Power conversion device

Abstract

To provide a power conversion device having a regeneration function and capable of improving stability as a device by enabling continuance of operation also at an increased DC voltage.SOLUTION: A power conversion device that performs conversion of electric power between an AC unit and a DC unit to which a load is connected via a plurality of semiconductor switching devices, comprises: a voltage detection circuit 70 that detects a DC voltage of the DC unit (a smooth capacitor 3); a controller 71 that controls a conduction width command for each semiconductor switching device so that a deviation between a detected DC voltage value detected by the voltage detection circuit 70 at activation of the device and a detected DC voltage value detected after the activation of the device is 0, and outputs a conduction width command as the result of the control; and a conduction width command limiter 72 that limits the conduction width command output from the controller 71 to 0° to 120. Each semiconductor switching device is driven with a switching pattern of 120-degree circulation scheme having a conduction width of the limited conduction width command.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A circuit example of the power conversion device handled in the present invention is shown in FIG. 11. In FIG. 11, 2 is composed of semiconductor switching devices R+, S+, T+, R-, S-, T- connected in a three-phase bridge configuration, and is a forward power conversion unit that converts the AC power of an AC power supply (1; AC section), not shown, into DC power. A smoothing capacitor 3 (DC section) and a load 4 are connected in parallel to the DC side of the forward power conversion unit 2.

[0003] The circuit in FIG. 11 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 section and the DC section can be adjusted, and the current waveform of the AC section and the voltage waveform of the DC section can be arbitrarily adjusted.

[0004] 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.

[0005] FIG. 12 shows the switching pattern of the 120-degree conduction method. The upper arms R+, S+, T+ turn on the semiconductor switching device of the phase where each phase voltage becomes maximum, and the lower arms R-, S-, T- turn on the semiconductor switching device of the phase where each phase voltage becomes minimum.

[0006] The 120-degree conduction method has the advantages of less loss generated in the semiconductor switching device and a simple control circuit, but has the disadvantages that the power amount cannot be adjusted and the current waveform of the AC section and the voltage waveform of the DC section cannot be arbitrarily controlled.

[0007] Particularly, since the waveform cannot be arbitrarily controlled, in a power conversion device having a regeneration function by a 120-degree current conduction method, when an AC voltage drop occurs, an excessive current (hereinafter sometimes referred to as an input current) flows from the DC part to the AC part. When the peak value of the input current 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 reducing the stability of the device.

[0008] This phenomenon can be avoided by adopting a PWM control method. However, there are cases where it is not easy to adopt the PWM control method because the switching loss of the semiconductor switching device increases and the control circuit becomes complex. A method that can be realized with the same number of switching operations and a simple control circuit is required.

[0009] Therefore, a related proposed method described in Patent Document 1 has been proposed to suppress the flow of an excessive input current from the DC part to the AC part even when the AC voltage drops.

[0010] Fig. 13 shows the switching operation in the related proposed method described in Patent Document 1, and Fig. 14 shows the effect when the related proposed method is mounted. Fig. 13(a) is the switching pattern of the 120-degree current conduction method in normal times (the same as Fig. 12), and Fig. 13(b) is the switching pattern of the 120-degree current conduction method when the AC voltage drops.

[0011] When the AC voltage is within the normal range, the switching of the 120-degree current conduction method similar to Fig. 12 shown in Fig. 13(a) is performed. When the AC voltage drops, the conduction width of each semiconductor switching device is narrowed as shown in Fig. 13(b).

[0012] That is, in Fig. 13(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.

[0013] Also, the ON period of the upper arm S+ is set to be a period from a time t3' which 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" which is a predetermined time earlier than the time t5 when the maximum voltage switches from the S phase to the T phase.

[0014] Also, the ON period of the upper arm T+ is set to be a period from a time t5' which 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 in the figure) which is a predetermined time earlier than the time when the maximum voltage switches from the T phase to the R phase.

[0015] Also, the ON period of the lower arm S- is set to be a period from a time (not shown in the figure) which 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" which is a predetermined time earlier than the time t2 when the minimum voltage switches from the S phase to the T phase.

[0016] Also, the ON period of the lower arm T- is set to be a period from a time t2' which 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" which is a predetermined time earlier than the time t4 when the minimum voltage switches from the T phase to the R phase.

[0017] Also, the ON period of the lower arm R- is set to be a period from a time t4' which 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" which is a predetermined time earlier than the time t6 when the minimum voltage switches from the R phase to the S phase.

[0018] Therefore, the conduction width of each semiconductor switching device in Fig. 13(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. 13(b) is not included).

[0019] According to the related proposed method in Fig. 13, compared with the 120° current conduction method, the conduction timing is delayed and conduction occurs after the power supply voltage of each phase has risen. Therefore, the potential difference (hereinafter referred to as ΔV) between the DC part and the AC part at the start of conduction can be reduced, and excessive input current flowing from the DC part to the AC part is suppressed.

[0020] By narrowing the conduction width of each semiconductor switching device when the AC voltage drops in this way, excessive current flow is suppressed as shown in Fig. 14(b) which shows the current behavior during voltage drop. Note that Fig. 14(a) shows the current behavior when controlled by a normal switching pattern, and excessive current occurs during voltage drop.

Prior Art Documents

Patent Documents

[0021]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0022] As a proposed method for realizing the method of narrowing the conduction width of the semiconductor switching device when the power supply voltage drops as described in Fig. 13(b), for example, Patent Document 1 describes configuring a control block as shown in Fig. 15.

