JPH04506895A - Circuits and components with switch protection - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] W Circuits and components with switch protection Mamehiki Ohmi The present invention relates to circuits and components with switch protection, and more particularly, to circuits and components with switch protection. Although not specified, it has a switching element that is switched under load conditions. It relates to a mechanism for protecting this type of circuit.

l rice thorns food r ri Semiconductor devices used in power circuits are considered to form two specific groups. It will be done. The first group consists of thyristors (SCR) or triacs (trade name). devices, which are switched on via control electrodes. but cannot be switched to the off state by the same electrode. Rather, self- natural or forced diversion. The second group is gate turn-off. futhyristors (GTOs), power transistors and insulated gate field effect transistors It consists of devices such as transistors (ICFETs), and these devices can be switched to both on and off states.

The invention focuses on circuits that include a second group of semiconductor power devices.

This type of semiconductor power device is used in rectifier, chopper and inverter circuits. is known to be useful for its switching ability to supply electrical loads. Used for waveform synthesis. In the design of such circuits, consideration must be given to There are not many performance design criteria.

In the off state, the device operates at a voltage above some limited, primarily It has a withstand voltage characteristic that causes electron avalanche breakdown. Electron avalanche breakdown is a small number of Occurs when carriers remove additional minority carriers, which causes the device to Switched to on state.

In addition to the rate of change in withstand voltage in the off state, the rate of voltage change over time dv/dt It is also important. In the off-state, if the voltage increases too quickly with respect to time, Automatically changes to the on state.

Another thing to consider is the critical rate of increase in on-state current d i / It is dt. If the rate of change of current is too high, junction heating or direct electronic snow Due to the breakdown, deleterious effects will occur on the semiconductor power device. this question The problem can be alleviated to some extent by using a series inductor.

Known pulse width modulation (PWM) systems have a frequency different from that of the input. It is designed to synthesize output waveforms of one or more phases. current Improvements in semiconductor power devices in terms of ratings and dv/d ranges are PWM It was possible to increase the switching frequency. However, the switching frequency is high As a result, the problem of no-acceleration wave number interference (CRFI) arises.

The on-state of this type of device is There are also issues related to the frequency of switching between the It is clear that there is a need to absorb the amount of energy in the snapper circuit. Ru.

If the applied load is inductive, the current flow lags behind the applied voltage and is free-holed. Even with methods such as providing yield diodes, the amount of energy is higher than that of semiconductor power devices. It will be consumed by the chair. This energy is in the form of heat, so cooling It is necessary to consider the circuit design in this respect. Semiconductor devices are well protected If not, undesirable joint heating may occur which may eventually lead to failure.

One strategy to alleviate such problems is to use high frequency resonant sources (i.e. (in power), assists in the switching of semiconductor power devices, and controls dv/dt. The switching between the on and off states is fixed. The disadvantage is that it is performed only at commutation points. This point is especially important at any given time. This is not advantageous for PWM circuits where device switching is desired. In particular, variable frequency What if several outputs are combined? That's right. As a result, the benefits of high natural frequencies are weakened. In addition, it also introduces undesirable modulation noise. results in a tinging sensitivity limit.

Lord Mamehiki Wataru Blood It is an object of the invention that at any desired time, e.g. Even if the The objective is to cause state changes to be made in order to switch devices in a manner that is easy to use.

According to one aspect of the invention, the switching device has a fixed frequency and One or more frequencies different from the input depending on the switching device. a control circuit adapted to produce an output of greater than or equal to an electrical load connected to the output or each output; one output or each output of the control circuit; The switching device is connected to the power supply and cooperates with the load to change states. and a resonant circuit that can put the control circuit in an advantageous state for the operation of the vise. To provide an electrical circuit with switch protection consisting of:

Most preferably, the controlled circuit is capable of operating using a pulse width modulation method. be.

According to another aspect of the invention, the load connected to one or more outputs of the A resonant circuit is provided which is used in combination with a control circuit having a control circuit. This resonant circuit is one or The resonant circuit is applied to be connected to each output, and this resonant circuit is connected to at least one A controllable semiconductor device connected in anti-parallel in series with an inductive element. a capacitive element connected between the output and the reference voltage; formed by at least one of the inductive elements, at least one of the inductive elements and a load. series resonant circuit, which allows the control circuit to switch between the on and off states. placed in a favorable position to switch.

According to still another aspect of the invention, the switch has a fixed frequency input and A method for protecting a control circuit containing a control device is provided. This control circuit is one or more frequencies supplied to the load and different from the input of the switching device. It is applied to generate an output higher than that, and the protection method for this control circuit is the process of providing a resonant circuit connected to one or each output; resonant in cooperation with the load; A control circuit for actuation of a switching device when the circuit operates and changes state. It consists of a step of bringing the condition into an advantageous state.

