JP6717117B2 - Charge/discharge control method, battery system and storage battery system - Google Patents

Description

The present invention relates to a charge/discharge control method, a battery system and a storage battery system.

For example, a DC/DC converter and an inverter are mounted on a power conversion device that is provided between a storage battery and an AC power line and performs DC/AC power conversion. Further, a smoothing capacitor is connected to the DC bus connecting them. In this type of traditional power converter, for example, a DC/DC converter converts a voltage output from a storage battery into a voltage equal to or higher than a peak value (peak value) of an AC voltage and outputs the voltage to a DC bus. An AC voltage is generated from the voltage of the DC bus. In such a power converter, the DC/DC converter and the inverter constantly perform high-frequency switching operation.

On the other hand, there has been proposed a power conversion device capable of significantly reducing power loss due to high-frequency switching operation (see, for example, Patent Document 1 (FIGS. 10 and 11)). In such a power converter, the DC voltage output from the storage battery and the instantaneous value of the AC voltage are constantly compared in magnitude to generate a waveform of the AC voltage by the DC/DC converter at the time (phase) when boosting is required. On the other hand, the inverter stops high frequency switching and only performs the necessary polarity reversal. On the contrary, the DC/DC converter is stopped at the time (phase) when the step-down is required, the output voltage of the storage battery is simply passed, and the waveform of the AC voltage is generated by the inverter.

In this way, the DC/DC converter and the inverter can share the role of step-up/step-down. Further, as a result, a "minimum switching conversion system" can be executed in which a high-frequency switching quiescent period is generated in one of the DC/DC converter and the inverter within the AC half cycle, and the number of times of switching as a whole is reduced. .. Similarly, when the storage battery is charged, the “minimum switching conversion method” that reduces the number of times of switching as a whole can be executed.

In order to realize such minimum switching conversion, it is necessary that the capacitance of the capacitor connected to the DC bus is a small capacitance of “μF class”. This is because the voltage appearing on the DC bus is not a flat DC voltage but a composite waveform in which the DC voltage is superimposed with the phase portion around the peak value of the AC waveform. The capacitor connected to the DC bus is required to have a small capacity that does not smooth the phase portion around the peak value of this AC waveform.

JP, 2005-149882, A

It is known that in the power conversion device that executes the above-described minimum switching conversion method, the current (discharge current/charge current) flowing in the storage battery becomes a pulsating current. This is because the capacitor has a small capacity as described above. Further, the pulsating current causes the voltage across the storage battery being discharged or charged to be a DC voltage including pulsation. As described above, the current or voltage having a pulsating waveform is more likely to cause a detection error due to sampling than a flat DC voltage. If an error occurs, the charge/discharge control may be affected and the storage battery may be over-discharged or over-charged.

In view of such a problem, it is an object of the present invention to more accurately detect a current or voltage having a pulsating waveform and improve control accuracy.

The present disclosure includes the following inventions. However, the present invention is defined by the claims.
According to one expression as a charge control method, the present disclosure is a charge/discharge control method in the case where a current and a voltage related to charging or discharging a battery have a pulsating waveform, and the pulsating waveform is sampled at a predetermined cycle. A charging/discharging control method for obtaining a value obtained by averaging an effective value based on a detected value obtained by the sampling for a predetermined period and controlling charging/discharging based on the averaged value.

Further, the present disclosure is, in one expression as a battery system, a power conversion device that is provided between a battery and the battery and an alternating current circuit, and that current and voltage related to charging or discharging of the battery have a pulsating waveform. And, the power conversion device, the pulsating waveform is sampled at a predetermined cycle, the value obtained by averaging the effective value based on the detection value obtained by the sampling in a predetermined period, to the averaged value A battery system that controls charging and discharging based on the above.

