A high-voltage cascade inverter non-disturbance closing and cooling control circuit and method

Abstract

The present invention discloses a non-disturbance closing and cooling control circuit and method for a high-voltage cascade frequency converter, and relates to the field of power electronics application technology. The control circuit includes: a high-voltage cascade power unit, a high-voltage cascade frequency converter control system, a phase-shifting transformer, a three-phase voltage acquisition circuit, and a variable frequency power supply switching module; wherein the high-voltage cascade power unit is used to connect a number of power units in series to provide a high-voltage output; the high-voltage cascade frequency converter control system is used to control the non-disturbance closing pre-charging and cooling control functions of the high-voltage frequency converter; the phase-shifting transformer is used to provide an isolated power supply for each level of power units; the three-phase voltage acquisition circuit is used to detect the sampling signal of the high-voltage side input voltage; the variable frequency power supply switching module is used to set the non-disturbance closing pre-charging logic. The present invention solves the problem of low-voltage pre-charging and high-voltage non-disturbance closing in the prior art, reduces the transformer power-on impact current, and ensures that the DC bus capacitor in the power unit is charged at the rated voltage during the low-voltage pre-charging process.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics applications, and in particular to a high-voltage cascade inverter non-disturbance closing and cooling control circuit and method. Background Art

[0002] High-voltage frequency conversion technology is widely used in the field of industrial electric traction, especially the chain topology structure is more common. High-voltage direct power-on will impact the DC bus capacitor. The existing high-voltage pre-charging technology has the advantage of simple operation, but the high-voltage switch and charging components are expensive and large in size. After low-voltage pre-charging, it is also easy to generate a large inrush current due to the problem of asynchrony.

[0003] For example, Chinese patent CN101860225A discloses an AC inverter pre-charging circuit for a high-voltage frequency converter and a control method thereof, and provides an AC inverter pre-charging circuit for a high-voltage cascade frequency converter. An AC inverter device is used to replace the existing current-limiting resistor to generate an excitation current to excite the transformer, thereby avoiding the influence of the transformer excitation current on the pre-charging. Since the low-voltage side charging power supply and the high-voltage side power supply are not matched, high-voltage disturbance-free closing cannot be achieved, and the impact current at the moment of transformer power-on cannot be controlled. In addition, after charging is completed, the AC inverter device is in a non-working state, and the economy is poor.

[0004] For example, Chinese patent CN216752545U discloses a pre-charging and fan power supply circuit and a high-voltage inverter, which integrates the pre-charging circuit and the fan power supply circuit together to reduce costs and the size of the high-voltage inverter. However, this solution does not involve a non-intrusive high-voltage closing method, and it is impossible to realize the auxiliary winding to power the cooling fan, resulting in the inability to switch to the transformer auxiliary winding for power supply in the event of a low-voltage inverter failure or an external power supply failure.

[0005] In summary, the traditional technical solutions cannot achieve the functions of high-voltage non-intrusive closing and transformer power-on surge current suppression. No effective solutions have been proposed for the problems in the related technologies. Summary of the invention

[0006] Based on this, it is necessary to provide a high-voltage cascade inverter non-disturbance closing and cooling control circuit and method to address the above technical problems.

[0007] In a first aspect, the present invention provides a high-voltage cascade inverter non-disturbance closing and cooling control circuit, the control circuit comprising: a high-voltage cascade power unit, a high-voltage cascade inverter control system, a phase-shifting transformer, a three-phase voltage acquisition circuit and a variable frequency power supply switching module;

[0008] Among them, the high-voltage cascade power unit is used to connect several power units in series to provide high-voltage output;

[0009] High-voltage cascade inverter control system, used to monitor the internal system parameters of the high-voltage inverter and control the non-intrusive closing pre-charging and cooling control functions of the high-voltage inverter;

[0010] Phase-shifting transformer, used to provide isolated power supply for each level of power unit;

[0011] A three-phase voltage acquisition circuit is used to detect the sampling signal of the high-voltage side input voltage;

[0012] The variable frequency power supply switching module is used to set the disturbance-free closing pre-charging logic and perform the disturbance-free closing pre-charging and variable frequency cooling control operations.

[0013] Furthermore, the control circuit also includes: a three-phase low-voltage power supply and a three-phase heat dissipation cooling fan;

[0014] Among them, the three-phase low-voltage power supply is used to provide power for the pre-charging of the high-voltage inverter, and serves as a backup power supply with the 380V auxiliary winding after the high-voltage switch is closed; the three-phase heat dissipation cooling fan is used to provide air cooling for the high-voltage inverter.

[0015] Furthermore, the high-voltage cascade power unit includes 3*n power units, and the 3*n power units are respectively connected in series to form three n-level three-phase power groups, the input side of each level of the three-phase power group is connected to the secondary winding of the corresponding phase-shifting transformer, the output end of each level of the three-phase power group is connected in series, the output end of the first level of the three-phase power group that is not connected to other power units is connected to form a three-phase midpoint, and the output end of the nth level of the three-phase power group that is not connected to other power units is the high-voltage output U, V, W.

