Drive circuit for a brushless motor

Abstract

A drive circuit for a brushless motor is described. The drive circuit includes a converter for connection to phase windings of the motor and a controller. The converter includes a plurality of branches, each branch including a high side switch and a low side switch. Each switch includes four states: (i) on, in which the switch is conductive in both a first direction and a second direction, (ii) D1, in which the switch is conductive only in the first direction, (iii) D2, in which the switch is conductive only in the second direction, and (iv) off, in which the switch is not conductive in either the first direction or the second direction. The controller controls the states of the switches to configure the converter into one of a plurality of configurations.

Description

Technical Field

[0001] This invention relates to a drive circuit for a brushless motor. Background Technology

[0002] The drive circuit for a brushless motor is responsible for controlling the excitation of the motor's phase windings. When powered by AC voltage, the drive circuit typically includes a rectifier, an active power factor correction (PFC) stage, and link capacitors. The rectifier, active PFC stage, and link capacitors together output a relatively stable DC voltage to excite the phase windings. Summary of the Invention

[0003] This invention provides a drive circuit for a brushless motor, the drive circuit comprising: a converter for connecting to a phase winding of a motor, wherein the converter includes a plurality of branches, each branch including a high-side switch and a low-side switch, each switch including four states corresponding to: (i) ON, wherein the switch is conducting in both a first direction and a second direction; (ii) D1, wherein the switch is conducting in the first direction and not conducting in the second direction; (iii) D2, wherein the switch is not conducting in the first direction and is conducting in the second direction; (iv) OFF, wherein the switch is not conducting in either the first direction or the second direction; and a controller for controlling the states of the switches to configure the converter to one of a plurality of configurations, the plurality of configurations including: a first configuration, wherein: (i) the high-side switches of the first branch and the second branch are ON, and The first configuration is as follows: (i) the low-side switches of the first and second branches are open, or (ii) the low-side switches of the first and second branches are closed, and the high-side switches of the first and second branches are open; (ii) the high-side switches of the first and second branches are closed, one of the low-side switches of the first and second branches is open, and the other low-side switch is one of D1 and D2; and (iii) the low-side switches of the first and second branches are closed, one of the high-side switches of the first and second branches is open, and the other high-side switch is one of D1 and D2; and (iv) the controller configures the converter from the first configuration to the second configuration and from the second configuration to the third configuration.

[0004] By providing a switch that can be controlled in both directions (i.e., can be turned on in both directions and can be turned off in both directions), the drive circuit can apply a voltage of either polarity to the phase winding, regardless of the voltage polarity across the converter. That is, regardless of the polarity of the supply voltage, the drive circuit can apply a positive voltage to the phase winding to energize it in a first direction (e.g., from left to right) and can apply a negative voltage to it to energize it in a second, opposite direction (e.g., from right to left). Therefore, the drive circuit can be used with an AC power supply without requiring a rectifier, PFC stage, or DC link capacitor.

[0005] However, having a switch that is not conductive in either direction presents a challenge when managing the induced energy stored in the motor, as well as any energy the motor may generate. Therefore, the controller configures the converter with a series of settings to ensure that the drive circuitry safely transitions from one operating state to the next.

[0006] The controller configures the converter to a first configuration, wherein (i) the high-side switches of the first and second branches are turned on and the low-side switches of the first and second branches are turned off, or (ii) the low-side switches of the first and second branches are turned on and the high-side switches of the first and second branches are turned off. Therefore, the current in the phase windings freewheels around (i) the high-side loop of the converter or (ii) the low-side loop of the converter.

[0007] The controller configures the converter from a first configuration to a second configuration, wherein in the second configuration (i) the high-side switches of the first and second branches are turned on, one of the low-side switches of the first and second branches is turned off, and the other low-side switch is one of D1 and D2; or (ii) the low-side switches of the first and second branches are turned on, one of the high-side switches of the first and second branches is turned off, and the other high-side switch is one of D1 and D2. Therefore, the current in the phase windings continues to freewheel around (i) the high-side loop of the converter or (ii) the low-side loop of the converter.

[0008] The controller then configures the converter from the second configuration to the third configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch are open, one of the low-side switch of the first branch and the high-side switch of the second branch is closed, and the other of the low-side switch of the first branch and the high-side switch of the second branch is one of D1 and D2. Current in the phase windings is then transferred to the power supply. The only change occurring in the second configuration is that one of the previously closed switches is now open.

[0009] In the second configuration, one of the switches is in either state D1 or D2. By placing the switch in the diode state (i.e., D1 or D2), the converter can safely switch from the second configuration to the third configuration. Specifically, the converter can safely switch from the second configuration to the third configuration simply by switching one of the switches from on (second configuration) to off (third configuration). A path is then provided for the current in the phase winding to be transferred to the power supply via the switch in the diode state.

[0010] Therefore, a configuration sequence is provided for safely transitioning from a state in which the phase current freewheels around the converter (first configuration) to a state in which the phase current is transferred to the power supply (third configuration).

[0011] The controller may include an input for receiving a signal indicating the polarity of the voltage, and the controller may configure the converter in second and third configurations such that the state of the switch is one of D1 and D2 depending on the polarity of the voltage. Therefore, if the voltage polarity is positive, the switch state is D2, and if the power supply voltage polarity is negative, the switch state is D1. Selecting D1 or D2 causes the switch to be reverse biased by the power supply voltage. Therefore, shoot-through along the branch of the converter with the switch in diode state can be avoided.

[0012] The plurality of configurations may include a fourth configuration in which the high-side switch of the first branch and the low-side switch of the second branch are open, and the low-side switch of the first branch and the high-side switch of the second branch are closed. The controller then configures the converter from the third configuration to the fourth configuration. Therefore, the phase windings are excited by the power supply voltage across the converter. Furthermore, current is driven through the phase windings in the opposite direction to that during freewheeling. Therefore, the current in the phase windings is commutated. Thus, a sequence of configurations is provided for safely transitioning from a state where current freewheels through the phase windings in a first direction (first configuration) to a state where current is driven through the phase windings in the opposite direction (fourth configuration).

[0013] The multiple configurations may include an alternative fourth configuration, in which the high-side and low-side switches of the first and second branches are in the open state. The controller then configures the converter from the third configuration to the fourth configuration. In the third configuration, where phase current is transferred to the power supply, the converter can safely switch to the fourth configuration when the phase current reaches zero (e.g., after a period of time or by monitoring the phase current). In the fourth configuration, where all switches are open, the drive circuit can safely switch to another state, including being open.

[0014] The controller may include an input for receiving a signal indicating the current in the converter, and when the current amplitude is zero, the controller can configure the converter from a third configuration to a fourth configuration. This ensures a safe transition from the third to the fourth configuration. Attached Figure Description

[0015] Embodiments will now be described by way of example with reference to the accompanying drawings, in which:

[0016] Figure 1 This is a block diagram of the motor system;

[0017] Figure 2 This is a schematic diagram of the motor system;

[0018] Figure 3 The different states of the motor system switch are shown in detail;

[0019] Figure 4 This is the first example of a configuration sequence for the converter in a motor system;

[0020] Figure 5 This is the second example of a converter configuration sequence;

[0021] Figure 6 This is the third example of a converter configuration sequence;

[0022] Figure 7 This is the fourth example in the converter configuration sequence;

[0023] Figure 8 This is the fifth example in the converter configuration sequence;

[0024] Figure 9 It shows the use of Figure 8 Example waveforms of power supply voltage, reverse EMF, and phase current when the configuration sequence is shown;

[0025] Figure 10 It shows the use of Figure 8 The configuration sequence is another example waveform of power supply voltage, reverse EMF, and phase current;

[0026] Figure 11 This is the sixth example in the converter configuration sequence;

[0027] Figure 12 It shows the use of Figure 8 or Figure 11 Example waveforms of power supply voltage, reverse EMF, and phase current when the configuration sequence is shown;

[0028] Figure 13 Example waveforms of power supply voltage, reverse EMF, and phase current caused by incorrect timing of phase excitation of the motor system are shown.

