Power converter

Abstract

To provide an inexpensive and highly reliable power conversion device.SOLUTION: A power conversion device according to an embodiment includes a converter 4 for converting AC voltage supplied from an AC power supply 10 into DC voltage to output it; a filter circuit 2 provided between the AC power supply 10 and the converter 4; a voltage detector 12 for detecting the output voltage of the AC power supply 10; a current detector 14 for detecting the input current of the converter 4; detection circuits 16, 18 for detecting a detected value obtained from at least one of the voltage detector 12 and the current detector 14 as a digital signal; a state estimation circuit 20 for calculating an estimated value of the state quantity of the filter circuit 2 on the basis of a state equation including the elements of the detection circuits 16, 18 and the filter circuit 2, using the output voltage value of the AC power supply 10, the input current value of the converter 4, and the voltage command value of the converter 4; and control circuits 22, 24 for compensating the voltage command of the converter 4 using the estimated value calculated by the state estimation circuit 20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a power conversion device. [Background technology]

[0002] In power conversion devices such as PWM converters, filters are often installed to suppress harmonics. For example, LCL filters are frequently used to reduce the effects of harmonics caused by element switching. When an LCL filter is used, harmonics caused by element switching can be significantly reduced compared to when an L filter is used. However, due to resonance phenomena in the LCL circuit, not only can power supply harmonics exceed regulatory limits, but the control may become unstable, potentially leading to protective shutdowns and a decrease in the reliability of the power conversion device.

[0003] To reduce the effects of resonance, methods are known that passively suppress resonance by adding a resistor (damping resistor) to the filter circuit, and methods that actively suppress resonance by measuring and controlling the capacitor current or voltage in the filter circuit. In the active resonance suppression method, the effects of resonance can be attenuated in the same way as when a resistor is provided in the LCL filter by using the measured signal to provide feedback to compensate for the voltage command value.

[0004] As described above, resonance suppression can be achieved by adding components such as resistors and sensors to the LCL filter. However, passive resonance suppression by adding resistors leads to larger equipment, increased circuit losses, and higher costs, while active resonance suppression by adding sensors also leads to increased costs.

[0005] For example, if estimated values ​​of the capacitor current and capacitor voltage used for active resonance suppression can be obtained, resonance suppression can be achieved without adding any additional equipment. However, when obtaining these estimated values ​​by inversely calculating the voltage-current equation including the LCL filter, solving the differential equation increases the influence of noise included in the measured values. Using estimated values ​​heavily influenced by noise in the control of power converters could lead to a decrease in control performance or instability of the control system. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-106843 [Overview of the project] [Problems that the invention aims to solve]

[0007] The embodiments of the present invention have been made in view of the above circumstances, and aim to provide an inexpensive and highly reliable power conversion device. [Means for solving the problem]

[0008] The power conversion device according to this embodiment includes: a converter that converts an AC voltage supplied from an AC power source into a DC voltage and outputs it; a filter circuit provided between the AC power source and the converter; a voltage detector that detects the output voltage of the AC power source; a current detector that detects the input current of the converter; a detection circuit that detects the detected value obtained from at least one of the voltage detector and the current detector as a digital signal; a state estimation circuit that calculates an estimated value of the state quantity of the filter circuit based on a state equation including the elements of the detection circuit and the filter circuit, using the output voltage value of the AC power source, the input current value of the converter and the voltage command value of the converter; and a control circuit that compensates the voltage command of the converter using the estimated value calculated by the state estimation circuit. The state equation includes a delay element in the detection circuit and a delay element until the voltage command value of the converter is reflected in the output voltage of the converter. . [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram showing one example configuration of a power conversion device according to one embodiment. [Figure 2] Figure 2 shows an example of the relationship between the input / output values ​​of the LCL filter and the values ​​recognized by the controller in the power conversion device of the first embodiment. [Figure 3] Figure 3 is a block diagram illustrating an example configuration of an observer for a power converter according to the first embodiment. [Figure 4] Figure 4 shows an example of the relationship between the input / output values ​​of the LCL filter and the values ​​recognized by the controller in the power conversion device of the second embodiment. [Figure 5] Figure 5 shows an example of the relationship between the input / output values ​​of the LCL filter and the values ​​recognized by the controller in the power conversion device of the third embodiment. [Figure 6] Figure 6 shows an example of the relationship between the input / output values ​​of the LCL filter and the values ​​recognized by the controller in the power conversion device of the fourth embodiment. [Modes for carrying out the invention]

[0010] Figure 1 is a schematic diagram showing one example configuration of a power conversion device according to one embodiment.

