JP2007202342A - Digital converter and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital converter capable of controlling an input current precisely over a wide range, while a simple arrangement in which an inexpensive general coil can be used, and to provide its control method. <P>SOLUTION: The digital converter 1 is provided with a booster chopper 4, configured so that three circuits 4a-4c having substantially the same coils L1-L3 and switching elements Q1-Q3; a rectifying circuit 2 for supplying an input current to each of the coils L1-L3; and a one-chip microcomputer 3 for PWM-controlling each of the switching elements Q1-Q3. While determining whether a mode is a continuous mode, at which the input current into each of the coils L1-L3 is not interrupted during control cycle or an discontinuous mode at which it is interrupted during the control cycle, the PWM control is executed with a different algorithm, on the basis of a result of determination. At the same time, the switching elements Q1-Q3 are subsequently driven so that their phases are shifted by 120 degrees. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a digital converter using a step-up chopper, and more particularly to an apparatus that can realize PWM control with high efficiency and low loss without using expensive circuit elements and a control method therefor.

The applicant has previously proposed a device capable of realizing precise PWM control without using an expensive coil (Patent Document 1).
Japanese Patent Application No. 2004-268135

  The invention described in Patent Document 1 includes a step-up chopper provided with a coil and a switching element, a rectifier circuit that supplies an input current to the coil, and a computer circuit that performs PWM control of the switching element in a predetermined control cycle. In this case, PWM control is performed with a different algorithm based on the determination result while determining whether the input current to the coil is a continuous mode in which the current is not interrupted during the control cycle or a discontinuous mode in which the current is interrupted in the middle of the control cycle. .

  According to the present invention, it is possible to perform precise PWM control over a wide range of input current while having a simple configuration. In addition, since all can be realized by software control, the power factor correction circuit as in the case of hardware control can be omitted, and since a general coil can be used, there is an advantage that the entire apparatus can be downsized at low cost.

  However, as the current of the power supply increases, the heat loss of the switching element also increases, and the heat generation becomes a problem. In the above invention, the carrier frequency for PWM control cannot be extremely increased because almost all the processing is performed by software, and the ripple component superimposed on the input current is also a problem.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-efficiency, low-loss digital converter and its control method without using expensive circuit elements.

  In order to achieve the above object, a digital converter according to the present invention includes a step-up chopper configured by connecting N circuits in which substantially the same coil and switching elements are connected in series, and inputs to the coils. A digital converter comprising a rectifier circuit that supplies current and a computer circuit that PWM-controls each switching element in a predetermined control cycle, wherein the input current to the coil is continuous during the control cycle. While determining whether it is a mode or a discontinuous mode that is interrupted in the middle of a control cycle, the PWM control is executed with a different algorithm based on the determination result, while the switching elements are sequentially shifted in phase by 360 / N degrees. To be driven.

  The present invention is preferably configured such that the DC output voltage of the step-up chopper can be obtained from a single capacitor that is charged when the switching elements are turned off. In the present invention, the determination of the continuous mode or the discontinuous mode may be performed in every control cycle, or may be performed once in a plurality of control cycles. In any case, it is preferable to determine whether the current mode is the continuous mode or the discontinuous mode. In this control cycle, the coil charging start current Iv (n−2), the AC input voltage Vac (n−1) to the boost chopper, And the measured value of the DC output voltage Vdc (n−1) of the step-up chopper, the control time Ton (n−1) of the PMW wave in the current control cycle, and the inductance value of the coil.

  The control time of the PMW wave means the control on time Ton (n−1) in the embodiment, but is not particularly limited. If the OFF time of the switching element is PWM controlled, the control time is controlled. This is the off time. Further, the inductance value of the coil is preferably corrected in accordance with the measured value of the coil current.

  In the present invention, preferably, the control time Ton (n) of the PMW wave should be determined using an arithmetic expression corresponding to the determination result of the continuous mode or the discontinuous mode. More preferably, the control time Ton (n) of the PMW wave in the next control cycle is determined using the predicted value Iav (n) of the coil average current in the next control cycle as an arithmetic element. Here, the predicted value Iav (n) of the coil average current is determined by the integration of the predicted value Vac (n) of the AC input voltage and the integration parameter β, and the integration parameter β is the target value of the DC output voltage Vdc. It is preferably determined by PI (Proportional-Integral) control based on a deviation Verr from Vo.

  The number N of circuits connected in parallel is not particularly limited, but it is preferable that the control on time Ton is limited to Ton <360 / N in terms of angle in order to avoid the overlapping ON operation of each switching element. . In this sense, the number N is preferably 1 <N ≦ 3.

  The computer circuit according to the present invention also includes an AD converter that digitally converts an analog input signal, and a timer that can automatically output a pulse wave having an arbitrary pulse width based on setting data to various registers. A chip microcomputer is preferred. The AD conversion unit preferably adopts a configuration that digitally converts a group of analog input signals based on a command from the timer unit, in other words, a configuration that operates without receiving a command from the CPU. More preferably, the AD conversion unit should be configured to notify the CPU when the necessary digital conversion processing is completed.

  Moreover, this invention is a control method of the digital converter which comprises each technical element of Claims 1-5.

  According to the present invention described above, a high-efficiency and low-loss digital converter can be realized without using expensive circuit elements.

  Hereinafter, the present invention will be described in more detail based on examples. FIG. 1 is a circuit configuration diagram showing a digital converter 1 under software control, which is incorporated as a part of a motor control system. In this digital converter 1, a single-phase AC voltage (for example, 200 V) is rectified by a full-wave rectifier circuit 2 to become a pulsating current, and then a step-up chopper 4 that is PWM (Pulse Width Modulation) controlled by a one-chip microcomputer 3. It is converted into a predetermined DC voltage Vdc (for example, 350V). The three-phase motor M is driven by an inverter circuit 5 controlled by the one-chip microcomputer 3.

