JPH0118444B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an improvement of a coil power supply device for an electromagnet for a final stage accelerator (synchrotron) for accelerating electrons, protons, etc. to high energy. [Prior Art] In recent years, in the field of particle physics, accelerators that accelerate electrons, protons, etc. to high energies have come to be used as an important research tool. The synchrotron is used to generate the magnetic field for the final stage of the accelerator, and the coil power supply for the main electromagnet rapidly changes the load current in a fixed pattern and is operated repeatedly, with high precision.・High power factor and high reliability are required. As a power supply device for the coil of such an electromagnet, the one shown in FIG. 1 has conventionally been used. In Figure 1, 1 is an AC power supply, 2 is a power converter that converts AC to DC or DC to AC, 3a is a DC reactor for current smoothing, and 4 is an electromagnetic coil consisting of a resistor 4a and an inductance 4b. be. The operation of the conventional device will be explained based on FIG. In FIG. 1, the power converter 2 consists of a three-phase thyristor bridge, and by controlling the firing angle α of the thyristors constituting the bridge, the AC voltage input from the AC power source 1 can be adjusted to any positive or negative voltage. It is well known that continuous conversion to DC voltage is possible. By the way, the coil current i _n required in a synchrotron, for example, is a triangular wave as shown in FIG. 3a. Therefore, both ends of the coil 4 (P-N)
The voltage V _n to be applied to is V _n when the current starts up.
= L _n di _n /dt + R _n i _n and positive polarity (N is the reference potential), and the control angle α of the thyristor is operated at 90° or less. Also, the voltage required to reduce the current is
Since the polarity is opposite to V _n =-L _n di _n /d _t +R _n i _n , the thyristor is operated so as to delay the control angle α by 90° or more. In this way, by controlling the firing α of the thyristor of the power converter 2, a triangular wave current can be supplied to the coil 4. In addition, the DC reactor 3a
is for smoothing the voltage ripples generated by controlling the firing angle of the thyristor of the power converter 2, and passing a current with less ripple to the coil 4. [Problems to be Solved by the Invention] Incidentally, the coil power supply for the synchrotron electromagnet as described above requires highly accurate control of the set value of the coil current. For example, when starting up a triangular wave current, an accuracy of the order of ±10 ^-3 is required for the current setting value (triangular wave current reference) within a range of about a few percent to 100% of the maximum value of the coil current. Ru. On the other hand, in the above-mentioned conventional power supply device, the voltage ripple of the power converter 2 cannot be sufficiently attenuated by the DC reactor, especially in the current region around a few percent at the beginning of the rise of the triangular wave current, and the set value There was a problem in that it was not possible to obtain a coil current that followed the current with high precision. Therefore, when applied to a power supply device for a synchrotron, for example,
A problem occurred that made it impossible for the beam to enter the system. Note that the ripple of the current supplied to the coil 4 is
Although it is possible to attenuate by enlarging the DC reactor 3a, this is contrary to the control responsiveness and economical efficiency of the power converter 2, and is practically impossible. This invention was made in order to solve the above-mentioned problems of the conventional devices, and provides a power supply device that can obtain highly accurate coil current by attenuating the voltage ripple generated by a power converter to a minimum. It is intended to. [Means for Solving the Problems] A coil power supply device according to the present invention includes an LC filter that attenuates ripple voltage generated by a power converter and obtains the required coil current accuracy, and a resonance point of this LC filter. A filter device consisting of an RC filter that makes the voltage applied to the coil non-oscillatory is provided. [Operation] In this invention, when the frequency of the ripple voltage generated by the power converter is _r , the ratio _p / _r of the resonance frequency _p of the LC filter and the above _r is selected according to the required current accuracy, and , 1/ _p < R _p C _p between the reactance L _f of the LC filter, the resistance value R _p of the RC filter, and the capacitance C _p of the capacitor.
