Variable speed inverter drive for jet fan motors in road tunnels

Abstract

To provide a variable-speed inverter drive device capable of solving a voltage drop by reducing the diameter of a long cable and increasing the input voltage to the long cable, and preventing overvoltage application due to load fluctuations.SOLUTION: In a variable-speed inverter drive device 100 for inverter driving a road tunnel jet fan electric motor 300 connected via a long cable 200 of several hundred meters or more by an inverter device 110, in a connection configuration of the inverter device 110-the long cable 120-the jet fan electric motor 300, a jet fan motor overvoltage prevention device 150 having a drive voltage estimation device 130 and an overvoltage prevention control device 140 is provided on the inverter device 110 side, the drive voltage estimation device 130 estimates the drive voltage applied to the jet fan electric motor 300 through the long cable 200, and on the basis of the estimation result, the overvoltage prevention control device 140 controls the output voltage of the inverter device 110.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a variable speed inverter drive device for a motor for a jet fan in a road tunnel, which controls the operation of the jet fan for ventilating the road tunnel. [Background technology]

[0002] In the electrical equipment of jet fans in road tunnels, there are often long cables of several hundred meters between the power supply and the jet fan induction motor (hereinafter sometimes abbreviated as jet fan), and in conventional technology, cable voltage drop when the jet fan is operating at rated output is a problem. In conventional technology, measures have been taken to increase the diameter of long cables to keep the voltage drop in long cables to 7% or less. At present, cable lengths rarely exceed 1 km, but in the future, cable lengths are expected to reach around 3 km, which would further increase the cable voltage drop and, as a result, require even longer cables with larger diameters. If a large-diameter cable is used for such long cables, the cable cost cannot be ignored.

[0003] Conventional jet fan operation is often based on the so-called "multiple-unit operation control," which is a control method that controls the on / off of multiple jet fans and adjusts the air volume inside a tunnel by increasing or decreasing the number of operating fans (Patent Document 1: JP 2004-19250 A, etc.). When using this jet fan multiple operation control, a current approximately five times the rated current is required to start the jet fans, and the cable voltage drop is approximately five times as large. As a result, the applied voltage to the jet fan motor drops by 30% or more, which often results in insufficient starting torque and tends to lengthen the time it takes to start the jet fans.

[0004] To avoid the above problems with controlling the number of jet fans, the first solution in the prior art is to use a relatively expensive special squirrel-cage induction motor as the motor used for the jet fan, but this first solution cannot be adopted because it increases the cost of the motor used for the jet fan.

[0005] Next, the second solution used in the prior art to avoid the above problems with controlling the number of jet fans is to use larger diameter cables. However, when the cable length reaches 3 km, the cost of the cable increases. The cost of the cable is higher than the cost of the control panel used for operation and the jet fans themselves. Roughly speaking, the cost is about three times the cost of the control panel and more than twice the cost of the jet fans themselves. Therefore, this second solution in the prior art cannot be adopted either.

[0006] Next, as a third conventional solution to avoid the above problems of controlling the number of jet fans, one possible solution is to increase the input voltage to the long cable. If the cable diameter of a long cable is reduced to reduce cable costs, the voltage drop in the long cable will increase, but this solution involves increasing the input voltage to the long cable to compensate for the increased voltage drop.

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-19250 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0008] However, the third solution to the problem of cable voltage drop in long cables during controlled operation of jet fans using the prior art, that is, increasing the input voltage to the long cables, also had problems.

[0009] For example, if the long cable is 3 km long, the jet fan motor operates at 50 Hz, 50 kW, and has a rated power supply voltage of 440 V, a diameter of 200 mm2 is recommended. If we then verify the cost savings of reducing the diameter of the long cable to 100 mm2, the voltage drop will be approximately double that of the 200 mm2 case, resulting in a voltage drop of approximately 30% across the long cable. As a result, the applied voltage to the jet fan motor will be 300 V, which would be insufficient to operate the motor. If the power supply voltage is increased to 500 V, the voltage drop across the long cable will be approximately 20%, resulting in a voltage drop of 400 V across the jet fan motor, which will allow operation without any problems.

[0010] However, when using the jet fan number operation control, as mentioned above, a current approximately five times the rated current is required to start the jet fan, and the cable voltage drop is approximately five times as large. As a result, the applied voltage to the jet fan motor drops by 30% or more, which often results in insufficient starting torque and tends to lengthen the time it takes to start the jet fan. As described above, when controlling the number of jet fans, the starting current is large and lasts for a long time, so this third measure cannot be adopted when controlling the number of jet fans in the conventional method.

[0011] In contrast, the jet fan inverter drive device developed and adopted by the present applicant and others requires a starting current equal to or less than the rated current, making it easy to increase the output voltage of the inverter device, and enabling the cable diameter to be reduced, thereby reducing the cable current and voltage drop of long cables. In other words, cable costs can be significantly reduced. The present invention applies this jet fan inverter drive device.

[0012] In general-purpose inverter power supplies, it is assumed that the induction motor to be controlled is located relatively close, and in most cases the cable length is 50m or less. In this environment, it is sufficient to use the variable voltage variable frequency (VVVF) output function of the general-purpose inverter power supply device to operate the induction motor to be controlled using so-called "V / f control." However, even when voltage drop becomes a problem when using long cables, from several hundred meters to several kilometers, such as in the case of jet fan drive control for long-distance road tunnels, the problem of cable voltage drop can be solved by setting the output voltage of the inverter device higher by the amount of the cable voltage drop so that the "V / f control" voltage is applied to the induction motor that is the object of control.

[0013] In conventional technology, when multiple jet fans are operated, a constant current of the motor's rated current always flows through the long cable. In contrast, in inverter-driven operation, which is the premise of this invention, the current flowing through the long cable decreases in proportion to the square of the jet fan's rotation speed. In other words, for example, if the jet fans are operating at 70% rotation speed, the voltage drop in the cables will drop to 49%. However, with inverter operation, all jet fans installed in the tunnel are operated at the same speed according to the required ventilation volume, so they are designed so that operation at around 70% is sufficient under normal circumstances. In an emergency (fire), 100% operation is assumed, but the vast majority of operations are normal, and the voltage drop in the cables will be up to around 49%.

[0014] For example, consider a tunnel with four jet fans. In the case of conventional technology for controlling the number of units, if the design is for two units to operate under normal circumstances, the motor rated current flows through two of the four long cables, and no current flows through the remaining two. On the other hand, in the case of inverter operation using the inverter device assumed in this invention, the same ventilation capacity can be achieved by operating four jet fans equally at 70% rotation speed. In this state, 49% (70% squared) of the motor's rated current flows through the four long cables, and the voltage drop in the cables drops to 49% of that in the case of multiple-unit operation. The reason for this state is that the number of long cables used during normal operation is different. Considering only the cable voltage drop during normal operation, inverter operation does not require the use of long cables with a larger diameter than in the case of multiple-unit operation, which is a great advantage.

