CN101917126B - Voltage-equalizing and power-equalizing control method for multi-module cascade solid-state transformer - Google Patents

Abstract

The invention discloses a voltage-equalizing and power-equalizing control method for a multi-module cascade solid-state transformer (SST). An SST power main circuit part applied in the method comprises an input stage, an intermediate stage and an output stage, wherein a common duty ratio control policy based on single-phase d-q vector control is adopted in the input stage so as to realize the unit power factor of an input end of an electric network; a control policy based on voltage feedforward and voltage feedback is introduced for each module in the intermediate stage, the voltage feedforward is used as a reference of the voltage feedback, and an error between the voltage feedforward and the voltage feedback is used as a reference of inner current loop of the module after being output by a voltage PI adjuster. The two control policies of the front stage and the intermediate stage interact so as to realize the functions of voltage and power equalization of each SST module, electrical network side unit power factor, high electrical network current sine degree, low switching tube voltage stress and the like.

Description

A kind of multi-module cascade solid-state transformer voltage-equalizing and power-equalizing control method

Technical field

The present invention relates to power electronic technology in application on power system, relate in particular to a kind of multi-module cascade SST (solid-state transformer) voltage-equalizing and power-equalizing control method.

Background technology

The conventional electric power transformer is since by invention, and because of its reliable operation, characteristic of simple structure has become indispensable important component part in the electric power system, and number of applications is huge.But there is remarkable shortcoming in it: volume is big, heaviness; It is constant etc. that output voltage can't be kept; Its major function is to realize isolating and the electric pressure conversion, and function is simple, and the electrical network quality of power supply is not improved ability.

The notion of solid-state transformer is suggested for a long time, and it mainly is to realize voltage transitions and NE BY ENERGY TRANSFER through electrification electronic device and power electronic technology.Its outstanding feature is to improve the electrical network quality of power supply, improves the power factor and the output end voltage of input.Therefore solid-state transformer has the advantage that is more suitable for the intelligent grid construction than traditional transformer, has good development potentiality.

In recent years because the develop rapidly of power electronic device makes power electronic technology become possibility in application on power system.Present power electronic device still can not satisfy the requirement of distribution grade, and this also is one of key factor that always limits solid-state transformer development, can use the mode of cascade module to remedy the deficiency of individual module electric pressure.But all pressures that cascade system can be introduced each intermodule and equal power imbalance problems possibly cause the whole SST system can't operate as normal, must realize voltage and power equalization through certain control strategy.

The applied main power topology of control mode of the present invention is well positioned to meet the requirement of voltage levels through the mode of multi-module cascade, but control mode before this or too complicated, or can not well realize all pressing the function of equal power.Control mode of the present invention can not only realize all pressing the requirement of equal power can guarantee that control mode is simple simultaneously, realizes easily.

Summary of the invention

The objective of the invention is to be directed against voltage and the unbalanced deficiency of power that exists in the existing cascade module, a kind of multi-module cascade solid-state transformer voltage-equalizing and power-equalizing control method is provided.

The objective of the invention is to realize: a kind of multi-module cascade solid-state transformer voltage-equalizing and power-equalizing control method through following technical scheme; The SST power main circuit part of its application is formed by three grades: input stage is the active AC/DC rectifier of high frequency; Intergrade is a high-frequency isolation type DC/DC converter, and output stage is a high frequency DC/AC inverter.The input stage AC side adopts the multimode series connection; Corresponding each module input of intergrade of HVDC output termination of each module of input stage; 400 volts of direct currents of each module output parallel connection output of intergrade, the output stage high-frequency inverter becomes output 220 volts/50 hz ac to 400 volts of DC convertings.This may further comprise the steps:

(1) input stage adopts principal and subordinate dq conversion control mode: the SST input stage is a plurality of module series connection, confirms that one of them is a primary module, and this step comprises following substep:

(a) the primary module output voltage is sampled, sampled value and set-point compare, and their error is through the benchmark of Voltage loop PI as d shaft current ring;

(b) conversion obtains the d axle to the input current sampled value through dq, two components of q axle, and wherein the used phase reference of dq conversion is obtained through the PLL phase-locked loop by the input voltage sampled value, and then the d axle divides quantitative response active current component, and the q axle divides quantitative response reactive current component;

(c) as benchmark, error is sent into d shaft current PI to the d axle with above-mentioned Voltage loop PI output; The q axle is with 0 as benchmark, and error is sent into q shaft current PI, then diaxon PI output valve is carried out decoupling zero and anti-dq conversion, obtains modulating wave.

