JPH10341588A - Current zerocross detection of inductive load, and optimization of voltage mode pwm drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the zerocross of the current of an inductive load without monitoring the current of an exclusive detective resistor in series with inductive load. SOLUTION: To detect the zero-cross of the current of the inductive load Ls driven in voltage mode through the half bridge consisting of a switch on high order side and a switch on low order side driven in opposite phases to each other by PWM signals, the voltage value at the output node A of the half bridge is compared with a fixed reference voltage value Vref, and the direction of the current in the inductive load Ls is judged from the comparison result. The comparison results are sampled cyclically during the period when both the switches mentioned above are off. Then, the zero cross can be detected by the inversion of the comparative value between the two continuous samplings.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for detecting a current zero crossing of a PWM electronically switched inductive load without monitoring a current, and more particularly, to a voltage mode for optimizing the driving of a sensorless brushless motor. The method and its circuit.

[0002]

2. Description of the Related Art When driving an electronic switching motor (stepper) or a general sensorless brushless motor,
It is important that the drive current pulse input to the phase winding of the motor and the back electromotive force (BEMF) generated in the winding of the rotor be completely synchronized. This means that the induced BEMF signal of each phase winding is detected by a comparator, the signal is masked for the winding where the driving current flows, and the zero crossing of the BEMF generated in the winding when the driving current does not flow is detected. This can usually be achieved by detection. Such devices are described in Italian patent application 1,253,685 and European patent application 95
No. 8302188.4.

In a driving device having a predetermined sine wave characteristic, if there is no switching phase in which a driving current is not supplied to at least one of the motor windings, a problem arises that a zero crossing is detected simultaneously with driving synchronization. I do. However, this problem can be overcome by a method for reproducing BEMF signals as described in European Patent Application 968 30440.2.

Such a conventional device is controlled in a current mode by controlling the current in each winding in a linear manner by a mutual inductance loop circuit using current sensing resistors functionally connected in series to the windings. I have. On the other hand, there is known a voltage-mode driving device which operates with a simpler circuit. This solution involves digitally storing in a dedicated register such that the periodic scan rate of the recorded digital data, which is typically a sinusoidal reference signal sample value converted to a PWM signal, is synchronized with the rotor speed. This is suitable for an apparatus that uses a predetermined driving characteristic.

[0005]

In a voltage mode control device, it is necessary to consider a phase angle between a current and a voltage due to a response characteristic of a driving load in an induction winding. In a normal BEMF signal reproducing apparatus, it is impossible to dynamically correct the phase angle over the entire range of the rotor speed. In the predetermined correction that is performed as a result, optimal synchronization over the entire speed range cannot be guaranteed, and thus inefficiency and torque reduction of the device occur.

Therefore, in the above-described application example and a general switching induction load driving device, it is necessary to detect the zero crossing of the current of the inductive load without monitoring the current of the dedicated detection resistor in series with the inductive load. It is obvious.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a method for detecting a change in a slip direction, that is, a change in a current direction of an inductive load controlled in a voltage mode of a pulse width modulation (PWM) device. The present invention relates to a detection method and a circuit.

The method of the present invention detects a voltage change at a drive node of an inductive load, that is, outputs a voltage value at an output node of a half-bridge power stage during a period in which both power switches of the power stage are off. Is compared with a fixed reference voltage value that can be set arbitrarily and is within a normal voltage fluctuation range of the output node using a comparator that can periodically sample the output node. The sample output is masked until read (sample). During this period, drive P
It is periodically the same as the period of the WM signal and can be detected in each PWM drive cycle during the delay time between when the lower element is switched off and when the higher element is switched on.

Due to the inductive nature of the load, in each switching operation, the current of the load continues to flow in the same direction as the drive phase that has just ended, preferably the dual power supply half-bridge transistor is a DMOS integrated device, Specifically, a dedicated recirculating diode, such as that included in an integrated transistor structure, is recirculated. When the two power transistors of the power stage are off, the current slip direction causes the voltage at the drive node of the winding to rise until the recirculating diode connected in parallel to each power transistor reaches a threshold voltage. Or it is shifted to the ground voltage.

With such a method, periodic information on the current direction is obtained, and it is found from the detection of currents in opposite directions at two consecutive samples that a zero crossing of the current of the inductive load has occurred.

