DE4233573A1 - Self-regulated current rectifier with quasi=resonant d.c. voltage intermediate circuit - contains resonant circuit choke between constant voltage source and power switches forming triggering resonant circuit with capacitor - Google Patents

Abstract

The current rectifier contains a resonant circuit choke in the line from a constant voltage source to rectifier power semiconductor switches. The choke forms a resonant circuit with a capacitor between the switch ports on the d.c. side to switch the switches when the intermediate circuit voltage approaches null. The choke is bridged by a series circuit contg. a clamp capacitor and a clamp power switch and antiparallel clamp diode. The resonant circuit capacitor (Cr) is connected in series with a resonant circuit switch (Ts) bridged by a diode (Ds) conducting in the direction of the constant dc voltage (Ud). USE/ADVANTAGE - Cost of power switches is reduced, high losses in the semiconducting clamp switches avoided and full utilisation of the constant dc voltage ensured.

Description

The invention relates to a self-commutated converter according to the Preamble of claim 1. This converter can both as itself guided rectifier as well as self-guided inverter will. Such a converter is known from the reference "R. W De Doncker, J. P. Lyons "An Auxiliary Quasi-Resonant DC Link Inverter" in: IEEE PESC Con. Proc. 1991, pp. 248 to 253 "known.

Self-commutated power converters are nowadays with power half that can be switched off conductor switches, such as transistors, GTOs or IGBTs. Current and voltage occur simultaneously with each switching operation Switch element that cause a high switching power loss (so-called hard switching).

Since the switching power dissipation increases proportionally with the switching frequency, is an increase in the switching frequency to improve the output behavior tens of the converter during hard switching only by improving the Switching properties of the power semiconductor switches used possible.

Another problem arises from those occurring at the moment of switching high current and voltage steepness, which leads to increased electromag net interference and insulation problems in the with the current connected machines.

One way to avoid the disadvantages listed above is Using a resonant converter circuit. Here, the  Power semiconductor switch always in the current or voltage zero crossing one vibrating, feeding voltage switched (so-called soft switching).

This allows a significant reduction in switching losses and thus achieve an increase in the switching frequency.

Disadvantages of the resonant converter circuit are the high voltage and Current load of the power semiconductor switch. One way the soft To achieve switching without the power semiconductor switch with very high Stressing voltage is the use of a resonant converter circuit with active voltage limitation (Active Clamped Resonant DC Link Inverter). Such a converter is known from the reference "D. Devan, C. Sibinski "Zero Switching Loss Inverters For High Power Application" in: IEEE-IAS Con. Rec. 1987, pp. 627 to 634 ". The known so-called Active Clamped Resonant DC Link Inverters limit the voltage load the power semiconductor switch by connecting a clamp capacitor via clamp power semiconductor switch to a freely selectable value of about 110% to 200% of one from a constant DC voltage source provided intermediate circuit voltage.

The converter specified at the beginning (a so-called auxiliary quasi Resonant DC Link Inverter) limits the voltage load to DC link voltage value.

However, the Active Clamped Resonant DC Link Inverter has the following Disadvantages on:

• - The clamp power semiconductor switch switches at the resonant circuit frequency, which is four to five times higher than the output switching frequency. That condemned gently a high switching power loss.
• - In addition to the load current in the DC link, the resonant circuit choke is loaded with a higher resonant circuit current.
• - The vibration in the DC link must be maintained continuously. This is difficult under all operating conditions, for example with over load or short circuit and means a continuously occurring power loss on the clamp power semiconductor switch.  
• - The usual pulse width modulated control method cannot be used there is a switching of the power semiconductor switches in the converter is not possible at all times (the zero crossing of the voltage in the DC link must be waited for).
• - The converter circuit needs an additional start to start help since the clamp capacitor before normal operation of the current richters must first be charged to the clamp voltage. He can not charged via the power semiconductor switches of the converter will.

The auxiliary quasi-resonant DC link inverter specified at the beginning avoids the disadvantages of the Active Clamp Resonant DC Link Inverter listed above. However, there are the following disadvantages:

• - High transmission losses in the clamp power semiconductor switch, since this is the entire output current must lead.
• - High additional expenditure on power semiconductor switches in order to find suitable ones Time to activate the resonant circuit.
• - Full utilization of the DC voltage in the DC link is due to the Circuit geometry not possible.

The invention is therefore based on the object of a converter Specify the type mentioned above, the additional effort in performance semiconductor switches for the targeted triggering of the resonant circuit process between The resonant circuit choke and the resonant circuit capacitor reduce the high throughput avoid losses in the clamp power semiconductor switch and a full off guaranteed use of constant DC voltage.

This object is achieved according to the invention by the ge in claim 1 identified features solved.

Advantageous embodiments of the self-commutated converter according to the Invention are characterized in the remaining claims.

Exemplary embodiments of the invention are described below with reference to the drawing are explained.  