[0011] The power converter in this embodiment is connected between an AC power source (system power source) 10 and a DC load 8, and converts the AC voltage supplied from the AC power source 10 into a DC voltage and supplies it to the DC load 8.

[0012] The power conversion device of this embodiment includes an LCL filter (filter circuit) 2, a converter 4, a voltage detector 12, a current detector 14, and a controller. The controller includes a current detection circuit 16, a voltage detection circuit 18, an observer (state estimation circuit) 20, and a control circuit. The control circuit includes a damping controller 22, a PWM control circuit 24, and a subtractor 26.

[0013] The controller comprises at least one processor and memory storing a program executed by the processor, and can realize various functions through software or a combination of software and hardware.

[0014] Converter 4 converts the AC voltage supplied from the AC power supply via the LCL filter 2 into a DC voltage and outputs it. Converter 4 is a PWM (Pulse Width Modulation) converter and includes a capacitor 6 inserted between the high-potential DC terminal and the low-potential DC terminal. The switching elements of converter 4 are controlled by gate signals supplied from the controller.

[0015] The voltage detector 12 detects the output voltage (AC voltage) of the AC power supply 10. The value detected by the voltage detector 12 is supplied to the controller.

[0016] The current detector 14 detects the value of the alternating current input to the converter 4. The value detected by the current detector 14 is supplied to the controller.

[0017] The LCL filter 2 is installed between the AC power supply 10 and the converter 4. The LCL filter 2 is a filter circuit comprising coils 2L1 and 2L2 and a capacitor 2C. Coils 2L1 and 2L2 are connected in series between the AC power supply 10 and the AC terminal of the converter 4. One end of the capacitor 2C is electrically connected between coils 2L1 and 2L2. The other end of the capacitor 2C is grounded.

[0018] The current detection circuit 16 converts the analog signal of the current value detected by the current detector 14 into a digital signal and detects it as a digital value. The current detection value of the digital signal detected by the current detection circuit 16 is supplied to the observer 20.

[0019] The voltage detection circuit 18 converts the analog signal of the voltage value detected by the voltage detector 12 into a digital signal and detects it as a digital value. The current detection value of the digital signal detected by the voltage detection circuit 18 is supplied to the observer 20.

[0020] The observer 20 is a state estimation circuit that calculates an estimated value of the state quantity of the LCL filter 2 from the voltage command value, the output value of the current detection circuit 16, and the output value of the voltage detection circuit 18. The voltage command value is, for example, a value input from a higher-level control device of the power conversion device to the controller and corresponds to the desired output voltage value of the converter 4.

[0021] In the present embodiment, the observer 20 outputs an estimated value of the voltage of the capacitor 2C of the LCL filter 2, an estimated value of the current, or both of these as an estimated value of the state quantity of the LCL filter 2 by using the extended system model of the LCL filter 2 as follows.

[0022] Here, the continuous-time state space model of the LCL filter 2 can be expressed by Equation (1).

[0023]

Equation

[0024] Also, v cov (t) is the input voltage of the converter 4, i cov (t) is the output current of the converter 4, v c (t) is the voltage of the capacitor 2C, i c (t)(=i cov (t)-i g(t)) is the current through capacitor 2C, v g (t) is the output voltage of AC power supply 10, i g (t) is the output current of the AC power supply 10.

[0025] Note that equation (1) assumes either a three-phase AC system (fixed coordinate system) or a dq coordinate system (rotating coordinate system), and that the various matrices and vectors have been transformed according to the coordinate system.

[0026] A typical observer can be designed using equation (1). However, current detection circuits 16 and voltage detection circuits 18 that perform A / D conversion often include filters such as low-pass filters to remove high-frequency noise and prevent aliasing. These filters attenuate high-frequency components from the signal recognized within the controller, resulting in a delay.