[0029] Figure 14 The diagram details four arrangements of specific converter configurations, depending on the polarity of the supply voltage and phase current; and

[0030] Figure 15This is the seventh example in the converter configuration sequence. Detailed Implementation

[0031] Figure 1 and 2 The motor system 10 includes a brushless motor 20 and a drive circuit 30. The motor system 10 is powered by an AC power supply 40, such as a household power supply.

[0032] The brushless motor 20 is a permanent magnet motor, and among other things, includes phase windings 21 and a position sensor 22. The position sensor 22 senses the angular position of the rotor of the motor 20 and outputs a signal POS. Suitable examples of the position sensor 22 include a Hall effect sensor or an optical encoder.

[0033] The drive circuit 30 includes a pair of power lines 31, an input filter 32, a converter 33, a voltage polarity detector 34, a current sensor 35, a current polarity detector 36, a gate driver 37, and a controller 38.

[0034] Power line 31 is intended to connect to the live wire and neutral terminal of AC power supply 40. Therefore, power line 31 carries AC voltage.

[0035] The input filter 32 includes a capacitor C1 and an inductor L1. The capacitor C1 is used to smooth the relatively high switching effects of the converter. Additionally, the capacitor C1 provides storage for any energy generated by the motor 2; this will be discussed in further detail below. The capacitor C1 is not required to smooth the base frequency AC voltage. Therefore, a capacitor with relatively low capacitance can be used. The inductor L1 is used to smooth any residual current ripple. The inductor L1 is designed to reduce ripple at the motor frequency, so an inductor with relatively low inductance can be used, especially when the motor 20 operates at relatively high speeds or has a relatively high number of poles.

[0036] Converter 33 is a single-phase full-bridge converter, sometimes referred to as an H-bridge converter. Converter 33 is connected to the phase winding 21 of motor 20 and includes two branches connected in parallel across power line 31. Each branch includes high-side switches SW1 and SW3 and low-side switches SW2 and SW4.

[0037] Each of switches SW1-SW4 is bidirectional and includes four states: ON, D1, D2, and OFF. When the switch is ON, it conducts in both the first and second directions. When the switch is in the D1 state, it conducts in the first direction but not in the second. Conversely, when the switch is in the D2 state, it does not conduct in the first direction but conducts in the second. Therefore, D1 and D2 can be considered as diode states. Figure 2In the specific arrangement of the switches shown, the first direction can be considered downward (i.e., D1 = downward conduction) and the second direction can be considered upward (i.e., D2 = upward conduction). Finally, when the switch is in the open state, the switch does not conduct in either the first or the second direction.

[0038] Figure 3 The different states of each switch and the equivalent circuit are shown.

[0039] Compared to a MOSFET with a body diode or an IGBT with an equivalent anti-parallel diode, a bidirectional switch has two additional switching states. For example, when the MOSFET is on, the switch is bidirectionally conductive. When the MOSFET is off, the switch continues to be unidirectionally conductive due to the inherent body diode. Unlike the bidirectional switch described above, the MOSFET does not have an open-circuit state where the switch is not conducting in either direction. Furthermore, while the MOSFET can conduct in the first direction (i.e., through the body diode) only when it is off, the switch cannot conduct only in the second opposite direction.

[0040] As described in more detail below, the advantage of providing a converter 33 with a bidirectional switch is that the switch can be controlled regardless of the polarity of the voltage on the power line, allowing voltages of either polarity to be applied to the phase windings. Therefore, the drive circuit can be used with an AC power supply without the need for a rectifier. However, the lack of an anti-parallel diode presents challenges when managing the induced energy stored in the motor and any energy that the motor may generate.

[0041] Each switch may include a gallium nitride switch, which has a relatively high breakdown voltage, making it well-suited for operation at supply voltage. However, other types of bidirectional switches capable of being controlled in both directions can be used.

[0042] Voltage polarity detector 34 detects the polarity of the supply voltage and outputs a signal V_POL. V_POL can be a digital signal that is logically high when the supply voltage polarity is, for example, positive, and logically low when the polarity is negative. Suitable examples of voltage polarity detector 34 include a ground-referenced comparator or a commercially available integrated package that may provide electrical isolation.

[0043] The current sensor 35 includes a pair of sensing resistors R1 and R2, each located in a branch of the converter. The voltage across the sensing resistors R1 and R2 is output as current sensing signals I_SENSE1 and I_SENSE2. These signals provide measurements of the current in the converter and phase windings. Although the current sensor includes a pair of sensing resistors, it should be understood that other devices, such as current transducers or current transformers, can be used to sense the current in the converter and phase windings.

[0044] Current polarity detector 36 detects the polarity of the current in converter 33 and phase winding 21 and outputs a signal I_POL. I_POL can be a digital signal; for example, the digital signal is logically high when the current polarity is positive and logically low when the polarity is negative. Figure 2 In the schematic diagram, the polarity of the current can be considered positive when it flows through the phase winding 21 from left to right, and negative when it flows through the phase winding 21 from right to left. In one example, the current polarity detector 36 may include a comparator with I_SENSE1 and I_SENSE2 as inputs.

[0045] Gate driver 37 is responsible for driving switches SW1-SW4 of converter 33. The illustrated embodiment of gate driver 37 includes a pair of half-bridge drivers 37a and 37b, each half-bridge driver 37a and 37b responsible for driving the switching of a corresponding branch of converter 33. However, it is conceivable that gate driver 37 may include a single full-bridge driver. Each of the half-bridge drivers 37a and 37b includes multiple input terminals for receiving input signals and multiple output terminals for outputting gate signals. In response to the input signal, half-bridge drivers 37a and 37b generate gate signals for driving the switching of a branch of the converter. Each switch includes two gates, therefore half-bridge drivers 37a and 37b generate a pair of gate signals for each switch.

[0046] Controller 38 is responsible for controlling the operation of motor system 10. Controller 38 includes multiple input terminals for receiving input signals and multiple output terminals for outputting control signals. The input signals received by controller 38 include a position signal POS, a voltage polarity signal V_POL, a current polarity signal I_POL, and current sensing signals I_SENSE1 and I_SENSE2. In response to the input signals, controller 38 generates and outputs four control signals S1-S4. Each control signal controls the state of a corresponding switch SW1-SW4 of converter 33. Each switch has four states: ON, D1, D2, and OFF. Therefore, each control signal has four levels. The control signals are output to gate driver 37, which drives switches SW1-SW4 in response. As described below, controller 38 outputs control signals to configure converter 33 into one of several different configurations.

[0047] The operation of motor system 1 will now be described.

[0048] To excite phase winding 21, controller 38 configures converter 33 to have the high-side switch of the first branch and the low-side switch of the second branch turned on, and the low-side switch of the first branch and the high-side switch of the second branch turned off. The specific selection of the switches depends on the desired excitation direction and the polarity of the power supply voltage, and is determined by signal V_POL. For example, to excite phase winding 21 from left to right, switches SW1 and SW4 are turned on when the polarity of the power supply voltage is positive, and switches SW2 and SW3 are turned on when the polarity of the power supply voltage is negative. Conversely, to excite phase winding 21 from right to left, switches SW2 and SW3 are turned on when the polarity of the power supply voltage is positive, and switches SW1 and SW4 are turned on when the polarity of the power supply voltage is negative.

[0049] Therefore, the controller 38 can configure the converter 33 so that the phase winding 21 can be energized in either direction regardless of the polarity of the power supply voltage; that is, a voltage of either polarity can be applied to the phase winding 21. Thus, the drive circuit 30 can use the AC power supply voltage to energize the phase winding 21 without requiring a rectifier or PFC stage.

