A main fan control method and system based on cascade energy storage converter

Abstract

The present invention provides a main fan control method based on a cascade energy storage converter, comprising: when the main fan is in a cold standby state, the cascade energy storage converter adopts a strong inertia voltage and current double closed-loop control strategy to drive the main fan to start at reduced voltage; after the main fan runs stably, the main fan is switched to the main power grid for grid-connected operation after pre-synchronization; when the main power grid in which the main fan and the cascade energy storage converter are grid-connected loses power, the cascade energy storage converter disconnects from the main power grid and drives the main fan to start at high speed; when the main power grid resumes power supply, the main fan is switched to the main power grid for grid-connected operation after pre-synchronization. The present invention can reduce the impact of the direct start of the main fan on the main power grid, and achieves the effect of not stopping the main fan when the main power grid is out of power.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine ventilation systems, and in particular relates to a main fan control method based on a cascade energy storage converter. Background Art

[0002] With the deepening of electrification in the coal industry and the high requirements for safe production, ventilation systems are playing an increasingly important role in coal mine production. Once power failure occurs, it is very likely that ventilation will not work properly, causing extremely serious safety accidents. In particular, the main fan is the most important equipment in the ventilation system of a coal mine, known as the "lungs of the mine", so ensuring the stable operation of the main fan has become one of the important tasks of the power supply system.

[0003] At present, the dual power supply mode commonly used in coal mine power supply systems is mostly diesel-generated main fan systems. However, the diesel-generated system has a weak resistance to the main fan motor current surge, which easily causes overcurrent at startup. At the same time, the diesel-generated main fan is in cold standby state most of the time. The time from when the main power grid is cut off to normal startup is at the minute level, which cannot meet the demand of the main fan not stopping when the power is off. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a main fan control method based on a cascaded energy storage converter to solve the above-mentioned technical problems.

[0005] In a first aspect, the present invention provides a main fan control method based on a cascaded energy storage converter, comprising:

[0006] When the main fan is in cold standby state, the cascaded energy storage converter adopts a strong inertia voltage and current double closed-loop control strategy to drive the main fan to start at reduced voltage, wherein the voltage loop obtains the three-phase current reference signal of the AC side of the cascaded energy storage converter, and the current loop obtains the three-phase voltage reference signal of the cascaded energy storage converter output;

[0007] After the main fan runs stably, it is pre-synchronized and then switched to the main grid for grid-connected operation;

[0008] When the main power grid in which the main fan and the cascade energy storage converter are connected and operated loses power, the cascade energy storage converter disconnects from the main power grid and drives the main fan to start on the fly;

[0009] When the main grid resumes power supply, the main fan is switched to the main grid for grid-connected operation after pre-synchronization.

[0010] Furthermore, the formula for obtaining the three-phase current reference signal of the AC side of the cascaded energy storage converter by the voltage loop is: ;

[0011] In the formula, , , is the three-phase current reference signal, , , is the three-phase voltage reference signal of the AC side of a given cascaded energy storage converter; , , The three-phase voltage actually output by the cascaded energy storage converter on the AC side; , , is the three-phase current actually outputted by the cascaded energy storage converter on the AC side; is the Laplace operator; is the grid-connected reactance; PR is the transfer function of a bandpass filter with adjustable bandwidth and coefficient, which plays a strong inertia role; is the maximum limiting current.

[0012] Furthermore, the current loop obtains the formula for the three-phase voltage reference signal output by the cascaded energy storage converter as follows:

[0013] ;

[0014] In the formula, is the current loop coefficient, ; is the grid angular frequency, , , It is the three-phase voltage reference signal finally output by the cascaded energy storage converter; The transfer function is a bandpass filter with a coefficient of 1 and an adjustable bandwidth, which plays a role in voltage stabilization.

