JP7412388B2 - power converter - Google Patents

Description

The present application relates to a power conversion device.

Power conversion devices installed in hybrid vehicles (HEVs), electric vehicles (EVs), etc. are required to be smaller and lower in cost.
In an on-vehicle power conversion device that controls output power based on input power, a current transformer (CT) is used for current detection with the aim of reducing size and cost. When using a current transformer, the detected current value may deviate from the actual current value. For example, Patent Document 1 listed below discloses a technique for correcting errors caused by detected current using a field effect transistor (FET) in a current detection circuit using a current transformer.

Japanese Patent Application Publication No. 2014-119354

In order to read the current value converted into voltage through the current transformer, a smoothing circuit consisting of a filter resistor and a filter capacitor is installed after the current transformer to avoid the use of a high-speed AD converter that is usually combined with a microcomputer, for example. A microcomputer reads the voltage smoothed by this smoothing circuit. However, the above technique cannot take into account current detection errors caused by differences in frequency components extracted by the smoothing filter, and errors still occur. For example, when the duty ratio is narrow, the high frequency component of the overall input current increases, and the detected voltage value after filtering by a smoothing circuit for AD conversion tends to decrease.

This application is intended to solve the above-mentioned problems, and corrects the current value based on the duty ratio of the drive signal that drives the semiconductor switching element of the power conversion circuit, thereby correcting the difference in frequency components of the obtained current. An object of the present invention is to obtain a power conversion device that suppresses detection errors that occur.

The power conversion device disclosed in this application includes a power conversion circuit having a semiconductor switching element, a current transformer for converting and detecting the input current of the power conversion circuit into a voltage, and A power converter that includes a smoothing circuit that performs smoothing and a control section that uses the output voltage of the smoothing circuit as input to control a drive signal that drives a semiconductor switching element, and corrects the output voltage of the smoothing circuit based on the duty ratio of the drive signal of the semiconductor switching element. In the device, the control unit obtains in advance the true input current and the output voltage of the smoothing circuit when the duty ratio is varied from the minimum value when the duty ratio is narrow to the maximum value when the duty ratio is wide, and calculates the true input current. It has a storage section that stores the correlation between the current and the output voltage of the smoothing circuit as a coefficient for correcting when converting the smoothed output voltage into a current value of the current transformer ,
Let the output voltage of the smoothing circuit of the true input current be V_flat_real,
Let the output voltage of the smoothing circuit when the duty ratio is narrow be V_flat,
Let the current duty ratio be duty,
If the maximum duty ratio, which is the maximum value when the duty ratio is large, is duty_large, then based on the following formula (1),

V_flat_real=V_flat×(duty_large/duty) (1)

The ratio between the current duty ratio and the maximum duty ratio is set as a gain, and the output voltage of the smoothing circuit is multiplied by the gain to correct the output voltage of the smoothing circuit with respect to the input current.

According to the power conversion device of the present application, a power conversion device capable of detecting accurate current values can be realized.

1 is a diagram showing a circuit configuration of a power conversion device according to a first embodiment; FIG. 3 is a diagram showing an example of a frequency spectrum of an input current in the power conversion device according to the first embodiment. FIG. FIG. 3 is a diagram showing the correlation between the input current and the output voltage of the smoothing circuit in the power conversion device according to the first embodiment. FIG. 2 is a diagram illustrating an example of a hardware configuration of a control unit in a power conversion device according to an embodiment.

Embodiment 1.
Embodiment 1 will be described below.
FIG. 1 is a block diagram showing an example of a power conversion device 1 according to the first embodiment. As shown in FIG. 1, it has a current transformer 11, a reset resistor 12, a voltage dividing resistor 13, a diode 14, a filter resistor 15, and a filter capacitor 16, and further includes a semiconductor switching element 17a connected to the rear stage of the current transformer 11, 17b, 17c, 17d, a transformer 18, diodes 19a, 19b, 19c, 19d, and a smoothing reactor 20. The power conversion circuit 100 constitutes a DC/DC converter, and control drivers 101a, 101b, 101c, and 101d are connected to each of the semiconductor switching elements 17a to 17d. A sensor circuit 300 is connected to the input side of the power conversion device 1, and a sensor circuit 400 is connected to the output side thereof.

