CN110797910B - Control method for improving low voltage ride through capability of matrix converter system - Google Patents
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Abstract
The invention discloses a control method for improving the low voltage ride through capability of a matrix converter system, which comprises the following steps: 1) Detecting whether the power grid voltage drops or not by sampling and calculating the three-phase voltage of the power grid in real time, calculating the highest rotating speed value of the system which can operate under the motor load under the working condition that the load is the motor load after the power grid voltage drops, and switching the system into a traversing control mode if the rotating speed of the motor is greater than the highest rotating speed value; 2) During the crossing period, the clamping capacitor is used as an energy conversion mechanism, and the crossing is realized by maintaining the voltage of the clamping capacitor to be constant; 3) When switching to the traversing control through the step 1), the system is switched from the normal working mode to the traversing mode; and subtracting the square of the clamping capacitor voltage with the output of the voltage ring PI controller and the damping coefficient times as an input reference value of the motor q-axis current controller. The control method can realize the low voltage ride through capability of the system which does not stop running after the voltage of the power grid drops, inhibit the overcurrent phenomenon of the system, and enable the system to quickly recover running after the voltage of the power grid is recovered.
Description
Technical Field
The invention relates to the technical field of power converter control of a driving motor, in particular to a control method for low voltage ride through capability of a matrix converter system.
Background
The motor system generally adopts a power grid as an input power supply, and is influenced by factors such as line short circuit, ground fault, overload and the like, and the power grid can have power quality problems such as voltage drop, short-time interruption, voltage change and the like. Among the various power quality problems, voltage sag is the most frequent type of fault that severely affects the sustained operation capability of the motor system. Once the motor system is stopped, for some important industrial occasions, the production process is interrupted, and serious economic loss is caused. In this regard, the motor system is required to have a Low Voltage Ride-through (LVRT) capability of 0.06-0.6 s for non-stop operation under the condition that the power grid Voltage drops by 10% -30% of rated value.
Matrix Converter-permanent magnet synchronous motor system (MC-PMSM) is a type of motor system with high power density, motor regenerated energy capable of feeding power grid, sinusoidal input current waveform and flexible and adjustable power factor. The development of the technical level has important significance for breaking through key technologies of the high-integration motor system. However, the power topology is free of large-capacity energy storage elements, so that the output side of the system is extremely susceptible to the input side. When the grid voltage drops and the system does not have LVRT capability, the system needs to be shut down for operation. In this regard, various solutions are proposed by domestic and foreign specialists and scholars. These schemes can be divided into three categories:
1) The energy storage device is added in the topological structure to realize crossing, such as super capacitor, battery or flywheel. Under normal conditions, the power grid charges the energy storage device, and after the power grid fails, the energy storage device supplies power to the system to maintain the normal operation of the system;
2) The system topology structure is modified to realize the crossing, for example, three switching devices and a direct current energy storage capacitor are added in the traditional MC topology, and a virtual voltage type inverter is formed by combining three switches in the MC, so that the crossing is realized by a method of keeping the capacitor voltage and the motor magnetic flux constant;
3) The LVRT control is applied based on the load inertia principle, an auxiliary circuit is designed to realize the crossing, and the method can be divided into two types, namely, the input filter capacitor is utilized to store energy, three IGBTs are added in a topological structure at the same time, the power grid is isolated from the system through the IGBTs after the power grid fails, the power grid does not transmit energy to the system any more, and zero-power control is adopted to realize the crossing; secondly, the clamp capacitor is used for storing energy to realize crossing, and the crossing method is divided into 3 modes: the method adopts a mode of applying clamping capacitor voltage or effective grid voltage by magnetic linkage hysteresis control, a mode of switching in three modes of clamping loop freewheeling, zero vector freewheeling and non-zero vector freewheeling in one control period, and a mode of switching in two circuit loops by current hysteresis control.
The existing method for increasing the energy storage device and modifying the topology weakens the advantages of compact system volume and high power density to a certain extent, the method for realizing the crossing by utilizing the rotational inertia mechanical energy of the motor focuses on the design of a crossing strategy, the hysteresis control effect is poor, and the control quantity has larger fluctuation during the crossing.
