CN86101150A - The torque that is used for induction motor control is determined - Google Patents

Abstract

An induction AC motor control device comprises two kinds of methods determining motor torque: when electromotor velocity is lower than a certain predetermined speed, use the form of repeatedly deciding the corresponding direct current power input of torque of electromotor velocity formulation into each, determine torque; And when electromotor velocity is higher than this predetermined speed,, carry out the mathematical computations of various power losses, thereby try to achieve the torque of motor then according to direct current power input and frequency inverter.

Description

The torque that is used for induction motor control is determined

In general the present invention be when driving an induction motor with direct supply by transverter, determines motor output torque.

People know that when with the direct supply driven induction motor, the power of being defeated by induction motor meets following relation:

Power input=DC voltage * DC current (1)

DC voltage wherein and dc current measurement get up very convenient.

The output power of motor equals its power input and deducts whole power losses in the electric motor drive system, and the output torque of motor can be write as following formula:

Output torque=(power input-power loss)/(frequency inverter) (2)

Wherein do not comprise the rotor loss.

Utilize formula 2, an output torque sensor is contained on the motor reel exports torque,, just can measure the power loss of motor drive with experimental technique when known power input to measure.

But, in a variety of motor applications, do not wish on motor reel, to adorn a torque sensor and measure the output torque.

Another kind of prior art in order to the sensing equipment power loss, requirement predicts the alternating voltage and the alternating current of motor.For a three-phase induction motor, require to predict all three-phase voltages and all three-phase currents.Perhaps only predict the electric current of the voltage of two-phase and two-phase and derive the voltage and current of third phases according to these known parameters.But when going wrong during operation under the frequency of the variation of motor.

The invention provides the method for a definite AC motor output torque, use known DC input voitage and direct current input current.In this process, can use two kinds of methods, or determine motor output torque by looking into torque and the rotation speed relation table worked out in advance.Or according to selected motor running speed, utilization motor mathematical model to determine the power of electric motor loss, is made the output torque of motor then, and motor alternating voltage or motor alternating current are not measured in the actual output torque of not removing the actual measurement motor yet.

Optimum implementation of the present invention will be illustrated with example referring to the accompanying drawing of back.

Fig. 1 represents in the prior art, by transverter, drives a three-phase current motor with direct supply.

Fig. 2 represents in another prior art, promotes the vehicle orbital motion with a motor.

Fig. 3 schematically shows the present invention and determines device in order to the torque feedback of controlling a three-phase alternating-current induction motor.

Fig. 4 A, 4B, 4C, 4D represent a process flow diagram, in order to determine the torque feedback among Fig. 3, its method is to use the mathematical model of an electric-motor drive device.

Fig. 5 A, 5B, 5C represent a process flow diagram, feed back in order to obtain torque to be determined according to the torque rotary speed relation table.

Fig. 6 schematically illustrates according to the present invention, is the transverter and the clamping device of control of induction outfit.

Fig. 7 represents to illustrate that prior art GTO(Gate Turn On control gate connects switch) current information when connecting.

Fig. 8 represents to illustrate the current information when prior art GTO disconnects.

Fig. 1 represents a kind of prior art that is used on the three-phase current motor torque control unit, comprising a direct supply 10, give a transverter 12 power supplies, supply with AC motor 14 after turning to three-phase alternating current, this motor links to each other with a load 16, and this load can be a transport vehicle.A torque sensor 18 links to each other with the output shaft of AC motor 14, in order to predict the motor output torque 37 that flows to load 16.Power controller 26(also is called vehicle control device) input signal be from transport vehicle driver's the assisted instruction 24 and the weight 28 of transport vehicle, and transport vehicle wheel diameter 31.Power controller 26 produces a torque instruction 30, transport vehicle 16 quickens according to the acceleration of assisted instruction 24 regulations so that AC motor 14 produces desired torque, impulsion limiter 24 is received torque instruction 30 and it is limited, with the torque instruction 22 that provides in impulsion, to be restricted, and be defeated by motor controller 20.Motor controller 20 produces GTO enabling pulse 38 and gives transverter 12, so that torque feedback signal 37 matches with restricted torque instruction 22 in impulsion.

In Fig. 2, be decorated with several transport vehicles that on track 17, travels 16.Power supply 10 is by one the 3rd track 19 and current-collector 21 and communicate with contained transverter 12 on each car 16.Motor 14 links to each other with the driving wheel of car and moves along track 17 to promote vehicle 16.Torque sensor 18 links to each other with motor 14, to provide torque feedback signal 37 to motor controller 20.

In Fig. 3, be decorated with the control device of electric motor that a suitable the present invention uses, in order to control a three-phase current motor, motor that promotes a large amount of passenger vehicles of carrying for example, vehicle drivers can provide the vehicle assisted instruction to power controller 26.This instruction just converts a torque instruction signal 30 to, and passes to a signal limiter 32 to avoid producing irrational torque instruction after balance car weight and wheel diameter.Having one dashes forward towards limiter 34, make it be created in the torque instruction 22 that is restricted in the impulsion according to desirable impulsion rate 36, in order that do not allow the passenger be got excited, 38 pairs of torque feedback signals 40 of a torque feedback determinator are checked, its method is, the DC voltage 43 and the DC current 44 measuring system power inputs that provide according to power supply 10, also according to frequency inverter 48, synthesis mode 50, and the tach signal 52 that provides of a velocity gauge 54 that links to each other with propulsion motor 14, the output torque of motor 14 is estimated.Torque feedback signal 40 leads to the negative value input end of a summer 58, in impulsion limited torque instruction signal 22 then lead to summer 58 on the occasion of input end.Signal 40 and signal 22 compare in summer 58.The torque error signal 60 of comparative result gained leads to a motor controller 62.Vehicle control initiating signal 64 from the driver can make propulsion motor 14 change or not change.Other are the synthesis models 50 of DC line voltage 43 and transverter for measuring the required input signal of torque feedback signal, motor controller 62 output braking thyristor initiating signals 68, instruction drag angle 70, instruction frequency inverter 48 and instruction transverter voltage percentage 74, with these signals all to transverter and the braking synthesizer 76, this device also has a state of a control signal 78 in addition as its input and output signal, to provide synthesis model signal 50 to motor controller 62 and torque feedback determinator 38, when motor 14 is in on-position and be subjected to the extra voltage of transformer braking circuit 80 supplies simultaneously, state of a control signal 78 just works, to keep synthesis model to be in the six step modes, and prevent to change to accurate six step modes or PWM(Pulse Width Modulation pulse-length modulation) go in the mode, transverter and braking synthesizer 76 are defeated by transverter 12 with transverter GTO enabling pulse 82, to brake GTO enabling pulse 86 and be defeated by braking circuit 80, in the power propelling with in braking, transverter 12 all drives motor, and in the time need moving bigger retarding torque, just make braking circuit 80 its effects of performance to motor 14 than basic rotating speed.

In Fig. 4 A, 4B, 4C and 4D, be decorated with a process flow diagram, in order to according to motor 14 available power and motors speed, feed back to determine torque.If velocity gauge frequency 52 is lower than 12 hertz, then, determine the torque of motor according to experimental data with the lattice of tabling look-up.If the velocity gauge frequency more than 14.5 hertz, thinks that then motor torque is several functions that can ask power loss.These power losses comprise the stator loss, and the loss of friction pectinid, and other similar losses in the calculating, deduct these loss sums with power input, again divided by frequency inverter, just draw the output torque of motor, as shown in Equation (2).In the rotor current loss is not included in.Between 12 hertz and 14.5 hertz, available above-mentioned same computing method is come the calculating motor torque, in order that the usefulness of a magnetic hysteresis band for stable control is arranged.

To the square frame 100 among relevant Fig. 4 A, power input multiply by the AC line electric current with AC line voltage and calculates.Power input can just can be born, and whether depends on that motor is just in regenerative braking or current drawn from the line of electric force.In square frame 102, judge the torque relevant, at the last calculating torque that once whether once was used to Speedometer Drive.Form digitizing and empirical have been tabled look-up in these torques, and as the function of power input with the speed increment of selecting, the function that is lower than 14.5 hertz slow running part is stored in the computing machine, because when slow running, torque and power input are not linear relations.When motor operated in more than 12 hertz, the pattern of rated output loss was gratifying.For this cause, verifying of 102 pairs on square frame used look-up table to determine whether program.If it is sure answering, then in square frame 104, do once to verify, to determine whether that velocity gauge frequency 52 is greater than 14.5 hertz.If answer in the square frame 102 negate, then in square frame 106, do once to verify, be less than or equal to 12 hertz to determine whether velocity gauge frequency 52.If the answer in the square frame 104 is negated, or the answer in square frame 106 is sure, then the look-up table program is just transferred to square frame 108.If the answer in the square frame 104 is sure, or the answer in the square frame 106 is negated that then the power loss computing method at square frame 109 just begins to use in square frame 110.A feature here is set, using the power loss computing method with sign, thereby when passing through this program, whether look-up table should uses to verify should to get suitable approach next time.In square frame 112, for the power loss in the computing system, need know motor root mean square (RMS) value electric current, and motor current is determined as the function of a parameter.This parameter is exactly to slide premultiplication to pass the voltage of motor, and divided by the design voltage of motor, this design voltage is to obtain according to the every hertz of voltage ratio that equals constant.Every hertz of voltage ratio is 9.33 in the representative instance of a propulsion motor.For example equal at 100 hertz at 9.33 o'clock with voltage and frequency ratio, motor needs the voltage of 933 hints to line approximately under this ruuning situation.Voltage is that 600 volts direct supply can only be supplied with the about 468 volts line of the motor of feeding to line voltage.The ratio of these two voltages is exactly in order to determine the multiplier factor of motor current.The slippage function is provided by a form of working out in advance in this respect of tabling look-up.This form can with on record motor model be added on the motor relation of sine voltage and set up.For certain given motor slippage, under the condition that the supposition motor temperature remains unchanged, a certain specific motor current is arranged, in square frame 114, the conducting of transverter switchgear loss also will be calculated, no matter its synthetic and on-off mode why, can be used same formula.The conducting loss can be represented by the formula:

