Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
  • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
  • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
  • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
  • H02P23/0077—Characterised by the use of a particular software algorithm

Definitions

• the invention relates the control of an AC motor via a simple means with respect to both frequency and voltage.
• Utilisation of a microprocessor allows for optimization of the motor controller to the motor and load, thereby developing a simple, efficient drive system.
• AC motor speed controllers inverters, drives
• l*-* limiting the widespread use of such a product.
• the invention disclosed herein is an AC Motor Speed Controller, that provides total control over the output characteristics of the AC motor by the control of frequency and voltage to the said motor at, below, or above it nominal ratings.
• the invention provides the ability to control Speed of said motor throughout the application of frequency applied to the motor as demanded by the controlling function.
• the invention allows the voltage to be controlled to the motor which develops Torque.
• the combination of Speed and Torque determines Horsepower.
• individual control of both frequency and voltage which can be preprogrammed, it allows for characterization of the output Volts-per-Hertz curve to the motor (output of the controller) thereby providing effective control of the Speed, Torque and Horsepower developed by the motor.
• Such control can be predetermined and preset or controlled by changing load conditions if the controller is programmed to do such.
• the controller consists of two basic sections, the Power Section and the Logic Section.
• the Power Section's function is to handle all of the main power utilized by the Motor (00) itself.
• This consists of a Power Rectifier (20), Filter Capacitor(s) (10-23) and three Phase Modules (40,50,60).
• This allows for the incoming single or three phase AC to be rectified to DC and filtered. If operated off of a straight DC source, such as battery pack, direct connection to the Phase Modules would occur.
• the Phase Modules, at the direction and control of the Logic Section then output and convert the DC to Variable Frequency and Variable Voltage (through the use of a Pulse Width Modulation Technique [PWM]) which is then outputed to the Motor (00) for control.
• Dynamic Braking (80) is automatically introduced on a scaled level under a controlled deceleration.
• the Logic Section (30) controls the Power Section based on desired operating Speed, Current Feedback, and Voltage Feedback signals and predetermined preprogrammed requirements.
• the Logic Section consists of the following: the Microprocessor (30-7) which is preprogrammed and active throughout the controlling function, monitoring external functions such as Current, Voltage, and Speed command signals to output the appropriate signals to the driver circuits which in turn drive the three Phase Modules
• voltage Feedback circuit (90) monitors output voltage and outputs a voltage that is proportional to the output current of the Inverter to the motor.
• the Electronic Fault Protector circuit (70) monitors currents in and out of the DC buss, incoming line conditions and buss voltage conditions and “shuts down" the Microprocessor (30-7) and Drivers (30-13) to the Phase Modules (40,50,60) when preset trip levels are exceeded.
• the overall controller provides a very simple and controllable means for determining the Speed, Torque and Horsepower output characteristic of the controlling AC motor.
• Phase driver 40,50,60 schematic Dynamic braking schematic
• FIG. 1 details out the Block Diagram and Schematic of the AC Motor Speed Controller.
• Incoming power consisting of single phase or three phase AC, 115 V, 208 V, or 380 V, enters into the Power Rectifier 20.
• a pre-charge is applied to Filter Capacitor 10-2 while the main DC Buss 10-12 (+) and 10-11 (-) are applied to Phase drivers 40,50,60.
• Phase Drivers at the control and direction of Logic/Driver 30 control the Motor ( 00) .
• the Phase Drivers apply the Frequency and Voltage to the AC Motor 00, thereby controlling Speed, Torque, and Horsepower.
• Dynamic Braking Module 80 also under the control and direction of the Logic/Driver 30 absorbs the regenerative energy from the Motor 00 during deceleration.
• Base Drive Transformer 10-1 is the AC power supply for the low voltage DC power supplies in the Power Rectifier 20 and the Logic/Driver 30.
• Sensing Devices 10-6 and 10-7 monitor the forward and regenerative current in the main DC buss 10-11/10-12 which are fed back into the Logic/Driver 30.
• the Logic/Driver 30 is controlled via operator commands.
• the Forward/Reverse 10-5, Master Speed Potentiometer 10-4 and Start/Stop/Reset 10-3 are manual control inputs while serial link 10-27 represents an external computer command link.
• Figure 2 represents the Power Rectifier Block 20. It consists of four or six diodes (for single or three phase input power) 20-1 through 20-6 which are wired in a full bridge rectifier configuration. Resistor 20-7 acts as a
• Diode 20-18 is a flyback diode to clamp the inductive energy of relay coil Kl during turn off.
