CN104716656B - Cascading static synchronous reactive compensator topology with energy exchange unit and control method thereof - Google Patents

Abstract

The invention discloses a cascading static synchronous reactive compensator topology with an energy exchange unit and a control method thereof, and relates to the power unit capacitor voltage balance control technology of a cascaded reactive compensation device. The cascading static synchronous reactive compensator topology with the energy exchange unit and the control method thereof aim at solving the problems existing in the method adopted by an existing star connection cascade converter for the capacitor voltage unbalance among phases that the output current of the converter changes and breaks the control reliability and extracting of positive and negative sequence components has lowpass filtering and influences the dynamic performance of the cascading static synchronous compensator. The cascading static synchronous reactive compensator topology comprises N-1 power modules which adopt the star connection, and the N is a positive integer; the N power module adopts the energy exchange unit EEU, the energy exchange unit EEU is connected with a star point, the energy exchange unit EEU comprises a three-phase bridge and two common capacitors, and the three-phase bridge and the common capacitors adopt the star connection. The cascading static synchronous reactive compensator topology with the energy exchange unit and the control method thereof are used in the cascaded reactive compensation device based on the power unit.

Description

There is the cascade Static Synchronous reactive-load compensator topology of energy conversion unit and its control Method

Technical field

The present invention relates to the power cell capacitor voltage balance control technology of cascade connection type reactive power compensator.

Background technology

Reactive power compensator based on cascade of power units is due to without step-up transformer, can reduce device volume and work( Consumption, occupies more and more important position in middle pressure (common 6kV, 10kV) power quality controlling.In practical application, cascade is idle Compensation device often selects star connection, as shown in Figure 1.Compared with delta connection, required for same nominal voltage devices Submodule number less, converter output current harmonics are less.

The subject matter that star connection cascade converter exists is that three alternate capacitor voltage balance problems are relatively difficult to resolve certainly.Work as level The connection each power model of STATCOM is in suspended state, when carrying out reactive-load compensation, a power frequency period internal power module charge and discharge electric energy Amount is identical, and module capacitance voltage can keep stable.But under non-ideal conditions, such as current break, module device parameter is not When consistent, module capacitance voltage is by imbalance, if not taking responsible measures, this uneven expansion further leads to convert Device controls unsuccessfully.

Module capacitance Voltage unbalance includes two parts：Capacitance voltage between single-phase internal module is uneven, and with Capacitance voltage between phase is uneven.For the former, there is the solution more than comparison at present, wherein most popular solution bag Include sequence, voltage modulated ripple compensates and the direct method of adjustment of module conducting dutycycle, its overall thought is to each module Charge and discharge process carries out trickle adjustment, the holding capacitor balance of voltage, will not change converter output voltage, by these sides simultaneously Method has solved this problem substantially.

But uneven for capacitance voltage between phase and phase, current solution is simultaneously few.In terms of existing document, main The solution wanted is to propose method by Japanese scholars Akagi, that is, adjust often mutually total output voltage, by superposition and converter The consistent voltage of output current phase place, in the different real components of three alternate generations, to change the energy stores between three-phase, puts down Capacitance voltage between weighing apparatus three-phase.But the voltage of the method superposition can cause the change of converter output current, converter simultaneously Three-phase output voltage also not releveling, its neutral potential differs and is set to zero, this destroys the reliability of control.Domestic have scholar By positive-negative sequence detached method, out-of-balance current voltage is controlled, but the extraction of positive and negative order components has LPF ring Section, can have a strong impact on the dynamic property of cascade STATCOM.

Content of the invention

The invention aims to solve existing star connection cascade converter for phase and phase between capacitance voltage uneven Using method there is converter output current and change, destroy control reliability, the extraction of positive and negative order components exist LPF, A kind of problem of impact cascade STATCOM dynamic property, there is provided cascade Static Synchronous with energy conversion unit Reactive-load compensator topology and its control method.

