CN105067905B - A kind of frequency converter power electronics controllable load method based on gird-connected inverter - Google Patents

A kind of frequency converter power electronics controllable load method based on gird-connected inverter Download PDF

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CN105067905B
CN105067905B CN201510423191.7A CN201510423191A CN105067905B CN 105067905 B CN105067905 B CN 105067905B CN 201510423191 A CN201510423191 A CN 201510423191A CN 105067905 B CN105067905 B CN 105067905B
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frequency converter
inverter
load
connected inverter
power
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CN105067905A (en
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吴跨宇
蔡慧
宣晓华
黄晓明
楼伯良
卢岑岑
卢嘉华
熊鸿韬
沈轶君
陆海清
马智泉
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Zhejiang Electric Power Co Ltd
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Abstract

The invention discloses a kind of frequency converter power electronics controllable load methods based on gird-connected inverter.When frequency converter is tested at present, energy-dissipating type loads not only wastes the electric flux of test process completely, and be difficult to accurate simulation frequency converter the load characteristic with subsidiary engine.The present invention directly connects fictitious load of the three-phase grid-connected inverter as frequency converter using the output terminal in frequency converter, and main circuit structure is the preposition transformer set gradually from front to back, uncontrollable rectifier device, intermediate dc capacitance, inverter, wave filter and postposition transformer;By the given value of current signal of given different three-phase grid-connected inverter, to simulate different load current characteristics;Three-phase grid-connected inverter is controlled using the current inner loop strategy based on pi regulator in two-phase rotating coordinate system.The present invention can apply in the test of big-power transducer, and in whole process, nearly all energy can also feed back to power grid;It can realize reactive power equilibrium control.

