WO2022041363A1

WO2022041363A1 - Power electronic device control initialization method

Info

Publication number: WO2022041363A1
Application number: PCT/CN2020/116987
Authority: WO
Inventors: 李周; 詹若培
Original assignee: 东南大学溧阳研究院; 东南大学
Priority date: 2020-08-26
Filing date: 2020-09-23
Publication date: 2022-03-03
Also published as: CN112086989B; CN112086989A

Abstract

A power electronic device control initialization method, comprising: (1) before a target control strategy starts up, measuring the electric quantity from an actual system to carry out state acquisition, collecting real-time electric quantity data, and obtaining setting value information required by a control loop; (2) according to the setting value information required by the control loop in step (1), setting an initial value of an integrator in the control loop, and locking the initial value of the integrator before starting up control; and (3) setting a target control strategy reference value as an electric quantity measurement value obtained in step (1); and a control system sends a control start signal to a modulation and valve group control to start the control strategy. By means of setting the initial value of the integrator in the control system and controlling a target reference value when the control strategy is initialized, the method can reduce circuit impact, improve the rapidity and stability with which the power electronic device controls during start-up, and provide more application scenarios for the power electronic device. The method can be widely applied in the field of power electronics.

Description

A kind of power electronic equipment control initialization method

technical field

The invention belongs to the technical field of power electronics, and relates to a control initialization method for power electronic equipment.

Background technique

With the development of power electronic technology, power electronic equipment such as VSC-HVDC (high voltage direct current transmission technology based on voltage source converter), DFIG (double-fed induction motor), SVC (static reactive power compensator), STATCOM (static Synchronous compensator), etc., have been widely used in power systems. In control strategies for these power electronic devices, integrators are often used in the control loop. The zero-error control is realized in different control strategies through the integrator, and different control objectives are achieved. During the startup of the valve control of the equipment, or in the process of switching the control strategy, if the control strategy is started with the same settings as the normal operation, it will have a great impact, overvoltage and overcurrent will easily occur, and the system stability will be difficult to achieve. maintain. In order to ensure the stability of the control start-up process, the current and voltage need to be limited within a certain range, and at the same time, the start-up speed of the control strategy needs to be improved. Combining the above two points, the control strategy of power electronic equipment needs a suitable control initialization method.

In order to realize the control strategy initialization, the traditional control initialization method first sets the control target reference value to be the same as the actual value to reduce the influence of control startup, and after the system is stabilized, the reference value will be changed to the ideal value. At the same time, since the initial value of the integrator is unknown before the control strategy for the power electronic device starts, it will bring unpredictable problems, so the output value of the integrator needs to be reset to zero. However, clearing the initial value of the integrator is one of the reasons for the circuit shock during the control start-up process, which leads to a larger shock at the start of some control strategies, thus increasing the difficulty of control start-up. This is because the initial value of the integrator is cleared, and the output value of the integrator is zero, which causes the control quantity to be different from the corresponding electrical quantity in the actual circuit.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention provides a control initialization method for power electronic equipment. In the control initialization method, the initial value of the integral is considered according to the actual circuit model to reduce the impact caused by the start of the control strategy, which can improve the control of power electronic equipment. The strategy's startup stability, while improving the startup speed, enables power electronic devices to have more application scenarios.

In order to achieve the above object, the present invention provides the following technical solutions:

A power electronic equipment control initialization method, comprising the following steps:

(1) Before the target control strategy is started, state acquisition is carried out from the actual system measurement electrical quantity, and the real-time electrical quantity data related to the control part is collected; through the real-time electrical quantity data, the setting value information required by the control loop is obtained;

(2) According to the setting value information required by the control loop in step (1), realize the setting of the initial value of the integrator in the control loop, and lock the initial value of the integrator before starting the control;

(3) The target control strategy reference value is set as the electrical quantity measurement value obtained in step (1), and the control system sends the control start signal to the modulation and valve group control to start the control strategy.

Further, the following steps are also included:

(5) When the control strategy is started, the lock on the initial value of the control loop integrator is released, the control loop works normally, and the next initialization can be performed thereafter.

