JP6629077B2 - Pseudo-synchronous force-voltage converter and its controller - Google Patents

Description

  The present invention relates to a voltage-type converter that converts DC power into AC power and supplies AC power to a power system.

  In a power system, the inertia of a synchronous machine plays an important role for stable operation of the system. That is, the synchronous machine contributes to stable operation of the power system by operating in synchronization with the power system by the synchronizing force.

  On the other hand, renewable energies such as solar power generation systems are being introduced into electric power systems. Basically, renewable energy is temporarily stored, converted into AC power by an inverter, and supplied to a power system. In the future, it is expected that a large number of power electronics devices (voltage-type converters) that convert renewable energy into AC power will be connected to the power system. However, such power electronics devices, unlike synchronous machines, have essentially no inertia or synchronization power. For this reason, there is a concern that the synchronizing power in the power system will decrease as the number of power electronics devices increases. Therefore, a method has been proposed in which a power electronic device simulates the behavior of a synchronous machine to stabilize a power system with a reduced synchronizing force (for example, see Non-Patent Documents 1 and 2).

Keita Noguchi, Yutaka Sasaki, Yoshifumi Zoka and Naoto Yurino, "System Stabilization Control Using Synchronous Power Inverter", Proceedings of the 2013 Annual Conference of the China Association of Electrical and Information Engineers, pp. 67-68, 2013 Shinya Sekizaki, Yuki Nakamura, Yutaka Sasaki, Yoshifumi Zoka, Naoto Yurino, "Construction of Experimental System for System Stabilization Using Inverters" . 59-60, 2014

  A conventional voltage-type converter that simulates the behavior of a synchronous machine uses a PLL (Phase Locked Loop) for synchronizing with a system. However, the voltage converter of the PLL system has a problem that it is unstable in an area (weak grid) far from a large-scale power supply.

  In view of the above problems, an object of the present invention is to make a voltage type converter simulate the behavior of a synchronous machine without using a PLL.

  A pseudo-synchronous force-voltage converter and its controller according to one aspect of the present invention are as follows. That is, the controller of the voltage-type converter that converts the DC power to the AC power and supplies the AC power to the power system has a governor command for droop-controlling the voltage-type converter so that the output frequency of the voltage-type converter becomes the target frequency. A governor that controls the value, and an output that calculates the output voltage phase of the voltage-type converter from the command value and the measured value, the target frequency, and the governor command value of the active power output of the voltage-type converter based on the fluctuation equation of the synchronous machine. A voltage phase calculation unit, a regulator unit that controls a modulation rate of the voltage-type converter so that a voltage of the power system becomes a target voltage, and a pulse modulation signal based on the modulation rate and the output voltage phase, and generates the pulse modulation signal. Switching control of the switching element in the inverter in the voltage-type converter according to It is obtained by a control unit.

  According to this, the voltage type converter can be controlled based on the oscillation equation of the synchronous machine, and the governor and the regulator can maintain the frequency and voltage of the power system.

  In the above controller, the inverter may be a single-phase inverter.

  According to this, the controller can control the single-phase voltage type converter.

  In the above controller, the output voltage phase calculation unit may calculate an actual measured value of the active power output of the voltage type converter from each measured value of the DC voltage and the DC current on the input side of the inverter.

  According to this, it is possible to easily and stably calculate the actual measured value of the active power output of the voltage type converter.

  In addition, the pseudo-synchronous force-voltage converter converts a power storage device, a DC / DC converter that converts a DC voltage supplied from the power storage device into an arbitrary DC voltage, and an output voltage of the DC / DC converter into an AC voltage. It is provided with an inverter and the above-mentioned controller which controls switching of a switching element in the inverter.

  According to the present invention, it is possible to simulate the behavior of a synchronous machine in a voltage type converter without using a PLL, and it is possible to operate stably even in a weak grid.

