JPH0359671B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention connects two separately excited bridge converters together with a capacitor on the alternating current side to form an alternating current intermediate circuit, and operates the converter. A power conversion device (hereinafter also referred to as ICB) that performs commutation operation using an alternating current voltage established at This invention relates to a firing angle control method.
Generally, in such a system, it is desired that commutation failure is prevented and stable operation is always performed regardless of the load state.

[Problems with conventional technology]

Figure 1 shows an energy transfer converter (ICB)
This is a configuration diagram showing the general configuration of 1.ICB, 2.
3 is a separately excited bridge converter, 4 is a capacitor,
5 and 6 are coils, 10 is an oscillator 11, a pulse generator 12, a firing angle adjuster 13 and a pulse generator 1
This is an ignition device consisting of four components. The main circuit configuration of this ICB is as shown in the figure with the reference numeral 1.
The basic components are pulse separately excited converters CONVA(2), CONVB(3) and a three-phase capacitor 4 (capacitance: C). As mentioned above, this device transfers the energy of CONVACONVB by adding a phase difference θ to the firing of the two converters CONVA and CONVB. In this case, the energy is transferred between coil 5 and coil 6. will be given and received.
The ignition control is performed by the ignition device 10. For example, one of the two converters (CONVA) is fixedly ignited by a signal from the external oscillator 11, and the other converter (CONVB) is A method is adopted in which the oscillator is ignited by shifting it by θ in the leading or lagging direction with respect to the reference phase indicated by the oscillator. In addition, the commutation of converters CONVA and CONVB is performed by the voltage v _c of capacitor 4, and the phase difference θ
It is known that if ignition is applied arbitrarily, depending on the load conditions of the two converters, the reverse bias voltage and time necessary for commutation of the thyristor may not be obtained, which may cause commutation failure. There is.

This can be considered as follows.
In other words, the capacitor voltage v _c that controls commutation in this device is a voltage generated by operating two converters, and this is an approximately sinusoidal AC voltage equal to the ignition frequency of the converters. . Looking at it from another perspective, it can be said that in stable operating conditions, the two converters CONVA and B perform so-called power commutation using this capacitor voltage v _c as a power source. This is clearly shown in FIGS. 2B to 2D. In addition, the second
Figure A shows the currents i _A , i _B , i _C and voltage in the AC intermediate circuit of ICB.
FIG. 3 is a circuit diagram showing the relationship between v _c . That is, the second B
The figure shows the relationship between input currents i _A and i _B , capacitor current i _c , and capacitor voltage v _c for one phase when CONVA and CONVB are fired in the same phase. As can be seen from this figure, when CONVA and B are fired in the same phase (θ=0), the so-called firing phases α _A and α _B based on the capacitor voltage v _c are both 90°.
Further, FIG. 2C shows the waveform when ignition is performed with CONVB advanced by θ with respect to CONVA. In this case, α _A > 90°, α _B < 90°,
It can be seen that CONVA operates as an inverter and CONVB operates as a rectifier. That is, in this case, power is supplied from CONVA to CONVB.

Generally speaking, when a converter that commutates the power supply is operated as an inverter, if the phase control angle α increases to nearly 180°, the thyristor will not be able to obtain sufficient reverse bias time, which often leads to commutation failure. This is well known and applies to the present device as well. For example, as shown in Figure 2D, if θ=90° where i _A << i _B , then CONVA
The firing phase α _A of α _A becomes 180°, making it impossible to obtain the reverse bias time. Therefore, when such an ignition phase occurs, this device causes commutation failure and cannot continue stable operation. To prevent this, conventional methods detect the capacitor voltage v _c and use this as a reference.
I tried to find the actual firing angles α _A and α _B of CONVA and CONVB. Then, when α _A and α _B become larger than predetermined values, the device is stopped, or the phase difference θ (θ
= α _A − α _B ) in the zero direction. However, it is not easy to determine the ignition phase of the converter with respect to the capacitor voltage without time delay, and the detection circuit has also tended to be complicated. Further, it is not preferable to proceed with the protection process in the direction of stopping each time.

[Purpose of the invention]

This invention was made under these circumstances, and it is possible to prevent commutation failure and ensure stable operation at all times, regardless of the load condition of the energy transfer converter (ICB). The purpose of this invention is to provide a method for controlling ignition limitation.

[Key points of the invention]

This invention detects the DC currents I _S and I _L of the two converters in the above-mentioned ICB, and
Find these ratios (I _L /I _S ) or the distribution ratio (I _L /I _S +I _L ) for their sum, and calculate these ratios (or distribution ratios) determined from the commutation margin angle necessary for the converter. The actual phase difference θ is limited and controlled based on the relationship with the maximum value of the phase difference θ between the two converters to prevent commutation failure.

[Practical example of the invention]

FIG. 3 is a block diagram showing an embodiment of the present invention. That is, the main circuit has the same configuration as in Fig. 1, and its ignition method is the same as in Fig. 1, in which converter A (2) is fixedly ignited by oscillator 11, and converter B (3) is ignited in a fixed manner. Using the signal from the oscillator 11 as a synchronizing signal, firing is performed with a phase shift of θ with respect to the reference phase of the oscillator, that is, the firing phase of CONVA. However, in this case, the limiter 23 is set so that the phase difference angle θ is within the range of the maximum and minimum values allowed.
It is characterized in that it has a configuration that prevents commutation failure, and the maximum value of the phase difference angle θ,
The minimum value is determined by the DC current detectors 7 and 8, the adder 24,
It is obtained as follows using the divider 21, pattern generator 22, etc. Note that FIG. 4 is a waveform diagram depicting AC input currents i _A , i _B and capacitor current i _C of CONVA and CONVB with the same polarity as FIG. 2A, focusing on their fundamental wave components.

