JPH0216119B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a PWM (pulse width modulation) control device for a DC servo motor. Conventionally, in this type of PWM control system, four semiconductor switches Tr ₁ , Tr ₂ , Tr ₃ are used as shown in FIG.
and Tr ₄ are arranged and connected in the form of a bridge, and a driver is configured such that a pair of opposing connection points of the bridge is connected to a power supply terminal, and a DC servo motor M is connected between the other pair of opposing connection points. Two sets of semiconductor switches (a set of Tr ₁ and Tr ₄ , and a set of Tr ₂ and Tr ₃ ), one set being the semiconductor switch installed on the opposite side of the bridge, are arranged alternately as shown in Figure 2. A method is adopted in which the average value _n of the voltage v _n applied to the DC servo motor M is adjusted by turning it ON/OFF and adjusting the ratio of ON and OFF times. PWM control determines this ON/OFF time ratio in response to a command value. A conventionally widely used PWM control method is a method that compares a triangular wave carrier signal S _c and a command value S _i as shown in FIG. In Figure 3, a is S _c
(solid line) and Si (dashed line), and when _b is large (Si(1)), c is
When S _i is 0 (S _i (2)), d is small when S _i is small (S
(3)) respectively. In this method, a pair of switching elements installed corresponding to the case of S _i >S _c is turned ON and the other pair is turned OFF. Conversely, if S _i < S _c , ON/
Inverts the OFF state. Due to this ON/OFF operation, DC power supply voltage V _d or -V _d is applied to v _n . Depending on the S _i level, the time ratio at which V _d and -V _d are applied changes, _{and n} is controlled in accordance with S _i .
Since this conventional PWM is a method of adjusting v _n using only two types of voltages, V _d and -V _d ,
An increase in the pulsation of the motor current i _n is unavoidable. The pulsation of i _n increases motor loss and leads to an increase in motor size. The pulsation of i _n also causes motor noise. As a measure to suppress this pulsation, ON/
There are ways to increase the OFF repetition frequency or insert a reactor in series with the motor. The former has a limit due to the current switching speed of the switching element. The latter is associated with a large and heavy reactor, and is not preferred from the standpoint of reducing the size and weight of the device. The present invention improves the conventional servo driver.
The aim is to solve the problem of motor current pulsation, which is a drawback of PWM control, by simply improving PWM control without making the driver larger or more expensive. In conventional PWM, the reason why the current ripple increases is that _n is adjusted by only two voltages, +V _d and -V _d . Naturally, if the types of voltages applied to the motor are increased, the pulsation of i _n should decrease. Focusing on this point, the present invention has been developed to improve the conventional method, which uses one type of triangular carrier signal.
Unlike PWM, by increasing the number of carrier signals to two types, it is possible to apply zero voltage to the motor in addition to ±V _d , making it possible to suppress the pulsation of i _n to a small level. First, the operating principle of the present invention will be explained. Semiconductor switching elements Tr ₁ , Tr ₂ , Tr ₃ and
In a servo driver having a configuration in which Tr ₄ is arranged in a bridge shape as shown in Fig. 1, there are four operating modes (see Fig. 4) that can be operated without shorting the DC power supply. Mode: Elements in ON state (Tr ₁ and Tr ₄ ), Elements in OFF state (Tr ₂ and Tr ₃ ) Mode: Elements in ON state (Tr ₂ and Tr ₃ ), Elements in OFF state (Tr ₁ and Tr ₄ ) Mode: Elements in ON state (Tr ₁ and Tr ₃ ), Elements in OFF state (Tr ₂ and Tr ₄ ) Mode: Elements in ON state (Tr ₂ and Tr ₄ ), Elements in OFF state (Tr ₁ and Tr ₃ ) The v _n obtained by each mode of operation is v _n =v _d for mode, v _n =−v _d for mode, and v _n =0 for mode. Therefore, by implementing PWM that includes a mode or a mode in addition to the mode, the pulsation of _in can be suppressed. PWM using mode 1 or 2 can be achieved by increasing the number of carrier signals to two (Figure 5a). The two carrier signals Sc ₁ and S _c2 have the same frequency, always S _c1 > S _c2 , and S _c2
The maximum value S _c2-nax and the minimum value S _c1-nio of S _c1 are S _c2-nax >
Set the range in which the S _c1-nio relationship is maintained. The ON/OFF of semiconductor switch elements Tr ₁ and Tr ₂ is controlled by a carrier signal.