Disclosure of Invention
Aiming at the prior art, the invention aims to solve the technical problems that when the system does not have low voltage ride through capability after the voltage of the power grid drops, the system is stopped to cause the interruption of operation, and meanwhile, the procedures of system correction, positioning and the like after the power grid is recovered also cause time delay, so that serious economic loss can be caused in important occasions.
In order to solve the technical problems, the invention provides a control method for improving the low voltage ride through capability of a matrix converter system, which comprises the following steps:
step one, detecting whether the voltage of a power grid drops, and judging whether to switch to pass through control: detecting whether the power grid voltage drops by sampling and calculating the three-phase voltage of the power grid in real time, calculating a maximum rotating speed value of a system which can stably run under a motor load after the power grid voltage drops under the working condition that the load is the motor load when the power grid voltage drops, switching the system into a traversing control mode if the rotating speed of the motor is greater than the maximum rotating speed value, otherwise, continuing to run according to the control mode before failure;
step two, designing a low voltage ride through operation auxiliary circuit: during the crossing period, the clamping capacitor is used as an energy conversion mechanism, and the crossing is realized by maintaining the voltage of the clamping capacitor to be constant;
step three, designing a low voltage ride through controller: the low voltage ride through controller is structured such that when switching to ride through control by step one, the system is switched from a normal operating mode to a ride through mode; the voltage PI controller is connected with the motor q-axis current controller through the voltage loop, the voltage of the voltage loop PI controller is equal to the voltage of the clamping capacitor, and the voltage of the clamping capacitor is equal to the voltage of the motor q-axis current controller.
Further, the control method for improving the low voltage ride through capability of the matrix converter system according to the present invention comprises:
in the first step, when the power grid voltage drops, the dropping depth h is calculated:
in U RMS For sampling the obtained effective value of the power grid voltage, U RMS_N Is an effective value of the power grid in a normal state;
calculating the highest rotating speed n of the motor capable of stably running under different dropping depths and different loads after the voltage of the power grid drops max Is represented by the expression:
wherein R is s The resistor is a motor stator resistor; l (L) s The stator inductance is the motor stator inductance; psi phi type f The permanent magnet flux linkage amplitude value of the motor; n is the motor rotation speed; p is the pole pair number of the motor; t (T) L Is the motor load; u (U) m Inputting phase voltage amplitude values for the matrix converter;
The motor is set to stably operate at the rotating speed of n r/min before the power grid faults, and the load is T L Under the working condition of N.m, calculating T after the voltage of the power grid drops L Maximum rotational speed value n at which the system can be operated under load max If n>n max And switching the system to a crossing control mode, otherwise, continuing to operate the system according to the control mode before the fault.
In the second step, the motor and the clamping capacitor perform bidirectional energy circulation during the crossing period, two ends of a diode in the topological structure clamping circuit of the matrix converter system are connected in anti-parallel with a switching device, and the switching device is always in a conducting state during the crossing period.
In the third step, the design method of the low voltage ride through controller includes:
during the crossing period, the motor works in a generator state, the motor convention is adopted in the direction defined by each physical quantity of the motor, and a unified mathematical model of the motor and an inversion stage of the matrix converter is established:
in the formula, v d 、v q D, q-axis components of the stator voltage; i.e d 、i q D, q-axis components of the stator current; c (C) cla Is a clamping capacitor; v cla A clamping capacitor voltage; r is R L An energy discharging resistor which is a clamping capacitor;
the parameters of the voltage loop PI controller are designed by adopting the concept of active damping, and definition is defined
Wherein i is q1 B is the output of the voltage ring PI controller a Is a damping coefficient;
control of i during traversal d =0, will i q Substituting the expression of the (2) into the established unified mathematical model of the motor and the matrix converter inverter, and configuring the poles to the expected closed-loop bandwidth beta to obtain the voltage v c 2 la Controlled object transfer function with respect to q-axis current:
and the transfer function of the controlled object is combined with the voltage loop PI controller, and parameters of the voltage loop PI controller are obtained through parameter setting, so that the design of the low-voltage ride-through controller is completed.
The control method for improving the low voltage ride through capability of the matrix converter system can be applied to the fields of matrix converters, motor control and the like. Compared with the prior art, the invention has the beneficial effects that:
(1) And the occurrence of the overcurrent phenomenon of the system during the voltage drop of the power grid is restrained.