Show it

Fig. 1 shows the basic structure of a converter according to the invention with quasi-resonant DC voltage circuit,

Fig. 2 voltage and current waveforms of selected components of the circuit shown in Fig. 1,

Fig. 3 shows the profile of the currents in time by the clamp power semiconductor switch and the resonant circuit switch in the circuit of Fig. 1 in its specific assignment,

Fig. 4 shows a further circuit arrangement according to the invention and

Fig. 5 shows the time course of the currents through the clamp power semiconductor switch and the resonant circuit switch in the circuit arrangement according to FIG. 4 in their special time assignment.

In Fig. 1, a converter with quasi-resonant DC voltage intermediate circuit is shown. Power semiconductor switches T1 to T6 (here indicated as ICBTs) and anti-parallel rework diodes D1 to D6 form the three strands of the converter between the supply lines of the intermediate circuit voltage Ud, which are connected via a constant voltage source (for example an uncontrolled mains converter with a downstream capacitor). provided. The AC-side (load-side) outputs of the converter are labeled U, V, W.

In the intermediate circuit, that is between the constant voltage source and the Power converter, is a resonant circuit consisting of a resonant circuit choke Lr and an oscillating circuit capacitor Cr, in series with an oscillating circuit switch Ts and an oscillating circuit diode Ds connected in parallel with it. A Clamp circuitry consists of a clamp capacitor Cc and a clamp Power semiconductor switch Tc with a diode Dc connected in antiparallel to it. The resonant circuit switch Ts is shown here as an IGBT. Advantageously However, it can also be designed as a thyristor.  

The clamp capacitor Cc must be dimensioned larger than the oscillator circular capacitor Cr. A relation is favorable in which the clamp capacitor Cc 10. . . Is 20 times larger than the resonant circuit capacitor Cr. The clamp Capacitor Cc must have a clamp voltage Uc of approximately 10% to 40% the intermediate circuit voltage Ud can be charged.

If one or more strings are to be switched in the converter, first the clamp power semiconductor switch Tc and the oscillator circuit switch Ts switched on. Since the resonant circuit capacitor Cr on the Value Ud + Uc is charged, no current initially flows in it. Through the The resonant circuit choke Lr flows a linearly increasing current from the Clamp-Kon capacitor Cc via the clamp power semiconductor switch Tc.

When the current through the resonant circuit choke Lr has reached a value that sufficient energy storage for the oscillation of the resonant circuit guaranteed, the clamp power semiconductor switch Tc is turned off. The current in the resonant circuit choke Lr now flows over the power half conductor switch Ts and discharges the resonant circuit capacitor Cr. The resonant circuit switch Ts becomes a few microseconds later than the clamp power half conductor switch Tc now also switched off. If he is trained as a thyristor is not even a shutdown command because the current through it automatically becomes zero.

The energy in the resonant circuit choke Lr is via the rework diodes D1 to D6 fed back into the DC link. During the rework diodes D1 to D6 carry current, the desired switching commands given to the power semiconductor switches of the converter. You switch now that the DC link voltage has dropped to zero, below zero voltage around. This is the optimal prerequisite for switching without nen Significant switching losses created in the converter.

The forward losses in the clamp power semiconductor switch Tc and in the oscillation Circular switches Ts are also minimal, since they only turn on in the short time fall, which is required for the oscillation process in the intermediate circuit.  

The switching losses in the clamp power semiconductor switch Tc and in the oscillation Circular switches Ts are also minimal. The clamp power semiconductor switch Tc only switches on the clamp voltage Uc below zero current (the switch-on current increases linearly from zero). When switched off, its voltage increases borders linearly through the resonant circuit capacitor Cr.

The resonant circuit switch Ts is only loaded with the clamp voltage Uc. This causes minimal switching losses. The tension becomes The resonant circuit switch Ts is dimensioned smaller in accordance with the clamp voltage Uc (10% to 40%) than the other power semiconductor switches in the converter.

The resonant circuit capacitor Cr is then again via the resonant circuit inductor Lr, the resonant circuit diode Ds and the intermediate circuit (voltage source Ud) charged. Its voltage is determined by the clamp diode Dc and the Clamp capacitor Cc limited to the value Ud + Uc.

The charge on the clamp capacitor Cc can be easily via the Clamp power semiconductor switches Tc and the power semiconductor switches T1 to T6 of the converter can be determined. If overloaded, the clamp Power semiconductor switch Tc switched on a few microseconds longer than it would be necessary for the reversal process. This is about the resonant circuit throttle Lr removed more charge from the clamp capacitor Cc. At sub The charge of the clamp capacitor becomes the power semiconductors accordingly switch T1 to T6 of the converter briefly in the zero voltage interval switched on. As a result, the Clamp-Kon capacitor Cc fed more charge.

In Fig. 2, the previously indicated voltage and current waveforms are shown:

The curves of current i _T1 and voltage u _T1 at the power semiconductor switch T1 over time t are shown in detail.

The time course of the voltage u _T4 at the power semiconductor switch T4, which alternately switches the line U of the converter with the power semiconductor switch T1, and the course of the current i _D4 through the reverse diode _D4 connected in reverse to the power semiconductor switch T4 are shown in chronological order.

