Power converter

Abstract

To provide a power conversion device which can suppress variation in an output voltage due to a sudden load change.SOLUTION: A power conversion device 100 comprises: an AC-DC converter 101 which converts AC power into first DC power; a DC-DC converter 102 which converts the first DC power into second DC power; and a control circuit 110 which controls an intermediate output voltage V1 of the AC-DC converter 101 on the basis of an output voltage command value. The control circuit 110 corrects the output voltage command value of the AC-DC converter 101 on the basis of a rate of a change in an output voltage V2 of the DC-DC converter 102 and a rate of a change in an output current Io of the DC-DC converter 102.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power conversion device.

Background Art

[0002] In Patent Document 1, in a three-phase inverter that drives a motor load, a method is described in which the motor speed and torque are detected, the output power of the three-phase inverter is calculated in real time, and it is fed forward to the current command value of a boost chopper connected to the front stage of the three-phase inverter. Thereby, when the rotational speed or torque of the motor changes suddenly, the current command value of the boost chopper is immediately corrected, and fluctuations in the input voltage of the three-phase inverter, that is, the output voltage of the boost chopper, can be suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A power conversion device including an AC-DC converter that full-wave rectifies and boosts an AC power supply and an isolation-type DC-DC converter that converts the DC power output by the AC-DC converter into another isolated DC power is known. Such a power conversion device is widely used as a power supply device for data centers, industrial equipment, etc. Also, in a power supply device, in order not to impair the performance of a device connected as a load, it is often required that the output voltage and output current do not fluctuate even when the load power changes suddenly.

[0005] In this context, the method described in Patent Document 1 is based on the assumption of an AC load, such as a motor load, and cannot be easily applied directly to a DC load. Furthermore, because feedforward control is performed at all times, there is a possibility that the control in a steady state may become unstable. In addition, a common problem in circuit configurations where an AC-DC converter and a DC-DC converter are connected is the fluctuation of the intermediate DC voltage input from the AC-DC converter to the DC-DC converter during sudden load changes.

[0006] In typical DC-DC converters, there is an upper limit to the ratio of the output voltage to the input voltage, i.e., the boost ratio. Therefore, for example, if the output voltage of the DC-DC converter decreases due to a sudden increase in load, the output of the DC-DC converter increases, and the intermediate DC voltage controlled by the AC-DC converter also decreases almost simultaneously. In other words, the input voltage of the DC-DC converter decreases. As a result, it becomes difficult to generate the required DC voltage within the driving capability of the DC-DC converter, which exacerbates the decrease in the DC voltage output from the DC-DC converter. Therefore, in order to suppress fluctuations in the output voltage caused by sudden load changes, it is necessary to suppress fluctuations in the intermediate DC voltage without affecting the steady-state control.

[0007] Therefore, one of the objectives of the present invention is to provide a power conversion device that can suppress fluctuations in output voltage caused by sudden changes in load.

[0008] The aforementioned and other objects and novel features of the present invention will become apparent from the description herein and the accompanying drawings. [Means for solving the problem]

[0009] A brief overview of a representative embodiment of the invention disclosed in this application is as follows: A power conversion device according to one embodiment includes an AC-DC converter that converts AC power to a first DC power, a DC-DC converter that converts the first DC power to a second DC power, and a control circuit that controls the output voltage of the AC-DC converter based on an output voltage command value. The control circuit corrects the output voltage command value of the AC-DC converter based on the rate of change of the output voltage of the DC-DC converter and the rate of change of the output current of the DC-DC converter. [Effects of the Invention]