• Resistor 20-15 is a base clamp resistor. Diodes 20-11 and
• Figure 3 represents the Logic/Driver 30 section which handles all of the signal commands to run the Motor 00 based on operator commands and Motor 00 load conditions, it is the unit which determines operating Frequency (Speed), Output Voltage (Torque) and Horsepower. In addition, it protects the AC Motor Controller from overload and fault conditions.
• the main controlling element of the Logic/Driver 30 is the Microprocessor 30-7 which has four analog inputs (30-33,
• Microprocessor 30-7 The operating and control elements of the Microprocessor 30-7 are further defined in Section B (Software) that follows.
• the six main output lines 30-44 control the Phase Drivers 40, 50, and 60, via buffer device 30-13 and the six output transistors 30-26 through 30-13.
• Resistor bank 30-31 acts as a pull up device- while resistors 30-14 through 30-19 act to limit base drive to the output transistors.
• Resistors 30-20 through 30-25 are base clamp resistors.
• Switches 30-10 and 30-11 are operator selectable to determine low frequency Voltage Boost settings. Resistors 30-8 and 30-9 act as pull down devices. Low frequency Boost is used to increase voltage applied to Motor 00 at low frequencies (12 Hz and below) which increase Motor 00 load, friction of the mechanical system and resistivity components of the Motor 00. The amount of Voltage Boost for a given Frequency and Switch combination (30-10 and 30-11) is predetermined and software controlled.
• the four Analog controlling input signals to the Microprocessor 30-7 are as follows: 1) Speed command signal 30-42 which determines the operating speed (frequency) to the Motor 00 (maximum operating speed is software controlled); 2) Acceleration/Deceleration signal 30-43 as determined by operator adjustable potentiometer 30-12 set the rates at which the output frequency to the Motor 00 changes as the speed command 30-42 varies; 3) Voltage Feedback signal 30-33 feeds back an analog signal proportional to the actual output voltage to the motor 70;
• Start/Stop/Reset command signal is given by operator control push button 10-3 inputting a digital signal 20-41 into the Microprocessor 30-7.
• 30-2 is a pull up resistor.
• Signal 30-41 is also used to reset Fault Protector 70.
• Forward/Reverse command signal is given by operator control switch 10-5 inputting signal 30-45 into microprocessor 30-7.
• Resistor 30-3 acts as a pull up resistor.
• Dynamic braking signal is generated out of the Microprocessor 30-7 via current limiting resistor 30-46 turning on transistor 30-48. 30-47 is acting as a base clamp resistor.
• the Dynamic Braking signal is a pulse width modulated (PWM) signal, where a high (or 1 equiv.) turns on transistor 30-48 causing the Dynamic Braking section 80 to turn on, absorbing energy from the main buss 10-11/10-12.
• PWM pulse width modulated
• the Dynamic Braking provides a constant torque braking and therefore the PWM duty cycle is predetermined and proportional to the selected deceleration rate. The faster the rate of deceleration the larger the duty cycle (percentage of high output over the entire period) and therefore the greater the absorbed energy via section 80. The slower the rate of deceleration would result in a smaller duty cycle.
• the Reset line 30-39 enables (if high) or disables (if low) the Microprocessor 30-7.
• a charge current is generated from the Microprocessor 30-7 into line 30-39 charging capacitor 30-5 via diode 30-6.
• Microprocessor 30-7 Upon reaching a full charge level.
• Microprocessor 30-7 begins operation. Should a faujt occur via an overload detected by t._e Electronic Fault Protector 70, line 30-39 goes immediately to zero.
• Diode 30-6 acts as a blocking diode so that the charge on capacitor 30-5 does not slow down the zero going signal from the Fault protector 70. This allows the Microprocessor 30-7 to immediately shut down.
• resistor 30-4 discharges capacitor 30-5.
• Voltage comparitor 30-35 is used as a latch device upon initial power up.
• Line 30-37 is a fixed voltage reference to comparitor 30-35.
• Logic/Drive 30 line 30-49 is high. Approximately two seconds later 30-49 goes low causing the output of the voltage comparitor 30-35 to go low latching up, via feedback, to the non-inverting input of 30-35.
• Output signal 30-36 is then sent to the Power Rectifier 20.
• Figure 4 represents the Phase Drivers 40, 50 and 60. All three Phase Drivers are identical with the exception of resistors 40-9 and 40-10 which generate a voltage feedback signal off of Phase Drive 40 and 50 via line 10-9 or 10-10. These two signals feedback to Logic/Driver 30 (Voltage Feedback section 90) to generate an error signal which represents the output voltage applied to Motor 00.
