fluctuation of the reactive power.

5. The complex vector current loop decoupling control method based on the stationary coordinate system as claimed in claim 3, wherein the step 5 determines the complex vector decoupling loop according to the calculated delay time, specifically as follows:

(5.1) the delay time caused by signal sampling and PWM inertia element is tau_dGenerally, the following are selected:

wherein f is_sFor the switching frequency, as the switching frequency decreases, the corresponding delay time will increase.

(5.2) Positive sequence vector under alpha and beta coordinate system in time domainAnd positive sequence vector under dq coordinate systemThe following relationships exist:

according to the determined delay time tau_dThe positive sequence delay link under the dq coordinate system can be obtained asThe time delay link is converted into an alpha beta coordinate system to obtain

(5.3) delay time τ according to equation (5.1)_dThe positive sequence time delay link under the dq coordinate system can be obtainedComprises the following steps:

then the negative sequence time delay link under the corresponding dq coordinate systemComprises the following steps:

where ω is the grid voltage fundamental angular frequency.

(5.4) converting the delay link into an alpha beta coordinate system to obtain G_{αβ_d}(s) is;

(5.5) controlled object G 'added with delay link'_{VIENNA_αβ}(s) is expressed as:

the delay link also influences the coupling between the active power and the reactive power of the system when the voltage of the power grid is unbalanced, and the coupling degree between the active power and the reactive power is more serious along with the reduction of the switching frequency.

(5.6) according to the delay element of the VIENNA rectifier given in (5.4), a positive sequence delay compensation element can be assumedThe expression of (a) is:

whereinTo delay compensate the angle, there are now:

knowing the positive sequence time s ═ j ω, the delay compensation angle at this time can be calculatedThe positive sequence delay compensation procedure isNegative sequence delay compensation link obtained by the same way

For convenience of calculation, the delay compensation link is usually subjected to euler transform:

(5.7) consider that the VIENNA rectifier is modeled in the α β coordinate system at low switching frequencies, albeit with current i_aAnd i_βThere is no coupling between the two, but there is still coupling inside the system, and this coupling cannot be eliminated by the traditional proportional resonant controller, so a reduced-order resonant controller is designed to realize decoupling inside the system.

According to the step (5.2), a positive sequence complex vector decoupling controller under the alpha and beta coordinate system can be deducedIs composed of

Negative sequence complex vector decoupling controller obtained by same methodComprises the following steps:

wherein k is_pIs a proportionality coefficient, k_iIs the resonance coefficient, k_rIs the resonance coefficient.

In order to realize the simultaneous control of positive and negative sequence components under an alpha-beta coordinate system in a non-ideal power grid and avoid current i under the alpha-beta coordinate system_aAnd i_βThe positive and negative sequence separation link can obtain the complex vector current controller G added with the delay compensation_αβ(s) is

6. The complex vector current loop decoupling control method based on the static coordinate system as claimed in claim 3, wherein step 5 derives a coupling coefficient relationship under the non-ideal grid condition, which can visually represent the coupling analysis between the active power and the reactive power to verify the effectiveness of the complex vector current controller, and the specific results are as follows:

(6.1) the current loop closed loop transfer function G(s) without considering the power grid voltage disturbance is as follows:

wherein G is_{VIENNA_αβ}(s) is a VIENNA rectifier object transfer function in an alpha beta coordinate system; g_αβ(s) is the current controller transfer function; re(s) is the real component of the current loop closed loop transfer function; im(s) is the imaginary component of the current loop closed loop transfer function.

The current feedback value i under the alpha beta coordinate system can be obtained according to the formula_α(s)、i_βThe relationship between(s) is:

(6.2) if the active power command and the reactive power command change according to the step response, and u (t) is the step response change, the active power command p₀(t) pu (t), reference reactive power q₀(t) qu (t). According to a reference current calculation formula, the alpha and beta axis reference current in the time domain can be obtainedIs composed of

Alpha-beta axis reference current under frequency domain can be obtained by Laplace transformationIs composed of

(6.3) substituting the current feedback value i in the alpha beta coordinate system_α(s)、i_β(s) availability

Wherein

Transforming the reverse Laplace to time domain to obtain A (t), B (t), C (t), D (t), and current feedback value i of alpha-beta coordinate system in time domain_α(t)、i_β(t)：

(6.4) obtaining the expressions of the instantaneous active power p (t) and the reactive power q (t) according to the calculation formula of the instantaneous complex power in claim 4, wherein the expressions are respectively

Substituting the current feedback value and the positive and negative sequence voltages under the corresponding alpha and beta coordinate system to obtain the current feedback value

(6.5) coupling coefficient H₁、H₂Are respectively as

Introducing an unbalance concept, defining the unbalance lambda as the ratio of the negative sequence component amplitude to the positive sequence component amplitude, and obtaining a simplified coupling coefficient expression as follows:

Technical Field

The invention belongs to the technical field of control in power electronic transformation technology, and particularly relates to a complex vector current loop decoupling control device and method under a static coordinate system.