(2) The system is continuously operated during the passing period, the motor is operated in a constant power state, and the motor is operated as a generator to charge the clamping capacitor and maintain the constant voltage of the capacitor, and the rotating speed of the motor is reduced with constant acceleration basically and is not reduced to zero.
(3) When the power grid voltage drops, the system does not need to stop running, and when the power grid voltage is recovered, the system can be started from a non-zero rotating speed and non-zero magnetic flux state.
Drawings
FIG. 1 is a flow chart of a control method of the present invention;
FIG. 2 is a control block diagram of the control method of the present invention;
FIG. 3 is an IMC-SPMSM system torque-speed operating range;
FIG. 4 is a schematic block diagram of a ride-through control decision;
FIG. 5 is a block diagram of a voltage closed-loop control architecture during a ride-through phase;
FIG. 6 is a ride-through waveform of the system at 300r/min and 0 N.m for a motor at a grid sag depth of 10%;
FIG. 7 is a ride-through waveform of the system at 300r/min and 15 N.m for a motor at a grid sag depth of 10%;
FIG. 8 is a ride-through waveform of the system at 300r/min and 0 N.m for a motor at 20% grid sag depth;
FIG. 9 is a ride-through waveform of the system at 300r/min and 15 N.m for a motor at 20% grid sag depth.
Detailed Description
The invention will now be further described with reference to the accompanying drawings and specific examples, which are in no way limiting.
The invention relates to a control method capable of improving the low voltage ride through capability of a matrix converter system, as shown in fig. 1, comprising the following steps:
step one, detecting whether the voltage of a power grid drops, and judging whether to switch to pass through control:
whether the grid voltage drops or not is detected by sampling and calculating the three-phase voltage of the grid in real time, and when the grid voltage drops, the dropping depth h is calculated:
in U RMS For sampling the obtained effective value of the power grid voltage, U RMS_N Is an effective value of the power grid in a normal state;
calculating the highest rotating speed n of the motor capable of stably running under different dropping depths and different loads after the voltage of the power grid drops max Is represented by the expression:
wherein R is s The resistor is a motor stator resistor; l (L) s The stator inductance is the motor stator inductance; psi phi type f The permanent magnet flux linkage amplitude value of the motor; n is the motor rotation speed; p is the pole pair number of the motor; t (T) L Is the motor load; u (U) m Inputting phase voltage amplitude values for the matrix converter;
Assuming that the motor runs at the rotating speed n (r/min) in a steady state before the power grid faults, and the load is T L Under the working condition of (N.m), calculating T after the voltage drop of the power grid L Maximum rotational speed value n at which the system can be operated under load max If n>n max The system is switched to a crossing control mode, otherwise, the system continues to operate according to the control mode before failure;
step two, designing a traversing auxiliary circuit:
during the crossing period, the clamping capacitor is used as an energy conversion mechanism, and the crossing is realized by maintaining the voltage of the clamping capacitor to be constant; in order to realize bidirectional energy circulation between the motor and the clamping capacitor, two ends of the diode are reversely connected with a switching device in parallel, and the switching device is always in a conducting state when passing through the device;
step three, designing a crossing controller:
when the first step is switched to the traversing control, the system is switched from the normal working mode to the traversing mode; the voltage PI controller is connected with the motor q-axis current controller through the voltage loop, the voltage of the voltage loop PI controller is equal to the voltage of the clamping capacitor, and the voltage of the clamping capacitor is equal to the voltage of the motor q-axis current controller.
