JP7524134B2 - Power Supplies - Google Patents

Description

The present invention relates to a power supply device that drives a capacitive load.

In recent years, dielectric elastomer actuators have been developed as free-form actuators in various fields such as haptics. Dielectric elastomer actuators are inexpensive to manufacture and are highly efficient at converting electrical energy into mechanical energy.

A dielectric elastomer actuator is a capacitive load with a capacitor structure, which generates a displacement according to the applied voltage. Therefore, it is necessary to apply a voltage according to the displacement to be generated. In other words, to drive a capacitive load, a power supply device is required that can arbitrarily control the voltage and can pass positive and negative currents. A power supply device with a bridge-configured output stage meets these conditions (see, for example, Patent Document 1).

Special Publication No. 2003-524361

However, power supplies with a bridge-configured output stage are often used as high-power power supplies (for example, the power supply in Patent Document 1 is intended for use in radio frequency bands for processing materials through induction heating, dielectric heating, and plasma excitation), and are not suitable for driving dielectric elastomer actuators as is. In other words, dielectric elastomer actuators are intended for use in devices that come into contact with the human body in the haptics field, devices for grasping products, and the like. Therefore, safety is considered important for power supplies that drive dielectric elastomer actuators.

The present invention was made in consideration of these problems, and its purpose is to provide a highly safe power supply device that can freely control the voltage and can pass both positive and negative currents.

In order to achieve the above object, the power supply device according to the present invention is configured as follows.
The power supply device of the present invention is a power supply device for driving a capacitive load, comprising a first power supply unit that outputs a DC voltage, and an input capacitor that is charged by the DC voltage from the first power supply unit, and a resonant second power supply unit that converts the DC voltage of the input capacitor into an AC voltage by on/off operation of bridge-connected switching elements and supplies it to the capacitive load, and regenerates the charge stored in the capacitive load to the input capacitor when the AC voltage drops, wherein the first power supply unit is configured with a smaller current capacity than the second power supply unit, and the overcurrent threshold at which the first power supply unit starts overcurrent protection is set to a lower value than the overcurrent threshold at which the second power supply unit starts overcurrent protection.

The power supply device of the present invention has the advantage that even if the capacitive load is short-circuited or the second power supply unit is broken, the load current flowing through the capacitive load is automatically suppressed to a small value, thereby ensuring safety.

1 is a block diagram showing a configuration of an embodiment of a power supply device according to the present invention; 2 is a diagram showing overcurrent protection characteristics by the first current control unit and the second current control unit shown in FIG. 1; 2 is a waveform diagram showing a sine wave output from the second power supply unit shown in FIG. 1 . 2 is a waveform diagram showing a sine wave output from the second power supply unit shown in FIG. 1 . 2 is a diagram showing the on/off states of a high-side switching element and a low-side switching element shown in FIG. 1 and a current path for charging and discharging a capacitive load. FIG. 2 is a waveform diagram showing a sine wave output from the second power supply unit shown in FIG. 1 . 2 is an equivalent circuit diagram of the capacitive load shown in FIG. 1 when a short-circuit fault occurs.

A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

Referring to FIG. 1, the power supply device 1 of this embodiment includes a first power supply unit 2 and a second power supply unit 3, and applies a positive or negative single-sided voltage and any voltage (DC, sine wave, square wave, etc.) to the capacitive load CL.

The first power supply unit 2 is a DC-DC converter that converts the input voltage Vin input from the DC power supply E to the input terminal Tin1 into a DC output voltage Vout1 and supplies it from the output terminal Tout1 to the second power supply unit 3. Note that while the first power supply unit 2 shown in FIG. 1 is an example configured as a flyback type switching power supply, it may be configured in other ways, such as a forward type.

The first power supply unit 2 includes a transformer 21, a switching element 22, an output rectifier smoothing circuit 23, a first voltage control circuit 24, a first current control circuit 25, and a driver 26.

The transformer 21 has a primary winding and a secondary winding, and the polarity of the primary winding and the polarity of the secondary winding are set to be opposite. The primary winding of the transformer 21 is connected between the positive terminal of the DC power source E and the switching element 22. As a result, the DC power source E is applied to the primary winding of the transformer 21 as the input voltage Vin.

The switching element 22 is, for example, an N-type MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The switching element 22 may be an IGBT (Insulated Gate Bipolar Transistor) or a BJT (Bipolar Transistor). The drain of the switching element 22 is connected to the primary winding of the transformer 21, and the source of the switching element 22 is connected to the ground terminal. As a result, the input voltage Vin is output to the secondary winding of the transformer 21 during the off period by the on/off operation of the switching element 22 connected via the primary winding of the transformer 21.