Further, the present disclosure is, in one expression, as a storage battery system, a storage battery, and a power conversion device that is provided between the storage battery and an AC circuit, and in which a current and a voltage related to charging and discharging of the storage battery have a pulsating waveform. , The power converter is a cycle other than a cycle that is a natural number multiple of one cycle of the pulsation waveform, the pulsation waveform is sampled, the effective value based on the detection value obtained by the sampling in a predetermined period. It is a storage battery system that obtains an averaged value and controls charging/discharging based on the averaged value.

According to the present invention, it is possible to more accurately detect a current or voltage having a pulsating waveform and improve control accuracy.

It is an example of a circuit diagram of a storage battery system according to an embodiment. It is a figure which shows an example of the voltage waveform which showed the operation|movement when a power converter device is charging the storage battery, for example. It is a figure which shows an example of the voltage waveform which showed the operation|movement when a power converter device is discharging the storage battery notionally. The upper graph is a waveform diagram (horizontal axis is time t) showing an example of the pulsating current, and the lower graph is the terminal voltage of the storage battery when such a pulsating current flows to the storage battery. It is a waveform diagram which shows an example. It is the graph which plotted the pulsating current detected as a result of measuring pulsating current for 100 ms with a sampling cycle of 0.1 ms. It is the graph which plotted the pulsating current detected as a result of measuring pulsating flow for 100 ms with the sampling period of 1 ms. It is the graph which plotted and connected the pulsating current detected as a result of measuring pulsating current for 100 ms with a sampling period of 10 ms. It is the graph which connected and plotted the pulsating current detected as a result of measuring pulsating current for 100 ms with a sampling period of 15 ms. It is a figure showing the pulsating current of 100Hz (2 times 50Hz, a solid line) and 120Hz (2 times 60Hz, a broken line). It is a graph which shows the error of the average value and true value based on sampling when a sampling cycle is changed in the range of 0-0.1 [s].

[Summary of Embodiment]
The gist of the embodiment of the present invention includes at least the following.

(1) This is a charging/discharging control method in the case where a current and a voltage related to charging or discharging a battery have a pulsating waveform, in which the pulsating waveform is sampled at a predetermined cycle, and the detected value obtained by the sampling is used. A charging/discharging control method for obtaining a value obtained by averaging an effective value based on a predetermined period and controlling charging/discharging based on the averaged value.

By executing such a charge/discharge control method, it is possible to obtain a detection value with high accuracy even with a current or voltage having a pulsating waveform. Thereby, the accuracy of control in charging or discharging can be improved.

(2) In the charge/discharge control method of (1), the predetermined cycle is, for example, a cycle other than a cycle that is a natural multiple of one cycle of the pulsating waveform.
If the sampling cycle is a cycle that is a natural multiple of one cycle of the pulsation waveform, the same value will be detected each time. Therefore, by avoiding this, the values of the pulsation waveform can be detected in a uniform phase. Therefore, by averaging, it is possible to accurately obtain the detected value.

(3) Further, in the charge/discharge control method of (1) or (2), when the sampling period is changed, a change characteristic appearing in an error between the averaged value and a true value is grasped in advance, and You may make it select the sampling period with which an error becomes relatively small.
In this case, an averaged value with less error can be obtained.

(4) One aspect as an object includes a battery, and a power conversion device that is provided between the battery and an AC electric path and has a pulsating waveform of current and voltage related to charging or discharging of the battery. The power conversion device samples the pulsating waveform at a predetermined cycle, obtains an average value of effective values based on the detection value obtained by the sampling for a predetermined period, and charges and discharges based on the averaged value. It is a battery system that controls.

By executing such charge control or discharge control, it is possible to obtain a detected value with high accuracy even with a current or voltage having a pulsating waveform. Thereby, the accuracy of control at the time of charging or discharging in the battery system can be improved.