The control drivers 101a to 101d receive drive signals Dra, Drb, Drc, and Drd output from the first control section 200a, and drive the semiconductor switching elements 17a to 17d. The semiconductor switching elements 17a to 17d are, for example, self-extinguishing semiconductors such as MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors), or wide bandgap semiconductors. It may be a semiconductor.

The control section 200 is separated into a first control section 200a and a second control section 200b, and the second control section 200b has a storage section 200c.
Generally, the first control unit 200a is configured with a general-purpose IC to reduce cost. In the general-purpose IC, for example, the drive signals Dra to 17d of the semiconductor switching elements 17a to 17d are set so that the output voltage value Vout obtained by the output side sensor circuit 400 approaches the output voltage command value V ^* from the second control unit 200b. Controls the duty ratio of Drd.

The semiconductor switching elements 17a to 17d are driven by PWM control by the first control section 200a. The first control unit 200a generates drive signals Dra to Drd. The drive signals Dra to Drd are connected to the gates of the semiconductor switching elements via control drivers 101a to 101d. Further, the second control unit 200b also monitors the input voltage value Vin detected by the sensor circuit 300 and the output voltage value Vout detected by the sensor circuit 400, for example, for overvoltage detection of the input/output voltage. The second control unit 200b is, for example, a microcomputer.

The current of the current transformer 11 is converted into a voltage via the voltage dividing resistor 13, smoothed via a smoothing circuit composed of filter elements of a filter resistor 15 and a filter capacitor 16, and inputted to the second control unit 200b. be done. By smoothing through filter processing using a smoothing circuit, the second control unit 200b does not require a high-speed AD converter, and can reduce costs. The second control unit 200b converts the voltage output through the filter resistor 15 and the filter capacitor 16 into a current value of the current transformer 11, and outputs the current value to the outside of the power conversion device 1.

The second control section 200b includes a storage section 200c that stores coefficients for correction when converting the output voltage smoothed by the filter resistor 15 and the filter capacitor 16 into a current value of the current transformer 11. ing.

Below, a method of correcting the detected current with respect to the duty ratio of the drive signals Dra to Drd of the semiconductor switching elements 17a to 17d will be explained. When the duty ratio detected by the second control unit 200b is narrower than a predetermined duty ratio (also referred to as "narrow duty ratio") , the detected input current is corrected to increase. When the duty ratio is narrow, the input current will have many high frequency components. However, high frequency components of the detected input current value that has been AD-converted via the filter resistor 15 and filter capacitor 16 that constitute the smoothing circuit are cut off (see FIG. 2). When the duty ratio is narrow, high-frequency current components are dominant. Note that the time when the duty ratio is much larger than the predetermined duty ratio described above is also referred to as the time when the duty ratio is wide.

Since the detected input current value is equal to the sum of squares of the spectrum below the cutoff frequency fc, the detected input current value is output as a value smaller than the true input current. Therefore, by compensating for the high frequency component of the input current smoothed through the filter resistor 15 and filter capacitor 16 through the above-described correction, it is possible to solve the problem in which the input current is detected as decreasing when the duty ratio is narrow.

