THE APPLICATION OF THYRISTOR AC POWER CONTROLLER IN BEPC

THE APPLICATION OF THYRISTOR AC POWER CONTROLLER IN BEPC

MODULATORS

L. Shen, Accelerator Centre, IHEP, Beijing, China

Abstracts

Thyristor AC power controller is first applied in

BEPC modulator. Here introduce the situation of its

application. We applied initially thyristor AC power

controller to BEPC individual modulators in 1995. We

discovered that the thyristor AC power controller has a

lot of advantage compared with induction voltage

regulator, so we applied thyristor AC power controller to

whole basically modulator in 1999. We have done the

overall observe for them in this term. Now they are

working well in BEPC modulators.

1. Introduce

The modulator is an important equipment in Linac.

Our modulator is line-type modulator. Its output pulse

high-voltage is 270KV, 350KV, output peak power is

80MW, 150MW. Before, we use induction voltage

regulator as voltage regulation. Now, we make use of

thyristor AC power controller to regulate output voltage.

It has a lot of advantage. For example, Its volume is

smaller, its weight is lighter, it can save electric energy

and so on.

2. Main circuit of thyristor AC power

controller

The three-phase ac input to the modulator can be any

level from 0 to 380V by the use of thyristor AC power

controller. The main circuit of Thyristor AC power

controller is shown in Figure 1.

Figure 1: The main circuit of thyristor AC power

controller

There are six thyristors. When this thyristor is

triggered by pulse, it will operate. There are six trigger

signal. They are arranged in order. These are A+
C-

B+
A-
C+
B-
A+. The phase difference is 60

each other. This six ordinal trigger pulse are produced by

control circuit of thyristor AC power controller. Output

voltage of thyristor ac power controller can be any level

from 0 to 380V by means of adjusting thyristor’s

conduction angle.

3. Control circuit of thyristor AC power

controller

There is automaton in control circuit of thyristor AC

power controller. It is shown in Figure 2.

Figure 2: Control principle of thyristor AC power

controller

It can improve modulator’s output stability by the

dc high-voltage feedback system. It only has a little

change when power line voltage has a large change.

Table 1 is shown the measure result of modulator’s

output stability.

Table 1: Modulator’s output stability

No add de-Q’ing

Modulator’s

number

The change of

power line

voltage

The change of

modulator’s

output

6# 1.4% 0.4%

10# 1.2% 0.4%

The input of AC enters thyristor AC power controller

through three 100A filters which decouple the noise from

the ac lines. Thus preventing possible RFI. Thyristor

work in on-off state. They will produce a large

harmonics interference, so must use filter to prevent this

interference into the power circuit. These harmonics

flowing into the power system source impedance

produce 0.35% distortion of Sine wave. This amount of

distortion is acceptable from the standpoint of

interference with communications and control system.

4. Low-frequency transient suppressor

network

Low-frequency transient suppressor network

connected from line to line of the primary of rectifier

transformer was improved. Three thyrite resistors added.

They are shown in Figure 3.

Figure 3: Improved low-frequency transient suppressor

The function of the three thyrite resistors are to

provide a low-impedance load for the transient over

voltage, to reduce the current in low-frequency transient

suppressor network, to prevent resistors of transient

suppressor network to take off from line because of over

hot.

5. Saving