CN113169686A - Method for controlling brushless permanent magnet motor - Google Patents
Method for controlling brushless permanent magnet motor Download PDFInfo
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- CN113169686A CN113169686A CN201980076821.4A CN201980076821A CN113169686A CN 113169686 A CN113169686 A CN 113169686A CN 201980076821 A CN201980076821 A CN 201980076821A CN 113169686 A CN113169686 A CN 113169686A
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- 238000000034 method Methods 0.000 title claims abstract description 56
- 230000005284 excitation Effects 0.000 claims abstract description 44
- 230000008859 change Effects 0.000 claims abstract description 11
- 238000005259 measurement Methods 0.000 claims description 52
- 230000007423 decrease Effects 0.000 claims description 19
- 238000004804 winding Methods 0.000 description 60
- 239000008186 active pharmaceutical agent Substances 0.000 description 13
- 230000004044 response Effects 0.000 description 9
- 230000000638 stimulation Effects 0.000 description 7
- 238000010586 diagram Methods 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
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- 230000005355 Hall effect Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
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- 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
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/14—Electronic commutators
- H02P6/15—Controlling commutation time
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- 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
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
- H02P25/022—Synchronous motors
- H02P25/03—Synchronous motors with brushless excitation
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- 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
- H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
- H02P6/08—Arrangements for controlling the speed or torque of a single motor
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Abstract
A method for controlling a brushless permanent magnet electric machine (14) includes measuring (102) an input power of the electric machine 14. The method comprises comparing (104) the measured input power with a target input power. The method includes applying (106) a first calibration factor to an excitation time parameter of the electric machine (14) to match the measured input power to a target input power. The method includes applying (116, 120) a second calibration factor to the excitation time parameter to change the speed of the motor (14). The method includes energizing the motor (14) according to an energization time parameter.
Description
Technical Field
The present invention relates to a method of controlling a brushless permanent magnet motor.
Background
Brushless permanent magnet motors include phase windings that are energized by a power source such that a magnetic field induced in the windings drives rotation of a rotor of the motor. Commutation of the phase winding occurs relative to the zero crossing of the back emf induced in the winding and it is known to advance the commutation of the winding by a so-called advance angle so that commutation of the winding occurs prior to the zero crossing of the back emf induced in the winding. The phase current is driven into the phase winding for a period of time commonly referred to as the on period, or for a predetermined periodic ratio referred to as the duty cycle.
It has previously been proposed to use a look-up table to determine the desired advance angle, conduction period and duty cycle.
Disclosure of Invention
According to a first aspect of the present invention there is provided a method of controlling a brushless permanent magnet electric machine, the method comprising: measuring the input power of the motor; comparing the measured input power with a target input power; applying a first calibration factor to an excitation time parameter of the motor to cause the measured input power to substantially match the target input power; applying a second calibration factor to the excitation time parameter to change the speed of the motor; and exciting the motor according to the excitation time parameter.
The method according to the invention may in principle be advantageous in that the method comprises applying a first calibration factor to an excitation time parameter of the electric machine such that the measured input power substantially matches the target input power; applying the second calibration factor to the excitation time parameter to change the speed of the motor and exciting the motor according to the excitation time parameter.
In particular, for brushless permanent magnet motors that operate, for example, as fans or compressors, peak operating efficiency may occur when the motor is operating at its peak speed at a given input power. Applying the first calibration factor to the excitation time parameter may ensure that the motor is operating at the target input power, while applying the second calibration factor may enable the speed to be varied to cause the motor to operate at or near its peak operating speed at the given target input power, thereby ensuring that the motor is operating at or near its most efficient operating point for the given target input power.
Using the first and second calibration factors in response to the measured input power may eliminate or reduce the need to use a look-up table or equation to determine the desired excitation time parameter, thereby causing the motor to operate at the desired input power with maximum efficiency for that input power. The lack or reduction of the need for a look-up table or equation may simplify the processing requirements and/or memory requirements of the processor used to control the motor, which may result in the use of a physically smaller and/or cheaper processor, i.e., a less expensive processing method than devices known in the art.
The method according to the first aspect of the invention may also enable the motor to optimise its own control parameters in use and may therefore minimise or eliminate the need for line end calibration of the motor during manufacture.
The method can comprise the following steps: measuring input power of a phase winding of the motor; and exciting a phase winding of the electric machine according to the excitation time parameter.
The method may include applying a first calibration factor until the measured input power substantially matches the target input power. The method may include applying a second calibration factor to the excitation time parameter once the measured input power substantially matches the target input power.
The method may include applying a first calibration factor in response to the measured input power. The method may include applying the first calibration factor before applying the second calibration factor.
The method may include applying a second calibration factor to the excitation time parameter to cause the motor to operate substantially at peak speed for the measured input power.
Operating substantially at peak speed refers to the motor operating at or near its peak operating speed for the target input power. The method may control the motor to operate at a speed within 10%, within 5%, within 4%, within 3%, within 2%, or within 1%, or within 0.5% or within 0.1% of the peak operating speed for the measured input power.
