CN102545677B - Parallel three-phase grid-connected inverter adopting mutual reactors and control method for three-phase grid-connected inverter - Google Patents

Abstract

The invention relates to a control method of a parallel three-phase grid-connected inverter using coupling reactors, belonging to the technical field of power grid inverters. It overcomes the shortcomings of traditional parallel grid-connected inverters, such as large volume and weight, high cost, low efficiency, narrow application range, complex control, and poor reliability. Two sets of three-phase grid-connected inverters in the inverter of the present invention are connected in parallel, and capacitors are connected in parallel on the shared DC bus, and the two AC signal output terminals belonging to the same phase in the two sets of three-phase grid-connected inverters They are respectively connected together through a set of coupling reactors and connected to the power grid. In the three-phase grid-connected inverter of the present invention, due to the use of coupling reactors, two sets of three-phase grid-connected inverters with the same structure are coupled to each other, and for each three-phase grid-connected inverter , There is also mutual coupling between the d-axis and q-axis components. In order to eliminate these effects, the control method of the present invention adopts a feed-forward decoupling control strategy while using a current loop.

Description

Control Method of Parallel Three-phase Grid-connected Inverter Using Coupling Reactor

technical field

The invention belongs to the technical field of grid inverter, and in particular relates to a three-phase grid-connected inverter.

technical background

With the enhancement of people's awareness of environmental protection and the increasing shortage of energy, the new energy industry represented by wind energy and solar energy has made great progress. In order to transmit the electrical energy converted from wind energy, solar energy, etc. to the grid, it is usually necessary to convert it into electrical energy whose amplitude, frequency, and phase are consistent with the grid, so as to realize the grid-connected operation of the system. In order to increase the power level of grid-connected inverters, reduce production costs, and improve system reliability, the parallel operation of inverters has received extensive attention. Under the condition of not increasing the current stress of a single power switch, the total current can be multiplied through the parallel connection technology, so that the development of a three-phase grid-connected inverter with a higher power level becomes a reality. In addition, when the total power is constant, power switching devices with lower power levels can be used, thereby greatly reducing production costs. At the same time, the parallel scheme facilitates modular design, shortens the production cycle, and broadens the application range of power modules. Moreover, after the carrier phase shift (CPS) technology is adopted, the harmonics of the total current after parallel connection can be greatly reduced, thereby reducing the capacity of the filter and reducing the production cost. In addition, the parallel scheme makes the N+1 redundant design a reality, which improves the reliability of the system. Combined with the hot-swap technology, it has greater advantages.

In a single converter system, since there is no zero-sequence circulation channel, there is no circulation problem, but in a parallel system, if there is a circulation channel, serious circulation problems will occur. The circulating current only flows between the parallel converters. Its existence increases the loss, reduces the system efficiency, and makes the power device heat up seriously, or even burn it out. Moreover, the circulating current will cause the problem of uneven current, so that the current stress borne by the power device will be unbalanced, which will affect its service life and limit the increase in the capacity of the entire system. At the same time, the circulating current will distort the three-phase current, which will increase the total harmonic distortion (THD), making the system unable to meet the grid-connected requirements. In addition, the high-frequency circulating current will cause serious electromagnetic interference (electromagnetic interface, EMI) problems.

In order to solve the circulation problem, scholars at home and abroad have carried out in-depth research. Traditionally, the AC side is usually used to use an isolation transformer solution or an appropriate software solution to suppress zero-sequence circulating current.

Document 1 (Dixon J W, Ooi B T.Series and parallel operation of hysteresis current-controlledPWM rectifiers[J].IEEE Transaction on Industry Applications, 1989, 25(4):644-651) multiple converters with the same structure When used in parallel, the input of each converter is isolated by the isolation transformer on the AC side, which improves the power level of the converter and eliminates the problem of zero-sequence circulating current, but the use of isolation transformers greatly increases the volume, weight and cost of the system.

Document 2 (Yoshihiro Komatsuzaki. Cross current control for parallel operating three phase inverter[C]. Power Electronics Specialists Conference, Taipei, China, 1994) and Document 3 (SFukuda, K Matsushita. A control method for parallel-connected multiple. inverter systems and Variable Speed Drive, London, England, 1998) control the parallel converter as a whole, which suppresses the circulation from the control method, but the control in this way is complicated, and it is difficult to realize when more modules are connected in parallel.