Further, in the step (2), after the initial value of the integrator is locked, the initial value of the integrator in the control loop is equal to the set value of the integrator.

Further, the setting value information required by the control loop includes: the control target reference value and the setting value of the integrator.

Further, the activation of the control strategy includes: activation of the control strategy when the device valve is unlocked and switching of the device control strategy.

Further, the power electronic equipment includes: STATCOM static synchronous compensator, SVC static reactive power compensator, TCSC controllable series compensator, UPFC unified power flow controller, DFIG double-fed induction motor, and HVDC high-voltage direct current transmission system.

Further, when applied to the amplitude and phase control of VSC, the initial value of the integrator is set as follows:

where Us is the AC voltage at the PCC point of the converter, Ps and Qs are the active power and reactive power at the PCC point, respectively, and X is the commutation impedance.

Further, the output of the integrator is:

In the formula, K _I and K _P are the proportional coefficients set by the integrator and the proportional link, the time t ₀ is the unlocking time, the time t ₁ is a certain time after the actual operation, and U _sref is the reference value of the AC voltage.

Further, when applied to the grid-side control structure of the DFIG doubly-fed wind turbine, the four integrators are set in the following ways:

Directly measure i _sdref (t ₀ ), i _sqref (t ₀ ), and calculate U _kd (t ₀ ) and U _kq (t ₀ ) by the following formulas:

In the formula, P _s is the active power on the grid side of the converter, U _s is the RMS AC voltage on the grid side of the converter, U _c is the RMS AC voltage at the PCC point, t ₀ is the start time of the control strategy, and Q _s is the grid side Reactive power, i _sd and i _sq are the d and q axis components of the grid-side AC current respectively, X _c is the equivalent impedance of the commutation inductance, and R is the equivalent resistance of the converter.

Further, the outputs of the four proportional integrators satisfy:

In the formula, t ₀ is the start time of the control strategy, t ₁ is a certain time when the control strategy is in normal operation, V _dc is the DC voltage of the converter, V _dcref is the DC voltage reference value, Q _sref is the reactive power reference value, i _sdref is the d-axis current reference value, and i _sqref is the q-axis current reference value.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

The invention realizes that when the control strategy is initialized, the initial value of the integrator in the control system and the reference value of the control target are adjusted, the circuit impact is reduced, the rapidity and stability of the power electronic equipment control during startup are improved, and the power electronic equipment is improved. It provides more application scenarios and can be widely used in the field of power electronics.

Description of drawings

1 is a schematic diagram of a power electronic device control initialization method of the present invention;

Fig. 2 is the flow chart of the power electronic equipment control initialization method of the present invention;

3 is a schematic diagram for verifying the flexible straight grid-connected system of the microgrid of the present invention;

Figure 4 is a schematic diagram of the amplitude and phase control of the flexible DC transmission;

Fig. 5 is a simulation result diagram for verifying the microgrid via the flexible straight grid-connected system of the present invention, wherein (a) is the AC busbar voltage (effective value) of the microgrid, (b) is the frequency of the microgrid AC bus, and (c) is the The active power of the PCC point of VSC1, (d) is the a-phase current of VSC1, (e) is the DC voltage of VSC1;

6 is a schematic diagram for verifying the grid-side control of the doubly-fed fan of the present invention;

Figure 7 shows a control loop with an integrator.

detailed description

The technical solutions provided by the present invention will be described in detail below with reference to specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

The invention provides a control initialization method for power electronic equipment. When the control strategy of the power electronic equipment needs to be started, in order to reduce the impact of the start-up process, it is adopted before the target control strategy is started to perform initialization. One or more control loops of the power electronic equipment control system include an integrator, which uses a certain control strategy to control the valve stage, thereby realizing the corresponding functions of the power electronic equipment. A control loop with an integrator is generally shown in Figure 7. In the figure, the input variable r _n (t) of a control loop of the control system obtains the output variable c _n (t) through the integrator, and its output value is continuously integrated from the initial control time, and is related to the initial value of the integration. The startup of the power electronic equipment control strategy includes the process of starting the control strategy when the valve control of the equipment is unlocked, and switching the equipment control strategy. It should be noted that the startup refers to the startup of a certain control strategy, and does not mean the startup of the power electronic device. The power electronic device may be in an operating state, and the operating state does not necessarily need to be a steady state.

