JP2015162951A - bidirectional converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bidirectional converter capable of suppressing the occurrence of reverse currents in a start-up time in the case of continuously controlling step-up/step-down or charging/discharging.SOLUTION: The bidirectional converter includes: a switch element Q1 connected to the positive electrode side of an input/output terminal T1 and one end of a coil L; a switch element Q2 connected to the negative electrode side of the input/output terminal T1 and one end of the coil L; a switch element Q3 connected to the positive electrode side of the input/output terminal T2 and the other end of the coil L; and a switch element Q4 connected to the negative electrode side of the input/output terminal T2 and the other end of the coil L. In a normal time, the switch elements Q1 and Q2 are configured to complementarily operate, and the switch elements Q3 and Q4 are configured to complementarily operate, and to bidirectionally convert a voltage and power. In a fixed period from a start-up time to the normal time, at least one of the switch elements Q1 to Q4 which are turned on in the normal time is turned off, and at least one combination between the combination of the switch elements Q1 and Q2 and the combination of the switch elements Q3 and Q4 is not configured to complementarily operate.

Description

  The present invention relates to a bidirectional converter that converts voltage and power in both directions and outputs the result.

  Since the Great East Japan Earthquake, attention has been focused on so-called renewable energy such as solar power generation and wind power generation, and in particular, the introduction of solar panels used for solar power generation has been accelerated. On the other hand, these renewable energies have a problem that can be a factor that disturbs the system voltage because the output depends on the weather and the climate, and the supply and demand of power do not always match.

  As one of countermeasures against such problems, peak shift using a storage battery is being studied. This is a system that supplies demand to the grid via PCS (Power Conditioning System) and stores excess energy in the storage battery. The demand exceeds the power generation. In this case, the energy stored in the storage battery is released to match the output of renewable energy with the actual power demand.

  When actually using a storage battery, a process is required in which the storage battery is charged to store energy, and discharged from the storage battery as necessary to release energy. The above process is generally performed by a bidirectional DC / DC converter. However, in two power conversions of charge / discharge, a conversion loss occurs in each. For this reason, in order to effectively use energy, a bidirectional DC / DC converter that can perform power conversion with higher efficiency is required.

  The bidirectional converter has four operations in terms of circuit operation: (1) step-down charge, (2) step-up discharge, (3) step-up charge, and (4) step-down discharge when there is no restriction on the input / output voltage relationship. Need to do. These operations include, for example, four power semiconductor elements, a magnetic component (coil), and two input / output terminals, and two power semiconductor elements are connected in cascade to each of the two input / output terminals. This can be realized by a bidirectional converter having a circuit configuration in which each of the midpoints of the elements are connected by magnetic components. However, in this case, the operation pattern of each switch is different for each of the operations (1) to (4), and the switch element operated by a PWM (pulse width modulation) signal for controlling the amount of power conversion is also included. , (1) to (4) for each operation, the control becomes complicated.

  In order to simplify the control, the voltage relationship is limited in advance, for example, by limiting the operating range to a condition where the voltage of the rechargeable battery is always lower than the system voltage, the necessary operation is (1) step-down charging and (2) It is possible to limit the boost discharge to two. On the other hand, in this case, it is necessary to lower the setting range of the storage battery in consideration of the operation margin, and since the current peak value increases accordingly, transmission loss and switching loss may increase, and efficiency may decrease. . In general, the efficiency of the converter tends to show higher efficiency as the voltage conversion rate is closer to 1, and therefore, this high efficiency region cannot be set as the operation range.

  When the operation range is not limited for higher efficiency, the control becomes complicated with four operation modes as described above. Patent Document 1 discloses a method for simplifying control to cope with such a problem. Patent Document 2 describes an example of continuous control of a bidirectional converter.

  FIG. 13A is a block diagram showing a conventional bidirectional converter, and shows a main circuit unit 100 and a switching control unit 200. A diagram equivalent to the block diagram showing the main circuit portion (step-up / step-down portion) and the switching control portion of the bidirectional converter disclosed in Patent Document 1 is created and shown as FIG. 13A. For the sake of explanation, it is assumed in FIG. 13A that a storage battery is connected to the voltage source A, and a PCS or the like is connected to the voltage source B via a DC bus wiring. Accordingly, the following description will be made on the assumption that discharging is performed when current flows in the direction from the voltage source A to the voltage source B, and charging is performed when current flows in the direction from the voltage source B to the voltage source A.

  The conventional bidirectional converter includes a main circuit unit 100 and a switching control unit 200. The main circuit unit 100 includes switch elements S1 to S4 and a magnetic component (coil) M. The switching control unit 200 includes a PWM signal distribution unit. 220. Further, a capacitor C1 is connected in parallel with the switch elements S1 and S2, and a capacitor C2 is connected in parallel with the switch elements S3 and S4.

  The switching control unit 200 generates a control signal that changes in the range of 0% to 200%. This control signal is compared with a reference value by the PWM signal distributor 220. When the current direction is charging and the control signal is 100% or less of the boost reference value, the switching control unit 200 drives the switch element S2 with the corresponding PWM signal, turns off the switch elements S1 and S4, and switches The device S3 is turned on to perform boost charge. On the other hand, when the control signal changes and exceeds 100% of the boost reference value, the switching control unit 200 drives the switch element S3 with the corresponding PWM signal and turns off the other switch elements S1, S2, and S4. To. Similarly, when the current direction is discharge, the switch element S4 is driven by a PWM signal in the case of step-up and the switch element S1 is driven in the case of step-down. As described above, the control range can be simplified and a cheaper controller can be used by expanding the control signal fluctuation range and sharing the control of the switch elements S1 to S4 corresponding to the two operations.

  However, in the above-described control, although the boosting and bucking processes are shared in the process of deriving the control value, the charging and discharging processes in which the direction of current is reversed remain separate.

  FIG. 13B is a diagram showing an example of operation waveforms of the conventional bidirectional converter shown in FIG. 13A. The upper part of FIG. 13B shows the inductor current when the discharge direction is positive, and the lower part shows the operation waveforms of the switch elements S1 to S4 during the boost discharge. The lower part of FIG. 13B shows an example of a change in the operation waveform when the direction of current is switched from discharging to charging by the method described in Patent Document 1.

  FIG. 13B will be briefly described. From the state in which the switch S4 for controlling the amount of current for boosting discharge is driven by the PWM signal, the duty of S4 is reduced as a previous step to reduce the discharge current to zero. Next, in order to start the charging current, S1 that was in the on state is turned off, and the duty of the step-down charging switch element S3 is gradually increased from the minimum to increase the charging current.

JP 2012-205427 A JP 2012-244642 A

  In the case of constructing a power storage system combined with photovoltaic power generation using a bidirectional converter, the direction of the current flowing through the bidirectional converter can change frequently when the power generation amount, that is, the supply amount and the demand amount are close to each other. In such a case, in the method described in Patent Document 1, it is necessary to increase the charging current flowing in the reverse direction after reducing the discharge current to 0 as described above. For this reason, in the bidirectional converter, there is a possibility that the response is delayed and the fluctuation range of the control voltage is increased. In order to suppress this, it is effective to connect larger capacity electrolytic capacitors to the input / output terminals as the capacitors C1 and C2. However, this method is not preferable because it causes an increase in cost.

  That is, a bidirectional converter used in a power storage system combined with power generation of renewable energy such as solar power generation is required to have a method for continuously charging and discharging, which is not described in Patent Document 1. Therefore, there is a demand for a control method that can suppress the change of the direction of the current, that is, the current that flows in the reverse direction (reverse current). Neither Patent Document 1 nor Patent Document 2 discloses a method for suppressing reverse current.

  The present invention relates to a bidirectional converter that can suppress the generation of reverse current at start-up when the buck-boost or charge / discharge is continuously controlled in a bidirectional converter that converts voltage and power bidirectionally. The purpose is to provide.

  The bidirectional converter according to the present invention has the following characteristics.

