JP6768753B2 - Motor control device - Google Patents

Description

An embodiment of the present invention relates to a motor control device that detects a phase current by a current detecting element arranged in a DC portion of an inverter circuit.

When detecting the current of each phase of U, V, and W in order to control the motor, there is a technique of detecting the current using one shunt resistor inserted in the DC part of the inverter circuit. To detect all three-phase currents with this method, a three-phase PWM signal so that two or more phases of current can be detected within one cycle of a PWM (Pulse Width Modulation) carrier. The pattern needs to be generated. Therefore, a motor control device has been proposed that can always detect currents of two or more phases without increasing noise by shifting the phase of the PWM signal within one cycle (Patent Document 1).

In addition, as a method of generating braking torque in the motor to decelerate the motor, a short-circuit brake that generates braking torque with the motor current generated by the induced voltage by conducting all the switching elements on the lower arm side of the inverter circuit at the same time, and electric power There is a regenerative brake or the like that generates braking torque by generating electricity and regenerating it in an inverter circuit (Patent Document 2).

Japanese Unexamined Patent Publication No. 2012-70519 Japanese Unexamined Patent Publication No. 2006-129663

However, when the short-circuit brake is performed in the configuration of Patent Document 1, there is a problem that the current cannot be detected because the current does not flow through the shunt resistor arranged in the DC portion of the inverter circuit.

Therefore, also in the current detection method disclosed in Patent Document 1, a motor control device capable of applying braking torque to the motor while detecting currents of two or more phases as much as possible is provided.

In the motor control device of the embodiment, the motor is driven via an inverter circuit that converts direct current into three-phase alternating current by controlling on / off of a plurality of switching elements connected by a three-phase bridge according to a predetermined PWM signal pattern. ,
A current detection element that is connected to the DC side of the inverter circuit and generates a signal corresponding to the current value.
A PWM signal generator that determines the rotor position based on the phase current of the motor and generates a three-phase PWM signal pattern so as to follow the rotor position.
A current detection unit that detects the phase current of the motor based on the signal generated in the current detection element and the PWM signal pattern is provided.
The PWM signal generation unit generates a three-phase PWM signal pattern so that the current detection unit can detect a two-phase current at two points in the carrier cycle of the PWM signal. To do
For one of the three-phase PWM signals, the duty pulse is increased or decreased in both the lagging side and the leading side with reference to an arbitrary phase of the carrier wave period.
For the other one phase, the duty pulse is increased or decreased in one direction of the lag side and the lead side with reference to an arbitrary phase of the carrier period.
For the remaining one phase, the duty pulse is increased or decreased in the direction opposite to the direction with reference to an arbitrary phase of the carrier period.
By setting the duty of the three-phase PWM signals to be the same, a braking control unit that generates braking torque in the motor is further provided.

A functional block diagram according to the first embodiment and showing a configuration of a motor control device. The figure which shows the duty pulse waveform of the three-phase PWM signal at the time of performing a general short-circuit brake. The figure which shows the three-phase pulse waveform when the d-axis voltage Vd and the q-axis voltage Vq are both set to zero when three-phase modulation is performed by vector control. The figure which shows the state which added the phase shift in Patent Document 1 to the three-phase pulse waveform shown in FIG. The figure which shows each phase voltage corresponding to the vector pattern (1)-(4) shown in FIG. The figure which shows the q-axis voltage Vq corresponding to the vector patterns (1) to (4) shown in FIG. 4 and the sum thereof. The figure which shows the d-axis voltage Vd corresponding to the vector patterns (1) to (4) shown in FIG. 4 and the sum thereof. Each signal indicating the speed change when both the upper phase (U +, V +, W +) and the lower phase (U-, V-, W-) of each phase PWM signal are turned off when the motor is rotating. Waveform diagram Waveform diagram of each signal showing the speed change of the motor when short-circuit braking is performed according to the waveform shown in FIG. Waveform diagram of each signal showing the speed change of the motor when short-circuit braking is performed according to the waveform shown in FIG. A flowchart showing interrupt processing in the brake control unit according to the second embodiment (No. 1). Flowchart showing interrupt processing in the brake control unit (Part 2) The figure which shows the three-phase pulse waveform which added the phase shift in Patent Document 1 at the time of performing two-phase modulation.