Brief description of the drawing Figure 1 shows one form of ideal pulse width modulation to generate waveforms in contrast to the prior art. It is a diagram.

FIG. 2 is a diagram showing a single-phase inverter arranged in one particular state, and is based on the present invention. It was constructed using the following methods.

FIG. 3 is a diagram showing another state of the single-phase inverter of FIG. 2.

Figure 4 shows the current and voltage waves during operation of one route of the bridge circuit shown in Figure 2. It is a detailed view of the shape.

FIG. 5 is a diagram showing another embodiment in which the present invention is applied to a three-phase circuit.

It's childish Pulse Width Variable IM (PWM) Control for Applying a Preferred Embodiment to an Inductive Load Although described with respect to an inverter, the invention need not be limited to this type of application; Rectifiers, choppers, cycloconverters, switched power supplies and other similar It goes without saying that the present invention can be similarly applied to circuits for applied devices.

Figure 1 shows a simple example of pulse width modulation technology, output waveform ■0 is the positive half cycle. a number of voltage pulses V with a potential of Vs+ and, in the negative half cycle, a potential of Vs-; Two half cycles are synthesized by n. In other words, the synthesized The pulse is approximated by the output waveform ■0 sine wave. The number and width of the various pulses Vn are It can be changed depending on the desired frequency of the output waveform VO. Maximum possible output frequency The range of possibilities depends on how quickly the switching devices that synthesize the waveforms are turned on or off. Determined by whether you can do it. Pulse width modulation techniques are well known.

Referring to FIG. 2, the single-phase full-wave PWM control inverter bridge circuit 10 has an inductive load. 50 is shown. A resonant circuit 30 is connected to both ends of the output of the bridge circuit 10. The outputs are represented as terminals VA and VB.

This circuit configuration can switch from on to off at any point in the output voltage waveform. can be switched from an off state to an on state.

The voltage sources of the bridge circuit 10 are two DC supply voltages S+ and Vs-. straight There are also devices that supply voltage with a frequency other than current, such as a cycloconverter. Can be used similarly.

The bridge circuit 10 is in the form of a piebora junk silane transistor (BJT) 12. It consists of two branches consisting of a pair of switching devices of the same type.

The first branch is by transistors QIA and Q2A, and the second branch is by transistors QIA and Q2A. Each transistor is configured by transistors QIB and Q2B. Each transistor The terminal 12 is equipped with a freewheeling diode 14, and DIA, D2A, t)I The above transistors B and D2B are shown as branches of the bridge circuit. , other semiconductor devices that can be switched off via a control voltage, e.g. It can also be used equivalently in place of GTO or IGFET.

The central connection point 16 of each branch is connected to a resistor R3A and an inductor L connected in parallel. It is connected to each snapper circuit consisting of SA, R3B and LSB. resistance Output terminals VA and VB are formed after the parallel connection circuit of the inductor and the inductor. There is. At the output terminal, a capacitor 20 (C3I -C34) and further connected to either the supply voltage Vs+ or Vs-. has been done.

A state in which an inductive load 50 is connected between output terminals VA and VB is shown. between the output terminals Further, a part of the resonant circuit 30 is also connected. Resonant circuits are symmetrical and connected in series. It consists of an anti-parallel connection circuit of two pairs of transistors/diodes, which Connected in series with inductor LC. Each transistor 22 is QCI.

QC2, and the diode 24 is designated DCl, DC2.

For convenience of explanation, the snapper circuit 18 will be ignored here. Snatsupa circuit has a small value and does not significantly affect the operation of the bridge circuit 10.

The example in FIG. 2 shows the conduction states of transistors QIA and Q2B. This state is shown in Figure 1. Any particular pulse of the pulse Vn in the positive half cycle of the output voltage waveform VO so that It also corresponds to In this state, the load current IL is equal to the supply voltage S as shown in the figure. + through an inductive load 50 back to the input supply voltage Vs-. Between output terminals VA and VB The voltage appearing at is due to the voltage drop across resistors R3A and R38 as well as the transistor Considering the voltage drop between the collector emitter of QIA and Q2B, it is close to 2xVs. It becomes.

The control electronics for the base terminals of the individual transistors 12.22 are not shown. However, each transistor is all processed by appropriate circuitry under the control of a digital processing unit. Driven.

The negative half cycle of vO shown in FIG. 1 is the output terminal VA.

Transistors Q2A and QIB are connected so that the polarity of the voltage appearing between VB is reversed. This can be achieved by switching.