The cascade Static Synchronous reactive-load compensator topology with energy conversion unit of the present invention, this cascade Static Synchronous Reactive-load compensator topology includes N-1 power model, and N is positive integer, and N-1 power model adopts Y-connection；This cascade is quiet Only the n-th power model of synchronous reactive-load compensator topology adopts energy exchange unit EEU, energy exchange unit EEU and star Point connects, and energy exchange unit EEU includes a three-phase bridge and two shared electric capacity C_N1、C_N2, three-phase bridge and two shared electric capacity C_N1、C_N2Using Y-connection, the Y-connection point O of energy exchange unit EEU is zero-potential point.

The control method of the cascade Static Synchronous reactive-load compensator topology with energy conversion unit of the present invention, this control The detailed process of method processed is：

Step 1, detection energy exchange unit EEU DC voltage U_DCN, by U_DCNWith DC side reference voltage U_DCref ^*Phase Subtract, difference adjusts output voltage adjustment angle θ obtaining energy exchange unit EEU through PI₀；

Step 2, detection A, B, C three phase capacitance voltage, obtain three phase capacitance average voltage U_avgx, by U_avgxAnd three-phase electricity Hold voltage reference value to subtract each other, difference adjusts through PI and obtains each phase output voltage adjustment angle θ_x；

Step 3, detection three-phase current i_a、i_b、i_c, obtain i through 3/2 conversion_dAnd i_q, and then obtain the electric angle of output current Degree θ_i；

Step 4, output voltage adjustment angle θ according to energy exchange unit EEU₀With each phase output voltage adjustment angle θ_x Difference be superimposed with electrical angle θ of output current_i, then deduct pi/2, obtain energy exchange unit EEU output voltage angle, θ^*；

Step 5, basis obtain energy exchange unit EEU output voltage angle, θ^*Square wave is adopted to energy exchange unit EEU Control；

Step 6, the capacitance voltage to the N-1 power model in every phase front are modulated using PSPWM, complete there is energy quantitative change The balance changing the cascade Static Synchronous reactive-load compensator topology of unit controls.

Advantages of the present invention：The open a kind of New Topological of present invention cascade STATCOM (STATCOM) and its Modulation and balance control strategy.Different from traditional topology, at neighbouring star tie point it increased one by three-phase bridge and The energy exchange unit (EEU) that common capacitor is constituted.Wherein, energy exchange unit adopts square-wave frequency modulation, and remaining module adopts Carrier-shifted PWM (PSPWM) is modulated, and by changing the modulating wave electromagnetic point of energy exchange unit, realizes converter alternate Capacitor voltage balance.Topology proposed by the invention and control method are conducive to cascading the capacitor voltage balance of reactive-load compensator, By the improvement of topological structure, actively increase an energy exchange unit for the energy transmission between three-phase, and by special The modulation and control realization capacitive coupling balance of voltage.With respect to traditional capacitance voltage balancing control method, the method is passed through Increased sub-fraction circuit, make whole system more reliable and more stable.

Brief description

Fig. 1 is the structured flowchart of typical case's cascade Static Synchronous reactive-load compensator topology；

Fig. 2 is the structural frames of the cascade Static Synchronous reactive-load compensator topology with energy conversion unit of the present invention Figure；

Fig. 3 is energy exchange unit EEU and other unit output voltages, converter overall output voltage and output current are closed It is schematic diagram；

Fig. 4 is the flow chart element of the control method of cascade Static Synchronous reactive-load compensator topology with energy conversion unit Figure；

Fig. 5 is a phase output voltage schematic diagram of energy exchange unit EEU and converter；

Fig. 6 is load current and compensates current diagram；

Fig. 7 is average capacitor voltage schematic diagram；

Fig. 8 is the capacitance voltage of three capacitance voltages and energy exchange unit EEU in a phase.

