CN105098804A - Method and device for controlling three-phase unbalanced current of virtual synchronous generator - Google Patents

Abstract

The invention discloses a method and a device for controlling three-phase unbalanced current of a virtual synchronous generator. The method comprises the following steps: establishing a rotor movement equation of the virtual synchronous generator (VSG) and a virtual excitation equation of the VSG; decomposing unbalanced voltage of a power grid into positive sequence voltage, negative sequence voltage, zero sequence voltage and corresponding phase-sequence current, and decomposing active power and reactive power output by the VSG to analyze an encountered imbalance problem; calculating a reference instruction of dq axis current according to the output three-phase voltage signal; and converting the reference instruction of the current into a pulse-width modulation (PWM) voltage modulation signal through a self-designed current inner ring, and controlling the virtual synchronous generator to run through the PWM voltage modulation signal, so as to enable the output three-phase current of the virtual synchronous generator to reach the balance. According to the control method disclosed by the embodiment of the invention, the VSG can still output three-phase balanced current when the three-phase voltage of the power grid is unbalanced, so that the operation safety of the power grid can be relatively well ensured; and the method and the device are safe, reliable, simple and convenient.

Description

The control method of the three phase unbalance current of virtual synchronous generator and device

Technical field

The present invention relates to power control technology field, particularly a kind of control method of three phase unbalance current of virtual synchronous generator and device.

Background technology

The output of distributed power source is generally the alternating current of direct current or non-power frequency, therefore needs to be connected with electrical network by combining inverter.Because traditional combining inverter belongs to static equipment, inertia and Damper Braces can not be provided for electrical network, therefore cannot participate in electrical network and regulate, along with the increase of distributed power source permeability, will inevitably the stability of serious threat operation of power networks.

In recent years, the combining inverter based on virtual synchronous generator (VSG, VirtualSynchronousGenerator) controls to receive publicity.The basic thought of VSG is the characteristic of simulation synchronous generator, the equation of rotor motion of imitation synchronous generator and field regulation characteristics is utilized to control inverter, inverter is made to have the characteristic similar to synchronous generator, to be reached for the object that electrical network provides inertia and damping to support.

In reality, there is the phenomenon of three-phase imbalance in the impact that line voltage is vulnerable to the factors such as laod unbalance, short trouble, open-phase operation, VSG there will be the problems such as current overload, power oscillation, current imbalance in this case, threatens its safe and stable operation.Therefore, consider that the control research of VSG under three-phase imbalance line voltage has great importance.At present, both at home and abroad to the concern of this problem with study less, mainly control to imitate conventional inverter.But, control to be calculated by power outer shroud directly to obtain current inner loop reference instruction due to conventional inverter, and VSG needs power instruction to control by being converted into voltage reference value after simulation synchronous generator operation logic, there is difference in the two input/output interface, control mechanism etc., therefore traditional control method cannot be directly used in VSG unbalanced operation and control.

Summary of the invention

The present invention is intended to solve one of technical problem in above-mentioned correlation technique at least to a certain extent.

For this reason, one object of the present invention is the control method of the three phase unbalance current proposing a kind of virtual synchronous generator, and this control method can make VSG still can export three-phase equilibrium electric current when electrical network imbalance of three-phase voltage, and realizes simple.

Another object of the present invention is the control device of the three phase unbalance current proposing a kind of virtual synchronous generator.

For achieving the above object, one aspect of the present invention embodiment proposes a kind of control method of three phase unbalance current of virtual synchronous generator, comprises the following steps: set up the equation of rotor motion of VSG and the virtual excitation equation of VSG of electromagnetic property that imitate synchronous generator mechanical property; Line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, and the active power exported by VSG according to described positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current and reactive power are decomposed into average weight and wave component, the power fluctuation faced by running when unbalanced source voltage with analyzing virtual synchronous generator and three-phase current unbalance; Calculate the reference instruction of dq shaft current according to three-phase voltage signal, equal the set point of virtual synchronous generator to make described average weight and suppress negative-sequence current; And the reference instruction of described electric current is converted into PWM (PulseWidthModulation, pulse width modulation) voltage modulation signal, and control described virtual synchronous generator operation by described PWM voltage modulation signal, thus the output three-phase current of described virtual synchronous generator is made to reach balance.

According to the control method of the three phase unbalance current of the virtual synchronous generator of embodiment of the present invention proposition, by line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, power fluctuation faced by running when unbalanced source voltage according to their relationship analysis virtual synchronous generator and three-phase current unbalance, and by calculating the reference instruction of dq shaft current, thus make average weight equal the set point of virtual synchronous generator and suppress negative-sequence current, finally by with reference to instruction morphing be PWM voltage modulation signal, the three-phase current realizing virtual synchronous generator reaches the object of balance, even if VSG still can export three-phase equilibrium electric current when electrical network imbalance of three-phase voltage, thus ensure the stability of operation of power networks better, not only safe and reliable, and it is simple and convenient.

In addition, the control method of the three phase unbalance current of virtual synchronous generator according to the above embodiment of the present invention can also have following additional technical characteristic:

Further, in one embodiment of the invention, described VSG equation of rotor motion is:

$J\frac{d\mathrm{\ω}}{dt}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0),$

Wherein, J is virtual rotation inertia, and ω is the virtual angular speed of VSG, T _mand T _ebe respectively virtual machine torque and electromagnetic torque, D is damping coefficient, ω ₀for the reference value of synchronous angular velocity.

Further, in one embodiment of the invention, the virtual excitation equation of described VSG is:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e,$

Wherein, M _ffor the maximum of mutual inductance between rotor with a phase stator, i _ffor the size of exciting current, K is the inertia coeffeicent of excitation regulation.

Further, in one embodiment of the invention, the reference instruction of dq shaft current according to following formulae discovery:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right],$

Wherein, for the dq component of forward-order current, L and R is total inductance between inverter to electrical network and all-in resistance, and s is differential operator, and ω is the virtual angular speed of VSG.

Further, in one embodiment of the invention, by 2 subharmonic voltages generated in trapper filtering decomposable process, described positive sequence voltage is obtained to decompose.

The present invention on the other hand embodiment proposes a kind of control device of three phase unbalance current of virtual synchronous generator, comprise: build module, for setting up the equation of rotor motion of VSG and the virtual excitation equation of VSG of electromagnetic property that imitate synchronous generator mechanical property; Decomposing module, for line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, and the active power exported by VSG according to positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current and reactive power are decomposed into average weight and wave component, the power fluctuation faced by running when unbalanced source voltage with analyzing virtual synchronous generator and three-phase current unbalance; Computing module, for calculating the reference instruction of dq shaft current according to three-phase voltage signal, equals the set point of virtual synchronous generator to make described average weight and suppresses negative-sequence current; And control module, for the reference instruction of described electric current is converted into PWM voltage modulation signal, and control described virtual synchronous generator operation by described PWM voltage modulation signal, thus make the three-phase current of described virtual synchronous generator reach balance.

According to the control device of the three phase unbalance current of the virtual synchronous generator of embodiment of the present invention proposition, by line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, thus analyzing virtual synchronous generator run when unbalanced source voltage faced by power fluctuation and three-phase current unbalance, and by calculating the reference instruction of dq shaft current, thus make average weight equal the set point of virtual synchronous generator and suppress negative-sequence current, finally by with reference to instruction morphing be PWM voltage modulation signal, the three-phase current realizing virtual synchronous generator reaches the object of balance, even if VSG still can export three-phase equilibrium electric current when electrical network imbalance of three-phase voltage, thus ensure the stability of operation of power networks better, not only safe and reliable, and it is simple and convenient.