In addition, the voltage u _Tc and the current i _{Tc of} the clamp power semiconductor switch Tc are shown over time t in relation to these current and voltage profiles in their temporal relationship.

The same applies to the voltage u _Ts and i _{Ts of} the resonant circuit switch Ts.

Finally, the time profiles of the voltage u _Ccr at the resonant circuit capacitor Cr and the current i _Cr through it are shown.

It can be seen that the smooth switching of the power semiconductor switches T1 and T4 always takes place when the intermediate circuit voltage, ie the voltage u _Cr at the resonant circuit capacitor _Cr oscillates through zero.

Above is Fig. 1 noted that the resonant circuit switch Ts may be formed as a thyristor. Since the current commutation from the clamp power semiconductor switch Tc to the resonant circuit switch Ts is very fast and thyristors need a certain amount of time to switch fully th (ignition delay time), difficulties can arise, especially at higher operating frequencies.

In Fig. 3, the course of the current i _Tc through the clamp power semiconductor switch Tc and the course of the current i _Ts through the resonant circuit switch Ts is shown for the commutation time. Thereafter, the current i _Ts must increase very quickly when the clamp power semiconductor switch Tc is controlled in the blocking state, ie the current i _Tc quickly becomes zero.

A slow switching oscillation is necessary for such a rapid current rise circuit switch Ts - such as B. a thyristor - but not suitable because of this (as mentioned above) takes a certain amount of time to build up electricity.

Fig. 4 shows a circuit arrangement with which the rapid current commutation from the clamp power semiconductor switch Tc to the resonant circuit switch Ts is avoided, with which the use of a thyristor as the resonant circuit switch Ts is possible without problems.

For this purpose, the series connection of the clamp capacitor Cc and the clamp power semiconductor switch Tc with the clamp diode connected in anti-parallel is not - as shown in FIG. 1 - the resonant circuit choke Lr but - accordingly FIG. 4 - the resonant circuit capacitor Cr is connected in parallel. The clamp capacitor Cc is placed with its one connection directly to the negative pole of the intermediate circuit voltage Ud, so that additional para-critical inductances when connected to the (usually designed as a capacitor battery of an intermediate circuit converter) constant voltage source are avoided. The resonant circuit switch Ts and the antiparallelge switched resonant circuit diode Ds are each connected with their one power connection directly to the resonant circuit reactor Lr and with their other connection to the power connection of the clamp power semiconductor switch Tc directly connected to the resonant circuit capacitor Cr.

With the circuit arrangement shown in FIG. 4, the courses of the currents i _Tc and i _Ts shown over time t in FIG. 5 result. The current i _Ts can be slowly built up together with the current i _Tc through the clamp power semiconductor switch Tc and already flows in full when the clamp power semiconductor switch Tc is switched off, thus allowing the use of a thyristor as an oscillating circuit switch Ts.

Of course, the circuit variant shown in FIG. 4 is also suitable for a fast-switching resonant circuit switch.

Claims (5)

1. Self-commutated converter with quasi-resonant DC voltage intermediate circuit, which in the supply line from a constant DC voltage source to the bridged th with an antiparallel feedback diode, can be switched off via its control connection, power semiconductor switches of the inverter have a resonant circuit choke, which together with one between the DC-side connections the power semiconductor switch-connected resonant circuit capacitor forms a resonant circuit for switching the power semiconductor switch at a zero-intermediate circuit voltage and in which the resonant circuit choke is connected through the series connection of a clamp capacitor limiting the voltage in the resonant circuit with a clamp power semiconductor switch and a clamp diode that is connected in antiparallel , characterized in that the resonant circuit capacitor (Cr) is connected in series with a resonant circuit switch (Ts) which is characterized by a in the direction of constant DC voltage (Ud) polarized resonant circuit diode (Ds) is bridged ( Fig. 1). 2. Self-commutated converter according to claim 1, characterized, that the clamp capacitor (Cc) 10 to 20 times the capacity of Has resonant circuit capacitor (Cr). 3. Self-commutated converter according to one of claims 1 or 2, characterized, that the clamp capacitor (Cc) before the start of switching the power semiconductor switch (T1 to T6) to a (clamp) voltage (Uc) of 10% up to 40% of the voltage (Ud) of the constant direct voltage source is loaded. 4. Self-commutated converter according to one of claims 1 to 3, characterized, that the resonant circuit switch (Ts) is formed by a thyristor.   5. Self-commutated converter according to one of claims 1 to 3, characterized in that the series connection of the voltage in the resonant circuit limiting capacitor (Cc) with the clamp power semiconductor switch (Tc) and this anti-parallel connected clamp diode (Dc) instead of To bridge the resonant circuit choke (Lr), the resonant circuit capacitor (Cr) is connected in parallel and the resonant circuit switch (Ts) designed as a transistor with its one power connection directly to the resonant circuit choke (Lr) and with its other power connection directly to the clamp power semiconductor switch (Tc) is connected ( Fig. 3).