DE3639495A1 - Circuitry for the switches of pulse-controlled invertors and DC semiconductor controllers for multi-quadrant operation - Google Patents

Abstract

For a device for the deliberate discharge of the circuitry capacitors for the electronic switches of a pulse-controlled invertor and DC semiconductor controller for multi-quadrant operation, in the case of which the series circuit formed by a first diode having the same forward direction as the switch and a discharge capacitor is connected in parallel with each switch, in the case of which a second diode having the opposite forward direction is connected in parallel with each switch, a branch pair being connected between the positive and negative DC terminals and the junction point of the two branches of a branch pair being connected to the output terminal of the pulse-controlled invertor and DC semiconductor controller for multi-quadrant operation (phases R or Y or B for invertors which produce three phase), the object exists of preventing undesirable discharging of the switching-off discharge capacitors, in order thus to reduce the power loss of the switching-off discharge circuitry. This is achieved in that the series circuit formed by a resistor (R1, R2) and an electronic auxiliary switch (T11, T12) having the same forward direction as the switches (T1, T2) is connected in parallel with each capacitor (C1, C2 in Figure 4), the auxiliary switch being switched on while the switch is conducting, and the disconnection taking place while the switch is conducting in the event of this being an auxiliary switch which can be disconnected, in such a manner that the discharge of the ... Original abstract incomplete. <IMAGE>

Description

The invention relates to a device according to the common Preamble of the independent claims 1 and 2.

. It shows the Figure 1 is a simplified schematic diagram of a three-phase, that is, one of three inverter branch pairs 10 existing transistor-inverter that _d to the input terminals 1 and 2 with a DC voltage + U, - U _d is supplied and at the outputs 3 , 4 and 5 emits a three-phase voltage U _R , U _S , U _T for supplying a load. The transistors of the pair of branches 10 are denoted by T 1 and T 2 , those of the other pair of branches by T 3 and T 4 as well as T 5 and T 6 . The return diodes lying parallel to the transistors are marked with D 1 . . . D 6 designated. The direction of power flow can also be reversed as shown.

The amplitude of the fundamental oscillation of the three-phase voltage output can be adjusted by switching the semiconductor switches (transistors T 1 to T 6 ) of the inverter several times per period. This is the control principle of so-called "pulse inverters" or in general of "pulse inverters".

To achieve the lowest possible harmonics, but one of the  The ratio becomes the ideal sinusoidal shape of the approximate output current the on and off duration of the semiconductor switch over a period varies according to the output voltage, cf. for example the PhD thesis by T.M. Undeland "Electrical power conversion with transistors ", University of Trondheim, October 1977.

Pulse inverters are preferably used to feed three-phase motors used.

2, it shows the Fig., The principle of pulse forming for controlling a pulse-controlled inverter. The illustration 2a shows three control voltages U _RC , U _SC and U _TC shifted by 120 ° el and a triangular scanning auxiliary voltage U _t . The amplitudes of the control voltages and the auxiliary voltage are compared with one another; depending on the result, whether the control voltage or the auxiliary voltage is greater, the control signals for the conduction of the transistors of the inverter are formed. These control signals are reproduced for the transistors T 1 and T 2 in the illustration 2b, where they are denoted by S 1 and S 2 .

The times t ₁,. . . t ₄ are certain switching states of the inverter branch pair with the transistors T 1 and T 2 , which are explained with reference to FIGS . 6 and 7.

The representations 2c and 2d show the output voltages of the inverter at the terminals 3 and 4 with respect to a fictitious center of the input DC voltage + U _d , - U _d . Figure 2e shows the linked output voltage U _{RS of} the inverter between terminals 3 and 4 . The course of the fundamental oscillation of the output voltage for the modulation state of the inverter shown is shown in dashed lines.

There is shown in FIG. 3, the circuit of the inverter branch pair 10 with the representation of the usual Beschaltungs- (relief) network 20 and 30. 20 represents the switch-off relief (RCD circuit) for limiting the voltage steepness d u / d t after switching off the semiconductor switch with the aid of the capacitor C 1 , which is connected in series with the diode D 11 in parallel with the switch T 1 . The reference symbols T 1 , T 2, etc. correspond to those in FIG. 1. A resistor R 1 is connected in parallel with the diode D 11 . The diode D 11 has the same forward direction as the switch T 1 . Correspondingly, the RCD circuit for the switch T 2 consists of the capacitor C 2 in series with the diode D 21 and the resistor R 2 in parallel with the diode 21 . The series connection is parallel to the switch T 2 .

At 30 is a switch-on relief by means of a choke L 1 to limit the current steepness when switching on the semiconductor switch T 1 . This choke lies between the connection of the output of the switch T 1 and the reverse current diode and the feed line to the output terminal 3 . A choke L 2 is correspondingly provided for the transistor T 2 .

S 1 , S 2 indicate the control signals for the semiconductor switches already mentioned for FIG. 2.

Circuits (relief networks) have the task of stress of power semiconductor switches (HL switches), for example To reduce transistors during switching operations.

There are circuits that serve to relieve the switch-on and there are which serve to relieve the switch-off.