<π _p L _f C _p and the ripple voltage of the power converter is attenuated to a minimum. [Embodiment of the Invention] An embodiment of the invention will be described below. In FIG. 2, 1 is an AC power source, and 2 is a power converter made of a thyristor converter, which is composed of a forward converter 2a that converts AC to DC and an inverse converter 2b that converts DC to AC. The forward converter 2a and the inverse converter 2b each include a three-phase thyristor bridge. 3 is a filter for absorbing the voltage ripple output from the power converter and for initially charging the voltage necessary for starting up the current, and includes a DC reactor 3a, capacitors 3b, 3
c, and a resistor 3d. 4a and 4b are the resistance and inductance of the electromagnetic coil 4, respectively. 5 and 6 are fired when the coil current rises,
A switch, such as a gate turn-off thyristor, which is extinguished when the current falls; 7 and 8 are diodes which become conductive when the coil current falls; 9
1 is a current sensor such as a DC CT or a shunt that detects a coil current, and 1 to 8 above constitute the main circuit of the present coil power supply device. In FIG. 2, reference numeral 10 is a voltage sensor composed of a voltage divider or the like for detecting the voltage output from the power converter 2, 11 is activated by a trigger signal given from an external device (not shown), and a switch 5,
6 ignition and extinguishing timing and current reference circuit 12
This is a control timing generation circuit for generating a triangular wave current reference _iref by energizing the current reference iref. 13, 16,
18 is an adder for adding and subtracting control signals;
14 is a current controller, 15 is a coil voltage V _n
This is a voltage reference circuit that determines the output voltage reference V _ref based on the pre-estimated load characteristics and current reference i _ref
The error ε between the current reference i _ref generated by the adder 13 and the coil current i _n detected by the current sensor 9 is corrected by the temperature change of the current sensor 9 and the coil 4. be done. 17 is a voltage controller; 19 is a phase control circuit that determines the control angle α of the forward converter 2a and the inverse converter 2b; 20
is a gate circuit that generates a firing pulse to be sent to the forward converter 2a and the inverse converter 2b. 21 is a CT for detecting alternating current; 22 is an overcurrent limiter that is energized by the overload current detected by the CT 21 and operates to limit the output of the power converter 2. The above-mentioned circuits 12 to 19 and 22 can be constructed by analog circuits such as operational amplifiers, or digital circuits such as microprocessors and minicomputers. The above elements 9 to 22 constitute a control circuit of the present coil power supply device. FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram explaining the operation of the present invention. The operation of the present invention will be explained based on FIGS. 2 and 3. Factors that determine the accuracy of the current output from the coil power supply device are the voltage ripple generated by the power converter 2 and the followability (responsiveness) of the control circuit to the current reference i _ref . Now, if the required current accuracy is defined by the degree of tracking with respect to the current reference setting value, ε=|i _ref −i _n |/i _ref ...(1) However, ε: Accuracy of coil current ( Tolerance) i _ref : Coil current setting value i _n : Can be expressed as coil current. The part that requires the highest current accuracy in the electromagnetic coil is the rising portion of the triangular wave current, ie, the portion that is several percent of the maximum value of the coil current. In this part, for example, the current accuracy ε' required for an electromagnetic coil for a synchrotron is ε'≒1/100 |I _ref −I _M |/I _ref <10 ^-5 ...(2) However, I _ref : Maximum coil current setting value I _M : Maximum coil current value In equation (2), 1/100 is a rough numerical representation of several percent of the maximum coil current value, and
10 ^-5 or less is the current accuracy ε generally required for electromagnetic coils for synchrotrons.