  A first input / output terminal connected to the first external device, a second input / output terminal connected to the second external device, a coil, a positive electrode side of the first input / output terminal, and the coil A first switch element connected between one end of the first input / output terminal, a second switch element connected between the negative electrode side of the first input / output terminal and the one end of the coil, and the second switch element A third switch element connected between the positive electrode side of the input / output terminal and the other end of the coil; and a third switch element connected between the negative electrode side of the second input / output terminal and the other end of the coil. A fourth switch element. In a steady state, the first switch element and the second switch element operate complementarily, and the third switch element and the fourth switch element operate complementarily, and the first input / output Voltage and power are converted from a terminal to the second input / output terminal or from the second input / output terminal to the first input / output terminal. During a certain period from the start to the steady state, at least one of the first switch element to the fourth switch element that is on during the steady state is turned off, and the first switch element and the At least one of the second switch element set and the third switch element / fourth switch element set does not operate in a complementary manner.

  ADVANTAGE OF THE INVENTION According to this invention, in the bidirectional | two-way converter which converts a voltage and electric power bidirectionally, when controlling buck-boost or charging / discharging continuously, generation | occurrence | production of the reverse current at the time of starting can be suppressed. A converter can be provided.

It is a block diagram of the bidirectional | two-way converter by Example 1 of this invention. It is the table | surface which put together the operation pattern of switch element Q1-Q4 in four operation | movement. It is a table | surface which shows the operation pattern in four operation | movement at the time of steady state of the switch elements Q1-Q4 of the bidirectional | two-way converter in Example 1. FIG. It is the table | surface which put together the table | surface of FIG. 2B. It is a figure which shows the current waveform at the time of starting by the boost discharge of the bidirectional | two-way converter of Example 1 with the operation waveform of each switch element Q1-Q4. It is a figure which shows an example of the outline of a waveform until the bidirectional | two-way converter of Example 1 starts by a pressure | voltage fall discharge, and transfers to pressure | voltage rise discharge after that. It is a figure which shows an example of the outline of a waveform until the bidirectional | two-way converter of Example 1 starts by step-down discharge, and transfers to step-up charge after that. It is a figure which shows an example of the outline of a waveform until the bidirectional | two-way converter of Example 1 starts by pressure | voltage rise discharge, and transfers to pressure | voltage fall discharge after that. It is a figure which shows an example of the outline of a waveform until the bidirectional | two-way converter of Example 1 starts by pressure | voltage rise discharge, and transfers to step-down charge after that. It is a figure which shows an example of the outline of a waveform until the bidirectional | two-way converter of Example 1 starts by step-up charge, and transfers to step-down charge after that. It is a figure which shows an example of the outline of a waveform until the bidirectional | two-way converter of Example 1 starts by pressure | voltage rise charge, and transfers to pressure | voltage fall discharge after that. It is a figure which shows an example of the outline of a waveform until the bidirectional | two-way converter of Example 1 starts by step-down charge, and transfers to step-up charge after that. It is a figure which shows an example of the outline of a waveform until the bidirectional | two-way converter of Example 1 starts by step-down charge, and transfers to step-up discharge after that. It is a figure which shows an example of an operation | movement when the bidirectional | two-way converter by Example 2 of this invention starts with a boost discharge. It is a block diagram which shows the conventional bidirectional | two-way converter. It is a figure which shows the example of an operation | movement waveform when the direction of an electric current of the conventional bidirectional converter switches. It is a figure explaining the outline | summary of the control flow of the bidirectional | two-way converter by Example 1. FIG. It is a figure which shows the structural example of the system using the bidirectional | two-way converter by this invention in the electrical storage system combined with photovoltaic power generation.

  The present invention is a system that realizes a peak shift in combination with a storage battery (for example, a storage battery and a PCS) in order to effectively use a so-called renewable energy power generation facility whose output is not always stable, such as solar power generation. In a system including a bidirectional DC / DC converter that connects them), it is possible to perform high-speed switching of operation such as step-up / step-down or charge / discharge under a high-efficiency voltage condition without generating a reverse current at startup. A simple bidirectional converter. In addition, since the present invention realizes the above control by a simpler method, it is possible to use a cheaper controller for the bidirectional converter, and to reduce the design cost of the bidirectional converter and the man-hour for creating the control program. Also contribute.

  The bidirectional converter according to the present invention includes four switch elements. In a steady state, the first switch element and the second switch element operate complementarily, and the third switch element and the fourth switch element complement each other. To work. During a certain period from the start to the steady state, at least one of the first switch element to the fourth switch element that is on during the steady state is turned off, and the first switch element and the second switch element are combined. Then, at least one of the third switch element and the fourth switch element does not operate in a complementary manner.

  ADVANTAGE OF THE INVENTION According to this invention, the reverse direction current at the time of starting can be suppressed in the bidirectional | two-way converter which performs switching control in the case of the voltage conditions of a buck-boost or charge / discharge, or the change of a current direction. For this reason, the bidirectional converter according to the present invention can respond to a change in operating conditions such as step-up / step-down or charging / discharging at high speed. Further, by applying the same control at the time of high load, it is possible to suppress the power consumption of the bidirectional converter and improve the efficiency.

  Hereinafter, a bidirectional converter according to an embodiment of the present invention will be described with reference to the drawings. The bidirectional converter according to the embodiment of the present invention is a DC / DC converter that converts voltage and power in both directions and outputs the converted voltage and power.

  A bidirectional converter according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram of a bidirectional converter according to Embodiment 1 of the present invention. In FIG. 1, a non-insulated bidirectional DC / DC converter is shown as an example. As shown in FIG. 1, the bidirectional converter 1 includes a main circuit unit 10 that converts power and a switching control unit 20 that controls the main circuit unit 10, and includes a first input / output terminal T1 and a second input / output terminal T2. And an input / output terminal T2. The first input / output terminal T1 is connected to the first external device, and the second input / output terminal T2 is connected to the second external device.

  The configuration of the main circuit unit 10 will be described. A first switch element Q1 and a second switch element Q2 connected in cascade are connected to the first input / output terminal T1, and a first capacitor C1 is connected in parallel with the switch elements Q1 and Q2. Is connected. The first switch element Q1 is connected to the positive electrode side of the first input / output terminal T1, and the second switch element Q2 is connected to the negative electrode side of the first input / output terminal T1. A third switch element Q3 and a fourth switch element Q4 connected in cascade are connected to the second input / output terminal T2, and a second capacitor C2 is connected in parallel with the switch elements Q3 and Q4. Is connected. The third switch element Q3 is connected to the positive electrode side of the second input / output terminal T2, and the fourth switch element Q4 is connected to the negative electrode side of the second input / output terminal T2.

  A coil L, which is a magnetic component, is connected to a connection portion between the first switch element Q1 and the second switch element Q2 and a connection portion between the third switch element Q3 and the fourth switch element Q4. Further, since the bidirectional converter 1 is a non-insulated type, the negative electrode sides of the first input / output terminal T1 and the second input / output terminal T2 are both connected to a common reference potential. The bidirectional converter 1 in FIG. 1 is sometimes called an H-bridge type circuit because of its shape.

  In this embodiment, a voltage source A is connected as a first external device to the first input / output terminal T1, and a voltage source B is connected as a second external device to the second input / output terminal T2. Shall be. Here, for the following explanation, it is assumed that a storage battery is connected to the voltage source A, and a DC bus wiring on the system (for example, PCS) side is connected to the voltage source B. For this reason, when the current i flowing through the bidirectional converter 1 flows from the voltage source A toward the voltage source B, discharge occurs, and conversely, when the current i flows from the voltage source B toward the voltage source A, charging occurs. That is, discharging is performed when output from the second input / output terminal T2 to the voltage source B, and charging is performed when outputting from the first input / output terminal T1 to the voltage source A. At this time, the direction of the current i flowing through the bidirectional converter 1 is “positive” in the case of discharging and “negative” in the case of charging. In addition, the voltage of a storage battery is represented by Vbat, and the voltage of the DC bus on the system side is represented by Vrail. The voltage Vbat is the voltage at the first input / output terminal T1, and the voltage Vrail is the voltage at the second input / output terminal T2.