Background

The VIENNA rectifier is a three-level topology, and has the biggest characteristics of small quantity of switching devices, low voltage stress borne by a switching tube, low input current harmonic distortion rate, high power density, high reliability, no need of setting driving dead time and the like, and is widely applied to medium-high voltage high-power level electric energy conversion occasions. However, since the rectifier generates a large power loss when operating at a medium-high power, the switching frequency needs to be reduced to increase the output power of the system. However, the problem of coupling aggravated by the rectifier control system can be generated while the switching frequency of the power device is reduced. For the problem of coupling of a control system, related decoupling current control technologies such as feedforward decoupling, feedback decoupling, internal model decoupling, deviation decoupling, complex vector decoupling and the like are widely concerned, however, under the condition of low switching frequency, the coupling of the control system is intensified under the influence of digital control delay, and the decoupling methods can reduce cross coupling but cannot completely offset.

Aiming at the decoupling problem of the VIENNA rectifier under low switching frequency, at present, research of many scholars mainly focuses on decoupling control of the rectifier by adopting a PI controller under the condition of a balanced power grid, however, the decoupling control under the balanced power grid fails when the voltage of the power grid is unbalanced, so that the decoupling of a current loop is incomplete, and the stability of a system is influenced.

Disclosure of Invention

The invention aims to provide a complex vector current loop decoupling control device and method under a static coordinate system, so as to realize the decoupling of a system under an unbalanced power grid and effectively improve the dynamic regulation performance of a VIENNA rectifier.

The technical solution for realizing the purpose of the invention is as follows: a complex vector current loop decoupling control device under a static coordinate system comprises a VIENNA rectifier, a digital processing control module and a driving circuit, wherein the digital processing control module comprises a sampling unit, a voltage control unit, a reference current calculation unit, a complex vector current control unit and a sine pulse width modulation unit;

the sampling unit respectively collects voltage signals of an upper capacitor and a lower capacitor on the direct current side of the VIENNA rectifier, three-phase voltage signals on the alternating current side of the VIENNA rectifier and three-phase current signals on the alternating current side of the VIENNA rectifier;

the voltage control unit processes the voltage signals of the upper capacitor and the lower capacitor on the direct current side into active power reference signals;

the reference current calculation unit processes the active power reference signal and the voltage and current signals obtained after coordinate transformation into a current reference signal under a static coordinate system;

the complex vector current control unit processes the current reference signal to obtain a modulated wave signal, and the modulated wave signal is sent to the sine pulse width modulation unit;

the output end of the sine pulse width modulation unit is connected to each switching tube of each phase bridge arm in the three-level VIENNA rectifier through the driving circuit.

Preferably, the digital processing control modules are chips of TMS320F28377D and EPM 1270T.

A complex vector current loop decoupling control method under a static coordinate system comprises the following steps:

step 1, in each switching period, a sampling unit of a digital control module respectively collects three-phase voltage e at an alternating current side_a、e_b、e_cAlternating side three-phase current i_a、i_b、i_cCapacitor voltage U on the DC side_C1And the capacitor voltage U under the DC side_C2；

Step 2, according to the signals collected in the step 1, converting alternating-current side voltage and alternating-current side current in a static abc coordinate system into a static alpha beta coordinate system through Clark, comparing direct-current side capacitor voltage with a voltage reference signal, obtaining an error signal through proportional-integral adjustment, and multiplying the error signal by the voltage reference signal to obtain an active power reference signal;

step 3, extracting a grid voltage characteristic value according to the obtained active power reference signal, and calculating a reference current to obtain a reference current i under an alpha beta coordinate system^* _α、i^* _β；

Step 4, according to the switching frequency f of the three-level VIENNA rectifier_sDetermining the delay time tau of a system_dComprises the following steps:

step 5, determining a complex vector decoupling loop according to the calculated delay time, and verifying the effectiveness of the complex vector current controller through the coupling coefficient analysis of the system;

step 6, converting the obtained current i_α、i_βComparing with reference current, and obtaining a three-phase modulation signal u through a complex vector decoupling loop and Clark inverse transformation_a、u_b、u_c；

And 7, generating a pulse width modulation signal by the three-phase modulation signal through a sine pulse width modulation unit, and controlling the work of a VIENNA rectifier switching tube through a driving circuit.