During the crossing period, the motor works in a generator state, the motor convention is adopted in the direction defined by each physical quantity of the motor, and a unified mathematical model of the motor and an inversion stage of the matrix converter is established:
in the formula, v d 、v q D, q-axis components of the stator voltage; i.e d 、i q D, q-axis components of the stator current; c (C) cla Is a clamping capacitor; v cla A clamping capacitor voltage; r is R L An energy discharging resistor which is a clamping capacitor;
the parameters of the voltage loop PI controller are designed by adopting the concept of active damping, and definition is defined
Wherein i is q1 B is the output of the voltage ring PI controller a Is a damping coefficient;
control of i during traversal d =0, will i q Substituting the expression of the (2) into the established unified mathematical model of the motor and the matrix converter inverter, and configuring the poles to the expected closed-loop bandwidth beta to obtain the voltage
Controlled object transfer function with respect to q-axis current:
and the transfer function of the controlled object is combined with the voltage loop PI controller, and parameters of the voltage loop PI controller are obtained through parameter setting, so that the design of the low-voltage ride-through controller is completed. The parameter setting method is a plurality of engineering design methods, which belong to common knowledge of the industry personnel (Yuan Lei, shen Jianqing, showcon, et al, design of a nonsingular terminal sliding mode observer of an inserted permanent magnet low-speed synchronous motor [ J ]. Physical school newspaper, 2013,62 (3): 030501.), and are not repeated here.
Examples:
the invention aims at an Indirect MC-surface-mounted PMSM (IMC-SPMSM) system, and a control block diagram of the system is shown in figure 2. The implementation method specifically comprises the following steps:
step one, detecting whether the voltage of a power grid drops, and judging whether to switch to pass through control:
the mathematical model of the SPMSM in the d-q coordinate system of rotor field orientation is shown below.
The stator voltage equation is
The stator flux linkage equation is
The torque equation and the motion equation are
T e ＝1.5pψ f i q (3)
Wherein u is d 、u q D, q-axis components of the stator voltage; i.e d 、i q D, q-axis components of the stator current; psi phi type d 、ψ q D, q-axis components of the stator flux linkage; l (L) s Is a stator inductance; psi phi type f Is the permanent magnet flux linkage amplitude; r is R s Is a stator resistor; p is the pole pair number; omega r For the electrical angular velocity, ω, of the motor rotor r =pn×pi/30, n being the motor speed; t (T) e 、T L The motor electromagnetic torque and the load torque are respectively; j is the moment of inertia.
In the IMC-SPMSM system, when the power grid voltage drops to a depth of h, the constraint relation which is to be met by the voltage applied by the motor stator end is that
Wherein U is the voltage amplitude of a stator phase; u (U) m Inputting a phase voltage amplitude for the IMC;
u gd 、u gq is the d, q axis component of the grid voltage.
The current flowing into the stator winding of the motor is limited by the maximum output current of IMC, namely
Wherein I is the stator current amplitude; i omax The maximum output current amplitude is IMC.
Substituting the formula (1) and the formula (2) into the formula (5) and solving to obtain the expression of the highest rotating speed of the motor which can stably run under different dropping depths and different loads, wherein the expression is as follows
In the method, in the process of the invention,
employing i d In the vector control mode of =0, the stator current amplitude i=t L /1.5pψ f 。
Employing i d Vector control=0, where the stator current vector I takes different magnitudes I (i.ltoreq.i omax ) The torque-rotation speed working range of the IMC-SPMSM system running in four quadrants under different voltage drop depths can be obtained by using the formulas (6) to (7), as shown in figure 3.
And detecting whether the grid voltage drops or not by using dq conversion and low-pass filtering methods. When the voltage of the power grid is detected to drop, whether the system is switched to the LVRT control mode or not is judged by comparing the original steady-state working point of the system with the torque-rotating speed operation range of the system after the voltage drops, and the judgment principle block diagram is shown in figure 4. In the figure, F sag Is a voltage drop signal; f (F) RT The switching signal is controlled for system traversal.
Step two, design of low voltage ride through operation auxiliary circuit
During the crossing period, the clamping capacitor is used as an energy conversion mechanism, and the crossing is realized by maintaining the voltage of the clamping capacitor to be constant; the diode in the prior system topological structure clamping circuit only has unidirectional conductivity, and in order to realize bidirectional energy circulation between the motor and the clamping capacitor, two ends of the diode are reversely connected with a switching device S in parallel 2 And the switching device is always in an on state at the crossing device as shown in fig. 2.