[0010] According to the above embodiment, it becomes possible to suppress fluctuations in output voltage caused by sudden changes in load. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing an example of the configuration of a power conversion device according to Embodiment 1. [Figure 2] Figure 1 is a flowchart illustrating an example of the processing steps in the control circuit. [Figure 3] This block diagram shows an example of the control circuit configuration in Figure 1. [Figure 4] These waveform diagrams show examples of operation during sudden load changes in the power converter shown in Figures 1 and 3. [Figure 5] Figure 1 is a circuit diagram showing a detailed configuration example of the AC-DC converter. [Figure 6] Figure 1 is a circuit diagram showing a detailed configuration example of the DC-DC converter. [Figure 7] This is a schematic diagram showing an example configuration of a power conversion device according to Embodiment 2. [Figure 8] Figure 7 is a flowchart showing an example of the processing steps in the control circuit. [Figure 9] Figure 7 is a block diagram showing an example of the control circuit configuration. [Figure 10]In the power conversion device according to Embodiment 3, it is a flowchart showing an example of the processing content of the control circuit in FIG. 1. [Figure 11] In the power conversion device according to Embodiment 3, it is a waveform diagram showing an example of the operation when the load suddenly changes.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. In all the drawings for explaining the embodiments, the same members are generally denoted by the same reference numerals, and repeated explanations thereof are omitted.

[0013] (Embodiment 1) <Outline of the Power Conversion Device> FIG. 1 is a schematic diagram showing a configuration example of the power conversion device according to Embodiment 1. The power conversion device 100 shown in FIG. 1 includes an AC-DC converter 101, a DC-DC converter 102, an intermediate smoothing capacitor 104, an output smoothing capacitor 106, a control circuit 110, and various sensors. Among the various sensors, voltage sensors 107 and 108 and a current sensor 109 are included.

[0014] The power conversion device 100 is configured, for example, by mounting components constituting each block shown in FIG. 1 on a wiring board. The control circuit 110 is realized, for example, by components such as a microcontroller, an FPGA (Field Programmable Gate Array), or an ASIC (Application Specific Integrated Circuit).

[0015] The AC-DC converter 101 converts the AC power input from the three-phase AC voltage source 111 into the first DC power. Specifically, the AC-DC converter 101 takes the AC voltage Vac as an input and outputs an intermediate output voltage V1 that becomes a DC voltage. The intermediate smoothing capacitor 104 is connected to an intermediate node 103 that serves as the output node of the AC-DC converter 101 and the input node of the DC-DC converter 102. The intermediate smoothing capacitor 104 smooths the intermediate output voltage V1, which is a DC voltage, or in other words, the first DC power. The voltage sensor 107 detects the intermediate output voltage V1.

[0016] The DC-DC converter 102 converts the first DC power into the second DC power. That is, the DC-DC converter 102 takes the intermediate output voltage V1 that becomes a DC voltage as an input and outputs an output voltage V2 that becomes a DC voltage. The output smoothing capacitor 106 is connected to the output node 105 of the DC-DC converter 102 and smooths the output voltage V2, which is a DC voltage, or in other words, the second DC power. The voltage sensor 108 detects the output voltage V2. Also, the current sensor 109 detects the output current Io of the DC-DC converter 102. The output power, that is, the output voltage V2 and the output current Io, are supplied to a load not shown. The load is, for example, a DC load.

[0017] The control circuit 110 controls the AC-DC converter 101. A normal value V1ref0 of the intermediate output voltage command value is set in the control circuit 110. In the specification, the intermediate output voltage command value is referred to as V1ref. The control circuit 110 controls the intermediate output voltage V1 of the AC-DC converter 101 based on the intermediate output voltage command value V1ref and controls it so that the intermediate output voltage V1 becomes equal to the intermediate output voltage command value V1ref. Specifically, the control circuit 110 controls the current-carrying rate of the switching element included in the AC-DC converter 101 via the signal line 112 and controls the magnitude of the intermediate output voltage V1 by adjusting the AC power input from the three-phase AC voltage source 111.

[0018] Next, we will explain the operation during a sudden load change. Here, we will assume a case where the load increases rapidly. A sudden increase in load can be rephrased as a sudden increase in the output current Io. When the output current Io increases rapidly, charge is drawn from the output smoothing capacitor 106, and the output voltage V2 decreases. At this point, the control circuit 110 receives the detected value of the output voltage V2 via the signal line 113, and further receives the detected value of the output current Io via the signal line 114.

[0019] The control circuit 110 calculates the rate of change of the output voltage V2, dV2 / dt, and the rate of change of the output current Io, dIo / dt. Then, based on the rate of change of the output voltage V2, dV2 / dt, and the rate of change of the output current Io, dIo / dt, the control circuit 110 corrects the intermediate output voltage command value V1ref of the AC-DC converter 101.

