CN103199547A - Pulse-width modulation (PWM) rectifier and static synchronous compensator combined operation system and control method thereof - Google Patents

Abstract

The invention discloses a pulse-width modulation (PWM) rectifier and static synchronous compensator combined operation system and a control method thereof. The PWM rectifier and static synchronous compensator combined operation system is formed by a plurality of PWM rectifiers, a static synchronous compensator and an upper computer monitoring platform. Each PWM rectifier is formed by a three-phase bridge type inverter circuit, a connecting reactor, a direct current side capacitor, direct current side load and a controller. The static synchronous compensator is formed by a three-phase bridge type inverter circuit, a connecting reactor, a direct current side capacitor and a controller. On the condition that three-phase network voltage is unbalanced, the PWM rectifiers input negative-sequence current to restrain double frequency existing in direct current side voltage to fluctuate. The static synchronous compensator inputs negative-sequence current opposite to the negative-sequence current inputted by the PWM rectifiers and ensures three-phase equilibrium of grid-side current. The PWM rectifier and static synchronous compensator combined operation system can restrain the double frequency in the direct current side voltage of the PWM rectifiers to fluctuate and can also maintain the three-phase equilibrium of the grid-side current on the condition that three-phase network voltage is unbalanced.

Description

PWM rectifier and static var compensator combined operation system and control method thereof

Technical Field

The invention relates to a PWM rectifier and static var compensator combined operation system and a control method thereof.

Background

Under the influence of unbalanced load and three-phase power grid faults, the voltage of the three-phase power grid is always in an unbalanced state. In order to enable the three-phase PWM rectifier to normally operate under the condition of unbalanced voltage of the three-phase grid, many scholars research control strategies of the PWM rectifier under the condition of unbalanced voltage. According to different control targets, the control strategies of the PWM rectifier under the condition of voltage unbalance are divided into two types: the first kind of control strategy aims at maintaining the three-phase balance of the input current of the PWM rectifier, and needs to ensure that the output voltage of the PWM rectifier contains a negative sequence voltage component which is the same as the three-phase power grid voltage, and the negative sequence voltage component acts with the input current to generate instantaneous input power with double frequency fluctuation, so that the double frequency fluctuation occurs to the DC side voltage of the PWM rectifier; the second type of control strategy aims at inhibiting the double frequency fluctuation of the voltage at the direct current side, and needs to control the PWM rectifier to input negative sequence current and maintain the constant input instantaneous power. Under the condition that the three-phase power grid voltage is unbalanced, two control targets are mutually contradictory and are difficult to unify. According to different application occasions, the two types of control strategies have certain application values. In the occasions with higher requirements on the direct current power supply, such as electrolysis, electroplating and the like, a second type of control strategy is often applied, namely the quality of the electric energy on the alternating current side is sacrificed to inhibit the double-frequency fluctuation of the voltage on the direct current side.

PWM rectifiers are widely considered to be a three-phase grid-friendly load. People often neglect the power quality problem of the PWM rectifier, even add a power quality control function to the PWM rectifier, and rarely research the power quality problem and the control mode generated by the PWM rectifier. However, on the occasion that a plurality of PWM rectifiers are connected in parallel, the quality problem of electric energy generated by the PWM rectifiers cannot be ignored, a large amount of negative sequence current flows into a three-phase power grid, the loss of the power distribution network is increased, and the normal operation of other equipment of the power distribution network is threatened. The static synchronous compensator based on the full-control device is an ideal negative sequence treatment device, and has important significance in researching the combined operation of a plurality of parallel PWM rectifiers and the static synchronous compensator.

Disclosure of Invention

The invention aims to solve the technical problem that in order to overcome the defects of the prior art, the invention provides a combined operation system of a PWM rectifier and a static var compensator, which can inhibit the double frequency fluctuation of the DC side voltage of the PWM rectifier and maintain the three-phase balance of the grid side current.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a PWM rectifier and static reactive compensator combined operation system comprises a plurality of PWM rectifiers and a static synchronous compensator, wherein each PWM rectifier comprises a three-phase bridge type inverter circuit, a direct current side capacitor, a direct current side load and a controller, the three-phase bridge type inverter circuit, the direct current side capacitor and the direct current side load are sequentially connected, the controller controls the on-off of a switch tube in the three-phase bridge type inverter circuit, and the three-phase bridge type inverter circuit is connected into a three-phase power grid through a connecting reactor; the static synchronous compensator comprises a three-phase bridge type inverter circuit, a direct-current side capacitor and a controller, wherein the three-phase bridge type inverter circuit is connected with the direct-current side capacitor, the three-phase bridge type inverter circuit is connected into a three-phase power grid through a connecting reactor, and the controller controls the on-off of a switch tube in the three-phase bridge type inverter circuit; and the controller of the PWM rectifier and the controller of the static synchronous compensator are both connected to an upper computer monitoring platform.