The output rectifier smoothing circuit 23 includes a rectifier diode D1 and an output capacitor Cout, and the output capacitor Cout is connected between both terminals of the secondary winding of the transformer 21 via the rectifier diode D1. As a result, the AC voltage induced in the secondary winding of the transformer 21 is rectified and smoothed by the output rectifier smoothing circuit 23, and is supplied to the second power supply unit 3 via the resistor R1 and the backflow prevention diode 4 as the DC output voltage Vout1.

Resistor R1 is a current detection resistor that detects the output current Iout1 (input current to the second power supply unit 3) output from the first power supply unit 2, and the voltage across it is input to the first current control circuit 25. Resistor R1 may also be provided on the low side.

The backflow prevention diode 4 is a diode for preventing the backflow of charge from the second power supply unit 3 to the first power supply unit 2, and has an anode connected to the output terminal Tout2 of the second power supply unit 3 and a cathode connected to the input terminal Tin2 of the first power supply unit 2.

The first voltage control circuit 24 is a circuit that generates a control signal that controls the on/off state of the switching element 22, and controls the output voltage Vout1 to a desired constant voltage using the control signal. The control signal generated by the first voltage control circuit 24 is input to the gate of the switching element 22 via the driver 26, and the switching element 22 is turned on and off based on the control signal.

The first current control circuit 25 monitors the output current Iout1 by the voltage across resistor R1, and has an overcurrent protection (OCP) function that controls the on/off of the switching element 22 via the driver 26 to limit the power supplied to the second power supply unit 3 when the output current Iout1 rises and reaches the overcurrent threshold I_oc1.

The overcurrent protection characteristics of the first current control circuit 25 are not particularly limited, and may be the drooping characteristics shown by the solid line in FIG. 2(a), the V-shaped characteristics shown by the dotted line in FIG. 2(a), or the V-shaped characteristics shown by the dashed line in FIG. 2(a).

The second power supply unit 3 is a resonant DC-AC converter with a bridge-configured output stage that converts the output voltage Vout1 of the first power supply unit 2 into an arbitrary (sine wave, rectangular wave, triangular wave, direct current, etc.) output voltage Vout2 and supplies it to a capacitive load CL. Note that while the second power supply unit 3 shown in FIG. 1 is configured as a half-bridge circuit, it may also be configured as a full-bridge circuit.

The second power supply unit 3 includes an input capacitor Cin, a Hi (high side) switching element 31, a Low (low side) switching element 32, a reactor L1, a second voltage control circuit 33, a second current control circuit 34, and a Hi/Low (high side/low side) driver 35.

The input capacitor Cin is, for example, an electrolytic capacitor, and its positive terminal is connected to the input terminal Tin2 (cathode of the backflow prevention diode 4) to which the output voltage Vout1 from the first power supply unit 2 is input, and its negative terminal is connected to the ground terminal. Note that the capacitance of the input capacitor Cin is preferably sufficiently large relative to the capacitance of the capacitive load CL.

The high-side switching element 31 and the low-side switching element 32 are, for example, composed of an N-type MOSFET. The high-side switching element 31 and the low-side switching element 32 may be an IGBT (Insulated Gate Bipolar Transistor) or a BJT (Bipolar Transistor). A series circuit (half-bridge circuit) of the high-side switching element 31 and the low-side switching element 32 is connected between the positive terminal of the input capacitor Cin and the ground terminal. The drain of the high-side switching element 31 is connected to the positive terminal of the input capacitor Cin, and the source of the high-side switching element 31 is connected to the drain of the low-side switching element 32, and the source of the low-side switching element 32 is connected to the ground terminal.

Diodes DH and DL are connected between the drain and source of the high-side switching element 31 and the low-side switching element 32, respectively. The cathodes of the diodes DH and DL are connected to the drains and the anodes to the sources. Note that, as in this embodiment, when the high-side switching element 31 and the low-side switching element 32 are configured, for example, with N-type MOSFETs, the diodes DH and DL can be parasitic diodes of the high-side switching element 31 and the low-side switching element 32.

The connection point X between the high-side switching element 31 and the low-side switching element 32 is connected to the output terminal Tout2 via a reactor L1 and a resistor R2. A capacitive load CL is connected between the output terminal Tout2 and the ground terminal.

Resistor R2 is a current detection resistor that detects the output current Iout2 output from the second power supply unit 3, and the voltage across it is input to the second current control circuit 34. Resistor R2 may also be provided on the low side.

The second voltage control circuit 33 is a circuit that generates a control signal that controls the on/off of the high-side switching element 31 and the low-side switching element 32, and controls the output voltage Vout2 to an arbitrary voltage by the control signal. The control signal generated by the second voltage control circuit 33 is input to the gates of the high-side switching element 31 and the low-side switching element 32 via the high/low driver 35, and the high-side switching element 31 and the low-side switching element 32 are turned on and off based on the control signal.