[0020] In detail, the control circuit 110 compares each rate of change dV2 / dt and dIo / dt with predetermined thresholds dV2_th and dIo_th. The control circuit 110 then determines that there has been a sudden increase in load if the rate of change of the output voltage V2 dV2 / dt exceeds the threshold (first threshold) dV2_th and the rate of change of the output current Io dIo / dt exceeds the threshold (second threshold) dIo_th. If the control circuit 110 determines that there has been a sudden increase in load, it corrects the intermediate output voltage command value V1ref from the normal value V1ref0. More specifically, the control circuit 110 corrects the intermediate output voltage command value V1ref to be higher than the normal value V1ref0 based on, for example, the difference between the rate of change of the output current Io dIo / dt and the threshold dIo_th.

[0021] This instantly increases the output power of the AC-DC converter 101, suppressing the decrease in the intermediate output voltage V1. Additionally, the output power of the DC-DC converter 102 increases, slowing the decrease in the output voltage V2. Meanwhile, the control circuit 110 compares the rate of change of the output voltage V2, dV2 / dt, with a predetermined threshold (third threshold) dV2_th. When the rate of change of the output voltage V2, dV2 / dt, becomes smaller than the threshold dV2_th, the control circuit 110 sets the correction amount to the intermediate output voltage command value V1ref to zero. In other words, the control circuit 110 returns the intermediate output voltage command value V1ref to its normal value V1ref0.

[0022] By using the control described above, fluctuations in the intermediate output voltage V1 can be suppressed during sudden load changes, and the DC-DC converter 102 can generate the required output voltage V2 within the range of its driving capability. As a result, fluctuations in the output voltage V2 can be suppressed. Furthermore, the correction of the intermediate output voltage command value V1ref is started when both the rate of change of the output voltage V2 dV2 / dt and the rate of change of the output current Io dIo / dt exceed a threshold, and ends in a steady state where the rate of change is small. Therefore, unlike when using, for example, feedforward control, it becomes possible to stabilize the control in a steady state.

[0023] The rate of change is the amount of change in the detected value during one detection cycle. For example, it can be calculated by dividing the difference between the detected value at the start and end of the detection cycle by the detection cycle time. The first threshold used for the output voltage V2 when starting the correction of the intermediate output voltage command value V1ref and the third threshold used for the output voltage V2 when ending the correction may be the same value or different values. When different values ​​are used, for example, setting the third threshold to a value smaller than the first threshold may prevent chattering and other issues.

[0024] <Control circuit details> Figure 2 is a flowchart showing an example of the processing content of the control circuit in Figure 1. For example, the control circuit 110 can select whether to enable or disable the correction function for the intermediate output voltage command value V1ref mentioned above. When the correction function is enabled, the control circuit 110 repeatedly executes the flow shown in Figure 2 for each control cycle. This flow may be realized, for example, by a processor in a microcontroller or the like executing a program stored in memory, or by incorporating the circuit into an FPGA or ASIC.

[0025] In Figure 2, the control circuit 110 first determines whether the rate of change of the output voltage V2, dV2 / dt, exceeds the threshold (first threshold) dV2_th (step S101). More specifically, the control circuit 110 determines whether the absolute value of the rate of change dV2 / dt |dV2 / dt| exceeds the threshold dV2_th. The rate of change dV2 / dt becomes negative in the case of a sudden load increase, which is one type of sudden load change, and positive in the case of a sudden load decrease, which is another type of sudden load change.

[0026] Next, the control circuit 110 determines whether the rate of change of the output current Io, dIo / dt, exceeds the threshold (second threshold) dIo_th (step S102). More specifically, the control circuit 110 determines whether the absolute value of the rate of change dIo / dt| |dIo / dt| exceeds the threshold dIo_th. The rate of change dIo / dt becomes positive in the case of a sudden increase in load and negative in the case of a sudden decrease in load.

[0027] If the rate of change of the output voltage V2, dV2 / dt, exceeds the threshold dV2_th, and the rate of change of the output current Io, dIo / dt, also exceeds the threshold dIo_th (step S102: YES), the control circuit 110 determines that a sudden load change has occurred. In this case, the control circuit 110 calculates a correction amount for the intermediate output voltage command value V1ref and reflects it in the normal value V1ref0 (step S103). In this specification, the correction amount for the intermediate output voltage command value V1ref is called ΔV1ref.