Preferably, the controller is a DSP.

As a preferred scheme, the upper computer monitoring platform comprises an industrial personal computer, and the industrial personal computer is communicated with the controller through an Ethernet.

The control method of the combined operation system of the PWM rectifier and the static var compensator under the condition of unbalanced three-phase power grid voltage comprises the following steps:

1) detecting three-phase network voltage u_sa、u_sb、u_scTransformed matrix C_abc/dq ⁺Obtaining fundamental wave positive sequence active component U of three-phase power grid voltage under DQ rotating coordinate system through low-pass filtering_d ⁺And fundamental positive sequence reactive component U_q ⁺And according to U_d ⁺And U_q ⁺Obtaining the amplitude U of the positive sequence voltage of the fundamental wave_S ⁺And initial phase angle theta⁺：

$\left\{\begin{array}{c}{U_s}^{+}=\sqrt{{\left({U_d}^{+}\right)}^2+{\left({U_q}^{+}\right)}^2}\\ {\mathrm{\θ}}^{+}=\arctan \frac{{U_q}^{+}}{{U_d}^{+}}\end{array}\right.,$

2) Will three-phase network voltage u_sa、u_sb、u_scTransformed matrix C_abc/dq ^-Obtaining a fundamental wave negative sequence active component U under a DQ rotation coordinate system through low-pass filtering_d ^-And fundamental negative sequence reactive component U_q ^-And according to U_d ^-And U_q ^-Obtaining the amplitude U of the fundamental wave negative sequence voltage_S ^-And initial phase angle theta^-：

$\left\{\begin{array}{c}{U_s}^{-}=\sqrt{{\left({U_d}^{-}\right)}^2+{\left({U_q}^{-}\right)}^2}\\ {\mathrm{\θ}}^{-}=\arctan \frac{{U_q}^{-}}{{U_d}^{-}}\end{array}\right.,$

3) Detecting the DC side voltage U of the jth PWM rectifier_jdcAnd an input current i_ja、i_jb、i_jc(ii) a j represents any one of a plurality of PWM rectifiers;

4) the DC side voltage U_jdcWith given value U of DC side voltage_jdc ^*Comparing, and adjusting the error by a PI regulator to obtain the amplitude I of the positive sequence component of the current of the jth PWM rectifier_j ⁺The amplitude I of the positive sequence component of the current_j ⁺Substituting the input negative sequence current amplitude I of the jth PWM rectifier_j ^-In the expression, the amplitude I of the current negative sequence component of the jth PWM rectifier is obtained_j ^-(ii) a Wherein,

5) amplitude I of current positive sequence component of jth PWM rectifier_j ⁺Are respectively related to the sine signal sin (ω t + θ)⁺）、sin（ωt+θ⁺-2π/3）、sin（ωt+θ⁺+2 pi/3) to obtain the instantaneous value of the three-phase positive sequence current; amplitude I of negative sequence component of jth PWM rectifier_j ^-Are respectively related to the sine signal sin (ω t + θ)^-+π）、sin（ωt+θ^--π/3）、sin（ωt+θ^-+ pi/3) to obtain the instantaneous value of the three-phase negative sequence current;

6) superposing the three-phase positive sequence current instantaneous value and the three-phase negative sequence current instantaneous value, and then superposing the superposed value and the actual input current instantaneous value i of the PWM rectifier_ja、i_jb、i_jcComparing the error of the two values with a proportionality coefficient K, and then multiplying the error with a feedforward quantity u of the three-phase power grid voltage_sa、u_sb、u_scSuperposed with DC side voltage U_jdcDividing to obtain a modulated signal u_ja、u_jb、u_jFinally modulating signal u_ja、u_jb、u_jcComparing with the triangular carrier, modulating to obtain PWM signal S of the jth PWM rectifier_j1、S_j2、S_j3、S_j4、S_j5、S_j6；

7) Detecting the current i of a load connected to a three-phase network_la、i_lb、i_lcTransformed matrix C_abc/dq ^-Obtaining a fundamental wave negative sequence active component I under a DQ rotation coordinate system through low-pass filtering_ld ^-And fundamental negative sequence reactive component I_lq ^-Is then transformed into a matrix

