CN115189560A - Bipolar multi-flat-top magnetic field current sequence generation device and control method - Google Patents

Bipolar multi-flat-top magnetic field current sequence generation device and control method Download PDF

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CN115189560A
CN115189560A CN202210656428.6A CN202210656428A CN115189560A CN 115189560 A CN115189560 A CN 115189560A CN 202210656428 A CN202210656428 A CN 202210656428A CN 115189560 A CN115189560 A CN 115189560A
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voltage
current
energy storage
bridge arm
storage capacitor
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丁洪发
张聃帝
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H02M1/322—Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock

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Abstract

The invention discloses a bipolar multi-flattop magnetic field current sequence generating device and a control method, and belongs to the technical field of power electronics and the field of repeated flattop magnetic fields. The device comprises: the high-voltage bus pre-stage circuit comprises a high-voltage bus pre-stage circuit, a high-voltage energy storage capacitor, a low-voltage bus pre-stage circuit, a low-voltage energy storage capacitor group, a multi-level switch network, a high-voltage switch circuit, a first bridge arm, a second bridge arm and an inductive load arranged between the middle points of the first bridge arm and the second bridge arm. According to the invention, the low-voltage energy storage capacitor group and the high-voltage energy storage capacitor are simultaneously arranged at two ends of the H bridge to respectively provide high voltage and different low voltage for the inductive load, the level value closest to the load voltage is output through the multi-level switch network, and the current conversion rate can be reduced while the current flat top value is maintained, so that the switching frequency is reduced, the heating of devices is further reduced, and the reliability of the system is increased.

Description

Bipolar multi-flat-top magnetic field current sequence generation device and control method
Technical Field
The invention belongs to the technical field of power electronics and the field of repeated flat-top magnetic fields, and particularly relates to a bipolar multi-flat-top magnetic field current sequence generation device and a control method.
Background
The strong magnetic field is used as an extreme environment, and provides many opportunities for discovering new properties and new phenomena of substances for scientific research in the fields of physics, chemistry, biology and the like.
The pulsed flat-top high-intensity magnetic field (also called long pulsed magnetic field) is a high-intensity magnetic field with the advantages of high stability of the steady-state high-intensity magnetic field and low energy consumption (compared with the steady-state magnetic field) of the pulsed high-intensity magnetic field, can keep higher stability in the flat-top stage, provides a high-intensity magnetic field with small ripple factor, small electromagnetic interference and small power consumption to provide conditions for corresponding scientific experiments, and can effectively reduce the influence of the magnetic field on the environment of experimental equipment and a measurement and control system. The method can be widely applied to a plurality of scientific research fields such as nuclear magnetic resonance, neutron diffraction, magnetic refrigeration, electromagnetic forming, electromagnetic welding, terahertz, electromagnetic emission, plasma compression and the like and industrial production fields. The method is an important direction for the research and development of future magnetic fields, and the main research direction is to pursue larger magnetic field strength, longer flat-top pulse width, higher repetition frequency and higher stability.
In the field of medical application, such as transcranial magnetic stimulation transmitting coils and gradient coils for magnetic resonance imaging, a plurality of flat-top magnetic field current pulses with different current values and durations are often required to be continuously introduced into the coils, which can be called as a magnetic field current sequence, and each current pulse in the magnetic field current sequence is expected to reach a set value quickly, so that heating is reduced, and the energy utilization rate is increased.
In a traditional method, a high-voltage H bridge is often used, and a load is discharged through a high-voltage capacitor connected with a preceding stage circuit of a high-voltage bus, so that the current can rapidly rise and fall. However, in the stage of maintaining the flat-top current, since the high-voltage capacitor is still connected to the load, the rising and falling rate of the current is very fast, and in order to control the flat-top current in a relatively accurate current range (generally within one thousandth), the switching device must be turned on and off at a very high switching frequency for pulse width modulation, which causes very large switching loss and severe heat generation of the switching device, thereby affecting the lifetime and reliability of the switching device. If the switching frequency is to be reduced, the switching frequency must be shared by the series-parallel connection of the switching devices, which in turn increases the size and complexity of the whole circuit.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a bipolar multi-flat-top magnetic field current sequence generation device and a control method, and aims to reduce the loss of a switching device and improve the reliability of the device.