[0023] In Fig. 15, the same parts as in Fig. 11 are denoted by the same reference numerals. 41 is a voltage detector that detects the three-phase AC voltage of the AC power supply 1 and is composed of, for example, an instrument transformer. 42 is a voltage detection circuit that obtains and outputs a voltage detection value from the detection output of the voltage detector 41. 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 supply voltage.

[0024] 44 is a voltage detection circuit that detects the DC voltage of the smoothing capacitor 3 in the DC part and outputs a DC voltage detection value. 60 uses 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 DC voltage detection value is equal to or higher than a set voltage, obtains the conduction width corresponding to the differential voltage, and determines a 120-degree current conduction method switching pattern of the obtained conduction width. It is a voltage-switching pattern calculator.

[0025] 30 is a semiconductor switching device drive circuit that drives each semiconductor switching device of the forward power conversion unit 2 in the switching pattern determined by the voltage-switching pattern calculator 60.

[0026] An example of the conduction width pattern used in the voltage-switching pattern calculator 60 is shown in FIG. 16. 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 of FIG. 16 to narrow the conduction width, an increase in the input current when the power supply voltage drops can be suppressed. However, the settings of the pattern in FIG. 16 (such as the conduction width change start point and the point where the conduction width becomes 0° (differential voltage value)) need to be adjusted on-site according to the installation environment and operating conditions.

[0027] The operation time chart of the control block of the related proposed method shown in FIG. 15 is shown in FIG. 17. In the top row of FIG. 17, the effective value of the power supply voltage (Vac), in the second row from the top, the DC voltage detection value Vdc, in the third row from the top, the conduction width determined by the voltage switching pattern calculator 60, and in the bottom row, the peak value of the input current flowing from the DC part to the AC part are shown respectively.

[0028] First, when the system starts at time ta, the effective value of the power supply voltage Vac and the DC voltage detection value Vdc rise. At this time, regardless of the conduction width, an input current corresponding to the potential difference flows from the AC part to the DC part.

[0029] Next, when the power supply voltage drops at time tb, the conduction width is narrowed instantaneously. As a result, the rise of the input current at time tb is suppressed.

[0030] Next, when the load regeneration starts at time tc, the input current starts to flow from the DC part to the AC part.

[0031] Next, when the power supply voltage recovers at time td, regardless of the conduction width, an input current corresponding to the potential difference flows from the AC part to the DC part.

[0032] Next, when the power supply voltage drops at time te, the conduction width is narrowed. As a result, the increase in the input current at time tf is suppressed.

[0033] Next, when the amount of regeneration from the load further increases at time tf, the conduction width is narrowed as the DC voltage rises. As a result, it becomes impossible to regenerate to the power supply side, resulting in an overvoltage.

[0034] In the conduction width pattern used in the related proposed method of FIG. 15 as described above, when the power supply voltage drops (times tb and te in FIG. 17), the conduction width is narrowed to prevent the input current from becoming excessive. However, in the situation where the amount of regeneration from the load side increases (time tf in FIG. 17), with the preset conduction width pattern, it is impossible to regenerate to the power supply side. When the DC bus voltage rises, the conduction width is further narrowed and the operation moves in the direction of reducing the regeneration amount. Therefore, there is a risk of damage to the device due to the rise in the DC bus voltage or the operation stop by the safety device of the device.

[0035] The present invention solves the above problems, and its object is to prevent the input current from becoming excessive from the DC part to the AC part in the DC voltage drop situation, and to prevent the input current and the DC voltage from becoming excessive in the DC voltage rise situations such as load regeneration and increase in the load regeneration amount. It is to provide a power conversion device that can do so.

[0036] Specifically, in a power conversion device having a regeneration function, the operation is made continuous even when the DC voltage rises, aiming to improve the stability of the device.

Means for Solving the Problems

[0037] The power conversion device according to claim 1 for solving the above problems is A power conversion device capable of performing power running operation and regeneration operation, and performing power conversion between an AC part and a DC part to which a load is connected by a plurality of semiconductor switching devices, A DC voltage detection circuit for detecting the DC voltage of the DC part, A control unit that controls the conduction width command of the semiconductor switching device so that the deviation between the DC voltage detection value detected at the time of device startup and the DC voltage detection value detected after device startup becomes zero by the DC voltage detection circuit, and outputs the conduction width command of the control result; A conduction width command limiter that limits the conduction width command output from the control unit to 0° to 120°; The semiconductor switching device is driven by a 120-degree current conduction method switching pattern having a conduction width of the conduction width command limited by the conduction width command limiter.

[0038] The power conversion device according to claim 2, in claim 1, At the time of device startup, the control unit initializes the conduction width command of the semiconductor switching device to 0°, then latches the DC voltage detection value, and controls the conduction width command of the semiconductor switching device so that the deviation between the latched DC voltage detection value and the DC voltage detection value detected after device startup becomes zero, and outputs the conduction width command of the control result.

[0039] The power conversion device according to claim 3, In a power conversion device capable of power running operation and regeneration operation, and performing power conversion between an AC part and a DC part to which a load is connected by a plurality of semiconductor switching devices, A DC voltage detection circuit that detects the DC voltage of the DC part; A regeneration operation necessity determination unit that determines the necessity of the regeneration operation based on the DC voltage detection value detected by the DC voltage detection circuit and the load current detection value obtained by detecting the current flowing through the load; A control unit that controls the conduction width command of the semiconductor switching device so that the deviation between the DC voltage detection value detected by the DC voltage detection circuit when the regeneration operation necessity determination unit determines that the regeneration operation is necessary and the DC voltage detection value constantly detected by the DC voltage detection circuit becomes zero, and outputs the conduction width command of the control result; A conduction width command limiter that limits the conduction width command output from the control unit to 0° to 120°; The semiconductor switching device is driven by a 120-degree conduction mode switching pattern having a conduction width of a conduction width command limited by the conduction width command limiter.