(First Embodiment)
Hereinafter, the first embodiment will be described with reference to FIGS. 1 to 7. Since this embodiment is based on the configuration of Patent Document 1, the same parts as those disclosed in Patent Document 1 are designated by the same reference numerals, description thereof will be omitted, and different parts will be described. .. FIG. 1 is a diagram corresponding to FIG. 1 of Patent Document 1, and is a functional block diagram showing a configuration of a motor control device. The difference from Patent Document 1 is that the PWM signal generation unit 21 instead of the PWM signal generation unit 9 includes the brake control unit 22. When a brake command is given by a higher-level control device or the like, the brake control unit 22 corresponding to the braking control unit applies braking torque to the motor 6 while maintaining a state in which a two-phase current can be detected by the shunt resistance 4 as much as possible. Control to generate.

Next, the operation of this embodiment will be described with reference to FIGS. 2 to 7. FIG. 2 is a duty pulse waveform of a three-phase PWM signal when performing a general short-circuit brake. If both the d-axis voltage Vd and the q-axis voltage Vq are set to zero during two-phase modulation by vector control, the pattern is such that the FETs 5U- to 5W- on the lower arm side are turned on at the same time. At this time, the dq-axis voltage equation in the steady state is as follows.
Vd = 0 = R × Id−ω × Lq × Iq… (1)
Vq = 0 = R × Iq−ω × Ld × Id + ω × φ… (2)
R: Resistance [Ω]
ω: Motor angular velocity [rad / sec]
Id: d-axis current [A]
Lq: q-axis inductance [H]
Iq: q-axis current [A]
Ld: d-axis inductance [H]
φ: Induced voltage [line-to-line Vrms / Hz]

In equations (1) and (2), the currents Id and Iq can be calculated by giving an arbitrary angular velocity ω, and the torque Tall of the short-circuit brake can be obtained based on the equation (5).
Tm = √ (3/2) × P × φ × IQ… (3)
Tr = 3/2 × P × (Ld-Lq) × Id × Iq… (4)
Tall = Tm + Tr ... (5)
Tm: Magnet torque P: Pole logarithm Tr: Reluctance torque

Since the angular velocity ω decreases due to the braking operation, the second and third terms on the right side of Eq. (2) decrease. As a result, the q-axis current Iq increases in the negative direction and the brake torque increases. During this short-circuit braking, a current corresponding to the rotation speed flows through the motor 6. However, in such a signal pattern, in the configuration in which the shunt resistor 4 is arranged in the DC portion of the inverter circuit 3 as in the present embodiment, the two-phase current cannot be detected within one cycle of PWM control.

FIG. 3 is a three-phase pulse waveform when both the d-axis voltage Vd and the q-axis voltage Vq are set to zero when three-phase modulation is performed by vector control, and is a three-phase pulse waveform as in Patent Document 1. This is the case where the phase of the phase pulse is not shifted. The pattern in which the FETs 5U + to 5W- on the upper arm side are turned on at the same time and the pattern in which the FETs 5U- to 5W- on the lower arm side are turned on at the same time each have a waveform with a duty ratio of 50%. In this case as well, as in the case of FIG. 2, a current corresponding to the rotation speed flows through the motor 6, but the two-phase current cannot be detected within one cycle of PWM control.

Therefore, in the present embodiment, the three-phase pulse waveform shown in FIG. 4 is output by adding the phase shift performed in Patent Document 1 to the three-phase pulse waveform shown in FIG. That is, the pulse V + of the V-phase upper arm extends the pulse to the left in the figure, and the pulse U + of the U-phase upper arm extends to the left and right in the figure with reference to the central phase of the PWM control cycle which is the valley of the triangular wave which is the U-phase carrier. The pulse is extended in the direction, and the pulse W + of the W phase upper arm extends the pulse in the right direction in the figure.