is less than 10 ^-3 . The frequency of the triangular wave current of the electromagnetic coil is usually several Hz or less, and if high frequency ripple voltage does not occur in the output of the power converter 2, the required control can be achieved by devising the control of the power converter 2. Current accuracy can be obtained. However, when using a thyristor converter as a power converter to control the firing angle α of the thyristor and obtain the desired DC output voltage, a ripple voltage that is an integral multiple of the AC power source is always generated, and the current required by the electromagnetic coil is Accuracy is not satisfied. In the case of a three-phase bridge, the frequency _r of this voltage ripple is _r = 6 _s , where _s is the frequency of the AC power supply. The ripple △i _n of the coil current generated by this voltage ripple is generally expressed as 2π _r・L _n ≫ _{R n} , where the value of the inductor 4b of the coil 4 is L n and the value of the resistor 4a is R _n . Therefore, it is expressed as △i _n ≒△V/2π _r・L _n ……(3). Therefore, with respect to voltage ripple, the required current accuracy can be obtained by reducing the ripple value ΔV itself applied to the coil 4 and increasing the ripple frequency _r . For this purpose, the forward converter 2a and the inverse converter 2b of the power converter 2 are a combination of a plurality of three-phase bridges, so that the ripple value ΔV is small and the ripple frequency _r is large. For example, in a 12-phase converter that combines two 3-phase bridges and a 24-phase converter that combines four 3-phase bridges, the ripple value △V naturally decreases as the number of phases increases, but the ripple frequency _r , _r = 12, _r = 24. By increasing the number of phases of the power converter in this way, it is possible to attenuate the ripple current △i _n generated in the coil current to some extent, but it is also possible to reduce the ripple current △i _n so that it can be ignored in terms of current accuracy. In order to achieve this, it is necessary to provide a filter 3 at the output end of the power converter 2. If the value of the DC reactor 3a constituting the filter 3 shown in FIG. At both ends, the value △Vm is expressed by the following formula:
becomes. △Vm＝△V×(o/r) ² ...(4) However, _p = 1/2π√ Therefore, for example, in the case of a 24-phase converter, if the frequency _s of the AC power supply is 60Hz, the ripple frequency _r is
If the resonance frequency _p of the filter is selected to be 1/100 or less of _r , the voltage ripple generated by the power converter 2 will be 10 ^-5 or less at both ends of the coil 4, which fully satisfies the required accuracy of the coil current. can. In other words, in equation (3), the reactance Lm of the coil 4b is generally several tens to several hundreds of mH, and the thyristor converter is of 12 or 24 phase type for reasons of economy and manufacturability. The ripple frequency _r is 720Hz for 12 phases and 1440Hz for 24 phases,
In the end, the denominator on the right side of equation (3) becomes a value of 100 to 1000, and △i _n /I _ref ≒△V _n /(100 to 1000)・I _ref <10 ^-5 ……(
5) △i _n ≒△V _n / (100 to 1000) < 10 ^-5 ...(6). On the other hand, from equation (4), if _p / _r = 1/100, △
Since V _n is 10 ^-4 , △i _n ≒10 ^-4 / (100 to 1000) ≒ (10 ^-6 to 10 ^-7 ) ＜
10 ^-5 , which fully satisfies the required accuracy of the coil current. Note that the accuracy of the coil current is the sum of the error (accuracy) in the fundamental wave part of the triangular wave caused by power converter control and the ripple error (accuracy), so the error due to ripple should be one order of magnitude less than the required accuracy. It is necessary to keep it. Therefore, the ratio _p / _r of _p and _r should be set to an appropriate value depending on the required current accuracy, for example, as in the above embodiment.
To obtain a current accuracy of 10 ^-5 , it is necessary to keep _p / _r = 1/100 or less. On the other hand, if the required current accuracy is 10 ^-3 ,
By selecting _p / _r = 1/10 or less, △V _n = △V × 10 ^-2 , as in the above example, and △i _n ≒△V _n / (100 to 1000) ≒ 10 ^-2 /(100 to 1000) ≒ (10 ^-4 to 10 ^-5 ) < 10 ^-3 , so a current accuracy of 10 ^-3 is obtained. However, the LC filter shown above has _p
It is an unstable circuit that has a resonance point at the frequency of . Now, if the input voltage of the LC filter is e _i and the output voltage is e _p , then e _p = 1/SC _f /SL _f +1/SC _f e _i ...(7) = 1/1 + S ² L _f C _f e _i ...(8) Here, if we set S=jω, e _p =1/1−ω ² L _f C _f e _i ...(9) Therefore, as is clear from equation (9), In the case of ω ² 1/L _f C _f , e _p /e _i ≫1, and the output signal is larger than the input signal. That is,

A voltage with a frequency near [Equation] will be amplified and cause vibration, but since a triangular wave coil current flows, the power converter 2 generates a microscopic step-shaped output voltage. , for a step voltage containing all frequencies, the output of the filter, i.e.
