MOTOR CONTROL CIRCUIT FOR ELECTRIC MOTOR

Abstract

A motor control circuit for an electric motor with a first node, wherein the motor control circuit includes a first resistive shunt device configured to be coupled to the first node.

Description

The present disclosure relates to a motor control circuit for an electric motor. BACKGROUND Fig. 1A is a schematic representation of a known brushless direct current (BLDC) motor 100. The BLDC motor 100 comprises a rotor 102 and a stator 104. The stator 104 comprises three phase circuits 108, 110, 112. Each of the phase circuits 108, 110, 112 comprises a wire coil. Brushless DC motors (BLDC) are characterized by high efficiency and excellent controllability and are used in many applications. During operation, current typically flows through two of the three coils, while the third is in a high-impedance state, as shown in Fig. 1A, where the phase circuit 112 is in the high-impedance state. In the high-impedance state, no current flows through the phase circuit 112. This creates a tristate node with parasitic impedance, which tends to oscillate. The BLDC motor can be a delta BLDC motor 100. Fig. 1B is an equivalent circuit diagram of the BLDC motor 100, arranged as a typical delta BLDC motor. The BLDC motor 100 comprises the three phase circuits 108, 110, 112, each of which includes a wire coil that can be represented by an inductor with an inductance Lm in series with a resistor Rm. Each phase circuit 108, 110, 112 is coupled to two of the three nodes v0, v1, v2. It is evident that the nodes can be referred to as "pins". For each node v0, v1, and v2, a motor driver with a half-bridge can apply the required voltage to control the current flow through the motor windings represented by the three Lm-Rm networks. Further control patterns 114, 116, and 118 are shown for each of the nodes v0, v1, and v2. Fig. 1C is a schematic representation of the motor network, which is represented by the equivalent circuit diagram of Fig. 1B, combined with a typical switching network for the three motor phases 108, 110, 112. The switching network includes the transistors M1, M2, M3, M4, M5, M6. For example, if the current flow is chosen to run from node v0 to node v2, transistors M1 and M6 are switched on, while the remaining transistors remain switched off. This current path is designated with the reference numeral 120. In each switching phase, there is a pair of transistors that is in the off state. In this example, both transistors at node v1 (M3 and M4) remain off. They therefore do not provide a current path, but instead create a parasitic capacitance in series with the inductor-resistor (LR) network. For current to flow from node v0 to node v2, there is a parasitic capacitance 122 of transistor M3 and a parasitic capacitance 124 of transistor M4. Transistors M1-M6 can be power field-effect transistors (FETs). The parasitic capacitances (represented by parasitic capacitors 122, 124) can result from a gate-drain capacitance (denoted as "Cgd"), a gate-source capacitance (denoted as "Cgs"), and / or a drain-source capacitor (denoted as "Cds") of the respective power FETs. Fig. 1D is an equivalent small-signal circuit diagram of the motor network and the switching network of Fig. 1C for the current path 120 from node v0 to node v2. The parasitic capacitance C1 is representative of the parasitic capacitors 122, 124. The circuit in Fig. 1D also includes a shunt current source 126 for reducing overshoot or oscillation. The shunt current source 126 is coupled in series with a switch S0. This illustrates a known technique for solving this problem by using a shunt current source connected between the tristate node (node ​​V1) and ground GND. However, using a current source is not very effective for reducing oscillation, requires a large chip area, and increases power loss. SUMMARY It is desirable to provide an improved system that reduces or overcomes one or more of the problems mentioned above. According to a first aspect of the disclosure, a motor control circuit for an electric motor is provided, comprising a first node, wherein the motor control circuit includes a first resistive shunt device configured to couple with the first node. Optionally, the electric motor includes a variety of motor phase circuits, which include a first phase circuit coupled to the first node. Optionally, the electric motor includes a stator that incorporates a variety of motor phase configurations. Optionally, the electric motor includes: i) a rotor; or ii) a rotor and a stator; or iii) electric magnets. Optionally, the electric motor can be a direct current (DC) motor. Optionally, the electric DC motor is a brushless electric DC motor. Optionally, the first resistive shunt device is configured to provide a current flow path from the first node. Optionally, the current flow path from the first node to another node can have constant voltage or constant potential. Optionally, the first resistive shunt device is configured to provide the current flow path from the first node in order to dampen voltage oscillations at the first node. Optionally, the first resistive shunt device is configured to