[0040] The power conversion device according to claim 4, in claim 3, When the device is starting up or when the regeneration operation execution command is off when the device is not starting up, and the previous value of the load current detection value is greater than a set load current margin value and the current value of the load current detection value is smaller than the load current margin value, the DC voltage detection value of the DC voltage detection circuit is latched. After the latching of the DC voltage detection value or when the regeneration operation execution command is off and the previous value of the load current detection value is not greater than the set load current margin value and the current value of the load current detection value is not smaller than the load current margin value, When the DC voltage detection value other than at the time of latching is greater than a value obtained by adding a set voltage margin value to the latched DC voltage detection value, it is determined that a regeneration operation is required and the regeneration operation execution command is turned on. When the device is not starting up and the regeneration operation execution command is not off, and the DC voltage detection value other than at the time of latching is smaller than a value obtained by adding the voltage margin value to the latched DC voltage detection value and the current value of the load current detection value is greater than the load current margin value, it is determined that a regeneration operation is not required and the regeneration operation execution command is turned off. It is characterized by outputting the on or off regeneration operation execution command.

[0041] The power conversion device according to claim 5, in claim 4, When the regeneration operation execution command output from the regeneration operation necessity determination unit changes from off to on, the control unit latches the DC voltage detection value, determines whether the regeneration operation execution command is on, and when the regeneration operation execution command is on, controls the conduction width command of the semiconductor switching device so that the deviation between the latched DC voltage detection value and the DC voltage detection value other than at the time of latching becomes zero, and outputs the conduction width command of the control result or, when the regeneration operation execution command is not on, outputs the conduction width command with the conduction width command set to zero.

[0042] The power conversion device according to claim 6 is a power conversion device capable of performing a power running operation and a regeneration operation, and performing power conversion between an AC part and a DC part to which a load is connected by a plurality of semiconductor switching devices. A DC voltage detection circuit that detects the DC voltage of the DC part; A power supply voltage effective value calculation unit that detects the power supply voltage of the AC part and calculates its effective value; When the effective value of the power supply voltage after the device is started, calculated by the power supply voltage effective value calculation unit, exceeds the effective value of the power supply voltage at the time of device startup, the excess ratio is multiplied by the first DC voltage detection value detected at the time of device startup to obtain a second DC voltage detection value, and the conduction width command of the semiconductor switching device is controlled so that the deviation between the second DC voltage detection value and the DC voltage detection value detected after the device is started becomes zero, and a control unit that outputs the conduction width command of the control result; A conduction width command limiter that limits the conduction width command output from the control unit to 0° to 120°; The semiconductor switching device is driven by a 120-degree current conduction method switching pattern having the conduction width of the conduction width command limited by the conduction width command limiter.

[0043] The power conversion device according to claim 7 is as described in claim 6, The control unit is characterized in that, at the time of device startup, after initializing the conduction width command of the semiconductor switching device to 0°, it latches the effective value of the power supply voltage at the time of device startup and the first DC voltage detection value at the time of device startup.

Advantages of the Invention

[0044] (1) According to the invention described in claims 1 to 7, it is possible to prevent the input current from the DC part to the AC part from becoming excessive in the DC voltage drop phase, and to prevent the input current and the DC voltage from becoming excessive in the DC voltage rise phase such as during load regeneration or when the load regeneration amount increases. (2) According to the invention described in claims 3 to 5, the regeneration operation can be performed only when it is determined that the regeneration operation is necessary. (3) According to the invention described in claim 5, since the power supply regeneration operation can be started when the voltage always rises by the voltage margin value from the DC voltage detection value immediately before the start of regeneration, the difference between the effective value of the AC power supply voltage and the DC voltage detection value during the power supply regeneration operation does not increase, and it is possible to prevent the input current from the DC part to the AC part from becoming excessive at the start of the power supply regeneration operation. (4) According to the invention described in claims 6 and 7, it is possible to prevent the input current from the DC part to the AC part from becoming excessive in the power supply voltage recovery phase after the power supply voltage has risen.

Brief Description of the Drawings

[0045]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Mode for Carrying Out the Invention

[0046] 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.

Example

[0047] The DC voltage from system startup to load connection is determined only by the power supply voltage. In Embodiment 1, a method is proposed in which the power supply voltage at system startup and the DC voltage in the equilibrium state are used as target values, and the conduction width is controlled so as to always maintain the DC voltage.

[0048] FIG. 1 is a control block diagram in Embodiment 1, and the same parts as in FIG. 15 are denoted by the same reference numerals. 70 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.

[0049] 71 is a controller that performs the control operation of FIG. 2 described later. At the time of system startup, it latches the steady-state value of the DC voltage detection value (hereinafter also referred to as Vdc * ), and thereafter uses Vdc * as the command value, and constantly controls the conduction width command so that the deviation from the detected DC voltage detection value (Vdc) becomes 0, and outputs it to the conduction width command limiter 72.

[0050] The conduction width command limiter 72 limits the conduction width command from the controller 71 to a value between 0° and 120° and outputs it to the semiconductor switching device drive circuit 73.