[0016] Furthermore, the high-voltage cascade inverter control system includes: a pre-charging and cooling control module, a low-voltage inverter pulse control and fault monitoring module, a power unit monitoring module and a logic control module; wherein the pre-charging and cooling control module is used to control the pre-charging function and cooling control function of the high-voltage inverter, and calculate the system parameters obtained by monitoring, and call different functional modules to execute the pre-charging and cooling control operation of the high-voltage inverter; the low-voltage inverter pulse control and fault monitoring module is used to control the pulse output of the low-voltage inverter, and receive the fault information of the low-voltage inverter, and perform processing using the logic control model; the power unit monitoring module is used to monitor the voltage and temperature of each level of power unit; the logic control module is used to complete the logic control function of the pre-charging process and cooling control.

[0017] Further, the phase-shifting transformer includes: a plurality of secondary windings, a 380V auxiliary winding and a high-voltage side input circuit;

[0018] Among them, the secondary winding is used to connect to the input side of several levels of power units; the 380V auxiliary winding is used to connect to the variable frequency power supply switching module and serve as a backup power supply for the three-phase low-voltage power supply; the high-voltage side input circuit is used to provide the high-voltage side input voltage to form a high-voltage input A, B, and C three-phase voltage, and is connected to the three-phase voltage sampling circuit and input into the three sampling channels of the high-voltage cascade inverter control system respectively.

[0019] Further, the variable frequency power supply switching module includes: a three-phase low voltage frequency converter, a contactor K1, a contactor K2, a contactor K3 and a contactor K4;

[0020] Among them, the three-phase low-voltage inverter is used to convert the frequency and voltage of the three-phase alternating current, and execute the disturbance-free closing pre-charging and variable frequency cooling control of the high-voltage inverter; contactor K1, contactor K2, contactor K3 and contactor K4 are all used to execute the disturbance-free closing pre-charging logic and switch the power supply mode of the high-voltage inverter.

[0021] Furthermore, one side of contactor K1 is connected to the 380V auxiliary winding and one side of contactor K4, the other side of contactor K1 is connected to one side of contactor K3 and the output end of the three-phase low-voltage inverter, the input end of the three-phase low-voltage inverter is connected to one side of contactor K2 and the other side of contactor K4, the other side of contactor K2 is connected to the three-phase low-voltage power supply, and the other side of contactor K3 is connected to the three-phase heat dissipation cooling fan.

[0022] Furthermore, the high-voltage cascade inverter control system controls the opening and closing of contactor K1, contactor K2, contactor K3 and contactor K4; the high-voltage cascade inverter control system is connected to the three-phase low-voltage inverter by switching quantity to output data and instructions, and the high-voltage cascade inverter control system controls the opening and closing of the switch tube in the three-phase low-voltage inverter by outputting pulses.

[0023] Furthermore, the high-voltage cascade inverter control system can control the rated output voltage of the three-phase low-voltage inverter to be synchronized with the high-voltage side input voltage, that is, the phase and phase sequence of the three-phase voltage under the rated frequency output state of the three-phase low-voltage inverter are consistent with the phase and phase sequence of the high-voltage side input voltage.

[0024] In a second aspect, the present invention further provides a method for controlling the non-disturbance closing and cooling of a high-voltage cascade inverter, the control method comprising the following steps:

[0025] S1, when contactor K1, contactor K2, contactor K3 and contactor K4 are all disconnected, set as the initial state of the variable frequency power supply switching module, and after the high-voltage cascade inverter control system receives the pre-charging start instruction, close contactor K1 and contactor K2; the three-phase low-voltage inverter is in hot standby state;

[0026] S2, using the high-voltage cascade inverter control system to detect the sampling channel, and based on the three-phase high-voltage phase sequence, setting the output phase sequence of the three-phase low-voltage inverter;

[0027] S3, the high-voltage cascade inverter control system controls the variable frequency power supply switching module to perform pre-charging based on a preset charging time;

[0028] S4, real-time detection of system parameters during the pre-charging process, and based on a preset charging completion threshold, identification of fault signals during the pre-charging process, and switching of protection states;

[0029] S5, detecting the phase between the high-voltage side input circuit and the variable frequency power supply switching module in real time, and controlling the variable frequency power supply switching module based on the phase change to trigger a high-voltage closing command;

[0030] S6, controls the QF switch of the high-voltage side input circuit to close, and controls the high-voltage cascade inverter to enter the hot standby state after the high-voltage cascade inverter control system detects that there is no fault.

[0031] Furthermore, the high-voltage cascade inverter control system controls the variable frequency power supply switching module to perform pre-charging based on a preset charging time, including the following steps:

[0032] S31, setting the start time of the three-phase low-voltage inverter as the charging time;

[0033] S32, using the high-voltage cascade inverter control system to output a pulse signal to the three-phase low-voltage inverter, controlling the three-phase low-voltage inverter to output a three-phase voltage, and gradually increasing it along the V / F curve;

[0034] S33, the voltage amplitude of the 380V auxiliary winding and the secondary winding in the phase-shifting transformer gradually increases to charge the power units at each level.