provide the current flow path from the first node to dampen voltage oscillations at the first node when the first node is in a tristate state. The first node in the tristate is optional if the first phase switch is in a high impedance state. Optionally, the first resistive shunt device includes a resistive element of the first shunt device. Optionally, the first resistive shunt device includes a first shunt device switch coupled to the resistive element of the first shunt device. Optionally, the first resistive shunt device is coupled with a constant potential. Optionally, the first resistive shunt device includes a first active load configured to adapt to voltage oscillations at the first node. Optionally, the first active load is configured to adapt to voltage oscillations at the first node based on a frequency of voltage oscillations across device, process, temperature and / or supply voltage corners. Optionally, the motor control circuit includes a switching network configured to switch between different switching states in order to control the current flow through each of the multitude of motor phase switching circuits. Optionally, the switching network includes a half-bridge with one or more switching network switches and / or one or more switching network diodes. Optionally, each of the switching network switches includes a switching network transistor. Optionally, each of the switching network transistors includes at least one transistor and / or each of the switching network transistors includes one or more diodes. Optionally, each of the switching network transistors includes a bipolar transistor, an IGBT and / or a thyristor. Optionally, each of the switching network transistors includes a p-type or an n-type MOSFET. Optionally, the switching network is configured to be coupled with a first voltage rail to a first supply voltage and a second voltage rail to a second supply voltage. Optionally, the first supply voltage can be positive or negative, and the second supply voltage can also be positive or negative. Optionally, the first phase circuit includes a first phase circuit coil with a first coil inductance and a first coil resistance. Optionally, the first resistive shunt device includes a resistive element of the first shunt device, and the resistance of the resistive element of the first shunt device is greater than the resistance of the first coil resistance. Optionally, the first resistive shunt device is configured to provide a current flow path from the first node to dampen voltage oscillations at the first node, and the resistance of the resistive element of the first shunt device is sufficient to provide critical damping of the voltage oscillations. Optionally, the variety of motor phase circuits includes a second phase circuit coupled to a second node and a third phase circuit coupled to a third node. Optionally, the motor control circuit includes a second resistive shunt device configured to be coupled to the second node, and / or a third resistive shunt device configured to be coupled to the third node. Optionally, the first phase switch is coupled with the third node, and / or the second phase switch is coupled with the first node, and / or the third phase switch is coupled with the second node. Optionally, the first phase circuit includes a first phase circuit coil with a first coil inductance and a first coil resistance, the second phase circuit includes a second phase circuit coil with a second coil inductance and a second coil resistance, and the third phase circuit includes a third phase circuit coil with a third coil inductance and a third coil resistance. Optionally, the motor control circuit includes a switching network configured to switch between different switching states to control the current flow through each of the multitude of motor phase circuits. Optionally, the switching network includes a half-bridge with one or more switching network switches and / or one or more switching network diodes. Optionally, the half-bridge includes a first switching network switch configured to be coupled to a first voltage rail and the third node, a second switching network switch configured to be coupled to the third node and a second voltage rail, a third switching network switch configured to be coupled to the first voltage rail and the first node, a fourth switching network switch configured to be coupled to the first node and the second voltage rail, a fifth switching network switch configured to be coupled to the first voltage rail and the second node, and a sixth switching network switch configured to be coupled to the second node and the second voltage rail. Optionally, the first phase circuit is coupled with the third node, the second phase circuit is coupled with the first node, and the third phase circuit is coupled with the second node. Optionally, the first resistive shunt device is configured to provide the current flow path from the first node to dampen voltage oscillations at the first node when the first node is in a tristate. The first node in the tristate is optional if the switching network is in a first switching state in which current can flow