CN102182630B - Method for braking in series for frequency-conversion speed-regulating wind power generation water pumping system - Google Patents

Abstract

The invention relates to a method for braking in series for a frequency-conversion speed-regulating wind power generation water pumping system. A braking unit which is composed of a braking resistor and an electronic switch in parallel is connected to the positive electrode of a direct current bus in a frequency-conversion controller, and is connected with the flat wave capacitor of the direct current bus in series; a control unit in the frequency-conversion controller detects the voltage Udc1 of the input end of the direct current bus, the voltage Udc2 of the output end of the direct current bus and the operation state of a water pump; when the water pump operates at a full speed, and the voltage Udc1 of the input end is greater than a limited value ULtd, the control unit regulates the on-state duty ratio Don of the electronic switch so as to further regulate the power ad pressure drop of the braking unit, thus the voltage Udc2 of the output end is stable at the limited value ULtd; and at the same braking capacity, the wind power generation water pumping system adopting the serial braking method provided by the invention has greater safe operation region, and the water pumping system can keep normal operation at a greater wind speed.

Description

Frequency control of motor speed type wind-power electricity generation water pumping system tandem brake method

Technical field

The present invention relates to frequency control of motor speed type wind-power electricity generation water pumping system, especially a kind of braking method that is applied in high wind speed condition down coversion regulable speed type wind-power electricity generation water pumping system belongs to technical field of wind power generation.

Background technique

Water pumping of the wind-force is widely used in human livestock drinking water, agricultural and pasture irrigation, preparing salt by working up seawater and breed, desert treatment etc., is one of Wind Power Utilization several kinds of forms the earliest, has a long history.The construction and development of the outlying areas without electricity of China, the control of large stretch of desert and improvement press for the solution problem of water consumption.With set up electrical network or adopt photovoltaic water-raising system to compare, the construction of water pumping of the wind-force system easily, take up an area of less, cost is low, can produce good economic and social benefit.

The tradition water pumping of the wind-force is main with Purely mechanical, and the mechanism of special-purpose wind energy conversion system, transmission and water pump is complicated, and rate of fault is higher, and water lift efficient is low.

The wind power generation water pumping system has increased one-level electric energy conversion links; The structure and the electric energy conversion links of wherein frequency control of motor speed type wind-power electricity generation water pumping system are as shown in Figure 1; By streamlined fixed pitch blade wind energy conversion system 1, magneto alternator (permanent-magnet synchronous generator; PMSG) 2, frequency-variable controller 3 and universal electric centrifugal pump 4 constitute, energy conversion efficiency obviously improves, system layout is flexibility more.Comprise rectifying unit 31, boosting unit 33, brake unit 32 and 34 4 controlling units of inversion unit in the frequency-variable controller 3.The AC rectification that it sends magneto alternator 2 earlier becomes direct current, and (maximum power point tracking, MPPT) algorithm is electric with the frequency-changing AC that dc inverter becomes to optimize again, control of pump 4 rotating speeds according to MPPT maximum power point tracking then.Because under different wind speed, the output voltage of magneto alternator 2 significantly changes with rotating speed, is complementary and keeps relative stability in order to guarantee DC bus-bar voltage and water pump 4 operating voltages, introduces boosting unit 33 and brake unit 32 at DC side.

During normal wind speed, the control of wind-driven generator according to the power coefficient of wind energy conversion system capturing wind energy to greatest extent, is converted into electric energy usually.But; Because system often is in the high wind environment above rated wind speed in the practical application; So must implement electric braking control accurately; To guarantee that rotating speed and output power are stable, the wind energy conversion system rotating speed is too fast, generator output voltage is too high otherwise possibly cause, and causes frequency-variable controller and load equipment to damage.

According to aerodynamics, fixed pitch wind turbine output mechanical power P _mFor:

$P_m=\frac{1}{2}{C}_P\left(\mathrm{\λ}\right)\mathrm{\ρ\π}{r}^2{v}^3---\left(1\right)$

$\mathrm{\λ}=\frac{\mathrm{\πr}}{30v}n---\left(2\right)$

In the formula, ρ: air density (kg/m ³); V: wind speed (m/s); R: pneumatic equipment blades made radius (m);

C _p(λ): power coefficient; λ: tip speed ratio; N: wind energy conversion system rotating speed (rpm)

The typical C of fixed pitch wind turbine _P-λ characteristic curve is as shown in Figure 2.The wind energy conversion system of variable-speed operation is kept and is obtained maximal wind-energy utilization factor C _PmaxBest tip speed ratio λ _OptBe constant, just irrelevant with wind speed.Therefore, under optimal operational condition, the rotating speed of wind energy conversion system is directly proportional with wind speed, and output power is directly proportional with the cube of wind speed.If ignore the power loss of generator, then the output power of generator equates with the output power of wind energy conversion system.By C _p-λ characteristic curve can obtain the relation curve of wind-driven generator output power and rotating speed under the different wind speed, and is as shown in Figure 3.

