Device and method for controlling the speed of a load commutation inverter using a firing angle

Abstract

The present invention relates to a load rectification inverter speed control device and method, and more specifically, to a load rectification inverter speed control device and method using a firing angle. According to one embodiment of the present invention, the present invention can overcome the limitations of conventional methods and improve speed control characteristics because the speed controller bandwidth is not limited by the current controller and torque overshoot caused by the zero-point component of the existing current controller can be prevented.

Description

Technology Field

[0001] The present invention relates to a load rectification inverter speed control device and method, and more specifically, to a load rectification inverter speed control device and method using a firing angle. Background Technology

[0003] IGBT and SiC devices are commonly used in high-capacity power conversion systems. Among these, thyristors are generally used because they can withstand high capacities. Load Commutation Inverters (LCIs) are employed when configuring power conversion devices for driving high-power motors. Conventional technology utilizes DC current control via a rectifier to adjust torque magnitude when controlling motor speed using a load commutation inverter. However, the bandwidth of a DC current controller composed of a rectifier is limited by factors such as digital filters and the inductance of the DC link. Additionally, overshoot may occur due to the zero point of the DC current controller. Due to these characteristics, the DC current controller limits the speed controller bandwidth to a low level during speed control, contains components that induce torque ripple, and can delay the steady-state entry time.

[0004] To solve this problem, a technology is needed that can control the speed of the load rectifier inverter using the firing angle without DC current control.

[0005] The background technology of the present invention is disclosed in Korean Registered Patent No. 10-2598225. The problem to be solved

[0007] The present invention proposes a method for controlling speed by generating torque using the adjustment angle, which is the control degree of freedom of a load rectifier inverter, without passing through a current controller. means of solving the problem

[0009] According to one aspect of the present invention, a load rectification inverter speed control device using a firing angle is provided.

[0010] A load rectification inverter speed control device using a firing angle according to one embodiment of the present invention may include a thyristor converter that rectifies the line voltage of a three-phase grid and controls the magnitude and polarity of the rectified voltage by adjusting the firing angle of the converter; a thyristor inverter that controls the phase angle of the current supplied to the motor using the firing angle of the inverter; a DC link unit that stores energy and suppresses harmonics between the thyristor converter and the thyristor inverter; a motor unit that operates with an AC voltage applied from the thyristor inverter; and a load rectification inverter firing angle control unit that receives a speed command from the motor unit and a DC current from the DC link unit, generates a firing angle command response, and outputs a maximum torque.

[0011] According to another aspect of the present invention, a load rectification inverter speed control method using a firing angle is provided.

[0012] A load rectification inverter speed control method using a firing angle according to an embodiment of the present invention may include the steps of: inputting a difference value between a speed command value and a current speed value to generate and output a command torque; inputting the command torque and a DC current to output an adjustment angle; inputting the DC current to calculate and output a maximum inverter firing angle; inputting a difference value between the maximum inverter firing angle and the adjustment angle to generate and output a new firing angle, which is the firing angle of the inverter; inputting a difference value between the DC current and a DC rated current to generate a DC current command and output a DC voltage command to control the DC current; and inputting the DC voltage command to calculate and output a firing angle of the converter. Effects of the invention

[0014] According to one embodiment of the present invention, the present invention can overcome the limitations of conventional methods and improve speed control characteristics because the speed controller bandwidth is not limited by the current controller and torque overshoot caused by the zero-point component of the existing current controller can be prevented.

[0015] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the composition of the invention described in the description or claims of the present invention. Brief explanation of the drawing

[0017] FIG. 1 is a drawing for explaining the overall driving system configuration of a load rectifier inverter according to one embodiment of the present invention. FIG. 2 is a drawing for explaining a load rectification inverter adjustment angle speed control block diagram according to an embodiment of the present invention. FIG. 3 is a flowchart illustrating a control method of a load rectification inverter adjustment angle speed control system according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a vector diagram of a wound rotor synchronous motor (WRSM) drive system according to an embodiment of the present invention. FIG. 5 is a drawing for explaining a 3D table showing the change in q-axis current according to DC current and adjustment angle according to one embodiment of the present invention. FIG. 6 is a drawing showing the change in arc extinction angle according to the adjustment angle, according to one embodiment of the present invention. FIG. 7 is a diagram showing parameter values ​​of a 15MW wound-type synchronous motor according to one embodiment of the present invention. FIG. 8 is a diagram showing the speed control simulation results of a 15MW wound-type synchronous motor according to one embodiment of the present invention. FIG. 9 is a diagram showing the poles and zeros of the DC current control method, which is a conventional method, and the adjustment angle control method of the present invention, according to one embodiment of the present invention. FIG. 10 is a diagram showing the speed control system bandwidth of the conventional DC current control method and the adjustment angle control method of the present invention, according to one embodiment of the present invention. Specific details for implementing the invention