To achieve the above object, according to one aspect of the present invention, there is provided a bipolar multi-mesa magnetic field current sequence generating device, comprising: the high-voltage bus pre-stage circuit comprises a high-voltage bus pre-stage circuit, a high-voltage energy storage capacitor, a low-voltage bus pre-stage circuit, a low-voltage energy storage capacitor group, a multi-level switch network, a high-voltage switch circuit, a first bridge arm, a second bridge arm and an inductive load arranged between the middle points of the first bridge arm and the second bridge arm;
the high-voltage bus pre-stage circuit is connected with a high-voltage energy storage capacitor in parallel, the high-voltage switch circuit is connected with the high-voltage energy storage capacitor in series, and two ends of the high-voltage energy storage capacitor are respectively connected to two ends of the first bridge arm and the second bridge arm;
the low-voltage bus preceding-stage circuit is connected with the low-voltage energy storage capacitor bank in parallel, and two ends of the multi-level switch network are connected to two ends of the first bridge arm and the second bridge arm respectively;
the low-voltage energy storage capacitor bank comprises N energy storage capacitors connected in series, the N energy storage capacitors connected in series divide the voltage of the low-voltage energy storage capacitor bank into N continuous voltage intervals, the multi-level switch network comprises a first clamping diode and N switch units connected in series, the first clamping diode is connected with the N switch units in series, and N is greater than 1,N switch units which are connected with the N energy storage capacitors in the low-voltage energy storage capacitor bank in a one-to-one corresponding manner in series.
Furthermore, each switch unit comprises an IGBT and a second clamping diode, and capacitors in the low-voltage energy storage capacitor bank are connected in series with the IGBTs and the second clamping diodes in the switch units in a one-to-one correspondence mode to form a pi-type network structure.
Further, the voltage V of the low-voltage energy storage capacitor bank L And voltage V of the high-voltage energy storage capacitor H Respectively satisfy:
V L ＞I max R m
Figure BDA0003688085740000031
wherein, I max A maximum current value, R, output for said device m Resistance of an inductive load, L m An inductance value of an inductive load, c min Is the minimum value of the rate of change of current.
Further, the first bridge arm comprises a first upper bridge arm (7) and a first lower bridge arm (8) which are connected in series, and the second bridge arm comprises a second upper bridge arm (9) and a second lower bridge arm (10) which are connected in series;
the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm respectively comprise a discharging branch and a current storage compensation branch, and the discharging branch and the current storage compensation branch are connected in parallel in an opposite direction.
Further, the discharging branch comprises an IGBT, and the current storage compensation branch comprises a freewheeling diode.
Further, the high-voltage switch circuit comprises an IGBT and a freewheeling diode, and the IGBT and the freewheeling diode are connected in anti-parallel.
Further, the capacitance of the N energy storage capacitors connected in series in the low-voltage energy storage capacitor bank is equal.
The control circuit controls the on-off of all the switch tubes in the multi-level switch network, the high-voltage switch circuit, the first bridge arm and the second bridge arm.
According to another aspect of the present invention, there is provided a control method of the apparatus according to any one of the first aspect, comprising:
before discharging, reading the current magnitude I of each flat-top current in the set magnetic field current sequence k And duration of each flat-top current Δ T k Wherein k =1,2, … …, N;
in the discharging process, when two adjacent flat-top currents are switched, the high-voltage switch circuit is conducted, the magnitude of the two flat-top current values is judged, and the two flat-top current values are recorded as I k 、I k+1 If I is k ＜I k+1 The first upper bridge arm and the second upper bridge arm are conducted, the positive voltage of the high-voltage energy-storage capacitor is applied to two ends of the inductive load, and the power is suppliedThe flow rises; if I k ＞I k+1 The first lower bridge arm and the second lower bridge arm are conducted, reverse voltage of the high-voltage energy storage capacitor is applied to two ends of the inductive load, and current is reduced;
when each flat-top current state is detected, the high-voltage switch circuit is switched off, and the current magnitude I of each flat-top current is determined k Determining a steady-state voltage I of an inductive load k R m Corresponding voltage intervals in the N continuous voltage intervals of the low-voltage capacitor bank enable corresponding switch units in the multi-level switch network to be conducted, corresponding voltage is provided for an inductive load, and each flat-top current state is maintained within a set fluctuation range until a set duration time delta T is reached k 。
Further, during each plateau current state, each plateau current state is maintained by hysteresis modulation.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) The invention discloses a bipolar multi-flat-top magnetic field current waveform sequence generation device and a control method, wherein a low-voltage energy storage capacitor group and a high-voltage energy storage capacitor are arranged at two ends of an H bridge simultaneously, the high-voltage energy storage capacitor provides high voltage for a load to realize rapid rise and fall of current, the low-voltage energy storage capacitor group is used for providing different low voltages, a level value closest to the load voltage is output through a multi-level switch network, and the current flat-top value is maintained while the current conversion rate can be reduced, so that the switching frequency is reduced, the heating of a device is further reduced, and the reliability of a system is increased.