(d) other are from module and the shared same modulating wave of primary module, and triangular carrier is the phase shift certain angle successively, and carrier wave and triangular wave relatively obtain the drive signal of each module.

(2) each module controls mode of intergrade is identical; Adopt electric voltage feed forward rear feed control method, realized that the ratio of intergrade input and output voltage is followed relation: promptly

this step comprises following substep:

(a) intergrade input and output voltage is sampled, input voltage sampled signal and output voltage sampled signal are compared, error is through Voltage loop PI, as the benchmark of current inner loop;

(b) input current is sampled, current sampling data and electric current loop fiducial value are compared, error compares with triangular carrier through electric current loop PI then, produces the switching tube drive signal.If electric current loop PI output valve is being for just, power forward flow then, otherwise power reverse flow.

(3) output stage adopts the SPWM control method, and the SPWM control method as modulating wave, relatively produces switching tube drive signal with triangular carrier with sine wave, guarantees that like this output voltage is sinusoidal wave.

The invention has the beneficial effects as follows: this control method can realize realizing between each cascade module of tandem type SST all pressing and equal power, can realize functions such as grid side unity power factor, power network current sine degree is high, switch tube voltage stress is low simultaneously.Than before control mode, this control mode makes preceding 2 stage converter collaborative work, each module of public realization that cooperatively interacts is all pressed equal power, this control mode control algolithm is simple simultaneously, advantage is obvious when module is a lot.This control mode is significant to the development of quickening electric power electric transformer.

Description of drawings

Fig. 1 is an input stage primary module control block diagram of the present invention;

Fig. 2 is a mid-stage voltage feedforward rear feed control block diagram of the present invention;

Fig. 3 is input stage 3 a module inputs series connection control block diagram of the present invention;

Fig. 4 representes intergrade 3 module output Parallel Control block diagrams of the present invention;

Fig. 5 is a three module cascade SST power main circuit instance graph.

Embodiment

The SST power main circuit part that multi-module cascade solid-state transformer voltage-equalizing and power-equalizing control method of the present invention is used is formed by three grades: input stage is the active AC/DC rectifier of high frequency; Intergrade is a high-frequency isolation type DC/DC converter, and output stage is a high frequency DC/AC inverter.In order to satisfy the requirement of high voltage and high power level; The input stage AC side adopts the multimode series connection; Corresponding each module input of intergrade of HVDC output termination of each module of input stage; 400 volts of direct currents of each module output parallel connection output of intergrade, the output stage high-frequency inverter becomes output 220 volts/50 hz ac to 400 volts of DC convertings.But power two-way flow.

Multi-module cascade solid-state transformer voltage-equalizing and power-equalizing control method of the present invention may further comprise the steps:

(1) input stage adopts principal and subordinate dq conversion control mode.

The SST input stage is a plurality of module series connection, confirms that one of them is a primary module, and input stage primary module control block diagram is as shown in Figure 1.V among the figure _C1Be primary module output voltage sampled value; i _aBe the input current sampled value; e _aBe the input voltage sampled value; The PLL module is a phase-locked loop; Am/dq and dq/am module are respectively dq conversion and anti-dq conversion module.

