CN107592026A - The control strategy of the two level traction rectifier devices based on VSM - Google Patents
The control strategy of the two level traction rectifier devices based on VSM Download PDFInfo
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Abstract
The invention discloses a kind of control strategy of the two level traction rectifier devices based on VSM, by imitating the mechanical model of synchronous machine, controls rectifier input voltagee abFrequency, control virtual machine torque and then control rectifier active power of outputP eWith the voltage of DC sideV dc.Traction rectifier device input voltage is controlled by the electromagnetic model for imitating synchronous machinee abAmplitude and Traction networks output reactive powerQ, add voltage and frequency support link so that rectifier can participate in the regulation of supply conductor voltage and frequency.The present invention can make traction rectifier utensil have the external characteristics of synchronous machine, possesses certain damping characteristic, the vibration of damping system, electric locomotive can be made also to be actively engaged in the regulation of supply conductor voltage and frequency while self-operating situation is met, the stability of trailer system is enhanced, is played a significant role in the control of traction rectifier device.
Description
Technical Field
The invention relates to the technical field of electric traction and electric transmission, in particular to a control strategy of a two-level traction rectifier based on VSM.
Background
Modern alternating current electric locomotives generally adopt an AC-DC-AC mode, single-phase alternating current is rectified into direct current at the front end through a PWM rectifier, and the PWM rectifier has the advantages of low power harmonic content, high power factor, capability of realizing bidirectional flow of energy and the like. However, research in power systems shows that power electronic devices have the advantage of rapid response and correspondingly lack inertia and damping characteristics, so that more and more power electronic devices are connected to a power grid, and the inertia and damping characteristics of the whole power grid are reduced. Similar problems can exist in a traction system if the traction network is considered a special microgrid and the electric locomotive is considered a special distributed energy source. In the field of distributed power generation, an effective measure at present is a Virtual Synchronous Machine (VSM) technology, that is, a three-phase inverter is used to simulate the external characteristics of a synchronous machine, and the three-phase inverter is equivalent to a synchronous generator. However, for a special system such as a traction system, related research is relatively few, the traction rectifier is essentially a single-phase rectifier, and is neither a three-phase system nor an inverter system, and how to apply the virtual synchronous machine technology to the single-phase two-level traction rectifier is still to be researched further.
In addition, the control strategy of the traditional traction rectifier generally adopts direct current control or dq decoupling control, and the two control methods can realize better direct current side voltage control and grid side current phase control, but only consider the electric locomotive as a passive load and do not have the capability of actively participating in the regulation of the amplitude and the frequency of the traction grid voltage. In the power system, the traditional power generation equipment is a synchronous motor, can provide support for the voltage and frequency of a power grid, and can adaptively adjust and output reactive power and active power when the voltage amplitude and the frequency of the power grid fluctuate, so that a certain support function is provided for the power grid. The traction rectifier based on the virtual synchronous machine technology can also autonomously participate in the regulation of the traction network through a voltage and frequency regulation part.
Disclosure of Invention
The invention relates to a control strategy of a two-level traction rectifier based on VSM, which can enable the traction rectifier to have the external characteristics of a synchronous machine, have certain damping characteristics and damp oscillation of a system, and enable an electric locomotive to actively participate in the regulation of voltage and frequency of a traction network while meeting the self running condition. The technical scheme is as follows:
the control strategy of the two-level traction rectifier based on the VSM is characterized in that a mechanical model of the two-level traction rectifier simulating a synchronous machine is established, the direction of current flowing into the rectifier is the positive direction of the current, and the equation of the mechanical model is as follows:
in the formula, T m 、T e 、T d Respectively a virtual mechanical torque, a virtual electromagnetic torque and a damping torque; j is rotational inertia; omega 0 Is the actual traction net angular velocity; d p Is the damping coefficient;the electrical angular velocity of the virtual synchronous machine is the angular velocity of the input voltage of the rectifier;
determining the angular velocity of the input voltage of a rectifierTo achieve rectifier input voltage e ab The frequency of (2).
