KR820000337B1 - Voltage limitation and energy rehound circuit for current source inverter - Google Patents

Abstract

A capacitor(C4) and the first diode(D11) are comprised as a voltage limitation circuit, capacitors(C5,C6) are connected with the both ends of the capacitor(C4), a thyristor (S4), a inverter(L3), a thyristor(S5) and a inductor(L4) are connected with the both ends of capacitors (C5,C6) in series, a inductor(Lrl), a diode(C14), a inductor(Lr2) and a diode (D15) are connected with input power source, separately, and the center part of that and the both ends of the capacitor (C4) are connected together.

Description

Voltage Limit and Energy Feedback Circuit of Current Source Inverter

1a, b is a conventional square wave current source inverter circuit,

2 is an embodiment configuration of the inverter of the present invention,

3 is a specific circuit diagram illustrating the present invention,

4a, b, c, and d are diagrams illustrating step by step operations of FIG.

5 shows one method of controlling the input voltage of the voltage limiting circuit according to the present invention to be changed according to a reference voltage.

6 is an oscillo-gram showing the operation of the voltage limit and energy feedback circuit in accordance with the present invention,

7 is an oscillogram of line voltage and phase current of a motor.

The present invention relates to a voltage limiting and energy feedback circuit of a novel batch reflux inverter associated with a current source inverter.

The general purpose of the present invention is to increase the reliability of the inverter by controlling the voltage spike of the new current-type single-reflux inverter independent of load fluctuations, and to use a system with a low-voltage reverse-blocking two-terminal thyristor (hereinafter referred to as thyristor). The present invention relates to a voltage limiting and energy feedback circuit for absorbing and re-feeding spike energy generated at every instant of reflux during operation of the inverter.

Conventional current source inverter shows the square wave inverter method proposed by Mr. WARD (Ref. 1) and STEIGERWALD (Ref. 2) as shown in FIG. The basic configuration of the WARD inverter consists of thyristors (T ₁ , T ₃ , T ₅ and T ₄ , T ₆ , T ₂ ) and diodes (D ₁ , D ₃ , D ₅ and D ₄ , D ₆ , D ₂₎ It consists of the connection of the capacitors C at the series connection points of), thus requiring 6 elements each in one inverter. On the other hand, the inverter of STEIGERWALD is formed by connecting one capacitor (C) to the connection point of two auxiliary thyristors (T _p , T _n ) connected in series at both ends of the power at the center of the motor connected to the six main butters. It is. The advantage of these methods is that the circuit is simple, the control is simple, and the quadrant operation of the motor is possible. However, their disadvantage is that the load tolerance is very small and the upper limit of the operating frequency is low. In addition, the peak spike voltage value varies greatly depending on the load and operating speed, and thyristors having a fairly high breakdown voltage should be used.

[references]

E. Ward, Inverter Suitable for Operation of a Range of Frequency, Proceedings IEEE Vol. III, No. 8, Aug., 1964.

2. R.L. Steigerwald, “Characteristics of a Current-fed Inverter with Commutation Applied Through Road Neutral Point,” IEEE Trans. Ind. Appl., IA 15, Sep. Oct., 1979.

In the present invention, by employing a new reflux circuit of the new method not only solved the shortcomings of the existing circuits to enable a very wide range of operation, but also to control the spike voltage arbitrarily and constant in spite of the fluctuations in load, it is more reliable in terms of reliability. It is proposed a new method of voltage limiting and energy feedback circuit which is improved and at the same time more economically advantageous by making use of low voltage withstand pressure thyristor.

The inverter configuration diagram of the present invention is shown in FIG. That is, the present invention is composed of a converter, a current source reactor and an inverter, and the reflux on the inverter is made by an independent batch reflux circuit, and the voltage limit and energy for absorbing and re-recharging the energy of the voltage spike generated at each reflux In addition to the feedback circuit, the entire system is constructed. In a circuit such as the first diagram described above, the change of the phase current of the motor occurs while charging the capacitor (s) with the reflux operation, which causes various disadvantages. However, when the reflux is generated at a high speed by using the batch reflux method as in the present invention, there is almost no change in the phase current between these periods, and occurs mainly at the moment after the reflux. At this time, increase the potential difference between phases for a short time as possible, but the maximum value is limited to any suitable potential according to the relationship with the input voltage, which can lead to a rapid change of current between phases. Will have. However, in the circuit for limiting to a constant voltage, energy flows at each reflux, and thus, by storing it for a while and immediately feeding it back to the power supply, it is possible to increase the efficiency and to effectively control the voltage. The part responsible for such an operation is called a voltage limiting and energy feedback circuit, and the following conditions must be particularly satisfied in the operation. First, the four-phase operation of the motor will not be unreasonable. Second, it should not have any influence on the operation of the other circuits.

