JPH0119596Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an inverter device that turns switching elements on and off to obtain an alternating current output, and particularly relates to an inverter device that has a function of protecting the switching elements from destruction due to overcurrent.

[Technical background of the invention and its problems]

2. Description of the Related Art Controlling the rotational speed and torque of an electric motor using an inverter has been widely used from the viewpoints of controllability, reliability, versatility, and cost. Transistors are generally used as switching elements in such inverters because transistors have excellent characteristics such as self-extinguishing properties, low saturation loss, and high-speed switching characteristics. . When comparing transistors with such superior advantages to thyristors, transistors have a problem in that they have lower withstand capability than thyristors, and are particularly inferior in terms of overload capability.

However, when applying such a transistor to an inverter device in the power field, for example,
Protection from destruction of the transistor is more difficult to coordinate against overcurrent than overvoltage.

FIG. 1 shows the configuration of a conventional sine wave approximation PWM type inverter device. In Figure 1, 1 is a rectifier circuit consisting of rectifier diodes Da to Df, and 2 is a DC reactor _L1 and a smoothing capacitor.
This smoothing circuit 2 and the rectifier circuit ₁ constitute a DC power supply 3. 4
is an inverter main circuit, to which DC voltage is supplied from the DC power supply 3. The inverter main circuit 4 includes transistors Tr ₁ to Tr 6 as switching elements in each arm of a three-phase bridge circuit, flywheel diodes D ₁ to _{D 6 ,} and resistors to protect the transistors from surges generated during load switching.
It consists of a series circuit of R ₁ to R ₆ and capacitors C ₁ to C ₆ , and includes transistors Tr ₁ and Tr ₄ , Tr ₂ and Tr ₅ ,
The interconnection points of Tr ₃ and Tr ₆ are designated as U, V, and W phase output terminals T _U , _TV , and _TW . Transistor Tr ₁
The control circuit 5 applies a control signal set so that the inverter output voltage waveform is constant with respect to the output frequency to the bases B ₁ to B ₆ of Tr ₆ , and outputs by performing sine wave approximation PWM switching. A three-phase alternating current voltage is formed at terminals T _U , _TV and T _W . Furthermore, the frequency of the AC output is changed by controlling the switching period of each transistor Tr ₁ to Tr ₆ . Further, an overcurrent detection resistor _Rs1 is connected to the line _LN . 6 detects the overcurrent based on the voltage across the overcurrent detection resistor R _s1 , and depending on the detection, the transistor
This is a protection circuit that stops the operation of Tr ₁ to Tr ₆ .
Here, for ease of understanding, regarding the current waveform flowing through a single-phase inverter, Fig. 2 shows some details of Fig. 1, and Figs. 3 and 4 show waveforms of each part.
This will be explained with reference to figures. Transistor Tr ₂ and
With Tr ₄ off and transistor Tr ₅ on,
When the control signal Sc shown in FIG. 3 is inputted to _the base B ₁ of _the transistor Tr ₁ , the current Idt shown in FIG.
This current Idt acts as a load on the transistor Tr ₁ to generate a current Ir ₁ having a waveform shown in b in FIG. 3, and a current I _WM having a waveform shown in c in FIG. 3 in the motor winding _WM . Therefore, a line current I _LN having a waveform shown in e in FIG. 3 is generated in the line L _N. In addition, in Figure 3b,
Ia is the current I _WM generated in the motor winding _WM , Ib is dv/dt
The current Idt is generated by . Further, the line current I _LN is the sum of the current Tr ₁ flowing through the transistor Tr ₁ and the recovery current of the flywheel diode D ₄ . The input side of photocoupler PC 1 is connected to both ends of overcurrent detection resistor R _s1 connected to line L _N via resistor R ₁₁ , and the output side of photocoupler _{PC 1 is} connected to ground via resistor R ₁₂ . Further, a flip-flop 7 is connected to the output side of the photocoupler PC ₁ and constitutes a part of the protection circuit 6. The current e in Figure 3 is applied to the overcurrent detection resistor R _s1 .
When I _LN flows, a voltage with the same waveform as e in Figure 3 is generated across the overcurrent detection resistor R _s1 , and this voltage activates the photocoupler PC ₁ , and the input side of the photocoupler PC ₁ is activated. If the filter capacitor C ₁₁ shown in FIG. 2 is not present, a voltage V _D having a waveform shown in FIG. 3 f is generated across the output resistor R ₁₂ of the photocoupler PC ₁ . At this time, the current Idt shown in FIG. 3d can be considered as a rated current and will not directly destroy the transistor.