[0051] The semiconductor switching device drive circuit 73 drives the semiconductor switching device of the forward power conversion unit 2 by a 120-degree current conduction method switching pattern having the conduction width of the conduction width command limited by the conduction width command limiter 72.

[0052] In FIG. 2 showing the control flow of the controller 71, first in step S1, it is determined whether it is at the time of system startup. If it is at startup (True), after initializing the conduction width to 0° in step S2, the DC voltage detection value Vdc * is latched in step S3.

[0053] After the execution of step S3, or if it is determined in step S1 that it is not at the time of system startup (False), in step S4, Vdc * - Vdc is input to a PI controller or the like as a deviation, and the conduction width command is controlled so that the deviation becomes 0.

[0054] Thereafter, in step S5, the conduction width command of the control result is output and the process ends.

[0055] The operation time chart of the control block in FIG. 1 above is shown in FIG. 3.

[0056] In Fig. 3, the topmost shows the effective value of the power supply voltage (Vac), the second row from the top shows the DC voltage detection values Vdc (solid line), Vdc * (dashed line; latched at startup as the command value), the third row from the top shows the conduction width generated by the controller 71 (dashed line), the conduction width generated by the conduction width command limiter 72 (solid line), and the bottom row shows the peak value of the input current flowing from the DC part to the AC part, respectively.

[0057] First, when the system starts at time t1, the effective value of the power supply voltage Vac and the DC voltage detection value Vdc rise. At this time, regardless of the conduction width, an input current corresponding to the potential difference flows from the AC part to the DC part.

[0058] Next, at time t2, it is initialized with a conduction width of 0° (step S2 in Fig. 2), and at time t3, Vdc * is latched (step S3 in Fig. 2), and at time t4, the conduction width control is started (steps S4 and S5 in Fig. 2).

[0059] Next, when the power supply voltage drops at time t5, both the effective value of Vac and Vdc decrease, and the deviation between Vdc and Vdc * becomes large, and the conduction width generated by the controller 71 enters the negative region. As a result, the input current from the DC part to the AC part is suppressed.

[0060] Next, when the load regeneration starts at time t6a, the DC voltage detection value Vdc gradually rises, and the deviation from the Vdc * latched at startup gradually becomes smaller, and the conduction width generated by the controller 71 gradually approaches 0°.

[0061] Next, at time t6b when the deviation between Vdc and Vdc * becomes almost 0, the conduction width takes a positive value, and the input current starts to flow from the DC part to the AC part.

[0062] Next, when the power supply voltage recovers at time t7, the conduction width expands.

[0063] Next, when the power supply voltage drops at time t8, the conduction width narrows. As a result, the increase in the input current is suppressed.

[0064] Next, when the load regeneration amount further increases at time t9, the conduction width widens. This prevents Vdc from rising to an overvoltage.

[0065] Next, when the power supply voltage recovers at time t10, the conduction width widens.

[0066] Next, when the power supply voltage rises at time t11, the potential of the DC part is pushed up by the power supply voltage, so the deviation between Vdc and Vdc * becomes large. Although the conduction width generated by the controller 71 continues to widen in an attempt to reduce the deviation, the deviation does not shrink. At this time, the conduction width generated by the conduction width command limiter 72 continues to widen but is finally limited to 120°. Also, at this time, regardless of the conduction width, an input current corresponding to the potential difference is supplied from the AC part to the DC part.

[0067] Next, when the power supply voltage recovers at time t12, since the conduction width generated by the conduction width command limiter 72 has expanded to 120°, a large input current is supplied from the DC part to the AC part, resulting in an overcurrent.

[0068] By the above operation, it is possible to prevent the input current from becoming excessive from the DC part to the AC part in the power supply voltage drop phase, and to prevent the input current and the DC voltage from becoming excessive in the DC voltage rise phases such as during load regeneration or when the load regeneration amount increases.

Example

[0069] Due to load fluctuations, the load current and the DC voltage change. In the second embodiment, a method is proposed in which the regeneration operation is performed only when it is determined that the power supply regeneration operation is necessary based on the load current and the DC voltage. Also, during the regeneration operation, the DC voltage at the start of the regeneration operation is set as the target value, and control is performed to maintain that DC voltage.

[0070] FIG. 4 is a control block diagram in the second embodiment, and the same parts as those in FIG. 1 are denoted by the same reference numerals.

[0071] The difference between FIG. 4 and FIG. 1 is that a regeneration operation necessity determination module 80 for determining the necessity of the regeneration operation is newly provided based on the DC voltage detection value detected by the voltage detection circuit 70 and the load current detection value obtained by detecting the current flowing through the load 4, and instead of the controller 71, when the determination module 80 determines that the regeneration operation is necessary, the conduction width command of the semiconductor switching device is controlled so that the deviation between the DC voltage detection value detected by the voltage detection circuit 70 and the DC voltage detection value constantly detected by the voltage detection circuit 70 becomes zero, and a controller 81 for outputting the conduction width command of the control result is provided. Other parts are configured in the same manner as in FIG. 1.

[0072] In the regeneration operation necessity determination module 80 realized by an arithmetic element such as a CPU, the necessity of the power regeneration operation is always determined based on the sign and magnitude of the load current and the magnitude of the DC voltage, and a regeneration operation execution command is sent to the controller 81 (hereinafter, the load current is denoted as IL, and the DC voltage latched in the regeneration operation necessity determination module 80 is denoted as Vdc´).