Document 4 (Li Jianlin, Gao Zhigang, Hu Shuju, et al. Application of parallel back-to-back PWM converters in direct-drive wind power generation systems [J]. Power System Automation, 2008, 32(5): 59-62) proposed an independent DC bus The topological structure eliminates the circulating current channel on the hardware, solves the circulating current problem, and makes the system control relatively simple, but this topology is only suitable for special motors with electrical isolation. When the motor is a commonly used three-phase motor There are still serious circulation problems, and the machine-side circulation and grid-side circulation are coupled with each other, which limits its application occasions. In addition, due to the separation of DC buses in this topology, the voltages of the two buses must be controlled separately, which increases the volume of the system and is not conducive to modular design.

Document 5 (Li Rui, Xu Zhuang, Xu Dianguo. Circulation analysis and control of parallel permanent magnet direct drive wind power system [J]. Chinese Journal of Electrical Engineering, 2011, 31(6): 38-45) proposed a parallel variable Inverter topology, the isolation transformer is omitted on the AC side, and a zero-sequence circulator controller is designed to suppress the zero-sequence circulating current and greatly improve the power level of the converter. However, due to the small zero-sequence circulating current impedance, zero-sequence It is relatively difficult to solve the sequence circulation problem. In addition, the use of zero-sequence circulation controller increases the complexity of the control system.

Contents of the invention

In order to overcome the shortcomings of traditional parallel-connected grid-connected inverters such as large volume and weight, high cost, low efficiency, narrow application range, complex control, and poor reliability, the present invention proposes a parallel-connected three-phase grid-connected inverter using coupling reactors. A converter and a control method for the three-phase grid-connected inverter.

The parallel-connected three-phase grid-connected inverter using coupling reactors described in the present invention is composed of two sets of three-phase grid-connected inverters with the same structure and three sets of coupling reactors. Grid inverters share a common DC bus, and capacitors are connected in parallel on the DC bus; the two sets of three-phase grid-connected inverters with the same structure are connected in parallel with each other, and the two sets of three-phase grid-connected inverters with the same structure belong to The two AC signal output ends of the same phase are respectively connected together through a set of coupling reactors and connected to the power grid.

The power switches in the two sets of three-phase grid-connected inverters with the same structure are realized by IGBT.

The control method of the above-mentioned three-phase grid-connected inverter is as follows: the DC bus voltage signal measured by the voltage sensor is used as the DC voltage feedback value U _dc , and the difference between the DC bus voltage given value U _dcref and the DC voltage feedback value U _dc is input To the voltage loop PI controller, after being processed by the voltage loop PI controller, _idref is obtained, and the _idref is weighted to obtain two current given values i _d1ref and i _d2ref , and the two current given values i _d1ref , i _d2ref respectively serve as the current given value of the d-axis current loop controller of the two sets of grid-connected three-phase inverters;

At the same time, the three-phase current signals of the two sets of grid-connected inverters are respectively measured by current sensors, and the three-phase current signals are transformed by coordinates to obtain the d-axis currents i _d1 and i of the two sets of grid-connected inverters _d2 and q-axis current i _q1 , i _q2 ; the d-axis current i _d1 , i _d2 and q-axis current i _q1 , i _q2 are respectively used as the feedback value of the d-axis current loop and the feedback value of the q-axis current loop to realize the d-axis Closed-loop control of the current loop and closed-loop control of the q-axis current;

The feedback value i _d1 , i _d2 of each d-axis current loop is respectively different from the corresponding current given value i _d1ref , i _{d2ref ,} adjusted by PI, and then added to the corresponding feedforward compensation amount to obtain u _d1 , u _d2 ;

The feedback value i _q1 , i q2 _of each q-axis current loop is different from the corresponding current given value i _q1ref , i _q2ref respectively, adjusted by PI, and then added to the corresponding feedforward compensation amount to obtain u _q1 , u _q2 ;

The u _d1 , u _d2 and u _q1 , u _q2 are used as the output signals of the current loop controller, and the output signals are inversely transformed by Park to obtain the voltage reference in the two-phase stationary coordinate system, and the voltage reference is used as the SVPWM module The input generates the duty ratio signal of the three-phase bridge arm, and then obtains the six-way control PWM signal of two sets of grid-connected three-phase inverters to realize the control of the grid-connected inverters;

The feedback values i _d1 and i _d2 of each d-axis current loop are respectively different from the corresponding current given values i _d1ref and i _d2ref , adjusted by PI, and then added to the corresponding feedforward compensation amount to obtain u _d1 , u _d2 , the corresponding feedforward compensation amounts are _ed +ωL ₁ ′i _q1 –ωMi _q and _ed +ωL ₂ ′i _q2 –ωMi _q respectively, and _ed is the d-axis feedforward component of grid voltage , ω is the grid synchronous angular velocity; L ₁ ′ is the equivalent inductance of the three-phase branch of the first set of three-phase grid-connected inverter; L ₂ ′ is the three-phase branch of the second set of three-phase grid-connected inverter, etc. Effective inductance; M is the three-phase inductance between two sets of three-phase inverters.