The method may comprise measuring the speed of the motor before and/or after applying the second calibration factor.
Measuring the input power of the motor, e.g., the input power of a phase winding of the motor, may include measuring a supply voltage and/or phase current through the motor. Measuring the input power of the motor may comprise measuring a supply voltage and/or a supply current. Measuring the supply current may be beneficial compared to measuring the phase current (e.g., the current through a phase winding of the motor), as it may provide a more accurate measurement of the current driven into the motor, as switching losses may not need to be taken into account.
The energization time parameter may include a parameter that defines when a phase winding of the motor is commutated, and/or when energization of the motor (e.g., a phase winding of the motor) begins, and/or how long the motor (e.g., a phase winding of the motor) is energized. Energization of the motor may include driving phase currents through phase windings of the motor.
The excitation time parameter may comprise an advance angle, e.g. a phase angle at which commutation of a phase winding of the electrical machine occurs, and thus a phase angle at which excitation of the phase winding begins. The advance angle may be measured with respect to the zero crossing of the back emf induced in the phase winding. Although referred to as an advance angle, which may mean that commutation of the phase winding occurs before a zero crossing of the back emf induced in the phase winding, the advance angle may comprise a positive, negative or zero value. Thus, commutation of the phase winding may occur before, after or in synchronism with the zero crossing of the back emf induced in the phase winding. In case the advance angle is negative, the advance angle may alternatively be referred to as a delay angle, since commutation of the phase winding may be delayed with respect to a zero crossing of the back emf induced in the phase winding.
The excitation time parameter may comprise a conduction period, e.g. a time period during which excitation of the motor occurs. The excitation time parameter may comprise a duty cycle, for example, defining a ratio of excitation occurrence frequencies within a period. The excitation time parameter may comprise an advance angle and an on-period, or may comprise an advance angle and a duty cycle. The excitation time parameter may include a sine wave amplitude or other waveform amplitude.
The first calibration factor may comprise a first advance angle calibration factor and/or a first on-period calibration factor and/or a first duty cycle calibration factor. The second calibration factor may comprise a second advance angle calibration factor and/or a second conduction period calibration factor and/or a second duty cycle calibration factor. The method may comprise applying a first advance angle calibration factor to the advance angle and/or applying a first conduction period calibration factor to the conduction period and/or applying a first duty cycle calibration factor to the duty cycle. The method may comprise applying a second advance angle calibration factor to the advance angle and/or applying a second conduction period calibration factor to the conduction period and/or applying a second duty cycle calibration factor to the duty cycle. The first advance angle calibration factor may be proportional to the first conduction period calibration factor and/or the first duty cycle calibration factor. The second advance angle calibration factor may be proportional to the second conduction period calibration factor and/or the second duty cycle calibration factor.
The first calibration factor may increase the advance angle and/or increase the conduction angle and/or increase the duty cycle. By increasing the advance angle, the measured power can be increased because the current can be driven into the phase winding at an earlier point in time. By increasing the conduction angle, the measured power can be increased because current can be driven into the phase winding for a longer period of time. By increasing the duty cycle, the measured power can be increased because current can be driven into the phase winding for a greater percentage of the period. The first calibration factor may reduce the advance angle and/or reduce the conduction angle and/or reduce the duty cycle. By reducing the advance angle, the measured power can be reduced because the current can be driven into the phase winding at a later point in time. By reducing the conduction angle, the measured power can be reduced because current can be driven into the phase winding in a shorter period of time. By reducing the duty cycle, the measured power can be reduced because current can be driven into the phase winding for a smaller percentage of the period.
The second calibration factor may increase and/or decrease the advance angle and/or the conduction angle and/or the duty cycle.
The target input power may include a power set by a user. For example, the target input power may include power set by a user switching a switch.
The method may include operating the brushless permanent magnet motor using an initial excitation time parameter relationship in response to a comparison of the measured input power to a target input power, for example, prior to applying the first calibration factor. This may be beneficial because it may move the measured input power closer to the target input power before applying the first calibration factor, and thus may avoid the need for a large calibration factor, which may lead to unstable operation and/or inefficiency. Applying the first calibration factor to the excitation time parameter of the electric machine may include applying the first calibration factor to the excitation time parameter of the initial excitation time parameter relationship. The initial excitation time parameter relationship may comprise a relationship between at least one excitation time parameter and the input power, e.g. which excitation time parameter or combination of excitation time parameters realizes which input power.
The method may include a first closed control loop for applying a first calibration factor and a second closed control loop for applying a second calibration factor. The method may include a first closed control loop for ensuring that the measured input power substantially matches the target input power. The method may include a second closed control loop for varying the speed of the motor. The method can comprise the following steps: a first closed control loop for varying the measured input power through the motor, and a second closed control loop for varying the speed of the motor. The first closed control loop may comprise an outer control loop and the second closed control loop may comprise an inner control loop. The first closed control loop may operate on a faster time scale than the second closed control loop. This may be beneficial because the first closed control loop may react quickly to ensure that the measured input power substantially matches the target input power, while the second closed control loop may be calibrated to achieve the most efficient operating point for a given measured input power.