In addition, the control device of the three phase unbalance current of virtual synchronous generator according to the above embodiment of the present invention can also have following additional technical characteristic:,

Further, in one embodiment of the invention, described VSG equation of rotor motion is:

$J\frac{\mathrm{d\ω}}{\mathrm{dt}}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0),$

Wherein, J is virtual rotation inertia, and ω is the virtual angular speed of VSG, T _mand T _ebe respectively virtual machine torque and electromagnetic torque, D is damping coefficient, ω ₀for the reference value of synchronous angular velocity.

Further, in one embodiment of the invention, the virtual excitation equation of described VSG is:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e,$

Wherein, M _ffor the maximum of mutual inductance between rotor with a phase stator, i _ffor the size of exciting current, K is the inertia coeffeicent of excitation regulation.

Further, in one embodiment of the invention, the reference instruction of dq shaft current according to following formulae discovery:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right],$

Wherein, for the dq component of forward-order current, L and R is total inductance between inverter to electrical network and all-in resistance, and s is differential operator, and ω is the virtual angular speed of VSG.

Further, in one embodiment of the invention, described decomposing module, also for 2 subharmonic voltages by generating in trapper filtering decomposable process, obtains described positive sequence voltage to decompose.

The aspect that the present invention adds and advantage will part provide in the following description, and part will become obvious from the following description, or be recognized by practice of the present invention.

Accompanying drawing explanation

Above-mentioned and/or additional aspect of the present invention and advantage will become obvious and easy understand from accompanying drawing below combining to the description of embodiment, wherein:

Fig. 1 is the flow chart of the control method of the three phase unbalance current of virtual synchronous generator according to the embodiment of the present invention;

Fig. 2 is VSG underlying topology syndeton schematic diagram according to an embodiment of the invention;

Fig. 3 is the structural representation of current inner loop control according to an embodiment of the invention;

Fig. 4 is the structural representation adding the VSG control that negative-sequence current suppresses according to an embodiment of the invention;

Fig. 5 is in prior art when single-phase short circuit, the current output waveform schematic diagram under VSG controls;

Fig. 6 is according to an embodiment of the invention when single-phase short circuit, the current output waveform schematic diagram under VSG controls;

Fig. 7 be prior art and according to one embodiment of the invention when single-phase short circuit, the contrast schematic diagram of the power output under VSG controls; And

Fig. 8 is the structural representation of the control device of the three-phase current of virtual synchronous generator according to the embodiment of the present invention.

Embodiment

Be described below in detail embodiments of the invention, the example of described embodiment is shown in the drawings, and wherein same or similar label represents same or similar element or has element that is identical or similar functions from start to finish.Be exemplary below by the embodiment be described with reference to the drawings, be intended to for explaining the present invention, and can not limitation of the present invention be interpreted as.

In addition, term " first ", " second " only for describing object, and can not be interpreted as instruction or hint relative importance or imply the quantity indicating indicated technical characteristic.Thus, be limited with " first ", the feature of " second " can express or impliedly comprise one or more these features.In describing the invention, the implication of " multiple " is two or more, unless otherwise expressly limited specifically.

In the present invention, unless otherwise clearly defined and limited, the term such as term " installation ", " being connected ", " connection ", " fixing " should be interpreted broadly, and such as, can be fixedly connected with, also can be removably connect, or connect integratedly; Can be mechanical connection, also can be electrical connection; Can be directly be connected, also indirectly can be connected by intermediary, can be the connection of two element internals.For the ordinary skill in the art, above-mentioned term concrete meaning in the present invention can be understood as the case may be.

In the present invention, unless otherwise clearly defined and limited, fisrt feature second feature it " on " or D score can comprise the first and second features and directly contact, also can comprise the first and second features and not be directly contact but by the other characterisation contact between them.And, fisrt feature second feature " on ", " top " and " above " comprise fisrt feature directly over second feature and oblique upper, or only represent that fisrt feature level height is higher than second feature.Fisrt feature second feature " under ", " below " and " below " comprise fisrt feature directly over second feature and oblique upper, or only represent that fisrt feature level height is less than second feature.

Describe control method and the device of the three phase unbalance current of the virtual synchronous generator proposed according to the embodiment of the present invention with reference to the accompanying drawings, describe the control method of the three phase unbalance current of the virtual synchronous generator proposed according to the embodiment of the present invention first with reference to the accompanying drawings.With reference to shown in Fig. 1, this control method comprises the following steps:

S101, sets up the equation of rotor motion of VSG and the virtual excitation equation of VSG of electromagnetic property that imitate synchronous generator mechanical property.

Further, in one embodiment of the invention, VSG equation of rotor motion is:

$J\frac{d\mathrm{\ω}}{dt}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0),$

Wherein, J is virtual rotation inertia, and ω is the virtual angular speed of VSG, T _mand T _ebe respectively virtual machine torque and electromagnetic torque, D is damping coefficient, ω ₀for the reference value of synchronous angular velocity.

Further, in one embodiment of the invention, the virtual excitation equation of VSG is:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e,$

Wherein, M _ffor the maximum of mutual inductance between rotor with a phase stator, i _ffor the size of exciting current, K is the inertia coeffeicent of excitation regulation.

Particularly, first the underlying topology structure that virtual synchronous generator techniques is corresponding is determined: this distributed generation system can comprise inverter, LCL filter, grid-connected port power calculates, VSG control algolithm calculates, SVPWM (SpaceVectorPulseWidthModulation, space vector pulse width modulation) modulates 5 subsystems.Virtual synchronous generator (VSG) technology is by imitating the mechanical property of synchronous generator and electromagnetic property, making inverter have the characteristic similar to synchronous generator, to be reached for the object that electrical network provides inertia support and damping to support.

Wherein, the equation of rotor motion of synchronous generator mechanical property is simulated:

$J\frac{d\mathrm{\ω}}{dt}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0)---\left(1\right)$

In formula: J is virtual rotation inertia, the moment of inertia of simulation synchronous generator rotor; ω is the virtual angular speed of VSG; T _mand T _ebe respectively virtual machine torque and electromagnetic torque; D is damping coefficient, the damping of simulation generator amature; ω ₀for the reference value of synchronous angular velocity, be generally 314rad/s.Separate formula can obtain virtual angular velocity omega, obtains rotor angle θ through integration _o.

Further, virtual synchronous generator three-phase output voltage amplitude:

V _o＝M _fi _fω(2)

M _fthe maximum of mutual inductance between rotor with a phase stator, i _fit is the size of exciting current.

Further, the virtual excitation equation of the VSG of analog electrical magnetic characteristic:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e---\left(3\right)$

K is the inertia coeffeicent of excitation regulation.

S102, line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, and the active power exported by VSG according to positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current and reactive power are decomposed into average weight and wave component, the power fluctuation faced by running when unbalanced source voltage with analyzing virtual synchronous generator and three-phase current unbalance.

Further, in one embodiment of the invention, by 2 subharmonic voltages generated in trapper filtering decomposable process, positive sequence voltage is obtained to decompose.