Further, by controlling the virtual machine torque T m Controlling virtual electromagnetic torque T e Further control the active power P of the rectifier e ：
Virtual mechanical torque T m The device consists of two parts:
T m ＝T 0 +△T
T 0 controlling the dc side voltage to track a given value for the output of the PI controller, expressed as:
T 0 ＝(K p +K i /s)(V dc _ ref -V dc )
in the formula, K p And K i Proportional coefficient and integral coefficient of PI controller; s is a differential operator, V dc Is a DC side voltage, V dc _ ref Is a given value;
Δ T is the frequency support component, expressed as:
△T＝k f (ω 0 -ω 0 * )
in the formula, k f As a frequency adjustment factor, omega 0 * Adjusting the virtual mechanical torque T by the delta T for the rated angular speed of the traction network when the frequency of the traction network fluctuates m ；
When the system is in a stable state, T is provided m ＝T e Virtual electromagnetic torque T e Comprises the following steps:
T e ＝P e /ω
in the formula, omega is the actual angular speed of the input voltage of the rectifier; when the system is in a steady state, the system is controlled by omega 0 Instead of ω, i.e.:
T e ＝P e /ω 0
by regulating the rectifier output active power P e And provides support for the traction net frequency.
Furthermore, a virtual electromagnetic model simulating a two-level traction rectifier of the synchronous machine is established, and the input voltage e of the rectifier is obtained according to the electromagnetic relation between the stator and the rotor of the traditional synchronous generator ab Expression (c):
in the formula, M f Is a mutual inductance between a virtual field winding and a stator winding, i f For virtual excitation current, θ is the virtual synchronous machine electrical angle, i.e. the phase of the rectifier input voltage, from which the angular velocity of the rectifier input voltageObtaining an integral;
exciting current i f Considered as a constant value, then:
thereby realizing the rectifier input voltage e ab Amplitude ofAnd (4) controlling.
Further, virtual mutual inductance M f With virtual field current i f Product of (M) f i f The method is obtained by reactive link deviation, namely:
M f i f ＝∫(Q set +△Q-Q)/kdt
in the formula, Q set The command reactive power is obtained, delta Q is the reactive deviation of a voltage support link, Q is the actual output reactive power of the network side, and 1/k is an integral coefficient;
to achieve the same phase of the network side voltage and current, Q is adjusted set If not =0, then
M f i f ＝∫(△Q-Q)/kdt
The reactive support link is as shown in the formula:
△Q＝D q (V g_rms -V * g_rms )
in the formula, V g_rms And V * g_rms Respectively the actual effective value and the rated effective value of the network side voltage, D q Is a reactive power regulating coefficient.
Furthermore, the network side reactive power Q and the rectifier input active power P e The calculation is carried out by a second-order generalized integral method to obtain:
wherein s is a complex variable; omega 0 * Determining the resonant frequency of the system for the rated angular speed of the traction network; k is a radical of formula 0 Determining the bandwidth and response time of the system for adjusting the coefficient; e.g. of the type α For the input voltage e of the rectifier ab Same phase component, e, calculated by SOGI β Is e ab A virtual quadrature phase component of; v. of gα For traction network voltage v g The same phase component, v, calculated by the SOGI gβ Is v is g A virtual quadrature phase component of (a); i.e. i α The same phase component i calculated by SOGI for the input current i of the rectifier β Is the virtual quadrature phase component of i.