The method may include controlling a brushless permanent magnet motor operating in a steady state. The method may include controlling a brushless permanent magnet motor operating at a speed in excess of 20 krpm. The method may include controlling a single-phase brushless permanent magnet motor.
Applying the second calibration factor may include making a first measurement of the speed of the motor, applying the first polarity calibration factor to a stimulation time parameter of the motor, making a second measurement of the speed of the motor; and:
i) if the second measurement is greater than the first measurement, continuing to apply the first polarity calibration factor and then measuring the speed of the motor until the speed of the motor decreases;
ii) if the second measurement is less than the first measurement, applying a second polarity calibration factor having a polarity opposite the first polarity calibration factor, continuing to apply the second polarity calibration factor, and then measuring the speed of the motor until the speed of the motor decreases.
This may be advantageous because applying the first calibration factor to the excitation time parameter may ensure that the motor is operating at the target input power, while applying the first or second polarity calibration factor may ensure that the motor is operating at or near its peak operating speed at a given measured input power, thereby ensuring that the motor is operating at or near its most efficient operating point for a given measured input power.
In the case where the second measurement is greater than the first measurement, this may indicate that the motor has moved closer to its most efficient operating point for a given power. The application of the first polarity calibration factor and subsequent measurement of the speed of the motor continues until the speed of the motor decreases, possibly indicating that the motor is operating at or near its peak speed at a given power. In the case where the second measurement is less than the first measurement, applying a second polarity calibration factor having a polarity opposite that of the first polarity calibration factor may ensure that the speed at which the motor is operated increases and that the motor has moved closer to its most efficient operating point for a given power. Continuing to apply the second polarity calibration factor and then measuring the speed of the motor until the speed of the motor decreases may indicate that the motor is operating at or near its peak speed at a given power.
Applying the second calibration factor may include applying a positive polarity calibration factor to the excitation time parameter, making a first measurement of the speed of the motor, applying a negative polarity calibration factor to the excitation time parameter, making a second measurement of the speed of the motor; and
i) if the second measurement is greater than the first measurement, continuing to apply the negative polarity calibration factor and subsequently measuring the speed of the motor until the speed of the motor decreases;
ii) if the second measurement is less than the first measurement, reapplying the positive polarity calibration factor, continuing to apply the positive polarity calibration factor, and then measuring the speed of the motor until the speed of the motor decreases.
This may be advantageous because applying the first calibration factor to the excitation time parameter may ensure that the motor is operating at the target input power, while applying the positive or negative polarity calibration factor may ensure that the motor is operating at or near its peak operating speed at a given measured input power, thereby ensuring that the motor is operating at or near its most efficient operating point for a given measured input power.
Measuring the speed of the motor may include measuring the speed of the rotor of the motor, for example, by utilizing a position sensor of the motor or an estimated position of the rotor.
The value of the second calibration factor may be selected to be small enough to prevent significant overshoot beyond the peak operating speed of the motor for a given measured input power. For a given measured input power at the operating point, it can be ensured that the motor is operating at or near its most efficient operating point. In a closed loop system, the method may comprise substantially continuously varying the speed of the motor, for example, such that the speed of the motor oscillates around a peak operating speed. In this way, the controller of the motor may substantially continuously search for the peak operating speed of the motor for a given input power.
According to another aspect of the invention, there is provided a data carrier comprising machine readable instructions for operating one or more processors of a controller of a brushless permanent magnet motor to measure an input power of the motor, compare the measured input power to a target input power, apply a first calibration factor to a stimulation time parameter of the motor to substantially match the measured input power to the target input power, apply a second calibration factor to the stimulation time parameter to vary a speed of the motor, and stimulate the motor according to the stimulation time parameter.
According to another aspect of the present invention, there is provided a brushless permanent magnet motor comprising a controller configured to measure an input power of the motor, compare the measured input power to a target input power, apply a first calibration factor to a stimulation time parameter of the motor to substantially match the measured input power to the target input power, apply a second calibration factor to the stimulation time parameter to vary a speed of the motor, and stimulate the motor according to the stimulation time parameter.
The motor may comprise a current sensor for measuring the supply current. When the motor is connected to the power source, the current sensor may be located between an inverter of the motor and the power source. This may be beneficial because it may provide a more accurate measurement of the input current, for example, as compared to a current sensor located between the inverter and the zero voltage rail. The current sensor may be located on the high side rail.
Preferred features of each aspect of the invention may be equally applicable to other aspects of the invention where appropriate.
