AC-DC power conversion device

Abstract

To provide an AC-DC power conversion device capable of preventing an increase in current amount at AC voltage reduction.SOLUTION: An AC-DC power conversion device has a regeneration function and converts AC power of an AC power supply 1 to DC power by a plurality of semiconductor switch devices R+, S+, T+, R-, S-, T-. The AC-DC power conversion device includes a current-switching pattern calculator 21, using a current versus conduction width characteristic set so as to narrow conduction width of the semiconductor switch devices when being set current or higher, for detecting current of the AC power supply 1 and calculating an effective value to determine conduction width corresponding to the detected current effective value, and determining a switching pattern of a 120-degree conduction method of the determined conduction width, and drives the semiconductor switch devices by using the determined switching pattern.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an AC-DC power conversion device having a regeneration function.

Background Art

[0002] A circuit example of the power conversion device dealt with in the present invention is shown in FIG. 1. In FIG. 1, 2 is a forward power conversion unit configured by connecting semiconductor switching devices R+, S+, T+, R-, S-, T- in a three-phase bridge, and converts the AC power of an AC power supply (1), not shown, into DC power.

[0003] A smoothing capacitor 3 and a load 4 are connected in parallel to the DC side of the forward power conversion unit 2.

[0004] The circuit in FIG. 1 is a circuit capable of both motoring operation and regeneration operation, and by switching the semiconductor switching devices R+, S+, T+, R-, S-, T- at an arbitrary timing, the power between the AC part and the DC part can be adjusted, and the current waveform of the AC part and the voltage waveform of the DC part can be arbitrarily adjusted.

[0005] As a method for determining the switching pattern of the semiconductor switching devices R+, S+, T+, R-, S-, T- of this circuit, there is a 120-degree conduction method. FIG. 2 shows the switching pattern of the 120-degree conduction method. For the upper arm R+, S+, T+, the semiconductor switching device of the phase where each phase voltage becomes maximum is turned ON, and for the lower arm R-, S-, T-, the semiconductor switching device of the phase where each phase voltage becomes minimum is turned ON.

[0006] Conventionally, as a PWM control method of a power conversion device, for example, the one described in Patent Document 1 has been proposed.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] The 120-degree through-flow method has the advantages that the loss generated in the semiconductor switching device is small and the control circuit is simple. On the other hand, it has the disadvantages that the adjustment of the power amount cannot be performed and the current waveform of the AC part and the voltage waveform of the DC part cannot be arbitrarily controlled.

[0009] Particularly, because the waveform cannot be arbitrarily controlled, when the AC voltage drops under the condition of constant load power, an excessive current flows from the DC part to the AC part as shown in FIG. 3 showing the behavior when the input voltage drops. When the amount of current increase at this time reaches a level at which the device cannot be safely driven, it is necessary to stop the device, which is a factor that reduces the stability of the device.

[0010] This phenomenon can be avoided, for example, by adopting the PWM control method of Patent Document 1. However, there are cases where it is not possible to easily adopt the PWM control method because the loss generated in the semiconductor switching device increases and the control circuit becomes complicated. A method that can be realized with the same number of switchings and a simple control circuit is required.

[0011] The present invention solves the above problems, and an object thereof is to provide an AC-DC power conversion device capable of preventing an increase in the amount of current when the AC voltage drops.

Means for Solving the Problems

[0012] The AC-DC power conversion device according to claim 1 for solving the above problems is An AC-DC power conversion device having a regeneration function and converting the AC power of an AC power supply into DC power by a plurality of semiconductor switching devices, Using the current-conduction width characteristic set to narrow the conduction width of the semiconductor switching device when the current is equal to or greater than the set current, the current of the AC power supply is detected, the effective value is calculated, the conduction width corresponding to the detected effective value of the current is obtained, and a switching pattern calculation unit that determines a 120-degree current conduction method switching pattern of the obtained conduction width is provided. It is characterized in that the semiconductor switching device is driven by the determined switching pattern.

[0013] The AC-DC power conversion device according to claim 2 In an AC-DC power conversion device that has a regeneration function and converts AC power of an AC power supply into DC power by a plurality of semiconductor switching devices, Using the differential voltage-conduction width characteristic set to narrow the conduction width of the semiconductor switching device when the differential voltage between the voltage detected for the DC voltage of the AC-DC power conversion device and the voltage detected for the AC voltage and the effective value calculated is equal to or greater than the set voltage, the conduction width corresponding to the differential voltage is obtained, and a switching pattern calculation unit that determines a 120-degree current conduction method switching pattern of the obtained conduction width is provided. It is characterized in that the semiconductor switching device is driven by the determined switching pattern.