The invention has the beneficial effects that:
1) The method can better control the voltage stability of the direct current side, and can quickly track a given value when the reference voltage or the load of the direct current side is suddenly changed; the output reactive Q of the network side can be controlled to be 0, so that the current of the network side and the voltage of the network side are controlled to be in the same phase, and the unit power factor operation is realized;
2) The method is different from the direct current control or dq decoupling control of the traditional traction rectifier, but adopts a control strategy of a virtual synchronous machine to enable the traction rectifier to have the external characteristics of the synchronous machine, obtains the frequency and the phase of the input voltage of the rectifier through active feedback, obtains the amplitude of the input voltage of the rectifier through reactive feedback, and synthesizes the two to finally obtain the modulation voltage;
3) The control link of the invention is added with a frequency support link, when the frequency of the traction network is lower than the rated frequency of the traction network, the virtual mechanical torque is reduced, thereby reducing the active power absorbed by the traction rectifier from the traction network, and when the frequency of the traction network is about the rated frequency, the virtual mechanical torque is increased, thereby increasing the active power absorbed by the traction rectifier traction network; the active power required by the traction network can be adjusted according to the actual frequency of the traction network while the self operation is met, so that the support is provided for the frequency of the traction network;
4) The control link of the invention is additionally provided with a voltage supporting link, when the voltage amplitude of the traction network is equal to a rated value, the unit power factor operation is realized, namely Q =0; when the voltage amplitude of the traction network deviates, the traction rectifier can independently and properly adjust the reactive power absorbed by the traction rectifier, and a certain support is provided for the voltage amplitude of the traction network; when the actual voltage amplitude of the traction network is greater than the rated value, the rectifier absorbs the reactive power Q >0, and when the actual voltage amplitude of the traction network is less than the rated value, the rectifier absorbs the reactive power Q <0, namely the traction rectifier outputs the reactive power to the traction network;
5) The invention realizes active-frequency control by simulating the mechanical equation of the synchronous machine, and the mechanical equation reflects the damping characteristic of the synchronous machine, so that the traction rectifier also has the damping characteristic similar to the synchronous machine, the oscillation of the system can be damped, and the amplitude of the oscillation is controlled by adjusting the damping coefficient, thereby improving the capability of the traction rectifier for coping with the abnormal state of the traction network and improving the stability of the system;
6) The invention can realize the bidirectional flow of power, the electric locomotive can be equivalent to a synchronous generator in a regeneration state, and the power can be more friendly as a synchronous machine and fed back to a traction network;
7) The virtual synchronous machine model of the single-phase two-level traction rectifier is constructed, so that the traditional VSM technology is expanded, the VSM technology is not only suitable for a three-phase inverter, but also can be adopted by the single-phase rectifier, and a synchronous machine scheme can be adopted no matter the single-phase rectifier is traditional distributed power generation equipment or electric equipment such as an electric locomotive, so that the uniformity of an electric power system is improved.
Drawings
FIG. 1: the two-level traction rectifier topological diagram in the embodiment of the invention.
FIG. 2: the embodiment of the invention discloses a system control block diagram.
FIG. 3: the SOGI block diagram in the embodiment of the invention.
FIGS. 4a-4c: in the embodiment of the invention, when the traction rectifier works under the traction working condition, the system responds to the waveform.
FIG. 5: in the embodiment of the invention, the traction rectifier works under the traction working condition and the regeneration working condition, and the voltage and the current on the network side have the same phase (figure 5 a); the grid side voltage and current are in opposite phase (5 b).
FIG. 6: the damping characteristic in the embodiment of the invention responds to the waveform.
FIG. 7 is a schematic view of: the voltage support experiment in the embodiment of the invention.
FIGS. 8a-8b: frequency support experiments in the embodiments of the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific embodiments. A control strategy of a two-level traction rectifier based on VSM can realize direct current side voltage control and network side voltage and current are in the same phase. The traction rectifier is changed from a passive load to a load which can automatically participate in the adjustment of the voltage amplitude and the frequency of the traction network, and the traction rectifier has certain damping characteristics, so that the oscillation of a system can be damped, and the stability of the system is improved. The traction rectifier is used for simulating the synchronous machine, so that the electric locomotive has the external characteristics of the synchronous machine, the electric locomotive can be regarded as special distributed power generation equipment, and the uniformity of an electric power system is improved.
(1) Circuit equivalent of two-level traction rectifier and synchronous generator
The control strategy of the VSM-based two-level traction rectifier in this embodiment is shown in fig. 1, and specifically includes: neglecting the traction transformer, taking the output voltage of the secondary side of the traction network transformer as the input voltage v of the traction network g ，v g Filtered inductor L s And line impedance R s And single-phase two-level PWM rectifierConnected with each other, the output end of the rectifier is connected with a filter capacitor C for 2 times 2 And an inductance L 2 The two ends of the load are connected with a supporting capacitor C d In traction condition, the Load is simplified to Load 1 Pure resistance, load simplified to Load under regenerative braking conditions 2 Resistance plus dc power. When the Load is Load 1 When the traction rectifier works under the traction working condition, the operation is similar to the VSM working in a charging mode, namely, the power grid charges the direct-current side storage battery; when Load is Load2, the traction rectifier operates in a regenerative braking mode, which is equivalent to an inverter, and the normal operation mode of the VSM is the same. Thus, the traction rectifier can also be controlled to mimic the external characteristics of the synchronous generator.