Drawings
For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:
FIG. 1 is a block diagram of an electric motor system according to the present invention;
FIG. 2 is a schematic view of the motor system of FIG. 1;
FIG. 3 details an enable state of an inverter of the motor system of FIG. 1 in response to a control signal issued by a controller of the motor system;
FIG. 4 is a first schematic block diagram illustrating a method in accordance with the present invention;
FIG. 5 is a second schematic block diagram illustrating the inner control loop of the method of FIG. 4;
FIG. 6 is a schematic diagram illustrating the change in velocity in response to an applied calibration factor in accordance with the present invention;
FIG. 7 is a schematic view of an alternative embodiment of an electric motor system according to the present invention;
fig. 8 is a schematic block diagram illustrating another method in accordance with the present invention.
Detailed Description
The motor system 10 of fig. 1 and 2 is powered by a DC power source 12 and includes a brushless motor 14 and a control circuit 16.
The motor 14 includes a four-pole permanent magnet rotor 18 that rotates relative to a four-pole stator 20. Although described herein as a four-pole embodiment, those skilled in the art will recognize that the teachings of the present application are applicable to other embodiments of brushless permanent magnet motors, such as an eight-pole embodiment. The wires wound around the stator 20 are coupled together to form a single phase winding 22. Although described herein as a single phase motor, those skilled in the art will appreciate that the teachings of the present application may also be applied to a multi-phase motor, such as a three-phase motor.
The control circuit 16 includes a filter 24, an inverter 26, a gate driver module 28, a current sensor 30, a voltage sensor 32, a position sensor 34, and a controller 36.
The filter 24 includes a link capacitor C1 that smoothes out relatively high frequency fluctuations due to switching of the inverter 26.
The gate driver module 28 drives the opening and closing of the switches Q1-Q4 in response to control signals received from the controller 36.
The current sensor 30 includes a shunt resistor R1 positioned between the inverter and the zero voltage rail. The voltage across the current sensor 30 provides a measure of the current in the phase winding 22 when connected to the power source 12. The voltage across the current sensor 30 is output as signal I SENSE to the controller 36.
The voltage sensor 32 includes a voltage divider R2, R3 positioned between the DC voltage rail and the zero voltage rail. The voltage sensor outputs a signal V _ DC to the controller 36 that represents a scaled down measure of the supply voltage provided by the power supply 12.
The position sensor 34 comprises a hall effect sensor located in a slot opening of the stator 20. The sensor 34 outputs a digital signal HALL that is a logic high or low depending on the direction of the magnetic flux passing through the sensor 34. The HALL signal thereby provides a measure of the angular position of rotor 18. Embodiments are also contemplated in which the position sensor 34 is omitted and a sensorless control scheme is implemented. Such sensorless control schemes are known and will not be described herein for the sake of brevity. In such a sensorless scheme, the HALL signal may be replaced by a back emf signal representing the period of back emf.
The controller 36 includes a microcontroller having a processor, a memory device, and a plurality of peripherals (e.g., an ADC, a comparator, a timer, etc.). In an alternative embodiment, controller 36 may comprise a state machine. The storage device stores instructions for execution by the processor and control parameters used by the processor during operation. The controller 36 is responsible for controlling the operation of the motor 14 and generates control signals S1-S4 for controlling each of the four power switches Q1-Q4. The control signals are output to the gate driver module 28, which in response drives the opening and closing of the switches Q1-Q4.
FIG. 3 summarizes the enabled states of the switches Q1-Q4 in response to the control signals S1-S4 output by the controller 36. Hereinafter, the terms "set" and "clear" will be used to indicate that the signals are logically pulled up and pulled down, respectively. As shown in fig. 3, the controller 36 sets S1 and S4 and clears S2 and S3 to energize the phase winding 22 from left to right. Conversely, the controller 36 sets S2 and S3 and clears S1 and S4 to energize the phase winding 22 from right to left. The controller 36 clears S1 and S3 and sets S2 and S4 to freewheel the phase winding 22. Freewheeling causes the current in the phase winding 22 to recirculate around the low-side loop of the inverter 26. In this embodiment, the power switches Q1-Q4 are capable of conducting in both directions. Thus, the controller 36 closes both low-side switches Q2, Q4 during freewheeling such that current flows through the switches Q2 and Q4, rather than the less efficient diodes. It is contemplated that inverter 26 may include power switches that conduct in only a single direction. In this case, the controller 36 will clear S1, S2, and S3 and set S4 to freewheel the phase winding 22 from left to right. The controller 36 would then clear S1, S3, and S4 and set S2 to freewheel the phase winding 22 from right to left. The current in the low side loop of the inverter 26 then flows down through the closed low side switch (e.g., Q4) and up through the diode of the open low side switch (e.g., Q2).
In the event that the speed of rotor 18 is above a predetermined threshold, for example above 60krpm, controller 36 operates in a steady state mode. The speed of the rotor 18 is determined by the interval between successive edges of the HALL signal, which is hereinafter referred to as the HALL period.