  A ripple suppression capacitor Cin is connected between the (+) output terminal of the full-wave rectifier circuit 2 and the ground line, and between the (−) output terminal of the full-wave rectifier circuit 2 and the ground line, A shunt resistor r for current detection of the boost chopper 4 is connected.

  In this embodiment, three step-up choppers 4a to 4c are connected in parallel, and each step-up chopper 4a to 4c is controlled to turn on with a phase delay of 120 degrees. That is, the step-up chopper 4 includes switching elements Q1 to Q3 that are turned on by three types of PWM waves (PWM1 to PWM3) having different phases, coils L1 to L3 and diodes D1 to D3 corresponding to the switching elements Q1 to Q3, and , And a single smoothing capacitor C that is charged when each of the diodes D1 to D3 is conducted.

  In this embodiment, an insulated gate bipolar transistor IGBT (Insulated Gate Bipolar Transistor) is used as the switching elements Q1 to Q3, but they are all the same element. The same applies to the coils L1 to L3 and the diodes D1 to D3, and the coils L1 to L3 and the diodes D1 to D3 are the same element.

  As illustrated, the coils L1 to L3 and the switching elements Q1 to Q3 are connected in series, and the pulsating flow output (Vac) of the full-wave rectifier circuit 2 is commonly supplied to the coils L1 to L3. Further, three types of PWM waves (PWM1 to PWM3) having different phases are supplied to the gate terminals of the switching elements Q1 to Q3, and the collector terminals are connected to the anode terminals of the diodes D1 to D3. The emitter terminals of the switching elements Q1 to Q3 are connected to the earth line, the cathode terminals of the diodes D1 to D3 are commonly connected to the smoothing capacitor C, and the other end of the smoothing capacitor C is connected to the earth line. Has been.

  Since the step-up chopper 4 of the embodiment is configured as described above, when any switching element Qi is turned on, the pulsating input voltage Vac is generated by the switching element Qi and the coil Li connected in series with the switching element Qi. A short circuit is caused and a charging current flows through the coil Li. In the case of the present embodiment, the switching elements Q1 to Q3 are turned on with a 120-degree phase delay, so that a charging current with a 120-degree phase delay flows through each coil Li (see FIG. 17).

  Then, when the switching element Qi corresponding to the coil Li changes from the ON state to the OFF state in a state where the charging current is flowing through any one of the coils Li, the corresponding diode Di is turned on and the coil Li is discharged. A current flows through a path of the coil Li → the diode Di → the smoothing capacitor C, and the smoothing capacitor C is charged. Since this operation is executed in each of the coils L1 to L3 with a phase delay of 120 degrees, a smoothed DC voltage Vdc is obtained from the smoothing capacitor C.

  The operating current of each step-up chopper 4 is detected from the shunt resistor r connected to the (−) output terminal of the full-wave rectifier circuit 2. In this embodiment, the operation of the A / D converters (AD1, AD4) is detected. By defining the timing, only the current during the ON operation of the switching element Q1 is detected (see FIGS. 7A and 7C). In other words, in this embodiment, the charging current of the first coil L1 is detected through the shunt resistor r.

  As shown in the figure, the charging current I of the first coil L1, the input AC voltage Vac, and the output DC voltage Vdc are input to the one-chip microcomputer 3 through the signal input units IN1 to IN3, respectively. Each of the input signals is digitally converted by the A / D converters AD1 to AD4. The A / D converter AD1 and the A / D converter AD4 acquire the charging current I of the first coil L1 at different timings.

  The signal input unit IN1 is composed of an OP amplifier circuit that receives the voltage across the shunt resistor r, and functions as a current detection sensor together with the shunt resistor r. Further, the signal input unit IN2 and the signal input unit IN3 are configured by a resistance voltage dividing circuit and an OP amplifier amplifier circuit.

  The data acquired through the signal input units IN1 to IN3 and the A / D converters AD1 to AD4 are arithmetically processed by the one-chip microcomputer 3, and the ON time of the PWM signal (hereinafter referred to as control on time) is calculated. The PWM signals (PWM1 to PWM3) output from the one-chip microcomputer 3 are supplied to the gate terminals of the switching elements Q1 to Q3 through each buffer circuit DR. The one-chip microcomputer 3 is connected to the inverter circuit 5 through the signal input unit IN4 and the signal output unit OUT2, and controls the three-phase motor M by inverter.

  Hereinafter, prior to describing the specific control operation of the one-chip microcomputer 3, the control principle of the first boost chopper 4a will be described. FIG. 2 is a time chart illustrating the relationship between the first PWM wave (PWM1) output from the one-chip microcomputer 3 and the current flowing through the coil L1 of the first boost chopper 4a. Hereinafter, the first boost chopper 4a will be described. The inductance values of the coils L1 to L3 are all the same, and the circuit operations of the other boost choppers 4b and 4c are also the same.

  As shown in the figure, a triangular wave due to a coil charging current and a coil discharging current flows in the coil L1, but the energy stored in the coil L1 is sufficient and the continuous current flows (see FIG. 2A). Since there is insufficient energy, there is a discontinuous mode (see FIG. 2B) in which the current is interrupted in the middle.

  In this embodiment, since different PWM control is performed depending on which operation mode is in use, first, a determination formula for determining the operation mode will be described. In the time chart of FIG. 2, it is assumed that the current time is the control cycle (n−1). Then, it is considered that the control on time Ton (n) in the next control cycle (n) is determined based on the measured value in the control cycle (n−1). Note that the frequency of the AC input voltage is 50 Hz or 60 Hz, but in order to control it sufficiently quickly, in this embodiment, the control cycle T is set to 45.6 μS.

