MXPA96003940A - Method and apparatus for controlling an mo - Google Patents

Abstract

The present invention relates to a voltage controller for an induction motor having at least one stator phase, said controller being characterized in that it comprises: pulse signal means for producing an electrical pulse signal in said stator phase as a function of an engine driving frequency, resulting in a magnitude of current in said stator phase such that said current magnitude varies in response to varying load conditions for said motor; monitoring means for monitoring the magnitude of current in said stator phase, means for calculating a current reference as a function of a motor driving frequency and a desired motor speed, change signal means electrically connected to the monitoring means and means for calculating the current reference to produce a change signal related to the difference between the current magnitude in the stator phase and current reference; and manipulation means electrically connected to said shift signal means and said pulse signal means to produce a motor driving frequency for the pulse signal means which varies in magnitude in response to the signal of change

Description

METHOD AND APPARATUS FOR CONTROLLING AN ENGINE BACKGROUND OF THE INVENTION The invention relates to a controller controlling an engine, and particularly to an operator to control an induction motor, and very particularly to a controller to control an induction motor in a flow bob. It is known to provide an air management system such as a heating, ventilating or air conditioning ("HVAC") system with a blower or a fluid pump that pushes or pulls air through a heat exchanger or an electric coil. to heat or cool the air, respectively, and transfer the air through a system or conduits and vents to a room or rooms where a thermostat is located. The thermostat provides feedback to the system to indicate the temperature in the room or rooms. In this way, the air temperature in those rooms is controlled. The blower includes a motor and the HVAC system usually also includes a controller to control the motor - in response to various parameters such as the room air temperature, the air flow rate, the speed of the engine and engine torque. It is also known that the efficiency of the transfer < Heat in the air and the heat exchanger or cooling coil depends directly on the air flow rate through the heat exchanger or the cooling coil. Still, it is known that the efficiency of the heat transfer procedure can be increased to the inax Linus by maintaining the flow velocity at a specific fixation point. The fixation point or flow velocity at which the heat transfer is most efficient is determined empically (typically) by the manufacturer of the HVAC system), and is programmed into the system thermostat. However, since the vents in the system open or close, the load on a motor changes, thus changing the motor speed, the blower output and the stator current. The exchange loads experienced by the engine make it extremely difficult to accurately control the output of the donor sun. Many techniques have been developed to control the air flow rate and a blower in an HVAC system and have consistently revolutionized the use of a direct current motor with permanent magnet brushes. Direct current motors with permanent wiper blades have been used because they are relatively easy to control and provide good performance in low power air handling applications. However, DC motors with permanent brushes are typically more expensive and less bulky than other types of motors such as induction motors. A known method for controlling a direct-current motor with a permanent brush is shown and described in the patent of F.U.A. No. 4.9 B, H9fi.

BRIEF DESCRIPTION OF THE INVENTION Accordingly, the invention provides a method and apparatus for controlling an engine, and particularly a method and apparatus for operating an induction motor in an HVAC system to provide performance comparable to that of a direct current motor. with permanent brushes at a lower cost. The motor has at least one stator phase and a controller is provided to supply electric power to the stator phase so that the mechanical output generated by motor is substantially constant regardless of any variations in the motor load. . The controller can be used to control any motor in any application where it is desired to maintain a constant mechanical output regardless of variations in load on the motor. Such applications may include, as in the preferred embodiment of the invention, a fluid pump to maintain a constant fluid flow despite varying load collisions. Nevertheless, the invention is not limited to fluid pumps. The invention could also be applied to, for example, a L-belt conveyor pulser motor to maintain a constant conveyor belt speed in response to varying load conditions. The controller includes pulse signal means to produce an electrical impulse signal in the stator phase resulting in a current flow in the stator phase such that the current flow varies in response to varying load conditions for the motor. , means for monitoring the flow of current in the stator phase, means of change signal for producing a change signal related to changes in the current flow, and manipulation means electrically connected to the signal means of change and the impulse signal means for changing the electric pulse signal in response to the signal means of the change. The invention also provides a method for controlling an engine having at least one stator phase, and the method including the steps of producing an eLectpco pulse signal in the stator phase resulting in a current flow in the stator phase. stator, in such a way that the current flow vanes in response to the variable load conditions for the motor, monitoring the current flow in the stator phase, producing a change signal in relation to the changes in the current flow, and changing the electrical impulse signal in response to the shift signal means. A major advantage of the invention is to provide a fluid pump of an HVAC system that provides substantial fluid flow between constant regardless of variations in the load on the fluid pump. Another advantage of the invention is to provide a fluid pump which uses an induction motor and a controller so that the LINE-induced motor generates a substantially constant flow of fluid irrespective of load variations. Another advantage of the invention is to provide a controller for an induction motor, said controller changes the torque of the motor only in response to the stator current. Another advantage of the invention is to provide a method for controlling an induction motor in a fluid pump to provide a substantially constant fluid flow irrespective of load variations on the motor. Other features and advantages of the invention are set forth in the detailed description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of the motor controller and a motor controlled by the controller. Figure 2 is a graphical illustration showing the relationship between the stator current and the frequency of the electrical stimulus used to power the motor.

