PWM actuator control with pulse regulation

A driver circuit for generating a sequence of pulses of a drive voltage from a supply voltage is described. The drive voltage is used for operating an electrical actuator, such as an electrical engine or machine. The driver circuit comprises means for providing an amplitude indication of an amplitude of the supply voltage, which is used for generating a first pulse of the sequence of pulses. Furthermore, the driver circuit comprises an integration unit configured to integrate the amplitude indication for a duration of the first pulse, thereby generating an integrated voltage. In addition, the driver circuit comprises a comparator configured to compare the integrated voltage with a reference voltage, thereby generating a comparator signal. Furthermore, the driver circuit comprises a control unit configured to terminate the first pulse in dependence of the comparator signal.

TECHNICAL FIELD

The present document relates to the control of an actuator, such as an electrical engine or machine. In particular, the present document relates to the control of such an actuator using pulses.

BACKGROUND

If an electrical engine (also referred to as a motor or machine) is driven with current and voltage pulses as drive signals, wherein the pulses are derived from a power supply, noise on the power supply may cause modulation of the drive signals. The modulation of a drive signal for an engine typically leads to a modulation of the motion of the engine.

SUMMARY

The present document addresses the technical problem of providing an efficient driver circuit for an actuator, which is configured to derive drive signals (notably drive voltages) from a noisy supply, which allow for a stable operation of the actuator. According to an aspect, a driver circuit for generating a sequence of pulses of a drive voltage from a supply voltage is described. The drive voltage may be used for operating an electrical actuator (e.g. an electrical engine or machine). The supply voltage may exhibit variations (e.g. due to noise). The driver circuit may be configured to generate a sequence of pulses, with pulses having a constant energy, even in the presence of variations of the supply voltage. By doing this, a stable operation of the actuator may be ensured, even if the supply voltage exhibits variations.

The driver circuit comprises means for providing an amplitude indication of an amplitude of the supply voltage. In particular, an amplitude indication may be provided for the amplitude of the temporal portion of the supply voltage, which is used for generating a first pulse of the sequence of pulses. The means for providing an amplitude indication may be configured to convert a voltage drop across the actuator into a current. The voltage drop across the actuator typically corresponds to (e.g. is equal to) the amplitude of the first pulse. The conversion may be performed such that the current is proportional to the voltage drop across the actuator (and therefore proportional to the amplitude of the first pulse). In such a case, the amplitude indication may correspond to such a current.

The driver circuit may further comprise an integration unit which is configured to integrate the amplitude indication for a duration of the first pulse, thereby generating an integrated voltage. The integration unit may start cumulating the amplitude indication at the beginning of the first pulse. Furthermore, the integration unit may terminate the accumulation of the amplitude indication, when the first pulse is terminated. As such, the integrated voltage is typically indicative of the amplitude-times-duration product of the first pulse, which is indicative of the energy of the first pulse.

The integration unit may comprise a capacitor (for cumulating the amplitude indication). Furthermore, the integration unit may comprise a reset switch which is arranged in parallel to the capacitor and which is configured to discharge the capacitor, subsequent to the termination of the first pulse. The reset switch may be controlled by the control unit of the driver circuit. By using the reset switch, the integration unit may be reset in preparation for a pulse that is subsequent to the first pulse.

In addition, the driver circuit comprises a comparator which is configured to compare the integrated voltage with a reference voltage, thereby generating a comparator signal. The reference voltage may be indicative of a target energy which is to be provided to the actuator using the first pulse. As such, the comparator may be configured to determine whether the cumulated amplitude indication (i.e. the integrated voltage) corresponds to the target energy or not.

The comparator may be configured to set the comparator signal at a time instant at which the integrated voltage becomes equal to the reference voltage. In other words, the comparator signal may be set as soon as the integrated voltage becomes equal to the reference voltage. As such, a time instant may be detected at which the energy of the first pulse corresponds to the target energy.

The driver circuit may comprise a control unit which is configured to terminate the first pulse in dependence of the comparator signal. In particular, the control unit may be configured to terminate the first pulse as soon as the comparator signal is set, i.e. as soon as the comparator determines that the energy of the first pulse corresponds to the target energy.

Hence, the driver circuit may be configured to generate a sequence of pulses having pulses which exhibit a pre-determined target energy, thereby enabling a stable operation of the actuator. This may be achieved even through the supply voltage exhibits variations.