By comparing the magnitude of command value S _i with either S _c1 or S _c2 , Tr ₃ and Tr ₄ are set to the remaining carrier signal and command value.
Determined by comparing the size of S _i . For example Tr ₁ and Tr ₂
If S _c1 and S _i and Tr ₃ and Tr ₄ are determined by comparing S _c2 and Si, each element ON/OFF is determined as shown in the table below.

[Table] If you decide to turn ON as shown in the table above, if S _i > S _c1 , the servo driver's operation mode will be. Also S _c1
>S _i >S _c2 , it becomes a mode, and S _c2 >S _i , it becomes a mode. These three types of modes do not always appear. If S _i is relatively large and intersects only with S _c1 (FIG. 5b), the operating modes of the servo driver are alternately repeated. When S _i crosses both S _c1 and S _c2 near 0 (FIG. 5c), the modes are sequentially repeated. When S _i is small and intersects only with S _c2 , the mode and mode are repeated in FIG. 5d. In any S _i , since a mode where v _n =0 is used, the alternating current component included in the V _n waveform is reduced compared to conventional PWM, and the pulsation of i _n can be reduced. The carrier signals S _c1 and S _c2 used in the present invention are:
The shape of the wave is not limited to a triangular wave in which the rising slope and the falling slope are equal, and furthermore, the shape is not limited to mutually equal shapes. As long as the amplitude, frequency, and average level of the carrier signal do not change, changing both slopes will only change the timing at which each operating mode appears and will not affect _n . The invention can also be implemented with sawtooth wave carriers that are extremely different on both slopes, for example in FIG. 6, provided that S _c1 >S _c2 and S _c2-nax >S _c1-nio hold. The reason why there are two types of carrier constraints S _c1 > S _c2 and S _c2-nax > S _c1-nio is that when both carriers intersect, a power supply short circuit mode appears, so to avoid this, S _c1 > S _c2 and if there is a region where S _i within the control range does not intersect with either carrier, a dead zone will appear where _n does not change for S _i , so S _c2-nax > S _c1 This is to specify _-nio . The relationship between S _i and _n obtained by the PWM of the present invention is not a linear relationship within the control range (-V _d ≦v _n ≦V _d ). S _i =S _c2-nax and S _i =S _c1-nio
The amount of change _{in n} with respect to S _i changes after . Normally, the servo driver is not used alone, but is incorporated into a feedback control loop, so even if S _i and _n are not in a linear relationship,
This is compensated by feedback and is not a big problem. For applications where it is a problem that S _i and _n do not have a linear relationship, the present invention can be applied by correcting a part of the carrier signal waveform.
PWM can have a function where S _i and _n are proportional. First, the reason why S _i and _n do not have a linear relationship will be explained. In FIG. 1, the connection point between Tr ₁ and Tr ₂ is assumed to be point x, and the connection point between Tr ₃ and Tr ₄ is assumed to be point y. The average value of the potentials at points x and y from the negative terminal of the power supply _{is x} ,
Let v _y be the amplitude of both carriers, and V _c be the amplitude of both carriers. S _i =
0, if the carrier signal is determined so that _n = 0, then S _c2-nax = −S _c1-nio = V _p
It is. Using _these values to represent _x and _y , the range _x = V _{d y} = 0 S _{c1 -nax (} = V _c - _{V p )} S _i S _c2-nax (=V _p ) range _x = V _d /V _c S _i +V _d /V _c V _{p y} =0 S _c2-nax (=V _p )S _i S _c1-nio (=-V _p ) range _x = V _d /V _c S _i +V _d /V _c V _{p y} = -V _d /V _c S _i +V _d /V _c