In the illustrated embodiment, transistors QIA, Q2B are conductive and capacitor C32 , SC3 begins to be charged with a voltage of about 2xVs.

First, a transistor is used for the purpose of creating an off state in the waveform generated by pulse width modulation Consider the case where QIA and Q2B are switched off.

This condition causes the transistor to start blocking its base terminal. This is achieved by operating the gate through the Is the load 50 inactive? , the current IL flowing through the transistor is delayed and the forward biased die It is necessary to recognize the path passing through DIA and D2A.

The voltage of output terminals VA and VB is diode DIB.

It will change at a control rate of IL/(2xC3) until D2A becomes conductive. Out The voltage between power terminals VA and VB is its zero reference value, and the load current IL is The current continues to flow for a limited time until the charged energy of the capacitors C32 and C33 disappears.

It is usual to provide a further on-state long before the load current IL has substantially decreased. It is. That is, it is preferable to maintain the load current IL. On state and off state The switching between the two states is clearly shown in FIG.

Now, considering the switch-on process, again the transistors QIA, A, Q It is appropriate to take a look at 2B. Capacitors C32 and C33 are charged The charge is not completely dissipated following the on-state. If the resonant circuit 30 is provided If not, this charge would cause a large inrush current during switch-on to the transformer. generated by the transistor, which can cause considerable damage to the transistor. .

The switch-on operation will be explained in more detail with reference to FIG. 31 and FIG. Transistor QC2 is activated before transistors QIA, Q2B are switched on. As a result, the inductance LC forms a parallel circuit with the load 50. Daio DC2 is forward biased, and capacitors C32 and C33 are now charged. A second path is created in which the absorbed energy does not pass through the load 50. Transistor QC2 Following switch-on, until the current flowing through LC is equal to the load current IL (Vs” It increases linearly at a rate of 10Vs-)/LS.

Figure 4 shows the nearly continuous load current IL, which is connected to the inductor LC and the output terminals VA, VB. Between A and B in Figure 4, the magnitude is equal to the load current IL. represents an increase in the current flowing through the inductor IC up to the point where it becomes , the current flowing through the inductor LC and the capacitors SC2, S0 Resonance for a period of 1/(4χπ×F〒CxC3)) due to the resonant circuit formed between 3 It continues to increase along trajectory B-C. The load voltage changes from half wave to sine waveform between B and C. continues to increase until

Point C is when transistors QIA and Q2B are switched on, and VA and Vs+ There is no voltage difference between VB and Vs~ in the drawing, therefore, transistor Q IA and Q2B are not overly stressed.

The current flowing through the inductor LC is linear between CD at the ratio of (Vs“-Vs-)/LC. decreases and reaches zero. At zero point, transistor QC2 is turned off .

The maximum current flowing through the inductor LC is (Vs”-Vs-) x (CS/L C Atonal. Die t-1'DcI, DC2 is each transistor connected in series with this. Block QC1 and QC2 in opposite directions.

In the illustrated embodiment, transistor QC2 switches transistors QIA and Q2B. It is used to switch on. On the contrary, transistor QCI is a transistor It is used to switch on the stars Q2A and QIB. Transistor QCI , QC2 is shown as a pibora junction transistor, but for example GTO, I(:, easily integrated into other types of semiconductor devices such as FETs or SCRs) It can be replaced. It has no specific requirement to be turned off by the control electrode It's for a reason. A single triac is used in place of both transistors QC1 and QC2 You can also

Transistor 22 and diode 24 of resonant circuit 30 have their ratings in order of load. Must match directional current rating, but benefits from low stress switching and High switching frequency in conjunction with PWM methods due to no need for commutation clamp rails When operated at wave numbers, the extra cost becomes well worth it.

Snatsupa circuit 18. Let us return to the R3A/LSA and R3B/LSB elements. Ru. These elements take into account the loss in the resonant circuit 30, and the bridge transistor This prevents instantaneous transient currents when the star 12 is switched on. That is, each branch There is always a small residual voltage across the complementary capacitor of the circuit (e.g. QIA, C32). However, this causes an inrush current when the state of the transistor 12 changes. This inrush current The current can be adjusted by the parallel connection circuit of the resistor and inductance of the snapper circuit 18. can disappear.

Although not shown, the bridge circuit 10 is equipped with an interlock, and the snapper circuit A bridge occurs unless the forward voltage determined by 18 falls below the maximum safe level. transistors QIA/Q2B and Q2A/QIB are not switched on. It is most preferable to ensure that

In the above embodiment, the switch operation of transistors QIA, Q2A and QC2 is The operation corresponds to a positive half cycle of the composite output waveform Vo. Completion required during negative half cycle An elementary action will occur.

