CN101944747A - Low-voltage failure crossing method of brushless cascading double-fed wind power generator set - Google Patents

Abstract

The invention provides a low-voltage failure crossing method of a brushless cascading double-fed wind power generator set, comprising a crowbar circuit (controlling a winding from short-circuit to protect the circuit) controlling a winding AC side and a charge leakage circuit which is back to back of a DC side of a current transformer; the crowbar circuit ensures to release the residual energy incapable of being input into an electricity grid when the electricity grid has a low-voltage failure, and can control a winding end to limit the voltage and the current; the charge leakage circuit ensures the voltage of the DC side to be stable under any condition, and also ensures to release the residual active power at the DC end, thereby protecting the hardware. In a low-voltage failure, the current transformer of the electricity grid end simultaneously inputs reactive power to the electricity grid, thereby satisfying the low-voltage crossing standard and providing assistance for recovering the electricity grid to be normal.

Description

The low voltage failure traversing method of brushless cascade double-fed wind power generator group

Technical field:

The present invention relates to a kind of special machines and be applied in the method that the low voltage failure in the wind generator system passes through, can realize that brushless cascade double-fed wind power generator continues maintenance work when low-voltage, unnecessary active power release is made it not flow into electrical network, the voltage and current of restriction control winding terminal, keep the stable of current transformer dc terminal, and send the standard that reactive power fault when satisfying low-voltage is passed through to electrical network.

Background technology:

Double feedback electric engine is widely used in wind power generation field, and once because the advantage on cost and the volume has occupied the market share above 50%, yet in recent years because of the inferior position that it is safeguarded and low-voltage is passed through, the market share decreases.

Brushless cascade double feedback electric engine is as an improvement version of double feedback electric engine, and it has kept all advantages of double feedback electric engine, and has removed the very high brush of maintenance requirement, greatly reduces maintenance cost, has strengthened the reliability of system.

The principle of brushless cascade double feedback electric engine just was suggested in 20 beginnings of the century, adopted the method for two induction machine cascades to realize low-speed running.At the beginning of the nineties, the design of modernized brushless cascade double feedback electric engine finalizes the design almost.This motor adopts two groups of independently stator winding, uses different level logarithms to prevent each other coupling.Rotor adopts special similar squirrel-cage design, and two stator winding simultaneously can be coupled.The speed of motor is determined jointly by the driving frequency of two stator winding.

Generally speaking, one group of stator winding is connected and fixed the electrical network of frequency and voltage, is called the power winding; Another group stator winding connects the current transformer of variable-frequency variable-voltage, is called the control winding; In other words, consider that the power winding is a fixed frequency, spinner velocity is finally determined by the frequency of control winding.

If brushless cascade double feedback electric engine is applied in the wind generator system, the fault in the time of must considering low-voltage is passed through.The existing fault crossing technology mainly is to consider traditional motor topology, but never occurs at the scheme that the low voltage failure of brushless cascade double-fed wind-force electrical machinery passes through, and has therefore limited the application of brushless cascade double feedback electric engine in the wind power generation of reality.This patent has been described the brand-new low voltage failure based on brushless dual-feedback wind power generator of a cover and has been passed through control system; this control system has adopted crowbar circuit (protection of control short circuit in winding) and drain charge circuit; the release of the active power that the brushless double feed induction generator produces when having solved low-voltage and the safety operation of current transformer, brushless cascade double-fed wind power generator group still keeps operation when having guaranteed the generation low voltage failure.In system's operation, inject reactive power to satisfy the requirement that low voltage failure passes through to electrical network.

Summary of the invention:

The objective of the invention is: a kind of low voltage failure ride through system at brushless cascade double-fed wind power generator group is provided, promptly when line voltage reduces, guarantees that still generator normally moves.

Design of the present invention is: the unnecessary active power that generator produces is released on the drain charge resistance of interchange and direct current, guarantees the safety operation of current transformer and motor.Electrical network end current transformer adopts the vector control algorithm based on the line voltage synchronous coordinate system, carries reactive power to electrical network, and the system of assurance satisfies the technical indicator that low voltage failure passes through.

According to the foregoing invention design, technical scheme of the present invention is made up of following link:

First link is: the present invention adopts a crowbar circuit at the control winding terminal of brushless cascade double-fed generator, limits the voltage and current of control winding when low voltage failure takes place simultaneously.The crowbar circuit adopts the control mode of hysteresis.

Second link is: the present invention adopts a drain charge circuit in the DC side of current transformer, when operate as normal and low voltage failure keep the stable of dc voltage when taking place, realize the trouble free service of current transformer.The drain charge circuit adopts the control mode of hysteresis or PWM.

The 3rd link is: the present invention injects reactive power to electrical network in the vector control algorithm of electrical network end current transformer employing based on the line voltage synchronous coordinate system when low voltage failure takes place, satisfy the standard that low-voltage is passed through.