Further, in step 3, according to the active power reference signal, a grid voltage characteristic value is extracted and reference current calculation is performed to obtain reference current i in an alpha beta coordinate system^* _α、i^* _βThe method comprises the following steps:

non-ideal grid voltage e_a(t)、e_b(t)、e_c(t) can be decomposed into positive and negative sequence components, and the expression under the abc coordinate system is:

wherein subscripts a, b, c represent a phase a, b phase, c phase; superscript +, -respectively represents positive sequence component and negative sequence component;representing the magnitude of the positive sequence component,representing the magnitude of the negative sequence component; omega is the fundamental angular frequency of the grid voltage;

the network side voltage e under the alpha beta coordinate system can be obtained through Clark transformation_α(t)、e_β(t) is:

wherein the content of the first and second substances,represents the magnitude of the positive sequence component in the alpha beta coordinate system,representing the magnitude of the negative sequence component in the α β coordinate system.

According to the nature of the Clark transformation,rotates counterclockwise with an angular velocity omega relative to the alpha axis in the alpha beta coordinate system,clockwise at an angular velocity ω relative to the α axis in the α β coordinate system;is stationary relative to the fundamental positive-sequence rotational coordinate system,relative rest with the fundamental frequency negative sequence rotating coordinate system;

the fundamental frequency positive sequence rotation coordinate system rotates anticlockwise with an angular velocity omega relative to the alpha axis in the alpha beta coordinate system; the fundamental frequency negative sequence rotating coordinate system rotates clockwise with an angular velocity omega relative to the alpha axis in the alpha beta coordinate system;

defining: characteristic value of network voltageAre respectively asProjections on a d axis and a q axis in a fundamental frequency positive sequence rotating coordinate system; characteristic value of network voltageAre respectively asProjections on a d axis and a q axis in a fundamental frequency negative sequence rotating coordinate system;

similarly, the current characteristic value can be obtained through the steps

According to the instantaneous reactive power theory, the complex power s (t) can be expressed as:

wherein j is a complex number unit, p (t) is instantaneous active power, q (t) is instantaneous reactive power, e_α、e_βRespectively three-phase network voltage e_a、e_b、e_cAlpha-axis component, beta-axis component, i after Clark transformation_a、i_βAre respectively three-phase currents i_a、i_b、i_cAlpha-axis component and beta-axis component after Clark transformation;

three-phase voltage and current are represented as direct current quantities under a two-phase dq rotating coordinate system, the derivation process of reference current can be effectively simplified, and the network-access instantaneous active power p (t) and the network-access instantaneous reactive power q (t) can be obtained according to the formula:

in the formula, p_c2(t)、p_s2(t) is a coefficient corresponding to a second harmonic contained in the instantaneous active power; p is a radical of₀(t) is the dc component in the net-entry instantaneous active power; q. q.s_c2(t)、q_s2(t) is a coefficient corresponding to a second harmonic contained in the instantaneous reactive power; q. q.s₀(t) is the dc component in the network-entry instantaneous reactive power;

the specific expressions are respectively as follows:

when the coordinate system is changed back to the α β coordinate system, the expression is:

wherein

After integration, it can be represented in matrix form as:

inverse solution matrix equation, by which reference current can be obtained under different control targetsAnd introducing a coefficient k into the reference current expression, the reference current expression can be simplified as follows:

wherein

Different controls are realized mainly by changing the k value in the control process: when k is-1, constant active power control is mainly used for eliminating secondary fluctuation of active power; when k is 0, the negative sequence current is restrained, and the output three-phase current is balanced; when k is 1, the constant reactive power control mainly eliminates the secondary fluctuation of the reactive power.

Further, in step 5, the complex vector decoupling loop is determined according to the calculated delay time, which is specifically as follows:

the delay time brought by signal sampling and PWM inertia link is tau_dGenerally, the following are selected:

wherein f is_sFor the switching frequency, as the switching frequency decreases, the corresponding delay time will increase.