Specific embodiment

Specific embodiment one：With reference to Fig. 2, present embodiment is described, there is described in present embodiment energy conversion list The cascade Static Synchronous reactive-load compensator topology of unit, this cascade Static Synchronous reactive-load compensator topology includes N-1 power model, N is positive integer, and N-1 power model adopts Y-connection；The n-th power mould of this cascade Static Synchronous reactive-load compensator topology Block adopts energy exchange unit EEU, energy exchange unit EEU and star point to connect, and energy exchange unit EEU includes a three-phase Bridge and two shared electric capacity C_N1、C_N2, three-phase bridge and two shared electric capacity C_N1、C_N2Using Y-connection, energy exchange unit EEU Y-connection point O be zero-potential point.

Specific embodiment two：With reference to Fig. 4, present embodiment is described, there is described in present embodiment energy conversion list Unit cascades the topological control method of Static Synchronous reactive-load compensator, and the detailed process of this control method is：

Step 1, detection energy exchange unit EEU DC voltage U_DCN, by U_DCNWith DC side reference voltage U_DCref ^*Phase Subtract, difference adjusts output voltage adjustment angle θ obtaining energy exchange unit EEU through PI₀；

Step 2, detection A, B, C three phase capacitance voltage, obtain three phase capacitance average voltage U_avgx, by U_avgxAnd three-phase electricity Hold voltage reference value to subtract each other, difference adjusts through PI and obtains each phase output voltage adjustment angle θ_x；

Step 3, detection three-phase current i_a、i_b、i_c, obtain i through 3/2 conversion_dAnd i_q, and then obtain the electric angle of output current Degree θ_i；

Step 4, output voltage adjustment angle θ according to energy exchange unit EEU₀With each phase output voltage adjustment angle θ_x Difference be superimposed with electrical angle θ of output current_i, then deduct pi/2, obtain energy exchange unit EEU output voltage angle, θ^*；

Step 5, basis obtain energy exchange unit EEU output voltage angle, θ^*Square wave is adopted to energy exchange unit EEU Control；

Step 6, the capacitance voltage to the N-1 power model in every phase front are modulated using PSPWM, complete there is energy quantitative change The balance changing the cascade Static Synchronous reactive-load compensator topology of unit controls.

Specific embodiment three：Present embodiment is described further to specific embodiment two, adjusts energy described in step 1 Output voltage adjustment angle θ of amount crosspoint EEU₀It is able to maintain that the capacitance voltage of energy exchange unit EEU is stable.

Specific embodiment four：Present embodiment is described further to specific embodiment two, adjusts each described in step 2 Phase output voltage adjustment angle θ_xIt is capable of the capacitive coupling balance of voltage.

Specific embodiment five：Present embodiment is described further to specific embodiment two, obtains energy described in step 4 Amount crosspoint EEU output voltage angle, θ^*The exchange of energy exchange unit EEU power component energy can be controlled, thus changing The energy stores of each phase electric capacity.

Specific embodiment six：Present embodiment is described further to specific embodiment two, to every phase described in step 6 The capacitance voltage of front N-1 power model is modulated being able to ensure that the electric capacity electricity of the N-1 power model in every phase front using PSPWM Flatten weighing apparatus.

Specific embodiment seven：Present embodiment is described further to specific embodiment two, to energy described in step 5 The modulation system that crosspoint EEU carries out square wave control is：

Wherein, S_NIt is the switch function of energy exchange unit EEU, M_xIt is the modulating wave of N-1 power model, v_refAFor A phase Output voltage amplitude, V_DCNIt is the DC voltage of N-1 power model, V_DCiRepresent the capacitance voltage in i-th power model.

The present invention proposes a kind of cascade STATCOM topological structure with energy exchange unit, such as Fig. 2.Open up with traditional Flutter (Fig. 1) difference, at neighbouring star tie point, it increased an energy exchange being made up of three-phase bridge and common capacitor Unit EEU.The size of capacitance voltage represents in electric capacity the energy of storage, in New Topological, by can to the control of EEU To exchange the energy of electric capacity storage in three-phase, so that capacitance voltage is adjusted.