Particularly, analyze when unbalanced source voltage, the operation problem that VSG may occur: line voltage is decomposed into positive sequence, negative phase-sequence, zero-sequence component, just, sequence, residual voltage act on respectively generation positive and negative, zero-sequence current.Because without center line in VSG, so zero-sequence current cannot circulate, so output current is only decomposed into positive sequence and negative phase-sequence two components, be designated as i respectively ⁺, i ^-.

The instantaneous active power that VSG exports can be expressed as:

p＝v·i＝v ⁺·i ⁺+v ^-·i ^-+(4)

v ⁺·i ^-+v ^-·i ⁺+v ⁰·i ⁺+v ⁰·i ^-

V in formula ⁺, v ^-, v ⁰be respectively three order components of VSG port voltage, order components mark herein all represents three-phase voltage vector." " represents the inner product of three phasor1s.The three-phase component of residual voltage is identical, is decided to be zero, i.e. v with the positive sequence of symmetry and the inner product one of negative-sequence current ⁰i ⁺=v ⁰i ^-=0, therefore (4) formula can abbreviation be:

p＝v ⁺·i ⁺+v ^-·i ^-+v ⁺·i ^-+v ^-·i ⁺(5)

Be shown with table of natural sines:

V ⁺, V ^-be respectively the amplitude of positive sequence, negative sequence voltage; I ⁺, I ^-be respectively the amplitude of positive sequence, negative-sequence current; the phase angle difference between a phase positive sequence voltage with a phase forward-order current, namely the rest may be inferred for remaining phase angle difference.

From (6) formula, voltage, the electric current of the voltage of positive sequence, electric current and negative phase-sequence can produce constant active power; Positive sequence voltage and negative-sequence current, forward-order current and negative sequence voltage can produce with the active power of 2 times of power frequency fluctuations.Therefore, active power can be decomposed into average weight and wave component the expression formula of the two is:

$\left\{\begin{array}{c}\stackrel{\‾}{p}=v^{+}\·i^{+}+v^{-}\·i^{-}\\ \tilde{p}=v^{+}\·i^{-}+v^{-}\·i^{+}\end{array}\right.---\left(7\right)$

In like manner can derive the average weight of reactive power and the expression formula of wave component:

$\left\{\begin{array}{c}\stackrel{\‾}{q}=\left|v^{+}\×i^{+}\right|+\left|v^{-}\×i^{-}\right|\\ \tilde{q}=\left|v^{+}\×i^{-}\right|+\left|v^{-}\×i^{+}\right|\end{array}\right.---\left(8\right)$

In formula: "×" represents the multiplication cross of vector.

From (7), (8) formula, if control current three-phase balance, then electrical network negative sequence voltage and forward-order current effect still can produce power fluctuation; And if the wave component controlling power output is 0, then negative-sequence current can not be 0.Therefore, three-phase balance and power invariability can not reach simultaneously.But in Practical Project, when current balance type, be set as and set value of the power P* by the average weight of power output, Q* is identical, positive sequence voltage so in wave component and negative-sequence current effect item will be eliminated, and therefore can reach the effect reducing meritorious and reactive power fluctuation.

S103, calculates the reference instruction of dq shaft current according to three-phase voltage signal, equal the set point of virtual synchronous generator to make average weight and suppress negative-sequence current.

Further, in one embodiment of the invention, according to the reference instruction of following formulae discovery dq shaft current:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right],$

Wherein, for the dq component of forward-order current, L and R is total inductance between inverter to electrical network and all-in resistance, and s is differential operator, and ω is the virtual angular speed of VSG.

Particularly, by the three-phase voltage signal v of VSG algorithm output _ocalculate the reference instruction of dq shaft current, while playing suppression negative-sequence current effect, make the average weight of power stage identical with VSG set point.

Wherein, with reference to shown in Fig. 2, in circuit shown in Fig. 2, ignore the effect of capacitive branch, analyze its positive sequence circuit, then positive sequence voltage, the pass of electric current under dq coordinate system are:

$\left[\begin{array}{c}{v}_{od}\\ v_{oq}\end{array}\right]=\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]+\left[\begin{array}{cc}Ls+R& -\mathrm{\ω}L\\ \mathrm{\ω}L& Ls+R\end{array}\right]\left[\begin{array}{c}{i}_d^{+}\\ i_q^{+}\end{array}\right]---\left(9\right)$

In formula: v _od, v _oqthat VSG algorithm exports v _odq component; with it is the dq component of electrical network positive sequence voltage and forward-order current; L and R is total inductance between inverter to electrical network and all-in resistance; S is differential operator.Due to v _oonly have positive sequence component, therefore can be directly used in calculating.

From (1) formula and (3) formula, VSG is by regulating v _oautomatic control is meritorious identical with set point with reactive power, as long as so the electric current calculated is consistent with voltage swing relation and real circuits, power can be made identical with set point.For eliminating negative-sequence current, the forward-order current in desirable (9) formula is as the current reference value exported, and its expression formula is:

$\begin{array}{c}\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]={\left[\begin{array}{cc}Ls+R& -\mathrm{\ω}L\\ \mathrm{\ω}L& Ls+R\end{array}\right]}^{-1}\left(\left[\begin{array}{c}{v}_{od}\\ v_{oq}\end{array}\right]-\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]\right)\\ =\frac{1}{{(Ls+R)}^2{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}(Ls+R){\mathrm{\Δv}}_d^{+}+{\mathrm{\ωL\Δv}}_q^{+}\\ (Ls+R){\mathrm{\Δv}}_q^{+}+{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right]\end{array}---\left(10\right)$

In formula: $\left[\begin{array}{c}\mathrm{\Δ}{v}_d^{+}\\ {\mathrm{\Δv}}_q^{+}\end{array}\right]=\left[\begin{array}{c}{v}_{od}\\ {\mathrm{\ν}}_{oq}\end{array}\right]-\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right].$

Because VSG has the closed-loop control of outer voltage, Current calculation need not simulate side circuit completely, as long as the fundamental relation symbolizing electric current and voltage dq axle component guarantees that positive-negative relationship is not put upside down, and just can achieve effective control.The second-order system of (10) and (Ls+R) are used to the final-value theorem of step response, can be by current-order computational short cut:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right]---\left(11\right)$

Further, above-mentioned computational process needs the positive sequence component of line voltage, therefore the positive-negative sequence component of line voltage will be separated.

Under dq coordinate system, the expression formula that line voltage is decomposed into positive-negative sequence component is:

$\left[\begin{array}{c}{e}_d\\ e_q\end{array}\right]=\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]+R(-2\mathrm{\ω}t)\left[\begin{array}{c}{e}_d^{-}\\ e_q^{-}\end{array}\right]---\left(12\right)$

In formula: $R\left(\mathrm{\θ}\right)=\left[\begin{array}{cc}cos\mathrm{\θ}& -sin\mathrm{\θ}\\ sin\mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right].$

As can be seen here, in dq coordinate system, former three-phase alternating current positive sequence voltage can become direct voltage, and former three-phase alternating current negative sequence voltage can become 2 subharmonic voltages, trapper therefore can be utilized to filter out 2 subharmonic voltages, reach the effect isolating positive sequence voltage.The transfer function of trapper can be:

$F\left(s\right)=\frac{s^2+{\mathrm{\ω}}_n^2}{s^2+\frac{{\mathrm{\ω}}_n}{Q}s+{\mathrm{\ω}}_n^2}---\left(13\right)$

In formula: ω _nbe trap angular frequency, be designed to 2 times of power frequency angular frequencies; Q is quality factor.It is noted that Q can not obtain too little, otherwise filter effect can be very poor; Q also should not obtain excessive, otherwise trapper response is too slow, worsens dynamic effect.