Positive sequence vector under alpha and beta coordinate system under time domainAnd positive sequence vector under dq coordinate systemThe following relationships exist:

according to the determined delay time tau_dThe positive sequence delay link under the dq coordinate system can be obtained asThe time delay link is converted into an alpha beta coordinate system to obtain

According to delay time tau_dThe positive sequence time delay link under the dq coordinate system can be obtainedComprises the following steps:

then the negative sequence time delay link under the corresponding dq coordinate systemComprises the following steps:

where ω is the grid voltage fundamental angular frequency.

Converting the delay link to alpha-beta coordinate system to obtain G_{αβ_d}(s) is;

adding a controlled object G 'after a delay link'_{VIENNA_αβ}(s) is expressed as:

the delay link also influences the coupling between the active power and the reactive power of the system when the voltage of the power grid is unbalanced, and the coupling degree between the active power and the reactive power is more serious along with the reduction of the switching frequency.

According to the delay link of the VIENNA rectifier, a positive sequence delay compensation link can be assumedThe expression of (a) is:

whereinTo delay compensate the angle, there are now:

knowing the positive sequence time s ═ j ω, the delay compensation angle at this time can be calculatedThe positive sequence delay compensation procedure isNegative sequence delay compensation link obtained by the same way

For convenience of calculation, the delay compensation link is usually subjected to euler transform:

considering that the VIENNA rectifier is modeled in the alpha beta coordinate system under the condition of low switching frequency, although the current i_aAnd i_βThere is no coupling between the two, but there is still coupling inside the system, and this coupling cannot be eliminated by the traditional proportional resonant controller, so a reduced-order resonant controller is designed to realize decoupling inside the system.

According to the relation between the positive sequence vectors in the alpha beta coordinate system and the dq coordinate system, the positive sequence complex vector decoupling controller in the alpha beta coordinate system can be deducedIs composed of

The negative sequence complex vector solution can be obtained by the same wayCoupler controllerComprises the following steps:

wherein k is_pIs a proportionality coefficient, k_iIs the resonance coefficient, k_rIs the resonance coefficient.

In order to realize the simultaneous control of positive and negative sequence components under an alpha-beta coordinate system in a non-ideal power grid and avoid current i under the alpha-beta coordinate system_aAnd i_βThe positive and negative sequence separation link can obtain the complex vector current controller G added with the delay compensation_αβ(s) is

Further, step 5 deduces a coupling coefficient relationship under the non-ideal grid condition, and the coupling analysis between the active power and the reactive power can be visually represented to verify the effectiveness of the complex vector current controller, and the specific results are as follows:

the current loop closed loop transfer function G(s) without considering the grid voltage disturbance is as follows:

wherein G is_{VIENNA_αβ}(s) is a VIENNA rectifier object transfer function in an alpha beta coordinate system; g_αβ(s) is the current controller transfer function; re(s) is the real component of the current loop closed loop transfer function; im(s) is the imaginary component of the current loop closed loop transfer function.

The current feedback value i under the alpha beta coordinate system can be obtained according to the formula_α(s)、i_βThe relationship between(s) is:

if the active power command and the reactive power command change according to the step response, and u (t) is set as the step response change, the active power command p₀(t) pu (t), reference reactive power q₀(t) qu (t). According to a reference current calculation formula, the alpha and beta axis reference current in the time domain can be obtainedIs composed of

Alpha-beta axis reference current under frequency domain can be obtained by Laplace transformationIs composed of

Substituting the current feedback value i under the alpha beta coordinate system_α(s)、i_β(s) availability

Wherein

Transforming the reverse Laplace to time domain to obtain A (t), B (t), C (t), D (t), and current feedback value i of alpha-beta coordinate system in time domain_α(t)、i_β(t)：

The instantaneous complex power calculation formula of claim 4 is used to obtain the expressions of instantaneous active power p (t) and reactive power q (t), which are respectively

Substituting the current feedback value and the positive and negative sequence voltages under the corresponding alpha and beta coordinate system to obtain the current feedback value

Coefficient of coupling H₁、H₂Are respectively as

Introducing an unbalance concept, defining the unbalance lambda as the ratio of the negative sequence component amplitude to the positive sequence component amplitude, and obtaining a simplified coupling coefficient expression as follows:

compared with the prior art, the invention has the remarkable advantages that: (1) the control is carried out under a static reference coordinate system, so that the calculation complexity and unnecessary time delay and errors are reduced; (2) the coupling between active power and reactive power under the non-ideal power grid condition can be effectively improved, the dynamic performance of the system is improved, and the control system is simple and easy to realize.