[0015] For example, if the long cable is 3 km long, the jet fan is 50 Hz, 50 kW, and the voltage applied to the long cable is 440 V, if the recommended long cable with a diameter of 200 mm2 is used, the voltage drop will be about 10%, and the input voltage of the jet fan will be 400 V. If a long cable with a diameter of 100 mm2 is used to halve cable costs, the voltage drop will increase by approximately 30%. If the voltage applied to the long cable remains at 440 V, the voltage applied to the jet fan induction motor after passing through the long cable with a diameter of 100 mm2 will drop to 300 V, making it inoperable. If the voltage applied to the long cable is increased to 500V, the voltage drop will be approximately 20%, and the voltage applied to the jet fan induction motor through the long cable with a diameter of 100mm2 will be 400V, making it possible to operate. Here, the voltage drop is approximately twice that of the long cable with a diameter of 200mm2, but by increasing the voltage applied to the long cable, the operation of the jet fan induction motor will not be affected. Furthermore, even if a long cable with a diameter of 60 mm2 is used, if the voltage applied to the long cable is increased to 560 V, the voltage drop in the long cable will be approximately 30%, but the voltage applied to the jet fan induction motor will be 400 V, making it possible to operate. As mentioned previously, raising the voltage applied to the long cable is not possible when operating multiple units because the starting current is large, but it is possible with inverter operation.

[0016] In this way, compared to the number of units operation control in the prior art, inverter operation using the inverter device that is the premise of the present invention has the advantageous advantage of being able to operate while keeping the cable diameter of the long cable small and reducing cable costs.

[0017] However, if measures are taken to increase the voltage applied to the long cable, which serves as the input voltage, it becomes necessary to prevent overcurrent from being applied to the induction motor in the event of an abnormality.For example, if the rated voltage of a jet fan induction motor is 400V, the voltage of 500V applied to the long cable is 1.25 times the rated voltage of the induction motor, and the voltage of 560V applied to the long cable is 1.6 times the rated voltage of the induction motor, so measures are essential to prevent this voltage from being directly applied to the induction motor. In other words, if the load on the jet fan were to suddenly decrease, the current to the induction motor would suddenly decrease, and the voltage of the induction motor would potentially become overvoltage. If an overvoltage is applied to the induction motor, there is a risk that the induction motor will break down or deteriorate.

[0018] The present invention aims to provide a variable speed inverter drive device for jet fan motors in road tunnels that solves the problem of cable voltage drop in long cables that occurs when operating with controlled number of units in the above-mentioned prior art by increasing the input voltage to the long cables through the adoption of inverter drive operation as a premise of the present invention, and that further provides a jet fan motor overvoltage prevention device that effectively prevents the risk of overvoltage being applied to the induction motor due to fluctuations in the jet fan load. [Means for solving the problem]

[0019] In order to achieve the above object, the variable speed inverter drive device for a jet fan motor in a road tunnel according to the present invention is a variable speed inverter drive device that uses an inverter device including an AC / DC converter that converts a three-phase commercial power input from AC to DC, and an inverter circuit that converts the DC to three-phase AC with variable frequency and voltage, to inverter-drive a jet fan motor in a road tunnel that is connected via a long cable of several hundred meters or more, and is characterized in that in the connection configuration of the inverter device - the long cable - the jet fan motor, a jet fan motor overvoltage prevention device is provided on the inverter device side, which includes a drive voltage estimating device and an overvoltage prevention control device, and the drive voltage estimating device estimates the drive voltage to be applied to the jet fan motor from the inverter device via the long cable, and the overvoltage prevention control device controls the output voltage of the inverter device based on the result of the estimation of the drive voltage to the jet fan motor by the drive voltage estimating device. In the above-mentioned inverter device-long cable-jet fan motor connection configuration, the long cable has a voltage drop of more than 7%, and the voltage applied from the inverter device to the long cable is a voltage that compensates for the voltage drop of the long cable, and is a high voltage that is 1.07 times or more the rated voltage of the jet fan motor.

[0020] With the above configuration, the problem of cable voltage drop in long cables is solved by increasing the input voltage to the long cables through the adoption of inverter drive operation, which is the premise of the present invention, and further, by providing a jet fan motor overvoltage prevention device, it is possible to effectively prevent the risk of overvoltage being applied to the induction motor due to fluctuations in the jet fan load.

[0021] The drive voltage estimation device estimates the drive voltage applied to the jet fan motor via the long cable from the inverter device by inputting the output current and output frequency of the inverter device and using the impedance of the long cable and the motor power factor of the jet fan motor. On the other hand, when the drive voltage applied to the jet fan motor exceeds the allowable voltage of the jet fan motor and becomes an overvoltage, the overvoltage prevention control device controls whether to lower the output voltage of the inverter device using a predetermined voltage command pattern or temporarily stop the output voltage of the inverter device.

[0022] Here, there are several possible configurations for the variable speed inverter drive device for the jet fan motor in the road tunnel. The first pattern is a connection configuration of inverter device - long cable - jet fan motor, in which the output voltage of the inverter device is increased and input to the long cable without providing a step-up transformer. A three-phase AC noise filter may be provided between the inverter device and the long cable. The three-phase AC noise filter preferably includes, for example, an in-phase reactor, an LC filter connected in series to the in-phase reactor, and a feedback loop from the LC filter to the input side of the inverter circuit of the inverter device.

[0023] In this first pattern, the drive voltage estimation device takes the output current and output frequency of the inverter device as input, and can estimate the drive voltage applied to the jet fan motor via the long cable from the inverter device using the impedance of the three-phase AC noise filter, the impedance of the long cable, and the motor power factor of the jet fan motor. Specifically, when the output current of the inverter device is Iinv, the output frequency is f, the resistance component of the three-phase AC noise filter and the long cable is R, the inductance component is L, and the motor power factor of the jet fan motor is cosθ, the drive voltage (Vfan) applied to the jet fan motor estimated by the drive voltage estimation device is approximated by the following [Equation 3].

number

[0024] Next, the second pattern of a variable speed inverter drive device for a jet fan motor in a road tunnel is a configuration in which a three-phase AC noise filter and a step-up transformer are installed between the inverter device and the long cable in a connection configuration of inverter device-long cable-jet fan motor. In this way, if a step-up transformer is provided in the downstream of the inverter, even if there is an upper limit to the inverter output voltage, adding a step-up transformer (for example, a 440V / 500V or 440V / 560V step-up transformer) makes it easy to increase the voltage applied to long cables. In this way, adding an appropriate step-up transformer in the downstream of the inverter is equivalent to boosting the output voltage of the inverter to a desired voltage.