[0027] For example, if the resonant frequency of LCL filter 2 is low, the observer can estimate the state of the filter circuit and suppress resonance without being affected by the delay caused by LCL filter 2. However, considering the size and cost of LCL filter 2 and the frequency band in which harmonics are restricted, it is difficult to lower the resonant frequency to a level where it is not affected by the delay. If there is a large delay in the signal used by the observer, the observer will not be able to obtain accurate estimates, leading to a decrease in control performance and instability of the control system.

[0028] Figure 2 shows an example of the relationship between the input / output values ​​of the LCL filter and the values ​​recognized by the controller in the power conversion device of the first embodiment. Here, i cov '(t) is the converter current recognition value, v g '(t) is the AC power supply voltage recognition value, v covREF Let (t) be the converter voltage command.

[0029] The converter current value i is the output of LCL filter 2. cov (t) is the converter current recognition value i, which is detected by the controller via the current detection circuit 16. covIt is recognized as '(t). If the current detection circuit 16 has the characteristics of a low-pass filter, the converter current recognition value i cov '(t) is the converter current value i cov A phase lag occurs compared to (t).

[0030] Also, the AC power supply voltage value v g Similarly, the AC power supply voltage is recognized by the controller via the voltage detection circuit 18. g It is recognized as '(t). AC power supply voltage value v g (t) is an input to the LCL filter 2, so on the block diagram shown in Figure 2, the AC power supply voltage recognition value v g The AC power supply voltage value v is obtained when (t) passes through the reverse system of the voltage detection circuit 18. g It will be entered as (t).

[0031] Also, the converter voltage value v cov If a sensor for measuring (t) is provided, it will be recognized by the controller via the voltage detection circuit 18, but in most cases, measurement is not performed using a sensor. Therefore, in the block diagram of Figure 2, the command value is the converter voltage command value v covREF (t) is converted to the converter voltage value v via a delay until the voltage is reflected. cov (t) is generated and input to LCL filter 2.

[0032] From the above, it can be concluded that the input and output signals of the LCL filter 2 shown in equation (1), which is the target of the observer design, do not perfectly match the input and output signals recognized by the software calculation unit. The greater the delay relative to the underlying signal, the lower the estimation performance of the observer designed based on equation (1).

[0033] Therefore, in the power conversion device of this embodiment, the observer 20 is not an observer that targets equation (1), but rather an expanded model of the LCL filter 2 that includes delay elements in the detection circuit and delay elements from the command value to the voltage reflection. By designing the observer 20 to target this expanded model, the effects of delay are taken into consideration when calculating the estimated values ​​of the state variables of the LCL filter 2.

[0034] Let the state-space model of the LCL filter 2 shown in equation (1) be denoted as (A, B, C, 0), and the state-space model of the voltage detection circuit inverse system be denoted as (A f1 ,B f1 ,C f1 ,D f1 ), the state-space model of the current detection circuit 16 is (A f2 ,B f2 ,C f2 If we set ,0, then the expanded version of the LCL filter 2 including the delay element can be shown by equation (2).

[0035]

number

[0036]

number

[0037] However, the state-space model of the inverse system of the voltage detection circuit (A f1 ,B f1 ,C f1 ,D f1 Regarding this, if the original voltage detection circuit 18 is composed of a low-pass filter intended for high-frequency noise removal, it is conceivable that the inverse system would result in an improper system, potentially increasing the effect of noise through differentiation. Therefore, it is desirable to suppress excessive differentiation by imperfect differentiation or the like and create a proper system.

[0038] Also, in equation (2), x c(t) is the state vector in the expanded system of the LCL filter 2, y c (t) is the output vector in the expanded version of the LCL filter 2. Here, the converter voltage command v covREF (t) is the actual converter output voltage v cov The delay before it is reflected in (t) is not included in equation (2) and will be described later. Observer 20 is an expanded version of the LCL filter 2 that includes the delay element shown in equation (2) above (A c ,B c ,C c Designed for ,0).