(2) By connecting the discharging branch and the current storage compensation branch in reverse parallel, on the basis of the generation of a multi-flattop magnetic field current sequence, the bipolar current of positive current and negative current can be realized, and the application scene is wider.
Drawings
FIG. 1 is a schematic diagram of a circuit for generating an adjustable bipolar multi-mesa current waveform sequence according to an embodiment of the present invention;
FIG. 2 is a circuit topology diagram for generating an adjustable bipolar multi-mesa current waveform sequence in accordance with an embodiment of the present invention;
FIG. 3 is a schematic diagram of typical waveforms of an adjustable bipolar multi-mesa current waveform sequence in an embodiment of the present invention.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:
the method comprises the following steps of 1-a high-voltage bus preceding stage circuit, 2-a high-voltage energy storage capacitor, 3-a low-voltage bus preceding stage circuit, 4-a low-voltage energy storage capacitor group, 5-a multi-level switch network, 6-a high-voltage switch circuit, 7-a first upper bridge arm, 8-a first lower bridge arm, 9-a second upper bridge arm, 10-a second lower bridge arm and 11-an inductive load.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the present invention, the terms "first", "second", and the like in the description and the drawings are used for distinguishing similar objects, and are not necessarily used for describing a particular order or sequence.
As shown in fig. 1 and fig. 2, the bipolar multi-flattop magnetic field current waveform sequence generating device of the present invention mainly comprises:
the system comprises a high-voltage bus preceding-stage circuit 1, a high-voltage energy storage capacitor 2, a low-voltage bus preceding-stage circuit 3, a low-voltage energy storage capacitor group 4, a multi-level switch network 5, a high-voltage switch circuit 6 and an H bridge;
the H bridge comprises a first bridge arm, a second bridge arm and an inductive load 11 arranged between the middle points of the first bridge arm and the second bridge arm;
the high-voltage bus pre-stage circuit 1 is connected with the high-voltage energy-storage capacitor 2 in parallel, and the high-voltage switch circuit 6The high-voltage bus pre-stage circuit 1 is connected with the high-voltage energy storage capacitor 2 in series, and two ends of the high-voltage energy storage capacitor 2 are connected to two ends of the first bridge arm and the second bridge arm in parallel, wherein the high-voltage bus pre-stage circuit 1 is used for providing high voltage V for the high-voltage energy storage capacitor 2 H ；
The low-voltage bus preceding-stage circuit 3, the low-voltage energy storage capacitor bank 4 and the multi-level switch network 5 are connected in parallel and then connected to two ends of the first bridge arm and the second bridge arm in parallel, and the low-voltage bus preceding-stage circuit 3 is used for providing low voltage V for the low-voltage energy storage capacitor bank L The low-voltage energy storage capacitor group 4 comprises N low-voltage energy storage capacitors connected in series, and the N low-voltage energy storage capacitors connected in series are used for converting the low voltage V L Division into 0-V L N consecutive voltage intervals in between; the multi-level switch network 5 comprises a first clamping diode and N switch units connected in series, wherein the first clamping diode is connected in series with the N switch units connected in series, and N more than 1,N switch units are connected in series with N energy storage capacitors in the low-voltage energy storage capacitor group 4 in a one-to-one correspondence manner. Specifically, each switch unit comprises an IGBT and a second clamping diode, and capacitors in the low-voltage energy storage capacitor group 4 are connected in series with the IGBTs and the second clamping diodes in the switch unit in a one-to-one correspondence manner to form a pi-type network structure, that is, one low-voltage energy storage capacitor in the low-voltage energy storage capacitor group, the IGBT in one switch unit and the second clamping diode form a pi-type network structure.