[0025] In this second pattern, the drive voltage estimation device takes the output current and output frequency of the inverter device as input, and can estimate the drive voltage applied to the jet fan motor via the long cable from the inverter device using the impedance of the three-phase AC noise filter, step-up transformer, and long cable, the step-up ratio of the step-up transformer, and the motor power factor of the jet fan motor. Specifically, when the output current of the inverter device is Iinv, the output frequency is f, the resistance components of the three-phase AC noise filter, step-up transformer, and long cable are R, their inductance components are L, the motor power factor of the jet fan motor is cosθ, and the step-up ratio of the step-up transformer is α, the drive voltage (V) applied to the jet fan motor estimated by the drive voltage estimation device is approximated by [Equation 4].

number

[0026] Here, the step-up transformer can be an isolation transformer. When an insulating transformer is used as the step-up transformer, the circuit configuration can be simplified. For example, the three-phase AC noise filter can be simplified to just an LC filter, and the long cable can be an unshielded cable. [Effects of the Invention]

[0027] The variable-speed inverter drive device for jet fan motors in road tunnels of the present invention can advantageously solve the problem of cable voltage drop in long cables by increasing the input voltage to the long cables through the adoption of inverter-driven operation as a premise of the present invention. Furthermore, by providing a jet fan motor overvoltage protection device, it is possible to effectively prevent the application of overvoltage to the induction motor due to fluctuations in the jet fan load. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a block diagram illustrating a basic configuration of a variable speed inverter driving device 100 for a jet fan motor for a road tunnel according to a first embodiment of the present invention. [Figure 2] FIG. 10 is a diagram illustrating a simulation result in the configuration of the first embodiment. [Figure 3] FIG. 3 is a diagram showing the results of simulating the operating state when normal operation is possible with the operating pattern of Case 4 in FIG. 2. [Figure 4] FIG. 10 is a diagram showing the results of a simulation in the case where an abnormality occurs in a configuration in which the jet fan electric motor overvoltage protection device 150 is not provided in the configuration of the first embodiment. [Figure 5] 10 is a diagram showing the results of a simulation in the case where an abnormality occurs in the configuration of the first embodiment, which includes the jet fan electric motor overvoltage protection device 150. FIG. [Figure 6] FIG. 10 is a block diagram illustrating a basic configuration of a variable speed inverter driving device 100a for a jet fan motor for a road tunnel according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a diagram illustrating a simulation result in the configuration of the second embodiment. [Figure 8] FIG. 8 is a diagram showing the results of simulating the operating state when normal operation is possible with the operating pattern of Case 4 in FIG. 7. [Figure 9] 10 is a diagram showing the results of a simulation in the case where an abnormality occurs in the configuration of the second embodiment, which includes a jet fan electric motor overvoltage protection device 150. FIG. [Figure 10] FIG. 10 is a block diagram illustrating the basic configuration of a variable speed inverter driving device 100b for a jet fan motor for a road tunnel according to a third embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

[0029] Hereinafter, embodiments of the variable speed inverter drive device for a jet fan motor in a road tunnel according to the present invention will be described with reference to the drawings. However, it goes without saying that the scope of the present invention is not limited to the specific applications, shapes, numbers, etc. shown in the following embodiments. Hereinafter, the configuration of the variable speed inverter drive device 100 of the first embodiment is the first pattern configuration described in the section on means for solving the problems of the invention, in which a three-phase AC noise filter is provided between the inverter device and the long cable, but a step-up transformer is not provided. In other words, this is a pattern in which the output voltage of the inverter device is increased and the input voltage is applied to the long cable. Hereinafter, the configuration of variable speed inverter drive device 100a of Example 2 is the second pattern configuration described in the section on means for solving the problems of the invention, in which a three-phase AC noise filter and a step-up transformer are provided between the inverter device and the long cable. In other words, this is a pattern in which the output voltage of the inverter device is increased by the step-up transformer and the input voltage is applied to the long cable. Example 1

[0030] 1 shows an example of a variable speed inverter driving device 100 for a jet fan motor for a road tunnel according to a first embodiment of the present invention. 1 is a block diagram illustrating the basic configuration of a variable speed inverter drive device 100 for a jet fan motor for a road tunnel according to Example 1 of the present invention. A long cable 200, a jet fan motor 300, the road tunnel, etc. are also shown in a simplified manner.

[0031] As shown in FIG. 1, the variable speed inverter drive device 100 for a jet fan motor in a road tunnel is configured with an inverter device 110, a three-phase AC noise filter 120, a jet fan motor overvoltage prevention device 150 including a drive voltage estimation device 130 and an overvoltage prevention control device 140.

[0032] First, the long cable 200 will be described. A cable with a voltage drop of more than 7% is used as the long cable 200. In other words, in the present invention, an expensive long cable 200 with a large diameter is not used, but rather a cable with a smaller diameter than that recommended in the prior art is actively used.

[0033] When a cable with a voltage drop exceeding 7% is used, the voltage applied to long cable 200 drops significantly, so the output voltage on the inverter device 110 side is increased to compensate for the voltage drop in long cable 200. In other words, the jet fan motor 300 will be required to handle a high voltage that is 1.07 times or more the rated voltage. For this reason, variable speed inverter drive device 100 for a jet fan motor in a road tunnel according to the present invention is configured to include jet fan motor overvoltage prevention device 150, which includes drive voltage estimator 130 and overvoltage prevention control device 140.

[0034] In this configuration example, it is preferable that the long cable 200 is a shielded cable as a countermeasure against harmonics. If an isolation transformer is used in the input stage to cut harmonics, the long cable 200 may be an unshielded cable, and this configuration will be described later in Example 3.

[0035] A variable speed inverter drive device 100 for a jet fan motor in a road tunnel will now be described. First, the inverter device 110 will be described. The inverter device 110 is a variable frequency / variable voltage three-phase AC power supply device that receives a three-phase commercial power supply as input and converts it into a power supply having a desired frequency and a desired voltage. The inverter device 110 is configured to include a so-called converter circuit 111 and an inverter circuit 112 .

[0036] First, a converter circuit 111 (abbreviated as CNV in the figure) converts the input three-phase AC commercial power supply from AC to DC, and then an inverter circuit 112 (abbreviated as INV in the figure) converts the DC converted by the converter circuit 111 into a three-phase AC power supply with variable frequency and voltage. This inverter device 110 itself may be a commercially available product. However, there are few examples of its use as a power supply device for road tunnels, and the only application example is by the applicant of this application.