[0039] Observer 20 will be considered in discrete time because it performs digital control executed by software. Equation (2) State-space model (A c ,B c ,C c Since (0) is a continuous-time system, we discretize it and obtain a discrete-time state-space model (A d ,B d ,C d We obtain the converter voltage command v. covREF (k) and converter voltage v cov The discrete-time relationship with (k) is the converter voltage command v covREF After (k) is calculated, the actual converter voltage v is calculated in the next step. cov If this is reflected in (k), then equation (6) below holds. v cov (k+1) = v covREF (k) (6) Equation (6) above represents the converter voltage command v covREF (k) to converter voltage v cov It can also be considered as a delay before it is reflected in (k), and in discrete-time state-space models (A d ,B d ,C d By extending equation (0) and equation (6), the entire extended system including the delay shown in Figure 2 can be represented.

[0040] The entire extended system including the delay is represented by a discrete-time state-space model (A e ,B e ,Ce , 0), each matrix can be expressed by equations (7), (8), and (9). [Number]

[0041] Here, matrix B d1 , B d2 is the matrix of equation (10) obtained by dividing the input matrix of the discrete-time state space model (A d , B d , C d , 0) for each input signal. B d = [B d1 B d2 (10) From the above, by designing an observer for the discrete-time state space model (A e , B e , C e , 0), which is the overall augmented system including the delay element, the state of the LCL filter 2 can be estimated considering the influence of the delay.

[0042] Also, the continuous-time state model of the LCL filter 2 that performs the converter current feedback shown in equation (1) is observable, and the observability is not lost even in the discrete-time state space model (A e , B e ​​​​​​​​​​​​​​​​​​​​​​​​​​The output vector of ,0) is e(k)(=y e (k)-y e * (k=y e (k)-C e x e * When (k) is set, if the observer gain matrix K is appropriately designed, the output error e(k) can be made 0, and the state vector x e * (k) Discrete-time state-space model (A e ,B e ,C e It can be treated as an estimator of the state vector (0). The observer gain matrix K is determined to obtain the desired estimation performance and can be obtained using methods such as the pole placement method or solving the Riccati equation as an optimal problem.

[0044] Figure 3 is a block diagram illustrating an example configuration of an observer for the optimal control device of the first embodiment. Observer 20 estimates the capacitor voltage v c * (k), or the estimated value of the capacitor current i c * (k) is output to the damping controller 22. Figure 3 shows that the observer 20 outputs the estimated value i of the capacitor current. c * This example shows how to output (k).

[0045] Observer 20 obtains the state vector x based on equation (11). e * From (k), the output matrix C h Estimated value of the capacitor current i extracted by c * Output (k). Note that the output matrix C h is the state vector x e * (k) Estimated value of converter current i cov * (k), Estimated value of capacitor voltage v c * (k), Estimated value of power supply current ig * Using element (k), estimate the capacitor current i c * (k)(=i cov * (k)-i g * This is the matrix that extracts (k).

[0046] The damping controller 22 estimates the capacitor voltage v c * (k), or the estimated value of the capacitor current i c * The compensation amount is calculated using (k) and output to the subtractor 26. The damping controller 22 is set to obtain the desired damping performance and may be a filter with constants or specific frequency characteristics. For example, the estimated capacitor current i is sent from the observer 20 to the damping controller 22. c * The value of (k) is input, and the damping controller 22 estimates the constant gain as i. c * The value obtained by multiplying (k) is fed back as the compensation amount.

[0047] The subtractor 26 outputs the voltage command v of the converter. covREF The value obtained by subtracting the compensation amount output from the damping controller 22 from the value of (k) is the compensated voltage command v covREF Output (k) to the PWM control circuit 24. The PWM control circuit 24 receives the compensated voltage command v covREF By comparing the modulated wave generated from (k) with the carrier wave, the gate signal for converter 4 is generated and output to converter 4.

[0048] As described above, an observer 20 based on an expanded system model that includes delay elements in detection circuits 16 and 18 and delay elements from the voltage command value to the output voltage value of converter 4 can be used to calculate estimated values ​​of the state variables of the LCL filter 2 that take delay elements into account. In the power converter of this embodiment, it is possible to add a damping term to the closed loop by feeding back compensation values ​​obtained through a predetermined controller based on the estimated values ​​calculated as described above, thereby enabling resonance suppression in the LCL filter 2.

