JPH10285988A - Current detector and current controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current controller directly sampling a load current at variable timing, capable of being followed up to a current change at high speed and using a PWM amplifier. SOLUTION: The device has a PWM amplifier 2 for driving load 1, a mean- current value detector 3 for detecting the mean current value of load 1, and a controller 5 setting the pulse width of a PWM signal output from the PWM amplifier 2 in response to the difference of a detected mean current value and a command current value from the outside. The mean-current value detector 3 has a current sensor 31 for detecting the actual current value of the load 1, a sampling-pulse generating circuit 32 for generating sampling pulses S2 at timing, when the mean current value is obtained on the basis of a load- current waveform determined by the period T0, and pulse width T1 of the PWM signal and the impedance ZL of the load 1, and a current-value sampling circuit 33 for sampling the actual current value acquired by the current sensor 31 by sampling pulses S2 and obtaining the mean current value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a current detector for a PWM amplifier that drives a load by pulse width control, and a current controller for controlling the current of the load.

[0002]

2. Description of the Related Art Conventionally, a PWM amplifier has been used for a motor drive circuit or the like in an NC machine tool. PW
The load current of a motor or the like driven by the M amplifier is controlled by a control loop that controls the pulse width of the PWM amplifier so that the difference between the command current value from the outside and the current value detected by the load becomes zero. . When the load includes a large inductance such as a motor, the current has a large ripple within the pulse period of the PWM amplifier. Therefore, if the current value is sampled at a constant sampling point of the pulse cycle, an error from the average current value within one cycle increases, and high-precision control cannot be performed. Therefore, in order to obtain an average current value excluding the influence of the ripple, a filter is conventionally provided in the output of the current detector. In the case of a digital controller (discrete control system), after removing a ripple by a filter, the detected current value is converted into digital data by an A / D converter and fed back.

[0003]

However, in the conventional method using a filter for obtaining an average current value, there is a problem that a time delay in the filter adversely affects high-speed performance and cannot follow a high-speed change in current. In addition, since the ripple of the current changes depending on the load, it is necessary to optimize the filter according to the load in order to follow a high-speed current change, and there is a problem that the filter configuration is complicated.

The present invention has been made in consideration of the above circumstances, and is capable of following a high-speed current change by directly sampling a load current including a ripple at a variable sampling timing at which an average current value can be obtained. It is an object of the present invention to provide a current detection device for a PWM amplifier and a current control device using the PWM amplifier.

[0005]

SUMMARY OF THE INVENTION The present invention is a current detecting device for a PWM amplifier for driving a load by pulse width control, comprising: a current sensor for detecting an actual current value of the load;
Sampling pulse generating means for generating a sampling pulse at a timing at which an average current value is obtained based on a load current waveform determined by a period T0 and a pulse width T1 of the PWM signal and an impedance ZL of the load; Current value sampling means for sampling an actual current value obtained by the sensor to obtain an average current value.

The present invention also provides a PWM amplifier for driving a load, an average current value detecting means for detecting an average current value of the load, an average current value detected by the average current value detecting means, and an external command. Control means for setting a pulse width of a PWM signal output from the PWM amplifier in accordance with a difference from a current value, wherein the average current value detection means detects an actual current value of the load. A current sensor, a period T0 and a pulse width T of the PWM signal;
Sampling pulse generating means for generating a sampling pulse at a timing at which an average current value is obtained based on a load current waveform determined by the load impedance ZL, and an actual current value obtained by the current sensor by the sampling pulse. And a current value sampling means for obtaining an average current value.

In the present invention, the sampling pulse generating means may be, for example, a maximum current value Imax obtained by a load impedance ZL when T1 / T0 and T1 = T0.
Sampling pulses at the timing at which the average current value is obtained from the pulse width T1 are generated based on the relationship between the average current value as a function of and the timing at which this average current value is obtained.

When a load including an inductance is driven by a PWM amplifier, a current waveform including a ripple is represented by PWM
The sampling timing at which the average current value is obtained can be known in advance from the current waveform, which is uniquely determined by the period T0, pulse width T1, and load impedance of the M signal.
Therefore, in the present invention, the average current value can be immediately detected without using a filter by sampling the current value from the load current including the ripple at the sampling timing at which the average value is obtained. The sampling timing according to the load current waveform is
For example, the pulse width T1 can be stored in a memory or the like in advance in relation to the load current waveform, and the pulse width T1 can be read out as an address, or can be calculated in real time by a simple algorithm. In this manner, according to the present invention, a current control device capable of directly and accurately detecting an average current value at a variable sampling timing according to a load and capable of following a high-speed current change is obtained. be able to.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a current control circuit according to an embodiment of the present invention, specifically, a motor drive circuit used for an NC machine tool or the like. This current control device includes a PWM amplifier 2 for driving a load 1, an average current value detection circuit 3 for detecting an average current value Iav of the load 1, and an average current value Iav detected by the average current value detection circuit 3. A subtractor 4 for obtaining a difference value ΔI from an external command current value I0; and a pulse width control signal S1 is output in accordance with the obtained difference value ΔI to set a pulse width of a PWM signal output from the PWM amplifier 2. And a controller 5 that performs the operation.

The average current value detection circuit 3 includes a current sensor 31 for detecting the actual current value Id of the load 1, a period T0 and a pulse width T1 of the PWM signal, and an impedance ZL of the load 1.
A sampling pulse generation circuit 32 that generates a sampling pulse S2 at a timing at which an average current value is obtained based on a load current waveform determined by the load current waveform, and an actual current value Id obtained by the current sensor 31 using the sampling pulse S2 to sample A current value sampling circuit 33 for obtaining the value Iav.

