CN105322554A - Prediction method for capacitor voltage fluctuation in direct current side of chain type STATCOM (static synchronous compensator) - Google Patents

Abstract

The invention discloses a prediction method for capacitor voltage fluctuation in a direct current side of a chain type STATCOM (static synchronous compensator). The prediction method comprises a step of obtaining the direct current side reactive power, a step of integral resetting and a step of limiting amplitude; the step of obtaining the direct current side reactive power is carried out by superposition between the reactive power of the chain type STATCOM in switching with a power grid, and the reactive power on a connected electric reactor to obtain instantaneous reactive power on a direct current capacitor; the step of integral resetting is carried out by performing integral processing on the instantaneous reactive power on the direct current capacitor to obtain the direct current side voltage fluctuation, and resetting the integral value in the voltage fluctuation theory zero crossing point to eliminate the integral error accumulation; and the step of limiting amplitude can restrain the shielding action on the capacitor voltage transient state error by the prediction method in the reactive instruction change transient process. The method can be applied to the direct current side voltage closed loop control of the chain type STATCOM; the second harmonic generation component in the direct current side capacitor voltage feedback value of the chain type STATCOM is eliminated, a third harmonic current instruction generated by introducing the second harmonic generation component into the direct current side capacitor voltage regulator is avoided, and the third harmonic generation component in the grid connection current of the chain type STATCOM is effectively reduced.

Description

A kind of chain type STATCOM DC capacitor voltage volatility forecast method

Technical field

The invention belongs to voltage control technical field, more specifically, relate to chain static synchronous compensator (staticsynchronouscompensator, STATCOM) DC capacitor voltage volatility forecast method.

Background technology

Electricity Generation system generally adopts diode rectification or Thyristor Controlled rectification to form DC power supply, has that power factor is low seriously waits power quality problem with harmonic pollution in power distribution network.Chain type STATCOM adopts H bridge cascade connection multi-level topology, direct screening can carry out dynamic passive compensation and power quality controlling in mesohigh power distribution network, has the advantage that modularization, easily expansion, idle continuous adjustment, compensate function are various.

Chain type STATCOM DC capacitor voltage generally adopts self-excitation mode, relies on closed loop feedback to control to maintain the stable of capacitance voltage.Because chain type STATCOM and power system reactive power exchange and three phase capacitance independence, DC capacitor voltage is by the fluctuation of generation two times of power frequencies, this voltage fluctuation introduces DC voltage closed-loop control by feedback element, make the harmonic component producing frequency tripling in active current instruction, worsen the chain type STATCOM grid-connected current quality of power supply.In Voltage Feedback passage, add filtering process, voltage fluctuation can be suppressed the impact of current harmonics, but reduce the dynamic responding speed of system, have impact on the stability of closed-loop system, limit the span of controling parameters, easily cause capacitance voltage self-oscillation.

Summary of the invention

For above defect or the Improvement requirement of prior art, the invention provides a kind of chain type STATCOM DC capacitor voltage volatility forecast method, its object is to the impact that elimination voltage fluctuation of capacitor controls chain type STATCOM DC side.

For achieving the above object, according to one aspect of the present invention, provide a kind of chain type STATCOM DC capacitor voltage volatility forecast method, comprise and obtain DC side reactive power, integral processing and amplitude limiting processing, specific as follows:

(1) pass through line voltage u _swith referenced reactive current i _cbe multiplied, the reactive power q that acquisition chain type STATCOM and electrical network exchange _s;

By by referenced reactive current i _cdifferential obtains the voltage u on inductance _l; By by inductive drop u _lwith referenced reactive current i _cbe multiplied, obtain the reactive power q on inductance _l;

By the reactive power q that above-mentioned chain type STATCOM and electrical network exchange _swith the reactive power q on inductance _lsuperposition, obtains the reactive power instantaneous value q of input direct-current lateral capacitance _c;

(2) pass through the reactive power instantaneous value q of input direct-current lateral capacitance _cwith coefficient be multiplied, the capacitance voltage rate of change of acquisition; Integral processing is carried out to this capacitance voltage rate of change, obtains the fluctuation u of capacitance voltage _d2;

