Adaptive commutation for preventing current reversal in motor drives

Abstract

Embodiments of the present disclosure relate to adaptive rectification for preventing current reversal in motor drives. A voltage regulator receives an input voltage and generates a regulated output voltage. A first feedback network compares a feedback signal to a reference signal to assert / de-assert a first pulse control signal when the reference signal is higher / lower than the feedback signal. A second feedback network compares the output voltage to a threshold signal to assert / de-assert a second control signal when the threshold signal is higher / lower than the output voltage. A charge pump is enabled if the second control signal is de-asserted and timed by the first pulse control signal to generate a supply voltage higher than the input voltage. A first pass element is enabled when the second control signal is asserted and selectively activated when the first pulse control signal is asserted. A second pass element is selectively activated when the second control signal is de-asserted.

Description

Technical Field

[0001] This application relates to adaptive rectification for preventing reverse current in motor windings, and more particularly to adaptive rectification for reducing power dissipation in motors. Background Technology

[0002] Reverse current in motor windings can occur due to the back electromotive force voltage induced in the windings by the motor's rotation. Reverse current is more likely when the motor is running under a small load, and the average current through the windings is correspondingly small. Furthermore, reverse current is more likely when the motor is running at high speeds and the back electromotive force is correspondingly high. Additionally, high current ripple can cause reverse current when the motor has a relatively small inductance. Summary of the Invention

[0003] The electric motor operates by energizing its windings and supplying current to a first end of the windings in a first direction and drawing current from a second end of the windings. Energization of the windings occurs during a first time period of the on-time, corresponding to the duty cycle of a control signal (pulse width modulation (PWM) signal) used to indicate motor operation. During the remainder of the duty cycle (off-time), the active energization of the windings ends. Conversely, current in the windings recirculates through the windings in the first direction.

[0004] During recirculation, current tends to reverse to the opposite direction. If the current reverses, the motor operates less efficiently. Therefore, it is advantageous to prevent current recirculation after the current has reversed to the opposite direction. Furthermore, it is advantageous to allow current to recirculate through the bidirectional conductive path of the transistor (in a conductive state) rather than through the body diode or freewheeling diode (in a non-conductive state).

[0005] During the recirculation cycle, current is initially allowed to recirculate through the transistor's conduction path in a first direction, and the direction of the current is monitored. If the current direction is opposite to a second direction, the transistor is turned off to prevent current from flowing through the transistor in the opposite direction. Attached Figure Description

[0006] Figure 1 The system includes a motor and a control stage.

[0007] Figure 2 An electrical model of the phases of an electric motor is shown.

[0008] Figure 3A An example of half-bridge level control is shown.

[0009] Figure 3B An example of half-bridge level control is shown.

[0010] Figure 4A and Figure 4B The diagram illustrates the power dissipation of the motor, the power dissipation of the high-side transistor, and the power dissipation of the low-side transistor relative to the current flowing through the windings when the half-bridge stage is operated according to adaptive rectification technology.

[0011] Figure 5A and Figure 5B The diagram shows the power dissipation of the motor, the power dissipation of the high-side transistor, and the power dissipation of the low-side transistor relative to the current through the windings when the half-bridge stage is operated according to synchronous rectification.

[0012] Figure 6A and Figure 6B The diagram shows the power dissipation of the motor, the power dissipation of the high-side transistor, and the power dissipation of the low-side transistor relative to the current through the windings when the half-bridge stage operates according to quasi-synchronous rectification.

[0013] Figure 7 An example of half-bridge stage control is shown when current is recirculated through the high-side transistor.

[0014] Figure 8A An attenuation mode selection level according to one embodiment is shown.

[0015] Figure 8B The attenuation mode selection level according to an embodiment is shown. Detailed Implementation

[0016] Figure 1 A system 100 including a motor 102 and a control stage 104 is shown. The control stage 104 includes a sequencing stage 106, a drive stage 108, a decay mode selection stage 110, and a half-bridge stage 112. The motor 102 may be a multiphase (e.g., three-phase) brushless direct current (DC) motor (BLDC). Therefore, the motor 102 may include multiple phases, denoted herein as U, V, W.

[0017] Half-bridge stage 112 includes multiple half-bridges 114a, 114b, 114c corresponding to multiple phases of motor 102. Each half-bridge 114a, 114b, 114c includes a respective high-side transistor 116a, 116b, 116c and a respective low-side transistor 118a, 118b, 118c. High-side transistors 116a, 116b, 116c each have a first conductive terminal coupled to voltage supply node 120 and a second conductive terminal coupled to the corresponding half-bridge node 122a, 122b, 122c. Low-side transistors 118a, 118b, 118c each have a first conductive terminal coupled to the corresponding half-bridge node 122a, 122b, 122c and a second conductive terminal coupled to ground 124. Figure 1As shown, a sensing resistor 126 can be coupled between the second conductive terminals of the low-side transistors 118a, 118b, and 118c and ground 124 to generate a current-sensing voltage representing the current passing through them. The high-side transistors 116a, 116b, and 116c and the low-side transistors 118a, 118b, and 118c each have a control terminal coupled to the driver stage 108. Furthermore, transistors 116a, 116b, 116c, 118a, 118b, and 118c each have a freewheeling diode (body diode) connected in parallel with them.

