JP5731328B2 - Inverter device and MR device - Google Patents

Description

  The present invention relates to an inverter device including a plurality of inverter bridges connected in series, and an MR (Magnetic Resonance) device including the inverter device.

  Conventionally, the MR apparatus includes a gradient magnetic field generator. FIG. 1 schematically shows a configuration example of a gradient magnetic field generator. This gradient magnetic field generator is, for example, an inverter device including an inverter bridge 20 including a plurality of switching elements. A bus power supply 10 having a voltage Vbus (for example, 800 V) is connected to the input side of the inverter device, and a gradient coil 30 that is an inductance load is connected to the output side. A control unit 50 is further connected to the inverter bridge 20, and a current sensor 40 is connected to the gradient coil 30. The control unit 50 performs feedback control of the switching operation of the inverter bridge 20 so that the difference between the current It of the target current waveform and the current Ir of the actual current waveform due to the output of the current sensor 40 becomes small.

  Specifically, this feedback control is performed by selecting a switching element that performs substantial switching for transmitting power, and adjusting the on-duty ε when switching the selected switching element, thereby adjusting the output voltage. It is to control the sign and magnitude. In the example of FIG. 1, when switching elements Qa and Qb are selected and switching is performed in synchronization with an on-duty ε, the output voltage Vout becomes + ε · Vbus. Further, when the switching elements Qc and Qd are selected and switching is performed in synchronization with the on-duty ε, the output voltage Vout becomes −ε · Vbus.

  Here, consider the relationship between the current I of the gradient coil 30 and the output voltage Vout of the inverter bridge 20. If the current I is passed through the gradient coil 30 with a trapezoidal pulse waveform, the current I of the gradient coil 30 and the output voltage Vout of the inverter bridge 20 have a relationship as shown in FIG. When the current I and the voltage Vout have the same polarity, power is supplied from the inverter bridge 20 to the gradient coil 30, and when the polarities are opposite, power is regenerated from the gradient coil 30 to the inverter bridge 20. It will be.

  By the way, the current waveform desired to flow through the gradient coil 30 generally includes a steep rise and fall. In order to increase or decrease the current I at high speed, it is necessary to increase the absolute value of the output voltage Vout of the inverter bridge 20. In order to increase the absolute value of the output voltage Vout, it is necessary to increase the voltage Vbus of the bus power supply 10 connected to the input side of the inverter bridge 20.

  However, if the inverter bridge 20 is always driven by a high voltage bus power supply, power consumption increases due to internal resistance, a dummy load for stabilization, or the like, which is not preferable. In addition, the actual current waveform that flows through the gradient coil 30 generally has a flat portion, and the ratio of the steep rising and falling portions is not so large.

  Therefore, as one of the improvement measures, consider using an inverter bridge series circuit in which a plurality of inverter bridges having different input power supply voltages are connected in series, and changing the utilization ratio between the inverter bridges according to the required output voltage.

  For example, as shown in FIG. 3, the first inverter bridge 21 connected to the first bus power supply 11 having a relatively high power supply voltage Vbus1 (for example, 700V), and a voltage having a relatively low power supply voltage. An inverter bridge series circuit 25 is prepared in which a second inverter bridge 22 connected to a second bus power supply 12 that is Vbus2 (for example, 100 V) is connected in series. A gradient coil 30 is connected to the output side of the inverter bridge series circuit 25. And the control part 51 selects the switching element in each of the 1st and 2nd inverter bridges 21 and 22 so that the required output voltage Vout can be obtained according to the current waveform of the target gradient coil 30, The on-duty α and β are adjusted when the selected switching element is switched to control the output voltages V1 (= ± α × Vbus1) and V2 (= ± β × Vbus2) of the respective inverter bridges. (See Patent Document 1, FIG. 3, etc.).

  In this way, the first inverter bridge 21 by the first bus power supply 11 with the high voltage Vbus1 can be used only when necessary, and the gradient coil 30 can be used while suppressing power consumption. It becomes possible to flow a current with a target current waveform. Note that the on-duty α may be set to 0 so that the output of the first inverter bridge 21 is completely cut off.

