JPH0352565A - Pulse width modulation type supply voltage - Google Patents

Abstract

PURPOSE:To miniaturize semiconductor elements and to prevent breakdown by heightening carrier-frequency to modulate the pulse width when it is detected that the instantaneous value of an electric current supplied to the load from a pulse width modulation type supply voltage is in excess of a specific upper limited value. CONSTITUTION:Control error (rho), resulting from subtraction 12 of target value from controlled variable (f) of the load 10, is corrected by a PID corrector 14 to make a signal (a), and it is inputted to a PWM signal making circuit 16. PWM modulation of the signal (a) is made by a triangle wave from a carrier oscillation circuit 18 at the making circuit 16, a pulse train (b) is outputted, and DC power 22 supplies an electric current ir to the load 10 intermittently through a gate circuit 24 and drive circuit 20. The current ir detected by a CT 26 is compared (28) with a reference value, when it is in excess of a specific value, a signal (c) is outputted, and a pulse (d) for a short period (tau) is outputted from a monostable oscillator 30. OR 32 of the signal (c) and pulse (d) is made, and the gate circuit 24 is closed only for the period (tau) to stop the drive circuit 20. According to the constitution, the PWM modulation is equivalent to the modulation executed by carrier of high frequency, and the rising of a load current is prevented.

Description

[Detailed Description of the Invention] Purpose of the Invention (Industrial Application Field) The present invention (industrial field of application) This invention relates to a pulse width modulated voltage source that can be approximated.

(Prior Art) Conventionally, a pulse width modulation (PWM) type voltage source has been used to extract desired power from a DC power source with a constant voltage value.

The operation of this pulse width modulated voltage source is to connect the DC voltage source and the load intermittently based on a pulse signal with a predetermined period T, and at that time, the current waveform is set to the target pulse width of the pulse signal. Modulate the power so that the power supplied to the load is adjusted.

With the development of semiconductor switching elements such as transistors and thyristors, PWM
This makes it possible to increase the predetermined frequency during modulation, and is used in a wide range of fields.

(Problems to be Solved by the Invention) As described above, due to the characteristics of the semiconductor switching element, which is one of the essential constituent elements, the following problems remain unsolved.

When the time constant of the load is small, the ripple rate of the PWM-controlled current increases and exceeds the maximum allowable current value of the semiconductor switching element that constitutes the pulse width modulated voltage source.
This will lead to element destruction.

This phenomenon also occurs when the time constant of the load fluctuates over a wide range, for example when driving a variable reluctance motor or solenoid actuator, or when starting a normal electric motor. type voltage source (upper) It is generally used as a power source for a load that has a somewhat large inductance component.

In addition, dynamic braking is known as a braking method for electric motors, etc., but when dynamic braking is performed when a pulse width modulated voltage source is used as a power source for the electric motor, the electromotive force generated by the electric motor causes the above-mentioned Similarly, there is a possibility that a large current exceeding the maximum allowable current value momentarily flows through the semiconductor switching element.

In order to avoid destruction of semiconductor switching elements due to the above phenomenon, when manufacturing pulse width modulated voltage sources, we use semiconductor switching elements with a large maximum allowable current value that has a high margin for the load. .

However, in order to increase the maximum allowable current value of a semiconductor switching element, it is necessary to increase the size of the element itself, and a pulse width modulated voltage source using a plurality of such elements synergistically becomes larger and heavier.

Furthermore, semiconductor switching elements with a large maximum allowable current value are expensive, which will push up the prices of various devices containing pulse width modulated voltage sources. The present invention has been made in order to solve the above-mentioned unresolved problems with pulse width modulated voltage sources, and uses a semiconductor switching element that is appropriate for the load while avoiding overcurrent damage to the semiconductor switching element. The purpose of this invention is to provide a pulse width modulated voltage B that is inexpensive and highly versatile, achieving a smaller and lighter power supply section.

Structure of the Invention (Means for Solving the Problems) Means configured by the present invention to solve the above problems (connecting a DC voltage source and a load using a signal obtained by pulse width modulating a target current waveform with a carrier wave of a predetermined frequency) in a pulse width modulated voltage source that intermittently controls the current flowing through the load to approximate the average current waveform flowing through the load to the target current waveform, comprising: instantaneous value detection means for detecting an instantaneous value of the current flowing through the load; The gist is a pulse width modulated voltage source characterized by comprising: carrier frequency correction means for increasing a predetermined frequency of the carrier wave when the detection result of the instantaneous value detection means exceeds a predetermined upper limit value. (Function) Carrier frequency correction means (table) in the drive device of the present invention When the instantaneous value of the load current detected by the instantaneous value detection means exceeds a predetermined upper limit value, the carrier frequency of the pulse width modulation is increased. The degree of current modulation is improved only when the constant is small, and the current ripple rate is kept low.

Further, since the carrier frequency correction means (above) is operated based on the detection result of the instantaneous value detection means, the carrier frequency is kept low in a normal state where the ripple rate of the load current is small.