In the three-phase grid-connected inverter of the present invention, due to the use of coupling reactors, two sets of three-phase grid-connected inverters with the same structure are coupled to each other, and for each three-phase grid-connected inverter , There is also mutual coupling between the d-axis and q-axis components. In order to eliminate these effects, the present invention adopts a feed-forward decoupling control strategy when designing the current loop.

Since the two sets of three-phase grid-connected inverters are connected in parallel, the two sets of three-phase grid-connected inverters use a common voltage outer loop and a separate current inner loop.

In the above control method, the current reference i _q1ref and i _q2ref of the q-axis current loop controller are generally zero, so as to ensure that the grid-connected inverter has the greatest ability to feed active power to the grid under a certain capacity, and realize unity power factor Grid-connected, the q-axis current given i _q1ref and i _q2ref can also be given by the reactive power demand of the grid, so as to realize the reactive power compensation of the system to the grid.

The power level of the inverter described in the present invention is doubled, the design of the control system is simplified, the isolation transformer is omitted, the volume and weight of the converter are greatly reduced, the cost is reduced, and the Zero-sequence circulation solves the problems of uneven current and waveform distortion caused by zero-sequence circulation, improves efficiency and reliability, and makes parallel-connected three-phase grid-connected inverters applicable to high-power wind power generation, solar power generation and gas turbine power generation and other occasions.

The present invention adopts the parallel connection scheme of coupling reactors. First, the coupling reactor only has a damping effect on the differential mode component of the branch current of the parallel converter, and has no damping effect on its common mode component, so it has an independent current sharing effect, so that The current stress of each parallel converter tends to be consistent, thus laying a foundation for improving the power level of the converter. At the same time, under ideal conditions, the branch currents of the two parallel inverters are equal, and no magnetic flux is generated for the coupling reactors connected in parallel on different sides. Therefore, compared with the traditional reactor, the volume of the coupling reactor can be greatly reduced. In addition, the coupling reactor can suppress the zero-sequence circulating current.

The characteristics of the present invention are: two sets of three-phase grid-connected inverters with the same structure are connected in parallel through coupling reactors, so that the power level of the inverters is doubled; the two parallel inverters use exactly the same The control structure simplifies the design of the control system; since the isolation transformer is omitted, the volume and weight of the converter are greatly reduced, and the cost is reduced; at the same time, the circulating current is suppressed, and the uneven current between two parallel converters is solved. Waveform distortion and other problems have improved efficiency and reliability, making parallel three-phase grid-connected inverters applicable to high-power wind power generation, solar power generation, and gas turbine power generation.

Description of drawings

Fig. 1 is a topological structure of a parallel three-phase grid-connected inverter using coupling reactors according to the present invention.

Fig. 2 is a decoupling equivalent circuit schematic diagram of the topology of the parallel-connected three-phase grid-connected inverter using coupling reactors according to the present invention.

Fig. 3 is a schematic diagram of an equivalent circuit in a synchronous rotating coordinate system of the topology structure of the parallel three-phase grid-connected inverter using coupling reactors according to the present invention.

Fig. 4 is a control schematic diagram of the control method of the three-phase grid-connected inverter according to the present invention.

Detailed ways

Specific Embodiments 1. Refer to Figures 1, 2 and 3 to illustrate this embodiment. The parallel-connected three-phase grid-connected inverter using coupling reactors described in this embodiment consists of two sets of three-phase grid-connected inverters with the same structure Composed of three sets of coupling reactors, the two sets of three-phase grid-connected inverters with the same structure share a common DC bus, and capacitors are connected in parallel on the DC bus; the two sets of three-phase grid-connected inverters with the same structure Connected in parallel with each other, the two AC signal output terminals belonging to the same phase in two sets of three-phase grid-connected inverters with the same structure are respectively connected together through a set of coupling reactors and connected to the power grid.

The power switches in the two sets of three-phase grid-connected inverters with the same structure described in this embodiment can be realized by using IGBTs.

