JPH09162804A - High speed insulated amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and precisely detect current at high speed with comparatively easy constitution by modulating the pulse width of the analog detection signal of current, digitizing it, demodulating it through the optical communication module and an optical fiber and outputting it to the control circuit of a low voltage-side. SOLUTION: A pulse width modulation circuit 12 modulating the pulse width of the analog detection signal of current flowing in the unit of a high voltage- side and digitizing it, an optical communication module 13 transmitting the signal which is pulse-modulated and a demodulation circuit 14 outputting a demodulation signal to the control circuit are provided. The pulse width modulation circuit 12 is constituted by a triangular wave generator 12a and a PWM comparator 12b. The analog signal of current flowing in the unit on the high voltage-side is pulse width-modulated by the pulse width modulation circuit 12 and is digitized. The modulated signal is demodulated by the demodulation circuit 14 on the output side through the optical communication module 13 and the optical fiber and is outputted to the control circuit on the low voltage- side, which controls the current of the unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a safe and high-speed control analog signal between a main circuit of a device on the high voltage side and a control circuit on the low voltage side for controlling the device. The present invention relates to a high-speed isolation amplifier having an insulation function for performing transmission processing on the.

[0002]

2. Description of the Related Art Conventionally, the main circuit of equipment on the high voltage side,
As a circuit for feeding back a control signal to a control circuit on the low voltage side for controlling the device, there is an isolation amplifier having a function of electrically insulating the two. And recently, because the high-speed switching device has come to be used for the current control of the main circuit side,
High-speed response and high-precision characteristics are now required.

For example, in a drive control of an electric motor for a winder for winding paper, fibers, films, etc., an accelerator for traveling control of a forklift truck, etc., instead of the conventional phase control by a thyristor such as SCR, When an FET (field effect transistor), an IGBT (insulated gate bipolar transistor) or the like that can be controlled at high speed is used, a chopping control method is used for such an element instead of the phase control. In this chopping control method, the current change rate is large and the electric time constant is equivalently small compared to the phase control. Therefore, in order to perform constant tension control and overcurrent protection operation properly, An isolation amplifier with high-speed response is required.

Concretely, consider a case where a DC shunt motor having a rated voltage of 220 V, a rated current of 20 A, an armature resistance (Ra) of 1 Ω, and an armature inductance (La) of 3 mH is chopper-controlled by a 300 V DC power source. And the armature time constant τ = La / Ra = 3 mH / 1Ω = 3 mS, but if a 300 V DC chopper power supply is used, the equivalent electric time constant τ ′ = τ / {power supply voltage / (rated current × armature resistance )} = 3 mS ÷ 300 V / (20 A × 1 Ω) = 3 mS ÷ 15 = 200 μS That is, when the current feedback control is performed by the chopper control, the phase delay (detection delay) of the feedback system is τ ′ =
Considering the stability of control for 200μS, 20μ
It is necessary to make it about S or less.

Further, in order to provide electrical insulation (isolation) in the isolation amplifier, (1) a direct current transformer (DCCT) by electromagnetic induction or a high frequency transformer (AM)
(Modem), (2) Hall element by Hall effect, (3)
There is a method such as photo coupling due to photoelectron emission. However, the DCCT is difficult in terms of resolution and linearity, and the AM modem is inferior in high-frequency transmission characteristics (about 5 KHz is a limit) and is not suitable for high-speed control, and the Hall element is capacitively coupled. Is large, noise is likely to occur. Further, there are an analog method and a digital method in the photocoupling, but the former is not preferable because of a large change over time, and the latter is mostly the latter, which is subjected to modulation / demodulation (modem) processing in a digitized state. In this digital system, there are an FM modem system and a high speed A / D conversion modem system.