S104, is converted into PWM voltage modulation signal by the reference instruction of electric current, and controls virtual synchronous generator operation by PWM voltage modulation signal, thus makes the three-phase current of virtual synchronous generator reach balance.

Particularly, by current-order computing module, original VSG voltage is exported the current reference instruction input needed with current inner loop to couple together.Generally control electric current under dq rotating coordinate system, adopt feed forward decoupling control strategy, its control block diagram as shown in Figure 3.I in figure _d, i _qand e _d, e _qthe actual value that the measured value being respectively VSG port current and line voltage obtains through abc/dq coordinate transform; for the reference instruction of dq shaft current; it is the modulation wave signal of inverter output voltage.Due to the existence of PI controller, the indifference that Fig. 3 can realize VSG port current controls.

In an embodiment of the present invention, the VSG of the embodiment of the present invention is by the method simulating the electromagnetism of synchronous generator, mechanical property realizes basic controlling, secondly when unbalanced source voltage, by line voltage being decomposed into the sequence electric current of positive sequence, negative phase-sequence, residual voltage and correspondence, thus two kinds of operation problems that analysis VSG control method may occur: power fluctuation and three-phase current unbalance, then by the three-phase voltage signal v of VSG algorithm output _ocalculate the reference instruction of dq shaft current, while playing suppression negative-sequence current effect, make the average weight of power stage identical with VSG set point, finally, because the output current of VSG is determined by output voltage indirectly, so ring controller in design current, be used for by instruction morphing for the current reference that obtains be PWM voltage modulation signal.The embodiment of the present invention does not rely on the type of Voltage unbalance when suppressing negative-sequence current, all can have good performance when the balance of voltage and various uneven type, and design is comparatively simple, is easy to Project Realization.

Particularly, the control method of the three phase unbalance current of the virtual synchronous generator of the embodiment of the present invention has the following advantages:

1, can when unbalanced source voltage effectively control VSG export three-phase equilibrium electric current, playing simultaneously and reducing meritorious and reactive power oscillation, suppress power transient to impact, reduce the effect of fault current amplitudes.

2, do not rely on the uneven type of line voltage, and do not affect performance when VSG normally works.

3, control structure is simple, is easy to Project Realization.

In sum, the embodiment of the present invention more effectively can ensure that VSG exports three-phase equilibrium electric current, and is easy to Project Realization.

Be described in detail with the control method of a specific embodiment to the three phase unbalance current that the embodiment of the present invention proposes below.In one particular embodiment of the present invention, the embodiment of the present invention comprises the following steps:

1) the underlying topology structure that virtual synchronous generator techniques is corresponding is determined: this distributed generation system comprises inverter, LCL filter, grid-connected port power calculates, VSG control algolithm calculates, SVPWM modulates 5 subsystems.Virtual synchronous generator (VSG) technology is by imitating the mechanical property of synchronous generator and electromagnetic property, making inverter have the characteristic similar to synchronous generator, to be reached for the object that electrical network provides inertia support and damping to support.Setting inverter be three-phase three brachium pontis without bus, direct voltage is 700V, and ac line voltage effective value is 381V, and inverter switching frequency is the L of 10kHz, filter inductance _s, R _sfor 2mH and 0.1 Ω, filter capacitor C=40 μ F, line parameter circuit value L _lS, R _lSfor 2mH and 0.1 Ω, the given meritorious set point 10kW of inverter, idle set point 5kvar.

The equation of rotor motion of simulation synchronous generator mechanical property:

$J\frac{d\mathrm{\ω}}{dt}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0)---\left(1\right)$

In formula: J is virtual rotation inertia, the moment of inertia (choosing according to Practical Project) of simulation synchronous generator rotor; ω is the virtual angular speed of VSG; T _mand T _ebe respectively virtual machine torque and electromagnetic torque; D is damping coefficient (choosing value according to the actual requirements), the damping of simulation generator amature; ω ₀for the reference value of synchronous angular velocity, be generally 314rad/s.(1) formula of solution can obtain virtual angular velocity omega, obtains rotor angle θ through integration _o.

Virtual synchronous generator three-phase output voltage amplitude:

V _o＝M _fi _fω(2)

M _fthe maximum (choosing according to the actual requirements) of mutual inductance between rotor with a phase stator, i _fit is the size of exciting current.

The virtual excitation equation of VSG of analog electrical magnetic characteristic:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e---\left(3\right)$

K is the inertia coeffeicent (choosing according to the actual requirements) of excitation regulation.

2) analyze when unbalanced source voltage, the operation problem that VSG may occur: line voltage is decomposed into positive sequence, negative phase-sequence, zero-sequence component, just, sequence, residual voltage act on respectively generation positive and negative, zero-sequence current.Because without center line in VSG, so zero-sequence current cannot circulate, so output current is only decomposed into positive sequence and negative phase-sequence two components, be designated as i respectively ⁺, i ^-.

The instantaneous active power that VSG exports can be expressed as:

p＝v·i＝v ⁺·i ⁺+v ^-·i ^-+(4)

v ⁺·i ^-+v ^-·i ⁺+v ⁰·i ⁺+v ⁰·i ^-

V in formula ⁺, v ^-, v ⁰be respectively three order components of VSG port voltage, order components mark herein all represents three-phase voltage vector." " represents the inner product of three phasor1s.The three-phase component of residual voltage is identical, is decided to be zero, i.e. v with the positive sequence of symmetry and the inner product one of negative-sequence current ⁰i ⁺=v ⁰i ^-=0, therefore (4) formula can abbreviation be:

p＝v ⁺·i ⁺+v ^-·i ^-+v ⁺·i ^-+v ^-·i ⁺(5)

Be shown with table of natural sines:

V ⁺, V ^-be respectively the amplitude of positive sequence, negative sequence voltage; I ⁺, I ^-be respectively the amplitude of positive sequence, negative-sequence current; the phase angle difference between a phase positive sequence voltage with a phase forward-order current, namely the rest may be inferred for remaining phase angle difference.

From (6) formula, voltage, the electric current of the voltage of positive sequence, electric current and negative phase-sequence can produce constant active power; Positive sequence voltage and negative-sequence current, forward-order current and negative sequence voltage can produce with the active power of 2 times of power frequency fluctuations.Therefore, active power can be decomposed into average weight and wave component the expression formula of the two is:

$\left\{\begin{array}{c}\stackrel{\‾}{p}=v^{+}\·i^{+}+v^{-}\·i^{-}\\ \tilde{p}=v^{+}\·i^{-}+v^{-}\·i^{+}\end{array}\right.---\left(7\right)$

In like manner can derive the average weight of reactive power and the expression formula of wave component:

$\left\{\begin{array}{c}\stackrel{\‾}{q}=\left|v^{+}\×i^{+}\right|+\left|v^{-}\×i^{-}\right|\\ \tilde{q}=\left|v^{+}\×i^{-}\right|+\left|v^{-}\×i^{+}\right|\end{array}\right.---\left(8\right)$

In formula: "×" represents the multiplication cross of vector.