[0037] The three-phase AC noise filter 120 is a filter circuit that removes noise contained in the three-phase AC power supply with the desired variable frequency and variable voltage generated by the inverter device 110. In this example, as shown in Fig. 1, the filter is configured to include an in-phase reactor 121, an LC filter 122 connected in series to the in-phase reactor 121, and a feedback loop 123 extending from the LC filter 122 to the input side of the inverter circuit 112 of the inverter device 110.

[0038] The operating principle of this three-phase AC noise filter 120 can be explained as follows. First, by providing the common-mode reactor 121, the common-mode voltage at the input terminal of the long cable 200 can be kept low. Next, the LC filter 122 and the feedback loop 123 function as a low-pass filter to produce a sine wave, so that the high frequency current at the input terminal of the long cable 200 can be reduced. In the second embodiment, in the case of the second pattern in which the step-up transformer 160 is added, if an insulating transformer is used as the step-up transformer 160, the three-phase AC noise filter 120 may be configured with only the LC filter 122, which will be described later in the second embodiment.

[0039] The drive voltage estimation device 130 is a device that estimates the value of the drive voltage when the power supply voltage given from the inverter device 110 passes through the long cable 200 and is applied to the jet fan motor 300 at the end of the cable. 1, the output current (Iinv) and output frequency (f) of the inverter device 110 are input as variables. Also, known constants include the combined impedance (resistance component R, inductance component L) of the three-phase AC noise filter 120 and the long cable 200, and the motor power factor (cos θ) of the jet fan motor 300. Based on these data, it is necessary to estimate the drive voltage Vfan that is applied to the jet fan motor 300 via the long cable 200 from the power supply voltage from the inverter device 110.

[0040] The estimation process of the drive voltage estimation device 130 is summarized as follows. First, if the resistance component of the combined impedance of the three-phase AC noise filter 120 and the long cable 200 is R and the inductance component is L, the following [Equation 5] can be derived.

number

number

[0041] The voltage drop Vdrop through the three-phase AC noise filter 120 and the long cable 200 is approximated by the following [Equation 7].

number

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[0042] If the jet fan motor 300 and the three-phase AC power supply are star-connected, then the relationship between the line voltage and the phase voltage is given by the following [Equation 9]. Therefore, if the voltage drop Vdrop is incorporated, the drive voltage Vfan applied to the jet fan motor 300 can be approximated by the following [Equation 10].

number

number

[0043] From the above flow, the result of the estimation process of the drive voltage estimation device 130 is obtained by [Equation 10]. In this [Equation 10], the power factor cosθ may be a constant value of the rated power factor. The remaining resistance component R and inductance component L can also be set to known values, and estimates can be obtained immediately using the output voltage Vinv and output current Iinv of the inverter device 110.

[0044] Next, the overvoltage prevention control device 140 will be described. The overvoltage prevention control device 140 is a component of the jet fan motor overvoltage prevention device 150, and works in conjunction with the drive voltage estimation device 130 to check the drive voltage Vfan applied to the jet fan motor 300 estimated by the drive voltage estimation device 130, and if the drive voltage Vfan exceeds the allowable voltage of the jet fan motor 300 and becomes an overvoltage, the device takes control measures to prevent overvoltage.

[0045] Here, the control measure for preventing overvoltage is a control measure for reducing the output voltage of the inverter device 110 using a predetermined voltage command pattern. For example, there is a control measure for reducing the output voltage by a fixed percentage (for example, 1%) every control period (for example, every 0.1 seconds). Also, for example, a control measure may be taken to temporarily stop the output voltage of the inverter device 110. This temporarily shuts off the application of power. That is, the drive voltage estimation device 130 and the overvoltage prevention control device 140 work together to prevent the drive voltage Vfan applied to the jet fan motor 300 from becoming an overvoltage.

[0046] Below is a simulation of the operation of the overvoltage prevention control device 140 in an abnormal situation where an overvoltage is applied to the jet fan motor 300 in a configuration in which the variable speed inverter drive device 100 for jet fan motors in road tunnels of the present invention is applied, and the results thereof.

[0047] In this example, the specifications of the jet fan motor 300 used in the simulation were rated frequency 50 (Hz), rated voltage 400 (V), rated output 50,000 (W), slip ratio 2.5%, motor efficiency 0.939 (%), and power factor 0.860 (%).

[0048] The cable lengths used in the simulation were five patterns: short range 0m (thin cable diameter 100mm2), medium range 800m (thin cable diameter 100mm2), long range 3000m (thick cable diameter 200mm2), long range 3000m (thin cable diameter 100mm2), and long range 3000m (ultra-thin cable diameter 60mm2).

[0049] The operation control used in the simulation is V / f control for the inverter device, and in order to avoid magnetic saturation as a motor, the output voltage Vinv is controlled according to the inverter output frequency f so that the ratio of the drive voltage Vfan applied to the jet fan motor 300 to the frequency f is kept approximately constant as shown in Figure 3. In addition, torque boost is performed at the start of operation. Here, torque boost is a control that applies a voltage of f=fstart, Vstart when starting the jet fan motor 300, and raises the frequency and voltage so that the rated frequency (frated) and rated voltage (Vrated) are reached in about 20 seconds. In order to increase the starting torque, the voltage Vstart at start-up is set slightly higher than the proportional value (rated voltage Vrated × (fstart / frated)).

[0050] The simulation was carried out for six patterns, from Case 0 to Case 5. Case 0 is a general-purpose short-range case with a cable length of 50 m or less, and since the voltage drop due to the cable can be ignored, the simulated drive voltage Vfan and drive current Ifan are the motor characteristics themselves. Case 1 is a simulation of a tunnel of about 800 m that is commonly seen today, in which the configuration recommended by conventional technology is adopted. Case 2 simulates the configuration recommended by the prior art for a long tunnel, which is the premise of the present invention, with a long cable 200 of 3,000 m. In other words, it is a simulation of a case where a large-diameter cable of 200 mm2 is used for a cable length of 3 km, and the output voltage of the inverter device 110 is boosted by only about 10% (440 V applied), and a countermeasure against voltage drop is taken by increasing the diameter of the cable. Case 3 simulates the case where the tunnel assumed by the present invention is long and the long cable 200 is 3000 m long, and measures to increase the output voltage of the inverter device 110 of the present invention are not taken, but the voltage is increased by only about 10% (440 V applied), and a thin 100 mm2 long cable 200 is simply used. Case 4 simulates the case where the tunnel assumed by the present invention is long and the long cable 200 is 3000 m long, and measures are taken to increase the output voltage of the inverter device 110 of the present invention (500 V applied), and a thin 100 mm2 long cable 200 is used. Case 5 goes further and simulates the case where the tunnel assumed in this invention is long and the long cable 200 is 3000 m long, and measures are taken to further increase the output voltage of the inverter device 110 of this invention (560 V applied), and an extremely thin long cable 200 with a diameter of 60 mm2 is used.