Do not have electricity storage unit in the wind-power electricity generation water pumping system among the present invention, the electromotive power output of wind-driven generator and the input electric power of water pump keep balance.Definition rated wind speed v _NThe maximum output of wind-driven generator is rated power P under the condition _GN, corresponding rotating speed is rated speed n _N, output voltage is voltage rating U _N, and the rated power P of water pump _PNInput electric power during for the water pump full speed running, P usually _PN＜P _GN

During normal wind speed, the rotating speed through regulating water pump remains on the running state of system on the maximum power point, and output voltage is lower than U _NWhen wind speed is high, the maximum output power P of wind-driven generator _MaxGreater than P _PNThe time, the water pump full speed running, the real output of generator is restricted to P _PN, system mode will depart from maximum power point, and output voltage then increases with rotating speed.Keeping the condition of system stable operation is the characteristics of output power curve P of wind-driven generator _GMust with load characteristic curve P _LIntersect, and meet the following conditions at the intersection point place:

dP _L/dn＞dP _G/dn (3)

As shown in Figure 3, wind speed is v ₂The time, on the corresponding characteristics of output power curve two points and P are arranged _PNEquate, but the B point does not satisfy the condition of formula (3), so system will stably operate in the A point, rotating speed and output voltage are far longer than n _NAnd U _NGenerally speaking, high rotating speed is also little to the mechanical structure influence of small wind turbine, and HV then possibly constitute a serious threat to the frequency-variable controller of electrification electronic device.

In order to make system in the high wind environment, can continue operation, improve the utilization ratio of system, guarantee the safety of inverter circuit simultaneously, need take suitable brake measure, wind energy conversion system rotating speed and DC bus-bar voltage are controlled in the reasonable range.As the electric braking control of miniature wind power generation system, adopt parallelly connected braking circuit as shown in Figure 4 usually, with reference to Fig. 4, by braking resistor R _BAnd the braking circuit that switching device S is composed in series is connected between the both positive and negative polarity of dc bus, becomes the parallel connection relation with the flat wave capacitor of dc bus, and inductance L and diode D are the devices shared with boosting unit 33 among Fig. 4, through the conducting dutycycle D of by-pass cock device S _On, control brake power changes the system load characteristic curve.

What withstand voltage level was minimum in the system is the switching device in the frequency-variable controller, must implement control, makes the output end voltage U of dc bus _Dc2Be no more than limit value U _LtdWhen adopting parallelly connected brake control method, because the input terminal voltage U of dc bus _Dc1The output end voltage U of ≈ dc bus _Dc2, in order to suppress U effectively _Dc2, must make the stabilized (steady-state) speed of wind-driven generator be lower than corresponding speed limit n _Ltd, the desirable operating point track of system is like 0BB ' B among Fig. 5 " shown in.Among Fig. 5, system's realization maximum wind power was caught when curve 0B represented to hang down wind speed, and output power is directly proportional with the cube of rotating speed; Horizontal linear BB ' expression is along with wind speed increases, wind-driven generator receive water pump rated power restriction and can not Maximum Power Output, rotating speed and output voltage all raise, but are lower than speed limit n _LtdVertical line B ' B " the expression wind speed further raises, braking circuit action, with the wind-driven generator stabilization of speed at n _LtdThe stalling current waveform is discontinuous width-modulation pulse, braking force P _BPWith load total output P _LPBe respectively

$P_{\mathrm{BP}}={\mathrm{<figure-callout\; id="1"\; label="U\; dc"\; filenames="HDA0000052857830000021.png"\; state="\{\{state\}\}">U</figure-callout>}}_{\mathrm{dc}}^1{D}_{\mathrm{on}}/R_B---\left(4\right)$

P _LP＝P _PN+P _BP (5)