Obtaining the load side current negative sequence component instantaneous value i_la ^-、i_lb ^-、i_lc ^-Obtaining the command current i of the static synchronous compensator by taking the inverse_ca1 ^*、i_cb1 ^*、i_cc1 ^*；

8) Amplitude I of negative sequence component of input current of PWM rectifier_j ^-After the summation of the upper computer, the sigma I is obtained_j ^-The signals are sent to a static synchronous compensator by an upper computer monitoring platform in a communication mode and then respectively matched with a sine signal sin (omega t + theta)^-）、sin（ωt+θ^-+2π/3）、sin（ωt+θ^--2 pi/3) to obtain the command current i_ca2 ^*、i_cb2 ^*、i_cc2 ^*；

9) Static synchronous compensator command current i_ca1 ^*、i_cb1 ^*、i_cc1 ^*PWM rectifier command current i_ca2 ^*、i_cb2 ^*、i_cc2 ^*Weighting the two parts of command current to obtain the final command current i_ca ^*、i_cb ^*、i_cc ^*：

$\left\{\begin{array}{c}{i_{\mathrm{ca}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{ca}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{ca}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\\ {i_{\mathrm{cb}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{cb}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{cb}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\\ {i_{\mathrm{cc}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{cc}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{cc}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\end{array}\right.$

Wherein eta is₁、η₂The weights are obtained by two instruction current obtaining modes;

10）detecting DC side voltage U of static synchronous compensator_cdcAnd an input current i_ca、i_cb、i_cc，U_cdcWith given value U of DC side voltage_cdc ^*Comparing, adjusting the error of the two by PI adjuster to obtain the amplitude I of the current positive sequence component_c ⁺Amplitude of the positive sequence component of the current I_c ⁺Are respectively related to the sine signal sin (ω t + θ)⁺）、sin（ωt+θ⁺-2π/3）、sin（ωt+θ⁺+2 pi/3) to obtain the instantaneous value of the three-phase positive sequence current;

11) will command current i_ca ^*、i_cb ^*、i_cc ^*Superposed with the instantaneous value of the positive sequence current and then with the instantaneous value i of the actual input current of the static synchronous compensator_ca、i_cb、i_ccComparing the error value with the feedforward quantity u of the three-phase network voltage after multiplying the error value by the proportionality coefficient K_sa、u_sb、u_scSuperimposing the value with the DC side voltage U_cdcDividing to obtain a modulated signal u_ca、u_cb、u_ccFinally modulating signal u_ca、u_cb、u_ccComparing with triangular carrier, modulating to obtain PWM signal S of static synchronous compensator_c1、S_c2、S_c3、S_c4、S_c5、S_c6。

Compared with the prior art, the invention has the beneficial effects that: the invention can inhibit the double frequency fluctuation of the DC side voltage of the PWM rectifier, maintain the three-phase balance of the grid side current and achieve the purpose of improving the electric energy quality of the DC side and the AC side simultaneously. The command current of the static synchronous compensator is obtained through two modes, and the reliability is higher.

Drawings

FIG. 1 is a block diagram illustrating the structure of an embodiment of the present invention;

FIG. 2 is a control block diagram of a PWM rectifier according to an embodiment of the present invention under a three-phase grid voltage imbalance condition;

FIG. 3 is a block diagram of a static synchronous compensator according to an embodiment of the present invention.

Detailed Description

As shown in fig. 1, the combined operation system according to an embodiment of the present invention includes a plurality of PWM rectifiers and a static synchronous compensator, and is characterized in that the PWM rectifiers include a three-phase bridge inverter circuit, a dc side capacitor, a dc side load, and a controller, the three-phase bridge inverter circuit, the dc side capacitor, and the dc side load are connected in sequence, the controller controls on/off of a switching tube in the three-phase bridge inverter circuit, and the three-phase bridge inverter circuit is connected to a three-phase power grid through a connecting reactance; the static synchronous compensator comprises a three-phase bridge type inverter circuit, a direct-current side capacitor and a controller, wherein the three-phase bridge type inverter circuit is connected with the direct-current side capacitor, the three-phase bridge type inverter circuit is connected into a three-phase power grid through a connecting reactor, and the controller controls the on-off of a switch tube in the three-phase bridge type inverter circuit; and the controller of the PWM rectifier and the controller of the static synchronous compensator are both connected to an upper computer monitoring platform.

The controller is a DSP.