Description

A kind of frequency converter power electronics controllable load method based on gird-connected inverter
Technical field
The present invention relates to power electronics field, particularly a kind of frequency converter power electronics based on gird-connected inverter can Control load method.
Background technology
Either due to technique or energy-efficient needs, frequency converter obtains on the subsidiary engine of thermal power plant Turbo-generator Set A large amount of application is arrived.Frequency converter input supply voltage fluctuates the stable operation that can influence frequency converter, to promote low voltage frequency converter High-low voltage ride-through capability, at present frequently with auxiliary voltage support device mode solve shake electricity to frequency converter stable operation It influences.
For examine a kind of subsidiary engine low voltage frequency converter reactance voltage fluctuating level itself and height after additional supporting device is configured, Whether low-voltage crossing ability meets related specifications requirement, needs to carry out the testing results under input supply voltage fluctuation operating mode.Become The fictitious loads such as magnetic hysteresis dynamometer machine, excitation electromotor may be used in frequency device when testing, but energy-dissipating type load not only wastes completely The electric flux of test process, and be controlled response speed and qualitative effects, it is difficult to accurate simulation frequency converter with subsidiary engine Load characteristic.On the other hand, limit by the factors such as radiate for energy-dissipating type load and power consumption levels are limited, be only limitted to small-power and become Frequency device simple test application can not be applied to the test of big-power transducer, and dump energy cannot return during the test Power grid is fed to, causes the waste of the energy.Meanwhile this test mode be difficult to analog inverter the accurate spy with auxiliary load Property.
Invention content
For accurate analog inverter actual operating mode, test load when meeting the operation of big-power transducer quota will It asks, the present invention provides a kind of frequency converter power electronics controllable load method based on gird-connected inverter, can be with analog inverter institute band Practical auxiliary load characteristic, and realize test device power back off power grid green test.
The technical solution adopted in the present invention is:A kind of frequency converter power electronics controllable load based on gird-connected inverter Method directly connects fictitious load of the three-phase grid-connected inverter as frequency converter in the output terminal of frequency converter, forms frequency converter test With load system, main circuit structure is the preposition transformer set gradually from front to back, uncontrollable rectifier device, intermediate dc electricity Appearance, inverter, wave filter and postposition transformer;The output current of three-phase grid-connected inverter is passed through by given value of current signal deciding The given value of current signal of given different three-phase grid-connected inverter, to simulate different load current characteristics;It is rotated using two-phase Current inner loop strategy based on pi regulator controls three-phase grid-connected inverter in coordinate system.
The load torque of motor has relationship with frequency, in simple terms, a certain kind of 0,1,2, -1 power of torque and frequency It is proportional.And load torque is directly proportional to electric current, so obtaining different loads after treatment by the frequency signal of frequency converter Given value of current signal, different load characteristics is simulated with this.This given value of current signal is exactly watt current Setting signal.
Reactive current Setting signal can be set as 0, and the power factor of such three-phase inverter is 1.Certainly, some occasions need Output reactive power, then can be set as needed reactive current Setting signal.
In conventional test methodologies, due to the presence of machine winding time constant, its control response speed is limited, it is impossible to fast Speed, all kinds of auxiliary load characteristics of accurate simulation;The angle converted from energy, frequency converter directly connects motor and generator, can be with The effect of the two is considered as and is offset each other.Therefore, the present invention is proposed without motor and generator, straight in the output terminal of frequency converter Fictitious load of the three-phase grid-connected inverter as frequency converter is connect, so as to constitute a kind of new frequency converter load for testing system System.Analysis shows gird-connected inverter load, which can provide adjustable operating current, carrys out fictitious load fluctuation, it was demonstrated that using grid-connected Inverter load method builds the feasibility of transducer testing system.The controllability that gird-connected inverter load has, can be with mould Intend different types of load characteristic.Wherein, inverter realizes test device power back off as energy feedback to the channel of power grid The green test of power grid.
The power electronics controllable load method can simulate different load characteristics, it have it is loaded accurately and fast and appoint The analog capability for load characteristic of anticipating.In addition, gird-connected inverter load is also easy to improve power grade, meet big-power transducer Test request.
Further, two transformers have isolation features, make the interval of frequency converter, inverter and power grid three From being improved the safety of load system and simplify design.
Further, when setting watt currentIt is non-zero, and change at any time, reactive currentIt is 0, when reaching stable The loading condition of only active power acting can be simulated, fictitious load only absorbs active power from power grid at this time.
Further, the line voltage of inverter need to be more than the secondary side line voltage of postposition transformer, overcome output filter electric Pressure drop in sense, so that inverter returns to power to power grid.
Further, the input direct-current voltage of inverter need to be more than output line voltage amplitude, and otherwise inverter can not export the phase Hope power to power grid.
Further, the variation range that the intermediate dc capacitance voltage allows is as follows:
Wherein, UdmFor the rated voltage of intermediate dc capacitance, UdTFor inverter is made to export the input threshold of 380V line voltages Voltage, UsLine voltage for frequency converter output;KT2For the no-load voltage ratio of postposition transformer, KT2< 1 plays antihypertensive effect;Consider power device Pressure drop (output power is bigger, and the pressure drop on inductance is bigger) in the loss and inductance of part needs to improve threshold voltage UdT, introduce Proportionality coefficient k, general k > 1.
Compared to traditional excitation electromotor load method and generator loading method, the invention has the advantages that:It can be While testing high power load, volume being reduced, reducing cost, entire transducer testing system becomes very succinct;In test Nearly all energy can feed back to power grid;Load characteristic is controllable, has preferable practicability.
Description of the drawings
Fig. 1 is gird-connected inverter support structures figure of the present invention.
Fig. 2 is inner ring control block diagram (abc expression a-b-c three-phase static coordinate systems, the dq expressions of three-phase inverter of the present invention Two-phase rotating coordinate system;ia、ib、icThe respectively line current of net side A, B, C phases;L is inductance;IdFor watt current, IqIt is idle Electric current;For watt current reference value,For reactive current reference value;Uga、UgbRespectively net side A, B phase voltage;VdIt is active Voltage, VqFor reactive voltage;θ is the angle of d-q coordinate system d axis and a-b-c coordinate system a axis, and PLL represents phaselocked loop, UdFor centre DC capacitor C2Voltage, PWM represent pulse width modulation).
Fig. 3 is that the watt current order of three-phase inverter of the present invention gives block diagram.
Specific embodiment
Referring to Fig. 1, the present invention provides a kind of frequency converter power electronics controllable load method based on gird-connected inverter, main circuit Structure is divided into preposition transformer, uncontrollable rectifier device, intermediate dc capacitance, inverter, wave filter and postposition and becomes from front to back Six parts of depressor.Two of which transformer have isolation features, be all isolated between frequency converter, inverter, power grid three, make be The safety of system is improved and simplifies design.
General frequency converter output line voltage virtual value Usm=380V, the no-load voltage ratio for not connecing preposition transformer or preposition transformer are When 1, after uncontrollable rectifier, DC capacitor C2Rated voltage be Udm≈ 513V, this, which is obviously smaller than, makes inverter export 380V The input threshold voltage U of line voltagedT.There are two types of solutions thus:First, preposition transformer boosting, increases the output of frequency converter Voltage, this will improve the resistance to pressure request of subsequent device;Second is that postposition transformer pressure-reducing, the output voltage of gird-connected inverter is reduced. Obviously, second method is more reasonable.
It is designed to simplify, takes the no-load voltage ratio K of preposition transformerT1=1.If the no-load voltage ratio of postposition transformer is KT2, grid line voltage It is Us=380V, then the secondary side voltage of postposition transformer is
UT2l=KT2Us (1)
Therefore C2The variation range that voltage allows
Due to frequency converter output voltage and C2The relationship of voltage is directly proportional, also substantially directly proportional with frequency setting instruction, So variation range of frequency
Therefore minimum given frequency can be obtained
More than analysis result shows frequency converter frequency in fminAnd fNBetween when changing, gird-connected inverter index of modulation m<1, It can export and it is expected power, the normal work of gird-connected inverter load at this time.
If take fmin=30Hz, k=1.15, then K is obtained by formula (5) finallyT2≈ 0.5, at this time UT2l=190V, UdT ≈310V.In the case where formula (5) other parameters are constant, fminAnd KT2It is directly proportional.
Referring to Fig. 2, for ease of the performance of the anti-loading variation of test frequency converter, by inverter fed to the power of power grid (electric current) size must be adjustable, situation about being fluctuated with simulating grid auxiliary load.Since the time constant of power electronic equipment is small, Fast response time, gird-connected inverter can simulate different load characteristics by power (electric current) signal feeding, it has load The accurately and fast analog capability with arbitrary load characteristic.This is the great advantage of gird-connected inverter load.It is in addition, grid-connected inverse Become device load to be also easy to improve power grade, meet the test request of big-power transducer.It, can be with when actual device designs Various types of fluctuations of load are designed as required, without departing from the rated power of gird-connected inverter.
The present invention controls gird-connected inverter by the current inner loop strategy based on pi regulator in two-phase rotating coordinate system, It can be provided directly with work(electric current and reactive current.As shown in Fig. 2, when setting watt currentIt is non-zero, and change at any time, Reactive currentIt is 0, the loading condition of only active power acting can be simulated when reaching stable, fictitious load is from power grid at this time Absorb active power.
Referring to Fig. 3, the Setting signal of watt current comes from the frequency output signal of frequency converter.By to current order Setting or control can simulate the load characteristic of different type motor.Enable the watt current of gird-connected inverterSetting and frequency conversion The frequency setting order of device can be obtained into certain functional relation after standardization as watt current setting order:Work as change The frequency setting of frequency device is greater than or equal to fminWhen, gird-connected inverter load can export the power directly proportional to frequency converter frequency, I.e. load has controllability.Certainly, the no-load voltage ratio K of corresponding different postposition transformerT2, fminAlso it is different, KT2It is smaller, then fmin Also smaller, debugging range when frequency converter is tested is wider..Phase angle signal is obtained by voltage signal through PLL phaselocked loops, using electric current Signal obtains I by abc-dq coordinate transformsdAnd Iq, by IdWithPI controls are carried out, obtain VdAnd VqSignal, then Carry out the anti-coordinate transforms of dq-abc.It can make external input signal synchronous with internal oscillator signal in this way, accurately control inverse Become device.
If gird-connected inverter will export the line voltage of determining numerical value, it is desirable that its input direct-current voltage need to be more than some threshold Value, otherwise inverter, which can not export, it is expected power to power grid.For three-phase voltage type inverter circuit, input direct-current voltage need to be more than Output line voltage amplitude.Inverter returns to power to power grid, needs to overcome the pressure drop on output filter inductance, so inverter Line voltage need to be more than postposition transformer secondary side line voltage.

