JPH0216110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a rectifier that generates a variable DC voltage.

[Conventional technology]

Figure 1 shows the basic configuration of a three-phase full-wave rectifier, where 1 is a 3-phase AC power supply, 2, 3, and 4 are R, S, and T phases of this 3-phase AC power supply, and 5 is a 3-phase AC power supply. Phase full wave rectifier unit, 6, 7, 8 are the input lines of the 3 phase full wave rectifier unit U phase, V phase, W phase, 9,
10 are the output lines P and N of the three-phase full-wave rectifier unit 5, UP is the thyristor on the U-phase P side, and VP is the V
The thyristor on the phase P side, VN is the thyristor on the V phase N side, WP is the thyristor on the W phase P side, WN is the thyristor on the W side N
The side thyristor is shown. Note that the R, S, and T phases of the three-phase AC power supply 1 and the input lines U, V, and W phases of the three-phase full-wave rectifier unit 5 are given different names to make the explanation easier to understand later. Usually R and U, S and V, T
and W are connected.

Figure 2 shows the output voltage waveform and the temporal change in the conduction thyristor due to conventional general ignition control when a three-phase full-wave rectifier as shown in Figure 1 is operated with an inverter to generate a negative variable DC voltage. As is clear from the figure, for a constant DC output voltage, each thyristor is symmetrically controlled to fire at the same phase angle α. As is well known, such a rectification method controls the phase of current with respect to voltage, so if the absolute value of the output voltage is small, the power factor is poor and a large amount of reactive power is generated.

[Summary of the invention]

As mentioned above, the present invention is a three-phase full-wave rectifier using a thyristor as a rectifying element as shown in FIG.
When a negative variable DC output voltage is generated by inverter operation using symmetrical phase control as shown in Figure 2, the power factor is poor and large reactive power is generated, especially when the absolute value of the output voltage is small. This was done to improve the power factor in the low output range (area where the absolute value of the output voltage is small), and to provide a rectification method and ignition control method that generate less reactive power. .

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, 51, 52, and 53 are first, second, and third three-phase full-wave rectifier units, respectively, and L
1a, L1b, L2a, L2b, L3a, L3b
each indicates a reactor. The internal configurations of the first to third three-phase full-wave rectifier units 51 to 53 are the same as the three-phase full-wave rectifier unit 5 in FIG.
The connection of input lines to the three-phase AC power supply 1 is such that the first three-phase full-wave rectifier unit 51 connects R-U, S-V, T
-W, the second three-phase full-wave rectifier unit 52 is S-U, TV, R-W, and the third three-phase full-wave rectifier unit 53 is T-U, RV, S-W. - They are connected by switching the phases to make a W connection,
In addition, the output lines P of each unit 51 to 53,
N are reactors L1a, L1b, L2, respectively
They are mutually connected in parallel via a, L2b, L3a, and L3b.