[0018] Sequencing stage 106 has inputs coupled to drive stage 108 and outputs coupled to the inputs of attenuation mode selection stage 110. Drive stage 108 has outputs coupled to control terminals coupled to high-side transistors 116a, 116b, 116c and low-side transistors 118a, 118b, 118c. Attenuation mode selection stage 110 has outputs coupled to the inputs of drive stage 108. Sequencing stage 106, drive stage 108, and attenuation mode selection stage 110 may be part of one or more controllers for motor 102.

[0019] Sequencing stage 106 generates and outputs one or more enable signals to enable commutation of the half-bridge corresponding to a phase of motor 102. Sequencing stage 106 also outputs a pulse width modulation (PWM) signal representing the commutation period. Sequencing stage 106 may also output a signal to driver stage 108 indicating the desired current direction in motor 102. Driver stage 104 receives one or more enable signals and PWM signals, and controls high-side transistors 116a, 116b, 116c and low-side transistors 118a, 118b, 118c based on one or more enable signals and PWM signals. Controlling the high-side transistors 116a, 116b, 116c and the low-side transistors 118a, 118b, 118c includes sending drive signals (HSU, HSV, HSW, LSU, LSV, LSW) to the corresponding control terminals of the high-side transistors 116a, 116b, 116c and the low-side transistors 118a, 118b, 118c to put the transistors into an on or off state.

[0020] If one or more enable signals enable the first half-bridge 114a (phase U), the driver stage 104 controls the first half-bridge 114a to commutate according to a PWM signal that depends on the current through that phase. The driver stage 104 turns on the low-side transistor 118b (phase V) of the second half-bridge 114b (or, if the high-side transistors 116a, 116b, 116c are used for current recirculation, then the high-side transistor 116b of the second half-bridge 114b is turned on). If the current reverses, the driver stage 104 controls the first half-bridge 114a and the second half-bridge 114b according to adaptive rectification. The driver stage 104 puts the third half-bridge 114c (phase W) in a high-impedance state while both the high-side and low-side transistors 116c, 118c are turned off. Depending on the enabled half-bridge represented by one or more enable signals, the driver stage 104 similarly alternates between different half-bridge pairs used for current flow.

[0021] The attenuation mode selection stage 110 receives multiple signals. One of these signals represents the voltage at each of the half-bridge nodes 122a, 122b, and 122c. The attenuation mode selection stage 110 compares the voltages at the two half-bridge nodes 122a, 122b, and 122c used for current circulation. The result of the comparison indicates the current direction in a phase of the motor 102. Based on this comparison, the attenuation mode selection stage 110 outputs a control signal to drive state 108. The control signal indicates to drive state 108 the current direction in that phase, or whether to operate the half-bridge stage 112 with synchronous (first mode) or quasi-synchronous (second mode) rectification. As described herein, drive state 108 operates transistors 116a, 116b, 116c, 118a, 118b, and 118c based on the control signal. When the current reverses, drive state 108 operates the transistors to prevent current recirculation.

[0022] Multiple windings of the motor 102 can be positioned on the stator (not shown) of the motor 102. The motor 102 can be a synchronous motor, and the speed of the motor can be synchronized with the frequency of the current in the windings. Rotation is achieved in response to the magnetic field generated by the current passing through the multiple windings.

[0023] Each of the plurality of windings has a corresponding first end and a second end. The plurality of windings can be coupled in a star configuration in the motor, whereby the first ends of the plurality of windings are coupled to each other. The second ends of the plurality of windings are coupled to half-bridge nodes 122a, 122b, and 122c, respectively. The displacement between the magnetic field generated by the current flowing through the plurality of windings and the magnetic field generated by the permanent magnet of the rotor produces the torque that causes the motor to rotate.

[0024] Figure 2An electrical model of the phases of motor 102 is shown. The windings of each phase U, V, W of motor 102 can be represented as series-coupled inductors 128a, 128b, 128c (denoted as 'Lm'), resistors 130a, 130b, 130c (denoted as 'Rm'), and voltage sources 132a, 132b, 132c (denoted as 'V'). BEMF (t)'). As described herein, the first end of the winding is coupled to a star-configured node 134, and the second end of the winding acts as a motor lead and is coupled to corresponding half-bridge nodes 122a, 122b, and 122c. Voltage sources 132a, 132b, and 132c represent the back electromotive force (EMF) voltage induced in the winding by the rotation of the motor. The level of the back EMF voltage is proportional to the rotational speed of the rotor. When the angular displacement between the rotor and stator magnetic fields is approximately 90°, the back EMF voltage is opposite to the current flowing through the winding.