Figure 3 is a graphical illustration showing the relationship between voltage < The stator and the frequency of the electrical stimulus. Figure 4 is a graphic illustration showing the relationship between the fluid flow velocity and the corresponding motor energizing current. Before explaining in detail one embodiment of the invention, it should be understood that the invention is not limited to its application to the details of the construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention may have other modalities and be practiced or carried out in various ways. Also, it should be understood that the phraseology and terminology used herein are for description purposes and should not be considered as limiting.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY Illustrated schematically in Figure 1 of the drawings is a motor controller 10 and motor 14. Although the controller can be used to control any motor in any application, the motor of the preferred embodiment is a three-phase induction motor employed. in a fluid pump. Most particularly, the fluid pump of the preferred embodiment is a blower - for use in an HVAC system. As indicated above, in HVAC systems, it has been shown that the heat transfer efficiency between the heat exchanger - or the cooling coil and the air passing through - the heat exchanger or cooling coil is directly dependent on the flow velocity of the air passing through the heat exchanger or cooling coil.

In addition, it has been determined that the efficiency of the heat exchanger is maximized at a specific air flow rate (usually determined by the design characteristics of the heating element or cooling coil). The motor 14 includes a stator (not shown) having three phase windings, and a rotor (not shown) mounted to rotate about a rotor axis (not shown). As is commonly known in the art, the energization of the stator phases causes the rotation of the rotor. The motor 14 also includes a shaft 18 connected to the rotor for rotation therewith. An impeller or blower 22 is mounted on the shaft 18 so that the fan 22 rotates, the air is pulled or forced onto the heat exchanger unit (not shown) and from there it is supplied to a system of conduits (not shown) to distribute the air to the room or rooms. A series of switches 26 selectively electrically connect the motor 14 to the power (typically direct current derived from normal AC line voltage) in response to control signals produced by the controller 10. The controller 10 it includes a thermostat 30 that is located inside the room or rooms that are going to be heated or cooled. The thermostat 10 monitors the air temperature of the room and generates, in response to the air temperature of the room, control signals to start the operation of the motor. The controller 10 also includes a microprocessor 34 connected to the thermostat 30 to control the temperature of the room. receive the control signals from the thermostat. The microprocessor 34 is also connected to the switches 26 that supply power to the motor 14 to control the switches 26 and to energize the motor 14 whereby the fan 22 supplies a volume of constant air flow rate despite any change in the loading conditions experienced by the engine 14. Typically, said load changes occur when opening or closing the vents in the duct system. As is commonly known in the art, a series of impellers 38 are connected between the power switches 26 and the microprocessor 34. The microprocessor 34 includes decoder 42 for receiving control signals from the thermostat and includes signaling means. of pulse or power supply means connected to the decoder 42 to produce an electrical impulse signal or electrical stimulus resulting in current flow in the stator phase. Although various means are suitable for producing the electrical impulse signal, the pulse signal means of the preferred embodiment include a current converter 46 connected to the de-energizer 42 and a current command computer 50 connected to the current converter. 46. The microprocessor also includes change serial methyls to produce a change signal related to changes in the stator current flow. Although various means for generating the change signal are suitable, in the preferred embodiment the change signal means includes a comparator 54 connected to the current command calculator 50. The microprocessor also includes manipulation means connected to the comparator and the signal means of pulse to change the electrical impulse signal in response to the output of the comparator 54. Although various means for changing the electrical impulse signal are appropriate, the manipulation means of the preferred embodiment include a current regulator or integrator 58 connected to the comparator 54 and a summing node 62 connected to the current regulator 58. Improved composition of emulsion at summing node 62 has an output which is fed back through a delay element 66 to one in rada of summing node 62 and to the calculator - of current command 50. The output of node of sums 62 is also connected to a frequency converter at voltage 70. A modulator of amplitude of course 72 is connected to the converter-frequency to voltage 70. The modulator of amplitude of pulse 72 is connected to interrupting impellers 38 to output signals for them and selectively connects the phases of ino + or 14 to electrical energy. The contactor 10 also includes monitoring means for monitoring the current flow in the stator phase. Any known means for monitoring- or measuring the stator current is appropriate. In the preferred embodiment, the monitoring means is a current detector 74 connected to at least one of the phases of the motor for detecting phase current of the motor. The current detector 74 is connected to the comparator 54 to transmit the phase current to the comparator 34. During operation, the initiator processor 54 controls the motor 14 using the ratio between the stator current, stator