[0073] FIG. 5 shows an outline of the control flow of the regeneration operation necessity determination module 80. First, in step S11, it is determined whether or not it is at the time of system startup. If it is at startup (in the case of True), the DC voltage detection value of the voltage detection circuit 70 is latched in step S12.

[0074] If the determination result in step S11 is not at startup (in the case of False), it is determined in step S13 whether or not the regeneration operation execution command is off.

[0075] If the determination result in step S13 is True (in the case where the regeneration operation execution command is off), in step S14, it is determined whether or not the previous value of the load current detection value is larger than the set load current margin value (0 + margin < IL previous value) and the current value of the load current detection value is smaller than the load current margin value (IL current value < 0 + margin).

[0076] When the determination result in step S14 is True, the DC voltage detection value Vdc´ is latched in step S12.

[0077] After the process of step S12 or when the determination result in step S14 is False, in step S15, it is determined whether the DC voltage detection value Vdc other than during latching is greater than the value obtained by adding the voltage margin set for the latched DC voltage detection value Vdc´.

[0078] As a result, when Vdc is greater than Vdc´ + margin, the regeneration operation execution command is turned on in step S16. When the determination result in step S15 is False (when Vdc is not greater than Vdc´ + margin), the process of step S16 is bypassed.

[0079] When the determination result in step S13 is False (when the regeneration operation execution command is not off), in step S17, it is determined whether the DC voltage detection value Vdc other than the latch is less than the value obtained by adding the voltage margin value to the latched DC voltage detection value Vdc´ and whether the current value of the load current detection value IL is greater than the load current margin value (0 + margin).

[0080] When the determination result in step S17 is True (for example, when in the power running state and it is determined that there is no regeneration operation), the regeneration operation execution command is turned off in step S18. When the determination result in step S17 is False, the process of step S18 is bypassed.

[0081] Next, in step S19, the regeneration operation execution command that has been turned on or off according to the processes of steps S15, S16, S17, and S18 is output to the controller 81, and the process ends.

[0082] In the controller 81 of FIG. 4, at the rising edge of the above-described regeneration operation execution command, the DC voltage detection value is latched. While the regeneration operation execution command is ON, the latched DC voltage detection value Vdc' is used as the command value, and the conduction width command is controlled so that the deviation from the DC voltage detection value Vdc that is constantly detected becomes zero, and is output to the conduction width command limiter 72.

[0083] FIG. 6 shows an outline of the control flow of the controller 81. In FIG. 6, first, in step S21, it is determined whether or not the regeneration operation execution command output from the regeneration operation necessity determination module 80 has risen from OFF to ON.

[0084] If the determination result in step S21 is True (when it has risen from OFF to ON), in step S22, the DC voltage detection value Vdc * is latched, and then in step S23, it is determined whether or not the regeneration operation execution command is ON.

[0085] If the determination result in step S21 is False (when the regeneration operation execution command has not risen from OFF to ON), the process of step S22 is bypassed.

[0086] If the determination result in step S23 is True (when it is ON), in step S24, Vdc * -Vdc is input to a PI controller or the like as a deviation, and the conduction width command is controlled so that the deviation becomes zero.

[0087] If the determination result in step S23 is False (when the regeneration operation command is OFF), in step S25, the conduction width command is set to zero.

[0088] Next, in step S26, the conduction width command of the control result processed in step S24 or the conduction width command of zero after the process of step S25 is output to the conduction width command limiter 72, and the process ends.

[0089] The operation time chart of the control block in FIG. 4 is shown in FIG. 7. In FIG. 7, the uppermost row shows the effective value of the power supply voltage (Vac), the second row from the top shows the DC voltage detection values Vdc (solid line), Vdc * (dashed line; latched at startup and used as the command value), Vdc´ (very thin dashed line; latched within the regeneration operation necessity determination module 80), the third row from the top shows the conduction width (solid line) generated by the controller 71 and the conduction width command limiter 72, the internal calculation value of the conduction width (dashed line), and the lowermost row shows the peak value of the input current flowing from the DC part to the AC part, respectively.

[0090] First, when the system starts up at time t1, the effective value of the power supply voltage Vac and the DC voltage detection value Vdc rise and increase to 100% respectively.

[0091] Next, at time t3, Vdc´ is latched.

[0092] Next, when the power supply voltage drops at time t4, both the effective value of Vac and Vdc drop to 50%, and the deviation between Vdc and Vdc´ becomes large.

[0093] Next, when the load regeneration starts at time t5, Vdc gradually increases.

[0094] Next, when the power supply regeneration operation start time t6 arrives, a value of 100% Vdc appears due to latching, the conduction width command is widened to 30°, and the input current from the DC part to the AC part rises to 100%. * The value appears, the conduction width command is widened to 30°, and the input current from the DC part to the AC part rises to 100%.

[0095] Next, when the power supply voltage recovers at time t7, the effective value of Vac rises to 100%, the conduction width rises to 60°, the input current becomes smaller than 100% for a moment but then returns to 100% again.

[0096] Next, when the power supply voltage drops at time t8, the effective value of Vac drops to 50%, and the conduction width is narrowed from 60° to 30°. At this time, the deviation between Vdc and Vdc * becomes large for a moment but then returns to almost zero deviation again, and the input current rises to around 140% for a moment but is then suppressed to 100% again.

[0097] Next, when the load regeneration amount further increases at time t9, the input current rises to 150%, and the conduction width is widened from 30° to 60°. At this time, Vdc becomes momentarily larger than Vdc * but the deviation between the two becomes almost 0 again, preventing Vdc from rising to an overvoltage.