The first bridge arm comprises a first upper bridge arm 7 and a first lower bridge arm 8 which are connected in series, the second bridge arm comprises a second upper bridge arm 9 and a second lower bridge arm 10 which are connected in series, the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm respectively comprise a discharging branch and a current storage compensation branch, and the discharging branch and the current storage compensation branch are connected in reverse parallel;
specifically, the high-voltage energy storage capacitor 2 is a high-voltage energy storage capacitor C H (ii) a Preferably, the N low-voltage energy storage capacitors connected in series have the same capacitance parameter, and the voltage V of the low-voltage energy storage capacitor group is adjusted L Divided into N equal voltage intervals.
When the high-voltage switch circuit 6 is in a conducting state, high voltage is provided for an inductive load through the high-voltage energy storage capacitor 2, so that current can quickly rise and fall; when the high-voltage switch circuit 6 is in a disconnected state, the multi-level switch network 5 is in a working state, namely, the low-voltage bus is divided by the low-voltage energy storage capacitor group, and when the load steady-state voltage falls in a corresponding voltage interval, corresponding switch units in the multi-level switch network work to provide corresponding low voltage for the inductive load.
The high-voltage switch circuit 6 includes an IGBT and a freewheeling diode, and the IGBT and the freewheeling diode are connected in reverse parallel, and the high-voltage output and the low-voltage output are switched by turning on and off the high-voltage switch circuit 6.
The discharging branch comprises an IGBT, and the current storage compensation branch comprises a freewheeling diode.
The on-off of all the switch tubes is controlled by a control circuit, in the embodiment, the control circuit is an upper computer, and for convenience of description, the reference positive direction of the load current is shown in fig. 1 and fig. 2. Before discharging, the upper computer reads the current values of a plurality of flat-top currents in the required current sequence and the information of the duration time of each flat-top current. During discharge, the circuit has four states: a current-up state, a current-down state, a current-hold state, and a rest state. When the high-voltage switch circuit 6, the first upper bridge arm and the second lower bridge arm are conducted, the inductive load bears the high voltage V of the positive high-voltage energy-storage capacitor H The load current will rise rapidly, and the current rise state is at this moment; when the high-voltage switch circuit 6, the second upper bridge arm and the first lower bridge arm are conducted, the inductive load bears the high voltage-V of the reversed high-voltage energy-storage capacitor H The load current will drop rapidly, and the current drop state is at this moment; when the high-voltage switch circuit 6 is turned off and the multi-level switch network works, the voltage born by the inductive load can be rapidly switched within a certain range, and the current continuously rises and falls within a set error range (fluctuation amplitude) so as to maintain the current, namely a current maintaining state, namely a flat-top current state. When all the switches are closed, namely all the switch tubes in the multi-level switch network, the high-voltage switch circuit, the first bridge arm and the second bridge arm are closed, the current in the circuit is 0, the load bearing voltage is 0, the current can be maintained at 0, and the circuit is in a resting state at the moment. The circuit will be at four according to the read current sequenceIn which states it switches to output the desired sequence of currents. This circuit can also output a triangular wave if the time for the flat top current state is set to 0.
Specifically, in this embodiment, the low-voltage energy storage capacitor bank includes three low-voltage capacitors as an example for specific description. In the whole topology, the preceding stage circuit of the high-voltage bus can be regarded as the voltage V H The voltage source of the low-voltage bus pre-stage circuit can be regarded as the voltage V L The low-voltage energy storage capacitor bank comprises C connected in series L1 To C L3 The multi-level switching network comprises three IGBTs (S) L1 To S L3 ) And four clamping diodes (D) L1 To D L4 ) The high-voltage switch circuit comprises a high-voltage switch S H And its freewheeling diode D H The inductive load comprises a load resistor R connected in series m And an inductance of L m The first upper bridge arm comprises an IGBT switching tube T 1 And a reverse parallel freewheeling diode D 1 The first lower bridge arm comprises an IGBT switching tube T 2 And a reverse parallel freewheeling diode D 2 The second upper bridge arm comprises an IGBT switching tube T 3 And a reverse parallel freewheeling diode D 3 The second lower bridge arm comprises an IGBT switching tube T 4 And a reverse parallel freewheeling diode D 4 . It should be noted that, in other embodiments, the low-voltage energy storage capacitor group may also be other multiple low-voltage capacitors connected in series, the structure of the multi-level switch network changes according to the number of capacitors of the low-voltage energy storage capacitor group, one low-voltage capacitor is added to each series connection of the low-voltage energy storage capacitor group, and a switch unit connected in series is correspondingly added to the multi-level switch network, that is, an IGBT and a second clamping diode are added, where the added low-voltage capacitor, the added IGBT and the second clamping diode are connected in a pi-type network.
