CN2396568Y - Self-phase-change inverter - Google Patents

Abstract

The utility model discloses a self-commutated inverter, composed of a common commutation circuit and a three-phase bridge type inverter circuit. When a direct current power supply Ud which is obtained by rectifying alternating current is added to the positive and a negative busbars of the common commutation circuit and the three-phase bridge type inverter circuit, the self-commutated inverter can generate three-phase alternating current with adjustable frequency according to preset control logic, and the three-phase alternating current can be used for a variable frequency speed control system of a three-phase induction motor. Charging voltage on a capacitor is controllable, so that overvoltage for commutation can be dropped, and the control system can be greatly simplified.

Description

A kind of self commutated inverter

The utility model relates to a kind of converting means that is used for power supply, is specially the self commutated inverter that direct current that a kind of handle obtains through rectification is transformed to the adjustable three-phase alternating current of voltage to frequency, is used for the frequency conversion speed-adjusting system of three-phase induction motor.

Three-phase inverter, at present three-phase inverters that adopt series diode formula three-phase inverter or band auxiliary triode thyristor bridge more, it is phase-splitting commutation mode.The used commutating capacitor of series connection secondary tubular type three-phase inverter is more, voltage on the commutating capacitor can not artificially be controlled its height, till when charging current equals zero, because of the very high requirement of withstand voltage of charging voltage to switching device very high, be applied in high voltage (3,6,10kV) high-power (more than the 800kW) frequency conversion system, need be provided with huge commutation overvoltage absorption piece, and cause that thus power loss own strengthens; The three-phase inverter of band auxiliary triode thyristor bridge, exist voltage on capacitor uncontrollable equally, and the high defective of commutation overvoltage, this inverter is owing to be two three-phase bridge parallel connections, thereby need 12 road trigger impulses, thereby make its control system complexity according to certain logical relation work.

The purpose of this utility model provides a kind of self commutated inverter, this self commutated inverter is because the charging voltage on the capacitor is controlled, thereby the commutation overvoltage is descended greatly, the requirement of withstand voltage of main switching device is reduced greatly, and saved heavy overvoltage absorption piece; This self commutated inverter only needs eight road trigger impulses simultaneously, and control system is greatly simplified.

To achieve these goals, it is public commutation mode that the utility model changes phase-splitting commutation mode, it is made of public commutation circuit and three-phase inverter bridge circuit, three commutating capacitors participate in commutation simultaneously at each commutation beat, thereby the realization of controlling for charging voltage on the commutation capacitor provides the condition that makes things convenient for.

Self commutated inverter of the present utility model is compared with present normally used series diode formula three-phase inverter and band auxiliary triode thyristor bridge three-phase inverter, and effect and advantage that it has are:

1, the quantity of commutating capacitor has reduced 1/2, and the charging voltage on the capacitor controlled (is condition to satisfy the commutation requirement), [is limited in 1.25-thereby the commutation overvoltage level is descended greatly -scope in], the silicon controlled requirement of withstand voltage of main switching device is reduced greatly, can save heavy overvoltage absorption piece, its power loss is greatly reduced.

2, two thyristor arm T are partly adopted in its commutation of this self commutated inverter ₇, T ₈And three-phase diode bridge (D ₁-D ₆) constitute, can save that four road trigger impulses form and amplification system, control system is simplified.

3, this self commutated inverter is specially adapted in the high voltage large capcity frequency conversion speed-adjusting system, as is applied in the 1250kW/6kV asynchronous motor dragging system of thermal power plant, and its operational effect is good.

Below in conjunction with accompanying drawing the utility model is explained

Fig. 1: circuit block diagram of the present utility model

Fig. 2: circuit theory diagrams of the present utility model

Fig. 3: the utility model and commutation capacitor voltage sensor applied in any combination figure

Fig. 4: control logic graph of a relation of the present utility model

Power supply U of the present utility model _dBe the dc power supply that three-phase alternating-current supply obtains through the three-phase bridge controlled rectification, power supply U _dThe utmost point connect thyristor T respectively ₁, T ₃, T ₅, T ₇Anode, T ₁Negative electrode connect capacitor C ₁An end, the A phase of motor M, thyristor T ₄Anode, T ₃Negative electrode connect capacitor C ₂An end, the B phase of motor M, thyristor T ₆Anode, T ₅Negative electrode connect capacitor C ₃An end, motor M C mutually and thyristor T ₂Anode; Thyristor T ₇Anode connect diode D respectively ₁, D ₃, D ₅Positive pole; Power supply U _dNegative pole connect thyristor T ₄, T ₆, T ₂, T ₈Negative electrode, D ₁, D ₃, D ₅Negative pole respectively by A ', B ', C ' with diode D ₄, D ₆, D ₂Positive pole and C ₁, C ₂, C ₃The other end be connected D ₄, D ₆, D ₂Negative pole and thyristor T ₈Anode be connected.