Parallel connection braking force P _BPBy DC bus-bar voltage, braking resistor R _BAnd conducting dutycycle D _OnDecision does not have direct relation with the operate power of water pump.Can know by formula (4) and formula (5), work as D _OnRemain unchanged, the load characteristic curve P in parallelly connected braking circuit when work _LPBe a quadratic curve that raises up with rotating speed, reduce R _BOr increase D _On, can both accelerate the speed that raises up of load characteristic curve, the stable operating point that makes system is moved to the left along the output power curve of wind-driven generator, and rotating speed and output voltage descend thereupon, thereby guarantee the safety of system.Work as D _On=1 o'clock, parallelly connected braking circuit provided maximum brake power, corresponding load power curve P _LPmaxWith straight line B ' B " intersection point be A ', braking force does

$P_{\mathrm{BP}\max }=U_{\mathrm{Ltd}}^2/R_B---\left(6\right)$

System's control must guarantee that the stationary value of DC bus-bar voltage is no more than U _Ltd, and the required braking force of system is less than the maximum brake power P of parallelly connected braking circuit _BPmaxTherefore, in case confirm rational P according to the designing requirement of system _BPmax, just there is a safe operation zone in system, shown in the dash area among Fig. 5.Suppose that wind speed is by v ₁Rise to v ₂, control system will increase D gradually _On, adjustment bearing power curve finally makes system stability in A ' point; If wind speed continues to increase to v ₃The time, the required braking force of system exceeds the maximum capacity of parallelly connected braking circuit, and system will operate in A, and " point has run off the safe operation zone, and frequency-variable controller faces the danger of overload, overvoltage.

The parallel connection braking method is control brake power effectively; Realize the slow-speed of revolution operation of wind-driven generator under the high wind speed through the rotating speed that suppresses wind-driven generator; Prevent to produce overvoltage; But because the maximum output of wind-driven generator is directly proportional with the cube of wind speed, wind speed slightly increase the rapid increase that will cause output power, so require braking circuit must have enough big capacity.On the other hand, the constant and output power of the rotating speed of magneto alternator increases, and mean that the output current equal proportion increases, and overcurrent very easily causes the permanent demagnetization of permanent magnet in the generator.

Summary of the invention

The purpose of this invention is to provide a kind of frequency control of motor speed type wind-power electricity generation water pumping system tandem brake method, use this braking method, under identical braking capacity, water pumping system can keep normal operation under bigger wind speed; And can effectively reduce the probability of the permanent demagnetization of permanent magnet in the magneto alternator.

Frequency control of motor speed type wind-power electricity generation water pumping system tandem brake method of the present invention is following:

To be connected by the brake unit that braking resistor and electronic switch compose in parallel on the positive pole of dc bus in the frequency-variable controller, with the flat wave capacitor formation series relationship of dc bus;

Control unit in the frequency-variable controller detects the input terminal voltage U of said dc bus _Dc1With output end voltage U _Dc2, and the running state of water pump, as water pump full speed running and said input terminal voltage U _Dc1Greater than limit value U _LtdThe time, control unit is regulated the conducting dutycycle D of said electronic switch _On, and then the power and the pressure drop of adjusting brake unit, make said output end voltage U _Dc2Be stable at limit value U _Ltd

Said control unit is preferably according to said output end voltage U _Dc2With said limit value U _LtdDeviation, employing ratio, integral control mode are regulated conducting dutycycle D _On

Said input terminal voltage U _Dc1High more, control unit makes conducting dutycycle D _OnMore little.

The warp experiment when wind speed is 10m/s, is adopted the parallel connection braking, and braking force reaches 0.99KW, and dynamo current is up to 3.87A, and the braking force of employing tandem brake has only 0.25W, and dynamo current has only 1.45A; When wind speed is 14m/s, adopt the parallel connection braking, braking force reaches 3.19KW; Dynamo current is up to 7.40A, and brake unit and generator seriously transship, and adopts the braking force of tandem brake to have only 0.70W; Dynamo current has only 1.35A, and system still moves normally.It is thus clear that, compare with adopting the parallel connection braking, under identical braking capacity, adopt the wind-power electricity generation water pumping system safe operation zone of tandem brake method of the present invention bigger, water pumping system can keep normal operation under bigger wind speed; And because dynamo current is very little, permanent magnet can permanently not demagnetize in the magneto alternator.

Description of drawings

Fig. 1 is the theory diagram of frequency control of motor speed type wind-power electricity generation water pumping system.

Fig. 2 is the typical C of fixed pitch wind turbine _P-λ characteristic curve.

Fig. 3 is the relation curve of wind-driven generator output power and rotating speed under the different wind speed.