The topology of the parallel-connected three-phase grid-connected inverter using coupling reactors described in this embodiment is shown in Figure 1. The electric energy transmitted by the previous stage is filtered and stored by the capacitor C connected in parallel on the shared common DC bus. After the voltage is stabilized, it is sent to the subsequent parallel-connected three-phase grid-connected inverter. Each set of three-phase grid-connected inverter consists of three bridge arms, the three bridge arms of the first set of three-phase grid-connected inverter are A ₁ , B ₁ , and C ₁ , and the second set of three-phase grid-connected inverters are The three bridge arms of the inverter are A ₂ , B ₂ , and C ₂ . Two sets of three-phase grid-connected inverters are connected in parallel. _k1 and L _k2 (k=a,b,c) are then connected together, and then connected to the power grid. There is coupling between the inductors L _k1 and L _k2 , the mutual inductance is M _k (k=a,b,c), and it is a parallel circuit on different sides; R _ak , R _bk , R _ck (k=1,2) are respectively K sets of three-phase grid-connected inverters include the line resistance of each phase including inductance resistance; U _dc is the bus DC voltage of the shared shared DC bus.

See Figure 2 for the decoupling equivalent circuit of the topology shown in Figure 1, in which L _ak ′=L _ak +M _a , L _bk ′=L _bk +M _b , L _ck ′=L _ck +M _c (k=1,2), and usually take L _ak =L _bk =L _ck =L _k ,R _ak =R _bk =R _ck =R _k (k=1,2),M _a =M _b =M _c =M _; i _l is the direct current transmitted by the previous stage; i _ak , i _bk , i _ck (k=1,2) are the three-phase grid-connected branch currents of the k-th set of three-phase grid-connected inverter; e _a , e _b , e _c are the three-phase voltages of the grid respectively.

When selecting the mutual inductance M, it can neither be too small nor too large. If it is too small, it will reduce the effect of the coupling reactor on suppressing the zero-sequence circulating current. If it is too large, it will increase the coupling between the two parallel inverters, thereby increasing the control efficiency. Difficulty, after trade-off consideration, the present invention takes the typical value of coupling coefficient k as 0.415, then the mutual inductance M is:

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}\sqrt{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0.415</span>}\sqrt{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the above formula, k is the coupling coefficient, L ₁ is the three-phase self-inductance of the first three-phase grid-connected inverter, and L ₂ is the three-phase self-inductance of the second three-phase grid-connected inverter.

See Figure 3 for the equivalent circuit in the synchronous rotating coordinate system of the topological structure shown in Figure 1, in which L _k ′=L _ak ′=L _bk ′=L _ck ′(k=1,2); i _dk , i _qk (k=1,2) are the d-axis and q-axis grid-connected branch currents respectively; d _dk , d _qk , d _zk (k=1,2) are the duty ratios of the d-axis, q-axis, and z-axis respectively; e _d , e _q are d-axis and q-axis voltages of the power grid respectively; ω is the synchronous angular velocity of the power grid.

It can be seen from Figure 3 that the d-axis current components i _d1 and i _d2 are coupled together through the inductor –M and the controlled voltage source (–ωMi _q ), which increases the difficulty of control. Due to the symmetry of the d-axis and q-axis, similar conclusions can be drawn for the q-axis current component. It can be seen from the z-axis equivalent circuit in the figure that the zero-sequence circulating current impedance is (L ₁ +L ₂ +R ₁ +R ₂ +2M), and the formula R ₁ is the included inductance of the first three-phase grid-connected inverter The equivalent resistance of the three-phase line including the resistance, _R2 is the equivalent resistance of the three-phase line including the inductance resistance of the second set of three-phase grid-connected inverter. However, when using ordinary three-phase reactors, the zero-sequence circulating current impedance is only (L ₁ +L ₂ +R ₁ +R ₂ ), so when using coupling reactors, the zero-sequence circulating current resistance is relatively large, which plays a role in suppressing zero-sequence circulating current. Especially for high-frequency zero-sequence circulating current effect is more obvious. Its use saves the bulky isolation transformer and complex zero-sequence circulating current controller on the AC side, reduces the production cost, reduces the size and weight of the grid-connected inverter, and simplifies the design of the control system, improving the parallelism. performance of grid inverters.

