Full-control static frequency converter for starting motor

Abstract

The invention belongs to the field of frequency converter topological structures for motor starting, and particularly relates to a full-control static frequency converter for motor starting. Each bridge arm of at least one of the network bridge unit and the machine bridge unit adopts a full-control type power electronic device series topology; in the series topology, the value of the number of the full-control power electronic devices is determined according to the ratio of the product of the set safety coefficient twice the root number and the power grid line voltage peak value to the rated voltage of the full-control power electronic devices. According to the invention, the number of the full-control power electronic devices in each series topology can be adjusted according to actual demands. Compared with a modularized multi-level topology, under the condition that actual requirements are met, the number of full-control type power electronic devices is remarkably reduced, and the equipment cost and the size are remarkably reduced.

Description

Technical Field

[0001] This invention belongs to the field of inverter topologies for motor starting, and specifically relates to a fully controlled static inverter for motor starting. Background Technology

[0002] Pumped storage, as an important component of the new power system, plays three major roles: ensuring the safety of the large power grid, facilitating the consumption of clean energy, and promoting the optimized operation of the power system. It is currently the most technologically mature, widely used, and economically optimal flexible power source, playing a crucial role in the clean and low-carbon energy transition. Currently, pumped storage power station units are started using thyristor-type pumped storage static starter (SFC) devices.

[0003] However, because thyristors are semi-controlled devices, their inherent topology limits their use as inverters for starting pumped-storage power station motors. This results in significant harmonic interference to the power grid during motor startup and operation, along with low control accuracy and poor dynamic performance. Therefore, some researchers have proposed using fully controlled power electronic devices as static inverters (SIDs) for starting pumped-storage power station motors. The switching state of fully controlled power electronic devices is entirely determined by control signals. Using fully controlled SIDs allows for more complex control algorithms and higher control accuracy. Compared to semi-controlled SIDs, they offer significant advantages in control performance, adjustment range, efficiency, stability, and application flexibility, making them a more popular choice for static starting inverters. Currently, the topology of fully controlled SIDs used for starting pumped-storage motors is typically a modular multilevel topology. This topology consists of numerous sub-modules connected in series, each containing a fully controlled power electronic device. However, when using a modular multilevel topology, the number of fully controllable power electronic devices is relatively fixed due to the limitations of standardized submodules (for example, it must be increased in integer multiples of the number of fully controllable power electronic devices in the standardized submodule). This often results in a large redundancy in the actual number of fully controllable power electronic devices in practical applications, which often leads to larger equipment size and higher cost. Summary of the Invention

[0004] The purpose of this invention is to provide a fully controlled static frequency converter for motor starting, which solves the problem that the number of fully controlled power electronic devices in the existing fully controlled static frequency converters is relatively fixed due to the limitation of standardized sub-modules, and that there is a large redundancy.

[0005] To achieve the above objectives, the present invention provides a fully controlled static frequency converter for motor starting, the frequency converter comprising a network bridge unit and a machine bridge unit, characterized in that each arm of at least one of the network bridge unit and the machine bridge unit adopts a series topology of fully controlled power electronic devices; in the series topology, the number of fully controlled power electronic devices is determined according to the ratio of the product of a set safety factor of √2 and the peak value of the grid line voltage to the rated voltage of the fully controlled power electronic devices.

[0006] Beneficial Effects: Compared to existing fully controlled static inverters for motor starting, this invention primarily improves the topology of the fully controlled power electronic devices in the inverter's bridge and motor bridge units. Existing fully controlled static inverters for motor starting use a modular multilevel topology, which often leads to significant redundancy due to the need to meet the requirements of standardized submodules. This invention, however, uses a series topology on at least one arm of the bridge unit and motor bridge unit (the number of series topologies is determined by the ratio of the product of a safety factor of √2 and the grid line voltage to the rated voltage of the fully controlled power electronic devices). Therefore, with minimal redundancy, the number of fully controlled power electronic devices in each series topology can be adjusted according to actual needs. Compared to the aforementioned modular multilevel topology, this invention significantly reduces the number of fully controlled power electronic devices while still meeting the actual requirements, resulting in a significant reduction in equipment cost and size.