  Each of the first to fourth switch elements Q1 to Q4 includes an IGBT (Insulated Gate Bipolar Transistor) and diodes 13a to 13d connected in parallel. The collector terminal of the switch element Q1 is connected to the positive electrode side of the first input / output terminal T1. The emitter terminal of the switch element Q1 and the collector terminal of the switch element Q2 are connected to one end of the coil L. The emitter terminal of the switch element Q2 is connected to the negative electrode side of the first input / output terminal T1. The collector terminal of the switch element Q3 is connected to the positive electrode side of the second input / output terminal T2. The emitter terminal of the switch element Q3 and the collector terminal of the switch element Q4 are connected to the other end of the coil L. The emitter terminal of the switch element Q4 is connected to the negative electrode side of the second input / output terminal T2.

  The positive terminal of the first capacitor C1 is connected to the collector terminal of the switch element Q1, and the negative terminal of the first capacitor C1 is connected to the emitter terminal of the switch element Q2. The positive terminal of the second capacitor C2 is connected to the collector terminal of the switch element Q3, and the negative terminal of the second capacitor C2 is connected to the emitter terminal of the switch element Q4. Also, diodes 13a to 13d for preventing reverse current are connected between the collectors and emitters of the first to fourth switching elements Q1 to Q4, respectively. Diodes 13a-13d have their anodes connected to the emitter side of switch elements Q1-Q4 and their cathodes connected to the collector side of switch elements Q1-Q4.

  The main circuit unit 10 can detect the voltage Vbat, the voltage Vrail, and the current i (inductor current i) flowing through the coil L. The voltage Vbat and the voltage Vrail can be obtained by detecting the voltages of the first capacitor C1 and the second capacitor C2, respectively. The inductor current i can be detected by using a shunt resistor or the like. However, in this embodiment, it is necessary to detect the direction in which the inductor current i flows. Therefore, the direction of the current can be determined as in HCT (Hole Current Transducer). Detection is performed using a determinable element. The detection circuit for the voltage Vbat, the voltage Vrail, and the inductor current i is not shown in FIG.

  The switching control unit 20 includes a control unit 21, a PWM signal generation unit 22, a reverse current side output off unit 23, and AND circuits A1 to A4, and generates drive signals for the switch elements Q1 to Q4.

  The control unit 21 receives the voltage Vbat of the voltage source A detected by the main circuit unit 10, the voltage Vrail of the voltage source B, and the current i (inductor current i) flowing through the coil L. These values are converted into digital values and input to the control unit 21. Conversion to a digital value may be performed using an IC (integrated circuit) of a dedicated ADC (Analog Digital Converter, AD converter). When the control unit 21 incorporates an ADC function, the control unit 21 performs the conversion. Also good. And the control part 21 outputs the control signal for determining the duty of each switch element Q1-Q4 to the PWM signal generation part 22 in order to control the inductor electric current i with the detection value input according to the operating conditions. . In the case of the bidirectional converter of this embodiment, the operating conditions of the four switch elements Q1 to Q4 differ depending on the direction of the inductor current i and the magnitude relationship between the voltages of the two voltage sources A and B. For this reason, the control signals of the switch elements Q1 to Q4 take values corresponding to 0 to 200%.

  The PWM signal generation unit 22 assigns a value of 0 to 200% to each of the switch elements Q1 to Q4 according to the received control signal.

  The control value for determining the duty is obtained by general PI control. For example, in the case of constant voltage control in which the voltage Vrail of the voltage source B is constant, the target current command value is calculated by performing PI control by feeding back the difference between the input voltage Vrail and the target voltage. Further, the control value necessary for determining the duty is calculated by feeding back the difference from the detected current i and performing the PI control. Since the current i covers positive and negative values, the charge / discharge current is controlled, and the operation of the bidirectional converter can be realized. On the other hand, if the purpose is to charge the storage battery and control the state of charge, the current command value is derived by PI calculation with the target of control of the target voltage as the voltage Vbat of the voltage source A, and the operating range of the current command value It is possible to operate the converter according to the purpose by controlling.

  In addition, although PI control was mentioned as an example as a control system, PID control etc. can also be used as needed, such as required precision and response speed.

  Here, the following control is considered as the simplest switch control of the bidirectional converter having the H-bridge type circuit configuration.

  When performing step-down discharge, that is, control of flowing current from voltage source A to voltage source B with voltage Vbat> voltage Vrail, switch elements Q2, Q3, and Q4 are turned off, and switch element Q1 is driven by a PWM signal to perform duty Take control. While the switch element Q1 is on, a current is passed from the voltage source A to the voltage source B through the diode 13c connected in parallel with the switch element Q1, the coil L, and the switch element Q3. When the switch element Q1 is off, the energy stored in the coil L circulates to the voltage source B via the diode 13b parallel to the switch element Q2, the coil L, and the diode 13c parallel to the switch element Q3. .

  When performing control of boosting discharge, that is, control of flowing current from voltage source A to voltage source B with voltage Vbat <voltage Vrail, switch element Q1 is turned on, switch elements Q2, Q3 are turned off, and switch element Q4 is turned on by PWM. The duty is controlled by driving with a signal. A current returning to the voltage source A is generated through the switch element Q1, the coil L, and the switch element Q4 while the switch element Q4 is on. During the period when the switch element Q4 is off, the current commutated from the switch element Q4 to the diode 13c parallel to the switch element Q3 is supplied to the voltage source B by the energy stored in the coil L.

  When performing step-down charging, that is, controlling the current to flow from the voltage source B to the voltage source A with the voltage Vbat <voltage Vrail, the switch elements Q1, Q2, and Q4 are turned off, and the switch element Q3 is driven by the PWM signal to generate a duty cycle. Take control. While the switch element Q3 is on, a current flows from the voltage source B to the voltage source A via the switch element Q3, the coil L, and the diode 13a connected in parallel with the switch element Q1. When the switch element Q3 is off, the energy stored in the coil L circulates to the voltage source A through the diode 13d parallel to the switch element Q4, the coil L, and the diode 13a parallel to the switch element Q1. .

  When performing step-up charging, that is, control for passing a current from the voltage source B to the voltage source A with the voltage Vbat> the voltage Vrail, the switch element Q3 is turned on, the switch elements Q1 and Q4 are turned off, and the switch element Q2 is PWMed Duty control is performed by the signal. A current returning to the voltage source B is generated through the switch element Q3, the coil L, and the switch element Q2 while the switch element Q2 is on. During the period when the switch element Q2 is OFF, the current commutates from the switch element Q2 to the diode 13a in parallel with the switch element Q1 by the energy stored in the coil L, and is supplied to the voltage source A.

  FIG. 2A is a table summarizing the operation patterns of the switch elements Q1 to Q4 in the above four operations. In FIG. 2A, “PWM” indicates that duty control is performed, and indicates an operation pattern that is an operation waveform that is driven by a PWM signal and switched between on and off. “ON” indicates an operation pattern in which the operation waveform is on and constant (H), and “OFF” indicates an operation pattern in which the operation waveform is off and constant (L). Only one switch element needs duty control in each operation mode, and the other switch elements are fixed to ON or OFF. Different switch elements perform duty control in each operation mode.

  When the discharge is confirmed again, when the voltage Vbat decreases and the potential difference between the voltage Vbat and the voltage Vrail approaches from the state in which the voltage Vbat> the voltage Vrail and the switch element Q1 is PWM controlled with an arbitrary duty, the duty of Q1 is increased. It becomes the direction to expand. Further, when the potential is reversed and voltage Vbat <voltage Vrail, Q1 is turned on, that is, the duty is 100%, and the duty of Q4 is increased from 0%. Q4 during duty control of Q1 is an off state, that is, 0% duty. Therefore, with respect to a control value that varies between 0 and 200%, 0 to 100% of the control value is applied as a duty to Q1, and more than that is fixed at a duty of 100%. ˜200% is shifted to 0 to 100% and applied as duty, and below that is fixed at 0% duty. In this way, it is possible to determine the duty of Q1 and Q4 required for the step-up / down discharge with a single control value including the on and off states.

  The charging can be considered in the same manner, and the duty of Q2 and Q3 necessary for the step-up / step-down charging can be determined by using a control value that varies between 0 to 200% with respect to Q2 and Q3.