(3) to the fluctuation u of the capacitance voltage that step (2) integral processing obtains _d2carry out amplitude limit, obtain DC capacitor voltage volatility forecast value

${\tilde{u}}_d=\left\{\begin{array}{c}{\tilde{u}}_{dmax},u_{d2}>{\tilde{u}}_{dmax}\\ u_{d2},-{\tilde{u}}_{dmax}\≤u_{d2}\≤{\tilde{u}}_{dmax}\\ -{\tilde{u}}_{dmax},u_{d2}\≤-{\tilde{u}}_{d\max }\end{array}\right.;$

Wherein, N is the cascade number of chain type STATCOM, for the set point of DC capacitor voltage, C is the capacitance of DC bus capacitor; Wherein, the set point of DC capacitor voltage is determined according to device withstand voltage ability, as adopted the IGBT of 1700V electric pressure, DC capacitor voltage set point 800 ~ 1000V, for amplitude limit value; Amplitude limiting processing can suppress idle instruction to change in transient process this Forecasting Methodology to the shielding action of capacitance voltage transient state deviation.

Preferably, in above-mentioned steps (2), also comprise the process that integrator zero setting resets, be specially: rectification is carried out to line voltage unit synchronizing signal sin (ω t), obtain absolute synchronization signal | Syn|, by this absolute synchronization signal with relatively, the square wave R of two frequencys multiplication is obtained _e, the theoretical zero crossing of corresponding capacitance voltage two harmonic of this square wave rising edge; The rising edge of this square wave is adopted to reset, integrator zero setting to eliminate the error accumulation that integral processing causes.

Preferably, the amplitude limit value in step (3) amplitude limiting processing step for:

${\tilde{u}}_{dmax}=\left|\frac{N}{4{\mathrm{\ωu}}_d^{*}C}(U_s{I}_{cmax}-{\mathrm{\ωLI}}_{cmax}^2)\right|;$

Wherein, ω is electrical network angular frequency, U _sfor line voltage effective value, L is that chain type STATCOM connects inductance value, I _cmaxfor the maximum offset current effective value of chain type STATCOM.

In general, the above technical scheme conceived by the present invention compared with prior art, can obtain following beneficial effect:

(1) chain type STATCOM DC capacitor voltage volatility forecast method provided by the invention, owing to eliminating two harmonics in chain type STATCOM DC capacitor voltage value of feedback, two harmonics are avoided to introduce DC capacitor voltage adjuster, thus apply chain type STATCOM DC capacitor voltage volatility forecast method provided by the invention, effectively can reduce the frequency tripling harmonic component in chain type STATCOM grid-connected current;

(2) chain type STATCOM DC capacitor voltage volatility forecast method provided by the invention, introduces integral reset function in its preferred version, resets, effectively can eliminate the accumulation of integral error at the theoretical zero crossing of voltage fluctuation of capacitor to integrated value;

(3) chain type STATCOM DC capacitor voltage volatility forecast method provided by the invention, amplitude limiting processing can suppress this Forecasting Methodology in idle instruction change transient process to the shielding action of capacitance voltage transient state deviation, to further shorten voltage dynamic adjustments response delay time.

Accompanying drawing explanation

Fig. 1 is real single-phase chain type STATCOM main circuit topological structure figure;

Fig. 2 is the chain type STATCOM double-closed-loop control block diagram of prior art;

The chain type STATCOM DC capacitor voltage volatility forecast method schematic diagram that Fig. 3 provides for embodiment;

Fig. 4 is integral reset signature waveform in embodiment;

The application of the chain type STATCOM DC capacitor voltage volatility forecast method that Fig. 5 provides for embodiment;

Fig. 6 is the oscillogram adopting chain type STATCOM double-closed-loop control method to obtain;

The oscillogram that the chain type STATCOM DC capacitor voltage volatility forecast method that Fig. 7 provides for employing embodiment obtains.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearly understand, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein only in order to explain the present invention, be not intended to limit the present invention.In addition, if below in described each execution mode of the present invention involved technical characteristic do not form conflict each other and just can mutually combine.