[0025] Torque and the average value of the current through the winding (I) phase，avg The torque is positively correlated with the rotor and stator magnetic fields. Furthermore, the torque depends on the angular displacement between the rotor and stator magnetic fields. Typically, the torque is maximum when the angular displacement is 90°. The torque reaches its minimum when the magnetic fields are aligned and the angular displacement is 0°. The torque can be expressed as:

[0026] Tq∝I phase，avg ×f(θ) Equation (1)

[0027] Where f(θ) is a function relating the rotor and stator magnetic field displacement to torque.

[0028] Control stage 104 can drive motor 102 according to a six-step sequence technique, in which a pair of windings is energized one at a time according to the sequence of six possible current directions, each of which corresponds to a stator magnetic field vector. Control stage 104 can commutate the current to different winding pairs based on sensor readings or sensorless techniques (e.g., back EMF zero-crossing detection). The commutation current allows the angular displacement between the two magnetic fields to be kept within the desired optimal range. Control stage 104 can select the subsequent pair to energize based on the desired motor direction.

[0029] The driver stage 108 can operate transistors 116a, 116b, 116c, 118a, 118b, and 118c between on and off states based on one or more PWM signals using a six-step sequence technique. Furthermore, the driver stage 108 can directly or indirectly regulate the average current (I0). phase，avg To adjust the torque.

[0030] Figure 3A An example of control for half-bridge stage 112 is shown. The corresponding sides (first side (side 1) and second side (side 2)) of the first and second half-bridges 114a and 114b are shown in... Figure 3A As shown in [the image]. It should be noted that, although in [the image]... Figure 3A The first and second half-bridges 114a and 114b, corresponding to phases U and V respectively, are shown in the diagram, but the controls described herein can be used for any other pair of half-bridges, phases, or sides for operating the motor 102.

[0031] The attenuation mode selection stage 110 includes a first comparator 136a. The first comparator 136a has a first input (e.g., a non-inverting input) coupled to a first half-bridge node 122a and a second input (e.g., an inverting input) coupled to a second half-bridge node 122b. The first comparator 136a also has an output. A pair of windings 138a corresponding to the U and V phase windings are coupled between the half-bridge nodes 122a and 122b. This pair of windings 138a is modeled as a series-coupled inductor, resistor, and voltage source. The inductance, resistance, and voltage source of this pair of windings 138a are a collection of inductors 128a and 128b, resistors 130a and 130b, and voltage sources 132a and 132b, respectively.

[0032] While the first and second half-bridges 114a and 114b are operating during the PWM cycle, the third half-bridge 114c is in a high-impedance state. During the high-impedance state, the third high-side transistor 116c and the third low-side transistor 118c of the third half-bridge 114c are not turned on (turned off).

[0033] During the on-time of the PWM cycle, driver stage 108 turns on the first high-side transistor 116a and turns off the first low-side transistor 118a. Additionally, driver stage 108 turns off the second high-side transistor 116b and turns on the second low-side transistor 118a. During the on-time, driver stage 108 charges winding 138a by applying the supply voltage of voltage supply node 120 to winding 138a. Current flows from the first half-bridge node 122a through winding 138a to the second half-bridge node 122b. The first half-bridge 114a supplies current, and the second half-bridge 114b absorbs current.

[0034] When the on-time of the PWM cycle ends and the off-time of the PWM cycle begins, driver stage 108 uses synchronous rectification to switch the operation from current charging to current recirculation. At the start of the off-time, driver stage 108 switches the first high-side transistor 116a to a non-conducting state and the first low-side transistor 118a to a conducting state. Driver stage 108 keeps the second half-bridge 114b in the same state as during the on-time. Therefore, driver stage 108 short-circuits the second terminal of winding 138a. The short circuit allows winding 138a to discharge.

[0035] During each of the above commutation periods, the driver stage 108 can introduce an intermediate period, commonly referred to as the dead time, in which both the high-side transistor 116a and the low-side transistor 118a of the first half-bridge 114a are in a non-conducting state.

[0036] The current through winding 138a can be reversed. Because the magnitude of the current is not constant, a reverse direction may occur. The current is susceptible to ripple caused by the characteristics of the motor, the supply voltage, and the back electromotive force. In particular, when motor 102 operates at relatively low torque and uses a correspondingly low average current (I0), the current may reverse. phase，avg When the current is reversed, it is more likely to occur. For example, the low average current can be less than 1 ampere (A).

[0037] If the current reverses, the driver stage 108 does not use synchronous rectification to operate the half-bridge stage 112 during the entire turn-off time. The driver stage 108 ends synchronous rectification (first rectification mode) and uses quasi-synchronous rectification (second rectification mode) to operate the half-bridge stage 112 in response to the current reversal.