In practical design, the circuit parameter design needs to consider the following aspects:
the maximum current value output by the multi-flat-top current waveform sequence generating device under the normal working condition is set as I max In order to make the circuit control the rising and falling of the current to maintain the stability of the current in the flat-top current maintaining stage, the low-voltage bus pre-stage circuitThe voltage must be larger than the load steady-state voltage when the output current takes the maximum value, namely the voltage V of the front-stage circuit of the low-voltage bus L The requirements are as follows:
V L ＞I max R m (1)
setting the waveform requirement for switching between different plateaus to have a minimum rate of change of current (including rise and fall) of c min The voltage V of the preceding stage circuit of the high-voltage bus H Need to satisfy
Figure BDA0003688085740000081
Wherein i m Is the current value of the inductive load,
Figure BDA0003688085740000082
indicating the derivation of the current value of an inductive load, R m Resistance of an inductive load, L m The inductance value of the inductive load.
The specific technical solution of the present invention is described in the generation of a typical current waveform as shown in fig. 3, taking the direction of the load current in the figure as a reference direction, assuming that the stability of the flat top current must satisfy the fluctuation amplitude less than σ (percentage):
(1) Before each discharge, the upper computer reads the current magnitude I of each flat-top current in the set magnetic field current sequence (i.e. the current sequence of the waveform shown in FIG. 3) 1 To I 5 And the duration of each flat-top current, Δ T 1 To Δ T 5 If not continuous plateau current, the interval between plateaus is also read, e.g. plateau current duration Δ T 2 The flat-top and flat-top current duration of 3 The flat tops are discontinuous, and a time interval with 0 current is arranged in the middle.
(2) In the discharging process, when switching between different flat-top currents (i.e. in the current rising state or the current falling state) is performed, the magnitude between the two flat-top current values before and after the current rising state or the current falling state is determined to determine whether the current rises or falls next. If it is an ascending switch toNew plateau, i.e. the current of the latter plateau being greater than the current of the former plateau, e.g. from I 4 Switch to I 5 Then turn on S H 、T 1 And T 3 Inductive load L m And R m Bear the positive voltage + V of the high-voltage energy-storage capacitor H The current rises rapidly with a current rise rate of (V) H -i m R m )/L m (ii) a If the current is switched to a new plateau, i.e. the latter plateau current is smaller than the former plateau current, e.g. from I 1 Switch to I 2 Then turn on S H 、T 2 And T 4 Inductive load L m And R m Bear the reverse voltage-V of the high-voltage energy-storage capacitor H The current rapidly decreases at a current decrease rate of (-V) H -i m R m )/L m 。
(3) When in flat-top current state, S is closed H According to the current value I of the flat top current k (k =1,2,3,4,5) to determine the steady-state voltage I of the load k R m Within which voltage range of the low-voltage capacitor bank, in the embodiment, three capacitance parameters of the low-voltage capacitor bank are completely the same, so that the voltage V of the low-voltage bus is reduced L Equally dividing the data into three equal parts, and controlling a multi-level switch network to output 0,V L /3，2V L /3，V L Four voltages, by controlling the two half-bridges, -V can be output L ，-2V L /3，-V L /3，0，V L /3，2V L /3，V L There are seven kinds of voltage. For example, when in the first plateau current state, if the steady state voltage I of the load 1 R m Satisfies 2V L /3＜I 1 R m ＜V L While maintaining T 1 And T 4 Is turned on, at this time, S is turned on L3 The load is subjected to a voltage of V L The current will be equal to (V) L -I 1 R m )/L m The current rise rate of (2) slowly rises; when rising to I 1 At (1 +0.5 sigma), S is turned off L3 Opening S L2 The voltage born by the load is 2V L /3, current will be as follows (I) 1 R m -2V L /3)/L m Current reduction rate ofSlowly decreases when decreasing to I 1 (1-0.5. Sigma.), S is turned off L2 Opening S L3 The current rises again, and the process is repeated until the duration of the flat-top current reaches the specified value, the working process of the current values in other ranges is similar, if the current value I of the flat-top current is k In the reverse direction, the switch tube T is maintained 2 And T 3 And conducting.