[0035] Furthermore, the system parameters in the pre-charging process are detected in real time, and based on a preset pre-charging completion threshold, a fault signal in the pre-charging process is identified, and the switching protection state includes the following steps:

[0036] S41, real-time detection of the DC bus voltage of each power unit, and the output voltage and output power of the three-phase low-voltage inverter;

[0037] S42. When contactor K1 is closed and contactor K3 is disconnected, when the output voltage and output frequency of the three-phase low-voltage inverter reach the rated voltage and rated frequency, if the DC bus voltage of each power unit is greater than the charging completion threshold, a synchronization instruction is sent to the three-phase low-voltage inverter. If the DC bus voltage of each power unit does not reach the charging completion threshold, a pre-charging fault signal is issued and contactor K1 and contactor K2 are disconnected.

[0038] Furthermore, the high-voltage cascade inverter control system detects the three-phase low-voltage inverter fault and the three-phase low-voltage power supply fault in real time, controls the contactor K1, the contactor K2, the contactor K3, and the contactor K4 through the logic control module, and drives the cooling system to operate. The cooling system operation steps include:

[0039] When the three-phase low-voltage power supply fails while contactor K1 is disconnected and contactor K3 is closed, the high-voltage cascade inverter control system disconnects contactor K2 and closes contactor K4, using the 380V auxiliary winding to provide power for the three-phase low-voltage inverter and continue to control the operation of the three-phase heat dissipation cooling fan in a closed loop;

[0040] When the three-phase low-voltage inverter fails, the high-voltage cascade inverter control system disconnects the contactor K2 and the contactor K4, and then closes the contactor K1 and the contactor K3, and directly drives the three-phase heat dissipation cooling fan to operate through the 380V auxiliary winding.

[0041] Furthermore, the three-phase low-voltage inverter adopts PID regulation control output, and the speed of the three-phase heat dissipation cooling fan is closed-loop controlled by calculating the average temperature and the parameter adjustment amount, wherein the expression for calculating the average temperature and the parameter adjustment amount includes:

[0042]

[0043]

[0044] Where, T avr Represents the average temperature of all power units; T alarm Indicates the set power unit alarm temperature threshold; T Ai represents the temperature of the i-th power unit in phase A; T Bi represents the temperature of the i-th power unit in phase B; T Ci represents the temperature of the i-th power unit in phase C; n represents the number of power units in each phase; S represents the complex frequency variable; k i , k p represents the closed-loop control parameter; Δf represents the parameter adjustment amount output by the high-voltage cascade inverter control system to the three-phase low-voltage inverter.

[0045] Furthermore, the phase between the high-voltage side input circuit and the variable frequency power supply switching module is detected in real time, and based on the phase change, the variable frequency power supply switching module is controlled to trigger the high-voltage closing instruction, including the following steps:

[0046] S51, when the three-phase low-voltage inverter is started to the charging time, the high-voltage cascade inverter control system is used to detect the three groups of channel voltages of the sampling channel, and the A phase of the high-voltage side input circuit and the A phase of the three-phase low-voltage inverter are calculated;

[0047] S52, adjust the phase of phase A of the three-phase low-voltage inverter. When the phase of phase A of the three-phase low-voltage inverter is consistent with the phase A of the high-voltage side input circuit, control the three-phase low-voltage inverter to stop output, disconnect contactor K1, and trigger the high-voltage closing command.

[0048] The beneficial effects of the present invention are:

[0049] 1. The present invention solves the problem of low-voltage pre-charging and high-voltage non-disturbance closing in the prior art, reduces the transformer power-on impact current, can ensure that the DC bus capacitor in the power unit is charged at the rated voltage during the low-voltage pre-charging process, reduces the impact of high-voltage power-on on the DC bus capacitor, and does not require a charging resistor, thereby reducing energy consumption.

[0050] 2. The present invention realizes closed-loop temperature control of the cooling fan, reduces the operating current of the cooling fan, reduces energy consumption, and reduces noise; at the same time, it has a high degree of automation and is simple and reliable to implement; and it can increase the service life of the DC bus capacitor, cooling fan, and transformer in the power unit, and reduce implementation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0052] Figure 1 It is a circuit schematic diagram of a non-disturbance closing and cooling control circuit of a high-voltage cascade inverter according to an embodiment of the present invention;

[0053] Figure 2 It is a schematic diagram of a power unit in a non-disturbance closing and cooling control circuit of a high-voltage cascade inverter according to an embodiment of the present invention;

[0054] Figure 3 It is a system block diagram of a high-voltage cascade inverter control system in a high-voltage cascade inverter non-disturbance closing and cooling control circuit according to an embodiment of the present invention;

[0055] Figure 4 The present invention is a flowchart of a method for non-disturbance closing and cooling control of a high-voltage cascade inverter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0057] See also Figure 1-Figure 3, provides a high-voltage cascade inverter non-disturbance closing and cooling control circuit, the control circuit includes: a high-voltage cascade power unit, a high-voltage cascade inverter control system, a phase-shifting transformer, a three-phase voltage acquisition circuit and a variable frequency power supply switching module.