[0098] Next, when the power supply voltage recovers at time t10, the effective value of Vac rises to 100%, and the conduction width is widened to 90°. At this time, the input current drops momentarily but then returns to 150% again.

[0099] Next, when the load regeneration ends at time t11, the conduction width becomes 0°, and the input current becomes 0%. Next, when the device stops at time t12, the effective value of Vac and Vdc become 0.

[0100] By the above operation, since the conduction width is automatically controlled so that the DC voltage is kept constant at the value at the start of the regeneration operation, in the power supply voltage drop phase (times t4, t8), the input current is prevented from becoming excessive by narrowing the conduction width, and also in the DC voltage rise phase such as at the start of load regeneration (time t5) or when the load regeneration amount increases (time t9), it is possible to prevent the input current and the DC voltage from becoming excessive by controlling to an appropriate conduction width that maintains the balance between the power supply voltage and the DC voltage (the same effect as in Embodiment 1).

[0101] Also, when starting the power supply regeneration operation during the operation of the system, if the power supply regeneration operation is started with Vdc being excessive with respect to the effective value of Vac, an excessive input current will flow. However, in this method, since the power supply regeneration operation is always started when the DC voltage Vdc' has risen by the margin from just before the start of regeneration (the determination result in step S15 of FIG. 5), the difference between the effective value of Vac and Vdc at the start of the power supply regeneration operation does not become large unless the margin is set too large, and it is possible to suppress the input current from becoming excessive at the start of the power supply regeneration operation.

[0102] In addition, since the conduction width gradually expands to an appropriate conduction width from 0° after the start of the power regeneration operation (time t6), it is possible to suppress the input current from becoming excessive at the start of the power regeneration operation.

[0103] As described above, according to the first and second embodiments, by adjusting the conduction width of the semiconductor switching device according to the DC voltage value, it is possible to prevent an increase in the current amount during a decrease in the AC voltage and an increase in the voltage during an increase in the DC voltage, and to prevent damage to the device and unnecessary device stoppage.

[0104] In addition, compared with the configuration of FIG. 12, since a power supply voltage detection circuit becomes unnecessary, the device can be miniaturized and the cost can be reduced.

Embodiment

[0105] In the control method of the first embodiment, it is possible to prevent the input current from the DC part to the AC part from becoming excessive in the situation of a decrease in the power supply voltage, and to prevent the input current and the DC voltage from becoming excessive in the situation of an increase in the DC voltage such as during load regeneration or an increase in the load regeneration amount. However, in the situation where the power supply voltage exceeds the value at the start (time t11 in FIG. 3), since the conduction width is widened beyond the conduction width necessary for regeneration on the power supply side, in the subsequent situation where the power supply voltage recovers (time t12 in FIG. 3), there is a risk of damage to the device due to an excessive input current and operation stop by a safety device of the device.

[0106] Therefore, in the third embodiment, similar to the first embodiment, in the situation of a decrease in the AC power supply voltage, it is possible to prevent the input current from the DC part to the AC part from becoming excessive, and in the situation of an increase in the DC voltage such as during load regeneration or an increase in the load regeneration amount, it is possible to prevent the input current and the DC voltage from becoming excessive, and to prevent the input current from the DC part to the AC part from becoming excessive in the situation of recovery of the power supply voltage after the power supply voltage has risen.

[0107] FIG. 8 is a control block diagram in Embodiment 3, and the same parts as those in FIG. 1 are denoted by the same reference numerals. 101 is a voltage detector that detects the three-phase AC voltage of the AC power supply 1 and is composed of, for example, an instrument transformer. 102 is a voltage detection circuit that obtains a voltage detection value from the detection output of the voltage detector 101 and outputs it. 103 is a voltage effective value calculator that calculates the effective value of the voltage detection value from the voltage detection circuit 102 and outputs the effective value of the power supply voltage.

[0108] 104 is a voltage detection circuit that detects the DC voltage of the smoothing capacitor 3 in the DC part and outputs a DC voltage detection value.

[0109] 105 is a controller that performs the control operation of FIG. 9 described later. At the time of system startup, it latches the steady-state value of the effective value of the power supply voltage (hereinafter also referred to as Vac) * and the steady-state value of the DC voltage detection value (hereinafter also referred to as Vdc * (the first DC voltage detection value)), and thereafter, the value obtained by multiplying the excess ratio of the effective value of the power supply voltage (Vac) with respect to Vac * by Vdc * (hereinafter also referred to as Vdc ** (the second DC voltage detection value)) is used as a command value, and the conduction width command is always controlled so that the deviation from the detected DC voltage detection value (Vdc) becomes 0, and is output to the conduction width command limiter 106.

[0110] The conduction width command limiter 106 limits the conduction width command from the controller 105 to a value between 0° and 120° and outputs it to the semiconductor switching device drive circuit 107.

[0111] The semiconductor switching device drive circuit 107 drives the semiconductor switching device of the forward power conversion unit 2 according to a 120-degree conduction mode switching pattern having the conduction width of the conduction width command limited by the conduction width command limiter 106.

[0112] In FIG. 9 showing the control flow of the controller 105, first, at step S31, it is determined whether it is the time of system startup. If it is the startup time (True), then at step S32, after initializing the conduction width to 0°, at step S33, the effective value of the power supply voltage Vac * and the detected value of the DC voltage Vdc * are latched.