The electrical model of the synchronous machine, i.e. its loop voltage of each phase satisfies the formula (1):
in the formula: l is a radical of an alcohol s Is a synchronous inductance of a synchronous generator; r s Is a synchronous resistor of a synchronous generator; e.g. of the type abc Is the transient electromotive force, v, of a synchronous generator abc Is the terminal voltage of the synchronous generator, i abc Is the synchronous current of the synchronous generator.
For a traction rectifier, if the direction of current flowing into the rectifier is defined as the positive direction of current, the voltage equation of the loop satisfies the formula (2):
in the formula: l is s A filter inductor; r s Is the line impedance; v. of g The voltage of the traction network after passing through the traction inverter; e.g. of the type ab The input voltage of the rectifier is also the modulation voltage of the control link, and i is the loop current.
When only one phase of the synchronous machine is considered, it can be found by comparing fig. 1 that the filter inductance of the traction rectifier can be equivalent to a synchronous generatorThe synchronous inductance and the loop equivalent resistance of the motor can be equivalent to the synchronous resistance of a synchronous generator and the input voltage e of a rectifier ab Can be equivalent to the transient electromotive force of a synchronous generator. By means of VSM-based control, the external characteristics of the traction rectifier can be equivalent to one phase of a synchronous machine as shown in fig. 1.
(2) Virtual electromagnetic model of two-level traction rectifier
According to the electromagnetic relationship between the stator and the rotor of the traditional synchronous generator, the input voltage of the rectifier is obtained:
M f is a mutual inductance between the virtual field winding and the stator winding, i f Is a virtual excitation current, theta is a virtual synchronous machine electrical angle, namely the phase of the input voltage of the rectifier,is the electrical angular velocity of the virtual synchronous machine, i.e. the angular velocity of the rectifier input voltage.
To simplify the analysis, the excitation current i is measured f Considered as a constant value, then:
the virtual mutual inductance M f And virtual exciting current i f Product of (D) M f i f Derived from reactive link deviation, i.e. M f i f ＝∫(Q set +△Q-Q)/kdt。
Q set To command reactive power; different from the VSM technology, the traditional VSM technology mainly aims at realizing the tracking of the instruction active power and reactive power under the grid-connected condition, so that the fed back reactive power is the power at the output side of the inverter and is not the power at the grid side; for the traction rectifier, the control objective is that the network side voltage and current are in phaseI.e. the net side input reactive power is 0, so here Q is the net side actual output reactive power and not the rectifier input side reactive power; to achieve the same phase Q of the network side voltage and current set =0, so M f i f Can be simplified to be represented as:
M f i f ＝∫(△Q-Q)/kdt (5)
M f i f initial value isV g * Rated voltage amplitude of traction network, f 0 * The traction network is rated for a frequency, here 50Hz.
And delta Q is reactive deviation of a voltage supporting link, if the actual effective value of the voltage on the network side is equal to the rated effective value delta Q =0, the part is specifically stated in the voltage supporting section, and 1/k is an integral coefficient.
(3) Mechanical model of two-level traction rectifier
Because the traction rectifier is in a traction working condition under most conditions, current flows into the traction rectifier, and only in a regenerative braking working condition, the current flows into the traction rectifier and flows into a power grid, the direction of the current flowing into the traction rectifier is specified to be the positive direction of the current, and the direction of a circuit specified by the traditional VSM is opposite to the direction of the current, so that the power signs are just opposite, further the signs of the virtual electromagnetic torque, the mechanical torque and the damping torque are also opposite, and the mechanical model of the traction rectifier is obtained as follows:
in the formula: t is m 、T e And T d Virtual mechanical torque, electromagnetic torque and damping torque; j is a virtual moment of inertia; d p In order to be a damping coefficient of the damping,for rectifier input voltage acceleration, i.e. virtual synchronous angular velocity, omega 0 Is the actual angle velocity of the traction wire.