At this time, as shown in FIG. 4, four types of voltage vector patterns (1) to (4) are generated. The phase voltage in each voltage vector pattern is shown in FIG. Further, the q-axis voltage Vq in this case is shown in FIG. 6, and the d-axis voltage Vd is shown in FIG. The d-axis voltage Vd and the q-axis voltage Vq are generated in each voltage vector pattern, and the d-axis voltage Vd and q are the total values of the four voltage vector patterns (1) to (4) over an electric angle of 0 to 360 degrees. The shaft voltage Vq becomes zero. Therefore, it is possible to realize a short-circuit brake similar to the conventional d-axis voltage Vd and q-axis voltage Vq = 0. That is, a short-circuit brake similar to the three-phase pulse waveform shown in FIG. 3 acts on the motor 6. Then, for example, if the timing for detecting the current is two points, the lag side and the lead side near the central phase, the W phase current (-) can be detected in the period near the lag side from the central phase, and the vicinity of the same lead side. The V-phase current (-) can be detected during the period of.

FIG. 8 shows the speed when the upper phase (U +, V +, W +) and the lower phase (U−, V−, W−) of each phase PWM signal are turned off when the motor 6 is rotating. Show change. At this time, since the motor 6 is in the free run state, it takes 22.5 s to stop the motor 6. FIG. 9 shows the case where the short-circuit brake shown in FIG. 3 is applied, and the time until the motor 6 stops is 3.39 s. On the other hand, FIG. 10 shows a case where short-circuit braking is performed by the three-phase pulse waveform shown in FIG. 4 of the present embodiment. Since the upper arm side short circuit and the arm side short circuit are switched in the middle of the control cycle, the time until the motor 6 stops is 4.37 s, which is slightly longer than the case of FIG. 6, but is sufficient than the case of FIG. It can be said that it is short.

As described above, according to the present embodiment, when the MOSFETs 5U ±, V ±, W ± constituting the inverter circuit 3 are on / off controlled according to a predetermined PWM signal pattern, the shunt resistance 4 is on the DC bus 2b side of the inverter circuit 3. The PWM signal generation unit 21 determines the rotor position θ based on the phase current of the motor 6, and generates a three-phase PWM signal pattern so as to follow the rotor position θ. When the current detection unit 7 detects the phase current of the motor 6 based on the signal generated in the shunt resistor 4 and the PWM signal pattern, the PWM signal generation unit 21 has the current detection unit 7 at two points in the carrier cycle. A three-phase PWM signal pattern is generated so that a two-phase current can be detected at the timing.

Specifically, one of the three-phase PWM signals increases or decreases the duty pulse in both the lagging side and the advancing side with reference to the intermediate phase of the carrier period, and the other one phase is in the lagging direction from the reference. The duty pulse is increased or decreased, and the remaining one phase increases or decreases the duty pulse in the direction advancing from the reference. Then, the brake control unit 22 sets the duty of the three-phase PWM signals to be the same when applying the braking torque to the motor 6. This makes it possible to apply braking torque to the motor 6 while detecting three-phase currents as much as possible even in a configuration that employs a one-shunt current detection method.

Further, the brake control unit 22 easily generates a braking torque in the motor 6 by setting the output voltage command values Vd and Vq in the vector control to zero and setting the duty of the three-phase PWM signal to 50%. be able to.

(Second Embodiment)
Next, the second embodiment will be described with reference to FIGS. 11 to 13. In the second embodiment, the form of the brake to be operated is changed according to the rotation speed of the motor 6. In the following description, "shift 2 PWM" means phase shift control of a three-phase pulse in Patent Document 1, and "normal PWM" is 3 centered on a generally performed reference phase. It means that the phase duty pulse is generated symmetrically. The interrupt processing shown in FIGS. 11 and 12 is executed every PWM cycle.

In the interrupt process shown in FIG. 11, when the short-circuit brake command is input (S1; YES), the brake control unit 22 performs "shift 2 PWM" in the three-phase modulation (S2). That is, the short-circuit brake is performed by outputting the three-phase pulse waveform shown in FIG. 4 of the first embodiment. If the short-circuit brake command is not input (NO), the drive control of the normal motor 6 is performed (S6).