[0018] The present invention is susceptible to various modifications and may have various embodiments; therefore, specific embodiments are illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention. In describing the present invention, detailed descriptions of related prior art are omitted if it is determined that such detailed descriptions may unnecessarily obscure the essence of the invention. Furthermore, singular expressions used in this specification and claims should generally be interpreted as meaning "one or more" unless otherwise stated.

[0019] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0020] The terms used herein are used merely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0021] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0023] FIG. 1 is a drawing for explaining the overall driving system configuration of a load rectifier inverter according to one embodiment of the present invention.

[0024] Referring to FIG. 1, a synchronous motor drive system using a load commutation inverter (LCI) includes a thyristor converter (110), a thyristor inverter (120), a DC link section (130), a motor section (140), and a load commutation inverter firing angle control section (200).

[0025] The thyristor converter (110) and the thyristor inverter (120) are each symmetrically configured with six thyristor rectifiers.

[0026] The thyristor converter (110) is a thyristor rectifier connected to a three-phase grid.

[0027] The thyristor converter (110) is the line-to-line voltage on the three-phase grid side. Rectifies, and the firing angle of the converter The magnitude and polarity of the rectified voltage can be controlled by adjusting it.

[0028] The thyristor inverter (120) is a thyristor rectifier connected to the motor unit (140).

[0029] The thyristor inverter (120) is the firing angle of the inverter The phase angle of the current supplied to the motor is controlled using [this].

[0030] The DC link section (130) is composed of a DC link inductor.

[0031] The DC link inductor is required to store energy and suppress harmonics between the thyristor converter (110) and the thyristor inverter (120) and is composed of a large inductance.

[0032] DC link inductance has a large value to maintain continuous current mode, increase reliability, and reduce harmonics. However, large inductance has the disadvantage of causing phase lag and limiting dynamics.

[0033] The motor unit (140) operates with an alternating current voltage applied from a thyristor inverter (120).

[0034] The load rectifier inverter firing angle control unit (200) receives the speed command of the motor unit (140) and the DC current of the DC link unit (130) as inputs, generates a firing angle command response, and outputs the maximum torque.

[0036] FIG. 2 is a drawing for explaining a control device of a load rectification inverter adjustment angle speed control system according to one embodiment of the present invention.

[0037] In Fig. 2 is the motor speed command value, is the current speed of the motor, is the commanded torque (q-axis current command if the motor inductance is symmetrical), is the adjustment angle, is the DC link current, is the DC link rated current, is the maximum inverter firing angle, is the DC link current command, is the DC link voltage command, is the firing angle of the inverter (new firing angle), is the firing angle of the converter.

[0038] Referring to Fig. 2, the commanded torque (q-axis current), which is the output value of the speed controller, is generated solely through inverter-side adjustment angle control. Through the analyzed table, an adjustment angle and a corresponding firing angle command can be generated to generate the commanded torque at a specific DC current, thereby enabling torque generation solely through inverter-side firing angle control without DC current control. Consequently, the current controller of the lower loop can be eliminated during speed control to remove delay and zero-point components, and the dynamic characteristics of speed control can be improved by relaxing bandwidth limitations.

[0039] Referring to FIG. 2, the load rectification inverter firing angle control unit (200), which receives the speed command of the motor unit (140) and the DC current of the DC link unit (130) from the control unit of the load rectification inverter adjustment angle speed control system and generates a firing angle command response to output maximum torque, includes a speed control unit (210), a current-torque-adjustment angle table unit (220), a maximum inverter firing angle calculation unit (230), a new inverter firing angle calculation unit (240), a DC current control unit (250), and a converter firing angle calculation unit (260).

[0040] The speed control unit (210) is the speed command value of the motor unit (140) and current speed Receive the difference value as input and command torque Generates and outputs a response. Command torque is the q-axis current command when the inductance of the motor part (140) is symmetrical.

[0041] The current-torque-adjustment angle table section (220) is the commanded torque, which is the output value of the speed control section (210). and DC current of the DC link section (130) Receives the adjustment angle Prints.

[0042] The current-torque-adjustment angle table section (220) can be configured as a 3D table.