[0058] The high-voltage cascade power unit is used to connect several power units in series to provide high-voltage output, and the schematic diagram of the power unit is as follows Figure 2 shown.

[0059] In the description of the present invention, the high-voltage cascade inverter includes 3*n power units, and the 3*n power units are connected in series to form an n-level three-phase power group. The input side of each level of the three-phase power group is connected to the secondary winding of the corresponding phase-shifting transformer. The output end of each level of the three-phase power group is connected in series. The output end of the first level of the three-phase power group that is not connected to other power units is connected to form a three-phase midpoint. The output end of the nth level of the three-phase power group that is not connected to other power units is a high-voltage output U, V, W. By analogy, the nth level power unit A n , B n , C n One end of the output is connected to the n-1th power unit A n-1 , B n-1 , C n-1 , forming a high voltage output terminal.

[0060] Specifically, Figure 1 As shown, the high-voltage cascade power unit includes several levels (1, 2, 3...n), each level of the power unit includes three power units, and each power unit is connected to the secondary winding of the phase-shifting transformer. Among them, the three power units of the first level are power unit A 1 、Power unit B 1 and power unit C 1 ; The three power units of the second stage are power unit A 2 、Power unit B 2 and power unit C 2 ; The three power units of the nth level are power unit A n 、Power unit B n and power unit C n .

[0061] The high-voltage cascade inverter control system is used to monitor the internal system parameters of the high-voltage inverter and control the non-disturbance closing pre-charging and cooling control functions of the high-voltage inverter.

[0062] In the description of the present invention, Figure 3 As shown, the high-voltage cascade inverter control system includes: a pre-charging and cooling control module, a low-voltage inverter pulse control and fault monitoring module, a power unit monitoring module and a logic control module.

[0063] Among them, the pre-charging and cooling control module is used to control the pre-charging function and cooling control function of the high-voltage inverter, calculate the system parameters obtained by monitoring, and call different functional modules to execute the pre-charging and cooling control operation of the high-voltage inverter. The low-voltage inverter pulse control and fault monitoring module is used to control the pulse output of the low-voltage inverter, receive the fault information of the low-voltage inverter, and perform processing using the logic control model. The power unit monitoring module is used to monitor the voltage and temperature of each level of power unit. The logic control module is used to complete the logic control function of the pre-charging process and cooling control.

[0064] Phase-shifting transformer is used to provide isolated power supply for each level of power unit.

[0065] In the description of the present invention, the phase-shifting transformer includes: a plurality of secondary windings, a 380V auxiliary winding and a high-voltage side input circuit.

[0066] The secondary winding is used to connect to the input side of several power units. The 380V auxiliary winding is used to connect to the variable frequency power supply switching module and serve as a backup power supply for the three-phase low-voltage power supply. The high-voltage side input circuit is used to provide high-voltage side input voltage to form high-voltage input A, B, C three-phase voltages, and is connected to the three-phase voltage sampling circuit to be input to the three sampling channels V of the high-voltage cascade inverter control system. a 、V b 、V c .

[0067] The three-phase voltage acquisition circuit is used to detect the sampling signal of the high-voltage side input voltage.

[0068] The variable frequency power supply switching module is used to set the disturbance-free closing pre-charging logic and perform the disturbance-free closing pre-charging and variable frequency cooling control operations.

[0069] In the description of the present invention, the variable frequency power supply switching module includes: a three-phase low voltage frequency converter, a contactor K1, a contactor K2, a contactor K3 and a contactor K4.

[0070] Among them, the three-phase low-voltage inverter is used to convert the frequency and voltage of the three-phase AC power and perform the non-disturbance closing pre-charging and variable frequency cooling control of the high-voltage inverter. Contactors K1, K2, K3 and K4 are all used to execute the non-disturbance closing pre-charging logic and switch the power supply mode of the high-voltage inverter.

[0071] In addition, the three-phase low-voltage inverter VFC realizes electrical connection with different power supplies and different output loads through contactors K1, K2, K3, and K4, and can be completely isolated from the circuit in case of failure without affecting the normal operation of the high-voltage inverter.

[0072] In the description of the present invention, one side of the contactor K1 is connected to the 380V auxiliary winding and one side of the contactor K4, the other side of the contactor K1 is connected to one side of the contactor K3 and the output end of the three-phase low-voltage inverter, the input end of the three-phase low-voltage inverter is connected to one side of the contactor K2 and the other side of the contactor K4, the other side of the contactor K2 is connected to the three-phase low-voltage power supply, and the other side of the contactor K3 is connected to the three-phase heat dissipation cooling fan.

[0073] In the description of the present invention, the high-voltage cascade inverter control system controls the opening and closing of contactors K1, K2, K3 and K4. The high-voltage cascade inverter control system is connected with the three-phase low-voltage inverter to output data and instructions, and the high-voltage cascade inverter control system controls the opening and closing of the switch tube in the three-phase low-voltage inverter by outputting pulses.

