POWER CONVERSION DEVICE, POWER CONVERSION CONTROL METHOD, AND POWER CONVERSION CONTROL PROGRAM

Abstract

To suppress a fluctuation in a DC voltage outputted from a converter.SOLUTION: A power conversion device 100 includes a converter 21 that converts AC voltage Vs to DC voltage Vdc, smoothing capacitors 22, 23, 32, 33 for suppressing a fluctuation in the DC voltage Vdc, and an inverter 31 that converts to AC power the DC voltage Vdc stored in the smoothing capacitors 22, 23, 32, 33. The device includes DC voltage detectors 25, 26 that detect the DC voltage Vdc, a current detector 7 that detects AC power source-side current I_c, a DC voltage controller 52 that generates a converter input current command AVROUT so as to adjust the DC voltage Vdc to be equal to a DC voltage command value Vref, a converter output current controller 53 that controls the converter AC voltage so as to adjust the AC power source-side current I_c to be equal to the generated converter input current command AVROUT, and an adder 56 that adds a converter-side power compensation value to the converter input current command AVROUT.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a power conversion device including a converter and an inverter, and more particularly to a power conversion device, a power conversion control method, and a power conversion control program capable of suppressing converter DC voltage fluctuations that accompany sudden load changes. [Background technology]

[0002] There are known power conversion devices that convert the power of an AC power source into variable-voltage, variable-frequency power. The main circuits of these power conversion devices are composed of a converter that converts AC voltage into DC voltage, a DC circuit equipped with a large-capacity smoothing capacitor, and an inverter that converts DC into AC. In particular, the smoothing capacitor occupies a large volume proportion of the entire power conversion device, and reducing its size is essential to making the power conversion device more compact.

[0003] One of the functions of a smoothing capacitor is to suppress DC voltage fluctuations caused by mismatches in power transfer between the converter and the inverter. Therefore, if DC voltage fluctuations can be reduced separately, the capacitor capacity can be reduced, making it possible to make the device more compact. For example, Patent Documents 1 and 2 disclose the following technologies. (1) The output current of the converter is controlled according to the output value of a DC voltage controller that controls the DC voltage to a predetermined value, thereby controlling the DC voltage to a constant value (see Patent Document 1). (2) A signal corresponding to a change in load (power) on the inverter side is transmitted to the converter, and the current of the converter is controlled using the transmitted signal (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 61-109491 [Patent Document 2] Japanese Patent Application Publication No. 3-245793 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 2 discloses a technique for transmitting a signal corresponding to a load (power) change on the inverter side to a converter and controlling the output current of the converter using the transmitted signal. However, the technique described in Patent Document 2 requires a transmission circuit for transmitting and receiving a current command between the converter and the inverter. These transmission circuits use wiring and signal transmission and reception circuits, so that it is necessary to add components to the power conversion device.

[0006] In particular, in power conversion devices applied to steel rolling plants, one converter may apply a DC voltage to multiple inverters. In this case, the number of transmission circuits for connecting the converters and the inverters is required to be equal to the number of inverters connected to one converter.

[0007] In addition, the use of a transmission circuit causes a transmission delay when transmitting and receiving a current command signal, so the current command signal received by the converter is delayed relative to the current command signal transmitted by the inverter. In this case, the converter uses the delayed received signal to control the current, causing a mismatch in power transmission and reception between the converter and the inverter, resulting in fluctuations in the output DC voltage.

[0008] The present invention has been made in consideration of the above circumstances, and has an object to provide a power conversion device, a power conversion control method, and a power conversion control program that can suppress fluctuations in the DC voltage output by a converter. [Means for solving the problem]

[0009] The present invention relates to a power conversion device (100) including a converter (converter power conversion unit 21) that converts an AC voltage (Vs) into a DC voltage (Vdc), a smoothing capacitor (22, 23, 32, 33) for suppressing fluctuations in the DC voltage, and an inverter (31) that converts the DC voltage charged in the smoothing capacitor into AC power, the power conversion device (100) including a DC voltage detector (25, 26) that detects a potential difference of the smoothing capacitor, a current detector (7) that detects an AC power supply side current (I_c) of the converter, and a converter power conversion unit (21) that converts a DC voltage detection signal (Vdc) by the DC voltage detector (25, 26) into a DC voltage command value (Vref) of the converter. output A DC voltage controller (52) that generates a current command (AVROUT), and a converter output a converter output current controller (current controller 53) for controlling a DC voltage (Vdc) output by the converter so that an AC power supply side current (I_c) of the converter coincides with a current command (AVROUT); a converter side DC power current calculation unit (73) for calculating a converter side DC power current estimate value (Idch_c) from the AC power supply side current (I_c) of the converter; a fluctuating power current calculation unit (74) for calculating a fluctuating power current estimate value (ΔIdch) from a DC voltage detection signal (Vdc) of the converter; and an inverter side DC power current estimate value (Idch_i) obtained by subtracting the fluctuating power current estimate value (ΔIdch) from the converter side DC power current estimate value (Idch_c). a filter power compensation gain adjustment unit (76) that adjusts a filter time constant and a compensation amount; and an inverter side DC power current adjustment value (Idcfil_i) outputted from the filter power compensation gain adjustment unit. a converter side power compensation conversion unit (75) that multiplies the input current command (AVROUT) by an inverse conversion gain (1 / Kdc) to generate a converter side power compensation value (POBSOUT); and The result of the addition is output to the converter output current controller (current controller 53). and an adder (56) for The fluctuating power current calculation unit (74) differentiates the DC voltage detection signal (ΔIdch) of the converter with the capacitance (C) of the smoothing capacitor. The symbols and letters in parentheses are symbols and the like given in the embodiments and do not limit the present invention. Effect of the Invention