Fig. 1 is single-phase chain type STATCOM main circuit topological structure figure, and main circuit adopts single-phase H bridge construction as concatenation unit, and each concatenation unit is followed in series to form Multilevel Inverters, is connected with electrical network through linked reactor.By changing output voltage amplitude and the phase place of Multilevel Inverters, regulating chain type STATCOM grid-connected current to make it contrary with load reactive current phase place, thus reaching the object of reactive power compensation.

Fig. 2 is chain type STATCOM double-closed-loop control block diagram of the prior art; Its voltage regulator is according to capacitance voltage set point u _d ^*with value of feedback u _ddifference generate active current instruction I _p, by I _pbe multiplied with line voltage unit synchronizing signal sin (ω t), obtain the instantaneous value i of active current instruction _p ^*; By the instantaneous value i of active current instruction _p ^*with referenced reactive current i _q ^*superposition, obtains chain type STATCOM current-order i _c ^*; By chain type STATCOM current-order i _c ^*with current feedback values i _crelatively, error delta i is obtained _c, this error generates the modulation signal u of Multilevel Inverters through current regulator _r; For balancing the capacitance voltage of each concatenation unit, introduce voltage balancing control, deviation according to capacitance voltage is finely tuned each concatenation unit modulation signal, generate each concatenation unit modulation signal, multiplex pulse width modulated (PulseWidthModulation is generated again through phase-shifting carrier wave modulation, PWM) signal, drives corresponding switching device in main circuit.

Chain type STATCOM AC and electrical network carry out reactive power exchange, its line voltage u _s=U _ssin (ω t), grid-connected current the reactive power that chain type STATCOM and electrical network exchange i _crefer to grid-connected current peak value, t refers to time variable;

The cocommutative reactive power of usual chain type STATCOM linked reactor be can not ignore; The cocommutative reactive power of linked reactor $q_L=u_L{i}_c-L\frac{{\mathrm{di}}_c}{dt}{i}_c=-\frac{1}{2}{\mathrm{\ωLI}}_c^{2}sin\left(2\mathrm{\ω}t\right);$ Wherein, u _lrefer to the pressure drop on linked reactor;

Then inject the reactive power of DC bus capacitor $q_c=q_s+q_L=\frac{1}{2}(U_s{I}_c-{\mathrm{\ωLI}}_c^2)sin\left(2\mathrm{\ω}t\right);$ Each concatenation unit DC capacitor voltage balance, the power fluctuation that DC bus capacitor is total wherein N is concatenation unit quantity;

Due to AC and power balance of DC side, q _c=q _d, namely thus, two times of power frequency fluctuations that the capacitance voltage caused by the reactive power injecting idle DC bus capacitor occurs, its two harmonic $u_{d2}=\frac{N}{2u_{d}C}\∫\left(U_s{I}_c-{\mathrm{\ωLI}}_c^2\right)\sin \left(2\mathrm{\ω}t\right)dt\≈-\frac{N\left(U_s{I}_c-{\mathrm{\ωLI}}_c^2\right)}{4{\mathrm{\ωu}}_d^{*}C}\cos \left(2\mathrm{\ω}t\right);$

Its voltage regulator adoption rate-integration (proportional-integral, PI) controls, DC deviation during employing integral processing elimination stable state between capacitance voltage value of feedback and set point; In voltage deviation, two harmonics account for leading, the active current instruction obtained after PI regulating and controlling $I_p-{\stackrel{\‾}{I}}_p+{\tilde{I}}_{p}sin(2\mathrm{\ω}t+\mathrm{\θ});$

Wherein, maintain chain type STATCOM capacitance voltage to stablize the required real component injected, it is the real component that in voltage deviation, two harmonics produce through pi regulator; By I _pbe multiplied with line voltage synchronizing signal, obtain the instantaneous value i of active current instruction _p ^*,

$i_p^{*}=I_{p}sin\left(\mathrm{\ω}t\right)={\stackrel{\‾}{I}}_{p}sin\left(\mathrm{\ω}t\right)+\frac{1}{2}{\tilde{I}}_{p}sin(\mathrm{\ω}t+\mathrm{\θ})+\frac{1}{2}-{\tilde{I}}_{p}sin(3\mathrm{\ω}t+\mathrm{\θ});$