In the configuration shown in Figure 2, a filter capacitor _C11 is inserted on the input side of the photocoupler _PC1 to remove the above current Idt, and the output voltage of the photocoupler _{PC1 is}
The peak value of _VD is suppressed. Photocoupler without and with filter capacitor C ₁₁
The waveforms of the output voltage V _D of PC ₁ are shown in FIGS. 4a and 4b, respectively. By inserting the filter capacitor C ₁₁ , the peak value of the output voltage V _D will decrease from V _D2 to V′ _D2 , but the steady-state value of the output voltage V _D will increase from V _D1 to V′ _D1 . Therefore, a transmission time delay of t ₁ occurs compared to the case where the filter capacitor C ₁₁ is not provided. For this reason, if you insert a filter capacitor C ₁₁ ,
There is a problem that the detection operation of the protection circuit 6 is delayed, but in the absence of the filter capacitor _C11 , it is difficult to distinguish between the current Idt, which has a high peak value caused by dv/dt in response to load fluctuations, and the short-circuit current. This may cause the protection circuit 6 to malfunction, and the transistors Tr ₁ to Tr ₆ cannot be reliably protected from destruction.

[Purpose of invention]

The present invention was developed in view of the above circumstances, and its purpose is to detect the current flowing through the switching element, and when an overcurrent flows, to quickly and quickly cut off the control signal to the switching element using a protection circuit. It is an object of the present invention to provide an inverter device that can prevent the protection circuit from malfunctioning, thereby reliably protecting the switching elements from destruction.

[Summary of the idea]

The present invention is configured to switch the overcurrent response level of the protection circuit only when the switching element is turned on.

[Example of idea]

An embodiment of the present invention will be described below with reference to FIGS. 3, 5, and 6.

In FIG. 5, 8 is a single-phase inverter main circuit that is supplied with power from a DC power source 9, which consists of four transistors Tr ₇ to Tr ₁₀ as bridge-connected switching elements and a flywheel diode.
It consists of a series circuit of D ₇ to D ₁₀ , resistors R ₇ to R ₁₀ , and capacitors C ₇ to C ₁₀ , and a transistor
The interconnection points of Tr ₇ and Tr ₉ , Tr ₈ and Tr ₁₀ are output terminals.
T ₁ and T ₂ , and a motor winding _WM is connected between the output terminals T ₁ and T ₂ . A control signal set so that the inverter output voltage waveform is constant with respect to the output frequency is applied to the transistors Tr ₇ to Tr ₁₀ from a control circuit (not shown) to perform sine wave approximation PWM switching.
A single-phase AC voltage is formed at T ₁ and T ₂ . In addition, a line L _N connecting the DC power supply 9 and the inverter main circuit 8
An overcurrent detection resistor _Rs2 , which is an overcurrent detection element, is interposed in series. The input side of photocoupler PC ₂ is connected to both ends of this overcurrent detection resistor R _s2 via a resistor R ₁₃ for voltage level adjustment, and a resistor R ₁₄ is connected between the output side of this photocoupler PC ₂ and the ground.
and R ₁₅ series circuits are connected. Therefore,
Photocoupler PC ₂ produces output voltages Va and Vb (Va>Vb) at points a and b in FIG. 5, respectively. Now,
In the following, a protection circuit 10 including a photocoupler PC ₂ and the like will be described. That is, 11 and 1
2 is an AND circuit, one input terminal of the AND circuit 11 is connected to point a, and the other input terminal is connected to the output terminal Q of a monostable multivibrator 13 which is a switching circuit; The input terminal of the monostable multivibrator 13 is connected to the point b, and the other input terminal is connected to the output terminal of the monostable multivibrator 13. The trigger input terminal T of the monostable multivibrator 13 has transistors Tr ₇ to Tr _10.
A control signal S ₀ (see FIG. 6a) given to the controller is inputted. AND circuit 11, 12
The outputs of the flip-flops 14 and 15 are respectively applied to flip-flops 14 and 15, and the outputs from the respective output terminals of these flip-flops 14 and 15 are applied to both input terminals of an AND circuit 16, respectively. The flip-flops 14 and 15 are initialized when the switch 17 is turned on. Also, AND circuit 1
When the output of Tr 6 is the signal “1”, the transistor Tr ₇
Control signals for each base B ₇ to B ₁₀ of Tr ₁₀ to Tr 10
The configuration is such that the supply of the control signal S ₀ is allowed, and when the output of the AND circuit 16 is a signal "0", the supply of the control signal S ₀ is cut off.