[0049] Furthermore, in the power conversion device of this embodiment, resonance suppression in the LCL filter 2 can be performed using measured values ​​such as the input current value of the converter and the output voltage value of the AC power supply, which are measured by existing sensors, eliminating the need to add any new equipment. In other words, according to this embodiment, an inexpensive and highly reliable power conversion device can be provided.

[0050] Next, the power conversion device of the second embodiment will be described in detail with reference to the drawings. In the following description, components similar to those in the first embodiment described above will be denoted by the same reference numerals and their descriptions will be omitted. The power conversion device of this embodiment differs from the first embodiment in the configuration of the observer 20 described above. This embodiment differs from the first embodiment in that the voltage detection circuit 18 does not include the characteristics of a low-pass filter, or has a configuration in which the delay can be ignored.

[0051] Figure 4 shows an example of the relationship between the input / output values ​​of the LCL filter and the values ​​recognized by the controller in the power conversion device of the second embodiment. The converter current value i is the output of LCL filter 2. cov (t) is the converter current recognition value i, which is detected by the controller via the current detection circuit 16. cov It is recognized as '(t). If the current detection circuit 16 has the characteristics of a low-pass filter, the converter current recognition value i cov '(t) is the converter current value i cov A phase lag occurs compared to (t).

[0052] In this embodiment, the delay in the voltage detection circuit 18 is negligible, and the AC power supply voltage value v g The AC power supply voltage v is detected by the controller via the voltage detection circuit 18. g It can be recognized as (t). Also, the converter voltage command value v covREF (t) is the converter voltage value v through a delay before the voltage is reflected. cov (t) is generated and input to LCL filter 2.

[0053] Based on the above, in the power conversion device of this embodiment, the observer 20 is designed for an expanded model of the LCL filter 2 that includes the delay element of the current detection circuit 16 and the delay element from the command value to the voltage reflection, and calculates estimated values ​​of the state variables of the LCL filter 2 that take into account the effects of the above delays.

[0054] In this embodiment, since we are dealing with an expanded model of the LCL filter 2 that does not include the voltage detection circuit inverse system, each matrix of the state-space model shown in equation (2) can be expressed by equations (12), (13), and (14).

number

[0055] By discretizing the expanded system model represented by equations (12), (13), and (14) above, as in the first embodiment, and considering the converter voltage command delay, a discrete-time state-space model (A) is obtained, which is the overall expanded system including the delay element. e ,B e ,C e ,0) can be obtained. The observer 20 of this embodiment uses this discrete-time state space model (A e ,B e ,C e It can be designed based on (0), and the observer's state equation can be expressed by equation (11).

[0056] According to the observer 20 designed as described above, it is possible to calculate estimated values ​​of the state variables of the LCL filter 2 considering the delay element, and to feed back the product of the calculated estimated values ​​multiplied by a predetermined gain (or the value obtained by passing it through a predetermined transfer function) to add a damping term to the closed loop, thereby enabling resonance suppression in the LCL filter 2. Furthermore, in this embodiment, the observer 20 can be made less dimensional than in the first embodiment, thereby reducing the computational load on the software.

[0057] Furthermore, in the power conversion device of this embodiment, resonance suppression in the LCL filter 2 can be performed using measured values ​​such as the input current value of the converter and the output voltage value of the AC power supply, which are measured by existing sensors, eliminating the need to add any new equipment. In other words, according to this embodiment, an inexpensive and highly reliable power conversion device can be provided.

[0058] Next, the power conversion device of the third embodiment will be described in detail with reference to the drawings. The power conversion device of this embodiment differs from the first embodiment in the configuration of the observer 20 described above. This embodiment differs from the first embodiment in that the current detection circuit 16 does not include the characteristics of a low-pass filter, or has a configuration in which the delay can be ignored.

[0059] Figure 5 shows an example of the relationship between the input / output values ​​of the LCL filter and the values ​​recognized by the controller in the power conversion device of the third embodiment. In this embodiment, the delay in the current detection circuit 16 is negligible, and the converter current value i is the output of the LCL filter 2. cov (t) is the converter current value i detected by the controller via the current detection circuit 16. cov It is recognized as (t).