(5) Another aspect as an object includes a storage battery, and a power conversion device that is provided between the storage battery and an AC electric line and has a pulsating waveform of a current and a voltage related to charging and discharging of the storage battery. The power conversion device samples the pulsation waveform in a cycle other than a cycle that is a natural multiple of one cycle of the pulsation waveform, and averages effective values based on the detection values obtained by the sampling in a predetermined period. A storage battery system that obtains a value and controls charging and discharging based on the averaged value.

By executing such charge/discharge control, it is possible to obtain the detection value with high accuracy even with a current or voltage having a pulsating waveform. As a result, the accuracy of charge/discharge control in the storage battery system can be improved.

[Details of Embodiment]
Hereinafter, details of embodiments of the present invention will be described with reference to the drawings.

<<Circuit configuration example>>
FIG. 1 is an example of a circuit diagram of a storage battery system according to an embodiment. In the figure, the power conversion device 1 is provided between the storage battery 2 and the AC electric circuit 3, and in the state where the DC voltage of the storage battery 2 is lower than the peak value (peak value) of the AC voltage of the AC electric path 3, Bidirectional power conversion can be performed. A load 4L of a customer in which the power conversion device 1 is installed and a commercial power system 4P are connected to the AC power line 3.

The power conversion device 1 includes a DC-side capacitor 5, a DC/DC converter 6, an intermediate capacitor 9, an inverter 10, and a filter circuit 11 as main circuit components of the power conversion unit 20. The DC/DC converter 6 includes a DC reactor 7, a high-side switching element Q1 and a low-side switching element Q2, and constitutes a DC chopper circuit. As the switching elements Q1 and Q2, for example, MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) can be used. The switching elements Q1 and Q2 of the MOSFET have diodes (body diodes) d1 and d2, respectively. The switching elements Q1 and Q2 are controlled by the control unit 14.

The high voltage side of the DC/DC converter 6 is connected to the DC bus 8. The intermediate capacitor 9 connected between the two lines of the DC bus 8 has a small capacity (100 μF or less, for example, several tens of μF), and exhibits a smoothing action for a voltage switched at a high frequency (for example, 20 kHz). However, it does not exert a smoothing effect on a voltage that changes at a frequency about twice the commercial frequency (100 Hz or 120 Hz).

The inverter 10 connected to the DC bus 8 includes switching elements Q3 to Q6 forming a full bridge circuit. These switching elements Q3 to Q6 are, for example, MOSFETs. In the case of MOSFET, the switching elements Q3 to Q6 have diodes (body diodes) d3 to d6, respectively. The switching elements Q3 to Q6 are controlled by the control unit 14.

A filter circuit 11 is provided between the inverter 10 and the AC electric circuit 3. The filter circuit 11 includes an AC reactor 12 and an AC-side capacitor 13 provided on the load 4L side (right side in the drawing) of the AC reactor 12. The filter circuit 11 blocks passage of high-frequency noise generated in the inverter 10 so that the high-frequency noise does not leak to the AC electric circuit 3 side.

As a circuit element for measurement, a voltage sensor 15 and a current sensor 16 are provided on the low voltage side (left side in the figure) of the DC/DC converter 6. The voltage sensor 15 is connected in parallel with the storage battery 2 and detects the terminal voltage of the storage battery 2. Information on the detected voltage is provided to the control unit 14. The current sensor 16 detects a current flowing through the DC/DC converter 6. The current flowing through the DC/DC converter 6 is also a current flowing through the storage battery 2 if the current flowing through the DC side capacitor 5 is ignored. Information on the detected current is provided to the control unit 14. A voltage sensor 17 is connected in parallel to the intermediate capacitor 9. The voltage sensor 17 detects the voltage across the intermediate capacitor 9, that is, the voltage of the DC bus 8. Information on the detected voltage is provided to the control unit 14.

On the other hand, on the AC side, a current sensor 18 that detects the current flowing through the AC reactor 12 is provided. Information on the current detected by the current sensor 18 is provided to the control unit 14. Further, a voltage sensor 19 is provided in parallel with the AC side capacitor 13. Information on the voltage detected by the voltage sensor 19 is provided to the control unit 14.