[0028] In step S103, specifically, the control circuit 110 calculates a correction amount proportional to the difference between the rate of change of the output current Io dIo / dt and the threshold value dIo_th. In this case, the correction amount ΔV1ref becomes positive when the rate of change of the output current Io dIo / dt is positive, and becomes negative when the rate of change of the output current Io dIo / dt is negative. The control circuit 110 may also correct the intermediate output voltage command value V1ref based on the difference between the rate of change of the output voltage V2 dV2 / dt and the threshold value dV2_th instead of the output current Io. However, using the output current Io allows for a faster response than using the output voltage V2, so from this viewpoint, it is preferable to use the output current Io.

[0029] On the other hand, if the rate of change of the output voltage V2 dV2 / dt does not exceed the threshold dV2_th (step S101: NO), or if the rate of change of the output current Io dIo / dt does not exceed the threshold dIo_th (step S102: NO), the control circuit 110 determines that the operation of the power converter 100 is in a steady state. In this case, the control circuit 110 sets the intermediate output voltage command value V1ref to the normal value V1ref0 by setting the correction amount ΔV1ref of the intermediate output voltage command value V1ref to zero (step S104).

[0030] Through the flow described above, the control circuit 110 can correct the intermediate output voltage command value V1ref of the AC-DC converter 101 to the opposite polarity to the direction of fluctuation of the output voltage V2 of the DC-DC converter 102. Furthermore, in the steady state, i.e., when the rate of change dV2 / dt or rate of change dIo / dt is small, the correction amount ΔV1ref of the intermediate output voltage command value V1ref becomes zero. Therefore, stable control becomes possible in the steady state.

[0031] FIG. 3 is a block diagram showing a configuration example of the control circuit in FIG. 1. In FIG. 3, differentiator 301 receives the detected output current Io, calculates the rate of change dIo / dt, and outputs it. Comparator 302 receives the rate of change dIo / dt from differentiator 301 and a preset threshold value dIo_th. Comparator 302 compares the rate of change dIo / dt with the threshold value dIo_th, and when |dIo / dt|≧dIo_th, outputs a high-level detection signal 303, and when |dIo / dt|<dIo_th, outputs a low-level detection signal 303.

[0032] Similarly, differentiator 306 receives the detected output voltage V2, calculates the rate of change dV2 / dt, and outputs it. Comparator 307 receives the rate of change dV2 / dt from differentiator 306 and a preset threshold value dV2_th. Comparator 307 compares the rate of change dV2 / dt with the threshold value dV2_th, and when |dV2 / dt|≧dV2_th, outputs a high-level detection signal 308, and when |dV2 / dt|<dV2_th, outputs a low-level detection signal 308.

[0033] Adder 305, similar to the case of comparator 302, receives the rate of change dIo / dt from differentiator 301 and the threshold value dIo_th. Adder 305 is also a difference detector, and by calculating the difference between the rate of change dIo / dt and the threshold value dIo_th, for example, calculates a correction amount ΔV1ref proportional to the difference. Specifically, assuming |dIo / dt|≧dIo_th, adder 305 calculates a positive-pole correction amount ΔV1ref when the rate of change dIo / dt is positive, and calculates a negative-pole correction amount ΔV1ref when the rate of change dIo / dt is negative.

[0034] The correction amount calculator 304 outputs the correction amount ΔV1ref from the adder 305 as the correction signal 309 when both detection signals 303 and 308 are at a high level. On the other hand, the correction amount calculator 304 outputs zero as the correction signal 309 when at least one of the detection signals 303 and 308 is at a low level. The adder 310 outputs the intermediate output voltage command value V1ref by adding the correction amount ΔV1ref based on the correction signal 309 to the normal value V1ref0 of the intermediate output voltage command value V1ref. Note that the input to the adder 305 may be either the rate of change dV2 / dt from the differentiator 306 or the threshold value dV2_th, as described in Figure 2.