[0043] An explanation of this follows in Figure 4 below.

[0044] The maximum inverter firing angle calculation unit (230) is the DC current of the DC link unit (130). Receives the maximum inverter firing angle Calculate and output. Maximum inverter firing angle It can be expressed as shown in mathematical formula 4 below.

[0045] The new inverter firing angle calculation unit (240) calculates the maximum inverter firing angle calculated by the maximum inverter firing angle calculation unit (230). Adjustment angle, which is the output value of the current-torque-adjustment angle table section (220). Receive the difference value as input and the new firing angle of the inverter. Prints.

[0046] New inverter firing angle It can be expressed as shown in mathematical formula 5 below.

[0047] The DC current control unit (250) controls the DC current of the DC link unit (130). and DC rated current DC current command receiving the difference value Generate and DC voltage command Outputs DC current Controls.

[0048] The converter firing angle calculation unit (260) is the DC voltage command of the DC current control unit (250) Receives the converter's firing angle as input Calculate and output.

[0049] That is, the thyristor converter (110) controls the firing angle of the converter to adjust the DC voltage of the DC link unit (130) to be synthesized. By controlling the DC voltage, the DC current of the DC link unit (130) can be controlled. The firing angle of the converter can be expressed as Equation 1 below.

[0050] [Equation 1]

[0051]

[0052] In Equation 1, is the line-to-line voltage of the converter.

[0053] The thyristor inverter (120) uses the firing angle of the inverter to control the phase angle of the current supplied to the motor. The phase delay is determined by .

[0054] The firing angle of the converter and the firing angle of the inverter are limited to a range from 0 to . Generally, the firing angle of the inverter is set to a maximum value to transmit maximum power.

[0055] Equations 2 to 4 below are expressed as the commutation angle required for thyristor commutation , the thyristor extinction margin angle , and the minimum lead angle of the phase current with respect to the phase voltage respectively.

[0056] In high-power systems with a low resistance ratio, the change in the commutation angle is determined by the DC current and the firing angle of the inverter , and the change in is very small. The thyristor extinction margin angle is generally a constant value, and is added to prevent commutation failure caused by abnormal conditions.

[0057] ​[Mathematical Formula 2]

[0058]

[0059] In mathematical formula 2 is the inverter line voltage, is electric speed, is the rectification reactance.

[0060] The ignition angle of the present invention represents the rectification delay angle of the thyristor converter.

[0061] Mathematical Equation 3 is an inequality representing the firing angle range to prevent rectification failure.

[0062] [Mathematical Formula 3]

[0063]

[0064] Equation 4 is the maximum inverter firing angle, which is the maximum value in Equation 3. It represents the maximum inverter firing angle. DC current It depends on the inverter's firing angle. This is the maximum inverter firing angle, which is the maximum value. When set to this, the inverter can generate maximum power under the leading power factor conditions resulting from the rectification characteristics of the thyristor.

[0065] [Mathematical Formula 4]

[0066]

[0067] The new roll call of the inverter is the maximum inverter firing angle of mathematical formula 4. Reduce the adjustment angle by σ.

[0068] Therefore, in the proposed method of the present invention, the firing angle of the inverter, which is a new firing angle including the adjustment angle σ, Defines as in mathematical formula 5.

[0069] [Mathematical Formula 5]

[0070]

[0072] FIG. 3 is a flowchart illustrating a control method of a load rectification inverter adjustment angle speed control system according to one embodiment of the present invention.

[0073] In step S305, the load rectifier inverter speed control device has the speed command value of the motor part (140). and current speed Input the difference value to command torque Generates and outputs a response. Command torque is the q-axis current command when the inductance of the motor part (140) is symmetrical.

[0074] In step S310, the load rectifier inverter speed control device commands torque and DC current of the DC link section (130) Adjust angle by entering Prints.

[0075] In step S315, the load rectifier inverter speed control device controls the DC current of the DC link section (130). Input the maximum inverter firing angle Calculate and output.

[0076] In step S320, the load rectification inverter speed control device has a maximum inverter firing angle. and adjustment angle Input the difference value to obtain the new firing angle of the inverter. Creates and outputs.

[0077] In step S325, the load rectifier inverter speed control device controls the DC current of the DC link section (130). and DC rated current DC current command by entering the difference value Generate and DC voltage command Outputs DC current Controls.

[0078] In step S330, the load rectifier inverter speed control unit [commands] the DC voltage command Input the converter's firing angle Calculate and output.