through one or both of the second and third phase circuits and no current may flow through the first phase circuit. Optionally, the switching network is in the first switching state when the first and sixth switching network switches are in an on state and the second, third, fourth and fifth switching network switches are in the off state. According to a second aspect of the disclosure, an electric motor device is provided which includes an electric motor with a first node and a motor control circuit with a first resistive shunt device configured to couple with the first node. It is obvious that the electric motor of the second aspect may include features described in connection with the first aspect, and may include further features as described here, according to the understanding of experts. According to a third aspect of the disclosure, a method for providing a motor control circuit for an electric motor with a first node is provided, wherein the method includes providing the motor control circuit with a first resistive shunt device configured to couple with the first node. It is evident that the procedure of the third aspect may include a use and / or provision of the features described in connection with the first aspect and / or the second aspect, and may include further features as described here, according to the understanding of experts. BRIEF DESCRIPTION OF THE DRAWINGS The disclosure is described in detail below by way of example and with reference to the accompanying drawings, wherein: Fig. 1A is a schematic representation of a known brushless direct current (BLDC) motor, Fig. 1B is an equivalent circuit of the BLDC motor of Fig. 1A, Fig. 1C is a schematic representation of the motor network, represented by the equivalent circuit of Fig. 1B, combined with a typical switching network for the three motor phases, Fig. 1D is a small-signal equivalent circuit of the motor network and the switching network of Fig. 1C when one of the nodes is in the tristate; Fig. 2A is a timing diagram showing simulation results for a practical implementation of the motor network and the switching network of Fig. 1C, Fig. 2B is another timing diagram showing simulation results for a practical implementation of the motor network and the switching network of Fig. 1C; Fig.Figure 3A is a schematic representation of an electric motor and a motor control circuit according to a first embodiment of the present disclosure; Figure 3B is a schematic representation of a specific embodiment of the stator and the motor control circuit according to a second embodiment of the present disclosure; Figure 3C is a schematic representation of an electric motor with the stator and the motor control circuit 301 according to a third embodiment of the present disclosure; Figure 3D is an equivalent circuit diagram of the electric motor and the motor control circuit of Figure 3C; Figure 4A is a schematic representation of a specific embodiment of the stator and the motor control circuit according to a fourth embodiment of the present disclosure; Figure 4B is a small-signal equivalent circuit diagram of the motor network and the switching network of Figure 4A; and Figure 4B is a small-signal equivalent circuit diagram of the motor network and the switching network of Figure 4A.Fig. 5A is a time diagram with simulation results for a practical implementation of the stator and motor control circuit of Fig. 4A as part of the electric motor of Fig. 3C, Fig. 5B is a time diagram with simulation results for a practical implementation of the stator and motor control circuit of Fig. 4A as part of the electric motor of Fig. 3C, and Fig. 5C is a frequency diagram with the simulation results of Fig. 5B in the frequency domain. DETAILED DESCRIPTION Fig. 2A is a time graph 200 with simulation results for a practical implementation of the motor network and the switching network of Fig. 1C. It shows the voltage at node v1 when node v1 is in the tristate region (when the switches are configured as described with respect to Fig. 1C), without shunt current source 126 (curve 202) and with shunt current source 126 (curve 204). A highlighted section shows the graph over a different time frame to illustrate the difference between curves 202 and 204. Fig. 2A shows the overshoot of node v1 in the tristate region, caused by the parasitic capacitances of the power FETs M3 and M4. Curve 204 shows this current damped with the shunt current source 126 as a current source of 1 mA, and curve 202 shows the undamped case. It is obvious that, since the system in Fig. 1C is symmetrical, the phase circuits 108, 110, 112 all behave approximately the same, so that the curves 202, 204 also show the behavior that would occur for nodes v0 and v2 if they were in the tristate. Fig. 2B is another timing diagram 206 with simulation results for a practical implementation of the motor network and the switching network of Fig. 1C . If the voltage pulses have a low amplitude, the damping with the shunt current source 126 works well, but if the voltage increases, the damping is no longer sufficient and the oscillation can increase drastically. The voltage at node v1 is shown