Conducting loss=4.05 * motor current (3)

In square frame 116, carry out the calculating of switching losses, calculate in PWM(pulse-length modulation with first formula) or the switching losses of standard in six steps.The average frequency of switching here is 400 hertz.Carrier frequency is that 400 hertz switching losses is:

Switching losses=312+1.2 * motor current (4)

Switching losses in six step operations is smaller, because average frequency of switching is not 400 hertz, so switching losses can calculate according to following relation:

Switching losses=0.009 * motor current * the transverter in six steps

Frequency (5)

In square frame 118, calculate the energy loss of buffer circuit.This loss is the energy loss that is connected across in the buffer circuit at GTO switchgear two ends, i.e. ohmic loss and capacitance loss in the buffer circuit charging and discharging.In PWM or accurate six step operations, the buffer circuit loss can be calculated as follows

Buffer circuit loss=((1.0 * 10 ^-5* V ²)+

（1.35×10 ⁵×I ²）〕×F （6）

Wherein V is an AC line voltage, and I is a motor current, and F is a switching frequency.For PWM and accurate six steps, can make the mean value of F equal 400 hertz, for six step operations, the buffer circuit loss is:

Buffer circuit loss=((6.0 * 10 ^-6* V ²)+

（5.3×10 ^-5×I ²）〕×F （7）

In square frame 120, calculate the loss of transverter, this loss equals loss of conduction, switching losses and buffering loss sum.

Now, shown in Fig. 4 B, be necessary the loss of calculating motor.At first at square frame

Stator resistance loss=3 * stator resistance * (motor current) ²(8)

This is the I of three windings of stator ²The R loss.In square frame 124, calculate core losses constant at voltage but under the frequency change.Still use the motor design voltage here.With motor 14 is example, and this motor has 45 hertz basic rotating speed and equals 9.33 volts every hertz constant voltage ratio.Parameter in the first core losses formula can be calculated as follows:

Core losses=1864 * (frequency inverter)/45 (9)

For the six step methods of operation, there is not desirable voltage place in whole frequency range, be more than the constant volt, to move, then the core losses formula is provided by following formula:

Core losses=1.162 (motor voltage)/(frequency inverter) 1.6 * frequency inverter (10)

The spuious loss of controlled motor can utilize the formula in the prior art to calculate, that is: in square frame 126

Spuious loss=2.12 * motor torque (11)

Motor torque wherein be exactly before calculated torque.

In square frame 128, carry out the calculating of harmonic losses, in calculating, use series of forms and formula.It is extremely difficult setting up an accurate loss model for harmonic losses.Therefore, adopt the method for a simplification to calculate harmonic losses, in the hope of an approximate value.When calculating harmonic losses, to set up form and formula that microprocessor will be used earlier.For this reason, make AC motor under laboratory condition, under different rotating speeds and load, turn round.On each operating point, measure the transverter power input, motor output torque, and motor root mean square (RMS) value electric current.According to these data, just can use relevant formula, carry out the calculating of the every other loss except harmonic losses.Output power of motor can be exported taking advantage of and deriving of torque and frequency inverter from motor.Deduct this output power and just obtain the loss of being left from power input, this loss of being left should be approximately equal to harmonic losses, as long as the loss formula of deriving has rational precision.The harmony loss that estimates on all operating points is made form and formula, so that microprocessor can be used it for the calculating of harmonic losses at last through the arrangement layout.

For a certain AC motor kinematic train, the layout of harmonic losses data arrangement.Can provide form for each Waveform Synthesis Technology.Every kind of such form is with the harmonic losses under the zero load and an operational factor associated.For the PWM synthesis mode, form is expressed as loss the function of frequency inverter.For accurate six step synthesis modes, loss is expressed as the percentile function of command voltage.For the synthetic operation of six steps, loss is the function of frequency inverter by table.When motor had a certain torque, experimental data showed that the harmonic losses amount has just increased.Find following formula in whole motor full and down scope, to represent harmonic losses approx

Harmonic losses=1+ (slip-frequency)/(rated slip frequency) * 1.2 * table value (11A)

In square frame 128, carry out checking of synthesis mode.According to the synthesis mode that adopts, select in three forms for use, to obtain motor in similar ruuning situation but the harmonic losses during no-load.Only with this table value and slip-frequency and the rated slip frequency harmonic losses of (11A) calculating motor by formula just.

In square frame 130, carry out the calculating of motor loss, this loss is obtained as following sum, i.e. stator loss, core losses, spuious loss and harmonic losses.

In square frame 132, carry out the pectinid loss and calculate.The pectinid loss is made up of two parts, and a part is a fan loss.Another part is the loss of rotor pectinid.The rotor windage loss is in a four-pole motor, and available following formula calculates:

Pectinid loss=599 * ((rotations per minute (RPM))/1800) ³(12)

Wherein 1800 are basic frequencies of motor.Under this basic frequency.The pectinid loss is 599 watts.In square frame 134, carry out the friction loss of friction rotor loss and motor 14 usefulness fans, available following formula calculates:

Friction loss=(104 * (rotations per minute (RPM)))/1800 (13)

Wherein 104 watts, people know it is friction loss under 1800 rev/mins base speed, suppose that simultaneously under this base speed, friction loss is directly proportional with speed.In square frame 136, rub and lose the calculating of sum with pectinid.The loss sum that Here it is obtains in square frame 132 and 134.

In square frame 138, once check.Look at that whether the transformer in braking circuit 80 is not by short circuit.When motor 14 was done the transformer running under braking in six step modes, situation will be such.When motor is not done the transformer running under braking, in square frame 140, be that thyristor is obtained brake loss with following formula:

Brake loss=4.05 * motor current (14)

If transformer braking is arranged, then in square frame 142, the calculating transformer brake loss.

The transformer brake loss comprises the following, i.e. buffer circuit and GTO switching losses, GTO and the loss of circuit diode current flow, diode bridge loss, transformer ohmic loss, and transformer core loss.More than each square frame 133,135,137,139 of providing according to Fig. 4 C of every loss and the formula of 141 regulations calculated one by one.In square frame 144, carry out the calculating of power loss.Power loss is the following sum, it is the motor loss that square frame 130 is obtained, the friction pectinid loss of obtaining in the square frame 136, the brake loss of obtaining in the square frame 140 or 142, and the inverter losses of in square frame 120, obtaining, in square frame 146, carry out the calculating of corrected output, this power rate of just can passing on Gong.Equal power input or square frame 100 calculate power, deduct square frame 144 calculate power loss.In square frame 148, make torque feedback TEF equal corrected output divided by frequency inverter (rate of can passing on Gong is divided by stator frequency).Because division arithmetic carries out in square frame 148, and division arithmetic can cause the situation of overflowing when frequency inverter is very little, therefore in square frame 150, determine to have or not the situation of overflowing to take place.If register overflows, its result is wrong, because be still staying in the register than lower part of result, and most important information has been lost.Like this, in square frame 152, will once check, look at that torque is positive or negative.If torque is born, motor is in the running under braking mode.If torque is positive, motor is in the power method of operation torque to take place.If torque is positive, then in square frame 154, be fixed in maximum positive torque.If torque is born, then in square frame 156, be fixed in maximum negative torque.In this way protect, in case in the calculating of limited figure place, make a mistake, once return then and reset.

In flow chart 108 shown in Fig. 4 A, call in the program that is called schedule method shown in Fig. 5 A.In square frame 160, set a sign operation and using the torque form, in square frame 162, once check, look at whether velocity gauge frequency 52 is less than zero, whether carries out towards negative direction to conclude operation, if situation is like this really, then several computings are just skipped and have not been done.When vehicle was in the rollback campaign of starting forward, friction brake was released, and with open loop power supply motor, so that vehicle travels forward, at this moment, velocity gauge frequency 52 may be less than zero.If velocity gauge frequency 52 is negative, program just carries out the transition to square frame 164.In square frame 164, carry out the open loop of a torque according to predetermined slippage and calculate.Know that the velocity gauge frequency greater than zero, then once checks if in square frame 162, examine in square frame 166, look at that whether limited impulsion torque instruction 22 is less than zero.Under the running under braking mode, situation is should be so.If situation is like this really, then in square frame 168, once check, look at that whether velocity gauge frequency 52 is less than a minimum frequency values.For this low-limit frequency, retarding torque can be calculated, and simultaneously, schedule method also is adaptable.Operate under the very low velocity gauge frequency for a van, wish usually vehicle is applied friction catch.