I _p ^*containing third-harmonic component, for eliminating two harmonics in chain type STATCOM DC capacitor voltage value of feedback, avoid two harmonics to introduce DC capacitor voltage adjuster and produce triple harmonic current instruction, frequency tripling harmonic component in effective reduction chain type STATCOM grid-connected current, the DC capacitor voltage volatility forecast method that embodiment provides is as shown in Figure 3;

Concrete, by by line voltage u _swith referenced reactive current i _cbe multiplied, the reactive power q that acquisition chain type STATCOM and electrical network exchange _s; By referenced reactive current i _cdifferential obtains the voltage u on inductance _l; By inductive drop u _lwith referenced reactive current i _cbe multiplied the reactive power q obtained on inductance _l; By the reactive power q that chain type STATCOM and electrical network exchange _swith the reactive power q on inductance _lsuperposition, obtains the reactive power instantaneous value q of input direct-current lateral capacitance _c; Again by the reactive power instantaneous value q of input direct-current lateral capacitance _cwith coefficient be multiplied, and carry out integral processing, obtain the volatility forecast value of capacitance voltage $u_{d2}=\frac{N}{2u_d^{*}C}\∫q_{c}dt;$

Owing to there is metrical error and the error of calculation, integral processing expands the DC component that error accumulation causes in Output rusults, have influence on the control of capacitance voltage DC component, for this reason, in embodiment, also comprise reset processing in integral processing step, integral element is resetted, to eliminate error accumulation at capacitance voltage two harmonic theoretical zero crossing.

Be implemented as follows: rectification is carried out to line voltage unit synchronizing signal sin (ω t) and obtains absolute synchronization signal | Syn|, with relatively, the square wave R of two frequencys multiplication is obtained _e, utilize the reset function in the rising edge activation integral treatment step of this square wave, signature waveform as shown in Figure 4, the zero crossing of corresponding capacitance voltage two harmonic of the rising edge of square wave;

Thus, beyond two harmonic zero moment, idle instruction sudden change will cause capacitance voltage actual value transient state to depart from capacitance voltage set point, the transient state deviation of capacitance voltage is passed to voltage feedback value in time, be conducive to the response speed improving voltage-regulation, avoid DC capacitor voltage to occur temporary overvoltage.In transient process, predicting the outcome of voltage fluctuation of capacitor also will produce larger being biased, and produces shielding action to the transient state deviation of capacitance voltage.Although the biased zero that two harmonics can predict the outcome by the introducing of integral reset function in half power frequency period, but the actual deviation of capacitance voltage will be shielded by voltage prediction link before reset function effect, be difficult to arrive voltage regulator, cause voltage deviation to can not get timely suppression; For addressing this problem, embodiment carries out amplitude limit by predicting the outcome to two harmonics, shortens voltage dynamic adjustments response delay time further.

Amplitude limit value according to the maximum offset current I of chain type STATCOM _cmaxdetermine,

${\tilde{u}}_{dmax}=\left|\frac{N}{4{\mathrm{\ωu}}_d^{*}C}\left(U_s{I}_{cmax}-{\mathrm{\ωLI}}_{cmax}^2\right)\right|;$

In embodiment, amplitude limiting processing is realized by analog circuit; After amplitude limiting processing, predicting the outcome of chain type STATCOM DC capacitor voltage volatility forecast method as follows:

${\tilde{u}}_d=\left\{\begin{array}{c}{\tilde{u}}_{dmax},u_{d2}>{\tilde{u}}_{dmax}\\ u_{d2},-{\tilde{u}}_{dmax}\≤u_{d2}\≤{\tilde{u}}_{dmax}\\ -{\tilde{u}}_{dmax},u_{d2}\≤-{\tilde{u}}_{d\max }\end{array}\right.;$

When transient state deviation is larger, exceed amplitude limit value part very fast is passed to voltage regulator, participate in closed-loop adjustment, increase further to suppress voltage deviation.Shown in Fig. 5, be the application scenarios signal of the chain type STATCOM DC capacitor voltage volatility forecast method that embodiment provides, predict the outcome by DC capacitor voltage detected value is deducted voltage fluctuation of capacitor, obtain the DC component of DC capacitor voltage participate in DC voltage closed-loop control by this DC component, avoid capacitance voltage two harmonic introduce DC capacitor voltage adjuster and produce triple harmonic current instruction, the frequency tripling harmonic component in chain type STATCOM grid-connected current can be reduced.