The second current control circuit 34 monitors the output current Iout2 using the voltage across resistor R2, and when the output current Iout2 reaches the overcurrent threshold I_oc2, it has an overcurrent protection (OCP) function that controls the on/off of the Hi-side switching element 31 and the Low-side switching element 32 via the Hi/Low driver 35 to limit the power supplied to the capacitive load CL.

The overcurrent threshold I_oc1 at which the first current control circuit 25 initiates overcurrent protection is set to a value lower than the overcurrent threshold I_oc2 at which the second current control circuit 34 initiates overcurrent protection, as shown in FIG. 2.

The characteristics of the overcurrent protection by the second current control circuit 34 are not particularly limited, and may be the drooping characteristics shown by the solid line in FIG. 2(b), the V-shaped characteristics shown by the dotted line in FIG. 2(b), or the V-shaped characteristics shown by the dashed line in FIG. 2(b).

In the second power supply unit 3, an LC filter circuit is formed by a reactor L1, an input capacitor Cin, and a capacitive load CL. As shown in FIG. 3, the high-side switching element 31 and the low-side switching element 32 are alternately turned on and off, and the duty ratio is controlled to output the desired output voltage Vout2. Note that the output voltage Vout2 shown in FIG. 3 is a waveform when a sine wave is output.

As shown in Figures 4 and 5, the on/off operation of the high-side switching element 31 and the low-side switching element 32 is performed with a dead time period (periods T1 and T3) in between, during which both are in the off state, in order to suppress through current when they are simultaneously on. From the top, Figure 4 shows the on/off state of the high-side switching element 31, the on/off state of the low-side switching element 32, the drain current of the high-side switching element 31, the drain current of the low-side switching element 32, and the reactor current of the reactor L1. Figure 5 shows the on/off states of the high-side switching element 31 and the low-side switching element 32 during periods T1 to T4b shown in Figure 4, and the current path that charges and discharges the capacitive load CL.

In the second power supply unit 3, during periods T1 and T2a shown in Figures 4 and 5, when it is desired to lower the voltage of the capacitive load CL (when the voltage is dropping), the charge stored in the capacitive load CL is extracted, and the extracted charge is regenerated as the regenerative current Ire to the input capacitor Cin. In other words, the second power supply unit 3 can reuse unnecessary charge.

In the power supply device 1 of this embodiment, the backflow prevention diode 4 prevents the backflow of charge from the second power supply unit 3 to the first power supply unit 2. This prevents the output voltage Vout1 of the first power supply unit 2 from increasing due to the regenerative energy of the regenerative current Ire. This improves dynamic regulation because the switching operation of the first power supply unit 2 is not stopped as the output voltage Vout1 increases.

The relationship between the input current to the second power supply unit 3, that is, the output current Iout1 of the first power supply unit 2, the output current Iout2 of the second power supply unit 3, and the regenerative current Ire is expressed as follows:
Iout1=Iout2−Ire (Formula 1)
It is expressed as:

In the case of a capacitive load CL, if there is no loss in the circuit, all the charge stored in the capacitive load CL is regenerated and returned to the input capacitor Cin, so charge can be exchanged between the input capacitor Cin and the capacitive load CL without loss. In this case, the current supply capacity required of the first power supply unit 2 is only to initially charge the input capacitor Cin of the second power supply unit 3, and thereafter the output current Iout1 of the first power supply unit 2 becomes zero.

In reality, due to energy consumption in the resistance components of the circuit and the capacitive load CL, output current Iout2 > regenerative current Ire, so it is necessary to supply current even after charging the input capacitor Cin. However, since the charge charged in the capacitive load CL is reused by the regenerative current Ire, as shown in Figure 6, the output current Iout1 of the first power supply unit 2 can be small compared to the output current Iout2 supplied to the capacitive load CL. Note that Figure 6 shows the waveform when a sine wave is output, where (a) shows the output voltage Vout2 of the second power supply unit 3, (b) shows the output current Iout2 of the second power supply unit 3, and (c) shows the input current of the second power supply unit 3 (output current Iout1 of the first power supply unit 2).

Therefore, the first power supply unit 2 can be configured with a smaller current capacity than the second power supply unit 3. And because the first power supply unit 2 can have a smaller current capacity than the second power supply unit 3, as described above, the overcurrent threshold I_oc1 at which the first power supply unit 2 starts overcurrent protection is set to a lower value than the overcurrent threshold I_oc2 at which the second power supply unit 3 starts overcurrent protection. This ensures safety even when the capacitive load CL has a short-circuit fault or when the second power supply unit 3 has a fault.

Figure 7 shows an equivalent circuit when the capacitive load CL is short-circuited, with a resistance component RL connected in parallel to the capacitive load CL. Under normal conditions, the resistance component RL has a negligible large value, but in the event of a short-circuit fault, it becomes too small to be ignored. The resistance component RL = 0 Ω represents a complete short-circuit fault state.