  Hereinafter, the circuit equation will be described with the inductance value of the coil L1 as L. The circuit equation during coil charging (switching element ON) is Vac (n−1) = L × {Ip (n−1) −Iv (n−2)} / Ton (n−1) (Equation 1 ) Here, Iv (n-2) is a coil charging start current, Ip (n-1) is a coil charging peak current, and Ton (n-1) is a control ON time, and each value in the control cycle (n-1). It is. Vac (n−1) is an input voltage in the control cycle (n−1). Since the control cycle T (= 45.6 μS) is sufficiently short with respect to the power supply frequency, Vac (n−1) is constant. Can be regarded as a value.

  On the other hand, the circuit equation at the time of coil discharge (switching element OFF) is Vdc (n−1) −Vac (n−1) = L × {Ip (n−1) −Iv (n−1)} / Toff (n -1) (Expression 2). Here, Vdc (n-1) is the voltage across the capacitor C, Iv (n-1) is the coil current at the end of the current control cycle (coil charging start current of the next control cycle), Toff (n-1). Are OFF times, which are values in the control cycle (n−1), respectively.

  If Ip (n−1) is eliminated from (Equation 1) and (Equation 2) and Iv (n−1) is solved, Iv (n−1) = Iv (n−2) + T / L × [{Vac (N−1) −Vdc (n−1)} + Ton (n−1) × Vdc (n−1)] (Equation 3) The control period T is T = Ton (n−1) + Toff (n−1).

  In the above (Formula 3), if Iv (n−1)> 0, the continuous mode is selected, and if Iv (n−1) = 0, the discontinuous mode is selected. However, (Formula 3) uses the coil charging start current Iv (n-2) in the current control cycle (n-1), and the coil charging start current Iv (n-1) in the next control cycle (n). Therefore, if the charging start current Iv (n−2) is not accurate, the determination of the continuous mode or the discontinuous mode will be wrong. That is, if Iv (n−2) is determined by a prediction calculation based on the control on time (Ton (n−2)) in the immediately preceding control cycle, an error is accumulated by the calculation of (Equation 3). As a result, the control instruction value itself may diverge from the target. Therefore, in this embodiment, the input current AD1 at the start of coil charging is measured for each control cycle.

  However, since a time delay Ts inevitably occurs from the start of the control cycle to the time of acquisition of the input current (see FIG. 8C), the measured value AD1 is corrected in consideration of this time delay Ts and coil charging is started. The current is Iv (n−2). Now, assuming that the current measurement value at the timing Ts of the control cycle (n−1) is AD1, the inclination (Δi / Δt) of the coil charging current is Δi / Δt = e / from the relationship of L × Δi / Δt = e. L. Here, e is voltage, i is current, and t is time.

  Therefore, the amount of increase in current at the time delay Ts can be calculated as Vac (n−1) / L × Ts. Using this value, Iv (n−2) = AD1−Vac (n−1) / L × Ts (Expression 4) Substituting (Equation 4) into (Equation 3), Iv (n-1) = AD1- [Vac (n-1) * Ts + T * {Vdc (n-1) -Vac (n-1)} −Ton (n−1) × Vdc (n−1)] / L (Expression 5), and input at the final timing of the current control cycle (n−1) (= start timing of the next control cycle) The current value Iv (n-1) can be accurately determined based on the measured value AD1 of the input current at the start timing of the current control cycle (n-1).

  Then, depending on whether or not the coil charging start current Iv (n-1) of the next control cycle obtained in this way is positive, it is possible to accurately determine whether it is a continuous mode or a discontinuous mode, and an optimal control corresponding to that mode. Is possible. That is, the measured values of the AC input voltage Vac (n-1), the DC output voltage Vdc (n-1), and the input current AD1 in the current control cycle (n-1) and the previous control cycle are determined. On the basis of the control on time Ton (n−1), it can be determined whether the control for the continuous mode or the control for the discontinuous mode should be performed. In addition, about the calculation procedure of the above (Formula 1)-(Formula 5), supplementary description is carried out to FIGS.

  By the way, the DC output voltage Vdc (n−1) does not necessarily need to be updated every control cycle. Therefore, in this embodiment, Vdc (i) whose value is updated every 1 mS is used ( (See step ST30 in FIG. 9). Therefore, the discriminant of the present embodiment is, precisely, Iv (n-1) = AD1- [Vac (n-1) * Ts + T * {Vdc (i) -Vac (n-1)}-Ton (n −1) × Vdc (i)] / L (Expression 5 ′).

  Furthermore, the average value Vdc for the past 0.5 seconds calculated by the process of step ST38 in FIG. 9 may be used as the DC output voltage. In this case, Iv (n−1) = AD1− [Vac (n−1) × Ts + T × {Vdc−Vac (n−1)} − Ton (n−1) × Vdc] / L. The discriminant of equation 5 ″) is adopted.

<Discontinuous mode>
Next, a method for calculating the control on time Ton (n) based on the coil average current Iav during each control cycle will be described. First, the control on time Ton (n) in the discontinuous mode is calculated (see FIG. 2B).

  The circuit equation at the time of charging the coil is Vac (n) = L × {Ip (n) −Iv (n−1)} / Ton (n), but Iv (n−1) = 0 because of the discontinuous mode. In the end, Vac (n) = L × Ip (n) / Ton (n) (Formula 6). Here, Vac (n) is the AC input voltage, Ip (n) is the current value at the coil charging peak, Iv (n−1) is the current value at the start of coil charging, and Ton (n) is the control on time. .