Specifically, the sampling pulse generating circuit 32 averages the pulse width T1 based on various load current waveform data determined by the period T0 of the PWM signal, the pulse width T1, and the impedance ZL of the load 1. The memory includes a memory configured to output a timing at which a current value is obtained. Using the pulse width control signal S1 obtained by the controller 5 as an address signal, timing data from which an average value of load current including ripple is obtained is read out from the memory, and a sampling pulse S2 is generated at a timing corresponding to the timing data. Occur.

FIG. 2 shows the pulse period T of the PWM amplifier 2.
O shows the relationship between the set pulse width T1 and the load current waveform including the ripple. The current value obtained when the PWM amplifier 2 is always on during the period T0 is the maximum current value Imax. The current waveform has an initial current value I1 of the pulse period T0.
, The impedance Z including the inductance of the load 1
The pulse width increases to I2 with the waveform determined by L, and the set pulse width T
A ripple waveform that decreases from the timing of 1 is drawn. At this time, the average current value Iav during the period T0 intersects this current waveform at two points P1 and P2. These points P1, P
If the actual current value Id is sampled at any one of the sampling points 2, the average current value Iav can be immediately obtained without using a filter.

The timings P1 and P2 are not fixed but change according to the current waveform. The current waveform has the pulse period TO, the set pulse width T1, and the load impedance Z as described above.
It depends on L. Specifically, for example, the average current value Iav is
Load impedance Z when T1 / T0 and T1 = T0
As a function with the maximum current value Imax obtained by L, it is expressed by the following equation (1).

[0014]

## EQU1 ## Iav = (T1 / T0) Imax

From various data satisfying this relationship, if, for example, the pulse period T0 and the maximum current value Imax are fixed, a linear relationship between the pulse width T1 and the average current value Iav is obtained, and the average current value Iav at that time is obtained. Is also determined. Therefore, in the sampling timing generation circuit 32, the pulse width control signal S corresponding to the pulse width T1
With 1 as an address, data of the timing P1 or P2 at which the average current value Iav is obtained is stored in a memory in advance. Thereby, based on the pulse width control signal S1 obtained from the controller 5, it is possible to generate the sampling pulse S2 for reading out the timing data and detecting the average current value.

In order to actually correspond to various loads, it is necessary to consider that the maximum current value Imax varies depending on the load. Therefore, for example, using the pulse width T1 and the maximum current value Imax as the row and column addresses, respectively, the average current value I
The timing data at which av is obtained is stored. The current sensor 31 is provided with a maximum value detecting function, and the pulse width T
If the timing data determined by 1 and the maximum current value Imax is read, the actual current value can be sampled at the point where the average current value is always obtained.

As described above, according to this embodiment, the actual current value including the ripple is directly sampled at an appropriate variable sampling timing, so that the current can be reduced without a time delay as in the case of using a filter. , It is possible to detect the average current value in response to the high-speed change of the current and perform high-precision current control. In the embodiment, the case where the sampling timing generation circuit 32 is configured by a memory has been described. However, a simple algorithm can be calculated by a high-speed processor without using a memory.

[0018]

As described above, the PWM according to the present invention is provided.
In the current detection device of the amplifier, the actual current value including the ripple is directly sampled at an appropriate variable sampling timing according to the load and the pulse width of the PWM signal, and the average current value is obtained. The average current value can be detected at high speed in response to a high-speed change in current. In addition, by configuring a current control device incorporating such a current detection device, it is possible to perform high-precision current control.

[Brief description of the drawings]

FIG. 1 shows a current control device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of average current value detection according to the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Load, 2 ... PWM amplifier, 3 ... Average current value detection circuit, 4 ... Subtractor, 5 ... Controller, 31 ... Current sensor, 32
... Sampling timing generation circuit, 33 ... Current value sampling circuit.

Claims (3)

[Claims] 1. PW for driving a load by pulse width control
A current sensor for detecting an actual current value of the load, an average current based on a load current waveform determined by a period T0 and a pulse width T1 of the PWM signal and an impedance ZL of the load. Sampling pulse generating means for generating a sampling pulse at a timing at which a value is obtained, and current value sampling means for sampling an actual current value obtained by the current sensor by the sampling pulse to obtain an average current value. Current detection device. 2. The method according to claim 1, wherein the sampling pulse generating means includes:
Load impedance ZL when 1 / T0 and T1 = T0
Generating a sampling pulse at a timing at which the average current value is obtained from the pulse width T1, based on a relationship between the average current value as a function of the maximum current value Imax obtained at the time and the timing at which the average current value is obtained. The current detection device according to claim 1, wherein 3. A PWM amplifier for driving a load, an average current value detecting means for detecting an average current value of the load, an average current value detected by the average current value detecting means, and an external command current value. A current control device for setting a pulse width of a PWM signal output from the PWM amplifier in accordance with a difference between the average current value detection device, a current sensor for detecting an actual current value of the load; A sampling pulse generating means for generating a sampling pulse at a timing at which an average current value is obtained based on a load current waveform determined by a period T0 and a pulse width T1 of the PWM signal and an impedance ZL of the load; Current value sampling to obtain the average current value by sampling the actual current value obtained by the current sensor Current control device being characterized in that a stage.