FR2522901A1 - ALTERNATE CURRENT MOTOR CONTROL SYSTEM CURRENT CONTROL PULSE WIDTH MODULE - Google Patents

Abstract

MOTOR CONTROL SYSTEM FOR REGULATING THE SPEED AND TORQUE OF AN ALTERNATIVE CURRENT MOTOR. IT INCLUDES AN INVERTER 24 CURRENT CONTROL MODULE IN PULSE WIDTH, A FIRST CONTROL LOOP 30 WHICH MAINTAINS THE VALUE OF THE VOLTAGE AT THE MOTOR TERMINALS Whatever the variations in load conditions and a second control loop 58 to stabilize THE MOTOR FREQUENCY. APPLICATIONS TO ALTERNATIVE CURRENT MACHINES.

Description

The present invention relates to

  control of AC machines, and more particularly

  specifically to current machine control systems

  rectifier comprising a current-controlled inverter.

  In applications of AC machines where it is desired to have a control of the

  speed and torque of the machine, systems are used

  In general, a system with

  Inverter control system comprises a variable frequency DC / AC inverter fed by a DC power source, supplying variable frequency current to a synchronous or induction AC machine. Such inverters most often have a DC power supply. multi-pair configuration

  switching devices, switching devices

  each pair being connected in series and each pair of series-coupled switching devices connected to a DC power source Connected to the junction of each series-coupled switching device a respective phase of the machine Alternating current is supplied

  by the inverter to the machine when the devices of

  mutation of each pair are alternately and successively

made conductive.

  The object of the present invention is to provide a simplified control system which can be used in applications requiring speed control.

  but does not require precise torque regulation.

  Another object of the present invention is

  the realization of a control system which makes it possible

  maintain an engine operation in the presence of a cyclic load more stable than that which one usually has

  in open loop operation with a common inverter

sent in tension.

  The present invention, in a first form, provides interposable motor control between a source of electrical power and the stator of an AC motor. The motor control comprises a current-controlled inverter comprising current regulators.

  which compare sinewave reference waves produced

  by a wave generator at a real line current

  corresponding motor to produce error signals.

  These error signals are compared to a hysteresis band and pulse-width modulated signals are sent.

  the inverter to maintain error signals in the

  hysterisis band A first control loop maintains the value of the voltage at the motor terminals regardless of the variations of the conditions

  The flow of the motor is determined in the first

  control loop by integrating the detected voltage at the output of the inverter The motor flow is rectified and compared with a reference flow that can be constant, if it is desired to operate with a constant voltage / frequency ratio to obtain an error signal The error signal is amplified and used to control

the current input of the inverter.

  In another embodiment of the present invention,

  addition, a second control loop can be added.

  To stabilize the motor frequency The active component of the motor line current is determined and increases in this active component cause short reductions in the frequency of the inverter.

  allows the stabilization of the motor rotor in case of

pumping.

  The following description refers to

  annexed figures which respectively represent:

  Figure 1, a representation partly sketchy

  partly functional, of the present invention; FIG. 2, a phase diagram showing the relation between the line voltages with respect to the neutral and the air gap flux of the motor; and FIG. 3, the wave diagrams of the input and output signals of the synchronous rectifier of the

figure 1.

  Figure 1 depicts a motor control to

  alternating current An inverter controlled by current

  Modulated pulse generator 8 comprises a wave generator supplying to each of the three current regulators 12, 14 and 16 reference sinusoidal signals, these reference signals being in three-phase relationship with each other. the frequency of the three sinusoidal signals generated by the wave generator varies according to a frequency control signal

  and an amplitude control signal applied to the gen-

  Wave regulator The current regulators 12, 14 and 16, in addition to the inputs connected to the wave generator, each have an input connected to the current sensors 18, 20 and 22, which are themselves connected to the output of the transmitter. inverter 24 Current regulators provide modulated pulse width signals to the inverter 24 DC source 26 supplies power to the inverter The output of the inverter consisting of three lines A, B and C is connected

  to winding the motor stator 28.