  Here, paying attention to the table of FIG. The switches necessary for control at the time of discharging are Q1 and Q4, and Q2 and Q3 are in the off state. The switches of the upper and lower arms (the combination of Q1 and Q2 or the combination of Q3 and Q4) are dangerous because the voltage source is short-circuited when the two are turned on at the same time, but it is not necessarily a problem if only one of the switches is turned on. . Therefore, the expected operation is examined by assuming the case of inputting a signal in which the arm and the on / off state are inverted with respect to the operations of Q2 and Q3 in the steady state.

  In the case of step-down discharge, since Q1 is “PWM” and Q4 is “OFF”, if Q2 is set to complementary PWM control of Q1 and Q3 is set to “ON”, the off period of Q2 is the same as before and is on. There is no problem even if the period is on during the period through the parallel diode 13b. Also, the point where Q3 is turned on is not a problem because the current always flows through the parallel diode 13c. Note that Q2 being complementary PWM control of Q1 means that the operation of Q2 is PWM control in which on and off are reversed with respect to Q1.

  In the case of step-up discharge, since Q1 is “ON” and Q4 is “PWM”, Q2 does not change when “OFF”, and Q3 is complementary PWM control of Q4. The off period of Q3 is the same as before, and the on period is a period in which Q4 is turned off and commutates to the diode 13c in parallel with Q3. Note that Q3 is complementary PWM control of Q4 means that the operation of Q3 is PWM control in which on and off are reversed with respect to Q4.

  The same can be said for the step-down charge and the step-up charge as in the case of the step-down discharge and the step-up discharge.

  FIG. 2B shows these operations as a table, and summarizes the operation patterns of the switch elements Q1 to Q4 when a signal with ON / OFF inverted is input. From FIG. 2B, it can be seen that the step-down discharge and the step-up charge are such that the PWM of Q1 and Q2 is inverted, that is, Q1 and Q2 perform complementary operations. Considering this, the operations of the switch elements Q1 to Q4 are the same. Similarly, in the boost discharge and the step-down charge, the operation of each of the switch elements Q1 to Q4 is the same considering that the operations of Q3 and Q4 are complementary. As operating conditions, the former is voltage Vbat> voltage Vrail, the latter is voltage Vbat <voltage Vrail, and the voltage conditions are the same. From this, the control of FIG. 2B means that the determination process of charging / discharging is unnecessary.

  FIG. 2C is a table summarizing the table of FIG. 2B obtained by combining the control value having the fluctuation range of 0 to 200% and the complementary operation in this way. With the switch control shown in FIG. 2C, it is possible to control the bidirectional converter without making the determinations of the step-up / step-down and the charge / discharge.

  As described above, in the PWM signal generation unit 22, the duty signal PD1 corresponding to the value of 0 to 100% and the value of 100 to 200% according to the 0 to 200% signal input from the control unit 21. A corresponding duty signal PD2 is output. The signal PD1 is input to the AND circuits A1 and A2 that output the driving signals Q1 and Q2, respectively, with one side inverted (A2 side in FIG. 1), and the signal PD2 is an AND that outputs the driving signals Q3 and Q4, respectively. One of the circuits A3 and A4 (A4 side in FIG. 1) is inverted and input.

  In the above description, it has been described that the operation mode determination is not required on a regular basis by driving with the complementary signals obtained by inverting the signals of the upper and lower arms (the combination of Q1 and Q2 and the combination of Q3 and Q4). However, there are cases where complementary driving becomes a problem under some operating conditions.

  For example, at the start of step-down discharge, when Q3 is turned on when complementary driving is performed, Q1 of PWM control is turned off and Q2 is turned on, the duty of Q1 is small and sufficient energy is supplied to the coil L. Otherwise, after the discharge current flowing through the path of the diode 13b, the coil L, and the diode 13c becomes 0, the voltage Vrail of the voltage source B is applied to the voltage of the path of the Q3, the coil L, and Q2 on the contrary. A current flows. For this reason, a reverse current is generated in the coil L. Depending on the initial duty, an overcurrent may occur in the reverse direction before the stable state is entered, and the system may be destroyed. For this reason, at the time of starting, in order to suppress the reverse current, it is necessary to turn off the switch element that flows the reverse current.

  For this reason, the control unit 21 determines the direction of the inductor current i and the reverse current suppression period, and sends a signal for turning off the switch element that flows the reverse current to the reverse current side output off unit 23. Output.

  The reverse current side output off unit 23 has two outputs (usually on (H) output) for stopping the discharge current or charge current control switch according to the received contents, Turn off (L). The two outputs are input to AND circuits A1 and A4 that output Q1 and Q4 on the discharge control side, and AND circuits A2 and A3 that output Q2 and Q3 on the charge control side.

  Therefore, as described above, at the start of the step-down discharge mode, a signal for suppressing the charging current is output from the reverse current side output off unit 23 to stop Q2 and Q3, and an overcurrent in the charging direction is generated. The bidirectional converter 1 is activated while suppressing the above. The signal for suppressing the current in the reverse direction is canceled for a certain period or after the current reaches a certain value, so that it is not necessary to determine charge / discharge and step-up / down, which are features of this embodiment. The converter 1 can be controlled.

  In FIG. 1, the outputs of the AND circuits A1 to A4 are drawn so as to drive the switch elements Q1 to Q4 of the main circuit unit 10 as they are. However, in practice, the gate terminals of the switch elements Q1 to Q4 are connected. A buffer or an external gate driver circuit for supplying a current necessary for driving is connected in between. However, this is not shown in FIG. 1 because it deviates from the essence of the control operation of the bidirectional converter 1. Similarly, it is necessary to set a dead time between the signals of the upper and lower arms, but the description thereof is also omitted.

  FIG. 2B is a table summarizing the operation patterns of the switch elements Q1 to Q4 when a signal with ON / OFF inverted is input as described above. The switching elements Q1 to Q4 of the bidirectional converter in the present embodiment perform operation patterns in four operations according to the table of FIG. The four constant operations are step-down discharge, step-up discharge, step-down charge, and step-up charge. As described above, in FIG. 2B, “PWM” indicates an operation pattern that is driven by a PWM signal and has an operation waveform that is switched on and off, and “ON” indicates an operation pattern that has an operation waveform that is constant on (H). “OFF” indicates an operation pattern in which the operation waveform is constant OFF (L). “PWM” with an overline indicates a complementary operation pattern of “PWM” without an overline, that is, an operation pattern in which on and off are reversed with respect to “PWM” without an overline.

  From the table of FIG. 2B, it can be seen that the switch element Q1 and the switch element Q2 perform complementary operations (operations in which on and off are reversed), and the switch elements Q3 and Q4 perform complementary operations. Further, from the table of FIG. 2B, it can be seen that the control of the step-down discharge and the step-up charge are identical and the control of the step-up discharge and the step-down charge are identical except that the operation pattern of “PWM” is complementary.

  In the table of FIG. 2B, the operation pattern of the part with a gray background is that, as will be described later, the switch element that is on is turned off for a certain period from the start to the steady state. This is an operation pattern for preventing the complementary operation from being performed.

  FIG. 14 is a diagram for explaining the outline of the control flow of the bidirectional converter according to this embodiment.

  The switching control unit 20 of the bidirectional converter 1 activates the bidirectional converter 1 after receiving the activation signal of the bidirectional converter 1 (S10), and starts control after performing necessary processing such as selection of an operation mode ( S20) A current command value is calculated from the input value.

  Several cycles from the start-up may be a control cycle for computation only due to the response time. As a result, when the current command value changes from an initial value of 0 to a significant value, charging or discharging is determined by the sign of the current command value (current direction), so the main circuit unit 10 detects the current direction (S30). ).

  The switching control unit 20 determines the direction of the reverse current to be suppressed, and outputs a signal for turning off the switch element that passes the current of the suppression direction from the reverse current side output off unit 23 to suppress the reverse current. Control continues (S40).

  Thereafter, the switching control unit 20 determines whether or not to end the control for suppressing the reverse current (S50).

  The switching control unit 20 is configured so that when a certain period of time until reaching a steady state has elapsed since startup (that is, when a period when it is considered that there is no risk of generating reverse current has passed, or when the current reaches a predetermined reference value) The control for suppressing the reverse current is terminated (S60).