Japanese Patent No. 4362176

  However, in such a gradient magnetic field generator, depending on the current waveform of the gradient coil 30, the balance between the inverter bridges when the inverter bridge series circuit 25 supplies power to the gradient coil 30, and the gradient coil 30. When power is regenerated in the inverter bridge series circuit 25, a phenomenon occurs in which the balance between the inverter bridges of the power is different.

  For example, as shown in FIG. 4, a case is considered in which a current is passed through the gradient coil 30 with a triangular wave current waveform in which the current value rises relatively slowly and then falls sharply.

  When the current I is gradually increased, the output voltage Vout only needs to be kept relatively small on the + (positive) side, so that only the second inverter bridge 22 with a low input power supply voltage or the main (main) ) And the first inverter bridge 21 having a high input power supply voltage can be rested. In this case, the power applied to the gradient coil 30 is relatively small, and the second inverter bridge 22 is mainly responsible.

  On the other hand, when the current I is fully increased and then decreased sharply, the output voltage Vout needs to be instantaneously increased on the − (negative) side. Therefore, the first and second inverter bridges 21 and 22 Must drive both. In this case, the electric power regenerated from the gradient coil 30 is relatively large, and the electric power is regenerated at a large rate to the first inverter bridge 21 that outputs a larger voltage.

  That is, in the first inverter bridge 21, a large amount of power is suddenly regenerated from a state where there is almost no power applied to the gradient coil 30. On the other hand, in the second inverter bridge 22, relatively small power is regenerated from a state in which relatively small power is applied to the gradient coil 30. That is, when the inverter bridge series circuit 25 supplies power to the gradient coil 30, the balance between the inverter bridges of the power, and when the power is regenerated from the gradient coil 30 to the inverter bridge series circuit 25, This means that the balance between power inverter bridges is different.

  In this case, in the first inverter bridge 21, the regenerated electric power is much higher than the electric power to be applied. Therefore, the first bus power supply 11 cannot absorb the surplus power, and the power supply voltage rises and is unstable. Will work.

  As described above, depending on the current waveform flowing through the gradient coil 30, the imbalance between the power supplied to the inverter bridge and the regenerated power may increase extremely. When this imbalance increases, the first bus power supply 11 and / or the second bus power supply 12 cannot absorb the imbalance, and the output voltages V1 and V2 cannot be controlled to the intended voltages. As a result, the bus power supply itself becomes unstable, and the current waveform of the gradient coil 30 is also distorted.

  Such a phenomenon is not limited to the gradient magnetic field generator of the MR device, and is an inverter device having a plurality of inverter bridges connected in series when an inductive load is driven with a desired current waveform. It is what happens.

  Due to such circumstances, in an inverter device including a plurality of inverter bridges connected in series, when the inductance load is efficiently driven by changing the utilization factor between the inverter bridges, the input power supply voltage of the inverter bridge is changed. A technique to stabilize it is desired.

  The invention of the first aspect is an inverter bridge series circuit in which a plurality of inverter bridges are connected in series on the output side, and at least one of the input power supply voltages of each inverter bridge is different from other input power supply voltages The bridge series circuit, the inductive load connected to the output side of the inverter bridge series circuit, and the output voltage of the inverter bridge series circuit are voltages that allow a current to flow through the inductive load with a desired current waveform. And a control unit that controls the on-duty of each of the plurality of inverter bridges, wherein the control unit converts the current value in the desired current waveform to positive / negative and current differential value positive / negative. The inverter bridge series circuit applies to the inductive load. Inverter devices for controlling the respective on-duties so as to correct the imbalance between the balance between inverter bridges of power and the balance between inverter bridges of power regenerated from the inductance load to the inverter bridge series circuit I will provide a.

  According to a second aspect of the invention, the inverter bridge series circuit includes a first inverter bridge having a relatively high input power supply voltage and a second inverter bridge having a relatively low input power supply voltage in series on the output side. An inverter device according to the first aspect, which is a connected circuit, is provided.

  According to a third aspect of the present invention, when the current value in the desired current waveform is positive and the current differential value is positive, the control unit decreases the on-duty of the first inverter bridge, and the second An inverter device according to the second aspect of the present invention that performs control to increase the on-duty of the inverter bridge is provided.