The current rise rate d i / d t is limited by means of an inductor for switch-on relief and the voltage rise speed d u / d t at the HL switch is limited by a capacitance for switch-off relief. In both cases, a reduction in the power loss occurring during switching is achieved by reducing either the current or the voltage load during the switching process of the HL switch. In terms of circuitry, the switch-on relief is carried out with a choke that forms a series circuit with the HL switch. The switch-off is relieved by connecting a capacitor in parallel to the HL switch. When the HL switch is switched off, this capacitor forms a shunt to the HL switch, via which the load current can flow for a short time until the capacitor is fully charged.

The capacitor is charged when the driving load voltage reaches is. Then the load current changes to a return diode, such as the Example in every inverter branch with voltage intermediate circuit is.

To ensure a short-circuit-like discharge when the HL switch is switched on again of the switch-off relief capacitor via the HL switch To avoid this, it is common to limit the discharge current with a resistor. However, this measure also requires a low impedance Bridging the discharge resistance to the bypass effect when switching off not to hinder. This is usually done with a diode reached, which is arranged parallel to the discharge resistor. Such one complete switch-off-relief network is as RCD circuit widespread, compare for example the references:

• 1. "Handbook II - Transistors in Power Electronics", Thomson- Components, pages 55 to 59,
• 2. "IEEE Transactions on Industry Applications" Vol. IA-16 (1980) No. 4, Pages 513 to 515, essay William McMurray "Selection of Snubbers and Clamps to Optimize the Design of Transistor Switching Converters ".

The invention has for its object a device of the beginning specified type that indicate an undesired discharge of the switch-off Avoids relief capacitors, thereby reducing the power loss to reduce the switch-off discharge circuit.

This is according to the invention by the characterizing part of patent claim 1 Features listed and alternatively by the in the characterizing part of the claim 2 listed features solved.

The device according to the invention can be used especially in converters with high switching frequency the semiconductor switch not only the Efficiency can be increased effectively, but also to the same extent  the heat dissipation problem of the wiring can be reduced. Furthermore the current load on the wiring elements is reduced accordingly.

Undesired discharge of the capacitor can occur in such circuits take place in which a flyback diode in parallel for conventionally (i.e. RCD wiring) high performance Switch is arranged. Performs in such switch arrangements Return diode current, the capacitor also discharges through the Discharge resistance as if the connected HL switch was switched on would. This leads to a loss of energy from

E _v = 1/2 C · U _c ²,

which one can lead to considerable losses at high switching frequencies.

Discharge of the capacitor is only required, however, if the HL switch is live to be completely discharged before the HL switch is switched off. Thus, the current, which was previously carried by the HL switch, can continue to flow after switching off via the capacitor until it is charged to the driving voltage, as a result of which the voltage rise rate d u / d t at the switching off or switched off HL switch to the value

is reduced. The one occurring during the shutdown period of the HL switch Power loss (switch-off power loss) is reduced accordingly, whereby the desired switch-off relief is achieved.

Operating states in which there are undesirable discharges of the capacitor, comes, for example occur in all pulse inverters with appropriate HL switch control on (inverter with voltage intermediate circuit) or generally in pulse converters, such as, for example can be used to supply multi-phase machines.

The device according to the invention is described below Embodiment explained in more detail with reference to the drawing.  

They show

Fig. 4 shows a device according to the invention,

Fig. 5 shows a further alternative device according to the invention,

FIG. 6a to 6d switching states in an inverter branch pair with conventional wiring and the

Fig. 7a to 7d switching states in an inverter branch pair, according to the device of the invention.

FIG. 4 shows a pair of branches of the inverter, as has already been described for FIG. 3. The same designations have been chosen for the same components.

In contrast to the device according to FIG. 3, however, the resistor R 1 lying parallel to the diode D 11 and the resistor R 2 lying to the diode D 21 are omitted.

Parallel to the relief capacitor C 1 is a series circuit consisting of a resistor R 11 and an electronic auxiliary switch T 11 .

In the other branch, in parallel with the relief capacitor C 1, there is a series circuit consisting of a resistor R 21 and an electronic auxiliary switch T 21 .

The auxiliary switches T 11 and T 21 have the same forward direction as the transistors T 1 and T 2, respectively.

The control signals for the auxiliary switches are labeled S 11 and S 21 , respectively.

Before going into detail about the switching function of the auxiliary switches, the alternative device according to the invention according to FIG. 5 will first be described.

In Fig. 5, which shows only one branch of the pair of branches, there is no parallel connection of a resistor (R 11 or R 21 ) in series with an auxiliary switch (T 11 or T 21 ) to the relief capacitor (C 1 or C 2 ) .

This is the series connection of a resistor  1 and an auxiliary switch  11 parallel to the diodeD 11 placed.

The series connection of resistor and auxiliary switch can also be compared the representation inFig. 4 andFig. 5 be reversed. Is practical but to prefer the representation shown in these figures, since then the desk(T 1 respectivelyT 2nd) and the auxiliary switch(T 11 respectively T 21st inFig. 4th  11 inFig. 5) are at the same potential.