Step three, design of low voltage ride through controller
The method of the invention realizes the crossing by maintaining the voltage of the clamping capacitor constant. To design a voltage loop controller, a unified mathematical model of the inverter stage and SPMSM in fig. 2 is first established. During crossing S 1 、S 2 Is always in a conducting state, and the conducting voltage drop is ignored in the modeling process. A unified model is described by adopting a switching function method, a motor adopts motor convention, power device loss is ignored, and the motor is connected with AC and DC through kirchhoff voltage lawThe power balance of the flow side is carried out, and the unified model of the inversion stage and the SPMSM in the d-q coordinate system is obtained through coordinate transformation
Wherein C is cla Is a clamping capacitor; v cla A clamping capacitor voltage; r is R L An energy discharging resistor which is a clamping capacitor;
in order to maintain the voltage of the clamping capacitor constant during the passing period, the motor works in a generator state, and the energy emitted by the motor is consumed in R L Above, it can be seen that the motor is operated in a constant power state, and the electromagnetic power of the motor can be expressed as P em ＝T e ×ω r And/p. The motor speed gradually drops during the passing period, so that the SPMSM electromagnetic torque T e Increasing. Due to T e And i only q In order to reduce copper loss of motor during crossing, i is adopted d Control =0.
The motor works in a constant power state during the passing, and when the copper of the motor is ignored, the power P emitted by the motor 2 ＝P em Then
P 2 ＝1.5ψ f i q ω r (9)
The parameters of the voltage loop PI controller are designed by adopting the concept of active damping, and definition is defined
Wherein i is q1 The output of the voltage loop PI controller; b (B) a Is the damping coefficient. Will i q Substituting the obtained product into a unified model type (8)
The pole of formula (10) is configured to a desired closed loop bandwidth beta, and a voltage can be obtained
Controlled relative to q-axis currentThe object transfer function is
By comparing equation (10) with equation (11), the damping coefficient B can be obtained a ＝(2/R L -βC cla )/3u q 。
Adopts the traditional PI regulator, and adopts the transfer function expression as
Can get +.>
The block diagram of the voltage closed-loop control obtained by this combination (10) is shown in fig. 5.
Wherein,,
a reference value that is the square of the clamp capacitance voltage; k (K) pu And K iu The proportional gain and the integral coefficient of the voltage loop PI controller are respectively, the current loop is equivalent to a first-order inertia link, T i Is the current loop time constant.
Through PI parameter setting, K can be obtained pu And K iu Is a value of (2).
The low voltage ride through control method of the matrix converter system has been experimentally verified on a 6kW prototype. The input voltage drop depth of the system is 10%, the motor operates at 300r/min, LVRT experiment waveforms under the conditions of 0 N.m and 15 N.m of loads are respectively shown in figures 6-7, the input voltage drop depth of the system is 20%, the motor operates at 300r/min, and LVRT experiment waveforms under the conditions of 0 N.m and 15 N.m of loads are respectively shown in figures 8-9.
From fig. 6-9, it can be seen that the experimental process is divided into 3 parts, (1) a steady state operation phase of the system before failure, (2) a LVRT transition phase, and (3) a system re-acceleration phase after recovery of the grid voltage.
When the input voltage of the system drops, the system is switched from the normal control mode to the LVRT control strategy through the processes of voltage detection, judgment and the like. The voltage of the power grid drops by 10 percent (20 percent) during the passing period, the voltage reference value of the clamping capacitor drops by 10 percent (20 percent) on the basis of the steady-state value, the waveform can show that the voltage value is maintained near the expected value, the overcurrent phenomenon does not occur in the system, i d Maintain around 0, i q Is negative. Analysis shows that the SPMSM operates as a generator to give C clamp Supplying power and maintaining v cla Is constant. The motor speed is reduced substantially at constant acceleration, while as can be seen from equation (9), i as the speed is reduced q The absolute value is gradually increasing. When the grid voltage is restored, the motor is quickly started from a non-zero rotating speed and a non-zero magnetic flux state. The motor is always in a controlled state in the whole traversing process, and no overcurrent phenomenon occurs. It can be seen that the control method of the present invention improves the low voltage ride through capability of the matrix converter system.
Although the embodiment of the present invention is described with reference to the surface-mounted permanent magnet synchronous motor, the present invention is not limited to the above-described specific embodiments, which are merely illustrative, but not restrictive, and many modifications, such as low voltage ride through method under driving of matrix converters of dc motor, asynchronous motor, and other synchronous motor, may be made by those skilled in the art based on the teaching of the present invention and the known technology in the art, without departing from the spirit of the present invention, which are all within the scope of the present invention.