With reference to Fig. 2-Fig. 8 explanation, the output voltage of the every phase of cascade converter is submodule output voltage in all phases Sum, each submodule output voltage is by modulation controlling.The output voltage of converter can be by the electric capacity of each module Voltage and the index of modulation represent：

U_j=(V_DC1M₁+V_DC2M₂+…+V_DC(N-1)M_N-1)+V_DCNM_N, j=A, B or C (1)

Front N-1 module is entirely H bridge type topology, and its three-phase output voltage passes through PWM method such as phase-shifting PWM (PSPWM) it is modulated.EEU also can adopt PWM, but it only has 2 level output (+V_DCN/ 2 and-V_DCN/ 2), this be with The different place of other modules, so it is difficult in the modulation (such as PSPWM) participate in other modules.Can also from above formula Go out, if switch harmonic can not be offset by other modules, n-th module is operated in needs of a relatively high opening during PWM mode Close frequency.In order to reduce switching frequency harmonic, the present invention adopts square-wave frequency modulation to EEU module, and other modules adopt PSPWM to adjust System.

Hypothesis A phase output voltage amplitude is v_refA, using its modulation system such as formula (2) during square-wave frequency modulation Suo Shi, θ in formula^*It is EEU module modulating wave electromagnetic point.S_NIt is the switch function of n-th module, M_xIt is the modulating wave of other modules, for same phase shift Triangular carrier is compared to obtain corresponding switching pulse.

Adjustment θ^*Angle can achieve capacitor voltage balance, and principle is as shown in Figure 3.Taking A phase as a example, in reactive-load compensation, Hypothesis A phase output current is i_A, output voltage is u_A, then i_AWith u_AElectromagnetic point differs 90 degree.Assume EEU unit output voltage Differ as θ it is known that when θ is for pi/2 with current angle,

And work as 0<θ<During pi/2, W>0；When-pi/2<θ<When 0, W<0.Therefore, by being controlled to θ, you can so that energy is handed over Change unit charge or discharge.Simultaneously as shown in remaining submodule modulating wave such as formula (2), that is, the total output voltage of A phase keeps not Become, during pure reactive-load compensation, it differs 90 degree with current angle, in a power frequency period, total active of A phase is exchanged for 0.Its complement submodule Block output voltage deducts energy exchange unit voltage for reference voltage, therefore, if a power frequency period self-energy crosspoint Energy exchange is more than 0, then the energy exchange of remaining submodule will so pass through to adjust the output electricity of energy exchange unit less than 0 Pressure angle, θ, you can reach the purpose of adjustment remaining module capacitance voltage of A phase.

Meanwhile, in order to keep energy exchange unit (EEU) its voltage stable it is also desirable to the energy exchange to this unit is entered Row controls, and equally realizes also by its reference voltage of control and output current angle.

Finally, the capacitor voltage balance scheme of this converter is as shown in Figure 4.First, the electricity to energy exchange unit (EEU) Pressure carries out closed-loop control, obtains EEU output voltage adjustment angle θ₀, then three phase capacitance average voltage is carried out with PI closed loop control System, obtains output voltage adjustment angle θ of each phase EEU_x, finally, this adjustment angle is superimposed with the angle, θ of each phase current_i, and subtract Remove pi/2, that is, obtain EEU output voltage angle, θ^*.

Afterwards, it is modulated according to shown in formula (2).Finally, in order to balance the electric capacity electricity of other power cells in phase Pressure, using conventional method in other documents, adjusts to the modulating wave of each power cell further, and superposition is electric with this unit Press the component proportional to the difference of this phase average cell voltage.