[0113] If it is after the execution of step S33 or if it is determined at step S31 that it is not the time of system startup (False), then at step S34, it is determined whether Vac exceeds Vac * . If it exceeds (True), then at step S35, the value obtained by multiplying the excess ratio of Vac with respect to Vac * by Vdc * is calculated as Vdc ** . If it does not exceed (False), then at step S36, Vdc ** is initialized with Vdc * .

[0114] The excess ratio is given by the following formula. Excess ratio = (Vac - Vac * ) / Vac * After the execution of step S35 or step S36, at step S37, by inputting Vdc ** - Vdc as a deviation to a PI controller or the like, the conduction width command is controlled so that the deviation becomes 0.

[0115] Thereafter, at step S38, the conduction width command of the control result is output and the process ends.

[0116] The operation time chart of the control block in FIG. 8 above is shown in FIG. 10. In FIG. 10, the uppermost line is the effective value of the power supply voltage Vac (solid line), Vac * (dashed line; the value latched at startup), the second line from the top is the detected value of the DC voltage Vdc (solid line), and the value obtained by multiplying Vdc * by the excess ratio of the effective value of the power supply voltage (Vac) with respect to Vac * as Vdc **(Dashed line), the third line from the top shows the conduction width (dashed line) generated by the controller 105, the conduction width (solid line) generated by the conduction width command limiter 106, and the bottom line shows the peak value of the input current flowing from the DC part to the AC part respectively.

[0117] First, when the system starts at time t1, the effective value of the power supply voltage Vac and the detected value of the DC voltage Vdc rise. At this time, regardless of the conduction width, an input current corresponding to the potential difference flows from the AC part to the DC part.

[0118] Next, at time t2, it is initialized with a conduction width of 0° (step S32 in FIG. 9), and at time t3, Vac * and Vdc * are latched (step S33 in FIG. 9), and at time t4, the conduction width control is started (steps S37, S38 in FIG. 9).

[0119] Next, when the power supply voltage drops at time t5, both the effective value of Vac and Vdc decrease, and the deviation between Vdc and Vdc * becomes large, and the conduction width generated by the controller 105 enters the negative region. As a result, the input current from the DC part to the AC part is suppressed.

[0120] Next, when the load regeneration starts at time t6a, the detected value of the DC voltage Vdc gradually rises, and the deviation from the Vdc * latched at startup gradually becomes smaller, and the conduction width generated by the controller 105 gradually approaches 0°.

[0121] Next, at time t6b when the deviation between Vdc and Vdc * becomes almost 0, the conduction width takes a positive value, and an input current starts to flow from the DC part to the AC part.

[0122] Next, when the power supply voltage recovers at time t7, the conduction width expands. Next, when the power supply voltage drops at time t8, the conduction width narrows. As a result, the increase in the input current is suppressed. Next, when the load regeneration amount further increases at time t9, the conduction width increases. This prevents Vdc from rising to an overvoltage.

[0123] Next, when the power supply voltage recovers at time t10, the conduction width increases. Next, when the power supply voltage rises at time t11 and it is detected that the effective value of the power supply voltage Vac exceeds the effective value of the power supply voltage Vac latched at startup, * the ratio of the excess of Vac over Vac is multiplied by Vdc * to calculate a value Vdc * (step S35 in FIG. 9), and conduction width control is continued with the calculated Vdc ** as the command value. ** This prevents the conduction width from expanding beyond the conduction width necessary for regeneration to the power supply side. At this time, an input current corresponding to the potential difference is supplied from the AC part to the DC part regardless of the conduction width.

[0124] Next, when it is detected at t12 that the power supply voltage has recovered and the effective value of the power supply voltage Vac no longer exceeds the effective value of the power supply voltage Vac latched at startup, Vdc

[0125] is initialized with Vdc * (step S36 in FIG. 9), and conduction width control is continued with the initialized Vdc ** as the command value. * ** **

[0126] ​As described above, in the embodiment of FIG. 8, similar to Embodiment 1, it is possible to prevent the input current from becoming excessive from the DC part to the AC part during the power supply voltage drop phase, and to prevent the input current and the DC voltage from becoming excessive during the DC voltage rise phase such as during load regeneration or an increase in the load regeneration amount. Also, in the phase where the power supply voltage exceeds the value at startup (time t11 in FIG. 10), it is possible to prevent the conduction width from being expanded beyond the conduction width necessary for regeneration to the power supply side, and in the subsequent phase where the power supply voltage recovers (time t12 in FIG. 10), it is possible to prevent damage to the device due to excessive input current and the operation stop by the safety device of the device. (The peak value of the input current at time t12 is lower in FIG. 10 than in FIG. 3).

[0127] As described above, according to the third embodiment, in the power supply voltage rise phase, by increasing the DC voltage command value by the rate of increase of the power supply voltage, it is possible to prevent the conduction width from being expanded beyond the conduction width of the semiconductor switching device necessary for regeneration to the power supply side.

[0128] Also, as in step S37 of FIG. 9, Vdc ** -Vdc is input as a deviation to a general PI controller or the like, and the conduction width command is controlled so that the deviation becomes zero. By adopting such a structure, a general PI controller or the like only needs to be adjusted once, and it is possible to cope even when the load regeneration amount or the power supply voltage fluctuates. Also, during regeneration, in order to adjust the conduction width so as to keep the DC voltage Vdc constant, unlike the 120-degree current conduction method, the driving / regeneration loop where the DC voltage Vdc drops due to excessive regeneration to the power supply side and the DC voltage Vdc rises due to supply from the power supply side is repeated will not occur.