[0014] The AC-DC power conversion device according to claim 3, in claim 2 The switching pattern calculation unit A current estimation calculator that calculates a current estimation value based on a current estimation pattern in which an estimated current corresponding to the differential voltage is set, the load power, and a power source impedance adjustment coefficient; Using the current-conduction width characteristic set to narrow the conduction width of the semiconductor switching device when the calculated current estimation value is equal to or greater than the set current conduction width change start point current, the conduction width corresponding to the current estimation value is obtained, and a current-switching pattern calculator that determines a 120-degree current conduction method switching pattern of the obtained conduction width; It is characterized by comprising the above.

Effect of the Invention

[0015] (1) According to the invention described in claims 1 to 3, it is possible to prevent an increase in the current amount during a decrease in the AC voltage and prevent unnecessary device stoppage, improving stability. (2) According to the invention described in claim 1, since the conduction width is determined based on the detected current, the current amount can be directly adjusted. (3) According to the invention described in claim 2, the system can be assembled very simply. (4) According to the inventions described in claims 2 and 3, the switching pattern can be determined without performing current detection.

Brief Description of the Drawings

[0016]

Figure 1

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Figure 12

Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment examples. In this embodiment example, in a power conversion device having a regeneration function, for example, as shown in FIG. 1, when the power supply voltage fluctuates, particularly when the AC voltage drops, an excessive current is suppressed from flowing, and the operation can be continued, thereby improving the stability of the device.

[0018] FIG. 4 shows the switching operation according to this embodiment example. FIG. 4(a) is a switching pattern of the 120-degree conduction method during normal times, and FIG. 4(b) is a switching pattern of the 120-degree conduction method when the AC voltage drops.

[0019] When the AC voltage is within the normal range, the switching of the 120-degree conduction method similar to FIG. 2 shown in FIG. 4(a) is performed. However, when the AC voltage drops, the conduction width of each semiconductor switching device is narrowed as shown in FIG. 4(b) to suppress the flow of an excessive current (during this protection operation, the power supplied from the AC power supply to the load is suppressed).

[0020] That is, in FIG. 4(b), the ON period of the upper arm R+ is set as the period from a time t1' that is a predetermined time later than the time t1 when the maximum voltage switches from the T phase to the R phase to a time t2" that is a predetermined time earlier than the time t3 when the maximum voltage switches from the R phase to the S phase.

[0021] Also, the ON period of the upper arm S+ is set as the period from a time t3' that is a predetermined time later than the time t3 when the maximum voltage switches from the R phase to the S phase to a time t4" that is a predetermined time earlier than the time t5 when the maximum voltage switches from the S phase to the T phase.

[0022] Also, the ON period of the upper arm T+ is set to be a period from a time t5' that is a predetermined time later than the time t5 when the maximum voltage switches from the S phase to the T phase to a time (not shown) that is a predetermined time earlier than the time when the maximum voltage switches from the T phase to the R phase.

[0023] Also, the ON period of the lower arm S- is set to be a period from a time (not shown) that is a predetermined time later than the time when the minimum voltage switches from the R phase to the S phase to a time t1" that is a predetermined time earlier than the time t2 when the minimum voltage switches from the S phase to the T phase.

[0024] Also, the ON period of the lower arm T- is set to be a period from a time t2' that is a predetermined time later than the time t2 when the minimum voltage switches from the S phase to the T phase to a time t3" that is a predetermined time earlier than the time t4 when the minimum voltage switches from the T phase to the R phase.

[0025] Also, the ON period of the lower arm R- is set to be a period from a time t4' that is a predetermined time later than the time t4 when the minimum voltage switches from the T phase to the R phase to a time t5" that is a predetermined time earlier than the time t6 when the minimum voltage switches from the R phase to the S phase.

[0026] Therefore, the conduction width of each semiconductor switching device in FIG. 4(b) is the period during which the switching pattern of the upper arm is ON and the switching pattern of the other phase of the lower arm is ON (that is, the shaded period in FIG. 4(b) is not included).

[0027] By narrowing the conduction width of each semiconductor switching device in this way when the AC voltage drops, as shown in FIG. 5(b) which shows the current behavior when the voltage drops, the flow of excessive current is suppressed. Note that FIG. 5(a) shows the current behavior when controlled by a normal switching pattern, and excessive current occurs when the voltage drops.

Example

[0028] Fig. 6 shows the control block diagram of the first embodiment. In the first embodiment, the current value of the AC section is detected, and the effective current value is calculated. Based on this calculation result, the conduction width is determined, and the switching pattern is determined. Since this method uses current detection, the current amount can be directly adjusted. However, since a current detector is required, it is an effective method in a system that already has a current detection circuit.

[0029] In Fig. 6, the same parts as those in Fig. 1 are denoted by the same reference numerals. 11 is a current detector that detects the three-phase AC current of the AC power supply 1 and is composed of, for example, current transformers provided in each phase.