In view of the above, the present invention creates a circuit as shown in FIG. 3 and the operation of energy feedback is shown in FIG. 4 in order. As a method of limiting the voltage by temporarily storing energy, a capacitor C ₄ having a sufficient capacity is used. The operation thereof is described in relation to the operation of the collective reflux circuit, but it will be mentioned here for a while.

The operation of the collective reflux circuit is to turn off and turn off the main thyristors in the inverter. Therefore, the current change between phases of the motor occurs after the reflux is completed, and the current flows into the capacitor C ₄ through the diode D ₁₁ . As a result, the voltage of the capacitor C ₄ is increased, and if the value is large enough, the voltage across the capacitor C ₄ , which is changed by one-time charging, will be small. However, if the charging is continued as the reflux operation is continued in the non-discharge state, the voltage across the capacitor C ₄ will continue to rise and become very high, and thus the effect of the voltage limit will not be obtained.

Therefore, the charge of the capacitor (C ₄ ) must be discharged out in an appropriate amount in an appropriate way, there may be a variety of methods. For example, it can be solved by a heat loss using a resistor or it can be returned to the power supply. In order to increase the efficiency of the system, it is preferable to a method for re-feeding back to the power source, and the present invention will be described with reference to FIG. 3, which is an embodiment of the present invention.

That is, the voltage limiting circuit is composed of the capacitor C ₄ and the diode D ₁₁ so that a part of the load side current charges the capacitor C ₄ through the diode D ₁₁ during the period in which the phase current change occurs during reflux. The maximum value of the spike voltage generated at is limited to the voltage across the capacitor (C ₄ ). Capacitors C ₅ and C ₆ are connected to both ends of capacitor C ₄ , respectively, and thyristor S ₄ , inductor L ₃ , and thyristor S between both ends of capacitors C ₅ and C ₆ . ₅ ) and an inductor L ₄ are connected. In addition, one end of the capacitor (C ₅ , C ₆ ) and the inductor (L _r1 , L _r2 ) and the diodes (D ₁₄ , D ₁₅ ) are connected in series to the input power, respectively, and the diodes (D ₁₂ , D ₁₃ ) Are respectively connected to both ends of the capacitor (C ₄ ) and the inductor (L _r1 , L _r2 ).

Therefore, the thyristors S ₄ and S ₅ discharge the voltages across the capacitors C ₅ and C ₆ , respectively, and once discharged, current flows to the power supply while discharging the capacitor C ₄ . As the voltage across (C ₅ , C ₆ ) and capacitor (C ₄ ) are the same, the energy of inductor (L _r1 , L _r2 ) is _reduced while recharging capacitor (C ₄ ) through diode (D ₁₂ , D ₁₃ ). It was designed to continue to produce energy feedback until discharged.

Hereinafter, the operation of the present invention will be described with reference to FIG. 4.

In section I, the capacitors C ₄ , C ₅ , C ₆ are charged with the polarity as indicated in the figure. When the thyristors S ₄ and S ₅ are simultaneously turned on in the section II, the voltages of the capacitors C ₅ and C ₆ discharge through the inductors L ₃ and L ₄ at very high speeds, respectively. When the sum of the voltages across the capacitors C ₄ , C ₅ , and C ₆ is higher than the power supply voltage, it is moved to the section III. In section III, current flows to the power supply through the diodes D ₁₄ and D ₁₅ and the inductors L _r1 and L _r2 , so that the capacitor C ₄ discharges and immediately indicates the process of energy feedback. If the value of inductance L _r (= L _r1 + L _r2 ) is much larger than inductor L ₃ (L ₄ ), the turn-off time of thyristors S ₄ and S ₅ is sufficiently long. When the voltages of the capacitors C ₅ and C ₆ are recharged in the same direction as in the section I, and their respective sizes are the same as the voltages across the capacitor C ₄ , the energy of the inductor L _r which discharged less until then is discharged. The energy feedback is continued while recharging the capacitor C ₄ through the diodes D ₁₂ and D ₁₃ . This is the operation process of section IV, and when the current of inductance L _r reaches zero, it returns to section I. Again, the diodes D ₁₄ and D ₁₅ are in the off state, thus preventing the discharge of the capacitors C ₅ and C ₆ so that the operation of the next cycle can be stably continued. If a faster energy feedback is required, the thyristors S ₄ and S ₅ can be turned on and on before the current of the inductor L _r becomes zero in section IV. In this case, the thyristors S ₄ and S ₅ ) Turn-off time should be considered.