Drawings

FIG. 1 is a schematic structural diagram of a complex vector current loop decoupling control system based on a static coordinate system.

FIG. 2 is a control block diagram of a complex vector current loop decoupling control system based on a static coordinate system.

Fig. 3 is a schematic diagram of a main circuit structure of the VIENNA rectifier.

Fig. 4 is a schematic diagram of coupling coefficients without considering system delay by using the conventional proportional resonance control and the decoupling control method of the present invention in the embodiment of the present invention. Wherein (a) adopts the traditional proportional resonance to control the coupling coefficient H₁The (b) is the control of the coupling coefficient H by using the traditional proportional resonance₂The (c) is a coupling coefficient H adopting the decoupling control method of the invention₁The (d) is a coupling coefficient H adopting the decoupling control method of the invention₂Schematic representation.

Fig. 5 is a schematic diagram of a coupling coefficient considering system delay by using a conventional proportional resonance control and the decoupling control method of the present invention in the embodiment of the present invention. Wherein (a) is coupling coefficient H of conventional proportional resonant controller₁The (b) is the coupling coefficient H of the traditional proportional resonant controller₂The (c) is a coupling coefficient H adopting the decoupling control method of the invention₁The (d) is a coupling coefficient H adopting the decoupling control method of the invention₂Schematic representation.

FIG. 6 is a waveform of three-phase AC voltage, three-phase AC current, DC-side voltage and power under grid-connected conditions of a VIENNA rectifier, wherein (a) is a waveform of three-phase AC voltage, three-phase AC current, DC-side voltage and power at a switching frequency of 5kHz after the method of the present invention is used; (b) waveform diagrams of three-phase alternating voltage, three-phase alternating current, direct-side voltage and power at a switching frequency of 2.5kHz after the method of the present invention is used.

Fig. 7 is a waveform diagram of three-phase ac voltage, three-phase ac current, dc-side voltage, active power and reactive power at a switching frequency of 5kHz before and after the use of the method of the present invention, wherein (a) is a waveform diagram of three-phase ac voltage, three-phase ac current, dc-side voltage, active power and reactive power before the use of the control method of the present invention; (b) the waveform diagrams of three-phase alternating voltage, three-phase alternating current, direct-current side voltage, active power and reactive power after the control method of the invention is used.

Fig. 8 is a waveform diagram of three-phase ac voltage, three-phase ac current, dc-side voltage, active power and reactive power at a switching frequency of 2.5kHz before and after the use of the method of the present invention, wherein (a) is a waveform diagram of three-phase ac voltage, three-phase ac current, dc-side voltage, active power and reactive power before the use of the control method of the present invention; (b) the waveform diagrams of three-phase alternating voltage, three-phase alternating current, direct-current side voltage, active power and reactive power after the control method of the invention is used.

Detailed Description

The invention is described in further detail below with reference to the figures and the embodiments.

With reference to fig. 1, the complex vector current loop decoupling control device based on the stationary coordinate system of the present invention includes a VIENNA rectifier, a digital processing control module and a driving circuit, wherein the digital processing control module includes a sampling unit, a voltage control unit, a reference current calculation unit, a complex vector current control unit and a sinusoidal pulse width modulation unit.

The system comprises a sampling unit, a reference current generation unit, a complex vector current decoupling control unit, a VIENNA rectifier and a VIENNA rectifier, wherein the sampling unit is used for respectively acquiring voltage signals of an upper capacitor and voltage signals of a lower capacitor on a direct current side of the VIENNA rectifier and three phase current signals on an alternating current side of; sampling the obtained voltage signals of the upper capacitor and the lower capacitor on the direct current side, and obtaining an active power reference signal through a voltage control unit; the active power reference signal and the voltage and current signals obtained after coordinate transformation are processed by a reference current generation unit under a static coordinate system to obtain a current reference signal under the static coordinate system; the complex vector current decoupling control unit processes the current reference signal to obtain a modulated wave signal, and sends the modulated wave signal to the sinusoidal pulse width modulation unit, and the output end of the sinusoidal pulse width modulation unit is connected to each switching tube of each phase bridge arm in the three-level VIENNA rectifier through a driving circuit; the digital processing control module adopts TMS320F2808 and EPM1270T chips.