The control unit 14 includes, for example, a CPU (Central Processing Unit), and the CPU executes a software (computer program) to realize a necessary control function. The software is stored in the storage device (not shown) of the control unit 14.

The storage battery 2 is provided with, for example, a BMS (Battery Management System) 21. The BMS 21 can provide the control unit 14 with information such as the current flowing through the storage battery 2, the voltage across the storage battery 2, and the state of charge (SOC) of the storage battery 2.

<<Outline of charge/discharge operation (minimum switching conversion method)>>
The power conversion device 1 described above is capable of discharging the power of the storage battery 2, converting the power from direct current to alternating current, and supplying power to the alternating current electrical path 3. On the contrary, the power conversion device 1 can perform conversion from AC to DC and charge the storage battery 2 based on the power of the commercial power system 4P.

In either case of charging or discharging, the inverter 10 and the DC/DC converter 6 alternately perform switching operation during the AC 1/2 cycle (or during 1 cycle). Such a switching conversion method can be called a minimum switching conversion method. The power conversion device 1 that performs the control of the minimum switching conversion method can reduce the total number of high frequency switching operations due to the idle period occurring in the high frequency switching of the switching elements Q1 to Q6. Thereby, the efficiency of power conversion can be significantly improved.

For example, when charging the storage battery 2, the inverter 10 cooperates with the AC reactor 12 to boost the voltage, and the DC/DC converter 6 exhibits a “through” function of simply passing a voltage/current. In some cases, the inverter 10 only performs rectification, and the DC/DC converter 6 performs step-down. The AC reactor 12 when the inverter 10 boosts voltage is also a part of the inverter 10.

On the other hand, when the storage battery 2 is discharged, the DC/DC converter 6 boosts the voltage, the inverter 10 performs the non-inversion passage or the inversion passage of the polarity, and the DC/DC converter 6 exhibits the “through” function. Then, the inverter 10 exhibits a step-down inverter function (including necessary polarity reversal).

The minimum switching conversion method is a known control method that is also described in detail in Patent Document 1 described above, and thus a detailed control theory is omitted, but it will be briefly described with a voltage waveform diagram.

<<Charging operation seen from voltage waveform diagram>>
FIG. 2 is a diagram showing an example of a voltage waveform conceptually showing the operation of the power conversion device 1 configured as described above, for example, when the storage battery 2 is being charged.
(A) shows the absolute value of the AC voltage target value Vinv* and the DC voltage target value Vg'. The AC voltage target value Vinv* is a value that should be a voltage at the input end (AC side) of the inverter 10 during the charging operation based on the AC voltage Va. If the impedance of the AC reactor 12 is ignored, Vinv*=Va. The DC voltage target value Vg′ is a value that takes the voltage drop of the DC reactor 7 into consideration in the storage battery voltage Vg. If the impedance of the DC reactor 7 is ignored, Vg'=Vg.
The control unit 14 compares these two voltages and controls the inverter 10 and the DC/DC converter 6 based on the comparison result.

here,
(#1) In the period of time t0 to t1, t2 to t3, t4 to t5, the absolute value of the AC voltage target value Vinv* becomes smaller than the DC voltage target value Vg' (or becomes Vg' or less).
(#2) Further, for example, in the period from time t1 to t2 and t3 to t4, the absolute value of the AC voltage target value Vinv* is equal to or higher than the DC voltage target value Vg′ (or is larger than Vg′).
Therefore, the conversion unit (the DC/DC converter 6 or the inverter 10) that mainly performs the switching operation is changed depending on whether it is (#1) or (#2).
When Vg′=|Vinv*|, it is necessary to include it in either (#1) or (#2). Therefore, hereinafter, the absolute value of the AC voltage target value Vinv* is the DC voltage target value Vg′. Description will be made focusing on the case where it is smaller and the case where the absolute value of the AC voltage target value Vinv* is larger than the DC voltage target value Vg′.