A. the primary module output voltage is sampled, sampled value and set-point compare, and their error is through the benchmark of Voltage loop PI as d shaft current ring;

B. conversion obtains the d axle to the input current sampled value through dq, two components of q axle, and wherein the used phase reference of dq conversion is obtained through the PLL phase-locked loop by the input voltage sampled value, and then the d axle divides quantitative response active current component, and the q axle divides quantitative response reactive current component;

As benchmark, error is sent into d shaft current PI to the c.d axle with above-mentioned Voltage loop PI output; The q axle is with 0 as benchmark, and error is sent into q shaft current PI, then diaxon PI output valve is carried out decoupling zero and anti-dq conversion, obtains modulating wave.

D. other are from module and the shared same modulating wave of primary module, and triangular carrier is the phase shift certain angle successively, and carrier wave and triangular wave relatively obtain the drive signal of each module.

(2) each module controls mode of intergrade is identical, adopts electric voltage feed forward rear feed control method

Individual module control block diagram is as shown in Figure 2.H wherein _{V_1}And H _{V_2}Be electric voltage feed forward and feedback factor; H _{I_1}And H _{I_2}All be the current feedback coefficient, PI _vIt is Voltage loop proportional integral device; PI _vIt is electric current loop proportional integral device; v _{PI, c}It is electric current loop proportional integral output valve; Work as v _{PI, c}＞0 o'clock, the power forward flow was worked as v _{PI, c}＜0 o'clock, the power reverse flow.k _PWMBe the PWM modulation gain, G _{I_1}And G _{I_2}Be respectively forward and reverse transfer electric current and shift to the transfer function between the angle; Z _{O_1}And Z _{O_2}It is the equiva lent impedance of prime and back level.

A. intergrade input and output voltage is sampled, input voltage sampled signal and output voltage sampled signal are compared, error is through Voltage loop PI, as the benchmark of current inner loop;

B. input current is sampled, current sampling data and electric current loop fiducial value are compared, error compares with triangular carrier through electric current loop PI then, produces the switching tube drive signal.If electric current loop PI output valve is being for just, power forward flow then, otherwise power reverse flow.

Intergrade has realized that the ratio of intergrade input and output voltage is followed relation: i.e.

through adopting electric voltage feed forward rear feed control method

(3) output stage adopts the SPWM control method.

The SPWM control method as modulating wave, relatively produces switching tube drive signal with triangular carrier with sine wave, guarantees that like this output voltage is sinusoidal wave.The SPWM control method can be divided into two kinds of unipolarity and bipolar SPWM, and these two kinds of methods respectively have pluses and minuses, can select wherein a kind of use by demand.

The effect of output stage is that the output dc voltage with the prime intergrade converts the industrial frequency AC civil power into, realizes being incorporated into the power networks.This grade is little to the equal power influences of all pressures of whole SST system, and be comparatively ripe with period control method, is not key content of the present invention.

The control of above-mentioned input stage and intergrade interacts, and collaborative work can realize that each rectifier converter output voltage of connecting all presses the equal power delivery that realizes each road module simultaneously., power bi-directional all can realize above-mentioned functions when flowing.

Describe the present invention in detail below in conjunction with instance, it is more obvious that the object of the invention and effect will become.

Fig. 5 is the single-phase SST power of an a kind of three module cascade main circuit instance graph.Following its detailed operation of surface analysis and control procedure.