If the velocity gauge frequency is higher than the low-limit frequency in the square frame 168, and the calculating of retarding torque is essential.Program just goes to square frame 170,, establishes a parameter A here, makes it equal the velocity gauge frequency, makes a numerical digit equal 1/64 hertz therein.In square frame 172, establish a B parameter, make its integral part that equals A, this removes A with 64 and gets.As long as A equals arbitrary number in 0 to 63, the result is exactly a round values 0.As long as A is the arbitrary number in 64 to 127, the result is exactly a round values 1, and other in square frame 174, establish a parameters C by that analogy, make it equal an interval distance.This is interval apart from the initial point that rises from first form, up to the initial point corresponding to the form of velocity gauge frequency integral part.Because each table has 32 train values, in square frame 174, take advantage of round values B with 32, just can choose desired form.If round values is zero, is exactly first form.If round values is 1, it is multiply by 32 just draw address 32.The IP address of Here it is second form.Other by that analogy.In square frame 176, determine a parameter D, the practice is that the IP address with first form is added on the parameters C, and C is exactly the interval distance of that form.If first form is since zero point, parameters C is exactly the IP address of this form.But, apart from the initial point address that is added to first form, just obtain the initial point address that a pointer D points to required form interval because first form can begin somewhere from other.In square frame 178, call in the torque calculation list procedure.This routine uses selected form, and fetches a torque value from form, and this torque value is decided to be E and is called the torque low value in square frame 180.In square frame 180, be decided to be E and be called the torque low value.In square frame 182, establish a parameter F, make it equal D and add 32,32 top address that are added to stand-by form, be in order to enable form of F.In square frame 184, call in the torque calculation list procedure again, in square frame 186, obtain the high value G of torque.Like this, parameter E provides the pairing torque low value of certain frequency that equals velocity gauge frequency integral part, and parameter G then provides and equals 1 and add the high value of the pairing torque of the upper frequency of velocity gauge frequency integral part.After obtaining these two the pairing torque values of pointing out by certain velocity gauge frequency integral part of direct current power input, just can between these two torque values, carry out intermediate interpolated, in the hope of torque value corresponding to the velocity gauge actual frequency.This intermediate interpolated is by square frame 188,190, and 192,194 and 196 finish.For obtaining the slope of straight line between torque E and G, in square frame 188, make this slope of torque/speed frequency equal the poor of parameter G and E.In square frame 190, if Parameter H, make it equal B and take advantage of 64, in square frame 192, the fraction part of velocity gauge frequency or make rotating speed surplus part be calculated, this part equals the velocity gauge frequency and deducts Parameter H, because deduct 64 surpluses of taking advantage of integral part B just should equal to be left from original number.This surplus is exactly the difference of velocity gauge frequency or claims fraction part.In square frame 194, establish a parameter J, it is poor to make it equal total torque, and this just should be added to that part on the torque low value E for trying to achieve total torque.This part also equal in square frame 188, to calculate straight slope multiply by the poor of velocity gauge reading, again divided by 2 ⁶Just 64, in square frame 196, this fraction part of torque is added on the torque low value, just draw calculate the torque feedback.

In Fig. 5 C, provide the process flow diagram of torque calculation list procedure.Selected form has 32 tabular items, in the form last list be exactly be used for packed data and dividing remove calculate the scale factor of performance number.In square frame 200, calculate to such an extent that the power proportions factor is read as last tabular item in the form.The middle table of form list corresponding to null value calculate power, and first or uppermost tabular item be corresponding to regenerating power, and last or nethermost tabular item are corresponding to consumption power.Like this, the scope that form is summarized is from uppermost negative power, through zero power, up to nethermost on the occasion of power.In square frame 202, establish a parameter M, make it equal to calculate to such an extent that power is removed by (8 * scale factor L).The power input that parameter M is just scaled.In square frame 204, establish a parameter N, make it equal scaled power input M and multiply by 2 ^-8Suitably to dwindle numerical value, to make the number that draws at last between one 15 and 14 and represent the interval distance of form mid point, in square frame 206, once check, look at that whether number N are greater than 14.If the numerical value of N then in square frame 208, makes N equal 14 greater than 14, mean that tabulated value 14 is needed, if the numerical value of N is just once checked less than 14 in square frame 210, whether the numerical value of looking at N because from zero power count, has 15 tabular items less than 1.If the numerical value of N is less than 1, this just represents that number N should be fixed on one 15 in square frame 212.In square frame 214, in form, select a tabulated value, its address because before the form mid point, has 15 tabular items for the interval distance apart from the form mid point adds the uppermost address 15 of form, and is interval apart from can just bearing, and depends on which part of use table.Establish again a R equal this tabulated value multiply by take advantage of several 2 ⁶It is turned to desired torque unit of measurement.In square frame 216, establish a parameter P, make its equal to show in next bigger tabulated value multiply by 2 ⁶Like this, just from form, successively obtain two tabulated values.The all corresponding different direct current power input of in these two torque values each, 0 corresponding direct current power input more less wherein than P, actual direct current power input is between these two direct current power inputs, in order to obtain torque, must between these two torque values, carry out intermediate interpolated corresponding to the actual DC power input.This intermediate interpolated is finished in square frame 218,220,222.In square frame 218, obtain the difference of two tabulated values and draw the value of slope Q.In square frame 220, the fraction part of torque value is to multiply by 2 with tabulated value N ⁸And with this product from calculated originally power in the method that deducts obtain.This difference is between actual DC power input and the direct current power input corresponding to torque R.With slope Q and this difference power, and then multiply by 10 ^-8With the value that contracts, just obtain a value of representing the difference of two torques.These two torques, one is the torque R corresponding to the actual DC power input.In square frame 222, torque margin is added on the torque R, just obtain the value of torque feedback.Then, from this torque calculation list procedure reposition.

The output torque of motor determines according to the direct current input parameter, rather than relies on the voltage and current of measuring AC motor or lean against and adorn a torque sensor on the motor and determine.When the velocity gauge frequency is less than or equal to 14.5 hertz, just determine that with schedule method torque, the supposition of its basis are, if the voltage that applies is constant substantially, when the power of some enters motor, motor must send a certain size torque.The motor torque of trying to achieve can have nearly 5% variation, this is because the error of loss in calculating, and other factors that do not take in cause, as temperature effect etc., but control is used for electric motor for vehicle, and this precision is enough.Up to the basic rotating speed of motor, motor is in the running status of every hertz of constant voltage from low speed.When the voltage of motor is known, between motor output torque and direct current power input, certain corresponding relation is just arranged.Here the torque that provides and the form of power relation calculate, and work out a motor mathematical model in the calculating earlier, calculate various corresponding power relations again.In than the higher velocity range of basic rotating speed, voltage changes, because the transverter working voltage is for normal or owing to applied braking.For the operation of this speed of hyper-base, it is not satisfied using the result of the form gained of torque and power relation.A method of share is the relation of rated output loss and motoring, with calculate power loss in power input, deduct, poor with frequency inverter again except that this, so just obtain the output torque of motor, when rotating speed is higher, power input is bigger, some error during power loss is calculated, influence to motor output torque calculation is also not very big, when rotating speed is low, transverter and power of electric motor loss account for a big chunk of total power input, and during power loss was calculated, the error that size is identical can cause the mistake that is difficult to accept to the motor output torque of being asked.From about 12 hertz to basic rotating speed, the result that the method for two kinds of calculating motor torques provides is more or less the same, but loses the list data that computing method does not need the required a large amount of storages of schedule method.Therefore, when near 12 hertz, more be suitable for and adopt the loss computing method.

If motor is lower than under 10 hertz of situations in the velocity gauge frequency and brakes, then just no longer include funtcional relationship between torque and the power input.In other words, corresponding each power input value has more than one torque value corresponding with it.Therefore, can not use in two torquemeter algorithms any one in the hope of operating in the output torque of the motor of braking under the low frequency very.But, for the vehicle that transports lot cargo, under low like that speed, be more suitable for carrying out friction catch, therefore, above said situation will can not become problem, under the sort of situation, can suppose that torque and motor slippage are proportional, motor torque be carried out an open loop estimate.But controller will not use this estimation, because under low like that frequency, not plan to make controller to carry out the closed loop motor braking.This estimation is just to include for complete.In addition, if the velocity gauge frequency is born, the expression heavy-duty truck falls back.Opposite with desirable direction of motion.At this moment, because same reason can not be carried out correct torque calculation.The sort of vehicle is finished from returning back to turn over the open loop control operation, and in this operation, the torque that the also unfavorable usefulness of controller is calculated for the sake of completeness, is here estimated torque as the function of slippage.

For the look-up table that application of torque is calculated, prepared the form that a cover is made up of 16 different forms and be used for searching.Each form is applicable to from 0 to 15 different rotating speeds meter frequency.Wherein 0 to 15 is integer hertz values of velocity gauge frequency, and motor torque is the function of power input and rotating speed or velocity gauge frequency.In this method, need to use 16 two-dimentional forms to have the effect of three-dimensional table, this one dimension of rotating speed is wherein provided jointly by several tables.Each is shown all layouts and becomes 31 different power points, makes that for each performance number a corresponding torque value is all arranged.Performance number is lined up 31 different numerical value, the tabular item of form central authorities be null value calculate power, 15 negative power meter train values are arranged or claim the braking power value before central table is listd, also have 15 positive tabulated values after central table is listd, the 32nd tabulated value is a scale factor that is used for packed data, stores the respective torque value in each place.Each form is all done enough greatly, to cover the output torque value of most possible appearance.In higher velocity range, look-up table is more suitable, in this scope, 100 kilowatts of may have maximum output torque at the power of 50 to, and at slow-revving one, 3 kilowatts of just has of the power of possibility fully loaded output.The direct current power input has big like this variation range, will need very large form.In order to reduce the form size, just use a scale factor to indicate wattage poor of each form intersite.For example, has difference between two adjacent places, and at slow-revving one, 3.3 kilowatts of at high-revolving of 0.2 kilowatt of of two of may only the have an appointment difference of adjacent intersites up to one.According to a motor mathematical model, adopt to break away from the mode of master routine with the rated output loss, carry out the calculating of various losses.These losses when quilt has closed get up and be added to the power that motor torque sends after, its result equals to supply with the power input of this system.Use the account form of this disengaging master routine, each integer velocity gauge frequency is calculated, just can draw a form, this form is illustrated under this velocity gauge frequency, the relation between torque and the power input.