[0038] During synchronous rectification, the attenuation mode selection stage 110 compares the voltage at the end of winding 138a to indicate the direction of the current through winding 138a. For example... Figure 3A As shown, the first comparator 136a of the attenuation mode selection stage 110 receives a first voltage across the first half-bridge node 122a and a second voltage across the first half-bridge node 122b. The first voltage may represent the voltage drop (VDS1) across the first low-side transistor 118a, and the second voltage may represent the voltage drop (VDS2) across the second low-side transistor 118b. When the first low-side transistor 118a is turned on, the first voltage may be the total resistance (also known as the drain-source on-resistance (R)) between the current through the winding 138a and the conductive terminals of the first low-side transistor 118a. DS(on) The second voltage can be the product of the current through winding 138a and the drain-source on-resistance (R) of the second low-side transistor 118a. DS(on) The product of ).

[0039] The second conductive terminals of low-side transistors 118a and 118b are coupled to each other. Therefore, if the first voltage is less than the second voltage, the current does not reverse. Current flows from the second low-side transistor 118b to the first low-side transistor 118a through their common coupling, and from the first low-side transistor 118a to the second low-side transistor 118b through winding 138a.

[0040] If the current does not reverse, the attenuation mode selection stage 110 continues to use synchronous rectification operation of the half-bridge stage 112. The attenuation mode selection stage 110 continues to compare the first and second voltages during the off-time.

[0041] Conversely, if the first voltage is greater than the second voltage, the current flows in the opposite direction. Current flows from the first low-side transistor 118a to the second low-side transistor 118b through their common coupling, and from the second low-side transistor 118b to the first low-side transistor 118a through winding 138a. If the first and second voltages are the same, no current flows through winding 138a (or the current rating is 0A).

[0042] If the current reverses, the attenuation mode selection stage 110 responds by dynamically switching operation to quasi-synchronous rectification. The attenuation mode selection stage 110 outputs a control signal, commanding the driver stage 108 to turn off the first low-side transistor 118a. The first low-side transistor 118a becomes non-conductive, preventing current from flowing in the reverse direction.

[0043] Alternatively, driver stage 108 turns off the second low-side transistor 118b. The second low-side transistor 118b becomes non-conductive, preventing current from flowing as... Figure 3B The reverse flow is shown in the control example.

[0044] The attenuation mode selection stage 110 can compare the first and second voltages and output a control signal during the off-time of the PWM cycle of the PWM signal. The attenuation mode selection stage 110 can avoid comparing the first and second voltages and outputting a control signal during the on-time of the PWM cycle. Furthermore, the attenuation mode selection stage 110 can switch the operation from quasi-synchronous rectification to synchronous rectification in response to detecting that reverse direction has stopped during the off-time of the PWM cycle.

[0045] As described herein, operating the half-bridge stage 112 using adaptive rectification is superior to operating it using only synchronous rectification or only quasi-synchronous rectification during the turn-off time. Operating the half-bridge stage 112 using adaptive rectification results in less power dissipation compared to operating it using only quasi-synchronous rectification. Furthermore, operating the half-bridge stage 112 prevents the current reversal observed in synchronous rectification.

[0046] Power dissipation of winding 138a and current (I) through the winding phase，RMS The root mean square (RMS) of the power dissipation is positively correlated with the root mean square (RMS) of the power. Power dissipation is expressed as:

[0047] P d ∝i phase，RMS· Equation (2)

[0048] The reverse current reduces the current through the winding (I) phase，RMS The average value of the current (RMS) is lower, resulting in lower torque. However, current reversal contributes positively to the RMS of the current and leads to increased power consumption. Preventing current reversal reduces the mismatch between the average current and RMS and improves the efficiency of motor 102.

[0049] Furthermore, the power dissipated in response to current flowing through the freewheeling diode of the first low-side transistor 118a (when the first low-side transistor 118a is turned on) is higher than the power dissipated due to current flowing through the conductive path of the first low-side transistor 118a (when the first low-side transistor 118a is not turned on).

[0050] In exclusive synchronous rectification, the first low-side transistor 118a is turned on during the off-time. Recirculating current flows through the first low-side transistor 118a. Therefore, the power consumed by the recirculating current flowing through the first low-side transistor 118a is less than the power consumed by alternatively using a freewheeling diode to allow current to flow. However, when the current reverses, the first low-side transistor 118a is turned on, allowing reverse current to flow.