[0074] In the description of the present invention, the output voltage of the three-phase low-voltage inverter is synchronized with the high-voltage side input voltage, and the phase and phase sequence of the three-phase voltage under the rated frequency output state of the three-phase low-voltage inverter are consistent with the phase and phase sequence of the high-voltage side input voltage.

[0075] In the description of the present invention, the control circuit also includes: a three-phase low-voltage power supply and a three-phase heat dissipation cooling fan.

[0076] Among them, the three-phase low-voltage power supply is used to provide power for the pre-charging of the high-voltage inverter, and serves as a backup power supply with the 380V auxiliary winding after the high-voltage switch is closed.

[0077] Three-phase heat dissipation cooling fan is used to provide air cooling for high-voltage inverters.

[0078] See also Figure 4 The present invention also provides a method for controlling the non-disturbance closing and cooling of a high-voltage cascade inverter, the control method comprising the following steps:

[0079] S1. When contactor K1, contactor K2, contactor K3 and contactor K4 are all disconnected, the initial state of the variable frequency power supply switching module is set, and after the high-voltage cascade inverter control system receives the pre-charge start instruction, contactor K1 and contactor K2 are closed; the three-phase low-voltage inverter is in hot standby state.

[0080] S2. Use the high-voltage cascade inverter control system to detect the sampling channel and set the output phase sequence of the three-phase low-voltage inverter based on the three-phase high-voltage phase sequence.

[0081] S3. The high-voltage cascade inverter control system controls the variable frequency power supply switching module to perform pre-charging based on a preset charging time.

[0082] In the description of the present invention, the high-voltage cascade inverter control system controls the variable frequency power supply switching module to perform pre-charging based on a preset charging time, including the following steps:

[0083] S31, setting the starting time of the three-phase low-voltage inverter to the charging time, that is, the starting time of the three-phase low-voltage inverter VFC from 1 Hz to 50 Hz.

[0084] S32, using the high-voltage cascade inverter control system to output a pulse signal to the three-phase low-voltage inverter, controlling the three-phase low-voltage inverter to output a three-phase voltage, and gradually increasing it along the V / F curve.

[0085] S33, the voltage amplitude of the 380V auxiliary winding and the secondary winding in the phase-shifting transformer gradually increases to charge the power units at each level.

[0086] S4. Real-time detection of system parameters during the pre-charging process, and based on a preset charging completion threshold, identification of fault signals during the pre-charging process, and switching of protection states.

[0087] In the description of the present invention, the system parameters in the pre-charging process are detected in real time, and based on the preset pre-charging completion threshold, the fault signal in the pre-charging process is identified, and the switching protection state includes the following steps:

[0088] S41, real-time detection of the DC bus voltage of each power unit, and the output voltage and output power of the three-phase low-voltage inverter.

[0089] S42. When the output voltage and output frequency of the three-phase low-voltage inverter reach the rated voltage and rated frequency, if the DC bus voltage of each power unit is greater than the charging completion threshold, a synchronization command is sent to the three-phase low-voltage inverter. If the DC bus voltage of each power unit does not reach the charging completion threshold, a pre-charging fault signal is issued and contactor K1 and contactor K2 are disconnected.

[0090] In the description of the present invention, the high-voltage cascade inverter control system detects the three-phase low-voltage inverter fault and the three-phase low-voltage power supply fault in real time, controls the contactor K1, the contactor K2, the contactor K3, and the contactor K4 through the logic control module, and drives the cooling system to operate. The cooling system operation steps include:

[0091] S431. When contactor K1 is disconnected and contactor K3 is closed, when the three-phase low-voltage power supply fails, the high-voltage cascade inverter control system disconnects contactor K2 and closes contactor K4, and uses the 380V auxiliary winding to provide power for the three-phase low-voltage inverter, and continues to control the operation of the three-phase heat dissipation cooling fan in a closed loop.

[0092] S432. When the three-phase low-voltage inverter fails, the high-voltage cascade inverter control system disconnects the contactor K2 and the contactor K4, and then closes the contactor K1 and the contactor K3, and directly drives the three-phase heat dissipation cooling fan to operate through the 380V auxiliary winding.

[0093] In the description of the present invention, the three-phase low-voltage inverter adopts PID regulation control output, and the speed of the three-phase heat dissipation cooling fan is closed-loop controlled by calculating the average temperature and the parameter adjustment amount, wherein the expression for calculating the average temperature and the parameter adjustment amount includes:

[0094]

[0095]

[0096] Where, T avr Represents the average temperature of all power units; T alarm Indicates the set power unit alarm temperature threshold; T Ai represents the temperature of the i-th power unit in phase A; T Bi represents the temperature of the i-th power unit in phase B; T Ci represents the temperature of the i-th power unit in phase C; n represents the number of power units in each phase; S represents the complex frequency variable; k i , k p represents the closed-loop control parameter (k i represents the integral parameter, k p represents the proportional parameter); Δf represents the parameter adjustment amount (modulation wave frequency adjustment amount) output by the high-voltage cascade inverter control system to the three-phase low-voltage inverter.