The upper computer monitoring platform comprises an industrial personal computer which is communicated with the controller through an Ethernet to monitor the running state of the system in real time and respond to faults.

When the three-phase network voltage is unbalanced, the three-phase network voltage u_sa,u_sb,u_scRespectively as follows:

$\left\{\begin{array}{c}{u}_{\mathrm{sa}}={U_s}^{+}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{+})+{U_s}^{-}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{-})\\ u_{\mathrm{sb}}{=U_s}^{+}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{+}-2\mathrm{\π}/3)+{U_s}^{-}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{-}+2\mathrm{\π}/3)\\ u_{\mathrm{sc}}{=U_s}^{+}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{+}+2\mathrm{\π}/3)+{U_s}^{-}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{-}-2\mathrm{\π}/3)\end{array}\right.---\left(1\right)$

wherein, U_s ⁺、θ⁺Amplitude and initial phase angle, U, of the positive sequence component of the three-phase network voltage, respectively_s ^-、θ^-The amplitude and the initial phase angle of the negative sequence component of the three-phase power grid voltage are respectively. Let the jth PWM rectifier input current i_aj,i_bj,i_cjRespectively as follows:

$\left\{\begin{array}{c}{i}_{\mathrm{aj}}={I_j}^{+}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{+})+{I_j}^{-}\sin (\mathrm{\ωt}+{{\mathrm{\δ}}_j}^{-})\\ i_{\mathrm{bj}}{=I_j}^{+}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{+}-2\mathrm{\π}/3)+{I_j}^{-}\sin (\mathrm{\ωt}+{{\mathrm{\δ}}_j}^{-}+2\mathrm{\π}/3)\\ i_{\mathrm{cj}}{=I_j}^{+}\sin (\mathrm{\ωt}+{\mathrm{\θ}}^{+}+2\mathrm{\π}/3)+{I_j}^{-}\sin (\mathrm{\ωt}+{{\mathrm{\δ}}_j}^{-}-2\mathrm{\π}/3)\end{array}\right.---\left(2\right)$

wherein, I_j ⁺、θ⁺Is the amplitude of the positive sequence component of the PWM current, θ⁺The controller can ensure that the input current positive sequence component of the PWM rectifier is in the same phase with the voltage positive sequence component of the three-phase power grid; i is_j ^-、θ_j ^-The amplitude and the initial phase angle of the negative sequence component of the input current of the PWM rectifier are respectively.

Input power p of PWM rectifier_jComprises the following steps:

the first term on the right of the equation is the power generated by the action of the positive sequence voltage and the positive sequence current, the second term is the power generated by the action of the negative sequence voltage and the negative sequence current, the third term is the power generated by the action of the positive sequence voltage and the negative sequence current, and the fourth term is the power generated by the action of the negative sequence voltage and the positive sequence current. The first two power are constants, and the last two power fluctuate twice frequency with time. Chinese forgetInput power p of PWM rectifier_jI.e. the input power of the DC side capacitor, input power p_jThe presence of double frequency fluctuations will result in dc side voltage fluctuations. To suppress the DC side voltage fluctuation, the input power p is adjusted_jThe third term and the fourth term in the expression are cancelled, then:

$\left\{\begin{array}{c}{I_j}^{-}=\frac{{I_j}^{+}{U_s}^{-}}{{U_s}^{+}}\\ {{\mathrm{\δ}}_j}^{-}={\mathrm{\θ}}^{-}+\mathrm{\π}\end{array}\right.---\left(4\right)$

namely, the phase of the negative sequence component of the input current of the rectifier is opposite to that of the negative sequence component of the three-phase grid voltage, and the amplitude is in direct proportion to the product of the positive sequence current and the negative sequence voltage and in inverse proportion to the amplitude of the positive sequence voltage.

From the above analysis, it can be known that the PWM rectifier is controlled to input a certain amount of negative sequence current, so that the double frequency fluctuation of the dc side voltage caused by the unbalance of the three-phase grid voltage can be suppressed. However, the quality problem of electric energy generated by a plurality of PWM rectifiers cannot be ignored, a large amount of negative sequence current flows into a three-phase power grid, the loss of the power distribution network is increased, and the normal operation of other equipment of the power distribution network is threatened. The static synchronous compensator provided by the invention provides a negative sequence current opposite to the PWM rectifier so as to maintain a network side current i_sa,i_sb,i_scAnd (4) balancing three phases. Amplitude I of input negative sequence current of static synchronous compensator_c ^-And initial phase angle delta_c ^-Comprises the following steps:

$\left\{\begin{array}{c}{I_c}^{-}=\mathrm{\Σ}{I_j}^{-}=\frac{{U_s}^{-}}{{U_s}^{+}}\mathrm{\Σ}{I_j}^{+}\\ {{\mathrm{\δ}}_c}^{-}={\mathrm{\θ}}^{-}\end{array}\right.---\left(5\right)$

wherein, Σ I_j ^-Inputting the sum of the amplitudes of the negative-sequence currents, Σ I, for a plurality of PWM rectifiers_j ⁺The sum of the amplitudes of the positive sequence currents is input to a plurality of PWM rectifiers.