[0035] <Operation of power converters during sudden load changes> Figure 4 is a waveform diagram showing an example of operation during a sudden load change in the power converter shown in Figures 1 and 3. Figure 4 shows, as an example, the operation waveform during a sudden load increase. Figure 4 also shows, as a comparative example, the waveform when the method of the embodiment is not used, indicated by a dotted line. The operation shown in Figure 4 will now be explained.

[0036] At time t1, the load increases rapidly, and the output current Io begins to increase. During the period from time t1 to time t2, the output voltage V2 decreases due to the increase in output current Io. Consequently, the output of the DC-DC converter 102 increases, and the intermediate output voltage V1 also decreases almost simultaneously. During this period from time t1 to time t2, the rate of change of both the output current Io and the output voltage V2 is small, so the intermediate output voltage command value V1ref remains at its normal value V1ref0.

[0037] At time t2, both the rate of change of the output current Io and the rate of change of the output voltage V2 exceed the threshold. Consequently, correction of the intermediate output voltage command value V1ref begins. During the period from time t2 to time t3, a correction amount ΔV1ref is calculated based on the difference between the rate of change of the output current Io dIo / dt and the threshold value dIo_th, and the intermediate output voltage command value V1ref becomes higher. As a result, the output of the AC-DC converter 101 increases, and the decrease in the intermediate output voltage V1 can be suppressed compared to the comparative example.

[0038] At time t3, the rate of change of the output current Io, dIo / dt, reaches its peak. During the period from time t3 to time t4, the correction amount ΔV1ref decreases as the rate of change dIo / dt decreases. At time t4, the output of the DC-DC converter 102 stabilizes the decrease in output voltage V2. Consequently, as the rate of change of output voltage V2, dV2 / dt, falls below the threshold, the correction amount ΔV1ref returns to zero. This operation suppresses the decrease in the intermediate output voltage V1 more effectively than in the comparative example, and as a result, reduces the fluctuation range of the output voltage V2.

[0039] <Details of each converter> Figure 5 is a circuit diagram showing a detailed configuration example of the AC-DC converter in Figure 1. The AC-DC converter 101 shown in Figure 5 has a boost chopper type configuration that includes a full-wave rectifier circuit 401, an inductor 402, a switching element 403, and a diode 404. The full-wave rectifier circuit 401 rectifies the three-phase AC voltage Vac into a DC voltage by performing full-wave rectification using a diode bridge consisting of six diodes D1 to D6.

[0040] Inductor 402 stores power from the full-wave rectifier circuit 401 when the switching element 403 is ON. Conversely, when the switching element 403 is OFF, the power stored in inductor 402 is transmitted to the intermediate smoothing capacitor 104 via diode 404. The magnitude of the intermediate output voltage V1 is controlled by the current flow rate of the switching element 403. The ON / OFF state of the switching element 403 is controlled by a signal line 112 from the control circuit 110 shown in Figure 1.

[0041] The AC-DC converter 101 is not limited to the circuit configuration shown in Figure 5; for example, it may be a 3-phase PWM converter or other circuit configurations. Also, in the example in Figure 5, the switching element 403 is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), but it is not limited to this and may be an IGBT (Insulated Gate Bipolar Transistor) or other element.

[0042] Figure 6 is a circuit diagram showing a detailed configuration example of the DC-DC converter in Figure 1. The DC-DC converter 102 shown in Figure 6 is a resonant converter, which is a type of isolated DC-DC converter. The primary side of the DC-DC converter 102 is provided with a full-bridge circuit 501 consisting of switching elements Q10 to Q13, an inductor 502, the primary winding of a transformer 503, and a capacitor 504. On the other hand, the secondary side of the DC-DC converter 102 is provided with a full-bridge circuit 506 consisting of switching elements Q20 to Q23, an inductor 505, and the secondary winding of a transformer 503.

[0043] In the full-bridge circuit 501, alternating current flows through the transformer 503 by alternately switching on the switching elements Q10 and Q13 and the switching elements Q11 and Q12. In the full-bridge circuit 506, the current transmitted by the transformer 503 is synchronously rectified and then charges the output smoothing capacitor 106 by alternately switching on the switching elements Q20 and Q23 and the switching elements Q21 and Q22.