If power input drops between 2, just from form, take out two torque values, the power input that one of them correspondence is lower, another is corresponding to higher power input.Suppose torque and the power relation of being in line between these two torque values, actual power input is carried out intermediate interpolated, just can obtain the output torque.The velocity gauge frequency also supposes it is 0,1,2 ... or in 15 hertz of these tittles one.Because the velocity gauge frequency seldom may just in time equal an integer, therefore need make more intermediate interpolated and calculate to determine the torque under the actual speed frequency.Intermediate interpolated is performed such: at first according to current power input, make two torque values of two integer velocity gauge frequency correspondences.These two integer velocity gauge frequencies are from being clipped in the middle actual speed meter frequency up and down, and each above-mentioned torque value all uses the said intermediate interpolated method in front to determine.Had these two each all be from two velocity gauge frequency meters calculate middle torque value, just use the intermediate interpolated method to obtain again between the last torque value of feedback between the torque value in the middle of two, for instance, if the velocity gauge frequency equals 10 1/2 hertz, obtain the torque value under 10 hertz and 11 hertz earlier, between these two torque values, carry out intermediate interpolated again to obtain the output torque.

Give power input with a dimensioning, make a numerical digit equal 7.6294 * 10 ^-3Watt, the yardstick of torque is that a numerical digit equals 0.1146 pound of Foot.The byte that plays the yardstick effect in the form is to set like this, makes a numerical digit equal 15.625 watts of each form points.In the byte form, have 255 available digits, but the numerical value in the table of bytes can not be measured with the unit identical with the unit of tolerance torque, this is because torque can be up to 800 pounds of Foot, this will need the numerical digit more than 255, like this, each form torque value equals 0.1146 * 2 ⁶Pound Foot.

In Fig. 6, be decorated with the synoptic diagram of transverter and brake line.These two intercouples to control an induction motor, and transverter 12 comprises that two switches of GTO-1 and GTO-2 link to each other with direct supply 10, and is excitatory with the magnetic pole A to motor 14.Two switch GTO-3 also link to each other with direct supply 10 with GTO-4 in addition.Excitatory with magnetic pole B to motor 14.Switch GTO-5 links to each other with direct supply 10 equally with GTO-6, and is excitatory with the magnetic pole C to motor 14.Also be decorated with the braking circuit 80 of the phase A of motor 14 among the figure.Phase B and C mutually have and the identical braking circuit of A mutually, but do not draw in the drawings.Also be decorated with voltage buffer circuit 250 and the current buffering circuit 252 of GTO-1 among the figure.

Also be decorated with thyristor TH-1 and TH-2 among Fig. 6, be used in braking circuit 80, its effect is with transformer 254 short circuits.Thyristor buffer circuit 256 also is drawn among Fig. 6, and the purposes of GTO switch GB1 is that when thyristor TH1 and not conducting of TH2, modulating brake circuit 80 is defeated by motor 14 voltages.GTO switch and GB1 are furnished with a voltage buffer circuit 258 and a current buffering circuit 260.Circuit diode DB1 comprises a buffer circuit 262.The elementary winding of 264 pairs of transformers 254 of diode bridge works.

The energy of being drawn when in Fig. 7, being decorated with the GTO switch connection.

Be decorated with the energy of being drawn when the GTO switch disconnects among Fig. 8.

SG800E * 21 type GTO switches that each electrode of transverter uses a Toshiba to produce.The gate current of this GTO is 5 amperes, and the di/dt of anode is then decided by the electrode inductance, as the L of electrode A ₁, inductance L ₁Be 7 microhenrys, when the voltage of electric current 46 is 600 volts, the value that this inductance provides di/dt is the every microseconds of 85 peaces, or 0.16 watt of each pulse, as shown in Figure 7, connection each time for the switch GTO-1 of the electrode A of transverter 12 just has 0.16 watt power loss, and this loss is multiplied by per second and connects number of times and just draw the power loss of representing with the per second wattage.

Turn-offing loss is what to determine with the curve shown in Fig. 8.Suppose that this curve is a straight line, the electric current that the slope of this straight line be multiply by the GTO switch of flowing through just draws the energy loss of each shutoff, then this energy loss be multiply by turn-off number of times in the per second and just obtains shutoff loss in the per second.

In order to estimate the torque of AC motor, use a microprocessor and DC input voitage and direct current input current are measured by an analog-to-digital converter.These two parameters are taken advantage of the power input that together just obtains transverter and braking circuit.From power input, deduct every other every loss in the system except the motor rotor ohmic loss, microprocessor just can draw the useful part in the power that motor produces torque, then, remove this net horsepower with frequency inverter, just can make the torque of motor.If the rotor resistance loss is also included within the system loss, will replace frequency inverter to come calculating torque with the rotor mechanical motion frequency.

Calculate system loss can be divided into four basic groups.First group comprises the loss that occurs in the transverter, and this part is divided into GTO and diode current flow loss, GTO switching losses, and the loss in the buffer circuit again.Second group of loss of system comprises the energy loss in the AC motor, wherein is divided into stator resistance loss, magnetic energy loss unshakable in one's determination, harmonic losses and spuious loss again.The 3rd group of loss of system comprises various mechanical losses in the AC motor, wherein can be divided into motor friction loss and pectinid loss again.The 4th group of loss of system is just in Motor Control, just occur when comprising optional braking circuit, comprising the transformer brake loss, this loss can have a great difference each other, this will see whether current transformer is less than using but by the short circuit of thyristor institute, or current use of transformer and thyristor is turn-offing not, if transformer is by the thyristor short circuit, the transformer brake loss includes only the conducting loss of thyristor.If transformer is not by the short circuit of thyristor institute, the transformer brake loss comprises all semi-conductive bufferings and switching losses in the braking circuit, the conducting loss except that the bridge circuit diode in all semiconductors, the conducting loss of bridge circuit diode, the ohmic loss in the transformer, and the core losses of transformer.The method of asking of total system loss is earlier the loss in every group to be added up, and all each group losses are added up just obtains the total losses of system again.

In order to calculate every group system loss, must derive and wait to ask the relation between each known parameters in loss and the system, a variety of losses all are the functions of motor current.Microprocessor can directly be read root mean square (PMS) value of motor current, (independent electric current is to the line of electric pressure converter, connection converter and steering logic assembly but owing to the cost costliness of finishing the required parts of this function, and root-mean-square value (RMS) voltage determining circuit), so work out a relation between motor machine rms current and a lot of parameter, these many parameters are: the slip-frequency of each known variables, motor voltage and the V/F voltage that equals constant.This relation is according to following principle, and promptly when air-gap flux remained unchanged, electric current was the known function of slip-frequency, disregards influence of temperature variation.At air-gap flux is under the ratings situation, relation between motor current and slip-frequency can be stored in the form for the microprocessor access, promptly when motor had specified air-gap flux, microprocessor just can be found out the value of motor current according to known slip-frequency.If slip-frequency remains unchanged, motor current is directly proportional with voltage on being added in motor.Like this, even motor is not under the specified air-gap flux situation, also can calculate motor current, used equation is as follows:

Motor current=F(slippage) * (motor voltage)/(motor designs voltage (DFS)) (16)

F(slippage wherein) be the relation of motor current and slip-frequency, and motor designs voltage is for producing the required voltage of specified air-gap flux.After carrying out table lookup and aforementioned calculation, microprocessor just provides the good estimation of a current electric current of motor.Then, just this motor current value is used in several losses calculating.

Unidirectional transmission diode in the transverter and the conducting among GTO loss can be regarded the function of motor current approx as, the product of instantaneous conducting loss electric current that equals to pass through and the voltage drop that produces by this device in GTO or the diode.But there is no need to calculate instantaneous conducting loss, therefore only need the average conducting loss in definite semiconductor devices.The average voltage drop that the GTO of conduction average current value produces is about 1.8 volts, and the average voltage drop that the diode of conduction average current value produces is about 1.2 volts.Though the voltage drop of these two kinds of devices has slightly variation with the size of conduction current, but still supposes that 1.8 and 1.2 volts of these two constants are available.Suppose that voltage reduces to 1.8 volts of constants, the conducting loss in the transverter among all GTO can be calculated as follows:

GTO conducting loss=1.8 * (0.9 * motor current)/4 * 6 (17)

Wherein, loss is with watt representing that motor current is represented with the root mean square ampere.0.9 being used for a rms current value is average current value, the 4th, because each GTO on average has only the conducting of 1/4 time, 6 then is one to have six GTO in the transverter, and this formula can be simplified to following formula:

GTO conducting loss=2.43 * motor current (18)

In like manner, suppose 1.2 volts of constant voltage drops, the conducting of all unidirectional transmission diodes loss can be calculated as follows in the transverter:

Diode current flow loss=1.2 * (0.9 * motor current)/4 * 6 (19)

Wherein, loss is with watt representing that motor current is represented with the root mean square ampere.0.9 being used for a rms current value is average current value.The 4th, because each diode on average has only 1/4 time conducting, 6 then is because one have six unidirectional transmission diodes in the transverter.Above formula becomes following formula through simplifying:

Diode current flow loss=1.62 * motor current (20)

These formula are in fact just partly set up, and have only the conducting of 1/4 time because wherein suppose each diode and each GTO.In fact, drag in servicely at motor, the ON time of GTO is greater than 1/4, and the ON time of diode is then less than T.T. of 1/4.In fact this trickle skew of the two ON time has increased the loss of GTO, has but reduced the loss of diode, but for simplicity, this difference has been ignored, and when braking, situation is just in time opposite.The effect of ignoring this ON time skew, converter deblocking loss equal the conducting loss that GTO adds diode at last, or

Converter deblocking loss=4.05 * motor current (3)

No matter synthesis mode how, all use this formula.