The illustrated bridge circuit 10 is not self-starting, but rather has a starting circuit and a capacitor. It is necessary to charge the C51-4. This starting circuit consists of a pair of relatively low current FEs. It can be constructed with a T or BJT and a series resistor.

As mentioned above, the transistor 22, the diode 24 and the input in the resonant circuit 10 The inductor LC has a double structure as shown in the figure, and the internal An intermediate point is provided to make this intermediate point the zero voltage reference level. This allows the transition The voltage rating of the star can be halved.

If the bridge circuit 10 is a half-wave bridge, it includes transistors QIB and Q2B. No branch is required, so the output terminal VB can simply be connected to the zero voltage reference level. Bye.

Furthermore, as another example, a three-phase inverter 60 shown in FIG. It is shown in a block diagram, and an inductive load 55 is also shown in a block diagram. A common example of the above embodiments. The swing circuit 30 is provided as three equivalent circuits 70, each with an output phase φA- Connected to φC.

Transistors QC5-10 are configured symmetrically and have a pair of danks between the outputs of each phase. They are connected by diode 72. Each pair has a common connection point to the neutral point N. There is. The neutral point N is also connected to each third output phase via an inductor LCI-3. It is. As explained in the single-phase example, the functions of capacitors C3l-CS4 are as follows: This is accomplished by six interphase capacitors provided within the inverter 60.

This embodiment changes one simultaneous state from the current state to the diagonally opposite state. other The combination of all states will reverse the bridge transistor in the three-phase inverter 60. It is necessary to switch off from the

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Claims (13)

[Claims] (1) Has a fixed frequency input and includes a switching device. , the input and one or more outputs at different frequencies by a switching device. a control circuit adapted to generate a force; one or each output of said control circuit; an electrical load connected to the output; connected to one output or each output of the control circuit and operated in cooperation with the load; and upon a change of state, the control circuit for actuation of the switching device. Electrical with switch protection consisting of a resonant circuit capable of being brought into favorable conditions; circuit. (2) The control circuit is operable by a pulse width modulation (PWM) method. The circuit according to item 1. (3) Favorable conditions control the rate of rise of off-state voltage and limit the rate of rise of on-state current. control and further minimize the static off-state voltage for switching devices. The switching circuit according to item 1. (4) the resonant circuit is symmetrical and forms one or each output; A circuit according to claim 1, which is separately controllable for positive and negative half-cycle waveforms. Road. (5) The resonant circuit cooperates with an inductive element and a capacitive element connected in series. 5. The circuit of claim 4, comprising semiconductor devices connected in parallel. (6) The resonant circuit is a blocking diode connected in series with each semiconductor device. 6. The circuit of claim 5, further comprising a code. (7) The circuit according to claim 2, wherein the pulse width modulation control circuit is a full wave inverter. (8) in conjunction with a control circuit having a load connected to one or more of its outputs; a resonant circuit connected to one or each output; and the resonant circuit is connected in series with at least one inductive element. a combinational circuit of controllable semiconductor devices connected in anti-parallel; a capacitive element connected between the output and the reference voltage; at least one of the capacitive elements; and a series resonant circuit formed by at least one of the inductive elements and the load; and thereby enable the control circuit to switch between the on state and the off state. Characterized by being placed in an advantageous situation. (9) Claims for use in conjunction with control circuits that enable the use of pulse width modulation (PWM) methods. Resonant circuit according to item 8. (10) Advantageous conditions for multiple semiconductor switching devices in a PWM control circuit Controls the rate of increase in off-state voltage at either end, and controls the rate of increase in on-state current. control, and also a static off state across either end of the semiconductor switching device. 10. The switching circuit of claim 9, which minimizes voltage. (11) A control having a fixed frequency input and including a switching device. A method for protecting a control circuit, the control circuit being supplied to a load and to produce one or more outputs at a different frequency than the input of the switching device. This control circuit protection method is applied to providing a resonant circuit connected to one or each output; A switching device operating said resonant circuit in cooperation with a load upon a change of state. placing the control circuit in a favorable state for operation of; It is characterized by consisting of. (12) The control circuit may be operable by a pulse width modulation (PWM) method. The circuit according to claim 11. (13) The operating step operates the semiconductor to connect the at least one capacitive element to the at least one capacitive element. Is it a process of forming a series resonant circuit composed of one inductive element and a load? consists of an increase in off-state voltage due to switching devices in the PWM control circuit. claim that the rate of rise of the rate and on-state current is controlled and the static off-state voltage is minimized. The method according to item 12.