1 is a configuration diagram of a pseudo-synchronous force-voltage converter according to an embodiment of the present invention. Control block diagram of controller of pseudo-synchronous force-voltage converter Schematic diagram of a single-phase microgrid for verification Graph showing the output frequency of each single-phase VSC in a single-phase microgrid Graph showing the output voltage of each single-phase VSC in a single-phase microgrid Graph showing the active power output of each single-phase VSC in a single-phase microgrid Schematic diagram of three-phase microgrid for verification Graph showing the output frequency of each single-phase VSC in a three-phase microgrid Graph showing the output voltage of each single-phase VSC in a three-phase microgrid Graph showing active power output of each single-phase VSC in a three-phase microgrid

  Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, an unnecessary detailed description may be omitted. For example, a detailed description of well-known matters and a repeated description of substantially the same configuration may be omitted. This is to prevent the following description from being unnecessarily redundant and to facilitate understanding of those skilled in the art.

  The inventors provide the accompanying drawings and the following description so that those skilled in the art can fully understand the present invention, and these are intended to limit the subject matter described in the claims. is not.

≫Configuration of quasi-synchronous force-voltage converter≫
FIG. 1 shows a configuration of a pseudo-synchronous force-voltage converter 10 according to an embodiment of the present invention. The “pseudo-synchronous force voltage type converter” refers to a voltage type converter (VSC: Voltage Source Converter) which simulates the behavior of a synchronous machine to have a pseudo-synchronous force. For the sake of convenience, the pseudo-synchronous force-voltage converter 10 is hereinafter simply referred to as VSC10.

  The VSC 10 is a power electronics device that converts renewable energy (RES) 11 into AC power and supplies AC power to a power system. For example, the VSC 10 includes a power storage device 1, a DC / DC converter 2, an inverter 3, and a controller 4.

  The power storage device 1 is a device that stores power supplied from the RES 11 and supplies power to the DC / DC converter 2. The power storage device 1 can be composed of, for example, an electric double layer capacitor, a lithium ion capacitor, a lead battery, or the like.

  DC / DC converter 2 receives power from RES 11 and power storage device 1, converts the power to an arbitrary DC voltage, and outputs the DC voltage. If the power supplied by the RES 11 is smaller than the output power of the DC / DC converter 2, insufficient power is supplied from the power storage device 1. Conversely, if the supply power of the RES 11 is larger than the output power of the DC / DC converter 2, the surplus power is charged to the power storage device 1.

  The inverter 3 has a plurality of IGBTs (Insulated Gate Bipolar Transistors) 31. The switching operation of these IGBTs 31 converts the DC voltage supplied from DC / DC converter 2 into an AC voltage. More specifically, inverter 3 is a single-phase inverter, and converts the output voltage of DC / DC converter 2 into a single-phase AC voltage. That is, VSC 10 is a single-phase VSC. Therefore, the VSC 10 can be connected to an arbitrary phase such as a micro grid. The AC output of the inverter 3 is filtered by a filter 12 to remove a harmonic voltage and a harmonic current, further transformed into an arbitrary AC voltage by a transformer 13 and supplied to a power system (not shown).

  The controller 4 generates a pulse-modulated gate signal and controls the switching of each IGBT 31 in the inverter 3. The controller 4 performs various digital operations according to the oscillation equation of the synchronous machine as described below, and can be realized by a CPU (Central Processing Unit) or the like. The control system of the controller 4 includes a governor for maintaining the frequency of the system and an AVR (Automatic Voltage Regulator) for maintaining the system voltage, and forms a pseudo inertia (virtual inertia) generation loop.

(Virtual inertia generation loop including governor)
The behavior of a synchronous machine, which is essentially a three-phase device, cannot be directly applied to a single-phase control system. In order to imitate the behavior of the synchronous machine in the single-phase VSC, it is assumed that one of the windings of the synchronous machine is connected to a single-phase system and the operation is performed with the other windings opened. In this case, the actual synchronous machine cannot maintain the synchronous operation, but the VSC enables the synchronous operation by the operation based on the internal dynamic rotation system model. In designing a new single-phase VSC control system based on this idea, a model based on the oscillation equation is adopted. The three-phase VSC control system can be constructed in a similar manner. Here, the fluctuation equation including the governor linearized near the equilibrium point of the VSC operation is given by equations (1) to (4).