The driver circuit may comprise a control switch which is configured to couple the actuator with the supply voltage. The control unit may be configured to generate a control signal for controlling the control switch, in dependence of the comparator signal. In particular, the control unit may be configured to generate a first control signal for opening the control switch, thereby terminating the first pulse. The first control signal may be generated in dependence of the comparator signal (as outlined above). Furthermore, the control unit may be configured to generate a second control signal for closing the control switch, thereby starting or initiating the generation of a pulse of the sequence of pulses. The second control signal may be generated in dependence of a pulse trigger signal (or clock signal), wherein the pulse trigger signal comprises triggers at a trigger frequency (or clock frequency), wherein the trigger frequency may be fixed.

As such, the drive circuit may be configured to provide a sequence of pulses at a trigger frequency, wherein the duration (or width) of the pulses may be varied, in order to ensure that the pulses exhibit a pre-determined target energy (even in case of a varying supply voltage).

The control unit may comprise a (or may correspond to a) gated D latch with a reset interface, a clock interface and an output interface. The comparator signal may be coupled to the reset interface, the pulse trigger signal may be coupled to the clock interface and/or the first pulse may be terminated using a control signal provided at the output interface. In particular, the first and/or second control signal may be provided at the output interface. As such, the control unit may be implemented in an efficient manner.

The means for providing an amplitude indication may comprise a resistor which is arranged between the actuator and the integration unit. In such a case, the amplitude indication may correspond to a current through the resistor. Alternatively, the means for providing an amplitude indication may comprise a current source which is controlled in dependence on a voltage drop across the actuator. In such a case, the amplitude indication may correspond to a current provided by the current source.

The driver circuit may comprise calibration means configured to calibrate the integration unit. By doing this, the accuracy of the driver circuit may be increased.

The driver circuit may comprise a full bridge with a plurality of control switches. The control unit may be configured to control the plurality of control switches using a control signal, in order to generate from the supply voltage pulses with reverse polarity for the sequence of pulses. By providing a full bridge, the actuator may be operated in an increased number of operation modes (e.g. in a forward and a reverse operation mode).

According to a further aspect, a method for generating a sequence of pulses from a supply voltage is described. The sequence of pulses is used for operating an electrical actuator. The method comprises providing an amplitude indication of an amplitude of the supply voltage, which is used for generating a first pulse of the sequence of pulses. Furthermore, the method comprises integrating the amplitude indication for a duration of the first pulse, thereby generating an integrated voltage. In addition, the method comprises comparing the integrated voltage with a reference voltage, thereby generating a comparator signal. The method comprises further terminating the first pulse in dependence of the comparator signal.

It should be noted that the methods and systems including its preferred embodiments as outlined in the present document may be used stand-alone or in combination with the other methods and systems disclosed in this document. In addition, the features outlined in the context of a system are also applicable to a corresponding method. Furthermore, all aspects of the methods and systems outlined in the present document may be arbitrarily combined. In particular, the features of the claims may be combined with one another in an arbitrary manner.

In the present document, the term “couple” or “coupled” refers to elements being in electrical communication with each other, whether directly connected e.g., via wires, or in some other manner.

DESCRIPTION

As indicated above, the present document is directed at the stable operation of an actuator (e.g. an electrical engine) using a noisy power supply. The power supply may e.g. provide voltages in the range of 5V or 10V. In particular, the present document is directed at providing an efficient driver circuit for such an actuator.

FIG. 1shows a block diagram of an example driver circuit100for an actuator150. The driver circuit comprises a control switch101which is configured to apply a drive voltage136to the actuator, wherein the drive voltage136is derived from a supply voltage131. The supply voltage131may have a nominal value and may exhibit variations around the nominal value. The drive voltage136may comprise a sequence of pulses for operating the actuator150. The pulses exhibit a temporal length and an amplitude. The power or energy for operating the actuator150is typically proportional to the product of the temporal length and the amplitude of a pulse. A stable operation of the actuator150may be achieved by operating the actuator150with a sequence of pulses, wherein the pulses of the sequence of pulses have constant energy.

The driver circuit100is configured to generate a drive voltage136with a sequence of pulses having equal energy using an integration unit120. The integration unit120is configured to monitor the integral of the amplitude of a pulse of the drive voltage136. As such, the integration unit120is configured to monitor the energy of a pulse of the drive voltage136. By doing this, the energy of the pulses may be kept constant, even if the supply voltage131is noisy. Variations of the supply voltages131may be regulated during the generation of a pulse and by consequence, noise from the supply voltage131may be suppressed.