[0050] To enable freewheeling in phase winding 21, controller 38 configures converter 33 in an alternative configuration where (i) the high-side switches of the first and second branches are on, and the low-side switches of the first and second branches are off, or (ii) the low-side switches of the first and second branches are on, and the high-side switches of the first and second branches are off. In both cases, a path is provided for the current in phase winding 21 to freewheel or circulate around converter 33. In the first scenario where the high-side switch is on, the current freewheels around the high-side loop of converter 33. In the second scenario where the low-side switch is on, the current freewheels around the low-side loop of converter 33. Figure 2 In the schematic diagram shown, the sensing resistors R1 and R2 of the current sensor are located in the lower part of the branch of converter 33. Therefore, by freewheeling around the low-side loop of converter 33, controller 38 can sense the current and excitation during freewheeling. However, freewheeling around the high-side loop of converter 33 is perfectly feasible, especially if current sensing is not required during freewheeling or if the current is sensed by other means.

[0051] During normal operation, the controller 38 can control the converter 33 to repeatedly switch between excitation and freewheeling. For example, the controller 38 can configure the converter 33 to excite the phase winding 21 for a set time period, or until the current in the phase winding 21 exceeds an upper threshold, at which point the controller 38 can configure the converter 33 to freewheel the phase winding 21. The freewheeling can then continue for a set time period, or until the current in the phase winding 21 drops below a lower threshold, at which point the controller 38 can configure the converter 33 to excite the phase winding 21. The process of sequentially exciting the phase winding 21 and freewheeling the phase winding 21 can then be repeated.

[0052] The switches SW1-SW4 of converter 33 do not have anti-parallel diodes, which poses a challenge when changing between excitation and freewheeling. For example, consider the case where switches SW1 and SW4 are on. To freewheel around the low-side loop of converter 33, switch SW1 would typically be turned off and then switch SW2 turned on. However, when SW1 is off, a path is no longer provided for the induced energy stored in motor 20. This problem does not occur with switches that include body diodes or anti-parallel diodes, as the diodes continue to provide a path. However, the lack of diodes poses a challenge not only for the induced energy stored in motor 20 but also for any energy that might be generated by motor 20. Therefore, controller 38 configures converter 33 with a series of configurations as it moves between different operating states.

[0053] Incentives to Continuous Flow

[0054] Let’s first consider the configuration sequence when moving from stimulus to regeneration.

[0055] The sequence begins with converter 33 in a first configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch of the converter are turned on, and the low-side switch of the first branch and the high-side switch of the second branch are turned off. This first configuration causes phase winding 21 to be energized by the power supply voltage. As described above, the energizing direction (i.e., the polarity of the applied voltage) will depend on which switch is turned on and the polarity of the power supply voltage.

[0056] Figure 4 (a) illustrates a specific example of the converter in a first configuration. In this specific example, switches SW1 and SW4 are turned on, and switches SW2 and SW3 are turned off. The power supply voltage is positive, so the phase windings are energized from left to right.

[0057] Then, controller 38 configures converter 33 to a second configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch are turned on, one of the low-side switch of the first branch and the high-side switch of the second branch is turned off, and the other of the low-side switch of the first branch and the high-side switch of the second branch is D1 or D2. The only change that occurs in the first configuration is that one of the previously turned-off switches is now D1 or D2. The specific selection of the switch will depend on whether freewheeling occurs around the high-side loop or the low-side loop of the converter. The specific selection of the diode state (i.e., D1 or D2) depends on the polarity of the supply voltage and is selected such that the switch is reverse biased by the supply voltage. Therefore, if the polarity of the supply voltage is positive, the switch changes from off to D2 (i.e., up-conducting). Conversely, if the polarity of the supply voltage is negative, the switch changes from off to D1 (i.e., down-conducting). Both switches remain on, so phase winding 21 continues to be energized in the second configuration.

[0058] Figure 4 (b) illustrates a specific example of the converter in the second configuration. In this particular example, the supply voltage polarity is positive, and freewheeling will occur around the low-side loop. Therefore, the low-side switch SW2 changes from open to closed (D2).

[0059] Then, controller 38 configures converter 33 to a third configuration, wherein (i) the low-side switches of the first and second branches are open, the high-side switch of the first branch is on, and the high-side switch of the second branch is D1 or D2, or (ii) the high-side switches of the first and second branches are open, the low-side switch of the second branch is on, and the low-side switch of the first branch is D1 or D2. The only change that occurs in the second configuration is that a previously on switch is now off. The specific selection of the switch from on to off depends on whether freewheeling occurs around the high-side loop or the low-side loop of converter 33. When converter 33 is in the third configuration, phase winding 21 is no longer energized by the supply voltage, and phase current freewheels or circulates around the high-side or low-side loop of converter 33.

[0060] Figure 4 (c) illustrates a specific example of the converter in the third configuration. Freewheeling occurs around the low-side loop, thus the high-side switch SW1 changes from on to off.

[0061] In the third configuration, current flows through the first switch in the ON state and the second switch in the diode state (i.e., D1 or D2). For example, in Figure 4In example (c), current flows downward through switch SW4 in the ON state and upward through switch SW2 in the diode state. With converter 33 in the third configuration, freewheeling can continue in this manner. However, conduction losses may be lower when the switches are ON compared to the diode state. Therefore, controller 38 can configure converter 33 in a fourth configuration, where (i) the high-side switches of the first and second branches are ON and the low-side switches of the first and second branches are OFF, or (ii) the low-side switches of the first and second branches are ON and the high-side switches of the first and second branches are OFF. The only change in the third configuration is that the switches previously in the diode state are now ON. When in the fourth configuration, current continues to freewheel around the high-side or low-side loop of converter 33. However, current now flows through the ON switches, thus reducing conduction losses.

[0062] Figure 4 (d) illustrates a specific example of the converter in the fourth configuration. Current continues to freewheel around the low-side loop of the converter, so both low-side switches SW2 and SW4 are turned on.

[0063] Continue to Incentive

[0064] Next, let's consider the configuration sequence from freewheeling to excitation. Furthermore, let's consider the case where the phase winding is excited in the same direction as the freewheeling phase current.

[0065] The sequence begins with converter 33 in the first configuration, wherein (i) the high-side switches of the first and second branches are turned on and the low-side switches of the first and second branches are turned off, or (ii) the low-side switches of the first and second branches are turned on and the high-side switches of the first and second branches are turned off. The phase current then freewheels around the high-side or low-side loop of converter 33.

[0066] Figure 5 (a) illustrates a specific example of the converter in a first configuration. In this specific example, high-side switches SW1 and SW3 are open, and low-side switches SW2 and SW4 are closed. Current then freewheels around the low-side loop of the converter.

[0067] Then, controller 38 configures converter 33 to a second configuration, wherein (i) one of the high-side switches of the first and second branches is turned on, and the other high-side switch is D1 or D2, and the low-side switches of the first and second branches are turned off, or (ii) one of the low-side switches of the first and second branches is turned on, and the other low-side switch is D1 or D2, and the high-side switches of the first and second branches are turned off. The only change that occurs in the first configuration is that one of the previously turned-on switches is now D1 or D2. The specific selection of the switch depends on the expected excitation direction, and therefore depends on the polarity of the supply voltage and the phase current. As described below, this particular switch is not used (i.e., not turned on) during excitation and is eventually turned off. The diode state of the selected switch (i.e., D1 or D2) is such that the phase current continues to freewheel around the high-side or low-side loop of the converter. Therefore, the selection of D1 or D2 depends on the branch of the converter to which the switch belongs and the polarity of the phase current. When the converter is in the second configuration, the phase current continues to freewheel around the high-side or low-side loop of converter 33. However, the current now flows through the first switch, which is in the ON state, and the second switch, which is in the diode state (i.e., D1 or D2).

[0068] Figure 5 (b) illustrates a specific example of the converter in the second configuration. In this particular example, switches SW1 and SW3 are open, switch SW4 is on, and switch SW2 is D2. Therefore, current continues to freewheel through switches SW2 and SW4 around the low-side loop of the converter.