  On the other hand, the circuit equation at the time of coil discharge is Vdc (n) −Vac (n) = L / Tcut (n) × {Ip (n) −Iv (n)}. Tcut (n) is a time until the current value Ip (n) in the coil charge peak state is discharged and becomes zero (see FIG. 2B). Since the circuit equation in the discontinuous mode is considered here, Iv (n) = 0, and Vdc (n) −Vac (n) = L / Tcut (n) × Ip (n) (Expression 7) ) The average value Iav (n) of the input current in this control cycle is Iav (n) = {Ip (n) × Ton (n) + Ip (n) × Tcut (n)} / (2 × T). (Formula 8)

  Then, when these (Equation 6) to (Equation 8) are solved for Ton (n), Ton (n) × Ton (n) = {2 × T × L × Iav (n) × (Vdc (n) −Vac (N))} / {Vac (n) × Vdc (n)} (Equation 9) In addition, the calculation process of (Formula 9) was shown in FIGS.

<Continuous mode>
Subsequently, the control ON time Ton (n) in the continuous mode is calculated (see FIG. 2A). A circuit equation at the time of coil charging is Vac (n) = L × {Ip (n) −Iv (n−1)} / Ton (n) (Equation 10). On the other hand, the circuit equation at the time of coil discharge is Vdc (n) −Vac (n) = L / Toff (n) × {Ip (n) −Iv (n)} (Equation 11). Here, Toff (n) = T−Ton (n), which is the time from the start of coil discharge to the start of coil charge in the next control cycle.

  The average current Iav (n) in this control cycle is Iav (n) = [{Ip (n) + Iv (n−1)} × Ton (n) + {Ip (n) + Iv (n)} × Toff. (N)] / {2 × T} (Expression 12) Here, when (Equation 10) to (Equation 12) are solved for Toff (n) while erasing Ip (n) and Iv (n), Toff (n) × Toff (n) = [2 × T × L * {Iv (n-1) -Iav (n)} / Vdc (n)] + T * T * Vac (n) / Vdc (n) (Formula 13) Therefore, Ton (n) Is calculated as Ton = T−Toff (n) (Equation 14). Note that (Equation 14) and other calculation processes are supplemented in FIGS. 15 to 16.

  In this embodiment, the control on-time Ton (n) is calculated using (Equation 9) or (Equation 14) according to the discontinuous mode or the continuous mode. Prediction parameters for the AC input voltage Vac (n), the DC output voltage Vdc (n), and the average input current Iav (n) in (n) are required.

The AC input voltage Vac (n) is predicted based on the current AC input voltage measurement value Vac (n-1) and the previous AC input voltage measurement value Vac (n-2). The difference between the control cycle (n-2) and the control cycle (n-1) measurement value is added to the current measurement value Vac (n-1) as follows. Vac (n) = 2 × Vac (n−1) −Vac (n−2) (Equation 15)
On the other hand, for the DC output voltage Vdc (n), an average value Vdc of past measurement values for the DC voltage is adopted. Although the calculation method of the average value Vdc is determined as appropriate, in this embodiment, the measured values for the past 0.5 seconds are averaged by the averaging process executed every 0.5 seconds to obtain the DC output voltage Vdc. (See step ST38 in FIG. 9). This DC output voltage Vdc is stored in an appropriate work area of the memory, and the value Vdc of this work area is updated every 0.5 seconds.

  Therefore, in this case, in the discontinuous mode, Ton (n) × Ton (n) = {2 × T × L × Iav (n) × (Vdc−Vac (n))} / {Vac (n) × On the other hand, in continuous mode, Toff (n) × Toff (n) = [2 × T × L × {Iv (n−1) −Iav (n)} / Vdc. ] + T × T × Vac (n) / Vdc (Equation 13 ′), Ton = T−Toff (n) (Equation 14 ′).

  However, instead of using the average value Vdc for 0.5 seconds, the value of Vdc (i) obtained from the output value AD3 of the A / D converter AD3 every 1 mS may be used. In this case, in the discontinuous mode, Ton (n) × Ton (n) = {2 × T × L × Iav (n) × (Vdc (i) −Vac (n))} / {Vac (n) × Vdc (i)} (Equation 9 ″) On the other hand, in continuous mode, Toff (n) × Toff (n) = [2 × T × L × {Iv (n−1) −Iav ( n)} / Vdc (i)] + T × T × Vac (n) / Vdc (i) (Equation 13 ″), Ton = T−Toff (n) (Equation 14 ″) Become. In FIG. 3, for convenience, the case where Vdc (i) is used is indicated by a solid line, and the case where the DC output voltage Vdc is used is indicated by a broken line.

  The predicted value of the average input current Iav (n) is Iav (n) = β × Vac (n) from the relationship with the predicted value of the AC input voltage Vac (n). Here, the gain β is adjusted by PI control so that the difference Verr becomes zero while comparing the reference value (target value) Vo of the DC output voltage with the above-mentioned averaged DC output voltage Vdc.

  That is, Verr = Vo−Vdc (Expression 16), and Vo = Vac (pk) + α (Expression 17). Here, the reference value Vo of the DC output voltage is set to a value obtained by adding the amount of boost α by the coil L to the peak value Vac (pk) of the AC input voltage (pulsating flow). By setting in this way, conversion with high efficiency according to the input voltage value is possible. In addition, since the amount of pressure boosted by the coil L can be reduced, it is possible to select an inexpensive and lightweight coil with an appropriate size that does not increase in size. The optimum inductance value of the coil L is generally determined based on a design formula of L = Vac × Vac × (Vdc−Vac) / {γ × Pac × Vdc / T}. Since the output voltage value Vdc is set in correspondence with the voltage value Vac, the inductance value of the coil always maintains an almost optimum value. In the above design formula, γ is the ripple content of the input current, T is the control period, Pac is the maximum input power, and Vac is the instantaneous value of the input voltage.