when node v1 is in the tristate region (when the switches are configured as described with respect to Fig. 1C) with the shunt current source 126 (curve 208). In the present example, the voltage oscillations have a larger amplitude than shown in Fig. 2A, so the damping provided by the shunt current source 126 is no longer sufficient when the average voltage of node v1 increases and the oscillation intensifies. Curve 210 shows the current flowing through the shunt current source 126 during operation. A higher current than required would lead to higher losses and an overdamped system at low voltages. A major disadvantage of the known solution with the shunt current source 126 is its limited effectiveness in damping overshoot. It should be noted that the magnetic fields can also induce a variable voltage at the node in the tristate when the rotor angle changes. This variable voltage can be seen in Fig. 2B (for ideal damping) and Fig. 5A. This voltage cannot be derived from the previously described simple equivalent circuit. Fig. 3A is a schematic representation of an electric motor 320 and a motor control circuit 301 according to a first embodiment of the present disclosure. The electric motor 320 comprises a node N1. The motor control circuit 301 comprises a resistive shunt device 306 configured for coupling with node N1. The electric motor 320 can include a variety of motor phase circuits 302, which include a phase circuit 304 coupled with a node N1. In the present embodiment, the electric motor 320 comprises a stator 300, which includes a plurality of motor phase circuits 302. It is evident that in further embodiments, the electric motor 320 may comprise a rotor or both a rotor and a stator. In a further embodiment, the electric motor 320 may include electric magnets, for example, if the electric motor 320 is a linear motor. The motor control circuit 301 can control the operation of the electric motor by applying a sufficient voltage to control the current flow through each of the phase circuits 302. The motor control circuit 301 can receive control signals, for example from a control device, and control the operation of the electric motor based on the received control signals. In the present example, the plurality of phase circuits 302 includes an N-th phase circuit 308 to illustrate that certain embodiments of this disclosure can include any number of phase circuits 302, according to the understanding of those skilled in the art. “N” denotes an integer, as is the usual notation. The motor control circuit 301 can include a resistive shunt device for each of the plurality of phases 302. In the present example, this is represented by an Nth resistive shunt device 309 coupled to a node of the Nth phase circuit 308. The stator 300 can be used with an electric direct current (DC) motor, for example with the electric brushless DC (BLDC) motor, as shown in Fig. 1A-1D. The phase circuit 304 can, for example, include a phase circuit coil with a coil inductance and a coil resistance. The resistive shunt device 306 can be configured to provide a current flow path from node N1. In particular, the resistive shunt device 306 can provide a resistive current path. The resistive shunt device 306 can provide a current flow path from node N1 to dampen the voltage oscillation at node N1 that can occur when node N1 is in the tristate. Node N1 can be in the tristate when phase circuits 304 and 310 are in a high-impedance state. Phase circuits 304 and 310 can be in the high-impedance state when stator 300 is configured so that no current can flow through phase circuit 312. While the phase circuits 304 and 310 are in the high impedance state, the stator 300 can be configured so that current can flow through one or more of the other phase circuits of the plurality of phase circuits 302. Fig. 3B is a schematic representation of a specific embodiment of the stator 300 and the motor control circuit 301 according to a second embodiment of the present disclosure. In the present embodiment, the plurality of phase circuits 302 further comprises a phase circuit 310 coupled to a node N2 and a phase circuit 312 coupled to a node N3. It is obvious that further embodiments of the stator 300 may include one or more further phase circuits. The motor control circuit 301 can include a resistive shunt device 314 configured to be coupled to node N2, which can be used to prevent oscillations at node N2 when, for example, node N2 is in the tristate. The resistive shunt device 314 can essentially function as described for the resistive shunt device 306, but with respect to node N2 instead of node N1, according to the understanding of those skilled in the art. In further specific embodiments, the resistive shunt device 314 can be implemented as for the embodiments of the resistive shunt device 306 described here, according to the understanding of those skilled in the art. The motor control circuit 301 can include a resistive shunt device 316 configured to be coupled to node N3, which can be used to prevent oscillations at node N3 when, for example, node N3 is in the tristate. The resistive shunt device 316 can essentially function as