Fig. 2 is a control block diagram of the PWM rectifier according to the present invention in the case of unbalanced three-phase grid voltage.

Detecting to obtain three-phase power grid voltage u_sa、u_sb、u_scTransformed matrix C_abc/dq ⁺Obtaining a fundamental wave positive sequence active component U under a DQ rotation coordinate system through low-pass filtering_d ⁺And fundamental positive sequence reactive component U_q ⁺And according to U_d ⁺And U_q ⁺Obtaining the amplitude U of the positive sequence voltage of the fundamental wave_S ⁺And initial phase angle theta⁺：

$\left\{\begin{array}{c}{U_s}^{+}=\sqrt{{\left({U_d}^{+}\right)}^2+{\left({U_q}^{+}\right)}^2}\\ {\mathrm{\θ}}^{+}=\arctan \frac{{U_q}^{+}}{{U_d}^{+}}\end{array}\right.---\left(6\right)$

Wherein: transformation matrix C_abc/dq ⁺The expression of (a) is:

$C_{{\mathrm{abc}/\mathrm{dq}}^{+}}=\frac{2}{3}\left[\begin{array}{ccc}\sin \mathrm{\ωt}& \sin (\mathrm{\ωt}-2\mathrm{\π}/3)& \sin (\mathrm{\ωt}+2\mathrm{\π}/3)\\ \cos \mathrm{\ωt}& \cos (\mathrm{\ωt}-2\mathrm{\π}/3)& \cos (\mathrm{\ωt}+2\mathrm{\π}/3)\end{array}\right]---\left(7\right)$

three-phase network voltage u_sa、u_sb、u_scTransformed matrix C_abc/dq ^-Obtaining a fundamental wave negative sequence active component U under a DQ rotation coordinate system through low-pass filtering_d ^-And fundamental negative sequence reactive component U_q ^-And according to U_d ^-And U_q ^-Obtaining fundamental waveAmplitude U of positive sequence voltage_S ^-And initial phase angle theta^-：

$\left\{\begin{array}{c}{U_s}^{-}=\sqrt{{\left({U_d}^{-}\right)}^2+{\left({U_q}^{-}\right)}^2}\\ {\mathrm{\θ}}^{-}=\arctan \frac{{U_q}^{-}}{{U_d}^{-}}\end{array}\right.---\left(8\right)$

Wherein the transformation matrix C_abc/dq ^-The required phase information ω t is derived from the A-phase grid voltage u_saObtaining, via a phase-locked loop:

$C_{{\mathrm{abc}/\mathrm{dq}}^{-}}=\frac{2}{3}\left[\begin{array}{ccc}\sin \mathrm{\ωt}& \sin (\mathrm{\ωt}+2\mathrm{\π}/3)& \sin (\mathrm{\ωt}-2\mathrm{\π}/3)\\ \cos \mathrm{\ωt}& \cos (\mathrm{\ωt}+2\mathrm{\π}/3)& \cos (\mathrm{\ωt}-2\mathrm{\π}/3)\end{array}\right]---\left(9\right)$

detecting and obtaining the DC side voltage U of the jth PWM rectifier_jdcAnd an input current i_ja、i_jb、i_jc。U_jdcWith given value U of DC side voltage_jdc ^*Comparing, obtaining the amplitude I of the current positive sequence component by the error through a PI regulator_j ⁺Then, by substituting formula (4), the amplitude I of the negative sequence component of the current can be obtained_j ^-. Amplitude I of the positive sequence component_j ⁺Are respectively related to the sine signal sin (ω t + θ)⁺）、sin（ωt+θ⁺-2π/3）、sin（ωt+θ⁺+2 pi/3) to obtain the instantaneous value of the three-phase positive sequence current; amplitude I of the negative sequence component_j ^-Are respectively related to the sine signal sin (ω t + θ)^-+π）、sin（ωt+θ^--π/3）、sin（ωt+θ^-And + pi/3) to obtain the instantaneous value of the three-phase negative sequence current. The positive sequence current instantaneous value is superposed with the negative sequence current instantaneous value and is superposed with the actual input current instantaneous value i of the PWM rectifier_ja、i_jb、i_jcComparing the error with the feedforward quantity u of the three-phase power grid voltage through a proportion link K_sa、u_sb、u_scSuperposed with the DC side voltage U_jdcDividing to obtain a modulated signal u_ja、u_jb、u_jc. Finally comparing with the triangular carrier wave, modulating to obtain a PWM signal S_j1、S_j2、S_j3、S_j4、S_j5、S_j6(ii) a Wherein K can be taken as L/T_sWherein L is an inductance value of the connecting reactor, T_sThe period is controlled for the DSP.