First, as shown in (b), during a period (t0 to t1, t2 to t3, t4 to t5) in which the absolute value of the AC voltage target value Vinv* is smaller than the DC voltage target value Vg', the control unit 14 causes the inverter to operate. The switching operation of 10 is performed, and boosting is performed in cooperation with the AC reactor 12. Note that the switching here means high-frequency switching of, for example, about 20 kHz, and does not mean low-frequency switching of a degree (twice the commercial frequency) for performing synchronous rectification (the same applies hereinafter).

On the other hand, in these periods (t0 to t1, t2 to t3, t4 to t5), in the DC/DC converter 6, the switching element Q1 is on and Q2 is off, and the voltage is directly passed (passed). There is. The vertical stripe pattern shown in (b) is actually a PWM (Pulse Width Modulation) pulse train, and the duty differs depending on the potential difference for boosting to the DC voltage target value Vg'. As a result, the voltage appearing on the DC bus 8 has a waveform as shown in (c).

Further, during a period (t1 to t2, t3 to t4) in which the absolute value of the AC voltage target value Vinv* is larger than the DC voltage target value Vg′, the control unit 14 stops the switching operation of the inverter 10, and instead, the DC The /DC converter 6 is caused to perform a switching operation to reduce the voltage. The inverter 10 that has stopped the switching operation is in a state of performing synchronous rectification or full-wave rectification by the diodes d1 to d4.
The vertical stripe pattern shown in (d) is actually a PWM pulse train, and the duty differs depending on the potential difference between the absolute value of the AC voltage target value Vinv* and the DC voltage target value Vg′. As a result of the step-down, the desired DC voltage target value Vg′ shown in (e) is obtained, and thus the storage battery 2 can be charged.

<<Discharge operation seen from voltage waveform diagram>>
FIG. 3 is a diagram showing an example of a voltage waveform conceptually showing the operation when the power conversion device 1 is discharging the storage battery 2.
(A) shows the absolute value of the AC voltage target value Vinv* and the DC voltage target value Vg'. The AC voltage target value Vinv* is a value that should be a voltage at the output terminal of the inverter 10 during the discharging operation based on the AC voltage Va. If the impedance of the AC reactor 12 is ignored, Vinv*=Va. The DC voltage target value Vg′ is a value that takes the voltage drop of the DC reactor 7 into consideration in the storage battery voltage Vg. If the impedance of the DC reactor 7 is ignored, Vg'=Vg.
The control unit 14 compares these two voltages and controls the inverter 10 and the DC/DC converter 6 based on the comparison result.

First, during a period (t1 to t2, t3 to t4) in which the absolute value of the AC voltage target value Vinv* is larger than the DC voltage target value Vg', the control unit 14 causes the DC/DC converter 6 to perform a switching operation to perform boosting. (FIG. 3(b)). As a result, the voltage shown in (c) appears on the DC bus 8.

On the other hand, during a period (t0 to t1, t2 to t3, t4 to t5) in which the absolute value of the AC voltage target value Vinv* is smaller than the DC voltage target value Vg', the control unit 14 causes the inverter 10 to perform a switching operation as an inverter. The voltage is reduced ((d) in FIG. 3). In addition to this switching operation, the inverter 10 inverts the polarity of energization at each cycle of a frequency (for example, 100 Hz) corresponding to twice the frequency of the AC circuit 3. This switching operation is extremely slow compared to the switching operation of 20 kHz, for example. On the other hand, while the inverter 10 is performing the switching operation (t0 to t1, t2 to t3, t4 to t5), in the DC/DC converter 6, the switching element Q1 is on or off and the switching element Q2 is off, The voltage/current is directly passed through the switching element Q1 or the diode d5 which is on.
As a result, the desired AC waveform shown in (e) is obtained.