[0069] Controller 38 configures converter 33 to a third configuration, in which the high-side switch of the first branch and the low-side switch of the second branch are turned on, one of the low-side switch of the first branch and the high-side switch of the second branch is D1 or D2, and the other of the low-side switch of the first branch and the high-side switch of the second branch is turned off. The only change in the second configuration is that a previously turned-off switch is now turned on. Furthermore, the turned-on switch is on the same branch as the switch in diode mode (either D1 or D2). Phase winding 21 is now energized by the power supply voltage via the two switches in the turned-on state. The switch in diode mode is now reverse-biased by the power supply voltage.

[0070] Figure 5 (c) shows a specific example of the converter in the third configuration. In this particular example, switches SW1 and SW4 are on, switch SW2 is D2, and switch SW3 is off.

[0071] It is conceivable that the excitation can continue in the third configuration without any further changes. However, if the polarity of the power supply voltage changes, a shoot-through will occur along the branch of converter 33 with the switch in diode state. Therefore, controller 38 configures converter 33 to a fourth configuration, in which the high-side switch of the first branch and the low-side switch of the second branch are turned on, and the low-side switch of the first branch and the high-side switch of the second branch are turned off. The only change that occurs in the third configuration is that the switch previously in diode state (i.e., D1 or D2) is now off.

[0072] Figure 5 (d) shows a specific example of the converter in the fourth configuration, where switches SW1 and SW4 are turned on and switches SW2 and SW3 are turned off.

[0073] The specific configuration sequence described here when moving from a freewheeling source to a stimulus is the reverse of the configuration sequence described above when moving from a stimulus to a freewheeling source. For example, it can be seen that... Figure 4 and Figure 5 The configuration sequences shown are inversely complementary. Therefore, it can be said that the controller 38 configures the converter 33 with a first sequence to excite the phase winding 21, and configures the converter 33 with a second inverse sequence to allow the phase winding 21 to freewheel.

[0074] Continue current to the reverse excitation (commutation)

[0075] Next, let's consider the configuration sequence from freewheeling to reverse excitation. In this case, the phase winding is excited in the opposite direction to the phase current, resulting in the current in the phase winding being commutated.

[0076] Similarly, the sequence begins with converter 33 in the first configuration, where (i) the high-side switches of the first and second branches are turned on and the low-side switches of the first and second branches are turned off, or (ii) the low-side switches of the first and second branches are turned on and the high-side switches of the first and second branches are turned off. Therefore, the phase current freewheels around the high-side or low-side loop of converter 33.

[0077] Figure 6 (a) illustrates a specific example of a converter in a first configuration, where switches SW1 and SW3 are open, while switches SW2 and SW4 are closed. Furthermore, current freewheels clockwise around the low-side loop of the converter.

[0078] Then, controller 38 configures converter 33 to a second configuration, wherein (i) the high-side switches of the first and second branches are turned on, one of the low-side switches of the first and second branches is D1 or D2, and the other low-side switch is off, or (ii) the low-side switches of the first and second branches are turned on, one of the high-side switches of the first and second branches is D1 or D2, and the other high-side switch is off. The only change compared to the first configuration is that one of the previously off switches is now D1 or D2. The specific selection of the switch depends on the expected excitation direction and therefore on the polarity of the supply voltage. As described below, this particular switch is used (i.e., turned on) during excitation and is eventually turned on. The specific selection of the diode state (i.e., D1 or D2) also depends on the polarity of the supply voltage and is selected such that the switch is reverse biased by the supply voltage. Therefore, if the polarity of the supply voltage is positive, the switch changes from off to D2 (i.e., up-conducting). Conversely, if the polarity of the supply voltage is negative, the switch changes from off to D1 (i.e., down-conducting).

[0079] Figure 6 (b) shows a specific example of the converter in the second configuration, where switches SW2 and SW4 are on (so the current continues to freewheel around the low-side loop of the converter), switch SW1 is off, and switch SW3 is D2.

[0080] The controller 38 configures the converter 33 to a third configuration, in which the high-side switch of the first branch and the low-side switch of the second branch are open, one of the low-side switch of the first branch and the high-side switch of the second branch is closed, and the other of the low-side switch of the first branch and the high-side switch of the second branch is either D1 or D2. The only change in the second configuration is that a previously closed switch is now open. Furthermore, the open switch is in the same branch as the switch in diode mode (either D1 or D2). When the converter 33 is in the third configuration, the induced energy stored in the motor 20 is transferred to the capacitor C1.

[0081] Figure 6 (c) shows a specific example of the converter in the third configuration, where switches SW1 and SW4 are off, switch SW2 is on, and switch SW3 is D2.

[0082] Finally, controller 38 configures converter 33 to a fourth configuration, in which the high-side switch of the first branch and the low-side switch of the second branch are open, and the low-side switch of the first branch and the high-side switch of the second branch are closed. The only change in the third configuration is that the switches previously in diode mode (i.e., D1 or D2) are now closed. When converter 33 is in the fourth configuration, phase winding 21 is energized by the power supply voltage in the opposite direction to the previous configuration. Any remaining induced energy stored in motor 20 is transferred to capacitor C1. When all the induced energy has been transferred to the capacitor, the current in the phase winding is reversed.

[0083] Figure 6 (d) shows a specific example of the converter in the fourth configuration, where switches SW1 and SW4 are off and switches SW2 and SW3 are on. Therefore, the phase windings are now energized from right to left.

[0084] From incentive to reverse incentive (reversal)

[0085] There may be situations where it is desired or necessary to reverse the excitation direction (i.e., the commutation phase winding) during excitation, and the controller can use the following sequence to configure the converter.

[0086] The sequence begins with converter 33 in the first configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch of the converter are turned on, and the low-side switch of the first branch and the high-side switch of the second branch are turned off. Therefore, the phase windings are energized in a direction that depends on the specific selection of the on / off switches and the polarity of the power supply voltage.

[0087] Figure 7 (a) illustrates a specific example of the converter in a first configuration. In this specific example, switches SW1 and SW4 are on, while switches SW2 and SW3 are off. The power supply voltage is positive, so the phase windings are energized from left to right.

[0088] The controller 38 then configures the converter 33 to a second configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch are turned on, and the low-side switch of the first branch and the high-side switch of the second branch are either D1 or D2. The only change that occurs in the first configuration is that the two previously open switches are now either D1 or D2. The specific selection of the diode state (i.e., D1 or D2) depends on the polarity of the power supply voltage and is selected such that the switch is reverse biased by the power supply voltage. Therefore, if the polarity of the power supply voltage is positive, the switch changes from open to D2 (i.e., upward conduction). Conversely, if the polarity of the power supply voltage is negative, the switch changes from open to D1 (i.e., downward conduction). When the converter 33 is in the second configuration, the phase winding 21 continues to be energized in the same direction as in the first configuration.

[0089] Figure 7(b) illustrates a specific example of the converter in the second configuration. In this particular example, the polarity of the power supply voltage is positive. Therefore, switches SW1 and SW4 are on, and switches SW2 and SW3 are D2 (i.e., up-conducting). Thus, the phase windings continue to be energized from left to right.

[0090] The controller 38 configures the converter 33 to a third configuration, in which the high-side switch of the first branch and the low-side switch of the second branch are open, and the low-side switch of the first branch and the high-side switch of the second branch are either D1 or D2. The only change in the second configuration is that the two previously closed switches are now open. When the converter is in the third configuration, the induced energy stored in the motor 20 is transferred to the capacitor C1 via the diode-state switch.

[0091] Figure 7 (c) shows a specific example of the converter in the third configuration, where switches SW1 and SW4 are open, and switches SW2 and SW3 are D2 (i.e., up-conducting). The induced energy stored in the motor is then transferred to the capacitor (not shown) via switches SW2 and SW3.