The coil current oscillates and the required accuracy cannot be achieved. As a countermeasure against vibration of this filter, a filter in which only a resistor R _p is inserted in parallel with the capacitor 3b of the LC filter can be considered. The relationship of the input signals in this case is e _p =Z _f ′/SL _f +Z _f ′e _i ……(10) =1/1+L _f ／ _RO S+L _f C _f S ² e _i ……(11) = 1/1+2ξωS+ω ² S ² e _i ...(12) However, Z _f ′=R _p /1+SR _p C _f ω ² =L _f C _f 2ξω=L _f /R _p It is well known that in equation (10), the non-oscillation condition in which the output signal does not become larger than the input signal is ξ1.0. Therefore, from equation (13), in order for the filter characteristics to become stable and non-oscillating, Organizing this, we need the following conditions: π _p L _f R _p ……(14). However, although the above-mentioned filter can be a non-oscillatory and stable filter, the power loss due to R _p is large and it is not practical. Therefore, the above filter characteristics are applied only to currents with a frequency of _p or more, and the triangular wave coil basic current below that (frequency is about _p / 10) shows the characteristics of an LC filter, as shown in Figure 2. The filter 3 shown in FIG. 1 is composed of an LC filter and an RC filter. The relationship between the input and output signals of this filter is as follows. e _p =1+C _p R _p S/1+C _{p R p} S+(L _f C _f C _p )S ² +L _f C _f R _p C _p
S ³ e _i ……(15) e _p /e _i =1+τ _f S/1+τ _f S+{(
1/2πfo) ² +τ _f /πfo}S ² +τ _f /(2πfo) ² ) S ³ …
…(18) Here, L _f C _f = (1/2π _p ) ² τ _f = C _p R _p R _p = π _p L _f C _p = τ _f /π _p L _fThe above equation (16) is non-standard. Vibratory, that is, if e _p /e _i can be made less than 1 for all frequencies, the resistance R _p
This reduces power loss and provides a stable filter. Therefore, as a result of conducting a simulation using an electronic computer based on equation (16), it was found that the following conditions were necessary. R _p π _p L _f ...(17) R _p C _p 1/ _p ...(18) Expressing equations (17) and (18) together, 1/ _p R _p C _p π _p L _f C _p ...(19) Reactor 3 that constitutes filter 3 in Fig. 2
a, capacitors 3b, 3c, and various resistors L _f ,
C _f , C _p , and R _p are under the above condition of _p / _r = 1/100,
It has the relationship shown in equation (19), but _p / _r =
Even if it is set to 1/10, a stable filter can be obtained by providing the relationship of equation (19). To give a specific numerical example, if _p = 30Hz, τ _f ≒1/ _p ≒0.03,

From [Formula], if L _f = 1 (mH), then C _f = 1/(2π _p ) ² L _f ≒0.028(F) R _p = π _p L _f ≒0.094 (Ω) C _p = τ _f / π _p L _f ≒0.32(F). On the other hand, it is necessary to solve the problem of the coil current following the current reference i _ref through control. FIG. 3 shows the steady operation of the coil power supply device according to the present invention, and it is assumed that the previous cycle is completed at time t ₁ and the next new cycle begins, and this new cycle is completed at time t ₄ . . Generally, the power supply device for the electromagnet coil in an accelerator is linked to the control of other devices, and the
As shown in the figure, a trigger signal tg having a constant period τ as shown in FIG. 3d is supplied from the main controller. Based on this signal tg, this coil power supply device periodically performs a predetermined operation. That is, the control timing generating circuit 11 activated by the trigger signal tg generates signals as shown in FIG. 3 f and g, and supplies them to the current reference circuit 12. Current reference circuit 12 consisting of an integrator using an operational amplifier or a digital circuit using ROM, etc.
When the signal supplied from the control timing generation circuit 11 (FIG. 3 f) is binary logic "1", the output is 0, and the time is determined by "1" of the signal g (FIG. 3 g).