[0080] FIG. 4 is a diagram illustrating a vector diagram of a wound rotor synchronous motor (WRSM) drive system according to one embodiment of the present invention.

[0081] The Wound Rotor Synchronous Motor (WRSM) is a motor primarily used in high-power applications, and the motor torque is the torque constant It is determined by. In this invention, since the magnetic resistance torque component of the WRSM is negligibly small, the motor torque q-axis current in the Rotor Reference Frame (RRF) coordinate system It is assumed to be proportional to.

[0082] q-axis current is the torque of the motor part (140) It can be seen through mathematical equation 6 that it is proportional to.

[0083] [Mathematical Formula 6]

[0084]

[0085] In Fig. 4 is the load angle of the motor part (140), and is the basic current component of the motor part (140).

[0086] Referring to Fig. 4, the current along the d-axis and current on the q-axis is the firing angle of the inverter in the rotor coordinate system of the vector diagram. and the load angle of the motor It can be expressed as shown in mathematical formula 7 below using .

[0087] [Mathematical Formula 7]

[0088]

[0089]

[0090] Referring to Fig. 4, Under the assumption that, the motor load angle The firing angle of the inverter and DC link current It can be expressed as shown in mathematical formula 8 below using .

[0091] [Mathematical Formula 8]

[0092]

[0093] electric motor torque The current on the q-axis in mathematical equation 6 representing Mathematical Equation 7 representing and the motor load angle If we substitute mathematical formula 8, which represents [it], it can be expressed as mathematical formula 9 below.

[0094] [Mathematical Formula 9]

[0095]

[0096] Equation 9 represents the motor torque as DC current and the firing angle of the inverter It can be expressed as. That is, the firing angle of the inverter The torque of this motor It can be seen that it is involved in.

[0097] Inverter firing angle in the torque equation The range of is It is smaller than.

[0098] Referring to Equation 8, the firing angle of the inverter and the load angle of the motor It can be seen that this is a proportional relationship, and referring to Equation 9, the firing angle of the inverter and the load angle of the motor As this increases, the torque of the electric motor It can be seen that it also increases.

[0099] In other words, the torque equation is go When it is more dominant, As increases over all intervals, it is a monotonically increasing function relationship, which can be expressed as in Equation 10 and holds under the condition of Equation 11.

[0100] [Mathematical Formula 10]

[0101]

[0102]

[0103] [Mathematical Formula 11]

[0104]

[0105] coefficient If is less than 1, maximum It generates maximum torque.

[0106] It is similar in magnitude to the product per unit of the basic current and inductance of the motor, and has a maximum value of 0.4 in the simulation and experimental motor of the present invention.

[0107] Therefore, maximum torque can be generated through maximum power factor control.

[0109] FIG. 5 is a 3D table diagram showing the change in q-axis current according to DC current and adjustment angle according to one embodiment of the present invention.

[0110] The present invention newly defines the adjustment angle σ. The adjustment angle σ is the actual firing angle of the inverter. and maximum inverter firing angle It is the difference. This is expressed by the mathematical formula 5 mentioned above.

[0111] [Mathematical Formula 5]

[0112]

[0113] Determine the adjustment angle σ to determine the firing angle of the inverter It can adjust the q-axis current It can also be adjusted. Q-axis current This can be determined through the mathematical formula 12 below.

[0114] [Mathematical Formula 12]

[0115]

[0116] Therefore, linearity can be ensured by analyzing the torque equation with the adjustment angle σ as in mathematical equation 13.

[0117] [Mathematical Formula 13]

[0118]

[0119] This relationship can be derived across all DC current regions through mathematical equation 13.

[0120] Referring to FIG. 5, the current-torque-adjustment angle table section (220) is configured in the form of a q-axis current 3D table for the adjustment angle and DC current through mathematical formulas 1 to 13.

[0121] Referring to FIG. 5, a torque controller can be newly configured to generate a firing angle command response for a commanded torque in a DC current state using interpolation.

[0122] Therefore, the present invention can control speed without passing through a DC current controller.

[0123] During actual operation, when the load rectifier inverter enters natural rectification mode, the current command is first raised to the rated current through converter current control. During this current raising process, the inverter-side firing angle control will be performed along the Maximum Torque Per Ampere (MTPA) path, which generates maximum torque, for the speed controller output value. This means controlling along the red line in Fig. 5.

[0124] Referring to Figure 5, the red line is the path of the Maximum Torque Per Ampere (MTPA).

