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英文原文
Application of Advanced One-cycle Control in STATCOM
0 Introductions
Static Synchronous Compensator (STATCOM) is a flexible AC transmission system, one of the core device, which through the power grid into or from the grid to absorb some of the reactive power, can stabilize the voltage, flicker suppression, power factor, etc. to improve. In order to ensure stable and reliable work of STATCOM, the control method of choice is very important. STATCOM current control methods used in the main have a direct current control and indirect current control, but most of these control methods involve a number of control parameters of the coordinated adjustment more difficult to achieve.
Embarks from the instantaneous power principle of detailed balance, infers the inverter output current to the output voltage transformation relationship, thus has omitted the electric current PI regulator, reduced the controlled variable adjustment order of complexity, but this method needs the known STATCOM installment the equivalent resistance and the equivalent inductance value, but these two parameter generally with difficulty precision measuring. Embarks from the STATCOM structure, establishes it under the dq coordinate system's differential equation, through the solution differential equation, obtains the STATCOM control relationship directly. But this control method needs to carry on the precise modeling to STATCOM, very inaccessibility.
Is insensitive based on single week control's static synchronous compensator (OCC-STATCOM) to system's frequency departure, installment Lu good is very high, simultaneously only need carries on the examination to the input current and the STATCOM concurrent side voltage then, the control structure is simple, receives the attention more and more. But as a result of the OCC-STATCOM main circuit power component existence inherent dead time, this will have the negative effect to its output's idle current peak-to-peak value and the phase, will thus reduce the installment the idle work compensation effect. This article carries on the analysis in view of the OCC-STATCOM principle of work and the existence question, through changes in the single week governing equation the duty factor to realize to the inverter power component dead area compensation, increases the STATCOM controller's precision.
1 One-cycle Control static synchronous compensator's principle
See Figure based on the single week control's single-phase STATCOM installment structure drawing 1, (sometimes installs is composed of the voltage inverter and the connection reactor connects reactor also to use to connect transformer to replace). Sometimes, in connects between the reactor and the
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inverter also installs outputs the filter to filter the high frequency burr signal which the inverter outputs. Its principle of work is, examines the STATCOM junction point electric current as well as the inverter concurrent side electric capacity voltage, controls inverter’s voltage output through the single week algorithm, realizes STATCOM to pour into suitable in advance or the lag idle current to the electrical network, achieves the regulating power factor the goal.
When STATCOM effective work, the power source side idle work output is 0, is equal after undergoing the compensation, the three-phase load for the pure resistance load, the net side current waveform completely tracks the voltage waveform. Considers the single-phase circuit, may obtain the ideal control goal expression
isR?Us
In the formula, Usis the installment junction point voltage; is is the net side electric current; R expresses after the control equivalent resistive load. Supposes single week control the switching period is T, the duty factor is D. When 0?t?DT, on the invertors the bridge arm break over, gets down the bridge arm to shut off; WhenDT?t?T, gets down the bridge arm break over, on the bridge arm shuts off. The theoretical analysis may know, when STATCOM effective work, is and the D relations are
2DUm?Um?Rsis (1)
In the formula, Um??Rs/R?UDC, Rs is the electric current sampling resistance value; Um is the invertors concurrent side voltage. Considered the turn-on frequency is bigger than the network voltage frequency far, in a switching period Um basic invariable, type (1) may realize through the single week control way. Takes single week constant of integrationTi?1/2T, may promote the single week governing equation is
1Ti?DT0Umdt?1DTUm?2DUm?Um?Rsis (2) TiMay result in OOC-STATCOM according to type (2) the control scheme to see Figure 2. In chart,UDCref, for direct-current side electric capacity voltage
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datum value; Um obtains by (UDCref?UDC) after the PI adjustment. The control circuit carries on the integral in each switching period to Um, when the integral valve conforms to type (2), the switching signal turn over, the integrated circuit repositions, waiting next cycle again integral, thus obtains satisfies-like (2) D.
Line impedanceAnti- feeling loadPower sourceConnects the reactor One-cycle ControlJunction point electric current cocurrent side voltage signal
Fig. 1 Configuration of STATCOM based on one-cycle control
Fig. 2 Principle scheme of one-cycle control
Fig. 3 Schematic of Inverter Bridge
2 dead area effects compensate
Because in the invertors main circuit's power on-off element is not the perfect switch, to prevent the invertors high and low bridge arm to occur goes nonstop to the short trouble, must establish a section of dead time in its driving
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signal, guaranteed after the identical bridge arm high and low two power tubes can shut off first, clears. Considers the single-phase circuit, supposes the control signal the dead time is td, the invertors output inductance electric current
iLinflow invertors direction for positive, The contra variant bridge schematic drawing see Figure 3. In the chart, M1?M4 is IGBT; VD1?VD4 for quick recovery after flow second-level tube. In td, the invertors output voltage size and
iL direction concern. When iL is positive, iL through VD1 and VD4 after flow, the invertors output voltage is ?UDC; When iL for negative, iLthrough
VD2 and VD3 after flow, the invertors output voltage is ?UDC. The dead area effect profile schematic drawing see Figure 4, on the output inductance L actual voltage waveform, the ideal voltage waveform as well as both the difference, like in Figure 4 (a), (b), (c) shows. Supposes k?td/T, when iLis positive, the
M1, M4 time delay break over to the electric circuit does not have the influence, but the M2, M3time delay break over, this time the duty factor becomes (D?k). Consideration type (2) may know, the duty factor change, the serious influence single week control control precision, namely because of the dead area existence, will cause the idle current which the invertors will output to contain the massive overtones, thus has affected the STATCOM work effect, for this reason, this article proposed one kind will improve the single week control policy.
（a）On L actual voltage waveform
（b）On L ideal voltage waveform