[0015] Further, the method of flying start includes:

[0016] When the main grid is powered off, the cascaded energy storage converter and the main fan are controlled to disconnect from the main grid, and the cascaded energy storage converter and the main fan are kept connected;

[0017] Detecting the amplitude of the voltage signal on the AC side of the cascaded energy storage converter through a phase-locked loop With angular frequency and initial phase , as the amplitude of the voltage reference signal of the initial state of flying car starting , angular frequency , initial phase , the formula is:

[0018] ;

[0019] Amplitude of the voltage reference signal , angular frequency As the magnitude of the main power grid and angular frequency The voltage rises until it returns to normal. The amplitude of the voltage reference signal output by the cascaded energy storage converter during the flying car start process and angular frequency The changes are as follows

[0020] ;

[0021] , are respectively the amplitude and angular frequency of the voltage reference signal at this moment; , are respectively the amplitude and angular frequency of the voltage reference signal at the previous moment;

[0022] in,, , is the rise coefficient, 0< <1,0< <1;

[0023] According to the amplitude of the voltage reference signal , angular frequency and initial phase , determine the three-phase voltage reference signal of the AC side of the cascaded energy storage converter given during the flying car starting process, the formula is:

[0024] .

[0025] In a second aspect, the present invention provides a main fan control system based on a cascade energy storage converter, comprising: a cascade energy storage converter, a main fan and a switch KM1;

[0026] The output AC side of the cascade energy storage converter is connected to the grid-in side of the main fan, and the switching switch KM1 is used to simultaneously control the connection between the main fan and the cascade energy storage converter and the main grid.

[0027] The beneficial effects of the present invention are as follows: a cascade energy storage converter and a strong inertia voltage-current dual closed-loop off-grid voltage control method are adopted, and the main fan is started off-grid when the main fan is in a cold standby state, thereby ensuring that the cascade energy storage device will not overcurrent due to impact load; the main fan of the coal mine is normally started and then connected to the grid for operation, thereby reducing the impact of the direct start of the main fan on the main power grid; when the main fan is connected to the grid and the main power grid loses power, the flying start of the main fan can be quickly achieved in combination with the flying start strategy, thereby achieving the effect of not stopping the main fan when the main power grid is out of power. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 is a schematic diagram of a control system according to an embodiment of the present invention;

[0030] Figure 2 It is a topological structure diagram of the cascade energy storage converter used in the present invention;

[0031] Figure 3 It is a topological structure diagram of a power unit of a cascaded energy storage converter used in the present invention;

[0032] Figure 4 is a schematic flow chart of a control method according to an embodiment of the present invention;

[0033] Figure 5 It is a simulation diagram of a control system of an embodiment of the present invention;

[0034] Figure 6 It is a simulation waveform diagram of a control method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0036] Figure 1 A main fan control system based on a cascade energy storage converter provided in an embodiment of the present invention includes: a main grid, a switching switch KM1, a cascade energy storage converter (PCS), and a main fan; the output AC side of the cascade energy storage converter is connected to the grid-in side of the main fan, and the switching switch KM1 is used to simultaneously control the connection between the main fan and the cascade energy storage converter and the main grid. When the switching switch KM1 is closed, the main fan and the cascade energy storage converter are connected to the main grid at the same time, and when the switching switch KM1 is disconnected, the main fan and the cascade energy storage converter are disconnected from the main grid at the same time.

[0037] The topological structure of the cascade energy storage converter mentioned in the present invention is as follows: Figure 2 As shown, Figure 3Each power unit of the cascade energy storage converter shown includes a filter reactor, a cascade H-bridge and a battery pack.

[0038] A main fan control method based on a cascade energy storage converter provided by an embodiment of the present invention can be based on Figure 1 The control system described. Figure 4 The control method comprises:

[0039] When the main fan is in cold standby state, the cascaded energy storage converter adopts a strong inertia voltage and current double closed-loop control strategy to drive the main fan to start at reduced voltage. Among them, the voltage loop obtains the three-phase current reference signal of the cascaded energy storage converter AC side, and the current loop obtains the three-phase voltage reference signal of the cascaded energy storage converter output;

[0040] After the main fan runs stably, it is pre-synchronized and then switched to the main grid for grid-connected operation;

[0041] When the main power grid in which the main fan and the cascade energy storage converter are connected and operated loses power, the cascade energy storage converter disconnects from the main power grid and drives the main fan to start on the fly;

[0042] When the main grid resumes power supply, the main fan is switched to the main grid for grid-connected operation after pre-synchronization.