From (7), (8) formula, if control current three-phase balance, then electrical network negative sequence voltage and forward-order current effect still can produce power fluctuation; And if the wave component controlling power output is 0, then negative-sequence current can not be 0.Therefore, three-phase balance and power invariability can not reach simultaneously.But in Practical Project, when current balance type, be set as and set value of the power P* by the average weight of power output, Q* is identical, positive sequence voltage so in wave component and negative-sequence current effect item will be eliminated, and therefore can reach the effect reducing meritorious and reactive power fluctuation.

3) design current command calculations: the three-phase voltage signal v that VSG algorithm is exported _ocalculate the reference instruction of dq shaft current, while playing suppression negative-sequence current effect, make the average weight of power stage identical with VSG set point.

3-1) computational methods: the effect ignoring capacitive branch in circuit shown in Fig. 2, analyze its positive sequence circuit, then positive sequence voltage, the pass of electric current under dq coordinate system are:

$\left[\begin{array}{c}{v}_{od}\\ v_{oq}\end{array}\right]=\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]+\left[\begin{array}{cc}Ls+R& -\mathrm{\ω}L\\ \mathrm{\ω}L& Ls+R\end{array}\right]\left[\begin{array}{c}{i}_d^{+}\\ i_q^{+}\end{array}\right]---\left(9\right)$

In formula: v _od, v _oqthat VSG algorithm exports v _odq component; with it is the dq component of electrical network positive sequence voltage and forward-order current; L and R is total inductance between inverter to electrical network and all-in resistance; S is differential operator.Due to v _oonly have positive sequence component, therefore can be directly used in calculating.

From (1) formula and (3) formula, VSG is by regulating v _oautomatic control is meritorious identical with set point with reactive power, as long as so the electric current calculated is consistent with voltage swing relation and real circuits, power can be made identical with set point.For eliminating negative-sequence current, the forward-order current in desirable (9) formula is as the current reference value exported, and its expression formula is:

$\begin{array}{c}\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]={\left[\begin{array}{cc}Ls+R& -\mathrm{\ω}L\\ \mathrm{\ω}L& Ls+R\end{array}\right]}^{-1}\left(\left[\begin{array}{c}{v}_{od}\\ v_{oq}\end{array}\right]-\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]\right)\\ =\frac{1}{{(Ls+R)}^2{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}(Ls+R){\mathrm{\Δv}}_d^{+}+{\mathrm{\ωL\Δv}}_q^{+}\\ (Ls+R){\mathrm{\Δv}}_q^{+}+{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right]\end{array}---\left(10\right)$

In formula: $\left[\begin{array}{c}\mathrm{\Δ}{v}_d^{+}\\ {\mathrm{\Δv}}_q^{+}\end{array}\right]=\left[\begin{array}{c}{v}_{od}\\ v_{oq}\end{array}\right]-\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right].$

Because VSG has the closed-loop control of outer voltage, Current calculation need not simulate side circuit completely, as long as the fundamental relation symbolizing electric current and voltage dq axle component guarantees that positive-negative relationship is not put upside down, and just can achieve effective control.The second-order system of (10) and (Ls+R) are used to the final-value theorem of step response, can be by current-order computational short cut:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right]---\left(11\right)$

3-2) positive sequence voltage extracts: above-mentioned computational process needs the positive sequence component of line voltage, therefore the positive-negative sequence component of line voltage will be separated.

Under dq coordinate system, the expression formula that line voltage is decomposed into positive-negative sequence component is:

$\left[\begin{array}{c}{e}_d\\ e_q\end{array}\right]=\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]+R(-2\mathrm{\ω}t)\left[\begin{array}{c}{e}_d^{-}\\ e_q^{-}\end{array}\right]---\left(12\right)$

In formula: $R\left(\mathrm{\θ}\right)=\left[\begin{array}{cc}cos\mathrm{\θ}& -sin\mathrm{\θ}\\ sin\mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right].$

As can be seen here, in dq coordinate system, former three-phase alternating current positive sequence voltage can become direct voltage, and former three-phase alternating current negative sequence voltage can become 2 subharmonic voltages, trapper therefore can be utilized to filter out 2 subharmonic voltages, reach the effect isolating positive sequence voltage.The transfer function of trapper is:

$F\left(s\right)=\frac{s^2+{\mathrm{\ω}}_n^2}{s^2+\frac{{\mathrm{\ω}}_n}{Q}s+{\mathrm{\ω}}_n^2}---\left(13\right)$

In formula: ω _nbe trap angular frequency, be designed to 2 times of power frequency angular frequencies; Q is quality factor.It is noted that Q can not obtain too little, otherwise filter effect can be very poor; Q also should not obtain excessive, otherwise trapper response is too slow, worsens dynamic effect.

4) design current inner ring transfers current-order to voltage instruction: with reference to shown in Fig. 4, by current-order computing module, original VSG voltage is exported the current reference instruction input needed with current inner loop and couples together.Generally control electric current under dq rotating coordinate system, adopt feed forward decoupling control strategy, its control block diagram as shown in Figure 3.I in figure _d, i _qand e _d, e _qthe actual value that the measured value being respectively VSG port current and line voltage obtains through abc/dq coordinate transform; for the reference instruction of dq shaft current; it is the modulation wave signal of inverter output voltage.Due to the existence of PI controller, the indifference that Fig. 3 can realize VSG port current controls.

Further, Fig. 5 is in prior art, during single-phase short circuit, and the current output waveform under VSG controls.When Fig. 6 is single-phase short circuit, in embodiments of the present invention, VSG controls lower current output waveform.Wherein, abscissa is the time, and unit is second, and ordinate is electric current, and unit is ampere.Do not use the present invention, three-phase current unbalance as seen, when using of the present invention, current balance type.When Fig. 7 is single-phase short circuit, in above-mentioned two situations, the contrast of power output.Wherein, abscissa is the time, and unit is second, and ordinate is active power and reactive power respectively, and unit is watt and weary.When not using of the present invention, regulation time is long, and amplitude is large, uses the present invention, can reduce transient state overshoot, improves the ability of VSG stable operation.

According to the control method of the three-phase current of the virtual synchronous generator of embodiment of the present invention proposition, by line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, thus analyzing virtual synchronous generator run when unbalanced source voltage faced by power fluctuation and three-phase current unbalance, and by calculating the reference instruction of dq shaft current, thus make average weight equal the set point of virtual synchronous generator, finally by with reference to instruction morphing be PWM voltage modulation signal, the three-phase current realizing virtual synchronous generator reaches the object of balance, even if VSG still can export three-phase equilibrium electric current when electrical network imbalance of three-phase voltage, thus ensure the stability of operation of power networks better, not only safe and reliable, and it is simple and convenient.

Secondly, the control device of the three phase unbalance current of the virtual synchronous generator proposed according to the embodiment of the present invention is described with reference to the accompanying drawings.With reference to shown in Fig. 8, this control device 10 comprises: build module 100, decomposing module 200, computing module 300 and control module 400.