[0129] As a result, the stability of control is improved. In the subsequent phase where the power supply voltage recovers, it is possible to prevent damage to the device due to excessive input current and the operation stop by the safety device of the device.

Explanation of Reference Numerals

[0130] 1... AC power supply 2... Forward power conversion unit 3... Smoothing capacitor 4…Load 70, 104…Voltage detection circuit 71, 81, 105…Controller 72, 106…Conduction width command limiter 73, 107…Semiconductor switching device drive circuit 80…Regeneration operation necessity determination module

Claims

1. In a power conversion device capable of performing a power running operation and a power regeneration operation, and performing power conversion between an AC section and a DC section to which a load is connected by a plurality of semiconductor switching devices, a DC voltage detection circuit for detecting the DC voltage of the DC section; a control unit that controls the conduction width command of the semiconductor switching device so that the deviation between the DC voltage detection value detected at the time of device startup and the DC voltage detection value detected after device startup becomes zero by the DC voltage detection circuit, and outputs the conduction width command of the control result; a conduction width command limiter that limits the conduction width command output from the control unit to 0° to 120°; A power conversion device, characterized in that the semiconductor switching device is driven by a 120-degree current conduction method switching pattern having a conduction width of the conduction width command limited by the conduction width command limiter.

2. The power conversion device according to claim 1, wherein the control unit initializes the conduction width command of the semiconductor switching device to 0° at the time of device startup, then latches the DC voltage detection value, and controls the conduction width command of the semiconductor switching device so that the deviation between the latched DC voltage detection value and the DC voltage detection value detected after device startup becomes zero, and outputs the conduction width command of the control result.

3. In a power conversion device capable of performing a power running operation and a power regeneration operation, and performing power conversion between an AC section and a DC section to which a load is connected by a plurality of semiconductor switching devices, a DC voltage detection circuit for detecting the DC voltage of the DC section; a regeneration operation necessity determination unit that determines the necessity of a regeneration operation based on the DC voltage detection value detected by the DC voltage detection circuit and the load current detection value obtained by detecting the current flowing through the load; a control unit that controls the conduction width command of the semiconductor switching device so that the deviation between the DC voltage detection value detected by the DC voltage detection circuit when the regeneration operation necessity determination unit determines that a regeneration operation is necessary and the DC voltage detection value constantly detected by the DC voltage detection circuit becomes zero, and outputs the conduction width command of the control result; a conduction width command limiter that limits the conduction width command output from the control unit to 0° to 120°; A power conversion device, characterized in that the semiconductor switching device is driven by a 120-degree current conduction method switching pattern having a conduction width of the conduction width command limited by the conduction width command limiter.

4. The regeneration operation necessity determination unit latches the DC voltage detection value of the DC voltage detection circuit when it is at the time of device startup or when the regeneration operation execution command is off when it is not at the time of device startup, and the previous value of the load current detection value is greater than a set load current margin value, and the current value of the load current detection value is smaller than the load current margin value. After latching the DC voltage detection value, or when the regeneration operation execution command is off and the previous value of the load current detection value is not greater than the set load current margin value, and the current value of the load current detection value is not smaller than the load current margin value. When the DC voltage detection value other than at the time of latching is greater than the value obtained by adding a set voltage margin value to the latched DC voltage detection value, it is determined that the regeneration operation is necessary and the regeneration operation execution command is turned on. When it is not at the time of device startup and the regeneration operation execution command is not off, and the DC voltage detection value other than at the time of latching is smaller than the value obtained by adding the voltage margin value to the latched DC voltage detection value, and the current value of the load current detection value is greater than the load current margin value, it is determined that the regeneration operation is not necessary and the regeneration operation execution command is turned off. The power conversion device according to claim 3, characterized in that it outputs the on or off regeneration operation execution command.

5. When the regeneration operation execution command output from the regeneration operation necessity determination unit changes from off to on, the control unit latches the DC voltage detection value, determines whether the regeneration operation execution command is on, and when the regeneration operation execution command is on, controls the conduction width command of the semiconductor switching device so that the deviation between the latched DC voltage detection value and the DC voltage detection value other than at the time of latching becomes zero, and outputs the conduction width command of the control result or the conduction width command with the conduction width command set to 0 when the regeneration operation execution command is not on. The power conversion device according to claim 4, characterized in that it does so.

6. In a power conversion device capable of performing power running operation and regeneration operation, and performing power conversion between an AC section and a DC section to which a load is connected by a plurality of semiconductor switching devices, A DC voltage detection circuit for detecting the DC voltage of the DC section; A power supply voltage effective value calculation unit for detecting the power supply voltage of the AC section and calculating its effective value; When the effective value of the power supply voltage after device startup calculated by the power supply voltage effective value calculation unit exceeds the effective value of the power supply voltage at device startup, the excess ratio is multiplied by the first DC voltage detection value detected at device startup to obtain a second DC voltage detection value, and the conduction width command of the semiconductor switching device is controlled so that the deviation between the second DC voltage detection value and the DC voltage detection value detected after device startup becomes zero, and a control unit that outputs the conduction width command of the control result; A conduction width command limiter that limits the conduction width command output from the control unit to 0° to 120°; A power conversion device characterized by driving the semiconductor switching device by a 120-degree current conduction method switching pattern having a conduction width of the conduction width command limited by the conduction width command limiter.

7. The power conversion device according to claim 6, wherein the control unit initializes the conduction width command of the semiconductor switching device to 0° at device startup, and then latches the effective value of the power supply voltage at device startup and the first DC voltage detection value at device startup.

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