The auxiliary switches are always switched on when the main switch T 1 or T 2 also carries current. They can be switched off within the operating time of the main switch when the discharge of the capacitor has reached the desired level or when it is completely discharged. A targeted discharge of the wiring capacitor is therefore possible. However, if a complete discharge is not required, for example if the load current is so small that the transistor can switch off within the so-called safe working areas (SOA or RSSOA) even without the capacitor being fully discharged, the auxiliary switch can also prematurely be switched off, whereby the power loss of the circuit is reduced even further.

In FIG. 4, the capacitor C is 1 (or R 2) unload 1 (or C 2) only via the auxiliary switch 11 T (or T 12) and the discharge resistor R.

In FIG. 5, the discharge takes place additionally on the HL-switch T 1 (discharge via T 1, T 11, R 1).

The line types of the auxiliary transistors shown in FIGS. 4 and 5 (T 11 and T 12 ), npn type in FIG. 4, pnp type in FIG. 5, are the emitter with regard to a common control reference potential of the respective main transistor T 1 or T 2 selected. Of course, other transistors or semiconductor switch types can also be used.

Auxiliary switch transistors only need a short time (for a few µs) lead relatively small discharge current of the circuit, which is usually accounts for only a fraction of the main current of the connected HL switch (1/10.. 1/20). Inexpensive transistors can therefore be smaller Power can be used.

Instead of transistors for the auxiliary switches, other semiconductor switches that can be switched off, such as GTO thyristors, can also be used. One can also use thyristors that cannot be switched off for the case. In the arrangement according to FIG. 4, however, only a complete discharge of the discharge capacitor is possible, since the discharge current cannot then be interrupted by the auxiliary switch.

In the arrangement of FIG. 5, the discharge current at the main switch T, however, can be interrupted 1 because through this also the discharge current flows.

In Figs. 6a to 6d, the switch states are in an inverter branch pair with conventional ON and OFF relief circuit, during a pulse period of t = t ₁ to t = t ₄ with the time reference in FIG. 2, Panel B occur. Here, the Fig. 6a 6b refers to the time t = t ₁, FIG. At the time t = t ₂, Fig. 6c at the time t = t ₃ and Fig. 6d on the time t = t ₄ . The load current is denoted by I _L and is drawn in with a large extension. The direction of the load current does not change during the time period shown.

With i _{c, E} and i _{c, A} , the discharge (index "E") or charge (index "A") currents of the relief capacitors are designated. They are shown in FIGS. 6c and 6d by solid, dashed lines.

FIGS. 7a to 7d of the invention show the switching conditions analogous to FIGS. 6a to 6d according to the institution.

So far, reference has been made to the pulse changing operation. Analogous relationships also apply to the semiconductor actuator for direct current in Multi-quadrant operation, see "Fundamentals of power electronics" by Prof. Dr.-Ing. K. Heumann, point 8.2.3 on pages 121 to 123, published in B.G. Teubner publishing house, Stuttgart 1975.

Claims (3)

1. Device for the targeted discharge of the wiring capacitors for the electronic switches of a pulse-controlled inverter and direct current semiconductor actuator for multi-quadrant operation, in which the series circuit of a first diode with the same forward direction as the switch and a relief capacitor is connected in parallel with each switch In parallel to each switch there is a second diode with the opposite forward direction, with a pair of branches between the positive and negative DC terminals and the connection point of the two branches of a pair with the output terminal of the pulse-controlled inverter and DC semiconductor actuator for multi-quadrant operation (strings R or S or T for Three-phase generating inverter) is connected, characterized in that in parallel with each capacitor (C 1 , C 2 in Fig. 4), the series connection of a resistor (R 1 , R 2 ) and an electronic auxiliary switch (T 11 , T 12 ) with the same Durchl aßrichtung as the switch (T 1 , T 2 ) lies, with the auxiliary switch being switched on while the switch is on, and in the event that it is a switchable auxiliary switch, the switch off while the switch is on so that the Discharge of the relief capacitor reaches a certain desired value. 2. Device for the targeted discharge of the wiring capacitors for the electronic switches of a pulse-controlled inverter and direct current semiconductor actuator for multi-quadrant operation, in which the series circuit of a first diode with the same forward direction as the switch and a relief capacitor lies parallel to each switch In parallel to each switch there is a second diode with the opposite forward direction, with a pair of branches between the positive and negative DC terminals and the connection point of the two branches of a pair with the output terminal of the pulse-controlled inverter and DC semiconductor actuator for multi-quadrant operation (strings R or S or T for Three-phase generating inverter), characterized in that in parallel with each first diode (D 11 in Fig. 4) the series connection of a resistor ( 1 in Fig. 5) and an electronic auxiliary switch ( 11 in Fig. 5) with the same passage Direction as the switch (T 1 ), with the auxiliary switch being turned on while the switch is on, and in the event that it is a switchable auxiliary switch, the shutdown takes place while the switch is on so that the discharge capacitor is discharged reached a certain desired value. 3. Device according to claims 1 or 2, characterized in that the two pairs of branches lead via a throttle (L 1 , L 2 ) to the connection point connected to the output terminal ( 3 ).