In the FM modem system, as shown in FIG. 5, the detected value from the shunt that detects the current of the equipment to be controlled is V / F converted, and the F value is passed through a high-speed photocoupler.
Bias frequency (carrier)
The frequency characteristic can be improved by increasing the value, but the fluctuation of the bias frequency becomes the fluctuation (drift) of the output 0 level, and the influence of the offset is large. If a PLL circuit or the like is used to correct this, the circuit configuration becomes complicated and the cost increases, and if the frequency decreases, the response becomes slow. Further, as shown in FIG. 6, the high-speed A / D conversion modem system performs high-speed A / D conversion on the detection value from the shunt that detects the current of the device to be controlled, and the high-speed D-coupled via the high-speed photo coupler. However, there is a drawback in that the resolution is insufficient, the number of wires is increased by the bit length, and the cost becomes high.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and performs chopper control using a high-speed switching device for current control of the main circuit of equipment on the high voltage side. In this case, the operation is stable even if there is a change in the bias frequency, high-speed, high-precision current detection is possible with a relatively simple structure at low cost, and constant tension control and overcurrent protection are properly performed. It is an object of the present invention to provide an amplifier which can be implemented and which electrically insulates the main circuit of a device on the high voltage side and its control circuit on the low voltage side.

[0008]

To achieve the above object, the present invention provides a high speed isolation amplifier for transmitting a control signal from a high voltage side device to a control device, wherein an analog signal from the high voltage side device is pulsed. A pulse width modulation circuit for performing width modulation and digitization, an optical transmission module for converting the pulse width modulated signal into an optical signal, an optical fiber for transmitting the optical signal from the optical transmission module to the optical reception module, and An optical receiving module for receiving an optical signal, a demodulation circuit for inputting a signal output from the optical receiving module, and the control device for inputting a control signal demodulated by the demodulation circuit.

In the above structure, the analog detection signal of the current flowing through the equipment on the high voltage side is pulse-width modulated by the pulse-width modulation circuit and digitized, and the pulse-width modulated signal is transmitted through the optical communication module and the optical fiber. Through the demodulation circuit on the output side,
It is output to the control circuit on the low voltage side that controls the current of the device. By pulse-width modulating the analog detection signal in this way, the operation is stable even if the bias frequency changes.
A fast response is made. Further, the detection signal from the high voltage side is transmitted to the low voltage side in an electrically insulated state.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a control circuit diagram in which the high-speed isolation amplifier of the present invention is embodied, and shows a case where the controlled object is a DC motor for a winder. In this control circuit, four power FETs (field effect transistors) 3 connected in a bridge were used for controlling the energization of the armature 2 of the main circuit of the DC motor 1 on the high voltage side, and had an electrical insulation function. The isolation amplifier 4 is used to feedback control the detected value of the current (torque) to the control circuit 5 on the low voltage side. To detect the current (torque), the current flowing through the armature 2 is detected by the shunt (resistor) 6. The control circuit 5 includes a current error amplifier 7 and a PWM (pulse width modulation circuit) 8. A current (torque) command and a feedback signal of a current (torque) detection value are input to the current error amplifier 7. The output of the PWM 8 is connected to the gate of the power FET 3 via the electrically insulating circuit 9.

FIG. 2 is a block diagram of the isolation amplifier 4, and FIG. 3 is a specific circuit diagram of the isolation amplifier 4. The isolation amplifier 4 transmits an amplifier 11 that amplifies the analog detection signal from the shunt 6, a pulse width modulation circuit 12 that performs pulse width modulation of the amplified analog signal to digitize it, and the pulse width modulated signal. The optical communication module 13 is a high-speed photocoupler, and the demodulation circuit 14 demodulates a signal at the output side of the optical communication module 13. The pulse width modulation circuit 12 includes a triangular wave generator 12a and a PWM comparator 12b. The demodulation circuit 14 is composed of an averaging circuit and is provided with an offset trimmer 15 for adjusting 0 volt. The demodulation output of the averaging circuit is given to the control circuit 5. The optical communication module 13 is composed of a light emitting diode and a phototransistor for receiving the emitted light so as to have an isolation function.

In the above-mentioned isolation amplifier 4, when the triangular wave generator 12a and the PWM comparator 12b are operational amplifier IC AD847 manufactured by Analog Devices and the high speed photocoupler 13 is TLP552 manufactured by Toshiba, The conversion speed of the width modulation was as fast as about 1 μS.