Specifically, the method for controlling the bipolar multi-flat-top magnetic field current sequence generation device comprises the following steps:
before discharging, reading the current magnitude I of each flat-top current in the set magnetic field current sequence k And duration of each flat-top current Δ T k Wherein k =1,2, … …, N;
in the discharging process, when two adjacent flat-top currents are switched, the high-voltage switch circuit is conducted, the magnitude of the two flat-top current values is judged, and the two flat-top current values are respectively marked as I k 、I k+1 If I k ＜I k+1 The first upper bridge arm and the second upper bridge arm are conducted, positive voltage of the high-voltage energy storage capacitor is applied to two ends of the inductive load, and current rises; if I k ＞I k+1 The first lower bridge arm and the second lower bridge arm are conducted, reverse voltage of the high-voltage energy storage capacitor is applied to two ends of the inductive load, and current is reduced;
when each flat-top current state is detected, the high-voltage switch circuit is switched off according to the current magnitude I of each flat-top current k Determining a steady-state voltage I of an inductive load k R m Corresponding voltage intervals in N continuous voltage intervals of the low-voltage capacitor bank enable corresponding switch units in the multi-level switch network to be conducted, corresponding voltage is provided for the inductive load, and each flat-top current state is maintained within a set fluctuation range until a set duration time delta T is reached k 。
Wherein, when each flat-top current state is in, each flat-top current state is maintained through hysteresis modulation.
The waveform sequence generated by the device can be widely applied to the medical fields of transcranial magnetic stimulation, nuclear magnetic resonance imaging and the like, and the rapid rise and fall of the load current are realized by discharging the inductive load through the high-voltage energy storage capacitor, so that the switching between different current values is rapid; and in the current maintaining stage, the inductive load is connected with the low-voltage energy storage capacitor bank, and different flat-top current values are regulated and maintained through hysteresis modulation. And finally, a series of bipolar multi-flat-top magnetic field current waveform sequences with accurately adjustable current values and durations can be generated according to requirements. Compared with the traditional method, the method has the advantages that the control strategy is reliable and accurate, and due to the fact that the high-voltage capacitor and the low-voltage capacitor are arranged, when the circuit states are different, different voltages are provided for the inductive load by the high-voltage capacitor or the low-voltage capacitor, the high voltage is provided for the inductive load by the high-voltage energy storage capacitor, the current can be guaranteed to rise and fall rapidly, different low voltages are provided for the inductive load by the low-voltage energy storage capacitor in the current maintaining stage, the current conversion rate is reduced, the switching frequency of a switching device can be greatly reduced, heating of the device is reduced, and the reliability of the system is improved.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A bipolar multi-flattop field current sequence generating device is characterized by comprising: the circuit comprises a high-voltage bus preceding-stage circuit (1), a high-voltage energy storage capacitor (2), a low-voltage bus preceding-stage circuit (3), a low-voltage energy storage capacitor group (4), a multi-level switch network (5), a high-voltage switch circuit (6), a first bridge arm, a second bridge arm and an inductive load (11) arranged between intermediate points of the first bridge arm and the second bridge arm;
the high-voltage bus pre-stage circuit (1) is connected with the high-voltage energy storage capacitor (2) in parallel, the high-voltage switch circuit (6) is connected with the high-voltage energy storage capacitor (2) in series, and two ends of the high-voltage energy storage capacitor (2) are respectively connected to two ends of the first bridge arm and the second bridge arm;
the low-voltage bus preceding-stage circuit (3) is connected with the low-voltage energy storage capacitor bank (4) in parallel, and two ends of the multi-level switch network (5) are respectively connected to two ends of the first bridge arm and the second bridge arm;
the low-voltage energy storage capacitor bank (4) comprises N energy storage capacitors connected in series, the N energy storage capacitors connected in series divide the voltage of the low-voltage energy storage capacitor bank into N continuous voltage intervals, the multi-level switch network (5) comprises first clamping diodes and N switch units connected in series, the first clamping diodes are connected with the N switch units in series, and N is greater than 1,N switch units which are connected with the N energy storage capacitors in the low-voltage energy storage capacitor bank (4) in a one-to-one corresponding mode.