The above control algorithm may be implemented in a DSP. The DSP also converts the running state of the PWM rectifier and the amplitude I of the negative sequence component_j ^-Uploading to an upper computer for monitoringA platform.

FIG. 3 is a control block diagram of the static synchronous compensator of the present invention.

Detecting to obtain three-phase power grid voltage u_sa、u_sb、u_scTransformed matrix C_abc/dq ⁺Obtaining a fundamental wave positive sequence active component U under a DQ rotation coordinate system through low-pass filtering_d ⁺And fundamental positive sequence reactive component U_q ⁺Obtaining the initial phase angle theta of the fundamental positive sequence voltage from equation (6)⁺. Three-phase network voltage u_sa、u_sb、u_scTransformed matrix C_abc/dq ^-Obtaining a fundamental wave positive sequence active component U under a DQ rotation coordinate system through low-pass filtering_d ^-And fundamental positive sequence reactive component U_q ^-Obtaining the initial phase angle theta of the fundamental positive sequence voltage from equation (8)^-. In which the phase information ω t required to transform the matrix is represented by the A-phase grid voltage u_saObtained via a phase locked loop.

Detecting and obtaining a load side current i_la、i_lb、i_lcTransformed matrix C_abc/dq ^-Obtaining a fundamental wave negative sequence active component I under a DQ rotation coordinate system through low-pass filtering_ld ^-And fundamental negative sequence reactive component I_lq ^-Is then transformed into a matrix

Obtaining the load side current negative sequence component instantaneous value i_la ^-、i_lb ^-、i_lc ^-Obtaining the command current i of the static synchronous compensator by taking the inverse_ca1 ^*、i_cb1 ^*、i_cc1 ^*In which the phase information ω t required to transform the matrix is represented by the A-phase grid voltage u_saObtaining, via a phase-locked loop:

$C_{{\mathrm{dq}}^{-}/\mathrm{abc}}=\left[\begin{array}{cc}\sin \mathrm{\ωt}& \cos \mathrm{\ωt}\\ \sin (\mathrm{\ωt}+2\mathrm{\π}/3)& \cos (\mathrm{\ωt}+2\mathrm{\π}/3)\\ \sin (\mathrm{\ωt}-2\mathrm{\π}/3)& \cos (\mathrm{\ωt}-2\mathrm{\π}/3)\end{array}\right]---\left(10\right)$

amplitude I of negative sequence component of input current of PWM rectifier_j ^-After the summation of the upper computer, the sigma I is obtained_j ^-Monitored by an upper computer in a communication modeThe platform is sent to a static synchronous compensator and then respectively connected with a sine signal sin (ω t + θ)^-）、sin（ωt+θ^-+2π/3）、sin（ωt+θ^--2 pi/3) to obtain the command current i_ca2 ^*、i_cb2 ^*、i_cc2 ^*。

Weighting the two parts of command current to obtain the final command current i_ca ^*、i_cb ^*、i_cc ^*：

$\left\{\begin{array}{c}{i_{\mathrm{ca}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{ca}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{ca}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\\ {i_{\mathrm{cb}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{cb}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{cb}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\\ {i_{\mathrm{cc}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{cc}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{cc}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\end{array}\right.---\left(11\right)$

Wherein eta is₁、η₂The weight, eta, of two instruction current acquisition modes₁、η₂And may take the value of 1.