The integration unit120is configured to provide an integral voltage137which is indicative of the cumulated or integrated amplitude of a pulse of the drive voltage136. Using a comparator102, the integral voltage137may be compared with a pre-determined reference voltage132, wherein the reference voltage132is indicative of the target energy of a pulse of the drive voltage136. In other words, the reference voltage132may be used to set the target energy of a pulse of the drive voltage136. Using an digital-to-analog converter, a digital reference signal may be converted into an analog reference voltage132. As such, a digital reference signal may be used to set the target energy of a pulse of the drive voltage136. The comparator102generates a comparator signal133which is set or reset as soon as the integral voltage137reaches the reference voltage132. Hence, the comparator signal133indicates the time instant at which a pulse of the drive signal136exhibits the target energy.

The driver circuit100further comprises a control unit103(which comprises e.g. a flip-flop or D latch). The control unit103is configured to generate a control signal135for the control switch101in dependence of the comparator signal133. In particular, the control unit103may be configured to generate a first control signal135for opening the control switch101(i.e. for terminating a pulse of the drive voltage136), as soon as the comparator signal133indicates that the pulse of the drive signal136exhibits the target energy.

Furthermore, the control unit103may be configured to generate the second control signal135based on a pulse trigger signal134, wherein the pulse trigger signal indicates that a pulse for the drive voltage136is to be generated. The control unit103may be configured to generate a second control signal135for closing the control switch101(i.e. for starting a pulse of the drive voltage136), in reaction to an appropriate trigger within the pulse trigger signal134.

As shown inFIG. 1, the integration unit120may comprise an operational amplifier121and a capacitor122. Furthermore, a reset switch123may be used to discharge the capacitor122. The capacitor122may be discharged subsequent to the termination of a particular pulse and prior to the start of a directly subsequent pulse.

The resistor110may be used to sense the amplitude of the drive signal136. In particular, the resistor110may be used to provide a current to the integration unit120, which is proportional to the voltage drop across the actuator150, i.e. which is proportional to the amplitude of a pulse of the drive voltage136.

Using the driver circuit100, the engine150may be started by setting the flip flop (i.e. the D latch)103, thereby closing the control switch101and thereby starting the generation of a pulse for the drive voltage136. The integration unit120starts to integrate the amplitude of the pulse. The integration time, until the time instant when the reference voltage132is reached, depends on the amplitude of the drive voltage136across the actuator150. As soon as the reference voltage132is reached, the flip flop103is reset and the integration unit120zeroed (using the reset switch123). The process restarts at the next clock pulse or trigger (provided by the pulse trigger signal134). Supply voltages132with a relatively high amplitude lead to relatively low integration times, which results in relatively short pulses, thereby maintaining the voltage-time product constant. The energy of a pulse for driving the actuator150is proportional to the reference voltage132. Consequently, the reference voltage132may be adjusted to set the desired energy level for each pulse of the drive voltage136.

Using the driver circuit100ofFIG. 1, the influence of supply voltage variations or noise on the energy which is applied to the actuator150may be suppressed.

FIGS. 2aand 2bshow example pulses of a drive voltage136. The pulse frequency of the sequence of pulses of a drive voltage136may be constant and may be set by the pulse trigger signal134.FIGS. 2aand 2bshow the amplitude201(measured in Volts) of pulses211,212over time202(measured in μs). As can be seen in FIG. a, the temporal length of a pulse211,212increases as the amplitude of the pulse211,212decreases (and vice versa). On the other hand, the amplitude-time product of a pulse211,212(which is indicative of the energy of the pulse) remains constant.FIG. 2bshows a sequence221of pulses. It can be seen that as the amplitude201of the pulses of the sequence221of pulses increases, the temporal length (or duration) of the pulses decreases (and vice versa). Hence, the driver circuit100may be used to regulate the pulse width (or duration) of the pulses of the drive voltage136in dependence on the amplitude of the voltage pulses which are applied to the actuator150, i.e. in dependence on the amplitude of the supply voltage131.

FIG. 3shows a block diagram of another driver circuit100. In the illustrated example, a full bridge is used to provide a drive voltage136to the actuator150with a reversible polarity. Either the control switches101,301may be used to generate the drive voltage136(by closing the control switches101,301, while leaving the control switches302,303open) with a first polarity, or the control switches303,302may be used to generate the drive voltage136(by closing the control switches303,302, while leaving the control switches101,302open) with a second polarity (which is reverse to the first polarity). By doing this, the actuator150may e.g. be operated in a forward and in a reverse direction, respectively.

Furthermore, the driver circuit100comprises a switch network with switches322,323,324,325for coupling the actuator150with a sensing unit110(which may comprise a voltage-current converter). When using the first polarity, the switches322and325may be closed. On the other hand, when using the second polarity, the switches323and324may be closed. By using the switch network, the subsequent sensing unit110may be limited to a single polarity.