Define i _zs as the system zero-sequence circulating current of the parallel-connected three-phase grid-connected inverter, and

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; zs</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="z"\; filenames="HDA0000135935880000021.png"\; state="\{\{state\}\}">z</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Then the zero-sequence circulation can be further expressed as:

$\frac{{\mathrm{<span\; class="notranslate">\; di</span>}}_{\mathrm{<span\; class="notranslate">\; zs</span>}}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="R"\; filenames="HDA0000135935880000021.png"\; state="\{\{state\}\}">R</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="L"\; filenames="HDA0000135935880000021.png"\; state="\{\{state\}\}">L</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; zs</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="L"\; filenames="HDA0000135935880000021.png"\; state="\{\{state\}\}">L</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; m</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; dc</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

Specific Embodiment 2. Referring to FIG. 4, this embodiment will be described. This embodiment describes the control method for the parallel-connected three-phase grid-connected inverter using coupling reactors described in the first embodiment, the control method is: using the DC bus voltage signal obtained by voltage sensor measurement as The DC voltage feedback value Udc, the difference between the DC bus voltage reference value Udcref and the DC voltage feedback value Udc are input to the voltage loop PI controller, and the idref is obtained after being processed by the voltage loop PI controller, and the idref is obtained after weight distribution. Two current given values id1ref, id2ref, the two current given values id1ref, id2ref respectively serve as the current given values of the d-axis current loop controllers of two sets of grid-connected three-phase inverters;

At the same time, the three-phase current signals of the two sets of grid-connected inverters are respectively measured by current sensors, and the three-phase current signals are transformed by coordinates to obtain the d-axis currents i _d1 and i of the two sets of grid-connected inverters _d2 and q-axis current i _q1 , i _q2 ; the d-axis current i _d1 , i _d2 and q-axis current i _q1 , i _q2 are respectively used as the feedback value of the d-axis current loop and the feedback value of the q-axis current loop to realize the d-axis Closed-loop control of the current loop and closed-loop control of the q-axis current;

The feedback value i _d1 , i _d2 of each d-axis current loop is respectively different from the corresponding current given value i _d1ref , i _{d2ref ,} adjusted by PI, and then added to the corresponding feedforward compensation amount to obtain u _d1 , u _d2 ;

The feedback value i _q1 , i q2 _of each q-axis current loop is different from the corresponding current given value i _q1ref , i _q2ref respectively, adjusted by PI, and then added to the corresponding feedforward compensation amount to obtain u _q1 , u _q2 ;

The u _d1 , u _d2 and u _q1 , u _q2 are used as the output signals of the current loop controller, and the output signals are inversely transformed by Park to obtain the voltage reference in the two-phase stationary coordinate system, and the voltage reference is used as the SVPWM module The input generates the duty cycle signal of the three-phase bridge arm, and then obtains six control PWM signals of two sets of grid-connected three-phase inverters to realize the control of the grid-connected inverters.

Specific Embodiment 3. This embodiment is a further limitation of the control method described in Specific Embodiment 2. In this embodiment, the process of weight distribution is: perform current weighting according to the power capacity of two sets of three-phase inverters Allocation, if the power capacity of two sets of three-phase inverters is equal, the equivalent allocation will be carried out, that is, i _d1ref =i _d2ref =0.5i _dref ; if the power capacity of two sets of three-phase inverters is not equal, then according to the power capacity Distribution is carried out in proportion, that is, i _d1ref =j·i _dref , i _d2ref =(1–j) i _dref , and j is the power capacity ratio of two sets of three-phase inverters.

Embodiment 4. This embodiment is a further limitation of the control method described in Embodiment 2. In this embodiment, the current given i _q1ref and i _q2ref values of the q-axis current loop controller are both 0 .

Embodiment 5. This embodiment is a further limitation of the control method described in Embodiment 2. In this embodiment, the feedback values i _d1 and i _d2 of each d-axis current loop are respectively related to the corresponding current given After the fixed values i _d1ref and i _d2ref are adjusted by PI after making difference, they are added to the corresponding feed-forward compensation amount respectively to obtain u _d1 and u _d2 , and the corresponding feed-forward compensation amount is respectively e _d +ωL ₁ ′ i _q1 –ωMi _q and _ed +ωL ₂ ′i _q2 –ωMi _q , e _d is the grid voltage d-axis feedforward component, ω is the synchronous angular velocity of the grid; L ₁ ′ is the first set of three-phase grid-connected inverter Three-phase branch equivalent inductance; L ₂ ′ is the three-phase branch equivalent inductance of the second set of three-phase grid-connected inverters; M is the three-phase mutual inductance between two sets of three-phase inverters.