  FIG. 3 is a control block diagram for explaining the above-described control operation. As shown in the figure, it is determined for each control cycle whether it is a continuous mode or a discontinuous mode. If it is a discontinuous mode, (Equation 9 ′ / Equation 9 ″) is used. The control on time Ton is calculated using Equation 14 ″). Then, the switching element Q1 of the first step-up chopper 4a is turned on by a PWM wave having a pulse width equal to the calculated control ON time Ton. The same applies to the other step-up choppers 4b and 4c, and the switching elements Q2 and Q3 are turned on by a PWM wave whose phase is delayed by 120 degrees.

  As described above, the control principle of the PWM control has been described based on FIGS. 2 and 3. Next, the one-chip microcomputer 3 that realizes the control operation of FIG. 3 will be specifically described.

  FIG. 4 illustrates an internal configuration diagram of the one-chip microcomputer 3. Here, a single-chip RISC microcomputer SH7046 (Renesas Technology Corp.) is used. The one-chip microcomputer 3 includes a CPU core 30, a clock generation unit 31, an AD conversion unit 32, and a multifunction timer pulse unit (MTU) 33. The clock generator 31 of this embodiment oscillates a 50 MHz system clock, and a 25 MHz peripheral clock PΦ obtained by dividing the system clock by two is supplied to the MTU 33. Then, the peripheral clock PΦ is supplied to the counter of the MTU 33 as it is as a counting clock (frequency 25 MHz) without being divided thereafter.

  FIG. 5 schematically illustrates the internal configuration of the AD conversion unit 32. The AD conversion unit 32 has 8-channel analog input terminals AN8 to AN15. The input analog signal is AD converted by a successive approximation method, and digital data after AD conversion (resolution 10 bits) is: Stored in data registers ADDR8 to ADDR15.

  In this embodiment, each analog signal indicating the operation state of the step-up chopper 4 is supplied to the above-described AD conversion unit 32 via the signal input units IN1 to IN3. It functions as 4-channel A / D converters AD1 to AD4. The 4-channel A / D converters AD1 to AD4 are set to operate in the continuous scan mode, and when the AD conversion start trigger (see FIG. 5) is received from the MTU 33, the A / D converters AD1 to AD4 are in that order. An AD conversion operation is executed.

  When all the AD conversion operations are completed, an interrupt signal (ADI interrupt) is set to be output to the CPU core 30. Therefore, the CPU core 30 performs arithmetic processing based on the AD-converted input data in the interrupt processing program caused by the ADI interrupt, and calculates the control on time Ton described above.

  FIG. 6 illustrates the internal configuration of an MTU (multifunction timer pulse unit) 33. The MTU 33 is composed of a 5-bit (channel_0 to channel_4) 16-bit timer, and can output a PWM wave having an arbitrary pulse width based on data set in various registers.

In the case of the present embodiment, each setting of the MTU 33 is as follows.
<Settings related to the AD conversion unit 32>
An AD conversion start trigger is generated by a compare match of TGRA_0 (channel 0 general register A). Note that, as described above, the AD conversion unit 32 of the one-chip microcomputer 3 starts the AD conversion operation by the AD conversion start trigger.
<Setting of interrupt request to CPU core 30>
An interrupt request signal is generated in the CPU core by a compare match of TGRA_0 (channel 0 general register A). In response to the interrupt request signal, the CPU core 30 writes a set value to TGRA_0 to TGRA_2 (general register A of channels 0 to 2) and TGRB_0 to TGRB_2 (general register B of channels 0 to 2). This set value is a numerical value that defines the rising timing and falling timing of the three-phase PWM wave output from the MTU 33.
<Settings related to the operation of the MTU 33>
[Setting (1)] Of channels 0 to 4, channels 0 to 2 are set to "synchronous operation". Then, the channel 0 counter clearing factor is set to “TGRA — 0 (channel 0 general register A) compare match”, and the channel 1 and 2 counter clearing factors are set to “synchronous clear”. Therefore, the timer counters TCNT_0 to TCNT_2 of the channels 0 to 2 are cleared in synchronization with the compare match of TGRA_0.
[Setting (2)] Channels 0 to 2 are set to “PWM mode 1”. In PWM mode 1, TGRA (general register A) and TGRB (general register B) are used in pairs, and a PWM wave is output from the TIOCA terminal (the PWM output terminal of MTU33) by a TGRA and TGRB compare match. The
[Setting (3)] In response to an interrupt request due to a TGRA_0 compare match, a CPU core is set in TGRA_0 to TGRA_2 (general register A of channels 0 to 2) and TGRB_0 to TGRB_2 (general register B of channels 0 to 2). 30 writes the set value. Specifically, 1140, 380, and 760 are written to TGRA_0 to TGRA_2 (general register A of channels 0 to 2), and Ton, 380 + Ton, and 760 + Ton are written to TGRB_0 to TGRB_2 (general register B of channels 0 to 2). Write. Note that Ton is a control ON time calculated for each control cycle.
[Setting (4)] The output level of the TIOCA terminal (the PWM output terminal of the MTU 33) changes at the time of TGRA (general register A) compare match and at the time of TGRB (general register B) compare match. Each output of TIOCA_0 to TIOCA_2 rises to an H level by a compare match of TGRA_0 to TGRA_2 and falls to an L level by a compare match of TGRB_0 to TGRB_2 by the initial setting to the TIOR (timer IO control register) of each channel. Set as follows.
[Setting (5)] The counting clock of the timer counter TCNT is set to 25 MHz (period 40 nS), which is the same as the peripheral clock PΦ.