[0010] According to the present invention, it is possible to suppress fluctuations in the DC voltage output by the converter. [Brief description of the drawings]

[0011] [Figure 1] 1 is an overall configuration diagram of a power conversion device according to a first embodiment of the present invention. [Diagram 2] 1 is a block diagram showing a converter unit and a control circuit according to a first embodiment of the present invention. [Diagram 3] 1 is an overall configuration diagram of a power conversion device according to a first comparative example of the present invention; [Figure 4] FIG. 4 is an overall configuration diagram of a power conversion device according to a second comparative example of the present invention. [Diagram 5] FIG. 11 is a block diagram showing a converter unit and a control circuit according to a second embodiment of the present invention. [Figure 6] FIG. 11 is an overall configuration diagram of a power conversion device according to a third embodiment of the present invention. [Figure 7] FIG. 11 is a block diagram showing a converter unit and a control circuit according to a third embodiment of the present invention. [Figure 8] FIG. 4 is a diagram showing a DC voltage waveform over time when a converter is started up. [Figure 9] FIG. 11 is an overall configuration diagram of a power conversion device according to a fourth embodiment of the present invention. [Figure 10] FIG. 13 is a block diagram showing a converter unit and a control circuit according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings, etc. The following embodiments show specific examples of the contents of the present invention, and the present invention is not limited to these examples. Various changes and modifications are possible by those skilled in the art within the scope of the technical ideas disclosed in this specification.

[0013] FIG. 1 is an overall configuration diagram of a power conversion device according to a first embodiment of the present invention.

[0014] The power conversion device 100 includes a converter unit 2 that converts AC power (three-phase AC power) from an AC power source 1 of voltage Vs into DC power, an inverter unit 3 that converts the DC power output by the converter unit 2 into desired AC power, an electric motor 4 driven by the AC power output by the inverter unit 3, a converter control device 5a that controls the converter unit 2, and an inverter control device 6 that controls the inverter unit 3.

[0015] The converter unit 2 is a so-called three-level converter, which converts AC power from the AC power supply 1 into DC power with a positive potential (first potential) level, a neutral point (zero) potential (second potential) level, and a negative potential (third potential) level. The inverter unit 3 is a so-called three-level inverter, which converts DC power with a positive potential (first potential) level, a neutral point (zero) potential (second potential) level, and a negative potential (third potential) level into AC power to be supplied to the electric motor 4. The positive potential levels of the converter unit 2 and the inverter unit 3 are connected by a P wiring 40, the neutral point potential levels are connected by a C wiring 41, and the negative potential levels are connected by an N wiring 42.

[0016] The converter unit 2 includes a converter power conversion section 21, a series circuit of a converter P-side smoothing capacitor 22 and a converter N-side smoothing capacitor 23 for suppressing fluctuations in DC voltage, a converter P-side DC voltage detector 25 for measuring the terminal voltage of the converter P-side smoothing capacitor 22, and a converter N-side DC voltage detector 26 for measuring the terminal voltage of the converter N-side smoothing capacitor 23. The converter P-side smoothing capacitor 22 and the converter N-side smoothing capacitor 23 have the same capacity, but they do not necessarily have to have the same capacity.

[0017] The converter power conversion unit 21 is configured to include four IGBT (Insulated Gate Bipolar Transistor) transistors T1, T2, T3, and T4, four commutation diodes D1, D2, D3, and D4, and two diodes D5 and D6 for each phase. Each phase of the AC power supply 1 is connected to the emitter of the transistor T2 and the collector of the transistor T3. The collector of the transistor T2, the emitter of the transistor T1, and the cathode of the diode D5 are connected, and the emitter of the transistor T3, the collector of the transistor T4, and the anode of the diode D6 are connected. A DC voltage is generated between the collector of the transistor T1 and the connection point of the anode of the diode D5 and the cathode of the diode D6, and a DC voltage is generated between the emitter of the transistor T4 and the connection point of the anode of the diode D5 and the cathode of the diode D6.

[0018] The converter P-side smoothing capacitor 22 is connected between the collector of the transistor T1 and the connection point of the anode of the diode D5 and the cathode of the diode D6. The converter N-side smoothing capacitor 23 is connected between the emitter of the transistor T4 and the connection point of the anode of the diode D5 and the cathode of the diode D6. The converter P-side DC voltage detector 25 measures the terminal voltage of the converter P-side smoothing capacitor 22. The converter N-side DC voltage detector 26 measures the terminal voltage of the converter N-side smoothing capacitor 23. The PN DC voltage signal Vdc is a signal that is the sum of the terminal voltage of the converter P-side smoothing capacitor 22 and the terminal voltage of the converter N-side smoothing capacitor 23.

[0019] Like the converter unit 2, the inverter unit 3 includes an inverter power conversion section 31, an inverter P-side smoothing capacitor 32, and an inverter N-side smoothing capacitor 33. Here, the inverter P-side smoothing capacitor 32 is connected in parallel with the converter P-side smoothing capacitor 22, and the inverter N-side smoothing capacitor 33 is connected in parallel with the converter N-side smoothing capacitor 23.

[0020] The converter control device 5a is composed of a CPU (Central Processing Unit) and a storage unit (not shown), and realizes the following functions by executing a program stored in the storage unit. The converter control device 5a controls the converter power conversion unit 21 so that the converted DC power has a desired value. The inverter control device 6 controls the inverter power conversion unit 31 so that the output torque and speed of the electric motor 4 satisfy desired characteristics.