A complex vector current loop decoupling control method under a static coordinate system comprises the following steps:

step 1, in each switching period, a sampling unit collects three-phase voltage e at an alternating current side_a、e_b、e_cAlternating side three-phase current i_a、i_b、i_cTransforming the alpha-beta-phase coordinate system to a static alpha-beta coordinate system through Clark transformation;

step 2, sampling capacitor voltage U on the direct current side_C1And the capacitor voltage U under the DC side_C2Comparing the active power reference signal with a voltage reference signal, obtaining an error signal through proportional-integral regulation, and multiplying the error signal by the voltage reference signal to obtain an active power reference signal;

the transfer function of the voltage loop PI controller is:

wherein k is_upIs a proportionality coefficient, k_uiIs an integral coefficient;

with reference to fig. 2, an active power reference signal P^*The expression is as follows:

wherein, U_dcIs the sum of the capacitor voltages on the dc side,is a DC side reference voltage;

step 3, extracting a grid voltage characteristic value according to the obtained active power reference signal, and calculating a reference current to obtain a reference current i under an alpha beta coordinate system^* _α、i^* _β；

Non-ideal grid voltage e_a(t)、e_b(t)、e_c(t) can be decomposed into positive and negative sequence components, and the expression under the abc coordinate system is:

wherein subscripts a, b, c represent a phase a, b phase, c phase; superscript +, -respectively represents positive sequence component and negative sequence component;representing the magnitude of the positive sequence component,representing the magnitude of the negative sequence component; omega is the fundamental angular frequency of the grid voltage;

the network side voltage e under the alpha beta coordinate system can be obtained through Clark transformation_α(t)、e_β(t) is:

wherein the content of the first and second substances,represents the magnitude of the positive sequence component in the alpha beta coordinate system,representing the magnitude of the negative sequence component in the α β coordinate system.

According to the nature of the Clark transformation,rotates counterclockwise with an angular velocity omega relative to the alpha axis in the alpha beta coordinate system,clockwise at an angular velocity ω relative to the α axis in the α β coordinate system;is stationary relative to the fundamental positive-sequence rotational coordinate system,relative rest with the fundamental frequency negative sequence rotating coordinate system;

the fundamental frequency positive sequence rotation coordinate system rotates anticlockwise with an angular velocity omega relative to the alpha axis in the alpha beta coordinate system; the fundamental frequency negative sequence rotating coordinate system rotates clockwise with an angular velocity omega relative to the alpha axis in the alpha beta coordinate system;

defining: characteristic value of network voltageAre respectively asProjections on a d axis and a q axis in a fundamental frequency positive sequence rotating coordinate system;

characteristic value of network voltageAre respectively asProjections on a d axis and a q axis in a fundamental frequency negative sequence rotating coordinate system;

the current characteristic value can be obtained in the same way

According to the instantaneous reactive power theory, the complex power s (t) can be expressed as:

wherein j isPlural units, p (t) instantaneous active power, q (t) instantaneous reactive power, e_α、e_βRespectively three-phase network voltage e_a、e_b、e_cAlpha-axis component, beta-axis component, i after Clark transformation_a、i_βAre respectively three-phase currents i_a、i_b、i_cAlpha-axis component and beta-axis component after Clark transformation;

three-phase voltage and current are represented as direct current quantities under a two-phase dq rotating coordinate system, the derivation process of reference current can be effectively simplified, and the network-access instantaneous active power p (t) and the network-access instantaneous reactive power q (t) can be obtained according to the formula:

in the formula, p_c2(t)、p_s2(t) is a coefficient corresponding to a second harmonic contained in the instantaneous active power; p is a radical of₀(t) is the dc component in the net-entry instantaneous active power; q. q.s_c2(t)、q_s2(t) is a coefficient corresponding to a second harmonic contained in the instantaneous reactive power; q. q.s₀(t) is the dc component in the network-entry instantaneous reactive power;

the specific expressions are respectively as follows:

when the coordinate system is changed back to the α β coordinate system, the expression is:

wherein

After integration, it can be represented in matrix form as:

inverse solution matrix equation, by which reference current can be obtained under different control targetsAnd introducing a coefficient k into the reference current expression, the reference current expression can be simplified as follows:

wherein

Different controls are realized mainly by changing the k value in the control process: when k is-1, constant active power control is mainly used for eliminating secondary fluctuation of active power; when k is 0, the negative sequence current is restrained, and the output three-phase current is balanced; when k is 1, the constant reactive power control mainly eliminates the secondary fluctuation of the reactive power.