The controller 36 commutates the phase winding 22 in response to the edges of the HALL signal. Each hall edge corresponds to a change in polarity of the rotor 18 and thus a change in polarity of the back emf induced in the phase winding 22. More specifically, each HALL edge corresponds to a zero crossing in the back emf. Commutation involves reversing the direction of current through the phase winding 22. Thus, if current flows through the phase winding 22 in a left-to-right direction, commutation involves exiting the winding from right to left.
The controller 36 may advance, synchronize or retard commutation with respect to HALL edges, and thereafter, the phase angle at which the controller 36 commutates the phase winding 22 will be referred to as an advance angle, regardless of whether commutation is advanced, synchronized or retarded. The period of time that current is driven into the phase winding 22 is hereinafter referred to as the conduction period, and the controller 36 may vary the conduction period to obtain desired operating characteristics.
The method according to the invention will now be described with reference to fig. 4 to 6.
During operation of the motor system 10, it may be desirable to drive a target input power into the phase winding 22. To ensure that the target input power is driven into the phase winding 22, the controller 36 calculates the measured power P _ SENSE at 102 from the equation P _ SENSE ═ V _ DC. I _ SENSE using the signal I _ SENSE received from the current sensor 30 and the signal V _ DC received from the voltage sensor 32. The measured power P SENSE is compared to the target input power, e.g. by a comparator or the like at 104. If the measured power P _ SENSE is not equal to the target input power, the controller 36 operates the electric machine 14 using the initial energization time parameter relationship, i.e., the initial combination of advance angle and conduction angle, to bring the measured power P _ SENSE closer to the target input power.
The controller 36 then changes the value of the advance angle for commutating the phase winding 22 and drives the phase current into the phase winding 22 for the conduction period at 106 in an attempt to calibrate any remaining error between the measured input power P SENSE and the target input power and communicates the new advance angle and conduction period to the gate drive module 28 via signals S1-S4. The gate drive module 28 then operates 108 the switches Q1-Q4 accordingly to commutate the phase winding 22 at the calibrated advance angle and provide phase current to the phase winding 22 for the calibrated conduction period. The signals I _ SENSE and V _ DC are again used to calculate the updated measured power P _ SENSE and to calibrate the advance angle and conduction period when needed.
Thus, calibrating the measured power P SENSE to correspond to the target input power to be driven into the phase winding 22 forms a closed outer feedback loop 110, the closed outer feedback loop 110 serving to ensure that the motor 14 operates at the desired input power. The use of a closed outer feedback loop 110 may ensure that the motor 14 operates at a substantially constant input power. The closed outer feedback loop 110 acts at a relatively fast rate to ensure that the desired input power is achieved.
For a motor operating at a particular input power, the most efficient operating point for the motor is when the motor is operating at its highest speed at that power. To ensure that this occurs, a closed internal feedback loop 112 is provided. A closed inner feedback loop 112 is schematically shown in fig. 5. The closed inner feedback loop 112 varies the advance angle and conduction period so that the maximum operating speed of the electric machine 14 is achieved at a desired constant input power, thus ensuring peak operating efficiency at a given input power.
In the presently preferred embodiment, once it is determined by the closed outer feedback loop 110 that the motor 14 is operating at a constant input power, the closed inner feedback loop 112 first measures the speed of the rotor 18 at 114 and the measured speed is stored by the controller 36. A first polarity calibration factor, e.g., plus or minus a specified number of degrees, is applied to the advance angle and the conduction angle at 116 before the speed of the motor 14 is measured again at 114.
If the speed of the motor 14 has increased between the initial measurement and the measurement after applying the first polarity calibration factor at 116, the controller 36 continues to apply the first polarity calibration factor at 116 and then measure the speed of the motor 14 at 114 until the speed of the motor 14 decreases. Once the speed of the motor 14 is reduced, the controller 36 determines that the peak speed, and therefore the peak operating efficiency, has been passed. The controller 36 then applies the opposite polarity calibration factor at 118 such that the speed of the motor 14 is increased and the opposite polarity calibration factor is applied until the speed of the motor 14 is again decreased, thereby reapplying the first polarity calibration factor at 116. This process is repeated so that the controller 36 continuously searches for peak speed, and thus peak operating efficiency, and the motor 14 effectively oscillates about its peak operating efficiency.
If the speed of the electric machine 14 has decreased between the initial measurement and the measurement after applying the first polarity calibration factor at 116, a second polarity calibration factor having a polarity opposite to the polarity of the first polarity calibration factor is applied to the advance angle and the conduction angle at 120 such that the speed of the electric machine 14 increases. The controller 36 continues to apply the second polarity calibration factor at 120 and then measures the speed of the motor 14 at 114 until the speed of the motor 14 decreases. Once the speed of the motor 14 is reduced, the controller 36 reapplies the first polarity calibration factor at 122 such that the speed of the motor 14 is increased, and applies the first polarity calibration factor at 122 until the speed of the motor 14 is again reduced. This process is repeated so that the controller 36 continuously searches for the peak operating efficiency and the motor 14 effectively oscillates about its peak operating efficiency.