[0092] Finally, controller 38 configures converter 33 to a fourth configuration, in which the high-side switch of the first branch and the low-side switch of the second branch are open, and the low-side switch of the first branch and the high-side switch of the second branch are closed. The only change in the fourth configuration is that the switches that were previously in diode mode (i.e., D1 or D2) are now closed. When converter 33 is in the fourth configuration, phase winding 21 is energized by the power supply voltage in the opposite direction to the previous configuration. Any remaining induced energy stored in motor 20 is transferred to capacitor C1. When all the induced energy has been transferred to the capacitor, the current in the phase winding is reversed.

[0093] Figure 7 (d) shows a specific example of the converter in the fourth configuration, where switches SW1 and SW4 are off and switches SW2 and SW3 are on. Therefore, the phase windings are now energized from right to left.

[0094] reactive current

[0095] When the rotor of motor 20 rotates, a back EMF is induced in the phase winding 21. Near the zero-crossing point of the power supply voltage, the amplitude of the back EMF may exceed the power supply voltage. Therefore, the amplitude and polarity of the phase current may become uncontrollable. Furthermore, the phase current at this time is mainly reactive because, in the case of a relatively low or no power supply voltage, the active power is relatively low or non-existent. This reactive current can be large and may affect the efficiency of the motor system. Motor 20 can be designed such that the motor's machine parameters, such as peak back EMF and phase inductance, help to mitigate the reactive current. However, this inevitably impairs the motor's performance. As will now be explained, the converter can be configured to maintain control of the phase current near the zero-crossing point of the power supply voltage. In this way, the motor design can be separated from considerations of reactive current.

[0096] In one example, controller 38 can configure converter 33 such that all switches SW1-SW4 are open at or near the zero-crossing of the supply voltage. Therefore, no phase current flows. Thus, there is no reactive power, but also no active power. However, the loss of active power is unlikely to be a problem. Even if phase current were present, the active power at or near the zero-crossing of the supply voltage would be low or zero because the amplitude of the supply voltage is low or zero. Therefore, the reduction in total active power due to the opening of all switches is likely to be small and unlikely to adversely affect the overall performance of the motor.

[0097] In motor systems with switches that include body diodes or anti-parallel diodes, phase currents cannot be controlled in this way. In particular, the diodes continue to provide a path for reactive current even when the switch is open. Therefore, the motor system described herein is able to control phase currents in a way that is simply impossible in other motor systems.

[0098] By disconnecting all switches of converter 33, there are now periods when no current is drawn from the supply voltage. Therefore, the harmonic content of the current drawn from the supply voltage may increase. Consequently, controller 38 can configure the converter in different ways so that the phase current remains under control while better shaping the current drawn from the supply voltage. Two configuration sequences will now be described.

[0099] Reactive current - first configuration sequence

[0100] The first sequence begins with converter 33 in the first configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch of the converter are turned on, and the low-side switch of the first branch and the high-side switch of the second branch are turned off. Therefore, the phase winding 21 is energized in a direction that depends on the specific selection of the turned-on switches and the polarity of the power supply voltage.

[0101] Figure 8(a) illustrates a specific example of the converter in a first configuration. In this specific example, switches SW1 and SW4 are on, while switches SW2 and SW3 are off. The power supply voltage is positive, so the phase windings are energized from left to right.

[0102] The controller 38 monitors the amplitude of the current in the phase winding via current detection signals I_SENSE1 and I_SENSE2. If the rate of change of the phase current amplitude is less than a threshold, the controller 38 configures the converter 33 to a second configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch are either D1 or D2, and the low-side switch of the first branch and the high-side switch of the second branch are off. The only change occurring in the first configuration is that the two previously on switches are now either D1 or D2. The specific selection of the diode state (i.e., D1 or D2) depends on the polarity of the power supply voltage and is selected such that the switch is forward biased by the power supply voltage. Therefore, if the polarity of the power supply voltage is positive, the switch changes from on to D1 (i.e., downward conduction). Conversely, if the polarity of the power supply voltage is negative, the switch changes from on to D2 (i.e., upward conduction).

[0103] Figure 8 (b) shows a specific example of the converter in the second configuration. The power supply voltage is positive, so switches SW1 and SW4 are D1, and switches SW2 and SW3 are open.

[0104] The controller 38 continues to monitor the amplitude of the current in the phase winding 21. If the amplitude of the phase current reaches zero, the controller 38 configures the converter 33 to a third configuration, in which all switches of the converter 33 are open. The controller keeps the converter 33 in the third configuration until the phase winding 21 is re-energized.

[0105] Now refer to Figure 9 Describe the implementation of this specific configuration sequence. Figure 9 The power supply voltage, the induced reverse EMF in the phase winding, and the phase current are shown.

[0106] At T0, the converter is configured in the first configuration, and the phase windings are energized (e.g., from left to right). In this particular example, the phase windings are energized when the reverse EMF has the opposite polarity to the supply voltage. Therefore, the supply voltage is boosted by the reverse EMF. The end result is an increase in current in the phase windings. In this particular example, the phase current polarity is positive. If the phase windings were energized in the opposite direction (e.g., from right to left), the phase current polarity would be negative. However, the behavior of the phase current amplitude (i.e., absolute value) is the same. Between T0 and T1, the amplitude of the reverse EMF decreases, transitions from zero, and then increases. The polarity of the reverse EMF has now changed and is therefore opposite to the supply voltage. Therefore, the rate of change of the phase current amplitude decreases during T0 to T1. At T1, the amplitude of the reverse EMF is the same as the supply voltage amplitude. Furthermore, as previously stated, the reverse EMF is opposite to the supply voltage. Therefore, the rate of change of the phase current is zero at T1. Between T1 and T2, the amplitude of the reverse EMF is greater than the supply voltage, thus reducing the amplitude of the phase current; that is, the rate of change of the phase current amplitude is now negative. When the rate of change of the phase current amplitude is less than a threshold, the controller configures the converter to a second configuration. In this particular example, the threshold is zero. Therefore, the converter is configured to the second configuration when the rate of change of the phase current amplitude becomes negative. In the second configuration, the previously switched-on switch is now in diode mode. The switch is forward biased by a combination of the supply voltage and the self-inductance voltage across the phase winding. Therefore, the current continues to flow in the same direction as before (e.g., from left to right). When the phase current amplitude reaches zero, the switch is now reverse biased by the reverse EMF. Therefore, the phase current is clamped to zero. Finally, between T2 and T3, the controller configures the converter to a third configuration. When all switches are now open, the phase current remains zero.

[0107] Using this specific configuration sequence, current continues to be drawn from power supply 40, thereby improving the shape of the current waveform. However, the phase current is always controlled. In particular, the switch is configured in diode mode, which clamps the current to zero and prevents reverse EMF from reversing the polarity of the phase current.

[0108] Figure 10 Another example of the implementation of this particular configuration sequence is shown.

[0109] Again, at T0, the converter is configured in the first configuration, the phase windings are energized, and the phase current rises. Between T0 and T1, the amplitude of the reverse EMF decreases, transitions from zero, and then increases. Therefore, the rate of change of the phase current amplitude decreases between T0 and T1. In T1, the amplitude of the reverse EMF is the same as the amplitude of the supply voltage, so the rate of change of the phase current is zero, and the amplitude of the reverse EMF is now opposite to the supply voltage. Between T1 and T2, the amplitude of the reverse EMF is greater than the supply voltage, so the amplitude of the phase current decreases. Again, in this particular example, when the rate of change of the phase current amplitude is less than zero, the controller configures the converter in the second configuration. Therefore, when the rate of change of the phase current amplitude becomes negative, the converter is configured in the second configuration. The switch is forward biased by a combination of the supply voltage and the self-induced voltage across the phase windings, so current continues to flow. Between T1 and T2, the amplitude of the reverse EMF rises, reaches its peak, and begins to decline. In T2, the amplitude of the reverse EMF is again the same as the supply voltage, so the rate of change of the phase current is zero. From T2 to T3, the amplitude of the power supply voltage is greater than that of the reverse EMF, therefore the amplitude of the phase current increases again. Therefore, compared to... Figure 9 In contrast to the example, the phase current never reaches zero. The controller then keeps the converter in the second configuration until the time for freewheeling or commutating the phase winding arrives.