described for the resistive shunt device 306, but with respect to node N3 instead of node N1, according to the understanding of those skilled in the art. In further specific embodiments, the resistive shunt device 316 can be implemented as for the embodiments of the resistive shunt device 306 described here, according to the understanding of those skilled in the art. It is obvious that in further embodiments in which the plurality of phase circuits 302 include additional phase circuits, each of the one or more of the additional phase circuits may also be coupled to a resistive shunt device of the motor control circuit 301, which may be implemented according to one of the embodiments of the resistive shunt device 306 as described here, and according to the understanding of those skilled in the art. Phase switch 304 can be coupled between node N1 and node N3. Phase switch 310 can be coupled between node N1 and node N2. Phase switch 312 can be coupled between node N2 and node N3. Fig. 3C is a schematic representation of the electric motor 320, comprising the stator 300, and the motor control circuit 301 according to a third embodiment of the present disclosure. It is obvious that in further embodiments, the stator 300 of the present embodiment can be implemented using one of the embodiments of the stator 300 described herein. It is also obvious that in further embodiments, the motor control circuit 301 of the present embodiment can be implemented using one of the embodiments of the motor control circuit 301 described herein. The electric motor 320 further comprises a rotor 322. It is evident that in a specific embodiment the motor control circuit 301 can be coupled to each of the nodes N1, N2, N3 to control the operation of the electric motor 320. The electric motor 320 can essentially function as described for the motor 100, but including the motor control circuit 301 of the present disclosure, which provides improved performance of the system in the event of voltage oscillations, for example at a tristate node. It is evident that further embodiments of the present disclosure may include other types of motors with phased circuits, which may be represented by an RL circuit (or similar) subject to overshoot with a fixed time constant, with the motor control circuit 301 of the present disclosure with the resistive shunt device 306 to reduce oscillations. For example, and as discussed above, the electric motor 320 can comprise a rotor and / or a stator. In certain embodiments, one or both of the rotor and the stator can comprise a variety of phase configurations that are subject to overshoot / oscillations. In another embodiment, the electric motor 320 can comprise electric magnets, for example, if the electric motor 320 is a linear motor. In a particular embodiment, the electric magnets can comprise a plurality of phased configurations that are subject to overshoot / oscillations. Fig. 3D is an equivalent circuit diagram of the electric motor 320 and the motor control circuit 301 from Fig. 3C . The phase circuit 304 can include a phase circuit coil 324 with a coil inductance Lm1 and a coil resistance Rm1, as represented by the inductor Lm1 and the resistance Rm1 coupled in series in the equivalent circuit of Fig. 3C. The phase circuit 310 can include a phase circuit coil 326 with a coil inductance Lm2 and a coil resistance Rm2, as represented by the inductor Lm2 and the resistance Rm2 coupled in series in the equivalent circuit of Fig. 3C. The phase circuit 312 can include a phase circuit coil 328 with a coil inductance Lm3 and a coil resistance Rm3, as represented by the inductor Lm3 and the resistance Rm3 coupled in series in the equivalent circuit of Fig. 3C. Fig. 4A is a schematic representation of a particular embodiment of the stator 300 and the motor control circuit 301 according to a fourth embodiment of the present disclosure. In the present embodiment, the resistive shunt device 306 comprises a resistive element Rs1 of the shunt device. The resistive element Rs1 of the shunt device can be a resistor. The shunt device 306 can further comprise a switch s1 that is coupled to the resistive element Rs1 of the shunt device. The resistive shunt device 306 can be coupled to GND; however, in further embodiments, the resistive shunt device 306 can be coupled to another constant potential, such as the supply voltage VDD. In the present example, the constant potential coupled to the resistive shunt device 306 is ground (GND). It is obvious that the resistive element Rs1 of the shunt device can be called shunt resistance Rs1 if the resistive element of the shunt device is the shunt resistance. In certain embodiments, the shunt resistor Rs1 can be coupled to GND (e.g., via switch s1), while in other embodiments, the shunt resistor Rs1 can be coupled to a different constant potential, such as the supply voltage VDD. This potential changes the losses in resistor Rs1, but not the time constant of the damping circuit. In an alternative embodiment, the resistive shunt device 306 can include an active load configured to adapt to voltage oscillations at node N1. The active load can be configured to adapt to