[0125] After controlling along the red line, the torque is controlled only through the adjustment angle while keeping the DC current command fixed. This means controlling along the blue line in Fig. 5.

[0126] Referring to Figure 5, the blue line is the current path resulting from adjusting the adjustment angle σ at the rated current.

[0127] The blue line represents the q-axis current as the adjustment angle σ increases. It indicates that it decreases.

[0128] It is reasonable to increase the adjustment angle σ because the current vector rotates counterclockwise under the same current magnitude.

[0129] Therefore, the operating point moves away from the MTPA path, which is the red line, and consequently, the q-axis current It decreases.

[0130] This is clearly different from conventional methods.

[0131] In the conventional method, the firing angle of the inverter maximum value Set to, and q-axis current and DC link current It is controlled to adjust. At this time, the DC link current is the converter's roll call angle Adjust it.

[0132] On the other hand, the present invention uses an adjustment angle control method that controls by adjusting the adjustment angle σ, which is a new control degree of freedom, on the inverter side.

[0134] FIG. 6 is a diagram showing the change in arc angle according to the adjustment angle according to one embodiment of the present invention.

[0135] Adjustment angle σ and extinction angle using mathematical formula 14 The relationship can be defined.

[0136] [Mathematical Formula 14]

[0137]

[0138] Referring to Equation 14, the adjustment angle σ is the rectification angle and clearance angle It can affect the clearance angle. A process is required to verify whether variations do not have a negative impact on system reliability. To this end, system characteristic coefficients Defines as mathematical formula 15.

[0139] [Mathematical Formula 15]

[0140]

[0142] Referring to Equation 15, the system characteristic coefficient is a system parameter , , , It depends on. , , , Is and It affects.

[0143] Therefore, referring to Fig. 6, the effect of a change in σ on system reliability is For different values ​​of and σ It can be evaluated by observing.

[0144] The present invention is, This varies from 0 to a maximum of 0.0604. In this range is the initial setting value in all operating areas It is maintained above.

[0145] In other words, the present invention can be concluded to mean that adjusting σ does not affect system reliability.

[0147] Referring to FIGS. 5 and 6, while the conventional method used the maximum firing angle as the firing angle of the inverter, the method of the present invention controls the torque by using the adjustment angle σ as a new degree of freedom.

[0148] The adjustment angle affects the overlap angle at the same current, but analysis results show that changes in the adjustment angle do not affect the reliability of the control system in all regions.

[0150] FIG. 7 is a diagram showing parameter values ​​of a 15MW wound-type synchronous motor according to one embodiment of the present invention.

[0152] FIG. 8 is a diagram showing the speed control simulation results of a 15MW wound-type synchronous motor according to one embodiment of the present invention.

[0153] The motor subject to simulation is a 15MW wound-rotor synchronous motor (WRSM), and the parameter values ​​are shown in Fig. 7.

[0154] Referring to Fig. 8, (a) represents DC current and (b) represents motor speed.

[0155] Referring to FIG. 8, the speed control performance using the conventional DC current torque generation method shown by the red line and the adjustment angle torque generation method of the present invention shown by the blue line is compared. Compared to the conventional method, the present invention reduces the speed overshoot phenomenon and significantly reduces the time required to satisfy steady-state requirements.

[0157] FIG. 9 is a diagram showing the poles and zeros of the DC current control method, which is a conventional method according to one embodiment of the present invention, and the adjustment angle control method of the present invention.

[0158] In Fig. 9, BW is the bandwidth.

[0159] The worst-case scenario occurs when transitioning from forced commutation to natural commutation, which can affect speed control dynamics. SCR system delay It is 6 times the motor operating speed, and the SCR system delay This is because it is maximized at the minimum natural rectification speed, which is 10% of the rated speed.

[0160] Referring to Fig. 9, the condition is set to 10% of the system's electrical synchronous speed. At this time, the delay component generated in the adjustment angle controller It can be expressed by mathematical formula 16.

[0161] [Mathematical Formula 16]

[0162]

[0163] Referring to Fig. 9, the adjustment angle controller is a closed-loop transfer function The poles and zeros obtained when compared to are shown. is the closed-loop transfer function of the open-loop function, and the open-loop function can be represented by the following mathematical equation 17.

[0164] [Mathematical Formula 17]

[0165]

[0166] In mathematical formula 17 is equivalent resistance, is inductance, is the time constant of the RL load And, is the switching period, is the converter's control period, is the time constant of the low-pass filter, The control rectifier delay and filter delay are integrated as the main delay element. It can be expressed as such, and in cases of hundreds of kilowatts or more Is It can be approximated as, is the integral time constant of the PI controller And, is proportional gain, is the integral gain.