When the capacitive load CL has a short-circuit fault, part of the charge that should be regenerated is consumed by the resistance component RL, and the regenerative current Ire decreases. The smaller the resistance component RL, the smaller the ratio of the regenerative current Ire to the output current Iout2. Therefore, considering the above (Equation 1), the input current to the second power supply unit 3, i.e., the output current Iout1 of the first power supply unit 2, and the output current Iout2 of the second power supply unit 3 become approximately equal.

Here, the first power supply unit 2 is configured with a smaller current capacity than the second power supply unit 3, and the overcurrent threshold I_oc1 of the first power supply unit 2 is set to a value lower than the overcurrent threshold I_oc2 of the second power supply unit 3. Therefore, the output current Iout1 of the first power supply unit 2 is limited to the output current Iout1 of the first power supply unit 2, and even if the capacitive load CL is short-circuited or the second power supply unit 3 is broken, the load current flowing through the capacitive load CL is automatically suppressed to a small value close to I_oc1, ensuring safety.

As described above, this embodiment provides a power supply device 1 for driving a capacitive load CL, comprising a first power supply unit 2 that outputs an output voltage Vout1 (DC voltage), and an input capacitor Cin that is charged by the DC voltage from the first power supply unit 2, and a resonant second power supply unit 3 that converts the DC voltage of the input capacitor Cin into an AC voltage by on/off operations of a bridge-connected Hi-side switching element 31 and a Low-side switching element 32 and supplies the AC voltage to the capacitive load CL, and regenerates the charge stored in the capacitive load CL as a regenerative current Ire to the input capacitor Cin when the AC voltage drops, wherein the first power supply unit 2 is configured with a smaller current capacity than the second power supply unit 3, and the overcurrent threshold I_oc1 at which the first power supply unit 2 starts overcurrent protection is set to a lower value than the overcurrent threshold I_oc2 at which the second power supply unit 3 starts overcurrent protection.
With this configuration, even if the capacitive load CL experiences a short-circuit failure or the second power supply unit 3 fails, the load current flowing through the capacitive load CL is automatically suppressed to a small value close to I_oc1, ensuring safety and providing a highly safe power supply device that can arbitrarily control the voltage and pass positive and negative currents.
In addition, when the capacitive load CL is short-circuited and Iout2 flows a current equal to or greater than a predetermined current Ith, the switching element 22 of the first power supply unit 2 is turned off by latch detection, thereby further improving safety.
In addition, when the capacitive load CL has short-circuited and Iout2 has flowed a current equal to or greater than a predetermined current Ith, the high side switching element 31 of the second power supply unit 3 is turned off and the low side switching element 32 is turned on, thereby further improving safety.

Furthermore, in this embodiment, a backflow prevention diode 4 is provided to prevent a backflow of charge from the second power supply unit 3 to the first power supply unit 2 .
With this configuration, the switching operation of the first power supply unit 2 is not stopped in response to an increase in the output voltage Vout1, improving dynamic regulation.

It is clear that the present invention is not limited to the above-described embodiments, and that each embodiment may be modified as appropriate within the scope of the technical concept of the present invention. Furthermore, the number, position, shape, etc. of the above-described components are not limited to the above-described embodiments, and may be any number, position, shape, etc. that is suitable for implementing the present invention. The same components are denoted by the same reference numerals in each drawing.

1 Power supply device 2 First power supply unit 3 Second power supply unit 4 Reverse current prevention diode 21 Transformer 22 Switching element 23 Output rectifier smoothing circuit 24 First voltage control circuit 25 First current control circuit 26 Driver 31 Hi side switching element 32 Low side switching element 33 Second voltage control circuit 34 Second current control circuit 35 Hi/Low driver CL Capacitive load Cin Input capacitor Cout Output capacitor D1: Rectifier diodes DH, DL Diode E DC power supply L1 Reactor R1, R2 Resistor

Claims (2)

A power supply device for driving a capacitive load, comprising:
A first power supply unit that outputs a DC voltage;
a resonant second power supply unit which includes an input capacitor charged by a DC voltage from the first power supply unit, converts the DC voltage of the input capacitor into an AC voltage by on/off operations of bridge-connected switching elements, and supplies the AC voltage to the capacitive load, and regenerates the charge stored in the capacitive load to the input capacitor when the AC voltage drops;
The first power supply unit has a smaller current capacity than the second power supply unit,
A power supply device, characterized in that an overcurrent threshold at which the first power supply unit initiates overcurrent protection is set to a value lower than an overcurrent threshold at which the second power supply unit initiates overcurrent protection. The power supply device according to claim 1, characterized in that it is provided with a backflow prevention diode that prevents a backflow of charge from the second power supply unit to the first power supply unit.

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