Specific Embodiment 6. This embodiment is a further limitation of the control method described in Embodiment 2. In this embodiment, the feedback values i _q1 and i _q2 of each q-axis current loop are respectively related to the corresponding current given value After i _q1ref and i _q2ref are adjusted by PI, they are added to the corresponding feedforward compensation amounts to obtain u _q1 and u _q2 respectively, and the corresponding feedforward compensation amounts are ωL ₁ ′i _d1 –ωMi _d and ωL ₂ ′i _d2 –ωMi _d , ω is the grid synchronous angular velocity; L ₁ ′ is the three-phase branch equivalent inductance of the first set of three-phase grid-connected inverter; L ₂ ′ is the second set of three-phase grid-connected inverter The equivalent inductance of the three-phase branch of the inverter; M is the three-phase mutual inductance between two sets of three-phase inverters.

Embodiment 7. This embodiment is a further limitation of the control method described in Embodiment 2. In this embodiment, the u _d1 , u _d2 and u _q1 , u _q2 are used as the output signals of the current loop controller, After the output signal is inversely transformed by Park, the voltage reference quantity in the two-phase static coordinate system is obtained, and the voltage reference quantity is used as the input of the SVPWM module to generate the duty ratio signal of the three-phase bridge arm, and then two sets of grid-connected three-phase inverters are obtained. The process of the six-way control PWM signal of the inverter is as follows: the u _d1 and u _q1 are inversely transformed by Park to obtain the voltage reference quantities u _α1 and u _β1 in the two-phase stationary coordinate system, and the voltage reference quantities u _α1 and u _β1 is used as the input signal of the SVPWM module to control the SVPWM module to generate three-phase duty ratio signals d _a1 , d _b1 , d _c1 , and generate 6 channels of PWM waves according to the three-phase duty ratio signals d _a1 , d _b1 , and d _c1 , the 6-way PWM wave is amplified as a set of 6-way PWM driving signals of a three-phase grid-connected inverter; the voltage u _d2 , u _q2 are inversely transformed by Park to obtain the voltage references u _α2 , u _β2 , the voltage references u _α2 and u _β2 are used as the input signals of the SVPWM module to control the SVPWM module to generate three-phase duty cycle signals d _a2 , d _b2 , d _c2 , and according to the three-phase duty cycle signal d _a2 , d _b2 , and d _c2 generate 6 channels of PWM waves, which are amplified and used as 6 channels of PWM driving signals for another set of three-phase grid-connected inverters.

Since the two sets of three-phase grid-connected inverters use a common voltage outer loop and an independent current inner loop, the function of the voltage loop is mainly to maintain the stability of the DC bus voltage, so that energy is transmitted from the DC side to the grid. Its output is given i _d1ref and i _d2ref respectively as the d-axis currents of two sets of three-phase grid-connected inverters after being distributed by current weight. In the case of a certain capacity of the three-phase grid-connected inverter, in order to transmit energy to the grid to the maximum, the q-axis current setting i _q1ref and i _q2ref of the two sets of three-phase grid-connected inverters are generally set to zero, so as to realize Unity power factor grid connection. i _q1ref and i _q2ref can also be given by the reactive power requirements of the grid for the system.

Due to the symmetry between the two sets of three-phase grid-connected inverters, and the symmetry between the d-axis and q-axis components of the current loop, the d-axis and q-axis of the two sets of three-phase grid-connected inverters A current loop controller can use the same control parameters.

Due to the use of coupling reactors, the two sets of three-phase grid-connected inverters are coupled to each other, and for each set of three-phase grid-connected inverters, there is also mutual coupling between the d-axis and q-axis components, as To eliminate these effects, a feed-forward decoupling control strategy should be used when designing the current loop. Taking the d-axis current loop controller of the first three-phase grid-connected inverter as an example, the decoupling term (ωL ₁ ′i _q1 –ωMi _q ) is compensated to the output of the PI regulator, so that the d-axis, q The decoupling between the axis components can also play the role of decoupling between the two grid-connected inverters. In addition, the grid voltage d-axis feedforward component _ed offsets the influence of the actual grid voltage, and then the d-axis output reference voltage u _d1 of the first set of three-phase grid-connected inverters is obtained. After obtaining the output reference voltage of the d-axis and q-axis, it is sent to the SVPWM module through coordinate inverse transformation, and then the three-phase duty ratio signal is obtained, so as to realize the control of the grid-connected inverter.

In the above control method, the voltage loop PI controller is a voltage loop controller of a common voltage outer loop used by two sets of three-phase grid-connected inverters.

The principle of the above control method is:

The three-phase current signals of two sets of grid-connected inverters are respectively measured by current sensors, which are the three-phase current signals i _a1 , i _b1 and i _c1 of the first set of three-phase grid-connected inverters, and the second set of three-phase parallel inverters The three-phase current signals i _a2 , i _b2 , i _c2 , of the grid inverter, and the three-phase voltages are u _a , _ub , _uc respectively.