2. The device according to claim 1, wherein each switch unit comprises an IGBT and a second clamping diode, and the capacitors in the low-voltage energy-storage capacitor bank are connected in series with the IGBTs and the second clamping diodes in the switch units in a one-to-one correspondence to form a pi-type network structure.
3. The apparatus of claim 2, wherein the voltage V of the low voltage energy storage capacitor bank L And voltage V of the high-voltage energy storage capacitor H Respectively satisfy:
V L ＞I max R m
Figure FDA0003688085730000011
wherein, I max A maximum current value, R, output for said device m Resistance of inductive load, L m An inductance value of an inductive load, c min Is the minimum value of the rate of change of current.
4. A device according to claim 3, characterized in that said first bridge leg comprises a first upper bridge leg (7) and a first lower bridge leg (8) connected in series, and said second bridge leg comprises a second upper bridge leg (9) and a second lower bridge leg (10) connected in series;
the first upper bridge arm, the first lower bridge arm, the second upper bridge arm and the second lower bridge arm respectively comprise a discharging branch and a current storage compensation branch, and the discharging branch and the current storage compensation branch are connected in parallel in an opposite direction.
5. The apparatus of claim 4, wherein the discharge branch comprises an IGBT and the current storage compensation branch comprises a freewheeling diode.
6. The apparatus of claim 5, wherein the high voltage switching circuit comprises an IGBT and a freewheeling diode, the IGBT and freewheeling diode being connected in anti-parallel.
7. The apparatus of claim 1, wherein the N series-connected energy storage capacitors in the low voltage energy storage capacitor bank have equal capacitance.
8. The device according to claim 1, further comprising a control circuit that controls on and off of all switching tubes in the multi-level switching network, the high-voltage switching circuit, the first leg, and the second leg.
9. A method of controlling the apparatus of any one of claims 1-8, comprising:
before discharging, reading the current magnitude I of each flat-top current in the set magnetic field current sequence k And duration of each flat-top current Δ T k Wherein k =1,2, … …, N;
in the discharging process, when two adjacent flat-top currents are switched, the high-voltage switch circuit is conducted, the magnitude of the two flat-top current values is judged, and the two flat-top current values are recorded as I k 、I k+1 If I is k ＜I k+1 The first upper bridge arm and the second upper bridge arm are conducted, positive voltage of the high-voltage energy storage capacitor is applied to two ends of the inductive load, and current rises; if I k ＞I k+1 The first lower bridge arm and the second lower bridge arm are conducted, reverse voltage of the high-voltage energy storage capacitor is applied to two ends of the inductive load, and current is reduced;
when each flat-top current state is detected, the high-voltage switch circuit is turned off, and the current magnitude I of each flat-top current is determined k Determining a steady-state voltage I of an inductive load k R m Corresponding voltage intervals in N continuous voltage intervals of the low-voltage capacitor bank enable corresponding switch units in the multi-level switch network to be conducted, corresponding voltage is provided for inductive loads, and each flat-top current state is maintained within a set fluctuation range until a set duration time delta T is reached k 。
10. The control method of claim 9, wherein each plateau current state is maintained by hysteresis modulation at each plateau current state.
CN202210656428.6A 2022-06-10 2022-06-10 Bipolar multi-flat-top magnetic field current sequence generation device and control method Pending CN115189560A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116614018A (en) * 2023-07-19 2023-08-18 华中科技大学 Heavy frequency flat-top pulse magnetic field generating device
CN116707494A (en) * 2023-07-27 2023-09-05 华中科技大学 Multi-waveform magnetic field generating device and control method

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116614018A (en) * 2023-07-19 2023-08-18 华中科技大学 Heavy frequency flat-top pulse magnetic field generating device
CN116614018B (en) * 2023-07-19 2023-09-19 华中科技大学 Heavy frequency flat-top pulse magnetic field generating device
CN116707494A (en) * 2023-07-27 2023-09-05 华中科技大学 Multi-waveform magnetic field generating device and control method
CN116707494B (en) * 2023-07-27 2023-10-20 华中科技大学 Multi-waveform magnetic field generating device and control method

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