[0043] The control method provided by the embodiment of the present invention adopts a cascade energy storage converter structure and a strong inertia voltage and current dual closed-loop off-grid voltage control method, combined with a flying start strategy, to realize the power outage and non-stop operation of the main fan of the coal mine. First, the present invention realizes the power outage and non-stop operation strategy of the main fan of the coal mine through the off-grid-grid switching operation of the main fan. When the main fan is in a cold standby state, a strong inertia voltage and current dual closed-loop off-grid voltage is used to drive the main fan to start at a reduced voltage, thereby reducing the impact of the main fan on the main power grid; when the main fan is running stably, the main fan is sent to the grid and connected to the grid for operation, thereby reducing the impact of the main fan directly starting on the main power grid. Secondly, when the main fan and the cascade energy storage converter are connected to the grid and the grid loses power, the cascade energy storage converter realizes the flying start of the main fan by switching the switch, thereby ensuring that the main fan runs without stopping the wind when the power is off. Finally, when the main power grid returns to normal, the main fan is switched to the grid for operation.

[0044] In this embodiment, on the basis that the switching switch KM1 is used to simultaneously control the connection between the main fan and the cascade energy storage inverter and the main power grid, after the main fan runs stably and pre-synchronizes, the main fan is switched to the main power grid for grid-connected operation by closing the switching switch KM1. After grid-connected operation, the cascade energy storage inverter adopts traditional PQ control to achieve grid-connected charging and discharging; when the main power grid in which the main fan and the cascade energy storage inverter are grid-connected loses power, the cascade energy storage inverter is disconnected from the main power grid by disconnecting the switching switch KM1, and the main fan is driven by the cascade energy storage inverter analog frequency converter to achieve flying start.

[0045] The strong inertia voltage and current dual closed-loop control strategy provided by the present invention is a proportional resonant control in a three-phase coordinate system, with the output voltage as the target and the output current as the limit, thereby ensuring that the cascaded energy storage converter will not overcurrent due to impact load, thereby ensuring that the main fan can be started without impact under cold standby.

[0046] The pre-synchronization operation of the present invention is used to ensure that the initial phase and amplitude of the cascaded energy storage converter are synchronized with the main power grid to reduce current impact.

[0047] Optionally, as an embodiment of the present invention, the formula for obtaining the three-phase current reference signal of the AC side of the cascaded energy storage converter by the voltage loop is: ;

[0048] In the formula, , , is the three-phase current reference signal, , , is the three-phase voltage reference signal of the AC side of a given cascaded energy storage converter; , , The three-phase voltage actually output by the cascaded energy storage converter on the AC side; , , is the three-phase current actually outputted by the cascaded energy storage converter on the AC side; is the Laplace operator; is the grid-connected reactance; PR is the transfer function of a bandpass filter with adjustable bandwidth and coefficient, which plays a strong inertia role; is the maximum limiting current.

[0049] Specifically, PR can be selected as a 2nd order bandpass filter:

[0050] ;

[0051] In the formula, is the attenuation coefficient, is the passband cutoff angular frequency, is the main grid angular frequency.

[0052] In this embodiment, the three-phase current reference signal , , , given the AC side three-phase voltage reference signal of the cascaded energy storage converter , , , the three-phase voltage actually output by the cascaded energy storage converter on the AC side , , , the three-phase current actually output by the cascaded energy storage converter on the AC side , , They are all instantaneous values, and the size of the instantaneous value depends on its frequency, amplitude and initial phase.

[0053] In this embodiment, since the main fan is started mainly by current and voltage, if the main fan is started directly under a strong power grid, the impact current is 5 to 10 times the rated current. In order to solve the impact current, you can generally choose a series resistor start b inverter start, and this embodiment adopts a fixed frequency current limiting start method to avoid overcurrent, without increasing the hardware cost.

[0054] Optionally, as an embodiment of the present invention, the formula for obtaining the three-phase voltage reference signal output by the cascaded energy storage converter by the current loop is:

[0055] ;

[0056] In the formula, is the current loop coefficient, ; is the main grid angular frequency, , , It is the three-phase voltage reference signal finally output by the cascaded energy storage converter; It is the transfer function of a bandpass filter with a coefficient of 1 and an adjustable bandwidth, which plays a role in voltage stabilization.