The above current and voltage parameters are transformed into coordinates to obtain the corresponding physical quantities i _d1 , i _q1 , i _z1 , i _d2 , i _q2 , i _z2 , u _d , u _q in the synchronous rotating coordinate system, where i _d1 and i _d2 are taken as d The feedback of the shaft current loop controller is adjusted by PI after making difference with the given value i _d1ref and i _d2ref respectively, and adding the respective compensation amount (e _d +ωL ₁ ′i _q1 –ωMi _q ), (e _d +ωL ₂ ′i _q2 –ωMi _q ) as the output voltage reference u _d1 and u _d2 of the d-axis current loop controller. The current setting of the q-axis current loop controller is generally zero, that is, i _q1ref =i _q2ref =0, to ensure that the grid-connected inverter has the maximum ability to feed active power to the grid under a certain capacity, and achieve unity power factor Grid-connected, i _q1ref and i _q2ref can also be given by the reactive power demand of the grid, so as to realize the reactive power compensation of the system to the grid. This embodiment adopts the former method. Feedback values i _q1 , i _q2 are respectively different from i _q1ref , i _q2ref and then adjusted by PI, adding their respective compensation amounts (ωL ₁ ′i _d1 –ωMi _d ), (ωL ₂ ′i _d2 –ωMi _d ) as Output voltage reference quantities u _q1 and u _q2 of the q-axis current loop controller. The voltage references u _d1 , u _q1 are inversely transformed by Park to obtain the voltage references u _α1 , u _β1 in the two-phase stationary coordinate system, which are used as the input of the SVPWM module to generate three-phase duty cycle signals d _a1 , d _b1 , d _c1 , In this way, 6 channels of PWM waves are generated, which are isolated by optical fibers and sent to the drive board, and finally the 6 channels of PWM driving signals for the first set of three-phase grid-connected inverters are obtained. The voltage references u _d2 , u _q2 are inversely transformed by Park to obtain the voltage references u _α2 , u _β2 in the two-phase stationary coordinate system, which are used as the input of the SVPWM module to obtain the three-phase duty cycle signals d _a2 , d _b2 , d _c2 , In this way, 6 channels of PWM waves are generated, which are isolated by optical fibers and sent to the drive board, and finally 6 channels of PWM driving signals for the second set of three-phase grid-connected inverters are obtained.

Claims (5)