<<Example of charge/discharge control method>>
Next, detection of the current flowing through the storage battery 2 during charging or discharging will be described. The charge/discharge control is performed by the control unit 14 based on the detected current so as to match it with the target value. Therefore, in order to improve the control accuracy, it is necessary to detect the current more accurately.

In the above-mentioned minimum switching conversion method, the current flowing through the storage battery 2 becomes a pulsating flow at the time of charging or discharging.
For example, assuming that the AC side instantaneous voltage v(t), effective value voltage V, instantaneous current i(t), effective value current I, instantaneous power p(t), power factor 1, frequency f, and time t are as follows: Like
v(t)=√2·V·sin(2πft) (1)
i(t)=√2·I·sin(2πft) (2)
p(t)=v(t)·i(t)=2VI·sin ² (2πft) (3)

Since the current ig(t) flowing in the storage battery 2 is basically a value obtained by dividing the AC instantaneous power p(t) shown in the equation (3) by the voltage Vg of the storage battery 2,
ig(t)=2 (VI/Vg)·sin ² (2πft) (4)
=(VI/Vg)·(1-cos(4πft)) (5)
=(VI/Vg)·(1+sin{(3π/2)+4πft}... (6)
Is. Expressions (5) and (6) represent that the current ig becomes a pulsating flow, and the pulsating frequency is twice the frequency on the AC side.
The voltage Vg of the storage battery 2 also has a smaller amplitude than the current, but pulsates in the same cycle.

The upper graph of FIG. 4 is a waveform diagram (the horizontal axis represents time t) showing an example of such a pulsating current. The average value of the current in one cycle τ of the pulsating flow in this case is the illustrated value I1. The cycle τ is 1/2 of one AC cycle of the commercial power system 4P. The lower graph is a waveform diagram showing an example of the terminal voltage of the storage battery 2 when such a pulsating current flows in the storage battery 2. The voltage pulsates in a cycle τ in synchronization with the current. The average value of the terminal voltage in the period τ is V1. As the charging progresses, the terminal voltage of the storage battery 2 rises and the average value rises from V1 to V2. Conversely, during discharge, the terminal voltage drops as the discharge progresses.

Next, the same pulsating current (effective value 20 [A], peak value 28.2 [A]) is taken as an example where the frequency of the AC electric circuit 3 is 50 Hz and the period of the pulsating current flowing in the storage battery 2 is 10 ms. ) Is a graph showing the results of measurement by changing the sampling period.

FIG. 5 is a graph in which the pulsating current detected as a result of measuring the pulsating current during a sampling period of 0.1 ms and 100 ms is plotted. Actually, the pulsating flow is measured over 1000 ms, but up to 100 ms is displayed due to space limitations (hereinafter, the same applies to FIGS. 6 to 8). The vertical axis represents the current [A]. In this case, the waveform is reproduced very faithfully to the actual pulsating flow.
Here, the effective value ig_RMS in a predetermined period T (T1 to T2) within 1000 ms, for example, is _calculated by the following equation (7).

A plurality of such effective values were acquired over 1000 ms, and the averaged value was 20.0 [A].

Next, FIG. 6 is a graph plotting the detected pulsating current as a result of measuring the pulsating current for 100 ms at a sampling period of 1 ms. The vertical axis represents the current [A]. Also in this case, the waveform is reproduced almost faithfully to the actual pulsating flow. However, as compared with FIG. 5, the sampling period is 10 times, so that a slight slight difference in height is seen in the peak value (peak value). A plurality of effective values for a predetermined period are acquired over 1000 ms, and the average value of these values is 20.0 [A], and there is no difference up to the first digit of the decimal point when the sampling cycle is 0.1 ms.

Next, FIG. 7 is a graph obtained by plotting and connecting the detected pulsating currents as a result of measuring the pulsating currents for 100 ms with the sampling period further increased to 10 ms. The vertical axis represents the current [A]. In this case, as is clear from comparison with FIGS. 5 and 6, the actual pulsating flow is not faithfully reproduced, but multiple effective values for a predetermined period are acquired over 1000 ms, and these are averaged. The value obtained was 20.0 [A], and there was no difference up to the first digit of the decimal point with the sampling periods of 0.1 ms and 1 ms.