  After completing the control for suppressing the reverse current, the switching control unit 20 causes the switch elements Q1 to Q4 to perform the complementary operation as illustrated in FIG. 2B or 2C, and shifts to the steady control (S70).

  As can be seen from FIG. 14, the control flow of the bidirectional converter according to the present embodiment is a simple one that detects the direction of the current after startup and suppresses the reverse current. It corresponds to.

  With reference to FIG. 3, a case of boost discharge will be described as an example, and a state of generation of a reverse current at the time of start-up (current reverse to the discharge current) and a method for avoiding it will be described.

  FIG. 3 is a diagram showing a current waveform at the time of start-up by step-up discharge of the bidirectional converter of this embodiment, together with operation waveforms of the switch elements Q1 to Q4. The current waveform of the bidirectional converter indicates the waveform of the current i (inductor current) flowing through the coil L (inductor L). When the bidirectional converter is activated, it is assumed that the bidirectional converter is in a steady state at time tc0. Note that the operation waveform indicated by the dotted line of the lower switch element Q3 in FIG. 3 shows a waveform when the steady operation is performed at the time of startup, and the dotted line in the upper graph shows the current waveform in this case. Since it is a step-up discharge, the system side DC bus (voltage source B) connected to the second input / output terminal T2 rather than the voltage Vbat of the storage battery (voltage source A) connected to the first input / output terminal T1. The voltage Vrail is higher.

  As shown in FIG. 2B, the drive waveform in the step-up discharge in the steady state is a complementary operation of the switch element Q3 and the switch element Q4 that are PWM controlled. Therefore, when the complementary waveform of the switch element Q3 indicated by the dotted line is input from the state where the duty of the switch element Q4 is small as shown in FIG. 3 according to the operation pattern of FIG. Is the dotted line in the upper graph of FIG. That is, when the switch elements Q1 to Q4 are operated in accordance with the steady operation pattern of FIG. 2B at the time of startup, current flows through the path of Q3, inductor L, and diode 13a during the on period of the long PWM operation of Q3. In this case, a charging current (reverse current) in the direction opposite to the discharge current flows, and the discharge cannot be controlled.

  That is, the current discontinuous mode in which the inductor current i flows discontinuously at the time of start-up (a control method in which there is a period during which no current flows as in the case of time t <tc0 in the current waveform in the upper stage of FIG. 3) When Q3 is operated in a complementary manner, a reverse current is generated while Q3 is on. Therefore, when the switch element Q3 is turned off at the time of start-up, the generation of charging current is suppressed, so that the amount of discharging current can be controlled. However, after the transition to the continuous current mode in which the inductor current i rises and flows continuously at time t = tc0 (the steady operation mode in which no current flows), the reverse is abrupt even if Q3 is turned on. Since the directional current does not increase, the control to turn off Q3 at the time of start-up can be canceled after shifting to the current continuous mode.

  The control unit 21 of the switching control unit 20 can determine whether or not the inductor current i has shifted from the current discontinuous mode to the current continuous mode. The control unit 21 monitors the inductor current i, and determines that the inductor current i has shifted from the current discontinuous mode to the current continuous mode when the inductor current i exceeds a predetermined reference value ith1 +. The reference value ith1 + can be arbitrarily determined based on a test performed in advance. In general, the current displacement Δi at time Δt is obtained as Δi = ΔV · Δt / L from the potential difference ΔV = | Vrail−Vbat | between the two voltage sources A and B. In this case, the margin is set in consideration of the margin.

  Further, during actual operation, the bidirectional converter 1 may be operated under various conditions. In some cases, the bidirectional converter 1 operates under a low load condition, and it may be assumed that the current does not easily shift to the continuous mode. For this reason, a time tso that can be regarded as sufficient for the inductor current i to rise is set in advance, and when this time tso elapses, it is considered that the operation has shifted to the steady operation and the generation of the reverse current is suppressed. You may cancel | release control which turns off a switch element. The time tso can be arbitrarily determined based on a test performed in advance.

  As described above, in the control to turn off the switch element in order to suppress the generation of the reverse current, the operation of the bidirectional converter has reached the steady state after the transition to the current continuous mode or after the elapse of the preset time tso. It is more practical to consider it as a cancellation.

  In the above, taking the case of the boost discharge as an example, the generation of the reverse current and the suppression method thereof have been described. Since the bidirectional converter 1 according to the present embodiment performs four operations as described above, the control for performing each operation will be described below with reference to FIGS. These explanations also describe how the complementary driving of the switch elements Q1 to Q4 functions when the operation is switched.

  4 to 11 are diagrams showing an example of the operation of bidirectional converter 1 shown in FIG. 4 to FIG. 11, the voltage at the two input / output terminals T <b> 1 and T <b> 2 is shown as the storage battery voltage Vbat and the system voltage Vrail connected to each other in the upper stage.

  4 to FIG. 11, the current (inductor current i) flowing through the inductor L (coil L) is shown. The sign of the inductor current i corresponds to the direction of the inductor current i, the discharge direction, that is, the direction from the storage battery (voltage source A) to the system (voltage source B) is positive, and the reverse charge direction is negative. . In the middle graph, the waveform of the control current (command value Iref) calculated by the control unit 21 of the switching control unit 20 is also shown. The command value Iref is a target value of the inductor current i. In general, the conversion power of the bidirectional converter 1 is reduced by controlling the operation waveforms of the switch elements Q1 to Q4 so that the inductor current i matches the command value Iref. Control. The time ts1 is the time when the switch elements Q1 to Q4 are actually driven after the control of the bidirectional converter 1 is started at time t = 0.

  The lower part of FIGS. 4 to 11 partially shows operation waveforms for several cycles of the switch elements Q1 to Q4 in three time zones including the time of startup.

  Hereinafter, the control and waveform of the bidirectional converter 1 will be described for each of FIGS. 4 to 11.

  FIG. 4 is a diagram illustrating an example of a schematic waveform until the bidirectional converter 1 starts at time t = 0 by step-down discharge and then shifts to step-up discharge.

  As shown in the upper voltage graph, at startup, the voltage Vbat of the storage battery is higher than the system voltage Vrail, and then the voltage of the storage battery decreases due to discharge, so that the magnitude relationship of the voltages is reversed at time t = tcv.

  The operation waveforms of the switch elements Q1 to Q4 are as follows. In the step-down discharge of FIG. 2B, Q1 is “PWM”, Q2 is “PWM” (complementary operation of Q1), Q3 is “ON”, and Q4 is “OFF”. And Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. In this control, in order to suppress reverse current at startup, Q2 and Q3 which are on in FIG. 2B are turned off, Q2 does not perform complementary operation with Q1, and Q3 does not perform complementary operation with Q4. . Therefore, as shown in the operation waveforms of the switch elements Q1 to Q4 in the lower part of FIG. 4, at the time of start-up, Q2 to Q4 are off, a PWM signal with a gradually increasing small duty is applied to Q1, and the inductor current i is Control is performed so as to be equal to the command value Iref.

  When the inductor current i exceeds the predetermined reference value ith1 + and shifts to the current continuous mode or does not reach the reference value ith1 +, if the predetermined time tso elapses, the operation of the switch elements Q1 to Q4 in the lower stage of FIG. As shown in the waveform, Q2 and Q3 are turned off at time t = ts2, and Q2 is “PWM” (complementary operation of Q1) and Q3 is “ON” as shown in the step-down discharge of FIG. 2B. Do. That is, Q1 and Q2 perform complementary operations, and Q3 and Q4 perform complementary operations.

  Thereafter, when the magnitudes of the voltages Vbat and Vrail are reversed at time t = tcv, the bidirectional converter 1 shifts to boost discharge, and as shown in the boost discharge of FIG. 2B, Q1 is “ON” and Q2 is “ “OFF”, Q3 is “PWM” (complementary operation of Q4), Q4 is “PWM”, Q1 and Q2 perform complementary operations to each other, Q3 and Q4 perform complementary operations to each other, and continue the discharge state.