[0051] Alternatively, in exclusive quasi-synchronous rectification, the first low-side transistor 118a is not turned on during the off-time. Current recirculates through the freewheeling diode of the first low-side transistor 118a. If the current is inverted and reversed, the freewheeling diode advantageously blocks the current flow. However, in the on-state, the freewheeling diode consumes more power than the first low-side transistor 118a. Therefore, the power consumed by the recirculated current through the first low-side transistor 118a is less than that by alternative use of the freewheeling diode. However, when the current reverses during synchronous rectification, the first low-side transistor 118a is turned on and allows reverse current to flow.

[0052] Figure 4A The diagram shows the power dissipation 402 of the motor 102, the power dissipation 404 of the high-side transistor 116a, and the power dissipation 406 of the low-side transistor 118a relative to the current 408 through the winding 138a when the half-bridge stage 112 operates according to the adaptive rectification technique described herein. The inductor (Lm) 128a is 100 microhenries (μH), the resistor (Rm) 130a is 0.1 ohms (Ω), and the voltage source (V... BEMF The 132a winding is 15 volts (V), and the power supply voltage is 24V. To promote higher torque, the current 408 through the 138a winding is relatively high. The current 408 through the 138a winding is maintained above 7.5A.

[0053] Due to the increased current 408, the risk of current reversal is low. The power 402 consumed by the motor 102 varies relative to the current 408 passing through the winding 138a. Furthermore, when the high-side transistor 116a is on, it consumes power 404 during the on-time of the PWM cycle, and when it is not on, it stops consuming power 404 during the off-time of the PWM cycle. Conversely, when the low-side transistor 118a is on, it consumes power 406 during the off-time of the PWM cycle, and when it is not on, it stops consuming power 406 during the on-time of the PWM cycle.

[0054] Because in Figure 4A There is no reverse current, and the average value and RMS of the current 408 through winding 138a are comparable. The low-side transistor 118a does not consume power excessively.

[0055] Figure 4B The diagram illustrates the power dissipation 402 of the motor 102 relative to the current 408 flowing through winding 138a, the power dissipation 404 of the high-side transistor 116a, and the power dissipation 406 of the low-side transistor 118a when the half-bridge stage 112 operates according to the adaptive rectification technique described herein. Inductor (Lm) 128a, resistor (Rm) 130a, voltage source (V... BEMF (t))132a and the power supply voltage is 24V with reference Figure 4A The same value as described. The current through winding 138A is 408, which is lower than... Figure 4A The current is 408 (for example, because the motor is running at a lower torque).

[0056] like Figure 4B As shown, current 408 is prevented from reversing. When current 408 flows through winding 138a, motor 102 consumes power 402. Furthermore, when low-side transistor 118a switches from on to off, low-side transistor 118a exhibits a peak in power dissipation 406. When the current is 0A, the power dissipations 402, 404, and 406 of motor 102, high-side transistor 116a, and low-side transistor 118a are negligible (and are prevented from flowing through winding 138a due to reverse direction).

[0057] Using the adaptive rectification technique described in this article Figure 4A and 4B During operation, the power dissipation 402 of the motor 102 is the main contributor to the total power dissipation. The power dissipation 404 of the high-side transistor 116a and the power dissipation 406 of the low-side transistor 118a are relatively small compared to the power dissipation 402 of the motor 102.

[0058] Figure 5A The diagram shows the power dissipation 502 of the motor 102, the power dissipation 504 of the high-side transistor 116a, and the power dissipation 506 of the low-side transistor 118a relative to the current 508 through the winding 138a when the half-bridge stage 112 is operated according to synchronous rectification. Inductor (Lm) 128a, resistor (Rm) 130a, voltage source (V... BEMF (t))132a and the value of the power supply voltage are compared with the reference. Figure 4A The same applies. The current 508 through winding 138a remains positive and is not blocked due to reverse rotation. Therefore, the power dissipation performance of synchronous rectification is the same as... Figure 4A The power dissipation performance of the adaptive rectification technology shown is the same. The power dissipation 502 of the motor 102, the power dissipation 504 of the high-side transistor 116a, and the power dissipation 506 of the low-side transistor 118a are respectively compared with the reference. Figure 4A The power dissipation 402 of the described motor 102, the power dissipation 404 of the high-side transistor 116a, and the power dissipation 406 of the low-side transistor 118a are the same.

[0059] Figure 5B The diagram shows the power dissipation 502 of the motor 102, the power dissipation 504 of the high-side transistor 116a, and the power dissipation 506 of the low-side transistor 118a relative to the current 508 through the winding 138a when the half-bridge stage 112 is operated according to synchronous rectification. Inductor (Lm) 128a, resistor (Rm) 130a, voltage source (V... BEMF (t))132a and the power supply voltage is 24V with reference Figure 4A The same value as described. For example... Figure 5B As shown, current 508 has a ratio Figure 5A The current 508 shown has a lower average value, therefore, current 508 is more likely to reverse.