Further, FIG. 8 is a graph obtained by plotting and connecting the detected pulsating currents as a result of measuring the pulsating current for 100 ms with the sampling period being increased by 50% in FIG. 7 to 15 ms. The vertical axis represents the current [A]. Also in this case, as in FIG. 7, the actual pulsating flow is not faithfully reproduced, but a plurality of effective values for a predetermined period are acquired over 1000 ms, and the averaged value is 20.1. It was [A], and there was an error of 0.1 [A] in one decimal place. However, if the sampling period is further lengthened, the error is expected to increase.

From FIGS. 5 to 8, when the sampling period is the same as the pulsating flow period (10 ms in this example) or about 50% increase, the error can be suppressed to a sufficiently small level by averaging the effective values. I understand. If the detection accuracy is given the highest priority, it is preferable that the sampling cycle is short, but in that case, the calculation processing load of the CPU of the control unit 14 becomes heavy, and therefore it is necessary to use a high-performance and high-priced CPU. Considering the cost performance of the power conversion device 1 as a whole, it is not enough to make the sampling period very small.

Therefore, it is practically possible to select a sampling period that is not significantly different from the pulsating flow period (for example, 0.1 times to 1.5 times) while using a relatively inexpensive CPU with an arithmetic processing capacity that is not too high. , Considered preferable.

As described above, as charge/discharge control when the current and voltage related to charging or discharging the storage battery 2 have a pulsating waveform, the pulsating waveform is sampled at a predetermined cycle, and the effective value based on the detected value obtained by sampling is determined. It is possible to obtain an averaged value in a predetermined period and control charging/discharging based on the averaged value.
By executing such charge/discharge control, it is possible to obtain the detection value with high accuracy even with a current or voltage having a pulsating waveform. Thereby, the accuracy of control in charging or discharging can be improved.

However, the sampling period has a value that should not be selected.
FIG. 9: is a figure showing the pulsating current of 100 Hz (2 times 50 Hz, a solid line) and 120 Hz (2 times 60 Hz, a broken line).
For example, focusing on the waveform of the solid line, if the sampling period is set to 10 ms (1 times the pulsating flow period) and sampling is started from time 10 ms, the same value is detected in succession as 20, 30, 40, 50 ms. This is the case (the solid circle in the figure). In this case, even if the effective values are averaged, they do not become reasonable values. Even if the sampling period is 20 ms (twice the pulsating flow period), 30 ms (three times the pulsating flow period), 40 ms (four times the pulsating flow period), the result is the same.

On the other hand, paying attention to the waveform of the broken line, assuming that the sampling period is 8.33 ms (one time of the pulsating flow period) and sampling is started from time 10 ms, (10+8.33) ms, (10+8.33×2) ms, (10+8.33×3)ms, and (10+8.33×4)ms, the same values are detected in succession (circle mark of broken line in the figure). In this case, even if the effective values are averaged, they do not become reasonable values. Even if the sampling period is set to 16.67 ms (twice the pulsating flow period), 25 ms (three times the pulsating flow period), 33.33 ms (four times the pulsating flow period), the result is the same.

That is, the sampling period to be avoided is a period that is a natural number multiple of one period of the pulsating waveform. Therefore, the predetermined cycle that should be the sampling cycle must be a cycle other than a cycle that is a natural multiple of one cycle of the pulsation waveform.
As a result, the value of the pulsating waveform can be detected evenly in phase. Therefore, the detected values can be obtained with high accuracy by taking the effective values and averaging them. As a result, the accuracy of charge/discharge control can be improved.