(1) first order rectification stage: use the series connection of three H bridge type PWM rectification circuits, three modules shared filter inductance of connecting.T under the normal operating conditions ₁₁, T ₁₃, T ₂₁, T ₂₃, T ₃₁, T ₃₃With T ₁₂, T ₁₄, T ₂₂, T ₂₄, T ₃₂, T ₃₄Complementary work.Satisfy and concern V _An=V _Ab+ V _Bc+ V _CnSuppose V _C1=V _C2=V _C3=V _d, each module can produce three level :-Vd, 0, Vd.With the 1#H bridge is example, works as T ₁₁, T ₁₄Conducting simultaneously and T ₁₂, T ₁₃When turn-offing simultaneously, V _Ab=V _dWork as T ₁₂, T ₁₃Conducting simultaneously and T ₁₁, T ₁₄When turn-offing simultaneously, V _Ab=-V _dWork as T ₁₁, T ₁₃Conducting simultaneously and T ₁₂, T ₁₄Turn-off simultaneously, or T ₁₂, T ₁₄Conducting simultaneously and T ₁₁, T ₁₃V when turn-offing simultaneously _Ab=0.All the other two H bridge operating states by that analogy.The control block diagram is as shown in Figure 3.In order to realize that the input current phase place follows input voltage, the zero static difference on the realization theory adopts single-phase dq conversion control mode, uses outer shroud Voltage loop, the control strategy of interior circular current ring in order to accelerate dynamic response simultaneously.The input current sampled value is carried out the dq conversion, and the phase reference of conversion is the phase place of input voltage.As primary module, the value of feedback of outer voltage is the output voltage of 1#H bridge with the 1# module, and relatively the back error is through Voltage loop PI with fiducial value, and Voltage loop PI output is as the benchmark of electric current loop d axle, and the benchmark of electric current loop q axle is 0.D, q axis error get into the d axle respectively and q axle PI passes through decoupling zero then, passes through anti-dq conversion again, obtains the modulating wave of sinusoidal shape, compares with triangular carrier then, obtains the drive signal of each switching tube.In order to reduce the input current ripple, 120 ° of the phase shifts successively of all the other two modules and the shared sinusoidal modulation wave of primary module, triangular carrier.Can improve equivalent switching frequency like this, reduce to import the volume of filter inductance, improve the power density of system.

(2) second level intergrade: use a kind of novel DAB bridge type topology, it is few that this topology has a passive component, and power density is high, and advantages such as the soft switch of switching tube can satisfy the power bi-directional transmission requirements again simultaneously, in high-power circuit, are used widely.Three DAB module output parallel connections, the input termination is the output of prime separately.Its control block diagram is shown in accompanying drawing 4.H wherein _{V_1}And H _{V_2}Be electric voltage feed forward and feedback factor; H _{I_1}And H _{I_2}All be the current feedback coefficient, PI _vIt is Voltage loop proportional integral device; PI _vIt is electric current loop proportional integral device; v _{PI, c}It is electric current loop proportional integral output valve; Work as v _{PI, c}＞0 o'clock, the power forward flow; Work as v _{PI, c}＜0 o'clock, the power reverse flow.k _PWMBe the PWM modulation gain, G _{I_1}And G _{I_2}Be respectively forward and reverse transfer electric current and shift to the transfer function between the angle; Z _{O_1}And Z _{O_2}Be prime and secondary equiva lent impedance.All the other the two modules each several part function and first module class are seemingly.

Can know that from the control block diagram this is a kind of novel control mode.In traditional feedforward or rear feed mode, fiducial value is generally definite value, can stablize input voltage or output voltage through electric voltage feed forward or rear feed usually.And this control mode compares feedforward value and rear feed value, carries out error then and amplifies.Control makes input and output voltage satisfy certain proportionate relationship like this, and ratio is by the feedforward coefficient decision of feedforward back.

Promptly $V_{\mathrm{Dc}\_11}=V_{\mathrm{Dc}\_21}=V_{\mathrm{Dc}\_31}=\frac{H_{v\_2}}{H_{v\_1}}{V}_{o\_\mathrm{Dc}}$

V wherein _{Dc_11}, V _{Dc_21}, V _{Dc_31}Being respectively the primary voltage of three DAB modules, also is the output voltage of first order rectification stage; V _{O_dc}It is the secondary voltage of three DAB modules.

Have and above-mentionedly know that rectification stage I#H bridge is a primary module, output voltage stabilization.