Transverter GTO switching losses is decided by synthesis mode, because loss is relevant with switching frequency.In PWM(pulse-length modulation) and accurate six step modes in, switching frequency is about 400 hertz, and in six step modes, switching frequency equals frequency inverter.Therefore, needing a formula is the usefulness in PWM and accurate six steps, needing another equation is the usefulness of the six step methods of operation, switching losses among the GTO can calculate according to the makers' data of GTO, switching losses is made up of two parts, and a part is to connect loss, and another part is to turn-off loss, GTO manufacturing plant provides the relation curve of connecting loss and anode di/dt, also provides to turn-off the relation curve that loses with anode current.The model of the GTO that the present invention is used is SG SG800E * 21, its loss curve as shown in Figure 7 and Figure 8, the connection of six GTO loss and turn-off loss from these curves can the induced representation transverter.The form of relational expression is as follows:

GTO connects loss=0.26 * (400/2) * 6=312 (22)

GTO shutoff loss=0.0011 * (0.9 * IM) * (400/2) *

6＝1.2×IM （4）

In above equation, several 0.26 takes to connect on the loss curve and equals 5 amperes corresponding to IGM, and anode di/dt equals the point of 85 amperes of every microseconds.The average frequency of switching of several 400 representatives in the following formula in the PWM and the accurate six step methods of operation, in the formula several 2 is owing to only in half of GTO turn-on time current flowing is arranged, this has just very reduced switching frequency with a factor 2 effectively, and several 6 in the following formula represented the number of GTO in the transverter.The rate of curve on the loss curve is turn-offed in several 0.0011 representatives; IM is motor root-mean-square value (PMS) electric current of representing with ampere.In six step synthesis modes, switching losses is smaller, and this is because switching frequency equals the transverter basic frequency, and is not equal to 400 hertz.Therefore, if use six step synthesis modes, will use other formula to calculate.In six step synthesis modes, when electric current was flowed through GTO, all GTO turn-offed, and therefore, effective switching frequency must not resemble at PWM with intending in the six step synthesis modes and be removed by 2.In addition, in six step modes, connect little the getting of loss and can ignore, because when motor current in the opposite direction flowed, each GTO connected originally.The result is, motor current changes direction and GTO begins conducting.Yet it will be very little in this case, connecting loss.In addition, in six step modes, the shutoff loss in the circulation of each switch is bigger because the electric current that is turned off under normal circumstances the root-mean-square value than motor current is bigger.The accurate numerical value of electric current is relevant with the phase angle between voltage and current.When GTO turn-offed, the current value estimation was about 1.4 times of motor current root-mean-square value, and this is owing to reasons such as higher hamonic wave cause.The switching losses formula of describing in the six step synthesis modes is as follows:

GTO connects loss=0 (23)

GTO turn-offs loss=0.0011 * 1.4 * IM * frequency inverter * 6

=0.009 * IM * frequency inverter (24)

Transverter GTO switching losses=0.009 * IM * frequency inverter (5)

Transverter buffering loss be included in six in the voltage buffer circuit loss and the loss in three current buffering circuits.Occur in loss in the voltage buffer circuit and be since GTO when turning on and off, the charging fully and the discharge of capacitor, the loss in the current buffering circuit are because the enhancing of electric current and weakening in the inductor when GTO turns on and off.In each transverter electrode, four kinds of different situations are arranged basically, electric energy is expended in buffer circuit.

First kind of situation is such, when motor current when negative, direction of current flow is to flow out motor, GTO-2 turn-offed before this, connected then.In this case, motor current flowed through before this diode D1 and L1, but after GTO-2 connects, the electric current GTO-2 that just flows through.Simultaneously, the voltage buffer condenser C2 that uses of GTO-2 must shed 600 volts of voltages; In this course, energy consumption equals 0.5 * C * V ²; The voltage buffer capacitor C1 that GTO-1 uses must charge to 600 volts of voltages; The electric current of L1 of flowing through must stop to flow; And diode D1 turn-offs.Connect GTO-2, the electric current of the L1 that flows through begins to reduce, and begins to reduce across the voltage on GTO-2 buffer condenser both sides.When the electric current one of the L1 that flows through reaches zero, this electric current just begins oppositely and the buffer condenser of GTO-1 is charged.In addition, diode D1 will could turn-off with about 2.5 microsecond times.Therefore, in this small time, D1 will be at contrary direction conduction current.The charging voltage of GTO-1 buffer condenser will be above DC line voltage, and this is because the existence of buffer inductor and circuit stray inductance.When GTO-1 buffer condenser voltage surpasses line voltage distribution, the electric current in L1 and the stray inductance just begins to reduce, and portion of energy is temporarily transferred in the capacitor, and remaining all consumes in R1.The energy of transferring in the capacitor is the reason of buffer condenser voltage overshoot, and the very fast consumption of the major part of energy is in R4 and R1, and the part of being left feeds back to direct supply.Be lost in buffer electrode resistance R 1, the energy among R4 and the R5 can prove by following formula and provide:

The buffering loss=(0.5 * C * V of first kind of situation ²)+

〔0.5×L×（IL ²+ID ²）〕

（25）

Wherein first representative is because the discharge loss of GTO-2 buffer condenser, second energy loss of representing charging of GTO-1 buffer condenser and the power consumption of buffering inductor, in the switch circulation at the end, be stored in the energy in the GTO-1 capacitor, can not think a kind of loss, because this is the energy that stores this moment.In above formula, C is the buffer capacitor that equals 2 microfarads; V is a DC line voltage; L represents buffer inductance (7 microhenry) and stray inductance (2 microhenry) sum, and therefore, L equals 9 microhenrys; IL is the peak point current that flows through L1, and this is the maximum current that reaches when giving the charging of GTO-1 buffer condenser, wherein is not counted in diode current; ID is the backward dioded peak point current of D1 of flowing through, and IL and ID are determined by following formula:

IL＝V×（C/L） ^0.5（26）

ID＝V/L×Trr （27）

Wherein, V, C, L is former all offered some clarification on, and Trr is the diode reverse recovery time, and its value is about 2.5 microseconds.In this buffering loss formula (25) above two formula substitutions, can represent the formula of an electrode loss, its form is as follows:

Buffering loss=C * V in first kind of situation ²+ 0.5 * (V ²/ L)

×Trr ²（28）

In second kind of situation, motor current is positive, and when GTO-1 will turn-off, electric current was flowing through GTO-1, and in this case, motor current flows in L1 at first.When GTO-1 turn-offed, the buffer condenser of GTO-1 began to charge with motor current.Simultaneously, the buffer condenser of GTO-2 begins discharge, and in resistance R 5, the energy of consumption equals 0.5 * C * V with energy consumption ², when GTO-1 buffer condenser both end voltage one reaches DC line voltage, the electric current in buffer inductor and the random thoughts inductance just begins to reduce.At this moment, the energy that is stored in these inductance equals 0.5 * L * I ², wherein I is a motor current, all this energy or consume in resistance R 1, or with the form of overshoot voltage, temporarily transfer in the buffer condenser of GTO-1.This temporarily overcharges capacitor and has consumed in resistance R 4 soon, and in second kind of situation, inverse current is unimportant among diode current and the L1, and the energy loss in second kind of situation can be expressed from the next:

Buffering loss=(0.5 * C * V in second kind of situation ²)+

（0.5×L×I ²） （29）

C wherein, V, L make explicit provisions in front; I wherein is a motor root-mean-square value electric current.

The third situation occur in motor current on the occasion of, and GTO-1 changes in the connection from shutoff, motor current flows in diode D2 at first, but have no progeny in the GTO-1 pass, motor current flow through GTO-1 and inductor L1, first kind of situation that the similar front of this situation was narrated, it is identical to prove that at this moment buffering loss formula and the buffering of first kind of situation lost formula.

The 4th kind of situation occur in when motor current be in the negative value and the GTO-2 that connects that flows through, then, GTO-2 just is turned off, electric current stops flowing through diode D1 and inductor L1, second kind of situation that this situation was narrated before similar, it is identical to prove that buffering loss this moment formula and the buffering in second kind of situation are lost formula.

In all contingent switch circulations, energy loss in the buffer circuit of an electrode has as previously discussed, in order to try to achieve power loss, these energy losses must be multiply by the number of times that p.s., this situation took place, multiply by the number of electrode in the transverter again.In PWM and accurate six step synthesis modes, the frequency that each took place of these four kinds of situations equals half of switching frequency, therefore, in PWM and accurate six step modes, is suitable for following formula:

Transverter buffering loss=(+2 * the second kind of situation of 2 * the first kinds of situation losses

Loss) * F/2 * 3 (30)

Or represent with following formula:

Transverter buffering loss=((2 * ((C * V ²)+(0.5 *

（V ²/L）×Trr ²）））+

（2×（（0.5×C×V ²）+

（0.5×L×I ²）））×

(F)/2 ×3 （31）

F wherein is a switching frequency.