[0057] Optionally, as an embodiment of the present invention, the method for flying car starting includes:

[0058] When the main grid is powered off, the cascaded energy storage converter and the main fan are controlled to disconnect from the main grid, and the cascaded energy storage converter and the main fan are kept connected;

[0059] Detecting the amplitude of the voltage signal on the AC side of the cascaded energy storage converter through a phase-locked loop With angular frequency and initial phase , as the amplitude of the voltage reference signal of the initial state of flying car starting , angular frequency , initial phase , the formula is:

[0060] ;

[0061] Amplitude of the voltage reference signal , angular frequency As the magnitude of the main power grid and angular frequency The voltage rises until it returns to normal. The amplitude of the voltage reference signal output by the cascaded energy storage converter during the flying car start process and angular frequency The change is as follows:

[0062] ;

[0063] , , are respectively the amplitude and angular frequency of the voltage reference signal at this moment; , are respectively the amplitude and angular frequency of the voltage reference signal at the previous moment;

[0064] in, , is the rise coefficient, 0< <1,0< <1; Rise coefficient , The specific value is determined according to the main fan characteristics, 0< <1,0< <1 is just a reference range, the specific value needs to be determined in conjunction with the specific fan model.

[0065] According to the amplitude of the voltage reference signal , angular frequency and initial phase , determine the three-phase voltage reference signal of the AC side of the cascaded energy storage converter given during the flying car starting process, the formula is:

[0066] .

[0067] In this embodiment, the characteristics of the frequency converter are simulated by a cascaded energy storage converter, and the main fan is directly controlled to run again by the cascaded energy storage converter when the main fan is rotating, without waiting for the main fan to stop.

[0068] In MATLAB / Simulink, build Figure 5The simulation model of a main fan control system based on a cascade energy storage converter is shown to illustrate the implementation effect of a main fan control method based on a cascade energy storage converter provided by an embodiment of the present invention. The simulation parameters in the control system are shown in Table 1, and the specific values ​​of the simulation parameters are not used as a limitation on the protection scope of the present invention;

[0069] Table 1 Simulation parameters

[0070]

[0071] Figure 6 Based on Figure 5 The simulation system shown executes the control method and outputs the three-phase voltage, current and main fan rotor frequency waveforms on the AC side of the cascaded energy storage converter. Figure 6 The specific time reflected by the waveform is only used for illustrating the effect and is not intended to limit the protection scope of the control method of the present invention.

[0072] Phase 1: After the cascade energy storage converter is turned on at 0.25s, it outputs a stable voltage on the AC side. At 0.5s, the main fan starts directly without load. Since the starting current of the main fan is 5 to 10 times the rated current (peak value 410A to 820A), which far exceeds the maximum rated current of 180A designed for the cascade energy storage converter, the current limit of the voltage loop limits the output current of the cascade energy storage converter. From 0.5s to 6s, the cascade energy storage converter outputs a constant peak current of 180A to drive the main fan to start. After the main fan starts, the voltage and current return to normal. The main fan runs at almost full power to test whether the control method can provide voltage support normally when the load increases. Therefore, at 6.2s, the main fan is simulated to add 95% of the rated load. It can be seen that the output current of the cascade energy storage converter increases. Since the current is lower than the limiting current, the output voltage is normal and not disturbed.

[0073] The second stage: at 7.2s, the AC side output voltage of the cascaded energy storage converter (voltage at point Us1) is pre-synchronized with the main grid voltage (voltage at point Us2), and the pre-synchronization is completed at 7.7s, and then the switch KM1 is closed. It can be seen that due to the influence of the pre-synchronization operation, the impact current of the cascaded energy storage converter is small at the moment of grid connection, which does not affect the normal operation of the control system.

[0074] Stage 3: 8.5s through disconnection Figure 5The middle switch cabinet KM2 simulates a power outage in the main grid. At the moment of power outage, the back electromotive force (voltage at point Us1) of the main fan decreases. The cascaded energy storage converter is shut down first, then the switch KM1 is disconnected, and the voltage amplitude, frequency and initial phase of the back electromotive force (voltage at point Us1) of the main fan are locked by a phase-locked loop. After the voltage interruption at point Us1 reaches 0.1s, a flying start is performed. During the 0.1s of voltage interruption, the main fan continues to rotate by its own mechanical inertia, and a flying start is performed with the state at 8.6s as the initial state. It can be seen that the voltage amplitude at point Us1 returns to normal after a short adjustment, and the rotor frequency begins to rise until the frequency returns to normal.