This ensures that the motor 14 is operating at or near its peak speed for the measured input power, and thus ensures that the motor 14 is operating at or near its most efficient operating point.
In particular, it can be seen from fig. 6 that the speed of the motor follows a curve which varies according to the applied calibration factor and which has a peak. If the first polarity calibration factor results in an increase in velocity relative to the initial velocity measurement, it can be inferred that the velocity is moving toward the peak velocity along the curve in FIG. 6. By continuing to apply the first polarity calibration factor, the speed of the motor 14 will increase along the curve. Once the decrease in speed is measured, it can be inferred that the speed of the motor 14 has passed its peak value, and a second opposite polarity calibration factor is applied so that the speed of the motor 14 increases along the curve. Once the measured speed is reduced, it can be concluded that the speed of the motor 14 has passed its peak value again, thus reapplying the first polarity calibration factor. In this manner, the motor 14 operates to search for peak speeds.
If the first polarity calibration factor results in a decrease in velocity relative to the initial velocity measurement, it can be inferred that the velocity is moving away from the peak velocity along the curve in FIG. 6. By applying a second polarity calibration factor having a polarity opposite to the polarity of the first polarity calibration factor, the speed of the motor 14 may be moved towards the peak along the curve of fig. 6. By continuing to apply the second polarity calibration factor, the speed of the motor 14 will increase along the curve. Once the decrease in speed is measured, it can be inferred that the speed of the motor 14 has passed its peak, thus ceasing to apply the second polarity calibration factor at 120 and reapplying the first polarity calibration factor to search for a peak, as described above.
Thus, the closed inner feedback loop 112 controls the operating speed of the motor 14 such that the motor 14 operates substantially at or near its peak operating speed and peak operating efficiency for a given measured input power. The value of the calibration factor used in the closed inner feedback loop 112 is small enough that when the application of the calibration factor is stopped (i.e. the speed of the motor decreases after a steady increase), the speed of the motor is still close enough to the peak speed, so it can be said that the speed is equal to or close to the peak speed.
The use of a closed outer control loop 110 and a closed inner control loop 112 may eliminate or reduce the need for the controller 36 to utilize look-up tables to obtain the advance angle and conduction angle required for the desired operating power at peak efficiency, and may allow for real-time calibration of the operating characteristics of the electric machine 14. This may eliminate or reduce the need for offline calibration of the motor 14, thereby saving time and cost.
It will be appreciated that alternative peak search algorithms and methods may be employed for the closed inner control loop 112 to find the peak operating speed and thus peak operating efficiency. For example, a positive polarity calibration factor may be applied to the advance angle and the conduction angle prior to a first measurement of the speed of the motor. A negative polarity calibration factor may then be applied to the advance angle and the conduction angle before a second measurement of the speed of the motor is made. If the second measurement is greater than the first measurement, the negative polarity calibration factor will continue to be applied to subsequent motor speed measurements until the motor speed decreases. If the second measurement is less than the first measurement, the positive polarity calibration factor will be reapplied to subsequent motor speed measurements until the motor speed decreases.
In this manner, the closed inner feedback loop 112 may control the operating speed of the motor 14 such that the motor 14 operates substantially at or near its peak operating speed and peak operating efficiency.
Although the above method applies a calibration factor to the advance angle and the conduction angle, it will be appreciated that this depends on the type of electric machine being controlled, and alternatively the method may for example comprise applying a calibration factor to the advance angle and the duty cycle.
In an alternative embodiment, shown schematically in fig. 7, current sensor 30 comprises a current sense resistor located on the high side rail between power supply 12 and filter 24. When connected to the power source 12, the voltage across the current sensor 30 provides a measurement of the input current. According to the foregoing embodiment, the voltage across the current sensor 30 is output as the signal I _ SENSE to the controller 36.
Positioning the current sensor 30 on the high side rail between the power source 12 and the filter 24 before the inverter 26 may provide a more accurate measurement of the input current and, therefore, allow a more accurate calculation of the measured input power, since switching losses need not be taken into account.
Although current sensor 30 is shown in fig. 7 as being located on the high side rail between power supply 12 and filter 24, it is also contemplated that current sensor 30 may be located on the low side rail between power supply 12 and filter 24, still allowing for more accurate power measurements than the position shown in fig. 2.
As described above, positioning the current sensor 30 between the power source 12 and the filter 24 may provide more accurate power measurements. However, removing the current sensor 30 from the position shown in fig. 2 means that the current sensor 30 is no longer used to provide a measurement of the instantaneous current in the phase winding 22. Measurement of the instantaneous current in the phase winding 22 is essential to the operation of the motor 10 and may be used to prevent an overcurrent event and thus prevent failure of the motor 10.