  The MTU 33 is set and operated as described above. FIG. 7A shows the relationship between the timer counters TCNT (TCNT_0 to TCNT_2) of the channels 0 to 2 and the general registers (TGRA_0 to TGRA_2, TGRB_0 to TGRB_2) in relation to the operation of the MTU 33, and The PWM wave output from a TIOCA terminal (TIOCA_0-TIOCA_2) is illustrated.

  As described above, in this embodiment, the timer counters TCNT_0 to TCNT_2 of the channels 0 to 2 are synchronously cleared at the time of a compare match of TGRA_0 set to the fixed value 1140. Therefore, each timer counter TCNT functions as a 1140 base counter that circulates from 0 to 1139. On the other hand, since the count clock of the timer counter TCNT is 25 MHz (period 40 nS), the timer counter circulates with 45.6 μS (= 1140 × 40 nS) as one period (control period T), and PWM control is performed. The carrier frequency is about 22 KHz.

  The TGRA (general register A) of channel 0 to channel 2 has 1140, respectively by the CPU core 30 caused by an interrupt generated at the time of a compare match of TGRA (TGRA_0) of channel 0 (that is, when each timer counter TCNT is synchronously cleared). 380 and 760 are written. Similarly, TGRB (general register B) of channel 0 to channel 2 is written with Ton, 380 + Ton, and 760 + Ton, respectively, by an interrupt generated at the time of a channel 0 TGRA (TGRA_0) compare match.

  Due to the above settings, TIOCA_0 (the TIOCA terminal of channel 0) rises to the H level as the timer counter TCNT is cleared. Thereafter, when the timer counter TCNT_0 of the channel 0 advances and coincides with Ton which is the value of TGRB_0 (general register B of the channel 0), the TIOCA_0 falls to the L level.

  The same applies to channel 1 and channel 2, and TIOCA_1 (TIOCA terminal of channel 1) rises to H level at the timing of timer counter TCNT_1 = 380, by the TGARA_1 compare match, and at the timing of timer counter TCNT_1 = 380 + Ton, It falls to L level by TGRB_1 compare match. Further, TIOCA_2 (TIOCA terminal of channel 2) rises to H level at the timing of timer counter TCNT_2 = 760 by the TGRA_2 compare match, and falls to L level at the timing of timer counter TCNT_2 = 760 + Ton by the compare match of TGRB_2. .

  Therefore, the PWM wave having the pulse width Ton is output from the TIOCA_0 to TIOCA_2 which is the output terminal of each channel with a phase delayed by 120 degrees (see FIG. 7A), and the switching elements Q1 to Q3 are The ON operation is performed based on the three-phase PWM wave having a phase shift.

  FIG. 7B illustrates the interrupt processing of the CPU core 30 based on the compare match of TGRA — 0 (channel 0 general register A). As described above, at the first timing of each control cycle (at the time of TGRA_0 compare match), the CPU core 30 applies a pulse width to TGRA_0 to TGRA_2 (general register A) and TGRB_0 to TGRB_2 (general register B) of the MTU 33. Writes a set value for the control on time Ton. The control on time Ton is a value calculated in the immediately preceding control cycle.

  FIG. 7C illustrates an AD conversion start trigger based on a compare match of TGRA — 0 (general register A of channel 0). As shown in the figure, at the first timing of each control cycle (when TGRA_0 is a compare match), an AD conversion start trigger is supplied from the MTU 33 to the AD conversion unit 32, and in response, the A / D converters AD1 to AD4 are continuously provided. The AD conversion operation is executed in this order by operating in the scan mode. When the A / D converter AD4 finishes AD conversion, it outputs an AD conversion end interrupt signal to the CPU core 30.

  As described above, the MTU 33 cooperates with the CPU core 30 and the AD conversion unit 32 to output three PWM waves whose phases are different by 120 degrees with a control period T of about 50 μS. 8 to 9 are flowcharts showing the processing contents of the one-chip microcomputer 3 that realizes the control operation of FIG. The control process shown in FIG. 3 includes a PWM wave output operation (see FIGS. 7A and 8A) performed by the MTU 33 repeated every 45.6 μS, and a timer interrupt TM_INT activated every 1 mS (FIG. 9). ) And an AD conversion end interrupt AD_INT (FIG. 8B) that is started when the AD conversion operation is completed.

  Hereinafter, the operation content of the MTU 33 is confirmed based on FIG. The timer counter TCNT is cleared in synchronization every 45.6 μS (= 1140 count clocks). At the time of this clearing, the CPU core 30 is interrupted, and the CPU core 30 defines the falling timing of each PWM wave by the writing process to TGRA_0 to TRGA_2 and TGRB_0 to TRGB_2 (see FIG. 7B). Further, when the timer counter TCNT is cleared, an AD conversion start trigger is supplied to the AD conversion unit 33 (see FIG. 7C). In addition, as described above, the three types of PWM waves are regenerated after the timer counter TCNT is cleared.

  Thereafter, when the AD conversion processing of the A / D converters AD1 to AD4 operating in the continuous scan mode is completed, an AD conversion end interrupt is applied to the CPU core 30. As shown in FIG. 8C, there is a time delay Ts from the start of the control cycle to the start of the first AD conversion, and the start of the fourth AD conversion from the start of the first AD conversion. Until there is a delay time Td.