  According to a fourth aspect of the invention, the control unit increases the on-duty of the first inverter bridge when the current value in the desired current waveform is positive and the current differential value is negative, and the second An inverter device according to the second aspect or the third aspect is provided that performs control to reduce the on-duty of the inverter bridge.

  According to a fifth aspect of the invention, the control unit reduces the on-duty of the first inverter bridge when the current value in the desired current waveform is negative and the current differential value is negative, An inverter device according to any one of the second to third aspects that performs control to increase the on-duty of the inverter bridge is provided.

  According to a sixth aspect of the invention, the control unit increases the on-duty of the first inverter bridge when the current value in the desired current waveform is negative and the current differential value is positive. An inverter device according to any one of the second to fourth aspects is provided that performs control to reduce the on-duty of the inverter bridge.

  According to a seventh aspect of the invention from the first aspect, the control unit performs feedback control of the on-duty so that a difference between the desired current waveform and the current waveform of the inductive load is reduced. An inverter device according to any one of the aspects is provided.

  According to an eighth aspect of the invention, the switching elements constituting the inverter bridge are IGBTs (insulated gate / bipolar transistors) or GTOs (gate / turn-off thyristors), respectively. An inverter device according to any one aspect is provided.

  According to a ninth aspect of the invention, the inductive load is a gradient coil for MR imaging, and the desired current waveform is a current waveform for generating a gradient pulse for MR imaging. To an inverter device according to any one of the eighth aspects.

  The tenth aspect of the invention provides an MR apparatus including the inverter device of the ninth aspect.

  According to the invention of the above aspect, the control unit balances between the inverter bridges of the power supplied to the inductive load from the inverter bridge series circuit in which a plurality of inverter bridges are connected in series, and the inverter bridge series circuit from the inductive load. Since the on-duty of each inverter bridge is controlled so that the imbalance with the balance between the inverter bridges of the regenerated power is corrected, the unstable operation due to the imbalance of each inverter bridge can be suppressed. The input power supply voltage of each inverter bridge can be further stabilized.

It is a figure which shows schematically the structural example of the conventional gradient magnetic field generator. It is a figure which shows the 1st example of the relationship between the current waveform and voltage waveform in a gradient coil. It is a figure which shows roughly the structural example of the conventional improved gradient magnetic field generator. It is a figure which shows the 2nd example of the relationship between the current waveform and voltage waveform in a gradient coil. It is a figure showing roughly composition of a gradient magnetic field generator concerning an embodiment of an invention.

  Embodiments of the invention will be described below. However, this does not limit the invention.

  FIG. 5 is a diagram schematically showing the configuration of the gradient magnetic field generator (inverter device) according to the present embodiment.

  As shown in FIG. 5, the gradient magnetic field generator 100 includes an inverter bridge series circuit 25, a gradient coil 30, a current sensor 40, and a control unit 52.

  The inverter bridge series circuit 25 is a circuit in which a first inverter bridge 21 and a second inverter bridge 22 are connected in series on the output side. In this example, each of the first and second inverter bridges 21 and 22 is a full bridge type. A first bus power supply 11 having a relatively high voltage Vbus1 as a power supply voltage is connected to the input side of the first inverter bridge 21. A second bus power supply 12 having a relatively low voltage Vbus2 as a power supply voltage is connected to the input side of the second inverter bridge 22. Each of the first and second inverter bridges 21 includes a plurality of switching elements. The high voltage Vbus1 is, for example, 700V, and the low voltage Vbus2 is, for example, 100V. Examples of the switching element include an IGBT (insulated gate bipolar transistor), a GTO (gate turn-off thyristor), a power MOSFET (field effect transistor), and a power bipolar transistor. The switching frequency of the inverter bridge is, for example, about 50 to 100 kHz.

  A gradient coil 30 that is an inductive load is connected to the output side of the inverter bridge series circuit 25. The gradient coil 30 generates a gradient pulse magnetic field corresponding to the current waveform of the gradient coil 30.

  The current sensor 40 detects a current flowing through the gradient coil 30. As the current sensor 40, for example, a non-contact Hall element can be considered.