It rises from t ₁ and generates a current reference corresponding to i _nax at time t ₂ , and due to the binary logic "0" of signal g, the current reference which was i _nax at time t ₂ becomes 0 at time t ₃ .
stand down. In this way, the current reference circuit 12 generates a triangular wave coil current reference. The voltage V _p required to start up the coil current at time t ₁ can be approximately expressed as V _p ≒ L _n dim/d _t = L _n i _nax / t ₂ − t ₁ , and how accurate is it at this time? It is no exaggeration to say that whether this voltage V _p can be applied to the coil 4 or not determines the accuracy required of this coil power supply device. Therefore, in the present invention, in addition to the switches 5 and 6 that conduct between the filter 3 and the coil 4 at time t ₁ and the major loop that is based on the current reference i _ref , a minor loop that is based on the voltage reference V _ref is provided. It is set up. In other words, the time in Figure 3
At t _p, the fall of the coil current i _n of the previous cycle is completed. At this point, the diode 7,
8 is off, switches 5 and 6 are also off, and the voltage V _c of filter capacitors 3b and 3c is
is V ₃ as shown in FIG. 3c, which is generally different from the voltage V _p required for the rise of the coil current _in . Therefore, during the period when the current reference i _ref is 0, t ₀ −t ₁
In this device, the filter capacitors 3b, _3b ,
3c is charged to V _p . The voltage reference V _ref at this time is calculated by the voltage reference circuit 5 based on the load characteristics taking into account the coil current reference i _ref and the temperature θ _n of the coil 4 . At time _t1 , the control timing circuit 11 sends ON signals to the switches 5 and 6 as shown in FIG. 3i.
g _po is generated and supplied to switches 5 and 6. Therefore, the switches 5 and 6 are conductive, and the voltage V _p of the capacitors 3b and 3c adjusted in the I mode is applied to the coil 4, so that a highly accurate current is applied to the coil 4 at the beginning of the rise of the coil current. Can be supplied. The second mode, ie, the coil current ramp-up period, continues until time _t2 , and during this period, the device operates as follows. When the switches 5 and 6 become conductive at time _t1 , a current _i.sub.n as shown in FIG. 3a begins to flow through the coil 4. This current is detected by the current sensor 9, compared with the current reference i _ref by the adder 13, and the current controller 14 →
The forward converter 2a is energized through the adder 16→voltage controller 17→phase control circuit 19→gate circuit 20. On the other hand, the adder 16 includes the voltage reference circuit 1
A voltage reference V _ref generated from 5 is input and compared with the voltage of coil 4 detected by voltage sensor 10 . At this time, the voltage reference V _ref is generated based on the load characteristics that take into account the coil current reference i _ref and the temperature θ _n of the coil 4, and the error of the temperature θ _c of the current sensor 9 and the coil current i _n with respect to the current reference. The voltage is corrected by ε, etc., and output from the voltage reference circuit 15. That is, the load characteristics estimated in advance change depending on the temperature of the coil 4, and the apparent characteristics change depending on the temperature characteristics of the current sensor 9, so it is necessary to correct them. In this way, the adder 16 → voltage controller 17 → adder 18 → phase control circuit 19 → gate is connected so that the difference between the voltage detected by the voltage sensor 10 and V _ref based on the output V _ref of the voltage reference circuit 15 becomes 0. Since the circuit 20→forward converter 2a operates, the voltage V _n of the coil 4 can be determined accurately with faster control than the measurer loop for the current reference i _ref . Therefore, the error ε of the coil current i _n with respect to the current reference i _rer
Since the voltage reference V _ref is also small, it is only necessary to correct the voltage reference V ref, so that a highly accurate coil current can be obtained with respect to the current reference. The above voltage reference circuit 15
can be constructed by a function generator using an operational amplifier, a microprocessor, a minicomputer, etc. The maximum value i _nax of the coil current i _n at time t ₂
When the third timing is reached, the control timing generation circuit 11
A signal g _pff is generated which turns off switches 5 and 6 as shown in FIG. j. For the switches 5 and 6, semiconductor devices having a self-extinguishing ability such as transistors, gate turn-off thyristors, and electrostatic induction thyristors, or thyristor devices having a commutation circuit can be used. The switches 5 and 6 are immediately turned off by the signal g _pff . At this time, the inductance 4b of the coil 4
The polarity of the voltage generated in the second mode is opposite to that in the first mode, and is larger than the output voltage V _c of the filter 3, so that the diodes 7 and 8 are conductive. this time
The period from time t ₂ to time t ₃ is the second mode, and the energy accumulated in the coil 4 in the second mode is converted into AC in the loop of coil 4 → diode 7 → DC reactor 3a → inverter 2b → diode 8 → coil 4. Regenerate to power supply 1. Therefore, the coil current i _n can be controlled to follow the current reference i _ref by the operation of the control circuit constituted by the above-mentioned 9 to 22 so that it becomes 0 at time t ₃ . From time _t3 , the first mode starts again, and the mode shifts to the above-mentioned first mode and second mode. In this manner, the present coil power supply device repeatedly operates the above operation at a period τ. In the above embodiment, the AC power supply 1 and the power converter 2 consisting of a forward converter 2a and an inverse converter, each based on a three-phase thyristor bridge, have been described, but as shown in FIG. Using a DC power supply 23 instead of the AC power supply, and instead of the power converter 2,
For example, a four-quadrant chopper 24 consisting of a single-phase bridge of transistors can also be used. In addition to the transistor 24, a gate turn-off thyristor, an electrostatic induction thyristor, etc. can also be used. In addition, as shown in FIG.