[0007] Furthermore, the method for determining the number of fully controlled power electronic devices in each series topology of the bridge unit and the machine bridge unit, based on the ratio of the product of a safety factor of √2 and the peak value of the grid line voltage to the rated voltage of the fully controlled power electronic device, includes:

[0008]

[0009] n = n0 + m

[0010] Where, n0 is the number of fully controlled power electronic devices required in each series topology of the bridge unit and the machine bridge unit; n is the determined value of the number of fully controlled power electronic devices in each series topology of the bridge unit and the machine bridge unit; k is the set safety factor; U L This refers to the rated value of the power grid line voltage. U represents the peak value of the grid line voltage. T is the rated voltage of the fully controlled power electronic device; m is the set redundancy value of the fully controlled power electronic device, m is greater than or equal to 0.

[0011] Furthermore, it also includes a soft start unit, an LC filter unit on the grid side, a DC bus capacitor unit, a braking unit, and an LC filter unit on the motor side.

[0012] Furthermore, the soft-start unit is used to connect in series between the power grid and the LC filter unit on the power grid side; the soft-start unit includes a soft-start resistor and a bypass switch connected in parallel with the resistor, so as to perform current-limited charging of the bus capacitor in the initial stage of system power-on.

[0013] Furthermore, the LC filter unit on the grid side is connected in series between the soft start unit and the bridge unit; the LC filter unit on the grid side is used to suppress harmonics in the bridge unit.

[0014] Furthermore, the DC bus capacitor unit and the braking unit are connected in parallel between the bridge unit and the machine bridge unit; the DC bus capacitor unit includes various series and parallel capacitors for smoothing and stabilizing the DC bus voltage.

[0015] Furthermore, the braking unit mainly consists of a power electronic switch and a resistor connected in series; the braking unit is used to release energy in a fault condition.

[0016] Furthermore, the LC filter unit on the motor side is connected in series between the bridge unit and the motor; the LC filter unit on the motor side is used to filter the output waveform of the bridge unit so as to achieve a sine wave output waveform. Attached Figure Description

[0017] Figure 1 This is an example diagram of the topology of a fully controlled static inverter for motor starting in an embodiment of the present invention.

[0018] Figure 2 A flowchart illustrating the control method of the fully controlled static inverter for motor starting in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] Example of a fully controlled static inverter for motor starting

[0021] This embodiment presents a fully controlled static inverter for motor starting. The bridge unit and motor bridge unit of this fully controlled static inverter are mainly composed of fully controlled power electronic devices with a defined topology. The number of fully controlled power electronic devices in a series topology is calculated based on actual needs; that is, the number of fully controlled power electronic devices required to be connected in series at each arm of the bridge unit and motor bridge unit. After obtaining this number, multiplying it by the number of phases and the number of arms yields the total number of fully controlled power electronic devices required to be connected in series in the entire bridge unit and motor bridge unit. Combining this with the situation of each series topology, the fully controlled power electronic device topology of the entire bridge unit and motor bridge unit is obtained. This embodiment designs the series topology of fully controlled power electronic devices according to actual needs, allowing for adaptive adjustment of the number of fully controlled power electronic devices within the series topology to meet the actual requirements for the number of fully controlled power electronic devices with minimal redundancy.

[0022] In the fully controlled static inverter, each arm of the bridge unit and the machine bridge unit adopts a series topology of fully controlled power electronic devices. In this series topology, the number of fully controlled power electronic devices is determined by the ratio of the product of the set safety factor of √2 and the peak value of the grid line voltage to the rated voltage of the fully controlled power electronic devices.

[0023] Beneficial effects

[0024] Specifically, such as Figure 1 As shown, this fully controlled static inverter includes a bridge unit and a motor bridge unit. The main components of both the bridge and motor bridge units are fully controlled power electronic devices with a defined topology (both the bridge and motor bridge units use a series topology of two-level or three-level devices based on fully controlled power electronic devices; the fully controlled devices can be IGBTs, IGCTs, etc.). At least one of the bridge units in both the bridge and motor bridge units uses a series topology of fully controlled power electronic devices (e.g.,...). Figure 1 As shown, TW is a separate series topology for the bridge unit, and TJ is a separate series topology for the machine bridge unit. The number of fully controlled power electronic devices in this series topology needs to be determined by calculation. The parameters required for the calculation include: setting a safety factor (which is usually taken as 2 to 3 based on engineering experience), the grid line voltage, and the rated voltage of the fully controlled power electronic devices.