• Logic/Driver 30 Voltage Feedback section 90
• the Phase Drivers operate as follows: Two input signals generated from the Logic/Driver 30 enter in via lines 10-17, 10-18, and 10-19 for the negative Pulse Width Modulation (PWM) drive and 10-20, 10-21, and 10-22 lines for the Positive Toggle drive.
• PWM Pulse Width Modulation
• the Logic/Drive 30 will cause a particular Phase Module to change state.
• the Logic/Driver 30 would remove the negative PWM drive (10-17, 10-18 or 10-19) wait a short period (approximately 150 microseconds) and then apply a Positive Toggle drive (low) (Ref. Fig. 10). When this occurs the high voltage PNP transistor 40-7 turns on into saturation via base drive resistor 40-5, turning on its paired Darlington Power
• Transistor 40-14 Resistors 40-6 and 40-8 act as base clamp resistors. Diode 40-12 is used to block any regenerative energy flowing from Motor 00 when transistor 40-15 is turned off. This forces the inductive energy through fast recovery diode 40-13. This allows for the operation of transistor 40-14 without negative base drive. Snubbing device may be necessary across transistors 40-14 and 40-15 depending upon devices specifications.
• Figure 5 represents the Dynamic Braking section, where line 10-26 feeds from the Driver/Logic 30 a Pulse Width Modulation signal as described earlier.
• transistor 80-3 turns on into saturation via base limiting resistor 80-2 causing current to flow via base resistor 80-4 turning on Darlington Power Transistor 80-5 into saturation.
• Resistors 80-1 and 80-5 act as base clamp resistors. Saturation of 80-5 causes main buss (10-11 and 10-23) current to flow through high wattage dump resistors 8 * 0-8 and 80-7. The rating of the dump resistors are such that they are well below required levels since a full 100% duty cycle is never applied.
• the Dynamic Braking PWM signal is proportional to the deceleration rate, that is, the shorter the deceleration rate the higher the duty cycle, and therefor an equal amount of energy is always absorbed or "dumped" during a braking cycle. Failure of 80-5 or high repetitive deceleration condition will cause fuse 80-6 to clear preventing damage due to overheating of dump resistors 80-7 and 80-8.
• Figure 8 represents the Electronic Fault Protector. It consists of four independent trip conditions indicated by four LEDs (70-39 through 70-42).
• the two buss current sensing devices 10-6 and 10-7 monitor forward and regenerative currents on the main buss 10-11 and 10-12. These two independent signals are referenced to 70-50 (2.5 volts) which is developed by voltage divider resistors 70-3 and 70-4. Potentiometers 70-1 and 70-2 allow for fine adjustment and calibration of current sensing signals. These current signals then enter voltage comparitors 70-12 through 70-15 whose output is high (open collector output device) via pull up resistor pack 70-30. Resistors 70-6 and 70-7 form a voltage divider which is referenced to 70-12 and 70-13.
• Resistors 70-9 and 70-10 act similarly to the above mentioned except that their voltage divider level is negative with respect to 70-50 which represents the forward buss current trip level. Together these two levels form a operating window for normal buss currents. If they are exceeded the output of the respective voltage comparitor will go low. Over voltage protection is achieved via voltage comparitor 70-16. Resistors 70-18 and 70-20 form a voltage divider off of the main buss voltage. Under normal conditions the output of 70-16 is high. If voltage level 70-52, representative of the main buss voltage, exceeds a preset level as determined by potentiometer 70-28, 70-17 will go low.
• a latch and shut down of the fault and drive outputs must occur. This is accomplished via voltage comparitors 70-31 through 70-34. All are referenced to 70-53 which is to be the established voltage divider made up of resistors 70-36 and 70-37. If any one of the four fault detector comparitors goes low (two sets of two are tied together) their respective follower comparitor (70-31 through 70-35) non-inverting inputs will be set low below voltage reference 70-53. This will cause their normally off output to turn on bringing the output low and latching the fault condition. In addition, one of four indicating LED's 70-39 through 70-42 will illuminate indicating which fault has occured.
• Figure 8 represents the Current Feedback section 80 shown in Logic/Driver 30. Signals from the Buss current sensing devices 10-6 and 10-7 are feed into 80-1 and 80-2 resistors which input into summing operational amplifier 80-5. The gain of the amplifier is set by resistor 80-4 so that under maximum conditions the 80-5 will not saturate. Filtering is done by capacitor 80-3. The non-inverting input of 80-5 is offset by potentiometer 80-7 and adjusted in such a manner as to have zero output voltage on 80-5 with no main buss current flow on 10-11 and 10-12. The output of 80-5 is then inputted into non-inverting input of operational amplifier 80-9 which is wired as a non-inverting amplifier utilizing resistors 80-10, 80-11 and 80-12 to set the gain. Potentiometer 80-12 is adjusted such that at desired current to be limited at Motor 00, 80-9 output voltage would be equal to 2.0 volts and is applied to Microprocessor 30-7 via line 30-34.