  A first control loop 30 has a differential amplification device 32 comprising a resistor 34 connected to the negative input terminal of an amplifier 36 and a resistor 38 connected to the positive terminal of this amplifier. The line voltage A is applied to the resistor 34 and the line voltage B to the resistor 38 A resistor 40 is connected between the positive terminal of the amplifier 36 and the ground A feedback resistor 41 is connected between the output of the amplifier 36 and the terminal negative entry of this

amplifier 36.

  The output signal of the different amplifier

  which is equal to the difference between the voltages of

  line A and B is applied to the input of integrator 42.

  The integrator 42 comprises a resistor 44 connected to its input. The other end of the resistor 44 is connected to an amplifier 46. A reaction resistor 48 and a reaction capacitor 50 are connected between the input and the output of the amplifier. 46 we pass the signal

  of the integrator through a redundant device

  52 and the resulting output signal is applied to the negative input terminal of a summing junction 54 A flow reference signal T * is applied to the positive input terminal of the summing junction 54 The output of the summing junction is connected to a flux regulator 56 whose output is connected

  at the amplitude control input of the wave generator 10.

  A second control loop 58 receives the line voltage C at an input of a disconnector-inverter 62. The other input of the disconnector-inverter 62 is applied to the line voltage C inverted by the signal inverter 64. the integrator 42 is connected to the positive input terminal of a comparator 66 whose terminal

  Negative input is grounded The output of the

  Controller 66 controls inverter switch 62 The synchronously rectified output signal of inverter switch 62 is passed through a smoothing low-pass filter 68 which itself is connected to a circuit 70 having a transfer function. ws / (s +) that makes disappear

  the steady-state value of the output signal of the

  smoothing and passing only transient variations A unity gain amplifier has a

  resistance 72 of value R connected to the input of the ampli-

  A resistor 74 of the same value R is connected between the input and the output of the amplifier 73. It is connected in series with the resistor 72 at the input of

  the gain amplifier unit a capacitor 71

  A further embodiment of the transfer function could be a capacitor in series with a grounded resistor, the output is connected to the negative input terminal of a summing junction 76.

  then finding between the resistor and the capacitor.

  The positive input of the summing junction 76 receives a command frequency F * controlled by an operator The error signal is applied to the control input of

  frequency of the wave generator 10.

  The operation of the circuit of FIG. 1 will now be described. The wave generator 10 supplies a reference sinusoidal signal to each current regulator 12, 14 and 16. These sinusoidal signals are in three-phase relationship with each other. the reference signal supplied to each current regulator to a corresponding motor line current signal to obtain an error signal The error signal is then applied to a comparator (not shown) located in the current regulator, and when this error signal is found out of a predetermined band of hysteresis on both sides

  of this band, logic signals "1" and "-l" are emitted.

  The logic pulse train "1" and "-1" of each current regulator form the pulse width modulated switching signals for the respective phases of the inverter. The inverter switching signals are applied to a single pulse. trigger circuit which controls the pairs of switches of the inverter, each pair being associated with a phase of the motor A logic signal "1", for example, associated with a pair of

  the inverter, close the upper switch, open the

  controller and connects the DC power source to the corresponding phase of the motor A logic signal "-l" of the same current regulator closes the lower switch,

  opens the upper switch and connects the power source

  continuously in reverse polarity at the phase of

  The repeated switching of the three pairs of switching

  inverter results in the supply of three-phase power to the motor, with the current supplied to each phase

  maintained within the predetermined hysterisis band

  For further details regarding

  regarding the operation of the inverter it can be referred to

  United States Patent Application No. 080479, entitled: "Current-controlled Pulse Width Modulation Inverter Control System".

  transistorized "and of which a brief description will be found

  below: it is an AC machine control system, comprising an AC machine and an inverter whose configuration comprises several pairs of transistors with the transistors of

  each pair coupled in series and each pair of

  in series coupled to a power source

  continued; this system is controlled by the current of the

  The transistors of each pair of transistors are

  tors of the inverter alternately conductors for furnace

  alternating current at the output of the inverter

  conformity with a current error signal, proportion-

  the difference in magnitude between a real phase current of the inverter and a reference sinusoidal signal, with inversion of the conduction state of the transistors of each pair whenever the error signal of the current exceeds a lower limit or higher hysterisis,

  these limits vary according to the actual phase current of the on-

  To control the speed and torque of the machine,

  the output voltage of the inverter is

  respectively, variations in amplitude and frequency of the sinusoidal reference signal according to the instructions of the operator. Control operation is obtained.

  the inverter by regulating the amplitude and frequency of

  quence of the reference sinusoidal signal according to a signal

  torque reaction of the machine and a reaction signal

flow of the machine.