V _p S _c1-nio (=-V _p ) S _i S _c2-nio (=-V _c +V _p ) range _x = 0 _y =-V _d /V _c S _i +V _d /V _c V _p S _{c2 -nio} (=-V _c +V _p )S _i range _x = 0 _y = V _d . Since the motor voltage _n = _x − _y , the range _n of S _i S _c1-nax = V _d S _c1-nax The range _n of S _i S _c2-nax = V _d /V _c S _i +V _d /V _c V _p S _c2-nax S _i S _c1-nio range _n = 2V _d /V _c S _i S _c1-nio S _c2-nio range _n = V _d /V _c S _i −V _d /V _c V _p S The range _n of _c2-nio S _i becomes -V _d , and compared to the change in _n for the change in S _i in the range S _c2-nax S _i S _c1-nio , the change in _n in the range on both sides The amount is reduced by 1/2. In other words, since there is a difference in the region of S _i where _x and _y change with respect to S _i , in the region where _x and _y both change with S _i and the region where only one of them changes, v with respect to S _i The amount of change in _n changes. From the above, in order to make the relationship between S _i and _n linear, _x in the area S _c1-nax S _i S _c2-nax
In addition, it is sufficient to double the amount of change of _y with respect to S _i in the area S _{c1-nio S i} S c2-nio. This can be achieved by correcting the carrier waveforms in both regions. For example, as shown in Fig. 7, while reducing the amplitude of S _c1 in the region of S _c1 > S _c2-nax to 1/2,
The carrier signal is corrected so that the amplitude of S _c1 in the region of S _c1-nio > S _c2 is also halved. When correction is performed in this way, _x for S _i of the corrected area,
The amount of change in v _y is doubled, the amount of change in _n is also doubled, and the relationship between _n and S _i becomes a straight line in the range where S _i and the carrier signal intersect (FIG. 8). The correction of the carrier waveform is not limited to the above correction. If the carrier amplitude in the area to be corrected becomes 1/2, the amount of change in _x and _y with respect to S _i is 2
Since the amplitude is doubled, the amplitude of the triangular wave in the area to be corrected only needs to be halved, and the points of S _c1-nax and S _c2-nio may change before and after correction (Figure 9). As explained in the explanation of the operating principle above,
In short, the present invention provides a PWM control method for a DC servo motor using four bridge-connected semiconductor switches as servo drivers. Using two unchained triangular wave carrier signals S _c1 and S _c2 (however, S _c1 > S _c2 ), these carrier signals S _c1 and S _c2 are compared with the command value S _i , and S _i > When S _c1 > S _c2 , positive DC voltage V _d ; when S _c1 > S _i > S _c2 , zero voltage; when S _c1 > S _c2 > S _i , negative DC voltage - V _d . The present invention is characterized in that the pulsation of the drive current of the DC servo motor is suppressed to a small level by controlling each semiconductor switch element of the servo driver so as to apply it to the DC servo motor. Furthermore, in the above PWM control method, the present invention provides carrier signals S _c1 ,
The maximum and minimum values of S _c2 are respectively S _c1-nax ,
When S _c2-nax , S _c1-nio , and S _c2-nio , the part of S _c1 in the range of S _c1 > S _c2-nax , the part of S _c2 in the range of S _c2 < S _c1-nio , the carrier of It is characterized by correcting the waveform so that the amplitude of those parts is 1/2 of that before correction. Hereinafter, the present invention will be explained in more detail with reference to Examples. FIG. 10 shows the configuration of a specific circuit for performing PWM control of the present invention. This circuit consists of a DC power supply 100 that is the energy source for the motor, four semiconductor switches 101, which are constructed by connecting transistors and diodes in antiparallel to form a bridge to form a servo driver.
102, 103 and 104, a DC servo motor 105, a triangular wave oscillator 1 that creates a carrier waveform, and a triangular wave generated by the triangular wave oscillator 1.
Adders 2 and 3 are used to create two types of carrier signals S _c1 and S _c2 that have the same frequency, phase, and shape but differ only in average level, and a comparison of the magnitudes of both carrier signals S _c1 and S _c2 and the command value S _i is performed. comparators 4 and 5 for inverting the output of the comparator, signal inverters 6 and 7 for inverting the output of the comparator, and ON/OFF signals S ₁ , S ₂ , S ₃ and It is composed of transistor drive circuits 11, 112, 113 and 114 that amplify _S4 and drive each semiconductor switch. Next, an overview of the operation of this embodiment will be explained.