The circuit diagram that Fig. 4 brakes for the parallel connection that existing frequency control of motor speed type wind-power electricity generation water pumping system is adopted.

The relation curve of wind-driven generator output power and rotating speed when Fig. 5 brakes for adopting parallel connection.

Fig. 6 is the circuit diagram of tandem brake of the present invention unit.

The relation curve of wind-driven generator output power and rotating speed when Fig. 7 is the employing tandem brake.

Fig. 8 is the theory diagram of the used frequency control of motor speed type wind-power electricity generation water pumping system of experiment.

Fig. 9 is the control flow chart of tandem brake in the experiment.

Figure 10-13 is for adopting the experimental result of tandem brake, is respectively the curve that the output power of curve, generator and water pump that curve, dc bus input terminal voltage and output end voltage that the frequency-variable controller output frequency changes with wind speed change with wind speed changes with wind speed, the curve that braking force changes with wind speed.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is further specified.

The present invention improves the brake unit of Fig. 1 and existing frequency control of motor speed type wind-power electricity generation water pumping system shown in Figure 4, has proposed the tandem brake method.With reference to Fig. 6, brake unit of the present invention is by braking resistor R _BS composes in parallel with electronic switch, is connected on the positive pole of dc bus, becomes series relationship with the flat wave capacitor of dc bus, has braking and dividing potential drop double action concurrently, and inductance L and diode D are the devices shared with booster circuit among the figure.The preferred IGBT of electronic switch S.

With reference to Fig. 1 and Fig. 6 the employing tandem brake is described below, the DC bus-bar voltage constant voltage control under high wind speed:

The input terminal voltage U of, dc bus low when wind speed _Dc1≤limit value U _LtdThe time, electronic switch S keeps on state, and the wind-power electricity generation water pumping system is with the MPPT mode operation; And when wind speed is high, U _Dc1＞U _LtdThe time; Water pump 4 full speed runnings under the prerequisite of guaranteeing machinery and electrical safety, allow wind-driven generator 2 speed-raising operations; The withstand voltage level that only needs corresponding raising generator 2 and rectifying unit 21; Electronic switch S carries out PWM, regulates the power and the pressure drop of brake unit, makes the output end voltage U of dc bus _Dc2=U _Ltd, the safety of assurance inversion unit 34.

During brake unit work, under the filter action of inductance L, the dc bus output current is smoother, and mean value does

I _dc2＝P _PN/U _dc2 (7)

The pressure drop and the power of braking circuit are respectively

U _dc1-U _dc2＝(1-D _on)R _BP _PN/U _dc2 (8)

$P_{\mathrm{BS}}=(1-D_{\mathrm{on}})R_B{P}_{\mathrm{PN}}^2/U_{\mathrm{dc}2}^2---\left(9\right)$

This shows the tandem brake power P during system stable operation _BSDirectly receive water pump rated power P _PNThe influence of size reduces D _OnOr increase R _B, can both make the tandem brake power P _BSIncrease.Load total output P _LSBe water pump rated power P _PNWith the tandem brake power P _BSSum is derived and can be got with formula (9) by formula (8)

P _LS＝P _PNU _dc1/U _dc2 (10)

The elongation line that the desirable running state track of system is like 0BB ' B among Fig. 7 " shown in, wherein 0BB ' part is identical with Fig. 5, and oblique line B ' B " is through the P-n coordinate origin.Can know by formula (8), for making U _Dc2=U _Ltd, D _OnShould be along with U _Dc1Increase and linearity reduces,

D _on＝1-(U _dc1-U _Ltd)U _Ltd/P _PNR _B (11)

Suppose that wind speed is by v ₁Rise to v ₂, wind-driven generator quickens, U _Dc1With U _Dc2All increase, so control system reduces D gradually _On, adjustment bearing power curve finally makes system stability in A ' point.

Work as D _On=0 o'clock, the tandem brake circuit provided maximum brake power P _BSmax, with this foundation as the braking circuit design.Can find out, in the tandem brake, the braking capacity of brake unit and braking resistor R _BResistance be directly proportional.

$P_{\mathrm{BS}\max }=R_B{P}_{\mathrm{PN}}^2/U_{\mathrm{Ltd}}^2---\left(12\right)$

Comparison diagram 5 can know that with Fig. 7 system's operating point is in the right side of output power curve peak point during tandem brake, and corresponding power coefficient is low, and generated output power is little, and required braking force is also little.Therefore, if two kinds of braking circuits have identical braking capacity in design, then adopting the system safety operation zone of tandem brake method big, is v at wind speed ₃The time still can safe operation.