[0044] The alternating current on the primary side is controlled sinusoidally by a series resonant circuit consisting of inductor 502, the excitation inductor of transformer 503, and capacitor 504. This suppresses the cutoff current of the switching elements, enabling highly efficient power conversion. The magnitude of the output voltage V2 is controlled, for example, by the switching frequency of each switching element. The on / off state of each switching element is controlled by the control circuit of the DC-DC converter 102, which is not shown in Figure 1. However, this control circuit may be implemented by the control circuit 110 shown in Figure 1.

[0045] The DC-DC converter 102 is not limited to the circuit configuration shown in Figure 6; for example, it may be a DAB (Dual Active Bridge) or a non-isolated chopper circuit. The DAB has a configuration similar to the example shown in Figure 6, but with the capacitor 504 removed. Also, in the example in Figure 6, each switching element is a MOSFET, but it is not limited to this and may be an IGBT or other element.

[0046] <Main effects of Embodiment 1> As described above, in the method of Embodiment 1, the correction amount ΔV1ref of the intermediate output voltage command value V1ref is controlled based on the rate of change of the output voltage V2 and the rate of change of the output current Io. This makes it possible to suppress fluctuations in the output voltage V2 caused by sudden load changes. Furthermore, by using a control that makes the correction amount ΔV1ref zero in the steady state, stable control can be performed in the steady state. As a result, a robust power conversion device can be realized.

[0047] (Embodiment 2) <Overview of a power converter> Figure 7 is a schematic diagram showing an example configuration of a power converter according to Embodiment 2. The power converter 200 shown in Figure 7 differs from the configuration example shown in Figure 1 in the following two points. The first difference is that a current sensor 601 is provided. The current sensor 601 detects the capacitor current Ic flowing through the output smoothing capacitor 106. The second difference is that the control circuit 110 receives the detected value of the capacitor current Ic from the current sensor 601 via the signal line 602, instead of the detected value of the output voltage V2 in Figure 1.

[0048] In other words, in Embodiment 1, the control circuit 110 calculated the rate of change dV2 / dt of the output voltage V2, but in Embodiment 2, the rate of change dV2 / dt is detected by the capacitor current Ic flowing through the output smoothing capacitor 106. Specifically, from the definition formula for capacitor capacitance C, the relationship between the capacitor voltage Vc and the capacitor current Ic is given by equation (1). Vc = ∫(Ic)dt / C …(1)

[0049] From equation (1), the capacitor voltage Vc is the integral of the capacitor current Ic. Therefore, the rate of change of the output voltage V2, dV2 / dt, can be replaced by the capacitor current Ic. Alternatively, the output voltage V2 can be calculated by integrating the capacitor current Ic. For this reason, even if the capacitor current Ic is used instead of the output voltage V2, the same operation as in Embodiment 1 can be achieved, and the same effect can be obtained. Furthermore, generally speaking, the capacitor current fluctuates more significantly than the capacitor voltage, making it easier to detect sudden changes in load.

[0050] In the configuration example shown in Figure 7, the voltage sensor 108, i.e., the sensor that detects the output voltage V2, is not provided. However, in practical use, this voltage sensor 108 is also provided. That is, the value of the output voltage V2 needs to be reasonably accurate in order to control the DC-DC converter 102. On the other hand, the value of the output voltage V2 can also be determined by calculation based on equation (1). However, in this case, the computational load increases, and errors may occur in the value of the output voltage V2 due to changes in the capacitor capacitance C over time, etc.

[0051] <Details of the control circuit> FIG. 8 is a flowchart showing an example of the processing content of the control circuit in FIG. 7. The flow shown in FIG. 8 is such that step S101 in FIG. 2 is replaced by step S201 in FIG. 8. In step S201, the control circuit 110 determines whether or not the capacitor current Ic exceeds a threshold value (first threshold value) dIc_th. Specifically, the control circuit 110 determines whether or not the absolute value |Ic| of the capacitor current Ic exceeds the threshold value dIc_th. The capacitor current Ic becomes the negative electrode, that is, the discharge direction, in the case of a sudden increase in the load, and becomes the positive electrode, that is, the charging direction, in the case of a sudden decrease in the load.