Example 1:

Referring to Figure 1 and Figure 2, the power electronic equipment control initialization method provided in this example includes the following steps:

(1) Before the target control strategy is started, the state is obtained from the measured electrical quantities of the actual system, and the real-time electrical quantity data related to the control part is collected. Through the real-time electrical quantity data, the setting value information required by the control loop is obtained. It should be noted that the real-time electrical quantity data is the electrical quantity necessary for the original control, and there is no need to add a new measurement interface, and the system collects the actual electrical quantity value at all times. The setting value information required by the control loop, including the control target reference value and the setting value of the integrator;

(2) According to the setting value information required by the control loop in (1), realize the setting of the initial value of the integrator in the control loop, and lock the initial value of the integrator before starting the control. This operation can ensure the integrator in the control loop. The output value of (t ₀ ) is equal to the initial value, that is, the setting value of the integrator, which can ensure that there is no deviation between the output value and the actual value when the control starts. The initial value of the integrator in the control loop is set, because the output of the integrator satisfies:

In the formula, t ₀ is the starting time of the control strategy, _t ₁ is a certain time when the control strategy is running normally, and rn (τ) is the input of the integrator. c _n (t ₀ ) is the initial value that the integrator needs to set, and it usually needs to be calculated according to the actual circuit and mathematical model of the system.

(3) Set the reference value of the target control strategy to the measured value of the electrical quantity obtained in (1). This operation can ensure that the deviation of the control loop input is 0. The control system sends the control start signal to the modulation and valve group control to start the control strategy;

(4) When the control strategy is started, the lock on the initial value of the control loop integrator is released, the control loop works normally, and the next initialization can be performed thereafter. It should be noted that the setting of the initial value of the integrator only sets and locks the initial value, and only takes effect at the moment of startup. Even if the lock is not released after startup, the operation will not be affected. It should be noted that at this time, the control target reference value of the control strategy is still equal to the measured value when the control is started. It is necessary to modify the reference value to the ideal value when the control strategy is gradually stabilized.

Application Example 1: The present invention will be further described in detail below with reference to specific embodiments, which are to explain rather than limit the present invention.

Referring to FIG. 3, it is an application of the present invention in the flexible direct current transmission VSC-HVDC, and FIG. 4 is a block diagram of amplitude and phase control. The figure shows a double-ended VSC-HVDC system, and the left end is an equivalent microgrid system, which includes generator sets, motor sets, and fixed loads and energy storage devices. The AC bus voltage is 500kV, the voltage source converter VSC AC voltage is 255kV, the DC voltage is ±250kV, and the DC capacitance is 500uF. The equivalent generator set outputs 375MW of active power, the equivalent motor set consumes 150MW of active power, and the fixed load is 225MW. At 10s, the VSC-HVDC is put into operation, the VSC at the micro grid end is controlled by amplitude and phase, and the VSC at the main grid end is controlled by constant DC voltage. Perform PSCAD simulation according to the model to obtain the microgrid AC bus and the dynamic characteristics of the microgrid side VSC, see Figure 5.

According to the control initialization method of the present invention, the AC bus voltage of the micro-grid is measured before 10s, and the phase and AC amplitude required for the amplitude-phase control are obtained as the control target reference value of the control strategy. According to the voltage of 229kV, the reference value U _sref of the AC voltage at the PCC point controlled by the amplitude and phase is set to 229kV, and the initial value of the integrator is set as follows:

where Us is the AC voltage at the PCC point of the converter, Ps and Qs are the active power and reactive power at the PCC point, respectively, and X is the commutation impedance. In this example, Ps=0, Qs=15MVar, X is set to 0.15pu, and the actual calculated value is 10.58ohm, so the AC outlet side voltage of the converter U _c (t ₀ )=228.3kV. At this time, the amplitude and phase control output is:

In the formula, K _I and K _P are the proportional coefficients set by the integrator and the proportional link, the time t ₀ is the unlocking time, the time t ₁ is a certain time after the actual operation, and U _sref is the reference value of the AC voltage. The AC outlet side voltage of the VSC is calculated or directly measured from the above process, and this voltage is used as the initial value of the amplitude-phase control integrator, and the initial value of the integrator is locked before the control strategy is started. At 10s, a control start signal is sent to the control loop and the VSC valve stage control, and then the initial value of the integrator is unlocked. It should be noted that the setting of the initial value of the integrator is only to set and lock the initial value, and only at startup It works instantly, and it will not affect the operation even if it is not unlocked after startup. It can be seen in Figure 5 that the unlocking of the VSC-HVSC is completed to stable operation in only 2.5s. During this process, the DC voltage oscillates slightly, the maximum drop is about 480kV, and the AC voltage is almost unchanged. The large change in active power is caused by the fact that VSC-HVDC guarantees a frequency of 50Hz in order to achieve amplitude and phase control. It can be seen that the original frequency of the microgrid is 49.8Hz. After connecting to the VSC, it provides 75MW of active power to the microgrid. The frequency is stable at 50Hz, the whole process is fast and smooth, the current has no overcurrent problem, and the voltage has no overvoltage problem. In addition, for the scenario where the microgrid is connected to the grid through VSC-HVDC, if the amplitude and phase control is adopted, and the traditional control strategy initialization method is used to connect to the grid, since the integrator is cleared, the AC outlet voltage amplitude and phase of the converter will be the same as the parallel one. If there is a large gap between the network points, it will cause system oscillation or even cause the system to collapse, making it difficult to realize grid connection. However, according to the above simulation, the present invention can realize a good micro-grid grid connection process under the control of VSC amplitude and phase, which reflects the function of the present invention providing more application scenarios for power electronic equipment.

Application Example 2:

Referring to Figure 6 for the grid-side control structure of the DFIG doubly-fed wind turbine, according to the grid-side control structure, when the doubly-fed wind turbine is in the process of starting, the converter needs to be unlocked, and the control strategy needs to be initialized. According to the initialization method of the present invention, its initialization process is as follows:

(1) Before starting the grid-side control strategy, measure the active power, reactive power, AC voltage and AC current on the grid side of the fan, so as to obtain the setting value information required by the control loop. These data are the electrical quantities necessary for the original control, and there is no need to add a new measurement interface.

(2) According to the setting value information required by the control loop in (1), realize the setting of the initial value of the integrator in the control loop, and lock the initial value of the integrator before starting the control. This operation can ensure the integrator in the control loop. The output value is equal to the actual value, and it can ensure that there is no deviation between the output value and the actual value when the control start occurs. For the grid-side control loop of the DFIG shown in Figure 6, the outputs of the four proportional integrators satisfy:

In the formula, t ₀ is the starting time of the control strategy, t ₁ is a certain time when the control strategy is running normally, V _dc is the DC voltage of the converter, Q _s is the grid-side reactive power, i _sd and i _sq are the grid-side reactive power, respectively The d and q-axis components of the AC current, V _dcref is the DC voltage reference value, Q _sref is the reactive power reference value, is _sdref is the d-axis current reference value, and i _sqref is the q-axis current reference value. During control initialization, i _sdref (t ₀ ) and i _sqref (t ₀ ) can be directly measured, and U _kd (t ₀ ) and U _kq (t ₀ ) need to be calculated. The calculation formula is:

In the formula, P _s is the active power on the grid side of the converter, U _s is the rms value of the AC voltage on the grid side of the converter, U _c is the rms value of the AC voltage at the PCC point, X _c is the equivalent impedance of the commutation inductance, and R is the commutation inductance. Current equivalent resistance. The tuning of the integrator in the initialization process is completed according to the above procedure.