[0167] In conventional controllers, as the bandwidth expands, the trajectory of the poles appears along the imaginary axis. However, the control method of the present invention ensures higher responsiveness and stability by directing the trajectory of the poles to the left of the real axis.

[0169] FIG. 10 is a diagram showing the speed control system bandwidth of the conventional DC current control method and the adjustment angle control method of the present invention according to one embodiment of the present invention.

[0170] Referring to FIG. 10, the speed control bandwidth of the present invention can be set about 6 times faster than the conventional method even under worst conditions. The control method of the present invention sets the DC current by taking into account the maximum torque and conduction loss.

[0171] In FIG. 10, the DC Current control system is a conventional method, and the Adjustable angle control system is the adjustable angle control method of the present invention.

[0173] The present invention has been described above with reference to its embodiments. Those skilled in the art will understand that the present invention may be embodied in modified forms without departing from the essential characteristics of the invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the invention is defined by the claims, not by the foregoing description, and all variations within the scope of the claims should be interpreted as being included in the invention. Explanation of the symbols

[0175] 110: Thyristor converter 120: Thyristor inverter 130: DC Link Section 140: Electric motor 200: Load Rectifier Inverter Firing Angle Control Unit 210: Speed ​​control unit 220: Current-Torque-Adjustment Angle Table Section 230: Maximum inverter firing angle calculation unit 240: New inverter firing angle calculation unit 250: DC current control unit 260: Converter firing angle calculation unit

Claims

Claim 1 A load rectification inverter speed control device comprising: a thyristor converter that rectifies the line voltage of a three-phase grid and controls the magnitude and polarity of the rectified voltage by adjusting the firing angle of the converter; a thyristor inverter that controls the phase angle of the current supplied to the motor using the firing angle of the inverter; a DC link unit that stores energy and suppresses harmonics between the thyristor converter and the thyristor inverter; a motor unit that operates with an alternating voltage applied from the thyristor inverter; and a load rectification inverter firing angle control unit that receives the speed command of the motor unit and the DC current of the DC link unit, generates a firing angle command response, and outputs a maximum torque. Claim 2 A load rectification inverter speed control device according to claim 1, wherein the load rectification inverter firing angle control unit comprises: a current-torque-adjustment angle table unit that receives a command torque and a DC current and outputs an adjustment angle; a maximum inverter firing angle calculation unit that receives the DC current and calculates and outputs a maximum inverter firing angle; and a new inverter firing angle calculation unit that receives the difference value between the maximum inverter firing angle and the adjustment angle and outputs a new firing angle, which is the firing angle of the inverter. Claim 3 In paragraph 2, the load rectification inverter firing angle control unit further comprises a speed control unit that receives the difference between the speed command value of the motor unit and the current speed value and outputs the commanded torque. Claim 4 In paragraph 2, the load rectifier inverter firing angle control unit further comprises a DC current control unit that receives the difference value between the DC current and the DC rated current, generates a DC current command, and outputs a DC voltage command to control the DC current, thereby forming a load rectifier inverter speed control device. Claim 5 In paragraph 2, the load rectification inverter firing angle control unit further comprises a converter firing angle calculation unit that receives a DC voltage command and calculates and outputs the firing angle of the converter, thereby forming a load rectification inverter speed control device. Claim 6 In paragraph 3, the speed control unit is a load rectifier inverter speed control device that generates a q-axis current command when the inductance of the motor unit is symmetrical. Claim 7 A load rectification inverter speed control method comprising: a step of inputting a command torque and a DC current to output an adjustment angle; a step of inputting the DC current to calculate and output a maximum inverter firing angle; and a step of inputting the difference value between the maximum inverter firing angle and the adjustment angle to generate and output a new firing angle, which is the firing angle of the inverter. Claim 8 In claim 7, the load rectifier inverter speed control method further comprises the step of generating and outputting the commanded torque by inputting the difference between the speed command value and the current speed value. Claim 9 In claim 7, the load rectifier inverter speed control method further comprises the step of controlling the DC current by inputting the difference value between the DC current and the DC rated current to generate a DC current command and outputting a DC voltage command. Claim 10 In claim 7, the load rectifier inverter speed control method further comprises the step of inputting a DC voltage command to calculate and output the firing angle of a converter.

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