[0060] Also, the AC power supply voltage value v g The AC power supply voltage is recognized by the controller via the voltage detection circuit 18. g It is recognized as '(t). AC power supply voltage value v g(t) is an input to the LCL filter 2, so on the block diagram shown in Figure 5, the AC power supply voltage recognition value v g The AC power supply voltage value v is obtained when (t) passes through the reverse system of the voltage detection circuit 18. g It will be entered as (t). Also, the converter voltage command value v covREF (t) is the converter voltage value v through a delay before the voltage is reflected. cov (t) is generated and input to LCL filter 2.

[0061] Based on the above, in the power conversion device of this embodiment, the observer 20 is designed for an expanded model of the LCL filter 2 that includes the delay element of the voltage detection circuit 18 and the delay element from the command value to the voltage reflection, and calculates estimated values ​​of the state variables of the LCL filter 2 taking into account the effects of the above delays.

[0062] In this embodiment, since we are dealing with an expanded model of the LCL filter 2 that does not include the delay in the current detection circuit, each matrix of the state-space model shown in equation (2) can be expressed by equations (15), (16), and (17).

number

[0063] The expanded system model represented by equations (15), (16), and (17) above is discretized in the same manner as in the first embodiment, and by considering the converter voltage command delay, a discrete-time state-space model (A) is obtained, which is the overall expanded system including the delay element. e ,B e ,C e ,0) can be obtained. The observer 20 of this embodiment uses this discrete-time state space model (A e ,B e ,C e It can be designed based on (0), and the observer's state equation can be expressed by equation (11).

[0064] According to the observer 20 designed as described above, it is possible to calculate estimated values ​​of the state variables of the LCL filter 2 considering the delay element, and to feed back the product of the calculated estimated values ​​multiplied by a predetermined gain (or the value obtained by passing it through a predetermined transfer function) to add a damping term to the closed loop, thereby enabling resonance suppression in the LCL filter 2. Furthermore, in this embodiment, the observer 20 can be made less dimensional than in the first embodiment, thereby reducing the computational load on the software.

[0065] Furthermore, in the power conversion device of this embodiment, resonance suppression in the LCL filter 2 can be performed using measured values ​​such as the input current value of the converter and the output voltage value of the AC power supply, which are measured by existing sensors, eliminating the need to add any new equipment. In other words, according to this embodiment, an inexpensive and highly reliable power conversion device can be provided.

[0066] Next, the power conversion device of the fourth embodiment will be described in detail with reference to the drawings. In the power conversion devices of the first to third embodiments described above, the controller controls the converter current i, which is the current flowing to the converter 4 side of the LCL filter 2 (the input current of the converter 4). c This is a control system that performs current control using the value of (t). In contrast, in the power converter of this embodiment, the controller controls the system current i, which is the current flowing to the AC power supply 10 side of the LCL filter 2 (output current of the AC power supply 10). g This is a control system that uses the value of (t) to stabilize the system.

[0067] In the power converter with the above configuration, the observer 20 can calculate an estimated value of the state variable of the LCL filter 2, taking into account the delay of the detection circuit and the delay until the voltage command value is reflected in the converter voltage value.

[0068] Figure 6 shows an example of the relationship between the input / output values ​​of the LCL filter and the values ​​recognized by the controller in the power conversion device of the fourth embodiment. In the power conversion device of this embodiment, if the continuous-time state-space model of the LCL filter 2 is expressed in the same way as in equation (1), then the state matrix A, input matrix B, state vector x(t), and input vector u(t) are the same. On the other hand, the output signal of the LCL filter 2 is the system current i g (t) is obtained, and the output matrix C changes. For example, if all phases of a three-phase AC system are represented by equation (1), the state matrix A is a 9-dimensional square matrix, and in the power converter of this embodiment, the output matrix C can be represented by equation (18).

[0069]

number

[0070] In other words, in the power converter of this embodiment, by simply changing the output matrix C in equation (1) to the matrix in equation (18), it becomes possible to design an observer 20 that takes delay into account, similar to the power converter of the first embodiment described above, and to calculate estimated values ​​of the state variables of the LCL filter 2.