  As shown in the middle graph of FIG. 4, during the execution of these controls, the direction of the inductor current i is always positive and does not change.

  FIG. 5 is a diagram showing an example of a schematic waveform until the bidirectional converter 1 starts at time t = 0 by step-down discharge and then shifts to step-up charging.

  As shown in the upper voltage graph, at startup, the storage battery voltage Vbat is higher than the system voltage Vrail, and the magnitude relationship of the voltage remains unchanged.

  The operation waveforms of the switch elements Q1 to Q4 are as follows. In the step-down discharge of FIG. 2B, Q1 is “PWM”, Q2 is “PWM” (complementary operation of Q1), Q3 is “ON”, and Q4 is “OFF”. And Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. In this control, in order to suppress reverse current at startup, Q2 and Q3 which are on in FIG. 2B are turned off, Q2 does not perform complementary operation with Q1, and Q3 does not perform complementary operation with Q4. . Therefore, as shown in the operation waveforms of the switch elements Q1 to Q4 in the lower part of FIG. 5, at the time of start-up, Q2 to Q4 are off, a PWM signal with a gradually increasing small duty is applied to Q1, and the inductor current i is Control is performed so as to be equal to the command value Iref.

  Even if the inductor current i exceeds the predetermined reference value ith1 + and shifts to the current continuous mode or does not reach the reference value ith1 +, the operation of the switch elements Q1 to Q4 in the lower stage of FIG. As shown in the waveform, Q2 and Q3 are turned off at time t = ts2, and Q2 is “PWM” (complementary operation of Q1) and Q3 is “ON” as shown in the step-down discharge of FIG. 2B. Do. That is, Q1 and Q2 perform complementary operations, and Q3 and Q4 perform complementary operations.

  Thereafter, even when the direction of the current is switched at time t = tci in accordance with the condition that the operation of the bidirectional converter 1 shifts from step-down discharge to step-up charge, Q2 remains in complementary operation of Q1, and Q3 is set to Q4. The battery automatically shifts to the charged state while performing the complementary operation. That is, as shown in the step-up charging in FIG. 2B, Q1 is “PWM” (complementary operation of Q2), Q2 is “PWM”, Q3 is “ON”, and Q4 is “OFF”.

  As shown in the middle graph of FIG. 5, the rising discharge current gradually decreases, and the direction of the current is reversed at time t = tci to switch to the charging current.

  FIG. 6 is a diagram illustrating an example of a schematic waveform until the bidirectional converter 1 is started at time t = 0 by boost discharge and then shifts to step-down discharge.

  As shown in the upper voltage graph, at startup, the voltage Vbat of the storage battery is lower than the system voltage Vrail, and then the voltage Vbat of the storage battery decreases due to discharge, and the system voltage Vrail further decreases more rapidly, so that the time t The magnitude relation of the voltage is reversed at = tcv.

  The operation waveforms of the switch elements Q1 to Q4 are as follows: Q1 is “ON”, Q2 is “OFF”, Q3 is “PWM” (complementary operation of Q4), Q4 is “PWM” in the boost discharge of FIG. And Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. In this control, in order to suppress the reverse current during startup, Q3 which is on in FIG. 2B is turned off, and Q3 does not perform complementary operation with Q4. Therefore, as shown in the operation waveforms of the switch elements Q1 to Q4 in the lower stage of FIG. 6, at the time of start-up, Q1 is on, Q2 and Q3 are off, and a PWM signal with a gradually increasing small duty is applied to Q4. Control is performed so that the inductor current i becomes equal to the command value Iref.

  Even if the inductor current i exceeds the predetermined reference value ith1 + and shifts to the current continuous mode or does not reach the reference value ith1 +, the operation of the switch elements Q1 to Q4 in the lower stage of FIG. As shown in the waveform, Q3 is turned off at time t = ts2, and as shown in the boost discharge in FIG. 2B, Q2 remains in the “OFF” operation, and Q3 is “PWM” (complementary operation of Q4). ). That is, Q3 performs a complementary operation of Q4.

  Thereafter, when the magnitudes of the voltages Vbat and Vrail are reversed at time t = tcv, the bidirectional converter 1 shifts to step-down discharge. As shown in step-down discharge in FIG. 2B, Q1 is “PWM”, and Q2 is “ PWM "(complementary operation of Q1), Q3 is" ON ", Q4 is" OFF ", Q1 and Q2 perform complementary operations, Q3 and Q4 perform complementary operations, and continue the discharge state.

  As shown in the middle graph of FIG. 6, during the execution of these controls, the direction of the inductor current i is always positive and does not change.

  FIG. 7 is a diagram illustrating an example of a schematic waveform until the bidirectional converter 1 is activated at time t = 0 by boost discharge and then shifts to step-down charging.

  As shown in the upper voltage graph, at startup, the storage battery voltage Vbat is lower than the system voltage Vrail, and the magnitude relationship of the voltages remains unchanged.

  The operation waveforms of the switch elements Q1 to Q4 are as follows: Q1 is “ON”, Q2 is “OFF”, Q3 is “PWM” (complementary operation of Q4), Q4 is “PWM” in the boost discharge of FIG. And Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. In this control, in order to suppress the reverse current during startup, Q3 which is on in FIG. 2B is turned off, and Q3 does not perform complementary operation with Q4. Therefore, as shown in the operation waveforms of the switch elements Q1 to Q4 in the lower part of FIG. 7, at the time of start-up, Q1 is on, Q2 and Q3 are off, and a PWM signal whose small duty gradually increases is applied to Q4. Then, control is performed so that the inductor current i becomes equal to the command value Iref.

  Even if the inductor current i exceeds the predetermined reference value ith1 + and shifts to the current continuous mode or does not reach the reference value ith1 +, the operation of the switch elements Q1 to Q4 in the lower stage of FIG. As shown in the waveform, Q3 is turned off at time t = ts2, and Q3 operates as “PWM” (complementary operation of Q4) as shown in the boost discharge in FIG. 2B. That is, Q1 and Q2 perform complementary operations, and Q3 and Q4 perform complementary operations.

  Thereafter, even when the direction of the current is switched at time t = tci in accordance with the condition that the operation of the bidirectional converter 1 shifts from step-up discharge to step-down charge, Q2 remains in complementary operation of Q1 and Q3 is set to Q4. The battery automatically shifts to the charged state while performing the complementary operation. That is, as shown in step-down charging in FIG. 2B, Q1 is “ON”, Q2 is “OFF”, Q3 is “PWM”, and Q4 is “PWM” (complementary operation of Q3).

  As shown in the middle graph of FIG. 7, the discharge current that has risen gradually decreases, and at time t = tci, the direction of the current reverses and switches to the charging current.

  FIG. 8 is a diagram illustrating an example of a schematic waveform until the bidirectional converter 1 is started at time t = 0 by step-up charging and then shifts to step-down charging.

  As shown in the upper graph, the voltage Vbat of the storage battery is higher than the system voltage Vrail at the time of start-up, and then the voltage of the storage battery increases due to charging, and the system voltage Vrail further increases rapidly. The voltage magnitude relationship is reversed at tcv.

  The operation waveforms of the switch elements Q1 to Q4 are as follows: Q1 is “PWM” (complementary operation of Q2), Q2 is “PWM”, Q3 is “ON”, and Q4 is “OFF” in the boost charge of FIG. And Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. In this control, in order to suppress the reverse current at startup, Q1 which is on in FIG. 2B is turned off, and Q1 does not perform complementary operation with Q2. Therefore, as shown in the operation waveforms of the switch elements Q1 to Q4 in the lower part of FIG. 8, at startup, Q1 and Q4 are off, Q3 is on, and a PWM signal with a gradually increasing small duty is applied to Q2. Then, control is performed so that the inductor current i becomes equal to the command value Iref.

  Even if the inductor current i exceeds the predetermined reference value ith1- and shifts to the current continuous mode or does not reach the reference value ith1-, when the predetermined time tso elapses, the lower switching elements Q1 to Q4 in FIG. As shown in the operation waveform, Q1 is turned off at time t = ts2, and Q1 performs the operation of “PWM” (complementary operation of Q2) as shown in step-up charging in FIG. 2B. That is, Q1 and Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. The reference value ith1− is a negative value that has the same absolute value as the reference value ith1 + but has the opposite sign.