[0021] Here, the operation of the power conversion device in this embodiment has two modes, power running and regeneration. The power running mode is, for example, an operation mode in which the motor is accelerated or a load is applied, and the inverter control device 6 operates to extract the power required by the motor 4 from the smoothing capacitor of the DC circuit. At this time, the DC voltage drops, so the converter control device 5a operates to take in AC power from the AC power source 1 to the DC circuit side so as to keep the DC voltage constant. On the other hand, the regeneration mode is, for example, an operation mode in which the motor is decelerated or a load is applied in reverse, and the inverter control device 6 operates to return the regenerative power generated by the motor 4 to the smoothing capacitor of the DC circuit. At this time, the DC voltage rises, so the converter control device 5a operates to return power from the DC circuit to the AC power source 1 so as to keep the DC voltage constant.

[0022] The power conversion device 100 further includes a current detector 7 that detects the input AC current (AC power supply side current) of the converter unit 2, a speed detector 8 that is directly connected to the electric motor 4 and detects the speed of the electric motor 4, and a current detector 9 that detects the output AC current (electric motor side AC current) of the inverter unit 3. When the inverter control device 6 performs regenerative control, the current detector 7 detects the output current of the converter unit 2.

[0023] The converter input current I_c detected by the current detector 7 and the PN DC voltage signal Vdc are input to the converter control device 5a. The converter control device 5a performs various calculation processes based on the input detection values, and outputs a control signal for controlling the converter power conversion unit 21.

[0024] Signals (output signals) of the detection values ​​detected by the speed detector 8 and the current detector 9 are input to the inverter control device 6. The inverter control device 6 performs various calculation processes based on the input detection values, and outputs a control signal for controlling the inverter power conversion unit 31.

[0025] The converter control device 5a includes a DC voltage command generator 51, a DC voltage controller 52, a current controller 53, a pulse generator 54, a power observer unit 55a, and an adder unit 56.

[0026] The DC voltage command generator 51 outputs a converter DC voltage command value Vref indicating the voltage value of the DC voltage to be output from the converter unit 2 to the DC voltage controller 52 .

[0027] The DC voltage controller 52 controls the converter based on the converter DC voltage command value Vref input from the DC voltage command generator 51 and the PN DC voltage signal Vdc input from the converter P-side DC voltage detector 25 and the converter N-side DC voltage detector 26. output The DC voltage controller 52 calculates a current command value AVROUT and outputs it to the adder 56. Specifically, the DC voltage controller 52 adjusts the converter P-side DC voltage detector 25 so that the total value (PN DC voltage signal Vdc) of the detection values ​​of the DC voltages input from the converter P-side DC voltage detector 25 and the converter N-side DC voltage detector 26 coincides with the converter DC voltage command value Vref. output The current command value AVROUT is calculated.

[0028] The adder 56 is a converter output The current command value AVROUT is added to a calculated value output by the power observer unit 55 a, and the result of the addition is output to the current controller 53 as a converter output current command value I_cref.

[0029] The current controller 53 converts the AC power supply side current of the converter power conversion unit 21 (=converter input current I_c detected by the current detector 7) into the converter input current I_c from the adder 56. outputA converter voltage command value is calculated so as to coincide with the current command value AVROUT and is output to a pulse generator 54.

[0030] The pulse generator 54 calculates a pulse signal for controlling the on / off of each switching element of the converter power conversion unit 21 so that the value of the converter output voltage by the converter power conversion unit 21 matches the converter output voltage command value input from the current controller 53, and outputs the pulse signal to the converter power conversion unit 21.

[0031] The inverter control device 6 includes a speed command generator 61 , a speed controller 62 , a current controller 63 , and a pulse generator 64 .

[0032] The speed command generator 61 outputs a speed command value indicating the speed at which the electric motor 4 is operated to the speed controller 62. The speed controller 62 calculates an inverter output current command value so that the speed detection value input from the speed detector 8 coincides with the speed command value input from the speed command generator 61, and outputs the inverter output current command value to the current controller 63.

[0033] The current controller 63 calculates an inverter voltage command value so that the inverter output current detection value input from the current detector 9 matches the inverter output current command value input from the speed controller 62, and outputs the calculated inverter voltage command value to the pulse generator 64.

[0034] The pulse generator 64 calculates a pulse signal for controlling the on / off of each switching element of the inverter power conversion unit 31 so that the value of the inverter output voltage by the inverter power conversion unit 31 matches the inverter output voltage command value input from the current controller 63, and outputs the pulse signal to the inverter power conversion unit 31.

[0035] Next, a description will be given of a configuration related to a power observer in the power conversion device 100. The converter control device 5a of the power conversion device 100 includes a power observer unit 55a, and outputs a calculation result to an adder unit .

[0036] The power observer unit 55a outputs a converter side power compensation signal POBSOUT based on the PN DC voltage signal Vdc input from the converter P-side DC voltage detector 25 and the converter N-side DC voltage detector 26 and the converter input current detection value output from the current detector 7. The adder unit 56 adds the converter side power compensation signal POBSOUT calculated by the power observer unit 55a to the converter input current command value output from the DC voltage controller 52.

[0037] FIG. 2 is a block diagram showing a converter unit and a control circuit according to the first embodiment of the present invention. As described above, the converter control device 5a (FIG. 1) includes the DC voltage command generator 51, the DC voltage controller 52, the adder 56, the current controller 53 (FIG. 1), the pulse generator 54 (FIG. 1), and the power observer unit 55a.

[0038] The current controller 53, the pulse generator 54 and the converter power conversion unit 21 are represented by a converter output current unit 70. output When the current command value I_cref and the converter power supply side current (= converter input current I_c) are controlled by the minor loop so as to match, the converter input current I_c is output The current command value I_cref is followed by a first-order lag transfer function, that is, the converter output current unit 70 is expressed by a first-order lag transfer function of the converter current controller response time constant Tcc.