• the Voltage Feedback section 90 of the Logic/Driver 30 is represented by Figure 9.
• the two feedback voltage signals generated off of Phase Modules 40 and 50 from voltage divider resistors 40-9 and 40-10 on lines 10-9 and 10-10 are applied to operational amplifier 90-7.
• 90-7 is wired as a differential amplifier via resistors 90-1 through 90-4. It output is applied to low-pass filter made up of resistor 90-5 and capacitor 90-6 and applied to operational amplifier 90-7 which is used as a non-inverting amplifier.
• the gain of 90-7 is controlled by resistors 90-8, 90-9, and 90-10.
• Potentiometer 90-10 acts as a Volts per Hertz adjustment and is calibrated for nominal operation at 30 Hz Motor 00 frequency to be 1.93 Volts. The output is applied to
• Microprocessor 30-7 where the signal is software linearized.
• the Logic/Driver 30 consists of several major functions of tasks; they are:
• Serial communications channel 9. Stand alone operator cc-htrol or remote control via serial channel
• the software will continuously execute within the main control loop/command interpreter once the system has been initialized and "started”. All time-critical functions, namely the Regulated Voltage Control Timing, Output Frequency Timing, and Electronic Circuit Breaker
• the system Initialization Function will configure and initialize all hardware that is under control of the Logic Driver. In addition, software variables are initialized, initial commands are received and various control inputs are
• the Serial Channel will provide a networking capability, so • " that various systems may be realized efficiently.
• Digital Ratioing is a prime candidate. Acceleration/Deceleration-General
• Acceleration/Deceleration is obtained by creating an artificial operating point and then incrementing/decrementing this operating point towards the desired operating speed.
• the speed signal is control input 10-4.
• Each interval movement takes a programmable number of time units to complete.
• a selection of preprogrammable values is available either through the serial channel or the accel/decel control input 30-12. In this way, the acceleration/deceleration time constant may be controlled.
• Dynamic braking occurs only during deceleration and provides a variable duty-cycle signal that engages circuitry to dissipate energy stored in large inertia loads.
• Deceleration will occur only whenever the unit is in current limit mode.
• This current limit control is 30-34.
• the Boost function will provide a greater than nominal volts/hertz curve over the low speed region of the drive to provide adequate break-away torque.
• Boost control selects: 30-10, 30-11
• PWM duty cycle on Phase Driver outputs 30-13 The voltage regulation routine executes once every time through the main loop.
• the main loop will measure voltage regulation error and determine the correct PWM interrupt handler to implement. Regulation is maintained around the voltage operating point.
• the voltage feedback signal may be passed through a look-up table, in order to linearize and expand its dynamic range. Next this value is compared against the voltage operating point and a difference is obtained. This difference is reflected in the PWM cycle in order to obtain voltage regulation.
• This valve is pre-staged for the interrupt handler.
• Output Frequency is generated with a six phase waveform.
• the frequency generator uses a precise time source that runs at 6 times the nominal frequency.
• the frequency interrupt handler will change the drivers sequence patterns appropriately. These patterns may be accessed in either a "forward” or “reverse” manner.
• This interrupt will actually provide the timing functions for voltage control. It turns the proper drivers off when the master timing clock (PWM frequency) occurs. It then takes the pre-staged, calculated voltage time delay value and loads a timer with the time delay. When this timer times out, the drivers are turned on for the remaining portion of the cycle. This routine will indicate that 1 unit of the master timing clock has occurred to the background loop as well, since the cycle frequency always remains constant.
• This routine will count the six times frequency clock and then sequence the Phase Driver modules through the 6-step waveform (normal PWM interrupt cycles occur simultaneously). The sequence will either progress in the forward or reverse directions. Whenever the drivers are sequenced, a time delay (anti-shoot through) is provided for the driver modules (30-13).
• This handler will immediately turn off all the drivers and reset the processor.
• the processor maintains a history of EFP occurances, so that many possible recovery schemes may be implemented.
• the system initialization function configures all hardware that is under control of the logic driver. This includes the various internal/external input/output ports (both analog and digital), hardware timers, serial channels (not implemented in this configuration). In addition software variables are initialized, including the voltage and frequency operating points, acceleration/deceleration default values and driver sequence index.
• the unit After the various flags and variables are initialized the unit will go into a loop which waits for the start button, 10-3, to be pressed.