  The control unit 52 basically includes the first and second inverter bridges 21 and 22 so that the output voltage Vout of the inverter bridge series circuit 25 becomes a voltage at which a current flows through the gradient coil 30 with a desired current waveform. , The selection of the switching element and the adjustment of the on-duty of switching for the selected switching element are performed. The desired current waveform is a current waveform for causing the gradient coil 30 to generate a target gradient pulse magnetic field.

  Further, the control unit 52 assumes that the output voltage Vout of the inverter bridge series circuit 25 is not changed, and the inverter bridge series circuit 25 has a gradient based on the positive / negative of the current value and the positive / negative of the current differential value in a desired current waveform. Corrects the imbalance between the balance between the inverter bridges when power is supplied to the coil 30 and the balance between the inverter bridges when the power is regenerated from the gradient coil 30 to the inverter bridge series circuit 25. Adjust the on-duty of each inverter bridge.

  In this example, the on-duty of the inverter bridge is the product of the main factor and the sub factor, and the control unit 52 controls the main factor α and the sub factor A for the first inverter bridge 21 and the second inverter bridge 22. The on-duty is adjusted by determining the main factor β and the sub-factor B with respect to substantially real time. Note that the sub-factors A and B are both parameters that are scaled with 1 as a reference value.

  The controller 52 receives a desired current waveform of the gradient coil 30 necessary for generating a target gradient pulse magnetic field and a current waveform of the gradient coil 30 actually measured by the current sensor 40. The control unit 52 adjusts the main factors α and β according to a predetermined rule so that the difference between the desired current waveform and the actually measured current waveform becomes small.

For example, assuming that the output voltage Vout of the inverter bridge series circuit 25 assumed from the current It of the target current waveform is the voltage Vout1,
Condition a: When 100V ≧ Vout1> 0V, the switching elements Q1, Q2, Q5, Q6 are selected as switching targets, and the on-duty main factors α, β are set to α: β = 1: Adjust while holding at 9.

  Condition b: When 800V ≧ Vout1> 100V, switching elements Q1, Q2, Q5, Q6 are selected as switching targets, and main factors α, β of the on-duty are fixed at β = 0.8. adjust.

  When the condition c is 0> Vout1 ≧ −100V, the switching elements Q3, Q4, Q7, Q8 are selected as switching targets, the main factors α, β of the on-duty are set, and the ratio is α: β = 1. : Adjust while holding at 9.

  Condition d: When −100V> Vout1> −800V, switching elements Q3, Q4, Q7, and Q8 are selected as switching targets, and main factors α and β of the on-duty are fixed to β = 0.8. While adjusting.

  Further, the control unit 52 makes a combination of whether the current value It is positive or negative in the desired current waveform and whether the current differential value dIt / dt (that is, the slope coefficient when the current waveform is expressed by a mathematical expression) is positive or negative. In response, the sub-factor A constituting the on-duty of the first inverter bridge 21 and the sub-factor B constituting the on-duty of the second inverter bridge 22 are determined.

  For example, when the condition 1: current value It> 0 and the current differential value dIt / dt> 0, the polarities of the current I and the voltage Vout are the same, and the inverter bridge series circuit 25 changes to the gradient coil 30. Since power is applied, sub-factor A is lowered and sub-factor B is raised.

  Condition 2: When the current value It> 0 and the current differential value dIt / dt <0, the polarities of the current I and the voltage Vout are reversed, and power is supplied from the gradient coil 30 to the inverter bridge series circuit 25. Since it is regenerated, sub-factor A is raised and sub-factor B is lowered.

  Condition 3: When the current value It <0 and the current differential value dIt / dt <0, the polarities of the current I and the voltage Vout are the same, and power is supplied from the inverter bridge series circuit 25 to the gradient coil 30. Given that, subfactor A is lowered and subfactor B is raised.

  Condition 4: When the current value It <0 and the current differential value dIt / dt> 0, the polarities of the current I and the voltage Vout are reversed, and power is supplied from the gradient coil 30 to the inverter bridge series circuit 25. Since it is regenerated, sub-factor A is raised and sub-factor B is lowered.