[0030] 12 is a current detection circuit that obtains and outputs a current detection value from the detection output of the current detector 11. 13 is an effective current value calculator that calculates the effective value of the current detection value from the current detection circuit 12.

[0031] 21 is a current-switching pattern calculator (switching pattern calculation unit) that obtains the conduction width corresponding to the effective current value calculated by the effective current value calculator 13 using the input current-conduction width characteristic set to narrow the conduction width of the semiconductor switching device when the set current is exceeded, and determines the 120-degree conduction method switching pattern (for example, Fig. 4(b)) of the obtained conduction width.

[0032] 30 is a semiconductor switching device drive circuit that drives each semiconductor switching device of the forward power conversion unit 2 with the switching pattern determined by the current-switching pattern calculator 21.

[0033] An example of the input current-conduction width characteristic used in the current-switching pattern calculator 21 is shown in Fig. 7. In Fig. 7, during the period when the current detection value (effective current value) is within the rated current of the device, the conduction width is the normal 120 degrees.

[0034] The conduction width change start point is set to be equal to or higher than the rated current of the device, and the point where the conduction width becomes 0° is set at a location that is decreased by only the protection margin with respect to the maximum allowable current value of the device (a current value that does not reach the maximum allowable current and is smaller by the protection margin).

[0035] By setting it in this way, while suppressing the increase in current during the decrease in AC voltage, the device can be continuously operated without reaching the maximum allowable current of the device.

[0036] In addition, in the example of FIG. 7, although the conduction width is linearly decreased during the period from the conduction width change start point until the conduction width becomes 0°, it is not limited to a linear decrease.

Example

[0037] FIG. 8 shows the control block diagram of Example 2. In this Example 2, instead of directly detecting the current value of the AC section, the current value is estimated from the AC voltage, DC voltage, load power, and power source impedance. This is a method of determining the conduction width based on this calculation result and determining the switching pattern. Since this method indirectly controls the AC current using the voltage detection value, the ability to suppress the increase in current is lower compared to Example 1. However, in a power conversion device using a 120-degree conduction method, it is common to perform only voltage detection without performing current detection, so it can be said that Example 2 is a more practical method.

[0038] In FIG. 8, the same parts as those in FIG. 6 are denoted by the same reference numerals. 41 is a voltage detector that detects the three-phase AC voltage of the AC power source 1 and is composed of, for example, an instrument transformer. 42 is a voltage detection circuit that obtains a voltage detection value from the detection output of the voltage detector 41 and outputs it. 43 is a voltage effective value calculator that calculates the effective value of the voltage detection value from the voltage detection circuit 42 and outputs the effective value of the power source voltage.

[0039] 44 is a voltage detection circuit that detects the DC voltage of the smoothing capacitor 3 in the DC section and outputs a DC voltage detection value.

[0040] 50 is a current estimation calculator that calculates an estimated current value as shown in FIG. 10 below based on a current estimation pattern (FIG. 9 described later) that sets an estimated current corresponding to the differential voltage between the DC voltage detection value and the effective value of the power supply voltage, and the input load power and the power supply impedance adjustment coefficient.

[0041] 22 is a current-switching pattern calculator (switching pattern calculation unit) that obtains a conduction width corresponding to the estimated current value calculated by the current estimation calculator 50 using a current-conduction width characteristic set to narrow the conduction width of the semiconductor switching device when the current is equal to or greater than the set current, and determines a 120-degree current conduction switching pattern (for example, FIG. 4(b)) of the obtained conduction width.

[0042] The current-conduction width characteristic in this current-switching pattern calculator 22 is, for example, obtained by changing the horizontal axis of FIG. 7 to the estimated current value estimated by the current estimation calculator 50.

[0043] Note that the current estimation calculator 50 and the current-switching pattern calculator 22 constitute the switching pattern calculation unit of the present invention.

[0044] In the configuration of the second embodiment, since the system cannot detect the current value of the AC section, it is necessary to estimate the current value. However, in order to estimate the current value, it is not easy to estimate because it is affected by the load situation and the power supply environment (power supply impedance, voltage value) of the device installation location.

[0045] Considering the case where the device is operating with a standard power supply impedance, rated input voltage, and rated output, the current flowing into the input becomes the device rated current. From this, when the DC voltage rises or the power supply voltage drops, the current amount increases. Therefore, by tabulating the current estimation pattern as shown in FIG. 9 in a data table, the current under a certain load condition can be estimated (this pattern is obtained through pre-tests, simulations, etc.).

[0046] Here, as shown in FIG. 10 which shows the details of the current estimation calculator 50, the final current estimation value can be obtained by considering the increase and decrease of the current due to the load power and the correction coefficient of the power supply impedance in the installation environment.

[0047] In FIG. 10, 51 is a subtractor that subtracts the effective value of the power supply voltage from the detected value of the DC voltage. 52 is a current estimator that takes the subtraction output (differential voltage) of the subtractor 51 as an input and estimates the current according to the current estimation pattern of FIG. 9.