Detecting and obtaining DC side voltage U of static synchronous compensator_cdcAnd an input current i_ca、i_cb、i_cc。U_cdcWith given value U of DC side voltage_cdc ^*Comparing, obtaining the amplitude I of the current positive sequence component by the error through a PI regulator_c ⁺And then respectively connected with the sine signal sin (ω t + θ)⁺）、sin（ωt+θ⁺-2π/3）、sin（ωt+θ⁺+2 pi/3) to obtain the instantaneous value of the three-phase positive sequence current. Command current i_ca ^*、i_cb ^*、i_cc ^*Superposed with the instantaneous value of the positive sequence current, and superposed with the instantaneous value i of the actual input current of the static synchronous compensator_ca、i_cb、i_ccCompared, the error is processed by a proportion link K,feed forward u from three phase network voltage_sa、u_sb、u_scSuperposed with the DC side voltage U_cdcDividing to obtain a modulated signal u_ca、u_cb、u_cc. Finally comparing with the triangular carrier wave, modulating to obtain a PWM signal S_c1、S_c2、S_c3、S_c4、S_c5、S_c6。

The above control algorithm may be implemented in a DSP.

Claims (4)

1. A PWM rectifier and static reactive compensator combined operation system comprises a plurality of PWM rectifiers and a static synchronous compensator and is characterized in that each PWM rectifier comprises a three-phase bridge inverter circuit, a direct-current side capacitor, a direct-current side load and a controller, the three-phase bridge inverter circuit, the direct-current side capacitor and the direct-current side load are sequentially connected, the controller controls the on-off of a switch tube in the three-phase bridge inverter circuit, and the three-phase bridge inverter circuit is connected into a three-phase power grid through a connecting reactance; the static synchronous compensator comprises a three-phase bridge type inverter circuit, a direct-current side capacitor and a controller, wherein the three-phase bridge type inverter circuit is connected with the direct-current side capacitor, the three-phase bridge type inverter circuit is connected into a three-phase power grid through a connecting reactor, and the controller controls the on-off of a switch tube in the three-phase bridge type inverter circuit; and the controller of the PWM rectifier and the controller of the static synchronous compensator are both connected to an upper computer monitoring platform.

2. The PWM rectifier and static var compensator operating in combination according to claim 1, wherein the controller is a DSP.

3. The PWM rectifier and static var compensator combined operation system according to claim 1, wherein the upper computer monitoring platform comprises an industrial personal computer, and the industrial personal computer is communicated with the controller through an Ethernet.

4. A method for controlling a system of a PWM rectifier and a static var compensator according to any one of claims 1 to 3 in case of an unbalanced three-phase grid voltage, the method comprising:

1) detecting three-phase network voltage u_sa、u_sb、u_scTransformed matrix C_abc/dq ⁺Obtaining fundamental wave positive sequence active component U of three-phase power grid voltage under DQ rotating coordinate system through low-pass filtering_d ⁺And fundamental positive sequence reactive component U_q ⁺And according to U_d ⁺And U_q ⁺Obtaining the amplitude U of the positive sequence voltage of the fundamental wave_S ⁺And initial phase angle theta⁺：

$\left\{\begin{array}{c}{U_s}^{+}=\sqrt{{\left({U_d}^{+}\right)}^2+{\left({U_q}^{+}\right)}^2}\\ {\mathrm{\θ}}^{+}=\arctan \frac{{U_q}^{+}}{{U_d}^{+}}\end{array}\right.,$

2) Will three-phase network voltage u_sa、u_sb、u_scTransformed matrix C_abc/dq ^-Obtaining a fundamental wave negative sequence active component U under a DQ rotation coordinate system through low-pass filtering_d ^-And fundamental negative sequence reactive component U_q ^-And according to U_d ^-And U_q ^-Obtaining the amplitude U of the fundamental wave negative sequence voltage_S ^-And initial phase angle theta^-：

$\left\{\begin{array}{c}{U_s}^{-}=\sqrt{{\left({U_d}^{-}\right)}^2+{\left({U_q}^{-}\right)}^2}\\ {\mathrm{\θ}}^{-}=\arctan \frac{{U_q}^{-}}{{U_d}^{-}}\end{array}\right.,$

3) Detecting the DC side voltage U of the jth PWM rectifier_jdcAnd input three-phase current i_ja、i_jb、i_jc(ii) a j represents any one of a plurality of PWM rectifiersA stage;

4) the DC side voltage U_jdcWith given value U of DC side voltage_jdc ^*Comparing, and adjusting the error by a PI regulator to obtain the amplitude I of the positive sequence component of the current of the jth PWM rectifier_j ⁺The amplitude I of the positive sequence component of the current_j ⁺Substituting the input negative sequence current amplitude I of the jth PWM rectifier_j ^-In the expression, the amplitude I of the current negative sequence component of the jth PWM rectifier is obtained_j ^-(ii) a Wherein,