  Thereby, when the inverter bridge series circuit 25 supplies power to the gradient coil 30, that is, when the above conditions 1 and 3 are satisfied, the contribution ratio of the first inverter bridge 21 having a high input power supply voltage tends to increase. Then, control for lowering the contribution rate is performed. Further, when the inverter bridge series circuit 25 receives power regeneration from the gradient coil 30, that is, when the above conditions 2 and 4 are satisfied, the rate of regeneration by the second inverter bridge 22 having a low input power supply voltage tends to increase. Therefore, the control to reduce the rate of regeneration is performed.

  As the control unit 52, for example, an IC such as a PLD or an ASIC can be considered.

  According to the gradient magnetic field generating apparatus 100 having such a configuration, the balance between the inverter bridges of the electric power that the inverter bridge series circuit 25 supplies to the gradient coil 30 and the inverter of the electric power that is regenerated from the gradient coil 30 to the inverter bridge series circuit 25. The imbalance with the balance between the bridges can be corrected, the unstable operation due to the imbalance of each inverter bridge can be suppressed, and the input power supply voltage of each inverter bridge can be further stabilized.

  Further, according to such a gradient magnetic field generator 100, the imbalance correction is performed actively by the control unit 52, so that a dummy load for stabilization can be made unnecessary or smaller. , Space saving and cost reduction are possible.

  The above embodiment is an example in which the inverter device according to the invention is applied to a gradient magnetic field generator for MR imaging. An MR device provided with such a gradient magnetic field generator is also an example of an embodiment of the invention. It is. The embodiments of the invention can be variously modified without departing from the spirit of the invention.

DESCRIPTION OF SYMBOLS 10 Bus power supply 11 1st bus power supply 12 2nd bus power supply 20 Inverter bridge 21 1st inverter bridge 22 2nd inverter bridge 30 Gradient coil 40 Current sensor 50-52 Control part 100 Gradient magnetic field generator (inverter apparatus)

Claims (10)

An inverter bridge series circuit in which a plurality of inverter bridges are connected in series on the output side, and at least one of the input power supply voltages of each inverter bridge is different from other input power supply voltages,
An inductive load connected to the output side of the inverter bridge series circuit;
A control unit that controls the on-duty of each of the plurality of inverter bridges so that an output voltage of the inverter bridge series circuit is a voltage that allows a current to flow through the inductance load with a desired current waveform. An inverter device,
Wherein the control unit includes a separate positive and negative current values of the desired current waveform, depending on the combination of the different sign of the current differential value, and the on-duty of the input supply voltage is relatively high inverter bridge, the input An inverter device that performs control to increase one of the on-duty of the inverter bridge whose power supply voltage is relatively low and to decrease the other .   The inverter bridge series circuit is a circuit in which a first inverter bridge having a relatively high input power supply voltage and a second inverter bridge having a relatively low input power supply voltage are connected in series on the output side. The inverter device according to 1.   The control unit decreases the on-duty of the first inverter bridge and increases the on-duty of the second inverter bridge when the current value in the desired current waveform is positive and the current differential value is positive. The inverter device according to claim 2 which performs control.   The controller increases the on-duty of the first inverter bridge and decreases the on-duty of the second inverter bridge when the current value in the desired current waveform is positive and the current differential value is negative. The inverter device according to claim 2 or 3, wherein control is performed.   The control unit lowers the on-duty of the first inverter bridge and increases the on-duty of the second inverter bridge when the current value in the desired current waveform is negative and the current differential value is negative. The inverter apparatus as described in any one of Claim 2 to 3 which performs control.   When the current value in the desired current waveform is negative and the current differential value is positive, the control unit increases the on-duty of the first inverter bridge and decreases the on-duty of the second inverter bridge. The inverter apparatus as described in any one of Claim 2 to 4 which performs control.   The inverter device according to any one of claims 1 to 6, wherein the control unit feedback-controls the on-duty so that a difference between the desired current waveform and the current waveform of the inductive load is reduced. .   The inverter device according to any one of claims 1 to 7, wherein the switching elements constituting the inverter bridge are each an IGBT (insulated gate bipolar transistor) or a GTO (gate turn-off thyristor). The inductance load is a gradient coil for MR imaging,
The inverter device according to any one of claims 1 to 8, wherein the desired current waveform is a current waveform for generating a gradient pulse for MR imaging.   An MR device comprising the inverter device according to claim 9.

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