In VSM, the output active power of the inverter is controlled to be a command value, and T m ＝P set ω, constant at steady state ω, so virtual mechanical torque T m Is a constant value. And for the traction rectifier, the control target is to control the DC side voltage V dc Tracking a given value V dc _ ref If the load on the DC side is not changed, when the voltage on the DC side is a given value, the output active power of the rectifier is also a constant value, so the virtual electromagnetic torque T e Also at a constant value, having T when the system is in a steady state m ＝T e . If frequency support is not considered, the output of the PI controller is taken as a virtual mechanical torque:
T m ＝T 0 ＝(K p +K i /s)(V dc _ ref -V dc ) (7)
in the formula, K p And K i Proportional coefficient and integral coefficient of the PI controller respectively.
Virtual electromagnetic torque T e ：
T e ＝P e /ω (8)
In the formula: p e The active power absorbed by the rectifier from the traction network, and omega is the actual angular speed of the rectifier input voltage, in general omega and omega 0 Not very deviated, omega is used as omega 0 Instead of the former
T e ＝P e /ω 0 (9)
Damping torque T d ：
D p The damping coefficient, which is the damping coefficient, determines the amplitude of the system oscillation.
The embodiment realizes active-frequency control by simulating the mechanical equation of a synchronous machine, and active power absorbed from a traction network through a rectifier, namely virtual electromagnetic power P e Fed back to the control unit to obtain the input of the rectifierVoltage e ab Angular velocity ofIntegration yields e ab Phase. The phase theta and the angular velocity obtained by the mechanical modelDerived from electromagnetic models ab Amplitude, voltage of the input of the rectifier combined
(4) Rectifier input active and network side reactive power calculation
The traditional VSM is a three-phase system, and the power calculation of the three-phase system is simpler
The system considered in this embodiment is a single-phase system, so the power calculation method in the conventional VSM scheme is no longer applicable, and the power solution is performed by using a second-order generalized integral method (SOGI), a block diagram of which is shown in fig. 3, and the SOGI transfer function can be represented by equation (12).
In the formula, s is a complex variable, omega 0 * Determining the resonant frequency, k, of the system for the nominal angular velocity of the traction network 0 The bandwidth and response time of the system are determined, here taken to be 1.57.
The scheme needs to calculate the input active power P of the rectifier e And network side reactive power Q:
(5) Voltage support
In the embodiment, the voltage support is added in the control loop, and the reactive power absorbed by the traction rectifier can be automatically adjusted according to the voltage amplitude of the traction network, so that the support is indirectly provided for the voltage of the traction network.
The reactive support link is as shown in the formula:
△Q＝D q (V g_rms -V * g_rms ) (14)
in the formula: v g_rms And V * g_rms Respectively the actual effective value and the rated effective value of the network side voltage, D q Is a reactive power regulating coefficient.
From the formula (5), Q =Δq in a steady state. If the actual effective value V of the traction network voltage g_rms Greater than rated effective value V * g_rms ，△Q>, 0, in steady state, Q&0, the traction rectifier absorbs the idle work from the net side; if the actual effective value V of the traction network voltage g_rms Less than rated effective value V * g_rms ，△Q&0, in steady state, Q&And (lt) 0, the traction rectifier releases the reactive power to the traction network. It can be seen that when the voltage of the traction network fluctuates and deviates from the rated value, the power factor of the network side is not 1, so that the Q variation should not be large to ensure that the system still has a high power factor. Design D of the present embodiment q During parameter design, the actual effective value V of the traction network voltage is assumed according to the following standard g_rms To a rated effective value V * g_rms The maximum is 10%, and the Q variation does not exceed 10% of the rated capacity of the traction rectifier.
(6) Frequency support
The VSM has the external characteristic of a synchronous machine, and can adjust output active power when the frequency of the power grid fluctuates, so that frequency support is provided for the power grid. According to the control strategy of the VSM-based two-level traction rectifier, the frequency support is added in the control loop, so that the traction rectifier can autonomously adjust the active power absorbed by the traction rectifier according to the frequency of a traction network, and the frequency support is indirectly provided for the traction network.