[0039] The converter side DC power current conversion unit 71 obtains the converter side DC power current Idc_c by multiplying the converter input current I_c output from the converter current unit 70 by the converter side DC power current conversion gain Kdc. That is, the ratio between the AC power supply side current (converter input current I_c) and the output DC current (converter side DC power current Idc_c) of the converter power conversion unit 21 is constant.

[0040] The subtractor 78 and the DC voltage unit 72 represent the voltage-current relationship of the four capacitors (inverter P-side smoothing capacitor 32, converter P-side smoothing capacitor 22, inverter N-side smoothing capacitor 33, and converter N-side smoothing capacitor 23). In other words, the capacitance C represents the total capacitance of the four capacitors. The subtractor 78 calculates the fluctuating power current ΔIdc by subtracting the inverter side DC power current Idc_i from the converter side DC power current Idc_c. The DC voltage unit 72 represents the four capacitors as a transfer function, and indicates that the PN DC voltage signal Vdc fluctuates due to the fluctuating power current ΔIdc.

[0041] The inverter-side DC power current Idc_i simulates a DC power current generated on the inverter side in response to motor load disturbances on the inverter side, etc.

[0042] Here, the converter output current section 70 is expressed by equation (1), the converter side DC power current conversion section 71 is expressed by equation (2), and the DC voltage section 72 is expressed by equation (3). I__c=I__cref×1 / (1+Tcc·S) ··(1) Idc_c=I__c×Kdc ········(2) Vdc=ΔIdc×1 / (C S) (3)

[0043] where Tcc is the converter current controller response time constant, Kdc is the converter side DC power current conversion gain, and C is the smoothing capacitor capacitance.

[0044] 2, power observer unit 55 a includes converter-side DC power current calculation unit 73 , fluctuating power current calculation unit 74 , converter-side power compensation conversion unit 75 , and subtractor 79 .

[0045] The converter side DC power current calculation unit 73 calculates a converter side DC power current estimate value Idch_c from the converter input current I_c output from the converter output current unit 70. The fluctuating power current calculation unit 74 calculates a fluctuating power current estimate value ΔIdch based on the PN DC voltage signal Vdc.

[0046] A subtractor 79 subtracts the fluctuating power current estimated value calculated by the fluctuating power current calculation unit 74 from the DC power current estimated value from the converter side calculated by the converter side DC power current calculation unit 73, and outputs the inverter side DC power current estimated value Idch_i.

[0047] Moreover, the converter side power compensation conversion unit 75 multiplies the inverter side DC power current estimated value Idch_i by the inverse conversion gain of the converter side DC power current conversion gain Kdc, and outputs the converter side power compensation signal POBSOUT.

[0048] The converter side DC power calculation unit 73 is expressed by equation (4), the fluctuating power current calculation unit 74 is expressed by equation (5), and the converter side power compensation conversion unit 75 is expressed by equation (6). Idch_c=I__c×Kdc ··········(4) ΔIdch=Vdc×C·S (5) POBSOUT=1 / Kdc×Idch_i (6)

[0049] As described above, the power observer unit 55a of this embodiment can estimate the power change on the inverter side from the input current (converter input current I_c) and DC voltage (PN DC voltage signal Vdc) on the converter side.

[0050] (First Comparative Example) FIG. 3 is a diagram showing the overall configuration of a power conversion device according to a first comparative example of the present invention. The power conversion device 101, like the power conversion device 100 (FIG. 1), includes a converter unit 2, an inverter unit 3, and an electric motor 4. However, the power conversion device 101 differs from the power conversion device 100 in that it includes a converter control device 5 (5e) and an inverter control device 6B. The inverter control device 6B includes a load compensation calculation unit 65 that calculates an inverter-side DC power current value from a current detection value and a voltage detection value of the motor, and outputs a value converted into a converter-side power compensation value.

[0051] The power compensation value on the converter side calculated by the load compensation calculation unit 65 is transmitted to the converter control device 5e using a transmission circuit composed of wiring and a signal transmission / reception circuit, and the converter power compensation value output from the DC voltage controller 52 is added to the adder 56 in the converter control device 5e. output By adding the power compensation value on the converter side to the current command value AVROUT, the fluctuation of the DC voltage due to the mismatch of the power transfer between the converter and the inverter is suppressed. Therefore, the power conversion device 102 needs a transmission circuit (load compensation calculation unit 65 and transmission line 66) for transmitting and receiving signals between the converter and the inverter.

[0052] In contrast, in the power conversion device 100 of the first embodiment (Figures 1 and 2), the inverter side DC power current value is estimated and calculated within the converter control device 5a, so there is no need to send and receive signals between the converter and the inverter, and the transmission circuit that was previously essential in the power conversion device 101 is no longer necessary.

[0053] Furthermore, with the power conversion device 100 of the first embodiment, even when there is a control response delay in the DC voltage controller of the converter that constitutes the power converter and a signal transmission delay between the converter and the inverter, the power conversion device 100 can suppress fluctuations in the DC voltage of the converter even in response to a sudden load change on the inverter side, such as a sudden change in the speed or load of the AC motor.

[0054] (Second Comparative Example) FIG. 4 is an overall configuration diagram of a power conversion device according to a second comparative example of the present invention, showing equipment in which one converter supplies DC power to a plurality of inverters.

[0055] A power conversion device 102 supplies DC power to a plurality of inverter units 3a, 3b, and 3c using one converter unit 2. In the power conversion device 102, each inverter control device 6a, 6b, and 6c calculates an inverter-side DC power current value according to the driving state of each electric motor 4a, 4b, and 4c controlled by the corresponding inverter, and transmits the converted value into a converter-side power compensation value from each inverter side to a converter control device 5f using a transmission circuit.

[0056] In this case, a transmission circuit is required for each inverter connected to the converter, and in equipment with a large number of connected inverters, it becomes difficult to implement the transmission circuits.