In six step synthesis modes, when motor current is timing, GTO-1 always disconnects, and when motor current when bearing, GTO-2 never connects.Therefore, first kind of situation and the third situation do not take place in six step synthesis modes.But second kind of situation and the 4th kind of situation but take place in six step modes.Its occurrence frequency equals switching frequency, i.e. the basic frequency of transverter.In addition, in six step modes, when switch carried out, motor current was high than motor root-mean-square value electric current usually, as described in calculating as above loss, motor current is at this switching point, can make it be approximately equal to 1.4 times of motor root-mean-square value electric current, therefore, in six steps synthetic in, because this situation is suitable for following buffering loss formula:

Transverter buffering loss=(2 * the second kinds of situation losses) * F * 3

（32）

Or write as

Transverter buffering loss=(2 * ((0.5 * C * V ²)+

（0.5×L×（1.4×I） ²）））

×F×3 （33）

For PWM and accurate six step modes, use an average frequency of switching that equals 400 hertz, the capacitor of one 2 microfarad equals the inductance of 9 microhenrys altogether, and the diode reverse recovery time that equals 2.5 microseconds, buffering loss formula can be simplified to following two formulas:

Transverter buffering loss (PWM and accurate six steps)=

（（1.0×10 ^-5×V ²）+（1.35×10 ^-5×I ²））×F

（34）

Transverter buffering loss (six steps)=

（（6.0×10 ^-6×V ²）+（5.3×10 ^-5×I ²）×F

（35）

Wherein, V is a DC line voltage, and I is a motor root-mean-square value electric current, and F is the transverter switching frequency, and for six step synthesis modes, F equals the transverter basic frequency.

First motor loss that will illustrate is the stator resistance loss.Therefore this loss is because motor stator has resistance, and when the motor fundamental current is flowed through stator, resistance is with regard to loss of energy, this loss by under establish an equation given:

Motor stator ohmic loss=3 * R * I ²(36)

Wherein, R is a stator resistance, and I is the motor fundamental current, represents with the root-mean-square value ampere.It is because in threephase motor that the factor 3 is added in the formula, and three windings are arranged on the stator.In fact, stator resistance raises with temperature and increases, and is measured motor temperature to compensate this variation but changes in resistance also causes in needs very much.Suppose that motor stator resistance is a constant, equal 0.0204 ohm, so the stator resistance loss is provided by following formula:

Motor stator ohmic loss=0.0612 * I ²(37)

Core losses in the motor is a magnetizing loss, magnetic flux in the motor changes along with the variation of motor sine-wave current, but because the magnetic hysteresis character of motor, when magnetic flux changes polarity chron, energy loss just takes place, when motor operates under the situation that every hertz of voltage is a constant, motor flux also remains a constant, therefore, core losses is directly proportional with the transverter fundamental frequency, utilize the data of the core losses that motor manufacturing plant provides, can derive the core losses formula of this special motors under the constant ruuning situation of every hertz of voltage, motor data shows, when motor operates in 45 hertz rated speed and 420 volts volume is routed under the line voltage condition, the core losses of motor is 1864 watts, and the core losses formula is as follows:

Core losses=1864 * (frequency inverter/45)

=4.14 * frequency inverter (38)

When motor is not to be under the constant ruuning situation of every hertz of voltage, above formula is just inapplicable, because magnetic flux no longer is a constant.Therefore, must derive another formula, wherein count the influence that motor flux changes.Following formula promptly can be used for this situation:

Core losses=1.162 * (V/F) ^1.6* F (39)

Wherein, V be motor line to line voltage, F is the fundamental frequency of transverter voltage waveform.

Spuious loss is that the motor that is not included within any other every loss of motor adds loss.A guestimate of this spuious loss shows that its size is proportional to the torque of motor.The data of the motor of using during this alternating electromotive force drags show that when torque was 768 pounds of Foot, the spuious loss of motor was 1630 watts.According to these data, can obtain a constant, with spuious loss and motor torque opening relationships, its form is as follows:

Spuious loss=C * motor torque

Or

Spuious loss/the motor torque of C=(40)

C＝1630/768＝2.12

Therefore have

Spuious loss=2.12 * motor torque (11)

Wherein, core losses is with a watt calculating, motor torque be calculate at last motor torque, be unit with pound Foot.

Harmonic losses is because the harmonic current in the motor causes, and makes the motor heat pyrexia that has a resistance.This loss is the function of Several Parameters, as the output torque of used synthesis mode, transverter fundamental frequency and motor.Derivation formula, related data and form and formula combined in order to calculate harmonic losses, these all are extremely difficult work.But a very accurate very time taking method is to use the root-mean-square value of all significant harmonics in spectrum analyzer and measuring voltage and the electric current.Spectrum analyzer can also be used to measuring the phase angle between the voltage and current of each harmonic wave.Known this three parameters, just can calculate the energy loss that each harmonic wave causes with following formula:

Harmonic power=V * I * COS(phase angle) (41)

After obtaining the power loss that each harmonic wave causes, power loss addition with all harmonic waves, just obtain the total losses that all each harmonics cause, must collect data in several running frequencies and motor torque point place, after collecting abundant information, just set up the correlationship between data, obtain the combination of table look-up form and formula with this, these forms and equation make microprocessor be calculated harmonic losses under all ruuning situation.

Another kind of much easier method is to measure the power input (being input into the power of transverter) of being defeated by whole AC drawing system, measure the motor output torque under each different running frequencies and motor load again, simultaneously also to measure other useful parameters, as motor current, motor temperature or the like.Following formula provides the loss of being left in the system, and this loss of being left equals harmonic losses approx, as long as the loss equation of deriving has rational degree of accuracy.This formula is as follows:

Loss=P-((T * the F)+loss of being left) (42)

Wherein P is a power input, T is a motor torque, F is the transverter fundamental frequency, in the formula " loss " this comprise in the system that except the rotor loss all cross the various losses of clearly stipulating at previous crops, this method of back once was used for setting up formula and the formulation form of tabling look-up, use for microprocessor, to carry out the calculating of harmonic losses in this AC drawing system.

Pectinid loss in the motor is when rotor rotation, because rotor and fan make air produce the caused loss of motion.As everyone knows, this loss is proportional to the cube of rotor speed, multiply by a proportionality constant again.This constant is to determine according to the data that motor designs teacher provides.For the motor that native system uses, the pectinid loss can be by following formulate,

Pectinid loss=599 * (revolutions per minute/1800) ³(12)

Rotations per minute wherein is the number of turns that the motor reel per minute rotates.

The friction loss of motor is when rotor rotation and since between motor reel and support friction caused.As everyone knows, this loss equals the product of rotor speed and a certain proportionality constant.Similar to the pectinid loss, this constant can be determined by the data that motor designs teacher provides.For motor used in the native system, friction loss can be by following formulate:

Friction loss=104 * (revolutions per minute/1800) (13)

Rotations per minute wherein is the number of turns that the motor reel per minute rotates.

If comprise the braking transformer in the system, the loss that transformer causes must be calculated, and calculate before being added to loss in go.If do not use the braking transformer, at this moment thyristor on the motor or primary winding one side is in on-state, thereby, then do not have electric current to flow in the control device of transformer and elementary winding one side thereof at this moment, thereby do not have power loss yet the primary short circuit in winding.But thyristor himself has a voltage drop just at the conducting motor current.Therefore, the conducting power loss is arranged in the thyristor.The average pressure drop of supposing thyristor is 1.5 volts, and each that see six thyristors again has only the half the time conduction current, and it is as follows to brake thyristor loss of conduction formula:

Braking thyratron conducting loss=1.5 * ((0.9 * I)/2)

×6＝4.05×I （14）

Wherein 1.5 is thyratron pressure drops, and I is the motor root-mean-square value electric current of representing with ampere.0.9 be that motor root-mean-square value electric current is turned to the motor average current, the 2nd, because each thyratron has only the half the time conducting, 6 then is the sum of thyratron in the braking circuit.

If the braking thyratron is not in on-state, each thyratron just turn-offs when its motor sine-wave current separately passes null value next time, when all thyratrons all turn-offed, the device of braking transformer and elementary winding one side thereof just had electric current to flow, thereby power loss is arranged.Under establish an equation, suppose that DC line voltage is 700 volts, rather than 600 volts of the nominal voltages of previous supposition.Use this more high voltage be suitable because when using the transformer braking, sizable electric current is reproduced out and returns DC line.In most of the cases, DC line is not accepted whole electric currents, and therefore, voltage will rise to above 600 volts of nominal voltages, arrives about 700 hint road voltages.

Buffering and switching losses in the braking circuit comprise the following: in the thyratron buffering course, loss, the GTO that causes owing to the charge and discharge of capacitor in the circuit connects loss, GTO turn-offs in loss, the GTO voltage buffering course, because the charging and the discharge of capacitor, in the loss and circuit diode voltage buffering course that causes owing to the increase and decrease of inductor current in the circuit in the loss that causes on the contrary, the GTO current buffering process, because the buffering that charge and discharge caused of capacitor loss in the circuit.