(3) Set the reference value of the converter DC voltage and grid-side reactive power to the measured value of the electrical quantity obtained in (1) to ensure that the deviation of the control loop input is 0. The control system sends the control start signal to the modulation and valve group control to start the control strategy;

(4) When the control strategy is started, the lock on the initial value of the control loop integrator is released, the control loop works normally, and the next initialization can be performed thereafter. It should be noted that the setting of the initial value of the integrator only sets and locks the initial value, and only takes effect at the moment of startup. Even if the lock is not released after startup, the operation will not be affected. At this time, the control target reference value of the control strategy is still equal to the measured value when the control is started, and when the control strategy is gradually stabilized, the reference value is modified to the standard value.

The above two application embodiments are only examples and should not be used as limitations of the present invention. The power electronic devices to which the present invention can be applied include but are not limited to the following devices shown in Table 1:

Table 1

The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims

A power electronic equipment control initialization method, characterized in that it includes the following steps:

(1) Before the target control strategy is started, the state is obtained from the actual system measurement electrical quantity, and the real-time electrical quantity data related to the control part is collected; through the real-time electrical quantity data, the setting value information required by the control loop is obtained;

(2) According to the setting value information required by the control loop in step (1), realize the setting of the initial value of the integrator in the control loop, and lock the initial value of the integrator before starting the control;

(3) The target control strategy reference value is set as the electrical quantity measurement value obtained in step (1), and the control system sends the control start signal to the modulation and valve group control to start the control strategy.
The power electronic device control initialization method according to claim 1, further comprising the following steps:

(4) When the control strategy is started, the lock on the initial value of the control loop integrator is released, the control loop works normally, and the next initialization can be performed thereafter.
The power electronic equipment control initialization method according to claim 1 or 2, characterized in that, after the initial value of the integrator is locked in the step (2), the initial value of the integrator in the control loop is equal to the setting value of the integrator.
The power electronic equipment control initialization method according to claim 1 or 2, wherein the setting value information required by the control loop includes: a control target reference value and a setting value of the integrator.
The power electronic device control initialization method according to claim 1 or 2, wherein the control strategy activation includes: control strategy activation when the device valve control is unlocked and switching of the device control strategy.
The power electronic equipment control initialization method according to claim 1 or 2, wherein the power electronic equipment comprises: STATCOM static synchronous compensator, SVC static reactive power compensator, TCSC controllable series compensator, UPFC unified power flow Controller, DFIG double-fed induction motor, HVDC high-voltage direct current transmission system.
The power electronic equipment control initialization method according to claim 1 or 2 is characterized in that, when applied in the amplitude and phase control of the VSC, the initial value of the integrator integral is set as follows:

where Us is the AC voltage at the PCC point of the converter, Ps and Qs are the active power and reactive power at the PCC point, respectively, and X is the commutation impedance.
The power electronic equipment control initialization method according to claim 1 or 2, wherein the output of the integrator is:

In the formula, K I and K P are the proportional coefficients set by the integrator and the proportional link, the time t 0 is the unlocking time, the time t 1 is a certain time after the actual operation, and U sref is the reference value of the AC voltage.
The power electronic equipment control initialization method according to claim 1 or 2 is characterized in that, when applied in the grid-side control structure of the DFIG doubly-fed wind turbine, the four integrators are set in the following ways:

Directly measure i sdref (t 0 ), i sqref (t 0 ), and calculate U kd (t 0 ) and U kq (t 0 ) by the following formulas:

In the formula, P s is the active power on the grid side of the converter, U s is the RMS AC voltage on the grid side of the converter, U c is the RMS AC voltage at the PCC point, t 0 is the start time of the control strategy, and Q s is the grid side Reactive power, i sd and i sq are the d and q axis components of the grid-side AC current respectively, X c is the equivalent impedance of the commutation inductance, and R is the equivalent resistance of the converter.
The power electronic equipment control initialization method according to claim 1 or 2, wherein the output of the four proportional integrator satisfies:

In the formula, t 0 is the start time of the control strategy, t 1 is a certain time when the control strategy is in normal operation, V dc is the DC voltage of the converter, V dcref is the DC voltage reference value, Q sref is the reactive power reference value, i sdref is the d-axis current reference value, and i sqref is the q-axis current reference value.