The frequency support can be expressed as:
△T＝k f (ω 0 -ω 0 * ) (15)
virtual mechanical torque is output T by PI controller 0 And the frequency support comprises:
T m ＝T 0 +△T (16)
when traction net frequency omega 0 Equal to nominal frequency omega 0 * At time, Δ T =0,T m ＝T m * (T m * Rated virtual machine torque), at steady state, there is T m ＝T e So that T e ＝T e * (T e * Rated virtual electromagnetic torque), P e ＝P e * (P e * To control rectifier power rating). When traction net frequency omega 0 Greater than nominal frequency omega 0 * Time, delta T>0，T m >T m * (ii) a At steady state, has T m ＝T e So that T e >T e * ，P e >P e * I.e. the traction rectifier increases the absorbed active power. When the traction network frequency is less than the rated frequency, delta T<, 0, T in steady state e <T e * ， P e <P e * I.e. the traction rectifier reduces the absorbed active power.
(7) Results of the experiment
Fig. 4a-4c are waveforms of system responses when the traction rectifier is operating in traction conditions. When t =0s, the system starts, the load on the DC side is R =6.268 omega, and the reference voltage on the DC side is V dc_ref =2800V; when t =5s, the load jumps to 3.136 Ω, and when V is greater dc_ref Keeping the original shape; t =15s, V dc_ref =3000V, dc-side voltage waveform as shown in fig. 4a, which can quickly track a given load jump and dc-side reference voltage jump; the reactive Q is as shown in fig. 4b, the reactive Q =0 in steady state, the grid side voltage and current are in phase as shown in fig. 4c, and the power factor is 1.
Fig. 5 shows the network side voltage and current waveforms of the traction rectifier operating under traction and regeneration conditions, and fig. 5a shows the traction condition with the network side voltage and current in phase and a power factor of 1; fig. 5b shows the traction condition with the grid side voltage and current in phase opposition, again achieving a power factor of 1.
FIG. 6 is a graph showing a response waveform of a damping characteristic, wherein the moment of inertia J is constant, and it can be seen from the graph that when the moment of inertia J of the system is constant, the dynamic response time of the system is constant, but the damping coefficient D is constant p The larger the oscillation amplitude of the system, the better the damping characteristic of the synchronous machine, and the provided control scheme enables the traction rectifier to have the capacity of damping the oscillation of the system.
Fig. 7 is a voltage waveform of a grid side in a voltage support experiment, wherein the voltage of a traction grid of the first 5s is equal to a rated voltage, and the reactive power Q =0 of an input rectifier in a steady state; when t =5s, the grid side voltage amplitude is reduced by 10%, and Q is equal to the reduced value&0, the rectifier provides reactive power to the traction network; when t =10s, the rated voltage is recovered, when t =15s, the amplitude of the voltage on the network side is increased by 10%, and at the moment, the reactive Q of the input rectifier> 0, i.e. the rectifier absorbs reactive power, V, from the traction network g When the fluctuation is less than 10%, the Q fluctuation is less than 10% of the total capacity of the traction rectifier, and the method can be used for adjusting the reactive power more systematically, so that voltage support is provided for the traction network.
FIGS. 8a-8b are frequency support experiments, i.e., different damping coefficients D p The response waveform of the lower virtual electromagnetic torque. As shown in fig. 8a, when t =0s, the system starts, at which time ω is 0 ＝ω 0 * When the system is stable, T e ＝T e * . At t =5s, the frequency fluctuates in the forward direction, i.e., ω 0 Greater than omega 0 * ，△T>0，T m >T m * At steady state, having T m ＝T e So that T e >T e * ，P e >P e * I.e. the traction rectifier increases the absorbed active power. As shown in FIG. 8b, Δ T is measured when the traction network frequency is less than the nominal frequency<, 0, T in steady state e <T e * ，P e <P e * I.e. the traction rectifier reduces the absorbed active power.