So

$V_{o\_\mathrm{dc}}=\frac{H_{v\_1\_\mathrm{DAB}\_1}}{H_{v\_2\_\mathrm{DAB}\_1}}\&CenterDot;V_{\mathrm{dc}\_11}=\frac{H_{v\_1\_\mathrm{DAB}\_1}}{H_{v\_2\_\mathrm{DAB}\_1}}\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="V\; C"\; filenames="HSA00000211439800012.png,HSA00000211439800031.png"\; state="\{\{state\}\}">V</figure-callout>}}_C$

$V_{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="HSA00000211439800012.png,HSA00000211439800021.png"\; state="\{\{state\}\}">C</figure-callout>}2}=\frac{H_{v\_2\_\mathrm{DAB}\_2}}{H_{v\_1\_\mathrm{DAB}\_2}}\&CenterDot;\frac{H_{v\_1\_\mathrm{DAB}\_1}}{H_{v\_2\_\mathrm{DAB}\_1}}\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="V\; C"\; filenames="HSA00000211439800012.png,HSA00000211439800031.png"\; state="\{\{state\}\}">V</figure-callout>}}_C$

$V_{\mathrm{<figure-callout\; id="3"\; label="C"\; filenames="HSA00000211439800031.png"\; state="\{\{state\}\}">C</figure-callout>}3}=\frac{H_{v\_2\_\mathrm{DAB}\_3}}{H_{v\_1\_\mathrm{DAB}\_3}}\&CenterDot;\frac{H_{v\_1\_\mathrm{DAB}\_1}}{H_{v\_2\_\mathrm{DAB}\_1}}\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="V\; C"\; filenames="HSA00000211439800012.png,HSA00000211439800031.png"\; state="\{\{state\}\}">V</figure-callout>}}_C$

From formula can obtain when each module feedback and feedforward be proportional numbers when equating, can guarantee that then the rectification stage output voltage is balanced.

(3) third level inverse cascade: also can adopt the H bridge-type structure; Adopt SPWM control, its input impedance can be approximately equal to

This level is that 50HZ exchanges with the 400V dc inversion, and while 400V direct current section can be used for regenerative resource and is incorporated into the power networks, and is the trend that intelligent grid is built.The H bridge-type structure is convenient to realize the transmitted in both directions of power, also can satisfy powerful requirement, can use one or more H bridge parallel connections.

(4) the balanced dynamic process analysis of voltage power: above formula has been described quiescent operation state in the ideal case; But in real system; There are many non-ideal factors; Like the difference of each module parasitic parameter, and various disturbance all can cause system to depart from quiescent point, and following surface analysis is in the dynamic voltage balancing adjustment process of whole system.

A certain moment V in the time of might as well supposing the power forward transmitted _C2＞V _C1, this moment 2#DAB PI _vValue will increase, and makes it shift to the angle and increase that power output increases, then V _C2Downward trend is arranged, simultaneously since the 2#DAB power output increase and make V _{O_dc}Raise, at this moment V _C1H _{V_1}＜V _{O_dc}H _{V_2}So 1#DAB shifts to the angle and reduces, power output reduces, and this moment, 1# rectification module input power was constant, makes V _C1Increase tendency is arranged, and simultaneously 3#DAB adjustment process and 1#DAB are similar, can know that from above-mentioned analysis 3 DAB make V through adjustment _C1Increase V _C2Reduce V _C3Increase, the three has the trend that reaches unanimity.But this moment is because V _C1The definite value height is exported in the voltage ratio rectification, so rectification stage 1# module closed loop makes the rectification stage output voltage V through adjustment _C1, V _C2, V _C3Descend.So V _C1, V _C2, V _C3Not only voltage can be tending towards equilibrium and can be stabilized in given output valve simultaneously, makes V _{O_dc}Remain on set-point.