Accordingly, the inventors of the present application have devised a method of measuring the instantaneous current in the phase winding 22 by providing a measurement of the instantaneous current through the low side power switch Q4. Although described herein with reference to the low-side power switch Q4, it will be appreciated that the following method may be used to provide a measure of the instantaneous current through any of the power switches Q1-Q4.
The low side power switch Q4 is an n-channel MOSFET that switches on resistor R when current flows through power switch Q4DS(ON)With a drain source above. The inventors of the present application have determined that R can be estimated using the following equationDS(ON)：
Where average phase V is the average phase current supplied to winding 22 and the average DC current is the average DC current measured at the power supply, for example using current sensor 30 located on the high side rail between power supply 12 and filter 24. The above equation assumes that the average dc current is approximately equal to the average phase current in the winding 22. By using average phase V and average DC current values, RDS(ON)The value of (A) will change in real time, so R can be consideredDS(ON)With a change in temperature.
The average phase voltage across the power switch Q4 may be estimated using the following equation:
where V Limit is V of the power switch Q4 used to set the current LimitDS(drain-source voltage) and Duty is the proportion of time that current is supplied to the phase winding 22.
The controller 36 will know V Limit and Duty, and thus the controller 36 will know the average phase V. The current sensor 30 may be used to measure the average DC current, and thus R may be estimatedDS(ON)。
It is possible, for example, to use the existing VDSSensing circuit to measure Q4, V across power switchDSThe voltage drop of (c). Then, V can be utilized according to the following formulaDSAnd RDS(ON)The instantaneous current through the power switch Q4 is calculated:
then, during operation of the brushless motor 14, the controller 36 may use IQ4(i.e., the instantaneous current through the power switch Q4) to determine whether the current flowing through the power switch Q4 exceeds the predetermined threshold set by V Limit and enable the controller 36 to act accordingly, such as by opening the switch Q1, to freewheel current through the low side of the circuit.
The method for calculating I is shown in the flow chart of FIG. 8Q4The method of (1). The method 200 includes setting V Limit, i.e., the maximum voltage allowed across the power switch Q4 (corresponding to the maximum current allowed through the power switch Q4), at 202, typically set by a control algorithm according to the operating mode of the brushless motor 14. The duty cycle of the current provided to the motor is measured by the controller 36 at 204, and the duty cycle and the V Limit are used to calculate the average phase V at 206. Is made asThe average DC current is measured at 208 by the current sensor 30 before the signal I SENSE is fed to the controller 36.
At 210, controller 36 uses the average phase V and the average DC current to estimate R of power switch Q4DS(ON). For example using an existing V at 212DSThe sensing circuit measures the voltage drop VDS across the power switch Q4. Then, at 214, the control algorithm uses RDS(ON)And VDSCalculation of IQ4。
Thus, the method 200 may be used to calculate the instantaneous current through the power switch Q4, which may then be used, for example, to prevent an over-current event. Additionally or alternatively, the instantaneous current may be used to determine the position of the rotor 18 without the position sensor 34, such as disclosed in WO 2013/132249. The method 200 may further be used to estimate the instantaneous current flowing through any of the power switches Q1-Q4 during freewheeling, while including only a single shunt resistor in the circuit, thereby achieving increased functionality with little or no additional cost.
Claims (9)
1. A method of controlling a brushless permanent magnet electric machine, the method comprising: measuring the input power of the motor; comparing the measured input power with a target input power; applying a first calibration factor to an excitation time parameter of the motor to match a measured input power to a target input power; applying a second calibration factor to the excitation time parameter to change the speed of the motor; and exciting the motor according to the excitation time parameter.
2. The method of claim 1, wherein the excitation time parameter comprises an advance angle and/or a conduction period and/or a duty cycle.
3. A method according to claim 1 or 2, wherein the brushless permanent magnet motor comprises a single phase motor.
4. A method according to any preceding claim, wherein applying a second calibration factor comprises making a first measurement of the speed of the motor; applying a calibration factor having a first polarity to an excitation time parameter of the motor; performing a second measurement of the speed of the motor; and:
i) if the second measurement is greater than the first measurement, continuing to apply the calibration factor having the first polarity and then measuring the speed of the motor until the speed of the motor decreases;
ii) if the second measurement is less than the first measurement, applying a second polarity calibration factor having a polarity opposite to the first polarity calibration factor, continuing to apply the second polarity calibration factor, and then measuring the speed of the motor until the speed of the motor decreases.
5. The method of any of claims 1-3, wherein applying the second calibration factor comprises applying a positive polarity calibration factor to the excitation time parameter; performing a first measurement of a speed of the motor; applying a negative polarity calibration factor to the excitation time parameter; performing a second measurement of the speed of the motor; and
i) if the second measurement is greater than the first measurement, continuing to apply the negative polarity calibration factor and then measuring the speed of the motor until the speed of the motor decreases;
ii) if the second measurement is less than the first measurement, reapplying the positive polarity calibration factor, continuing to apply the positive polarity calibration factor, and then measuring the speed of the motor until the speed of the motor decreases.