Claims (3)

1. a kind of frequency converter power electronics controllable load method based on gird-connected inverter, three are directly connect in the output terminal of frequency converter Fictitious load of the phase gird-connected inverter as frequency converter forms frequency converter load for testing system, and main circuit structure is in the past Preposition transformer, uncontrollable rectifier device, intermediate dc capacitance, inverter, wave filter and the postposition transformer set gradually backward;Three The output current of phase gird-connected inverter is given by given value of current signal deciding by the electric current of given different three-phase grid-connected inverter Signal is determined, to simulate different load current characteristics;Using the current inner loop plan based on pi regulator in two-phase rotating coordinate system Slightly control three-phase grid-connected inverter;
The line voltage of inverter need to be more than the secondary side line voltage of postposition transformer, and the input direct-current voltage of inverter need to be more than defeated Line voltage amplitude;
The variation range that the intermediate dc capacitance voltage allows is as follows:
Wherein, UdmFor the rated voltage of intermediate dc capacitance, UdTFor inverter is made to export the input threshold voltage of 380V line voltages, USLine voltage for frequency converter output;KT2For the no-load voltage ratio of postposition transformer, KT2< 1 plays antihypertensive effect;Consider the damage of power device Pressure drop in consumption and inductance needs to improve threshold voltage UdT, introduce proportionality coefficient k, k > 1.
2. the frequency converter power electronics controllable load method according to claim 1 based on gird-connected inverter, which is characterized in that Two transformers have isolation features, make to be isolated between frequency converter, inverter and power grid three.
3. the frequency converter power electronics controllable load method according to claim 1 based on gird-connected inverter, which is characterized in that When setting watt currentIt is non-zero, and change at any time, reactive currentIt is 0, can be simulated when reaching stable only active Power acting loading condition, at this time fictitious load only absorb active power from power grid.
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CN106026345B (en) * 2016-07-11 2018-06-12 合肥联信电源有限公司 A kind of voltage-sag prevention device of motor
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CN109270386A (en) * 2018-11-28 2019-01-25 天津农学院 Inverter Experimental device with energy recovery function
CN112840549B (en) * 2019-09-02 2023-08-01 东芝三菱电机产业系统株式会社 Testing device for inverter device
CN112152469A (en) * 2020-10-14 2020-12-29 浙江省机电产品质量检测所有限公司 Repetitive control method for three-phase AC electronic load
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