Figure 4 shows the three-phase full-wave rectifier unit 51 to Figure 3.
53 shows the ignition control method and output voltage waveform, A is single-phase mode (hereinafter referred to as mode'),
B and C show the output voltage waveform in the three-phase mode (hereinafter referred to as mode', which is further divided into B's _A mode and C's _B mode), the conduction thyristor, and the equivalent circuit of the three-phase full-wave rectifier unit. , D show a list of thyristor firing control in each mode. This invention operates by switching each three-phase full-wave rectifier unit to modes ', ' _A , and ' _B according to the output DC voltage level required in the inverter region, and operates each three-phase full-wave rectifier unit 51 to 53. The purpose is to obtain the composite output of That is, assuming that the thyristor is an ideal rectifying element, the value of the minimum control advance angle (γ limiter) is γ, the peak value of the line voltage of the three-phase AC power supply 1 is Em, and the DC output voltage of the three-phase full-wave rectifier unit is E. _d 〓, E _d 〓If the maximum value is E _dp , in the inverter region E _d 〓=E _n /π(1-cosγ) ~ −E _n /πcosγ
Therefore, E _dp is E _dp = 3/πEm, but if E _d 〓 = E _dp / 3 (1 - cos γ) ~ -2/3E _dp cos γ, mode ′, If mode ′ _A , In this case, the first to third three-phase full-wave rectifier units 51 to 53 are operated in mode ' _B , and the thyristors 11 to 16 constituting the first to third three-phase full-wave rectifier units are As shown in Figure 4, in mode ', VP and VN are phase-controlled according to the required output DC voltage level at a control angle α (0 < α < π - γ), and UP and
UN is fired at π−γ, WP and WN are always non-conducting, and in mode ′ _A , VP and VN are controlled at the control angle α(−
The phase is controlled by π/3+γ<α<-γ) and is also fired at π-γ, UP and UN are fired at 2/3π-γ, WP and WN are fired at π-γ, and mode ′ _B
In this case, UP and UN are phase controlled by control angle α (2/3π−γ<α<π−γ), and VP, VN, WP, and WN are controlled by π−γ.
Asymmetric ignition control is performed in each mode so that ignition is controlled at Further, as described above, the input lines of the first to third three-phase full-wave rectifier units 51 to 53 to the three-phase AC power supply 1 are shifted from each other, and are connected in parallel to each other via the reactors L1a to L3b. Therefore, the combined DC output current does not become discontinuous even under light loads. Figure 5 shows the control angle α and the output DC voltage when asymmetric ignition control is performed by switching to Mode ', Mode ' _A , and Mode ' _B according to the level of the output DC voltage E _{d 〓} as described above. In Figure 6, the horizontal axis shows the output voltage E _d 〓/E _dp , and the vertical axis shows the reactive power Q/E dp _.
This is a power circle diagram showing the relationship between E _dp and I _d (where Q is the fundamental wave reactive power and I _d is the output DC current), and for comparison, a and a according to the embodiment of the present invention are shown. In the case of three-phase full-wave rectification with conventional symmetrical control b
It shows. As is clear from FIG. 6, the radius of the arc in the power circle diagram is 1/3 that of the normal three-phase full-wave system according to the present invention.
The generation of reactive power has been significantly reduced. Also the 7th
The figure shows the relationship between the fundamental wave power factor cosφ ₁ and the output voltage, where a shows the case where the asymmetric control according to the present invention is used, and b shows the case where the normal three-phase full-wave system is used. As is clear from the figure, the fundamental wave power factor in the low-medium power range has been greatly improved.

In the above explanation, for simplicity, the three-phase full-wave rectifier unit was explained as the most basic one consisting of six thyristors, but depending on the voltage and current value, thyristor elements can be connected in series or parallel. An effect similar to that of the above embodiment can also be obtained by connecting one three-phase full-wave rectifier unit itself in anti-parallel connection so that output currents in opposite directions can be obtained in the series-parallel region. Furthermore, although the three-phase full-wave rectifier unit has been described using a thyristor as a constituent element, the same effect can be obtained by using other elements whose conduction phase can be controlled, such as a transistor or a gate turn-off thyristor. Also, as an example, the fourth
The reason for setting the case where the thyristor is phase controlled as explained based on the figure is to minimize the fluctuation of the rectified waveform when switching each mode and to obtain a smooth change. Even if the phase to be controlled is changed (for example, UP and UN are phase controlled in mode ', VP and VN are fired at π-γ)51~5
If each unit of 3 is changed in the same way, the effect of the present invention will not change.

〔Effect of the invention〕

As described above, according to the present invention, when performing inverter operation by connecting a plurality of rectifier units in parallel, each rectifier unit is switched to single-phase mode or three-phase mode depending on the required output DC voltage level. By controlling the switching elements constituting the switch asymmetrically, it is possible to obtain a rectification method that has a good power factor and generates little reactive power even in the low output voltage range, and also rectifies each phase of the input power supply. Since the units are connected in a staggered manner, it is possible to prevent unbalance on the power supply side due to asymmetric control.