Claims (5)
1. The control strategy of the two-level traction rectifier based on the VSM is characterized in that a mechanical model of the two-level traction rectifier simulating a synchronous machine is established, the direction of current flowing into the rectifier is the positive direction of the current, and the equation of the mechanical model is as follows:
in the formula, T m 、T e 、T d Respectively a virtual mechanical torque, a virtual electromagnetic torque and a damping torque; j is rotational inertia; omega 0 Is the actual traction net angular velocity; d p Is a damping coefficient;the electrical angular velocity of the virtual synchronous machine is the angular velocity of the input voltage of the rectifier;
determining the angular velocity of the input voltage of a rectifierTo achieve rectifier input voltage e ab The frequency of (2).
2. The VSM-based two-level traction rectifier control strategy of claim 1, wherein virtual mechanical torque T is controlled m Controlling virtual electromagnetic torque T e Further control the active power P of the rectifier e ：
Virtual mechanical torque T m The device consists of two parts:
T m ＝T 0 +ΔT
T 0 controlling the dc side voltage to track a given value for the output of the PI controller, expressed as:
T 0 ＝(K p +K i /s)(V dc _ ref -V dc )
in the formula, K p And K i Proportional coefficients and integral coefficients of the PI controller are respectively; s is a differential operator, V dc Is a DC side voltage, V dc _ ref Is a given value;
Δ T is the frequency support component, expressed as:
ΔT＝k f (ω 0 -ω 0 *)
in the formula, k f As a frequency adjustment factor, omega 0 * Rated angular velocity for the traction network;
delta T regulates the virtual machine torque T in the event of fluctuations in the traction network frequency m When the system is in a steady state, there is T m ＝T e Virtual electromagnetic torque T e Comprises the following steps:
T e ＝P e /ω
in the formula, omega is the actual angular speed of the input voltage of the rectifier; when the system is in a steady state, the system is controlled by omega 0 Instead of ω, i.e.:
T e ＝P e /ω 0
by regulating the rectifier output active power P e And provides support for the traction net frequency.
3. The VSM-based two-level traction rectifier control strategy of claim 1, wherein a virtual electromagnetic model is created to simulate a synchronous machine two-level traction rectifier, and the input voltage e of the rectifier is obtained based on the electromagnetic relationship between the stator and rotor of a conventional synchronous generator ab Expression (c):
in the formula, M f Is a mutual inductance between a virtual field winding and a stator winding, i f For virtual excitation current, θ is the virtual synchronous machine electrical angle, i.e. the phase of the rectifier input voltage, from which the angular velocity of the rectifier input voltageObtaining an integral;
exciting current i f Considered as a constant value, then:
thereby realizing the rectifier input voltage e ab Amplitude ofAnd (4) controlling.
4. The VSM-based control strategy of two-level traction rectifier of claim 3, wherein the virtual mutual inductance M f With virtual field current i f Product of (D) M f i f The method is obtained by reactive link deviation, namely:
M f i f ＝∫(Q set +ΔQ-Q)/kdt
in the formula, Q set The command reactive power is delta Q, the reactive deviation of a voltage support link is delta Q, the Q is the actual output reactive power of the network side, and 1/k is an integral coefficient;
to achieve the same phase of the network side voltage and current, Q is adjusted set If not =0, then
M f i f ＝∫(ΔQ-Q)/kdt
The reactive support link is as shown in the formula:
ΔQ＝D q (V g_rms -V * g_rms )
in the formula, V g_rms And V * g_rms Respectively the actual effective value and the rated effective value of the network side voltage, D q Is a reactive power regulating coefficient.
5. The VSM-based two-level traction rectifier control strategy of claim 4, wherein the grid-side reactive power Q and rectifier input active power P e Calculated by the second order generalized integral method (SOGI):
wherein s is a complex variable; omega 0 * Determining the resonant frequency of the system for the rated angular speed of the traction network; k is a radical of formula 0 Determining the bandwidth and response time of the system for adjusting the coefficient; e.g. of the type α For the input voltage e of the rectifier ab The same phase component, e, calculated by the SOGI β Is e ab A virtual quadrature phase component of; v. of gα For traction network voltage v g The same phase component, v, calculated by the SOGI gβ Is v is g A virtual quadrature phase component of; i.e. i α The same phase component i obtained by SOGI calculation of input current i of the rectifier β Is the virtual quadrature phase component of i.
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