[0051] The simulation results are shown in Figure 2. As shown in Figure 2, when comparing Case 3, Case 4, and Case 5, which simulate the case where a long cable 200 with a small diameter of 100 mm2 is used in a long tunnel with a length of 3,000 m, the following can be seen. In Case 3, if measures to increase the output voltage of the inverter device 110 applied in the present invention are not taken and the voltage is increased by only about 10% (440 V applied), as shown in Figure 2, the voltage drop in the long cable 200 reaches 31.2%, and as a result, the drive voltage Vfan applied to the jet fan motor 300 becomes about 300 V, which is clearly below the rated voltage and is at a level where it cannot be operated.

[0052] In Case 4, when the output voltage of the inverter device 110 applied in the present invention is increased by 25% (500 V applied), as shown in Figure 2, although the voltage drop in the long cable 200 increases to 21%, the drive voltage Vfan applied to the jet fan motor 300 becomes 395 V, which clearly enables operation at close to the rated voltage and can be said to be at an appropriate operating level. In Case 5, when the output voltage of the inverter device 110 applied in the present invention is increased by 40% (560 V applied), as shown in Figure 2, although the voltage drop in the long cable 200 increases to 29.2%, the drive voltage Vfan applied to the jet fan motor 300 becomes 396 V, which clearly enables operation at close to the rated voltage and can be said to be at an appropriate operating level.

[0053] 2, if measures are taken to increase the output voltage of the inverter device 110 of the present invention, a 100 mm2 thin cable or even a 60 mm2 ultra-thin cable can be used, whereas a 200 mm2 thick cable would be used in the conventional technology. Since cable cost is roughly proportional to the cable cross-sectional area, the cost of the 200 mm2 thick cable used in the conventional technology can be halved if a 100 mm2 thin cable can be used, and can be reduced to about one-third if a 60 mm2 ultra-thin cable can be used.

[0054] Next, the results of simulating the driving operation state of an actual jet fan motor 300 are shown. The operation pattern was as follows: forward rotation start at t = 10 seconds, accelerated operation until t = 30 seconds, reached the rated rotation speed at t = 30 seconds, decelerated from t = 40 seconds, and stopped at t = 60 seconds. Thereafter, reverse rotation start was started at t = 70 seconds, accelerated operation in reverse until t = 90 seconds, reached the rated rotation speed at t = 90 seconds, decelerated from t = 100 seconds, and stopped at t = 120 seconds.

[0055] FIG. 3 shows the results of simulating the operating state in Case 4 when normal operation is possible with the above operating pattern, in which the output voltage of the inverter device 110 applied in the present invention is increased by 25% (500 V applied). Figure 3 consists of an upper, middle, and lower panel, and in all cases the horizontal axis is the time axis, which is drawn on the same scale. 3 is a diagram showing changes in the rotation speed of the jet fan electric motor 300. The horizontal axis represents elapsed time (s), and the vertical axis represents the rotation speed. The center diagram in Fig. 3 shows changes in the drive voltage of the inverter device 110 and the output voltage of the jet fan motor 300. The solid line shows changes in the drive voltage (Vfan) of the jet fan motor 300, and the dotted line shows changes in the output voltage (Vinv) of the inverter device 110. In both figures, the horizontal axis represents elapsed time (s) and the vertical axis represents output voltage. The lower diagram of Fig. 3 is a diagram showing the input current of the jet fan motor 300. The horizontal axis represents elapsed time (s) and the vertical axis represents the input current.

[0056] In contrast to this normal operation pattern, a simulation was performed in which some abnormality occurred, causing a sudden decrease in the input current (Ifan) flowing to the jet fan motor 300, resulting in an overvoltage of the drive voltage (Vfan) of the jet fan motor 300. Here, a comparison is shown between a configuration equipped with the jet fan motor overvoltage protection device 150 employed in the present invention and a configuration not equipped with the jet fan motor overvoltage protection device 150 employed in the present invention.

[0057] First, for comparison, a simulation of an abnormality occurring in a configuration that does not include the jet fan motor overvoltage protection device 150 employed in the present invention will be shown. FIG. 4 shows the simulation results for a configuration that does not include the jet fan motor overvoltage protection device 150 employed in the present invention, in which the jet fan motor 300 is in a steady operating state and the motor load suddenly drops from 100% to 30% at t=35 seconds. Figure 4 also has an upper, middle, and lower diagram, but the horizontal axis in all cases is the time axis, and the time axis is drawn to the same scale. Figure 4 is similar to Figure 3, and the upper diagram in Figure 4 shows changes in the rotation speed of jet fan motor 300, and the middle diagram in Figure 4 shows changes in the drive voltage of inverter device 110 and the output voltage of jet fan motor 300. The lower diagram in Figure 4 shows the input current to jet fan motor 300. As shown in the waveform of the output voltage of the jet fan motor 300 in the middle diagram of Figure 4, a sudden decrease in the load on the jet fan motor 300, which occurred at t = 35 seconds, caused a sudden decrease in the input current (Ifan) flowing to the jet fan motor 300, and as a result of a sudden decrease in the cable voltage drop, a voltage abnormality occurred in which the drive voltage (Vfan) of the jet fan motor 300 became an overvoltage.

[0058] As shown in Figure 4, at t = 35 seconds, the input current (Ifan) flowing to the jet fan motor 300 suddenly decreases, but because the drive voltage (Vinv) supplied from the inverter device 110 remains the same, the drive voltage (Vfan) of the jet fan motor 300 suddenly rises from 395V to 462V, exceeding the rated voltage of 400V of the jet fan motor 300 and becoming an overvoltage. In the simulation shown in Figure 4, the situation in which the motor load suddenly decreases from 100% to 30% remains unchanged, so even during reverse rotation control after t = 70 seconds and in the steady operating state at t = 90 seconds, the drive voltage (Vfan) of the jet fan motor 300 rises to 462V, exceeding the rated voltage of 400V of the jet fan motor 300 and resulting in an overvoltage.

[0059] Next, a simulation of an abnormality occurring in a configuration equipped with the jet fan motor overvoltage protection device 150 employed in the present invention will be shown. FIG. 5 shows the simulation results for a configuration equipped with the jet fan motor overvoltage protection device 150 employed in the present invention, in which the jet fan motor 300 is in a steady operating state and the motor load suddenly drops from 100% to 30% at t=35 seconds. Figure 5 also has an upper, middle, and lower diagram, and the horizontal axis in all cases is the time axis, which is drawn to the same scale. Figure 5 is similar to Figure 4, and the upper diagram in Figure 5 shows changes in the rotation speed of jet fan motor 300, and the middle diagram in Figure 5 shows changes in the drive voltage of inverter device 110 and the output voltage of jet fan motor 300. The lower diagram in Figure 5 shows the input current to jet fan motor 300.