[0097] S5, real-time detection of the phase between the high-voltage side input circuit and the variable frequency power supply switching module, and based on the phase change, control of the variable frequency power supply switching module to trigger a high-voltage closing command.

[0098] In the description of the present invention, the phase between the high-voltage side input circuit and the variable frequency power supply switching module is detected in real time, and based on the phase change, the variable frequency power supply switching module is controlled to trigger the high-voltage closing instruction, including the following steps:

[0099] S51. When the three-phase low-voltage inverter is started to the charging time (started to 50Hz), the high-voltage cascade inverter control system is used to detect the three groups of channel voltages of the sampling channel, and calculate the A phase of the high-voltage side input circuit and the A phase of the three-phase low-voltage inverter.

[0100] Specifically, the high-voltage cascade inverter control system CS detects the sampling channel V a 、V b 、V c, the phase of phase A on the high voltage input side is calculated using the software phase-locked loop algorithm ; Phase A of three-phase low voltage inverter VFC ; Use PID regulation algorithm to control the A phase of the three-phase low-voltage inverter VFC ,when Phase A with high voltage input side When they are consistent, the high-voltage cascade inverter control system CS stops outputting pulse signals to the three-phase low-voltage inverter VFC, and controls the three-phase low-voltage inverter VFC to stop output.

[0101] S52, adjust the phase of phase A of the three-phase low-voltage inverter. When the phase of phase A of the three-phase low-voltage inverter is consistent with the phase A of the high-voltage side input circuit, control the three-phase low-voltage inverter to stop output, disconnect contactor K1, and trigger the high-voltage closing command.

[0102] In addition, after the high-voltage cascade inverter completes the pre-charging high-voltage disturbance-free closing, if contactors K2 and K3 are closed and contactor K4 is disconnected, the 380V power supply is supplied to the three-phase low-voltage inverter VFC input through contactor K2, and the three-phase low-voltage inverter VFC drives the cooling fan to operate with variable frequency through contactor K3; if contactors K3 and K4 are closed and contactor K2 is disconnected, the 380V auxiliary winding is supplied to the three-phase low-voltage inverter VFC input through contactor K4, and the three-phase low-voltage inverter VFC drives the cooling fan to operate with variable frequency through contactor K3.

[0103] S6, controls the QF switch of the high-voltage side input circuit to close, and controls the high-voltage cascade inverter to enter the hot standby state after the high-voltage cascade inverter control system detects that there is no fault.

[0104] To sum up, with the help of the above-mentioned technical scheme of the present invention, the present invention solves the problem of low-voltage pre-charging and high-voltage non-disturbance closing in the prior art, reduces the transformer power-on impact current, can ensure that the DC bus capacitor in the power unit is charged at the rated voltage during the low-voltage pre-charging process, reduces the impact of high-voltage power-on on the DC bus capacitor, and does not require a charging resistor, thereby reducing energy consumption; the present invention realizes closed-loop temperature control of the cooling fan, reduces the operating current of the cooling fan, reduces energy consumption, and reduces noise; at the same time, it has a high degree of automation and is simple and reliable to implement; and can increase the service life of the DC bus capacitor, the cooling fan, and the transformer in the power unit, and reduce implementation and maintenance costs.

[0105] It should be understood that, although the steps in the flowchart of the accompanying drawings are displayed in sequence as indicated by the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least a part of the steps in the flowchart of the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a part of the sub-steps or stages of other steps.