  Thereafter, when the magnitudes of the voltages Vbat and Vrail are reversed at time t = tcv, the bidirectional converter 1 shifts to step-down charging, and as shown in step-down charging in FIG. 2B, Q1 is “ON” and Q2 is “ “OFF”, Q3 is “PWM”, Q4 is “PWM” (complementary operation of Q3), Q1 and Q2 perform complementary operations, Q3 and Q4 perform complementary operations, and continue to be charged.

  As shown in the middle graph of FIG. 8, during the execution of these controls, the direction of the inductor current i is always negative and does not change.

  FIG. 9 is a diagram illustrating an example of a schematic waveform until the bidirectional converter 1 is activated at time t = 0 by step-up charging and then shifts to step-down discharge.

  As shown in the upper voltage graph, at startup, the storage battery voltage Vbat is higher than the system voltage Vrail, and the magnitude relationship of the voltage remains unchanged.

  The operation waveforms of the switch elements Q1 to Q4 are as follows: Q1 is “PWM” (complementary operation of Q2), Q2 is “PWM”, Q3 is “ON”, and Q4 is “OFF” in the boost charge of FIG. And Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. In this control, in order to suppress the reverse current at startup, Q1 which is on in FIG. 2B is turned off, and Q1 does not perform complementary operation with Q2. Therefore, as shown in the operation waveforms of the switch elements Q1 to Q4 in the lower part of FIG. 9, at startup, Q1 and Q4 are off, Q3 is on, and a PWM signal with a gradually increasing small duty is applied to Q2. Then, control is performed so that the inductor current i becomes equal to the command value Iref.

  Even if the inductor current i exceeds the predetermined reference value ith1- and shifts to the current continuous mode or does not reach the reference value ith1-, when the predetermined time tso elapses, the lower switching elements Q1 to Q4 in FIG. As shown in the operation waveform, Q1 is turned off at time t = ts2, and Q1 performs “PWM” (complementary operation of Q2) as shown in step-up charging in FIG. 2B. That is, Q1 and Q2 perform complementary operations, and Q3 and Q4 perform complementary operations.

  Thereafter, even when the direction of the current is switched at time t = tci in accordance with the condition that the operation of the bidirectional converter 1 shifts from step-up charging to step-down discharge, Q1 remains complementary to Q2 and Q3 is set to Q4. It automatically shifts to the discharge state while performing the complementary operation. That is, as shown in the step-down discharge in FIG. 2B, Q1 is “PWM”, Q2 is “PWM” (complementary operation of Q1), Q3 is “ON”, and Q4 is “OFF”.

  As shown in the middle graph of FIG. 9, the rising charging current gradually decreases, and the direction of the current is reversed at time t = tci to switch to the discharging current.

  FIG. 10 is a diagram illustrating an example of a schematic waveform until the bidirectional converter 1 starts at time t = 0 in step-down charging and then shifts to step-up charging.

  As shown in the upper voltage graph, at startup, the voltage Vbat of the storage battery is lower than the system voltage Vrail, and then the voltage of the storage battery is increased by charging, so that the magnitude relationship of the voltages is reversed at time t = tcv.

  The operation waveforms of the switch elements Q1 to Q4 are Q1 is “ON”, Q2 is “OFF”, Q3 is “PWM”, and Q4 is “PWM” (complementary operation of Q3) in the step-down charging of FIG. And Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. In this control, in order to suppress reverse current at startup, Q1 and Q4 which are on in FIG. 2B are turned off, Q1 does not perform complementary operation with Q2, and Q4 does not perform complementary operation with Q3. . Accordingly, as shown in the operation waveforms of the switch elements Q1 to Q4 in the lower part of FIG. 10, at the time of start-up, Q1, Q2, and Q4 are off, and a PWM signal with a gradually increasing small duty is applied to Q3. Control is performed so that i becomes equal to the command value Iref.

  Even if the inductor current i exceeds the predetermined reference value ith1- and shifts to the current continuous mode or does not reach the reference value ith1-, when the predetermined time tso elapses, the lower switching elements Q1 to Q4 in FIG. As shown in the operation waveform, Q1 and Q4 are turned off at time t = ts2, and Q1 is “ON” and Q4 is “PWM” (complementary operation of Q3) as shown in step-down charging in FIG. 2B. Perform the action. That is, Q1 and Q2 perform complementary operations, and Q3 and Q4 perform complementary operations.

  Thereafter, when the magnitudes of the voltages Vbat and Vrail are reversed at time t = tcv, the bidirectional converter 1 shifts to step-up charging, and as shown in step-down charging in FIG. 2B, Q1 is “PWM” (complement of Q2). Operation), Q2 is "PWM", Q3 is "ON", Q4 is "OFF", Q1 and Q2 perform complementary operations to each other, Q3 and Q4 perform complementary operations to each other, and continue to be charged.

  As shown in the middle graph of FIG. 10, during the execution of these controls, the direction of the inductor current i is always negative and does not change.

  FIG. 11 is a diagram illustrating an example of a schematic waveform until the bidirectional converter 1 starts at time t = 0 by step-down charging and then shifts to step-up discharge.

  As shown in the upper voltage graph, at startup, the storage battery voltage Vbat is lower than the system voltage Vrail, and the magnitude relationship of the voltages remains unchanged.

  The operation waveforms of the switch elements Q1 to Q4 are Q1 is “ON”, Q2 is “OFF”, Q3 is “PWM”, and Q4 is “PWM” (complementary operation of Q3) in the step-down charging of FIG. And Q2 perform complementary operations, and Q3 and Q4 perform complementary operations. In this control, in order to suppress reverse current at startup, Q1 and Q4 which are on in FIG. 2B are turned off, Q1 does not perform complementary operation with Q2, and Q4 does not perform complementary operation with Q3. . Therefore, as shown in the operation waveforms of the switch elements Q1 to Q4 in the lower part of FIG. 11, at the time of start-up, Q1, Q2, and Q4 are off, and a PWM signal with a gradually increasing small duty is applied to Q3. Control is performed so that i becomes equal to the command value Iref.

  Even if the inductor current i exceeds the predetermined reference value ith1- and shifts to the current continuous mode or does not reach the reference value ith1-, when the predetermined time tso elapses, the lower switching elements Q1 to Q4 in FIG. As shown in the operation waveform, Q1 and Q4 are turned off at time t = ts2, and Q1 is “ON” and Q4 is “PWM” (complementary operation of Q3) as shown in step-down charging in FIG. 2B. Do. That is, Q1 and Q2 perform complementary operations, and Q3 and Q4 perform complementary operations.

  Thereafter, even when the direction of the current is switched at time t = tci in accordance with the condition that the operation of bidirectional converter 1 shifts from step-down charging to step-up discharging, Q1 remains in complementary operation of Q2 and Q3 is set to Q4 It automatically shifts to the discharge state while performing the complementary operation. 2B, Q1 is “ON”, Q2 is “OFF”, Q3 is “PWM” (complementary operation of Q4), and Q4 is “PWM”.

  As shown in the middle graph of FIG. 11, the rising charging current gradually decreases, and the direction of the current is reversed at time t = tci to switch to the discharging current.

  As described above, in the four operations performed by the bidirectional DC / DC converter according to the present embodiment with reference to FIGS. 4 to 11, the specific control method for suppressing the reverse current at the start and the operation after the start The example in the case of switching was demonstrated. In the control method shown in the present embodiment, the control at the time of start-up is complicated, but in the steady state, Q1 and Q2 perform complementary operations with each other, and Q3 and Q4 perform complementary operations with each other. It is possible to make a high-speed response continuously without being conscious of it.

  At present, IGBT modules combining IGBTs and diodes are widely used. Therefore, in the circuit shown in FIG. 1, the diodes 13a to 13d connected in reverse to Q1 and Q2, and Q3 and Q4, respectively. An IGBT module having a two-element configuration may be used for the part.