Fig. 6 adopts the chain type STATCOM double-closed-loop control method shown in Fig. 2, and the oscillogram of acquisition, comprises grid voltage waveform and grid-connected current waveform; Fig. 7 is in the system-based shown in Fig. 2, adds the oscillogram that the DC capacitor voltage volatility forecast method shown in Fig. 5 obtains, comprises grid voltage waveform and grid-connected current waveform; Contrastingly the DC capacitor voltage volatility forecast method that Application Example provides makes grid-connected current sine degree tool have clear improvement, harmonic content reduces.

Those skilled in the art will readily understand; the foregoing is only preferred embodiment of the present invention; not in order to limit the present invention, all any amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (3)

1. a chain type STATCOM DC capacitor voltage volatility forecast method, is characterized in that, specifically comprise the steps:

(1) pass through line voltage u _swith referenced reactive current i _cbe multiplied, the reactive power q that acquisition chain type STATCOM and electrical network exchange _s;

By by referenced reactive current i _cdifferential obtains the voltage u on inductance _l; By by inductive drop u _lwith referenced reactive current i _cbe multiplied, obtain the reactive power q on inductance _l;

By the reactive power q that described chain type STATCOM and electrical network exchange _swith the reactive power q on inductance _lsuperposition, obtains the reactive power instantaneous value q of input direct-current lateral capacitance _c;

(2) pass through the reactive power instantaneous value q of input direct-current lateral capacitance _cwith coefficient be multiplied, the capacitance voltage rate of change of acquisition; Integral processing is carried out to described capacitance voltage rate of change, obtains the fluctuation u of capacitance voltage _d2;

(3) to the fluctuation u of described capacitance voltage _d2carry out amplitude limiting processing, obtain DC capacitor voltage volatility forecast value

${\tilde{u}}_d=\left\{\begin{array}{c}{\tilde{u}}_{dmax},u_{d2}>{\tilde{u}}_{dmax}\\ u_{d2},-{\tilde{u}}_{dmax}\≤u_{d2}\≤{\tilde{u}}_{dmax}\\ -{\tilde{u}}_{dmax},u_{d2}\≤-{\tilde{u}}_{d\max }\end{array}\right.;$

Wherein, N is the cascade number of chain type STATCOM, for the set point of DC capacitor voltage, C is the capacitance of DC bus capacitor, for amplitude limit value; Described amplitude limiting processing can suppress idle instruction to change in transient process this Forecasting Methodology to the shielding action of capacitance voltage transient state deviation.

2. chain type STATCOM DC capacitor voltage volatility forecast method as claimed in claim 1, it is characterized in that, in described step (2), also comprise the process that integrator zero setting resets, be specially: rectification is carried out to line voltage unit synchronizing signal sin (ω t), obtain absolute synchronization signal | _syn|, by this absolute synchronization signal with relatively, the square wave R of two frequencys multiplication is obtained _e, adopt the rising edge of described square wave to reset, integrator zero setting to eliminate the error accumulation that integral processing causes.

3. chain type STATCOM DC capacitor voltage volatility forecast method as claimed in claim 1 or 2, is characterized in that, the amplitude limit value in the described amplitude limiting processing step of step (3) for:

${\tilde{u}}_{dmax}=\left|\frac{N}{4{\mathrm{\ωu}}_d^{*}C}(U_s{I}_{cmax}-{\mathrm{\ωLI}}_{cmax}^2)\right|;$

Wherein, ω is electrical network angular frequency, U _sfor line voltage effective value, L is that chain type STATCOM connects inductance value, I _cmaxfor the maximum offset current effective value of chain type STATCOM.