Next, the operation of this embodiment having the above configuration will be explained with reference to FIG. 6 as well. At time t ₂ in FIG. 6, the transistor Tr ₈ and Tr ₉ are off, and the transistor Tr ₁₀ is on.
When the control signal S ₀ shown in FIG. 6a is input to the base B ₇ of Tr ₇ to turn on the transistor Tr ₇ , a current I _LN flows through the line L _N , and the corresponding overcurrent detection resistor R _s2 The photocoupler PC ₂ is driven by the voltage across it, and as a result, the photocoupler PC ₂ moves to points a and b.
The voltages Va and Vb (see FIG. 6b) are output at the points, respectively. At this time, the first shear cutoff setting current value L _OFF1
and second damping setting current value I _OFF2 (I _OFF1 > I _OFF2 )
The shear breakout output voltages V _OFF1 and V _OFF2 (see FIG. 6b) of the photocoupler PC ₂ corresponding to the respective values are determined as V _OFF1 /V _OFF2 =R ₁₄ +R ₁₅ /R ₁₅ . On the other hand, at time t ₂ the control signal S ₀
When is output, the monostable multivibrator 13 is triggered, and the monostable multivibrator 13 starts a timer operation for a certain period of time (determined by the time constant τ), and during the timer operation period, the sixth As shown in the figure, the output from the output terminal Q is inverted from the signal "1" to the signal "0", and the output from the output terminal is also inverted from the signal "0" to the signal "1". The time constant τ is set to be slightly larger than the time width of the current Idt (see FIG. 3c) that would occur if there was no filter capacitor on the input side of the photocoupler _PC2 . When the control signal S ₀ is applied to the transistor Tr ₇ to turn it on, the signal "1" outputted from the output terminal of the monostable multivibrator 13 in synchronization with this causes a signal to be sent to the AND circuit 12. input is enabled for a time τ, and after that time τ the monostable multivibrator 1
The input of the signal to the AND circuit 11 is enabled by the signal "1" outputted from the output terminal Q of No. 3. Therefore, during the period when the output voltage Va is rising significantly due to the current Idt shown in _{FIG .} Made, Vb＞
When V _OFF2 (i.e. Va>V _OFF1 ),
The output from the output terminal of the flip-flop 15 is inverted to "0" by the AND circuit 12, and thereby the output of the AND circuit 16 is inverted to "0", and the control signal S ₀ to the base B ₇ of the transistor Tr ₇ is generated.
supply is suddenly cut off. Furthermore, when the current I _LN flowing through the line L _N has reached a steady value, the current I _LN is detected using the output voltage Va, and Va>V _OFF2.
When this occurs, the output of the flip-flop 14 is inverted to "0" by the AND circuit 11, and the supply of the control signal _S0 is immediately cut off. The above operation is performed by transistors Tr8 to _Tr8 .
This is performed every time the control signal S ₀ is supplied to the base of Tr ₁₀ .

According to the embodiment described above, each time the control signal S ₀ is supplied to the bases B ₇ to B ₁₀ of the transistors Tr ₇ to Tr ₁₀ , the protection circuit 10 operates for a certain period τ corresponding to the timer time of the monostable multivibrator 13. Since it was configured to increase the overcurrent response level of
There is no risk that the protection circuit 10 will malfunction due to the line current I _LN with a high peak value caused by dv/dt, and there is no need for a filter capacitor on the input side of the photocoupler PC ₂ .
There is no delay in the detection operation as in the conventional case.

Note that the AND circuits 11 and 12 in the above embodiment
An analog switch or the like may be provided instead, or the invention may be applied not only to a single-phase inverter but also to a multi-phase inverter. Furthermore, although a resistor was explained as an overcurrent detection element, magnetoelectric conversion elements such as Hall elements,
Needless to say, the present invention can also be applied to a device using a current transformer or the like.

[Effect of idea]

According to the present invention, as described above, it is possible to detect the current flowing through the switching element, and when an overcurrent flows, the control signal to the switching element can be cut off extremely quickly by the protection circuit. It is therefore possible to provide an inverter device that can prevent malfunctions of the protection circuit and thereby reliably protect switching elements from destruction.

[Brief explanation of drawings]

Figures 1 to 4 are for explaining the conventional device. Figure 1 is a wiring diagram showing the overall configuration of the inverter device, Figure 2 is a wiring diagram showing the single-phase inverter in Figure 1, 3 and 4 are diagrams showing waveforms at various parts in FIG. 2. Further, FIG. 5 is an overall wiring diagram showing one embodiment of the present invention, and FIG. 6 is a diagram showing waveforms of various parts in FIG. In the figure, 8 is the inverter main circuit, Tr ₇ to Tr ₁₀ are transistors (switching elements), 9 is a DC power supply, R _s2 is an overcurrent detection resistor (overcurrent detection element), 1
0 is a protection circuit, and 13 is a monostable multivibrator (switching circuit).

Claims (1)

[Scope of utility model registration request] An inverter main circuit consisting of a switching element that is turned on and off by a control signal and connected in series with an overcurrent detection element between both terminals of a DC power supply, and an inverter main circuit that receives a signal from the overcurrent detection element and operates the switching element. and a protection circuit for stopping the switching element, each time the control signal is input to the switching element, a timer operation is performed for a certain period of time, and during the timer operation period, the overcurrent response level of the protection circuit is controlled. An inverter device characterized by being provided with a switching circuit that switches to increase the voltage.