Naturally, for example, during the energization phase, by periodically turning off one of the power supply elements for a time sufficient to detect the current direction, another sample frequency lower than the frequency of the PWM drive signal can be obtained. But it is possible to achieve the same result. In practice, given the normal capacitance of the output node of the power stage and the delay of the comparator,
The detection interval in the current direction in the load is preferably about 1 μs to 2 μs because about 500 ns to 1.5 μs is required for capacitance charging.

The information of the zero crossings obtained in this manner can be easily used to dynamically correct the synchronization signal used for the motor controlled by the PWM system, and when the load state or the rotation speed of the motor fluctuates. At the same time, accurate synchronization can be maintained.

Thus, according to the present invention, an inductive load driven in voltage mode using a half-bridge stage having a high-side switch and a low-side switch driven in opposite phases by a pulse width modulation signal is provided. In the current zero-crossing detection method, the step of comparing the voltage of the output node of the half-bridge stage with a constant reference voltage, and periodically sampling the result of the voltage comparison while both of the switches are in the off state. A step of determining a direction of a current in the inductive load and a step of detecting a zero crossing from inversion between two consecutive sample values are performed. The determination of the current direction is performed during a delay time from when one of the two switches forming the half-bridge stage is turned off to when the other is turned on, or when one of the two switches forming the half-bridge stage is energized. Can be executed by suspending for a short time.

According to the present invention, there is provided a method for synchronizing a pulse width modulation voltage mode driving of an inductive load through a half-bridge stage. The current zero crossing of the load is detected. Further, in a driving method for driving a phase winding of a sensorless brushless motor in a voltage mode by pulse width modulation synchronized with a zero crossing of a winding current, the zero crossing of the winding current is detected by the current zero tolerance detection method described above. It is characterized in that it is detected. In this case, the pulse width modulation drive of the phase winding can be performed with a sine voltage waveform digitally stored in a memory in advance.

Further, according to the present invention, a BEMF signal generated in a motor winding and out of phase with each other is detected or reproduced, and one or more predetermined periodic drive signals synchronized with the frequency of the BEMF signal are generated. Means (BE) for generating at least one synchronization signal for the means (SIN generator)
MF detector) and programmed speed (Target spee
means for modulating the amplitude of said periodic drive signal (SIN) according to the actual speed error signal for d) (Ampl.
And a means (P) for converting the periodic drive signal after the amplitude modulation into the same number of PWM signals for operating a power stage (power actuator unit) for driving the motor winding.
And a drive unit for a sensorless brushless motor (BL motor), comprising: a zero-crossing current in at least one winding, and modulating the synchronization signal (Synchro). Means for generating a signal indicating the phase angle between the current and the voltage (current Z.
C. (Determination unit). Means for generating a signal indicative of the phase angle between current and voltage to modulate the synchronization signal (Syncro) comprises a first input connected to an output node of a half-bridge driving one of the windings. At least one comparator (Cmp) having a terminal (+) and a second input terminal (-) connected to a constant reference voltage (Vref);
While one of the two power switches is turned off from the energized state and the other is kept off, the comparator (Cm
p) and a timing circuit that samples the output of p) and provides a zero-crossing signal each time two successive sampled values are inverted.

Various features and advantages of the present invention will become more apparent from the following description of embodiments with reference to the accompanying drawings.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a power stage for driving an inductive load, which is one of windings of a polyphase motor. The load is the inductance Ls and the resistance R
s and a back EMF generator Bemf that generates a sinusoidal voltage whose amplitude is proportional and synchronous with the angular velocity of the rotor.

The circuit example of FIG. 1 shows a full bridge circuit for connecting (accessing) each terminal of each winding of a motor. Of course, as is apparent from the following description, the present invention can be similarly applied to a half-bridge drive circuit.

In the PWM modulator shown in FIG. 1, for example, a sine wave drive voltage is applied to the power MOS elements LS1, LS2, HS
1, which are converted into PWM signals for controlling the switches indicated by HS2. Here, the induction winding of the motor (Ls to R
Due to the low-pass filter function of s), the PWM drive can be considered as an A class sine wave drive. Due to the effect of such a drive mode, it is synchronized with the position of the rotor, that is, synchronized with the sinusoidal BEMF voltage generated in the winding,
In this example, a current having a predetermined sine wave is supplied to each winding of the motor.