<AD conversion end interrupt AD_INT>
When the AD conversion operation is completed for all the A / D converters, the control operation is executed by the interrupt process AD_INT shown in FIG. First, output values AD1 and AD4 (input current to the coil L) of the A / D converters AD1 and AD4 are acquired (ST10). Next, the average value Iav (n−1) of the input current in the control cycle (n−1) is calculated by the average calculation (AD1 + AD4) / 2 (ST11). As shown in FIG. 8C, the input current value varies depending on the sampling point, so the accuracy as the average value (average current) of the input current is not high, but this average value Iav (n−1) Is used only for the correction of the inductance value described below, so that no particular problem occurs.

  When the average value Iav (n−1) of the input current is obtained, the inductance value of the coil L1 mounted on the circuit is specified based on the current value Iav (n−1). As shown in FIG. 10, the inductance value of the coil L <b> 1 often changes depending on the DC superimposed current (average current) flowing therethrough. Therefore, in this embodiment, the characteristics of the coil L1 mounted on the circuit are stored in advance in the memory, and the inductance value corresponding to the average value Iav (n−1) of the input current is used in each arithmetic expression. I am doing so.

  Therefore, highly accurate control is possible without using a large and expensive coil. In order to further improve the control accuracy, the current value Iav (n−1) obtained by the average calculation (AD1 + AD4) / 2 is used as the control on time Ton (n−1) in the control cycle (n−1). It may be corrected accordingly (see FIG. 3). In other words, the two sampling points AD1 and AD4 may be divided into the coil charging current AD1 and the coil discharging current AD4, or the control on time Ton (n−1) may be long, and both may be the coil charging current. Therefore (see FIG. 8C), more accurate control can be realized if the average current is corrected based on this point.

  Subsequently, the output value AD2 (AC input voltage Vac (n-1)) of the A / D converter AD2 is acquired (ST13). Then, Vac (n) is calculated based on the voltage prediction formula Vac (n) = 2 × Vac (n−1) −Vac (n−2) (ST14). Next, the output value AD3 (DC output voltage Vdc (n-1)) of the A / D converter AD3 is acquired (ST15).

  Subsequently, the input current command value Iav (n) is calculated by calculating Iav (n) = β × Vac (n) (ST16). Note that. A necessary value of the integration parameter β is updated every 1 mS in the timer interrupt process TM_INT shown in FIG. 9 and stored in an appropriate work area.

  Next, the acquired value AD1 from the A / D converter AD1, the inductance value L of the coil corrected in the process of step ST12, the AC input voltage value Vac (n−1) acquired in the process of step ST13, Based on the control ON time Ton (n-1) and the DC output voltage value Vdc (i) in this control cycle, and based on the discriminant of (Expression 5 ′), the coil charging start current Iv (n−1) Is calculated (ST17). Then, according to the value (whether positive or not) of the coil charging start current Iv (n−1), it is determined whether the control should be controlled as the continuous mode or the discontinuous mode (ST17). As described above, the discriminant of (Expression 5 ″) may be used instead of (Expression 5 ′).

  If Iv (n−1) ≦ 0 and the discontinuous mode is set, Iv (n−1) = 0 is set (ST19), (Equation 9 ′) or (Equation 9 ″). ) To calculate the control on time Ton (n) (ST20). On the other hand, if Iv (n−1)> and the continuous mode is set, the control on-time Ton (n) is calculated based on the arithmetic expression of (Expression 14 ′) (Expression 14 ″) (ST21). ).

  Then, on the condition that the calculated control ON time Ton (n) does not exceed the control upper limit value and the control lower limit value, the Ton in the PWM buffer area is set as the control ON time of the next control cycle (n). The value of (n) is set (ST22, 23). The Ton (n) written in the PWM buffer in this way is used at the time of interruption at the start of the next control cycle, and Ton, 380 + Ton is stored in TGRB_0 to TGRB_2 (the general register B of channels 0 to 2) of the MTU 33. , 760 + Ton is written.

  However, when the calculated control ON time Ton (n) exceeds the upper limit value or the lower limit value, the control upper limit value or the control lower limit value is set in the PWM buffer. The upper limit value is T / 3 with respect to the control cycle T. In this case, a control upper limit value that is less than T / 3 is used. The reason for providing such a restriction is that if the operation is performed in a state where Ton ≧ T / 3, a plurality of step-up choppers are operated in an overlapping manner, and the object of the present invention such as suppression of heat generation is hindered. is there.

<Timer interrupt TM_INT>
Next, the timer interrupt TM_INT started every 1 mS independently of the above-described AD conversion end interrupt AD_INT will be described with reference to the flowchart of FIG.

  In the timer interrupt TM_INT, first, Vdc (i), which is the output of the A / D converter AD3, is acquired (ST30). The A / D converter AD3 executes an AD conversion operation every 45.6 μS, but the timer interrupt INT1 acquires the AD converted output DC voltage every 1 mS. Hereinafter, the acquired DC voltage is expressed as Vdc (i).

  Next, the calculation of SUM ← SUM + Vdc (i) is executed, and the acquired value of the output DC voltage Vdc (i) is added to the average calculation buffer SUM in the work area (ST31). Also, the AC input voltage Vac (i), which is the output of the A / D converter AD2, is acquired (ST32), and the AC input voltage Vac (i) and the peak value Vac (pk) stored in the memory are obtained. Contrast (ST33).

  If Vac (i)> Vac (pk), the maximum wave height value Vac (pk) stored in the memory is updated by calculating Vac (pk) ← Vac (i) (ST34). After obtaining the peak value Vac (pk) of the AC input voltage in this way, the counter CT is decremented (−1) (ST35), and it is determined whether or not the counter value CT is zero (ST36).

  Here, when the counter value CT becomes CT = 0, the average value of the output DC voltage Vdc (i) is obtained by multiplying the value of the average calculation buffer SUM by 1/500 (ST37). Then, the DC output voltage Vdc is specified by this average value (ST38).