[0060] As shown in 5B, current 508 is reversed during operation of motor 102. When current 508 flows through winding 138a, motor 102 consumes power 502 regardless of the direction of current 508, resulting in increased power consumption compared to operation using the adaptive rectification technique described herein. Furthermore, high-side transistor 116a and low-side transistor 118a also consume more power.

[0061] Figure 6A The diagram shows the power dissipation 602 of the motor 102, the power dissipation 604 of the high-side transistor 116a, and the power dissipation 606 of the low-side transistor 118a relative to the current 608 through the winding 138a when the half-bridge stage 112 is operating under quasi-synchronous rectification. Inductor (Lm) 128a, resistor (Rm) 130a, voltage source (V... BEMF(t))132a and the value of the power supply voltage are compared with the reference. Figure 4A The same applies. The current 608 through winding 138a remains positive and is not blocked due to reverse polarity. Therefore, the power dissipation of motor 102 and high-side transistor 116a is similar to... Figure 4A The power dissipation performance of the adaptive rectification technology shown is quite good.

[0062] However, because the low-side transistor 118a is turned off and current 608 flows through the body diode of the low-side transistor 118a, the low-side transistor 118a consumes more power during the off-time of the PWM duty cycle. The body diode of the low-side transistor 118a dissipates more power than the conductive path of the low-side transistor 118a.

[0063] Figure 6B The diagram shows the power dissipation 602 of the motor 102, the power dissipation 604 of the high-side transistor 116a, and the power dissipation 606 of the low-side transistor 118a relative to the current 608 through the winding 138a when the half-bridge stage 112 is operating under quasi-synchronous rectification. Inductor (Lm) 128a, resistor (Rm) 130a, voltage source (V... BEMF (t))132a and the power supply voltage is 24V with reference Figure 4A The same value as described.

[0064] Similar to Figure 6A The current in the 608 is higher than that of the low-side transistor 118a during the turn-off time of the PWM cycle. Figure 4B The adaptive rectification technique dissipates more power because the low-side transistor 118a is turned off and current 608 flows through the body diode of the low-side transistor 118a. Figure 5B In contrast, quasi-synchronous rectification prevents the current from reversing.

[0065] The adaptive rectification technique described in this paper avoids current reversal. Adaptive rectification maximizes the ratio between the average current and the RMS current through the motor windings to minimize power dissipation. Current is recirculated to the switch instead of its freewheeling diode to reduce power consumption.

[0066] In one embodiment, the driver stage 108 or the attenuation mode selection stage 110 may use filtering and / or blanking to suppress or disable the transition between quasi-synchronous rectification and synchronous rectification that occurs within a defined time period. The use of filtering and / or blanking is advantageous because it prevents frequent switching between operating modes.

[0067] In one embodiment, driver stage 108 may switch from synchronous operation to quasi-synchronous operation at most once during the off-time of the PWM cycle. Therefore, when a control signal indicates that the operation will switch from synchronous operation to quasi-synchronous operation during the off-time, driver stage 108 switches to quasi-synchronous operation and maintains quasi-synchronous operation of half-bridge stage 112 until the end of the off-time.

[0068] Note that lower power dissipation allows for increased density of the control stage 104 (e.g., on a printed circuit board (PCB)). Furthermore, lower power dissipation allows for the use of fewer heatsinks, fewer ventilation devices, and the elimination of heatsinks and ventilation devices for cooling the control stage 104. Additionally, reduced power consumption lowers manufacturing costs because it allows for the use of a larger drain-source on-resistance (Rd) in the half-bridge stage 112. DS(on) This transistor has a lower drain-source on-resistance (R0). DS(on) Transistors are more economical.

[0069] Although an embodiment in which the current through the windings of motor 102 is recirculated through the low-side transistors 118a, 118b, 118c is described herein, different practices may be employed. For example, the current may be recirculated through the high-side transistors 116a, 116b, 116c.

[0070] Figure 7 An example of control of half-bridge stage 112 is shown when current is recirculated through high-side transistors 116a, 116b, and 116c. Figure 7 China and reference Figure 3A The similar elements have the same reference numerals. Figure 7 In this configuration, the first and second low-side transistors 118a and 118b are not turned on, and the first and second high-side transistors 116a and 116b are jointly coupled at the voltage source node 120 (which has a power supply voltage). A first voltage can be represented as the difference between the power supply voltage and the voltage drop (VDS1) across the first high-side transistor 116a, while a second voltage can be represented as the difference between the power supply voltage and the voltage drop (VDS2) across the second high-side transistor 116b.

[0071] When the first voltage is lower than the second voltage, current flows from the first high-side transistor 116a into the winding 138a and from the winding 138a to the second high-side transistor 116b. Conversely, when the first voltage is higher than the second voltage, current flows from the second high-side transistor 116b into the winding 138a and from the winding 138a to the first high-side transistor 116a. If in Figure 7The required current direction in the half-bridge stage 112 is counterclockwise, so the current reverses when the first voltage is higher than the second voltage. Therefore, during turn-off time operation, the decay mode selection stage 110 switches operation from synchronous rectification to quasi-synchronous rectification in response to detecting that the first voltage has become higher than the second voltage. It should be noted that various operations described herein with respect to the current recirculated through the low-side transistors 118a, 118b, 118c can be modified to accommodate the current recirculated through the high-side transistors 116a, 116b, 116c.