[0057] In contrast, when the converter control device 5a according to the first embodiment of the present invention is used, the total value of all inverter-side DC power current values ​​connected to the converter is estimated and calculated internally. This makes it possible to eliminate the need for a transmission circuit in the power conversion device 102 (FIG. 4).

[0058] As described above, in the first embodiment of the present invention, the inverter-side DC power current estimated value Idch_i is estimated and calculated only from the signal in the converter control device 5a, converted into the converter-side power compensation signal POBSOUT, and then added to the output of the DC voltage controller 52, thereby making it possible to suppress fluctuations in the DC voltage even when there is no transmission circuit between the inverter and the converter.

[0059] Second embodiment In the second embodiment, the power observer section of the first embodiment is modified to remove the influence of a noise signal included in the PN DC voltage signal Vdc.

[0060] FIG. 5 is a block diagram showing a converter unit and a control circuit according to a second embodiment of the present invention. The power observer unit 55b is obtained by adding a filter power compensation gain adjustment unit 76 to the power observer unit 55a (FIG. 2). The filter power compensation gain adjustment unit 76 performs filtering and compensation amount adjustment processing on the inverter side DC power current estimated value Idch_i to calculate the inverter side DC power current adjustment value Idcfil_i. The converter side power compensation conversion unit 75 inputs the inverter side DC power current adjustment value Idcfil_i, multiplies it by the inverse conversion gain of the converter side DC power current conversion gain Kdc, and outputs the converter side power compensation signal POBSOUT.

[0061] The function of the filter power compensation gain adjustment unit 76 is expressed by equation (7). Idcfil_i=Idch_i×Kb / (1+Tb·S) ···(7)

[0062] where Kb is the power compensation gain and Tb is the filter time constant.

[0063] Since the fluctuating power current calculation unit 74 performs differential calculation, if a noise signal is superimposed on the PN DC voltage signal Vdc, the noise signal may be amplified. If the converter is driven based on the compensation signal to which the amplified noise signal is applied, the DC voltage fluctuates, which may cause a fault to be detected and, in the worst case, may cause damage to the power conversion device.

[0064] The adder 56 also includes a converter output The current command value AVROUT and the converter side power compensation signal POBSOUT are added together to suppress the fluctuation of the PN DC voltage signal Vdc. However, since the control responses of the DC voltage controller 52 and the power observer unit 55a are different, the control may become unstable depending on the distribution ratio between the output of the DC voltage controller 52 and the output of the power observer unit 55a due to the relationship between stability and response.

[0065] Therefore, in consideration of the case where a noise signal is included in the PN DC voltage signal Vdc, a filter power compensation gain adjustment unit 76 is added between the subtractor 79 and the converter side power compensation conversion unit 75. The filter power compensation gain adjustment unit 76 is configured as the product of a filter (1 / (1+Tb·S)) for removing noise and a power compensation gain Kb for adjusting the sharing of the output of the DC voltage controller 52 and the output of the power observer unit 55b, and inputs Idch_i, calculates Idcfil_i, and outputs it.

[0066] As described above, in the second embodiment, a filter power compensation gain adjustment unit 76 is added that performs filtering on the inverter side DC power current estimated value and a process of adjusting the compensation amount by setting a power compensation gain Kb and calculating the inverter side DC power current adjustment value Idcfil_i. This removes the influence of a noise signal contained in the PN DC voltage signal Vdc, thereby making it possible to prevent an excessive compensation signal from being added to the output of the DC voltage controller 52.

[0067] In addition, by adjusting the power compensation gain Kb for the control responses of the DC voltage controller 52 and the power observer unit 55, which are individually designed, it is possible to optimally set the distribution ratio between the output of the DC voltage controller 52 and the output of the power observer unit 55. This makes it possible to optimize the overall control characteristics in terms of stability and responsiveness.

[0068] Third embodiment In the third embodiment, a technique for appropriately initially charging a smoothing capacitor will be described.

[0069] FIG. 6 is a diagram showing the overall configuration of a power conversion device according to a third embodiment of the present invention. The power conversion device 103 is obtained by adding a charging power source 80, a charging circuit 81, and a switching signal generating unit 57 to the power conversion device 100 (FIG. 1).

[0070] Before the converter unit 2 and the inverter unit 3 start operating, the charging power supply 80 and the charging circuit 81 charge (initial charge) the converter P-side smoothing capacitor 22, the converter N-side smoothing capacitor 23, the inverter P-side smoothing capacitor 32, and the inverter N-side smoothing capacitor 33.

[0071] The switching signal generating unit 57 outputs one of the following signals depending on the driving state of the converter: (a) a start timer at the time of initial charging, (b) a normal stop command, or (c) a failure stop command. The switching signal generating unit 57 has a timer unit 57a that outputs a start timer signal.

[0072] FIG. 7 is a block diagram showing a converter unit and a control circuit according to a third embodiment of the present invention. The power observer unit 55c is configured by adding a selection unit 77 to the power observer unit 55a (FIG. 2), which switches the output of the converter side power compensation signal based on the signals output from the switching signal generating unit 57, namely (a) a start-up timer at the time of initial charging, (b) a normal stop command, and (c) a fault stop command.

[0073] As described above, the power observer unit 55a, inside the converter controller, adds the converter side power compensation signal POBSOUT to the converter output current command value AVROUT output from the DC voltage controller 52, thereby suppressing fluctuations in the DC voltage of the converter even in response to a sudden change in the speed command of the controlled motor 4 or load fluctuations, and making it possible to make the PN DC voltage signal Vdc coincide with the converter DC voltage command value Vref.