FIG. 10 is a graph showing an error between a true value and a value averaged based on sampling (value obtained by averaging effective values) when the sampling cycle is changed in the range of 0 to 0.1 [s]. Is. In the figure, the error has a change in a narrow time width with sharp peaks and valleys as the sampling cycle increases, and a large change with 50 ms as one section when the whole is viewed as a large envelope. .. That is, the left half and the right half of the figure have similar change characteristics to each other around 0.050 [s].
Table 1 below summarizes the extra-large, large, medium, small, and minimum errors in the shorter sampling period (that is, in the left half of the figure) in association with the sampling period.

Therefore, in Table 1, it is preferable to select the sampling period from the sampling period range in which the error is “minimum”. Furthermore, it is more desirable that the number of samplings is N=30 or more, which statistically reflects the influence of variations.
Then, when the sampling cycle is changed, the change characteristic appearing in the error between the averaged value and the true value is grasped in advance, and the sampling cycle in which the error becomes relatively small is selected. Of course, it is necessary to avoid a natural multiple of the pulsating cycle.
This makes it possible to obtain an averaged value with less error.

《Others》
In addition, although the pulsating current has been described as an object from FIG. 6 onward, the pulsating voltage shown in the lower part of FIG. 4 is similarly obtained by averaging the effective value based on the detection value obtained by sampling over a predetermined period. By controlling the charging/discharging based on the averaged value, the accuracy of the control can be increased.

Also, in the case of a power conversion device configured by an inverter alone without using a DC/DC converter, the DC side has a pulsating flow. Therefore, also in this case, the charge/discharge control based on the averaged value can be similarly applied.
A battery system using a fuel cell instead of the storage battery is also conceivable. Also in this case, similarly, by applying the discharge control based on the averaged value, the accuracy of the discharge control of the fuel cell can be improved.

《Supplementary note》
It should be understood that the embodiments disclosed this time are exemplifications in all points and not restrictive. The scope of the present invention is shown by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

1 Power Converter 2 Storage Battery 3 AC Line 4L Load 4P Commercial Power System 5 DC Capacitor 6 DC/DC Converter 7 DC Reactor 8 DC Bus 9 Intermediate Capacitor 10 Inverter 11 Filter Circuit 12 AC Reactor 13 AC Side Capacitor 14 Controller 15 Voltage Sensor 16 Current sensor 17 Voltage sensor 18 Current sensor 19 Voltage sensor 20 Power converter 21 BMS
d1 to d6 diodes Q1 to Q6 switching elements

Claims (4)

A charging/discharging control method when a current and a voltage related to charging or discharging a battery have a pulsating waveform,
Sampling the pulsating waveform in a cycle other than a cycle that is a natural multiple of one cycle of the pulsating waveform,
Obtaining a value obtained by averaging the effective value based on the detection value obtained by the sampling in a predetermined period,
The charge/discharge is controlled based on the averaged value,
Charge/discharge control method. When the sampling cycle is changed, the change characteristics appearing in the error between the averaged value and the true value are grasped in advance,
The charge/discharge control method according to claim 1 , wherein the sampling period in which the error is relatively small is selected . A battery,
A power conversion device provided between the battery and an alternating current circuit, wherein the current and voltage relating to charging or discharging of the battery have a pulsating waveform,
The power conversion device samples the pulsation waveform in a cycle other than a cycle that is a natural number multiple of one cycle of the pulsation waveform, and averages an effective value based on a detection value obtained by the sampling in a predetermined period. A battery system that obtains and controls charging and discharging based on the averaged value . And 蓄 battery,
Wherein provided between the 蓄 battery and the AC circuit, and a power conversion device current and voltage is pulsating waveform of the charging and discharging of the 蓄 battery,
The power conversion device samples the pulsation waveform in a cycle other than a cycle that is a natural number multiple of one cycle of the pulsation waveform, and averages an effective value based on a detection value obtained by the sampling in a predetermined period. seeking to control the charging and discharging based on the value obtained by the averaging, 蓄 cell system.