Mysql Codeigniter Parcel System

Question

I need a system that registers multiple installments of title in my Mysql BD I have this code below that registers and repeats the Insert according to installments Qtde informed, but it happens that when choosing the date with day 30, arrives in February it jumps the month and goes to 2 March.. where the error is?

public function cad_despesa_funciona() {

    $nParcelas = '3';
    $dataPrimeiraParcela = '30/12/2017';
    //$dataemissao = date('Y-m-d');
    //$ndocumento = 'ndcu';
    //$titulo = 'titulo';
    //$valor = '500.00';

if($dataPrimeiraParcela != null && $nParcelas !=null){
    $dataPrimeiraParcela = explode('/',$dataPrimeiraParcela);
    $dia = $dataPrimeiraParcela[0];
    $mes = $dataPrimeiraParcela[1];
    $ano = $dataPrimeiraParcela[2];
} else {
    $dia = date("d");
    $mes = date("m");
    $ano = date("Y");
}

for($x = 1; $x <= $nParcelas; $x++){
     $dt_parcelas[$x] = date("Y-m-d",strtotime("+".$x." month",mktime(0, 0,0,$mes,$dia,$ano)));
    }
    var_dump($nParcelas);
    foreach ($dt_parcelas as $vencimento)
    {
        $dados = array(
            'titulo' => 'teste titulo',
            'ndocumento' => '123',
            'datavencimento' => $vencimento,
            'parcela' => '123',
            'formadepgto' => '2',
            'valor' => '50.00',
            'dataemissao' => '2017-10-25',
            'planodecontas' => '2',
            'status' => 'aberto',
            'parcelaatual' => '2'
        );
    $this->db->insert('sis_despesas', $dados);
    }
}

I have this other code tbm, only I could not adapt it in codeigniter, in direct php I managed to work with it, even if I’m not mistaken it takes the last day of February, instead of taking the next month, this is a monthly system, can not stay 1 month without.

    $parcelas = '3';
    $datavenc = '2017-12-30';
    $datavencimento = Array(date('Y' , strtotime($datavenc)), date('m' , strtotime($datavenc)), date('d' , strtotime($datavenc)));
    $data_array = Array($datavencimento[0], $datavencimento[1], $datavencimento[2]);
    $n = $data_array[1]-1;
    $v_i = $n;

for($i = 0; $i < $parcelas; $i++) {

    $v_i++;
    $v = strtotime ( '+'.$i.' month' , strtotime(implode("-", $data_array))) ;
    $nd = date ( 'Y-m-d' , $v );
    $p = explode("-", $nd);

if($v_i <= 12) {

    $base_mes = date("Y-m-t", strtotime($nd));
    $forma_data = $p[0].'-'.$v_i.'-01';
    $ultimo_dia_do_mes = date("Y-m-t", strtotime($forma_data));
    $b1 = explode("-", $base_mes); // EXPLODE DO BASE MES
    $b2 = explode("-", $ultimo_dia_do_mes); // EXPLODE DO ULTIMO DIA DO MÊS

if($b1[2]!=$b2[2]) {
        $gravarData = $b2[0] . "-" . $b2[1] . "-" . $b2[2] . " 00:00:00";
    } else {
        $gravarData = $b1[0] . "-" . $b1[1] . "-" . $data_array[2].  " 00:00:00";
    }
    //AQUI EU COLOCO O INSERT PARA O BD
    }
else {
} 
} 
}