Here, Δθ _VSC is a minute variation of the VSC output voltage phase from the equilibrium point, M _VSC is a pseudo inertia constant, _DVSC is a pseudo damping coefficient, K _VSC is a pseudo synchronization coefficient, P _m is a pseudo mechanical input, and P _m is a pseudo mechanical input. _e is the frequency of the electrical _{output, P gov} is governor _{output, K gov} is _{Gabanagein, T gov} the governor time constant, omega _ref is VSC frequency command value, omega _VSC is VSC output voltage. Equations (3) and (4) representing governor operation have a first-order lag characteristic, and the governor output P _gov is obtained from the deviation of ω _VSC from ω _ref .

In equations (1) to (4), the control system requires only _Pe as an input signal. Output voltage phase theta _VSC is calculated based on P _e computed by the sensor information. A stable synchronous operation of three-phase VSC and single-phase VSC, respectively, is possible to accurately calculate a three-phase and single-phase instantaneous effective power output P _e becomes important. For three-phase VSC, the instantaneous active power _{P e} can be easily calculated by dq / abc conversion. A method for calculating the instantaneous active power output of the single-phase VSC will be described below.

(DC side measurement method)
Since the instantaneous active power calculated by a single-phase voltage and current having an AC frequency of f _1ph [Hz] oscillates at 2f _1ph [Hz], it is difficult to stably calculate the instantaneous active power output of the single-phase VSC. It is. Further, when the microgrid is connected to or disconnected from the power system, the voltage phase jumps instantaneously. This phase jump also causes oscillation of the VSC output active power. (1) causes a variation of the active power output P variation of _e is [Delta] [theta] _VSC in formula, in order to unstable synchronous operation of VSC, single phase in order to suppress adverse effects on VSC operation by active power output variation VSC the active power output P _e of measuring the DC side. P _e is calculated as the product of the DC voltage V _DC of the VSC and the DC current I _DC P _e = V _DC I _DC . P _e is to include the switching noise in the power device, it employs a low pass filter, handle that removes switching noise as active power output.

(AVR)
The AVR for maintaining the VSC output voltage V _VSC controls the modulation rate m _{VSC of the} VSC based on the equations (5) and (6).

Here, K _AVR is an AVR gain, and T _AVR is a time constant. The modulation factor m _VSC is controlled by a first-order lag system so that V _VSC matches the command value V _ref . In order to improve the stability of the control system, the modulation rate m _AVR is obtained by the feedforward control system as the sum of the rated modulation rate 1.0 and the output of the first-order lag system. In order to avoid unstable fluctuation of the VSC output voltage, the modulation rate m _AVR is limited by upper and lower limits. The modulation rate is usually in the range of m _AVR = [0.0, 1.0], but over-modulation is possible by controlling m _max as needed.

(Control system)
FIG. 2 shows a control block of the controller 4. The control block embodies the equations (1), (3), (5), and (6).

  The controller 4 includes a governor 41, an output voltage phase calculator 42, a regulator 43, and a switching controller 44.

The governor unit 41 controls a governor command value (P _gov ) for droop-controlling the _VSC 10 so that the output frequency (ω _VSC ) of the _{VSC 10} becomes the target frequency (ω _ref ). That is, the governor 41 performs the calculation of the expression (3).

The output voltage phase calculation unit 42 determines the command value (P _m ) and the actual measurement value (P _e ) of the active power output of the VSC 10, the target frequency (ω _ref ), and the governor command value (P _gov ), the output voltage phase (θ _VSC ) of the _{VSC 10} is calculated. That is, the output voltage phase calculation unit 42 performs the calculation of the expression (1).

Here, the output voltage phase calculation unit 42 calculates the actual measurement value (P _e ) of the active power output of the VSC 10 from the actual measurement values (V _DC , I _DC ) of the DC voltage and DC current on the input side of the inverter 3 in the VSC 10. can do. In the case of a three-phase VSC, the output voltage phase calculator 42 can calculate the actual measured value (P _e ) of the active power output of the VSC 10 by dq / abc conversion.

The regulator unit 43 controls the modulation rate (m _VSC ) of the _VSC 10 so that the output voltage (V _VSC ) of the _{VSC 10} becomes the target voltage (V _ref ). That is, the regulator unit 44 performs the calculations of the equations (5) and (6).