The generation of thyristor buffer circuit loss is because when the GTO of primary winding one side turn-offed, the capacitor in its buffer circuit was recharged the voltage that reaches 700 * 0.9 volts of plus or minus.The polarity of voltage depends on sense of current in the transformer.Once supposed in above calculating that DC circuit voltage was 700 volts, supposed also that transformer number of turns ratio was 0.9.When GTO discharged, this capacitor must be eliminated its voltage fully.The frequency that each GTO turns on and off is the twice of transverter fundamental frequency.Therefore, each buffer circuit in each primitive period, has twice charging and twice discharge at transverter.The buffer resistance device is all passed through in each charging and each discharge.Energy loss in this resistor no matter be charging or discharge cycles, all equals 1/2 * C * V ², be the capacitance of the buffer condenser represented with farad with the C in the watt-second expression; V is the change in voltage in the capacitor, equals 700 * 1.1 volt.In order to obtain the power loss in all three thyristor buffer circuits, can use following formula:

Braking thyratron buffering loss=1/2 * C * (700 * 0.9) ²

×4×F×3

F wherein is the transverter fundamental frequency of representing with hertz, the 4th, and transverter is in each primitive period, the sum of charging and discharge cycles; The 3rd, the number of thyratron buffer circuit.When capacitance is 1 microfarad, more than be formulated as following form

Braking thyratron buffering loss=2.4 * F

Braking GTO connects the calculating of loss, and the calculating of connecting loss with transverter GTO is identical.On the curve that provides from GTO manufacturing plant, learn that anode current rate of growth di/dt equals the every microsecond of 85 peaces, make IGM equal 5 amperes again, from curve, can learn that also the energy loss of each pulse is 0.16 watt-second.According to this numerical value, can derive braking GTO connection and lose as follows:

Braking GTO connects loss=0.16 * F * 2 * 3

＝0.96×F

F wherein is the transverter fundamental frequency; The number of times that each braking GTO connects in F * 2nd, per second; The 3rd, the number of braking GTO in the system.

The computing method that braking GTO turn-offs the definite of loss and transverter GTO shutoff loss are identical.But for the sake of simplicity, suppose that the average anode current that GTO turn-offs is a constant that equals 350 amperes.The numerical value that uses 350 amperes can be obtained the loss that each pulse has about 0.5 watt-second on the curve that GTO manufacturing plant provides.Utilize this numerical value, the formula that can derive following expression braking GTO shutoff loss is as follows:

Braking GTO turn-offs loss=0.5 * 2 * F * 3

＝3×F

In the following formula, F is the transverter fundamental frequency; 2 * F is each braking GTO turn-off number of times in the per second; The 3rd, the number of braking GTO in the system.

The loss of braking GTO voltage buffering is similar to the loss of transverter GTO voltage buffering.When braking GTO turn-offed, if operating voltage is 700 volts, then the capacitor in the buffer circuit was charged to 700 volts of voltages.Charging is undertaken by a diode, therefore, to the capacitor charging, does not almost have what loss.When braking GTO was connected, capacitor must pass through a conductive discharge, and this voltage is eliminated.Energy loss in the resistance equals to be stored in the gross energy in the capacitor, and this gross energy is 1/2 * C * V ²This energy be multiply by the number of times of per second inner capacitor discharge, just multiply by braking GTO switching frequency or 2 and take advantage of the transverter fundamental frequency, multiply by the number (3) of braking GTO voltage buffer circuit again, it is as follows just to obtain power loss:

Braking GTO voltage buffering loss=1/2 * C * 700 ²* 2

×F×3

Use a buffer condenser that equals 2 microfarads easily, above equation can turn to following form:

Braking GTO voltage buffering loss=2.94 * F

As transverter voltage buffer condenser, the braking buffer condenser is owing to current buffering inductor and stray inductance, and in fact charging also reaches more than 700 volts.Yet this extra loss is included in the current buffering formula.

The loss of braking circuit current buffering is similar to the loss of transverter current buffering.When braking GTO connected, the electric current in the buffer inductor increased.When braking GTO turn-offed subsequently, this electric current reduced to zero again, and energy just consumes in the buffer resistance device, disregarded to be transferred to the energy that the voltage buffer condenser goes.When current increases, the energy of storing in the inductor reaches 1/2 * L * (0.9 * I) ², wherein L is an inductance, 0.9 is transformer number of turns ratio, the motor current when I is the GTO shutoff.Electric current when therefore, 1.1 * I is shutoff in the inductor.This energy be multiply by the number of times that electric current reduces in the per second internal inductance device, promptly brake GTO switching frequency or 2 and take advantage of the transverter fundamental frequency, multiply by the number (3) of braking GTO current buffering circuit again, it is as follows just to obtain the power loss formula:

Braking GTO current buffering loss=1/2 * L * (0.9 * I ²)

×2×F×3

Because the motor current that the transformer braking causes usually is near load current value, so in above-mentioned formula, establish the motor average current and be 400 amperes when GTO turn-offs.Like this, above-mentioned formula can further be simplified.If require loss to calculate higher degree of accuracy is arranged, then can use one and the proportional electric current of motor root-mean-square value electric current, and need not 400 amperes of these constants.If the current buffering inductance is 7 milihenries, add stray inductance 3 milihenries, above-mentioned being formulated as:

Braking GTO current buffering loss=3.9 * F

The loss of circuit diode buffering is to produce like this, and when braking GTO connected, the circuit buffer condenser just charged to 700 volts of line voltage distributions: when braking GTO turn-offed, capacitor just discharge turned to 0 value with 700 volts.The buffer resistance device is all passed through in charging and discharge.Therefore, turn on and off at every turn, all produce and equal 1/2 * C * 700 ²Loss.Have such switch number of times p.s. 4 * F time.In all three-phases of braking transformer circuit, circuit diode buffering wasted power, available following formulate:

Brake line diode buffering loss=1/2 * C * 700 ²* F

×3

Buffer condenser with a capacity is 0.5 microfarad more than is formulated as:

Brake line diode buffering loss=1.47 * F

Because all bufferings and the switching losses of braking transformer lines, can both be expressed as the function that a constant multiply by the form of transverter fundamental frequency, in order to save the computing time of microprocessor, these loss formula are put together, become a composite formula.This composite formula is exactly:

Brake switch loss=14.7 * F

The circuit diode of the every phase of braking circuit, when GTO turn-offs, the conducting electric current; And when GTO connected, GTO is the conducting electric current then.The instantaneous conducting loss of circuit diode equals the product of the immediate current of the instantaneous pressure drop of device itself and break-over of device.Because what need is the average power loss, 1.2 volts of just selected average diode drops.In addition, selected again average current that flows through diode.Utilize these to simplify, the summation conducting loss of all three circuit diodes can be determined by following formula:

Braking circuit diode current flow loss=3 * ((1/1.1) *

(0.9 * I)) * 1.2 * angle/180

Wherein, the 1.1st, transformer number of turns ratio; I is the root-mean-square value of motor current; 0.9 the root-mean-square value of motor current is turned to motor current mean value; 1/1.1 motor current mean value is turned to diode current mean value; 1.2 be the diode average pressure drop; Angle in the following formula is shown with kilsyth basalt; The angle representative is in per 180 degree, and braking GTO turn-offs shared angle; Angle/180 ° are diode current flow time shared percent in T.T..

It is definite that available similar approach is lost in braking GTO conducting, uses 1.8 volts as average GTO pressure drops.So it is as follows to obtain this loss formula:

Braking GTO conducting loss=3 * ((1/1.1) *

（0.9×I））×1.8×（180

-angle)/180

In this formula, original angle/180 have been replaced with (180-angle)/180, in order that represent the time percent that the GTO ON time is shared with the former.

Carefully have a look circuit diode and GTO conducting loss formula: if the pressure drop of these two devices is the same, then the conducting altogether of all circuit diodes and GTO loss just can turn to following formula in the braking circuit:

Braking conducting loss=3 * ((1/1.1) * (0.9 * I))

* voltage drop

This simple formula is greatly simplified two other formula of branch.Voltage drop in the formula is taken as 1.6 volts, and this is because diode drop is 1.2 volts and the pressure drop of GTO is 1.8 volts a cause.Selecting 1.6 volts and do not select 1.5 volts of actual mean value, is because under normal circumstances, and the GTO ON time is occupied bigger time percent than the diode current flow time.In this above formula of pressure drop substitution of 1.6 volts, this formula just turns to:

Braking conducting loss=3.9 * I

Diode in full wave bridge rectifier itself also has the conducting loss.No matter how GTO works, total two diodes at the conducting electric current.The pressure drop of supposing these diodes is 1.2 volts, and diode bridge conducting loss is provided by following formula in all three-phases:

Braking bridge circuit loss=3 * ((1/1.1) * (0.9 *

I））×1.2×2

Wherein, (1/1.1) * (0.9 * I) is the average current by diode; I is the root-mean-square value of motor current; 1.2 be pressure drop by a diode; 2 expressions all have two diodes at any time in conducting.This formula can be simplified to following formula:

Braking bridge circuit loss=5.9 * I

The transformer ohmic loss is I ²* R, wherein I is motor current or Secondary Winding electric current; R is the transformer all-in resistance, and this all-in resistance comprises primary winding resistance and Secondary Winding resistance.The elementary winding resistance here equal actual elementary winding resistance multiply by the number of turns than 0.9 square, to convert Secondary Winding one side.Suppose that the transformer temperature is 130 degree Celsius, transformer resistance is about 0.08 ohm.This numerical value changes with temperature, but in most of the cases, this variation can be ignored.The formula of calculating transformer ohmic loss is as follows:

Braking transformer ohmic loss=0.08 * I ²

Wherein I is the root-mean-square value of motor current.