[0060] As shown in Figure 5, even though the sudden load decrease of the jet fan motor 300 that occurred at t = 35 seconds caused a sudden decrease in the input current (Ifan) flowing to the jet fan motor 300 and a sudden decrease in the cable voltage drop, it can be seen that the increase in the drive voltage (Vfan) of the jet fan motor 300 is suppressed, and the occurrence of voltage abnormalities that could result in overvoltage is suppressed. In other words, as shown in Figure 5, at t = 35 seconds, the input current (Ifan) flowing to the jet fan motor 300 suddenly decreases, but the drive voltage estimation device 130 equipped on the inverter device 110 side, 3000 m away, immediately estimates that the drive voltage (Vfan) supplied to the jet fan motor 300 will increase and become an overvoltage, and based on the estimation result of the drive voltage estimation device 130, the overvoltage prevention control device 140 equipped on the inverter device 110 side, 3000 m away, appropriately reduces the output voltage (Vinv) of the inverter device 110, so that the drive voltage (Vfan) of the jet fan motor 300 can be kept to an increase of about 405 V, and it can be seen that it will only be about 5% higher than the rated voltage of the jet fan motor 300 and will not become an overvoltage.

[0061] In the simulation shown in Figure 5, the situation in which the motor load suddenly decreases from 100% to 30% remains unchanged, but even in the reverse rotation control after t = 70 seconds and in the steady operating state at t = 90 seconds, the drive voltage (Vfan) of the jet fan motor 300 is suppressed to about 405 V, which is only about 5% higher than the rated voltage of the jet fan motor 300 and does not become an overvoltage.

[0062] As described above, the variable speed inverter drive device 100 for a jet fan motor of the present invention is equipped with a jet fan motor overvoltage prevention device 150, so even if an abnormality such as a load fluctuation occurs when the inverter device is at a high voltage and the jet fan motor 300 is being operated, the drive voltage (Vfan) of the jet fan motor 300 can be controlled to an operable state. In this way, by taking measures to increase the output voltage of the inverter device 110 applied in the present invention, safe operation can be ensured even if the output voltage of the inverter device 110 is increased to 500V, 560V, etc., and the occurrence of a problem in which the drive voltage applied to the jet fan motor 300 becomes an overvoltage state when there is a load fluctuation can be suppressed.

[0063] An embodiment of the present invention has been illustrated and described above as Example 1. Here, a notable feature is that in the inverter 110-long cable 200-jet fan motor 300 connection configuration, the jet fan motor overvoltage protection device 150 is provided on the inverter 110 side. If it were assumed that the jet fan motor 300, which is 3000 m away, were to be directly monitored, there would be no suitable method for sending a control signal to control the output voltage of the inverter 110 installed in a power supply room 3000 m away. However, the variable-speed inverter drive device 100 for a jet fan motor of the present invention can constantly estimate the drive voltage applied to the jet fan 3000 m away using the drive voltage estimator 130 installed on the inverter drive device 110 side, thereby virtually monitoring it, and can then take measures against overvoltage using the overvoltage prevention control device 140. This technology is extremely advantageous for application in long-distance tunnels, such as 3000 m. Example 2

[0064] Second Embodiment An example of a variable speed inverter driving device 100a for a jet fan motor for a road tunnel according to the present invention will be shown. The configuration of variable speed inverter driving device 100a of embodiment 2 is the same as that of the variable speed inverter driving device described in embodiment 1, except that a three-phase AC noise filter and a step-up transformer are provided between the inverter device and the long cable. In other words, the output voltage of the inverter device is stepped up by the step-up transformer, and the input voltage is applied to the long cable.

[0065] 6 is a block diagram illustrating the basic configuration of a variable speed inverter drive device 100a for a jet fan motor for a road tunnel according to Example 2 of the present invention. Note that a long cable 200, a jet fan motor 300, a road tunnel, etc. are also shown in a simplified manner. There may be a pattern in which the step-up transformer is devised to be an insulating transformer, which will be described later in a third embodiment. In the second embodiment, the description of the same components as those in the first embodiment will be omitted as appropriate.

[0066] As shown in Figure 6, the variable speed inverter driving device 100a for a jet fan motor in a road tunnel according to the second embodiment is configured to include a step-up transformer 160 in addition to an inverter device 110, a three-phase AC noise filter 120, a jet fan motor overvoltage prevention device 150 including a driving voltage estimation device 130 and an overvoltage prevention control device 140. That is, as shown in FIG. 6, in the connection configuration of the inverter device 110-long cable 200-jet fan motor 300, a three-phase AC noise filter 120 and a step-up transformer 160 are provided between the inverter device 110 and the long cable 200.

[0067] Here, the inverter device 110, three-phase AC noise filter 120, drive voltage estimation device 130, overvoltage prevention control device 140, and jet fan motor overvoltage prevention device 150 shown in Figure 6 may be the same as those shown in Example 1, so their explanation will be omitted here.

[0068] The step-up transformer 160 receives the output voltage from the inverter device 110 as an input voltage, steps up the voltage at a predetermined step-up ratio, and outputs the voltage as an input voltage to the long cable 200 . In the configuration incorporating this step-up transformer 160, in the first embodiment, a measure was taken to increase the output voltage of the inverter device 110 to overcome the problem of a large voltage drop caused by thinning the diameter of the long cable, but in this second embodiment, the input voltage to the long cable is increased by boosting the output voltage of the inverter device 110 through the step-up transformer 160. By using the step-up transformer 160 in this way, it is no longer necessary to increase the output voltage of the inverter device 110 itself, and this can be applied even to inverter devices 110 whose specifications have a set upper limit on the output voltage.

[0069] In Example 1, in Case 4 shown in Figure 3, a case was assumed in which the long cable 200 was 3000 m long and had a small diameter of 100 mm2, and measures were taken to increase the voltage of the inverter device 110 to 500 V. However, if a step-up transformer 160 with a step-up ratio of 125% (400 V / 500 V) is used, the output voltage of the inverter device 110 can be 400 V. Furthermore, in Example 1, in Case 5 shown in FIG. 3, a case was assumed in which the long cable 200 was 3000 m long and had an extremely small diameter of 60 mm2, and measures were taken to increase the voltage of the inverter device 110 to 560 V. However, if a step-up transformer 160 with a step-up ratio of 140% (400 V / 560 V) is used, the output voltage of the inverter device 110 can be 400 V.