The switching control unit 44 generates a pulse modulation signal based on the modulation factor (m _VSC ) calculated by the regulator unit 43 and the output voltage phase (θ _VSC ) calculated by the output voltage phase calculation unit 42, and generates the pulse modulation signal. The switching control of the IGBT 31 in the inverter 3 in the VSC 10 is performed according to the signal. Specifically, the switching control unit 44 calculates m _VSC sin θ _VSC and generates a gate signal of the IGBT 31 by PWM (Pulse Width Modulation) modulation.

検 証 Verification results in microgrid operation≫
Next, verification results by numerical simulation performed on a microgrid operation by a single-phase VSC group in which a plurality of quasi-synchronous force-voltage converters 10 (hereinafter, referred to as a single-phase VSC or VSC) according to the present embodiment are interconnected will be described. .

(Single-phase microgrid)
FIG. 3 shows a single-phase microgrid model used for the calculation condition simulation. In this model, three single-phase VSCs are connected to the ab phase. Power is supplied to loads of three-phase and single-phase loads (ab-phase) by a three-phase infinite bus and VSC. The infinite bus is a three-phase balanced voltage source (line voltage: 6600 [V], frequency: 60 [Hz]). The load is modeled as a resistance. Three VSC is connected to the ab-phase via a transformer filter _{(R fil + jL} fil). The DC side of the VSC is modeled as a constant voltage source _VDC . The turns ratio of the transformer is 400/6600. The infinite bus is connected to the track via a switch. Table 1 shows parameters used for the simulation.

  In the numerical simulation, the three VSCs are connected to the system at time t = 0.00 [s], and a three-phase ground fault occurs at the connection point of the infinite bus at time t = 5.00 [s]. . Thereafter, at t = 5.05 [s], the switch (Switch gear) is opened, and the ground fault is eliminated. Thereby, this system shifts to the single operation of the microgrid operated by the three single-phase VSCs. From time t = 5.05 [s] to t = 10.0 [s], the single operation is continued, and the switch is closed at t = 10.0 [s]. The system is connected to the bus and the operation shifts to system interconnection operation. For the purpose of verifying the behavior of a VSC with a large disturbance, the closing operation of the switch is performed without synchronization between the microgrid and the infinite bus.

FIG. 4 shows the output frequencies of the single-phase VSCs # 1, # 2, and # 3. According to FIG. 4, the VSC frequency is oscillating at t = 5.05 [s] when the single-phase microgrid is disconnected from the infinite bus and at t = 10.0 [s] when the single-phase microgrid is reconnected to the infinite bus. I understand. The frequency decreases at t = 5.05 [s] due to the consumption of the pseudo inertia energy to compensate for the increase in demand due to the disconnection. Since the pseudo inertia constant M _VSC of VSC # 3 is small and VSC # 3 is connected to a line near the infinite bus, the frequency of VSC # 3 fluctuates most greatly.

  FIG. 5 shows the output voltage of the single-phase VSC. At t = 5.05 [s], the single-phase microgrid is disconnected from the infinite bus, but the voltage is maintained by the AVR. A voltage phase jump occurs at t = 10.0 [s] when the single-phase microgrid is reconnected to the infinite bus without phase synchronization, but the single-phase VSC loses synchronism by the proposed DC-side measurement method. The operation is continued in synchronism with the system without performing.

The active power output of the VSC is shown in FIG. System interconnection during operation (~t = 5.05 [s], t = 10.0 [s] ~) single-phase VSC of the output control is performed so as to be equal to the pseudo machine input _{P m.} At the time of the isolated operation after t = 5.05 [s], the three single-phase VSCs increase the active power output and converge to a new equilibrium point determined by the governor droop characteristic. At t = 10.0 [s] when the VSC is reconnected to the infinite bus, the active power output starts oscillating and gradually converges to the original value.