The sensing unit110may be used to sense the amplitude of the drive voltage136and to provide an amplitude indication (e.g. a current) which is indicative of the amplitude of the drive voltage136. In the illustrated example, the sensing unit110comprises a voltage divider (with the resistors311,312), as well as an operational amplifier313for controlling the sensing transistor314(or current source) which is arranged in series with a sensing resistor315). The resistor312may be a variable and/or controllable resistor.

Furthermore, the driver circuit100comprises a calibration switch321for coupling the input of the integration unit120with a calibration signal331. By doing this, systematical errors (notably of the integration unit120) may be removed.

The control signal135which is generated by the control unit103may be used to control the control switches101,301and/or302,303.

As such a full bridge (comprising the control switches101,301,302,303) may be used to drive the actuator150using two polarities. The switching network (comprising the switches322,323,324,325) may be used as a rectifier in front of the sensing unit110(or voltage/current converter) so that the input to the sensing unit110corresponds to the voltage across the actuator150. As a result of this, the sensing unit110may be limited to processing only a single polarity.

The example sensing unit110comprises a resistor divider311,312for attenuating the drive voltage136across the actuator150. The attenuated voltage is applied across the sensing resistor315to develop a current which is proportional to the amplitude of the drive voltage136. This current may then be integrated by the integration unit120to provide an integrated voltage137at the output of the integration unit120, which is proportional to the amplitude of the drive voltage136times the width or duration of the corresponding pulse of the drive voltage136.

An alternative to integrating an amplitude indication of the amplitude of the drive voltage136is to directly integrate the amplitude of the supply voltage131. In such a case, an offset for the voltage drop across the one or more control switches101,301should be taken into account when setting the reference voltage132.

By using the calibration switch321a calibration input may be provided, which allows errors within the integration unit120to be calibrated. The time constant of the integrator120is typically depend on the values of the resistor315or110and of the capacitor122. Furthermore, there may be mismatch and offset errors.

The additional input for calibration may be used to generate from a pre-determined voltage a time constant which is related to the reference clock (i.e. to the pulse trigger signal134) of the driver circuit100. By adjusting the time constant, the driver system100may be stabilized for different processes and temperatures.

FIG. 4shows a flow chart of an example method400for generating a sequence221of pulses211,212of a drive voltage136from a supply voltage131. The drive voltage136is used for operating an electrical actuator150(e.g. an electrical machine). The method400comprises providing401an amplitude indication of an amplitude of a temporal excerpt of the supply voltage131, which is used for generating a first pulse211of the sequence221of pulses211,212. For this purpose, the amplitude indication of the supply voltage131may be derived directly from the supply voltage131. Alternatively or in addition, the amplitude indication may be derived from the drive voltage136. In particular, the amplitude indication may be derived from the first pulse itself.

Furthermore, the method400comprises integrating402the amplitude indication for a duration of the first pulse211, thereby generating an integrated voltage137. The integration operation may start directly at the beginning of the first pulse211, and may be continued until the first pulse211is terminated. As such, the integrated voltage137may correspond to or may be proportional to the accumulation of the amplitude indication since the beginning of the first pulse211.

The method400may proceed in comparing403the integrated voltage137with a reference voltage132, thereby generating a comparator signal133. The reference voltage132may be indicative of the target energy of the first pulse211. The method400further comprises terminating404the first pulse211in dependence of the comparator signal133. By doing this, it may be ensured that the first pulse211exhibits the target energy.

As such, the driver circuits100described in the present document allow for a suppression of supply noise for a pulse driven actuator150. The compensation of the noise is performed directly at the actuator150, thereby compensating all possible errors. The measurement of the noise may be performed directly at the actuator150, thereby avoiding possible intermodulation with the on-resistance of the one or more control switches101,301of the driver circuit100. Using a calibration input, the time constant of the integration unit120of the driver circuit100may be calibrated. Furthermore, a temperature drift may be calibrated by a calibration channel. In addition, the pulse energy of a voltage pulse may be adjusted by modifying the reference voltage132on a pulse-by-pulse basis.

The driver circuits100do not require an additional regulator (e.g. a buck, boost or LDO regulator) for generating a noise-free drive voltage136from a noisy supply voltage131, thereby providing a power- and cost-efficient driver circuit100for an electrical actuator150. Using the described driver circuits100, noise on the supply voltage131(e.g. audio noise) does not cause current to flow into the coil of an actuator150. As such relatively simple digital driving of an actuator150may be provided.