In this embodiment, two types of carrier signals S _c1 and S _c2 are used, which have the same frequency, phase, and waveform shape, and differ only in signal average level. S _c1 and S _c2
The magnitude relationship of 4 is S _c1 > S _c2 . Carrier signal S _c1
The operation mode of the servo driver (Fig. 4) is determined by comparing the magnitudes of S _c2 and command value S _i . In this embodiment, in the region S _i >S _c1 , the motor voltage v _n =
Operation mode in which V _d (semiconductor switch 101
and 104 are ON, 102 and 103 are OFF), S _c1 >
In the region S _i > S _c2 , the operating mode is v _n =0 (semiconductor switches 102 and 104 are ON, 101
and 103 are OFF), and in the region S _i < S _c2 v _n =
Operation mode in which V _d (semiconductor switch 102
and 103 are ON, and 101 and 104 are OFF). When the servo driver is operated in the above mode depending on the magnitude relationship between the carrier waveform and the command value, if the command value S _i is relatively large, S _i and S _c1 will only intersect, so the motor voltage v As _n
V _d and 0 appear alternately. When S _i is around 0, S _c1
In the region of S _i that interlinks with both S c2 and S _c2 , the mode →
Three types of modes are executed sequentially in the order of mode → mode → mode, so the motor voltage v _n is
The voltages V _d , 0, −V _d , 0 appear sequentially. Also S _i
In the region where is small (negative side) and Si intersects only with S _c2 , −V _d and 0 appear in the motor voltage v _n . In all of these three regions, the motor voltage is lower than the conventional PWM in which ±V _d appears alternately due to the fact that v _n = 0 is included in the waveform of v _n that is repeatedly expressed at the period of the carrier frequency. Since the alternating current component included in v _n decreases, the pulsation of the motor current decreases. The decrease is large when S _i is around 0, where v _n =0 appears twice within one period. Next, along with FIG. 11 showing the operation of this embodiment,
The specific operation will be explained. The original form of the carrier signal is generated by the triangular wave oscillator 1 and determined by the triangular wave S _A. Since S _A is a waveform based on the 0 level, S _A is made into two types of carrier waveforms with different levels. S _B is a bias signal corresponding to the level difference of carrier signals. When the bias signal S _B and the triangular wave S _B are added by the adder 2, the output S _c1 becomes larger than S _A by the bias amount of S _B.
On the other hand, when S _A and S _B are subtracted by the adder 3, the output S _c2 becomes smaller than S _A by the bias amount of S _B. Comparing carrier signals S _c1 and S _c2 ,
The frequency, phase and shape are equal and both levels are S _B
differs by twice the bias value. These S _c1 and S _c2
This is a PWM carrier signal. When the magnitude relationship between S _c1 and command value S _i is compared by the comparator 4, S ₁ is obtained. On the other hand, the magnitude relationship between S _c2 and S _i is compared by a comparator 5, and its output is S ₃ . As shown in the above operating principle, the semiconductor switch 101 is
ON when S _i > S _c1 , OFF when S _i < S _c1 , semiconductor switch 1
02 is ON when S _i < S _c1 and OFF when _i > S _c1 , the semiconductor switch 103 is ON when S _i < S _c2 , and OFF when S _i > S _c2 , and the semiconductor switch 104 is _ON when S _i > S _c2 . ＜S _c2
It is OFF. Therefore, the high level/low level of _S2 is the ON/OFF level of semiconductor switches 101 and 102.
The OFF signal and the high level/low level of _S3 correspond to the ON/OFF signals of semiconductor switches 103 and 104. The transistor drive circuits 111, 112, 113 and 114 of each semiconductor switch drive the transistors when a high level signal is applied.
Turns it ON, and turns it OFF when a low level signal is given. When S ₁ is high level, semiconductor switch 10
Since it corresponds to the 1 ON state, S ₁ becomes the ON/OFF signal for the semiconductor switch 101 as it is. Similarly, when S ₃ is at a high level, it corresponds to when the semiconductor switch 104 is ON, so S ₃ remains unchanged as the semiconductor switch 10.