  According to the present invention described in FIG. 1, the first control loop 30 controls the voltage of the lines A and B. The differential amplifier 32 gives the

  difference B-A and integrator 42 incorporates this difference.

  In addition, the integrator 42 suppresses the hash ripple and much of the noise present in the circuit. The variable flow signal AB is rectified, filtered and compared to a set flow level Y *. resulting error signal is applied to a flow controller that provides minimum and maximum amplitude level output values with a gain between these two limits The minimum level value prevents zero flow operation (if using a motor induction) and the maximum limit is necessary

  to avoid overcurrent at the output of the inverter.

  The output signal of the flux regulator is used to control the input amplitude signal of the wave generator which in turn controls the inverter current. If the setpoint flow Y * is constant then an operation with a first order constant voltage / frequency ratio can be obtained.

  engine is increased and the engine is powered with a

  constant, the motor voltage drops This decreased voltage is detected by the first control loop

  which increases the amplitude of the motor current to compensate

  and restore tension to its previous value Egale-

  When the frequency varies, the integrator of the

  control key automatically compensates for variations

  frequency since the voltage must increase linearly

  with the speed The operation of the inverter

  with the first control loop has characteristics

  similar to those of a converter system of

  open-loop voltage while maintaining the characteristics

  inherent in a pulse-modulated pulse system.

  current-controlled generator ie variation of the width of the switching pulses of the inverter to maintain the residual current at a low level and thereby reduce the losses of the motor The control circuit operates on any three-phase motor simply by connecting the output terminals of the inverter to the terminals of the motor stator You can also use the inverter

  pulse width modulation with the first

  control key as a three-phase voltage source

  constant when used as a source of cou-

  rant, the flow integrator will have a unity gain and the

  time aunt of the integrator 42 will be relatively more

  large that the time constant in operation in cir-

Cooked order.

  The second control loop 58 operates to stabilize the motor in case of oscillations of the rotor

  or oscillations of pumping The oscillations of the rotor pro-

  come from the harmonics present at the output of the ondu-

  which causes oscillations in the torque, which is a problem especially at low speeds For a motor designed for 60 Hz, for example, the motor speed pulses are the most sensitive for an applied frequency of 10> Hz The second control loop 58 determines the

  active component of the motor stator current in application

  the total stator current of the line at one of the two input terminals of a disconnector-inverter 62 and applying the inverted current of the line C to the other input terminal The position of the disconnector 62 is determined by the comparator 66 which controls the zero crossings

  B-A flow in phase with the line current.

  For the proper operation of the synchronous inverter 62, it is necessary to have a signal that is in phase

  with the line voltage C of the motor By referring

  FIG. 2 showing the phase relationships between the voltages and the air gap flux of the motor, it can be seen that the difference between the line voltage A (taken with respect to the neutral) and the line voltage B ( taken with respect to the neutral) results in a line voltage of AB The voltage BA is out of phase with the voltage C The flux due to the voltage AB is in phase with the phase voltage C and with the active component the line current of phase C. The flow AB is determined by the signal of

  output of the integrator 42 of the first control loop

  When the flow A-B is positive, the disconnector 62

  pass the line current, when the flow is nega-

  tif, the disconnector 62 passes the line current

  negative of the signal inverter 64 Figure 3 shows

  the different waves involved in the

  3A represents the comparator flux signal, and FIG. 3B shows a current in phase with the voltage (in an induction motor generally the current is phase shifted by 300 with respect to the voltage at full load). means that the entire current is an active current FIG. 3C represents the output signal of the disconnector 62 operating as a rectifier

  synchronous when the conditions described in Figure 3B prevail

  FIG. 1D shows the current wave for a zero load with a phase shift of 900 of the current with respect to the voltage. The current of FIG. 3D has no active component. FIG. 3E represents the output signal. of the disconnector operating as a rectifier

  synchronous when the conditions described in Figure 3 D dominate.