[0074] However, since the power observer unit 55a calculates the converter side power compensation signal POBSOUT, which is a correction signal, by using the DC voltage detection value, even if the PN DC voltage signal Vdc fluctuates due to a factor other than the fluctuation of the inverter side DC power current Idc_i, it will erroneously recognize that the inverter side DC power current Idc_i has fluctuated and perform erroneous correction. If the converter is driven based on an erroneous correction signal, the DC voltage will fluctuate, causing a fault detection, and in the worst case, causing damage to the power conversion device.

[0075] Therefore, in order to prevent erroneous correction by the power observer when the value of the PN DC voltage signal Vdc fluctuates due to factors other than fluctuations in the inverter side DC power current Idc_i, the power observer section 55c does not add the converter side power compensation signal calculated by the power observer to the converter output current command output by the DC voltage controller, depending on the driving state of the converter unit 2.

[0076] FIG. 8 is a diagram showing the DC voltage waveform over time when the converter is started up. The vertical axis is the voltage [V] of the PN DC voltage signal Vdc, and the horizontal axis is time [t]. τ1 is the time from the start of charging to the completion of charging, and τ2 is the time from the completion of charging to the time when the DC voltage matches the converter DC voltage command value Vref. When starting up the converter, it is necessary to charge in advance the converter P-side smoothing capacitor 22, converter N-side smoothing capacitor 23, inverter P-side smoothing capacitor 32, and inverter N-side smoothing capacitor 33, which are connected to the converter and inverter.

[0077] In order to charge the converter P-side smoothing capacitor 22, the converter N-side smoothing capacitor 23, the inverter P-side smoothing capacitor 32, and the inverter N-side smoothing capacitor 33, the power conversion device 103 includes a charging power source 80 and a charging circuit 81. Also, it takes time from the completion of charging until the converter is started and the PN DC voltage signal Vdc matches the converter DC voltage command value Vref. In the sections τ1 and τ2 in Fig. 8, the PN DC voltage signal Vdc does not match the converter DC voltage command value Vref, so the DC voltage fluctuates due to a factor different from the fluctuation of the DC power current on the inverter side.

[0078] Therefore, in this embodiment, there is provided a start timer unit 57a that counts the power observer start waiting time TS, which is the sum of the section (τ1+τ2) from the start of charging until the DC voltage matches the command value and the preset dead time τ3 after matching the converter DC voltage command value Vref, and a selection unit 77 that outputs zero before the start timer unit 57a completes counting and switches to output the converter side power compensation signal POBSOUT after the counting is completed. This makes it possible to prevent an erroneous compensation signal from the power observer unit 55c from being added to the output of the DC voltage controller 52 when the converter is started up.

[0079] Furthermore, when performing maintenance on the power conversion device 103, it is necessary to transmit a normal stop command to the converter unit 2 to stop the converter unit 2. Furthermore, when a failure or abnormality occurs in the power conversion device 101 or the equipment, it is necessary to immediately bring the converter unit 2 to an emergency stop to ensure safety.

[0080] When the converter unit 2 is stopped, the converter controller receives a stop command and stops the pulse signal output from the pulse generator 54. As a result, the DC voltage control stops, causing the DC voltage to fluctuate.

[0081] As described above, the power observer unit 55c estimates the inverter side DC power current Idc_i, which is a correction signal, using the DC voltage detection value. Therefore, even if the value of the PN DC voltage signal Vdc fluctuates due to the converter being stopped, the power observer unit 55c will erroneously recognize that the inverter side DC power current Idc_i has fluctuated, and will perform erroneous correction.

[0082] Therefore, in this embodiment, when the selection unit 77 receives a normal stop command or a fault stop command from the switching signal generating unit 57, the selection unit 77 switches the output switch to set the converter side power compensation signal POBSOUT to zero, thereby preventing an erroneous compensation signal from the power observer unit 55c from being added to the output of the DC voltage controller 52 when the converter is stopped.

[0083] (Fourth embodiment) In the fourth embodiment, a technique for dealing with a voltage sag occurring in the AC power supply 1 will be described.

[0084] FIG. 9 is an overall configuration diagram of a power conversion device according to a fourth embodiment of the present invention. The power conversion device 104 has a configuration in which a synchronous power transformer 11 that steps down the voltage Vs of the AC power supply 1 and generates a synchronous power supply signal, and an instantaneous voltage drop amount calculation unit 58 that calculates the amount of instantaneous voltage drop of the AC power supply 1 from the synchronous power supply signal are added to the power conversion device 100 (FIG. 1) of the first embodiment.

[0085] The synchronous power transformer 11 is connected to the AC power source 1, and reduces the AC voltage supplied to the converter to a voltage that can be processed by the converter control unit, thereby generating a synchronous power signal. The instantaneous voltage sag calculation unit 58 calculates the voltage fluctuation amount of the AC power source 1 from the synchronous power signal generated by the synchronous power transformer 11.

[0086] FIG. 10 is a block diagram showing a converter unit and a control circuit according to a fourth embodiment of the present invention. The power observer unit 55e, in the power observer unit 55a (FIG. 2), receives as input a signal of the voltage fluctuation amount output from the instantaneous sag amount calculation unit 58, and varies the converter side DC power current conversion gain Kdc (KdcA) used in the converter side DC power current calculation unit 73 and the converter side power compensation conversion unit 75.

[0087] Here, the converter-side DC power current conversion gain KdcA is expressed by equation (8). KdcA=(√3×Vs) / Vdc ····(8)

[0088] Here, Vs is the voltage of the AC power supply 1, and Vdc is the DC voltage output by the converter unit 2.

[0089] The voltage Vs of the AC power supply 1 is normally supplied to the converter unit 2 at a constant voltage. Also, the DC voltage Vdc output by the converter unit 2 is controlled by a converter controller to be a constant value. Therefore, the converter side DC power current conversion gain Kdc (KdcB) of the converter side DC power current conversion unit 71, the converter side DC power current calculation unit 73, and the converter side DC power current conversion gain Kdc (KdcA) used in the converter side power compensation conversion unit 75, the voltage Vs of the AC power supply 1 and the DC voltage Vdc output by the converter unit 2 are normally constant fixed values.