Below, correction of the detected current using the ratio between the current duty ratio and the maximum duty ratio (predetermined maximum duty ratio) when the duty ratio is wide will be described. While the duty ratio varies depending on the input current value, the frequency component amount of the input current is proportional to the effective value of the input current, so the amount of current component reduced by the filter resistor 15 and filter capacitor 16 does not depend on the duty ratio. (See Figure 3). Therefore, the duty ratio is corrected using the ratio of the maximum duty ratio.
Generally, one cycle of the drive frequency in the drive signal of the semiconductor switching elements that make up the power conversion circuit is T, and the dead period is set to prevent short circuits between the upper and lower arms made up of the semiconductor switching elements. When the time is Td, the "maximum duty ratio" can be expressed as (T-2×Td)/T, and the "minimum duty ratio" can be expressed as the minimum pulse width of the drive signal that the controller 200a can output.
In addition, as shown in Figure 3, from a narrow duty ratio to a wide duty ratio, the input current and the smoothing circuit output voltage have a linear correlation with a certain slope. If you have obtained the "smoothing circuit output voltage and true input current" and "smoothing circuit output voltage and true input current when the duty ratio is wide", it is possible to calculate the input current from the current smoothing circuit output voltage. becomes. FIG. 3 shows this correlation. A calculation formula for determining the true input current using this relationship is formula (1), which will be described later. Therefore, this correlation is a precondition for equation (1).

Specifically, the true input current and the output voltage of the smoothing circuit consisting of the filter resistor 15 and the filter capacitor 16 are calculated when the duty ratio is varied from the minimum value when the duty ratio is narrow to the maximum value when the duty ratio is wide. The correlation between the true input current and the output voltage of the smoothing circuit is obtained in advance and stored in the storage unit 200c as a coefficient for correction when converting the smoothed output voltage into the current value of the current transformer. Based on the formula (1) below, the ratio between the current duty ratio and the maximum duty ratio is used as a gain, and the output voltage of the smoothing circuit is corrected by multiplying the output voltage of the smoothing circuit by this gain, and the detected value of the input current is Correct.
That is, regarding the correlation between the true input current and the output of the smoothing circuit, the coefficient is used in an arithmetic expression for deriving a correction value in a specific arithmetic relationship.
V_flat_real=V_flat×(duty_large/duty) (1)
In the above equation (1), V_flat_real is the output voltage of the smoothing circuit for the true input current, V_flat is the output voltage of the smoothing circuit when the duty ratio is narrow, duty is the current duty ratio, and duty_large is the maximum duty. Show the ratio. Here, "duty_large" in equation (1) is the time when the duty ratio is the largest among the wide range of duty ratios shown in FIG. Further, "duty_large/duty" in equation (1) represents the ratio between the current duty ratio and the maximum duty ratio.
In this way, by correcting in advance the amount that the output voltage detected by the smoothing circuit changes depending on the duty ratio using the input current, the output voltage of the smoothing circuit that corresponds to the correctly corrected input current is detected as a result. be done.

A method of measuring the duty ratio in the second control section 200b will be described below. The second control unit 200b measures the duty ratio of the drive signals Dra to Drd based on the detected input voltage value Vin and output voltage value Vout using the following equation (2). In equation (2), duty indicates the duty ratio of the drive signals Dra to Drd, Vin indicates the input voltage value, and Vout indicates the output voltage value.
duty=1-(Vin/Vout)...(2)
By measuring the duty ratio as described above in the second control unit 200b, the duty ratio can be measured without the need for additional parts to calculate the duty ratio by reusing the existing detection circuit. .

In this embodiment, the correlation between the true input current and the output voltage of the smoothing circuit when the duty ratio is wide is used as a reference, but the correlation between the true input current and the output voltage of the smoothing circuit when the duty ratio is narrow is used as the standard. Based on the correlation with the output voltage of the smoothing circuit, correction may be applied to reduce the input current detected when the detected duty ratio is large.

The first control section 200a, second control section 200b, and storage section 200c in this embodiment may be one control section. In general, the duty ratio is calculated by Equation (2) using input and output voltages, and also increases as the output current increases due to a voltage drop in a circuit section or the like. Therefore, if the first control section 200a, the second control section 200b, and the storage section 200c are integrated into one control section, the actual duty ratio can be known in the control section 200, so that the current value can be calculated with higher accuracy. Correction becomes possible.