The present invention has following conspicuous outstanding substantive distinguishing features and remarkable advantage compared with the prior art:

1. the method for passing through based on the low-voltage of brushless cascade double feedback electric engine does not at present exist, and can not be simply the low-voltage traversing method of traditional double feedback electric engine be directly used on the brushless cascade double-fed wind power generator.The present invention has made variation on hardware connection, computed in software and parameter are selected on the basis based on the low-voltage traversing method of feed machine, proposed a low-voltage traversing method that is suitable for brushless cascade double feedback electric engine.

2. crowbar circuit of the present invention determines whether conducting crowbar circuit according to the electric current of the control winding that measures, therefore when low voltage failure of electric network takes place, the crowbar circuit is in the alternation switch state, has improved the controllability and the dynamic property of whole system when fault takes place.The crowbar circuit need not connect by brush on hardware connects simultaneously, has improved the reliability of system greatly.

Description of drawings

Fig. 1 is the BDFM schematic diagram.

Fig. 2 is the current transformer allocation plan that brushless cascade double feedback electric engine comprises the voltage failure traversing method.

Fig. 3 is crowbar circuit control principle figure.

Fig. 4 is that DC side drain charge circuit adopts hysteresis control mode schematic diagram.

Fig. 5 is that DC side drain charge circuit adopts PWM control mode schematic diagram.

Fig. 6 is the motor side converter structure.

Embodiment

The vector control method and the principle of this brushless cascade double feedback electric engine are summarized as follows:

Fig. 1 is the schematic diagram of brushless cascade double feedback electric engine.Brushless cascade double feedback electric engine has two groups of stator winding, is respectively power winding and control winding.The power winding directly connects the electrical network of 50Hz fixed frequency, and the control winding connects electrical network by two way convertor.Can control rotating speed of motor by the frequency of regulating the control winding.If can limit the working range of motor, most energy flows into or outflow motor by the power winding, and the energy of fraction flows into or outflow motor by current transformer, therefore can reduce the capacity of current transformer, be generally about 1/3 of capacity motor, can reduce the loss of current transformer simultaneously greatly.Traditional double feedback electric engine has only one group of stator winding directly to connect the electrical network of 50Hz, and the rotor winding crosses carbon brush and current transformer is electrically connected.With respect to traditional double feedback electric engine, brushless cascade double feedback electric engine does not need to adopt perishable carbon brush structure, has therefore improved the reliability of system.

Fig. 2 comprises the current transformer allocation plan of voltage failure traversing method for brushless cascade double feedback electric engine.Brushless cascade double feedback electric engine 1 carries out mechanical connection by gearbox 2 and wind slurry 3, and stator winding is divided into power winding 4 and control winding 5, connects electrical network 6 and motor side current transformer 7 respectively.Current transformer is divided into electrical network end current transformer 8 and motor side current transformer 7.Electrical network end current transformer 8 is connected with electrical network 6 by reactor 9, and the software arrangements base is active power and the reactive power that the vector control algorithm control of line voltage synchronous coordinate system flows into electrical network.Motor side current transformer 7 is connected with control winding 5, and software arrangements is the vector control algorithm based on power winding stator magnetic linkage synchronous coordinate system, controls the speed of brushless cascade double feedback electric engine and the reactive power of power winding.Electrical network end current transformer 8 is connected by a DC side with motor side current transformer 7.

DC side comprises dc capacitor 10 and drain charge circuit 11.Drain charge circuit 11 is made up of 12, one full control electronic switches 13 of a drain charge resistance and a fly-wheel diode 14.Switch 13 can be any type of electronic switch, adopts IGBT (insulation gate pole bipolar transistor) usually.When switch 13 turn-offed, drain charge circuit 11 was closed, and system works is in normal condition, and all energy flow into electrical network end current transformer 8 and flow into electrical network 6 from motor side current transformer 7.When switch 13 conductings, the drain charge circuit working, some or all energy consumptions are on drain charge resistance 12.Switch 13 concrete switching algorithms can adopt hysteresis control and two kinds of methods of PWM control, see Fig. 3 and Fig. 4 respectively.In the moment that switch 13 turn-offs, the immediate current of drain charge resistance 12 is realized the loop by fly-wheel diode 14.