  In actual operation the current is not a pure sinusoid but includes harmonics that reduce

  the accuracy of the determinations of the active current Cepen-

  When the active component of the current is measured in this way, the accuracy is sufficient to obtain the stabilization. The output signal of the disconnector 62 is sent through a smoothing filter. The resulting waveform (FIG. 3B) is a much stronger signal. large at the output of the smoothing filter that the wave of Figure 3 E The active current is then applied to a unity gain amplifier having a transfer function ws / (s + w) where S is a complex variable of the transform from La Place and w

  a function of the frequency of the wave applied to the

  The characteristic of the transmission function

  It is necessary to suppress the DC component and to match increases in the input active current of the transfer function with abrupt and momentary variations of the output signal of the transfer function. The output of the circuit 70 is connected to act. as a counter-reaction to the frequency control signal When the current increases because the load increases under the effect of the first control loop, the second control loop detects the increase in

  the active component of the current and gives a brief impulse

  momentarily decreases the frequency of the wave generator's control By lowering the generator's input frequency, the rotor speed is reduced briefly and by a small amount, thus preventing the motor from immediately reaching the torque. Briefly lowering the frequency when the load increases acts like a

  counter-reaction stabilizing the rotor in case of oscilla-

pumping arrangements.

Claims (4)

  An interposable motor control between an electric power source (26) and the stator of a polyphase AC motor (28) for controlling the speed and torque of the motor, characterized in that it comprises:   an inverter (24) controlled by current   a wave generator (10) which provides polyphase reference signals varying in frequency and frequency.   amplitude in response to amplifier control signals   study and frequency respectively, ways of reacting   (18,20,22) to make proportional signals   at each line current of the motor and the regulating means   current (12, 14, 16) to compare each reference signal of the wave generator (10) with the corresponding line current signal from the feedback means (18, 20, 22), thereby obtaining a signal of 'fault   and the current regulator means (12, 14, 16) comprises   also providing means for comparing each error signal with a hysterisis band to provide pulse width modulated signals to the inverter (24) so that these error signals remain within the band of 'hysteresis; and a first control loop (30) for maintaining the value of the stator voltage of the motor (28)   during load variations comprising a means of inte-   grating (42) to provide a signal proportional to the motor flux (28) due to the output voltage of the inverter (24), a rectifying means (52) for rectifying this signal, a summing means (54) for determine the   difference between the output signal of the means of   (52) and a set-point flow signal to provide an error signal, and flow control means (56) providing a gain to the flow error signal, which signal is applied to the input of the input signal. amplitude control of the wave generator (10).   2 Motor control according to claim 1, characterized in that it comprises: a second control loop (58) for stabilizing the frequency of the rotor comprising a means (66) for determining the active component of the current, a means (70) ) to provide a brief output pulse in response to an increase in the active component of the   motor current, a summing means (76) for determining   undermine the difference between the output signal of the medium   (70) providing a brief pulse and a frequency signal.   setpoint, this difference signal being applied   to the frequency control input of the generator of on- (10).   3 Control according to claim 1, characterized   in that it comprises: a second control loop (58) for stabilizing the motor frequency including rectifying means (62) for rectifying a third output current of the inverter (24) which is in synchronism with the zeroing the flux produced by the difference between the first and second output voltages of the inverter (24), a smoothing filter (68) for smoothing the output signal of the synchronous rectifying means (62); and means (70) for providing a brief pulse in response to an increase of the active component of the third output of the inverter (24), which pulse acts as a feedback signal on frequency control.   Motor control according to claim 2 or 3, characterized in that the means (70) for providing a short pulse comprises a unity gain operational amplifier (73) and a capacitor (71) in series with the   input terminal of the amplifier (73).