5) amplitude I of current positive sequence component of jth PWM rectifier_j ⁺Are respectively related to the sine signal sin (ω t + θ)⁺）、sin（ωt+θ⁺-2π/3）、sin（ωt+θ⁺+2 pi/3) to obtain the instantaneous value of the three-phase positive sequence current; amplitude I of negative sequence component of jth PWM rectifier_j ^-Are respectively related to the sine signal sin (ω t + θ)^-+π）、sin（ωt+θ^--π/3）、sin（ωt+θ^-+ pi/3) to obtain the instantaneous value of the three-phase negative sequence current;

6) superposing the three-phase positive sequence current instantaneous value and the three-phase negative sequence current instantaneous value, and then superposing the superposed value and the actual input current instantaneous value i of the PWM rectifier_ja、i_jb、i_jcComparing the error of the two values with a proportionality coefficient K, and then multiplying the error with a feedforward quantity u of the three-phase power grid voltage_sa、u_sb、u_scSuperposed with DC side voltage U_jdcDividing to obtain a modulated signal u_ja、u_jb、u_jcFinally modulating signal u_ja、u_jb、u_jcComparing with the triangular carrier, modulating to obtain PWM signal S of the jth PWM rectifier_j1、S_j2、S_j3、S_j4、S_j5、S_j6；

7) Detecting the current i of a load connected to a three-phase network_la、i_lb、i_lcTransformed matrix C_abc/dq ^-Low pass filtering to obtain DFundamental negative sequence active component I under Q rotating coordinate system_ld ^-And fundamental negative sequence reactive component I_lq ^-Is then transformed into a matrix

Obtaining the load side current negative sequence component instantaneous value i_la ^-、i_lb ^-、i_lc ^-Obtaining the command current i of the static synchronous compensator by taking the inverse_ca1 ^*、i_cb1 ^*、i_cc1 ^*；

8) Amplitude I of negative sequence component of input current of PWM rectifier_j ^-After the summation of the upper computer, the sigma I is obtained_j ^-The signals are sent to a static synchronous compensator by an upper computer monitoring platform in a communication mode and then respectively matched with a sine signal sin (omega t + theta)^-）、sin（ωt+θ^-+2π/3）、sin（ωt+θ^--2 pi/3) to obtain the command current i_ca2 ^*、i_cb2 ^*、i_cc2 ^*；

9) Static synchronous compensator command current i_ca1 ^*、i_cb1 ^*、i_cc1 ^*PWM rectifier command current i_ca2 ^*、i_cb2 ^*、i_cc2 ^*Weighting the two parts of command current to obtain the final command current i_ca ^*、i_cb ^*、i_cc ^*：

$\left\{\begin{array}{c}{i_{\mathrm{ca}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{ca}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{ca}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\\ {i_{\mathrm{cb}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{cb}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{cb}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\\ {i_{\mathrm{cc}}}^{*}=({\mathrm{\η}}_1{i_{\mathrm{cc}1}}^{*}+{\mathrm{\η}}_2{i_{\mathrm{cc}2}}^{*})/({\mathrm{\η}}_1+{\mathrm{\η}}_2)\end{array}\right.$

Wherein eta is₁、η₂The weights are obtained by two instruction current obtaining modes;

10) detecting DC side voltage U of static synchronous compensator_cdcAnd an input current i_ca、i_cb、i_cc，U_cdcWith given value U of DC side voltage_cdc ^*Comparing, adjusting the error of the two by PI adjuster to obtain the amplitude I of the current positive sequence component_c ⁺Amplitude of the positive sequence component of the current I_c ⁺Respectively corresponding to sineSignal sin (ω t + θ)⁺）、sin（ωt+θ⁺-2π/3）、sin（ωt+θ⁺+2 pi/3) to obtain the instantaneous value of the three-phase positive sequence current;

11) will command current i_ca ^*、i_cb ^*、i_cc ^*Superposed with the instantaneous value of the positive sequence current and then with the instantaneous value i of the actual input current of the static synchronous compensator_ca、i_cb、i_ccComparing the error value with the feedforward quantity u of the three-phase network voltage after multiplying the error value by the proportionality coefficient K_sa、u_sb、u_scSuperimposing the value with the DC side voltage U_cdcDividing to obtain a modulated signal u_ca、u_cb、u_ccFinally modulating signal u_ca、u_cb、u_ccComparing with triangular carrier, modulating to obtain PWM signal S of static synchronous compensator_c1、S_c2、S_c3、S_c4、S_c5、S_c6。

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