Experiment:

The formation of experiment system for use in carrying is as shown in Figure 8; In order to improve conventional efficient; And the repeatability of assurance experimental condition; Wind energy conversion system is replaced by the simulation unit, with the characteristic curve driving wind-force simulated machine of wind-force analog controller according to wind energy conversion system under the different wind friction velocities, and then drags magneto alternator.In conjunction with the specification of experimental prototype, the selected equipment parameter is as shown in table 1.

Table 1 emulation and experimental system parameter

Fig. 9 is for the braking control flow chart, as water pump full speed running and U _Dc1＞U _LtdThe time, braking circuit is started working, according to U _Dc2With U _LtdDeviation, employing ratio, integral control mode are regulated D _On, make U _Dc2Be stable at U _LtdMore specifically, as water pump full speed running and said input terminal voltage U _Dc1Greater than limit value U _LtdThe time, control unit passes through formula

D _on＝1-(K _P+K _I/s)(U _dc2-U _Ltd)

Regulate conducting dutycycle D _On, K wherein _PBe scaling factor, K _IBe integral coefficient, s is differential calculation.

At first, utilize Matlab ^TM/ Simulink platform has carried out simulation calculation; For the fully effect of check braking circuit, the setting of maximum brake power is higher, is about 2.2kW; Corresponding parallelly connected braking resistor and tandem brake resistance are respectively 50 Ω and 500 Ω, and the limit value of DC bus-bar voltage is made as U _Ltd=330V.Table 2 is three kinds of simulation results under the wind speed.

When wind speed was 7m/s, the output power of wind-driven generator was near the rated power of water pump, and DC bus-bar voltage is in normal range (NR), and braking circuit is not worked, and system is with the MPPT mode operation.

When wind speed rose to 10m/s, the maximum output of wind-driven generator had surpassed the rated power of water pump, the water pump full speed running.The system of brakeless circuit not only DC bus-bar voltage is too high, and the loss of inverter circuit and pump motor obviously increases.When adopting the parallel connection braking, can control the wind-driven generator rotating speed effectively, make DC bus-bar voltage remain on U _LtdNear, but braking force is near 1kW.When adopting tandem brake, though the wind-driven generator rotating speed is high, U _Dc2Remain on U _LtdNear, and braking force only needs 0.25kW.

When wind speed continues to rise to 14m/s; The system of brakeless circuit is in dangerous running state fully, though the parallel connection braking can drag down rotating speed and voltage reluctantly, generator and braking circuit seriously transship; Have only tandem brake could guarantee system safety operation, and braking force only need 0.7kW.

Table 2 simulation result

Figure 10-13 is for adopting the experimental result of tandem brake method system, and wind speed range is 4～10m/s.Experimental result and simulation result coincide, and when wind speed reached 7m/s, system switched to running under braking pattern (water pump full speed running) by MPPT operating mode (pump speed control operation).Along with constantly increasing of wind speed, the output voltage of wind-driven generator and power increase, but U _Dc2Keep stable.

Claims (3)

1. frequency control of motor speed type wind-power electricity generation water pumping system tandem brake method is characterized in that:

To be connected by the brake unit that braking resistor and electronic switch compose in parallel on the positive pole of dc bus in the frequency-variable controller, with the flat wave capacitor formation series relationship of dc bus;

Control unit in the frequency-variable controller detects the input terminal voltage U of said dc bus _Dc1With output end voltage U _Dc2, and the running state of water pump, as water pump full speed running and said input terminal voltage U _Dc1Greater than limit value U _LtdThe time, control unit is regulated the conducting dutycycle D of said electronic switch _On, and then the power and the pressure drop of adjusting brake unit, make said output end voltage U _Dc2Be stable at limit value U _Ltd

2. braking method according to claim 1 is characterized in that: as water pump full speed running and said input terminal voltage U _Dc1Greater than limit value U _LtdThe time, control unit is according to said output end voltage U _Dc2With said limit value U _LtdDeviation, employing ratio and integral control mode are passed through formula

D _on＝1-(K _P+K _I/s)(U _dc2-U _Ltd)

Regulate conducting dutycycle D _On, K wherein _PBe scaling factor, K _IBe integral coefficient, s is differential calculation; Said input terminal voltage U _Dc1High more, control unit makes conducting dutycycle D _OnMore little.

3. braking method according to claim 1 is characterized in that: the braking capacity of brake unit is directly proportional with the resistance of braking resistor.

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