Claims

1. A high-voltage cascade inverter non-disturbance closing and cooling control circuit, characterized in that: The control circuit includes: a high-voltage cascade power unit, a high-voltage cascade inverter control system, a phase-shifting transformer, a three-phase voltage acquisition circuit and a variable frequency power supply switching module; Wherein, the high-voltage cascade power unit is used to connect several power units in series to provide high-voltage output; The high-voltage cascade inverter control system is used to monitor the internal system parameters of the high-voltage inverter and control the non-disturbance closing pre-charging and cooling control functions of the high-voltage inverter; The phase-shifting transformer is used to provide isolated power supply for each level of power units; The three-phase voltage acquisition circuit is used to detect the sampling signal of the high-voltage side input voltage; The variable frequency power supply switching module is used to set the non-disturbance closing pre-charging logic and perform non-disturbance closing pre-charging and variable frequency cooling control operations; The control circuit also includes: a three-phase low-voltage power supply and a three-phase heat dissipation cooling fan; The three-phase low-voltage power supply is used to provide power for the pre-charging of the high-voltage inverter, and serves as a backup power supply with the 380V auxiliary winding after the high-voltage switch is closed; The three-phase heat dissipation cooling fan is used to provide air cooling for the high-voltage frequency converter; The high-voltage cascade inverter control system includes: a pre-charging and cooling control module, a low-voltage inverter pulse control and fault monitoring module, a power unit monitoring module and a logic control module; The pre-charging and cooling control module is used to control the pre-charging function and cooling control function of the high-voltage inverter, calculate the system parameters obtained by monitoring, and call different functional modules to execute the pre-charging and cooling control operation of the high-voltage inverter; The low voltage inverter pulse control and fault monitoring module is used to control the pulse output of the low voltage inverter, receive fault information of the low voltage inverter, and perform processing using the logic control model; The power unit monitoring module is used to monitor the voltage and temperature of each level of power units; The logic control module is used to complete the logic control functions of the pre-charging process and cooling control; The phase-shifting transformer comprises: a plurality of secondary windings, a 380V auxiliary winding and a high-voltage side input circuit; The secondary winding is used to connect to the input side of several levels of power units; The 380V auxiliary winding is used to connect to the variable frequency power supply switching module and serve as a backup power supply with the three-phase low-voltage power supply; The high-voltage side input circuit is used to provide a high-voltage side input voltage to form a high-voltage input three-phase voltage of A, B, and C, and is connected to the three-phase voltage sampling circuit to be input into the three sampling channels of the high-voltage cascade inverter control system respectively; The variable frequency power supply switching module includes: a three-phase low voltage frequency converter, a contactor K1, a contactor K2, a contactor K3 and a contactor K4; The three-phase low-voltage inverter is used to convert the frequency and voltage of the three-phase alternating current and perform the non-disturbance closing pre-charging and variable frequency cooling control of the high-voltage inverter; The contactor K1, the contactor K2, the contactor K3 and the contactor K4 are all used to execute the non-intrusive closing pre-charging logic and switch the power supply mode of the high-voltage inverter; The three-phase low-voltage inverter adopts PID regulation control output, and the speed of the three-phase heat dissipation cooling fan is closed-loop controlled by calculating the average temperature and the parameter adjustment amount. The expression for calculating the average temperature and the parameter adjustment amount includes: Where, T avr Represents the average temperature of all power units; T alarm Indicates the set power unit alarm temperature threshold; T Ai represents the temperature of the i-th power unit in phase A; T Bi represents the temperature of the i-th power unit in phase B; T Ci represents the temperature of the i-th power unit in phase C; n represents the number of power units in each phase; S represents a complex frequency variable; k i , k p Represents closed-loop control parameters; Δf represents the parameter adjustment amount output by the high-voltage cascade inverter control system to the three-phase low-voltage inverter.

2. A high-voltage cascade inverter non-disturbance closing and cooling control circuit according to claim 1, characterized in that: The high-voltage cascade inverter includes 3*n power units, and the 3*n power units are respectively connected in series to form an n-level three-phase power group, the input side of each level of the three-phase power group is connected to the secondary winding of the corresponding phase-shifting transformer, the output end of each level of the three-phase power group is connected in series, the output end of the first level of the three-phase power group that is not connected to other power units is connected to form a three-phase midpoint, and the output end of the nth level of the three-phase power group that is not connected to other power units is a high-voltage output U, V, W.

3. A high-voltage cascade inverter non-disturbance closing and cooling control circuit according to claim 2, characterized in that: One side of the contactor K1 is connected to the 380V auxiliary winding and one side of the contactor K4, the other side of the contactor K1 is connected to one side of the contactor K3 and the output end of the three-phase low-voltage inverter, the input end of the three-phase low-voltage inverter is connected to one side of the contactor K2 and the other side of the contactor K4, the other side of the contactor K2 is connected to the three-phase low-voltage power supply, and the other side of the contactor K3 is connected to the three-phase heat dissipation cooling fan.

4. A high-voltage cascade inverter non-disturbance closing and cooling control circuit according to claim 3, characterized in that: The high-voltage cascade inverter control system controls the opening and closing of the contactor K1, the contactor K2, the contactor K3 and the contactor K4; The high-voltage cascade inverter control system is connected to the three-phase low-voltage inverter in switching quantity to output data and instructions, and the high-voltage cascade inverter control system controls the opening and closing of the switch tube in the three-phase low-voltage inverter by outputting pulses.

5. A high-voltage cascade inverter non-disturbance closing and cooling control circuit according to claim 4, characterized in that: The high-voltage cascade inverter control system can control the rated output voltage of the three-phase low-voltage inverter to remain synchronized with the high-voltage side input voltage, that is, the phase and phase sequence of the three-phase voltage under the rated frequency output state of the three-phase low-voltage inverter are consistent with the phase and phase sequence of the high-voltage side input voltage.