voltage oscillations at node N1 based on a frequency of the voltage oscillations across device, process, temperature, and / or supply voltage limits. The motor control circuit 301 can further comprise a switching network configured to toggle between different switching states to control the current flow through each of the plurality of motor phase circuits 304, 310, 312. The switching network can comprise a half-bridge with one or more switching network switches and / or one or more switching network diodes. In the present example, the half-bridge comprises switching network switches, each switching network switch comprising a switching network transistor M1, M2, M3, M4, M5, M6. In the present example, there is a first switching network transistor pair formed by transistors M1 and M2; a second switching network transistor pair formed by transistors M3 and M4; and a third switching network transistor pair formed by transistors M5 and M6. The stator 300 functions essentially as described for the circuit shown in Fig. 1C, but including the resistive shunt device 306 to reduce the problem of voltage oscillations. In the present example, the switching network transistors M1-M6 each comprise n-type MOSFETs. However, it is obvious that in further embodiments the switching network transistors M1-M6 can also comprise p-type MOSFETs. In further embodiments, each of the switching network transistors M1-M6 can comprise at least one transistor. In further embodiments, each of the switching network transistors M1-M6 can comprise one or more diodes. In further embodiments, each of the switching network transistors M1-M6 can comprise a bipolar transistor, an IGBT, and / or a thyristor. The motor control circuit 301 can be configured to be coupled to a voltage rail 400 with a supply voltage VDD and a voltage rail 402 with a supply voltage GND, which is ground. In certain embodiments, the voltage rail 400 can have a positive or negative supply voltage. In certain embodiments, the voltage rail 402 can have a positive or negative supply voltage. For example, the resistive shunt device 306 can be used for motor bridges with a positive and a negative supply rail, for example + / - VDD, where VDD is the supply voltage. In this case, the shunt resistor Rs1 can consume less power because ground (GND) is the midpoint. The resistance of the resistive element Rs1 of the shunt device can be greater than the resistance of the coil resistor Rm1. Preferably, the resistance of the damping resistor (provided by the resistive element Rs1 of the shunt device) is significantly greater than the parasitic resistance of the winding (the coil resistance Rs1). Otherwise, extreme power losses may occur. The resistive shunt device 306 can be configured to provide a current flow path from node N1 to dampen voltage oscillations at node N1, for example, when the node is in the tristate, as discussed above. The resistance of the resistive element Rs1 of the shunt device may be sufficient to provide critical damping of the voltage oscillations. In the present embodiment, the switching network transistor M1 is coupled to the voltage rail 400 and the node N3; the switching network transistor M2 is coupled to the node N3 and the voltage rail 402; the switching network transistor M3 is coupled to the voltage rail 400 and the node N1; the switching network transistor M4 is coupled to the node N1 and the voltage rail 402; the switching network transistor M5 is coupled to the voltage rail 400 and the node N2; and the switching network transistor M6 is coupled to the node N2 and the voltage rail 402. In the present embodiment, the phase circuit 304 is coupled to node N3; the phase circuit 310 is coupled to node N1; and the phase circuit 312 is coupled to node N2. As previously discussed, the resistive shunt device 306 can be configured to provide the current flow path from node N1 to dampen voltage oscillations at node N1 when node N1 is in the tristate. Node N1 can be in the tristate if the switching network is in a switching state where current can flow through one or both of the phase circuits 310, 312 and no current can flow through the phase circuit 304, so that the phase circuit 304 is in a high impedance state. In the present example, the switching network is in the switching state in which node N1 is in the tristate when the switching network transistors M1 and M6 are in an on state and the switching network transistors M2-M5 are in an off state. In this switching state, where the current flow is selected from node N3 to node N2, transistors M1 and M6 are switched on, while the remaining transistors remain in the off state. The current path is designated with the reference symbol 404. Fig. 4B is an equivalent small-signal circuit diagram of the motor network and the switching network of Fig. 4A for the current path 404 from node N3 to node N2. The parasitic capacitance C1 represents the parasitic capacitors of the switching network transistors M3 and M4. Instead of using a shunt current source (as shown, for example, in Fig. 1D), embodiments of this disclosure use a resistive shunt device. In the present example, the resistive shunt device 