• This button is dual function in that its meaning is toggled from start to start depending upon the running state of the motor controller. After the unit has "started”, a 1 second delay is provided to allow the start button to be returned inactive. Start will always delay 1 second and then provide 1 second delay before the unit returns to the start loop. After the 1 second delay various control inputs are measured and their initial values stored. These control inputs include: the accel/decel selection, 20-12; voltage feedback input, 30-33; boost value selection, 30-10 and 30-11; for/reverse direction selection, 10-5; master speed potentiometer input, 10-4; and the current limit input, 30-34.
• Acceleration/Deceleration is obtained by creating and maintaining two artificial operating points; one for voltage and one for frequency control. Separate voltage and *-*- ⁇ frequency operating points are maintained so that alternative voltage/freq curves can be implemented, such as those in the low end boost region. Except for the boost region these operating points will move in unison, so that a nominal volts/hertz curve can be maintained.
• the accel/decel input will choose from several preprogramed rates.
• the basic time unit used is the PWM period, 1 msec, in this particular implementation. 5
• Dynamic braking is activated whenever the unit is decelerated. Within the deceleration routine is the logic to PWM the dynamic braking output by counting 1 msec, time units. 0
• the unit will limit the current drawn by decelerating and lowering the speed temporarily. It does this by detecting the threshold window on control input 5 30-34, and then forcing the unit to decelerate until the current is at a safe level.
• the Boost Region is defined as below 12hz running frequency. Within this region are 4 tables with programmable voltage values. The routine will first detect whether it is within this 12hz boost region. (The region value is programmable at will). If it is, then the chosen table is selected and its voltage values are indexed by the operating frequency value. The boost value is compared to the voltage operating point. The voltage operating point is replaced if the boost value is greater. In this way each table may have a different programmable frequency relative to the other tables.
• the output voltage is regulated by varying the driver PWM duty cycle on a 1 msec. (1 cycle) basis.
• the implementation uses the voltage operating point (voppt) as the reference voltage and converts (A and D conversation of feedback) signal. This signal is "linearized” by use of a look-up table. An offset value (up-down counter) is incremented/decremented in the proper direction and then added/subtracted to the voltage operating point value. This method allows smooth adjustments, little or no oscillations.
• a sample counter can easily be incorporated which allows the updating of the voltage correction to be calibrated to a particular motor.
• the actual time count of the duty cycle is obtained from a a look-up table and prestaged for the timer interrupt handler. Likewise the selected output frequency indicated by foppt will index a loop-up table and load the frequency timer with the correct count for 6 times running frequency.
• the interrupts are not enabled until the first pass through the loop has occurred. This will allow the prestaged values to be computed and stored prior to interrupt activity.
• the stop button (start button once the unit is running) is examined every time through the main loop and the unit is stopped (all control outputs to drivers are turned off, interrupts are disabled) if so selected.
• the timing of the 1 msec PWM cycle is maintained by a timer and as interrupt handler, optimized for speed.
• This 1 msec time source is also used as an internal time base for accel/decel timing and main loop control.
• An interrupt sync flag is toggled by the background tasks and
• the routine will also load the voltage timer either the PWM duty cycle count calculated and prestaged by the background.
• the frequency interrupt will step through and select the driver patterns necessary for the 6 step waveform.
• the waveform may be sequenced in a forward or reverse direction.
• the direction indication may be either static, that is determined only once when the unit has started. Dynamic direction change involves decelerating the motor to zero speed, toggling the direction and then accelerating to the previous operating speed.
• 1 complement pair of Phase Drivers has the danger of shoot through (both transistors on for a brief period).
• the interrupt handler will delay the appropriate amount (programmable for different transistors) of time to avoid this condition by ensuring that 1 transistors has turned off before the other transistor has turned on.
• the electronic fault protector interrupt will actually activate the microprocessor's reset line, thus causing a system reset.
• the initialization routine will detect previous activity by checking for several specific values in several specific places. This detection will allow algorithms to be developed which modify how the unit will restart itself due to previous history. For instance, the unit may restart itself three times before it indicates a serious problem.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Ac Motors In General (AREA)

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• 1985
  • 1985-11-12 WO PCT/US1985/002237 patent/WO1986003075A1/fr not_active Application Discontinuation
  • 1985-11-12 JP JP50520085A patent/JPS62501953A/ja active Pending
  • 1985-11-12 EP EP19850905993 patent/EP0203145A4/fr not_active Withdrawn
  • 1985-11-12 AU AU50953/85A patent/AU5095385A/en not_active Abandoned

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