The sine wave drive voltage input to the input terminal of the PWM modulator in the voltage mode control device has the same frequency and phase as the detected and reproduced BEMF sine wave voltage. In practice, the sinusoidal current flowing through the winding, while having the same frequency, has a predetermined phase angle (delay) with respect to the driving sinusoidal voltage due to the LR effect, and φ = (ω
e * Ls) / Rs. Where ωe is the angular velocity in radians / second of the motor multiplied by the number of pole pairs. When the rotation speed of the motor is increased, the phase angle also becomes a large value, and the efficiency is reduced.

The correction of the increase in the phase angle with respect to the rotation speed of the motor can be executed when instantaneous information on the phase angle is available. In performing this correction, it is common to introduce a detection resistor connected in series to the winding as in a current mode control device, but the cost for the current detection circuit is required. Therefore, according to the basic feature of the present invention, even in the case of a voltage mode sensorless drive circuit without a current detection resistor, the phase angle variation with respect to the rotation speed is dynamically corrected to completely cover the entire motor speed. In order to achieve good synchronization, it is possible to detect the zero crossings of the current in the inductive load.

The method of the present invention detects the current direction in an inductive load periodically at a predetermined sample frequency, and when a change in the current direction is detected between two consecutive detection values, the zero crossing of the current is detected. It is a method of creating information. This detection can be performed by turning off the lower or higher power supply element for a very short time during one period of the energized phase, or by turning off one of the power supply elements of the driving half bridge and By sampling the detection result during a short delay time occurring between the time when another power supply element is turned on, the detection can be performed periodically and selectively.

In practice, the detection device of the present invention compares the voltage at the output node of the driving half-bridge with a predetermined constant reference voltage value that falls within the normal voltage fluctuations of the output node, and outputs the voltage. The result is sampled during a period when both of the two power elements of the half-bridge stage are off.

The inductive characteristics of the load due to the windings are as follows. Current can continue to be forced out towards or from the output node of the connected half-bridge. Then, after a delay from the time of turning off the power supply stage that can change the capacitance of the output node, the potential at the output node with respect to the power supply voltage or the ground voltage shifts, and the potential shift is detected by the comparator Cmp, and the direction of the current flow Is generated. The detection of the two opposite current directions in two consecutive sample periods utilizing this makes it clear that the winding current has a zero crossing.

The functional circuitry of the current direction sensor of the present invention is shown in FIGS. 2a and 2b, according to which each time the lower element is turned off before the higher element is turned on.
Sampling is performed at the cycle of the PWM signal. In the illustrated example, both the high-order element and the low-order element are MOS transistors.

The feature of the two circuit configurations shown is the recirculation diode in parallel with each power transistor (switch). If the power switch is an integrated DMOS transistor, the recirculating diode can be contained in an integrated transistor structure. As another example, a recirculating diode may be conventionally connected in parallel with the power element of each driving half-bridge of the inductive load.

In the illustrated example, when the lower element is off, the current of the inductive load Ls continuously flows in the same direction, and the potential of the node A is maintained until the respective recirculating diodes reach the on threshold. The potential is shifted to the power supply potential or the ground potential according to the direction.

The information on the current direction is set to 500 ns to 1.5 μs after the low-side element is turned off in accordance with the charging of the parasitic capacitance at the node A and the delay of the comparator Cmp.
It can be obtained by sampling the signal at the comparator output node after some delay. The state change between two consecutive samples provided by the comparator Cmp provides information indicating the zero crossing of the load current without monitoring the current.

A drive system for a standard sensorless brushless motor with an automatic synchronization corrector according to the present invention is shown in the block diagram of FIG. As shown in the figure, basically, the current Z.I.
C. The components other than the determination unit are configured by a standard drive loop circuit of a brushless motor (BL motor).

In the structure of this embodiment, the zero crossing of the BEMF electromotive force generated in the motor winding is detected by the BEMF detector. In the SIN generation unit, a SIN signal is created based on a BEMF zero-crossing synchronization signal called Syncro such that the reference sine wave signal (SIN) has the same frequency and phase as the BEMF voltage.