frequency and air flow rate shown in Figure 2. This relationship has been determined empirically and, as shown clearly in Figure 2, for a given air flow velocity, the ratio of the stator current versus the stator frequency is generally linear, that is, it can be defined by the linear equation: y = rnx + b; wherein y = command current of the desired stator during a period of current (T); x = stator command frequency during a previous period (w); m = slope of the current frequency curve (the slope is determined by the characteristics of the blower, for example, cage size, number of pallets, c + c); and b = the zero frequency or stator current without steady state load (T2). Knowing the desired air flow velocity at which the HVAC system is to be operated, the stator current of zero frequency T at the air flow rate and the stator command frequency w during the previous time, the microprocessor 34 can easily calculate the desired stator command current [at which the motor 14 must be energized to generate the desired air flow velocity output. If the stator-wanted command current I differs from the actual stator current Ta., Then the stator command frequency u can be adjusted to compensate for the difference, which is assumed to be the result of the change in load on the motor 14. In a broad sense, the controller can be used to control any motor where the relationship between the electrical signal used to energize the motor and the output of the motor is known. Very specifically, and referring to Figure 1, the decoder 42 receives the inputs of the thermostat and generates in response to the thermostat inputs an output which is indicative of a flow output at 1? T per second desired (l / segdßl, oadoa) for the motor blower. The current converter 46 receives The signal of l / Iegeiaußaetoß generates in response to the signal of I / I. "O" "_- 0" the value * of current of the stator of frequency 0 (la). The converter 46 can generate T ^ using a real time calculation, however, in the preferred mode, the current converter 46 is simply a memory-based query box that stores a current value of the stator. Frequency 0 separated for a number of different flow velocities. The relation between l / segtíß »or« < "T3" are shown in FIG. 4. The current converter 46 transmits the current of the stator frequency 0 to the current command calculator 50. At about the same time, the command frequency >; x, that is, the command frequency of the period of 0.6 seconds previous, is sent to the command calculator tle current 50 from the output of the node of sums 62 .. In response to the reception of the current of The 0 Tz loop station and the command frequency signal w, the current command calculator 50 generates a command current T, ie, the current at which the motor 14 must be energized for a given blower output. As indicated "• internally, the ratio used for this determination is shown in Figure 2. The command current I is fed to the comparator 54 and compared to the actual phase current Tx as measured by the current detector 74. The current comparator 54 produces a current error value (I) representing the difference between the stator phase current r-eal T and the desired stator phase current T2 for the velocity] / c, egaßBßaC | ß of desired air flow. The current error (T) is transmitted to the current regulator 58 which integrates the current-error signal I to generate a manipulation output (w) "I to manipulation output u is added to the frequency of previous command w to generate an updated command frequency Us ,. The updated command frequency w2 represents an updated frequency signal which is required in the output motor current Ex to maintain the output of the desired blower air flow rate. The command frequency 2 is transmitted to the frequency converter at voltage 70 which generates an updated command voltage. The frequency to voltage converter 70 uses the ratio shown in Figure 3 to generate the command voltage and this voltage is the input to the pulse amplitude modulator 72 together with the updated command frequency, the function performed with the frequency converter A voltage 70 can be driven using a time software based on the calculation based on the equation: where V is the updated voltage command, Kv is a constant to convert the frequency units to voltage units, and w2 is the command frequency. In the preferred mode, the results of the function are recalculated and, like the functions of the current converter 46 and the current command calculator 50, the function of the frequency converter to voltages is stored in a reference table based on memory. The command frequency (w2) is also assigned to the current command calculator 50 via the delay element 66 which produces a transmission delay of approximately 0.6 seconds. This period of delay is to explain the fact that the load in the HVAC system changes slowly as the vents open or close and the delay avoids the instability of the heater. In response to the updated command frequency u2 and the updated command voltage V, the pulse amplitude modulator 72 generates control signals for the impellers 38 that operate the switches 26 to generate an updated current output so that the motor 14 maintain the desired airflow speed output. The current detector 74 will continue to measure the phase current of the stator. c > ? the motor load of the blower remains the same from a range of 0.6 seconds to the next, then the phase current of the stator I will not change, and there will be no resultant current error signal I generated. As a result, the frequency output of command W? in addition node 62 will not change. Alternatively, if the blower motor load changes from a 0.6 second interval to the next, then a new current error signal I will be generated to produce a new calculation of the command frequency w2 as described above. 1. 5 Various aspects and advantages of the invention are set forth in claims.