1. A control method for a parallel-connected three-phase grid-connected inverter using coupling reactors, the parallel-connected three-phase grid-connected inverter using coupling reactors consists of two sets of three-phase grid-connected inverters with the same structure Composed of three sets of coupling reactors, the two sets of three-phase grid-connected inverters with the same structure share a common DC bus, and capacitors are connected in parallel on the DC bus; the two sets of three-phase grid-connected inverters with the same structure Connected in parallel with each other, the two AC signal output terminals belonging to the same phase in two sets of three-phase grid-connected inverters with the same structure are respectively connected together through a set of coupling reactors and connected to the power grid. The control method uses the DC bus voltage signal obtained by voltage sensor measurement as the DC voltage feedback value U _dc , and the difference between the DC bus voltage given value U _dcref and the DC voltage feedback value U _dc is input to the voltage loop PI controller. The voltage loop PI controller obtains _idref after processing, and the _idref obtains two current given values i _d1ref and i _d2ref after weight distribution, and the two current given values i _d1ref and i _d2ref are respectively used as two sets of grid-connected The current given value of the d-axis current loop controller of the three-phase inverter; At the same time, the three-phase current signals of the two sets of grid-connected inverters are respectively measured by current sensors, and the three-phase current signals are transformed by coordinates to obtain the d-axis currents i _d1 and i of the two sets of grid-connected inverters _d2 and q-axis current i _q1 , i _q2 ; the d-axis current i _d1 , i _d2 and q-axis current i _q1 , i _q2 are respectively used as the feedback value of the d-axis current loop and the feedback value of the q-axis current loop to realize the d-axis Closed-loop control of the current loop and closed-loop control of the q-axis current; The feedback value i _d1 , i _d2 of each d-axis current loop is respectively different from the corresponding current given value i _d1ref , i _{d2ref ,} adjusted by PI, and then added to the corresponding feedforward compensation amount to obtain u _d1 , u _d2 ; The feedback value i _q1 , i _{q2 of each q-axis current loop is different from the corresponding current given value i q1ref , i q2ref respectively} , adjusted by PI, and then added to the corresponding feedforward compensation amount to obtain u _q1 , u _q2 ; The u _d1 , u _d2 and u _q1 , u _q2 are used as the output signals of the current loop controller, and the output signals are inversely transformed by Park to obtain the voltage reference in the two-phase stationary coordinate system, and the voltage reference is used as the SVPWM module The input generates the duty ratio signal of the three-phase bridge arm, and then obtains the six-way control PWM signal of two sets of grid-connected three-phase inverters to realize the control of the grid-connected inverters; It is characterized in that: the feedback value i _d1 , i _d2 of each d-axis current loop is respectively different from the corresponding current given value i _d1ref , i _{d2ref ,} adjusted by PI, and then respectively compared with the corresponding feedforward compensation amount Perform addition to obtain u _d1 and u _d2 , and the corresponding feedforward compensation amounts are _ed +ωL ₁ ′i _q1 –ωMi _q and _ed +ωL ₂ ′i _q2 –ωMi _q respectively, and _ed is the grid voltage d axis feedforward component, ω is the grid synchronous angular velocity; L ₁ ′ is the three-phase branch equivalent inductance of the first set of three-phase grid-connected inverter; L ₂ ′ is the three-phase inductance of the second set of three-phase grid-connected inverter Phase branch equivalent inductance; M is the three-phase mutual inductance between two sets of three-phase inverters. 2. The control method of the parallel-connected three-phase grid-connected inverter using coupling reactors according to claim 1, wherein the process of weight distribution is: according to the power of two sets of three-phase inverters If the power capacity of the two sets of three-phase inverters is equal, the equivalent distribution is carried out, that is, i _d1ref =i _d2ref =0.5i _dref ; if the power capacities of the two sets of three-phase inverters are not equal, The power capacity is distributed in proportion, that is, i _d1ref =j· _idref , i _d2ref =(1–j)i _dref , and j is the power capacity ratio of two sets of three-phase inverters. 3. The control method of the parallel-connected three-phase grid-connected inverter adopting coupling reactor according to claim 1, characterized in that, the current given values of _iq1ref and _iq2ref of the q-axis current loop controller Both are 0. 4. The control method of a parallel three-phase grid-connected inverter using a coupled reactor according to claim 1, wherein the feedback values i _q1 and i _q2 of each q-axis current loop are respectively compared with the corresponding current The given values i _q1ref , i _q2ref are adjusted by PI after making a difference, and then added to the corresponding feedforward compensation amount to obtain u _q1 , u _q2 respectively, and the corresponding feedforward compensation amount is ωL ₁ ′i _d1 –ωMi _d and ωL ₂ ′i _d2 –ωMi _d , ω is the grid synchronous angular velocity; L ₁ ′ is the three-phase branch equivalent inductance of the first set of three-phase grid-connected inverter; L ₂ ′ is the second set of three-phase The three-phase branch equivalent inductance of the phase grid-connected inverter; M is the three-phase mutual inductance between two sets of three-phase inverters. 5. The control method of the parallel-connected three-phase grid-connected inverter using coupling reactors according to claim 1, characterized in that, the u _d1 , u _d2 and u _q1 , u _q2 are used as the current loop controller Output signal, the output signal is obtained after Park inverse transformation, the voltage reference in the two-phase stationary coordinate system, the voltage reference is used as the input of the SVPWM module to generate the duty ratio signal of the three-phase bridge arm, and then two sets of grid-connected The process of the six control PWM signals of the three-phase inverter is as follows: the u _d1 and u _q1 are inversely transformed by Park to obtain the voltage references u _α1 and u _β1 in the two-phase stationary coordinate system, and the voltage reference u _α1 and u _β1 are used as the input signals of the SVPWM module to control _the SVPWM module to generate three-phase duty cycle signals d _a1 , d _b1 , _{d c1 ,} and _generate 6 6 channels of PWM waves, the 6 channels of PWM waves are amplified as a set of 6 channels of PWM driving signals for a three-phase grid-connected inverter; the voltage u _d2 and u _q2 are inversely transformed by Park to obtain the voltage reference in the two-phase stationary coordinate system u _α2 , u _β2 , the voltage references u _α2 , u _β2 are used as the input signals of the SVPWM module to control the SVPWM module to generate three-phase duty ratio signals d _a2 , d _b2 , d _c2 , according to the three-phase duty cycle The ratio signals d _a2 , d _b2 , and d _c2 generate 6 channels of PWM waves, which are amplified and used as 6 channels of PWM driving signals for another set of three-phase grid-connected inverters.

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