Claims (3)
1. A control method for improving the low voltage ride through capability of a matrix converter system is characterized by comprising the following steps:
step one, detecting whether the voltage of a power grid drops, and judging whether to switch to pass through control: detecting whether the power grid voltage drops by sampling and calculating the three-phase voltage of the power grid in real time, calculating a maximum rotating speed value of a system which can stably run under a motor load after the power grid voltage drops under the working condition that the load is the motor load when the power grid voltage drops, switching the system into a traversing control mode if the rotating speed of the motor is greater than the maximum rotating speed value, otherwise, continuing to run according to the control mode before failure;
step two, designing a low voltage ride through operation auxiliary circuit: during the crossing period, the clamping capacitor is used as an energy conversion mechanism, and the crossing is realized by maintaining the voltage of the clamping capacitor to be constant; the two-way circulation of energy is carried out between the motor and the clamping capacitor during the passing period, two ends of a diode in the clamping circuit of the topological structure of the matrix converter system are connected in anti-parallel with a switching device, and the switching device is always in a conducting state during the passing period;
step three, designing a low voltage ride through controller: the low voltage ride through controller is structured such that when switching to ride through control by step one, the system is switched from a normal operating mode to a ride through mode; the voltage loop PI controller is used for realizing the crossing in a mode of maintaining the voltage of the clamping capacitor to be constant, the input of the voltage loop PI controller is the difference value between the square of the voltage of the clamping capacitor and the reference value of the square of the voltage of the clamping capacitor, subtracting the square of clamping capacitor voltage with the damping coefficient multiplied by the output of the voltage ring PI controller as an input reference value of the motor q-axis current controller, wherein the damping coefficient is B a ＝(2/R L -βC cla )/3u q Wherein R is L The energy-discharging resistor of the clamping capacitor, C cla For clamping capacitance u q Is the q-axis component of the stator voltage.
2. The method for controlling a matrix converter system to improve low voltage ride through capability according to claim 1, wherein in the first step, when the grid voltage drops, a drop depth h is calculated:
in U RMS For sampling the obtained effective value of the power grid voltage, U RMS_N Is in the normal state of the power gridAn effective value;
calculating the highest rotating speed n of the motor capable of stably running under different dropping depths and different loads after the voltage of the power grid drops max Is represented by the expression:
wherein R is s The resistor is a motor stator resistor; l (L) s The stator inductance is the motor stator inductance; psi phi type f The permanent magnet flux linkage amplitude value of the motor; n is the motor rotation speed; p is the pole pair number of the motor; t (T) L Is the motor load; u (U) m Inputting phase voltage amplitude values for the matrix converter;
The motor is set to stably operate at the rotating speed of n r/min before the power grid faults, and the load is T L Under the working condition of N.m, calculating T after the voltage of the power grid drops L Maximum rotational speed value n at which the system can be operated under load max If n>n max And switching the system to a crossing control mode, otherwise, continuing to operate the system according to the control mode before the fault.
3. The method for controlling a matrix converter system to improve low voltage ride through capability according to claim 1, wherein in the third step, the method for designing the low voltage ride through controller comprises:
during the crossing period, the motor works in a generator state, the motor convention is adopted in the direction defined by each physical quantity of the motor, and a unified mathematical model of the motor and an inversion stage of the matrix converter is established:
in the formula, v d 、v q D, q-axis components of the stator voltage; i.e d 、i q D, q-axis components of the stator current; c (C) cla Is a clamping capacitor; v cla A clamping capacitor voltage; r is R L An energy discharging resistor which is a clamping capacitor;
the parameters of the voltage loop PI controller are designed and defined by adopting the concept of active damping
Wherein i is q1 B is the output of the voltage ring PI controller a Is a damping coefficient;
control of i during traversal d =0, will i q Substituting the expression of the (2) into the established unified mathematical model of the motor and the matrix converter inverter, and configuring the poles to the expected closed-loop bandwidth beta to obtain the voltage
Controlled object transfer function with respect to q-axis current:
and the transfer function of the controlled object is combined with the voltage loop PI controller, and parameters of the voltage loop PI controller are obtained through parameter setting, so that the design of the low-voltage ride-through controller is completed.
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