[0052] FIG. 9 is a block diagram showing a configuration example of the control circuit in FIG. 7. The control circuit 110 shown in FIG. 9 has different input contents to the comparator 307 as compared with the configuration example shown in FIG. 3. That is, the comparator 307 inputs the capacitor current Ic from the current sensor 601 and a preset threshold value dIc_th. The comparator 307 compares the capacitor current Ic with the threshold value dIc_th, and outputs a high-level detection signal 308 when |Ic| ≧ dIc_th, and outputs a low-level detection signal 308 when |Ic| < dIc_th.

[0053] <Main effects of the second embodiment> As described above, by using the method of the second embodiment, effects similar to the various effects described in the first embodiment can be obtained. Also, as shown in FIG. 7, the differentiator 306 in FIG. 3 can be deleted, and the control circuit 110 can be simplified. Further, by detecting the capacitor current Ic instead of the output voltage V2, it may be possible to perform detection with higher sensitivity with respect to a sudden change in the load. As a result, the responsiveness may be further enhanced.

[0054] (Embodiment 3) <Details of the control circuit> Figure 10 is a flowchart showing an example of the processing content of the control circuit in Figure 1 in the power conversion device according to Embodiment 3. The flow shown in Figure 10 is executed repeatedly in each control cycle. The flow shown in Figure 10 differs from the flow shown in Figure 2 in the following respects: Step S103 in Figure 2 is replaced by step S301 in Figure 10, and steps S302 to S304 are added in Figure 10.

[0055] In step S301, the control circuit 110 calculates a correction amount ΔV1ref for the intermediate output voltage command value V1ref, similar to the case in step S103. However, unlike in step S103, the control circuit 110 does not reflect the correction amount ΔV1ref in the intermediate output voltage command value V1ref at this stage. After step S301, the control circuit 110 determines whether the correction amount ΔV1ref calculated in step S301 is greater than the correction amount calculated in the previous control cycle (step S302).

[0056] If the correction amount ΔV1ref calculated in the current control cycle is greater than the correction amount calculated in the previous control cycle (step S302: YES), the control circuit 110 outputs an intermediate output voltage command value V1ref that reflects the correction amount ΔV1ref calculated in step S301 (step S304). On the other hand, if the current correction amount ΔV1ref is smaller than the previous correction amount (step S302: NO), the control circuit 110 sets the current correction amount ΔV1ref to a correction amount that decreases at a constant rate with each control cycle. Then, the control circuit 110 outputs an intermediate output voltage command value V1ref that reflects the set correction amount (step S303).

[0057] In step S303, specifically, the control circuit 110 determines a correction amount ΔV1ref, which is obtained by reducing the correction amount from the previous control cycle by a predetermined amount. Then, the control circuit 110 adds this determined correction amount to the normal value V1ref0 of the intermediate output voltage command value V1ref. By using this flow, the correction amount ΔV1ref can be gradually converged to zero, and control can be made so that the correction amount ΔV1ref is not abruptly reset to zero. As a result, fluctuations in the intermediate output voltage V1 when returning from a sudden load change to a steady state can be suppressed.

[0058] Figure 11 is a waveform diagram showing an example of operation during a sudden load change in the power converter according to Embodiment 3. The waveform diagram shown in Figure 11 differs from the waveform diagram shown in Figure 4 in that the waveform of the correction amount ΔV1ref is different. At time t3, as in the case of Figure 4, the rate of change of the output current Io dIo / dt reaches a peak. Consequently, the correction amount ΔV1ref also reaches a peak.

[0059] At time t34, which marks the next control cycle, the correction amount ΔV1ref calculated in step S301 in Figure 10 is assumed to be smaller than the correction amount calculated at time t3, which is the previous control cycle. In this case, in step S303 shown in Figure 10, the control circuit 110 sets the correction amount ΔV1ref at time t34 to a correction amount obtained by reducing the correction amount calculated at time t3 by a predetermined reduction amount ΔV, for example.