EXAMPLES Hereinafter, in order to explain the present invention more specifically, examples will be given and explained.

(Embodiment) FIG. 1 is an electrical circuit diagram of a pulse width modulated voltage source which is an embodiment of the present invention. In this embodiment, a type in which the time constant of the load 10 changes over a wide range over time, such as a variable reluctance motor, will be exemplified and explained.

Pulse width modulated voltage yiIt. of this embodiment. The current supplied to the load 10 is subjected to PWM control in order to match a predetermined control amount of the load 10, for example, rotational torque, with a target value. Therefore, the actual control amount of the load 10 is taken out as feedback information and subtracted from the target value at the addition point 12.

The result of subtraction between the target value and the controlled variable, that is, the control deviation ρ, is
The signal is input to the PWM signal generation circuit 16 through a proportional-integral-derivative (PID) corrector 14 designed to have an appropriate transfer function in order to improve the responsiveness of the control system. Therefore, this P
The signal a input to the WM signal generation circuit 16 becomes a current pattern to be PWM modulated.

PWM signal generation circuit 16 (as well known, the above signal a
and a triangular wave of a predetermined frequency created by the carrier wave transmitting circuit 18, and outputs a pulse train signal obtained by PWM modulating the signal a. Figure 2 illustrates this relationship. As shown in the figure, this is a pulse train signal obtained by a simple comparison between the output signal bl & signal a from the PWM signal generation circuit 16 and a carrier wave, and the pulse train signal is the result of PWM modulating the signal a.

According to the conventional pulse width modulated voltage source, the signal b obtained in this manner is directly output as a switching timing signal to the drive circuit 20 constituted by semiconductor switching elements such as transistors or thyristors. The semiconductor switching element performs intermittent connection between the load 10 and the DC power supply 22.
A constant voltage DC power supply 22 can be used to flow a load current in a desired current pattern. That is, as shown in FIG. 3(A), since the switching operation based on the PWM modulated signal b is performed by the drive circuit 20,
Although the instantaneous value of the load current ir fluctuates, it is possible to obtain a load current that matches a desired current pattern on average.

In addition, in Figure 3 (A), the pulsation of the load current becomes smaller with time (as shown in the figure), the time constant of load 10 gradually increases as shown in the figure, indicating that the property of suppressing temporal changes in the current is This is based on the fact that the diagram was drawn assuming a rising load.In this way, the electrical properties of load 10 (like PWM
This has a large effect on the current waveform after modulation.

The above is a description of the case where a conventional pulse width modulated voltage source passes current to the load 10 having the characteristics assumed in this embodiment. In such a case, as shown in FIG. 3(A), when the time constant of the load 10 is small, the ripple rate of the current is large, and its instantaneous value becomes excessive, causing the semiconductor switching element constituting the drive circuit 20 to There is a possibility that the maximum allowable current value of 1 m may be exceeded and the drive circuit 20 may be destroyed.

Therefore, on the pulse width modulated voltage source 1 of this embodiment, the above PW
A configuration is adopted in which the output signal b of the M signal generation circuit 16 is input to the drive circuit 20 via the gate circuit 24. A gate signal of this gate circuit 24 is a comparator 28 that compares the detected value of the current detection coil 26 that detects the actual load current waveform with a predetermined reference value, and the output signal of the comparator 28 is directly or monostable oscillator. is created by an OR circuit 32 inputting via 30.

Next 1:. The signal waveforms of each part of the pulse width modulated voltage source of this embodiment configured in this manner will be explained based on FIG. 3(B).

The predetermined reference value given to the comparator 28 is set to a value corresponding to the maximum allowable current value of 1 m of the semiconductor switching element constituting the drive circuit 20 described above. Therefore, the output signal C of the comparator 28 When the detection output ir of the detection coil 26 exceeds the maximum allowable current value im (ir
≧im), falls to L level. A monostable oscillator 30i which inputs this signal C; ( uses the falling point when the signal C falls to the L level as a trigger signal to output a pulse signal d with a short period fL'lτ.Then, the signal C and the signal d
The OR circuit 321 which inputs the OR circuit 321 outputs the logical sum of these signals to the gate circuit 24 as a gate signal. On the other hand, the other input signal E of the gate circuit 24 is the signal b from the PWM signal generation circuit 16 which PWM-modulated the current pattern as in the conventional case. Therefore, the output of the signal b (upper) from the PWM signal generation circuit 16, which was conventionally input to the drive circuit 2o, is prohibited during the period when the gate circuit 24 closes the gate.

Then, the output signal e IL of this gate circuit 24 becomes a signal with a good modulation degree as shown in the composite PWM signal shown in FIG. 3 (as the frequency of the PWM modulated carrier wave increases,
This signal is input to the drive circuit 20.