[0025] The methods for determining the number of fully controlled power electronic devices in each series topology of the bridge unit and the machine bridge unit, based on the ratio of the product of the set safety factor (√2) and the peak value of the grid line voltage to the rated voltage of the fully controlled power electronic device, include:

[0026]

[0027] n = n0 + m

[0028] Where, n0 is the number of fully controlled power electronic devices required in each series topology of the bridge unit and the machine bridge unit; n is the determined value of the number of fully controlled power electronic devices in each series topology of the bridge unit and the machine bridge unit; k is the set safety factor; U L This refers to the rated value of the power grid line voltage. U represents the peak value of the grid line voltage. T denoted as , where is the rated voltage of the fully controlled power electronic device; 'm' is the set redundancy value of the fully controlled power electronic device, where m is greater than or equal to 0. When m equals 0, no redundancy is set for the fully controlled power electronic device. However, under normal circumstances, fully controlled power electronic devices are selected that have long-term short-circuit failure capability to ensure system reliability. Therefore, the number of devices connected in series needs to be designed with n+1 redundancy, so the value of m is 1, meaning one redundant fully controlled power electronic device is set for each bridge arm. In other embodiments, m can also take other values ​​to flexibly adapt to different redundancy requirements. In this embodiment, the grid line voltage (i.e., AC voltage) is a sine wave, and the voltage that the device withstands needs to be calculated based on the maximum AC voltage, that is, based on the peak value of the grid line voltage. Calculation. In this embodiment, as... Figure 1 As shown, the number of fully controlled power electronic devices in series topology contained in the bridge unit is 6. Then, one series topology is connected in series at the upper and lower bridge arms of the three-phase parallel branch of the bridge unit (i.e., two series topologies are connected in series for each phase).

[0029] Similarly, such as Figure 1 As shown, the number of fully controlled power electronic device series topologies included in the bridge unit is 6. Therefore, one series topology is connected in series at each of the upper and lower arms of the three-phase parallel branch of the bridge unit. In other embodiments, the corresponding arms of the series topology can be set only in the network bridge unit or the bridge unit, or the network bridge unit or the bridge unit can be set as a half-bridge module, in which case the number of fully controlled power electronic device series topologies included in the half-bridge module is 3.

[0030] In summary, the methods for obtaining the number of fully controlled power electronic devices connected in series in both the bridge unit and the machine bridge unit are as follows:

[0031] N = 3 * 2 * n

[0032] Where N is the number of fully controlled power electronic devices connected in series in the bridge unit or machine bridge unit; n is the number of fully controlled power electronic devices connected in series in a group.

[0033] In addition, the bridge unit and the mechanical bridge unit adopt PWM modulation. By comparing the modulated wave with a high-frequency triangular carrier wave, the output pulse sequence controls the switching transistors (i.e., individual series topologies) TW and TJ to achieve control of the output voltage and current. In the series connection of devices, the fully controllable devices in the same bridge arm unit use high-speed optical fiber to achieve synchronous triggering, and the pulses of the upper and lower bridge arm units in the same phase are interlocked to avoid shoot-through short circuit damage to the devices.

[0034] In this embodiment, it also includes a soft start unit, an LC filter unit on the grid side, a DC bus capacitor unit, a braking unit, and an LC filter unit on the motor side.

[0035] Specifically, such as Figure 1 As shown, the fully controlled static inverter includes a soft starter unit, an LC filter unit, a braking unit, a DC bus capacitor unit, and an LC filter unit, in addition to the network bridge unit and the machine bridge unit; wherein, the voltage level of the power grid connected to the input side of the soft starter unit is ≥10kV.

[0036] In this embodiment, the soft start unit is connected in series between the power grid and the LC filter unit on the power grid side; the soft start unit includes a soft start resistor and a bypass switch connected in parallel with the resistor, so as to perform current-limited charging of the bus capacitor in the initial stage of system power-on.