[0060] As this control is repeatedly executed in each control cycle, the correction amount ΔV1ref gradually converges to zero, as shown in Figure 11. In other words, the sharp decrease in the correction amount ΔV1ref, as shown at time t4 in Figure 4, can be eliminated. In the case of Figure 4, although not shown, the intermediate output voltage V1 may fluctuate in response to the sharp decrease at time t4. In Figure 11, such fluctuations in the intermediate output voltage V1 can be suppressed.

[0061] <Main effects of Embodiment 3> As described above, the same effects as those described in Embodiment 1 can be obtained by using the method of Embodiment 3. Furthermore, compared to Embodiment 1, fluctuations in the intermediate output voltage V1 when returning from a sudden load change to a steady state can be suppressed.

[0062] The present invention has been described in detail above based on embodiments, but the present invention is not limited to the embodiments described above and can be modified in various ways without departing from its essence. For example, the embodiments described above are described in detail in order to explain the present invention in an easy-to-understand manner and are not necessarily limited to those having all the described configurations. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add a configuration from another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with a configuration from another embodiment. [Explanation of Symbols]

[0063] 100, 200… Power converter, 101… AC-DC converter, 102… DC-DC converter, 106… Output smoothing capacitor, 110… Control circuit, Io… Output current, V1… Intermediate output voltage, V2… Output voltage, Vac… AC voltage, dIo_th, dV2_th, Ic_th… Threshold, ΔV1ref… Correction amount

Claims

1. An AC-DC converter that converts alternating current power to a first direct current power, A DC-DC converter that converts the first DC power to a second DC power, A control circuit that controls the output voltage of the AC-DC converter based on the output voltage command value, Equipped with, The control circuit corrects the output voltage command value of the AC-DC converter based on the rate of change of the output voltage of the DC-DC converter and the rate of change of the output current of the DC-DC converter. Power converter.

2. In the power conversion device according to claim 1, The control circuit corrects the output voltage command value of the AC-DC converter when the rate of change of the output voltage of the DC-DC converter exceeds a predetermined first threshold and the rate of change of the output current of the DC-DC converter exceeds a predetermined second threshold. Power converter.

3. In the power conversion device according to claim 2, The control circuit determines the correction amount for the output voltage command value of the AC-DC converter based on the difference between the rate of change of the output current of the DC-DC converter and the second threshold value. Power converter.

4. In the power conversion device according to claim 2, The control circuit determines the correction amount for the output voltage command value of the AC-DC converter based on the difference between the rate of change of the output voltage of the DC-DC converter and the first threshold value. Power converter.

5. In the power conversion device according to claim 2, The control circuit, when the rate of change of the output voltage of the DC-DC converter falls below a predetermined third threshold, sets the correction amount of the output voltage command value of the AC-DC converter to zero. Power converter.

6. In the power conversion device according to claim 3 or 4, The control circuit calculates a correction amount for the output voltage command value of the AC-DC converter for each control cycle, and if the correction amount calculated in the current control cycle is smaller than the correction amount calculated in the previous control cycle, it determines a correction amount that decreases at a constant rate for each control cycle. Power converter.

7. In the power conversion device according to claim 1, The control circuit corrects the output voltage command value of the AC-DC converter in the opposite polarity to the direction of variation of the output voltage of the DC-DC converter. Power converter.

8. In the power conversion device according to claim 1, Furthermore, it has a capacitor that holds the second DC power, The control circuit detects the rate of change of the output voltage of the DC-DC converter by the capacitor current flowing through the capacitor. Power converter.

9. An AC-DC converter that converts alternating current power to a first direct current power, A DC-DC converter that converts the first DC power to a second DC power, The second capacitor that holds DC power, A control circuit for controlling the AC-DC converter, Equipped with, The control circuit corrects the output voltage command value of the AC-DC converter based on the capacitor current flowing through the capacitor and the rate of change of the output current of the DC-DC converter. Power converter.

10. In the power conversion device according to claim 9, The control circuit corrects the output voltage command value of the AC-DC converter when the capacitor current exceeds a predetermined first threshold and the rate of change of the output current of the DC-DC converter exceeds a predetermined second threshold. Power converter.

11. In the power conversion device according to claim 10, The control circuit determines the correction amount for the output voltage command value of the AC-DC converter based on the difference between the rate of change of the output current of the DC-DC converter and the second threshold value. Power converter.

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