Wherein, module 100 is built for setting up the equation of rotor motion of VSG and the virtual excitation equation of VSG of electromagnetic property that imitate synchronous generator mechanical property.Decomposing module 200 is for being decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current by line voltage, and the active power exported by VSG according to positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current and reactive power are decomposed into average weight and wave component, the power fluctuation faced by running when unbalanced power supply with analyzing virtual synchronous generator and three-phase current unbalance.Computing module 300, for calculating the reference instruction of dq shaft current according to three-phase voltage signal, equals the set point of virtual synchronous generator to make average weight and suppresses negative-sequence current.Control module 400 for the reference instruction of electric current is converted into PWM voltage modulation signal, and controls virtual synchronous generator operation by PWM voltage modulation signal, thus makes the three-phase current of virtual synchronous generator reach balance.The control device 10 of the embodiment of the present invention is on the basis of traditional virtual synchronous generator control technology, increase design current inner ring and Current calculation with the control method of the operation problem suppressing electrical network imbalance of three-phase voltage and bring, make VSG still can export three-phase equilibrium electric current when electrical network imbalance of three-phase voltage.

Further, in one embodiment of the invention, VSG equation of rotor motion is:

$J\frac{d\mathrm{\ω}}{dt}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0),$

Wherein, J is virtual rotation inertia, and ω is the virtual angular speed of VSG, T _mand T _ebe respectively virtual machine torque and electromagnetic torque, D is damping coefficient, ω ₀for the reference value of synchronous angular velocity.

Further, in one embodiment of the invention, the virtual excitation equation of VSG is:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e,$

Wherein, M _ffor the maximum of mutual inductance between rotor with a phase stator, i _ffor the size of exciting current, K is the inertia coeffeicent of excitation regulation.

Further, in one embodiment of the invention, according to the reference instruction of following formulae discovery dq shaft current:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right],$

Wherein, for the dq component of forward-order current, L and R is total inductance between inverter to electrical network and all-in resistance, and s is differential operator, and ω is the virtual angular speed of VSG.

Further, in one embodiment of the invention, decomposing module 200 also for 2 subharmonic voltages by generating in trapper filtering decomposable process, obtains positive sequence voltage to decompose.

Particularly, the underlying topology structure that virtual synchronous generator techniques is corresponding is first determined: this distributed generation system can comprise inverter, LCL filter, grid-connected port power calculates, VSG control algolithm calculates, SVPWM modulates 5 subsystems.Virtual synchronous generator (VSG) technology is by imitating the mechanical property of synchronous generator and electromagnetic property, making inverter have the characteristic similar to synchronous generator, to be reached for the object that electrical network provides inertia support and damping to support.

Wherein, the equation of rotor motion of synchronous generator mechanical property is simulated:

$J\frac{d\mathrm{\ω}}{dt}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0)---\left(1\right)$

In formula: J is virtual rotation inertia, the moment of inertia of simulation synchronous generator rotor; ω is the virtual angular speed of VSG; T _mand T _ebe respectively virtual machine torque and electromagnetic torque; D is damping coefficient, the damping of simulation generator amature; ω ₀for the reference value of synchronous angular velocity, be generally 314rad/s.Separate formula can obtain virtual angular velocity omega, obtains rotor angle θ through integration _o.

Further, virtual synchronous generator three-phase output voltage amplitude:

V _o＝M _fi _fω(2)

M _fthe maximum of mutual inductance between rotor with a phase stator, i _fit is the size of exciting current.

Further, the virtual excitation equation of the VSG of analog electrical magnetic characteristic:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e---\left(3\right)$

K is the inertia coeffeicent of excitation regulation.

Further, analyze when unbalanced source voltage, the operation problem that VSG may occur: line voltage is decomposed into positive sequence, negative phase-sequence, zero-sequence component, just, sequence, residual voltage act on respectively generation positive and negative, zero-sequence current.Because without center line in VSG, so zero-sequence current cannot circulate, so output current is only decomposed into positive sequence and negative phase-sequence two components, be designated as i respectively ⁺, i ^-.

The instantaneous active power that VSG exports can be expressed as:

p＝v·i＝v ⁺·i ⁺+v ^-·i ^-+(4)

v ⁺·i ^-+v ^-·i ⁺+v ⁰·i ⁺+v ⁰·i ^-

V in formula ⁺, v ^-, v ⁰be respectively three order components of VSG port voltage, order components mark herein all represents three-phase voltage vector." " represents the inner product of three phasor1s.The three-phase component of residual voltage is identical, is decided to be zero, i.e. v with the positive sequence of symmetry and the inner product one of negative-sequence current ⁰i ⁺=v ⁰i ^-=0, therefore (4) formula can abbreviation be:

p＝v ⁺·i ⁺+v ^-·i ^-+v ⁺·i ^-+v ^-·i ⁺(5)

Be shown with table of natural sines:

V ⁺, V ^-be respectively the amplitude of positive sequence, negative sequence voltage; I ⁺, I ^-be respectively the amplitude of positive sequence, negative-sequence current; the phase angle difference between a phase positive sequence voltage with a phase forward-order current, namely the rest may be inferred for remaining phase angle difference.

From (6) formula, voltage, the electric current of the voltage of positive sequence, electric current and negative phase-sequence can produce constant active power; Positive sequence voltage and negative-sequence current, forward-order current and negative sequence voltage can produce with the active power of 2 times of power frequency fluctuations.Therefore, active power can be decomposed into average weight and wave component the expression formula of the two is:

$\left\{\begin{array}{c}\stackrel{\‾}{p}=v^{+}\·i^{+}+v^{-}\·i^{-}\\ \tilde{p}=v^{+}\·i^{-}+v^{-}\·i^{+}\end{array}\right.---\left(7\right)$

In like manner can derive the average weight of reactive power and the expression formula of wave component:

$\left\{\begin{array}{c}\stackrel{\‾}{q}=\left|v^{+}\×i^{+}\right|+\left|v^{-}\×i^{-}\right|\\ \tilde{q}=\left|v^{+}\×i^{-}\right|+\left|v^{-}\×i^{+}\right|\end{array}\right.---\left(8\right)$

In formula: "×" represents the multiplication cross of vector.

From (7), (8) formula, if control current three-phase balance, then electrical network negative sequence voltage and forward-order current effect still can produce power fluctuation; And if the wave component controlling power output is 0, then negative-sequence current can not be 0.Therefore, three-phase balance and power invariability can not reach simultaneously.But in Practical Project, when current balance type, be set as and set value of the power P* by the average weight of power output, Q* is identical, positive sequence voltage so in wave component and negative-sequence current effect item will be eliminated, and therefore can reach the effect reducing meritorious and reactive power fluctuation.

Further, by the three-phase voltage signal v of VSG algorithm output _ocalculate the reference instruction of dq shaft current, while playing suppression negative-sequence current effect, make the average weight of power stage identical with VSG set point.

Wherein, with reference to shown in Fig. 2, in circuit shown in Fig. 2, ignore the effect of capacitive branch, analyze its positive sequence circuit, then positive sequence voltage, the pass of electric current under dq coordinate system are:

$\left[\begin{array}{c}{v}_{\mathrm{\ω}}\\ v_{oq}\end{array}\right]=\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]+\left[\begin{array}{cc}LS+R& -\mathrm{\ω}L\\ \mathrm{\ω}L& LS+R\end{array}\right]\left[\begin{array}{c}{i}_d^{+}\\ i_q^{+}\end{array}\right]\left(9\right)$

In formula: v _od, v _oqthat VSG algorithm exports v _odq component; with it is the dq component of electrical network positive sequence voltage and forward-order current; L and R is total inductance between inverter to electrical network and all-in resistance; S is differential operator.Due to v _oonly have positive sequence component, therefore can be directly used in calculating.