This self commutated inverter is applied in the frequency conversion speed-adjusting system, can adapt to the AC asynchronous motor speed governing operation to different electric pressures and capacity, and the parameter of components and parts is selected and should be determined by different electric pressures and capacity.Given below is the parameter of each element in the frequency conversion speed-adjusting system of this self commutated inverter asynchronous motor of being applied to 1250KW/6KV:

Thyristor T ₁-T ₈Be KP630A/4000V triode thyristor, D ₁-D ₆Be the common rectifier diode of ZP200A/4000V, commutation electric capacity is C ₁=C ₂=C ₃=8 μ F/400KVar/12KV.

The supporting use that will be connected with the commutation capacitor voltage sensor of this self commutated inverter, Fig. 3 is this self commutated inverter and commutation capacitor voltage sensor applied in any combination figure, the commutation capacitor voltage sensor is powered on by commutating capacitor and flattens mean value detecting circuit and the minimum voltage identification circuit is formed, among Fig. 3 in the square frame I expression be the commutation capacitor voltage sensor, be the commutating capacitor pressing mean value detecting circuit that powers in the square frame II: $U_{\mathrm{cp}}=\frac{U_{c1}+{\mathrm{<figure-callout\; id="2"\; label="U\; c"\; filenames="Y9925023100091.png"\; state="\{\{state\}\}">U</figure-callout>}}_c+{\mathrm{<figure-callout\; id="3"\; label="U\; c"\; filenames="Y9925023100091.png"\; state="\{\{state\}\}">U</figure-callout>}}_c}{3}$ Be minimum voltage identification circuit on the commutating capacitor in the square frame III: | U _Min|=min{|U _C1|, | U _C1|, | U _C3|.

The supporting use because self commutated inverter is connected with the commutation capacitor voltage sensor has promptly guaranteed inverter at 0～55Hz frequency range reliably working, has limited the charging voltage value (U on the commutating capacitor again _CpAnd U _CminBy set-point U _nAnd U ₀Determine), thus the commutation overvoltage level is descended.

Fig. 4 is the control logic figure of this self commutated inverter to what show, and as can be seen from Figure 4, control logic makes thyristor T when first beat ₈, T ₁Conducting, electric current I _dBy the thyristor of conducting, motor winding and three capacitor C ₁, C ₂, C ₃Flow, in such cases voltage U _CpLinear increasing.Moment in second clock pulse appears, T ₇, T ₂Conducting, T ₈, T ₁At C ₁, C ₂, C ₃On remain the voltage effect under and turn-off electric current I _dBy thyristor T ₇, T ₂Flow with the motor winding, electric capacity recharges.Recharge the initial stage, polarity of voltage and electric current I on the electric capacity _dThe flow direction matches, thereby charging process is accelerated greatly.In second time interval, voltage | U _Cp| reach | U _n| set-point (E position among Fig. 4), and the minimum voltage value on the while capacitor (is U in this beat _C1) occur than set-point U ₀Bigger absolute value, voltage sensor on the capacitor produce the output logic element " with " conversion.Control logic perceives this signal, thyristor T ₇Control impuls is interrupted, and makes T ₃Conducting, T ₇Bearing back-pressure turn-offs.Electric current I _dAlong T ₂, T ₃Flow with the motor winding, voltage is established on the capacitor, and inverter work enters the 3rd pulse beat in the case, promptly enters normal operating conditions.

If the minimum voltage U on the capacitor of Fig. 4 E position _C1Absolute value less than | U ₀|, the conversion of voltage sensor will be postponed to be occurred, and inverter enters before the normal operating conditions in other words, must satisfy two agreements simultaneously, promptly | U _Cp| 〉=| U _n| and | U _Cmin| 〉=| U ₀|, only in this way could guarantee the reliable commutation of inverter.

Claims (1)

1. a self commutated inverter is characterized in that: the dc power supply U that the three-phase alternating current power supply obtains through the three-phase bridge controlled rectification _dPositive pole connect thyristor T ₁, T ₃, T ₅, T ₇Anode, T ₁Negative electrode connect capacitor C ₁An end, the A phase of motor M, thyristor T ₄Anode, T ₃Negative electrode connect capacitor C ₂An end, the B phase of motor M, thyristor T ₆Anode, T ₅Negative electrode connect capacitor C ₃An end, motor M C mutually and thyristor T ₂Anode, thyristor T ₇Negative electrode connect diode D ₁, D ₃, D ₅Positive pole; Power supply U _dNegative pole connect thyristor T ₄, T ₆, T ₂, T ₈Negative electrode, D ₁, D ₃, D ₅Negative pole respectively by A ', B ', C ' with diode D ₄, D ₆, D ₂Positive pole and C ₁, C ₂, C ₃The other end be connected D ₄, D ₆, D ₂Negative pole and thyristor T ₈Anode be connected.

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