Next, the brake control unit 22 determines whether or not the rotation speed of the motor 6 is less than a preset threshold value (S3). The rotation speed of the motor 6 may be detected based on a sensor signal output by a position sensor (not shown), or may use a rotation speed estimated by position sensorless control. Here, since it may be determined that the rotation speed of the motor 6 has decreased to some extent due to the action of the short-circuit brake, it may be determined whether or not the time after the start of the short-circuit brake exceeds the threshold value. If the rotation speed of the motor 6 is equal to or higher than the threshold value (S3; NO), the short-circuit brake is continued as it is (S5). On the other hand, when the rotation speed of the motor 6 becomes less than the threshold value (YES), a regenerative braking command is generated (S4).

In the interrupt process shown in FIG. 12, if the regenerative brake command has not been generated (S11; NO), the same process as in step S6 is performed (S18). On the other hand, if the regenerative braking command is generated (YES), the regenerative braking is performed (S12). In this case, the q-axis current command Iqref or the voltage command Vq is set to a negative value in the vector control. Then, during the execution of the regenerative braking, in steps S13 and S14, it is determined whether or not the maximum of the three-phase PWM duties exceeds the threshold values 1 and 2, respectively. The threshold value 1 is set within a range in which the current can be detected, and is set to, for example, 70%. Further, the threshold value 2 is set to a value lower than the threshold value 1 and within a range in which the current can be detected, and is set to, for example, 50%.

If the duty exceeds the threshold value 1 (S13; YES), two-phase modulation is performed by "normal PWM" (S14). If the duty is equal to or less than the threshold value 1 and exceeds the threshold value 2 (S15; YES), two-phase modulation is performed by “shift 2 PWM” (S16). The waveform of the three-phase pulse in this case is as shown in FIG. Then, if the duty is the threshold value 2 or less (S15; NO), three-phase modulation is performed by "shift 2 PWM" (S17).

That is, if the regenerative brake is applied while the rotation speed of the motor 6 is high, the DC voltage of the inverter circuit 3 rises, and an excessive voltage may be applied to the FET 5 and the rectifier circuit (not shown). Therefore, the short-circuit brake is first applied to shift to the regenerative brake when the rotation speed drops to some extent.

If the duty exceeds the threshold value 1 when shifting to the regenerative braking, two-phase modulation is performed by "normal PWM" with priority given to lowering the voltage faster by the braking action. When the duty becomes the threshold value 1 or less, the two-phase current can be detected by performing two-phase modulation by "shift 2 PWM", and the switching loss due to the FET 5 is reduced. When the duty becomes the threshold value 2 or less, the current detection rate is improved by performing three-phase modulation with "shift 2 PWM". The process shown in FIG. 12 may be performed as one interrupt process following the process shown in FIG.

As described above, according to the second embodiment, when the brake control unit 22 first generates the braking torque in the motor 6, after first setting the duty of the three-phase PWM signals to be the same and performing short-circuit braking. , The regenerative braking is performed by giving a command value to generate a negative torque to the motor 6. As a result, the voltage of the regenerated electric power can be lowered to protect the circuit elements and the like from overvoltage.

Specifically, when the regenerative brake is applied to the motor 6, the brake control unit 22 performs two-phase modulation by the PWM signal generation unit 21 when the PWM duty corresponding to the output voltage is higher than the threshold value 2, and PWM. When the duty becomes the threshold value 2 or less, three-phase modulation is performed. As a result, the switching loss in the inverter circuit 3 can be reduced when the voltage of the regenerative power is high, and the current detection rate can be improved when the voltage is low.

Further, when the PWM duty exceeds the threshold value 1 which is higher than the threshold value 2, the brake control unit 22 generates the duty pulses of the two-phase PWM signals so as to extend symmetrically from the reference phase, and the PWM duty is the threshold value 1. When the following occurs, one duty pulse of the two-phase PWM signal is generated so as to extend symmetrically from the reference phase, and the other duty pulse is generated so as to extend in any one direction from the reference phase. This makes it possible to improve the current detection rate during the period during which regenerative braking is performed by two-phase modulation.