Step 4, according to the switching frequency f of the three-level VIENNA rectifier_sDetermining the delay time tau of a system_dComprises the following steps:

step 5, determining a complex vector decoupling loop according to the calculated delay time, and verifying the effectiveness of the complex vector current controller through the coupling coefficient analysis of the system;

positive sequence vector under alpha and beta coordinate system under time domainAnd dq coordinate systemLower positive sequence vectorThe following relationships exist:

according to the determined delay time tau_dThe positive sequence delay link under the dq coordinate system can be obtained asThe time delay link is converted into an alpha beta coordinate system to obtain

According to delay time tau_dThe positive sequence time delay link under the dq coordinate system can be obtainedComprises the following steps:

then the negative sequence time delay link under the corresponding dq coordinate systemComprises the following steps:

where ω is the grid voltage fundamental angular frequency.

Converting the delay link to alpha-beta coordinate system to obtain G_{αβ_d}(s) is;

adding a controlled object G 'after a delay link'_{VIENNA_αβ}(s) is expressed as:

the delay link also influences the coupling between the active power and the reactive power of the system when the voltage of the power grid is unbalanced, and the coupling degree between the active power and the reactive power is more serious along with the reduction of the switching frequency.

According to the delay link of the VIENNA rectifier, a positive sequence delay compensation link can be assumedThe expression of (a) is:

whereinTo delay compensate the angle, there are now:

knowing the positive sequence time s ═ j ω, the delay compensation angle at this time can be calculatedThe positive sequence delay compensation procedure isNegative sequence delay compensation link obtained by the same way

For convenience of calculation, the delay compensation link is usually subjected to euler transform:

considering that the VIENNA rectifier is modeled in the alpha beta coordinate system under the condition of low switching frequency, although the current i_aAnd i_βThere is no coupling between the two, but there is still coupling inside the system, and this coupling cannot be eliminated by the traditional proportional resonant controller, so a reduced-order resonant controller is designed to realize decoupling inside the system.

According to the relation between the positive sequence vector under the alpha beta coordinate system and the positive sequence vector under the dq coordinate system in the time domain, the positive sequence complex vector decoupling controller under the alpha beta coordinate system can be deducedIs composed of

Negative sequence complex vector decoupling controller obtained by same methodComprises the following steps:

wherein k is_pIs a proportionality coefficient, k_iIs the resonance coefficient, k_rIs the resonance coefficient.

In order to realize the simultaneous control of positive and negative sequence components under an alpha-beta coordinate system in a non-ideal power grid and avoid current i under the alpha-beta coordinate system_aAnd i_βThe positive and negative sequence separation link can obtain the complex vector current controller G added with the delay compensation_αβ(s) is

The control block diagram of the complex vector current controller is shown in fig. 3.

The current loop closed loop transfer function G(s) without considering the grid voltage disturbance is as follows:

wherein G is_{VIENNA_αβ}(s) is a VIENNA rectifier object transfer function in an alpha beta coordinate system; g_αβ(s) is the current controller transfer function; re(s) is the real component of the current loop closed loop transfer function; im(s) is the imaginary component of the current loop closed loop transfer function.

The current feedback value i under the alpha beta coordinate system can be obtained according to the formula_α(s)、i_βThe relationship between(s) is:

if the active power command and the reactive power command change according to the step response, and u (t) is set as the step response change, the active power command p₀(t) pu (t), reference reactive power q₀(t) qu (t). According to a reference current calculation formula, the alpha and beta axis reference current in the time domain can be obtainedIs composed of

Alpha-beta axis reference current under frequency domain can be obtained by Laplace transformationIs composed of

Substituting the current feedback value i under the alpha beta coordinate system_α(s)、i_β(s) availability

Wherein

Transforming the reverse Laplace to time domain to obtain A (t), B (t), C (t), D (t), and current feedback value i of alpha-beta coordinate system in time domain_α(t)、i_β(t)：

According to the calculation formula of the instantaneous complex power, the expressions of the instantaneous active power p (t) and the reactive power q (t) can be obtained, wherein the expressions are respectively

Substituting the current feedback value and the positive and negative sequence voltages under the corresponding alpha and beta coordinate system to obtain the current feedback value

Coefficient of coupling H₁、H₂Are respectively as

The coupling coefficient only represents the coupling inside the system without considering the digital control delay, and the control method can effectively reduce the coupling inside the system by combining with the figure 4. Considering the digital control delay, the coupling coefficient includes the coupling condition of the system interior and the delay link, and combining with fig. 5, it can be seen that the control method of the invention can effectively reduce and also can effectively inhibit the coupling brought by the delay link.