306 comprises the resistive element Rs1 of the shunt device, which is a shunt resistor. In certain embodiments, improved overshoot damping and lower power consumption are achieved compared to conventional shunt current source technology, since the shunt resistance of the resistive element Rs1 of the shunt device is significantly higher than the resistance Rm1 of the motor winding. Furthermore, the resistive element Rs1 of the shunt device is simple and small to implement. It is obvious that the switch s1 is optional, and in a particular embodiment the switch s1 can be used to activate the damping function of the resistive element Rs1 of the shunt device only when the motor is switched on and the node N1 is in the tristate. It is evident that in further embodiments the order of the switch s1 and the resistive element Rs1 of the shunt device can be reversed, and in further embodiments the resistive element Rs1 of the shunt device can be divided into two or more parts, with the switch s1 being placed between parts of the resistive elements. Fig. 5A is a timing diagram with simulation results for a practical implementation of the stator 300 and the motor control circuit 301 of Fig. 4A as part of the electric motor 320 of Fig. 3C with a resistive shunt device for each of the phase circuits 304, 310, 312. For example, the stator 300 can be arranged as shown in Fig. 3B, with the resistive shunt device 306 coupled to node N1, the resistive shunt device 314 coupled to node N2, and the resistive shunt device 316 coupled to node N3. The following are shown: the voltage at node N3 (curve 500), the voltage at node N1 (curve 502), and the voltage at node N2 (curve 504). Fig. 5A shows the terminal voltages of the electric motor 320 with ideal damping. Fig. 5A shows the voltage at the three terminals N1, N2, N3 in the tristate, either stably connected to ground or pulsed. The following describes the detailed implementation of the specific embodiment of the stator 300 and the motor control circuit 301 of Fig. 4A as part of the electric motor 320 of Fig. 3C, with a resistive shunt device for each of the phase circuits 304, 310, 312 when the phase circuits 304, 310, 312 are in the tristate. The following equations and description refer to node N1 in the tristate. However, it is obvious that the following equations and description are also applicable to the other nodes N2 and N3 when they are in the tristate during the operation of electric motor 320. We initially assume that the motor 320 does not induce any voltages and that node N1 does not depend on the angle of the rotor 322. The variables used in the formulas are: • V3: Voltage of the motor control switching node N3 - either VDD or zero • V1: Voltage of the motor control tristate node N1 • Lm1: Equivalent inductance of each of the phase circuit 304 • Rm1: Equivalent resistance of the phase circuit 304 • C: Parasitic capacitance of the two switches M3, M4 at node N1 in tristate (labeled C1 in Fig. 4B). • Rs: Resistance of the shunt resistor Rs1 for reducing or eliminating voltage oscillation at node N1. The transfer function is: With direct current (DC), s approaches zero (s => 0): To keep the amplitude unchanged: Rs >> Rm1: Rewriting the equation with ω0, the natural frequency of the system (assuming Rs >> Rm1) is: Therefore: The damping ratio: 1) 0 < ζ < 1: (underdamped system): the system oscillates before settling at its final value. 2) ζ = 1: (critically damped system): the system reaches its final value without oscillation. 3) ζ > 1: (overdamped system): the system shows no oscillations. The step response is slower. In the present example, the resistance Rs of the shunt resistor Rs1 is preferably 2.5 kΩ to obtain a critically damped system. Fig. 5B is a time diagram with simulation results for a practical implementation of the stator 300 and the motor control circuit 301 from Fig. 4A as part of the electric motor 320 from Fig. 3C, and shows the voltage at node N1 in the time domain. The simulation results show a step response. The following are shown: the voltage at node N1 with a resistance Rs of the shunt resistor Rs1 of 2.5 kΩ (curve 506) and the voltage at node N1 with a resistance Rs of the shunt resistor Rs1 of 1 MΩ (curve 508). The voltage at node N3 is also shown (curve 510). Fig. 5C is a frequency diagram showing the simulation results of Fig. 5B in the frequency domain. The same designations for curves 506 and 508 are used in this diagram. In curve 506, the oscillation and the peak in the AC response have disappeared. For comparison, curve 508 was simulated with 1 MΩ, which effectively acts as an open circuit. With a constant current shunt, the equivalent resistance would be greater if VDD is higher, since V / I = R and R varies with V. The damping factor in equation (6) therefore decreases with increasing Rs due to an increase in VDD. Eventually, the reduction effect diminishes, and oscillation begins at higher voltages. If a higher current is selected, we have an overdamped system at low voltages, leading to the aforementioned slower response and higher current consumption. Therefore, embodiments of the present disclosure using a resistive shunt device overcome the problems of known systems with a shunt current source. Known systems, such as those shown in Figs. 1A-1D, have the following disadvantages: 1. They are not very effective at reducing overshoot or oscillations, especially at higher voltages. (The current source does not provide a constant RC value across the voltage range.) 