[0048] 53 is a normalization circuit that normalizes the input load power, and its output is multiplied by the output of the current estimator 52 in the multiplier 54.

[0049] The output of the multiplier 54 and the input power supply impedance adjustment coefficient are multiplied in the multiplier 55, and the current estimation value is output.

Example

[0050] FIG. 11 shows the control block diagram of Example 3. In the above Example 2, the current value was estimated from the power supply impedance, load power, input voltage, and DC voltage. However, in this Example 3, the switching pattern is directly determined from the AC power supply voltage and the DC voltage. This system needs to adjust the conduction width in a fitting manner according to the installation environment and operation method of the device, and it is difficult to operate in applications with large load fluctuations. On the other hand, it has the merit that the system can be assembled very simply.

[0051] In FIG. 11, the same parts as those in FIG. 8 are denoted by the same reference numerals. The difference between FIG. 11 and FIG. 8 is that instead of the current estimation calculator 50 and the current-switching pattern calculator 22, a voltage-switching pattern calculator 60 (the switching pattern calculation unit of the present invention) is provided which obtains the conduction width corresponding to the differential voltage by using a differential voltage-conduction width characteristic (conduction width pattern) set to narrow the conduction width of each semiconductor switching device when the differential voltage obtained by subtracting the effective value of the power supply voltage from the detected DC voltage value is equal to or higher than a set voltage, and determines a 120-degree current conduction type switching pattern of the obtained conduction width. Other parts are configured in the same manner as in FIG. 8.

[0052] An example of the conduction width pattern used in the voltage-switching pattern calculator 60 is shown in FIG. 12. When the difference between the DC voltage and the input voltage (AC side voltage) is large, the input current becomes excessive. Therefore, by using the conduction width pattern in FIG. 12 to narrow the conduction width, an increase in the input current can be suppressed. However, the settings of the pattern in FIG. 12 (such as the start point of the current conduction width change and the point (differential voltage value) where the conduction width becomes 0°) need to be adjusted on-site according to the installation environment and operating conditions.

[0053] Note that in the example of FIG. 12, the conduction width is linearly decreased in the period from the start point of the current conduction width change to when the conduction width becomes 0°, but it is not limited to a linear decrease.

Explanation of Reference Numerals

[0054] 1... AC power supply 2... Forward power conversion unit 3... Smoothing capacitor 4... Load 11... Current detector 12... Current detection circuit 13... Effective current calculator 21, 22... Current-switching pattern calculator 30... Semiconductor switching device drive circuit 41... Voltage detector 42, 44... Voltage detection circuit 43... Effective voltage calculator 50…Current Estimation Calculator 51…Subtractor 52…Current Estimator 53…Normalization Circuit 54, 55…Multiplier 60…Voltage - Switching Pattern Calculator R+, S+, T+, R-, S-, T-…Semiconductor Switching Device

Claims

1. In an AC-DC power conversion device that has a regeneration function and converts AC power from an AC power source into DC power by a plurality of semiconductor switching devices, using a current-to-conduction width characteristic set to narrow the conduction width of the semiconductor switching device when the current is equal to or greater than a set current, the current of the AC power source is detected, the effective value is calculated, the conduction width corresponding to the detected effective value of the current is obtained, and a switching pattern calculation unit that determines a 120-degree current conduction method switching pattern of the obtained conduction width is provided, An AC-DC power conversion device characterized by driving the semiconductor switching device with the determined switching pattern.

2. In an AC-DC power conversion device that has a regeneration function and converts AC power from an AC power source into DC power by a plurality of semiconductor switching devices, using a differential voltage-to-conduction width characteristic set to narrow the conduction width of the semiconductor switching device when the differential voltage between the voltage detected for the DC voltage of the AC-DC power conversion device and the voltage detected for the AC voltage and having its effective value calculated is equal to or greater than a set voltage, the conduction width corresponding to the differential voltage is obtained, and a switching pattern calculation unit that determines a 120-degree current conduction method switching pattern of the obtained conduction width is provided, An AC-DC power conversion device characterized by driving the semiconductor switching device with the determined switching pattern.

3. The switching pattern calculation unit includes a current estimation pattern in which an estimated current corresponding to the differential voltage is set, a current estimation calculator that calculates an estimated current value based on the load power and the power source impedance adjustment coefficient, and a current-switching pattern calculator that, using a current-to-conduction width characteristic set to narrow the conduction width of the semiconductor switching device when the calculated estimated current value is equal to or greater than a set current conduction width change start point current, obtains the conduction width corresponding to the estimated current value and determines a 120-degree current conduction method switching pattern of the obtained conduction width. The AC-DC power conversion device according to claim 2, characterized by comprising the above.

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