4 ON/OFF signal. On the other hand, when _S1 is at a low level, _the semiconductor switch 102 is ON, and when _S3 is at a low level, the semiconductor switch ₁₀₃ is ON. When the low level and high level are inverted, the inverted signal _S2 of _S1 turns on/off the semiconductor switch 102.
The inverted signal S4 of the signal _S3 is the inverted signal _S4 of the semiconductor switch 103.
Becomes an ON/OFF signal. The ON/OFF signals S ₁ , S ₂ , S ₃ , S ₄ generated in this way are transmitted to each semiconductor switch 101 , 102 , 103 , 104 and a dedicated transistor drive circuit 111 , 112 , 11 , respectively.
3, 114, the PWM operation of this embodiment described above is performed, and the pulsation of the motor current can be suppressed to a level smaller than that of conventional PWM. In this embodiment, an example is shown in which an operation mode in _which v _n = 0 is obtained, but S c2 is input instead of S _c1 as the input of comparator 4, and S _c1 is input instead of S _c2 of comparator 5. By doing so, the mode appears at the same time as the operating mode appears. However, since v _n =0 in both modes, the motor voltage does not change at all. Furthermore, in this embodiment, the phases of the two types of carriers are the same, but even if the phases are changed within a range where the two carriers do not intersect, v _n = V _d within one cycle,
The period of v _n = -V or v _n = 0 is the same, and v _n
The average value of remains unchanged. The only thing that changes is the timing at which those voltages are applied to the motor. In this example, S _i is S _c1 and S _c2 compared to the range of S _i where only S _{i and S c1 and S i and} S _c2 intersect _, respectively.
There is a characteristic that the amount of change in the motor voltage with respect to a change in the S _i level in the range of S _i that intersects with both is doubled. Making the amount of change in the average motor voltage equal to the change in the S _i level in the range where S _i intersects either S _c1 or S _c2 or both is to correct the waveforms of S _c1 and S _c2 . It's easy to do. As shown in Fig. 12, this correction is performed by connecting an amplifier whose amplification degree in the range above the maximum value of S _c2 is 1/2 and whose amplification degree in the range below is 1 to the signal line of S _c1 .
As shown in Figure 3, this is achieved by inserting amplifiers in the S _c2 signal line, each with an amplification factor of 1 in the range above the minimum value of S _c1 and an amplification factor of 1/2 in the range below it. can. As described above in detail using the embodiments, the PWM control method according to the present invention is different from the conventional PWM method in that PWM is performed using two types of carriers. By using two types of carriers in this way, the average value of the motor voltage was conventionally adjusted using only two types of voltage, positive and negative, but according to the present invention, the average value of the motor voltage was adjusted using only two types of voltage, positive and negative. In addition, it is possible to adjust the motor voltage using zero voltage, thereby reducing the alternating current voltage component included in the motor voltage waveform and suppressing the pulsation of the motor current. The present invention makes it possible to increase motor loss and, in some cases, reduce current pulsations that cause motor noise, without changing the size, weight, and price of the control device. ,
It is possible to manufacture a device with less loss and noise than conventional devices, and furthermore, the reduction in motor loss makes it possible to downsize the motor.

[Brief explanation of drawings]

Figure 1 is a DC servo drive circuit diagram using bridge-connected switches, Figure 2 is a diagram to explain the operation of the drive circuit in Figure 1, and Figure 3 is a diagram of a conventional PWM drive circuit.
A waveform diagram for explaining the control device, FIG. 4 is a diagram showing the operation mode of the servo driver, FIG. 5 is a waveform diagram for explaining the PWM control device according to the present invention, and FIG. 6 is a carrier waveform for the present invention. A diagram showing an example, FIG. 7 is a diagram showing a carrier waveform for making the command value and motor voltage proportional, and FIG.
FIG. 3 is a diagram showing the relationship between command value S _i and motor average voltage by PWM control. Figure 9 is a diagram showing the carrier waveform correction range for making the command value S _i and motor voltage _n proportional.
~ indicates carriers that have undergone waveform correction to make S _i and _n proportional. FIG. 10 is a diagram showing an embodiment of the PWM control device of the present invention, and FIG. 11 is a waveform diagram for explaining the operation of the circuit in FIG. 10. FIGS. 12 and 13 are diagrams showing the characteristics of an amplifier for creating a carrier signal that makes the motor voltage and command value proportional.