  When the DC output voltage Vdc is obtained in this way, the values of the average calculation buffer SUM and the counter CT are initialized (ST39), and the reference value (target value) Vo of the output DC voltage is calculated by calculating Vo ← Vac (pk) + α. Is calculated (ST40). α is a boosted amount in the coil L when compared with the peak value Vac (pk) of the input AC voltage. Then, the difference between the output reference voltage Vo and the output average voltage Vdc obtained from the measured value is calculated (ST41). Specifically, Verr (i) ← Vo−Vdc is calculated.

  Based on the above result, the command value β by the PI control is calculated, and the timer interrupt process INT1 is finished (ST42). Here, the calculation of the command value β is based on an arithmetic expression of β = Verr (i) × Kp + {Verr (i) × Ki + Verr (i−1) ′ × Ki}, where Verr (i−1) ′ × Ki is , The previous integration control value (i−1), which is a value calculated as Verr (i−1) ′ × Ki = Verr (i−1) × Ki + Verr (i−2) ′ × Ki.

  The content of the AD conversion end interrupt (FIG. 8B) described above is described as “INT1” in the control block diagram 3. Further, “A / D” is described in the operation of the AD conversion unit 33, and “MTU” is described in the operation of the MTU 33.

  As described above, in the digital converter 1 according to the embodiment, the three step-up choppers 4a to 4c are connected in parallel, and the switching elements Q1 to Q3 are sequentially turned on with delay, so that the switching elements are distributed and mounted. This makes it possible to effectively disperse the heat generation. In relation to these, the current capacity specification of each switching element can also be lowered.

Further, since the ripple of the input current is reduced, the capacitor Cin on the input side can be reduced in size. FIG. 16 illustrates this relationship, and shows the relationship between the currents I _{L1 to} I _L3 of the coils _{L1 to L3} and the output current I _ALL of the rectifier circuit 2, which is the sum of these.

  Moreover, the inductance value of each coil L1-L3 can also be reduced. That is, Vdc (n) and Iav (n) are relatively increased as the boost chopper operates in parallel as compared with the case where there is a single boost chopper, for example, from (Expression 9) and (Expression 14). The inductance value L can be reduced.

  In addition, since there is no hardware control circuit and all can be realized by software control, the power factor correction circuit and the like can be omitted, and downsizing can be achieved at low cost. In addition, since a common coil is used and its inductance value is corrected in real time and reflected in the arithmetic expression, high-precision control is possible at a low cost. Furthermore, in this embodiment, since control is performed by instantaneous response, it is possible to cope linearly with load fluctuations. Further, as shown in (Equation 9) and (Equation 14), since control based on feedforward is mainly performed, divergence with respect to the target value can be suppressed and control delay is small.

It is a circuit block diagram which shows the digital converter which concerns on an Example. It is a time chart explaining the relationship between a control period and the charging / discharging operation | movement of a coil. It is a control block diagram explaining the control operation of the digital converter which concerns on an Example. It is a block diagram which shows the internal structure of a one-chip microcomputer. It is a block diagram which shows the internal structure of an AD conversion part. It is a block diagram which shows the internal structure of MTU. It is a time chart explaining operation | movement of MTU. It is a flowchart which shows the operation | movement content of MTU and AD conversion interruption. It is a flowchart which shows the operation | movement content of a timer interruption. It is a characteristic view which shows the relationship between the inductance value of a coil, and an average current. It is drawing explaining the derivation | leading-out process of (Formula 5). It is drawing explaining the derivation | leading-out process of (Formula 5). It is drawing explaining the derivation | leading-out process of (Formula 9). It is drawing explaining the derivation | leading-out process of (Formula 9). It is drawing explaining the derivation process of (Formula 14). It is drawing explaining the derivation | leading-out process of (Formula 14). It is drawing explaining reduction of a ripple.

Explanation of symbols

L1 to L3 Coils Q1 to Q3 Switching element 1 Digital converter 2 Rectifier circuit 3 Computer circuit (one-chip microcomputer)
4a-4c Booster chopper

Claims (7)

A step-up chopper configured by connecting N circuits in which substantially the same coil and switching element are connected in series, a rectifier circuit for supplying an input current to each coil, and a predetermined control for each switching element A digital converter configured with a computer circuit that performs PWM control in a cycle,
While determining whether the input current to the coil is a continuous mode that is not interrupted during a control cycle or a discontinuous mode that is interrupted in the middle of a control cycle, the PWM control is executed with a different algorithm based on the determination result,
Each of the switching elements is sequentially driven with a phase shifted by 360 / N degrees. The digital converter according to claim 1, wherein the DC output voltage of the step-up chopper is obtained from a single capacitor that is charged when each switching element is turned off. Whether the current mode is the continuous mode or the discontinuous mode is determined in the current control cycle by measuring each value of the coil charging start current, the AC input voltage to the boost chopper, and the DC output voltage of the boost chopper, and the current control. The digital converter according to claim 1, wherein the digital converter is determined based on a control time of the PMW wave in a cycle and an inductance value of the coil. 4. The digital converter according to claim 1, wherein a control ON time Ton of each switching element in the PWM control is limited to Ton <360 / N in terms of angle. The computer circuit is a one-chip microcomputer having an AD conversion unit for digitally converting an analog input signal and a timer unit capable of automatically outputting a pulse wave having an arbitrary pulse width based on setting data to various registers The digital converter in any one of Claims 1-4. The digital converter according to claim 5, wherein the AD conversion unit is configured to digitally convert a group of analog input signals based on a command from the timer unit. A method for controlling a digital converter that realizes the operation according to claim 1.