(Other embodiments)
The timing at which the current detection unit 7 detects the two-phase current within the carrier cycle does not necessarily have to be based on the phase indicating the minimum or maximum carrier level, and the carrier can detect the two-phase current. It may be set based on an arbitrary phase of.
Further, the timing of detecting the current does not need to match the cycle of the PWM carrier, and the detection may be performed at a cycle of, for example, twice or four times the carrier cycle. Therefore, the current detection timing signal input to the current detection unit 7 does not have to be the carrier itself, and may be, for example, a pulse signal having a predetermined period synchronized with the carrier.

The shunt resistor 4 may be arranged on the positive bus 2a. Further, the current detection element is not limited to the shunt resistor 4, and for example, a CT (Current Transformer) or the like may be provided.
The switching element is not limited to the N-channel MOSFET, and a P-channel MOSFET, an IGBT, a power transistor, or the like may be used. The pulse width of each phase may be adjusted to be, for example, 20% within the range in which the two-phase current can be detected during short-circuit braking.
The order of switching between the short-circuit brake and the regenerative brake is not limited to the one in which the regenerative brake is performed after the short-circuit brake, but may be the order of the regenerative brake and the short-circuit brake, and may be repeated such as the short-circuit brake, the regenerative brake, and the short-circuit brake. ..
The set values of the threshold values 1 and 2 in the second embodiment may be appropriately changed according to the individual design.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

In the drawing, 3 is an inverter circuit, 4 is a shunt resistance, 5 is a power MOSFET, 6 is a motor, 7 is a current detection unit), 9 is a PWM signal generation unit, 21 is a PWM signal generation unit, and 22 is a brake control unit. ..

Claims (6)

In a motor control device that drives a motor via an inverter circuit that converts direct current into three-phase alternating current by controlling on / off of a plurality of switching elements connected by a three-phase bridge according to a predetermined PWM signal pattern.
A current detection element connected to the DC side of the inverter circuit and generating a signal corresponding to the current value,
A PWM signal generator that determines the rotor position based on the phase current of the motor and generates a three-phase PWM signal pattern so as to follow the rotor position.
A current detection unit that detects the phase current of the motor based on the signal generated in the current detection element and the PWM signal pattern is provided.
The PWM signal generation unit generates a three-phase PWM signal pattern so that the current detection unit can detect a two-phase current at two points in the carrier cycle of the PWM signal. To do
For one of the three-phase PWM signals, the duty pulse is increased or decreased in both the lagging side and the leading side with reference to an arbitrary phase of the carrier wave period.
For the other one phase, the duty pulse is increased or decreased in one direction of the lagging side and the leading side with reference to an arbitrary phase of the carrier wave period.
For the remaining one phase, the duty pulse is increased or decreased in the direction opposite to the direction with reference to an arbitrary phase of the carrier period.
A motor control device further comprising a braking control unit that generates braking torque in the motor by setting the duty of the three-phase PWM signals to be the same. The motor control device according to claim 1, wherein the braking control unit sets the duty of the three-phase PWM signal to 50% by setting the output voltage command value to zero, and generates braking torque in the motor. The motor control device according to claim 1 or 2, wherein the braking control unit generates a braking torque in the motor by giving a command value for generating a negative torque to the motor. When generating braking torque in the motor, the braking control unit first sets the duty of the three-phase PWM signals to be the same, and then gives a command value to generate negative torque in the motor. Item 3. The motor control device according to item 3. When the braking control unit gives a command value for generating a negative torque to the motor, if the output voltage is higher than the threshold value, the PWM signal generation unit performs two-phase modulation to generate a two-phase PWM signal pattern. The motor control device according to claim 3 or 4, wherein when the output voltage becomes equal to or lower than the threshold value, the PWM signal generation unit performs three-phase modulation. When the threshold value is set to the second threshold value, the braking control unit sets a first threshold value higher than the second threshold value.
When the output voltage is higher than the first threshold value, the duty pulses of the two-phase PWM signals are generated so as to extend symmetrically from the reference phase.
When the output voltage becomes equal to or lower than the first threshold value, one duty pulse of the two-phase PWM signal extends symmetrically from the reference phase, and the other duty pulse extends in any one direction from the reference phase. The motor control device according to claim 5, which is generated.