The core losses of transformer is that core losses is relevant with following Several Factors because the magnetic flux in the iron core constantly changes causes, promptly frequency, determine the magnetic flux density maximal value of excitation voltage, the shape of excitatory waveform, and the structure of transformer.The core losses formula of transformer used herein is as follows:

The loss of braking transformer core=

307×10 ^{（0.4345×V/F-1.272）}

Wherein, V is the root-mean-square value of transformer outlet end line to voltage between lines; F is the transverter fundamental frequency.

When frequency was very low, loss can account for the over half of system's general power.At this moment, in order to use this formula of (power input-loss)/frequency, (being formula I) comes calculating torque.In the hope of realizing the torque accurate Calculation of any kind, just need set up a very accurate loss model.In order to avoid this problem, develop one and overlap the form of tabling look-up, in order to set up the relation between torque and power input and the frequency.Also have a kind of different form of tabling look-up, take from zero to 15 every one hertz the pairing numerical value of velocity gauge frequency for looking into.Wherein each form is represented all is relation between torque and the power input.In the frequency range below being about 45 hertz basic rotating speed, for all rotating speeds and load condition, what add to motor all is identical voltage.Between motor torque and power input, exist a definite relation, just, when motor torque increased, power input also increased thereupon.Therefore, for calculating torque, just calculate power input simply, and utilize this torque/power relation to try to achieve answer.This method is still feasible actually.Use loss model to calculate these torque/power relations.This calculating off line under every kind of rotating speed is separately and exclusively carried out.Result calculated is weaved into the form of tabling look-up, for microprocessor online use when the calculating torque.

When frequency is higher, more be suitable for and adopt online loss computing method of carrying out, because this method has greater flexibility, as always do not require and under every hertz of constant voltage, move.When more than basic rotating speed, moving, this under the constant situation of every hertz of voltage operation be do less than, use also unusual difficulty of look-up table, because if think such work, microprocessor just must be made compensation to voltage difference, and this compensation is very difficult.

Though look-up table can carry out the torque calculation under the low frequency operating mode, and the online loss model computing rule that carries out can not, but,, in fact be difficult to carry out the calculating of retarding torque with any method according to read-only power input for the low-down frequency that is lower than 10 hertz.When operating in these low-down frequencies, the certain functional relation that do not existed between torque and the power input can be for the usefulness of calculating retarding torque.Under low like this frequency, do running under braking if wish motor,, can use a kind of Motor Control of open loop type owing to there is the difficulty of said determination torque.

The explanation of used numbering in the accompanying drawing

The event identification figure number

Direct supply 10 1

Power supply 10 2

Direct supply 10 3

Transverter 12 1

Transverter 12 3

AC motor 14 1

Three-phase current motor 14 3

Load 16 1

Load 16 3

Torque sensor 18 1

Motor controller 20 1

Power controller 26 1

Power controller 26 3

Limiter 32 3

Impulsion limiter 34 1

Impulsion limiter 34 3

The torque feedback determines 38 3

Velocity gauge 54 3

Motor controller 62 3

Transverter and braking synthetic 76 3

Clamping device 80 3

Calculate power=line voltage * line current 100 4A

Be used for last WAS torque-power meter 102 4A that calculate of torque

The velocity gauge frequency is greater than 14.5 hertz of 104 4A

Velocity gauge frequency≤12 hertz 106 4A

Look-up table 108 4A

Look-up table 108 5A

Loss method 109 4A

Operation instruction 110 4A of torque calculation loss method

Motor current=F(slippage) * the motor end points

The motor terminal of design when total voltage * V/F is constant

Point voltage F(slippage) is form 112 4A that table look-up

Conducting loss=4.05 * motor current 114 4A

Switching losses in PWM or the accurate six step modes=

312+1.2 * switch motor current

Electric current * frequency inverter 116 4A

Buffering loss in PWM or the accurate six step modes=

〔（1.0×10 ^-5×V ²）+

（1.35×10 ^-5×I ²）〕×F

Buffering loss=((6.0 * 10 in the six step modes ^-6

×V ²）+（5.3×10 ^-5×I ²）〕×F 118 4A

Inverter losses=conducting loss+switch

Loss+buffering loss 120 4B

Stator resistance loss=3 * stator resistance *

(motor current) ²122 4B

The constant scope inner iron core loss of V/F=

1864 * frequency inverter/45

Iron core more than the constant scope of V/F

Loss=1.162 * (

(motor voltage)/(frequency inverter)) ^1.6* frequency inverter 124 4B

Spuious loss=2.12 * torque, 126 4B

Harmonic losses=basis records in the system humorous

The ripple loss also is stored in three numbers in the form

According to 128 4B

Motor loss=stator resistance loss+

Core losses+spuious loss+harmonic losses 130 4B

The loss of pectinid loss=axle fan+

Rotor pectinid loss=599 *

((rotations per minute)/1800) ³132 4B

Switching losses=14.7 * frequency inverter, 133 4C

Friction loss=104 *

((revolutions per minute)/1800) 134 4B

Conducting loss=3.9 * motor current 135 4C

Friction and pectinid loss=friction loss+pectinid

Lose 136 4B

Bridge circuit loss=5.9 * motor current 137 4C

The braking transformer is by short circuit 138 4C

Transformer ohmic loss=0.08 *

(motor current) ²139 4C

Brake loss=4.05 * motor current, 140 4C

Transformer core loss=307 *

((0.4345 * (transformer voltage)/(frequency inverter))-1.272) 141 4C

10

Brake loss=switching losses+conducting loss+bridge

Path loss mistake+transformer ohmic loss+transformer fe

The heart loses 142 4C

Power loss=motor loss+friction loss

+ brake loss+inverter losses 144 4D

Corrected output=calculate power-power loss 146 4D

TEF=(corrected output)/(frequency inverter) 148 4D

Overflow 150 4D

Torque is negative 152 4D

TEF is fixed on maximum positive torque 154 4D

TEF is fixed on maximum negative torque 156 4D

The look-up table operation instruction

Calculating torque 160 5A

Velocity gauge frequency＜0 162 5A

The TEF=((nominal torque)/(rated slip)) 164 5A

* design slippage

TERJ＜0 166 5A

Retarding torque can calculate the time,

Velocity gauge＜minimum frequency 168 5A

A=velocity gauge frequency, 1 byte=1/64

Hertz 170 5B

B=integer (A/64)=table number 172 5B

C=from first show to gauge outfit interval apart from=

32×B 174 5B

D=first table is gone up address+C 176 5B most

Call in torque calculation table 178 5B

E=torque low value=rreturn value 180 5B

The next table of F=D+32=go up address 182 5B most

Call in torque calculation table 184 5B

High value=rreturn value 186 5B of G=torque

Torque slope=G-E 188 5B

H＝B×64 190 5B

I=rotating speed surplus=velocity gauge frequency-H 192 5B

J=total torque surplus=(torque slope *

I）2 ⁶194 5B

TEF=calculate torque=E+J 196 5B

L=calculate the table of the power proportions factor=at last

List 200 5C

Ratio power=M

(table that rated output is used)/(8 * scale factor L) 202 5C

N=to the interval of showing mid point apart from=

M×2 ^-8204 5C

N 14 206 5C

N＝14 208 5C

N -15 210 5C

N＝-15 212 5C

P=(is (15+N+ goes up table address most)

The tabulated value at place) * 2 ⁶214 5C

P=(is on (the last table of 15+N+1+ ground

The location) tabulated value of locating) * 2 ⁶216 5C

Q=torque slope=P-R 218 5C

Torque margin=((M-(N * 2 ⁸))

×Q〕×2 ^-8220 5C

TEF=rreturn value=R+ torque margin 222 5C

Claims (4)

1, a kind of method of definite AC motor output torque, this AC motor determines that by a transverter supply of electrical energy that is subjected to DC power supply the step of torque comprises:

Be defeated by the DC voltage and the electric current of motor according to power supply, determine the power input of this motor;

With a velocity gauge that output frequency is arranged, the rotational speed of motor sensor;

According to a mathematical model of motor, set up the relation of electromotor velocity and output torque, when velocity gauge frequency during,, determine that motor exports torque according to above-mentioned speed and torque relation greater than first preset frequency;

When the velocity gauge frequency is lower than above-mentioned first preset frequency, utilize the form of prefabricated definite motor speed and output torque relation, to determine the output torque of motor.

2, determine the method for motor output torque according to claim 1, wherein be higher than above-mentioned first when deciding frequency when the velocity gauge frequency, comprising: with the motor current is foundation, sets up the calculating of inverter losses; With the frequency inverter is foundation, sets up the calculating of motor loss; With the electromotor velocity is foundation, sets up the calculating of friction pectinid loss.

3, the method for claim 1, wherein calculating motor output torque comprises: with above-mentioned model is foundation, calculates each power loss sum in transverter and the motor; With calculate the power loss sum from the power input of motor, reduce, to determine the output torque of motor.

4, determine the method for output torque according to claim 1, wherein when the velocity gauge frequency is lower than above-mentioned preset frequency, comprise and work out the corresponding numerical value tables of several torques with power, the corresponding motor predetermined speed that is different from other forms of each form, and provide the motor output torque of respective motor power input value.

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