[0037] Specifically, the soft starter unit is connected in series between the power grid and the LC filter unit on the grid side (i.e., the input side of the soft starter unit is connected to the power grid, and the output side of the soft starter unit is connected to the input side of the LC filter unit). This soft starter unit includes a soft starter resistor and a bypass switch connected in parallel with the soft starter resistor. The voltage ratings of the soft starter resistor and the bypass switch are matched to the power grid voltage rating. The bypass switch is a high-voltage circuit breaker or a high-voltage contactor, equipped with electric control. This soft starter unit has three-phase input and three-phase output and is used to pre-charge the DC bus capacitor, that is, to perform current-limited charging of the bus capacitor during the initial power-on phase of the system, preventing excessive charging current from causing significant impact on power electronic devices and the capacitors to be charged, thereby improving the safety and reliability of the system.

[0038] In this embodiment, the LC filter unit on the power grid side is connected in series between the soft start unit and the bridge unit; the LC filter unit on the power grid side is used for harmonic suppression of the bridge unit.

[0039] Specifically, the input port of the fully controlled static inverter mainly consists of a soft starter unit, an LC filter unit, and a network bridge unit, and this port is connected to the power grid. The output side of the soft starter unit is connected to the input side of the LC filter unit, and the output side of the LC filter unit is connected to the input side of the network bridge unit. The LC filter unit is used to suppress harmonics in the network bridge unit, improve the power quality on the grid side, reduce DC side ripple, and suppress fault current.

[0040] In this embodiment, the DC bus capacitor unit and the braking unit are connected in parallel between the bridge unit and the machine bridge unit; the DC bus capacitor unit includes various series and parallel capacitors for smoothing and stabilizing the DC bus voltage.

[0041] Specifically, the DC bus capacitor unit and braking unit are connected in parallel between the network bridge unit and the machine bridge unit, while the network bridge unit and the machine bridge unit are connected in series, meaning the output side of the network bridge unit is connected in series to the input side of the machine bridge unit. The DC bus capacitor unit is used to smooth and stabilize the DC bus voltage and buffer the energy exchange between the power grid and the synchronous motor. Figure 1 The CZ designation indicates that the DC bus capacitor unit is mainly composed of multiple capacitors connected in series and parallel to meet the system voltage access requirements. The braking unit is used for rapid energy discharge in case of a fault, protecting the power electronic devices of the bridge unit and the mechanical bridge unit.

[0042] In this embodiment, the braking unit mainly consists of a power electronic switch and a resistor connected in series; the braking unit is used to release energy in a fault condition.

[0043] Specifically, the main components of the braking unit are a series-connected power electronic switch and a resistor. TZ represents a basic periodic unit of the power electronic switch, which can be selected from thyristors, IGBTs, IGCTs, or MMC submodules. The power electronic switch and resistor withstand the DC bus voltage.

[0044] In this embodiment, the LC filter unit on the motor side is connected in series between the bridge unit and the motor; the LC filter unit on the motor side is used to filter the output waveform of the bridge unit so that the output waveform is a sine wave.

[0045] Specifically, the output port of the fully controlled static inverter mainly consists of a bridge unit and an LC filter unit, which are connected to the synchronous motor. That is, the output side of the bridge unit is connected to the input side of the LC filter unit, and the output side of the LC filter unit is connected to the synchronous motor. The LC filter unit is used to filter the output waveform of the bridge unit to achieve a sine wave output waveform, improve power quality, and suppress fault current.

[0046] Generally, pumped storage power station motor startup refers to the pumped storage motor being in pumping motor mode. The fully controlled static inverter absorbs energy from the grid, performs AC / DC conversion through the grid bridge unit, and then performs DC / AC conversion through the machine bridge unit, driving the motor from 0Hz to 50Hz, and from 0rpm to the rated speed. The grid connection switch closes, the fully controlled static inverter disengages, and the pumped storage unit begins pumping water. For example... Figure 2 As shown, when starting a pumped-storage substation motor using a fully controlled static frequency converter, the steps for controlling the fully controlled static frequency converter include:

[0047] S1: According to the issued start command, the power grid charges the DC bus capacitor through the soft start resistor in the soft start unit and the anti-parallel devices in the bridge unit in an uncontrolled rectification manner; when the DC bus voltage reaches the set value, the bypass switch in the soft start unit is closed to control the DC bus voltage to operate in a regulated manner.