[0070] In the second embodiment, if the step-up transformer 160 is used, the estimation process in the drive voltage estimation device 130, that is, the process of estimating the drive voltage Vfan when the input voltage of the long cable 200 is applied to the jet fan motor 300 at the end of the long cable 200, is as follows: When the output current of the inverter device is Iinv, the output frequency is f, the resistance components of the three-phase AC noise filter, the step-up transformer, and the long cable are R, the inductance component thereof is L, the motor power factor of the jet fan motor is cos θ, and the step-up ratio of the step-up transformer is α, the drive voltage (V) applied to the jet fan motor 300 estimated by the drive voltage estimation device 130 is given by [Equation 12] via [Equation 11].

number

number

[0071] The simulation results shown in the first embodiment are shown in FIG. In the simulation results shown in Fig. 2 for Example 1, the output voltage Vinv of the inverter device 110 is increased, but in the simulation results shown in Fig. 7 for Example 2, the output voltage Vinv of the inverter device 110 is kept constant at 400 V, and the output voltage Vtr of the step-up transformer 160 is increased. The drive voltage Vfan applied to the remaining element, the jet fan motor 300, is the same as in Fig. 2. In other words, this shows that by adding the step-up transformer 160, the required increase in voltage can be achieved while the output voltage Vinv of the inverter device 110 remains constant at 400 V.

[0072] The diagram showing the results of simulating the operating state of normal operation when a 25% voltage boost (500 V applied) is performed in Case 4 of FIG. 2 is shown in FIG. 8 in Example 2, instead of FIG. 3 in Example 1. FIG. 8 shows the results of simulating the operating state when normal operation is possible with the above operating pattern, in which the output voltage of the inverter device 110 applied in the present invention is further boosted to a higher voltage by 25% (500 V applied) via a non-insulated step-up transformer 160a. Figure 8 has three panels, an upper panel, a middle panel, and a lower panel, and in all of them the horizontal axis is the time axis, and the time axis is drawn on the same scale. The upper diagram in Fig. 8 shows changes in the rotation speed of the jet fan electric motor 300. The horizontal axis represents elapsed time (s), and the vertical axis represents the rotation speed. The center diagram in Figure 8 shows changes in the drive voltage of inverter device 110, the output voltage of non-insulated step-up transformer 160a, and the output voltage of jet fan motor 300. The solid line shows changes in the drive voltage (Vfan) of jet fan motor 300, the dashed line shows changes in the output voltage (Vinv) of inverter device 110, and the dotted line shows changes in the output voltage of non-insulated step-up transformer 160a. In each case, the horizontal axis represents elapsed time (s) and the vertical axis represents output voltage. The lower diagram in Fig. 8 is a diagram showing the input current of the jet fan motor 300. The horizontal axis represents elapsed time (s), and the vertical axis represents the input current. Next, in the case of Case 4 in Figure 2 where a 25% boost (500 V applied) is performed (where the output voltage of the inverter device 110 is further boosted to a higher voltage via the non-insulated boost transformer 160a), the motor load suddenly drops from 100% to 30% at t = 35 seconds. Figure 9 in Example 2 is a diagram showing the simulation results instead of Figure 5 in Example 1. Like FIG. 8, FIG. 9 also has an upper, middle, and lower diagram, but in all cases the horizontal axis is the time axis and is drawn on the same scale. The upper diagram in FIG. 9 is a diagram showing the change in rotation speed of the jet fan motor 300, with the horizontal axis being the elapsed time (s) and the vertical axis being the rotation speed. The center diagram in Figure 9 shows changes in the drive voltage of inverter device 110, the output voltage of non-insulated step-up transformer 160a, and the output voltage of jet fan motor 300. The solid line shows changes in the drive voltage (Vfan) of jet fan motor 300, the dashed line shows changes in the output voltage (Vinv) of inverter device 110, and the dotted line shows changes in the output voltage of non-insulated step-up transformer 160a. In each case, the horizontal axis represents elapsed time (s) and the vertical axis represents output voltage. The lower diagram in Fig. 8 is a diagram showing the input current of the jet fan motor 300. The horizontal axis represents elapsed time (s), and the vertical axis represents the input current.

[0073] As described above, even with the configuration of the second embodiment, that is, a configuration in which the step-up transformer 160 (non-isolated step-up transformer 160a) is added to keep the output voltage Vinv of the inverter device 110 constant at 400 V and to increase the voltage as needed by the step-up transformer (non-isolated transformer 160a), it is clear that good operation can be ensured in the normal operating state shown in FIG. 8 and the operating state when an abnormality occurs shown in FIG. 9, similar to the first embodiment. Example 3

[0074] An example of a variable speed inverter driving device 100b for a jet fan motor for a road tunnel according to the present invention will be shown below. The third embodiment is a configuration example in which the step-up transformer shown in the second embodiment is replaced with an insulating step-up transformer 160b. The configuration of the variable speed inverter driving device 100b of the third embodiment is the same as that of the second embodiment, in that a three-phase AC noise filter and a step-up transformer are provided between the inverter device and the long cable, but the step-up transformer is an insulating step-up transformer 160b.

[0075] 10 is a block diagram illustrating the basic configuration of a variable speed inverter drive device 100b for a jet fan motor for a road tunnel according to a third embodiment of the present invention. A long cable 200b, a jet fan motor 300, the road tunnel, and the like are also shown in a simplified manner. In the third embodiment, the description of the same components as those in the first and second embodiments will be omitted as appropriate.

[0076] As shown in FIG. 10, the variable speed inverter driving device 100b for a jet fan motor in a road tunnel according to the third embodiment is configured to include an inverter device 110, a three-phase AC noise filter 120b, a jet fan motor overvoltage prevention device 150 including a driving voltage estimation device 130 and an overvoltage prevention control device 140, as well as an insulating step-up transformer 160b. That is, as shown in FIG. 10, in the connection configuration of the inverter device 110-long cable 200b-jet fan motor 300, a three-phase AC noise filter 120b and an insulating step-up transformer 160b are provided between the inverter device 110 and the long cable 200.

[0077] Since the insulating step-up transformer 160b is used, the in-phase current is cut, and the three-phase AC noise filter 120b requires only the LC filter 122, eliminating the need for the in-phase reactor 121 seen in FIG. 1 of the first embodiment and FIG. 6 of the second embodiment, and also eliminating the need for the feedback loop 123 from the LC filter 122 to the input side of the inverter circuit 112 of the inverter device 110. Furthermore, since the isolation step-up transformer 160 is used to cut harmonic components, the long cable 200b may be an unshielded cable. As described above, in the configuration of Example 3, compared to the basic configuration of Example 1, it is not necessary to take measures to increase the voltage of the output of the inverter device 110 by using a step-up transformer as in the configuration of Example 2. Furthermore, by using the insulating step-up transformer 160b, the configuration of the three-phase AC noise filter 120b is simplified, and the long cable may be an unshielded cable, which enables cost reduction.