Next, the operation of the pulse width modulation circuit 12 among the isolation amplifiers 4 constructed as described above will be described with reference to the time chart of FIG. The signal after amplification of the analog detection signal by the amplifier 11 is DVR, the triangular wave output of the triangular wave generator 12a is CAR, and P
Let DP be the comparison output of the WM comparator 12b, and
Consider the fluctuation of the comparison output DP when the detection signal DVR gradually increases as shown in the figure when the frequency of the triangular wave output which is the carrier is reduced from 100 KHz to 50 KHz which is half. The comparison output DP has a frequency of 1
At 00KHz, 2/7, 3/7, 1 cycle 10μS,
The duty fluctuates as 4.5 / 7, while the duty fluctuates as 4/14, 9/14, ... When the frequency is 50 KHz. The latter fluctuation output, when averaged, is substantially the same as the former fluctuation output. That is, this indicates that by performing pulse width modulation, the output is less affected even if the carrier frequency changes.

As described above, according to this embodiment, even if the carrier frequency of the pulse width modulation in the isolation amplifier 4 fluctuates, the influence on the output can be reduced with a relatively simple structure. High linearity and good resolution. Further, by setting this carrier frequency to a high frequency, high-speed response can be improved. Further, electrical insulation using the optical communication module 13 can secure about 5000 V at 10 MHz.

The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above-described embodiment, the optical communication module 13 is shown to include the light emitting diode and the phototransistor, but an optical fiber may be interposed between the light emitting diode and the phototransistor. The high voltage side and the low voltage side can be separated by a long distance, long distance transmission is possible, and a large insulation voltage can be given between them. As a result, for example,
It can also be applied to extraction of signals from high-voltage equipment of several hundred thousand volts class such as substations. Further, the power FET 3 is shown as a device capable of switching the electric motor 1 at high speed, but the device is not limited to this and may be an IGBT or the like.

[0016]

As described above, according to the high speed isolation amplifier having the insulation function according to the present invention, the analog detection signal of the current flowing through the equipment on the high voltage side is pulse-width modulated and digitized, and this signal is converted. By demodulating through the optical communication module and the optical fiber and outputting to the control circuit on the low voltage side, the carrier frequency becomes stable, and a high speed response is possible. Therefore, when performing chopper control using a high-speed switching device to control the current in the main circuit of the equipment on the high-voltage side, it is possible to inexpensively perform high-speed, high-precision current detection with a relatively simple configuration, and Tension control and overcurrent protection can be properly performed. Further, the main circuit of the device on the high voltage side and its control circuit on the low voltage side may be electrically insulated. Also, by interposing an optical fiber between the transmission and reception side optical communication modules, the high voltage side and the low voltage side can be separated by a long distance, and a large insulation voltage can be provided.

[Brief description of the drawings]

FIG. 1 is a control circuit diagram of a DC motor for a winder embodying a high-speed insulation amplifier of the present invention.

FIG. 2 is a block configuration diagram of the high-speed isolation amplifier.

FIG. 3 is a specific circuit diagram of the high speed isolation amplifier.

FIG. 4 is a time chart showing the operation of the pulse width modulation circuit.

FIG. 5 is a diagram of an FM modem system, which is an example of a conventional isolation amplifier.

FIG. 6 is a diagram of a high-speed A / D conversion modem system, which is an example of a conventional isolation amplifier.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC motor 3 FET 4 Insulation amplifier 5 Control circuit 12 Pulse width modulation circuit 12a Triangular wave generator 12b PWM comparator 13 Optical communication module 14 Demodulation circuit

Claims (1)

[Claims] 1. A high-speed isolation amplifier for transmitting a control signal from a high-voltage side device to a control device, and a pulse width modulation circuit for pulse-width-modulating an analog signal from the high-voltage side device to digitize it, and this pulse. An optical transmission module for converting a width-modulated signal into an optical signal, an optical fiber for transmitting the optical signal from the optical transmission module to the optical reception module, an optical reception module for receiving the optical signal, and an optical reception module A high-speed isolation amplifier including a demodulation circuit for inputting an output signal and the control device to which a control signal demodulated by the demodulation circuit is input.