Claims (1)

[Claims] 1. Two sets of two series-connected semiconductor switches are connected between the positive and negative terminals of a DC power supply, and two connection points of the two series-connected semiconductor switches are connected to DC servo motor drive terminals. In a PWM control device for a DC servo motor using a servo driver that
The waveforms are triangular waves whose amplitudes and frequencies are equal to each other and whose average voltage levels are different, where the first triangular wave with a higher average voltage level always has a higher instantaneous value than the second triangular wave with a lower average voltage level at the same time, and A triangular wave generation circuit that outputs two types of triangular waves as carrier signals in which the maximum value of the second triangular wave is within a range greater than the minimum value of the first triangular wave, and a magnitude comparison between the two carrier signals and a motor voltage command value. When the motor voltage command value is greater than both carrier signals, the motor receives a positive DC power supply voltage; when the motor voltage command value is between the two carrier signals, the motor receives zero voltage; A PWM control device for a DC servo motor, comprising a control circuit that determines the on and off timing of each semiconductor switch so that a negative DC power supply voltage is applied to the motor when the voltage is smaller than the signal. 2. Regarding the first triangular wave, the triangular wave generation circuit generates a portion of the voltage value that is greater than or equal to the maximum value of the second triangular wave,
A patent claim characterized in that the amplitude of each part of the second triangular wave having a voltage value lower than the minimum value of the first triangular wave is halved and output as a carrier signal. A PWM control device for a DC servo motor as described in Scope 1. 3 Connect the first and second switches in series,
The third and fourth switches are connected in series, and the two series-connected switches are connected between the positive and negative terminals of the DC power supply, and the connection point between the first and second switches and the third and fourth switches are connected between the positive and negative terminals of the DC power supply. a servo driver that drives a DC servo motor connected between the switch connection point of is always higher in instantaneous value at the same time than a second triangular wave having a low average voltage level, and the maximum value of the second triangular wave is within a range greater than the minimum value of the first triangular wave. A circuit that generates two types of triangular wave carrier signals, a triangular first carrier signal and a triangular second carrier signal with a low average voltage level, and a comparison between these carrier signals and a motor voltage command value. , a circuit that outputs first, second, third, and fourth control signals for controlling on/off of the first, second, third, and fourth switches, respectively; The second control signal turns on the first switch when the motor voltage command value is larger than the first carrier signal, and the second control signal turns on the second switch when the motor voltage command value is smaller than the first carrier signal. The third control signal turns on the third switch when the motor voltage command value is greater than the second carrier signal, and the fourth control signal turns on the speed command value. When the second carrier signal is smaller than the second carrier signal, the fourth switch is turned on. A PWM control device for a DC servo motor according to claim 1. 4 Connect the first and second switches in series,
The third and fourth switches are connected in series, and the two series-connected switches are connected between the positive and negative terminals of the DC power supply, and the connection point between the first and second switches and the third and fourth switches are connected between the positive and negative terminals of the DC power supply. a servo driver that drives a DC servo motor connected between the switch connection point of is always higher in instantaneous value at the same time than a second triangular wave having a low average voltage level, and the maximum value of the second triangular wave is within a range greater than the minimum value of the first triangular wave. A circuit that generates two types of triangular wave carrier signals: a triangular wave first carrier signal and a triangular wave second carrier signal with a low average voltage level; Carrier signal correction that halves the amplitude of the voltage value portion of the low second carrier signal that is greater than or equal to the maximum value, and the amplitude of the portion of the voltage value that is less than or equal to the minimum value of the first carrier signal for the second carrier signal. circuit, and first, second, third, and fourth switches that compare the magnitudes of these carrier signals and the speed command value and control the first, second, third, and fourth switches on/off, respectively. the first control signal turns on the first switch when the speed command value is greater than the first carrier signal, and the second control signal outputs a speed control signal. The third control signal turns on the second switch when the command value is smaller than the first carrier signal, and the third control signal turns on the third switch when the motor voltage command value is larger than the second carrier signal. The fourth control signal turns on the fourth switch when the motor voltage command value is smaller than the second carrier signal. A PWM control device for a DC servo motor.