Now, if the zero cross point of i _A is the time origin (t = 0), then i _A and i _B are i _A = I _Asio ω _c t ... (1) i _B = I _Bsio (ω _c t + θ) ... ...(2) Here, ω _c is the capacitor voltage angular frequency, and θ is the phase difference angle between the converters (θ: lead, θ<0: lag).

Therefore, since the capacitor current i _C is the sum of these, i _C = i _A + i _B = I _Asio ω _c t + I _Bsio (ω _c t + θ) I _Csio (ω _c t + β) (3). Here, I _C and β in equation (3) are I _C = √ ( _A + _Bcps ) ² + ( _Bsio ) ² ... (4) tanβ = I _Bsio θ / I _A + I _Bcps θ ... (5) This is what is required. Here, since tanβ=sinβ/cosβ=I _Bsio θ/I _A +I _Bcps θ from equation (5), the following relational expression is established: I _Asio β+I _Bsio (β−θ)=0 (6). Furthermore CONVA, CONVB
Let _{I S} and _{I L} be _{the direct} currents of I _Ssio β+I _Lsio (β-θ)=0 ...(9) It can be rewritten as follows.

Here, by setting k=I _L /I _S +I _L (10), the above equation (9) further becomes (1-k)sinβ+ksin(β-θ)=0 (11).

By the way, the relationship between firing angles α _A and α _B and β and θ is as follows from FIG. 4: α _A = π/2 + β (12) α _B = π/2 + β-θ (13). Since it is necessary for α _A and α _B to maintain commutation margin angle γ _nio , 0α _A π−γ _nio 0α _B π−γ _nio is required, and applying this to β and θ, −π/ The following conditions are obtained: 2βπ/2−γ _nio −π/2β−θπ/2−γ _nio (14). Further, the phase difference angle θ is −π/2θπ/2 (15) for control purposes.

Here, if we assume that γ _{nio =} 30° and find the area of θ that satisfies each equation (11), (14), and (15) with respect to k (distribution ratio), the fifth
It will look like the figure. Note that FIG. 5 is a pattern diagram showing the allowable range of the phase difference angle, in which the horizontal axis shows the distribution ratio indicated by k, and the vertical axis shows the operable phase difference angle θ.

Based on the above, the third example showing the embodiment of this invention
In the circuit shown in the figure, the DC currents I _S and I _L of CONVA(2) and CONVB(3) are detected by detectors 7 and 8, and the adder 24 and divider 21 detect k=I _L / _IL
+I _S is calculated and inputted into the pattern generator 22 which stores the pattern as shown in Fig. 5 to find the maximum value θ _nax and minimum value θ _nio of the allowable phase difference angle θ. Commutation failure is prevented by limiting θ based on the value using the limiter 23.

Although the embodiments of the present invention have been described above, the pattern generator does not need to exactly copy the curve shown in FIG. 5, but may be a pattern that approximates it on the safe side. Also, here, pattern generation is performed by finding k=I _L /I _S +I _L ; however,
The same thing happens with k'=I _L /I _S.
This is also clear from equation (9) above. In short, I _L and I _S
By determining the ratio or distribution ratio (I _L /I _S +I _L ), the operable range of the phase difference angle θ can be determined.

〔Effect of the invention〕

According to this invention, the maximum and minimum values of the allowable ignition phase difference angle θ are determined from the DC current ratio (or distribution ratio) of the two converters of the ICB, and θ is limited and controlled based on this. Because we are
Commutation failure is prevented regardless of the ICB load conditions, and safe operation is always possible. Furthermore, the phase difference angle θ is related to the energy transfer rate between the two converters, and when it is large, the transfer rate is also large, but in this invention, the phase difference angle θ is maximized while preventing commutation failure. This improves the functionality of the device.

[Brief explanation of drawings]

Figure 1 shows energy transfer converter (ICB)
Figure 2A is a circuit diagram showing the relationship between current and voltage in the AC intermediate circuit of the ICB.
Figures 2B to 2D are due to the difference in phase difference angle.
A waveform diagram for explaining the difference in current and voltage waveforms in the AC intermediate circuit of ICB. Figure 3 is a configuration diagram showing an embodiment of the present invention. Figure 4 shows the AC input current and capacitor of the two converters in Figure 3. A waveform diagram showing the phase relationship with the current, and FIG. 5 is a pattern diagram showing the allowable range of the phase difference angle between the two converters. Description of symbols, 1... Energy transfer converter (ICB), 2, 3... Separately excited bridge converter, 4
... Capacitor, 5, 6 ... Coil, 7, 8 ...
DC current detector, 11... Oscillator, 12, 14...
...Pulse generator, 13...Ignition angle adjuster, 21...
...Divider, 22...Pattern generator, 23...Limiter, 24...Adder.

Claims (1)

[Claims] 1. Two separately excited converters are connected to each other on the AC side, a capacitor is connected in parallel to the connection point, and each converter is operated, thereby converting based on the AC voltage established across the capacitor. In a power conversion device that performs current operation and transfers energy between two converters by shifting the firing phase of each converter from each other, the ratio of the DC currents of each converter or the Determine the distribution ratio of one DC current to the sum, determine in advance the range of firing phase difference angles of both converters that are allowable for the ratio or distribution ratio, and calculate the firing phase difference of both converters. Reverse bias voltage during commutation required for the elements constituting the converter by limiting the maximum and minimum values of , so that they do not exceed the permissible range in light of the determined ratio or distribution ratio, A firing angle limitation control method in a power converter, characterized by securing time and preventing commutation failure.