[0072] Figure 8A A decay mode selection stage 110 according to an embodiment is shown. The decay mode selection stage 110 is shown coupled to a half-bridge stage 112. In addition to a first comparator 136a, the decay mode selection stage 110 also includes second and third comparators 136b and 136c. The second comparator 136b has a first input (e.g., a non-inverting input) coupled to a second half-bridge node 122b and a second input (e.g., an inverting input) coupled to a second half-bridge node 122c. The second comparator 136b also has an output. The third comparator 136c has a first input (e.g., a non-inverting input) coupled to a first half-bridge node 122a and a second input (e.g., an inverting input) coupled to a third half-bridge node 122c. The third comparator 136c also has an output.

[0073] As described herein with respect to the first comparator 136a, the second comparator 136b indicates that the currents are reversed when the second and third phases are energized (e.g., according to a six-step sequence technique). The third comparator 136c indicates that the currents are reversed when the first and third phases are energized. The comparison results output from comparators 136a, 136b, and 136c are used by the attenuation mode selection stage 110 to output control signals to the drive stage 108.

[0074] Instead of using multiple comparators corresponding to different excitation phases, the attenuation mode selection stage 110 may include switches that selectively couple the comparator inputs to different phases.

[0075] Figure 8B A decay mode selection stage 110 according to an embodiment is shown. The decay mode selection stage 110 includes a comparator 140 and first and second switches 142a and 142b. The comparator 140 has first and second inputs and an output. The first switch 142a has a first terminal coupled to the first input of the comparator 140, and the second switch 142b has a first terminal coupled to the second input of the comparator 140. The first switch 142a has second and third terminals coupled to the first and second half-bridge nodes 122a and 122b, respectively. The second switch 142b has second and third terminals coupled to the second half-bridge node 122b and the second half-bridge node 122c, respectively.

[0076] The first and second switches 142a and 142b operate to couple the first and second inputs of comparator 140 to two different half-bridge nodes 122a, 122b, and 122c, respectively, for recirculating current through winding 138a. The comparison result output from comparator 140 is used by attenuation mode selection stage 110 to output a control signal to drive stage 108.

[0077] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments based on the detailed description above. Generally, the terminology used in the following claims should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted to include all possible embodiments and the full scope of the authorized equivalents of these claims. Therefore, the claims are not limited to this disclosure.

Claims

1. An electrical device, comprising: An electric motor includes multiple phases; as well as The control level includes: A half-bridge stage, comprising multiple half-bridges respectively coupled to the plurality of phases; and The driver level is configured as follows: The first and second half-bridges of the plurality of half-bridges are operated to rectify synchronously and allow current to pass in a first direction through windings corresponding to the first and second phases of the plurality of phases, the first half-bridge including a first half-bridge node and the second half-bridge including a second half-bridge node. Compare the first voltage of the first half-bridge node with the second voltage of the second half-bridge node; Based on a comparison of the first voltage and the second voltage, a first control signal is generated during synchronous rectification, the first control signal indicating that the direction of the current is changed to a second direction opposite to the first direction; and In response to receiving the first control signal, the synchronous rectification is terminated and the first and second half-bridges of the plurality of half-bridges are operated to rectify in a quasi-synchronous manner and prevent the current from passing through the winding in the second direction.

2. The electrical device according to claim 1, wherein the drive stage is configured as: Receive a second control signal indicating a pulse width modulation (PWM) period having an on-time and an off-time; and The first half-bridge and the second half-bridge are operated to rectify synchronously and quasi-synchronously during the off-time of the PWM cycle.

3. The electrical device according to claim 2, wherein the drive stage is configured as follows: During the on-time of the PWM cycle, the first half-bridge is operated to supply current to the winding, and the second half-bridge is operated to draw current from the winding.

4. The electrical equipment according to claim 1, wherein: The first half-bridge further includes a first high-side transistor coupled to the first half-bridge node, and a first low-side transistor coupled to the first half-bridge node, and The second half-bridge also includes a second high-side transistor coupled to the second half-bridge node and a second low-side transistor coupled to the second half-bridge node.

5. The electrical equipment according to claim 4, wherein: The control stage includes a comparator having a first input coupled to the first half-bridge node, a second input coupled to the second half-bridge node, and an output.