[0078] In the configuration according to Example 3, when the output voltage of the inverter device 110 applied in the present invention is further boosted via the isolation step-up transformer 160b to increase the voltage by 25% (500V applied), the simulation results of the operating state when normal operation is possible with the above operating pattern are similar to those in Figure 8 of Example 2. Also, when the voltage is boosted by 25% (500V applied) in Case 4 of Figure 2 (when the output voltage of the inverter device 110 is further boosted via the isolation step-up transformer 160b to increase the voltage), the simulation results of the motor load suddenly decreasing from 100% to 30% at t = 35 seconds are similar to those in Figure 9 of Example 2. Illustrations are omitted here. Even in the configuration according to the third embodiment, by adding the step-up transformer 160 (isolation step-up transformer 160b), the output voltage Vinv of the inverter device 110 is kept constant at 400 V, and the necessary voltage increase is performed by the step-up transformer (isolation step-up transformer 160b), it is possible to obtain the operating state of normal operation as shown in FIG. 8 and the operating state when an abnormality occurs as shown in FIG. 9, and it is found that good operation can be ensured as in the first embodiment.

[0079] While preferred embodiments of the present invention have been illustrated and described above, the present invention can be widely applied as a variable speed inverter drive device for a motor for a jet fan in a road tunnel that controls a ventilation system for the road tunnel. It will be understood that various modifications can be made without departing from the spirit and scope of the present invention, which is to be limited only by the appended claims. [Explanation of symbols]

[0080] 100, 100a, 100b Variable speed inverter drive device for jet fan motor 110 Inverter device 120,120b Three-phase AC noise filter 130 Driving voltage estimator 140 Overvoltage prevention control device 150 Jet fan motor overvoltage protection device 160 Step-up transformer 160a non-isolated step-up transformer 160b isolation step-up transformer 200,200b long cable 300 Jet fan motor

Claims

1. A variable speed inverter drive device that drives an electric motor for a jet fan in a road tunnel connected via a long cable by an inverter device, The long cable has a voltage drop of more than 7%, In the connection configuration of the inverter device, the long cable, and the jet fan motor, a jet fan motor overvoltage prevention device including a drive voltage estimation device and an overvoltage prevention control device is provided on the inverter device side; The drive voltage estimating device estimates a drive voltage applied to the jet fan motor from the inverter device through the long cable, A variable speed inverter drive device for an electric motor for a jet fan in a road tunnel, characterized in that the overvoltage prevention control device controls the output voltage of the inverter device based on the estimation result by the drive voltage estimation device.

2. In the connection configuration of the inverter device, the long cable, and the jet fan motor, 2. A variable speed inverter drive device for a jet fan motor in a road tunnel as described in claim 1, characterized in that the voltage applied from the inverter device to the long cable is a voltage that compensates for the voltage drop in the long cable and is a high voltage that is 1.07 times or more the rated voltage of the jet fan motor.

3. 3. A variable speed inverter drive device for a jet fan motor in a road tunnel as described in claim 1 or 2, characterized in that the drive voltage estimation device receives as input the output current and output frequency of the inverter device, and estimates the drive voltage to be applied to the jet fan motor from the inverter device through the long cable using the impedance of the long cable and the motor power factor of the jet fan motor.

4. In the connection configuration of the inverter device, the long cable, and the jet fan motor, 4. A variable speed inverter drive device for a motor for a jet fan in a road tunnel according to claim 1, wherein a three-phase AC noise filter is provided between the inverter device and the long cable.

5. 5. The variable speed inverter drive device for an electric motor for a road tunnel jet fan according to claim 4, wherein the three-phase AC noise filter comprises an in-phase reactor, an LC filter connected in series to the in-phase reactor, and a feedback loop from the LC filter to the input side of the inverter device.

6. 6. A variable speed inverter drive device for a jet fan motor in a road tunnel as described in claim 5, wherein the drive voltage estimation device receives as input the output current and output frequency of the inverter device, and estimates the drive voltage to be applied to the jet fan motor from the inverter device through the long cable using the impedance of the three-phase AC noise filter, the impedance of the long cable, and the motor power factor of the jet fan motor.

7. 7. A variable speed inverter drive device for a jet fan motor in a road tunnel as claimed in claim 6, wherein the drive voltage (Vfan) applied to the jet fan motor estimated by the drive voltage estimation device is approximated by [Equation 1], where Iinv is the output current of the inverter device, f is the output frequency, R is the resistance component of the three-phase AC noise filter and the long cable, L is the inductance component, and cos θ is the motor power factor of the jet fan motor. [Equation 1]

8. In the connection configuration of the inverter device, the long cable, and the jet fan motor, 3. A variable speed inverter drive device for a motor for a jet fan in a road tunnel according to claim 1 or 2, characterized in that a three-phase AC noise filter and a step-up transformer are provided between the inverter device and the long cable.

9. 9. A variable speed inverter drive device for a jet fan motor in a road tunnel according to claim 8, wherein the drive voltage estimation device receives as input the output current and output frequency of the inverter device, and estimates the drive voltage to be applied to the jet fan motor from the inverter device through the long cable using the impedances of the three-phase AC noise filter, the step-up transformer, and the long cable, the step-up ratio of the step-up transformer, and the motor power factor of the jet fan motor.

10. 10. The variable speed inverter drive device for a jet fan motor in a road tunnel according to claim 9, wherein the drive voltage (V) applied to the jet fan motor estimated by the drive voltage estimation device is approximated by [Equation 2], where Iinv is the output current of the inverter device, f is the output frequency, R is the resistance components of the three-phase AC noise filter, the step-up transformer, and the long cable, L is their inductance component, cos θ is the motor power factor of the jet fan motor, and α is the step-up ratio of the step-up transformer. [Equation 2]

11. 11. A variable speed inverter driving device for a motor for a jet fan in a road tunnel according to claim 9 or 10, wherein the step-up transformer is an insulating transformer.

12. 12. The variable speed inverter drive device for a motor for a jet fan in a road tunnel according to claim 11, wherein the three-phase AC noise filter is an LC filter, and the long cable is an unshielded cable.

13. A variable speed inverter drive device for a jet fan motor in a road tunnel as described in any one of claims 1 to 12, characterized in that the overvoltage prevention control controls whether to reduce the output voltage of the inverter device using a predetermined voltage command pattern or temporarily stop the output voltage of the inverter device when the drive voltage applied to the jet fan motor exceeds the allowable voltage of the jet fan motor and becomes an overvoltage.

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