  In the present embodiment, it has been described that IGBTs are used as the switch elements Q1 to Q4. Other switching elements such as power MOSFETs (Metal-Oxcide Silicon Field-Effect Transistors) and switch elements based on SiC (Silicon Carbide) and GaN (Gallium Nitride), which have been developed recently and are attracting attention for low loss. Even if it is used for Q1-Q4, it is clear that the same effect as the present embodiment can be obtained.

  A bidirectional converter according to Embodiment 2 of the present invention will be described with reference to FIG. The bidirectional converter according to the present embodiment has the same configuration as the bidirectional converter 1 of the first embodiment shown in FIG. Although the switch elements Q1 to Q4 of the bidirectional converter according to the present embodiment perform the same operations as the switch elements Q1 to Q4 of the bidirectional converter of the first embodiment, the operations described below can be performed.

  FIG. 12 is a diagram illustrating an example of the operation when the bidirectional converter according to the present embodiment is activated at time t = 0 by the boost discharge. Similarly to FIGS. 4 to 11, the upper stage shows the storage battery voltage Vbat and the system voltage Vrail, and the middle stage shows the inductor current i. In the lower part, operation waveforms for several cycles of the switch elements Q1 to Q4 are partially shown for three time zones.

  Hereinafter, the operation of the bidirectional converter according to the present embodiment will be described with reference to FIG. 6 illustrating the case where the bidirectional converter is started up by boosting discharge.

  As described with reference to FIG. 6 in the first embodiment, when the inductor current i exceeds the predetermined reference value ith1 + and starts the current continuous mode after starting with the boost discharge, the switch element Q3 is turned off at time t = ts2. (Operation for suppressing reverse current) is released. As shown in FIGS. 12 and 6, Q3 performs the operation of “PWM” (Q4 complementary operation) to perform the complementary operation of Q4.

  Further, when the discharge current increases and the inductor current i exceeds a predetermined second reference value ith2 + (time t = toff +), Q3 is turned off again. With this control, the power for switching Q3 can be reduced. Since Q3 is a switching element that does not contribute to the power conversion operation, it may be turned off. The second reference value ith2 + can be arbitrarily determined based on tests performed in advance, and has a larger absolute value than the reference value ith1 +.

  In general, such an operation complicates the control of the bidirectional converter. However, since the bidirectional converter according to the present embodiment has a function of turning off a switch element that does not participate in voltage and power conversion, such as Q3 at the time of step-up discharge, the second reference value ith2 + is set. When this reference value is exceeded, it is only necessary to add a process for turning off an appropriate switch element, and the control is not complicated.

  When the discharge current decreases and the inductor current i reaches the reference value ith1 + again (time t = ton +), Q3 is turned off. Q3 performs the operation of "PWM" (complementary operation of Q4) and performs the complementary operation of Q4, so that it can cope with the case where the direction of current is switched from discharging to charging. For this reason, the bidirectional converter according to the present embodiment has a feature that a high-speed response is possible.

  In the above description, the case of step-up discharge has been described as an example, but the case of step-down discharge can be similarly handled. In the case of charging, a second reference value ith2- having the same absolute value as that of the second reference value ith2 + but having the opposite sign (negative) is set, and the charging current By operating the switch elements Q1 to Q4 according to the values, the power consumption can be reduced even slightly.

  A bidirectional converter according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 15 is a diagram showing a configuration example of a system using the bidirectional DC / DC converter 1 according to the present invention in a power storage system combined with solar power generation.

  The solar cell 3 is connected to a high-voltage bus wiring 9 by a unidirectional DC / DC converter 5 and further connected to a load 6 via a DC / AC inverter 4. The energy generated by the solar cell 3 is supplied to the load 6. A storage battery 2 is connected to the high-voltage bus wiring 9 via a bidirectional DC / DC converter 1.

  The time and amount of power generation of the solar cell 3 cannot be controlled. For this reason, the energy generated by the solar cell 3 is charged and stored in the storage battery 2 when there is no demand for electric power. When it is necessary to supply electric power to the load 6, the energy generated by the solar cell 3 can be effectively used by discharging the storage battery 2.

  In FIG. 15, the DC / AC inverter 4 is connected only to the load 6, but it can also be connected to the system. In addition, even if the power storage system is configured using other power generation means, for example, a renewable energy source such as a wind power generator, instead of the solar cell 3, the effect of the bidirectional converter 1 according to the present invention can be obtained. Not too long.

  In addition, this invention is not limited to said Example, Various modifications are included. For example, the above-described embodiments are described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to an aspect including all the configurations described.

  DESCRIPTION OF SYMBOLS 1 ... Bidirectional converter, 2 ... Storage battery, 3 ... Solar cell, 4 ... DC / AC inverter, 5 ... Unidirectional DC / DC converter, 6 ... Load, 9 ... High voltage bus wiring, 10 ... Main circuit part, 13a- DESCRIPTION OF SYMBOLS 13d ... Diode, 20 ... Switching control part, 21 ... Control part, 22 ... PWM signal generation part, 23 ... Reverse current side output off part, 100 ... Main circuit part of the conventional bidirectional converter, 200 ... Conventional bidirectional converter Switching controller 220, PWM signal distributor, C1 first capacitor, C2 second capacitor, i inductor current, it1 +, it1-, it2 +, it2-, reference value, L coil, M, and so on. Magnetic component, Q1 ... first switch element, Q2 ... second switch element, Q3 ... third switch element, Q4 ... fourth switch element, S1-S4 ... switch element, T1 ... first Input and output terminal, T2 ... the second of input and output terminals, Vbat ... voltage of the battery, Vrail ... system side of the DC bus voltage.

Claims (7)

A first input / output terminal connected to the first external device;
A second input / output terminal connected to the second external device;
Coils,
A first switch element connected between a positive electrode side of the first input / output terminal and one end of the coil;
A second switch element connected between the negative electrode side of the first input / output terminal and the one end of the coil;
A third switch element connected between the positive electrode side of the second input / output terminal and the other end of the coil;
A fourth switch element connected between the negative electrode side of the second input / output terminal and the other end of the coil;
In a steady state, the first switch element and the second switch element operate complementarily, and the third switch element and the fourth switch element operate complementarily, and the first input / output Converting voltage and power from a terminal to the second input / output terminal or from the second input / output terminal to the first input / output terminal;
During a certain period from the start to the steady state, at least one of the first switch element to the fourth switch element that is on during the steady state is turned off, and the first switch element and the Of the second switch element set and the third switch element and fourth switch element set, at least one set does not operate in a complementary manner.
A bidirectional converter characterized by that. The predetermined period is
When outputting from the second input / output terminal to the second external device, the second switch element and the third switch element are turned off,
During the step-down operation, the first switch element is driven by a PWM signal and the fourth switch element is turned off.
During the step-up operation, the first switch element is turned on and the fourth switch element is driven with a PWM signal,
When outputting from the first input / output terminal to the first external device, the first switch element and the fourth switch element are turned off,
During the step-down operation, the second switch element is turned off and the third switch element is driven with a PWM signal,
During the step-up operation, the second switch element is driven with a PWM signal and the third switch element is turned on.
The bidirectional converter according to claim 1. When the fixed period has elapsed, the switch element that was turned off in the fixed period among the first switch element to the fourth switch element that is turned on in the steady state is turned on, and the steady state operation is performed.
The bidirectional converter according to claim 1.   The bidirectional converter according to claim 1, wherein the predetermined period is a period until a current flowing through the coil exceeds a predetermined value.   5. The bidirectional converter according to claim 1, wherein a current flowing through the coil, a voltage of the first input / output terminal, and a voltage of the second input / output terminal are detected.   The bidirectional converter according to claim 5, wherein a direction of a current flowing through the coil is detected. The certain period is a period until the current flowing through the coil exceeds a predetermined first value,
When the fixed period has elapsed, the switch element that was turned off in the fixed period from the first switch element to the fourth switch element that is turned on in the steady state is turned on, and the steady state operation is performed,
When the current flowing through the coil exceeds a predetermined second value that is greater than the first value, the switch element that was turned on when the fixed period has elapsed,
When the current flowing through the coil decreases and reaches the first value, the switch element that was turned off is turned on when the current flowing through the coil exceeds the second value;
The bidirectional converter according to claim 1.

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