[0048] S2: After the DC bus voltage is stabilized, the voltage is acquired through the output side of the bridge unit. Based on the acquired voltage, the initial position of the rotor is calculated, and the corresponding two-phase input current is provided to the two-phase windings of the synchronous motor to drive the motor to rotate from 0 rpm to the rated speed; and to drive the motor to run from 0 Hz to the rated frequency.

[0049] S3: When the motor speed reaches the rated speed and the motor frequency reaches the rated frequency, the speed of the motor is controlled according to the obtained acceleration and deceleration commands; when the motor phase is consistent with the grid phase, the motor grid connection switch is closed, and the pulse blocking of the fully controlled power electronic devices of the grid bridge unit and the machine bridge unit is controlled according to the obtained shutdown command; and the fully controlled static inverter is controlled to exit operation according to the obtained opening commands of the grid side input circuit breaker and the motor output side circuit breaker.

[0050] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or explanatory of the principles of the present invention, and do not constitute a limitation thereof.

Claims

1. A fully controlled static frequency converter for motor starting, comprising a network bridge unit and a machine bridge unit, characterized in that, Each arm of at least one of the bridge units, namely the network bridge unit and the machine bridge unit, adopts a series topology of fully controlled power electronic devices; in the series topology, the number of fully controlled power electronic devices is determined according to the ratio of the product of the set safety factor of √2 and the peak value of the grid line voltage to the rated voltage of the fully controlled power electronic devices.

2. The fully controlled static frequency converter for motor starting according to claim 1, characterized in that, The method for determining the number of fully controlled power electronic devices in each series topology of the bridge unit and the machine bridge unit, based on the ratio of the product of a safety factor of √2 and the peak value of the grid line voltage to the rated voltage of the fully controlled power electronic device, includes: n = n0 + m Where, n0 is the number of fully controlled power electronic devices required in each series topology of the bridge unit and the machine bridge unit; n is the determined value of the number of fully controlled power electronic devices in each series topology of the bridge unit and the machine bridge unit; k is the set safety factor; U L This refers to the rated value of the power grid line voltage. U represents the peak value of the grid line voltage. T is the rated voltage of the fully controlled power electronic device; m is the set redundancy value of the fully controlled power electronic device, m is greater than or equal to 0.

3. The fully controlled static frequency converter for motor starting according to claim 1, characterized in that, It also includes a soft start unit, an LC filter unit on the grid side, a DC bus capacitor unit, a braking unit, and an LC filter unit on the motor side.

4. The fully controlled static frequency converter for motor starting according to claim 3, characterized in that, The soft-start unit is connected in series between the power grid and the LC filter unit on the power grid side; the soft-start unit includes a soft-start resistor and a bypass switch connected in parallel with the resistor, so as to perform current-limited charging of the bus capacitor in the initial stage of system power-on.

5. The fully controlled static frequency converter for motor starting according to claim 3, characterized in that, The LC filter unit on the power grid side is connected in series between the soft start unit and the bridge unit; the LC filter unit on the power grid side is used to suppress harmonics in the bridge unit.

6. The fully controlled static frequency converter for motor starting according to claim 3, characterized in that, The DC bus capacitor unit and the braking unit are connected in parallel between the bridge unit and the machine bridge unit; the DC bus capacitor unit includes various series and parallel capacitors for smoothing and stabilizing the DC bus voltage.

7. The fully controlled static frequency converter for motor starting according to claim 3, characterized in that, The braking unit mainly consists of a power electronic switch and a resistor connected in series; the braking unit is used to release energy in a fault condition.

8. The fully controlled static frequency converter for motor starting according to claim 3, characterized in that, The LC filter unit on the motor side is connected in series between the bridge unit and the motor; the LC filter unit on the motor side is used to filter the output waveform of the bridge unit so that the output waveform is a sine wave.

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