2. Higher current consumption for the current source, as additional current is needed to generate the constant currents at nodes v0, v1, v2. 3. More space is required to accommodate a current mirror for shunt current sources. 4. A reference current is required. Exemplary embodiments of the present disclosure have the following advantages: 1. The use of resistors as a shunt device is more effective over the entire voltage range. 2. No additional current is required for bias current generation and current mirroring. The known system used multiple current mirrors to achieve a current multiplier in the microampere range from a central bias block to the milliampere range. 3. Reduced circuit footprint. Exemplary embodiments of this disclosure can provide the same reduction of overshoot for the entire VDD range (for a BLDC control device: VDD from 3 V to 26.4 V) and for a variable voltage at the node in tristate operation, depending on the rotor angle. The current implementation has yielded good results for the voltage range VDD from 3 V to 26.4 V. Furthermore, no additional power consumption is required in mirrors, and less space is needed. 1. The overshoot or oscillation for a motor pin in tristate when one end switches while a BLDC motor is rotating is almost completely eliminated. This is the case for the entire voltage range; even across curves, it is greatly reduced. 2. No additional power consumption (no additional current mirror required) is noticeable when the function is enabled. In summary, embodiments of the present disclosure can reduce overshoot / oscillation due to parasitic node capacitances in tristate and the inductance of the BLDC (brushless DC) motor more effectively than known systems. Various improvements and modifications can be made to the above without altering the scope of disclosure.

Claims

A motor control circuit for an electric motor with a first node, wherein the motor control circuit includes a first resistive shunt device configured to be coupled to the first node. The motor control circuit according to claim 1, wherein the electric motor comprises: a plurality of motor phase circuits comprising: a first phase circuit coupled to the first node. The motor control circuit according to claim 1 or 2, wherein the first resistive shunt device is configured to provide a current flow path from the first node. The motor control circuit according to claim 3, wherein the first resistive shunt device is configured to provide the current flow path from the first node in order to dampen voltage oscillations at the first node. The motor control circuit according to claim 2, comprising a switching network configured to switch between different switching states in order to control the current flow through each of the plurality of motor phase circuits. The motor control circuit according to claim 5, wherein the switching network comprises a half-bridge with one or more switching network switches and / or one or more switching network diodes. The motor control circuit according to claim 2, wherein: the first phase circuit comprises a first phase circuit coil with a first coil inductance and a first coil resistance; the first resistive shunt device comprises a resistive element of the first shunt device; and the resistance of the resistive element of the first shunt device is greater than the resistance of the first coil resistance. The motor control circuit according to claim 7, wherein: the first resistive shunt device is configured to provide a current flow path from the first node to dampen voltage oscillations at the first node; and the resistance of the resistive element of the first shunt device is sufficient to provide critical damping of the voltage oscillations. The motor control circuit according to claim 2, wherein the plurality of motor phase circuits comprises: a second phase circuit coupled to a second node; and a third phase circuit coupled to a third node. The motor control circuit according to claim 9, comprising: a second resistive shunt device configured to be coupled to the second node; and / or a third resistive shunt device configured to be coupled to the third node. The motor control circuit according to claim 9 or 10, comprising a switching network configured to switch between different switching states in order to control the current flow through each of the plurality of motor phase circuits. An electric motor device comprising: an electric motor with a first node; and a motor control circuit with a first resistive shunt device configured to be coupled to the first node. A method for providing a motor control circuit for an electric motor with a first node, wherein the method includes providing the motor control circuit with a first resistive shunt device configured to be coupled to the first node.

Images