[Brief explanation of drawings]

Figure 1 is a basic configuration diagram of a three-phase full-wave rectifier, Figure 2
The figure is an explanatory diagram showing the output voltage waveform and the time change of the conduction thyristor according to the conventional ignition control method when a variable DC output voltage is generated by inverter operation using the configuration shown in Fig. 1. FIG. 4 is a diagram illustrating the equivalent circuit, output voltage waveform, and ignition control method in each mode of the rectifier having the configuration shown in FIG. 3, and FIG. A characteristic diagram showing the relationship between the control angle α and the output voltage by the rectifier, FIG. 6 is a power circle diagram showing the relationship between the output voltage and reactive power, and FIG. 7 is the same diagram showing the relationship between the fundamental wave power factor and the output voltage. FIG. In the figure, 1 is the 3-phase AC power supply, 2 is the R phase of the 3-phase AC power supply, 3 is the S phase, 4 is the T phase, 5 is the 3-phase full-wave rectifier unit, and 6 is the U of the 3-phase full-wave rectifier unit. phase, 7
is the V phase, 8 is the W phase, 9 is the output line P of the 3-phase full-wave rectifier unit, 10 is the output line N, UP is the thyristor on the U-phase P side that constitutes the 3-phase full-wave rectifier unit, UN
is the thyristor on the U phase N side, VP is the thyristor on the V phase P side, VW is the thyristor on the V phase N side, and WP is the W thyristor.
Thyristors 51, 52, and 53 on the phase P side are No. 1, No. 2, and No. 3 three-phase full-wave rectifier units, respectively.
L1a, L1b, L2a, L2b, L3a, L3
b indicates a reactor. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A rectifier unit constituted by a plurality of switching elements whose conduction phase can be controlled is connected to an AC power source, and the switching elements are controlled to conduction to perform inverter operation, and a negative voltage is output from the output side of the rectifier unit. In a device designed to obtain a DC output voltage of
A plurality of the rectifier units are provided, the input ends of these rectifier units are respectively connected to the AC power source in mutually different phase relationships, and the output ends of the rectifier units are commonly connected via a reactor,
A rectifying device characterized in that each of the rectifying units described above is operated by switching to a single-phase operation mode or a multi-phase operation mode depending on the DC output voltage level that can be generated. 2. Each rectifier unit consists of a first, second, and third three-phase full-wave rectifier unit, and each of the three-phase full-wave rectifier units has a maximum DC output voltage that can be generated by E _dp and a minimum control advance. When the value of the angle (γ limiter) is γ, when the required output voltage value is E _dp /3 (1-cos γ) to -2/3E _dp cos γ, it is operated in mode ', which is the single-phase mode, The required output voltage value is In the _case of 2. The rectifier according to claim 1, wherein the rectifier is operated in ' _B mode, which is one of the three-phase modes. 3 Set the output end phases of the 3-phase AC power supply to R phase, S phase, and T phase.
phase, and the input terminal phases of the first, second, and third three-phase full-wave rectifier units are U phase, V phase, and W phase, respectively, and the output terminal of the three-phase AC power supply and the first, Second
The connections with the input terminal of the third three-phase full-wave rectifier unit are (R-U, S-V, T-W) and (S-W), respectively.
-U, T-V, R-W), (T-U, R-V, S-
W), and the positive output terminal P and load output terminal N of each three-phase full-wave rectifier unit are connected in parallel via a reactor, and each three-phase full-wave rectifier unit is configured. The U-phase P side of the switching element is UP, the U-phase N side is UN, the V-phase P side is VP, the V-phase N side is VN, and the W-phase P side is WP, W.
When the phase N side is WN, in mode ', each three-phase full-wave rectifier unit is connected to the above switching element.
VP and VN are phase controlled, UP and UN are ignited at 2/3π-γ, WP and WN are controlled to be constantly non-conducting, and in mode ' _A , each three-phase full-wave rectifier unit is controlled as described above. The switching elements VP and VN are controlled in phase, and are also fired at the phase angle π-γ.
UN is ignited at 2/3π-γ, WP and WN are ignited at π-γ, and in mode ' _B , each three-phase full-wave rectifier unit controls the phase of the switching elements UP and UN,
3. The rectifier device according to claim 2, wherein VP, VN, WP, and WN are controlled to fire at a phase angle of π-γ.