Step 6, converting the obtained current i_α、i_βComparing with reference current, and obtaining a three-phase modulation signal u through a complex vector decoupling loop and Clark inverse transformation_a、u_b、u_c；

Step 7, three-phase modulation signal u_a、u_b、u_cThe pulse width modulation signal is generated by the sine pulse width modulation unit, and the work of a VIENNA rectifier switching tube is controlled by a driving circuit.

The modulation rule of the VIENNA rectifier is as follows: as shown in FIG. 3, taking phase A as an example, in the positive half cycle of the modulated wave, when the carrier wave is larger than the modulated wave, S is set_a1、S_a2Conducting, the voltage of the A-phase bridge arm is 0, and when the carrier wave is less than the modulation wave, making S_a1、S_a2Turn off, the bridge arm voltage of A phase is U_dc2; in the negative half cycle of the modulated wave, when the carrier wave is smaller than the modulated wave, let S_a1、S_a2Conducting, the voltage of the A-phase bridge arm is 0, and when the carrier wave is greater than the modulation wave, making S_a1、S_a2Turn off, the bridge arm voltage of A phase is-U_dc/2. B. The modulation strategy of the C two phases is the same as that of the A phase.

Wherein U is_dcIs the voltage of the direct current bus at the output side of the VIENNA rectifier.

Example 1

In this embodiment, a three-phase VIENNA rectifier circuit is built by using a Simulink tool in MATLAB, and the input voltage is rectified by the three-phase VIENNA rectifier circuit to obtain direct current.

The electrical parameter settings during the simulation are as in table 1:

TABLE 1

The simulation mainly completes the comparative simulation of the traditional proportional resonance control method and the improved decoupling-based proportional resonance control method under two switching frequencies of 5kHz and 2.5 kHz. Before analyzing the dynamic performance of the VIENNA rectifier, simulation analysis is performed on the steady-state performance of the VIENNA rectifier under the power grid condition, and as can be seen from fig. 6, when the switching frequency is 5kHz and 2.5kHz, the control method can realize that three-phase current on the alternating current side is sinusoidal and the voltage on the direct current side is constant at a given voltage when the voltage of the power grid is unbalanced, which shows that the decoupling-based current control method designed by the invention can enable the VIENNA rectifier to normally operate when the voltage of the power grid is unbalanced.

Comparing the waveforms of the reactive power in fig. 7(a) and fig. 7(b) and fig. 8(a) and fig. 8(b), it can be seen that, by adopting the improved decoupling-based proportional resonance control method, when the active power suddenly changes, the transient change range of the reactive power average value is smaller and the time for recovering the stability is shorter than that of the conventional proportional resonance control method. Therefore, as can be seen from the comparison of the above figures, the decoupling-based proportional resonance control method provided herein can effectively reduce the coupling between the active power and the reactive power, and improve the dynamic performance of the system. Comparing fig. 7(a) and fig. 8(a), it can be found that when the conventional proportional resonance control method is adopted, after the switching frequency is reduced from 5kHz to 2.5kHz, it can be clearly seen that the amplitude of the reactive transient change is increased when the active sudden change occurs, and the time for recovering the stability is prolonged, which indicates that after the switching frequency is reduced, the coupling between the powers is aggravated by the delay link of the system. Moreover, as can also be seen from the comparison of the waveforms of the reactive power in fig. 8(a) and fig. 8(b), the decoupling-based proportional resonance control method proposed herein can effectively reduce the coupling between the active power and the reactive power, and improve the dynamic performance of the system.

In summary, the device and method for current loop decoupling control based on complex vectors in a static coordinate system are applied to a VIENNA rectifier under the condition of a low-switching-frequency non-ideal power grid, the control method determines a delay decoupling link through determination of delay time of the static coordinate system, coupling between active power and reactive power under the condition of the low-switching-frequency non-ideal power grid is effectively inhibited, positive and negative sequence decomposition of current in the static coordinate system is avoided through simplification of reference current, system calculation is simplified, and unnecessary delay and errors are avoided. The invention also deduces a relational expression of the coupling coefficient between the active power and the reactive power under the non-ideal power grid condition, and can visually display the coupling condition between the active power and the reactive power in the system.