(Three-phase microgrid with multiple single-phase VSCs)
FIG. 7 shows a three-phase microgrid model used for the simulation. This model has three single-phase VSCs, one for each of the ab, bc, and ca phases. The three-phase infinite bus and the VSC supply power to the three-phase load and the single-phase loads (ab, bc, and ca phases). The infinite bus is modeled as a three-phase balanced voltage source (line voltage: 6600 [V], frequency: 60 [Hz]). The load is a resistive load. The three VSCs are connected to the line via a filter and a transformer. The DC side of the VSC is modeled as a constant voltage source _VDC . The turns ratio of the transformer is 400/6600. The operation of the switch causes the microgrid to switch between grid-connected operation and isolated operation. Table 2 shows parameters used for the simulation. However, the parameters of single-phase VSC # 1 in Table 1 are used for all VSCs shown in FIG.

  The three VSCs are connected to the system at time t = 0.00 [s]. A three-wire ground fault occurs at t = 5.00 [s] and is eliminated at t = 5.05 [s]. When the switch is opened at t = 5.05 [s], the operation shifts to the single operation, and the three single-phase VSCs operate the three-phase microgrid. The three-phase microgrid reconnects to the infinite bus at t = 10.0 [s], but does not perform phase synchronization between the microgrid and the infinite bus.

  FIG. 8 shows the output frequencies of the single-phase VSCs # 1, # 2, and # 3. As shown in FIG. 8, the VSC of each phase operates independently during normal operation and single operation. FIG. 9 shows the output voltage of the single-phase VSC. During single operation, the three-phase equilibrium voltage is maintained by independent VSCs for each phase. FIG. 10 shows the active power output of the VSC. In the isolated operation after t = 5.05 [s], the three single-phase VSCs increase the active power output, and are transitioning to a new equilibrium point.

  The above verification results show that the VSC 10 according to the present embodiment performs an operation simulating the behavior of the synchronous machine. Further, since the VSC 10 according to the present embodiment does not use a PLL, it can operate stably even in a weak grid. In addition, since the VSC 10 according to the present embodiment can be realized as a single-phase VSC, it can be connected to an arbitrary phase, and can construct a three-phase microgrid that is strongly synchronized with the operation of the VSC group. . The flexibility of the VSC 10 according to the present embodiment that enables single-phase operation by independent VSC groups can greatly improve the resilience of the power system under various conditions including a failure.

  As described above, the embodiments have been described as examples of the technology in the present invention. For that purpose, the accompanying drawings and the detailed description have been provided.

  Therefore, among the components described in the accompanying drawings and the detailed description, not only those components that are essential for solving the problem, but also those that are not essential for solving the problem in order to exemplify the technology. May also be included. Therefore, it should not be immediately determined that the non-essential components are essential based on the fact that the non-essential components are described in the accompanying drawings and the detailed description.

  Further, since the above-described embodiment is for exemplifying the technology of the present invention, various changes, replacements, additions, omissions, and the like can be made within the scope of the claims or the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 Pseudo-synchronous force-voltage converter 1 Electric storage device 2 DC / DC converter 3 Inverter 4 Controller 41 Governor part 42 Output voltage phase calculation part 43 Regulator part 44 Switching control part

Claims (4)

A controller for a voltage-type converter that converts DC power to AC power and supplies AC power to a power system,
A governor unit that controls a governor command value for droop-controlling the voltage-type converter so that an output frequency of the voltage-type converter becomes a target frequency,
An output voltage phase calculation unit that calculates an output voltage phase of the voltage-type converter from a command value and an actual measurement value of the active power output of the voltage-type converter based on an oscillation equation of the synchronous machine, the target frequency, and the governor command value. When,
A regulator unit that controls a modulation rate of the voltage-type converter so that a voltage of the power system becomes a target voltage,
A controller configured to generate a pulse modulation signal based on the modulation factor and the output voltage phase, and to perform switching control of a switching element in an inverter in the voltage-type converter according to the pulse modulation signal.   The controller according to claim 1, wherein the inverter is a single-phase inverter.   3. The output voltage phase calculator according to claim 1, wherein the output voltage phase calculator calculates an actual measured value of the active power output of the voltage-type converter from each measured value of the DC voltage and the DC current on the input side of the inverter. controller. Power storage device,
A DC / DC converter for converting a DC voltage supplied from the power storage device into an arbitrary DC voltage;
An inverter for converting an output voltage of the DC / DC converter into an AC voltage;
A quasi-synchronous power-voltage converter comprising: the controller according to claim 1, wherein the controller controls switching of a switching element in the inverter.