[0090] However, the voltage Vs of the AC power supply 1 may fluctuate or drop instantaneously due to natural factors such as lightning strikes, or man-made factors such as an excessive load or a shortage of power supply capacity.

[0091] When the voltage Vs of the AC power supply 1 instantaneously fluctuates or drops, the converter-side DC power current conversion gain Kdc (KdcB) used in the converter-side DC power current conversion unit 71 according to equation (8) changes in response to the fluctuation or drop in the voltage of the AC power supply 1.

[0092] As described above, if the converter-side DC power current conversion gain Kdc (KdcA) used in the converter-side DC power current calculation unit 73 and the converter-side power compensation conversion unit 75 is set to a fixed value, when the voltage of the AC power source 1 fluctuates, it will not match the converter-side DC power current conversion gain Kdc (KdcB) of the converter-side DC power current conversion unit 71, resulting in erroneous correction. Driving the converter based on an erroneous correction signal will cause the DC voltage to fluctuate, leading to fault detection and, in the worst case, to damage the power conversion device.

[0093] Therefore, in this embodiment, the converter-side DC power current conversion gain setting value Kdc (KdcA) used in the converter-side DC power current calculation unit 73 and the converter-side power compensation conversion unit 75 is made variable based on the amount of instantaneous sag output from the instantaneous sag amount calculation unit 58.

[0094] As described above, in this embodiment, the converter-side DC power current conversion gain set value Kdc (KdcA) used in the converter-side DC power current calculation unit 73 and the converter-side power compensation conversion unit 75 is varied based on the amount of instantaneous sag output from the instantaneous sag amount calculation unit 58, so that it coincides with the converter-side DC power current conversion gain Kdc (KdcB) of the converter-side DC power current conversion unit 71, so that an accurate compensation signal can be added to the output of the DC voltage controller even if the voltage of the AC power supply 1 fluctuates.

[0095] Although each of the above embodiments has been described using a three-level device, the present invention is also applicable to a two-level device. [Explanation of symbols]

[0096] 1 AC power supply 2 Converter Unit 3 Inverter Unit 4,4a,4b,4c electric motor 5a, 5b, 5c, 5d, 5e Converter control device 6, 6a, 6b, 6c Inverter control device 7,9 Current detector 21 Converter Power conversion section (converter) 22 Converter P side smoothing capacitor 23 Converter N-side smoothing capacitor 25 Converter P side DC voltage detector 26 Converter N-side DC voltage detector 31 Inverter power conversion section (converter) 32 Inverter P side smoothing capacitor 33 Inverter N-side smoothing capacitor 55 Power Observer Section 51 DC voltage command generator 52 DC voltage controller 53,63 Current Controller 54,64 Pulse Generator 55a, 55b, 55c, 55d, 55e Power observer section 56 Addition section 57 Switching signal generator 57a Start timer section 58 Momentary sag calculation section 66 Transmission Line 70 Converter current section 72 DC voltage section 73 Converter side DC power current calculation unit 74 Variable power current calculation section 75 Converter side power compensation conversion section 76 Filter power compensation gain adjustment section 77 Selection section 80 charging power supply 81 Charging circuit 100, 101, 102, 103, 104 Power conversion device I_cref Converter output Current command value I_c Converter input current (AC power supply side current) Idc_c Converter side DC power current Idc_i DC power current on inverter side Vdc PN DC voltage signal (DC voltage) Idch_c Estimated converter side DC power current Idch_i Estimated inverter side DC power current POBSOUT Converter side power compensation signal AVROUT Converter output Current command value

Claims

1. A power conversion device including: a converter that converts an AC voltage into a DC voltage; a smoothing capacitor that suppresses fluctuations in the DC voltage; and an inverter that converts the DC voltage charged in the smoothing capacitor into AC power, a DC voltage detector for detecting a potential difference of the smoothing capacitor; a current detector for detecting a current on an AC power supply side of the converter; a DC voltage controller that generates a converter output current command so that a DC voltage detection signal by the DC voltage detector coincides with a DC voltage command value of the converter; a converter output current controller for controlling a DC voltage output by the converter so that a current on an AC power supply side of the converter coincides with the generated converter output current command; a converter-side DC power current calculation unit that calculates a converter-side DC power current estimate value from the AC power supply side current of the converter; a fluctuating power current calculation unit that calculates a fluctuating power current estimation value from a DC voltage detection signal of the converter; a filter power compensation gain adjustment unit that performs processing to adjust a filter time constant and a compensation amount for an inverter side DC power current estimate value obtained by subtracting the fluctuating power current estimate value from the converter side DC power current estimate value; a converter-side power compensation conversion unit that multiplies the inverter-side DC power current adjustment value output by the filter power compensation gain adjustment unit by an inverse conversion gain to generate a converter-side power compensation value; an adder that adds the converter side power compensation value to the converter output current command and outputs the addition result to the converter output current controller, The fluctuating power current calculation unit differentiates a DC voltage detection signal of the converter with the capacitance of the smoothing capacitor. A power conversion device comprising:

2. A power conversion device including: a converter that converts an AC voltage into a DC voltage; a smoothing capacitor that suppresses fluctuations in the DC voltage; and an inverter that converts the DC voltage charged in the smoothing capacitor into AC power, a DC voltage detector for detecting a potential difference of the smoothing capacitor; a current detector for detecting a current on an AC power supply side of the converter; a DC voltage controller that generates a converter output current command so that a DC voltage detection signal by the DC voltage detector coincides with a DC voltage command value of the converter; a converter output current controller for controlling a DC voltage output by the converter so that a current on an AC power supply side of the converter coincides with the generated converter output current command; a converter-side DC power current calculation unit that calculates a converter-side DC power current estimate value from the AC power supply side current of the converter; a fluctuating power current calculation unit that calculates a fluctuating power current estimation value from a DC voltage detection signal of the converter; a converter-side power compensation conversion unit that multiplies an inverter-side DC power current estimation value obtained by subtracting the fluctuating power current estimation value from the converter-side DC power current estimation value by an inverse conversion gain to generate a converter-side power compensation value; an adder that adds the converter side power compensation value to the converter output current command and outputs the addition result to the converter output current controller; A selection unit that selects an output value of the converter side power compensation conversion unit, the selection unit has a start-up timer unit that counts a time from the start of charging of the smoothing capacitor to the completion of charging, a time from the completion of charging to the time when the DC voltage detection signal coincides with the DC voltage command value, and a start-up time that is a sum of a preset dead time from the time when the DC voltage detection signal coincides with the DC voltage command value, Before the start-up timer unit completes counting, the selection unit switches the output of the converter-side power compensation conversion unit to zero, and after the start-up timer unit completes counting, the selection unit switches the output of the converter-side power compensation conversion unit to output the calculation result. A power conversion device comprising:

3. The selection unit switches the output of the converter side power compensation calculation unit to zero in response to a stop signal. The power conversion device according to claim 2 .

4. A power conversion device including: a converter that converts an AC voltage into a DC voltage; a smoothing capacitor that suppresses fluctuations in the DC voltage; and an inverter that converts the DC voltage charged in the smoothing capacitor into AC power, a DC voltage detector for detecting a potential difference of the smoothing capacitor; a current detector for detecting a current on an AC power supply side of the converter; a DC voltage controller that generates a converter output current command so that a DC voltage detection signal by the DC voltage detector coincides with a DC voltage command value of the converter; a converter output current controller for controlling a DC voltage output by the converter so that a current on an AC power supply side of the converter coincides with the generated converter output current command; a converter-side DC power current calculation unit that calculates a converter-side DC power current estimate value from the AC power supply side current of the converter; a fluctuating power current calculation unit that calculates a fluctuating power current estimation value from a DC voltage detection signal of the converter; a converter-side power compensation conversion unit that multiplies an inverter-side DC power current estimation value obtained by subtracting the fluctuating power current estimation value from the converter-side DC power current estimation value by an inverse conversion gain to generate a converter-side power compensation value; an adder that adds the converter side power compensation value to the converter output current command and outputs the addition result to the converter output current controller; A voltage drop amount calculation unit detects a voltage drop amount of the AC voltage, a power conversion device characterized in that gains of the converter-side DC power current calculation unit and the converter-side power compensation conversion unit are reduced or amplified in accordance with the amount of fluctuation or drop in the AC voltage detected by the instantaneous sag amount calculation unit.

5. A power conversion control method executed by a control device of a power conversion device including a converter that converts an AC voltage into a DC voltage, a smoothing capacitor for suppressing fluctuations in the DC voltage, an inverter that converts the DC voltage charged in the smoothing capacitor into AC power, a DC voltage detector that detects a potential difference of the smoothing capacitor, and a current detector that detects a current on an AC power supply side of the converter, a DC voltage controller that generates a converter output current command so that a DC voltage detection signal by the DC voltage detector coincides with a DC voltage command value of the converter; a converter output current controller for controlling a DC voltage output by the converter so that a current on an AC power supply side of the converter coincides with the generated converter output current command; a converter-side DC power current calculation unit that calculates a converter-side DC power current estimate value from the AC power supply side current of the converter; a fluctuating power current calculation unit that calculates a fluctuating power current estimate value by differentiating a DC voltage detection signal of the converter with respect to the capacitance of the smoothing capacitor; a filter power compensation gain adjustment unit that performs processing to adjust a filter time constant and a compensation amount for an inverter side DC power current estimate value obtained by subtracting the fluctuating power current estimate value from the converter side DC power current estimate value; a converter-side power compensation conversion unit that multiplies the inverter-side DC power current adjustment value output by the filter power compensation gain adjustment unit by an inverse conversion gain to generate a converter-side power compensation value; a converter side power compensation value added to the converter output current command and an adder that outputs the result of the addition to the converter output current controller,

6. A power conversion control program to be executed by a control device of a power conversion device including a converter that converts an AC voltage into a DC voltage, a smoothing capacitor that suppresses fluctuations in the DC voltage, an inverter that converts the DC voltage charged in the smoothing capacitor into AC power, a DC voltage detector that detects a potential difference of the smoothing capacitor, and a current detector that detects a current on an AC power supply side of the converter, a DC voltage controller that generates a converter output current command so that a DC voltage detection signal by the DC voltage detector coincides with a DC voltage command value of the converter; a converter output current controller for controlling a DC voltage output by the converter so that a current on an AC power supply side of the converter coincides with the generated converter output current command; a converter-side DC power current calculation unit that calculates a converter-side DC power current estimate value from the AC power supply side current of the converter; a fluctuating power current calculation unit that calculates a fluctuating power current estimate value by differentiating a DC voltage detection signal of the converter with respect to the capacitance of the smoothing capacitor; a filter power compensation gain adjustment unit that performs processing to adjust a filter time constant and a compensation amount for an inverter side DC power current estimate value obtained by subtracting the fluctuating power current estimate value from the converter side DC power current estimate value; a converter-side power compensation conversion unit that multiplies the inverter-side DC power current adjustment value output by the filter power compensation gain adjustment unit by an inverse conversion gain to generate a converter-side power compensation value; a converter side power compensation value added to the converter output current command and an adder outputting a result of the addition to the converter output current controller;

Images