The look at the process in the same operation that is energy fed back as soon capacitor (C ₄₎ principle that spreading the charge a small capacitor (C _5, C ₆₎ so as to keep constant the amount of charge in the thyristor (S _4, Each time S ₅ ) is turned on discontinuously, the voltage of capacitor C ₄ that is decreased once is related to its own voltage and capacity and the capacity of capacitors C ₅ and C ₆ . One possible reference voltage Vref for controlling the voltage across capacitor C ₄ to limit the spike voltage is shown in FIG. 5.

Here Vref is supposed to change almost linearly between V ₁ and V ₂ (V ₁ V _m V ₂ ; V _m = maximum input voltage) across the input voltage range. For example, for any given input voltage V _s1 , if the instantaneous voltage across capacitor C ₄ exceeds V _r1 , turn on thyristors S ₄ , S ₅ , otherwise leave it off. V ₁ is the reference voltage when V _s = 0 and needs to be considerably high even when the pressure voltage is low to obtain a clean step wave of the load current waveform by the reflux operation. Here, the voltage is about 50 volts. As a result, when the input voltage is low, the spike voltage becomes relatively larger than the back EMF of the motor, but becomes very small when the input voltage is high. 7 shows an oscillogram relating to the line voltage and the phase current of the 6-step current source inverter when the input voltage is low.

As such, the control method is so simple that independent control is possible without having to consider the operating conditions of the motor. 6 is an oscillogram of the experimental results of the energy feedback circuit. (a) shows the voltage across the capacitor (C ₄ ) and (b) shows the voltage across the capacitor (C ₆ ). As shown here, when the current flows with each reflux, when the voltage across the capacitor C ₄ increases and rises above a certain reference voltage, the thyristor S ₄ (S ₅ ) is turned on so that the capacitors C ₆ and C ₅ It can be seen that the voltage reverses at a rapid rate and at the same time the energy feedback begins. In addition, since the feedback period is very long compared to the discharge period, it can be seen that the discharge of the capacitor C ₄ occurs without a large spike current.

The operation of the voltage limiting and energy feedback circuits has been described so far. There are several advantages to using this approach: First, it is possible to use the thyristors with low breakdown voltage as the maximum voltage applied to the thyristor of the main inverter can always be reliably limited to any potential regardless of the load state. The low pressure-resistant thyristors are advantageous not only in terms of price but also in speed, and thus have less reflux energy and are advantageous for high speed operation. Second, since the amount of power handled in the energy feedback circuit is less than 10% of the total system power, the configuration of this part is possible at a very low price. That is, the inductance (L _r ) can be very small due to the small amount of current flowing, and the thyristors (S ₄ , S ₅ ) and diodes also have much smaller capacities than the main thyristors and do not require high breakdown voltage. . The capacity of the capacitor (C ₄ ) is only a little larger, there is no large current pulse flows and always charge only in a certain direction, it is possible to use an electrolytic capacitor can meet the low price condition as a whole. Third, the control method is not only simple, but the operation of the regenerative mode of the motor is prevented by only sending a gating pulse to the thyristors (S ₄ , S ₅ ). At this time, the capacitors (C ₅ , C ₆ ) this time acts as a good snubber (snubber) is a very safe off state of the thyristors is guaranteed. Therefore, the operation exchange between the motor and the generator can be made very quickly and effortlessly, and thus, the addition of the voltage limiting and energy feedback circuit of the present invention can obtain many benefits that are difficult to obtain in other ways.

Claims (1)

As described above and illustrated in the drawings, in the voltage limiting and energy feedback circuit of the current source inverter, the capacitor C ₄ and the first diode D ₁₁ form a voltage limiting circuit and the capacitor C ₄ capacitor across the (C _5, C ₆₎ is a yeolgyeol and the capacitor, the respective thyristor both ends of the _{(C 5, C 6) (} S 4) and the inductor (L ₃₎ and a thyristor (S ₅₎ and an inductor (L ₄₎ Are connected in series so that the inductor (L _r1 ), diode (D ₁₄ ) and inductor (L _r2 ) and diode (D ₁₅ ) are connected in series respectively to the input power source, and between the midpoint of the capacitor (C ₄ ) Voltage limiting and energy feedback circuit of the current source inverter, characterized in that the connection.

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