Between the control winding 5 of brushless cascade double feedback electric engine 1 and motor side current transformer 7, connected a crowbar circuit 15, guaranteed when low voltage failure of electric network, to control winding 5 current limlitings and to 7 pressure limitings of motor side current transformer.Crowbar circuit 15 is made up of bidirectional thyristor 16 and drain charge resistance 17.When electrical network generation low voltage failure, all IGBT of motor side current transformer 7 turn-off, bidirectional thyristor 16 conductings simultaneously, and all energy that the control winding produces are released in above the drain charge resistance 17.The selection of drain charge resistance 17 is very important, must guarantee that the voltage of control winding 5 is lower than dc voltage, thereby stop the fly-wheel diode quick charge of dc bus capacitor 10 by motor side current transformer 7, safeguards the stable of dc voltage.Drain charge resistance 17 must guarantee that simultaneously the electric current of control winding 5 is enough little, the intensification of restriction control winding 5.General drain charge resistance value is chosen as 2 to 5 times of whole leakage reactance of brushless cascade double feedback electric engine 1.

Fig. 3 is the control principle figure of crowbar circuit 15, adopts hysteresis control 18, detects the current i of control winding 5 ₂As input, if current i ₂Greater than the upper safety limit current i _H, illustrate that then electric current is excessive, need the thyristor 16 of conducting crowbar circuit 15, this moment, brushless cascade double feedback electric engine 1 was operated in uncontrollable cascade state; If current i ₂Less than the lower safety limit current i _L, then illustrative system is operated in safe condition, can turn-off the thyristor 16 of crowbar circuit 15, and this moment, brushless cascade double feedback electric engine was operated in controlled synchronous regime; If current i ₂Be in the upper safety limit current i _HWith the lower safety limit current i _LBetween the time, on off state is constant.

Fig. 4 is the fundamental diagram that dc terminal drain charge circuit 11 adopts hysteresis controller 19.As dc voltage v _DCSurpassed upper safety limit voltage v _HThe time, switch 13 complete conductings, the drain charge circuit is in running order; As dc voltage v _DCBe lower than lower safety limit voltage v _LThe time, switch 13 turn-offs, and the drain charge circuit is in closed condition; If dc voltage v _DCBe in upper safety limit voltage v _HWith lower safety limit voltage v _LBetween the time, on off state is constant.

Fig. 5 is the fundamental diagram that dc terminal drain charge circuit 11 adopts PWM controller 20.As dc voltage v _DCLower safety limit voltage v _LWith upper safety limit voltage v _HBetween the time, one of PWM controller 20 output and dc voltage voltage v _DCThe output variable 21 (scope from 0 to 1) that linear relationship is arranged, the sawtooth waveforms 23 (scope from 0 to 1) of a fixed frequency of saw-toothed wave generator 22 outputs simultaneously.PWM output 21 and sawtooth waveforms output 23 is the positive-negative input end of input comparator 24 respectively, and 25 pairs of switches 13 of the output of comparator 24 are controlled.As dc voltage v _DCBe in or be lower than lower bound operating voltage v _LThe time, switch 13 disconnects, and the drain charge circuit is not worked; As dc voltage v _DCSurpassed high limit operating voltage v _HThe time, switch 13 complete conductings, the drain charge circuit is in maximum drain charge capability state.

Fig. 6 is the principle of vector control figure based on line voltage synchronous coordinate axle of electrical network end current transformer 8.The main task of electrical network end current transformer 8 is that the assurance system continues the meritorious and reactive power of output to electrical network 6.

At first need to gather three-phase voltage v from electrical network 6 _Lu, v _LvAnd v _LwWith three-phase current i _Lu, i _LvAnd i _Lw, and, three-phase voltage and electric current are transformed to the two phase voltage v that are in rest frame respectively by carrying out 3 → 2 ' transformation matrixs 26 respectively _{L α}And v _{L β}With biphase current i _{L α}And i _{L β}The expression formula of transformation matrix 26 is:

$\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& -\frac{\sqrt{3}}{2}& \frac{\sqrt{3}}{2}\end{array}\right]$

Known two phase voltage v _{L α}And v _{L β}With biphase current i _{L α}And i _{L β}, active power P _lAnd reactive power Q _lCan obtain by power calculator 27.Being expressed as of power calculator 27:

$P_l=\frac{3}{2}(v_{\mathrm{l\α}}{i}_{\mathrm{l\α}}+v_{\mathrm{l\β}}{i}_{\mathrm{l\β}})$

$Q_l=\frac{3}{2}(v_{\mathrm{l\β}}{i}_{\mathrm{l\α}}-v_{\mathrm{l\α}}{i}_{\mathrm{l\β}})$

Simultaneously, based on the synchronous coordinate angle θ of voltage vector _lCan pass through v _{L α}And v _{L β}Carry out pole marks coordinate transform (i.e. 2 → θ conversion) 28 and obtain, expression formula is:

${\mathrm{\θ}}_l=\arctan \frac{v_{\mathrm{l\β}}}{v_{\mathrm{l\α}}}$

Before address, to be assurance systems continue the meritorious and reactive power of output to electrical network 6 to the main task of electrical network end current transformer 8.The purpose of active power control is to keep stable dc voltage v _DC, so the reference signal P of active power _l ^*Given by a PI (ratio/integration) controller 29.Being input as of PI controller 29 with reference to dc voltage v _DC ^*And measurement dc voltage v _DCThe control of reactive power is divided into the control of normal condition control and malfunction.When normal condition, with reference to reactive power Q _L0 ^*Setting must consider the reactive power Q of power winding terminal ₁Make the power factor of whole generating system satisfy the electrical network standard.When nonserviceabling, for the system that makes continues operation, with reference to reactive power Q _L1 ^*Setting must satisfy the electrical network standard to electrical network 6 input reactive powers, to strengthen the stability of network system.Selector switch 30 according to fault-signal from Q _L1 ^*And Q _L0 ^*Between select, determine final reference reactive power Q _l ^*

Consider at line voltage phasor coordinate system, the active power P of electrical network end current transformer _lAnd reactive power Q _lBe expressed as:

$P_l=\frac{3}{2}{v}_{\mathrm{ld}}{i}_{\mathrm{ld}}$

$Q_l=-\frac{3}{2}{v}_{\mathrm{ld}}{i}_{\mathrm{lq}}$

Therefore can be by control electrical network end current transformer output current i _LdAnd i _LqTo active power P _lAnd reactive power Q _lControl respectively.Control system adopts two PI controllers 31 and 32, and input is respectively with reference to active power P _l ^*With measurement active power P _l, and with reference to reactive power Q _l ^*With the measurement reactive power Q _l, be output as reference current i _Ld ^*And i _Lq ^*By one 2 → 3 conversion 33, with synchronous dq axle reference current i _Ld ^*And i _Lq ^*Be converted to three-phase reference current i _Lu ^*, i _LvAnd i _Lw ^*The formula of 2 → 3 conversion 33 is:

$\left[\begin{array}{cc}\cos \mathrm{\θ}& -\sin \mathrm{\θ}\\ \cos (\mathrm{\θ}-2\mathrm{\π}/3)& -\sin (\mathrm{\θ}-2\mathrm{\π}/3)\\ \cos (\mathrm{\θ}-4\mathrm{\π}/3)& -\sin (\mathrm{\θ}-4\mathrm{\π}/3)\end{array}\right]$

Wherein θ adopts the line voltage vector angle θ that obtains by polar coordinates conversion 28 _lFinal three-phase reference signal i _Lu ^*, i _LvAnd i _Lw ^*The input current transformer is to determine the final working point of current transformer.

Fig. 7 is the schematic diagram of motor side current transformer 7.Because electrical network end current transformer 8 has identical structure, therefore whole converter structure is called back to back structure.Here be the example explanation with motor side current transformer 7.Motor side current transformer 7 is made up of 6 switch I GBT 34 and 6 fly-wheel diodes 35.The frequency of three-phase output is by the frequency decision of the pwm control signal 36 of IGBT 34, and amplitude is by the duty ratio decision of pwm control signal 36.

Claims (4)

1. the low-voltage at brushless cascade double feedback electric engine is passed through protective circuit, in order to satisfy the system requirements that low voltage failure passes through.This protective circuit comprises:

Crowbar circuit at the control winding terminal of brushless cascade double feedback electric engine (control short circuit in winding protective circuit) is in order to shunting active power, the safety of protection motor side current transformer and motor itself;

The drain charge circuit of a current transformer dc terminal is in order to protection dc terminal electric capacity and shunting active power;

Employing is based on the electrical network end current transformer of the vector control algorithm of line voltage synchronous coordinate system, to provide reactive power to electrical network when the low voltage failure, satisfies the standard that low voltage failure passes through.

2. described according to claim 1, the crowbar circuit of current transformer is made up of three-phase bidirectional thyristor and three-phase protective resistance.As input, if the control winding current is lower than the lower safety limit electric current, then close by the drain charge circuit with the control winding current of brushless cascade double feedback electric engine for the controller of crowbar circuit; If the control winding current is higher than or equals upper safety limit electric current, then drain charge circuit turn-on.The mode of the logical employing of controller hysteresis determines the conducting or the shutoff of bidirectional thyristor in the crowbar circuit.

3. described according to claim 1, the dc terminal drain charge circuit of current transformer is made up of an IGBT (insulation gate pole bipolar transistor), a drain charge resistance and a fly-wheel diode.The drain charge circuit be control input with the dc voltage.If direct voltage is lower than lower safety limit voltage, then the drain charge circuit is closed; If tributary voltage is higher than or equals upper safety limit voltage, then drain charge circuit turn-on.Controller adopts the mode of hysteresis or PWM (pulse width modulation).

4. described according to claim 1, electrical network end current transformer electrical network just often to electrical network provide or absorbing reactive power to guarantee the requirement of power grid quality, when electrical network generation low voltage failure, provide reactive power to satisfy the standard that low voltage failure passes through to electrical network.

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