Claims (6)

1. the control method based on the cascade Static Synchronous reactive-load compensator topology with energy conversion unit, has energy conversion The cascade Static Synchronous reactive-load compensator topology of unit, this cascade Static Synchronous reactive-load compensator topology includes N-1 power mould Block, N is positive integer, and N-1 power model adopts Y-connection；The n-th work(of this cascade Static Synchronous reactive-load compensator topology Rate module adopts energy exchange unit EEU, energy exchange unit EEU and star point to connect, and energy exchange unit EEU includes one Three-phase bridge and two shared electric capacity C_N1、C_N2, three-phase bridge and two shared electric capacity C_N1、C_N2Using Y-connection, energy exchange unit The Y-connection point O of EEU is zero-potential point；

It is characterized in that, the detailed process of this control method is：

Step 1, detection energy exchange unit EEU DC voltage U_DCN, by U_DCNWith DC side reference voltage U_DCref ^*Subtract each other, poor Value adjusts output voltage adjustment angle θ obtaining energy exchange unit EEU through PI₀；

Step 2, detection A, B, C three phase capacitance voltage, obtain three phase capacitance average voltage U_avgx, by U_avgxWith three phase capacitance electricity Pressure reference value is subtracted each other, and difference adjusts through PI and obtains each phase output voltage adjustment angle θ_x；

Step 3, detection three-phase current i_a、i_b、i_c, obtain i through 3/2 conversion_dAnd i_q, and then obtain the electrical angle of output current θ_i；

Step 4, output voltage adjustment angle θ according to energy exchange unit EEU₀With each phase output voltage adjustment angle θ_xDifference It is superimposed with electrical angle θ of output current_i, then deduct pi/2, obtain energy exchange unit EEU output voltage angle, θ *；

Step 5, basis obtain energy exchange unit EEU output voltage angle, θ^*Square wave is adopted to control energy exchange unit EEU；

Step 6, the capacitance voltage to the N-1 power model in every phase front are modulated using PSPWM, complete with energy conversion list The balance of the cascade Static Synchronous reactive-load compensator topology of unit controls.

2. the controlling party of the cascade Static Synchronous reactive-load compensator topology with energy conversion unit according to claim 1 Method is it is characterised in that adjust output voltage adjustment angle θ of energy exchange unit EEU described in step 1₀It is able to maintain that energy is handed over The capacitance voltage changing unit EEU is stable.

3. the controlling party of the cascade Static Synchronous reactive-load compensator topology with energy conversion unit according to claim 1 Method is it is characterised in that adjust each phase output voltage adjustment angle θ described in step 2_xIt is capable of the capacitive coupling balance of voltage.

4. the controlling party of the cascade Static Synchronous reactive-load compensator topology with energy conversion unit according to claim 1 Method is it is characterised in that obtain energy exchange unit EEU output voltage angle, θ described in step 4^*Energy exchange unit can be controlled The exchange of EEU power component energy, thus change the energy stores of each phase electric capacity.

5. the controlling party of the cascade Static Synchronous reactive-load compensator topology with energy conversion unit according to claim 1 Method is it is characterised in that described in step 6, the capacitance voltage of the N-1 power model in every phase front is modulated using PSPWM can be true Protect the capacitor voltage balance of the N-1 power model in every phase front.

6. the controlling party of the cascade Static Synchronous reactive-load compensator topology with energy conversion unit according to claim 1 Method is it is characterised in that the modulation system carrying out square wave control to energy exchange unit EEU described in step 5 is：

$\left\{\begin{array}{c}{S}_N=\left\{\begin{array}{cc}1& 0\&le;{\mathrm{\&theta;}}^{*}<\mathrm{\&pi;}\\ -1& \mathrm{\&pi;}\&le;{\mathrm{\&theta;}}^{*}<2\mathrm{\&pi;}\end{array}\right.\\ M_x=\left(\frac{v_{refA}-S_N\frac{V_{DCN}}{2}}{\underset{i=1}{\overset{N-1}{\mathrm{\&Sigma;}}}{V}_{DCi}}\right),x=1,2,...,N-1\end{array}\right.$

Wherein, S_NIt is the switch function of energy exchange unit EEU, M_xIt is the modulating wave of N-1 power model, v_refAFor the output of A phase Voltage magnitude, V_DCNIt is the DC voltage of N-1 power model, V_DCiRepresent the capacitance voltage in i-th power model.