The synchronized predetermined SIN drive signal is BEM
F according to the difference between the speed indicated by the SPEED signal detected by the SPEED signal and the reference speed (Target Speed signal).
The amplitude is modulated by the modulator, and the resulting modulated drive (sine wave) signal is sent to the PWM modulator. Here, the signal (that is, a signal shifted by a plurality of phases) is converted into a PWM signal shifted in phase by the same number, and further, a full-bridge stage including two half bridges, which are driven in opposite phases, is a power actuator unit. Or
Input to each winding of the motor via a single half bridge.

The current Z.I. C. The determination unit detects a zero crossing of the winding current, and sends the detection information to the SIN generation unit. Here, since the synchronization signal Syncro is modulated in accordance with the phase angle between the current and the voltage, the driving signal SIN during each operating state of the motor.
Is actually synchronized to the zero crossing of the winding current.

[Brief description of the drawings]

FIG. 1 is a PWM drive circuit diagram of an inductive load.

2a and 2b schematically illustrate the basic concept of the circuit according to the invention.

FIG. 3 is a block diagram of a brushless motor driving circuit which is a synchronization optimizing circuit according to the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Pederazzini Giorgio Italy 27100 Pavia Viafossa Lumato 88

Claims (8)

[Claims] 1. A method for detecting a current zero-crossing of an inductive load driven in a voltage mode using a half-bridge stage having a high-side switch and a low-side switch driven in opposite phases by a pulse width modulation signal. Comparing the voltage at the output node of the half-bridge stage with a fixed reference voltage, and periodically sampling the result of the voltage comparison while the two switches are in the off state to change the direction of the current in the inductive load. A method for detecting a current zero crossing, comprising: performing a determining step and a step of detecting a zero crossing from inversion between two consecutive sample values. 2. The current zero-crossing detection method according to claim 1, wherein the determination of the current direction is performed during a delay time from when one of the two switches constituting the half-bridge stage is turned off to when the other is turned on. 3. The current zero-crossing detection method according to claim 1, wherein the determination of the current direction is performed by interrupting a short period of time for one of the two switches forming the half-bridge stage. 4. A method for synchronizing pulse width modulation voltage mode driving of an inductive load through a half-bridge stage, wherein the current flowing through the inductive load is obtained by the current zero-crossing detecting method according to claim 1. Wherein the current zero crossing of the inductive load is detected without monitoring. 5. A driving method for driving a phase winding of a sensorless brushless motor in a voltage mode by pulse width modulation synchronized with a zero crossing of a winding current, wherein the zero crossing of the winding current is determined. Any one of
A driving method characterized in that the detection is performed by the current zero tolerance detection method described in (1). 6. The driving method according to claim 5, wherein the pulse width modulation driving of the phase winding is executed with a sine voltage waveform digitally stored in a memory in advance. 7. A means (SIN generator) for detecting or reproducing a BEMF signal generated in a motor winding and out of phase with each other, and generating one or more predetermined periodic drive signals synchronized with the frequency of the BEMF signal. Means for generating at least one synchronization signal (BEMF detector) and means for modulating the amplitude of said periodic drive signal (SIN) according to an error signal of the actual speed with respect to a programmed speed (Target speed) (Ampl. Modulating unit) and the periodic drive signal after the amplitude modulation are converted into the same number of Ps for operating a power stage (power actuator unit) for driving the motor winding.
A driving device for a sensorless brushless motor (BL motor) including means for converting to a WM signal (PWM modulation unit), wherein a zero crossing of a current in at least one winding is detected, and the synchronization is performed. A drive device comprising: means (current ZC determining unit) for generating a signal indicating a phase angle between a current and a voltage to modulate a signal (Syncro). 8. A means for generating a signal indicative of a phase angle between a current and a voltage for modulating a synchronization signal (Syncro) is connected to an output node of a half-bridge driving one of the windings. A first input terminal (+) and a second input terminal (-) connected to a constant reference voltage (Vref)
And the output of the comparator (Cmp) while one of the two power switches constituting the half bridge is turned off from the energized state and the other is kept off. And a timing circuit that provides a zero-crossing signal each time two successive sampled values are inverted.