[0110] exist Figure 10 In the example, switches SW1 and SW4 can remain on continuously. In fact, keeping the switches on may be beneficial because conduction losses can be higher when the switches are in diode mode. Therefore, the controller can configure the converter to a second configuration when the rate of change of the amplitude of phase current (i) is less than a threshold, and the amplitude of phase current (ii) is less than another threshold. In this way, the efficiency of the motor system can be improved by switching to the second configuration only when the phase current is likely to drop to zero. Figure 10 In the example shown, another threshold can be set low enough that switches SW1 and SW4 remain on despite a momentary decrease in the amplitude of the phase current.

[0111] Reactive current - second configuration sequence

[0112] The second sequence again begins with converter 33 in the first configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch of the converter are turned on, and the low-side switch of the first branch and the high-side switch of the second branch are turned off. Therefore, the phase winding 21 is energized in a direction that depends on the specific selection of the on / off switch and the polarity of the power supply voltage.

[0113] Figure 11(a) illustrates a specific example of the converter in a first configuration. In this specific example, switches SW1 and SW4 are on, while switches SW2 and SW3 are off. The power supply voltage is positive, so the phase windings are energized from left to right.

[0114] Controller 38 monitors the amplitude of the phase current in converter 33. If the rate of change of the phase current amplitude is less than a threshold, controller 38 configures converter 33 to a second configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch are turned on, and the low-side switch of the first branch and the high-side switch of the second branch are either D1 or D2. The only change occurring in the first configuration is that the two previously open switches are now either D1 or D2. The specific selection of D1 or D2 depends on the polarity of the power supply voltage and is selected such that the switches are reverse biased by the power supply voltage. Therefore, if the polarity of the power supply voltage is positive, the switch changes from open to D2 (i.e., upward conduction). Conversely, if the polarity of the power supply voltage is negative, the switch changes from open to D1 (i.e., downward conduction).

[0115] Figure 11 (b) shows a specific example of the converter in the second configuration. The power supply voltage is positive, so switches SW1 and SW4 are on, and switches SW2 and SW3 are D2.

[0116] Then, controller 38 configures converter 33 to a third configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch are open, and the low-side switch of the first branch and the high-side switch of the second branch are either D1 or D2. The only change in the second configuration is that the two previously on switches are now off. The switches in diode mode (i.e., D1 or D2) are now forward biased by the self-induced voltage across the phase winding. The self-induced voltage is opposite to the supply voltage and the reverse EMF. Therefore, the amplitude of the phase current is reduced.

[0117] Figure 11 (c) shows a specific example of the converter in the third configuration, where switches SW1 and SW4 are now off, and switches SW2 and SW3 remain D2.

[0118] Controller 38 continues to monitor the phase current in the third configuration. When the phase current amplitude is zero, controller 38 configures converter 33 to the fourth configuration, in which all switches of converter 33 are open.

[0119] Clearly, the two configuration sequences described in this section are similar. The common concept of these two sequences is that the controller 38 initially configures the converter 33 with one pair of switches on (and the other pair off) to excite the phase winding and drive current through the phase winding 21 in a specific direction. The controller 38 monitors the phase current, and if the rate of change of the phase current amplitude is less than a threshold, the controller 38 configures the converter 33 to another configuration, where one pair of switches is in a diode state (and the other pair off), allowing the phase current to continue flowing in the same direction. Although the selection of the switches (i.e., SW1 / SW4 or SW2 / SW3) and the selection of the diode states (i.e., D1 or D2) differ in the two sequences, they share the commonality that when the phase current is zero, the switches are reverse-biased by the anti-EMF, thereby preventing the phase current polarity from reversing. Although the second sequence includes an additional configuration (i.e., the second configuration), only this additional configuration is needed to safely transition from the first configuration to the third configuration.

[0120] Although these two configuration sequences are similar, there are still differences. When the switch in the first sequence is in diode mode, the switching direction is the same as the power supply voltage direction (see, for example, see...). Figure 8 (b) Therefore, if the supply voltage subsequently exceeds the reverse EMF, the switch is forward biased, and the phase current rises, as... Figure 10 As shown in the example. Conversely, when the second sequence of switches is in diode mode, the switching direction is opposite to the direction of the power supply voltage (see, for example, see...). Figure 11 (b) Therefore, if the supply voltage subsequently exceeds the reverse EMF, the phase current continues to be clamped to zero. Another difference between the two sequences is that when the switches in the first sequence are in diode mode, the self-induced voltage across the phase winding is opposite only to the reverse EMF. Conversely, when the switches in the second sequence are in diode mode, the self-induced voltage across the phase winding is opposite to both the reverse EMF and the supply voltage. Therefore, the phase current decreases at a faster rate, and the controller has a longer time to disconnect all switches before the next event.

[0121] The two sequences mentioned above are not mutually exclusive, and the controller can use one or both sequences when controlling the excitation of the phase winding.

[0122] Polarity change of power supply voltage

[0123] Two configuration sequences have been described that provide better control over the phase currents near the zero-crossing point of the supply voltage. In particular, both sequences prevent phase current polarity reversal that can occur when the reverse EMF exceeds the supply voltage. As will now be explained, both configuration sequences also prevent phase current reversal in the event that the supply voltage polarity changes during excitation.

[0124] Let's consider the first of the two configuration sequences described above, namely... Figure 8 The configuration sequence shown. Figure 12 An example scenario showing a change in power supply voltage polarity during excitation is illustrated.

[0125] At T0, the controller configures the converter to the first configuration (e.g., SW1 / SW4 on, SW2 / SW3 off). Therefore, the phase windings are energized, and the phase current rises. At T1, the amplitude of the reverse EMF is the same as the amplitude of the supply voltage, so the rate of change of the phase current is zero. Between T1 and T2, the amplitude of the reverse EMF is greater than the supply voltage, so the amplitude of the phase current decreases. In this particular example, when the rate of change of the phase current amplitude is less than zero, the controller configures the converter to the second configuration. Therefore, the controller configures the converter to the second configuration shortly after T1 (e.g., SW / SW4 is D1, SW2 / SW3 off). At T2, the polarity of the supply voltage changes. Therefore, the supply voltage, along with the reverse EMF, is opposite to the self-induced voltage across the phase windings. At T3, the phase current has dropped to zero. Now, the switches in diode mode are reverse biased by the reverse EMF and the supply voltage. Therefore, regardless of the change in the polarity of the supply voltage, the phase current is clamped to zero. Then, at some point after T3, the controller configures the converter to the third configuration (i.e., SW1-SW4 disconnected).

[0126] Now let's consider the second configuration sequence, namely... Figure 11 The configuration sequence shown. As will become apparent, this situation is almost identical to that described above for the first configuration sequence. Refer again... Figure 12 .

[0127] At T0, the controller configures the converter to the first configuration (e.g., SW1 / SW4 on, SW2 / SW3 off). Therefore, the phase windings are energized, and the phase current increases. At T1, the amplitude of the reverse EMF is the same as the amplitude of the supply voltage, so the rate of change of the phase current is zero. Between T1 and T2, the amplitude of the reverse EMF is greater than the supply voltage, so the amplitude of the phase current decreases. When the rate of change of the phase current amplitude is less than zero, the controller configures the converter to the third configuration. Therefore, the controller configures the converter to the second configuration (e.g., SW1 / SW4 on, SW2 / SW3 D2), and then shortly after T1, to the third configuration (e.g., SW1 / SW4 off, SW2 / SW3 D2). Now, the supply voltage, along with the reverse EMF, is opposite to the self-induced voltage across the phase windings. However, at T2, the polarity of the supply voltage changes. The supply voltage now acts in the same direction as the self-induced voltage. However, the amplitude of the reverse EMF is significantly greater than the supply voltage, so the phase current continues to decrease. At T3, the phase current reaches zero. The switch, which is in diode mode, is now reverse biased by the reverse EMF. Therefore, the phase current is clamped to zero. Then, sometime after T3, the controller configures the converter in a different configuration (i.e., SW1-SW4 are off).