That is, by using the pulse width modulated voltage source of this embodiment, 1'
;L At the moment when the load current 1r reaches a value large enough to adversely affect the semiconductor switching elements constituting the drive circuit 20, the gate of the gate circuit 24 is closed and the output of the PWM signal b is interrupted for a short period τ. As a result of this, the load current 1r suddenly decreases in order to interrupt the connection between the drive circuit 20LL load 10 and the DC power supply 22, and a phenomenon in which the load current 1r exceeds the allowable maximum current im is avoided. After the interruption period ends, the gate of the gate circuit 24 becomes open, and the PWM signal b
supply of current is resumed.

Due to the operation of such a pulse width modulated voltage source, the load 10
12 The waveform of the supplied load current 1r becomes a pulsating current below the allowable maximum current value im, as shown in Figure 3 (B).
Destruction of the semiconductor switching elements constituting the drive circuit 20 due to large currents is avoided.

As described in detail above, according to the pulse width modulated voltage source of this embodiment, when the maximum value of If and load current 1r exceeds a predetermined reference value, the switching speed increases as if PWM modulation was performed using a high frequency carrier wave. This has the effect of preventing an abnormal increase in the load current 1r.

Moreover, such an increase in switching speed is limitedly carried out only when the load current 1r is about to become abnormally large; under normal conditions, the current due to the general switching speed 12 is increased as before. supply is carried out. Therefore, it is possible to use an inexpensive element with a continuous switching speed rating of a typical value as the semiconductor switching element constituting the drive circuit 20, and the average switching loss thereof can be kept small.

Furthermore, in this embodiment, a configuration is adopted in which the carrier frequency is increased in a pseudo manner using a simple circuit configuration such as a comparator 28, a monostable oscillator 30, an OR circuit 32, etc., without providing a plurality of carrier wave oscillation circuits 18 for tiPWM modulation. adopt. This makes it possible to manufacture a pulse width modulated voltage source with a simplified circuit configuration, small size, and low cost that exhibits the excellent effects described above. It should be noted that the present invention is not limited to the above-described embodiments, but may be embodied in various forms without departing from the spirit thereof. For example, {L In the above embodiment, the instantaneous value of the load current ir actually flowing through the load is detected to detect the point in time when the maximum allowable current value is 1 m or more, but the time constant of the load is detected or estimated and May be replaced. To explain based on the example described above, the time constant of the load 10 can be easily estimated from the rotation angle of the variable reluctance motor that is the load. Therefore, it is only necessary to control the frequency of the PWM carrier wave to increase when the time constant from the output of the encoder becomes less than or equal to a predetermined value.

Furthermore, in the above embodiment, in order to reduce the size and weight of the device, a configuration is adopted in which only one carrier wave transmission circuit 8 is provided, and a configuration is adopted in which the PWM modulation frequency is changed in a pseudo manner.
In order to strictly match the current pattern and the load current direct current 1':. The carrier wave transmitting circuit 18 may include a plurality of transmitting circuits having different transmitting frequencies.

Further, in the above embodiment, the carrier wave frequency is changed in two stages, but it may be changed in three or more stages. Such a configuration enables PWM modulation at a more optimal switching speed according to the characteristics of the semiconductor switching elements constituting the drive circuit 20 and the magnitude of the load current ir, thereby reducing switching loss, switching noise, continuous operation, etc. control accuracy is improved.

Effects of the Invention As described above in detail with reference to embodiments, the pulse width modulated voltage source of the present invention {1. can be reduced.

Therefore, it is possible to use a semiconductor switching element appropriate for the load, avoid overcurrent damage to the semiconductor switching element, and achieve a reduction in size and weight of the power supply section. Therefore, the pulse width modulated voltage source of the present invention can be manufactured at a very low cost and has excellent versatility that can be easily applied to various industrial equipment.

The pulse width modulated voltage source of the present invention (
A power supply unit that enables dynamic braking of motors to which it was difficult or impossible to apply conventional pulse width modulated voltage sources.Power supply unit whose load is a variable reluctance motor or solenoid actuator with large inductance changes. It is suitable for use as a t source for all kinds of industrial equipment.

[Brief explanation of drawings]

Figure 1 shows an electric circuit block of a pulse width modulated voltage source which is an embodiment of the present invention. Figure 2 shows an explanation of PWM modulation.
FIG. 3(A) shows an explanation of the load current waveform supplied to the load according to the prior art. FIG. 3(B) shows an explanation of the signal and current waveform of each part in the above embodiment. 10...Load 12...Additional point 14.
...PID corrector 16...PWM signal creation circuit 8.
...Carrier wave oscillation circuit 2 ... DC power supply 6 ... Current detection coil 0 ... Monostable oscillator

Claims (1)

[Scope of Claims] 1. Connection between a DC voltage source and a load is intermittently controlled by a signal obtained by pulse width modulating a target current waveform with a carrier wave of a predetermined frequency, and the average current waveform flowing through the load is set as the target current. A pulse width modulated voltage source that approximates a waveform, comprising: instantaneous value detection means for detecting the instantaneous value of the current flowing through the load; and when the detection result of the instantaneous value detection means exceeds a predetermined upper limit value, the predetermined frequency of the carrier wave is 1. A pulse width modulated voltage source comprising: means for correcting a carrier frequency to increase the carrier frequency;