6. A method for controlling the non-disturbance closing and cooling of a high-voltage cascade inverter, used to implement the non-disturbance closing and cooling control circuit of a high-voltage cascade inverter as claimed in any one of claims 1 to 5, characterized in that: The control method comprises the following steps: S1, when contactor K1, contactor K2, contactor K3 and contactor K4 are all disconnected, set as the initial state of the variable frequency power supply switching module, and after the high-voltage cascade inverter control system receives the pre-charging start instruction, close contactor K1 and contactor K2; the three-phase low-voltage inverter is in hot standby state; S2, using the high-voltage cascade inverter control system to detect the sampling channel, and based on the three-phase high-voltage phase sequence, setting the output phase sequence of the three-phase low-voltage inverter; S3, the high-voltage cascade inverter control system controls the variable frequency power supply switching module to perform pre-charging based on a preset charging time; S4, real-time detection of system parameters during the pre-charging process, and based on a preset charging completion threshold, identification of fault signals during the pre-charging process, and switching of protection states; S5, detecting the phase between the high-voltage side input circuit and the variable frequency power supply switching module in real time, and controlling the variable frequency power supply switching module based on the phase change to trigger a high-voltage closing instruction; S6. Control the QF switch of the high-voltage side input circuit to close, and after the high-voltage cascade inverter control system detects that there is no fault, control the high-voltage cascade inverter to enter a hot standby state.

7. A method for non-disturbance closing and cooling control of a high-voltage cascade inverter according to claim 6, characterized in that: The high-voltage cascade inverter control system controls the variable frequency power supply switching module to perform pre-charging based on a preset charging time, comprising the following steps: S31, setting the start time of the three-phase low-voltage inverter as the charging time; S32, using the high-voltage cascade inverter control system to output a pulse signal to the three-phase low-voltage inverter, controlling the three-phase low-voltage inverter to output a three-phase voltage, and gradually increasing it following the V / F curve; S33, the voltage amplitude of the 380V auxiliary winding and the secondary winding in the phase-shifting transformer gradually increases to charge the power units at each level.

8. A method for non-disturbance closing and cooling control of a high-voltage cascade inverter according to claim 7, characterized in that: The real-time detection of system parameters in the pre-charging process and identification of fault signals in the pre-charging process based on a preset charging completion threshold and switching the protection state include the following steps: S41, real-time detection of the DC bus voltage of each power unit, and the output voltage and output frequency of the three-phase low-voltage inverter; S42. When contactor K1 is closed and contactor K3 is disconnected, when the output voltage and output frequency of the three-phase low-voltage inverter reach the rated voltage and rated frequency, if the DC bus voltage of each power unit is greater than the charging completion threshold, a synchronization instruction is sent to the three-phase low-voltage inverter. If the DC bus voltage of each power unit does not reach the charging completion threshold, a pre-charging fault signal is issued and contactor K1 and contactor K2 are disconnected.

9. A method for non-disturbance closing and cooling control of a high-voltage cascade inverter according to claim 8, characterized in that: The real-time detection of the phase between the high-voltage side input circuit and the variable frequency power supply switching module, and based on the phase change, the control of the variable frequency power supply switching module to trigger the high-voltage closing instruction includes the following steps: S51, when the three-phase low-voltage inverter is started to the charging time, the high-voltage cascade inverter control system is used to detect the three groups of channel voltages of the sampling channel, and the A phase of the high-voltage side input circuit and the A phase of the three-phase low-voltage inverter are calculated; S52, adjust the phase of phase A of the three-phase low-voltage inverter. When the phase of phase A of the three-phase low-voltage inverter is consistent with the phase A of the high-voltage side input circuit, control the three-phase low-voltage inverter to stop output, disconnect contactor K1, and trigger the high-voltage closing command.

10. A method for non-disturbance closing and cooling control of a high-voltage cascade inverter according to claim 9, characterized in that: The high-voltage cascade inverter control system detects three-phase low-voltage inverter faults and three-phase low-voltage power supply faults in real time, controls contactors K1, K2, K3, and K4 through a logic control module, and drives the cooling system to operate. The cooling system operation steps include: When the three-phase low-voltage power supply fails while contactor K1 is disconnected and contactor K3 is closed, the high-voltage cascade inverter control system disconnects contactor K2 and closes contactor K4, using the 380V auxiliary winding to provide power for the three-phase low-voltage inverter and continue to control the operation of the three-phase heat dissipation cooling fan in a closed loop; When the three-phase low-voltage inverter fails, the high-voltage cascade inverter control system disconnects the contactor K2 and the contactor K4, and then closes the contactor K1 and the contactor K3, and directly drives the three-phase heat dissipation cooling fan to operate through the 380V auxiliary winding.

11. A method for non-disturbance closing and cooling control of a high-voltage cascade inverter according to claim 10, characterized in that: The three-phase low-voltage inverter adopts PID regulation control output, and the speed of the three-phase heat dissipation cooling fan is closed-loop controlled by calculating the average temperature and the parameter adjustment amount, wherein the expression for calculating the average temperature and the parameter adjustment amount includes: Where, T avr Represents the average temperature of all power units; T alarm Indicates the set power unit alarm temperature threshold; T Ai represents the temperature of the i-th power unit in phase A; T Bi represents the temperature of the i-th power unit in phase B; T Ci represents the temperature of the i-th power unit in phase C; n represents the number of power units in each phase; S represents a complex frequency variable; k i , k p Represents closed-loop control parameters; Δf represents the parameter adjustment amount output by the high-voltage cascade inverter control system to the three-phase low-voltage inverter.

Images