[0071] According to the observer 20 designed as described above, it is possible to calculate estimated values ​​of the state variables of the LCL filter 2 while considering the delay element, and to feed back the product of the calculated estimated values ​​multiplied by a predetermined gain (or the value obtained by passing it through a predetermined transfer function) to add a damping term to the closed loop, thereby enabling resonance suppression in the LCL filter 2.

[0072] Furthermore, in this embodiment as well, it is not always necessary to consider both the delay in the voltage detection circuit 18 and the delay in the current detection circuit 16. By applying equation (18) to the output matrix C in equation (12) or equation (17), it is possible to design the observer 20 in the same way as in the second and third embodiments, thereby reducing the computational load on the software.

[0073] Furthermore, in the power conversion device of this embodiment, resonance suppression in the LCL filter 2 can be performed using measured values ​​such as the input current value of the converter and the output voltage value of the AC power supply, which are measured by existing sensors, eliminating the need to add any new equipment. In other words, according to this embodiment, an inexpensive and highly reliable power conversion device can be provided.

[0074] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Note 1] A converter that converts the AC voltage supplied from an AC power source into a DC voltage and outputs it, A filter circuit is provided between the AC power supply and the converter, A voltage detector for detecting the output voltage of the AC power supply, A current detector for detecting the input current of the converter, A detection circuit that detects the detected value obtained from at least one of the voltage detector and the current detector as a digital signal, A state estimation circuit that calculates estimated values ​​of state quantities of the filter circuit based on a state equation including the elements of the detection circuit and the filter circuit, using the output voltage value of the AC power supply, the input current value of the converter, and the voltage command value of the converter. A power conversion device comprising: a control circuit that compensates for the voltage command of the converter using the estimated value calculated by the state estimation circuit. [Note 2] The power conversion device as described in Appendix 1, wherein the state estimation circuit estimates the state of the filter circuit based on a state equation including the elements of the detection circuit and the filter circuit, using the output current value of the AC power supply instead of the input current value of the converter. [Note 3] The power conversion device according to Appendix 1, wherein the state equation includes a delay element in the detection circuit and a delay element until the voltage command value of the converter is reflected in the output voltage of the converter. [Note 4] The power conversion device according to any one of Appendix 1 to Appendix 3, wherein the control circuit calculates a compensation amount for the voltage command of the converter using the product of an estimated value calculated by the state estimation circuit and a predetermined gain, and controls the converter using the value obtained by subtracting the compensation amount from the voltage command value of the converter. [Explanation of symbols]

[0075] 2…LCL filter, 2C…Capacitor, 2L1, 2L2…Inductor, 4…Converter, 6…Capacitor, 8…DC load, 10…AC power supply (grid power), 12…Voltage detector, 14…Current detector, 16…Current detection circuit, 18…Voltage detection circuit, 20…Observer, 22…Damping controller, 24…PWM control circuit, 26…Subtractor

Claims

1. A converter that converts the AC voltage supplied from an AC power source into a DC voltage and outputs it, A filter circuit is provided between the AC power supply and the converter, A voltage detector for detecting the output voltage of the AC power supply, A current detector for detecting the input current of the converter, A detection circuit that detects the detected value obtained from at least one of the voltage detector and the current detector as a digital signal, A state estimation circuit that calculates estimated values ​​of state quantities of the filter circuit based on a state equation including the elements of the detection circuit and the filter circuit, using the output voltage value of the AC power supply, the input current value of the converter, and the voltage command value of the converter. The system includes a control circuit that compensates for the voltage command of the converter using the estimated value calculated by the state estimation circuit, The power converter is characterized in that the state equation includes a delay element in the detection circuit and a delay element until the voltage command value of the converter is reflected in the output voltage of the converter.

2. The power conversion device according to claim 1, wherein the state estimation circuit estimates the state of the filter circuit based on the state equation including the elements of the detection circuit and the filter circuit, using the output current value of the AC power supply instead of the input current value of the converter.

3. The power conversion device according to claim 1 or 2, wherein the control circuit calculates a compensation amount for the voltage command of the converter using the product of an estimated value calculated by the state estimation circuit and a predetermined gain, and controls the converter using the value obtained by subtracting the compensation amount from the voltage command value of the converter.

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