[0128] It's conceivable that when the switch is still in diode mode, a situation might arise where the polarity-reversed power supply voltage could exceed the reverse EMF. Although in Figure 12 This scenario is unlikely to occur in the given condition, but it's conceivable that it might happen at lower speeds with smaller anti-EMF amplitudes. In this case, the switch would be forward biased by the supply voltage, and the phase current would rise again. However, the polarity of the phase current would remain unchanged. This situation is somewhat similar to... Figure 10 .

[0129] Incorrect timing

[0130] Phase winding 21 may be unintentionally energized at the wrong time. For example, noise in the position signal POS may cause the controller 38 to energize phase winding 21 at the wrong time. Incorrect timing of the energization may cause the phase current to flow in the opposite direction to the desired direction.

[0131] Figure 13An example of incorrect excitation timing is shown. At T0, the phase winding is excited by turning on switches SW1 and SW4. T0 should occur before the reverse EMF zero-crossing. However, for whatever reason, T0 occurs exactly after the reverse EMF zero-crossing. Therefore, the phase winding is excited when the reverse EMF is opposite to the supply voltage. Furthermore, at T0, the amplitude of the reverse EMF is greater than the amplitude of the supply voltage. Therefore, when the phase winding is excited (i.e., when switches SW1 / SW4 are turned on), the phase current is driven in the opposite direction to the direction expected by the reverse EMF. Therefore, in Figure 13 In the example, as expected, the phase current is negative, not positive.

[0132] Once the polarity of the phase current is sensed to be opposite to the expected polarity, the controller 38 can configure the converter 33 such that the switched-on switch is now in diode mode. The selection of diode mode (i.e., D1 or D2) ensures that a path continues to be provided for the phase current to flow from phase winding 21 to capacitor C1. Therefore, in Figure 13 In the example, the controller can configure switches SW1 and SW4 to D1 (i.e., down-conduct) shortly after T0.

[0133] Between T0 and T1, the amplitude of the reverse EMF increases, reaches a peak, and then decreases. However, throughout the entire T0-T1 period, the reverse EMF is greater than the supply voltage. Therefore, during the time period T0-T1, the amplitude of the phase current increases, despite its negative polarity. In T1, the amplitude of the reverse EMF is the same as the supply voltage, so the rate of change of the phase current is zero. Between T1 and T2, the amplitude of the supply voltage is greater than the reverse EMF. Furthermore, the reverse EMF becomes zero and increases the supply voltage. Therefore, the amplitude of the phase current decreases during the time period T1-T2. In T2, the phase current is zero and is then clamped by the switches. Then, shortly after T2, the controller 38 configures the converter 33 so that all switches are open.

[0134] Although the controller 38 can employ the above configuration sequence to manage phase currents with incorrect polarity, this situation can be completely avoided. In each of the above examples where the phase windings are energized, the sequence begins with the high-side switch of the first branch and the low-side switch of the second branch turned on, and the low-side switch of the first branch and the high-side switch of the second branch turned off. However, this sequence can alternatively begin with either D1 or D2 as the high-side switch of the first branch and the low-side switch of the second branch, and the low-side switch of the first branch and the high-side switch of the second branch turned off. The selection of D1 or D2 causes the switches to be forward biased by the supply voltage. Since the switches are activated in a diode state rather than an on state, the phase current is prevented from flowing in the wrong direction. The controller can then monitor the phase current, i.e., monitor the phase current via a current sensing signal. In the event of a rise in phase current, the controller can revert to one of the above configuration sequences. Specifically, the controller can configure the converter with the first configuration of the above sequence, wherein the high-side switch of the first branch and the low-side switch of the second branch are turned on, and the low-side switch of the first branch and the high-side switch of the second branch are turned off. Alternatively, if the phase current does not rise, the controller can configure the converter to open all switches in preparation for the next event.

[0135] In this particular configuration sequence, the switch first enters diode mode before being turned on. Therefore, this particular sequence cannot be used when the phase current has already flowed through the converter in the opposite direction (i.e., opposite to the excitation direction). As mentioned above, at or near the zero-crossing of the supply voltage, the phase current can be clamped to zero after each excitation cycle. Therefore, this configuration sequence can be used in combination with either of the two sequences described above in conjunction with reactive current.

[0136] closure

[0137] The motor system may need to be shut down at any time. Shutdown can occur as part of normal operation or as a response to a fault condition. If the converter's switches include body diodes or anti-parallel diodes, shutdown may simply require opening all switches. The diodes then provide a path for transferring the induced energy stored in the motor to the capacitors of the input filter. For this motor system 10, switches SW1-SW4 do not have such diodes, therefore the converter 33 must be configured in such a way that it can process the induced energy of the motor 20 before switches SW1-SW4 can be opened.

[0138] In response to shutdown, controller 38 configures converter 33 to a first configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch are D1 or D2, and the low-side switch of the first branch and the high-side switch of the second branch are open. The selection of the switches (i.e., SW1 / SW4 or SW2 / SW3) to the diode state depends on the polarity of the power supply voltage and the phase current, and is selected such that the induced energy stored in motor 20 is transferred to capacitor C1. The selection of the diode state (i.e., D1 or D2) depends on the polarity of the power supply voltage and is selected such that the switch is reverse biased by the power supply voltage. Therefore, if the polarity of the power supply voltage is positive, the switch switches to D2 (i.e., upward conduction). Conversely, if the polarity of the power supply voltage is negative, the switch switches to D1 (i.e., downward conduction). Therefore, the first configuration has four possible arrangements, such as... Figure 14 As shown in detail below.

[0139] Depending on the configuration of converter 33 immediately preceding its shutdown, controller 38 can configure converter 33 with one or more pre-configurations prior to the first configuration, allowing converter 33 to safely switch to the first configuration. For example, if switches SW1 and SW4 are on at the off point, the controller can configure the converter in a pre-configuration where switches SW1 and SW4 are on and switches SW2 and SW3 are in a diode state. Controller 38 then configures converter 33 to the first configuration, where, in this case, switches SW2 and SW3 are in a diode state, while switches SW1 and SW4 are off.

[0140] In the first configuration, the induced energy stored in the motor 20 is transferred to the capacitor C1, and the amplitude of the phase current decreases. When the current drops to zero, the current is clamped by the switch, and the controller 38 configures the converter 33 to a configuration where all switches are off.

[0141] As described above, the specific selection of the switch and diode states in the first configuration depends on the polarity of the power supply voltage. Specifically, the switch and diode states are selected such that the power supply voltage is opposite to the self-induced voltage across the phase winding. However, when converter 33 is in the first configuration, the polarity of the power supply voltage can be changed. In this case, controller 38 reconfigures converter 33 such that the power supply voltage continues to act opposite to the self-induced voltage.

[0142] When reconfiguring the converter, the controller 38 configures the converter 33 to a second configuration, wherein the high-side switch of the first branch and the low-side switch of the second branch are one of D1 and D2, and the low-side switch of the first branch and the high-side switch of the second branch are the other of D1 and D2. The only change that occurs in the first configuration is that the two previously open switches are now in a diode state. Furthermore, these two switches have diode states opposite to the other two switches. Thus, for example, if switches SW1 and SW4 are D1, then switches SW2 and SW3 are D2, and vice versa. Therefore, the converter 33 has a configuration in which all switches SW1-SW4 are in a diode state.

[0143] The controller 38 then configures the converter 33 to a third configuration, in which the high-side switch of the first branch and the low-side switch of the second branch are open, and the low-side switch of the first branch and the high-side switch of the second branch are either D1 or D2. The only change in the second configuration is that the two switches that were previously in diode mode in the first configuration are now open. The induced energy stored in the motor 20 continues to be transferred to the capacitor C1, thus reducing the amplitude of the phase current. When it drops to zero, the current is clamped by the switches, and the controller 38 configures the converter 33 to the final configuration in which all switches are open.