6. The electrical device of claim 4, wherein the drive stage is configured as follows: Operate the first and second half-bridges of the plurality of half-bridges to rectify synchronously through the following steps: The first high-side transistor and the second high-side transistor are controlled to be turned on, and the first low-side transistor and the second low-side transistor are controlled to be turned off, or The first low-side transistor and the second low-side transistor are controlled to be turned on, and the first high-side transistor and the second high-side transistor are controlled to be turned off.

7. The electrical device of claim 4, wherein the drive stage is configured as follows: The first half-bridge and the second half-bridge of the plurality of half-bridges are operated to perform quasi-synchronous rectification by controlling one of the first high-side transistor, the second high-side transistor, the first low-side transistor, and the second low-side transistor to be turned on and controlling the remaining transistors of the first high-side transistor, the second high-side transistor, the first low-side transistor, and the second low-side transistor to be turned off.

8. A controller for an electric motor, comprising: Multiple outputs, operable to be individually coupled to multiple transistor control terminals; as well as Multiple inputs, operable to be coupled to multiple half-bridge nodes of multiple half-bridges respectively, wherein the controller is configured to: The first half-bridge and the second half-bridge of the plurality of half-bridges are operated to rectify synchronously and allow current to pass through the windings of the motor in a first direction. The first half-bridge includes a first half-bridge node, and the second half-bridge includes a second half-bridge node. Compare the first voltage of the first half-bridge node with the second voltage of the second half-bridge node; as well as Based on a comparison of the first voltage and the second voltage, the direction of the current is detected to change to a second direction opposite to the first direction during synchronous rectification; as well as In response to detecting a change in the direction of the current to the second direction, the synchronous rectification ends and the first and second half-bridges of the plurality of half-bridges are operated to rectify in a quasi-synchronous manner and prevent the current from passing through the windings in the second direction.

9. The controller of claim 8, wherein the controller is configured to: Generate a control signal indicating the pulse width modulation (PWM) period with on-time and off-time; and The first half-bridge and the second half-bridge are operated to rectify synchronously and quasi-synchronously during the off-time of the PWM cycle.

10. The controller of claim 9, wherein the controller is configured to: During the on-time of the PWM cycle, the first half-bridge is operated to supply current to the winding, and the second half-bridge is operated to draw current from the winding.

11. The controller according to claim 8, wherein: The first half-bridge includes a first high-side transistor coupled to the first half-bridge node among the plurality of half-bridge nodes and a first low-side transistor coupled to the first half-bridge node among the plurality of half-bridge nodes, and The second half-bridge includes a second high-side transistor coupled to the second half-bridge node in the plurality of half-bridge nodes and a second low-side transistor coupled to the second half-bridge node in the plurality of half-bridge nodes.

12. The controller of claim 11, wherein the controller is configured to: The first and second half-bridges of the plurality of half-bridges are operated to rectify synchronously through the following steps: The first high-side transistor and the second high-side transistor are controlled to be turned on, and the first low-side transistor and the second low-side transistor are controlled to be turned off, or The first low-side transistor and the second low-side transistor are controlled to be turned on, and the first high-side transistor and the second high-side transistor are controlled to be turned off.

13. The controller of claim 11, wherein the controller is configured to: The first half-bridge and the second half-bridge of the plurality of half-bridges are operated to perform quasi-synchronous rectification by controlling one of the first high-side transistor, the second high-side transistor, the first low-side transistor, and the second low-side transistor to be turned on and controlling the remaining transistors of the first high-side transistor, the second high-side transistor, the first low-side transistor, and the second low-side transistor to be turned off.

14. A method for an electric motor, comprising: The first half-bridge and the second half-bridge of a plurality of half-bridges are operated to rectify in a first mode and allow current to pass through the windings of the motor in a first direction, the first half-bridge including a first half-bridge node and the second half-bridge including a second half-bridge node. Compare the first voltage of the first half-bridge node with the second voltage of the second half-bridge node; During synchronous rectification, the direction of the current is detected to change to a second direction opposite to the first direction based on a comparison of the first voltage and the second voltage; as well as In response to detecting a change in the direction of the current to the second direction, the synchronous rectification is terminated and the first and second half-bridges of the plurality of half-bridges are operated to rectify in a second mode and prevent the current from passing through the winding in the second direction.

15. The method of claim 14, comprising: Generate a control signal that indicates the pulse width modulation (PWM) period with on-time and off-time; Operate the first half-bridge and the second half-bridge to rectify in the first mode and the second mode during the off-time of the PWM cycle; as well as During the on-time of the PWM cycle, the first half-bridge is operated to supply current to the winding, and the second half-bridge is operated to draw current from the winding.

16. The method of claim 14, comprising: After operating the first and second half-bridges of the plurality of half-bridges in the second mode to rectify the current, the direction of the current is detected to change from the second direction to the first direction. as well as In response to detecting a change in the direction of the current from the second direction to the first direction, the first half-bridge and the second half-bridge of the plurality of half-bridges are operated to rectify in the first mode.

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