From (1) formula and (3) formula, VSG is by regulating v _oautomatic control is meritorious identical with set point with reactive power, as long as so the electric current calculated is consistent with voltage swing relation and real circuits, power can be made identical with set point.For eliminating negative-sequence current, the forward-order current in desirable (9) formula is as the current reference value exported, and its expression formula is:

$\begin{array}{c}\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]={\left[\begin{array}{cc}Ls+R& -\mathrm{\ω}L\\ \mathrm{\ω}L& Ls+R\end{array}\right]}^{-1}\left(\left[\begin{array}{c}{v}_{od}\\ v_{oq}\end{array}\right]-\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]\right)\\ =\frac{1}{{(Ls+R)}^2{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}(Ls+R){\mathrm{\Δv}}_d^{+}+{\mathrm{\ωL\Δv}}_q^{+}\\ (Ls+R){\mathrm{\Δv}}_q^{+}+{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right]\end{array}---\left(10\right)$

In formula: $\left[\begin{array}{c}\mathrm{\Δ}{v}_d^{+}\\ {\mathrm{\Δv}}_q^{+}\end{array}\right]=\left[\begin{array}{c}{v}_{od}\\ v_{oq}\end{array}\right]-\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right].$

Because VSG has the closed-loop control of outer voltage, Current calculation need not simulate side circuit completely, as long as the fundamental relation symbolizing electric current and voltage dq axle component guarantees that positive-negative relationship is not put upside down, and just can achieve effective control.The second-order system of (10) and (Ls+R) are used to the final-value theorem of step response, can be by current-order computational short cut:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right]---\left(11\right)$

Further, above-mentioned computational process needs the positive sequence component of line voltage, therefore the positive-negative sequence component of line voltage will be separated.

Under dq coordinate system, the expression formula that line voltage is decomposed into positive-negative sequence component is:

$\left[\begin{array}{c}{e}_d\\ e_q\end{array}\right]=\left[\begin{array}{c}{e}_d^{+}\\ e_q^{+}\end{array}\right]+R(-2\mathrm{\ω}t)\left[\begin{array}{c}{e}_d^{-}\\ e_q^{-}\end{array}\right]---\left(12\right)$

In formula: $R\left(\mathrm{\θ}\right)=\left[\begin{array}{cc}cos\mathrm{\θ}& -sin\mathrm{\θ}\\ sin\mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right].$

As can be seen here, in dq coordinate system, former three-phase alternating current positive sequence voltage can become direct voltage, and former three-phase alternating current negative sequence voltage can become 2 subharmonic voltages, trapper therefore can be utilized to filter out 2 subharmonic voltages, reach the effect isolating positive sequence voltage.The transfer function of trapper can be:

$F\left(s\right)=\frac{s^2+{\mathrm{\ω}}_n^2}{s^2+\frac{{\mathrm{\ω}}_n}{Q}s+{\mathrm{\ω}}_n^2}---\left(13\right)$

In formula: ω _nbe trap angular frequency, be designed to 2 times of power frequency angular frequencies; Q is quality factor.It is noted that Q can not obtain too little, otherwise filter effect can be very poor; Q also should not obtain excessive, otherwise trapper response is too slow, worsens dynamic effect.

Further, by current-order computing module, original VSG voltage is exported the current reference instruction input needed with current inner loop to couple together.Generally control electric current under dq rotating coordinate system, adopt feed forward decoupling control strategy, its control block diagram as shown in Figure 3.I in figure _d, i _qand e _d, e _qthe actual value that the measured value being respectively VSG port current and line voltage obtains through abc/dq coordinate transform; for the reference instruction of dq shaft current; it is the modulation wave signal of inverter output voltage.Due to the existence of PI controller, the indifference that Fig. 3 can realize VSG port current controls.

In an embodiment of the present invention, the VSG of the embodiment of the present invention is by the method simulating the electromagnetism of synchronous generator, mechanical property realizes basic controlling, secondly when unbalanced source voltage, by line voltage being decomposed into the sequence electric current of positive sequence, negative phase-sequence, residual voltage and correspondence, thus two kinds of operation problems that analysis VSG control method may occur: power fluctuation and three-phase current unbalance, then by the three-phase voltage signal v of VSG algorithm output _ocalculate the reference instruction of dq shaft current, while playing suppression negative-sequence current effect, make the average weight of power stage identical with VSG set point, finally, because the output current of VSG is determined by output voltage indirectly, so ring controller in design current, be used for by instruction morphing for the current reference that obtains be PWM voltage modulation signal.The embodiment of the present invention does not rely on the type of Voltage unbalance when suppressing negative-sequence current, all can have good performance when the balance of voltage and various uneven type, and design is comparatively simple, is easy to Project Realization.

Particularly, the control method of the three phase unbalance current of the virtual synchronous generator of the embodiment of the present invention has the following advantages:

1, can when unbalanced source voltage effectively control VSG export three-phase equilibrium electric current, playing simultaneously and reducing meritorious and reactive power oscillation, suppress power transient to impact, reduce the effect of fault current amplitudes.

2, do not rely on the uneven type of line voltage, and do not affect performance when VSG normally works.

3, control structure is simple, is easy to Project Realization.

In sum, the embodiment of the present invention more effectively can ensure that VSG exports three-phase equilibrium electric current, and is easy to Project Realization.

It should be noted that, the specific implementation of the device of the embodiment of the present invention and the specific implementation of method part similar, in order to reduce redundancy, be not described in detail herein.

According to the control device of the three phase unbalance current of the virtual synchronous generator of embodiment of the present invention proposition, by line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, thus analyzing virtual synchronous generator run when unbalanced source voltage faced by power fluctuation and three-phase current unbalance, and by calculating the reference instruction of dq shaft current, thus make average weight equal the set point of synchronous generator and suppress negative-sequence current, finally by with reference to instruction morphing be PWM voltage modulation signal, the three-phase current realizing virtual synchronous generator reaches the object of balance, even if VSG still can export three-phase equilibrium electric current when electrical network imbalance of three-phase voltage, thus ensure the stability of operation of power networks better, not only safe and reliable, and it is simple and convenient.

Describe and can be understood in flow chart or in this any process otherwise described or method, represent and comprise one or more for realizing the module of the code of the executable instruction of the step of specific logical function or process, fragment or part, and the scope of the preferred embodiment of the present invention comprises other realization, wherein can not according to order that is shown or that discuss, comprise according to involved function by the mode while of basic or by contrary order, carry out n-back test, this should understand by embodiments of the invention person of ordinary skill in the field.

In flow charts represent or in this logic otherwise described and/or step, such as, the sequencing list of the executable instruction for realizing logic function can be considered to, may be embodied in any computer-readable medium, for instruction execution system, device or equipment (as computer based system, comprise the system of processor or other can from instruction execution system, device or equipment instruction fetch and perform the system of instruction) use, or to use in conjunction with these instruction execution systems, device or equipment.With regard to this specification, " computer-readable medium " can be anyly can to comprise, store, communicate, propagate or transmission procedure for instruction execution system, device or equipment or the device that uses in conjunction with these instruction execution systems, device or equipment.The example more specifically (non-exhaustive list) of computer-readable medium comprises following: the electrical connection section (electronic installation) with one or more wiring, portable computer diskette box (magnetic device), random access memory (RAM), read-only memory (ROM), erasablely edit read-only memory (EPROM or flash memory), fiber device, and portable optic disk read-only memory (CDROM).In addition, computer-readable medium can be even paper or other suitable media that can print described program thereon, because can such as by carrying out optical scanner to paper or other media, then carry out editing, decipher or carry out process with other suitable methods if desired and electronically obtain described program, be then stored in computer storage.