Claims (18)

1. LP NOVEDñP. INVENTION CLAIMS A control for an engine having at least one stator phase, said controller comprising: pulse signal means for producing a pulse signal eLectpco in said stator phase, resulting in a current flow in said stator phase in such a manner that said current flow varies in response to varying load conditions ar-to said motor: reliable monitoring means monitor the current flow in said stator phase; shift signal means to produce a kill signal related to changes in the current flow; and manipulative means electrically connected to said shift signal means and said signal means to change the electrical impulse signal in response to the shift signal.
2. 2. A controller relies on an engine according to claim 1, further characterized in that said change signal means produce the change signal only in response to changes in the current flow.
3. 3. A motor controller according to claim 1, further characterized in that said electrical impulse signal is a pulse frequency and age.
4. 4. A motor rocker according to claim 1, further characterized in that said motor has a mechanical output and in that said motor-power controller, so that the mechanical output is substantially constant regardless of the varying loading conditions.
5. 5. A controller-pair-to an engine according to claim 1, further characterized in that said manipulation means are connected to the pulse signal means and to the signal means of change through a radar signal. Closed loop realization.
6. 6. A controller for a motor according to claim 1, further characterized in that said motor is a three-phase induction motor.
7. 7 - A controller - for an engine according to claim 1, further characterized in that said manipulation means changes the electric impulse signal periodically.
8. 8. A controller for an engine according to claim 1, further characterized in that said manipulation means changes the electric impulse signal approximately every 0.6 seconds.
9. 9. - A fluid pump for generating a fluid flow, said fluid pump comprising: a motor having at least one stator phase and which is exposed to variable load conditions; and a controlled) - to supply electrical energy to said stator phase - in such a way that said fluid flow is substantially constant IR independently of said variable load conditions; d. Controller-including power supply means for supplying power to the stator phase with an electrical stimulus, monitoring means for monitoring the current flow in said stator phase, and reliable manipulation means changing said electrical stimulus in response The flow is correct.
10. 10. A fl uid pump, co-formulated with the rei indication 9, further characterized because said motor includes a tree mounted rotatable about an axis and a fluid impeller mounted on said shaft so that the rotation of said tree produces the movement of the fluid.
11. 11. A fluid pump according to claim 10, further characterized in that said fluid pump is a blower in a HAVC system.
12. 12. A fluid pump according to claim 9, further characterized in that said manipulation means walk the electrical stimulus only in response to changes in said current flow.
13. 13. A fluid pump in accordance with the rei indication 9, further characterized in that said electrical stimulus is a pulse frequency and age.
14. 14. A fluid pump according to claim 9, further acted upon because said manipulation means are connected to the power supply means and to the monitoring means through a real path of closed loop locking.
15. 15. A fluid pump according to claim 9, further characterized in that said motor is a motor for induction of tests.
16. 16. A controller for an engine according to claim 9, further characterized in that said manipulation means changes the electric stimulus periodically.
17. 17. - A controller for an engine according to claim 9, further characterized in that said manipulation means changes the electric stimulus appropriately every 6 seconds.
18. 18. A method for controlling a motor having at least one stator phase, said method comprising the steps of: a) producing an electrical impulse signal in said stator phase resulting in a current flow in said phase of the stator in such a way that said current flow varies in response to the variable load conditions for said motor; b) monitoring said current flow in the stator phase: c) producing a change signal related to changes in said current flow; and d) changing said electrical impulse signal in response to said change signal. 1.9.- A method of confo idad with the reivindicaci n 10, further characterized in that step C further includes the step of producing a shift signal periodically to provide continuous control of said motor. ? ()

    20. - A method according to claim 18, further characterized in that step C further includes the step of producing said change signal approximately every 0.6 seconds to provide continuous control of said motor. 21.- A method of compliance with the reimbursement 10, further characterized in that said step a includes the step of calculating a desired stator current, and wherein said step c includes the step of calculating the difference between the desired stator current and the monitored current.