[0075] Stage 4: Closing at 11.4s Figure 5 The middle switch cabinet KM2 simulates the restoration of power supply of the main grid. When the cascaded energy storage converter detects that the main grid at point Us2 has returned to normal, it starts pre-synchronization. After the pre-synchronization is completed at 12.7s, the switch KM1 is closed and the main fan enters the grid-connected operation state again.

[0076] During the entire operation process, except for the startup process of the main fan, the rotor frequency of the main fan has been higher than 40Hz (80% of the rated speed), so that the main fan can continue to blow after the main power grid is cut off.

[0077] Although the present invention has been described in detail by referring to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention or any person skilled in the art who is familiar with the present invention may easily think of changes or substitutions within the technical scope disclosed by the present invention, and shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A main fan control method based on a cascaded energy storage converter, characterized in that: include: When the main fan is in cold standby state, the cascaded energy storage converter adopts a strong inertia voltage and current double closed-loop control strategy to drive the main fan to start at reduced voltage, wherein the voltage loop obtains the three-phase current reference signal of the AC side of the cascaded energy storage converter, and the current loop obtains the three-phase voltage reference signal of the cascaded energy storage converter output; After the main fan runs stably, it is pre-synchronized and then switched to the main grid for grid-connected operation; When the main power grid in which the main fan and the cascade energy storage converter are connected to the grid loses power, the cascade energy storage converter disconnects from the main power grid and drives the main fan to achieve flying start; the flying start method includes: When the main grid is powered off, the cascaded energy storage converter and the main fan are controlled to disconnect from the main grid, and the cascaded energy storage converter and the main fan are kept connected; Detecting the amplitude of the voltage signal on the AC side of the cascaded energy storage converter through a phase-locked loop With angular frequency and initial phase , as the amplitude of the voltage reference signal of the initial state of flying car starting , angular frequency , initial phase , the formula is: Amplitude of the voltage reference signal , angular frequency As the magnitude of the main power grid and angular frequency The voltage rises until it returns to normal. The amplitude of the voltage reference signal output by the cascaded energy storage converter during the flying car start process and angular frequency The change is as follows: , are respectively the amplitude and angular frequency of the voltage reference signal at this moment; , are respectively the amplitude and angular frequency of the voltage reference signal at the previous moment; in, , is the rise coefficient, 0< <1,0< <1; According to the amplitude of the voltage reference signal , angular frequency and initial phase , determine the three-phase voltage reference signal of the AC side of the cascaded energy storage converter given during the flying car starting process, the formula is: When the main grid resumes power supply, the main fan is switched to the main grid for grid-connected operation after pre-synchronization.

2. The main fan control method based on cascaded energy storage converter according to claim 1 is characterized in that: The formula for obtaining the three-phase current reference signal of the AC side of the cascaded energy storage converter by the voltage loop is: In the formula, , , is the three-phase current reference signal, , , is the three-phase voltage reference signal of the AC side of a given cascaded energy storage converter; , , is the three-phase voltage actually outputted on the AC side of the cascaded energy storage converter; , , is the three-phase current actually outputted by the cascaded energy storage converter on the AC side; is the Laplace operator; is the grid-connected reactance; is the maximum limiting current; in, is the attenuation coefficient, is the passband cutoff frequency, is the main grid angular frequency; It is a transfer function of a second-order bandpass filter with adjustable bandwidth and coefficient, and the second-order bandpass filter plays a strong inertia role.

3. The main fan control method based on cascaded energy storage converter according to claim 2 is characterized in that: The formula for obtaining the three-phase voltage reference signal output by the cascaded energy storage converter through the current loop is: In the formula, is the current loop coefficient, ; is the main grid angular frequency, , , It is the three-phase voltage reference signal finally output by the cascaded energy storage converter; The transfer function is a bandpass filter with a coefficient of 1 and an adjustable bandwidth, and the bandpass filter plays a role in voltage stabilization.

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