6. The method of any preceding claim, wherein the method comprises a first closed control loop for applying a first calibration factor and a second closed control loop for applying a second calibration factor, the first closed control loop comprising an outer control loop and the second closed control loop comprising an inner control loop.
7. A data carrier comprising machine readable instructions for operating one or more processors of a controller of a brushless permanent magnet motor to measure an input power of the motor; comparing the measured input power with a target input power; applying a first calibration factor to an excitation time parameter of the motor to match the measured input power to the target input power; applying a second calibration factor to the excitation time parameter to change the speed of the motor; and energizing the motor according to the energization time parameter.
8. A brushless permanent magnet electric machine comprising a controller configured to measure an input power of the electric machine; comparing the measured input power with a target input power; applying a first calibration factor to an excitation time parameter of the motor to match the measured input power to the target input power; applying a second calibration factor to the excitation time parameter to change the speed of the motor; and energizing the motor according to the energization time parameter.
9. A brushless permanent electrical machine according to claim 8, wherein the electrical machine comprises a voltage sensor for measuring a supply voltage and a current sensor for measuring a supply current, the current sensor being located between the supply and an inverter of the electrical machine when the electrical machine is connected to the supply.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1819005.8 | 2018-11-22 | ||
| GB1819005.8A GB2579185B (en) | 2018-11-22 | 2018-11-22 | A method of controlling a brushless permanent magnet motor |
| PCT/GB2019/052950 WO2020104764A1 (en) | 2018-11-22 | 2019-10-16 | A method of controlling a brushless permanent magnet motor |
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| Publication Number | Publication Date |
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| CN113169686A true CN113169686A (en) | 2021-07-23 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN201980076821.4A Pending CN113169686A (en) | 2018-11-22 | 2019-10-16 | Method for controlling brushless permanent magnet motor |
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|---|---|
| CN (1) | CN113169686A (en) |
| GB (1) | GB2579185B (en) |
| WO (1) | WO2020104764A1 (en) |
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| US5834910A (en) * | 1996-08-23 | 1998-11-10 | Honda Giken Kogyo Kabushiki Kaisha | Ac motor controlling apparatus |
| US5880574A (en) * | 1995-12-29 | 1999-03-09 | Honda Giken Kogyo Kabushiki Kaisha | Control system for electric vehicle |
| JP2008167525A (en) * | 2006-12-27 | 2008-07-17 | Sharp Corp | Motor driver and electrical equipment equipped therewith |
| US20100253274A1 (en) * | 2009-04-04 | 2010-10-07 | Dyson Technology Limited | Power tuning an electric system |
| US20140210379A1 (en) * | 2013-01-28 | 2014-07-31 | Makita Corporation | Power tool having a brushless motor and a control unit for controlling the brushless motor |
| US20180013369A1 (en) * | 2015-01-22 | 2018-01-11 | Denso Corporation | Control apparatus for rotary electric machine |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2469142B (en) * | 2009-04-04 | 2014-04-23 | Dyson Technology Ltd | High-speed electric system |
| GB2484289B (en) * | 2010-10-04 | 2013-11-20 | Dyson Technology Ltd | Control of an electrical machine |
| DE102011083907A1 (en) * | 2011-09-30 | 2013-04-04 | Robert Bosch Gmbh | Method for operating an electronically commutated electric motor |
| US9088238B2 (en) | 2012-03-06 | 2015-07-21 | Dyson Technology Limited | Method of determining the rotor position of a permanent-magnet motor |
-
2018
- 2018-11-22 GB GB1819005.8A patent/GB2579185B/en active Active
-
2019
- 2019-10-16 WO PCT/GB2019/052950 patent/WO2020104764A1/en active Application Filing
- 2019-10-16 CN CN201980076821.4A patent/CN113169686A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5880574A (en) * | 1995-12-29 | 1999-03-09 | Honda Giken Kogyo Kabushiki Kaisha | Control system for electric vehicle |
| US5834910A (en) * | 1996-08-23 | 1998-11-10 | Honda Giken Kogyo Kabushiki Kaisha | Ac motor controlling apparatus |
| JP2008167525A (en) * | 2006-12-27 | 2008-07-17 | Sharp Corp | Motor driver and electrical equipment equipped therewith |
| US20100253274A1 (en) * | 2009-04-04 | 2010-10-07 | Dyson Technology Limited | Power tuning an electric system |
| US20140210379A1 (en) * | 2013-01-28 | 2014-07-31 | Makita Corporation | Power tool having a brushless motor and a control unit for controlling the brushless motor |
| US20180013369A1 (en) * | 2015-01-22 | 2018-01-11 | Denso Corporation | Control apparatus for rotary electric machine |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2579185B (en) | 2021-06-09 |
| WO2020104764A1 (en) | 2020-05-28 |
| GB201819005D0 (en) | 2019-01-09 |
| GB2579185A (en) | 2020-06-17 |
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