That is, the control unit 200 obtains in advance the true input current and the output voltage of the smoothing circuit when the duty ratio is varied from the minimum value to the maximum value, and calculates the correlation between the true input current and the output voltage of the smoothing circuit. It has a storage unit 200c for storing information, uses the ratio of the current duty ratio to the maximum duty ratio as a gain, and corrects the detected value of the input current by multiplying the output voltage of the smoothing circuit by the gain.

Further, the control unit 200 obtains in advance the true input current and the output voltage of the smoothing circuit when the duty ratio is varied from the minimum value to the maximum value, and calculates the correlation between the true input current and the output voltage of the smoothing circuit. It has a storage unit 200c for storing the information, uses the ratio of the current duty ratio to the minimum duty ratio as a gain, and corrects the detected value of the input current by multiplying the output voltage of the smoothing circuit by the gain.

In addition, in Embodiment 1, an example of a full bridge DC/DC converter was shown as the power conversion circuit 100, but the circuit configuration is not limited to this, and any configuration that uses a smoothing circuit for AD conversion may be used. An LLC type or half bridge type DC/DC converter may be used.

Note that the control unit 200 includes a processor 201 and a storage device 202, as an example of hardware is shown in FIG. The storage device 202 includes, for example, a volatile storage device such as a random access memory, and a nonvolatile auxiliary storage device such as a flash memory. Further, an auxiliary storage device such as a hard disk may be provided instead of the flash memory. Processor 201 executes a program input from storage device 202 . In this case, the program is input from the auxiliary storage device to the processor 201 via the volatile storage device. Further, the processor 201 may output data such as calculation results to a volatile storage device of the storage device 202, or may store data in an auxiliary storage device via the volatile storage device.

Although this application describes exemplary embodiments, the various features, aspects, and functions described in the embodiments are not limited to the application of particular embodiments, and may be used alone or It is applicable to the embodiments in various combinations.
Accordingly, countless variations not illustrated are envisioned within the scope of the technology disclosed herein. For example, this includes cases in which at least one component is modified, added, or omitted.

Reference Signs List 1 power converter, 11 current transformer, 15 filter resistor, 16 filter capacitor, 17a to 17d semiconductor switching element, 100 power converter circuit, 200 control section, 200a first control section, 200b second control section, 200c storage section

Claims (2)

a power conversion circuit having a semiconductor switching element;
a current transformer for converting the input current of the power conversion circuit into voltage and detecting the voltage;
a smoothing circuit that smoothes the output of the secondary side of the current transformer;
A power conversion device including a control unit that controls a drive signal for driving the semiconductor switching element using the output voltage of the smoothing circuit as an input, and corrects the output voltage of the smoothing circuit based on the duty ratio of the drive signal of the semiconductor switching element. In,
The control unit obtains in advance the true input current and the output voltage of the smoothing circuit when the duty ratio is varied from a minimum value when the duty ratio is narrow to a maximum value when the duty ratio is wide, and It has a storage section that stores the correlation between the input current and the output voltage of the smoothing circuit as a coefficient for correcting when converting the smoothed output voltage into a current value of the current transformer ,
Let the output voltage of the smoothing circuit of the true input current be V_flat_real,
Let the output voltage of the smoothing circuit when the duty ratio is narrow be V_flat,
Let the current duty ratio be duty,
If the maximum duty ratio, which is the maximum value when the duty ratio is large, is duty_large, based on the following formula (1),

V_flat_real=V_flat×(duty_large/duty) (1)

A power conversion device characterized in that a ratio between a current duty ratio and a maximum duty ratio is used as a gain, and the output voltage of the smoothing circuit is multiplied by the gain to correct the output voltage of the smoothing circuit with respect to the input current. . The power conversion unit according to claim 1, wherein the control unit is separated into a first control unit that drives the semiconductor switching element and a second control unit that obtains the output of the smoothing circuit. Device.

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