Following relation is arranged between three rectification module through-put powers:

$P1:P2:\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="HSA00000211439800031.png"\; state="\{\{state\}\}">P</figure-callout>}3=k1:(\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="HSA00000211439800012.png,HSA00000211439800021.png"\; state="\{\{state\}\}">k</figure-callout>}2\&CenterDot;\frac{H_{v\_2\_\mathrm{DAB}\_2}}{H_{v\_1\_\mathrm{DAB}\_2}}\&CenterDot;\frac{H_{v\_1\_\mathrm{DAB}\_1}}{H_{v\_2\_\mathrm{DAB}\_1}}):(\mathrm{<figure-callout\; id="3"\; label="k"\; filenames="HSA00000211439800031.png"\; state="\{\{state\}\}">k</figure-callout>}3\&CenterDot;\frac{H_{v\_2\_\mathrm{DAB}\_3}}{H_{v\_1\_\mathrm{DAB}\_3}}\&CenterDot;\frac{H_{v\_1\_\mathrm{DAB}\_1}}{H_{v\_2\_\mathrm{DAB}\_1}})$

Wherein k1: k2: k3 is the ratio of three rectification module modulating waves.

Can know when ignoring between the modulating wave error and, just can realizing the transmission of 3 road constant powers from following formula when 3 DAB module feed-forward coefficients being set when identical with the feedback factor ratio.Simultaneously according to regenerative resource watt level on the 400V dc bus, this control strategy realizes that automatically power bi-directional flows, and guarantees that simultaneously each module all presses equal power.

More than analyze and can be generalized to the SST that the power main circuit is made up of any N AC/DC module input series connection and the parallel connection of N DC/DC output.

Claims (1)

1. multi-module cascade solid-state transformer voltage-equalizing and power-equalizing control method; The solid-state transformer power main circuit part of its application is formed by three grades: input stage is the active AC/DC rectifier of high frequency; Intergrade is a high-frequency isolation type DC/DC converter, and output stage is a high frequency DC/AC inverter; The input stage AC side adopts the multimode series connection; Corresponding each module input of intergrade of HVDC output termination of each module of input stage; 400 volts of direct currents of each module output parallel connection output of intergrade, the output stage high-frequency inverter becomes output 220 volts/50 hz ac to 400 volts of DC convertings; It is characterized in that it may further comprise the steps:

(1) input stage adopts principal and subordinate dq conversion control mode: the solid-state transformer input stage is a plurality of module series connection, confirms that one of them is a primary module, and this step comprises following substep:

(a) the primary module output voltage is sampled, sampled value and set-point compare, and their error is through the benchmark of Voltage loop PI as d shaft current ring;

(b) conversion obtains the d axle to the input current sampled value through dq, two components of q axle, and wherein the used phase reference of dq conversion is obtained through the PLL phase-locked loop by the input voltage sampled value, and then the d axle divides quantitative response active current component, and the q axle divides quantitative response reactive current component;

(c) as benchmark, error is sent into d shaft current PI to the d axle with above-mentioned Voltage loop PI output; The q axle is with 0 as benchmark, and error is sent into q shaft current PI, then diaxon PI output valve is carried out decoupling zero and anti-dq conversion, obtains modulating wave;

(d) other are from module and the shared same modulating wave of primary module, and triangular carrier is the phase shift certain angle successively, and carrier wave and triangular wave relatively obtain the drive signal of each module;

(2) each module controls mode of intergrade is identical, adopts electric voltage feed forward rear feed control method, has realized that the ratio of intergrade input and output voltage is followed relation: promptly

Wherein, V _InBe the intergrade input voltage, V _oBe intergrade output voltage, H _V-1Be the electric voltage feed forward coefficient, H _V-2Be the Voltage Feedback coefficient, this step comprises following substep:

(a) intergrade input and output voltage is sampled, input voltage sampled signal and output voltage sampled signal are compared, error is through Voltage loop PI, as the fiducial value of electric current loop;

(b) input current is sampled, current sampling data and electric current loop fiducial value are compared, error compares with triangular carrier through electric current loop PI then, produces the switching tube drive signal; If electric current loop PI output valve is being for just, power forward flow then, otherwise power reverse flow;

(3) output stage adopts the SPWM control method, and the SPWM control method as modulating wave, relatively produces switching tube drive signal with triangular carrier with sine wave, guarantees that like this output voltage is sinusoidal wave.

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