[0144] Figure 15 An example sequence during shutdown is shown. Figure 15 (a) illustrates the converter in a first configuration. In this particular example, the phase current polarity is positive (i.e., the current flows from left to right), and the supply voltage polarity is positive. Therefore, switches SW2 and SW3 are in diode state D2, and switches SW1 and SW4 are open. Switches SW2 and SW3 are forward biased by the self-induced voltage across the phase windings, so the phase current continues to flow from left to right, and the induced energy stored in the motor is transferred to the capacitor. Figure 15 (b) illustrates the converter in the second configuration. Previously open switches SW1 and SW4 are now in diode state D1. As described above, the converter is configured to the second configuration in response to a change in the power supply voltage polarity. Therefore, in this example, the power supply voltage polarity is now negative. Consequently, switches SW2 and SW3 are now forward biased by the power supply voltage, and switches SW1 and SW4 are reverse biased. Figure 15 (c) shows the converter in the third configuration, where switches SW2 and SW3 are open. Switches SW1 and SW4 are then forward biased by the self-induced voltage across the phase windings. Therefore, the phase current continues to flow from left to right, and the induced energy stored in the motor is transferred to the capacitor. Finally, although not shown, the converter is configured in its final configuration with all switches SW1-SW4 open when the phase current drops to zero.

[0145] Gate Driver

[0146] As described above, in the event of a fault, it may be necessary to disconnect the motor system 10. While it is generally expected that the controller 38 controls the shutdown sequence, a fault may exist within the controller 38. Therefore, the door driver 37 is also configured to shut down the motor system 10 in the event of a fault. This fault may occur due to a missing or conflicting control signal from the controller, or due to overcurrent on one or more switches.

[0147] Gate driver 37 receives signals V_POL and I_POL, which provide indications of the polarity of the power supply voltage and phase current, respectively. In the event of a fault, the gate driver uses these signals to shut down the motor system 10 using the same sequence described above; that is, gate driver 37 generates a sequence of gate signals that depends on the voltage and current polarities.

[0148] like Figure 14 As shown, the first configuration of the sequence has four possible permutations. Therefore, in response to a fault, the gate driver generates gate signals for: (i) driving the first pair of switches to D1 and driving the second pair of switches to open when the voltage polarity is positive and the current polarity is positive; (ii) driving the first pair of switches to D2 and driving the second pair of switches to open when the voltage polarity is negative and the current polarity is positive; (iii) driving the first pair of switches to open and driving the second pair of switches to D1 when the voltage polarity is positive and the current polarity is negative; and (iv) driving the first pair of switches to open and driving the second pair of switches to D2 when the voltage polarity is negative and the current polarity is negative.

[0149] although Figure 2 As not shown, gate driver 37 also receives an input signal that provides a measurement of the phase current amplitude. The input signal can be analog or digital. For example, the gate driver can receive current sensing signals I_SENSE1 and I_SENSE2. Alternatively, the input signal can be a digital signal that is logically high when the phase current is not zero and logically low when the phase current is zero. When the phase current amplitude is zero, the gate driver uses the input signal to drive all switches to open.

[0150] If the polarity of the power supply voltage changes in the first configuration, gate driver 37 configures converter 33 to a second configuration, and then a third configuration. In the second configuration, gate driver 37 generates gate signals for driving the first pair of switches to D1 and the second pair of switches to D2. More specifically, gate driver 37 generates gate signals for: (i) driving the first pair of switches to D1 and the second pair of switches to D2 when the current polarity is positive, and (ii) driving the first pair of switches to D2 and the second pair of switches to D1 when the current polarity is negative.

[0151] In the third configuration, gate driver 37 employs the same logic as in the first configuration. The polarity of the power supply voltage has changed, so different switch pairs are in different diode states, but the logic for determining which switch and which diode state (i.e., D1 or D2) remains unchanged. Therefore, the gate driver generates gate signals for: (i) driving the first pair of switches to D1 and driving the second pair of switches to open when the voltage polarity is positive and the current polarity is positive; (ii) driving the first pair of switches to D2 and driving the second pair of switches to open when the voltage polarity is negative and the current polarity is positive; (iii) driving the first pair of switches to open and driving the second pair of switches to D1 when the voltage polarity is positive and the current polarity is negative; and (iv) driving the first pair of switches to open and driving the second pair of switches to D2 when the voltage polarity is negative and the current polarity is negative.

[0152] While it is not unknown that gate drivers include fault protection logic, it is both unknown and unusual for gate drivers to monitor the polarity of voltage and / or current and then generate gate signals accordingly. Although the gate drivers described herein use the polarity of both the supply voltage and the phase current to generate gate signals, there are cases where gate drivers may use only the polarity of either the supply voltage or the phase current.

[0153] Using the drive circuit described herein, a motor can be driven using an AC power supply voltage without the need for a rectifier or PFC stage. This is made possible by providing a converter with a bidirectional switch. In particular, the switch can be controlled so that a voltage of either polarity can be applied to the phase windings regardless of the polarity of the power supply voltage. However, providing a bidirectional switch is not without its challenges. In particular, the lack of an anti-parallel diode presents a challenge when managing the induced energy stored in the motor and any energy that the motor may generate. Therefore, the controller configures the converter with different configuration sequences to ensure that the motor system safely transitions from one operating state to the next. While various configuration sequences have been described, the controller does not necessarily have to adopt every single one.

Claims

1. A drive circuit for a brushless motor, the drive circuit comprising: A converter for connection to the phase windings of the motor, wherein the converter includes multiple branches, each branch including a high-side switch and a low-side switch, and each switch including four states corresponding to: (i) ON, wherein the switch is on in both a first direction and a second direction; (ii) D1, wherein the switch is on in the first direction and not on in the second direction; (iii) D2, wherein the switch is not on in the first direction and is on in the second direction; (iv) OFF, wherein the switch is not on in either the first direction or the second direction; and A controller is configured to control the state of the switch to configure the converter into one of a plurality of configurations, the plurality of configurations including: In the first configuration, (i) the high-side switches of the first branch and the second branch are turned on and the low-side switches of the first branch and the second branch are turned off, or (ii) the low-side switches of the first branch and the second branch are turned on and the high-side switches of the first branch and the second branch are turned off. The second configuration is as follows: (i) the high-side switches of the first and second branches are turned on, one of the low-side switches of the first and second branches is turned off, and the other low-side switch is one of D1 and D2; or (ii) the low-side switches of the first and second branches are turned on, one of the high-side switches of the first and second branches is turned off, and the other high-side switch is one of D1 and D2; and In the third configuration, the high-side switch of the first branch and the low-side switch of the second branch are open, one of the low-side switch of the first branch and the high-side switch of the second branch is closed, and the other of the low-side switch of the first branch and the high-side switch of the second branch is one of D1 and D2. The controller configures the converter from a first configuration to a second configuration, and from a second configuration to a third configuration.

2. The driving circuit according to claim 1, wherein, The controller includes an input for receiving a signal indicating voltage polarity, and the controller configures the converter in a second and a third configuration such that the state of the switch is one of D1 and D2 depending on the voltage polarity.

3. The driving circuit according to claim 1 or 2, wherein: The plurality of configurations includes a fourth configuration in which the high-side switch of the first branch and the low-side switch of the second branch are disconnected, and the low-side switch of the first branch and the high-side switch of the second branch are connected. The controller configures the converter from a third configuration to a fourth configuration.

4. The driving circuit according to claim 1 or 2, wherein, The plurality of configurations includes a fourth configuration in which the high-side switches and low-side switches of the first and second branches are in an open state; and the controller configures the converter from the third configuration to the fourth configuration.

5. The driving circuit according to claim 4, wherein, The controller includes an input for receiving a signal indicating the current in the converter, and when the current amplitude is zero, the controller configures the converter from a third configuration to a fourth configuration.

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