Should be appreciated that each several part of the present invention can realize with hardware, software, firmware or their combination.In the above-described embodiment, multiple step or method can with to store in memory and the software performed by suitable instruction execution system or firmware realize.Such as, if realized with hardware, the same in another embodiment, can realize by any one in following technology well known in the art or their combination: the discrete logic with the logic gates for realizing logic function to data-signal, there is the application-specific integrated circuit (ASIC) of suitable combinational logic gate circuit, programmable gate array (PGA), field programmable gate array (FPGA) etc.

Those skilled in the art are appreciated that realizing all or part of step that above-described embodiment method carries is that the hardware that can carry out instruction relevant by program completes, described program can be stored in a kind of computer-readable recording medium, this program perform time, step comprising embodiment of the method one or a combination set of.

In addition, each functional unit in each embodiment of the present invention can be integrated in a processing module, also can be that the independent physics of unit exists, also can be integrated in a module by two or more unit.Above-mentioned integrated module both can adopt the form of hardware to realize, and the form of software function module also can be adopted to realize.If described integrated module using the form of software function module realize and as independently production marketing or use time, also can be stored in a computer read/write memory medium.

The above-mentioned storage medium mentioned can be read-only memory, disk or CD etc.

In the description of this specification, specific features, structure, material or feature that the description of reference term " embodiment ", " some embodiments ", " example ", " concrete example " or " some examples " etc. means to describe in conjunction with this embodiment or example are contained at least one embodiment of the present invention or example.In this manual, identical embodiment or example are not necessarily referred to the schematic representation of above-mentioned term.And the specific features of description, structure, material or feature can combine in an appropriate manner in any one or more embodiment or example.

Although illustrate and describe embodiments of the invention above, be understandable that, above-described embodiment is exemplary, can not be interpreted as limitation of the present invention, those of ordinary skill in the art can change above-described embodiment within the scope of the invention when not departing from principle of the present invention and aim, revising, replacing and modification.

Claims (10)

1. a control method for the three phase unbalance current of virtual synchronous generator, is characterized in that, comprises the following steps:

Set up and imitate the VSG equation of rotor motion of synchronous generator mechanical property and the virtual excitation equation of VSG of electromagnetic property;

Line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, and the active power exported by VSG according to described positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current and reactive power are decomposed into average weight and wave component, the power fluctuation faced by running when unbalanced source voltage with analyzing virtual synchronous generator and three-phase current unbalance;

Calculate the reference instruction of dq shaft current according to three-phase voltage signal, equal the set point of virtual synchronous generator to make described average weight and suppress negative-sequence current; And the reference instruction of described electric current is converted into PWM voltage modulation signal, and control described virtual synchronous generator operation by described PWM voltage modulation signal, thus make the three-phase current of described virtual synchronous generator reach balance.

2. the control method of the three phase unbalance current of virtual synchronous generator according to claim 1, is characterized in that, described VSG equation of rotor motion is:

$J\frac{d\mathrm{\ω}}{dt}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0),$

Wherein, J is virtual rotation inertia, and ω is the virtual angular speed of VSG, T _mand T _ebe respectively virtual machine torque and electromagnetic torque, D is damping coefficient, ω ₀for the reference value of synchronous angular velocity.

3. the control method of the three phase unbalance current of virtual synchronous generator according to claim 1, is characterized in that, the virtual excitation equation of described VSG is:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e,$

Wherein, M _ffor the maximum of mutual inductance between rotor with phase stator, i _ffor the size of exciting current, K is the inertia coeffeicent of excitation regulation.

4. the control method of the three phase unbalance current of virtual synchronous generator according to claim 1, is characterized in that, the reference instruction of dq shaft current according to following formulae discovery:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right],$

Wherein, for the dq component of forward-order current, L and R is total inductance between inverter to electrical network and all-in resistance, and s is differential operator, and ω is the virtual angular speed of VSG.

5. the control method of the three phase unbalance current of virtual synchronous generator according to claim 1, is characterized in that, by 2 subharmonic voltages generated in trapper filtering decomposable process, obtains described positive sequence voltage to decompose.

6. a control device for the three phase unbalance current of virtual synchronous generator, is characterized in that, comprising:

Building module, imitating the VSG equation of rotor motion of synchronous generator mechanical property and the virtual excitation equation of VSG of electromagnetic property for setting up;

Decomposing module, for line voltage is decomposed into positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current, and the active power exported by VSG according to described positive sequence voltage, negative sequence voltage, forward-order current and negative-sequence current and reactive power are decomposed into average weight and wave component, the power fluctuation faced by running when unbalanced source voltage with analyzing virtual synchronous generator and three-phase current unbalance;

Computing module, for calculating the reference instruction of dq shaft current according to three-phase voltage signal, equals the set point of virtual synchronous generator to make described average weight and suppresses negative-sequence current; And

Control module, for the reference instruction of described electric current is converted into PWM voltage modulation signal, and controls described virtual synchronous generator operation by described PWM voltage modulation signal, thus makes the three-phase current of described virtual synchronous generator reach balance.

7. the control method of the three phase unbalance current of virtual synchronous generator according to claim 6, is characterized in that, described VSG equation of rotor motion is:

$J\frac{d\mathrm{\ω}}{dt}=T_m-T_e-D(\mathrm{\ω}-{\mathrm{\ω}}_0),$

Wherein, J is virtual rotation inertia, and ω is the virtual angular speed of VSG, T _mand T _ebe respectively virtual machine torque and electromagnetic torque, D is damping coefficient, ω ₀for the reference value of synchronous angular velocity.

8. the control method of the three phase unbalance current of virtual synchronous generator according to claim 6, is characterized in that, the virtual excitation equation of described VSG is:

$K\frac{d\left(M_f{i}_f\right)}{dt}=Q*-Q_e,$

Wherein, M _ffor the maximum of mutual inductance between rotor with phase stator, i _ffor the size of exciting current, K is the inertia coeffeicent of excitation regulation.

9. the control method of the three phase unbalance current of virtual synchronous generator according to claim 6, is characterized in that, the reference instruction of dq shaft current according to following formulae discovery:

$\left[\begin{array}{c}{i}_d^{*}\\ i_q^{*}\end{array}\right]=\frac{1}{R^2+{\left(\mathrm{\ω}L\right)}^2}\left[\begin{array}{c}R\mathrm{\Δ}{v}_d^{+}+\mathrm{\ω}L\mathrm{\Δ}{v}_q^{+}\\ {\mathrm{R\Δv}}_q^{+}-{\mathrm{\ωL\Δv}}_d^{+}\end{array}\right],$

Wherein, for the dq component of forward-order current, L and R is total inductance between inverter to electrical network and all-in resistance, and s is differential operator, and ω is the virtual angular speed of VSG.

10. the control method of the three phase unbalance current of virtual synchronous generator according to claim 6, is characterized in that, described decomposing module, also for 2 subharmonic voltages by generating in trapper filtering decomposable process, obtains described positive sequence voltage to decompose.