By connecting diodes 5a, 6a in antiparallel to diodes 6 and connecting switches 7a, 8a in antiparallel to diodes 7, 8, a current can also flow through the coil 4 with a polarity opposite to that of the above embodiment. As described above, according to the present invention, a filter device that attenuates the ripple voltage generated by controlling a thyristor converter is provided by an LC filter consisting of a reactor L _f , a capacitor C _f , and a resistor R _p .
Consists of an RC filter consisting of a capacitor C _p ,
When the frequency of the ripple voltage is _r , the ratio between the resonant frequency _p of the LC filter and the above _r is selected according to the required current accuracy, and
Since the values of each reactor, capacitor, and resistor are selected so that 1/ _p < R _p C _p < π _p L _f C _p holds, voltage ripple can be attenuated to a minimum with a stable circuit. , has the effect of obtaining highly accurate coil current.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional coil power supply device, FIG. 2 is a diagram showing a coil power supply device according to an embodiment of the present invention, FIG. 3 is a diagram explaining the operation of the present invention, and FIG. 4 is a diagram showing a coil power supply device according to an embodiment of the present invention. FIG. 5 is a diagram showing another embodiment of the present invention. In the figure, 1 is an AC power supply, 2 is a power converter,
2a is a forward converter, 2b is an inverse converter, 3 is a filter, 3a is a DC reactor, 3b, 3c are capacitors, 3d is a resistor, 4 is a coil, 4a is the resistance of the coil, 4b is the inductance of the coil, 5, 6 is a switch, 7 and 8 are diodes, 9 is a current sensor, 10 is a voltage sensor, 11 is a control timing generation circuit, 12 is a current reference circuit, 13, 16, 18
is an adder, 14 is a current controller, 15 is a voltage reference circuit, 17 is a voltage controller, 19 is a phase control circuit, 20 is a goot circuit, 21 is a CT, 22
is an overcurrent limiter. 23 is a DC power supply, 24
is Chiyotsupa. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A thyristor converter for converting alternating current to direct current, which is formed by bridge-connecting a plurality of thyristor elements, and a switch element provided between a coil serving as a load, and a switch element and the above-mentioned thyristor converter. an LC filter consisting of a reactor L _f and a capacitor C _f and an RC filter consisting of a resistor R _p and a capacitor C _p , which are provided between the thyristor converter and attenuate the ripple voltage generated by the control of the thyristor converter; a current detector that detects the current flowing through the coil; a current controller that receives a current deviation signal between the current value detected by the current detector and a current reference and generates a control signal according to the current deviation signal; a voltage detector that detects the voltage applied to the coil; a phase control circuit that generates a phase control signal based on a voltage deviation signal between the voltage value detected by the voltage detector and a voltage reference; and the current deviation signal; It is equipped with a gate circuit that fires the plurality of thyristor elements according to the phase control signal of the phase control circuit, and when the frequency of the ripple voltage of the thyristor converter is _r , the resonance frequency of the LC filter is _p = 1/2π√ _f Select the ratio _p / _r of _f and the above _r according to the required current accuracy, and also select the above resistor R _p and capacitor.
A power supply device for a coil, characterized in that the value of C _p is selected to satisfy 1/ _p < R _p C _p < π _p L _f C _p .